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Full text of "Stirling, a book on steam for engineers;"

UNIVERSITY OF CALIFORNIA. 



QIKT OF" 






Class 



ENGRAVED AND PRINTED BY 
ROSENOW COMPANY, CHICAGO 



The Stirling Company 

Manufacturers of 

Water -Tube Safety Boilers for Stationary and Marine Use, 

Superheaters, Bagasse Furnaces and Conveyors, 

Chain Grate Stokers, Steel Stacks, 

and Breechings 

General Offices: 

Trinity Building, New York, N. Y., U. S. A. 

Works : Barberton, Ohio 



Sales Offices: 

Boston, Mass. ... . . Delta Building Toledo, Ohio 720 Monroe Street 

Philadelphia, Pa Betz Building Chicago, 111 Pullman Building 

Washington, D. C Colorado Building New Orleans, La Hennen Building 

Pittsburg, Pa. ... Germania Bank Building Atlanta, Ga Empire Building 

Cincinnati, Ohio . ... Ingalls Building San Francisco, Cal 32 First Street 

( Havana, Cuba . . Royal Bank of Canada Building 

Johannesburg, S. A. Yokohama, Japan Honolulu, H. I. 

Herbert Ainsworth A. S. Hay Von Hamm Young Co. 

35 Exploration Buildings 43 B-Yamashita-Cho Alexander Young Building 

Buenos Ayres, Argentine Republic 

La Cia de Fabricantes Extrangeros, Ltda. 

302, Calle Balcarce, 326 



Pub. No. 1205 



Stirling 



A Book on Steam for Engineers 



Edited by 
The Engineering Staff of The Stirling Company 




New York 

The Stirling Company 

Trinity Building 
1905 



Special Notice 

Realizing that it is practically impos- 
sible to avoid errors or misprints in 
the first edition of a work of this size, 
the publishers cordially invite those 
who note errors of any kind to report 
them, so that the necessary correc- 
tions may be made in future editions 
THE STIRLING COMPANY 



Copyright, 1905, by The Stirling Company 




Table of Contents 

PAGE 

The Stirling- Water-Tube Safety Boiler . . . . . 7 

Water-Tube versus Fire-Tube Boilers .... 35 

Works of The Stirling- Company 45 

Heat . 47 

Air 55 

Water 57 

Impurities in Boiler Feed Water ..... 59 

The Heating of Boiler Feed Water .... 67 

Steam 69 

Moisture in Steam 79 

Flow of Steam through Pipes and Orifices ... .87 

Superheated Steam and the Stirling Superheater . 93 

Combustion 105 

Fuels for Steam Boilers Ill 

Determination of Heating Value of Fuels .... 131 

Fuel Burning 141 

The Stirling-Chain Grate Stoker 159 

Utilization of Waste Heat 161 

Chimneys and Draft . . . . . . . 169 

Analysis of Flue-Gases . . . . . . . . 181 

Steam Boiler Efficiency 187 

Horse-Power Rating of Boilers 195 

Rules for Conducting Boiler Trials 201 

Table of Tests on Stirling Boilers 208 

Boilers for Mining Service ....... 209 

Principles of Steam Piping . . . . . . 213 

Boiler and Steam Pipe Coverings ..... 219 

Boiler Cleaning 223 

Care and Management of the Stirling Boiler . . 229 

Specifications for Masonry in Stirling Boiler Settings . 233 

Index . . 239 



135277 



The Stirling Water -Tube Safety Boiler 



Shortly after the invention of the double- 
acting steam engine by Watt, the develop- 
ment of the water-tube boiler began, but of 
the many designs which appeared during the 
succeeding half century none proved success- 
ful. Yet not all of the ideas underlying these 
early and crude designs were valueless, and 
after a long course of experimenting some 
of them were gradually worked out to a 
practical application, and the water-tube 
boiler then became a commercially successful 
steam generator. It was far from being 
perfect, however, as many of the most ad- 
vanced ideas of inventors could not be em- 
bodied in these early types of boilers, because 
of the lack of suitable material to construct 
the parts, and the then inadequate mechanical 
facilities for building such boilers. In con- 
sequence of these manufacturing limitations, 
the general design narrowed down to some 
arrangement in which steam was generated 
in slightly inclined tubes, and discharged 
into one or more upper drums. These parts 
were all easily made with the materials and 
mechanical facilities available at that time. 
One almost insuperable difficulty remained, 
and that was to devise safe and efficient means 
of providing passageway from the tube ends 
into the drums. Out of the hundreds of 
methods tried, but few proved to be even 
approximately successful, and there is yet 
to be found a method which can be considered 
entirely satisfactory. In consequence of the 
complexity of parts required in these various 
designs for connecting the tubes and the 
drums, cast iron was the only available 
material, and very unfortunately, its use for 
making such parts became common. 

The tendency to follow in the beaten track 
is well illustrated in this case, because until 
about two decades ago practically all of the 
various water-tube boilers which had achieved 
any success were more or less complicated 
developments of the general scheme of at- 
taching nearly horizontal tubes to a drum. 
In consequence, all of them were distinguished 
by a multitude of joints, caps, bolts, headers, 
water-legs, nipples, and other objectionable 
features, while practically all of them were 



compelled to use cast iron in headers, return- 
bends, and other parts of complicated shape 
subjected to high pressure. As steam pres- 
sures and the sizes of boilers were gradually 
increased, the defects of this general design 
were found to be many, and as each defect 
developed, further complication was intro- 
duced to correct it. 

These complications being inherent in the 
general design, it follows that their elimination 
demanded the development of a new type of 
boiler so essentially different, that, without 
introducing any new defects, it would be 
free from those affecting the older types whose 
possibilities of development had been ex- 
hausted. The problem of producing such a 
boiler received the earnest attention of many 
engineers, yet there was, and is now, but 
one satisfactory solution for that problem, the 
STIRLING WATER-TUBE SAFETY BOILER, as 
now manufactured and offered by THE STIR- 
LING COMPANY. 

Every great invention is the result of 
gradual evolution, and the Stirling boiler 
is no exception to this law. The first boilers 
of this type contained one mud drum and 
only two steam drums. These boilers were 
crudely constructed, and in their installation 
but little attention was paid to those minor 
details the aggregate of which constitute 
perfection. Crude, however, as these first 
boilers were, they conclusively demonstrated 
that the principle of the boiler is correct and 
that great possibilities lay in the development 
of its application. These points having been 
established, THE STIRLING COMPANY was 
formed, the boiler was developed, and its 
construction was perfected, but its principle 
was and always has been, the same. In its 
improved form, as described in the following 
pages, it has met every demand, and fulfilled 
every requirement. 

The Stirling Boiler ( Figs, i and 2 ) con- 
sists of three upper or steam drums, each 
connected by a number of tubes (called a 
"bank") to a lower or mud drum. Suitably 
disposed firetile baffles between the banks 
direct the gases into their proper course. 
Shorter tubes connect the steam spaces of all 



8 THE STIRLING WATER-TUBE SAFETY BOILER 

upper drums, also water spaces of front and plicity and eliminates the complication of 

middle drums. The boiler is supported on the older types. 

a structural steel framework, around which The Drums vary from 36 to 54 inches in 

is built a brick setting whose only office is diameter and are made of the best open 

to provide furnace space, and serve as a hearth flange steel. The plates extend the 




FIG. 1. THE STIRLING WATER-TUBE SAFETY BOILER-SECTIONAL SIDE ELEVATION 
THE RED, YELLOW AND BLUE SECTIONS RESPECTIVELY INDICATE-RED BRICK, FIRE-BRICK, AND CONCRETC 

housing to confine the heat. The entire entire distance between heads, hence there 
front is of metal of appropriate and artistic ape* no circular scams. The longitudinal 
design. These parts, together with the usual 'seams which are double or triple riveted 
valves and fittings, constitute the completed according to the working pressure to be car- 
boiler, which represents the acme of sin;- ried are so placed that they are not exposed 



FRONT ELEVATION AND SECTION 



to high temperature. The drum heads are 
hydraulically dished to proper radius; each 
drum is provided with one manhole, and the 
manhole plate and arch bars are of wrought 
steel; four manhole plates, which can be 



tions in them, as evidenced by the sectional 
view shown in Fig. 3. 

The Tubes are best lap- welded mild steel. 
They are slightly curved at the ends to permit 
them to enter the drums normally and to 




FIG. 2. THE STIRLING WATER-TUBE SAFETY BOILER-SECTIONAL FRONT ELEVATION 
THE RED, YELLOW AND BLUE SECTIONS RESPECTIVELY INDICATE RED BRICK, FIRE-BRICK, AND CONCRETE 



removed in ten minutes, give access to the 
entire interior of the boiler, and expose every 
tube end, rivet, and joint. The drum in- 
teriors are perfectly clear; there are no baffles, 
stays, tie-rods, mud pipes, or other obstruc- 



provide for free expansion of the boiler when 
at work. The tubes are expanded directly 
into reamed holes in tube sheets of the drums, 
hence the annular recess between tubes and 
the cast headers of some types of boiler is 



10 



THE STIRLING WATER-TUBE SAFETY BOILER 



eliminated, and failure of tubes by pitting 
through corrosion caused by accumulation 
of soot in these recesses is avoided. There are 
no short nipples and no tube joints in places 
which can be reached only by jointed handles 
on the tube expander, rendering it impos- 
sible to determine when the tube has been 
properly expanded. In the Stirling every 
tube end is visible and accessible. 

Steel Framework As the entire weight 
of boiler and contents is supported on the 
steel framework, cracking of the setting due 
to unequal settlements is obviated, and no 
blocking is needed when the brickwork has 
to be repaired. The design of framework 
can be modified to suit special conditions.* 



Furnace The design of the Stirling 
furnace is a distinct advance over previous 
practise, and offers advantages wholly un- 
obtainable under some types of boiler, and 
obtainable under the others only by a pro- 
hibitive increase in floor space. Referring 
to Figs i and 2 , it will be seen that a fire- 
brick arch is sprung over the grates and im- 
mediately in front of the first bank of tubes. 
The large trir.ngular space between boiler 
front, tubes, and mud drum, is available for 
combustion chamber, and for installation 
of sufficient grate surface to meet the require- 
ments of the lowest grades of fuel, all in 
marked contrast to boilers of the internally 
fired type, and many water-tube boilers in 




FIG. 3. SECTION THROUGH STEAM DRUM, SHOWING ABSENCE OF BAFFLES OR OTHER COMPLICATIONS 



Brick Setting This is so clearly shown 
by the cuts ( Figs, i and 2 ) that extended 
description is unnecessary. It is all plain, 
straight work, which can be done by any good 
brick mason who can read lucid instructions 
and a simple drawing. No special shapes or 
other material not found in open market are 
needed. Any necessary repairs to brickwork 
can be made without disturbing the boiler 
connections. The setting is provided with 
numerous doors of ornamental design ( Fig. 
4 ) , which give access to all parts for 
cleaning. 



which only the same grate surface is available 
whether the vertical rows contain few or 
many tubes. 

Kentf says: "Coal can be burned without 
s:noke, provided: 

(I) "The gases are distilled from the coal 
slowly. 

(II) "That the gases when distilled are 
brought into intimate contact with very hot air. 

(III) "That they are burned in a hot 1 1 re- 
brick chamber. 

(IV) "That while burning they are not 
allowed to come into contact with compara- 



*As an evidence of the direct advantages resulting from this manner of supporting the boiler. we 
refer to an explosion of natural gas in the furnace of a Stirling Boiler at the American Tin Plate Com- 
pany's plant at Elwood, Ind. Although the force of the explosion \vas sufficient entirely to demolish 
the brickwork, the boiler was uninjured in any way whatever. The brick was replaced and the boiler 
put into commission, without its having been necessary to make any repairs whatsoever to the 
bciler proper. A recent similar explosion under a boiler fired with oil at Works of Santa Monica, (Cal.) 
Brick & Tile Mfg. Co. showed precisely the same result brickwork completely demolished, but boiler 
uninjured. ''(Steam Boiler Economy, First Edition, p. 156. 



ADVANTAGES OF THE STIRLING CONSTRUCTION 



11 



tively cool surfaces, such as the shell or tubes 
of a steam boiler; this means that the gases 
shall have sufficient space and time in which 
to burn before they come into contact with 
the boiler surfaces." 

The first condition demands careful firing, 
and sufficient grate surface ; this grate surface 
is available in the Stirling furnace. 



carried in stock by all fire-brick dealers, in 
contrast to the special formed bricks (ob- 
tainable only from the manufacturer) re- 
quired by many types of water- tube boiler. 
Another marked advantage of the Stirling 
baffies is that since no tubes pass between or 
through the tiles ( see Fig. 5 ) , they are not 
pried apart and made leaky by distorted 





FIG. 4. CLEANING DOORS WITH ASBESTOS PACKING WASHERS 



The second requirement is preeminently 
met by introduction of the brick arch, which 
absorbs heat from the fire, becomes an incan- 
descent radiating surface similar to roof of a 
reverberatory furnace, heats up any air ad- 
mitted over the fuel, and ignites by radiation 
the gases distilled from the coal; it insures 
an even distribution of the gases, obviates 
their concentration at any one point and 
prevents the boiler from being chilled by 
inrush of cold air when the furnace doors 
are opened. 

The third requirement is met because the 
arch in combination with the furnace walls 
forms a fire-brick chamber of large capacity. 

The fourth requirement cannot be met by 
any internally- fired boiler, or water- tube 
boiler in which tubes form the roof of the 
furnace. In the Stirling furnace the gases 
do not come into contact with tubes until they 
pass out of the fire-brick chamber under the 
arch, and this chamber is of sufficient size to al- 
low the gases space and time in which to burn. 

Baffles and Course of Gases The baffle 
walls rest directly upon the tubes, and guide 
the course of the gases up the front bank, 
down the middle and up the rear bank, thus 
bringing them into such intimate contact 
with the boiler surface that the heat is 
quickly and thoroughly extracted from them. 
In no other boiler are the gases compelled 
to travel as far before reaching the stack, 
and the effect upon economy is evident. The 
baffles are made of plain rectangular firetile 



tubes; they can be removed and replaced 
without disturbing a tube. Baffles built 
across the tubes, as in many boilers, are 
damaged by pulling a faulty tube through 
them, and can be repaired in but one way by 
removal of every tube necessary to permit a 
man to crawl in and reach the defective spot. 








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FIG. 5. ELEVATION AND SECTION OF FIRETILE BAFFLES 
IN STIRLING BOILERS 

ADVANTAGES OF THE STIRLING 
CONSTRUCTION. 

Such advantages as have not already been 
named will now be pointed out. When com- 
parisons are made with other types, they 
are given not with the intention of attacking 
or disparaging those types, but merely to 



RAPID CIRCULATION OF WATER 



bring out the superior points of the Stirling 
water-tube safety boiler. 

Simplicity There are no details of 
complicated shape; no flat surfaces, tie-rods, 
water-legs, headers, return-bends, outside 
circulating pipes to plug up ; no multitudinous 
handhole plates to be removed and packed 
with gaskets, or be ground and scraped to a 
fit whenever boiler is opened; no baffles or 
mud pipes in the drums; no short nipples, 
seams exposed to heat, or parts inaccessible 
for cleaning. 

Expansion and Contraction In the 
Stirling the mud drum is not embedded in 
brickwork, but is suspended on the tubes 
which connect it with the upper drums. 



such as caused when one side of the furnace 
is being cleaned and other side is excessively 
hot, is taken up by the curve in the tube. 
The boiler therefore stays tight, and is 
entirely free from the stresses and frequent 
leaks caused by unequal expansion of straight 
tubes rigidly connected at each end to headers, 
water-legs, or large drums.* It will thus be 
seen that the bent tube performs in the boiler 
the same function as an expansion loop in a 
steam line, and that its successful introduc- 
tion in the Stirling boiler is a distinct and 
far-reaching advance in steam engineering. 

Rapid Circulation The path of the 
circulation in the Stirling is as follows: The 
water is fed into upper rear drum, passes 





FIG. 6. FORGED STEEL DRUM HEADS AND PADS FOR WATER COLUMN CONNECTIONS 



While in many water-tube boilers the weight 
of all the tubes and heavy headers must be 
supported by a single row of nipples in front 
and another row at the rear of the boiler 
which nipples frequently work loose owing to 
the vibrations ever present in a boiler when at 
work the method of suspension in the 
Stirling is radically different; here the mud 
drum is suspended on all the long tubes and 
the weight carried by each tube in supporting 
the drum and its contained water is only 
about forty pounds. Besides this the tubes 
are curved, so that each one may independ- 
ently of the others expand or contract 

In consequence of this construction, not 
only may the mud drum with perfect freedom 
move an amount representing the resultant 
expansion of the boiler, but any difference 
in expansion between the individual tubes, 



down the rear bank of tubes to the lower 
drum, thence up the front bank to forward 
steam drum. Here the steam formed during 
passage up the front bank disengages and 
passes through the upper row of cross tubes 
into the middle drum, while the solid water 
passes through the lower cross tubes into 
middle drum, then down the middle bank to 
lower drum, from which it is again drawn up 
the front bank to retrace its former course 
until it is finally evaporated. The steam 
generated in the rear bank passes through 
cross tubes to-the center drum. 

The temperature of gases in contact with 
the tubes will evidently be greatest at the 
bottom of the front bank, and gradually 
decrease as the gases proceed along their 
course to the breeching. Obviously then the 
velocity of water circulation and quantity of 



*For a remarkable illustration of the effects of unequal expansion of such tubes, see photograph, 
pp. 546-547, in Power, Sept. 1904. 




IMPOSSIBILITY OF FORMING STEAM POCKETS 



15 



steam generated will be a maximum in the 
front bank; in the rear bank there is a slow 
circulation downward equal to the quantity 
of water evaporated in the other two banks. 
The peculiar benefits arising from this action 
will be discussed under caption "Handling 
Impure Feed Water," page 19. 

Rapid circulation is essential for the follow- 
ing reasons: 

(1) To keep all parts of the boiler at 
practically the same temperature, thus elimi- 
nating severe stresses due to unequal expan- 
sion. 

(2) To permit quick raising of steam and 
rapid response to sudden demands on the 
boiler capacity. 



the lower tubes which then become over- 
heated, and buckle and leak, and finally burn 
out. So inadequate are these nipples and 
headers that recent experiments of M. Brull 
have shown that in boilers whose circulation 
is constricted by nipples or narrow water- 
legs, the circulation in the upper tubes 
reverses, that is, it goes from the front to rear 
instead of in the opposite way as intended.* 
In consequence of this, much matter sus- 
pended in the water is swept into the bottom 
tubes, which fact, in connection with the 
steam pockets, explains why those tubes so- 
rapidly fail. 

In the Stirling boiler there is no constriction 
of the circulation, as each tube discharges 






DRUM LUG MANHOLE AND ARCH BARS STEAM NOZZLE PAD 

FIG. 7. FORGED STEEL DETAILS OF THE STIRLING BOILER 



(3) To sweep away from the heating 
surfaces all steam bubbles as fast as formed, 
and thereby prevent "steam pockets" which 
quickly burn out the tubes. This is so par- 
ticularly the case where intense local heating 
occurs due to use of gas or oil fuel, that some 
types of boiler fairly well adapted to coal 
cannot be successfully used with these fuels. 

The third requirement is met only indif- 
ferently or not at all in those types of boilers 
in which tubes often numbering as many as 
eighteen, must discharge their entire content 
of steam and water through a narrow water- 
leg, or worse still, through a single nipple 
whose cross section is equal to that of but one 
tube. At 150 pounds gauge one cubic foot 
of water, when converted into steam, will 
have a volume of about 151 cubic feet. In 
consequence of this great increase in volume, as 
soon as the boiler is forced the nipple area 
becomes insufficient, steam pockets form in 



directly into the drums, without intervention 
of headers, nipples or water-legs. The nearly 
vertical position of the tubes also promotes 
rapid circulation, hence steam pockets cannot 
form, and a fruitful cause of interrupted 
service and tube renewals in other types is 
thus eliminated from the Stirling. The 
record of this boiler affords incontestable 
evidence on this point. To cite a case: In 
a plant using Stirling boilers in connection 
with water-power, the water-wheels failed 
and required several days for repairing. As 
the service could not be interrupted the only 
recourse was to operate the boilers continu- 
ously at over 100 per cent, above rating until 
the wheels could be repaired. Considerable 
damage to the boiler was expected as a 
matter of course. When the run was over it 
was found that the furnace lining had been 
melted down f and must be renewed, but no- 
damage of any kind to the boilers not even 



*Cf. "Appareil pour 1'dtude de la circulation dans les chaudieres a tubes d'eau, par M. Brull," 
Comptes Rendus de la Societe de I Industrie Minerale. Nov. -Dec., 1901. fOil fuel was used. 



BOILER EXPLOSIONS DUE TO CAST IRON 



17 



a leaky tube was noted, and not one penny 
was expended for repairing the boiler itself. 

Safety From the foregoing it is evident 
that the Stirling is preeminently a safety 
boiler. Since all parts are of wrought metal 
and either cylindrical or spherical in form, 
so that their strength can be accurately com- 
puted, and all flat surfaces, stay-bolts and 
braces have been discarded, all tendency 



too frequently allow small differences in first 
cost to lead to the purchase of boilers inhe- 
rently weak and dangerous. 

All serious explosions result from the sud- 
den liberation of the energy contained in 
large masses of steam and water. If a 
rupture occurs in the shell of a tubular, 
flue, or cylindrical boiler, the energy of all 
the steam and water within is suddenly 




FIG. 8. STEEL FIRING AND ASH-PIT DOORS OF THE STIRLING BOILER 



to distortion under pressure is avoided. 
The design once and forever eliminates 
from boiler construction any necessity for 
that most treacherous material and fruitful 
source of ruptures in other types 
cast iron whether confessedly such, or 
disguised under such trade names as "semi- 
steel," "composition," " flowed- steel, " 
"malleable metal," etc. In many countries 
the use of cast metal is forbidden by law. 
Purchasers too often fail to realize the 
enormous power contained in steam and 
water at a high temperature under pressure, 
and that the energy stored in boilers is 
sufficient to throw them straight upward a 
height of from one to four miles, and they 



released, to the destruction of the boiler 
itself, and frequently of its surroundings, 
with accompanying loss of life The same 
disastrous consequences attend a rupture 
in a water-tube boiler when the part giving 
away contains a large quantity of steam 
and water Thus, the bursting of headers 
in the horizontal type of water-tube boilers 
is frequently accompanied by the most 
destructive results, owing to the fact that, 
although they do not in themselves contain 
large volumes of water, they are connected 
with a number of tubes, which in the ag- 
gregate, contain a very large quantity of 
water and steam; and when the cast iron 
gives away, the rupture is not confined to 



HANDLING IMPURE FEED WATER 



19 



a single spot, but extends throughout the 
entire section of the header, thus instantly 
liberating the water and steam contained 
in all the tubes expanded into it. A rupture 
in cast iron must, of necessity, extend 
throughout its entire length or breadth; 
while a rupture in wrought iron, or soft 
steel, is local, and can be enlarged only 
by the continued application of force. None 
of the so-called "safety boilers" then, in 
which cast metal is used, are worthy of the 
name. The term can be applied only to 
boilers in which all possible points of rupture 



has been so reduced that baking of the 
scale to a flinty hardness is obviated, hence 
the deposit is soft and easily removed unless 
neglected for long periods of time. Even 
in this case the tube cannot be burned be- 
cause of the low - temperature of the gases 
surrounding it. 

Hence, before passing into the front 
bank the water is purified,* and the dan- 
ger of scale formation in the parts of 
the boiler that are subjected to the highest 
temperature is greatly reduced; consequently 
the interior of these tubes remains clean, 




FIG. 9. WATER COLUMN AND CONNECTIONS, WITH QUICK-CLOSING GAUGE GLASS FITTINGS 



are confined to portions such as the tubes, 
containing small masses of water, and which 
are constructed of a material in which 
such rupture will remain local. This con- 
dition is admirably fulfilled in the Stirling 
water-tube safety boiler. 

Handling Impure Feed Water In the 
course of the feed water from the feed drum 
to mud drum any precipitate formed under 
influence of the temperature and pressure 
must drop into the mud drum, which is 
protected from intense heat of the furnace, 
and acts as an excellent settling chamber. 
The scale-forming matter which crystallizes 
out under action of the temperature and 
pressure will deposit on the rear bank of 
tubes, but since the gases have passed two 
banks of tubes before reaching those where 
the deposit is formed, their temperature 



and heat is transmitted more rapidly to 
the water, thus not only preventing the 
tubes from becoming overheated and burned 
out, but at the same time maintaining 
the efficiency of the boiler If there are 
impurities in the feed water they must be 
deposited somewhere in the boiler, hence the 
only recourse is to devise means to deposit 
them where they will do the least harm. 
This is accomplished by settling the precip- 
itates where they can be blown off without 
gathering on the heating surface, and by 
causing the scale to form on the coolest 
heating surface where it will affect the 
economy the least, and remain so soft that 
its removal is easy. All this is accomplished 
to greater degree in the Stirling than in any 
other boiler, and in many types it is not 
accomplished at all. For example, in hor- 



*This explains why the water spaces in rear and middle drum are not connected. By compelling 
all the water to traverse the rear bank it is purified before reaching the parts of the boiler exposed to 
the highest temperatures. 



CLEANING THE INTERIOR OF THE BOILER 



21 



izontal water-tube boilersf the water is 
fed into upper drums, flows to the rear, 
then down the nipples to rear header (or 
water-leg), then into the tubes. Owing 
to the constricted area of nipple and header 
the velocity of water is multiplied in pro- 
portion to the number of tubes connected 
to one header. As the capacity of water 
to convey solids varies with the sixth power 
of the velocity,! only a small portion of 
the precipitates formed drops directly into 
the mud drum, while the balance is swept 
into the tubes. As the lower tube is the 
hottest, it draws in the greatest quantity 
of water, hence forms the greatest quantity 
of scale, to which is added the precipitate 
drawn in with the water. In consequence 
the deposit on the tubes is the sum of the 
scale and the precipitate. The most vital 
point, however, is that this deposit forms 
in greatest quantity in the hottest tubes and 
burns to a flinty hardness, consequently its 
removal is tedious and costly. Owing to the 
great heat on the bottom tubes, a small de- 
posit will invariably cause the tube to burn, 
bag, or crack. 

A most fruitful cause of burnt tubes is a 
piece of scale which becomes detached and 
falls on the bottom of the tube, and the spot 
under it is certain to burn out quickly The 
Stirling is free from this source of tube de- 
struction, because while the scale will not 
form in the hotter tubes unless the boiler is 
neglected, even if it does form owing to such 
neglect and a piece becomes detached it will 
slide down to the mud drum instead of lodging. 

Cleaning the Interior By removing 
four manhole plates, which can be done in ten 
minutes, the entire boiler interior is acces- 
sible for cleaning. From the preceding 
discussion it is evident that the precipitates 
are settled into the mud drum, whence they 
are blown off at intervals ;, the scale is prac- 
tically confined to the rear bank of tubes, and 
by reason of escaping the high temperatures 
it is soft and easily detached. Consequently 
it happens in most cases that only the rear 
bank needs cleaning each time the boiler 
is opened, while the others need only occa- 
sional attention. The scale is quickly and 
cheaply removed by a "turbine cleaner" 



consisting of a cutting tool driven by a 
water turbine attached to a hose, whose 
operation requires no labor beyond that 
necessary to guide the hose and cleaner 
attached, and shift it from one tube to an- 
other. Fig. 45* illustrates one of many 
designs of turbine cleaner on the market. 
So much progress has been made in the 
development of tube cleaners that the re- 
moval of scale from tubes (no matter whether 
they be straight or curved, or whether the 
scale be heavy or light), is merely a question 
of the selection of the tool or device best 
adapted to the work to be done. The 
matter is further discussed in the chapter on 
Boiler Cleaning, page 223. 

An objection occasionally urged against 
curved tubes by those who have neither had 
experience with them nor investigated their 
great advantage is that they are difficult 
to clean, and cannot be looked through. 
Neither objection has weight. The turbine 
cleaner traverses a straight or curved tube 
with equal facility If it did not, it would 
be impossible to clean some boilers whose 
tubes, though originally straight, distort 
in service an amount often exceeding the 
curves in the Stirling tubes. 

The thickness of scale in a tube cannot be 
judged by looking through the tube, because 
if the scale has evenly formed around the 
tube a difference of three-eighths of an inch 
in the bore cannot be detected by the eye 
at a point six feet away Where the in- 
crustation is heaviest on the bottom, due to 
deposit of precipitate and scale, as common 
in all horizontal water-tubes, the departure 
from the round bore can be seen, and this 
fact doubtless lead to the belief that abil- 
ity to see through a tube is an advantage. 
The actual fact is that the only way to know 
that there is no deposit on a tube is to pass 
through it a turbine tube cleaner, or a ball of 
proper size attached to a cord, and this test 
applies equally well to all tubes whether 
straight or curved. 

Every inch of surface in the Stirling boiler 
can be reached and cleaned, and the time 
required for opening, cleaning, closing and 
steaming up the boiler is often considerably 
less than that required merely to remove 



fAttempts have been made, but without success, to provide horizontal boilers with an equivalent 
of the Stirling mud drum, One such design is shown in Power, p. 565, Sept., 1904. *Page 225. 
JIf the velocity is tripled the carrying capacity is 729 times as great, etc. 



DURABILITY AND FREEDOM FROM REPAIRS 



23 



and refit the caps over tube ends in other 
types of boiler. 

Cleaning the Exterior Ample cleaning 
doors are provided both in the sides and rear 
of the setting, so that the exterior of the 
heating surfaces may be kept clean and all 
accumulations of soot, ashes, etc., blown 
off as rapidly as they form by using a steam 
blower-pipe which is furnished with every 
boiler.* 

The tubes being only slightly inclined 



of irregular shape and uncertain strength; 
stresses due to unequal expansion; multi- 
tudes of caps, joints and nipples, and simi- 
lar objectionable details, the Stirling boiler 
is free from parts liable to get out of order. 
The prevention of scale deposits in the hottest 
tubes; the perfect facilities for keeping the 
boiler clean; the rapidity of water circula- 
tion and impossibility of forming steam 
pockets, all combine to protect the tubes 
against burning out. Hence the necessity 




FIG. 10. IRON DOOR AND FRAME IN WALL OPENING OPPOSITE MUD DRUM 



from the vertical, there is no opportunity 
for soot and dust to settle on one side or on 
top of the tubes as in boilers of the hori- 
zontal type. Furthermore, the tubes are 
in parallel rows (not staggered as in some 
other types) and so arranged that it is pos- 
sible to pass the hand, and indeed, the whole 
arm, between two rows of tubes, and reach 
those in the last tier. The exterior surfaces, 
then, may with ease be thoroughly cleaned 
of soot and kindred deposits. 

Durability By reason of the elimination 
of thick plates and riveted joints exposed 
to the fire; cast metal of all kinds; parts 



of repairs to the boiler itself is extremely 
remote. The setting is simple and substan- 
tial and not subject to derangement other 
than the natural wear of furnace lining. 

In consequence the Stirling has earned an 
enviable reputation for durability and light 
cost of repairs. That this reputation is 
merited is evidenced by fact that according 
to statistics recently received from a plant 
operated by careful and intelligent engineers 
the records show that on basis of equal 
horse-power hours the tube renewals in the 
Stirling as compared with those on a promi- 
nent type of horizontal water-tube boiler 



*The importance of being able to clean a boiler thoroughly, outside as well as inside ,and of keeping it 
clean, was well demonstrated by a comparative test made by one of our engineers some time ago on a 
boiler which had been allowed to run some months without cleaning, and accumulate a thickness of 
one-eighth inch of soot on the tubes. Before cleaning the evaporation was found to be 8.04 pounds of 
water per pound of coal; and after cleaning the evaporation per pound of coal was 10.30, a gain of about 
28 per cent. 



STEAM AND WATER SPACE 



25 



of steel header construction were in ratio of 
i to 61, the relative maintenance account 
in other respects was as i to 3, and the labor 
of cleaning 6 to 35, all in favor of the Stir- 
ling.* 

Facility for Making Repairs Practically 
the only repairs needed to the Stirling boiler 
will be tube renewals, and unless the boiler 
is grossly neglected such renewals will be 




FIG. 11. PHOTOGRAPHS SHOWING DISTENTION OF TUBES 
AT POINT OF RUPTURE 

needed only after many years, as evidenced 
by fact that Stirling boilers have been in 
service for eight years, using hard coal, 
bituminous coal, natural and forced draft 
and oil fuel, without losing a tube or even 
developing a leak. Should tube renewals 
become necessary they are quickly and 
easily made. 

All tube failures reduce to four classes: 
(T) Pitting, which causes pin holes to 
be formed. 

(2) Defective welds, which cause the tube 
to open as in A, Fig n. 

(3) An initial bagging resulting in a 
rupture, as in B. 

(4) Scabbing and blistering as in C. 
In the first case, the tube is not enlarged, 

and may be drawn through a tube sheet, 
without disturbing other tubes, though 
usually with difficulty owing to deposits on 
the outer surface. 



In the other cases, the tubes become 
larger than their original size, hence they 
cannot be drawn through the tube sheet, 
water-leg or header, unless they are split 
and collapsed inch by inch for their entire 
length beyond the point of failure, and if 
they also pass through cross baffles the en- 
largement will pull out the bricks and de- 
stroy the baffle. To remove a tube in this 
way "is the work of days, and in consequence 
the actual method used is to cut out all 
tubes numbering at times half a dozen 
below the defective one and to avoid de- 
stroying the baffles these tubes are cut into 
several pieces. 

In the vertical types of water-tube boiler 
more recently introduced the tubes are 
crowded together so closely that not only is 
it necessary to cut out every tube in front 
of the defective one numbering at times 
nearly a dozen but the brickwork must 
be removed to gain access to the tubes 

Removal of tubes from the Stirling is ex- 
tremely simple. As the boiler is now con- 
structed the tubes are spaced as in Fig. 1 2 , 
and each alternate space is one-half inch 
wider than the tube diameter; to remove 
an inner tube it is merely necessary to cut 
the tube as near the tube-sheet as possible, 
pass it out through the wide space between 
the tubes, as indicated by the arrows in Fig. 
12, and then remove it from the setting 
through either the side or front doors pro- 
vided for that purpose. Consequently, any 
tube in the Stirling boiler as now constructed 
may be replaced without either disturbing 
any other tube, distorting the tube sheet, or 
damaging the firetile baffles. 




FIG. 12. TUBE SPACING IN STIRLING BOILERS 

Steam and Water Space Unless pro- 
vided with sufficient steam and water space, 
a boiler will be subject to sudden fluctuations 
of pressure; the water level will be unsteady, 



*Also see Table i, page 33, referring to boilers at World's Columbian Exposition. 



OPERATION AT HIGH AND LOW RATES OF EVAPORATION 



27 



and the steam will frequently be wet. Some 
prominent types of water-tube boiler use 
but one drum for from four to nine sections 
of tubes, but two drums from ten to sixteen 
sections, and three drums from eighteen 
to twenty-one sections. Hence for their 
entire range there are but three drum com- 
binations, and the steam and water space 
varies not with the boiler horse-power but 
in wide jumps between combinations. In 
the vertical water-tube boilers there is 
usually for all sizes but one top drum of very 
limited steam and water capacity. 

In the Stirling boiler there are three upper 
drums, which afford large steam and water 
spaces, and these vary strictly with the 
boiler horse-power, since increased capacity 
is gained, not by stacking up tubes in suc- 
cessive horizontal layers without increase 
of drum capacity, but by adding sections 
of tubes to the boiler width, and increasing 
the drum lengths in proportion 

Dry Steam The production of dry steam 
requires large disengaging surface; while 
in many types of boiler the effective disen- 
gaging surface is only a narrow strip over 
the nipples and water-legs (which explains 
why such boilers have to be provided with 
internal baffles of various kinds,*) in the 
Stirling the entire water surface of the 
three upper drums is available as disengaging 
surface, hence the steam does not disturb 
the water surface, and is dry. As there is 
no constriction of the water circulation, 
and as the middle drum from which the 
steam is drawn is somewhat higher than 
the other two drums, and the circulation 
of the water in this drum is downward, 
there is absolutely no spurting or geyser- 
like action of the water in this drum. The 
steam from the front and rear drum must 
also pass through hot circulating tubes which 
dry it before it reaches the central drum. 

Adaptation to Different Kinds of Fuel 
The large space available for furnace under 
the Stirling enables the grates to be pro- 
portioned for coal of the cheapest grade. 
By proper reduction of this grate surface, 
the requirements for better grades of coal 
can be exactly met. Should it be desired 
to burn wood, the most perfect form of 
wood furnace can be got simply by lowering 



the grates to level of firing floor. For burn- 
ing oil or gas, the only change needed from 
the standard furnace is to cover the grates 
with fire-brick so disposed as to admit the 
requisite quantity of air, and to provide 
at rear end of the grates a loose checkerwork 
wall of fire-brick against which the heat 
will impinge. Should it be necessary to 
change from oil or gas to other fuel, the 
Stirling furnace in an hour after shutting 
off the burners can be made ready for firing 
with coal, shavings or sawdust. For burning 
bagasse it is necessary only to provide 
proper feeding apparatus and suitable grates, 
and the furnace thus equipped may with 
equal success be used for other fuels. Con- 
sequently, with but trifling changes the 
Stirling furnace can be adapted to any kind 
of fuel, and in no case will there be any 
essential departure from the general design, 
or removal of the arch which forms the fire- 
brick chamber necessary for a perfect furnace. 

The Stirling furnace is also well adapted 
to installation of any of the various stokers 
in use, and to such modifications as are de- 
sirable when the boilers are installed in con- 
nection with coke ovens, heating furnaces, 
reverberatories for copper smelting, and 
other cases where the boilers are fired either 
wholly by waste gases, or partly by waste 
gases, and partly by hand. 

Possibility of Driving at both Low and 
High Rates of Evaporation without Great 
Loss of Fuel Economy This is a point of the 
highest importance in plants where peak loads 
occur. To install boiler capacity sufficient 
to handle the peak at regular rate of evapo- 
ration would require large initial cost, hence 
the usual procedure is to work the boilers 
above rating during the busy hours Unless 
the boiler can respond without material 
decrease in economy at the increased rate 
of working there will be large wastes of 
fuel. 

The Stirling boiler meets this require- 
ment to a degree not attainable with other 
types, because of its free circulation and 
the action of the rear bank of tubes. Here 
the gases come into contact with those parts 
of the boiler which receive the feed-water, 
hence the temperature difference between 
gases and water is a maximum, and the heat 



*See "A bad case of discharge of water with steam from water-tube boilers." Vol. XXVI, Transac- 
tions American Society of Mechanical Engineers. 



FUEL EFFICIENCY 



29 



is quickly abstracted from the gases. The 
economy therefore decreases very slowly 
as the rate of driving is increased, and this 
is evidenced by recent tests in which a Stir- 
ling boiler when driven at rates of 60 and 
100 per cent, above rating, showed diminu- 
tion in economy of but 5.11 and 7.66 per 
cent., respectively, below the efficiency at 
rating. 

Adaptation to Hot=Water Heating A 
unique illustration of the advantage result- 
ing from the absence of all constriction in 
the path of circulation in the Stirling boiler 
is afforded by the extensive use of this boiler 
in hot-water heating plants. For such work 
a free passage of the water in its course 
through the boiler is absolutely essential. 
This requirement is perfectly met in the 
Stirling, and the same boiler, according to 
the necessities of the plant, is used to generate 
steam at one time, and at other times to heat 
water which is pumped through the hot- 
water mains. 

Space Occupied The Stirling design is 
so flexible that the boiler can be and is built 
to meet the varying requirements of height, 
width and depth, so that a 200 horse-power 
boiler can be built to occupy from 12 to 22 
feet in height, 8 to 15 feet in width, and 14 
to 17 feet in depth. It is therefore equally 
well adapted to boiler-rooms having low 
ceilings and ample width, as well as to those 
having little width and ample height. More 
horse-power of the Stirling type can be in- 
stalled in a given number of cubic feet than 
of any other type on the market. 

BOILER EFFICIENCY 

Of all the terms relating to boiler perform- 
ance, none is so much talked of, yet so im- 
perfectly understood and erroneously applied 
as the word efficiency. It is therefore neces- 
sary that the different meanings of this 
word be clearly understood. 

"Fuel Efficiency" is the ratio between the 
heat absorbed by the boiler and the heat 
value of the fuel burned. In nearly all 
cases where the term boiler efficiency occurs 
it is used in this sense, yet this efficiency 
is quite secondary in importance to another 
which is thus defined: "The 'Commercial 
Efficiency,' or the 'Efficiency of Capital' 

*Thurston, "The Steam Boiler," page 475. 



employed in the maintenance of steam 
generating apparatus of a given power, is 
measured by the ratio of quantity of steam 
produced to the total cost of its continuous 
production. This efficiency is a maximum 
when that cost is a minimum."* Accordingly, 
the Stirling boiler will be considered with re- 
spect to both of the above named efficiencies. 

Fuel Efficiency The boiler can only ab- 
sorb heat, but the production of that heat 
depends upon the furnace, consequently the 
fuel efficiency is not properly boiler efficiency, 
but efficiency of the combination of boiler 
and furnace. A deficiency in either of these 
will affect the efficiency of the combination. 

The preceding discussion has set forth 
the capabilities of the Stirling furnace to 
handle each and any kind of fuel in use, 
and to insure complete combustion of the 
gases distilled from fuels containing high 
percentages of volatile matter, and to prevent 
extinguishment of the flame by contact 
with cool boiler surfaces over the fire. The 
Stirling furnace, therefore, leaves nothing 
to be desired, and its efficient performance 
is merely a matter of proper attention from 
the fireman. 

In regard to the Stirling boiler proper, it 
has already been shown: that the surfaces 
between the heat and water are thin, hence 
absort} the heat quickly; that the circulation 
is extremely rapid, so that the steam as 
fast as formed is carried away, and the 
heating surface kept covered with water; 
that the scale is formed on the coolest sur- 
faces where it affects the economy the least, 
and that its removal is so easy that every 
inch of surface of the boiler can be kept 
clean and efficient; that the course of the 
gases in contact with the tube surface is 
longer than in other types of boiler, so that 
the heat is thoroughly abstracted; that in 
the rear bank of tubes the coldest water 
comes in where the coldest gases go out, 
hence the flow of water and gas is in opposite 
directions in conformity with Rankine's 
law of economy; that leaky cross-baffles 
have been eliminated, hence there can be 
no short-circuiting of the gases to the stack; 
that the setting is simple and tight, hence 
air leakages are obviated; and that there 
are no exposed surfaces to cause loss by 
condensation. 




SHERRY BUILDING, NEW YORK, OPERATING 775 H. P. OF STIRLING BOILERS 

3 



COMPARISON OF TIME REQUIRED FOR CLEANING 



31 



In consequence of these features, the 
Stirling boiler develops a fuel efficiency as 
high as ever attained under any type of 
boiler, and with reasonable care its efficiency 
will continue unimpaired with use. 

In practically every case where efficiency 
tests are exhibited, they were made on 
boilers which were thoroughly cleaned and 
handled by an expert. That efficiencies thus 
obtained do not represent results obtainable 
in daily work will be evident upon consider- 
ing that the moment a boiler begins a run, 
its surface acumulates incrustation from 
the water. In the preceding part of this 
article it has been clearly shown that in 
many types of boiler the deposits form on 
the hottest tubes, where beside quickly de- 



Efficiency of Capital Invested Boilers 
are used to earn money, and what the boiler 
owner wants to know is "What boiler from 
the day I buy it until it goes to the scrap 
pile will return me the most money for every 
dollar I invest in buying and maintaining 
it?" Few realize that while a boiler may 
be efficient in fuel, it may still be a very 
undesirable investment. The chief factors 
which determine the excellence of a boiler 
are, in order of their importance: (i) 
Safety; (2) Cost of maintenance; (3) Cost of 
cleaning; (4) Fuel economy; (5) First cost. 

Each of these has been so fully discussed 
in its place that the further discussion of 
only two of them will readily indicate the 
bearing of the others. 





FIG. 13. COUNTERBALANCED STEEL FIRE DOORS AND FRAME 



stroying the tube, they affect the economy, 
which rapidly falls off as the length of the 
boiler run increases. In consequence it 
will be found that after several weeks the 
efficiency reaches a low figure out of all pro- 
portion to the efficiency of the boiler when 
clean. The effective efficiency of the run 
is only the average of the efficiencies at the 
beginning and end of the run a fact so 
seldom realized that a more general under- 
standing of it would prove of inestimable 
benefit to the boiler purchaser. 

In consequence of the difference between 
the Stirling and other types in the manner 
of depositing scale, it will be found that 
while when clean the two types of boiler 
may develop the same efficiency, the differ- 
ence at the end of the run will be largely 
in favor of the Stirling. Table 60, page 208, 
gives results of many tests on Stirling boilers. 



For the first case the financial aspect of 
the difference in time required for cleaning 
the various types will be considered. It 
has been shown that the time required to 
open, clean, close and steam up a Stirling 
is often less than that needed simply to 
remove and refit the caps in other types. 
The labor costs are frequently 5 to i , and the 
time the boiler is off 4 to i, both in favor 
of the Stirling. A point even more impor- 
tant, but which is frequently overlooked, 
is that every day a boiler is off for repairs 
means that much capital earning nothing, 
the capital being not only that invested in 
the boiler, but in piping connected to it, 
buildings housing it, and ground upon which 
it stands. Assume that cleaning is neces- 
sary every four weeks. In this time a Stirl- 
ing will be off one day, and the cap types 
be off four days. The difference, three days, 



CONCLUSIONS FROM PRECEDING DISCUSSION 



33 



is ten per cent, of a month, hence it follows 
that apart from the fourfold cost of cleaning 
the cap type boiler, that type will per annum 
produce ten per cent, fewer horse-power 
hours, or in other words, for the same output 
of steam ten per cent, greater capacity of cap 
type boilers than Stirlings will be necessary, 
disregarding the additional time lost by the 
cap types, owing to more frequent tube 
renewals. 

For the second case a comparative list 
of repairs of different types as installed at 
the World's Columbian Exposition, Chicago, 

TABLE 1 

A MEMORANDUM SHOWING CAUSES OF WITHDRAWAL 
FROM SERVICE, AND REPAIRS, ON SIX TYPES OF 
WATER-TUBE BOILERS, AT THE WORLD'S COLUM- 
BIAN EXPOSITION, FROM MAY i TO NOVEMBER 
i, 1893. 



STIRLING 2700 H. P. 


SQUARE HEADER 


July 5. Caulking Shell. 


TYPE 1500 H. P. 


Sep. 27. Burned Tube. 
Oct. 11. Burned Tube. 


July 12 Leaking Tubes. 
1 8 Burned Tubes. 




Aug. 5 Burned Tubes. 




8 Changing Tubes. 


SINUOUS HEADER 


10 Changing Tubes. 


TYPE 3000 H. P. 


1 1 Leaking Tubes. 
25 Changing Tubes. 


May 24. Three headers broke, 
one tube burst, No. 
7 boiler. 


Oct. 12 Putting in Tubes. 
15 Replacing Tubes. 
1 8 Replacing Tubes. 


June i. Tubes out of order. 
3. Bad Tubes. 


HEADER AND RETURN- 


8. Bad Tubes. 


BEND TYPE 1500 H. P. 


14. Tubes leaking. 
26. Replacing Tubes. 
July 17. Replacing Tubes. 
22. Replacing Tubes. 
Aug. 13. Tubes out. 
22. Changing Tubes. 
30. Leaking Tubes. 
Sep. 22. Burned Tubes. 
25. Burned Tubes. 
2Q. Changing Tubes. 
Oct. 8. Leaking Tubes. 
10. Leaking Tube?, 
ii. Burned Tubes. 
15. Burned Tubes. 


June 28. Replacing Tubes. 
July 5. Repairing Boiler. 
1 6. Replacing Tubes. 
22. Replacing Tubes. 
Aug. 15. Changing Tubes. 
30. Leaking Tubes. 
Sep. 8. Leaking Tubes. 
13. Leaking Tubes. 
15. Changing Tubes. 
215. Leaking Tubes. 
28. Burned Tubes. 
Oct. 8. Burned Tubes. 
17. Burned Tubes. 
19. Burned Tubes. 




24. Burned Tubes. 


SQUARE HEADER 
TYPE 3750 H. P. 


IRREGULARLY SHAPED 
HEADERS 1500 H. P. 
July 5 Repairs on Boilers. 


July 20. Replacing Tubes. 
25. Replacing Tubes. 
Aug. 3. Leaking Tubes. 
7. Leaking Tubes. 
29. Two Tubes out. 
Sep. o- Burned Tubes. 
12. Leaking Tubes. 


22 Burned Tube. 
28 Repairing Tube. 
Aug. i Repairs on Boilers. 
10 Replacing Tubes. 
13 Replacing Tubes. 
20 Working on Boilers. 
Oct. 17 Leaking Tubes. 


14. Burned Tubes. 
21. Leaking Tubes. 


WATER-LEG TYPE 


25. Leaking Tubes. 


4500 H. P. 


Oct. 5. Leaking Tubes. 


Sep. 24. Burned Tubes. 


10. Burned Tubes. 


28. Burned Tubes. 


15. Replacing Tubes. 


Oct. 4. Burned Tubes. 


26. Engineer in charge 


12. Burned Tubes. 


ordered fireman not 


15. Burned T'bs in 4B'lrs. 


to fire No. i Boiler. 


22. Burned Tubes. 


Cause not known. 


26. Burned Tubes. 



1893, will be presented, as evidence of the 
relative durability and repair account of 
the boilers when operating under identical 
conditions, with the same water and fuel. 
The purpose of this comparison being to 
illustrate the performance of types, and not 
of particular boilers, the names of the various 
competing boilers will be suppressed. 

Imitations One of the strongest testi- 
monials of the excellence of the Stirling boiler 
is the vigor with which attempts have been 
and are being made to imitate it. As the 
circulation in the Stirling is one of its most 
prominent advantages, some imitators at- 
tempt to reproduce this circulation to some 
degree, but with an altered arrangement 
and number of tube banks and drums. In 
other respects the constructive features 
peculiar to the Stirling boiler are copied as 
closely as is thought safe. 

In another class of imitations some part 
of the Stirling boiler, as for example two 
drums and their connecting tubes, is ex- 
ploited as a new type of boiler, and great 
stress is laid upon the fact that curved tubes 
are used. While the curved tubes are a 
great advantage, these abbreviated types 
have merely resurrected many ancient de- 
fects which the Stirling was designed to 
bury. Thus, if the water is fed into their 
upper drum, wet steam results; if fed into 
the lower drum, the hottest tubes rapidly 
scale up, just as in the horizontal type of 
water-tube boilers. Besides deficient steam 
and water space, none of these arrangements 
even remotely reproduce the effect of the 
feed drum and rear bank of tubes in the 
Stirling boiler. 

Conclusions The final judgment as 
to the merit of a boiler must rest with those 
who, by long experience with it, have as- 
certained its virtues or its failures, and from 
their verdict there can be no appeal. When 
judged by this standard, the finding is over- 
whelmingly in favor of the Stirling. No 
other boiler ever placed upon the market 
has so quickly met with popular favor, 
retained that favor, and had such phenom- 
enal sales. In consequence over 2,000,000 
horse-power are in use, in all parts of the 
world where the value of human life and 
the economical generation of steam are 
understood and appreciated. 



Water-Tube versus Fire-Tube Boilers 



In proportion as the use of steam has 
become more general and its economical 
generation has become better understood 
the water-tube boiler has rapidly displaced 
other types, until it is now used exclusively 
in all plants in which safety and economy 
are considered. Marine engineers, through 
excessive conservatism, have been slow in 
adopting the water-tube boiler, but the 
advantages of that type have been so clearly 
proved that to-day the use of water-tube 
boilers in the merchant marine is rapidly 
increasing, while the great naval powers, 
including the United States, have adopted 
for war vessels the water-tube boiler to the 
exclusion of other types. It must, there- 
fore, be evident that the water- tube boiler 
possesses advantages which make it superior 
to the types it has displaced, and some of 
these advantages will now be set forth. 

Safety The advent of high pressure was 
one of the strongest factors in forcing the 
adoption of the water-tube boiler. To make 
this clear, a gauge pressure of 200 Ibs., and 
an allowable stress of 12,000 Ibs. per square 
inch on boiler steel will be assumed, and 
neglecting the weakening effect of joints, 
the thickness of plate necessary for cylinders 
of various diameters will then be, 



DIA. CYLINDER, 

INCHES. 

3i 
36 
48 
60 
72 
108 

I2O 
144 



THICKNESS 
INCHES. 

. O2O 
0.300 

o . 400 

0.500 

o. 600 
o . 900 

1 . OOO 
I . 2OO 



The rapidity with which the plate thickness 
increases with the diameter is apparent; in 
practise all the above thicknesses, except 
the first, have to be augmented 30 to 40 
per cent, because of riveted joints. 

In water-tube boilers the drums seldom 
exceed 48 inches diameter, hence the thick- 
ness of plate required is never excessive. 
The thinner metal can be rolled of more 



uniform quality, the seams admit of better 
proportioning, and the joints can be more 
easily and perfectly fitted than when thicker 
plates are used. 

The 3^ inch tube is a standard size in the 
Stirling boiler, and for 200 Ibs. pressure a 
tube of No. 10 gauge is used. The thickness 
is 0.134 inch and with the same working 
stress as used in computing the above table 
the safe pressure would figure 1,072 Ibs. 
which will indicate the margin of safety. 

The essential constructive difference be- 
tween the water-tube and fire-tube types 
is that the former is composed of parts of 
relatively small diameter, and a rupture 
of a part must of necessity be local. The 
drums are so disposed that they are pro- 
tected from intense heat, and in the Stirling 
boiler there is a further advantage due to 
elimination of riveted joints exposed to 
high temperature. The greatest heat strikes 
on the tubes, hence the tubes are necessarily 
the parts which are most liable to wear and 
deterioration. If a tube fails it can instantly 
discharge only the water it contains, while 
the water in the other tubes must travel a 
considerable distance to reach the point 
of rupture. The quantity of water that 
can flow in a given time is limited by the 
bore of the tube, hence the results of a tube 
failure may cause inconvenience and require 
a shut down, but no considerable damage 
to property can be don?. 

Boilers of the shell type embody 'the un- 
desirable necessity of "putting one's eggs 
all in the same basket. " Not only are the 
shells subject to influences tending far more 
to rupture them than in case of drums in 
the water-tube type, but when they do 
rupture the whole body of contained water 
is liberated, and a disastrous and usually 
fatal explosion results. This is well evidenced 
in a recent case where a return tubular boiler 
made by a leading manufacturer, lately 
inspected and declared by competent au- 
thorities to be well constructed, and free 
from defects, exploded and killed 42 persons, 
besides causing large property loss. This 
typical case is merely one of a vast number 



QUICK STEAMING 



37 



which could be cited. The photograph on 
page 36 illustrates the disastrous results of 
the failure of a small return tubular boiler. 
This boiler was installed in a saw mill and 
exploded in November, 1904. The boiler 
house and the brick stack were both com- 
pletely demolished, and an empty boiler 
adjoining the exploded one was thrown 
outside the building and fell beside the shed 
in the background. It must therefore be 
remembered that when boilers explode, 
they wreck not only themselves but con- 
tiguous buildings, hence a water-tube boiler, 
in addition to its other advantages, is de- 
sirable as a matter of insurance against 
explosion. 

To the above mentioned advantages of 
the water-tube type the Stirling boiler adds 
additional advantages peculiar to itself. 
The elimination of all cast metal, compli- 
cated joints, riveted joints exposed to fire, 
stayed surfaces, and parts of irregular shape, 
increases the element of safety. A further 
advantage is the elimination of all com- 
pressive stresses. A cylinder subject to 
external pressure, as a fire-tube, or the in- 
ternally-fired furnace of certain types of 
boiler, will collapse under much less pressure 
than it could stand if applied internally; 
if any initial distortion from its true shape 
exists, the effect of the external pressure 
is to increase the distortion and collapse 
the cylinder, while an internal pressure tends 
to restore it to its original shape. 

Elimination of Temperature Stresses 
Stresses due to unequal expansion have been 
a fruitful source of trouble in fire-tube boilers, 
In water-legs, under internally-fired furnaces, 
and below the tubes, the circulation is de- 
fective. In consequence, leaks are common, 
and cause unsuspected corrosion in parts 
of the boiler that are not visible; stresses 
due to unequal expansion of the metal cannot 
be avoided, and these are often so excessive 
that the safety of the boiler is endangered, 
and many a disastrous explosion has been 
traced to this source. 

If the temperature on the fire and water 
sides of a plate be kept constant, the rate of 
transmission of heat is, within reasonable 
limits, but little affected by the plate thick- 
ness. In practical work such constant tem- 
peratures are not maintained, owing to 



fluctuations due to firing, and the variation 
in the demand for steam. If the furnace 
temperature be quickly increased in response 
to a sudden demand for steam, the plate 
itself must absorb the heat to elevate its 
temperature, hence if the plate be thick the 
heat transmission to the water must be 
sluggish, and the steam pressure cannot be 
quickly increased. An even more trouble- 
some feature in large shell boilers is the ab- 
solute necessity of firing them up very 
slowly, to allow their parts gradually to 
expand. This often takes 12 hours, and 
besides wasting fuel, it renders the boiler 
useless in emergencies. To diminish this 
evil artificial means of circulating the water 
are often used, such as " Hydrokineters " 
and circulating pumps, but they are merely 
slight palliations, and not remedies, as 
evidenced by the following statement from 
a prominent marine engineer : 

"Those of us who have had to do with 
the maintenance of Scotch boilers know 
what a continual round of expensive re- 
pairs have to be made at nearly every in- 
spection, and in almost every case the causes 
are due to straining because of unequal 
expansion. * * * There are Scotch 
boilers running at a working pressure of 150 
Ibs., upon the bottom of the shell of which 
the bare hand may be placed without any 
inconvenience. " 

These troubles are wholly obviated in the 
Stirling water-tube boiler. The metal ex- 
posed to heat is thin, hence the pressure 
rapidly responds to an increase in the furnace 
temperature. Circulation is rapid and takes 
place in a definite path which is arranged in 
conformity with the law of greatest economy. 
The rapid circulation practically equalizes 
the temperature in all parts of the boiler, 
and the arrangement of parts is such that 
temperature stresses are eliminated. Leaks 
and corrosion due to them are obviated, and 
the repair bill is lessened. 

Quick Steaming The thin metal in the 
tubes and the elimination of temperature 
stresses in the Stirling boiler permit steam 
to be raised so rapidly that in emergencies 
the boiler can be pressed into service and 
operated at a high capacity, long before a 
boiler of the shell type could safely be brought 
up to pressure. A unique illustration of 




FORD PLATE GLASS CO., TOLEDO, O., OPERATING 4.0OO H. P. OF STIRLING BOILERS 



EFFICIENCY DECREASED BY INCRUSTATION 



39 



the adaptability of the water-tube boiler in 
situations where sudden loads are to be 
encountered is afforded by a plant generating 
current for electric locomotives pulling trains 
through a long tunnel. When no train is 
passing there is no load on the plant, the 
engines turn slowly, and the boilers have 
little to do. A few moments before a train 
arrives a signal is given, the draft is turned 
on the boilers, steaming at full rate at once 
begins, the engines are speeded up, and the 
train upon arrival at the tunnel is at once 
pulled through. The method of operating 
the water-tube boilers saves a large amount 
of fuel which would be necessary for any 
other type of boiler which cannot almost 
immediately respond to sudden demands for 
steam. 

Cleaning In order that a boiler may be 
cleaned thoroughly it is necessary that every 
inch of its interior surface be accessible. 
This requirement cannot be met in fire-tube 
boilers. The tubes are nested together, 
and when incrustation forms upon them it 
can be removed only from such surfaces 
as can be reached. With a space between 
tubes often less than i\ inches all that can 
be done is to pass in the vertical spaces a 
thin sharp-pointed tool which can remove 
only a limited amount of the deposit on the 
side of the tube. In consequence nearly 
the entire tube circumference is inaccessible. 
The efficiency of the boiler rapidly falls off, 
and if the tubes get very hot they burn, so 
that frequent renewals are necessary. In 
the Scotch marine type, even when the engines 
operate condensing, tube renewals at inter- 
vals of six to seven years are necessary, and 
renewals in less than a year are sometimes 
required. In return tubulars operated with 
very bad water annual tube renewals are 
not uncommon. In the return tubular much 
sediment falls on the bottom sheets where 
owing to the great heat it bakes to such ex- 
cessive hardness that the only method of 
removing it is to chisel it out. This can be 
done only when sufficient tubes are omitted 
to leave space for a man to crawl in, and the 
discomforts under which he must work are 
apparent. Unless this deposit be removed, 
a burned and bagged plate will be the inevi- 
table result, and unless attended to in time 
an explosion will follow. 



The deposit of mud in water-legs of some 
types of boiler is an active agent in causing 
corrosion, and the difficulty of removing 
this deposit through hand holes is well 
known. A complete removal is practically 
impossible, and as a last resort to obviate 
corrosion it is common to make the bottom 
of the water-legs of copper. 

The soot and fine coal swept along by the 
draft will settle in the fire-tubes, and unless 
promptly removed it often hardens so that 
it must be cut out with a special form of 
scraper. It is not at all unusual, when 
soft coal is used, to find the fire-tubes half 
filled with soot, which not only renders use- 
less a large part of the heating surface, but 
diminishes the draft, so that it is difficult 
to develop the heat necessary to secure 
capacity from the heating surface that is 
left. 

The effects above named are diminished 
in varying degrees in some water- tube boilers, 
but are wholly obviated in the Stirling. The 
manner in which this boiler handles impure 
water and minimizes formation of scale has 
been described on page 19, and the methods 
of removing this scale are given in the chap- 
ter on Boiler Cleaning. Every inch of in- 
terior surface can be reached and kept clean. 

The deposit of soot on the outside of a 
horizontal tube is less than when deposited 
inside, but it is nevertheless sufficient greatly 
to reduce the effective heating surface. The 
nearly vertical tubes in the Stirling obviate 
this, since none of the fine material carried 
over by the draft can rest on the tubes, and 
the only deposit will be the soot or tarry 
matter which condenses from the gases. 
Even this can be blown off while the boiler 
is under pressure, while to expose the tube 
sheet of a fire-tube boiler when under steam 
would be a hazardous risk, because of the 
sudden contraction due to inrush of cold air. 

Efficiency What a boiler may do when 
clean, and what it does do when foul are 
very different things, and the magnitude of 
the difference is seldom understood by owners 
of boilers. It must be remembered that the 
moment a boiler begins work its heating 
surface begins to foul both inside and out. 
When a boiler has been operated several 
months without cleaning its efficiency may 
drop off by as much as 30 per cent, or more, 




ARMOUR INSTITUTE, CHICAGO, ILL., OPERATING 1 , 1 5O H. P. OF STIRLING BOILERS 



ADAPTABILITY OF THE WATER-TUBE TYPE 



41 



and in case of very bad water this result 
may happen in a much shorter time. The 
results will be worse in proportion as the 
deposits form on the hotter surfaces, yet in 
the return tubular type the sediment drops 
to the bottom of the shell, sweeps forward 
where the surfaces are hottest, and drops 
where it affects the economy the most. The 
tubes then foul up, and the impossibility 
of thoroughly cleaning them has been pointed 
out. The readiness with which deposit 
forms on crown sheets of fire-box boilers, 
and the large furnaces of internally-fired 
types is too well known to require comment. 

In the Stirling boiler the action is entirely 
different. The sediment is removed and 
blown out, and the scale forms on the coolest 
part of the boiler, as explained on page 19, 
hence the initial efficiency is not only higher 
than in the other types because of the su- 
periority of design, but it does not diminish 
so rapidly when the boiler is in use. 

Efficiency depends not only upon the degree 
to which the boiler absorbs heat, but also 
on the degree to which the furnace can de- 
velop the heat to be absorbed. The poorer 
the fuel the more impossible it is to develop 
its heating value when the gases, before the 
combustion is completed, come into contact 
with the shell as is the case in return tubulars, 
or with furnace walls surrounded by water, 
as in internally-fired types. The furnace 
must be practically enclosed in fire-brick, 
and this requirement is perfectly met in the 
Stirling furnace. The matter is further 
discussed in the chapters on "Fuel Burning" 
and "Steam Boiler Efficiency." 

Repairs The possession of great strength; 
the elimination of stresses due to uneven 
temperatures, and of leaks and the corrosion 
due to them; the protection of the drums 
from external heat; and prevention of de- 
posits on the hottest tube surfaces, all unite 
to obviate necessity of repairs. The tubes 
are the only parts in the Stirling boiler which 
may need renewal, and then only at infrequent 
intervals. Such renewals can be quickly 
and cheaply made. In fire-tube boilers 
tube renewals are a much more serious un- 
dertaking. As the tubes are enlarged by 
accumulations of hard deposit they cannot 
be drawn through the tube sheet unless they 
are collapsed inch by inch for their entire 



length; consequently it is usual to cut out 
all tubes necessary to give access to the de- 
fective one, and the tubes so cut are passed 
out of the manhole. In case of a bagged or 
blistered sheet the defective part must be 
cut out by hand, tap holes be drilled by 
ratchets, and as it is impossible to get space 
in which to drive rivets, a "soft patch" is 
necessary. This is only the sorriest of make- 
shifts, and usually will result in requiring 
the working pressure to be reduced, or a 
new plate to be put n. To do the latter the 
old plate must be cut out, a new one must be 
scribed to place so as to locate rivet holes, 
and in order to secure room in which to 
work when driving rivets the boiler must be 
retubed. The setting of course must be partly 
torn down, and then replaced, so that the 
final cost wil usually be considered greater 
than the initial cost of a Stirling boiler. In 
case of a rupture the water-tube boiler would 
lose a tube or two which can be quickly 
replaced; the fire-tube boiler will be so com- 
pletely demolished that the question of re- 
pairs will be shifted from the boiler to the 
surrounding property, and the damage done 
to this property will usually exceed many 
times the cost of a boiler of a type which 
would have eliminated all possibility of the 
explosion. The boiler purchaser must con- 
sider that not only are the current repairs of 
the Stirling much less than required for the 
fire-tube types, but that as a business prop- 
osition it is not wise to invest large sums 
m equipment which, through a possible 
accident to the boiler, may be either wholly 
destroyed, or so damaged that the cost of 
repairing it, and the loss of business until 
the repairs are made, would purchase boilers 
of absolute safety and leave a large margin 
beside. Add to this the possible loss of 
human life, and the true repair account to be 
considered when purchasing a boiler will 
receive more consideration than is usually 
accorded to it. 

Adaptability The super ority of the 
water-tube type when sudden loads are fre- 
quent has been pointed out. It is often con- 
tended that the fire-tube boiler is preferable to 
the water-tube when operating under variable 
loads, for the alleged reason that the greater 
amount of water in the shell type acts as a 
reservoir of heat, so that upon a reduction 



SPACE REQUIRED BY STIRLING BOILERS 



43 



in the steam pressure the stored heat imme- 
diately generates sufficient steam to meet 
the demand. In reply it need only be said 
that so far as the Stirling is concerned it 
often contains per square foot of heating 
surface, or per horse-power, as much water 
as the return tubular, and much more than 
some other types. Apart from this, the 
argument is also unsound. The total heat 
of steam at 150 Ibs. gauge pressure is 1193.5 
B. T. U., and at 100 Ibs., 1184.9 B. T. U.; 
difference 8.9 B. T. U. As the latent heat 
of steam at 100 Ibs. gauge is 876.5 B. T. U. 
it will be seen that a drop of 50 pounds 
would be necessary to provide heat enough 
to evaporate only one per cent, of the water 
in the boiler, consequently a drop of sufficient 
magnitude to have any practical influence 
in generating extra steam would go beyond 
the limits which any engineer would tolerate. 
The locomotive boiler, which is subjected to 
violent fluctuations of load often contains 
not over one-third as much water as a Stirling 
boiler developing the same power 

A defect of all shell types of boiler is that 
once they are built there can be no adjust- 
ment of draft areas to suit either the chimney 
to which the boilers are attached or the 
fuel which is to be burned. Many water- 
tube boilers are equally faulty in this re- 
spect. In the Stirling boiler it is possible 
to adjust the draft area to suit any condi- 
tions by shortening or lengthening the firetile 
baffles. To do this it is necessary merely to 
take out or to add on a few tiles, without 
changing bridge walls, or flame plates, or 
other parts difficult of access or expensive 
to alter. Consequently it is the work of 
only a few hours to adjust the draft areas 
in the Stirling to suit any new fuel which 
may have to be used, while such adjustment 
cannot be made at all in any type of fire- 
tube boiler. 

Space The cost of a boiler plant must 
include not only the boilers but the ground, 
the buildings, piping, stacks, breechings, 
coal bins, and everything else required to 
complete the plant ready to run. Obviously 
a saving in space occupied by the boiler 



will effect a saving in piping and buildings. 
The Stirling boi.er occupies so much less 
space than that required by fire-tube boilers 
of the same capacity that the saving thus 
made possible will often amount to consid- 
erable percentage of the cost of the boilers. 
For example, 175 H. P. is about the limit 
of size of the return tubular; a boiler of that 
capacity would be 78 inches diameter and 18 
ft. long, and when erected the setting would 
require a space 23 ft. long and 9 ft. 6 inches 
wide. A Stirling boiler of the same capacity 
can be installed in a space 16 ft. 3 inches long 
by 10 ft. wide, 18 ft. 10 inches long by 7 ft. 
wide, or in other lengths and widths to con- 
form to the requirements. 

In large installations the showing is still 
more marked in favor of the Stirling: thus 
three of the above tubulars would require 
a space 26 feet 6 inches wide by 23 feet deep. 
The equivalent 525 H. P. of Stirlings would 
require a space 23 by 16 feet, or 17 by 19 
feet, or intermediate widths and depths. 
Similarly, six of these tubulars would require 
a space 52 by 23 feet, while equivalent 
Stirling boilers could be placed in a space 
varying from 35 by 17 feet to 29 by 19 feet. 
The additional aisle space at the ends and 
rear would be the same for both. Because 
of the greater space required by shell boilers 
an attempt is often made to increase their 
heating surface by crowding the tubes very 
close. The effect of this is to increase the 
difficulty of removing scale from the tubes, 
and to cause excessive moisture in the steam. 

Should the growth of the plant require 
the substitution of larger boilers the water- 
tube type can be taken apart, removed and 
replaced by larger units, without alteration 
of buildings, and installation of expensive 
tackle. This is an item of great importance 
when boilers are installed under buildings, 
since fire-tube boilers installed in such places 
usually cannot be taken out, without either 
cutting them to pieces or tearing down parts 
of the building. 

Other important advantages of the water- 
tube over the fire-tube boilers will be pointed 
out in the chapters which follow. 




Z ui 



Works of The Stirling Company 



The Stirling Company manufactures Water- 
Tube Safety Boilers for both stationary and 
marine use, superheaters, chain grates, bag- 
asse furnaces and conveyors, stacks, breech- 
ings, etc. Its works are located at Barber- 
ton, Ohio, and occupy 60 acres; the shop 
floor space under roof is 300,000 square feet; 
there are 24 separate shops, and 28 other 
buildings. The shops and offices are con- 
structed of steel, brick, slate, and wood, on 
concrete foundations, and reflect the highest 
development in American factory construc- 
tion. Fire protection is afforded by the 
automatic sprinkler system, and fire hy- 
drants located throughout the grounds. 
These connect with the Company's private 
system of fire mains and pumps, and the 
City Service can be used in addition if nec- 
essary. 

The Works were started in 1890, since 
which time their valuation and capacity 
have increased over tenfold, yet the steady 
growth of the Company's business is such 
that constant additions to the equipment 
are demanded. Already the plant is the 
largest in the world which is devoted ex- 
clusively to manufacture of water-tube boil- 
ers. The boilers supplied by the Company 
are manufactured in its own Works, under 
the superintendence of its own engineers. All 
material is rigidly tested, and every precau- 
tion that years of experience can suggest is 
taken to insure that both the material and 
the workmanship of these boilers are of the 
highest grade obtainable. 

All parts of the plant are provided with 
standard gauge railway tracks and switches, 
and the Company owns an excellent equip- 
ment of locomotive cranes, cars, and buggies 
adapted to the special service to be performed. 



A unique feature of the works is an immense 
gantry crane with double cantilever arms 
spanning the entire drum yard. Another 
overhead crane operates through a distance 
of 600 feet from the foundry to the fitting 
shop, and passes directly into both buildings. 

The Works are equipped with steam, 
electric, hydraulic and pneumatic power 
supplied from a central station, and all 
buildings are electric lighted. The shop 
tools are for the most part electrically driven, 
while hydraulic power is used for riveting 
and flanging, and pneumatic power for 
caulking, etc. 

Many of the tools have been designed by 
the Company and embody every known 
improvement for accomplishing the result 
for which they are intended. The entire 
equipment is a striking example of modern 
American practise in economizing labor and 
material, and the Company is ever on the 
alert to adopt any method or improvement 
which may reduce cost of manufacture or 
increase the excellence of its product. 

In addition to the Stirling boiler as de- 
scribed in this catalog, the Company is ex- 
tensively engaged in the manufacture of 
water-tube boilers specially designed for 
marine use, and has already installed this 
type of boiler in the Russian cruiser Variag, 
the Russian battleship Retvizan, the United 
States battleships Maine, Virginia and 
Georgia, the cruisers Colorado and Pennsyl- 
vania, the monitor Nevada, the Imperial 
Ottoman cruiser Medjidia, a private steam 
yacht, and several of the largest vessels in 
use in the merchant marine. Work is now 
actively progressing on boilers for several 
steamships under construction for service on 
the Great Lakes. 



Heat 



Heat is a condition of matter caused by 
vibratory motion among its particles. Very 
hot bodies are those in which the vibrations 
are very rapid, and the hotter the body, 
the more rapid the vibrations. 

Temperature The temperature of a 
body is the measure of its capability of 
communicating to adjacent bodies sensible 
heat, or heat that may be felt. When two 
bodies of different temperature are placed 
into contact the hotter body becomes cooler, 
and the colder body hotter, until finally 
their temperatures equalize. This proves 
that heat can be transferred. 

Heat Effects When heat is added to 
or taken from a body, either the temperature 
of the body is altered, or its volume is varied, 
or its state is changed. Thus, if heat be 
added to water under atmospheric pressure,- 
the temperature of the water increases until 
it reaches 212 F. If more heat be added 
and the pressure remains unchanged, the 
temperature does not further increase, but 
the water evaporates into steam. Heat 
thus changes water from a liquid to a gaseous 
state. If heat be abstracted from water 
the temperature is reduced until it reaches 
32 F., after which any diminution of heat 
does not further decrease the temperature, 
until the liquid is converted into a solid, or 
ice. The quantity of heat passing from one 
body to another can thus be estimated by 
the effects produced. Therefore heat is 
something that can be both transferred and 
measured. 

The general effect of heat on a body is 
to increase its volume. If heat be abstracted 
from a body the contrary effect ensues, 
and the volume is diminished. Hence the 
general principle, to which, however, there 
are some exceptions, that heat expands and 
cold contracts. These effects, arising from 
a change of temperature, are produced in 
very different degrees according to the nature 
of the bodies. They are small in solids, 
greater in liquids, and greater still in gases. 

It is well known that the work expended 
in friction apparently is lost as regards 
mechanical work; that heat is developed 



when friction occurs; that the greater the 
friction the greater is the amount of heat 
produced. Experiments have proved that 
the amount of heat generated by friction 
is exactly equivalent to the amount of work 
lost, whence it is shown that heat like me- 
chanical work is one of the forms of energy. 
Thermometers In consequence of the 
uniform expansion of mercury and its great 
sensitiveness to heat, it is the fluid most 
commonly used in the construction of ther- 
mometers. In all thermometers the freez- 
ing and the boiling point of water, under 
mean atmospheric pressure at sea level, 

TABLE 2 
COMPARISON OF THERMOMETER SCALES 





Fahrenheit 


Centigrade 


Reaumur 


Absolute Zero . . . 


-460 . 66 


-273.70 


-218.96 







-17.77 


-14. 22 




IO 


-12.23 


-9-77 




20 


-6.67 


-5-33 




3 


I . I I 


-0.88 


Freezing Point . . 


32 


0. 


o . 


Maximum Density I 








of Water . . / f 


39 -i 


3-94 


3- J 5 




5 


10. 


8. 




75 


23.89 


19.11 




IOO 


37-78 


30.22 




200 


93-34 


74.66 


Boiling Point . . . 


212 


IOO. 


80. 




250 


121 . II 


96.88 




300 


148.89 


119.11 




350 


176.67 


141-33 



F - i e + 32 = i R + 32 

C = 5 (F - 32) - 3 R. 
R = I C = * (F - 32). 

are assumed as two fixed points, but the 
division of the scale between these two points 
varies in different countries,- hence there 
are in use three thermometers, known as 
the Fahrenheit, the Centigrade or Celsius, 
and the Reaumur. In the Fahrenheit the 
space between the two fixed points is divided 
into 1 80 parts; the boiling point is marked 
212, and the freezing point is marked 32, 



47 



48 



THE STIRLING WATER-TUBE SAFETY BOILER 



and zero is a temperature which, at the time 
this thermometer was invented, was incor- 
rectly imagined to be the lowest temperature 
attainable. In the Centigrade and the Reau- 
mur scales the distance between the two 
fixed points is divided into 100 and 80 parts, 
respectively. In each of these two scales 
the freezing point is marked o, and the boiling 
point is marked 100 in the Centigrade, and 
80 in the Reaumur. Each of the 180, 100, 
or 80 divisions in the respective thermom- 
eters is called a degree. 

Table 2 and appended formulas are useful 
for converting from one scale to another: 

Absolute Zero Experiments show that 
at 32 F. a perfect gas expands 492 1 . 66 part 
of its volume if its pressure remains constant, 
and its temperature is increased one degree. 
If this rate of expansion per degree held 
good at all temperatures (and experiment 
shows that it does above the freezing point), 
the gas, if its pressure remained the same, 
would double its volume if raised to a tem- 
perature of 32 + 492.66=524.66 Fah., while 
under a diminution of temperature it would 
shrink and finally disappear at temperature 
of 492.66-32=460.66 below zero Fah. 
While undoubtedly some change in the law 
would take place before the lower temper- 
atures could be reached, this is no reason 
why the law may not be used within the 
range of temperatures where it is known to 
hold good. From the preceding explanation 
it is evident that, under a constant pressure, 
the volume of a gas will vary as the number 
of degrees between its temperature, and the 
temperature of 460. 66 J Fah. To simplify 
the application of the law, a new thermomet- 
ric scale is constructed as follows: the point 
corresponding to 461 F. is taken as the 
zero point on the new scale, and the degrees 
are identical in magnitude with those on 
the Fahrenheit scale. Temperatures re- 
ferred to this new scale are called absolute 
temperatures, and the point 461 F. (= 
-273 C) is called the absolute zero. To convert 
any temperature Fahrenheit to absolute 
temperature, add 461 to the temperature 
on the Fahrenheit scale; thus 54 F. will be 
54r46i==5i5 absolute temperature; 113 
F. will likewise be equal to 113 + 461 
574 absolute temperature. If one pound of 
gas had a temperature of 54 F., and another 



pound had a temperature of 113 F., the 
respective volumes would be in the ratio of 
515 to 574, if the pressure on each were the 
same. 

British Thermal Unit The quanti- 
tative measure of heat is the British Thermal 
Unit. It is ordinarily written B. T. U., 
and is the quantity of heat required to raise 
the temperature of a pound of pure water 
one degree, at its point of maximum density, 
viz.: 39.1 F. In the metric system the 
unit is the calorie, or the heat necessary to 
raise the temperature of a kilogramme of 
water one degree Centigrade, at the point 
of maximum density. 

i B. T. U.=.2$2 Calorie 
_ B. T. U. 



Specific Heat The quantity of heat 
required to raise the temperature of unit 
weight of any substance one degree varies 
with the substance, and is called the specific 
heat of that substance. It is also the ratio 
of the heat so required to that required to 
heat the same weight of water. For solids, 
at ordinary temperatures, the specific heat 
is constant for each individual substance, 
although it is variable at high temperatures. 
In the case of gases a distinction must be 
made between specific heat at constant 
volume, and a constant pressure. 

Where merely specific heat is stated it 
implies specific heat at ordinary temperature, 
and mean specific heat refers to the average 
value of this quantity between the tem- 
peratures named. 

The specific heat of a mixture of gases 
is obtained by multiplying the specific heat 
of each constituent gas by the percentage 
of that gas in the mixture, and dividing the 
sum of the products by 100. The specific 
heat of a gas whose composition is CO, 13; 
COg, 0.4; 0, 8; N, 7 8. 6. is found as follows: 

CO, 13 X.2I7 2. 821 

CO Z , 0.4 X.2479 = .09916 

0, 8 X. 21751= 1.74008 
N, 78.6 X.2433 = 19.16268 
100. o 23.82292 

and 23.8229-^100 = .238 = specific heat of 
this gas. 

Latent Hea t Where the application 
of heat results in a change of state of a sub- 
stance, either from solid to liquid, or from 



BOILING POINT OF LIQUIDS 



49 



liquid to gaseous, there is an absorption of 
heat without any rise in temperature, and 
the heat thus absorbed is termed latent 
(or hidden), because it apparently disappears, 
and is not measurable by a thermometer. 
It is not lost, but reappears whenever the 
substance passes through the reverse cycle, 
from a gaseous to liquid, or from a liquid 
to a solid state. Latent heat is therefore 

TABLE 3 
SPECIFIC HEATS 

SOLIDS. 

Copper . -Q95 1 

Gold 0324 

Wrought Iron 1138 

Cast Iron 1298 

Steel (soft) 1165 

Steel (hard) -"75 

Zinc .0956 

Brass 939 

Glass IQ37 

Lead 0314 

Platinum 03 24 

Silver 0570 

Tin 0562 

Ice 5040 

Sulphur 2026 

Charcoal 2410 



LIQUIDS. 

Water 

Alcohol 

Mercury 

Benzine 

Glycerine 

Lead (melted) 

Sulphur (melted) 

Tin (melted) .... 

Sulphuric Acid 

Oil of Turpentine 

GASES. 

Air (at freezing point) 

Oxygen 

Nitrogen 

Hydrogen 

Superheated steam* . 
Carbon Monoxide -(CO) . 
Carbon Dioxide (CO 2 ) 
Olefiant Gas .... 
Blast Furnace Gas 
Chimney Gases (approx.) 



.0000 
. 7000 

0333 
.4500 

555 
. 0402 

.2340 
.0637 

335 
.4260 



At Constant 
Pressure. 


At Constant 
Volume. 


2375 


.1685 


2175 
.2438 


I55 1 
.1727 


3.4090 
.4805 
.2479 


2.4123 
346 

1758 


. 2170 


I S35 


. 4040 
.2277 


J 73 


II 
. 2/tO 





the quantity of heat which apparently dis- 
appears, or is lost to thermometric measure- 
ment, when the molecular constitution of 
body is being changed. It is expended in 
performing the work of overcoming the molec- 
ular cohesion of the particles of the sub- 
stance, and in overcoming the resistance of 
external pressure to change of volume of the 
heated body. 

If heat be applied to a pound of ice there 
will be a rise in temperature until the freezing 
point, 32 F., is reached. The ice will then 
begin to melt, but the temperature of the 
mixture of ice and water will remain 32 
F., as long as any particle of ice remains in 
it. Yet the melting process will absorb 
heat. The amount thus absorbed in changing 
the state of a pound of ice from ice at 32 
F., to water at 32 F. is 144 B. T. U. This 
is the latent heat of fusion of ice. If the 
application of heat be continued the tempera- 
ture of the water will rise, but it will now 
require about twice as many heat units to 
effect a rise of one degree as it did to accom- 
plish the same rise in the ice. The reason 
is that the specific heat of water is i.oo, 
while that of ice is only .504. When the 
water has reached a point of 212 F., there is 
a further absorption of heat with no increase 
of temperature. Boiling occurs, and the 
heat absorbed is expended in transforming 
the water into steam. Water at atmos- 
pheric pressure cannot be heated beyond 
212 F., and the steam which is formed is 
also at a temperature of 212 F., when the 
entire pound of water has been evaporated 
into steam, 965.8 B. T. U. have been usedin 
the operation. This is the latent heoi of 
evaporation of water. 

Ebullition The temperature of ebulli- 
tion of any liquid, or its boiling point, 
may be defined as that stage in the addition 

TABLE 4 

BOILING POINTS AT ATMOSPHERIC 

PRESSURE (Kent) 
(14.7 Ibs. absolute per square inch.) 

Ammonia. 140 F. Water 212 F. 

Bromin. . . 145 Average sea water 213.2 

Alcohol. . .173 Saturated brine. .226 

Benzine. ..212 Mercury 676 



*The specific heat of superheated steam is variable. See page 93. 



50 



THE STIRLING WATER-TUBE SAFETY BOILER 



of heat to the liquid at which the temperature 
of the liquid is no longer increased and the 
heat added is absorbed by converting the 
liquid into vapor. This temperature de- 
pends upon the pressure under which the 
liquid is evaporated; the greater the pressure 
the higher the temperature. 

Heat of the Liquid In the evaporation 
of any liquid, that quantity of heat which 
is absorbed in raising the temperature from 
32 F. to the temperature of ebullition cor- 
responding to the particular pressure at which 
the evaporation occurs, is the sensible heat, 
or the heat of the liquid. 

Total Heat of Evaporation The quan- 
tity of heat required to raise a unit weight 
of any liquid from the freezing point to a 
given temperature, and entirely to evaporate 
it at that temperature is the total heat of 
evaporation of the liquid for that particular 
temperature. It is the sum of the heat of 
the liquid, and the latent heat of evaporation. 
To recapitulate: The heat added to a 
body is divided up as follows: 

Total Heat = Heat to change the tempera- 
ture + heat to separate the 
molecules + heat to over- 
come the external pressure 
resisting an increase of volume 
of the body. 

In case of water which is converted into 
steam the total heat is divided as follows: 
Total Heat =Heat to change the tempera- 
ture of the water + heat 
to separate the molecules of 
the water + heat to over- 
come resistance to increase 
in volume of the steam. 
=Heat of the liquid + inner 
latent heat 4- outer latent 
heat. 
=Heat of the liquid + total 

latent heat of steam. 
= Total heat of evaporation. 
The Steam Tables, page 74 give the heat of 
the liquid and total latent heat through a 
wide range of temperatures. 

( I a s e s When heat is added to gases 
there is no inner work to be done, hence the 
total heat is that required to change the 
temperature plus that required to do the 
outer work. If the gas is not allowed to 
expand, as in case of gases heated at constant 



volume, the entire heat added is that re- 
quired to change the temperature only. 
Mechanical Equivalent of Heat The 

relation between heat and mechanical work 
has been experimentally determined by Joule, 
who found that the heat necessary to raise 
the temperature of one pound of water one 
degree Fahr. at its maximum density can 
perform work equal to the raising of 772 
pounds one foot high. This relation between 
heat and mechanical work is called the 
mechanical equivalent of heat, or Joule's 
equivalent. The latest experimental deter- 
mination of Rowland shows that the exact 
value is somewhat higher than 772, and 778 
foot-pounds is now usually accepted as the 
correct mechanical equivalent. 

Transfer of Heat Heat may be com- 
municated from one body to another in three 
different ways: viz., by radiation, conduction 
and convection. Radiation is the transfer of 
heat between bodies separated by a trans- 
parent medium. Conduction is the transfer 
or flow of heat from a hotter to a colder par- 
ticle in contact with it. Convection is the 
transfer of heat caused by the rise of heated 
particles in a mass of liquid or gas. The trans- 
fer of heat from a furnace to the boiler takes 
place by radiation, convection and conduction 
and the heat is distributed through the mass 
of water by convection, but the exact laws 
governing these methods of transfer are 
unknown. 

Temperature of Fire The following ta- 
ble, compiled by M. Pouillet, will enable the 
approximate temperature of a fire to be 
judged by its appearance. The temperature 
is practically the same for all kinds of com- 
bustibles under similar conditions. 



TABLE 5 



APPEARANCE 



OF FIRE. 

Red, just visible 

" dull . . . 

" cherry, dull . 

" full . 

clear 

Orange, deep . 
clear . 

White heat . . 
" bright . 
" dazzling 



TEMPERATURE 
FAHR. 

977 
1290 
1470 
1650 
1830 

2010 
2IQO 
2370 

2 55 
2730 



MERCURIAL PYROMETERS 



51 



Linear Expansion of Substances by 
Heat To find the increase in the length of a 
bar of any material due to an increase of tem- 
perature, multiply the number of degrees of 
increase of temperature by the co-efficient 
for 100 (Table 6) and by the length of the 
bar, and divide by 100. 

The expansion of metals per degree rise of 
temperature increases slightly as higher 
temperatures are reached, but for all practical 
purposes it may be assumed to be constant. 



1 i ) Mercurial Pyrometer for temperatures 
up to 800 Fahrenheit. 

( 2 ) Exp ansion Pyrometer for temperatures 
up to 1,500 Fahrenheit. 

(3) Melting points of metals which flow 
at various temperatures up to the melting 
point of platinum, 3,227 Fahrenheit. 

(4) Le Chatelier's thermo-electric py- 
rometer for temperatures up to 2,900 F. 

(5) Calorimetry for temperatures up to 
2,000 Fahrenheit. 



TABLE 6 

LINEAR EXPANSION OF SOLIDS AT ORDINARY TEMPERATURES 
(The tabular values are the fractional increase in length for a temperature increase of ioo c 

Fahrenheit or Centigrade.) 



NAME OF SUBSTANCE. 


COEFFICIENT 
PER 100 
FAHRENHEIT. 


COEFFICIENT 
PER IOO 
CENTIGRADE. 


Brass (cast) 


OOIO4 


00l88 


Brass, (wire) 


. OOIO7 


. OOI Q3 


Brick (fire) . 


OOO3 


oooc 


Copper, 


. OOOQ 


.0017 


Glass (English Flint) ... 


OOO4.!; 


00081 


Glass, (French white lead) 


00048 


' . 00087 


Gold 


. OOO8 


. 001 ; 


Granite (average) 


OOO47 


00085 


Iron (cast) .... 


OOO6 


OOI I 


Iron (soft forged) 


. OOO7 


OOI 2 


Iron (wire) 


OOO8 


0014 


Lead 


OOl6 


0029 


Mercury 


OO3 3 


0060 


Platinum 


ooo? 


0009 


Sandstone 


0006 


OOI I 


Silver 


OOI I 


OO2 


Slate, (Wales) 


0006 


OOI 


Water, (varies considerably with the temperature) .... 


.0086 


0155 



High Temperature Measurements 

The temperatures to be dealt with in steam 
boiler practise range from those of ordinary 
air and steam to the temperatures of burning 
fuel. The gases of combustion, originally 
at the temperature of the furnace, cool down 
as they pass through each successive bank 
of tubes in the boiler, to nearly the tem- 
perature of the steam, resulting in a wide 
range of temperatures through which definite 
measurements are sometimes required. 

Of the different methods devised for 
ascertaining these temperatures, five of 
the most important will be mentioned, viz.: 



Mercurial Pyrometers Mercury boils 
at 676 F. and atmospheric pressure, and for 
temperatures above 500 F. the ordinary 
mercurial thermometer cannot be used. 
For higher temperatures, up to 800 F., 
the space above the mercury is filled with 
nitrogen gas, and as the mercury expands, 
the gas is compressed, increasing the pressure 
and raising the boiling point. So constructed, 
mercurial pyrometers can be used for indi- 
cating temperatures not exceeding 800 F. 

Flue-gas temperatures are nearly always 
taken with such thermometers. The bulb 
of the instrument should project into the 



52 



THE STIRLING WATER-TUBE SAFETY BOILER 



path of maximum velocity of the gases in 
order that the average temperature may 
be obtained, and before a reading is taken, 
it is necessary to keep the thermometer 
inserted in the flue socket from seven to 
fifteen minutes depending on conditions. 
Sometimes these thermometers are made 
so that they can be permanently attached 
to the wall of the breeching or flue. 

This is the most accurate and by far the 
most preferable method of recording stack 
and uptake temperatures. 

Expansion Pyrometers Brass expands 
about 50% more than iron for the same 
increase in temperature; and for both the 
expansion is nearly proportional to the rise. 
In expansion pyrometers this phenomenon 
is utilized by enclosing a brass rod in an 
iron pipe, one end of the rod being rigidly 
attached to a cap at the end of the pipe, and 
the other end connected by a multiplying 
gear to a pointer moving around a graduated 
dial. The whole length of the pipe must 
be at a uniform temperature before the full 
amount of expansion is obtained. This, 
together with the fact that lost motion is 
likely to exist in the mechanism connected 
to the pointer, makes the expansion pyrom- 
eter unreliable; it is only when the instru- 
ment is thoroughly understood and care- 
fully calibrated that it can be depended 
upon. Its action is anomalous; for instance, 
if it is allowed to cool after being exposed 
to a high temperature, the needle will rise 
higher before it begins to fall. Similarly, 
a rise in temperature is first shown by the 
instrument as a fall. The explanation is 
that the iron, being on the outside, heats 
or cools more quickly than the brass. The 
readings are, therefore, valueless unless both 
the brass and iron are known to be of the 
same temperature. 

Melting Points of Metals When an 
approximate temperature is sufficient it 
can be found by introducing into the furnace 
or flue various metals of known melting 
points. The more common metals form a 
series in which the respective melting points 
differ by less than 100 to 200 F. and by 
using these in order, the temperatures can 
be fixed between the melting points of some 
two of them. This method lacks accuracy, 
but it suffices very well for approximate 



determination of the temperatures of the 
furnace, and in different parts of the tubes 
of a boiler. 

TABLE 7 

APPROXIMATE MELTING POINTS 
OF METALS 

Fah. 



Wrought Iron melts at about 


2825 


Steel (low carbon) 


2600 


Steel (high carbon) " 


2400 


Cast Iron (white) 


2200 


Cast Iron (grey) 


2000 


Copper 


1975 


Gun Metal 


I700 


Zinc 


764 


Antimony 


940 


Lead 


618 


Bismuth 


514 


Tin 


447 


Platinum 


3230 


Gold 


2056 


Silver 


1788 


Aluminum 


1172 



Thermo = Electric Pyrometers When 
wires of two different metals are joined at 
one end and heated, an electromotive force 
will be set up between the free ends of the 
wires. Its amount depends upon the com- 
position of the wires and upon the temper- 
ature. If a delicate galvanometer of high 
resistance be connected to the "thermal 
couple", as it is called, the deflection of 
the needle, after a careful calibration, will 
indicate the temperature very accurately. 

In the thermo-electric pyrometer of Le 
Chatelier, the wires are platinum and a 
10% alloy of platinum and rhodium, en- 
closed in porcelain tubes to protect them 
from the oxidizing influence of the furnace 
gases. The couple with its protecting tubes 
is called an "element". The elements are 
made in different lengths to suit conditions. 
It is not necessary for accuracy to expose 
the whole length of the element to the tem- 
perature to be measured, as the electro- 
motive force depends only upon the tem- 
perature of the juncture at the closed end 
of the protecting tube. The galvanometer 
can be located at any convenient point, 
since the length of the wires leading to it 
occasions practically no error. 



MEAN SPECIFIC HEATS OF SOLIDS 



S3 



The advantages of the thermo-electric 
pyrometer are: accuracy over a wide range 
of temperature, continuity of readings, and 
the ease with which observations can be 
taken. Its disadvantages are high first 
cost and extreme delicacy. 

Calorimetry This method derives its 
name from that fact that the process is the 
same as the determination of the specific 
heat of a substance by the water calorimeter, 
with the exception that in one the temper- 
ature is known and the specific heat is re- 
quired, while in the other the specific heat 
is known and the temperature is required. 
The temperature is found as follows: A 
given weight of some substance, such as 
iron, nickle, platinum, or fire-brick, is heated 
to the unknown temperature and then 
plunged into water and the rise in temper- 
ature noted. 
If: 

X = unknown temperature of substance, 
iv = weight of heated substance, Ibs. 
W = weight of water, Ibs. 
T = final temperature of water, 
t = temperature rise, or difference 
between initial and final tem- 
peratures of water, 
s = specific heat of cooled body, 

Wt 

Then: X=T + - [i] 

ws 



Table 8 gives the specific heats of some 
substances used in this method. For furnace 
temperature determination, the constants in 
the second column should be used. Specific 
heats increase with temperature, and author- 
ities differ as to the amount. 

TABLE 8 
MEAN SPECIFIC HEATS 

ORDINARY MEAN FOR HIGH 
SUBSTANCE TEMPERATURE TEMPERATURE 



Platinum 
Iron (cast) 
Nickel 
Fire-brick 



.032 
.130 
. 109 
. 200 



.038 
.180 
136 
. 260 



Example A piece of wrought iron bar, 
weighing one-half pound, is thrown into the 
furnace and heated to the temperature of the 
fire, and is then withdrawn and placed in a 
pail containing ten pounds of water. The 
original temperature of water was 60 F., and 
after the immersion of the iron, the tempera- 
ture rose 20. The temperature of the fur- 
nace by the formula was then X = 60 + 
.^ff = 2282 F., the specific heat of iron, 
0.18, being taken from the table. 

This method is affected by many sources 
of error, or else requires so many refinements 
of measurement that its results are usually 
very approximate. 



Air 



Pure Air is a mixture of oxygen and nitro- 
gen in following proportions: by volume 20.91 
parts oxygen to 79.09 parts nitrogen; by 
weight 23.15 parts oxygen to 76.85 parts 
nitrogen. Air in nature always contains 
other constituents such as dust, carbon 
dioxide, ammonia, ozone and water vapor. 

Air being perfectly elastic, the density of 
the atmosphere decreases in geometrical 
ratio with the altitude. This fact has an 
important bearing on proportions of furnaces 
and stacks located in high altitudes, as will 
later appear. The atmospheric pressure 
for different altitudes is given in Table 12*. 

Weight and Volume of Air These 
depend upon the pressure and temperature, 
as expressed in the formula 

Pv= 53 . 3 T [2] 

In which: P = absolute pressure in pounds 
per square foot, v = volume in cubic feet of 
one pound of air, and T = absolute temper- 
ature Fah. of the air. 

The weight of one cubic foot of air will be 
evidently -7 pounds. 

Example: Required the volume in cubic 
feet of a pound of air under 60.3 Ibs. per 
square inch gauge pressure, at 115 Fah. 
Here p = 144 X (14.7+ 60.3) = 10,800. T -- 
115+461=576, hence ^ = 5 rf|fip= 2.84 cu. 
ft. The weight per cubic foot will be ~?=^ 
= 0.35 Ibs. 

Table 9 gives weight and volume of air 
at different temperatures. 

The above formula will hold good if in 
place of the constant 53.3 the following con- 
stants be substituted for each gas : 

Oxygen = 48.257 
Nitrogen = 54.926 
Hydrogen= 770 . 322 

Specific Heat of Air This varies with 
the temperature. At 266 it is two per 
cent., and at 446 it is 5.68 per cent., higher 
than at 32, but the percentage of increase 
for such temperatures as exist in the boiler 
furnace, and along the path of the gases 
after they leave the furnace, is not known. 

Vapor in Air Air may carry as much as 
3% of vapor. This fact is of considerable 



TABLE 9 

VOLUME AND WEIGHT OF AIR AT 

VARIOUS TEMPERATURES, AND 

ATMOSPHERIC PRESSURE 



TEMPERATURE 


VOLUME OF 


WEIGHT OF 


IN DEGREES 


ONE POUND 


ONE CUBIC 


FAHR. 


CU. FT. 


FT. IN LBS. 


50 . . 


. . I 2.840 


.077884 


55 


. . i 2.964 


077J33 


60 . . . . 


i3-9 


.076400 


65 .. .. 


. . 13.216 


.075667 


70 . . 


-. I3-342 


.074950 


75 


.. 13.467 


.074260 


80 . . . . 


J 3-593 


073565- 


85 -. .- 


.. 13.718 


.072894 


90 . . 


13-845 


.072230 


95 - 


r 3-97 


.071580 


IOO 


. . 14.096 


.070942 


no 


.. 14-346 


.069698 


I 20 


. . 14-598 


.068500 


130 .. .. 


. . 14.849 


.067342 


140 


. . 15.100 


.066221 


150 . . . . 


I5-352 


.065140 


I 60 


.. 15.603 


.064088 


170 . . . . 


I5-854 


.063072 


180 .. 


. . 16.106 


.062090 


190 


16.357 


.061134 


200 


. . 16.606 


.060210 


2IO 


.. 16.860 


593 I 3 


212 


. . 16.910 


&5d?35 


22O 


. . 17.111 


.058442 


230 


. . 17.362 


057596 


240 


. . 17.612 


.056774 


250 . . 


.. 17.865 


055975 


260 


.. 18.116 


.055200 


270 .. .. 


.. 18.367 


054444 


280 . . 


.. 18.621 


053710 


290 


.. 18.870 


.052994 


300 


ig.I 21 


052297 


320 . . 


. . 19.624 


050959 


340 . . 


. . 2O. I 26 


.049686 


360 . . 


. . 20.630 


.048476 


380 .. .. 


.. 21.131 


047323 


4OO 


. . 21.634 


.046223 


425 .. .. 


. . 22.262 


.044920 


450 


. . 22.890 


.043686 


475 


.. 23.518 


.042520 


500 . . 


. . 24.146 


.041414 


525 - 


24.775 


.040364 


55 


25.403 


039365 


575 


. . 26.031 


.038415 


600 


. . 26.659 


375 I o 


650 . . . . 


27.913 


.035822 


700 


. . 29.172 


.034280 


750 .. .. 


. . 30.428 


.032865 



importance in solving problems relating to 
heating, drying and air compressing. Accord- 
ingly Table 10 gives the amount of vapor 
required to saturate air at different tem- 
peratures, its weight, expansive force, etc. 



*See page 58. 



56 



THE STIRLING WATER-TUBE SAFETY BOILER 



Q 



o 



ffi 

Oi 
CO 

C 



g ti 

X ^ 

3g 

Q O 



^ EH g 

3 $ 
M -? 



^ 3 



co 



t/ 



s ^ 

5^ <! 



fa 
O 



fa PH CO 

O S co 



O 

PH EH 



< fa 

H-l 

fa Q 

co <! 

EH 

ffl 

O 



Cubic Feet of 
Vapor from 1 Ib. 
of Water at its 


GJ 


to vo CS vO CO t^ M 
Qs CM vo vo O O ^" ^T to ^" M OO to T^- QN OO O PJ t^ 
OO vo O to M O ^ to vo O vo M O t~~- LO Tt to to O< 

O d VO M CO O ^t" tO CS M M M 
tO CS MM 


MIXTURES OF AIR SATURATED WITH VAPOR. 


Weight of Dry 
Air mixed with 
1 Ib. of Vapor, in 
Pounds. 

10 


M VO t^ O 

M OO t^- O ^ vo O CO O vo O GO vo vo O O HI vo O 

Tj" M T^- OO M M t^. VO tO ^ O O O ^J" Hi T}* hH M Tt" CO tO O 


d xO O to OO cs Tj* o CS O M vo M OO O ^ to W M 
O "3" O O f^ w CO vo *^* to cs M M 


Weight of Vapor 
mixed with 1 Ib. 
of Air, in Pounds. 

9 


p vo vo OM OOO M O\ r^ PO ^" M O ^^ to OO O to O <U 
O vo T^- t^ O M t^ OO O GO ^" vo OO t^ t^- O HI to O "^ to -*-* 

OOOOO OMMNPO TfvOCOMO PJMVOMP) O,5 

OOOOO OOOOO OOQMM pjto 1 ^}" t^ P^ oo T^ 


M CM HH 


Weight of Cubic Foot of the Mixture of Air 
and Vapor. 


Total Weight of 
Mixture in 
Pounds. 
8 


to M to vo OO P) vo OCMt~ OOOOOOO Tj-t^-Oto\O ^"OO 
\O *st" P* O OO t^ vo to PI O GO t^- vo to O GO vo PI O vo M vO 


OOOOO OOOOO OOOOO OOOOO OO 




Weight of the 
Vapor in Pounds. 

7 


OOOOO OOMMP1 pi to vo O GO O to O O vo O O 
OOOOO OOOOO OOOOO MMMpjpj toto 
OOOOO OOOOO OOOOO OOOOO OO 




Weight of the 
Air in Pounds. 
6 


\O "^" ^ O GO V O ^" cs O CO *-O ^O O^ V O w f^* W ^O GO O O O 
CO CO CO GO f""* J^** ^*** r~"* t^ 1 " >X O ^*O ''O *^"5 if) if) ^" ""^J" ^O C^ C 1 ) M O 
OOOOO OOOOO OOOOO OOOOO OO 




Elastic Force of 
the Air in the 
Mixture of Air 
and Vapor in 
Inches of 
Mercury. 
5 


GO GO OO t~~ O vo to M OO ^3" OO M" to M t* O OO HI O O "^1" O 


OOOOO OOOOOOO f- t~- O vo to M O t^> to O vo O 

PJP4PJCSP4 P)PJPP)P1 P)P)NP)P PJMMMM 


Elastic Force 
of Vapor in 
Inches of 


Mercury, 
(Regnault). 

4 


nzZS %zslzzs~z IIH1 H 


M M M M P) pq 


fjjfjfl ' 


Tj-piTj-t^M \OMt^tOO t^.^P)MO OCOCOGOO OM 


OOOOO OOOOO OOOOO OOOOO OO 




1^1 1 

>Qte 
^ 


" *-> Q 

i rt i 

* O 1 ~ H M 

5 6 c 

^>" C 


OOOOO OOQMM MMMPJPJ CSPJPlfOtO POtO 




~ 
2 ^ H 


OOOOO OOOOO OOOOO OOOOO OO 
M PI to ^ vo ^O r* OO ON O M C^ to Tf vo O X^ OO O O M 





Water 



Pure Water is a chemical compound of 
one volume of oxygen (O) and two of hy- 
drogen (H), and its chemical symbol is H 2 O. 

Weight The weight of water depends 
upon its temperature. Its weight at four 
temperatures much used in physical calcula- 
lations is as follows: 



TEMPERATURE 
FAHRENHEIT 



WEIGHT PER 
CUBIC FOOT 



At 32 or freezing 

point at sea level 62 .418 Ibs. 
At 39.1 or maximum 

density 62 .425 

At 62 or standard 

temperature 62.355 

At 212 or boiling 

point at sea level 59-760 



WEIGHT PER 
CUBIC INCH 

.03612 Ibs. 

.036125 ' 

.03608 

03458 " 



0.000040 to 0.000051 per atmosphere, at 
ordinary temperatures, decreasing however 
with an increase of temperature. 

Pressure due to Head The weight of 
water at standard temperature being 62.355 
Ibs. per cubic foot,* the pressure exerted 
by a column of any stated height may be 
determined; and conversely the height of 
the column producing any stated pressure 
can be computed. 

Pressure in pounds per square foot 
62.355 X height of column in feet. 

Pressure in pounds per square inch = 
.433 X height of column in feet. 

Height of column in feet = Pressure in 
pounds per square foot -^62.35 5. 

Height of column in feet = Pressure in 
pounds per square inch ^-.43 3. 



TABLE 11 



VOLUME AND WEIGHT OF DISTILLED WATER AT 
VARIOUS TEMPERATURES (Buet) 



Temper- 
ature 
Fahrenheit 


Relative 
Volume, 

Water at 
39-1 = r 


Weight 
per Cubic 
Foot. 
Pounds. 


Temper- 
ature 
Fahrenheit 


Relative 
Volume, 
Water at 
39.1 = ! 


Weight 
per Cubic 
Foot. . 
Pounds. 


Temper- 
ature 
Fahrenheit 


Relative 
Volume, 
Water at 
39.1 = ! 


Weight 
per Cubic 
Foot. 
Pounds. 


Temper- 
ature 
Fahrenheit 


Relative 
Volume, 
Water at 
39-i = i 


Weight 
per Cubic 
Foot. 
Pounds. 


32 


I . OOOI29 


62 . 42 


1 60 


I .02324 


6l . OI 


290 


I .08405 


57-59 


430 


I . 18982 


52-47 


39 - 1 


I . OOOOOO 


62.43 


170 


I . 0267 I 


60.80 


3 


I .09023 


57.26 


440 


1.19898 


52.07 


40 


I . 000004 


62 .42 


1 80 


1.03033 


60.59 


310 


I .09661 


5 6 -93 


45 


1.20833 


51.66 


50 


I .000253 


62 .41 


190 


I .03411 


60.37 


320. 


1.10323 


56-58 


460 


I . 21790 


51.26 


60 


I . 000929 


62.37 


200 


I .03807 


60. 14 


330 


I . IIO05 


56-24 


47 


I . 22767 


50.85 


70 


I . 001981 


62.30 


210 


I .04226 


59-89 


340 


I . 11706 


55-88 


480 


1.23766 


5-44 


80 


I .00332 


62 . 22 


212 


I .04312 


59-7 1 


35 


1.12431 


55-52 


490 


1.24785 


50.03 


90 


I .00492 


62 . 12 


22O 


I .04668 


59-64 


360 


1-13*75 


SS-i6 


5 


1.25828 


49.6l 


IOO 


I .00686 


62 .OO 


230 


1.05142 


59 37 


37 


1.13042 


54-79 


5 10 


I . 26892 


49-20 


no 


I . 00902 


61.87 


24O 


1-05633 


59-io 


380 


1.14729 


54-4i 


520 


1.27975 


48.79 


I2O 


I. 01143 


61 . 72 


250 


I .06144 


58-81 


390 


I-I553 8 


54-03 


530 


I . 29080 


48.36 


130 


I . 0141 1 


61.56 


26O 


I .06679 


58-52 


400 


I . 16366 


53-64 


540 


I -30204 


47-94 


140 


I . 01690 


61.39 


270 


1.07233 


58-21 


410 


I . 17218 


53-26 


550 


I-3I354 


47-5 2 


I <Q 


I . 01995 


61 . 20 


280 


I .07809 


57 .90 


420 


I . 18090 


52.86 








o 


s 7 \j 








J 1 s 




S 


j 









Compressibility Water is but slightly 
compressible, hence for all practical purposes 
it may be considered non-compressible. 
The coefficient of compressibility ranges from 



Impurities and Solvent Power Water 
in its natural state is never found absolutely 
pure. The composition of feed water to be 
used for boilers is of vital importance, the 



*Authorities differ concerning the weight of water. At 62 F. the range is from 62.291 to 62.360, 
and 62.355 is generally accepted as the most accurate. 



58 



THE STIRLING WATER-TUBE SAFETY BOILER 



impurities existing in such water affecting 
not only the economy, but also the durability 
of the boiler. In solvent power water has 
a greater range than any other liquid. For 
common salt this is nearly constant at all 
temperatures, while it increases with an in- 
crease of temperature for such impurities 
as magnesium and sodium sulphate. 

Sea water contains on an average about 
3.125 per cent, part of its weight of solid 
matter, whose composition will be approx- 
imately : 

Sodium Chloride 76% 

Magnesium Chloride 10 

Magnesium Sulphate 6 

Calcium Sulphate or Gypsum. 5 

Calcium Carbonate o 

Other Substances 2\ 

Total 100% 

The following are the Boiling Points and 
Specific Gravities of sea water of varying 
density : 

TAGE BOILING 

LT FAHRE1 

2I 3 

214 

2I S 

216 

217 
219. 

The boiling point of water decreases as the 
altitude above sea level is increased, as shown 
in Table 12. 

Specific Heat of Water The specific 
heat of water is unity at 39.1 F., but for 
other temperatures it is slightly greater. 
Rankine has constructed from Regnault's 
data the formula: Specific heat = 

1+0.000000309 (t - 39. i) 8 [3] 

In which t is the temperature Fah. In con- 
sequence of this variation of specific heat 
the heat of the liquid above 32 F. in any 
case is not exactly t 32, but is equal to t 32 
+ o. 000000103 X(t 39. i) 3 , where t is the 
temperature of ebullition. The heat of the 



liquid as computed for several temperatures 
by both methods is given below: 



PERCENTAGE 
OF SALT 
* 



3 

6 
9 

12 
IS 

18 



125- 
250 

375 
500 
625 

75 



POINT 


SPECIFIC 


IHEIT 


GRAVITY 


2 


I .029 


4 


1.058 


5 


1.087 


7 


i . 116 


9 


i-i45 


i 


1.174 



TEMP. FAH. 

60 
100 



T-32 

28 B.T. U. 

68 " " " 



RANKINE S FORMULA 



28.12 B. T. U. 
" " " 68.01 " " " 

150 118 ' 118.30 " " 

200 168 ' 168. 70 " " " 

212 180 " 180. 79 " " " 

It will thus be seen that the variation is 
entirely too slight to affect any but the most 
refined physical investigations, and that for 
all steam engineering work the heat of the 
liquid may be safely taken as / 32. 

TABLE 12 

BOILING POINT OF WATER AT 
VARIOUS ALTITUDES 



Boiling Point 
in degrees 
Fahrenheit. 


Altitude above 
Sea-Level. 
Feet. 


Atmospheric 
Pressure. 
Pounds per 
square inch. 


Barometer. 
Inches. 


184 


15,221 


8.19 


16.79 


I8 5 


14,649 


8-37 


17.16 


186 


14,075 


8.56 


17-54 


187 


I3,49 8 


8-75 


17-93 


188 


12,934 


8-94 


18.32 


189 


12,367 


9- J 3 


18.72 


190 


n,799 


9-33 


*9-*3 


191 


11,243 


9-53 


T 9-54 


192 


10,685 


9-74 


19.96 


J 93 


10,127 


9-95 


20.39 


194 


9-579 


10. 16 


20. 82 


195 


9,3! 


10.38 


21.26 


196 


8,481 


10.60 


21.71 


197 


7,932 


10.82 


22.17 


198 


7,38i 


11-05 


22 . 64 


199 


6,843 


11.28 


23.11 


200 


6,304 


11.52 


23-59 


201 


5,764 


II .76 


24.08 


202 


5-225 


12 .OI 


24.58 


203 


4,697 


12.25 


25.08 


2O4 


4,169 


12.51 


25 59 


2O5 


3,642 


12.77 


26 1 1 


2O6 


3-II5 


I3-03 


26. 64 


207 


2,589 


13.29 


27 18 


208 


2,063 


13-57 


27 73 


2O9 


r >539 


13 8 4 


28 29 


2IO 


1,025 


14 12 


28 85 


21 I 
212 


5 12 
Sea- Lev el 


14 41 
14 70 


29 42 
30 oo 



*Or one thirty-second part of the weight of the water and the salt held in the solution. 



Impurities in Boiler Feed Water 



Natural waters usually contain other sub- 
stances in solution or suspension. When 
the water is converted into steam, these 
substances, if solids, must be deposited 
somewhere in the boiler; if gases, they will 
pass out with the steam. The amount of 
solids deposited in a boiler is often aston- 
ishing; over 300 pounds per month will 
deposit in a 100 H. P. boiler using water 
containing only 7 grains per gallon. In the 
southwestern part of the United States 
where the water is often particularly bad, 
cases are known where boilers can be operated 
only two to three days between cleanings. 

The treatment of feed water belongs to 
the chemist rather than to the engineer, 
hence when the water causes trouble it will 
be economy to submit the case to a compe- 
tent chemist who makes a specialty of treating 
feed waters. His advice should be followed, 
since there are few cases where guessing 
is less successful than when treating feed 
waters. The following article is intended 
to convey such general information as will 
enable the reader to understand the effect 
of the impurities usually encountered, and 
to realize the necessity of referring the more 
difficult cases to an expert. 

Effect of Impurities According to the 
nature of the impurity it may produce one 
or several of the following results: 

(1) Precipitation of mud, etc. 

(2) Formation of scale. 

(3) Formation of scum which causes 
excessive priming or foaming. 

(4) Internal corrosion of the boiler. 

Effect of Mud and Scale Where pro- 
vision is made to catch the mud and blow 
it off before it settles on the heating sur- 
face, the only evil effect is the loss of heat 
due to blowing off. If the mud is carried 
along and deposited on the heating surfaces 
it may unite with the scale-forming matter, 
and the mass will be baked to a hardness 
which renders its removal difficult and 
costly. The arrangement of feed and mud 
drum in the Stirling boiler is particularly 
efficacious in precipitating mud and silt, 
and the boiler is successfully operating on 



waters which many other types of boiler are 
unable to use. 

The effect of scale depends largely upon its 
density. The scale formed by the carbonates 
is usually soft and porous, and its retarding 
effect upon heat transmission is small, hence 
unless present in large quantities its influence 
toward lowering boiler efficiency is less than 
commonly supposed. Sulphates and some 
other impurities form scales which are so hard 
that they can be removed only by cutting 
them loose, and so dense that they are 
impervious to water. Such scales are a 
source of positive danger which increases 
with the degree of temperature of the surface 
upon which they have formed, because the 
metal overheats and is liable to burn, crack, 
or bulge, thereby causing a rupture. The 
economy of the boiler is also seriously affected. 
Scale=forming Materials Those which 
occur most often and in largest quantity are 
Calcium carbonate (lime) . . . .CaCO 3 

Magnesium carbonate MgCO 3 

Calcium sulphate CaSO 4 

Magnesium sulphate MgSO 4 

The following are less frequently found, and 
usually in small amounts : 

Iron carbonate Fe 2 CO 3 

Magnesium chloride MgCl 2 

Calcium chloride CaCl 2 

Potassium chloride KC1 

Sodium chloride NaCl 

and, variously, iron oxide and hydroxide, 
calcium phosphate, silica, and organic matter. 
The carbonates of calcium and magnesium 
are but slightly soluble in water; they are 
usually combined with carbon dioxide as 
bicarbonates,CaH 2 (CO 3 ) 2 andMgH 2 (CO 3 ) 2 
respectively, which are quite soluble in cold 
water. Heating the water drives off the 
carbon doxide, CO 2 , and the bicarbonates 
decompose, precipitating, in the case of cal- 
cium the monocarbonate, CaCO 3 , and mag- 
nesium hydrate, Mg(OH) 2 , in the case of 
magnesium. This occurs between the tem- 
peratures 1 80 to 290 F. As the scale 
formed by calcium carbonate is porous and 
does not adhere strongly to the metal, it is 
not particularly troublesome unless present 



60 



THE STIRLING WATER-TUBE SAFETY BOILER 



in large quantity. The same is true of mag- 
nesium carbonate, but in the process of free- 
ing the carbon dioxide, CO 2 , the bicarbonate 
generally reduces to magnesium hydrate, 
Mg (OH), which not only follows the water 
currents and settles very slowly, but it 
cements together such other matter as it 
may encounter. The violent foaming which 
is often caused by carbonates of calcium and 
magnesium may cause far more trouble than 
the scale produced by these salts. 

The sulphates of calcium and magnesium 
are the most troublesome scale-forming 
impurities. They remain in solution until 
a temperature of about 302 is reached, when 



selves. They may, however, cause foaming, 
which will be greater as the solution becomes 
more concentrated. Frequent blowing off 
prevents their concentration, but wastes heat 
carried off by the hot water. 

A temperature of 302 F. corresponds to 
55 Ibs. gauge pressure, hence the reason 
why the rear bank of the Stirling boiler 
removes most of the scale-forming matter 
before the hotter parts of the boiler are 
reached is now evident. The water upon 
entering the feed drum is heated to the 
temperature corresponding to the boiler 
pressure, hence during its course through 
the rear tubes the scale will be deposited 



TABLE 13 
SOLUBILITIES OF SCALE-FORMING MINERALS 



' 


SOLUBLE IN 
PARTS OF PURE 
WATER AT 

3 2 F. 


SOLUBLE IN 
PARTS OF CAR- 
BONATED 
WATER, COLD. 


SOLUBLE IN 
PARTS OF PURE 
WATER AT 212 


INSOLUBLE IN 
WATER AT 


Calcium Carbonate 
Calcium Sulphate .... 
Magnesium Carbonate 
Calcium Phosphate 
Oxide of Iron .... 


62,500 

500 

5.500 


ISO 

'5 
1.333 


62,500 
460 
9,6OO 


302 F. 
302 F. 

212 F. 
212 F. 


Silica 








212 F. 













the calcium sulphate deposits in long, needle- 
like crystals, possessing active cementing prop- 
erties. These mingle with any other matter 
present to form a hard resisting scale. The 
^agnesium sulphate will deposit as a mono- 
hydrated salt, MgSO 4 H 2 O, and its presence 
is objectionable because it interferes with the 
removal of other impurities. 

The iron carbonate behaves much like 
calcium monocarbonate, CaCO 3 ,but it occurs 
so seldom and in such small quantities that 
its presence has little effect. 

The magnesium chloride precipitates as a 
hydroxide, which is objectionable because 
of its cementing properties. The other chlor- 
ides, calcium, potassium and sodium (com- 
mon salt) , give little trouble from incrustation 
unless allowed to concentrate beyond the 
point of saturation, when they are deposited 
and increase the bulk of the scale, although 
possessing no cementing properties them- 



and the purified water will pass into the hot- 
test tubes in the front bank. This feature 
is peculiar to the Stirling boiler. Here also, 
as in case of feed water heaters, the element 
of time affects the degree to which the im- 
purities can be removed, hence it is evident 
that the more the boiler is forced, the shorter 
the time the water can remain in the rear 
bank, hence the smaller the degree to which 
this water can be purified before passing 
into the front and middle banks. 

Scum may be due to vegetable matter, 
sewage, and light flocculent matter which 
gathers on top of the water. These form 
a glutinous skin on the water, which is 
raised by the steam, causing foaming or 
priming which may be so excessive as se- 
riously to interfere with operation of the 
engines. When animal and vegetable oils 
are used as components of the cylinder oil, 
and the hot-well water containing them 



HOW TO HANDLE IMPURE FEED WATER 



61 



is mixed with feed water containing soda, 
the oils are saponified, soap suds are formed, 
and violent foaming may result. The remedy 
is to use mineral oil. The scums are best 
handled by a surface blow-off. 

Pitting and Corrosion are usually caused 
by free acids which are either originally 
in the water or are liberated by splitting 
up some salt. The acids may be of vegetable 
origin derived from some adulterant of 
mineral oil, or the original water may have 
been polluted with acid due to discharge 
from industrial works, or drainage from 
mines; waters from swamps and bogs often 
contain humic or vegetable acids; sulphuric 
acid is often absorbed from the atmosphere, 
and found in drainage from coal and ore 
mines, particularly if the ores are sulphides. 

Magnesium chloride is generally thought 
to have a corrosive effect on boiler plate. 
Some assert that it is broken up by the boiling 
water into magnesium hydrate and hydro- 
chloric acid ; while others notably H . Ost , main- 
tain that water is partly decomposed by boil- 
ing, and the iron of the boiler is attacked by 
liberated oxygen, the magnesium chloride 
subsequently combining with the iron pro- 
toxide thus formed; the reaction being as 
follows : 

MgCl,+Fe(OH) 2 = FeCl 2 + Mg(OH) 2 

If Ost's theory is correct, corrosion takes 
place quite independently of the magne- 
sium chloride. 

Air absorbed by water is liberated by 
boiling, and produces corrosion. The pe- 
culiar activity of air under such circum- 
stances is due to the fact that whereas or- 
dinary air is a mixture of oxygen and nitrogen 
in the approximate ratio of i to 4, airr'-ssolved 
in water is a mixture of i part of oxygen 
and only 1.87 parts of nitrogen, owing to 
the greater solubility of oxygen. The deter- 
rent-effect of nitrogen as a dilutant is thus re- 
duced, and the mixture is correspondingly 
more active chemically. In the experiments 
of Lt. Comdr. W. F. Worthington, U. S. N., 
samples of iron and steel were supported 
on glass rolls in a porcelain bath of distilled 
water through which air was forced. The 
corrosion of the iron and steel was marked, 
in some cases occurring uniformly over 
the surface of the samples, and in other 
cases being confined to pits of small area, 



but of surprising depth. The temperature 
at which the oxygen most rapidly attacks 
the iron is lower than that of steam at the 
pressures now used, hence it will be found 
that pitting will occur much faster in a 
boiler that is moderately warm than when 
in full service; it also occurs in places where 
the circulation is defective, such as in water- 
legs. The rapid corrosion of feed pipes is 
similarly explained the temperature falls 
within the range in which oxygen rapidly 
attacks the iron. 

When water contains alkali, any copper 
used in the boiler will rapidly pit and corrode 
in parts where the circulation is defective. 
The oxygen attacks the copper and the alkali 
dissolves the copper oxide so formed, thus 
presenting a fresh surface to the action of 
the oxygen. With such waters copper fire- 
box plates one-half inch thick have been 
pitted through in five months. 

How to Handle Impure Feed Water 
There are three courses of procedure, viz.: 

(1) To neutralize the acids and remove 
the solids before the water enters the boiler. 

(2) To treat the water with chemicals 
after it has entered the boiler, with a' view 
of minimizing or preventing formation of 
incrustation and scale. 

(3) To evaporate the water and remove at 
regular intervals the deposits which form. 

Unless the water is of very good quality 
the first course is preferable, and the most 
economical in the end. The design of the 
equipment for efficient treatment will depend 
upon the character of the impurities in the 
water, and the work should be entrusted only 
to an expert. The necessary equipment is 
generally too expensive to be provided for 
small steam plants, and recourse must be 
had to the other methods. 

Free acids should receive attention before 
the water enters the boiler or heater. While 
milk of lime fed into the boiler will form 
a thin coating which to some extent prevents 
the acid from corroding the metal, the proper 
procedure is to neutralize the acid before 
the water is used. If free acid only is present, 
it may be neutralized by addition of carbonate 
of soda, but an excess of the carbonate 
may cause considerable priming. If scale- 
forming materials are present with the acid, 
more elaborate processes will be necessary. 



REMOVAL OF SCALE FROM BOILERS 



63 



If the water is suspected of containing acid, 
it should be tested by inserting blue litmus 
paper, which will turn red if acid is present. 
The water should then be submitted to a 
chemist, and the quantity of bicarbonate 
of soda required, or the necessity for more 
elaborate treatment, should be determined 
and prescribed by him. 

Heating Feed Water not only saves heat, 
but serves as a means of external purification 
more or less efficient according to the kind of 
impurities present. At the temperature of 
208 to 210 attainable in open or closed heat- 
ers some of the carbonates and other impuri- 
ties can be precipitated. Since sulphate of 
lime precipitates at 302, corresponding to 55 
Ibs. pressure, a live steam heater will remove 
most of it, if it be of sufficient size and kept 
clean. The element of time has considerable 
effect in precipitating impurities, hence the 
results will be better when both open and 
closed heaters are of sufficient size to allow 
the water to remain a considerable time under 
influence of the heat. 

Treatment after Water Enters the 
B o i 1 er The ob j ect of such treatment is to con- 
vert the scale-forming impurities into others 
which are less objectionable. This method 
affords a fertile field to the vendor of "com- 
pounds." When prepared by a chemist for a. 
particular water, such preparations may be of 
great benefit, but their use without adequate 
knowledge of what they contain and the 
effect of the ingredients on the impurities 
of the water, can be compared only with the 
use of "cure-alls" in medicine. When im- 
properly used they produce quite as much 
trouble as the impurities they are expected 
to neutralize. Even when properly com- 
pounded their office is to convert a certain 
amount of objectionable solids into a greater 
amount of less objectionable solids. If they 
fail they have only increased the evil they 
were expected to cure, hence the necessity 
of consulting a chemist when compounds are 
to be used. 

The Reagents used to Neutralize the 
Principal Impurities will now be given. 

Calcium and magnesium carbonates are 
precipitated to some extent by heat, because 
the carbon dioxide, CO 2 , necessary to hold 
them in solution is driven off. They may 
also be precipitated by caustic lime CaOH a 



which reduces them to the practically 
insoluble carbonates. Sodium hydroxide or 
caustic soda, NaOH, accomplishes the sams 
result. 

Magnesium and calcium sulphates and 
chlorides are convertible into carbonates by 
the use of soda-ash, Na 2 CO 3 . As carbon- 
ates, they are merely lesser evils than when 
sulphates. The resulting sodium sulphate 
or chloride, is harmless, requiring only oc- 
casional blowing off to prevent it from con- 
centrating. 

If the use of a solvent is necessary, there is 
in most plants no way of getting it into the 
boilers without shutting them down and 
introducing it through the manhole. If this 
is done only when the boilers are opened for 
cleaning no extra expense is involved, but, 
as a rule, the stoppages are so far apart that 
the introduction of the solvent accomplishes 
little, because in the natural course of run- 
ning it will be blown out long before the next 
charge is introduced. Small quantities of 
solution introduced at short intervals are 
more effective than a large quantity at longer 
intervals, and when the water is very bad 
a much greater quantity of the solvent can 
be used in a given time than is possible where 
large quantities are introduced at long 
intervals. With some waters a charge of 
30 pounds of soda-ash once a month might 
cause serious priming immediately after being 
introduced, while one pound a day could 
have no evil effect. 

The proper way to introduce the solvent is 
to attach to the feed pump suction an appa- 
ratus arranged to feed it just as cylinder oil is 
fed to an engine. There are many inex- 
pensive appliances of this kind on the market ; 
a satisfactory home-made appliance consists 
of a tee in the suction pipe, with a gate valve 
on the hot- well side of it, the outlet of the 
tee being turned upward, and connected 
to a nipple which in turn is connected to a 
vessel containing the solution. A valve is 
also placed in the nipple. By opening this 
valve and closing the valve in suction pipe, 
the solution is drawn into the pump and 
passed to the boiler. The action must be 
intermittent, and is not so efficient as when 
a continuous feed in small quantity is used. 

Removal of Scale Even with a system 
of purification it is practically impossible to 



64 



THE STIRLING WATER-TUBE SAFETY BOILER 



get the water absolutely pure, hence some 
deposit will form in course of time Without 
purification this deposit will form more or 
less rapidly according to character of the 
water, and its removal is essential to effi- 
ciency and durability of the boiler. The most 
efficient appliance for this work is a turbine 
tube cleaner, the construction of which is de- 
scribed in the chapter on Boiler Cleaning. 



of |-inch thickness will raise the temperature 
of the furnace plates about 300 degrees 
Fahrenheit. As grease offers ten times more 
resistance to heat, one would expect that .0125 
inch would have the same effect as this 
thickness of scale, but experience shows that 
the merest trace of grease, certainly less 
than o.ooi inch, or one-tenth of the above, 
can cause far more injury than scale."* 




4,000 H. P. OF STIRLING BOILERS, GUANICA CENTRALE, PUERTO RICO 



Extraction of Oil and Grease from Feed 
Water If feed water is taken from a hot- 
well the cylinder oil should be removed 
from it before it enters the boiler. In some 
districts where oil wells are common, much 
of the water available for boiler feed contains 
native oil. If this is allowed to enter the 
boilers, it will deposit on the hot surfaces, and 
these will inevitably be burned or blistered. 
The oil is also liable to cause heavy priming. 
"The peculiarity of grease deposits in boilers 
is that their effect is out of all proportion to 
their thicknesses. We have seen that scale 



Where the cylinder oil forms an emulsion 
with the hot- well water its removal is difficult, 
if not impossible, and the remedy is to select 
an oil which will not produce such emulsion. 
An oil extractor should be placed on the 
exhaust pipe, but while this, if properly 
looked after, will remove a considerable 
portion of the oil, the amount which passes 
through it is too great to be allowed to enter 
the boiler. Various devices are employed 
to extract the remainder of this oil. If an 
open heater is used it should be provided 
with an oil extracting device of liberal 



*Sec Water-Softening, by C. E. Stromeyer and W. B. Baron. Engineering, London, Dec. 25, 1903. 



CLASSIFICATION OF FEED WATERS 



65 



capacity. In some cases the water from con- 
denser or open heater is made to flow into 
a large box divided into compartments 
by vertical partitions, the water passing 
over one partition, then under the next, then 
over the third, etc., until it reaches the 
final compartment from which it is drawn 
by the feed pump. In each compartment 
is placed a basket made of wire netting, and 
loosely packed with hay, excelsior, etc., 
through which the water must pass. Each 
basket can be removed independently, and 
be charged with fresh filtering material. 
Each compartment is provided with surface 
and bottom blow-off. Another method is 



When oil has been allowed to enter the 
boiler it should at once be removed in the 
manner prescribed on page 228, 

Good and Bad Feed Water It is diffi- 
cult to judge of the quality of a feed water 
by the number of grains of solids per gallon, 
for the reason that whereas 50 grains of some 
soluble salt, such as sodium chloride, might 
be handled with success, only 8 grains of 
calcium sulphate might render the water 
unsuitable for boilers. The following clas- 
sification rates waters according to the num- 
ber of grains of incrusting solids (calcium 
carbonate, magnesium carbonate, magnesium 
chloride, etc.) per gallon. 



TABLE 14 
EFFECT OF, AND CORRECTIVES FOR, IMPURITIES IN FEED WATER (Norton} 



TROUBLESOME SUBSTANCE. 



TROUBLE. 



REMEDY OR PALLIATION. 



Sediment, mud, clay, etc. . . . 

Readily soluble salts 

Bicarbonates of lime, magnesia, iron 



Sulphate^of lime 



Chloride and sulphate of magnesium 
Carbonate of soda in large amounts 

Acid 

Dissolved carbonic acid and oxygen 

Grease (from condensed water) 
Organic matter (sewage) .... 
Organic matter 



Incrustation. 
Incrustation. 
Incrustation. 

Incrustation. 

Corrosion. 
Priming. % 
Corrosion. 
Corrosion. 

Corrosion. 

Priming. 

Corrosion. 



Filtration. Blowing off. 

Blowing off. 

Heating feed. Addition of caustic 

soda, lime, or magnesia, etc. 
Addition of carbonate of soda, barium 

chloride. 

Addition of carbonate of soda. 
Addition of barium chloride. 
Alkali. 
Heating feed. Addition of caustic 

soda or slacked lime. 
Slacked lime and filtering. Carbonate 

of soda. Substitute mineral oil. 
Precipitate with alum or ferric chloride 

and filter. 
Precipitate with alum or ferric chloride 

and filter. 



to insert into the feed pipe between the pump 
and the boiler two receptacles so piped that 
the water can be pumped through either 
of them while the other is being cleaned; 
these are arranged so that the water has 
to pass through layers of sponges, burlap, 
or other filtering material, which can easily 
be renewed. Whatever arrangement be a- 
dopted, it is necessary to renew the filtering 
material at regular intervals, and to ascertain 
by frequent inspection of the boiler that 
practically all the oil is removed from the 
feed water. 



Less than 8 grains*. . 
From 8 to 1 2 " ... 

12 to 15 ' ... 

15 to 20 " 

20 to 30 



. Very good 

.Good 

.Fair 

.Poor 

.Bad 



Greater than 30 grains. . . . Very bad 
Much smaller quantities of sulphates of 
calcium (lime) and magnesium will bring 
the quality of water lower down in the scale. 
For a rough comparison it may be said that 
one grain of these solids would be as harmful 
as two to three grains of the carbonates and 
chlorides above mentioned. 



*One pound avoirdupois = 7,000 grains. ^Similar result is caused by carbonates of calcium and 
magnesium. $Such water should not be used in a boiler unless first purified. 



The Heating of Boiler Feed Water 



Before the water fed into a boiler can be 
converted into steam it must be heated from 
its original temperature to that corresponding 
to the steam pressure. Steam at 160 Ibs. 
gauge pressure has a temperature of about 
370 Fahr., hence if the feed should be at a 
temperature of 60 degrees each pound of this 
water must absorb about 310 B. T. U. be- 
fore it can be converted into steam. This 
amount of heat is nearly 27% of the total 
heat needed. Obviously, then, if before the 
water is pumped into the boiler it can be 
made to absorb heat which otherwise would 
go to waste through the engine exhaust, or 
the flue-gases, it will be economy to save 
this heat, provided the cost of doing so is 
less than the value of the heat which is saved. 

The steam pressure and feed water tem- 
peratures before and after heating being 
known, the fuel saving can be computed by 
the following formula: 

100 (/ /, ) 



Fuel saving in per cent. - 



[4] 



in which t = temperature Fahr. of feed water 
after heating, t l =temperature Fahr. of feed 
water before heating, and //-total B. T. U. 
above 32 Fahr. per. pound of steam at the 
boiler pressure from Table 18, page 74. 

To effect this saving, money must be ex- 
pended for feed heating apparatus, piping, 
space in which to install them, and labor 
to operate them. The heating may be done 
by use of exhaust steam heaters, of either the 
open or closed type, according to character 
of the feed water, and nature of the plant; 
or by economizers, or by a combination of the 
two systems. Which of these to choose can 
be determined only after a study of the con- 
ditions in each case. For example, if the 
exhaust steam can all be used for heating, 
drying, ice-making, etc., its value when so 
utilized may exceed its value as a feed heat- 
ing medium, and an economizer should be 
considered. If the exhaust steam cannot be 
thus utilized, an open or closed heater can be 
considered, and here again the wisest selection 
can be made only after study of the conditions. 
When using certain feed waters heavily im- 
pregnated with mineral a closed heater may 



scale up so rapidly that its efficiency quickly 
falls off, and its cost of cleaning may be pro- 
hibitive, hence for such waters an open 
heater should be preferred. When engines 
work intermittently, as a mine hoist, a closed 
heater is not advisable, because the frequent 
coolings between hoists and the sudden heat- 
ing when each lift begins will soon loosen 
the tubes, or even pull them apart, hence 
an open heater or an economizer will give 
more satisfactory service 

Economizers are bulky, require a large 
amount of extra brickwork or an expensive 
metal housing, and frequently a considerable 
increase in the space necessary for heaters 
of the exhaust steam type. When comput- 
ing the net return on an economizer invest- 
ment, all these factors must be included. 
When the feed water is of a character that 
will quickly scale or incrust the economizer, 
and throw it out of service for cleaning 
during an excessive proportion of time, 
consideration must be given to the problem 
of purifying the water before it passes to the 
economizer, or the latter may fail to earn a 
profit on the investment. The character of 
fuel and type of boiler used also have more in- 
fluence on the economizer problem than com- 
monly supposed. The more wasteful the boiler, 
the greater the saving by using an economizer. 
When oil fuel is used under a large boiler of 
efficient design, the boiler efficiency may 
and often does exceed 80 per cent., thus 
leaving small opportunity for an economizer, 
and there are cases where economizers have 
been a source of profit while the boilers were 
fired with coal, but the net saving disappeared 
as soon as oil fuel was used, and the same 
would be the case with gas fuel. 

From the foregoing it is evident that general 
data as to the saving that can be effected by 
heating feed water, or detailed computations 
based on assumed conditions, can be of little 
practical use. Each case must be independ- 
ently worked out, which can be done in- 
telligently only after exhaustive study of 
each of the conditions affecting that case, 
including probable life and growth of the 
plant. When as a result of such a study 



68 



THE STIRLING WATER-TUBE SAFETY BOILER 



the different methods practicable for hand- 
ling the problem have been determined, the 
selection of the best one can be easily deter- 
mined by balancing the saving possible 
with each method against its first cost, depre- 
ciation, maintenance, and cost of operation. 



the advantage of the boiler; the capacity of 
the boiler is increased by the amount of heat 
added to the feed, and the stresses caused by 
feeding cold water into the boiler are reduced. 
Introduction of cold water into a boiler is 
also an occasional cause of priming. For 




BULL RIVETERS IN $RUM SHOP OP THE STIRLING COMPANY'S WORKS 



Thus far, only fuel saving has been con- 
sidered. But beside this, the benefits of 
heating feed water are many. The proper 
office of a boiler is to generate steam, and to 
do this most profitably it requires to be kept 
clean. By properly heating the feed water, 
most of the impurities can be eliminated to 



these reasons, heating of feed water is common 
even when fuel saving is not the main object, 
as in saw mills and in cases where feed water 
purification is necessary, as exemplified in 
the use of live steam heaters which purify, 
but considered as heaters only, save little or 
no fuel. 



Steam 



Gases and Vapors If the temperature 
of a gas be kept constant its pressure may be 
increased by making a corresponding decrease 
in its volume. Vapors, which are simply liquids 
converted into aeriform condition, can exist 
only in connection with a definite pressure 
corresponding to each temperature. Thus 
water vapor, or steam, of 150 pounds per sq. 
inch absolute pressure, can exist only under 
a temperature of about 358 F.; hence if the 
pressure of saturated steam be fixed its 
temperature also becomes fixed, and vice 
versa. 

Saturated Steam is steam which is at the 
maximum pressure and density possible at 
its temperature, or is steam in the condition 
in which it is generated from water with 
which it is in contact. If either the pressure 
be increased, or the temperature be decreased, 
some of the steam will immediately condense. 
Just so long as steam is of the same pressure 
and temperature as the water with which it 
can remain in contact without gaining or 
losing heat, it will remain saturated. 

Quality of Steam Dry saturated steam 
contains no water. In all practical cases 
saturated steam contains some water, which 
is suspended -in it, and the steam is then said 
to be wet. The percentage weight of the 
steam, in a mixture of steam and water, is 
called the quality of the steam. Thus if it be 
found that for each 100 pounds of the mixture 
there is f -pound of water the quality of steam 
will be 99.25. 

Superheated Steam If heat be added to 
steam out of contact with water, both tem- 
perature and pressure increase, provided the 
volume remains constant, or the temperature 
and volume increase if the pressure remains 
constant. Steam whose temperature exceeds 
that of saturated steam of the same pressure 
is called superheated steam and its properties 
approximate those of a perfect gas. 

Heat of the Liquid, Latent Heat, and 
Total Heat of Steam As explained in 
the chapter on Heat, the heat necessary 
to raise the water from 32 F. to point of 
ebullition is called heat of the liquid. The 
heat absorbed during the ebullition consists 



of that necessary to dissociate the molecules, 
or the inner latent heat; and that necessary 
to overcome the resistance to increase in 
volume, or the outer latent heat, and these 
two are the total latent heat of vaporization, 
as given in the Steam Tables, page 74. 

Relative Volume The relative volume 
of steam is the ratio between the volumes 
of an equal weight of steam, and of water 
at 39.1 F., and it is equal to the volume 
in cubic feet of one pound of steam multiplied 
by 62.425. Example: A pound of steam 
at 250 F. occupies a volume of 13.65 cubic 
feet, hence its relative volume is 
13.65X62.425=852.1. 

The Specific Volume of saturated steam 
is the volume in cubic feet of one pound 
of steam. 

Boiling Point The temperature of the 
boiling point of any liquid depends upon 
the pressure on the liquid. This fact is of 
great practical importance in steam con- 
densers, and in many operations requiring 
boiling in an open vessel, since in the latter 
case altitude has considerable influence. 
The relation between altitude and boiling 
point is shown in Table 12, page 58. 

Equivalent Evaporation from and at 
212 F. When comparing boiler tests, 
fuel performances, etc., it is usually found 
that neither the steam pressure nor the 
feed water temperature was the same in 
the various trials, hence it is necessary to 
establish some common basis to which all 
the trials can be reduced for purposes of 
comparison. The method of doing this 
is to transform the evaporation, as deter- 
mined under the actual feed temperature 
and steam pressure noted during the test, 
into an equivalent evaporation based upon 
a standard feed water temperature of 212 
F., and a steam pressure equal to normal 
atmospheric pressure at sea level (14.7 Ibs. 
absolute). Under these standard conditions 
the steam will be generated at a temperature 
of 212 from water at 212. The number 
of pounds of water which would be evaporated 
under the standard conditions by precisely 
the same amount of heat absorbed by the 



6g 



O 
H 
O 



STEAM PRESSURES, POUNDS BY GAUGE.* 












X ?5 


The values for intermediate pressures and feed water temperatures may, with sufficient accuracy for all practical purposes, be obtained by interpola- 
tion. If exact values are necessary they may be computed by the Formula 


f?Nf.'Sf. Ss2 ""2 U 5 " " 


M 


OOOOO 


OCO 1^ 

OCO 


o 


S 3 ~ f? ~ ? 0=0 o % S> 8 o 






f -0 

t t ~-. 

000 


o 

CO 








OOO 
TO". 


f? !? f? N S-^^"2 !?Z?"-2 


OOOOO 


OOOOO 


o f ~ c 







SSIifS 


t ~: (N o 


3- O u-. 
O3C 1- 


o 

o 


mil 8525% ss^ 


;::^ 


OOOOO 


o o o 

t O T 

- o o 
c- r c- 





3JJJJJJ JBHjfi SWS 


JJSfg 


lllll 


O 

o 5 c- 





SSS'** "M^O^ ^ "'-?"" o" 


~->' r - 




OOO 
CO 1~ C 





rairs- 8MS 5W25 




<- - - - o 

M 


000 
OOO 




o 


3 8 MM^^U ?^:2 




OOOOO 
00 CO f^ t^O 


c- ~ o 

OOO 

CO T C 

oo' ~^c 


M 8 OC 2 "2 U 2" M' 2 H 2 


OCO vC 10 t 
OOOOO 


OOOOO 


o 

o 


?**?? UUft ^82| 


OOOOO 


OOOOO 


00 t^-O 
000 




c 


jsssi H^ls ?!:!! 


00 l^O 10 Tj- 

OOOOO 


>-c - - - O 

OOOOO 


OOO 
rr . O- T 

CO t->C 

OOO 


o 

CO 








O "' O 

CO f-0 


f? S S 2~- - - 2" M ~ : 2 


*0 ?" 


fO fJ - O O 
OOOOO 


o 


ssss! 2?!S : 5H11? 


f'H'H 



~} N O O 


OOO 
00 r^ 10 


o 

o 


s^is ^^ur ^E:! 




, 

M H O O O 


000 

OCO CO 


o 


sass? 'S^^us' ^^nSo" 


OOOOO 


OOOOO 


OOO 


o 






CO ": 


C' I/-. - 


5"S S 2 1 'S^US' M^MSo 


OOOOO 


i- o oco 

OOOOO 


00-0 


o 






f 1 CO 


~2 f 


fi N M o O* 00 t^O v> ^ PO M O CO 


o"o o o o 


N *" O CX 


c ^ c 

OOO 


o 




OOOOO 


ooooo 


000 


o 










S 3 5 S* ~2 U? M : 2 o o 


OOOOO 


ft - CCO 
OOOOO- 


OOO 


o 
o 






-c - 


CO co'cc' 


a .". 8 .*' 2 . " 2 . M . 2 * 


OOOOO 


OOOOO 


000 


o 

o 


o 




o o 


>C - t^ 


. S . = ." "-"- :? "" . 


OOOOO 


sls 


000 




00 








ro O t 

t ~^ fo 


S S '" M^S^MM "nSoo" 


'o o o o o 


" O OCO J^ 


o 


OMMO OOOO^Qv oOoooor-t* 
M O O'OO *^O i/> ) MO ooo r* 


00 >0 10 Tf 
OOOOO 


CO f< 
M O OCO f~ 

o o coo 


OOO 

00 T O 

- -, o 

\O >O Tf 

000 


o 


S5SSS 55*8 -S>S^S 






OOO 



"0 


NN--., M H WOOO 


OOOOO 


ooooo 


OOO 
O <o 

o o 


jo -j- duiax 1 


MOOOO OOOOO OOOOO 


OOOOO 


OOOOO 


OOO 











J 



a 
o 



n 

ta 



965. 
re F 
he la 



a P 



ha 



-- 
o 



18, 
No 



from Ta 
he Steam 



= total heat of steam above 3 
ng this table in connection wit 



hich 
When 



FACTORS OF EVAPORATION 




71 



Doiler under the actual test conditions is 
called the equivalent evaporation from and at 
212; the quotient of the equivalent evapora- 
tion from and at 212, divided by the actual 
evaporation under test conditions, is the 
factor of evaporation. For example, suppose 
a boiler to evaporate water from a feed tem- 
perature of 60 F. into steam at 60 Ibs. 



pound of water, or the latent heat of evapora- 
tion, would have been needed, hence for each 
pound of water the boiler evaporated under 
the actual conditions, it could have evaporated 

-^ = 1. 1 88 Ibs. of water from and at 212. 

965.8 

Similarly, in another case it might be 
found that for each pound evaporated under 



TABLE 15 

PROPERTIES OF SATURATED STEAM FOR VARYING 
AMOUNTS OF VACUUM* 



Pressure 
Above 
Vacuum. 
Lbs. persq.in. 


Vacuum 
in 
Inches of 
Mercury 


Temperature, 
Degrees 
Fahrenheit. 


Heat of the 
Liquid above 
32 Fahrenheit, 
B. T. U. 


Latent Heat 
above 
32 Fahrenheit, 
B. T. U. 


Total Heat 
above 
32 Fahrenheit, 
B. T. U. 


Density or 
Weight per 
Cubic Foot, 
Pounds. 


-245 


29^ 


58.8 


26.84 


1072 . 6 


1099.5 


0.00077 


.490 


29 


79-3 


47.40 


1058.3 


1105.7 


o . 00152 


735 


28^ 


92 .0 


60 . 04 


1049 .6 


1109 .6 


0.00223 


.980 


28 


101.4 


69.47 


1043.1 


1112.5 


i .00294 


i-47 


27 


ii5-3 


83.36 


1033-4 


1116.8 


o. 00431 


i .96 


26 


125.6 


93-73 


1026 . i 


1119.8 


0.00566 


2-45 


2 5 


133-9 


IO2 . I 


1020 . 3 


1122.4 


0.00699 


2-94 


24 


140.9 


109 . I 


1015.5 


i 124. 6 


0.00829 


3-43 


23 


147.0 


II5-3 


IOI I . I 


1126.4 


0.00961 


3 9 2 


22 


!5 2 -3 


I2O.6 


1007 .4 


1128 .0 


o .01087 


4.41 


21 


J57-2 


125.6 


1003.9 


1129 . 6 


0.01218 


4.90 


20 


161.5 


129.9 


1000.9 


1130.9 


0.01342 


5-39 


19 


165.6 


134 


998.1 


1132.1 


0.01468 


5.88 


18 


169.4 


137.9 


995-3 


ii33-2 


0.01594 


6-37 


17 


172.8 


141.3 


992.9 


1134.2 


0.01719 


6.86 


16 


176.0 


144.5 


990.7 


II35-2 


0.01839 


7-35 


i5 


179.1 


147.6 


988.5 


1136.2 


o . 01963 


7.84 


U 


182. i 


150.6 


986.4 


H37-I 


0.02087 


8.82 


12 


187.5 


156.1 


982.7 


1138.7 


0.02334 


9.80 


TO 


192.4 


161 .0 


979-2 


I 140 . 2 


0.02576 


12.25 


5 


203.1 


171.8 


971.7 


IJ 43-5 


0.03178 


14. 69 





212 . I 


180.9 


965.3 


1146. 2 


0.03765 



gauge pressure. The total heat above 32 
in a pound of steam at 60 Ibs. gauge (74.7 
Ibs. absolute) is 1175.6 B. T. U. But since 
the water was originally at 60 instead of 
32, the heat added by the boiler was only 
ii7S.6-(6o-32) = 1147.6 B. T. U. Had this 
same heat been used to evaporate steam at 
atmospheric pressure from water already at a 
temperature of 212, only 965.8 B. T. U. per 



the actual conditions the same heat would 
evaporate 1.121 pounds of water from and 
at 212. The values 1.188 and 1.121 are 
the factors of evaporation, or the factor by 
which the number of pounds of water in the 
actual test is to be multiplied to find the 
equivalent number of pounds that could be 
evaporated from and at 212 F. with the same 
amount of heat. This factor for any set of 



*Partly from S. A. Reeve, The Thermodynamics o'f Heat Engines, 1903. 



72 THE STIRLING WATER 

conditions may be determined by the formula : 



965.8 

in which H=total heat of steam above 32 
from steam table; *=temperature Fah. of feed 
water. 

Table 16 gives the factors of evaporation 
for a large range of conditions, and for all 



-TUBE SAFETY BOILER 

changes according to altitude and the varia- 
tions of the barometer. Consequently cal- 
culations involving the properties of steam 
are based on absolute pressure, which is 
equal to the gauge pressure plus the atmos- 
pheric pressure in pounds per square inch. 
The latter is usually assumed to be equal 
to 14.7 pounds per sq. inch at sea level,* 



TABLE 17 

RATE OF VARIATION OF PROPERTIES OF SATURATED STEAM 
AT VARIOUS PRESSURES 



Abso- 
lute 
Pres- 
sure. 
Lbs. per 
sq. in. 


Temper- 
ature. 
Deg. Fahr. 


Increase in 
Temperature 
per Pound 
of Pressure. 
Deg. Fahr. 


Heat of the 
Liquid. 
B. T. U. 


Increase in 
Heat of the 
Liquid, per 
Pound of 
Pressure. 
B. T. U 


Latent 
Heat. 
B. T. U. 


Decrease in 
Latent Heat 
per Pound 
of Pressure. 
B. T. U. 


Total Heat. 
B. T. U. 


Increase in 
Total Heat 
per Pound 
of Pressure. 
B. T. U. 


Per Cent, of 
Total Heat 
as Heat of 
Liquid. 


20 


227.9 




196.9 




954-6 




"S^S 




17-3 






I .96 




1.98 




I. 3 8 




595 




40 


267 . I 




236.4 




927.0 




1163.4 




20.3 






1.2 7 




1.28 




.885 




390 




60 


2 9 2.5 




26l .9 




99-3 




1171.2 




22 . 4 






-965 




975 




.685 




. 290 




80 


3II.8 




281.4 




895.6 




1177.0 




23-9 






.830 




.825 




.580 




245 




IOO 


327.6 




297.9 




884. 




1181 . 9 




25.2 






.614 




.642 




45 6 




.186 




ISO 


358-3 




330-0 




861 .2 




1191.2 




27.7 






.468 




.492 




.348 




.144 




2OO 


38I-7 




354-6 




843.8 




1198.4 




29.8 






357 




373 




. 264 




. 109 




300 


417.4 




391-9 




817.4 




1209.3 




3 2 -4 






275 




.279 




195 




.084 




4OO 


444-9 




419.8 




797-9 




1217.7 




34-5 






22 5 




237 




. 169 




.068 




500 


467.4 




443-5 




781 .0 




1224.5 




35-5 






.179 




. 190 




135 




054 




750 


512.1 




490.9 




747-2 




1238.0 




39-6 






139 




.149 




.107 




-043 




1000 


546.8 




528.3 




720.3 




1248.7 




42.4 



except the most refined work the omitted 
values may be determined by interpolation. 

A Unit of Evaporation is the quantity 
of heat necessary to evaporate one pound 
of water at 212 into steam at the same 
temperature, and is equal to 965.8 B. T. U. 
Its symbol is U. E. 

Absolute and Gauge Pressures Steam 
gauges indicate the pressure above the at- 
mosphere. The atmospheric pressure 

*See Table 12, page 58. 



but for other levels it must be determined 
from the barometer reading at that place. 
Vacuum gauges indicate the difference, 
expressed in inches of mercury, between 
atmospheric pressure and the pressure inside 
the vessel to which the gauge is attached. 
For all rough purposes two inches height 
of mercury may be considered equal to 
pressure of one pound per square inch, hence 
for any reading of the vacuum gauge the 



STEAM TABLES 



73 



absolute pressure will be 14.7 -^X gauge 
reading in inches. Example: vacuum of 
24 inches will equal 14.7-12=2.7 Ibs. 
absolute per sq. inch. 

Table 15 gives the temperature, pressure 
and other properties of steam for varying 
amounts of vacuum, and exact pressures 
corresponding to each inch of reading of 
vacuum gauge. 

Economy of High Pressure Steam 
From the steam tables the following con- 
densed table of the heat needed at different 
pressures may be constructed. 



ABSOLUTE 
PRESSURE. 


TEMPER- 
ATURE F. 


HEAT OF 
LIQUID. 


LATENT 
HEAT. 


TOTAL 
HEAT. 


T 4-7 


212 


I80.8 


965.8 


II46.6 


20. o 


228 


196.9 


954-6 


IJ 5i-5 


IOO.O 


327.6 


297.9 


884.0 


1 181 . 9 


301.9 


4l8 


392.5 


816.9 


1209.4 



From this the following conclusions can 
be drawn. 

As the pressure and temperature increase, 
the latent heat decreases, but less rapidly 
than heat of the liquid increases, hence the 
total heat increases. The percentage in- 
crease of total heat is very small, being for 
the pressures of 20, 100 and 301.9 pounds 
absolute, only 0.43, 3.0 and 5.4 per cent, 
respectively, more than required for the 
pressure of 14.7 Ibs. The temperatures, 
however, increase at the rates of 7.5, 54.5 
and 97.1 per cent. The efficiency for a 
perfect steam engine is proportional to the 

tt. 
expression Sin which t and/j are absolute 



temperatures of steam at admission and 
exhaust, respectively. In actual engines 
the efficiency only approximates to the 
ideal, yet it will follow the same general 
law. Since the exhaust temperature cannot 
be lowered beyond present practise it follows 
that the only available method of increasing 
the efficiency is to raise the temperature 
at admission, which means either higher 
steam pressure, or use of superheated steam. 
As above shown, the increase in pressure 
will require but a trifling increase in fuel, 
hence the higher the pressure the greater 
the economy. 

Steam Tables Up to the present time 
an algebraic expression for the relation 
between saturated steam pressures, tem- 
peratures, and volumes, has not been pro- 
duced, except empirically. These relations 
have, however, been experimentally de- 
determined by Regnault, and from his data 
steam tables have been computed. These 
obviate the necessity of using empirical 
formulas. Such formulas may be found in 
standard works on Thermodynamics, and 
a number of them are given in Peabody's 
work below referred to. The following named 
tables cover all practical cases: 

Table 15 gives properties of saturated 
steam for varying amounts of vacuum. 

Table 17 shows variation in properties 
of steam at different pressures. 

Table 18 gives properties of saturated 
steam from 2 to 500 pounds absolute. These 
tables are based partly on Prof. Cecil H. 
Peabody's Tables of the Properties of Satu- 
rated Steam, which are generally accepted by 
engineers. 



74 



THE STIRLING WATER-TUBE SAFETY BOILER 



TABLE 18 
PROPERTIES OF SATURATED STEAM 



* Pressure above 
Vacuum. 
Lbs. per sq. in. 


Temperature, 
Degrees 
Fahrenheit. 


Heat of Liquid 
above 32Fahr. 
B. T. U. 


Latent Heat 
above 32 Fahr. 
B. T. U. 


Total Heat 
above 32 Fahr. 
B. T. U. 


Density, or Weight 
per Cubic Foot. 
Pounds. 


2 


126.3 


94-4 


1026. i 


1120.5 


0.00576 


4 


I53-I . 


121.4 


IOO7 . 2 


1128.6 


0.01107 


6 


170 . i 


138.6 


995- 2 


H33-8 


o . 01622 


8 


182.9 


I5I-5 


986.2 


H37-7 


0.02125 


10 


193-3 


161 .9 


979-o 


1140.9 


o . 02621 


12 


202 . o 


170.7 


972-9 


1143.6 


o . 031 i i 


14 


209 .6 


178.3 


967-5 


1145.8 


o . 03600 


14-7 


212 . O 


180.8 


965.8 


1146.6 


0.03760 


16 


216.3 


185.1 


962.8 


1147.9 


o . 04067 


18 


222 .4 


i9i-3 


958.5 


1149 .8 


0.04547 


20 


228.0 


196.9 


954-6 


"Si-5 


o . 05023 


22 


233-1 


202 .O 


95 1 - 


i J 53-o 


0.05495 


24 


237-8 


206.8 


947-6 


ii54-4 


0.05966 


26 


242 . 2 


211 . 2 


944-6 


H55-8 


o .06432 


28 


246.4 


215-4 


941.7 


ii57-i 


0.06899 


3 


25-3 


219.4 


938.9 


1158.3 


0.07360 


3 2 


254.0 


223.1 


936.3 


1159-4 


0.07821 


34 


257-5 


226. 7 


933-7 


i i 60 . 4 


o .08280 


36 


260. 9 


230.0 


93 J -5 


1161.5 


0.08736 


38 


264. i 


2 33-3 


929. 2 


1162.5 


o . 09191 


40 


267 . i 


236.4 


927 .0 


1163.4 


o . 09644 


42 


270. i 


239-3 


925.0 


1164.3 


o. 1009 


44 


272.9 


242 . 2 


923.0 


1165.2 


0.1054 


46 


275-7 


245.0 


921 .O 


1166.0 


o . 1099 


48 


278-3 


247.6 


919.2 


1166.8 


o. 1144 


5 


280.9 


250.2 


917.4 


1167 .6 


0.1188 


52 


283-3 


252.7 


9*5-7 


1168.4 


0.1233 


54 


285.7 


255-1 


914.0 


1169 . i 


o. 1277 


56 


288.1 


2 57-5 


912.3 


1169.8 


0.1321 


58 


290.3 


259-7 


910.8 


1170.5 


o . 1366 


60 


292.5 


26l .9 


909-3 


1171.2 


o. 1409 


62 


294.7 


264. I 


907.7 


1171.8 


0.1453 


64 


296.7 


266 . 2 


906. 2 


1172.4 


o. 1497 


66 


298.8 


268.3 


904.7 


1173.0 


0.1541 


68 


300.8 


270.3 


903-3 


1173.6 


0.1584 


70 


302.7 


272.2 


902 . I 


H74.3 


0.1628 


72 


304.6 


274.1 


9O0.8 


1174.9 


o. 1671 


74 


306.5 


276.0 


899.4 


II75-4 


0.1714 


76 


308.3 


277-8 


898.2 


1176 .0 


0.1757 


78 


310.1 


279.6 


896.9 


1176.5 


o. 1801 


80 


311.8 


28l .4 


895.6 


1177.0 


0.1843 


82 


3 I 3-S 


283.2 


894 4 


1177.6 


0.1886 


84 


315-2 


285.0 


893-1 


1178.1 


0.1930 


86 


316.8 


286.7 


891.9 


1178.6 


o.i973 


88 


318.5 


288.4 


890.7 


1179.1 


o. 2016 



*To reduce to 
above sea level, 



gauge pressures at 
subtract pressures 



sea level, subtract 
per square inch as 



14.7 from 
in Table 1 2 



pressures in this column. 
, page 58. 



In altitudes 



STEAM TABLES 
PROPERTIES OF SATURATED STEAM. CONTINUED 



75 



* Pressure above 
Vacuum. 
Lbs. Per sq. in. 


Temperature, 
Degrees 
Fahrenheit. 


Heat of Liquid 
above 32 J Fahr. 
B. T. U. 


Latent Heat 
above 32 Fahr. 
B. T. U. 


Total Heat 
above 32 Fahr. 
B. T. U. 


Density, or Weight 
Per Cubic Foot. 
Pounds. 


90 


320.0 


290 . o 


889.6 


1179.6 


o. 2058 


92 


321 .6 


291 .6 


888.4 


1180.0 


0. 2101 


94 


3 2 3-i 


293.2 


887.3 


1180.5 


o . 2144 


96 


324.6 


294.8 


886.2 


1 181 .0 


0.2186 


98 


326.1 


296 . 4 


885.0 


1181 .4 


o . 2229 


IOO 


327.6 


297-9 


884.0 


1 181 .9 


o. 2271 


102 


329.0 


299.4 


882.9 


1182.3 


0.2314 


IO4 


330-4 


300.9 


881.8 


1182.7 


0.2356 


106 


331-8 


32-3 


880.8 


1183.1 


0.2399 


108 


333- 2 


303-8 


879.8 


1183.6 


o . 2441 


no 


334-6 


305-2 


878.8 


i 184 . o 


o. 2484 


112 


335-9 


306.6 


877.8 


1184.4 


o . 2526 


114 


337-2 


308.0 


876.8 


1184.8 


0.2568 


116 


338.5 


39-4 


875.8 


1185.2 


o. 2610 


118 


339-8 


310.7 


874.9 


1185.6 


0.2653 


120 


34i-i 


312.0 


874.0 


1186.0 


0.2695 


122 


342.3 


3I3-3 


873-o 


1186.3 


0.2736 


I2 4 


343-5 


3 J 4-6 


872. i 


1186.7 


0.2779 


126 


344-7 


3I5-9 


871 .2 


1187.1 


o . 2820 


128 


345-9 


3J7- 1 


870.3 


1187.4 


o. 2862 


130 


347 - 1 


318.4 


869.4 


1187.8 


o. 2904 


132 


348.3 


319.6 


868.6 


1188.2 


o . 2946 


134 


349-5 


320.8 


867.7 


1188.5 


0.2988 


I 3 6 


35- 6 


322.0 


866.9 


1188.9 


0.3030 


138 


35 x -7 


323 2 


866.0 


1189 . 2 


0.3072 


I4O 


35 2 -9 


324-4 


865.1 


1189.5 


0-3 ri 3 


142 


354-o 


325-6 


864.3 


i 189 . 9 


0.3155 


144 


355- 1 


326.7 


863.5 


1190. 2 


o.3i97 


146 


35 6 - 1 


327-8 


862.8 


i 190 . 6 


0.3239 


148 


357-2 


328.9 


862.0 


1190.9 


o. 3280 


150 


358.3 


330.0 


861.2 


1191.2 


0.3321 


152 


359-3 


33 1 - 1 


860.4 


1191.5 


0.3363 


J 54 


360.3 


332-2 


859.6 


1191 . 8 


0.3405 


156 


361.4 


333-3 


858.9 


1192 . 2 


0.3447 


158 


362.4 


334-3 


858.2 


1192.5 


0.3488 


1 60 


363-4 


335-4 


857-4 


1192 .8 


0.3530 


162 


364-4 


336.4 


856.7 


1193.1 


0-3572 


164 


365-4 


337-5 


855-9 


II93-4 


0.3614 


166 


366.4 


338.5 


855-2 


II93-7 


0.3655 


168 


367-3 


339-5 


854.5 


1194.0 


o 3695 


170 


368.3 


340.5 


853-8 


ii94-3 


0.3737 


172 


369-2 


34i-5 


853-I 


i 194 . 6 


0.3778 


174 


370.2 


342.5 


852-3 


1194.8 


o. 3820 


176 


37 1 - 1 


343-5 


851.6 


1195.1 


o. 3862 


178 


372-1 


344-4 


851.0 


II95-4 


0.3904 


180 


373-o 


345-4 


850-3 


JI 95-7 


0-3945 



*To redtice to gauge pressures at sea level, subtract 14.7 from pressures in this column. In altitudes 
above sea level, subtract pressures per square inch as in Table 12, page 58. 



76 



THE STIRLING WATER-TUBE SAFETY BOILER 
PROPERTIES OF SATURATED STEAM. CONTINUED 



* Pressure above 
Vacuum. 
Lbs. per sq. in. 


Temperature, 
Degrees 
Fahrenheit. 


Heat of Liquid 
above 32Fahr. 
B. T. U. 


Latent Heat 
above 32 Fahr. 
B. T. U. 


Total Heat 
above 32 Fahr. 
B. T. U. 


Density, or Weight 
per Cubic Foot. 
Pounds. 


182 


373-9 


346.4 


849.6 


1196.0 


0.3987 


184 


374-8 


347-3 


848.9 


I 196 . 2 


o. 4029 


186 


375-7 


348.2 


848.3 


1196.5 


o. 4070 


1 88 


376.6 


349 2 


847.6 


1196.8 


0.4111 


190 


377-4 


35 - 1 


847.0 


II97.I 


0.4153 


192 


378.3 


35 1 o 


846.3 


"97-3 


0.4194 


194 


379-2 


35 J -9 


845.7 


1197.6 


0.4236 


196 


380.0 


352.8 


845.0 


1197.8 


0.4278 


198 


380.9 


353-7 


844.4 


1198. i 


0.4318 


200 


381-7 


354-6 


843-8 


1198.4 


0-4359 


2O2 


382.6 


355-4 


843-2 


1198.6 


0-4399 


2O4 


383-4 


356.3 


842.6 


1198.9 


0.4441 


206 


384-2 


357-2 


841.9 


1199.1 


o. 4482 


208 


385-1 


358.o 


841.4 


1199.4 


0.4524 


2IO 


385-9 


358.9 


840.7 


1199 . 6 


0.4565 


212 


386.7 


359-7 


840. 2 


1199.9 


0.4607 


214 


387.5 


360 . 6 


839.5 


i 200. i 


0.4648 


2x6 


388.3 


361-4 


839.0 


1200.4 


o . 4690 


218 


389.1 


362.2 


838.4 


i 200 . 6 


o 473 1 


22O 


389.8 


363-0 


837.8 


1200.8 


0.4772 


222 


390.6 


363-9 


837-2 


I2OI . I 


0.4813 


224 


39 x -4 


364.7 


836.6 


1201.3 


0.4855 


226 


392.2 


365-5 


836.1 


I2OI . 6 


0.4896 


228 


39 2 .9 


366.3 


835 5 


I2OI . 8 


0.4939 


230 


393.7 


367 i 


834-9 


1202 .O 


0.4979 


232 


394-5 


367 9 


834-3 


I2O2 . 2 


o. 5021 


234 


395-2 


368.6 


833-9 


I2O2 . 5 


o. 5062 


236 


395-9 


369-4 


833-3 


I2O2 . 7 


0.5103 


2 3 8 


396.7 


370.2 


832-7 


I2O2 .9 


0.5144 


24O 


397-4 


37 1 - 


832.2 


I2O3 . 2 


0.5186 


242 


398.1 


37 T -7 


831-7 


1203.4 


o. 5226 


244 


398.9 


372-5 


831.1 


1203 .6 


0.5268 


246 


399-6 


373-2 


830.6 


1203.8 


0-53 11 


248 


400.3 


374-0 


830.0 


1204.0 


0-5353 


250 


401 . o 


374-7 


829.5 


I2O4. 2 


0-5393 


252 


401 .7 


375-4 


829.1 


1204.5 


0-5433 


254 


402.4 


376.2 


828.5 


1204-7 


0-5475 


256 


403-1 


376.9 


828.0 


1204.9 


o 55 J 7 


258 


403.8 


377-6 


827-5 


I205.I 


0-5559 


260 


404-5 


378.4 


826.9 


1205.3 


o. 5601 


262 


405.2 


379-1 


826.4 


!205.5 


0.5642 


264 


405.8 


379-8 


825.9 


1205.7 


0.5684 


266 


406.5 


380.5 


825.4 


1205.9 


0.5726 


268 


407.2 


381-2 


824.9 


1206 . I 


0.5767 


270 


407-9 


381.9 


824.4 


1206.3 


0.5809 


?72 


408.5 


382.6 


823.9 


1206. 5 


0.5850 



*To reduce to gauge pressures at sea level, subtract 14.7 from pressures in this column, 
above sea level, subtract pressures per square inch as in Table 12, page 58. 



In altitudes 



STEAM TABLES 
PROPERTIES OF SATURATED STEAM. CONTINUED 



77 



*Pressure above 
Vacuum. 
Lbs. per. sq. in. 


Temperature, 
Degrees 
Fahrenheit. 


Heat of Liquid 
above 32 Fahr 
B.T. U. 


Latent Heat 
above 32 Fahr. 
B.T. U. 


Total Heat 
above 32 Fahr. 
B. T. U. 


Density, or Weight 
per Cubic Foot. 
Pounds . 


274 


409.2 


383.3 


823.4 


1206. 7 


0.5892 


276 


409 .8 


384.0 


822 .9 


1206 . 9 


0-5934 


278 


410.5 


384.6 


822.5 


1207 . i 


0.5976 


280 


411.1 


385.3 


822 .0 


1207.3 


o. 602 


282 


411.8 


386.0 


821.5 


1207.5 


o . 606 


284 


412.4 


386.6 


821.1 


1207.7 


o. 610 


286 


413- 


387-3 


820.6 


1207 . 9 


0.614 


288 


4I3-7 


388.0 


820.1 


1208. i 


0.618 


290 


4I4-3 


388.6 


819.7 


1208. 3 


o . 622 


292 


414.9 


389-3 


819.2 


1208.5 


0.627 


294 


4i5- 6 


390.0 


818.7 


1208 . 7 


0.631 


296 


416. 2 


390.6 


818.3 


1208 . 9 


0-635 


298 


416.8 


391-3 


817.8 


1209 . i 


0.639 


300 


4I7-4 


391-9 


817.4 


1209.3 


0.644 


302 


4l8.O 


392-5 


816.9 


1209 . 4 


0.648 


34 


418.6 


393-2 


816.4 


1209 . 6 


0.652 


306 


419.2 


393-8 


816.0 


1209 .8 


0-656 


308 


419.8 


394-4 


815.6 


I2IO . O 


0.660 


310 


420.4 


395- 


815.2 


I2IO. 2 


o. 664 


312 


421 . o 


395-7 


814.7 


1210.4 


0.668 


3U 


421 .6 


396.3 


814.2 


1210.5 


0.673 


3i6 


422 . 2 


396.9 


813.8 


1210.7 


0.677 


3i8 


422.8 


397-5 


8i3-4 


1210.9 


0.681 


320 


423-4 


398.1 


813.0 


I2II . I 


0.685 


322 


424.0 


398.7 


812.5 


121 I . 2 


0.690 


3 2 4 


424-5 


399-3 


812. i 


I2II.4 


0.694 


326 


425.1 


399-9 


811.7 


121 I . 6 


0.698 


328 


425-7 


400.5 


811.3 


I2II.8 


o. 702 


33 


426. 2 


401 . i 


810.8 


I2II.9 


0.707 


335 


427.6 


402 .6 


809.8 


1212 .4 


0.717 


35 


43J-9 


406.9 


806.8 


1213.7 


0.748 


375 


43 8 -4 


414.2 


801.5 


1215.7 


0.800 


400 


445- 2 


421.4 


796.3 


1217.7 


0-853 


45 


456.2 


433-4 


787.7 


1221 . I 


-959 


500 


466.6 


444-3 


779-9 


1224. 2 


1.065 



*To reduce to gauge pressures at 

above sea level, subtract pressures 

For relation between Heat of the 



sea level, subtract 14.7 from pressures in this column. 

per square inch as in Table 12, page 58. 

Liquid, Latent Heat, and Total Heat, see page 50. 



In altitudes 



Moisture in Steam 



Practically all saturated steam contains 
water, varying in amount from a fraction oi 
one per cent, when the steam is generated in 
a properly designed boiler fed with good 
water, to five per cent, or even more when 
the feed water is bad, or the boilers are of 
defective design. Not only is the heat 
absorbed by raising this water from the 
boiler feed temperature to the steam tem- 
perature practically wasted, but the water 
causes further loss by increasing the initial 
condensation in the engine cylinder; it also 
interferes with proper cylinder lubrication, 
causes knocking in the engine, and water 
hammer in the steam pipe. 

Quality of Steam The percentage weight 
of steam, in a mixture of steam and water, is 
called the quality of the steam. Thus steam 
of quality 99.5 contains one-half of one per 
cent, by weight of moisture. 

Calorimeters The apparatus used to de- 
termine the content of moisture in steam is 
called a calorimeter, though the name is inapt, 
since the instrument is in no sense a measurer 
of heat. The first form used was the "barrel 
calorimeter,'' in this apparatus liability of 
error is so great that its use is practically 
abandoned. Modern calorimeters are usually 
of either the throttling or separator type. 

Throttling Calorimeter Fig. 14 shows a 
section through a typical form of the instru- 
ment. Steam is drawn from the vertical 
pipe by a nipple arranged as later described, 
passes around the first thermometer cup as 
shown, then through a hole about ^-inch 
diameter in the disk as shown. It next 
passes around the lower thermometer cup, 
after which it is permitted to escape. Ther- 
mometers are inserted into the cups, which are 
then filled with cylinder oil, and when the 
whole apparatus is heated the temperature 
of the steam before and after passing through 
the hole in the disk is noted. 

The instrument and pipes leading to it 
should be thoroughly covered to diminish 
the radiation loss. 

When steam passes from a higher to a 
lower pressure, as in this case, no work has to 
be done in overcoming a resistance; hence, 



assuming there is no loss from radiation, the 
quantity of heat is exactly the same after 
passing the disk as it was ahead of it. Sup- 
pose that the higher steam pressure is 150 
Ibs. by gauge, and the lower pressure that of 
the atmosphere. The total heat in a pound 
of dry steam at the former pressure is 1193.5 
B. T. U. and at the latter pressure is 1146.6 
B. T. U., difference, 46.9 B. T. U. As this 
heat still exists in the steam of lower pressure, 




TO ATMOSPHERE - 

FIG. 14. THROTTLING CALORIMETER AND SAMPLING PIPE 

its effect is to superheat that steam. Assum- 
ing the specific heat of steam to be 0.48, the 

46.9 

steam will then be superheated - ^ = 97.7 

0.40 

degrees. Suppose, however, the steam had 
contained one per cent, of moisture. Before any 
superheating could occur, this moisture would 
have to be evaporated into steam of atmos- 
pheric pressure . Since the latent heat of steam 
at atmospheric pressure is965.8B.T.U.it fol- 
lows that the one per cent, of moisture would 
require 9.58 B. T. U. to evaporate it, leaving 
only 46.9 - 69.658 = 37.242 B. T. U. available 
for superheating, hence the superheat would 

37.242 
be => 77.6 as against 97.7 degrees in 

the preceding case. In a similar manner the 
degree of superheat for other amounts of 
moisture can be determined, and the action 
of the throttling calorimeter is based on this 
fact as will now be shown. 















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FORMULAS FOR THROTTLING CALORIMETER 



81 



Let H= total heat of steam at boiler press- 
ure. 

L = latent heat of steam at boiler press- 
ure. 

h = total heat of steam at reduced press- 
ure after passing the disk. 
*j = temperature of saturated steam at 

the reduced pressure. 
t a = temperature of steam after expand- 
ing through opening in the disk. 
0.48= specific heat of saturated steam. 

x = proportion of moisture in the steam. 
The difference between the B. T. U.'s in a 
pound of steam at boiler pressure and after 
passing the disk is the heat which must 
evaporate the moisture in the steam, and 
then do the superheating, hence 

Hh=xLo.4S(t 2 t 1 ), therefore 



H-h-o.. 



- *,) 



[6] 

i^, 

Almost invariably the lower pressure is ta- 
ken as that of the atmosphere where 
/t==ii46.6 and ^=212, hence the formula be- 
comes 

H 1146.6 0.48 (t z 212) 

For practical work it is more convenient to 
dispense with the upper thermometer in the 
calorimeter, and substitute an accurate steam 
guage whose readings are more easily noted. 

The value of x may be obtained, without 
computation, from Fig. 15. To illustrate 
its use, suppose that the steam gauge on the 
calorimeter indicated 160 pounds pressure, 
and that the temperature t z in the calorimeter 
after the steam had expanded was 304. 
Look on the bottom line of the chart and 
locate the vertical line over 304; look into 
the gauge pressure scale on the left side of the 
chart, and locate the horizontal line opposite 
1 60 pounds; these two lines intersect the- 
diagonal line indicating one-half of one per 
cent, of moisture. If instead of a steam gauge 
to indicate the pressure, a thermometer had 
been used to indicate the temperature of the 
steam before expanding, the temperature on 
the upper thermometer would have been 370, 
and the column of temperatures on the ex- 
treme left hand of the chart would be the one 
to use; the horizontal line opposite 370 will 
be found to be the same one which is opposite 



1 60 pounds pressure, hence as before the 
moisture will be one-half of one per cent. 

Sources of Error There are two. The 
first is that the specific heat of superheated 
steam, while given as 0.48, is far from being 
certain, and only future investigation can 
determine the true value. The second source 
of error is loss of heat by radiation. Evi- 
dently from the moment the steam enters 
the sampling nipple it is losing heat, hence 
when it passes through the small opening and 
into the lower pressure the heat available for 
evaporating moisture and superheating will 
be diminished by just the amount lost by 
radiation, hence the value of t z will be lower 
than it should be. This is sometimes cor- 
rected for as follows: A valve in the steam 
pipe beyond the calorimeter nipple is closed, 
and the steam left in a quiescent state for 
about ten minutes, and it is assumed that by 
doing this all the moisture in the steam will 
settle out, and that a sample of steam drawn 
from the pipe will be dry. Steam is then 
allowed to flow through the calorimeter and 
the temperature of the lower thermometer is 
noted. Let T denote this temperature. 
Since the sample of steam was assumed to be 
dry it follows that if there were no loss from 
radiation the value of T would be that due 
to all of the liberated heat being absorbed 
in superheating the steam of lower tempera- 
ture. There is, however, a loss by radiation, 
and the effect of this is to condense some of 
the steam of lower pressure, and the water 
thus formed must be evaporated before any 
superheating can be done. Let x 1 represent 
the proportion of water thus formed, then 
evidently 



L 

Now this amount of water was not in the 
steam originally, but was caused by con- 
densation in the instrument, hence the true 
amount of moisture in the steam, which may 
be denoted by X, will be 

H h 0.48 (t% ^) 
X=x-x - j 

H-h-o.48 (T-M 



L 

0.48 (T-t 9 \ 
L 



[8] 




JACOB RUPPERT ICE CO., NEW YORK, OPERATING 2, TOO H. P. OF STIRLING BOILERS 



SEPARATING CALORIMETER 



83 



The disadvantages of this method are: 
(i) It assumes that during the test the 
boiler pressure will remain the same as it was 
when T was determined, which is seldom 
practicable; (2) It assumes that the sample 
of steam drawn into the instrument when 
determining T was absolutely dry, although 
experiment has shown that this assumption 
is not necessarily true. Notwithstanding 
these facts, formula [8] is much used by 
engineers because of its simplicity and con- 
venience, and any error due to its use is of no 
practical significance. 

There are many forms of throttling calori- 
meter, all of which operate on precisely the 
same principle as the simple design shown in 
Fig. 14. An extremely convenient and com- 
pact design is shown in Fig. 16. It consists 
of two concentric cylinders screwed to a cap 
containing a thermometer cup. The steam 
pressure is measured by a gauge placed in the 
supply pipe, or any other convenient place. 




FIG. 16. COMPACT THROTTLING CALORIMETER 

Steam passes through the opening A , expands 
to atmospheric pressure, and its temperature 
at this pressure is measured by a thermometer 
placed in the cup C. To prevent radiation 
losses the annular space between the two 
cylinders is used as a jacket, and is supplied 
with steam through the hole B. 



The limits of the throttling calorimeter 
at sea level are from about four per cent, of 
moisture at eighty pounds pressure to six per 
cent, at 200 pounds pressure. If there is a 
greater content of moisture the liberated heat 
is insufficient to evaporate it and superheat 
the steam thus generated. 




FIG. 17. SEPARATING CALORIMETER 

Separating Calorimeter The separating 
calorimeter mechanically separates the en- 
trained water from the steam and collects it 
in a reservoir, where its amount is either 
indicated by a gauge glass or determined by 
draining it off and weighing it. The steam 
passes out of the calorimeter through an 
orifice of known size, so that either its total 
amount can be calculated or it can be weighed 
as later described. To avoid radiation errors 
the calorimeter should be well covered with 
non-conducting material. This instrument 
is not limited in capacity theoretically, but 
if the amount of moisture is very large, the 
readings should be checked by passing the 
discharged steam through a throttling calori- 



TAKING A CALORIMETER OBSERVATION 



85 



meter; that is, a small separator should be 
used between the steam pipe and a throttling 
calorimeter, and the sum of the percentages 
obtained from the two instruments be taken 
as the moisture in the steam. 

In the separating calorimeter, the amount 
of steam passing through the orifice can be 
determined by Napier's empirical formula, 
page 91. There is liability of considsrable 
erron in determining the area of such small 
orifices, and further, the flow of steam soon 
wears the orifice larger. A more accurate 
method of determining the weight of steam 
passing through is to convey it through a hose 
into a barrel of water resting on a platform 
scale. The weight of the barrel and contained 
water having been noted before and after the 
steam is run in, the difference is the weight 
of steam condensed. The moisture caught 
in the separating calorimeter can be weighed 
in the same way. If W is the weight of steam 
condensed, w the weight of moisture from the 
separating calorimeter, and x the per cent. 
of moisture in the steam, then 

IOOW 

'-wTw l9] 

Location of Sampling Nipple The prin- 
cipal source of inaccuracy in calorimeter 
determinations is failure to secure an average 
sample of steam. It is extremely doubtful 
whether such a sample is ever secured. To 
diminish the liability of error the instrument 
should be located as near as possible to the 
point where the sample is drawn off, and the 
sampling nipple should be placed as fully 
described in "Rules for Conducting Boiler 
Trials,'' Article XIV, page 204. 

Taking an Observation Locate the 
sampling nipple as above directed, attach the 
instrument as close to it as possible, and 



cover all exposed parts to prevent radiation. 
If the throttling calorimeter be used, locate 
the steam gauge on the pressure side, and the 
thermometer on the expansion side. To 
take an observation, note simultaneously the 
gauge reading and the thermometer reading, 
and from these the content of moisture may 
be determined directly from Fig. 15 or by 
use of formula [7]. If the separating calori- 
meter be used, attach to the separator outlet 
a piece of hose which terminates in a vessel of 
water on a platform scale graduated to read 
to j^ of a pound. Similarly connect the 
steam outlet to another vessel of water resting 
on an equally sensitive scale. Note in each 
case the weight of each vessel including the 
water it contains. When ready to take 
an observation, blow out the instrument 
thoroughly, so there will be no water in the 
separator. Then simultaneously close the 
separator drip and insert the steam hose into 
its vessel of water. When the separator has 
accumulated a sufficient quantity of water, 
close the valve at the main steam pipe, thus 
cutting off the supply of steam to the instru- 
ment, remove the steam hose from the vessel 
of water into which it was inserted, and 
empty the separator water into its vessel on 
the scale. Note the final weight of each 
vessel and contents, then the differences 
between final and original weights will be re- 
spectively, the weight of moisture collected 
by the separator, and the weight of steam 
from which this moisture was taken, hence 
the proportion of moisture can be computed 
from formula [9]. 

Before taking any calorimeter observations, 
steam should be allowed to flow through 
freely until the instrument is thoroughly 
heated up. 



Flow of Steam Through Pipes and Orifices 



Formulas for the flow of steam through 
pipes are based upon Bernoulli 's theorem for 
the flow of water through circular pipes with 
friction, modified by inserting the proper 
constants for steam. The loss of energy due 
to friction is given by Unwin (from Weis- 
bach) as 

* 

[10] 



If D represents the density or weight 
of steam per cubic foot, and p the loss of 
pressure in pounds per square inch, due 
to friction, then , -r\ 

P = [14] 

144 

and from [n], [13] and [14], 



where E is the energy loss in foot pounds, due Let dj=diameter of pipe in inches=i2d. 
to the friction of W units (of weight) of Let w=the flow in pounds per minute, 
steam passing through a pipe d feet in ( d ) z o 6w 

diameter and L feet long, with a velocity of then?f=6oi>X -I \ D, hence v = which 

(12) *0*D 

TABLE 19 
FLOW OF STEAM THROUGH PIPES 



Initial Gauge 


DIAMETER* OF PIPE IN INCHES. LENGTH OP PIPE = 240 DIAMETERS. 


Pressure, 
Pounds per 


* 


I 


li 


2 


ij 


3 


4 


5 


6 


8 


to 


12 


15 


18 


Square Inch. 


WEIGHT OF STEAM PEH MINUTE, IN POUNDS, WITH ONE POUND LOSS OF PRESSURE. 


i 


I .16 


2.07 


5-7 


10. 27 


15-45 


25.38 


46.85 


77-3 


H5-9 


211 .4 


34i i 


502.4 


804 


1177 


10 


I .44 


2-57 


7-1 


12.72 


19-15 


31 -45 


58.05 


95-8 


143.6 


262 . o 


422.7 


622.5 


996 


1458 


20 


1.70 


3-02 


8.3 


14-94 


22.49 


36.94 


68.20 


112. 6 


168.7 


307-8 


496.5 


731-3 


1170 


1713 


30 


1. 91 


3.40 


9-4 


16.84 


25.35 


41 .63 


76.04 


126.9 


190. i 


346.8 


559-5 


824.1 


1318 


1930 


40 


2. 10 


3.74 


10.3 


iS.SI 


27.87 


45-77 


84.49 


139-5 


209 .0 


381.3 


6i5.3 


906.0 


1450 


2122 


5 


2. 27 


4.04 


II . 2 


20. OI 


30.13 


49-48 


91 -34 


150.8 


226.0 


412. 2 


665.0 


979-5 


1567 


2294 


60 


2.43 


4.32 


II. 9 


21.38 


32.19 


52.87 


97.60 


161 . i 


241 . > 


440.5 


710.6 


046.7 


1675 


2451 


70 


2-57 


4.58 


12 .6 


22.65 


34-10 


56.00 


03.37 


170.7 


255-8 


466 . 5 


752.7 


108.5 


1774 


2596 


80 


2.71 


4.82 


13-3 


23.82 


35.87 


58.91 


08.74 


179-5 


269.0 


490.7 


791.7 


166.1 


1866 


2731 


90 


2.83 


5.04 


13.9 


24.92 


37-52 


61 .62 


13.74 


187.8 


281.4 


513-3 


828.1 


219.8 


I95i 


2856 


IOO 


2.95 


5.25 


14.5 


25.96 


39-07 


64.18 


18.47 


195-6 


293-1 


534.6 


862.6 


270. i 


2032 


2975 


I2O 


3.16 


5.63 


15.5 


27.85 


41 -93 


68.87 


27 . 12 


209.9 


314.5 


573-7 


925.6 


363.3 


2181 


3193 


ISO 


3.45 


6. 14 


17.0 


30.37 


45-72 


75-09 


38.61 


228.8 


343-0 


625.5 


1009. 2 


486.5 


2378 


3481 



v feet per second; g represents the accelera- 
tion of gravity (32.2) and / the coefficient 
of friction, which varies with the velocity 
to a certain extent, and with the size of the 
pipe. Some authorities consider both of 
these considerations negligible and treat / 
as a constant. In this article it will be 
regarded as varying according to the size of 
the pipe only, that is, 

/-^(i + ifa) ["I 

which relation was established by Unwin for 
a velocity of 100 feet per second. K is a 
constant experimentally determined and d 
the diameter of the pipe in feet. 

If h be the loss of head in feet, then 



when substituted in [15] gives 

f ? 6 ) w s L 
p = 0.04839 K \ i + \ 



The following experimental determinations 

of K have been made: 

K= . 005 for water. (Unwin) 
= .005 for air. (Arson) 
= . 0028 for air. (St. Gothard Tunnel Exp.) 
= . 0026 for steam. (Carpenter, Oriskany) 
= .0027 for steam. (G. H. Babcock) 

Using the value K=.OO27, and substitut- 
ing in [16] gives 

3.6) w*L 
p=o. 000131 ' 



Hence iv= 87 




[18] 



*Diametets up to 5 inches inclusive are actual internal diameters of standard pipe, per Table 61 , p. 213. 

87 




500 H. P. OF STIRLING BOILERS, HONOLULU BREWING & MALTING CO., LT'D., HONOLULU, H. 



RESISTANCE OF ELBOWS AND GLOBE VALVES 



89 



in which w=the flow in pounds per minute . 

p =difference in pressure between 

the two ends of the pipe, in 

pounds per square inch. 

D=density, or weight, per cubic 

foot of steam. 

d, =diameter of pipe in inches. 
L=length of pipe in feet. 
Table 19 is based on formula [18] and 
gives approximately the weight of steam 
per minute which will flow from various 
initial pressures, with one pound loss of 
pressure, through straight, smooth pipes, 
each having a length of 240 diameters. 



For any assumed pipe length and loss, 
the weight will be 



Example: Find the weight of steam 
of 100 Ibs. initial gauge pressure which will 
pass through a 6" pipe 720 feet long with a 
drop of 4 Ibs. Under the conditions in the 
Table, 293.1 Ibs. will pass, hence Q = 293.1 

j 240X6X4 ) * 
and Q, =293. H- - \ =239.3 Ibs 



720X12 

Table 20 is due to Mr. E. C. Sickles, who 
used formula [16] with Prof. Carpenter's 



TABLE 20 
FLOW OF STEAM THROUGH PIPES 

LENGTH OF PIPE ONE THOUSAND FEET 



DISCHARGE IN POUNDS PER MINUTE CORRESPONDING TO DROP IN 
PRESSURE ON RIGHT FOR PIPE DIAMETERS 


DROP IN PRESSURE IN POUNDS PER SQUARE INCH CORRESPOND- 
ING TO DISCHARGE ON LEFT; DENSITIES AND CORRES- 


IN INCHES IN TOP LINE. 


PONDING ABSOLUTE PRESSURES PER SQUARE 




INCH IN FIRST TWO LINES. 


Diameter.- 


12" 


10" 


8" 


6" 


4" 


3" 


2*" 


2" 


ii* 


I- 


Density. 
Pressure. 


.208 
90 


. 230 

100 


.284 
125 


.328 
150 


.401 
1 80 


-443 
200 


.506 

230 


548 
250 


Discharge 


2328 


443 


799 


371 


123- 


55-9 


28.8 


8.1 


6. Si 


52 


Drop 


18.10 


16.4 


13-3 


ii . i 


9-39 


8.50 


7-44 


6.87 




2165 


341 


742 


344 


114. 6 


51-9 


27 . 6 


6.8 


6.52 


-34 




15.60 


14-1 


II. 4 


9. 60 


8.09 


7-33 


6.41 


5-92 




1996 


237 


685 


318 


106. 


47 -9 


26.4 


5-5 


6. 24 


.16 




13-3 


12. O 


9-74 


8.18 


6.90 


6. 24 


5-47 


5-05 




1830 


134 


628 


292 


97.0 


43-9 


25.2 


4.2 


5-95 


.98 




ii . i 


IO.O 


8.13 


6.83 


S.76 


5-21 


4-56 


4-21 




1663 


3i 


571 


265 


88.2 


39-9 


24.0 


2-9 


5-67 


.80 




9.25 


8.36 


6.78 


5.69 


4.80 


4-34 


3.80 


3-51 




1580 


979 


542 


252 


83.8 


37-9 


22.8 


2.3 


5-29 


71 




8.33 


7-53 


6. io 


5.13 


4-32 


3-91 


3-42 


3.i6 




1497 


928 


Si4 


239 


79-4 


35-9 


21.6 


1.6 


5.00 


.62 




7.48 


6.76 


5.48 


4. 60 


3-88 


3-Si 


3-07 


2.84 




1414 


876 


48s 


226 


75- 


33.9 


20.4 


0.9 


4.72 


-53 




6.67 


6.03 


4.88 


4. io 


3.46 


3-13 


2.74 


2.53 




1331 


825 


457 


212 


70.6 


31-9 


19.2 


0.3 


4-43 


44 




5-91 


5-35 


4-33 


3-64 


3-07 


2.78 


2.43 


2.24 




1248 


873 


428 


199 


66.2 


23-9 


18.0 


9.68 


4-15 


35 




5-19 


4.69 


3-8o 


3-io 


2.69 


2.44 


2.13 


1.97 




1 164 


722 


400 


1 86 


61.7 


27.9 


16.8 


9-03 


3-86 


.26 




4-52 


4.09 


3-31 


2.78 


2.34 


2.12 


1.86 


1-72 




1081 


670 


37i 


172 


57-3 


25-9 


iS-6 


8.38 


3.68 


'7 




3-9 


3-53 


2.86 


2.40 


2 .02 


1.8 3 


i .60 


1.48 




908 


619 


343 


1 59 


52.9 


23-9 


14-4 


7-74 


3-40 


.08 




3-32 


3 -oo 


2.43 


2.04 


I .72 


1.56 


1.36 


1.26 




9IS 


567 


314 


146 


48.5 


21.9 


13-2 


7.10 


3 -ii 


0.99 




2.79 


2.52 


2.04 


1-72 


i -45 


I -31 


i .'5 


1 .06 




832 


516 


286 


132 


44- I 


20.0 


12 .0 


6.45 


2.83 


o .90 




2.31 


2 .OQ 


1 .69 


1.42 


I . 20 


I .08 


949 


.877 




748 


464 


257 


119 


39-7 


18.0 


io.. S 


5-8i 


2.55 


0.81 




1.87 


I . 69 


1-37 


i. IS 


-97 


.878 


.769 


.710 




665 


412 


228 


1 06 


35-3 


16.0 


9.6 


5.i6 


2. 26 


0.72 




1-47 


I - 33 


i .08 


905 


.762 


.690 


.604 


558 




582 


36i 


200 


92.8 


3-9 


14.0 


8.4 


4-52 


1.98 


0.63 




1. 13 


I .02 


.828 


.695 


.586 


531 


4S6 


.429 



To get the pressure drop for lengths other than 1,000 feet, multiply by lengths in feet-ri.ooo. 



To apply the table when the pipe lengths 
and the loss in pressure differ from those 
assumed, let L = the length, and d = ihe 
diameter of pipe, both in inches; I = the 
loss in pounds; Q = the weights as given 
in the table, and Q t = the weight under 
the changed conditions, then: 

For any length of pipe, if the weight of 
steam passing is the same as given in the 
table, the loss will be 



/=. 



240^ 



[19] 



If the pipe length is the same as assumed 
in the table, but the loss is different, then 
the quantity passing will be 



= Ql 



value K =0.0026. To use the table, assume 
a certain drop in pressure. Look for this 
drop in the column at the right under the 
heading "Drop in pressure in pounds;" 
next pass to the left along a horizontal 
line, until under heading "Discharge in 
pounds per minute" the tabular quantity 
which corresponds nearest to the quantity 
desired, is found; the size of pipe given at 
the top of the column in which the tabular 
quantity is located will be the one required. 
Elbows, globe valves, and a square ended 
entrance to the pipe, all offer resistance to 
the passage of the steam; it is convenient 
to consider this resistance equivalent to a 
length of straight pipe, and add these equiv- 
alent lengths to the straight portions of 



90 



THE STIRLING WATER-TUBE SAFETY BOILER 



the pipe line to obtain the total length to 
be used in the formulas. Complicated for- 
mulas for determining the equivalent length 
have been worked out, but in view of the 
varying proportions of valves and fittings 
such formulas are not worth the time it 
takes to apply them, and for all practical 
purposes it will be sufficiently accurate to 
allow for resistance at the entrance of a 
pipe a length equal to 60 times the diameter; 
for a right angled elbow a length of 40 di- 
ameters, and for a globe valve a length equal 
to 60 diameters. 



the pipe to 6,000 ft. per minute. When 
the pipes are long, this sometimes gives 
a greater drop in pressure than is desirable, 
and it is then best to check the sizes by refer- 
ring to the tables. 

In marine work, a velocity of 9,000 ft. 
per minute in steam pipes is very often 
used with excellent results, and there is no 
reason why this cannot be done in stationary 
practise, provided the boilers can be worked 
at a pressure sufficient to compensate for 
the drop in the pipe line. See the chapter 
on Steam Piping, page 213. 



TABLE 21 
FLOW OF STEAM INTO THE ATMOSPHERE 



Absolute Initial 
Pressure 
per Square Inch. 
Pounds . 


Velocity of Outflow 
at 
Constant Density, 
Feet per Second.* 


Actual Velocity 
of Outflow, 
Expanded . 
Feet per Second. 


Discharge 
per Square Inch of 
Orifice per Minute. 
Pounds. 


Horse-Power 
per Square Inch 
of Orifice if H.P.= 
30 Ibs. per Hour. 


2 5-37 


863 


1,401 


22. 8l 


45- 6 


3- 


867 


1,408 


26.84 


53-7 


40. 


874 


1,419 


35-i8 


70.4 


5- 


880 


1,429 


44.06 


88.1 


60. 


885 


J ,437 


5 2 -59 


105.2 


70. 


889 


i,444 


61 .07 


122 . I 


75- 


891 


i,447 


6 5-3 


130.6 


90. 


895 


i,454 


77-94 


r 55-9 


IOO. 


898 


!,459 


86.34 


172.7 


$ 


902 


1,466 


98.76 


J 97-5 


135- 


906 


i,47 2 


115.61 


231.2 


*55- 


910 


1,478 


132.21 


264.4 


165- 


912 


1,481 


140.46 


280.9 


2I 5- 


919 


i,493 


181.58 


363-2 



Drop in pressure in a steam pipe does 
not necessarily indicate a loss of energy, 
because the friction which causes the drop 
transforms the energy into heat, and this 
evaporates moisture and superheats the 
steam. The superheating effect is very 
slight ordinarily, but will be very manifest 
if the pressure drop is large, as illustrated 
in the throttling calorimeter. 

A common rule in laying out piping is 
to limit the velocity of the steam through 



Flow of Steam into the Atmosphere 

When steam is discharged into the atmos- 
phere, the velocity of outflow (at constant 
density and when the absolute pressures are 
greater than 1.73 times the atmospheric 
pressure) is as given in Table 21. 

The external pressure per square inch has 
been taken as that existing under the standard 
atmospheric pressure of 14.7 Ibs. absolute 
while the ratio of expansion in the nozzle 
itself has been taken as 1.624. 



*/. e., if the steam maintained the same density as it had at the initial pressure. 



FLOW OF STEAM THROUGH ORIFICES 



91 



Napier's approximate formula for the out- 
flow of steam into the atmosphere is 

t>& 

Pounds of steam per second = [2 2 1 

70 

In which p = absolute pressure in pounds 
per square inch, and a = area of orifice in 
square inches. This formula gives results 
which correspond very closely with those in 
Table 21 as shown below: 



f 


Discharge, Pounds, per Minute. 


By 

Table 21. 


By 
Napier's Rule. 


25-37 


22.81 


21.74 


40. 


35-18 


34-29 


60. 


5 2 -59 


5 J -43 


75- 


65-30 


64.29 


100. 


86.34 


85-71 


135- 


115.61 


H5-7 1 


165. 


140 . 46 


141-43 


2I 5- 


181.58 


184. 29 



Prof. Peabody conducted a series of ex- 
periments on flow of steam through tubes 
|-inch in diameter and -inch to ^-inch, and 
i^-inch long, with rounded entrances, in 



which the results agreed closely with Napier's 
formula, the greatest difference being an 
excess of the experimental over the cal- 
culated result, of 3.2 per cent. 

Flow of Steam from Orifices into a 
Pressure Above that of the Atmosphere 
The flow of steam of a higher towards a lower 
pressure increases as the difference of pressure 
is increased, until the external pressure be- 
comes only 58 per cent, of the absolute initial 
pressure. Below this point, the flow of steam 
is neither increased nor diminished by a re- 
duction of external pressure, even to the ex- 
tent of a perfect vacuum. Table 22, selected 
from Mr. Brownlee's data, illustrates this fact. 
The following formula is frequently used 
to determine the flow of steam through an 
orifice against a pressure greater than two- 
thirds the discharge : 

W=i. 9 AK(P-p)* p [23] 

where VF=weight of escaping steam in pounds 

per minute. 

A=&rea of orifice in square inches. 
K=o.g3 for a short pipe and 0.63 for 
an opening such as a hole in a 
plate or a safety valve. 
P = absolute pressure of steam, pounds. 

per square inch. 

p = difference in pressure between the 
two sides in Ibs. per square inch. 



TABLE 22 
FLOW OF STEAM THROUGH ORIFICES (Brownlee) 



Absolute Pres- 
sure in Boiler 
per Sq. In. 
Pounds. 


Absolute 
External Pressure 
per Square Inch. 
Pounds. 


Ratio of 
Expansion in 
Nozzle. 


Velocity of Out- 
flow at Constant 
Density. 
Feet per Second . 


Actual Velocity 
of Outflow 
Expanded . 
Feet per Second. 


Discharge per 
Square Inch of 
Orifice per Min. 
Pounds . 


75 


74 


I .012 


227.5 


230. 


16.68 


75 


72 


i-37 


386.7 


401 . 


28.35 


75 


70 


1.063 


49- 


521. 


35-93 


75 


65 


1.136 


660. 


749- 


48.38 


75 


61 .62 


1.198 


736. 


876. 


53-97 


75 


60 


i . 219 


765- 


933- 


56.12 


75 


5 


1-434 


873. 


1252. 


64- 


75 


45 


1-575 


890. 


1401 . 


65.24 


75 


43-46 


i . 624 


890.6 


1446.5 


65-3 


75 


IS 


i .624 


890.6 


1446.5 


65-3 


75 


o 


i .624 


890.6 


1446.5 


65-3 




FIG. 18. THE STIRLING SUPERHEATER BOILER AS INSTALLED FOR THE GENERAL ELECTRIC CO. 
16,000 H. P. OF STIRLING BOILERS OPERATED BY THIS COMPANY 



Superheated Steam and the Stirling Superheater 



Superheated steam is steam whose tem- 
perature exceeds that of saturated steam of 
the same pressure, and it is produced by 
adding additional heat to saturated steam 
which has been removed from contact with 
the water from which it was formed. Its 
properties approximate those of a perfect 
gas, and its thermal conductivity is lower 
than that of saturated steam. 

Superheated steam is used because : 

(1 ) There is always a loss of heat by radia- 
tion from steam pipes, and the heat so lost rep- 
resents an equivalent condensation when the 
pipe conveys saturated steam. Superheated 
steam cannot condense; it must first lose all 
of its superheat and be reduced to saturated 
steam. In consequence, if sufficiently super- 
heated it can lose the amount of heat repre- 
sented by radiation from the steam pipes, yet 
reach the engine perfectly dry. Since the 
thermal conductivity of superheated steam is 
less than that of saturated steam, the heat 
will not be so rapidly transmitted from the 
body of the steam to the walls of the pipe. 

(2) In an engine the steam is admitted into 
a space which has been cooled by the steam 
exhausted during the previous stroke. The 
heat necessary to warm the cylinder walls 
from the exhaust temperature to the tem- 
perature of the entering steam can be sup- 
plied only by the entering steam, hence if it 
be saturated some of it must condense. The 
amount thus condensed is seldom less than 
20 to 30 per cent, of the total weight of steam 
entering the cylinder. It is obvious, how- 
ever, that if an amount of heat more than 
sufficient to warm the cylinder walls could, 
by means of superheating, be imparted to the 
steam before it reached the engine, then even 
after the cylinder walls had been warmed up 
the steam would remain dry, and the initial 
condensation would thus be overcome. 

These properties of superheated steam 
have long been known, but their practical 
application has been slow, owing to con- 
structive difficulties. The recent successful 
development of the steam turbine, and of 
reciprocating engines adapted to the use of 
superheated steam, has rendered necessary 



the development of a simple, durable, effi- 
cient and safe steam superheater. The 
Stirling Company therefore inaugurated an 
exhaustive series of researches and experi- 
ments on superheated steam, and these have 
resulted in the development of a superheater 
which has produced a higher degree of super- 
heat than has yet been recorded as obtained 
from any other type of superheater installed 
in connection with a boiler. In addition 
to this, its constructive features are as 
radical an improvement over previous super- 
heaters as the Stirling boiler is over the types 
of boiler which preceeded it. 

Before describing the Stirling superheater 
the principles governing the amount of super- 
heating surface, and of the heating surface 
of the boiler to which the superheater is 
attached, will be explained and illustrated. 

Specific Heat of Superheated Steam 
The amount of fuel required to superheat 
steam, and the quantity of fuel that must be 
burned to produce this heat, are greater than 
is commonly supposed. The specific heat of 
superheated steam at atmospheric pressure 
and near the point of saturation was found by 
Regnault to be 0.48, and for the succeeding 
50 years it was thought that this value of 
the specific heat applied to higher pressures. 
Recent investigations both in this country 
and in Europe have shown that the specific 
heat is not constant, and that it is approxi- 
mately 0.65 for 100 superheat, and 0.75 
for 200 superheat. Using these values it can 
be calculated that the fuel used to gen- 
erate saturated steam must be increased 
by about the following percentages in order 
to superheat the steam to the degrees named. 

TABLE 23 
FUEL NEEDED FOR SUPERHEATING 



DEGREE OF 
SUPERHEAT 

75 
100 

150 

200 
2 5 



ADDITIONAL 
FUEL NEEDED 

5% 

7 
ii 

' '5 

20 







ll 


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rmW 
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SEt 


PURE IN DEGREES FAHRENHEIT OF HOT GASES SWEEPING HEATING SURFACE. 




~P 

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1 TEMPERA" 


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5 - > l B tS 


~ S3SWO AB H3AO Q3SSVd 


30tfJdnS ONIJ.V3H U3XVM JO J.N30 U3d 





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O 



TEMPERATURE OF GASES SWEEPING HEATING SURFACE 



95 



The degree of superheat being assumed, 
the amount of superheating surface required 
to produce it will depend upon where the 
surface is located in the path of the hot gases, 
between the furnace and breeching. This 
principle is of the utmost importance in super- 
heater design, hence it will be further illus- 
trated by means of the curve in Fig 19. In 
this the abscissas represent the temperature 
of the hot gases at different points in their 
path from the boiler furnace to the breeching ; 
the column on the extreme left indicates the 
per cent, of boiler heating surface passed over 
by the gases, and the adjoining column gives 
the amount of steam generated by the heat 
absorbed from the gases, this amount of 
steam being expressed as a per cent, of the 
total steam generated in the boiler. Ex- 
ample: When the gases are cooled to 700, 
they have passed over 60% of the boiler 
heating surface, and the heat they have 
given up has generated 90% of the steam 
which the boiler is producing. 

In drawing the curve, 10 square feet of 
heating surface have been taken as the 
equivalent of one boiler horse-power*, in con- 
formity with the usual practise of builders of 
water- tube boilers. The furnace temperature 
has been assumed as 2500 F., as the result 
of many experiments made by this Company's 
engineers. The breeching temperature of 
500. is assumed as a fair average of condi- 
tions for best economy. This temperature 
may appear to be too high, in view of the 
statement current in engineering literature, 
that for each reduction of 1 00 in the breeching 
temperature the boiler efficiency is increased 
6%. In order that this statement may be 
true the air supply per pound of fuel, the degree 
of completeness of the combustion, the losses 
by radiation and air leakages, the kind of 
fuel, and other factors, must remain un- 
changed a requirement which cannot be 
met in practise. A deficient air supply will 
cause the volatile matter in the fuel to pass 
off unburnt, and while this may lower the 
breeching temperature, it lowers the efficiency 
also. In consequence of these facts, and as 
further proved by many tests, a low breeching 
temperature does not necessarily indicate high 
efficiency, and an increase in the temperature 
often augments the efficiency, hence the 
temperature of 500 assumed in computing 

*See definition, page 195. 



the curve is very nearly that which gives the 
best results under average conditions. 

The curve connecting the furnace and 
breeching temperatures was plotted from an 
equation based upon the assumption that the 
heat transferred from the gases to the water 
is directly proportional to the difference in 
temperature; that is, if the temperature 
difference is 1000, each square foot of surface 
will absorb twice as much heat as it would 
with a temperature difference of 500. This 
was the original assumption of Rankine, and 
while its accuracy was later questioned, many 
hundred temperature measurements at differ- 
ent points along the path of the gases in 
Stirling boilers conform more closely to this 
curve than to any other. The liability of 
error is greatest at the lower portions of the 
curve where the temperatures are highest, 
because at these points large quantities of 
heat are transmitted directly from the glow- 
ing coals to the heating surface by radiation, 
while farther along the path of the gases the 
heat is transmitted by convection. This 
possible source of error, does not, however, 
effect either the part of the curve to be used 
in the following discussion, or the general 
conclusions to be deduced from it. 

In their path through the boilers the gases 
drop from 2500 to 500, a difference of 
2000. If equal drops in temperature rep- 
resented equal amounts of heat given out and 
absorbed by the boiler, then each 200 drop 
in temperature would represent 10% of the 
total heat absorbed by the boiler. This is 
not literally true, however, because the 
specific heat of the gases is greater at high 
than at low temperatures, but the difference 
is not sufficient to affect the important con- 
clusions to be drawn from the curve. Ac- 
cordingly, to determine the figures in the 
second column on the left side of Fig. 19, 
horizontal lines have been drawn for each 200 
drop in the gas temperatures, and the cor- 
responding per cent, of the total steam gener- 
ated, up to the point where each drop is noted, 
is written in the column. For example, when 
the gas temperature has dropped to 1500, 
then 19% of the heating surface has been 
passed over, and 50% of the total output 
of steam has been generated by this 19% 
of heating surface. If the gases were allowed 
to escape at this point instead of continuing 



HEATING SURFACE REQUIRED PER HORSE-POWER 



97 



through the boiler, then 40% of the total 
available heat would have been utilized, and 
the heating surface per boiler horse-power 
would be 3.8 square feet; here and in the 
following part of this article the term horse- 
power refers to the horse-power of the 
saturated steam boiler, or the saturated 
steam portion of the superheater boiler, 
without reference to the additional capacity 
represented by the superheater. 

Similarly the results for other drops in 
temperature can be calculated as follows : 

TABLE 24 



GAS TEM- 
PEKATURE. 


HEATING SUR- 
FACE PASSED 
OVER. 


STEAM 
GENER- 
ATED. 


HEATING SUR- 
FACE PER 
H. !. 


EFFICIENCY 
OF BOILER. 


I 5 00 


iQ# 


50 % 


3. 8 sq.ft. 


40% 


IOOO 


37 


75 


4- 9 


60 


75 


54 


87-5 


6.17 


70 


5 00 


100 


I OO 


10.00 


80 



The efficiency of 80% is possible with large 
boilers burning high grade coal, oil, or gas. 

Application of the Curve to the Prob= 
lemof Superheater Design A superheater 
maybe either independently fired, or be placed 
in the setting of a boiler and absorb heat 
from the furnace gases which sweep over its 
surface on their way through the boiler. 
The latter form of superheater is the one 
most generally used, hence the principles 
underlying the design of this form of super- 
heater will now be explained. 

In order that the superheater boiler may 
develop the same thermal efficiency as the 
standard boiler used for generating saturated 
steam, the furnace temperature, the breech- 
ing temperature, and the weight of flue-gases 
per pound of fuel, must be the same for either 
type of boiler. Assume that the superheater 
is to be located in the rear of the boiler, and 
that 100 of superheat will be required. 
From Table 23 this degree of superheat will 
require 7% more fuel than is required to 
generate an equal weight of steam. Re- 
ferring to the curve, Fig. 19, 7% of the total 
heat absorbed represents a drop of tempera- 
ture of 140, therefore, as the breeching 
temperature is to remain unchanged, the 
gases must enter the superheater at a tem- 
perature of 1 40+ 5 oo= 6 40. Locating this 



temperature on the curve, it is found to 
correspond to a point where 68% of the heat- 
ing surface of the boiler has been passed over 
by the furnace gases. Consequently 32% 
of the boiler heating surface of the standard 
boiler must be replaced by superheating 
surface sufficient to absorb 7% of the total 
heat absorbed by the boiler. The effect 
of this substitution will then evidently be a 
reduction of 7% in the weight of saturated 
steam generated, and a reduction of 32% 
in the heating surface of the boiler, so that 
68% of the heating surface of the saturated 
steam boiler generates 93% of the weight of 
steam produced by that boiler, and the 
heating surface per boiler horse-power will 



be =7-i3 square feet. It is evident that 

V O 

if more boiler heating surface per horse-power 
be installed, the gases will be cooled to a 
temperature below 640 before entering the 
superheater, in which case the required de- 
gree of superheat will not be obtained, hence 
it at once follows that the boiler heating 
surface of a superheater boiler must be 
proportioned in a different manner from that 
in a saturated steam boiler, as will more 
clearly be developed later on. 

Since the purpose of this investigation is 
to determine the relation between superheat- 
ing surface, and the heating surface of the 
saturated steam portion of the boiler to which 
the superheater is connected, it is to be under- 
stood that in the remainder of this chapter the 
term "boiler heating surface" denotes the 
heating surface of that part of the combina- 
tion of boiler and superheater which generates 
saturated steam, while the term "superheat- 
ing surface" refers to the surface which super- 
heats that steam after it is generated. 

If 200 of superheat be required, 15% of 
the total heat utilized must be absorbed by 
the superheater, which will correspond to a 
reduction of 300 in the gas temperature; 
this would require 50% of the heating surface 
of the saturated steam boiler to be replaced 
by superheating surface, and the remaining 
50% of the boiler surface would have a 
capacity of 85% of that of the saturated steam 

boiler, hence would have = 5.9 square 

8 5 

feet of boiler heating surface per horse- 
power. For 75 superheat, 25% of the boiler 




SUPERHEATER BOILERS, BURNING CRUDE OIL, EDISON ELECTRIC COMPANY, LOS ANGELES, CAL,, 
6.OOO H. P. OF STIRLING BOILERS OPERATED BY THIS COMPANY 

98 



LOCATION OF SUPERHEATER 



99 



heating surface would be replaced by the super- 
heater, and there would be 7.9 square feet 
of boiler heating surface. 

Instead of locating the superheater behind 
the boiler it may be inserted at some inter- 
mediate point in the path of the gases. For 
instance, assume that the superheater re- 
places three-tenths of the heating surface of 
the standard boiler, and is so placed that 
four-tenths of the amount of heating surface 
of the standard boiler is located ahead of the 
superheater, and the other three-tenths is 
placed behind it. Then the part of the curve 
between 40% and 70% in the left hand 
column will represent the cooling of the gas 
while passing over the superheater; the drop 
of temperature will be 300, which represents 
1 5% of the total heat absorbed, hence from 
Table 23 the degree of superheat will be 
200. The boiler will produce 85% as much 
steam as the saturated steam boiler, and 
the boiler heating surface per horse-power 

is =8.24 square feet. 

If 100 superheat were required and the 
ratio of boiler heating surface in front of and 
behind the superheater be kept as in the 
preceding case, the steam production will 
be 7% less than in the saturated steam boiler, 
and the gas temperature will be reduced 140 
in the superheater. The requirements can 
be met by substituting superheating surface 
in place of boiler heating surface between 
the points in the curve represented by 63% 
and 48% in the left hand column, and the 
boiler heating surface per horse-power will 

8 t; 
be = 9.14 square feet . 

93 

By removing the superheater farther for- 
ward, as for instance on that part of the 
curve represented between 21% and 32% 
in the left hand column, the steam production 
would be 15% less than in the saturated 
steam boiler, the reduction of gas temperature 
in the superheater will be 300, the superheat 
will be 200, and the boiler heating surface 

per horse-power will be =10.5 square feet. 

It will, however, be found that in almost 
the same proportion that the boiler heating 
surface per horse-power is decreased, the 
necessary superheating surface will increase, 
so that the sum of the boiler heating surface 



and superheating surface per boiler horse- 
power will be very nearly the same for any 
given degree of superheat. 

From the preceding discussion it follows 
that if a saturated steam boiler and a super- 
heater boiler are to be of identical fuel 
effiiciency the following laws will hold : 

(1) A superheater boiler must provide fewer 
square feet of boiler heating surface per horse- 
power than are required for a saturated steam 
boiler, provided the superheater is located at 
a point where at least 2 5 % of the boiler heating 
surface is placed between the superheater and 
the furnace. 

( 2 ) The boiler heating surface per horse- 
power will be decreased as the per cent, of boiler 
heating surface in front of the superheater 
is increased. 

(3) The position of the superheater remain- 
ing the same, the higher the superheat the less 
the boiler heating surface required per horse- 
power developed by the boiler heating surface. 

It therefore follows that the superheater 
may be placed either in the rear of all the 
boiler heating surface, or at some intermediate 
position with boiler heating surface ahead 
of and behind it. In the two cases the rela- 
tive amount of boiler heating and superheat- 
ing surface must vary if the results are to 
be the same. 

The kind of engine operated by the steam 
has, however, a vital bearing upon the loca- 
tion of the superheater. The engine may 
be either a steam turbine, or a reciprocating 
engine whose working parts are so designed 
as to permit the use of superheated steam. 
For the steam turbine the degree of super- 
heat is seldom less than 100, and is usually 
higher, while the maximum superheat which 
may be used has yet to be determined. In 
a reciprocating engine the superheat which 
may be used to advantage is limited by the 
design of the working parts, and any con- 
siderable increase augments the difficulty 
of lubrication, and may cause trouble with 
the packings, etc., hence the superheater 
should be so located that when the boiler 
is forced the steam temperature will not 
exceed the limit which is safe for such an 
engine. 

These requirements may be met by proper- 
ly locating the superheater. If it be placed 
in the middle pass of the boiler the close 



100 



THE STIRLING WATER-TUBE SAFETY BOILER 



proximity of the superheating surface and 
the furnace will cause the degree of super- 
heat to rise at times much faster than can 
occur when the superheater is placed in 
the rear pass. For this reason the super- 
heater located in the middle pass is to be 



Fig. 20 represents a vertical section of the 
boiler and superheater, as arranged for 
superheats not exceeding 100. The super- 
heater is located behind the boiler heating 
surface, and this design is particularly 
adapted to operating reciprocating engines. 



.;: -.-.. ... 




!...??" 

BBSS 



FIG. 20. SECTIONAL SIDE ELEVATION OF STIRLING BOILER WITH SUPERHEATER IN REAR PASS 



preferred for operating steam turbines where 
the superheat exceeds 100, while one located 
in the rear pass is most suitable for supplying 
steam to a reciprocating engine. 

The Stirling Superheater Boiler is de- 
signed in conformity with these principles. 



Fig. 21 represents the section used for 
degrees of superheat exceeding 100. The 
superheater is placed between the two 
banks of boiler heating surface, and by prop- 
erly proportioning the boiler heating and 
superheating surface, superheats up to 250 



SUPERHEATER IN MIDDLE PASS 



101 



can be obtained. In either case the super- 
heater consists of two drums connected 
by seamless- drawn tubes two inches in di- 
ameter. The construction is identical with 
that of the standard design of Stirling boiler, 
and all of the advantages of the bent tube 



Flooding the Superheater When de- 
sired the superheater may be flooded, and 
used to generate saturated steam. Fig. 22 
shows the arrangement of flooding pipe 
which connects the front steam drum with 
the lower superheater drum. \Y nen the 




f*sii&ff&fmwq&i#& _..-*- <a^% 

fo-ftr".?--. ' ; - :: "'--: ' ': -- ; * -^:;:&;^:?^ 

FIG. 21. SECTIONAL SIDE ELEVATION OF STIRLING BOILER WITH SUPERHEATER IN MIDDLE PASS 



are retained. In addition the joint between 
the tube ends and the drums is protected 
from high heat by a layer of asbestos cement 
which rests upon the lower drum, or is sup- 
ported on metal bars placed below the upper 
superheater drum. 



superheater is used for generating saturated 
steam the three compartments in the upper 
drum are thrown into communication by 
suitable valves so that each compartment 
can discharge its quota of saturated steam 
into the main pipe. 



102 



THE STIRLING WATER-TUBE SAFETY BOILER 



The advantages of this arrangement are 
obvious. The superheater boiler may, in 
emergencies, be used as a saturated steam 
boiler to operate other engines in the plant 
when those which use superheated steam 
are shut down. When a number of super- 



Course of the Steam in the Super- 
heater The upper drum in the superheater 
is divided into three compartments by 
means of two partitions, and the lower 
drum is similarly divided into two com- 
partments; each partition either contains 




FIG. 22. SIDE ELEVATION OF STIRLING SUPERHEATER BOILER, SHOWING FLOODING PIPE 



heater boilers are operated together, and 
it is desired to reduce the degree of super- 
heat, any one of these boilers may be used 
to generate saturated steam only, and this 
be mixed with the superheated steam to 
reduce the degree of superheat to any de- 
sired point. 



a manhole, or is removable, so that all 
parts of the drum are accessible. The 
steam enters one end compartment of the 
upper drum, and makes four passes through 
the tubes, as indicated in Fig. 23. 

Independently Fired Superheater Fig. 
24 represents the Stirling Independently 



REMOVING TUBES FROM SUPERHEATER BOILER 



103 



Fired Superheater. In this all the con- 
structive advantages of the Stirling boiler 
are retained. The saturated steam from 
the main boiler plant enters the rear super- 
heater drum, passes through the rear bank 
of tubes into the lower drum, thence to the 
upper drum, from which it passes into the 
pipe line. The furnace is similar to that 
used in the standard design of Stirling 
boiler. To protect the superheater tubes 
from the high temperature of the furnace 
a sufficient amount of boiler heating surface 
is located in front of the superheater to 




FIG. 23. SECTION THROUGH STIRLING SUPERHEATER, 
SHOWING PATH OF STEAM 

reduce the temperature of the gases to 1500 
by the time they reach the superheater 
tubes. Referring to the curve, Fig. 19, it 
will be noted that when the gas temperature 
reaches 1500 in the standard boiler, 19% of 
the boiler heating surface has been swept 
over by the gases, 50% of the steam produced 
by the boiler has been generated, and the 
boiler heating surface per horse-power is 
3.8 square feet. Consequently in the in- 
dependently fired superheater shown in 
Fig. 22 50% of the heat absorbed is used 
to generate steam which is added to the 
steam furnished by the main boiler plant, 



hence increases the capacity of the plant 
in proportion. The remaining 50% of the 
heat is absorbed by the superheater, and 
superheats both the steam from the main 
boiler plant and that from the front bank of 
water- tubes. If, for example, the degree 
of superheat is 150, then from Table 23 it 
will take 11% as much heat to superheat a 
pound of steam as to generate it from water 
in form of saturated steam, hence for each 
pound of saturated steam generated in the 
front bank of the superheater, 9 T 1 T pounds 
may be superheated, and 8j\ pounds are 
delivered from the boilers, therefore the 
superheater will generate about 12% of 
the amount of steam furnished by the main 
boiler plant. 

As a further precaution against any 
possible overheating of the superheater tubes 
nearest to the furnace, a flap valve is placed 
in the pipe conveying saturated steam to 
the superheater, as shown in Fig. 24. The 
spindle of this valve is connected by links 
to the superheater damper, so that the 
damper opening is regulated according to 
the quantity of steam flowing into the super- 
heater; if the steam flow stops, the valve 
drops to its seat, and the damper is closed. 

To provide for circulation in the water- 
tubes, four "downcomer" tubes are placed 
at each end of the drum, as shown in the 

section on line A B, Fig. 24. These 

are placed in a slot in the wall and are pro- 
tected from heat by the tile as shown. 

Independently Fired Superheaters can be 
furnished of any desired capacity, suitable 
for any superheat up to 250. 

Flooding Pipe The upper water drum 
and lower superheater drum are connected 
by piping, as shown in Fig. 22, hence, if 
desired, the superheater sections may be 
flooded, converting the whole into a satur- 
ated steam boiler. 

Removing Tubes from the Superheater 
Boiler The 3^-inch tubes in the boiler 
heating surface are alternately spaced 6| 
and 5^ inches; the 2-inch superheater tubes 
are alternately spaced 4^ and 3 inches. 
See Fig. 12.* This method of spacing per- 
mits any tube to be removed from the drums 
and be passed through the wider spacing, 
hence any tube in the boiler or superheater 
can be replaced without disturbing other tubes. 



104 



THE STIRLING WATER-TUBE SAFETY BOILER 



Cleaning An extremely important ad- 
vantage is that the superheater tubes may 
be cleaned by means of a turbine cleaner 
in precisely the same manner as the regular 
boiler tubes are cleaned. This point is of 
the utmost importance, since when using 
feed waters containing vegetable matter, 



vision is made for flooding the superheater 
and using it in emergencies to generate 
saturated steam, it is evident that for sat- 
isfactory service it is necessary that the super- 
heater tubes be just as readily cleaned as 
the water tubes. This requirement is per- 
fectly met in the Stirling superheater. 



SATURATED STEAM FROM BOILER PLANT 



SUPERHEATED STEAM 





FIG. 24. SECTIONAL SIDE ELEVATION OF THE STIRLING INDEPENDENTLY FIRED SUPERHEATER 



sewage, etc., some of this matter will be 
carried over into the superheater and de- 
posited upon the tubes, hence no form of 
superheater that cannot be readily cleaned 
will meet the requirements of successful 
use, considered as a superheater only. When, 
as in case of the Stirling superheater, pro- 



Superheaters for Boilers already In- 
stalled The Stirling Company manu- 
factures superheaters which may be attached 
to any Stirling boiler now in use, and will 
promptly furnish blue prints, prices, and 
full information on application from pros- 
pective purchasers. 



Combustion 



Combustion, as the term is used in steam 
engineering, is the rapid chemical combi- 
nation of oxygen with carbon, hydrogen and 
sulphur, with the accompaniment of heat 
and light. The substance which combines 
with the oxygen is the combustible.* The 
combustion is perfect when the combustible 
is oxidized to the highest possible degree; 
thus, conversion of carbon into carbon 
dioxide (C0 2 ) represents perfect combustion, 
while its conversion to monoxide (CO) is 
imperfect combustion, since the monoxide 
can be further burned and finally converted 
into CO S . 

Kindling Point As in many other chem- 
ical processes, a certain degree of heat is 
necessary to cause the union of the oxygen 
and combustible; the temperatures necessary 
to cause this union are the kindling temp- 
eratures, and are approximately as given 
in the following table by Stromeyer.f 

TABLE 25 
KINDLING TEMPERATURES 

Lignite Dust . . . 300 F. 
Sulphur . . . .470 
Dried Peat . . .435 
Anthracite Dust . 570 

Coal 600 

Cokes Red Heat 

Anthracite . . . " "75 
Carbon Monoxide . '1211 

Hydrogen . . . 1030 or 1290 
The Oxygen necessary for combustion 
is supplied from the air. Its density is 
1.10521, (Air = i); its weight 0.088843 Ibs. 
per cu. ft. at 32 F., and atmospheric pressure; 
its atomic weight is 16; a pound of air con- 
tains 0.2315 Ibs. of oxygen, and one pound 
of oxygen is contained in 4.32 Ibs. or air. 

Carbon (C), the most abundent com- 
bustible, has atomic weight of 12, and reaches 
the boiler furnace as a constituent of oil, 
gas, coal, charcoal, wood, etc. 

Hydrogen (H) occurs free in small quan- 
tity in some fuels, but is usually in combi- 
nation with the carbon. Its atomic weight 
is i; its density is 0.0692, (Air=i); and its 



weight per cubic foot at 32 F. and atmos- 
pheric pressure is 0.00559 Ibs. 

Sulphur (S, atomic weight 32) is found 
in most coals and in some oils. It is usually 
present in a combined form, either as sul- 
phide of iron, or sulphate of lime; in the 
latter form it has no heating value. Its 
presence in fuel is objectionable because 
the gases formed from its combustion attack 
the metal of the boiler and causes rapid cor- 
rosion, particularly in presence of moisture. 

Nitrogen (N) is drawn into the furnace 
with the air. Its atomic weight is 14; its 
density is 0.9701, (Air=i); its weight per 
cubic foot at 32 F. and atmospheric pressure 
is .07831 Ibs.; each pound of air at atmos- 
pheric pressure contains 0.7685 Ibs. of nitro- 
gen, and one pound of nitrogen is contained 
in 1.301 Ibs. of air. 

Nitrogen performs no useful office in com- 
bustion, and passes through the furnace 
without change. It dilutes the air, absorbs 
heat and reduces the temperature of the 
products of combustion and is the chief 
source of heat loss in furnaces. 

Combining Weights When chemical el- 
ements unite to form a new compound 
they do so in definite proportions which 
are always the same, and the union produces 
heat the quantity of which is also invariable. 
Thus, a pound of carbon, when carbon 
dioxide is formed, will always unite with 
2 pounds of oxygen, and give off 14,600 
B. T. U. As an intermediate step the carbon 
might unite with i^ times its weight of oxy- 
gen, and produce 4,450 B. T. U., but in its 
further conversion to CO 2 it would unite 
with an additional i times its weight of 
oxygen and evolve the other 10,150 B. T. U., 
since the heat developed in any chemical 
combination depends upon the initial and 
final states, and not upon any intermediate 
change. 

Calorific Value of Fuel The amount of 
heat liberated per pound of fuel undergoing 
perfect combustion is called the calorific value 
of the fuel. The methods of determining 
the calorific value will be treated in chapter 
on Determination of Heating Value of Fuels. 



*See foot-note, page 112. ^Marine Boiler Management and Construction, page 93. 



106 



THE STIRLING WATER-TUBE SAFETY BOILER 



Table 26 gives calorific values, air required, 
etc., for the elementary combustibles and 
several compounds. 

Hydrogen Available for Combustion 

During complete combustion the carbon 
will be converted into carbon dioxide, (CO 2 ); 
the hydrogen into water vapor, (H 2 O); 
and the sulphur into gas of the composition 
SO 2 . Not all the hydrogen shown by a fuel 
analysis is, however, available for heat pro- 
duction, since the oxygen shown by the an- 
alysis was united with part of the hydrogen 
in form of water, hence was already in com- 
bination before combustion was effected. 
Since water is H 2 O and the atomic weights 
of H and O are respectively i and 16, the 
weight of combined hydrogen will be one- 
eighth of the weight of the oxygen, hence 
the hydrogen available for combustion will 
beH-iO. 



Carbon . 
Hydrogen . 
Oxygen 
Nitrogen 


74-79% 
. . 4.98 
6.42 
i . 20 


Sulphur 
Water . . . . 
Ash 


3-24 
7.82 



IOO . OO% 



Substituting in the formula 

B. T. U. per pound. = 
14600X0.7479 

( 0.0642 

+62000 4 0.0408- 



+4000X0.0324 

= 13,650, very nearly. 

A calorimeter test showed 13480 B. T. U. 
for this coal, which illustrates the degree of 
accuracy to be expected of the formula. A 
more refined computation would involve a 



TABLE 26 
COMBUSTION DATA FOR CARBON, HYDROGEN, ETC. 



I 


2 


3 


4 


5 


6 


7 


8 


9 


10 


Oxidizable 
Substance, 
or Fuel. 


Chem- 
ical 
Symbol 


Atomic 
or Com- 
bining 
Weight 


Chemical Reaction. 


Product of 
Combustion. 


Oxygen 
per Ib. 
of Col. i 

Ibs. 


Nitrogen 
per lb.- 
of Col. i 
= 3.32XO 
Ibs. 


Air per Ib. 
of Col. i 
= 4.32XO 
Ibs. 


Gaseous 
Product 
per Ib. 
of Col. i 
= Col. i X 
Col. 8. Ibs. 


Heat 
Value 
per Ib. 
of Col. i 
B.T. U. 


Carbon 


C 


12 


C+2O=CO 2 


Carbon Dioxide 


2$ 


8.85 


it .52 


12.52 


14,600 


Carbon 


C 


12 


c+o=co 


Carbon Monoxide 


l| 


4-43 


5.76 


6.76 


4.4SO 


Carbon Monoxide 


CO 


28 


CO+O=CO 2 


Carbon Dioxide 


4/7 


i .90 


2 .47 


3 -47 


IO,I $O* 


Hydrogen 


H 


I 


2 H+O=H 2 O 


Water 


8 


26.56 


34- 56 


35 . 56 


62,000 


Methane 


CH 4 


16 


CH 4 +4O=CO2+2H2O 


Carbon Dioxide 




















and Water 


4 


13.28 


17.28 


18.38 


23,5<;o 


Sulphur 


S 


32 


S+2O=SO 2 


Sulphur Dioxide 


i 


3-33 


4.32 


5-32 


4,050 



Dulong's Formula The heating value 
of the various elements being known, the fol- 
lowing formula, due with slight modifications 
to Dulong, enables the heat of combustion 
of a fuel to be computed. 

Heating value of fuel per pound= 

14,600(7+62,000 ] H - > +4,oooS [24] 
( 8 ) 

C, H,0,and 5 are the proportionate parts, 
by weight, of carbon, hydrogen, oxygen and 
sulphur, respectively. The formula does not 
apply when the fuel contains carbon mon- 
oxide, (CO), but can be made to apply by 
adding the term 10,150 Cf, in which C is the 
proportionate weight of carbon which is con- 
verted into carbon monoxide. 

Assume, for example, a coal whose com- 
position is as follows: 



correction for heat expended in evaporating 
the water in the coal and superheating the 
resultant vapor to the breeching temperature. 
Air Required From Table 26 the air 
required can be readily calculated, thus: 
0.7479 CX2 . . . =1.9944 Ibs. O needed 

] 0.0498- ' 42 [ HX8 =0.3262 " " 
( 8 ) 

0.03248X1= . . . =0.0324 ' 

Total .... =2.3530 Ibs. O needed 
Since i pound of oxygen is contained in 
4.32 Ibs. of air, the total air needed will be 
2.353X4.32=10.165 Ibs. The weight of act- 
ual combustible is 

. 7479+. 040775+. 0324=. 82 pounds, 
hence the air required per pound of com- 
bustible is 10.165-^.82=12.4 Ibs. 



*Per pound of carbon in the monoxide; the heat value of a pound of carbon monoxide is 4.350 B. T. U. 
fOr by adding the term 4,350 CO if the weight of CO be known. 



HEAT LOSSES DUE TO EXCESS AIR 



107 



The air may be also found by following 
approximate formula: 

Weight of air per Ib. of fuel= 

S [25] 



in which the letters have same significance as 
in Dulong's formula above given. 

Table 27 gives the air supply for various 
fuels, calculated as above explained. 

TABLE 27 

CALCULATED NET QUANTITY OF AIR REQUIRED 
FOR COMBUSTION OF VARIOUS FUELS 



FUEL. 


WEIGHT OF GIVEN CONSTIT- 
UENT IN I LB. OF FUEL. 


POUNDS OF 
AIR REQUIRED 




CARBON. 


HYDRO- 


OXYGEN. 


PER LB. OF 
FUEL. 




% 


GEN % 


% 




Wood Charcoal 


93- 






II. 16 


Peat Charcoal . 


So. 






9.6 


Coke .... 


94- 






11.28 


Anthrarite Coal 


91-5 


3-5 


2 . 6 


12.13 


Dry Bituminous Coal 


87. 


5-0 


4.0 


12. 06 


Lignite .... 


70. 


5-0 


20 .0 


9-3 


Dry Peat . . . 


58. 


6.0 


31.0 


7.68 


Dry Wood . 


5. 




..... 


6.00 


Mineral Oil 


85. 






15-65 



The above values are useful for comparison 
with the air actually used in any given case. 
To produce perfect combustion with the 
calculated quantity of air would require that 



resistance to passage through the fuel in 
different places owing to ash, clinker, etc. 
Where such difficulties are absent, as when 
burning gas or oil fuel, the air supplied may 
be materially less than that required for coal. 
Experiment shows that under either natural 
or forced draft coal requires about 50% more 
than the net calculated amount of air, or 
about 1 8 pounds per pound of coal. If less 
is supplied the carbon burns to monoxide 
instead of dioxide, thus fails to develop its 
full heat value. An excess of air is also a 
source of waste, as it dilutes the products of 
combustion, and reduces the temperature 
by absorbing heat which is conveyed to the 
breeching. Table No. 28 by Coxe* indicates 
the magnitude of the heat losses due to ex- 
cess of air supply. By minimum air supply 
is meant the net calculated quantity, 

Temperature of the Fire If the heat due 
to combustion of the fuel and the weight 
and specific heat of the products of combustion 
be all known, the temperature of the furnace 
(neglecting heat lost by radiation and con- 
duction) can be calculated. Evidently, 

Heat of combustion in B. T. U= Weight 
of products of combustion X their specific 
heat X elevation of temperature of products 
in degrees. [26] 



TABLE 28 

SHOWING HEAT LOSSES WHEN BURNING 100 POUNDS OF ANTHRACITE 
WITH MINIMUM, AND TWICE THE MINIMUM AIR SUPPLY 

(100 pounds of anthracite are assumed equal to 1,313,080 B. T.U. T=chimney temperature. 
Atmospheric temperature assumed at 60 F.) 



TOTAL HEAT LOST IN GASES. 





T=400. 


T=500. 


T=6oo. 


T=700. 


T=8oo. 


B. T. U. 


% 


B. T. U. 


% 


B. T. U. 


% 


B. T. U. 


% 


B. T. U. 


% 


Minimum Air Supply 
Twice Minimum Air 


145.755 


1 1 .0 


I 7 I -754 


J 3 


!97.753 


15 


223.75 1 


I 7 .0 


249, 75 1 


19 .0 


Supply .... 


230,097 


J 7-5 


279,007 


21 


329,176 


2 5 


378,715 


28.8 


428,254 


32.6 



each particle of oxygen be brought into To illustrate, assume that the same coal 

intimate contact with the fuel. This cannot as in last problem is burned with the minimum 

be done in practise, because of the mixture supply of air. The sulphur and the small 

of the oxygen with nitrogen in the air, the quantity of oxygen needed to burn it may 

irregular thickness of the fire, and varying be neglected. Then: 

*See Thurston, Manual of Steam Boilers, p. 672. 



108 



THE STIRLING WATER-TUBE SAFETY BOILER 



Weight of CO 2 = . 7479+1. 9944 =2.7423 Ibs, 

Weight of H 8 0=o. 04077+ 

0.3262 = .3310 " 

Nitrogen carried in by 10.165 

Ibs. of air=io. 165X0. 7685 . =7.8118 

Total weight of products, in- 
cluding nitrogen .... 10.8861 



combustion with the minimum quantity of air, 
such a furnace temperature cannot possibly 
be reached in practise. To illustrate the 
diminution of furnace temperature due to 
excess of air supply, the preceding case will 
be worked out on basis of twice the minimum 
air supply. This gives the following result: 



TABLE 29 
COOLING EFFECT OF VARIOUS PERCENTAGES OF EXCESS AIR 



(Based on coal containing = 85$; [ = 2.5%; N = i#; Ash = 7.75#, and B.T. U. = 14, 750 
per pound. Temperature of external air = oF.) 









TEMPERATURE OF COM- 


PER CENT. OF AIR ADDED 


IDEAL TEMPERATURE 


LOSS OF TEMPERATURE 


BUSTION COMPARED 


TO THE MINIMUM 


OF COMBUSTION. 


DUE TO DILUTION. 


WITH THAT DEVEL- 


QUANTITY. 


DEGREES. 


DEGREES. 


OPED BY MINIMUM 








QUANTITY OF AIR. 


o (or Minimum Quantity) 


^,1^2 F 






10% Added 


J ' O 

4,710 


422 


9 I.8% 


20 


4,352 


780 


84.8 


3 


4,044 


1, 088 


78.8 


40 


3-777 


1.355 


73-6 


5 


3-543 


1,589 


69 .0 


60 


3,336 


1,796 


65.0 


70 


3>I53 


1,979 


61.4 


80 


2,988 


2,144 


58.2 


90 


2,840 


2,292 


55-3 


100 


2,705 


2,427 


5 2 -7 


125 


2,419 


2,7 J 3 


47-i 


150 


2,188 


2,944 


42 .6 


175 


1,997 


3, I 35 


38.9 


2OO 


1,837 


3, 2 95 


35-8 



= 0.59508 B. T. U. 



The mean specific heat of this mixture 
being unknown, the heat necessary to raise 
the mixture one degree will be now calculated. 
2.7423X0.217 (specific 

heatofCO 2 . . . 
0.3310X0.4805 (specific 

heat superheated steam. *= 0.15905 
7.8118X0.2438 (specific 

heat of N) . . . .= 1.90452 

Hence total heat to raise 

products one deg. F. =2.65865 B. T. U. 

The calculated calorific value of this coal 
was 13650 B. T. U., hence the elevation of 
temperature will be 2 ]" K = 5134 F. But 
because of the impossibility of getting proper 



B. T. U. for minimum air supply as 

already determined .... =2.65865 

Additional B. T. U. for 10.165 lbs - of 

air =10. 165 x 0.2375 = 2.41419 

B.T. U. required to raise products of 
combustion (including nitrogen) 

one degree =5.07284 

Hence elevation of furnace temperature = 
F. 



In the preceding computation the specific 
heat of air has been assumed as equal to 
.2438, its value at 32F., as is almost invar- 
iably done when computing furnace tem- 
peratures. It is known, however, that at 
high temperature the specific heat of air is 



(*) Heat to raise the water to boiling point is here neglected. The specific heat of superheated steam 
is also greater than here used. See p. 93. 



FUEL LOSSES DUE TO INCOMPETENT FIRING 



109 



considerably greater, and while exact deter- 
minations have not yet been made, enough 
has been done to show that at the usual 
furnace temperatures the specific heat closely 
approximates to 0.3. Assuming this value, 
the preceding computation would give a 
furnace temperature of 2220 which is more 
nearly correct than the temperature of 2690 
previously found. 



be burned only to carbon monoxide, which 
will develop less than one-third of the heat 
which is produced when the carbon is con- 
verted into carbon dioxide. 

This subject is of greatest practical im- 
portance, owing to the large and usually 
unsuspected loss of fuel due to incompetent 
or careless firing. Large sums of money are 
often spent on devices intended to save a few 




750 H. P. OF STIRLING BOILERS, ROBINSON'S CENTRAL DEEP, LIMITED, SOUTH AFRICA 



Table 29 further illustrates the cooling 
effect of excess air. In practical work the 
temperatures will be even less than given in 
the table, because of losses due to radiation, 
slicing fires and removal of ashes, and further 
fact that at high temperatures the specific 
heat of gases is probably greater than the 
values for lower temperatures, the only values 
at present available for use in making the 
computation. 

The temperature is also lowered by insuf- 
ficient air supply because the carbon will 



per cent, of fuel, while through careful atten- 
tion by a skilled fireman much greater savings 
could be effected without any expense what- 
ever. The computations are also valuable 
as indicating why boiler efficiencies, when 
gas or oil fuel is used, are often ten to fifteen 
per cent, higher than when burning coal, the 
difference being due to decrease in the excess 
of air used, and prevention of heat losses due 
to hot ashes, slicing fires, opening of fire 
doors, and admission of cold air into the 
furnace when burning coal. 



OF THE 

UNIVERSITY 



Fuels for Steam Boilers 



Fuels may be solid, liquid, or gaseous. 
Such representatives of each class as are used 
for firing steam boilers will be considered. 

Coal is the fossilized remains of prehistoric 
vegetable growth. In its stages from vege- 
table to almost pure carbon in the form of 
graphite, it was successively changed into the 
forms listed in Table 30. With each stage 
the content of carbon increases. 

TABLE 30 

APPROXIMATE CHEMICAL CHANGES, WOOD FIBRE 
TO ANTHRACITE COAL 



SUBSTANCE. 


CARBON. 


HYDROGEN. 


OXYGEN. 


Wood Fibre .... 


52.65 


5.25 


42 . 10 


Peat 


59-57 


5.96 


34-47 


Lignite 


66 . 04 


5-27 


28.69 


Earthv Brown Coal 


73.i8 


5.58 


21.14 


Bituminous Coal 


75.06 


5.84 


JO - JO 


Semi-bituminous Coal . 


89. 29 


5-05 


6.66 


Anthracite Coal . 


91.58 


3.96 


4.46 



Table 31 gives the approximate per- 
centages of carbon and volatile matter in the 
combustible portion of the general classes of 
coals. 

TABLE 31 

CLASSIFICATION OF COALS ACCORDING TO CON- 
STITUENTS IN THE COMBUSTIBLE* 





FIXED 


VOLATILE 




CARBON. 


MATTER. 


Anthracite 
Semi-anthracite 
Semi-bituminous . 


97 t092.5% 
92.5 to 87.5 
87-5 to 75 


3 to 7.5% 

7.5 to 12.5 

12 .5 tO 25 


Bituminous, Eastern . 


75 to 60 


2 5 tO 4O 


Bituminous, Western 
Lignite 


65 to 50 
under 50 


35 to 50 
over 50 



The percentages of ash and moisture in 
coal vary greatly. The ash ranges from three 
to thirty per cent.,- and the moisture from 
0.75 to 25 per cent, of the total weight of the 
coal, depending upon the locality where mined 
and the grade. 

Anthracite, or Hard Coal, ignites slowly, 
but when in a state of incandescence its radi- 
ant heat is very great. The name Anthracite 
may be applied to all those dry or non-bitu- 
minous coals which, possessing from three to 
seven per cent, of a gaseous matter, do not swell 
when burned. Its flame is quite short and 

*Kent's Steam Boiler Economy, page 42. 



of a yellowish blue tinge and it can be burned 
with practically no smoke. True or dry 
anthracite is characterized by few joints and 
clefts, and their squareness; great relative 
hardness and density; high specific gravity, 
ranging from 1.4 to 1.8: and semi-metallic 
luster. 

Anthracite is now classed and marketed 
according to sizes, the following division of 
mesh being adopted as standard at Wilkes- 
barre in 1891: 

Egg Coal must pass through 2}" mesh and not through 2" 
Stove " " " " 2" " " " " ii" 

Chestnut " " " ii" " " " " \" 

Pea Coal " " " 1" " " " " i" 

Buckwheat No. i must pass through \" mesh and not through \" 
Buckwheat No. 2 or rice, must pass throug'.i J" mesh and not 
through i". 

Semi=anthracite coal, because of its con- 
tent of seven to twelve per cent, of volatile 
combustible, kindles more readily and burns 
more rapidly than anthracite. It has less 
density, hardness, and metallic luster than 
anthracite and the usual specific gravity is 
about i .40. 

Semi=bituminous coal is softer, contains 
more volatile matter, kindles easier and burns 
more rapidly than anthracite. It gives an 
intense and free burning fire. 

Bituminous coals range in color from pitch 
black to a dark brown. Their luster is 
resinous or vitreous in the most compact 
specimens, and silky in those showing traces 
of vegetable fibre. The specific gravity is 
usually about 1.3. The distinctive charac- 
teristic of the bituminous coals is the emission 
of yellow flame and smoke when burning. 

Bituminous coals absorb moisture from the 
atmosphere. The surface moisture can be re- 
moved by ordinary drying, but a large portion 
of the water can be separated from the coal 
only by heating it to a temperature of about 
250 F. 

Bituminous coals are either caking or non- 
caking. The former when heated fuse to- 
gether and swell in size; the latter burn 
freely, do not fuse and are commonly known 
as "free burning'' coals. Caking coals are 
usually rich in volatile hydrocarbons and are 
valuable for gas manufacture. 



112 



THE STIRLING WATER-TUBE SAFETY BOILER 



Can n el Coal is a variety of bituminous 
coal, rich in hydrogen and hydrocarbon, and is 
exceedingly valuable as a gas coal ; it is bright 
flaming, burns without melting, and has a 
dull resinous luster. It is seldom used for 
steaming purposes, although it is sometimes 
mixed with Pocahontas coal when increased 
economy is desired at very high combustion 
rates. Cannel coal usually shows the follow- 
ing composition: 

Fixed carbon 26 to 55% 

Volatile Matter 42 to 64 

Earthy Matter 2 to 14 

The specific gravity is about 1.24. 

Lignite is vegetable matter in the earlier 
stages of conversion into coal. Its specific 
gravity is low, 1.2 to 1.23, and when freshly 
mined it contains as high as fifty per cent, of 



nite cause large stack losses, and in conse- 
quence it is a low grade fuel. 

Composition of Coal The uncombined 
carbon in coal is known as fixed carbon. 
There is also some carbon combined with 
hydrogen, and this, together with other 
gaseous substances driven off by the applica- 
tion of heat, constitutes the volatile portion 
of the fuel. The fixed carbon and the volatile 
matter constitute the combustible,* the 
other important ingredients entering into the 
composition of coal being moisture, and the 
refractory earths which form the ash. 

A large percentage of ash is undesirable, 
because it not only reduces the calorific value 
of the fuel, but in the furnace clogs up the air 
passages and prevents the rapid combustion 
necessary to high efficiency. If the coal also 



TABLE 32 

APPROXIMATE HEATING VALUE OF GENERAL GRADES OF COAL PER POUND 

OF COMBUSTIBLE, B. T. U. 





PER CENT. OF 


COMBUSTIBLE. 


HEATING VALUE PER 


KIND OF COAL. 


FIXED CARBON. 


VOLATILE MATTER. 


POUND OF COM- 
BUSTIBLE. 


Anthracite 
Semi-anthracite .... 


97.0 to 92.5 

02 S tO 87 C 


3 . o to 7.5 

7 <! to I 2 < 


14,600 to 14,800 
14 700 to ic 500 


Semi-bituminous .... 
Bituminous, Eastern 
Bituminous, Western 
Lignite 


87.5 to 75. 
75 . to 60. 
65. to 50. 
Under 50 


12.5 to 25. 
25 . to 40. 
35- to 50. 
Over 50 


15,500 to 16,000 
14,800 to 15,200 
13,500 to 14,800 
11,000 to 13,500 



moisture. Its appearance is not uniform, and 
varies from a light brown color of distinctly 
woody structure to specimens resembling 
hard coal. It is easily broken, will not stand 
much handling in transportation, rapidly 
absorbs moisture and if exposed to the 
weather it splits up into fine pieces like air 
slacked lime, which greatly increases the 
difficulty of burning it. It is non-caking 
and gives a bright but slightly smoky flame 
with moderate heat. 

Its composition is extremely variable, even 
in the same deposit; the ash may run as low 
as one per cent, and as high as fifty-eight per 
cent. The high content of moisture and 
large amount of air necessary for burning lig- 



contains an excessive quantity of sulphur, 
trouble will be experienced because sulphur 
is not only injurious to boiler steel, but unites 
with the ash to form a fusible slag or clinker 
which chokes up the grate bars and forms a 
solid mass, having imbedded in it large 
quantities of unconsumed carbon. Moisture 
in coal is more detrimental than ash in lower- 
ing furnace temperatures, because it is not 
only non-combustible, but it absorbs heat 
when it evaporates and is superheated to 
the temperature of the stack gases. 

Coal Tables The properties of the 
various classes of coals in the progression 
from lignite to anthracite are shown in Table 
32 . Data pertaining to the composition and 



*The oxygen and nitrogen contained in the volatile matter are not really combustible, but through 
custom the term combustible is generally applied to that part of the coal which is dry and free from 
ash, which includes the oxygen and nitrogen. 



UTILIZATION OF COAL DUST 



113 



calorific value of the principal coals in the 
United States are presented in Table 33. 
Preparation of this table has been difficult 
because of the dearth of reliable calorimeter 
tests on fuels from all the various localities. 
Published results are often unreliable be- 
cause of failure to specify whether these 
results apply to dry coal, or coal in its natural 
state, and also because of doubt as to the 
degree of accuracy of the calorimeter used. 
In many cases it has been necessary to com- 
pute the calorific value, but the results thus 
obtained are probably as nearly accurate as 
most of the others given, because of the 
variation in quality of samples, and dis- 
cordant results given by different calori- 
meters for samples taken from the same seam 
of coal. The tabular values are therefore to 
be regarded as approximations only, and in 
any important case a properly selected sample 
of the coal under consideration should 
be submitted to a competent chemist for 
determination of the calorific value. 

Attention is called to the difference between 
the calorific value of coal per pound of com- 
bustible and per pound of fuel. If a coal 
contains ninety per cent, of combustible, 
and has a thermal value of 14,500 B. T. U. 
per pound of combustible, the heating value 
per pound of coal will be 

14,500 x 0.90 = 13,050 B. T. U. 

In Table 33 only the calorific values per 
pound of combustible are given, and the 
value per pound of coal containing any given 
per cent, of ash and moisture can be quickly 
computed as above shown. 

Weathering of Coal produces results 
which vary with the kind of coal. Anthracite 
is but little affected, apart from the oxida- 
tion of the sulphur content, which is small. 
Since bituminous coals usually contain a 
higher percentage of sulphur than occurs in 
the anthracite, weathering will produce more 
rapid oxidation, which frequently gener- 
ates sufficient heat to cause spontaneous 
combustion. When this occurs the un- 
affected coal should at once be removed, 
and the heated coal be spread so that there 
may be a free circulation through it. When 
it is necessary to pile coal containing much 
sulphur, or expose it to the weather, the risk 
of spontaneous combustion may be dimin- 
ished by making the pile as shallow as pos- 



sible, and by inserting into it, at intervals 
of six to seven feet, pieces of pipe which 
stand vertically, and are open top and 
bottom, so as to promote the free circulation 
of air through the mass. 

Weathering destroys the coking property 
of coals; it also rapidly disintegrates some 
lignites and renders them difficult to burn on 
an ordinary grate. 

Sufficiently complete experiments to de- 
termine the relation between weathering of 
coal and the decrease in its heat value have 
not yet been made. The experiments thus 
far available indicate that there is some loss; 
probably the loss will be greater as the per 
cent, of volatile matter in the coal is in- 
creased. Besides this, the augmented dif- 
ficulty of burning weathered coals of low 
grade must be considered. 

It is bad practise to pile coal on the bare 
ground. When shoveled up, such coal will 
invariably be mixed with more or less dirt, 
gravel, etc., all of which promotes the forma- 
tion of clinkers and destruction of grates. 

Coal Dust The utilization of dust, slack, 
and small sizes of coal that would otherwise go 
to waste has been the subject of considerable 
investigation and experimentation, resulting 
in numerous processes for briquetting the 
material and burning it in the form of lump, 
as before described; another method which 
has come into favor in some localities is 
to pulverize the coal into a dust and use 
it as a fuel in this form. From data at 
present available it seems that advantages 
may be expected from such a fuel, since 
the utilization of the combustible portion 
is more complete than with solid fuel, the 
production of smoke is minimized, and the 
process admits of an adjustment of the air 
supply to a point very close to the theoretical 
quantity. This is due to the intimate ad- 
mixture of the air and fuel, and to the pos- 
sibility of maintaining a more nearly uni- 
form furnace temperature. The principal 
objections to the use of coal dust as a fuel 
are the liability of the feed pipes and pas- 
sages adjacent to the furnace to choke up, 
the difficulty of reducing the fuel to a uniform 
degree of fineness, liability of explosions 
in the furnace, and the gathering of dust 
on the boiler heating surface, thereby di- 
minishing its capacity and efficiency. 



114 



THE STIRLING WATER-TUBE SAFETY BOILER 



TABLE 33 

APPROXIMATE COMPOSITION AND CALORIFIC VALUE OF PRINCIPAL 

AMERICAN COALS 



LOCALITY WHERE MINED. 


PROXIMATE ANALYSES. 


Approx- 
imate 
Calorific 
Value in 
B. T. U. 
per Ih. 
of Com- 
bustible* 


Author- 
ity. 


Volatile 
Matter. 
Per Cent. 


Fixed 
Carbon. 
Per Cent. 


Moisture. 
Per Cent. 


Ash. Sulphur. 
Per Cent. Per Cent. 

1 


PENNSYLVANIA ANTHRACITES. 
















East middle field, Wharton bed . 


3.08 


86.40 


3-71 


6.22 


0.58 


I5,OOO 


(a) (b) 


" Mammoth bed. ". . , 


3.08 


86. 3 8 


4.12 


5-9 2 


0.49 


I5,OOO 


" " 


West middle field, Buck mountain bed . 


3-95 


82.66 


3-04 


9.88 


0.46 


1 5,70 


ii 


Seven foot bed , . 


3-Q8 


80.87 


3-41 


11.23 


o-S 1 


15,080 


" " 


Primrose bed 


3-7 2 


81.59 


5-54 


10.65 


0.50 


15,060 


" " 


Mammoth bed 


3-72 


81.14 


3.16 


11.08 


0.90 


15,060 


" " 


Northern field, Mammoth bed ... 


4-38 


83.27 


3-42 


8.20 


-73 


15,100 


" " 


Southern field, Mammoth bed 


4.28 


8 3 .8l 


3-9 


8.18 


0.64 


15,100 


" " 


Primrose bed 


4-i3 


87.98 


3.01 


4.38 


0.50 


I5.7 


" " 


Lykens Valley buckwheat . . . 


6.21 


76.QA 








I <.3OO 


" (c) 




6.8 


/ v y *r 

80.2 








J >O 

15,400 


\^ / 


a n 1 1 


5- 


81.0 








15.300 


" " 


PENNSYLVANIA SEMI-ANTHRACITE. 
















Loyalsock , 


8.10 


83-34 


1.30 


6.23 


1.03 


15,400 


(a) (b) 


Bernice basin 


3-56 


82.52 


0.96 


3-27 


0.24 


r 5.oso 


" " 


* ' *( 


8.56 


89-39 


1.97 


9-34 


1.04 


r 5.475 


" " 


SEMI-BITUMINOUS. 
















Bradford County Penna. 


16.95 


69.26 


0.82 


12.29 


0.67 


15,800 


(a) (d) 


Sullivan County 


I 3-3 


72.74 


3-24 


10.38 


0.61 


15,70 


" " 


Tioga County " 


20.50 


67.79 


1.65 


8.85 


1.26 


iS>7S 


" " 


Lycoming County 


I/-53 


72.42 


i. 06 


8.15 


0.84 


15,800 


<i 11 


Center County " 


22.60 


68.71 


0.60 


5-40 


2.69 


iS.? 00 


" " 


Huntington County . . . ... 


13-84 


78.46 


0.79 


6.00 


0.91 


15,70 


" " 


Blair County " 


27.27 


60.69 


i. 06 


8.66 


2.31 


iS.SS 


" " 


Cambria County, lower bed . 


21.21 


68.94 


0.74 


7-5 1 


1.98 


15,75 


" " 


upper bed . . . " 


17.18 


73-42 


1.14 


6.58 


1.41 


15,800 


" " 


Clearfield County, upper bed ..." 


23-94 


69.28 


0.70 


4.62 


1.42 


15,700 


11 n 


lower bed . . . " 


21. IO 


74.08 


0.81 


3-36 


0.42 


15,800 


11 11 


Somerset County " 


19.77 


67.78 


I-IS 


9.67 


1.61 


15,800 


" " 


Broad Top " 


17-38 


76.14 


0.78 


4.81 


0.88 


15,800 


i 11 


Cumberland Md. 


I9-I3 


72.70 


o-95 


6.40 


0.78 


15,820 


" (e) 


11 ii 


15-47 


73-5 1 


1.23 


9.09 


0.70 


15,820 


11 11 


" " 


JS-S 2 


74-28 


0.89 


9.29 


0.71 


15,800 


ii ii 


Pittsburg seam, George's Creek Valley 


19.19 


74.91 


o-59 


5-31 


0.63 


15,840 


" (0 


Bakerstown, 


17.17 


72-93 


0.60 


8.76 


0-59 


1:5,840 


II 11 


Upper Freeport, " 


17.07 


77.04 


1.02 


4.87 


0.83 


15,800 


II II 


Lower Kittanning, " 


16.92 


76.58 


0.74 


5.86 


0.68 


15,840 


1 11 


Pocahontas run of mine .... Va. 


18.30 


73.65 


0.80 


7-25 


o-57 


!5.7 8 o 


(g) 


" ' ' * ' " ' ' 


18.62 


75- 12 


0.63 


5-63 


o-57 


15.720 


' 




18.60 


75-75 


0.85 


4.80 


0.62 


15,800 





*Or coal dry and free from ash. 



AMERICAN COALS 



115 



TABLE 33 Continued 



LOCALITY WHERE MINED. 


PROXIMATE ANALYSED. 


Approx- 
imate 
Calorific 
Value in 
B. T. U. 
per lb. 
of Com- 
bustible. 


Author- 
ity. 


Volatile. 
Matter. 
Per Cent. 


Fixed 
Carbon. 
Per Cent. 


Moisture. 
Per Cent. 


Ash. 
Per Cent. 


Sulphur. 
Per Cent. 


New River district .... W. Va. 
















Quinnamont lump 


18.65 


79.26 


0.76 


I.I I 


0.23 


15,820 


(a) (h) 


slack 


17-57 


79.40 


0.83 


1.92 


0.28 


15.830 


" " 


Fire Creek 


22.J4 


75-02 


0.61 


1.47 


0-56 


15,800 


" " 


Longdale 


21.38 


72.32 


1.03 


5.27 


0.27 


15,800 


" " 


Nuttalburg 


2 5-35 


70.67 


i-35 


2.10 


0-57 


15.720 


" " 


Hawk's Nest 


21.83 


75-37 


i-93 


1.8 7 


O.26 


15,800 


" " 


Ansted 


32.6l 


63.10 


1.40 


2-15 


0.74 


!5.35o 


" " 


BITUMINOUS. 
















Jefferson County Penna. 


3 2 -53 


60.99 


I. 21 


3-76 


1. 00 


15.30 


(i) 


Indiana County 


29.26 


58.74 


0.98 


9.46 


i-73 


15.400 


<( 


Westmoreland County 


32.27 


59-23 


I.I4 


5-97 


i-5 


15,200 


< t 


Fayette County 


29-75 


60.47 


o-95 


7.04 


1.79 


15,400 


" 


Potter County 


32.28 


55-32 


1.72 


9.67 


I.OI 


15,100 


14 


McKean County 


34-49 


46.25 


2.25 


14.02 


2-97 


14,600 


" 


Clarion County 


38.60 


54.I5 


1.97 


4.10 


1.19 


14,700 


" 


Armstrong County 


42-55 


49.69 


1.18 


4-58 


2.OO 


14,000 


" 


Butler County 


39.88 


48.97 


1.91 


7.22 


1.97 


14,200 


" 


Lawrence County 


40-45 


52-51 


2. II 


3-25 


i-37 


14, 5 


" 


Beaver County 


39-04 


50.20 


1.96 


6.96 


2.OO 


14,50 


" 


Washington County .... 


37-n 


5-99 


1.16 


8.72 


2.06 


14,700 


" 


Greene County 


35-74 


SI-7S 


1.14 


9.10 


1-79 


14,800 


11 


Youghiogheny River 


36.49 


59-05 


1.03 


2.61 


1.81 


15,100 


" 


Connellsville 


30.10 


59.61 


1.26 


8.23 


0.78 


15.400 


" 


Upper Freeport seam . . . Pa. and O. 


37-35 


5 x -63 


i-93 


9.10 


2.89 


14,75 


(g) 


Jackson County Ohio. 


35-79 


52-78 


8.! 7 


3- 2 5 


M3 


14,140 




Middle Kittanning, Hocking Valley . " 


32-85 


48.74 


6.51 


8-93 


1-58 


14,080 


" 


MahoningCoal, Salinville " 


35-oo 


5-95 


3.i5 


10.90 


1.86 


i4,73o 


< ( 


Massillon " 


31-83 


64-25 


2-47 


i-45 


0.56 


15-075 


(a) 


Brier Hill " 


34.60 


56-30 


4.80 


4-3 




14,300 


(k) 


Big Stone Gap splint . . . Virginia. 


33-90 


59-25 


i. 80 


5-5 


0.71 


15,100 


(a) (c) 


Carbon Hill 


18.60 


71.00 


0.40 


IO.OO 




15,800 




Coal River 


35-89 

\J >J s 


58.89 


3-35 


I - 2 5 


0.62 


14,95 


" " 


Coal River splint 


33-33 


55- 2 5 


1.78 


9.02 


0.62 


15,000 


" " 


Cedar Grove, Kanawha Co. 


34.08 


60.67 


2.10 


2.50 


0.65 


15.^0 


' " 


Richmond coking coal ... " 


30-36 


58-30 


1.62 


10.58 




*5.35o 


" " 


South of James River .... 


32.24 


58.89 


1.48 


7.72 


i-45 


15,200 


" " 


Thacker W. Va. 


35-54 


56-24 


I. 3 8 


6.84 


i-39 


iS.^o 


(g) 


Coal Creek, Anderson County . .Tenn. 


34-86 


58.41 


1.29 


5-44 


O.2O 


*S,5 


(a) (c) 


Etna, Marion County " 


23-72 


63-94 


0-94 


11.40 


I.I9 


15,70 


a 


Franklin County . . . . ' . . " 


25-41 


62.00 


1.77 


10.82 


0.64 


*5>75 


" " 


Harriman " 


32-32 


62.31 




5-37 


0.84 


JS^S 


1 1 < i 


Melville, Hamilton Co " 


26.50 


67.08 


2.74 


3-68 


0.98 


^^S 





Morgan County 


34-55 


61.66 


!.6 7 


2.14 


0.88 


*5^5 


(i 



116 



THE STIRLING WATER-TUBE SAFETY BOILER 



TABLE 33 Continued 





PROXIMATE ANALYSES 


Approx- 
imate 








Calorific 




LOCALITY WHERE MINED. 


Volatile 
Matter. 
Per Cent. 


Fixed 
Carbon. 
Per Cent 


Moisture. 
Per Cent. 


Ash. 
Per Cent. 


[Sulphur. 
Per Cent. 


Value in 
B. T. U. 
per Ib. 
of Com- 


Author- 
ity. 














bustible. 




Newcombe, Campbell Co. . . . Tenn. 


33-77 


60.64 




3-59 


1 .20 


15,200 


(a) (c) 


Rhea County 


29.13 


61.68 


0.82 


7.07 


1.30 


1 SA5 





Rock wood, Roane Co. .... 


26.62 


60. II 


r -75 


11.52 


1.49 


15.050 


" " 


Scott County " 


34-53 


61.66 


1.67 


2.14 


0.88 


I5,2OO 


" " 


Tracy City, Suanee Co 


29.30 


61.00 


i. 60 


7.80 




r 5,45 


" " 


Boyd County .... Kentucky. 


33-77 


54-5 1 


3-27 


8.91 


I. 5 6 


14,95 


(a) (1) 


Carter County 


34.60 


55^5 


4.10 


4-77 


I-4I 


14,850 


" " 


Coalton County .... 


32.04 


55-59 


5- J 9 


6.71 


1.68 


15,100 


" " 


Floyd County 


36.70 


5 J -7o 


1.30 


10.30 


1.36 


14,400 


" " 


Greenup County .... 


35-00 


5 2 -34 


3-56 


9.02 


2-59 


14,600 


" " 


Johnson County .... 


38.04 


5 6 -30 


2.66 


3-oo 


1.29 


14,600 


" " 


Lawrence County .... 


35-70 


53-28 


4.60 


6.42 


i. 08 


14,600 


" " 


Martin County 


32.60 


62.68 


1.46 


3-26 




15.30 


" " 


Pike County 


26.80 


67.60 


i. 80 


3.80 


o-97 


15,600 


" " 


Bibb Co., Blockton, upper vein . . Ala 


34-oi 


59-5 1 


2.28 


3-25 


0-45 


1 S^5 


(c) 


Cahaba, Shelby County .... 


33-28 


63.04 


1.66 


2.02 


0-53 


15,400 


(m) 


Conglomerate " 


30.86 


64-54 


2.13 


2-47 


1.48 


15.45 


" 


Helena " 


29.44 


66. 81 


1. 21 


2-54 


0-53 


^.OS 


< < 


Pratt Co.'s Upper Jefferson Co. 


32.29 


59-50 


1.47 


6.73 


1.22 


i5. 2 5 


" 


Pratt Co. 's, Lower Jefferson Co. . 


30.68 


63.69 


i-S3 


4.10 


0.6l 


*545 


11 


Brazil Indiana. 


34-49 


50-30 


8.98 


6.28 


!-39 


i4,55o 


(a) 


Block Coal 


38-17 


52.27 


4.66 


5-89 




13,880 


(n) 


Big Muddy Illinois. 


3i-9 


53-o 


7-7 


7-4 




14,55 


(o) 


Carterville mine run 


34-n 


52-17 


4-87 


8.85 


0.85 


14,150 


(P) 


washed, No. i 


33-99 


54-21 


4.66 


7.14 


0.74 


!3,93 


' ' 


No. 2. 


35- 12 


55- or 


4-3i 


5-56 


0.86 


14,35 


" 


No. 4. 


33- 26 


55-29 


4.86 


6-59 


I-I5 


i3,94o 


" 


Collinsville, Madison Co. . 


45- 8 9 


3i-57 


9.20 


J3-34 


5-34 


13,080 


1 ' 


Danville, Vermilion Co 


43-7 


45-37 


4-78 


6-15 




14, 050 


" 


screenings 


33-So 


34.20 


9.40 


23.10 




13,760 


1 * 


Duquoin, Perry Co., lump 


34.61 


50-85 


9.14 


5-40 




14,110 


' ' 


nut 


38.91 


46.00 


7-43 


7.66 




L 3,098 


4 * 


slack 


35-95 


41.60 


6.05 


16.40 


S-M 


14,37 


" 


Glen Carbon, Madison Co., lump. 


39- T 3 


40.66 


7-85 


12.36 


4.87 


14,466 


' ' 


Girard, Macoupin Co 


34-39 


45-76 


9.70 


10.15 


3-5 


1 2,410 


' * 


La Salle 


39-40 


43-95 


8.22 


8-43 




14,600 




Mt. Olive 


38.33 


40.22 


9-63 


11.82 


6.78 


14,090 


(o) 


Mt. Olive 


33-i 


44.1 


8.1 


14.7 




13,70 


4 * 


Pana, Christian Co., nut 


39-43 


46.04 


5-30 


9-23 




13,860 


(P) 


Pana, Christian Co., slack . 


35-45 


39-35 


8-55 


16.65 


4-77 


13,100 


* 4 


St. John, paradise lump 


37.00 


51.10 


9-63 


2.27 




13,590 


* * 


Stanton, Macoupin Co., lump 


36.00 


48.00 


Dried 


16.00 




13.70 


* * 


Streator, average 


37-63 


45-93 


8.30 


8.14 




13,730 


4 ( 


lump 


39-40 


48.20 


Dried 


12.40 




14,400 





AMERICAN COALS 



117 



TABLE 33 Continued 



LOCALITY WHERE MINED. 


PROXIMATE ANALYSES. 


Approx- 
imate 
Calorific 
Value in 
B. T. U 
per lb. 
of Com- 
bustible 


Author- 
ity. 


Volatile 
Matter 
Per Cent 


I ixed 
Carbon 
Per Cent 


Moisture 
Per Cent 


Ash. 
Per Cent. 


Sulphui 
Per Cent 


Streator nut Illinois 


35- 6 


54-5 


Dried 


9.90 




I4,2OO 


(P) 


screenings .... 


38.40 


43.80 


Dried 


17.80 




14,100 


" 


Trenton Clinton Co 


30.4.0 


S2.OO 


1 3.^0 


4. 3O 


O.QO 


12,850 


" 


Vulcan, St. Clair Co., nut . 


o ^ 

30.86 


o 

45-9 


O O 

7-44 


*f*O 

16.61 


* y 
1.30 


12,440 


it 


Cleveland, Lucas Co Iowa 


39-7 6 


42.12 


6.66 


11.48 




I 1, 660 


(q) 


Cincinnati Co 


26.58 


40-03 


23-99 


9-i3 




14,850 


* ' 


Hiteman, Tyrone Co 


37-6^ 


44.69 


4.92 


12.76 




1 1 ,480 


" 


Steam coal, Beacon Co. 


O I O 

35- 6 4 


"T- . ^ -y 

38.09 


" ,7 

4.09 


/ 

20.37 




12,830 





Walnut block, Centerville 


37-77 


46.64 


5-52 


10.07 




12,460 


ii 


Smoky Hollow, Avery Co. 


39.02 


5 J -33 


6.29 


4-35 




II ,37 


" 


Whitebreast Fuel Co., Pekay . 


46.06 


46.89 


^ 


7-05 


2.8? 


14,020 


(y) 


Eldon Coal Co., Laddsdale 


42.72 


47.78 


3 ro 
w ^ 


9-5 


4.96 


i4,5 20 


" 


Mine No. 2, Hocking .... 


45.18 


45-34 


ts\ 
'3 "*00 


9.48 


3-98 


13,870 


" 


Des Moines Coal Co., Marquisville 


45.62 


50.29 


^ G 

o o 


4-09 


2-74 


12,560 


" 


Lunsden Coal Co., Bloomfield 


39.66 


53.46 


.< <% 

T3_ 5 


7.48 


2.38 


13,920 


" 


Whitebreast Fuel Co., Hilton . 


40.61 


48.21 


.215 * 

!'C ^ 


ii. 18 


3-26 


13,95 


" 


Block Coal Co., Centerville . . 


37-79 


54.85 


>^ J 8f 

c > 


7-36 


3-29 


13,690 


11 


Consolidation Coal Co., No. 10, Buxton " 


37-09 


50-83 


- 

> cs > 


12.08 


2.27 


13,690 


" 


Crowe Coal Co., Boone 


41.46 


50-33 


IS* 


8.21 


4.16 


13,860 


" 


Corey Coal Co., Lehigh 


37-98 


47.98 


""a*. 

^ G f- 


14.04 


5-90 


14,460 


" 


D. Lodwick, Mystic 


39-07 


54-91 


uS* 


6.02 


3-15 


13,690 


" 


Platt Coal Co., Van Meter . . 


40-54 


51.04 


eSi l 
M 


8.42 


3 .68 


i3,39o 


" 


Jasper Co. Coal Co., Colfax 


42.24 


50.27 


co.SS 


7-49 


3-08 


13, II0 


" 


Pittsburg Kansas. 


28.60 


60.32 


3.26 


7.28 




11,030 


(q) 


Weir City, No. i 


33-54 


58.41 


2.08 


5-97 




12,35 


" 


Weir City, No. 5 


33-77 


57-17 


2.70 


6.36 




12,850 


" 


Central C. & C. Co., No. 66, Macon Co. Mo. 


39.10 


41.83 


12. OO 


7-07 


3-44 


12^,580 


a) (r) 


Central C. & C. Co., No. 70, Macon Co. 


36.26 


43.16 


10.20 


10.38 


4-47 


^.iS 




Elliott Coal Co.. Randolph Co. . . 


36-32 


42.77 


11.15 


9.76 


3-55 


13,120 


11 (i 


Far. Consolidated, No. 6, Lafayette, Co. " 


36.14 


44.70 


n-95 


7.21 


2-57 


12,890 


<i 11 


Marceline Coal Co., Linn Co. ... " 


33-25 


47.27 


9-45 


10.03 


5-73 


13,420 


11 ii 


Mendota Coal Co., No. 2, Putnam Co. 


34-n 


39-85 


J7-59 


8-45 


3.21 


1,840 


11 11 


Murline Coal Co., Ray Co. 


37-35 


41.66 


I 3-7 


7.42 


1.92 


2,660 


ii 11 


Richmond & Camden Coal Co., Ray Co. " 


37-93 


42.99 


9-83 


9-25 


3-n 


2,620 


11 11 


Weir Coal Co., No. 3, Barton Co. . 


34-40 


53-98 


3.62 


8.00 


4.02 


5,000 


it ii 


Western Coal Co., No. 8, Barton Co. . 


35-73 


53-72 


2-35 


8.20 


4.10 


5,020 


11 K 


Hezron lump Colorado. 


37-52 


54-39 


Jried 


8.09 




2,970 


(8) 


Walsen run of mine 


36.02 


51.12 


Dried 


12.86 




2,130 




Bridgeport Coal Co., Wise Co. . Texas. 


31-93 


41.12 


12.21 


14.74 


J -73 


4,47 


(t) 


Cannel Coal Co . , Webb Co . . . 


48.84 


36.61 


3-46 


11.09 


2.09 


4,080 




Cisco, Eastland Co " 


34-86 


36.37 


13-44 


I 5-33 


2-54 


3,47 


" 


Eagle Pass, Maverick Co. . 


33-oS 


40.09 


9.40 


T 7-43 


1.28 


5,23 


" 


Rio Grande Coal Co. , Webb Co. . 


47-95 


38-89 


4.09 


9.07 


2-45 


2,720 


ii 


Strawn, Palo Pinto Co. 


3I-78 


42.04 


4.00 


22.18 


2-39 


5,600 


" 


Texas & Pacific Coal Co., Erath Co. 


33-2 


43-!5 


5-83 


17.82 


J-S 1 


5,000 


1 1 



118 



THE STIRLING WATER-TUBE SAFETY BOILER 



TABLE 33 Continued 





PROXIMATE ANALYSES. 


Approx- 
imate 








Calorific 
















Value in 


Author- 


LOCALITY WHERE MINED. 


Volatile 
Matter. 
Per Cent. 


Fixed 
Carbon. 
Per Cent. 


Moisture. 
Per Cent. 


Ash. 
Per Cent. 


Sulphur. 
Per Cent. 


B. T. L. 

per Ib. 
of Com- 


ity. 














bustible. 




LIGNITES AND LIGNITIC COALS 
















Calvert Bluff , Robertson Co. . . Texas- 


51.00 


IO.OO 


29.86 


9.14 


0.91 


I3,OOO 


(t) 


Como Coal Co., Hopkins Co. . 


45.88 


3-41 


33.87 


16.84 


0.68 


13,100 


" 


Glenn- Belto mine, Bastrop Co. . 


36.88 


21.22 


35-40 


6.50 


0-94 


13,530 


' * 


Houston Co. Coal Co 


33- 16 


J 9-93 


36.16 


IO -75 


0.40 


14,140 


' ' 


Lytle, Medina Co 


40.31 


18.50 


34-29 


6.90 


i .20 


I2,8OO 


' ' 


North Texas Coal Co. , Wood Co. . 


45- 21 


II. 60 


35-60 


7-59 


0-47 


13,460 


' ' 


Rockdale, Milam Co 


34.26 


22.73 


34-72 


8.29 


1.04 


13,100 


* * 


Timson Coal Co., Shelby Co. . 


39-53 


23-05 


31.96 


5-46 


1.46 


12,870 


' ' 


Cumberland Wyoming. 


44.27 


46.18 


3-65 


5-9o 


0.61 


I4,IOO 


(u) 


Hanna 


48.43 


36.37 


6.38 


8.82 


o-99 


13,440 


(v) 


Kemmerer 


36.16 


51-78 


5.80 


6.26 


0.60 


13,630 


(u) 


Rock Springs 


40.83 


48.30 


7.19 


3.68 


0.38 


13,900 


* 4 


Black Diamond .... Colorado. 


43-05 


39.01 


14.67 


3-27 


0.77 


10,507 


(c) 


Erie 


3 2 -7 r 


45-98 


18.57 


2-74 


0.52 


11,360 


* ( 


Canon City, vertical .... 


37- 61 


5^36 


7.01 


4-03 


i. 02 


13,097 


* * 


upper .... 


36.74 


47-93 


6.56 


8.76 


0.62 


I I ,1 70 


' * 


" lower 


37- 21 


49-54 


7.66 


5-59 


0.82 


11,644 


4 * 


Golden City, 5 foot seam . . " 


36.20 


42.08 


18.35 


3-37 


0-43 


8,154 


i l 


" 12 ' "... 


41-23 


38.46 


17.64 


2.67 


0.30 


9,947 


11 


Gunnison River 


12. 16 


84-65 


1-50 


2.29 


0.70 


14,240 


* * 


Marshall 


37-84 


46.43 


I3.I9 


2-54 


0.66 


11,478 


* * 


Mount Carbon 


36.91 


37-82 


20.38 


4.87 


0.40 


10,624 


* * 


South Park 


33-79 


58.62 


6.30 


1.28 


0.47 


12,204 


1 i 


Castle Gate . . Utah. 


IT 8 


Si .3 




6.9 




14,180 


(w) 


Black Diamond . . . .Washington. 


43.18 


J 

49.81 


4-32 


7 

2.69 


0.76 


13,600 


(x) 


Carbon Hill No. 4 Vein 


37.02 


49.12 


I. O2 


12.84 




14,600 


" 


Occidental, No. 6, Renton 


37-40 


52.55 


2. 02 


8.03 


0.68 


14,020 


4 * 


Renton Cooperative Co. No. 2 Vein " 


37.38 


53-6o 


3-44 


5-58 


o-73 


13,830 


" 


Roslyn mine, No. 4 . 


38.20 


49.40 


i .90 


10.50 


0.41 


14,590 


" 


Roslyn mine, Cle-Elum 


37-86 


48.30 


6-34 


7-59 


0.49 


U,730 


" 


Skaget Coal & Coke Co. . . 


26.67 


64.51 


o-53 


8.20 


0.68 


15,530 


" 


Wilkeson, C. & C. Co., No. i mine 


28.11 


6i.53 


0.63 


9-73 


2.09 


!5>59o 





REFERENCES: (a) B. T. U. computed by Table No. 49 and Fig. 27. (b) Analyses from Kent's Mechan- 
ical Engineer s Pocket-Book, p. 625. (c) Selected analyses. (d) Kent's Steam Boiler Economy, p. 59. 
(e) Kent's Pocket-Book, pp. 625-6. (f) Analyses by W. B. Clark, (g) Lord and Haas' researches, 
(h) Steam Boiler Economy, p. 65. (i) Ibid., p. 61. (k) Steam Boiler Economy, p. 46. (1) Ibid., p. 65. 
(m) Ibid., p. 67. (n) D. P. Jones, (o) Steam Boiler Economy, p. 73. (p) Twentieth Annual Coal Re- 
port, Illinois, 1902. (q) C. R. Richards, (r) Sixteenth Report of Coal Mine Inspector, Missouri, 1902. 
(s) Colorado Fuel and Iron Co. (t) Bulletin No. 15, University of Texas. (u) Union Pacific Coal Co. 
(v) Slosson and Colburn. (w) Carpenter, (x) Third Biennial Report of Bureau of Labor, State of Wash- 
ington, 1901-2. (y) Notes on Steam Generation with Imva Coal, by G. W. Bissell, M. E. in Bulletin No. 9. 
Engineering Experiment Station, Iowa State College. 



CALORIFIC VALUE OF WOOD 



119 



Patent or Pressed Fuels Among these 
may be classed fuels composed of the dust of 
some suitable combustible, pressed and ce- 
mented together by a substance possessing 
adhesive and inflammable properties. Such 
fuels, known as briquettes, are extensively 
used in France, and consist of carbon or soft 
coal, too small for ordinary commercial use, 
mixed with pitch and coal tar. They do 
not find much favor in this country, as the 
cost and difficulty of manufacture render 
them no more economical than coal. 

Coke is produced in three ways: (i) 
From gas coal, in gas retorts; (2) From gas 
or ordinary bituminous coal, in special ovens. 
(3) From petroleum, by carrying the dis- 
tillation of the residuum to a red heat. The 
process of manufacture necessitates expelling 
the hydrocarbon gases, hence coke is a porous 
product consisting almost entirely of carbon. 
It is a smokeless fuel, it readily attracts and 
retains water from the atmosphere, and if not" 
kept under shelter it may absorb twenty per 
cent, of its weight of moisture. 

TABLE 34 
ANALYSES OF AMERICAN COKES 

(Kentucky Geological Survey') 



WHERE MADE. 


NO. OF 

TESTS. 


FIXED 
CARBON. 


ASH. 


SULPHUR. 


Connellsville, Pa . 


3 


88.96 


9-74 


0.810 


Chattanooga, Tenn 


4 


80.51 


16.34 


i -505 


Birmingham, Ala. 


4 


87.29 


10.54 


i- 195 


Pocahontas, Va. 


3 


92.53 


5 74 


o. 597 


New River, W. Va. 


8 


92.38 


7.21 


o. 562 


Big Stone Gap, Ky. 


7 


93-23 


5-69 


0-749 



Coke from gas works is usually softer and 
more porous than other kinds. It ignites 
more readily and burns with less draft than 
is required for the combustion of coke pro- 
duced in ovens. It does not produce so 
intense a heat, hence it is not used extensively 
in factories where a smokeless fuel with great 
heat is needed. Oven coke is a dead gray 
black in color, porous and brittle, with a 
slightly metallic luster. It is used principally 
in blast furnaces, cupolas, smelting and other 
furnaces requiring a blast. Petroleum coke 
occurs in large irregular lumps, is a compro- 
mise in hardness between oven and gas-retort 
coke, blacker in color than either of the other 
classes and is used principally for making 
electric carbons. 



Peat contains a large amount of water, 
averaging seventy-five to eighty per cent., 
and occasionally reaching ninety per cent. 
It is unsuitable for fuel until dried, and its 
composition then varies little from that of 
wood. The proportion in which the various 
primary constituents exist in dried peat is 
about as follows: 



Carbon 

Hydrogen 

Oxygen. 

Nitrogen 

Ash 



58 to 60% 
6 

30 to 31 
1.25 to 1.5 
2.75 to 5 



Some peats have been known to show 
eleven per cent, of ash. In computing the 
heat of combustion, it must be borne in mind 
that peat as usually dried in the air contains 
from twenty-five to thirty per cent, of water. 
While large deposits of peat are found in this 
country it has not thus far been found 
profitable to utilize them in competition 
with coal. 

Wood is vegetable fiber which has not 
undergone geological changes, but usually 
the term is used to designate the compact 
substances familiarly known as tree trunks 
and limbs. When newly felled, wood con- 
tains moisture ranging from thirty to fifty per 
cent, by weight, and midway between these 
figures is considered a good average. After 
a year's ordinary drying in the atmosphere, 
the moisture is reduced to about eighteen to 
twenty-five per cent. 

Wood is usually classified as hard and soft. 
Hard woods include oak, maple, hickory, 
birch, walnut and beech. Soft woods con- 
sist of pine, fir, spruce, elm, chestnut, poplar 
and willow. Hard woods give less heat per 
pound than soft woods, contrary to general 
opinion. Gottlieb 's experiments proved that 
a pound of white pine has a heat value 8.25 
per cent, more than that of white oak. 
Weber's experiments with fir (soft) and oak 
(hard) gave the following results: 

FIR. OAK. 

Carbon 51-08% 5 -43% 

Hydrogen . . . . . 6.12 5.88 

Oxygen and Nitrogen .42.90 43 . 69 
Calorific Value, B. T. U. . 8,790 7,440 

From Table 36 it appears that about if 
Ibs. of dry wood have the same calorific value 
as one pound of bituminous coal; also that 



120 



THE STIRLING WATER-TUBE SAFETY BOILER 



the heating value of the same weight of 
various woods does not vary over ten per 
cent. The table is based on dry wood, but 
woods in ordinary air-dried condition contain 
about twenty to twenty-five per cent, of 
moisture, hence the available heat producing 
content will be twenty to twenty-five per cent. 

TABLE 35 
RELATIVE CALORIFIC VALUE OF WOODS 



WOOD. 


SPECIFIC 
GRAVITY. 


LBS. IN ONE 
CORD. 


LBS. COAL 
EQUIVALENT 
TO ONE CORD 
OF WOOD.* 


Hickory, shell bark 


I .OOO 


4469 


1910 


Oak, chestnut 


0.885 


3955 


1690 


Oak, white 


0.885 


3821 


1670 


Ash, white 


0.772 


3450 


1440 


Dogwood . 


0.8l5 


3643 


1560 


Oak, black 


0.728 


3254 


1390 


" red . 


0.728 


3254 


1 3 90 


Beech, white 


0.724 


3236 


1380 


Maple, hard (sugar) 


0.644 


2878 


1230 


Maple, soft 


0-597 


2668 


1140 


Cedar, red 


0.565 


2525 


1080 


Magnolia . 


o. 605 


2704 


1 1 60 


Pine, yellow 


0.551 


2463 


1060 


Sycamore . 


0.535 


2391 


IO2O 


Butternut . 


0.567 


2534 


1090 


Pine, New Jer ey 


0.478 


2137 


916 


pitch 


0.426 


1904 


812 


" white 


0.418 


1868 


800 


Poplar, Lombardy 


0.397 


1774 


761 


Chestnut . 


0.552 


2333 


I OOO 


Poplar, yellow 


0.563 


2516 


1080 



less than in the table, and of the heat pro- 
duced a part is absorbed in evaporating the 
water in the wood and superheating the steam 
thus formed. The heat so absorbed may be 
computed by formula, page 133, and the net 
calorific value of the wood may thus be deter- 
mined if the per cent, of water is known. As 



a general average one per cent, of water will 
make a reduction of one and one-half per cent, 
in the heating value of wood. Since a pound 
of average bituminous coal is equal in evapo- 
rative power to about one and three-fourths 
pounds of dry wood, or about two and one- 
third pounds of wood containing twenty-five 
per cent, of moisture, the value of a cord of 
wood expressed in pounds of coal may with 
sufficient accuracy for practical purposes 
be taken from Table 3 5 . 

Spent Tan, which consists of the fibrous 
portion of the bark, is thirty per cent, by 
weight of the original oak bark. The 
calorific value of dry tan, containing fifteen 
per cent, of ash, is 6,100 B. T. U. per pound, 
while tan in the average state of dryness con- 
tains thirty per cent, of water and has a 
heating value of 4,284 B. T. U. The con- 
ditions for burning tan and all other similar 
wet fuels require that they be surrounded with 
heated surfaces and burning fuel, in order that 
they may be dried rapidly, and thorough 
combustion be secured. 

Straw is one of the many inferior grades 
of fuel which are sometimes used when other 
fuels could be obtained only with difficulty 
and at greater cost. Table 37, on following 
page, gives the relative composition of wheat 
and barley air-dried straw. 

Such straws have a calorific value of 5411 
B. T. U. per pound according to Dulong's 
formula, [24] and weigh when pressed six to 
eight pounds per cubic foot. Experiments 



TABLE 36 
COMPOSITION AND CALORIFIC VALUES OF VARIOUS DRY WOODS (Gottlieb) 















CALORIFIC 


KIND OF WOOD 


CARBON 


HYDROGEN 


NITROGEN 


OXYGEN 


ASH 


VALUE B.T.U. 




% 


% 


% 


% 


% 


PER LB. 


Oak . . . . 


50.16 


6. 02 


0.09 


43-36 


-37 


8,316 


Ash . -, . . . 


4Q . 1 8 


6 . 27 


O . O7 


A -2 QI 


O . S7 


8,480 


Elm .... 


t^y 
48.99 


/ 

6. 20 


/ 
O.O6 


T^O 7 
44-25 


J J 1 
0.50 


v }*f-v * 

8,510 


Beech .... 


49 .06 


6. ii 


0.09 


44.17 


o-57 


8,591 


Birch .... 


48.88 


6.06 


O . IO 


44.67 


o . 29 


8,586 


Fir 


t;o . 36 


<; . 02 


o.o< 


4.3 . 30 


0.28 


0,063 


Pine .... 


o o 

50-31 


o y 
6 . 20 


J 

0.04 


T^O O7 

43.08 


o-37 


s * O 

9i53 


Poplar! 


49-37 


6. 21 


0.96 


41 .60 


1.86 


7,834t 


Willow t . . . 


49.96 


5-96 


0.96 


39-56 


3-37 


7,926! 



*On basis i Ib. coal = 2$ Ibs. wood. JValues according to Chevandier. fValues by Formula No. 24. 



CALORIFIC VALUE OF BAGASSE 



121 



in Russia show that winter wheat straw, 
dried at 230 F. gave a heating value of 
6,290 B. T. U. when dry and 5,448 B. T. U 
when containing ten per cent, of moisture. 

Other straws gave a calorific value varying 
from 6,750 B. T. U. per pound for flax to 
5,590 for buckwheat. 

TABLE 37 

COMPOSITION OF WHEAT AND BAR- 
LEY STRAWS 





WHEAT 


BARLEY 


MEAN 




STRAW 


STRAW 


VALUE 


Carbon . 


35-86% 


36.27% 


36.00 


Hydrogen 


. 5.01 


5-7 


5.00 


Oxygen . 


.37.68 


38.26 


38.00 


Nitrogen . 


o-45 


0.40 


0.50 


Ash . 


.5.00 


4-5 


4-75 


Water . . 


.16.00 


I5.50 


15-75 



Bagasse, or Megass, is the name given to 
refuse sugar cane after the juice has been 
extracted. It is used largely on sugar planta- 
tions as a fuel for generating the steam 
required in operating the mills; upon the 
efficient use of bagasse as a fuel depends to a 
great extent the success of sugar raising as a 
financial proposition, particularly where the- 
prices for sugar are low and the cost of coal 
delivered is high. 

The heating value of bagasse depends 
mostly upon the fibrous matter of the cane. 
This varies in different countries but in 
general is greater as the age of the cane is 
increased. In Cuba, Hawaii, and the West 
Indies, the cane is left standing from twelve 
months to two years and the fibrous matter 
will run from eleven to twenty per cent. In 
Louisiana, where the frosts require the cane 
to be harvested after a life not exceeding six 
and one-half months, the weight of the fiber 
will not be more than nine or ten per cent. 
The tropical canes therefore have a much 
greater fuel value, and even with inefficient 
machinery the mills can be operated solely 
by the bagasse produced. It is very seldom 
that such results can be obtained where the 
fiber is less than twelve per cent, of the weight 
of the cane; consequently in the sugar mills 
of the United States supplementary boilers 
fired with coal are required. The economy 
of the mill is estimated by the number of 



pounds of coal or wood required per ton of 
sugar produced. 

The average composition of Louisiana cane 
when ready to be ground is ten per cent, fiber 
and ninety per cent, juice. The juice con- 
sists of 

85 % Moisture 
10 % Sugar 
5 % Molasses, 

which makes the composition of sugar cane 
76.5 % Moisture 
9.0% Sugar 
4.5% Molasses 
10. o % Fiber 

In passing through the mills the content of 
juice extracted varies from 75% to 82% of the 
weight of cane, the average extraction being 
about 78%. Assuming 100 Ibs. of cane, 78 
Ibs. of juice will be extracted, leaving 22 Ibs. 
of bagasse, consisting of 10 Ibs. of fiber and 12 
Ibs. of juice; hence taking into account the 
composition of the juice as above given, the 
22 Ibs. of bagasse consist of 10.2 Ibs. moisture 
+ 1.2 Ibs. sugar +0.6 Ibs. molasses+io.o Ibs. 
fiber. 

Similarly, the composition of bagasse for 
other degrees of extraction may be computed, 
then reduced to percentages by weight of the 
bagasse itself, per following table : 



EXTRACTION 

75% 78% 80% 



or 



Moisture . . . .51 

Sugar 6 

Molasses .... 3 
Fiber 40 



46-37 42.5 

5-45 5- 

2-73 2.5 

45-45 5- 



Numerous experiments have shown the 
calorific value of the fiber contained in cane 
to be about 8,325 B. T. U. per pound of fiber; 
hence to obtain the calorific value of diffusion 
bagasse per short ton of cane, use the formula 

B. T. U. per short ton of cane= [27] 

2000X8325 X% of Fiber 
100 

Obviously the formula gives only the heat 
generated by the bagasse, and not the heat 
available for steam generating. All moist- 
ure must be evaporated and the result- 
ing vapor be superheated to the temperature 
of the stack gases. The heat so absorbed 
must be deducted from that calculated from 
the formula, to determine the available heat. 



122 



THE STIRLING WATER-TUBE SAFETY BOILER 



TABLE 38 
FUEL VALUES OF ONE POUND OF DIFFUSION BAGASSE 



Moisture in 
Bagasse. 
Per Cent. 


Heat Developed Per 
Pound of Bagasse. 
B. T. U. 


Heat Available Per 
Pound of Bagasse 
B.T.U. 


Pounds of Bagasse 
Equivalent to i Pound 
of Coal Containing 
14,000 B.T.U. 


Estimated Tem- 
perature of Fire. 
Fahr. 


o 


8,325 


8,325 


1.68 


2,465 


20 


6,660 


6,420 


2.18 


2,294 


3 


5,82) 


5,468 


2.56 


2,186 


40 


4,995 


4,5 l6 


3.10 


2,049 


50 


4,162 


3,563 


3-93 


1,870 


60 


3-33 


2,611 


5-4i 


1,627 


70 


2,497 


1,658 


8.44 


1,281 


75 


2,081 


.183 


11.90 


i,45 



TABLE 39 

VALUE OF ONE POUND OF MILL BAGASSE AT DIFFERENT EXTRACTIONS 
UPON CANE OF 10 PER CENT. FIBRE, AND JUICE CONTAINING 
15 PER CENT. SOLID MATTER 



PER CENT. 




FIBER. 


SUGAR. 


MOLASSES. 




PKR CENT. 








EXTRACTION OF 


MOISTURE IN 














WEIGHT OF 


BAGASSE 


PER CENT. 


FUEL VALUE 


PER CENT. 


FUEL VALUE 


PER CENT. 


FUEL VALUE 


CANE. 




IX BAGASSE 


B. T. U. 


IN BAGASSE 


B. T. U. 


IN BAGASSE 


B. T. U. 


(i) 


(a) 


(.0 


(4) 


(s) 


(6) 


(7) 


(8) 


9 


o.oo 


100 .00 


8,325 










85 


28.33 


66.67 


5,550 


3-33 


240 


i'.6 7 


116 


80 


42.50 


50 .00 


4,162 


5.00 


361 


2.50 


'74 


75 


51 .00 


40 . oo 


3,33 


6 . oo 


433 


"2 . OO 


209 


70 


56.67 


33-33 


2,775 


6.67 


482 


3-33 


232 


65 


60 . 71 


28.57 


2,378 


7-J5 


516 


3-57 


248 


60 


63-75 


25.00 


2,081 


7-50 


541 


3-75 


261 


55 


66 . i 2 


22.22 


1,850 


7.78 


562 


3-88 


270 


5 


68.00 


2O . OO 


1,665 


8.00 


578 


4.00 


278 


45 


69-55 


18.18 


1,513 


8.18 


59 1 


4.09 


284 


40 


70.83 


16.67 


1,388 


8-33 


601 


4.17 


290 


25 


73-67 


'3-33 


I , I I O 


8.67 


626 


4-33 


301 




75-0 


11.77 


980 


8.82 


637 


4.41 


307 





76.50 


IO . OO 


832 


9.00 


650 


4-5 






TOTAL HEAT 


HEAT REQUIRED 


HEAT AVAIL- 


POUNDS BAGASSE 






PER CENT. 
EXTRACTION OF 
WEIGHT OF 


DEVELOPED 
B. T. U. 
SUM OF COLUMNS 


TO EVAPORATE 

THE WATER 
PRESENT. 


ABLE FOR 
STEAM GEN- 
ERATION. 


REQUIRED TO 
EQUAL I LB. COAL 
CONTAINING 


COAL EQUIV- 
ALENT PEH 
TON OF CANE. 


TEMPERATURE 
OF FIRE. 


CANE 


4, 6 AND 8. 


B. T. U. 


B. T. U. 


14,000 B. T. U. 


POUNDS. 


FAHH. 




(o) 


do) 


(n) 


(12) 


(M) 


(14) 


90 


8,325 




8,325 


1.68 


119 


,465 


ST 


5,900 


339 


5,561 


2-52 


119 


,236 


80 


4,697 


509 


4,188 


3-34 


120 


,023 


75 


3,972 


6n 


3,361 


4.17 


120 


,862 


7 


3-489 


679 


2,810 


4.98 


120 


,732 


65 


3,142 


727 


2,415 


5.80 


121 


,612 


60 


2,883 


764 


2,119 


6.61 


121 


,513 


55 


2,682 


792 


T.Sgo 


7.40 


121 


,427 


5 


2,521 


815 


1,706 


8.21 


122 


.350 


45 


2,388 


833 


i,555 


9 .00 


122 


,284 


40 


2,279 


849 


i,43 


9-79 


123 


,222 


25 


2,037 


883 


I > 1 54 


12.13 


124 


,077 


15 


1,924 


899 


1,025 


13.66 


124 


,OO2 





1-795 


916 


879 


1 5 93 


126 


906 



VARIETIES OF PETROLEUM 



123 



Table 38 contains data relating to the heat 
developed, available heat, etc., per pound of 
diffusion bagasse of different contents of 
moisture, assuming the temperature of the 
air as 80 F. and that of the stack gases as 420. 
Reference thus far to the calorific value of 
bagasse has been confined to dtffusionbagas.se. 
In the diffusion process the cane is chopped 
into small pieces and subjected to a series of 
soaking processes, and the resulting bagasse 
contains only fiber and moisture. Mill- 
bagasse is the refuse left after the cane has 
been passed through the rolls. Not all of 
the juice is extracted, and the bagasse contains 
. fiber, moisture and juice. The juice contains 
combustible matter, viz., sugar and molasses. 
The composition of the bagasse will vary 
according to the per cent, extraction, as above 
shown. According to Dr. Atwater the calorif- 
ic value of sugar is 7,223 B. T. U. per lb., and 
that of molasses (dry matter only) is 6,956 
B. T. U. per lb. Thus a pound of mill- 
bagasse has a calorific value of 

8,325 X% Fiber+7,22jX % Sugar+6,056 X% Molasses r 2 ~| 

100 

and its available heating value will be this 
amount, less the B. T.U. 's necessary to drive 
off the contained moisture. 

Table 39 gives data pertaining to mill- 
bagasse of various extractions. Coal of 
14000 B. T. U. per pound is taken as a 
standard, and the coal ratios are obtained 
by dividing 14000 by the available heat per 
pound of bagasse. Coal equivalents per ton 
of cane are obtained by dividing the number 
of pounds of bagasse, resulting from the 
several extractions, by the coal ratio. Thus 
with an extraction of 75% there are 500 Ibs. 
of bagasse per (short) ton of cane, and 500 
^-4.17 (the coal ratio for 75% extraction) = 
120 pounds of coal, or the coal equivalent. 
The coal equivalents are practically the same 
for all degrees of extraction; in other words, 
sugar cane has an almost constant heating 
value, irrespective of how much juice is 
extracted from it. As the extraction grows 
less there is a greater weight of bagasse per 
ton of cane, and while a great part of this 
weight is due to water and is therefore non- 
combustible, the amount of juice left over is 
also greater and this contains combustible 
matter which more than compensates for the 
additional water present. Thus the coal 



equivalent of cane per ton actually increases 
as the degree of extraction grows less. 

A difficulty, however, is that large quan- 
tities of moisture render it difficult to burn 
the bagasse except in special furnaces. 
As the content of moisture increases the 
temperature of the fire decreases, and there 
is danger of a point being reached where 
the gases from the fuel will refuse to ignite. 
In Table 39, the highest attainable temp- 
erature resulting from the combustion of 
dry bagasse is 2,465 F., and of bagasse of 
75% extraction only 1862 F. The cal- 
culations are made on a basis of a pound 
of fiber requiring i2 Ibs. of air; sugar, 
9! Ibs., and molasses, 9^ Ibs.; which are 
twice the theoretical amounts for complete 
combustion. The methods of burning bag- 
asse will be treated in chapter on Fuel 
Burning. 

Corn is used as a fuel in some states when 
the crop is very abundant and the selling 
price is low. 

The following are calorimeter tests of 
various samples of corn: 

TABLE 40 
CALORIFIC VALUE OF CORN (Richards] 



HEATING VALUE IN B. T. U. 





MATERIAL. 


PER POUND 


PER POUND 


PER POUND 






OF 


OF DRY 


OF DRY 






MATERIAL. 


MATERIAL. 


COMBUST- 










IBLE. 


Yellow 


Dent Corn and Cob 


8,040 






" 


" 


8,202 


8,959 


9,085 


White 


Cob . . . 
Corn and Cob 


7,214 
7,841 


7,841 


7,958 


" 


Corn . 


8,382 


9.199 


9,301 




Cob . . . 


7.571 


8,174 


8,285 



Petroleum is practically the only oil 
which is sufficiently abundant and cheap 
to be used as a fuel under boilers. It pos- 
sesses many advantages over solid fuels, 
and its use is on the increase. 

Gasoline, Benzine, Kerosene, and other 
liquid oils distilled from petroleum are 
excellent fuels, but are too costly for use 
under boilers. The residuum after these 
have been distilled off is valuable as fuel. 

There are three kinds of petroleum in 
use, namely those which on distillation 
yield; (i) Paraffin; (2) Asphalt; (3) Olefin. 
To the first group belong the oils of the 
Appalachian Range and middle West. They 



124 



THE STIRLING WATER-TUBE SAFETY BOILER 



are dark brown with greenish tinge. Upon 
distillation they yield such a variety of 
light oils that their value is too great to 
permit their general use as fuels. 

To the second group belong the oils from 
California and Texas. These vary from 
reddish brown to jet black, and are used 
mostly for fuel. 

The third group comprises oils from 
Russia, which are also used more extensively 
for fuel than for any other purpose. 



contracts for purchase of oil should limit 
the content of water, else sufficient tankage 
should be provided to enable most of the 
water to be settled out of the oil before it is 
burned. A large content of water also 
causes trouble with the burners. 

Gasoline Test The content of water in 
fuel oil is often determined as follows: A 
burette or other tall vessel provided with 
glass stopper and graduated into 200 divis- 
ions is filled to the 100 mark with gasoline 



TABLE 41 
CALORIFIC VALUE OF CALIFORNIA OILS 





Per Cent 


Per Cent 


Specific 


Per Cent 


CALORIFI 
B. T. U. 


C VALUE, 
PER LB. 


KIND OF OIL. 


of 
Sulphur. 


of 

Silt. 


Gravity 
at 60 F. 


of 
Moisture. 


Oil as 
Fired. 


Oil Freed 
of Water. 


Whittier 


-975 


0.031 


0.9417 


i . 06 


18,428.4 


18,626 


1 * 


-735 


O . OIO 


0.9430 


i . 06 


18,478.8 


18,677 


* * 


I .010 


o . 024 


o . 9410 


74 


18,567.0 


18,705 


1 ' 


o . 960 


0.010 


0.9407 


.42 


18,578.7 


18,657 


Whittier and Los Angeles mixed 


0.980 


0.054 


0.9530 


4-93 


17,791.2 


18,714 


" i'ii ii i ( 


-955 


o . 048 


0.9529 


4 . 62 


17,887.5 


18,754 


it ii 1 1 ii ii 


0.845 


0.032 


0.9637 


8.71 


16,904. 7 


18,518 


ii i i ii ii ii 


o . 840 


o . 024 


o . 9629 


8.82 


16,956 . o 


18,596 


" " " 








A CA 


17,862 5 


18 607 
















i ii ii ii 








4.^6=; 


I 7 ,830 . O 


18,692 


,< <i 








4. 2 ? 


17,074. C 


18,772 


ii in 11 ii 








3.6? 


l8,O?Q . O 


18,710 


Los Angeles 








Q oo 


I 7 ,O3 C . O 


18,610 










o 87 


17,122 o 


18 007 


i< 








Q . l6 


17,241 . o 


18,970 


,. 








8 47 


16,980 . o 


18,551 


,. 








7 S 5 


18, T, c6 o 


iQ,8 c ? 


Kern Valley 








2.66 


10,410 .0 


IQ ,o =;o 


Fullerton 








2 O7 


19,686 . o 


20,102 

















In general, crude oils consist mostly of 
hydrogen and carbon, but contain small 
percentages of sulphur, nitrogen, arsenic, 
phosphorus, and silt. They also contain 
a content of water varying from less than 
one per cent, up to 50 per cent., depending 
upon the care that has been taken to sep- 
erate out the water which accompanies 
the oil when pumped from the well. Here 
as in all other fuels, the percentage of water 
affects the available heat of the oil, hence 



It is then filled to the 200 mark with the oil 
to be tested, which has first been slightly 
warmed. The two are thoroughly shaken 
together; any shrinkage below the 200 mark 
is made up by adding more oil, and the 
whole is then allowed to stand in a warm place 
(sometimes on an engine cylinder) for 24 
hours. The water and dirt settle to the 
bottom, and the number of divisions of each 
give their respective percentages, by volume, 
of the total. 



FLASH POINT OF OILS 



125 



Flash Point 142 F. 
Burning Point 181 F. 
Cold test 6 F. 



Prof. James E. Denton gives the following 
data as a result of his experiments with 
Beaumont (Texas) crude oil: 

Carbon 84.60% Sulphur 1.63% 
Hydrogen 10.90% Specific I 
Oxygen 2.87% Giavity' 

The Stirling Company has made various 
tests on boilers fired with California oil, 
samples of which were subjected to calori- 
meter test, with results as shown in Table 41 . 

Table 43 gives composition and calorific 
value of some oils as compiled from various 
sources. 

The nitrogen in petroleum varies from . 008 
to 1.10% while that of sulphur varies from 
to %- 



TABLE 43 
COMPOSITION AND CALORIFIC VALUES OF VARIOUS OILS 



Calorific Value of Petroleum Accurate 

data on this subject are scarce. A pound 
of oil free of water is usually considered to 
have a calorific value of from 18,500 to 
22,000 B T. U. Assuming the ultimate 
analysis of an average sample as Carbon 
84%, Hydrogen 14%, Oxygen 2%, and 
allowing for the combination of the oxygen 
with its equivalent of hydrogen to form 
water, the composition becomes Carbon, 84%, 
Hydrogen, 13 . 75%, Water, 2. 25%; and the 
heat value per pound of petroleum, free 
from water, is 

Carbon . .84 X 14,600=12,264 B. T. U. 

Hydrogen .1375X62,100= 8,625 B. T. U. 

Total, 20,889 B. T. U. 



KIND OF OIL. 


Per Cent of 
Carbon. 


Per Cent of 
Hydrogen. 


Per Cent of 
Oxygen. 


Specific 
Gravity. 


B. T. U 

per pound. 


Heavy Oil West Virginia 


82 c 


I 3 . 3 


T. . 2 


0.873 




Light Oil, West Virginia 
Heavy Oil, Pennsylvania 
Light Oil Pennsylvania 


84.3 
84.9 
82 o 


14.1 

J 3-7 
14.8 


1.6 
i . 04 

3 . 2 


0.8412 
0.886 
0.816 


21240 
19224 


Oil from Beaumont, Texas . 


86 8 


I T. . O 


O . O 


o . 920 




Oil from California 


84 o 


12.7 


I . 2 


O . Q2O 




Canada Crude 


84. T, 


1^.4 


2 . 3 




20410 


Ohio Crude 


80 2 


17 I 


2 . 7 




21600 


Oil from Parma, Italy 


84 o 


IT. . 4 


1.8 


0.786 




Oil from Hanover, Germany 


80.4 


12 . 7 


6.9 


o . 802 




Oil from Galicia, Austria 
Light Oil from Baku, Russia 
Heavy Oil from Baku, Russia . 
Refuse of Oil " " " . . 
Oil from Java 


82.2 

86.3 

86.6 
87.1 
87.1 


12 . I 
I 3 .6 
12.3 
II.7 
12 .O 


5-7 

0. I 

i . i 

I . 2 

o . g 


0.870 
0.884 
0.938 
0.928 
0.92^ 


18416 
22628 
19440 
22628 















The analysis and calorific value of the 
principal crude and residuum oils given by 
Mr. Orde are: 

TABLE 42 
ANALYSES OF OILS 





CARBON. 


HYDROGEN. 


OXYGEN, ETC. 


B. T. U. 




% 


% 


% 


Per Ib. 


Texas . . . 


85.66 


II .03 


3-31 


19,240 


Borneo . 
Caucasus 


87.8 
84.94 


10.78 
1 3 . p6 


1.24 
1.25 


18,830 
18,610 


Burmah 


86.4 


12. I 


i. 5 


18,865 



The Flash Point is the temperature at 
which an oil gives off inflammable gases. 
The flash points of the various oils are not 
given in the tables; in fact, data upon this 
subject are scarce. In general the light 
oils have a low flash point, while the heavy 
grades have a much higher flash point. 
This matter is of the utmost importance 
in determining the availability of oil as a 
fuel. The flash points of oils whose specific 
gravities are below 0.85 are generally below 
60 F., while those of oils whose specific 
gravity exceeds 0.85 are usually above 



126 



THE STIRLING WATER-TUBE SAFETY BOILER 



60 F. There are, however, many ex- 
ceptions to this rule, notably a certain 
Roumanian oil, whose specific gravity is 
0.899, an( i whose flash point is 240 F. The 
danger of explosion increases as the flash 
point is lowered, and the utmost care should 
be taken to lessen the possibility of the 
light vapors becoming ignited. When proper 
precautions are taken the use of oil is almost 
as safe as the use of coal. 

Gravity of Oils Fuel oils are often 
valued according to their gravity as indi- 
cated on the Beaume hydrometer, but the 
gravity is by no means an accurate measure 
of the relative calorific value. 

Petroleum as Compared with Coal 
Petroleum possesses the following advan- 
tages over coal: 

(1) Much lower cost for handling, as 
the oil is fed by simple, mechanical means, 
and cost of stoking, removing ashes, etc., 
is eliminated. 

(2) For equal heat value oil occupies 
less space than coal, and the storage space 
may be at considerable distance from the 
boilers without detriment. 

(3) Higher boiler efficiencies and capac- 
ities are obtainable, because the combustion 
is more perfect; the excess air supply is 
greatly lessened; the furnace can be kept 
at constant temperature because fires do not 
require cleaning nor furnace doors to be 
opened for firing; smoke can be wholly 
eliminated, and the boiler heating surfaces 
do not quickly foul with soot. 

(4) Intensity of the fire can be almost 
instantly regulated to conform to the demand 
for more or less steam. 

(5) Oil does not, like coal, deteriorate 
with age when stored. 

(6) Great reduction in number of men 
necessary around the plant, and freedom 
from dust, dirt and smoke, with their damage 
to adjoining property. 

The disadvantages of oil are: 

(1) It must have a high flash point to 
minimize danger of explosions. 

(2) City or town ordinances may impose 
onerous conditions regarding location and 
isolation of oil tanks. 

(3) The boiler repair bill will be high 
unless the boiler is specially adapted to use 
of oil. Whenever unatomized oil strikes 



the boiler surface, a burn, blister, or bag 
is almost sure to form, and in boilers of the 
tubular, or Scotch Marine type, such bag- 
ging may cause a serious explosion. Owing 
to the intense temperature in the fire-box, 
local overheating and burning of plates 
are also common in boilers which are either 
deficient in circulation or deposit scale 
on their hottest surfaces. Constriction of 
circulation will also inevitably cause "steam 
pockets" which rapidly burn out the tubes. 
For these reasons certain types of boilers 
which seem fairly well adapted to use of 
coal need excessive repairs when fired with 
oil. 

Many tables have been published which 
purport to show the number of barrels 
of oil equivalent to a ton of coal, and vice 
versa. For example, assuming a barrel of 
oil to weigh 310 Ibs., and a pound of oil 
to contain 20,000 B. T. U., the following 
table can be computed. 

TABLE 44 
COMPARISON OF OIL AND COAL 



B. T. U. PER LB. 
OF COAL. 


LBS. OF COAL 
EQUAL TO ONE 
BARREL OF OIL. 


BARRELS OF OIL EQUAL 
TO ONE SHORT TON 
OF COAL. 


IO,OOO 
I I ,OOO 
12,000 


620 

5 6 4 
5 J 7 


3- 2 3 

3-55 
3-87 


I3,OOO 


477 


4.19 


I4,OOO 
I5,OOO 


443 
4i3 


4.52 
4.84 



This and all similar computations based 
upon the relative calorific power of petro- 
leum and coal are of no practical value, for 
the reason that when burning oil, an effi- 
ciency ranging as high as 83% can be ob- 
tained with large boilers of good design, 
while with poorer grades of coal and smaller 
boilers the efficiency may fall to 65% or lower. 
The efficiency of either fuel will depend upon 
the size of the boilers, the adaptation of 
their grates and furnaces to the particular 
fuel used, the degree of intelligence of the 
men in charge, and other similar factors. 
Table 45, reproduced from Power, January 
1905, takes into account different boiler effi- 
ciencies, but it assumes a -fixed calorific value 
for oil, 18,500 B. T. U., hence this table like 



COMPARISON OF OIL AND COAL 



127 



others of similar nature, while very useful as a 
rough guide, cannot enable one to compute the 
saving possible by substituting one fuel for 
the other. The reason for this is as follows : 



The saving to be made may depend upon the 
labor which can be dispensed with, the 
available space for fuel storage, and facilities 
for conveying the oil by a pipe line, the 



TABLE 45 

EQUIVALENT HEAT VALUES OF COAL AND FUEL OIL, ALSO FACTORS FOR 

THE REDUCTION OF PLANT ECONOMY PER POUND OF COAL 

TO EQUIVALENT FIGURES PER GALLON 

AND BARREL OF FUEL OIL 





o' a 


11 


-q g 







c 


C sj 





fl 


POUNDS OF WATER EVAPORATED PER POUND OF COAL PER HOUR 




"3 


Jf 


E 3 

03 C 


5. i; 


FROM AND AT 212 FAHR. 




fe 


- ' C 


>X 


^ffi 






g 


t, 3 


fe 


SL, 






P4 


3 ^ 


^JT -' 


flj . 


































h 

b 


II -3 


|o| 


*gs 


5 


6 


7 


8 


9 


IO 


II 


12 


5 


6 


7 


8 


9 


IO 


I I 


12 


c 
o 


. c. 


"o N 


"* '<N 


































'S 


C 


-w C h " 


.2 S H 








8fi 


Sr3 . 


a 3 " 


c S " 








W 


I| 


lfi' S 


|5 


POUNDS OF OIL EQUAL TO ONE 


BARRELS OF OIL EQUAL TO ONE 


* 
'3 


"^ 7"; 


^53"H 
,u a o! 


-gig 


POUND OF COAL 


TON OF COAL 




ffi 


z 


z 


z 








70 


66 


12 . 64 


4247 


3955 


4746 


.5538 


6329 


. 71 20 


.7911 


.8702 


9493 


2.354 


2.825 


3-296 


3-767 


4.238 


4.709 


5-175 


5-651 


71 


67 


12.83 


4311 


.3897 


.4676 




.6235 


.7014 


7794 


.8573 


9353 


2.319 


2.783 


3-248 


3.711 


4- 175 


4. 640 


5-103 


5-567 


7 2 


68 


13.02 


4375 


.3840 


.4608 


.5376 


.6144 


. 69! 2 


.7680 


.8448 


.9216 


2.285 


2.742 


3- 200 


3-657 


4.114 


4-572 


5-028 


5-485 


73 


69 


13. 21 


4439 


-3785 


.4542 


5299 


.6056 


.6813 


7570 


.8304 


.9084 


2. 252 


2.703 


3- 154 


3-605 


4-054 


4.506 


4-956 


5.406 


74 


70 


13-40 


4502 


3731 


-4477 


-5224 


.5970 


.6716 


.7462 


.8208 


.8955 


2. 221 


2.665 


3-ioS 


3.554 


3-998 


4-442 


4-887 


5-331 


75 


71 


13.60 




.3676 


.4411 


.5147 


.5882 


.66l8 


7352 


.8088 


.882S 


2.188 


2 . 626 


3.064 


3.501 


3-939 


4-377 


4-8 5 


5- 252 


76 


72 


13-79 


4633 


-3625 


-4350 


.5076 


.5801 


.6526 


7251 


.7976 


.8702 


2. 158 


2.589 


3.022 


3-453 


3-885 


4-317 


4.748 


5-180 


77 


73 


13-98 


4697 


-3576 


.4291 


.5007 


.5722 


.6437 


7153 


.7868 


.8583 


2 . 129 


2.555 


2 . 980 


3.406 


3-832 


4.258 


4.683 


5 lot) 


78 


74 


14. 17 


476i 


-3528 


4234 


.4940 


5645 


.6351 


-7057 


.7762 


.8468 


2 . 100 


2 . 520 


2.941 


3-360 


3.78o 


4. 200 


4.621 


5.041 


79 


75 


14.36 


4825 


3481 


.4178 


.4874 


.5571 


. 6267 


.6963 


. 7660 


8352 


2.072 


2.487 


2.907 


3-3i6 


3.731 


4- 145 


4-559 


4-974 


80 


76 


14-55 


4889 


-3436 


4123 


.4811 


-5498 


.6l85 


.6872 


.7560 


8247 


2.045 


2.454 


2.863 


3-272 


3.682 


4.090 4-499 


4.909 




VALUES OF H 


VALUES OF J 


70 


66 


12 .64 


4247 


.0494 


.0593 


.0692 


.0791 


.0890 


.0988 


. 087 


. 187 


849.5 


707.8 


606. 7 


530.8 


471.8 


424.7 


386.0 


353-9 




67 


12.83 


43 I i 


.0487 


.0584 


.0682 


.0779 


.0877 


.0974 


. 071 


. 169 


862.2 


716.5 


615.8 


538.8 


478.8 


431 -0 


391 -9 


359-2 


72 


68 


13.02 


4375 


. 0480 


0576 


.0672 


.0768 


.0864 


. 0960 


. 056 


152 


875-0 


729. I 


625 .0 


546.9 


486.0 


437-5 


397-6 


364.5 


73 


69 


13.21 


4439 


.0473 


.0568 


.0662 


.0757 


.0853 


.0946 


. 038 


. 136 


887.8 


739-8 


634.1 


554-9 


492.0 


443-9 


403-4 


369-9 


74 


70 


13.40 


4502 


.0466 


-0559 


.0653 


.0746 


.0839 


.0932 


. 026 


. 119 


900.4 


750.3 


643. i 


562.7 


500. 2 


450.2 


409.2 


375-1 


75 


71 


13.60 


4569 


0459 


-0551 


.0643 


-0735 


.0827 


.0919 


. 01 I 


. 103 


913.8 


761.5 


652.7 


571- 


507.6 


456.9 


4I5-3 


380.7 


76 


72 


13-79 


4633 


-0453 


0544 


.0635 


.0725 


.O8l6 


.0906 


.0997 


. 088 


926. 6 


772.1 


661.8 


579- 


514.7 


463-3 


421 . i 


386.0 


77 


73 


13.98 


4697 


.0447 


-0536 


.0626 


-0715 


.0805 


. 0894 


.0983 


073 


939-4 


782.8 


671 .0 


587. 


521.8 


469. 7 


426.4 


391 -4 


78 


74 


14.17 


476i 


-0441 


.0529 


.0617 


.0705 


0794 


.0882 


.0970 


059 


952 . 2 


793 5 


680. i 


595- 


529.0 


476. i 


432.8 


396.7 


79 


75 


14.36 


4825 


-0435 


.0522 


. 0609 


.0696 


-0783 


.0870 


.0957 


044 


965.0 


804. i 


689.3 


603. 


536.1 


482.5 


438.6 


402 .0 


80 


76 


14-55 


4889 


.0429 


.0515 


.0601 


.0687 


.0773 


.0859 


- 1945 


. 031 


977-8 


8:4.8 


698.4 


611 . 


543-2 


488.9 


444-4 


407-4 



Net efficiency is determined by deducting from boiler efficiency 4 per cent., representing 
steam used for oil burners and oil pumps. 

One ton of coal weighs 2,000 pounds. One barrel of oil weighs 336 pounds. One gallon 
of oil weighs 8 pounds. One pound of oil contains 18,500 B.T.U. 

Equivalent gallons of oil per kilowatt hour= HXpounds of coal per kilowatt hour. 

J 



Equivalent kilowatt hours per barrel of oil = 



pounds of coal per kilowatt hour. 



PQ 



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o 



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g 
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128 



COMPARISON OF NATURAL GAS AND COAL 



129 



hours per day the plant operates, and the 
quantity of coal needed for banking fires, 
the possibility of operating an oil fired plant 
where a coal fired plant would be objection- 
able owing to smoke, and many other sim- 
ilar considerations, far more than on the 
relative calorific value of oil and coal. In 
consequence there is but one reliable method 
of determining the relative advantages of 
the two fuels, and that is by operating the 
plant with each fuel for an interval of time 
long enough to give accurate data regarding 
costs of every item entering into the problem. 
Any other method must necessarily be 
approximate to such a degree as to render 
it practically guesswork. 

Coal Tar usually has a value for other 
purposes far exceeding its fuel value, yet 
at times it is used to advantage for fuel. 
It differs from crude oil chemically, being 
lower in hydrogen and higher in carbon, 
and therefore of a lower calorific value. 
The following is an ultimate analysis of a 
tar made from a standard gas coal : 

Carbon 89 . 2 1 % 

Hydrogen 4.95 

Nitrogen I -5 

Oxygen 4.20 

Ash .06 

Sulphur 53 

B. T. U. per pound. . 15,388 

Water=Gas Tar is lighter than coal tar, 
and is the residuum of gas oil. Its analysis 
is as follows: 

Carbon . . . . . . 92 . 70% 

Hydrogen . . . . . 6. 13 

Nitrogen o . 1 1 

Oxygen 0.68 

Ash 05 

Sulphur .33 

B. T. U. per pound, . 17,296 

A gallon of coal tar weighs 10.33 Ibs., 
and a gallon of water-gas tar 9.58 Ibs. In 
actual tests the former has evaporated 11.91 
Ibs. of water per pound of fuel, and the latter 
14.9 Ibs., from and at 212. 

Natural Gas is pumped from the wells to 
the point where it is to be used. The gas 
leaves the pumping station in the field at 
pressures reaching 250 pounds per square 
inch; at the receiving station it is reduced 



to a pressure of 4 to 5 pounds before entering 
the distributing mains. At the boiler house 
this pressure is still further reduced by a 
valve controlled by the steam pressure. 
The final pressure at which the gas enters 
the burner is usually measured by a mercurial 
pressure gauge graduated to read in pounds 
and ounces per square inch. The charge 
for gas is based upon readings of a meter 
placed between the reducing valve and the 
burner. For purposes of comparison all 
observations should be based on gas re- 
duced to standard temperature of 32 F. 
and absolute atmospheric pressure of 14.7 
Ibs. per square inch. When the temper- 
ature and pressure corresponding to the 
meter readings are known, the volume of 
gas under standard pressure and temper- 
ature can be obtained by multiplying the 
number of cubic feet indicated on the meter 

by - - in which P= absolute pressure 

in pounds per square inch, and T absolute 
temperature F. of the gas at the meter. In 
boiler tests the evaporation should be re- 
duced to that per cubic foot of gas under 
standard pressure and temperature. 

The weight of natural gas is about 45.6 
Ibs. per i ,000 cubic feet under standard 
conditions. The composition varies con- 
siderably, even in the same field. Table 45 
gives analyses and calorific values of natural 
gases from various localities. 

Comparison of Natural Gas and Coal 
The same reasons which present any accu- 
rate comparison of the value of coal and 
petroleum without an actual test apply with 
equal force in case of coal and natural gas. 
The following table, based upon the assump- 
tion that one cubic foot of gas under standard 
conditions will evaporate .75 Ib. of water, 
will enable an approximate comparison to 
be made. 



WATER EVAPORATED 
PER POUND OF COAL 

7 
8 

9 

10 
ii 



NO. OF M CU. FT. GAS 
EQUAL 2,000 LBS. COAL 



21.3 

24.O 

26 . 7 
29-3 



Natural gas at 6 cents per 1,000 cubic 
feet will be equal in heating value to coal 
which evaporates 7 Ibs. of water per pound 
and costs $1.12 per ton. 




REPUBLIC IRON & STEEL CO. YOUNGSTOWN, O., OPERATING 1 1 ,3OO H. P. OF STIRLING BOILERS 



Determination of Heating Value of Fuels 



Methods The heating value of a fuel 
may be determined: (i) By calculation 
from a chemical analysis: (2) By burning a 
sample in a calorimeter. In the first method 
the calculation may be based on either an 
ultimate ana y sis or a proximate analysis. 
An ultimate analysis reduces the fuel to 
its elementary constituents of carbon, hy- 
drogen, oxygen, nitrogen, sulphur, and the 
ash and moisture. The work requires the 
services of a chemist, and for further par- 
ticulars the reader is referred to Stillman's 
Engineering Chemistry. A proximate anal- 
ysis determines only the per cent, of fixed 
carbon, volatile matter, moisture, and ash, 
but does not determine the ultimate com- 
position of the volatile matter. 

Caution in Interpreting Results of Ul- 
timate Analyses Reports of ultimate an- 
alyses sometimes give the percentages of 
constituents referred to weight of the sample 
less its weight of moisture. When the 
report gives the proportions in this way 
and also the per cent, of moisture originally 
in the sample, the true analysis can easily 
be obtained, as shown in following case: 



CHEMIST S TRUE 
REPORT ANALYSIS 



Carbon 
Hydrogen . 
Oxygen 
Nitrogen . 
Sulphur 
Ash . . 

Moisture . 



76.91 


72.25 


5-7 


4.76 


8.65 


8.125 


1.16 


i .09 


I . 21 


i . 135 


7 .00 


6.58 


100.00 




6.06 


6.06 



106.06 100.00 



The true analysis is obtained by dividing 
each of the apparent percentages, as reported, 
by the sum, 106.06. 

The per cent, of moisture determined by 
drying a large sample, immediately after 



it is taken from the coal pile, will almost 
invariably be larger than determined from 
the analysis, because in shipping the sample 
to the chemist, and preparing it for analysis, 
some of the moisture evaporates. 

The ultimate analysis resolves the fuel 
into its elementary constituents but does 
not reveal how these may have been com- 
bined in the fuel. The manner of their 
combination undoubtedly affects the cal- 
orific value, as fuels yielding identical ul- 
timate analyses often give different heating 
values when tested in a calorimeter. The 
difference is very slight, and a very close 
approximation to the heating value may 
be computed from the ultimate analysis. 

Calculations from an Ultimate Analy= 
sis The first formula for the calculation of 
heating values from the composition of a fuel 
is due to Dulong, and this, slightly modified, 
is used to-day. Other formulas have been 
proposed, some of which give more accurate 
results for particular classes of fuels, but 
most of them are based upon Dulong 's 
and are merely modifications of it. Du- 
long's formula* converted into British Units 
is 

Heating value in B. T. U. per lb.= 

14,500 C+62,ioo j H [29] 

( 8 ) 

The coefficients 14,500 and 62,100, repre- 
senting the heat of combustion of carbon 
and hydrogen, have been investigated by 
numerous experimenters who determined 
values which differ slightly from those 
above given. With a view of establishing 
some uniform practise the American So- 
ciety of Mechanical Engineers, in their 
"Rules for Conducting Boiler Trials, " Code 
of 1899, recommend the following; 

Heating value in B. T. U. per lb.= 

14,600(7 + 6 2,000 \H ->-+4,oooS [24] 
( 8 ) 



*Dulong's original formula in French units is 

Heat Value in Calories =8080^ + 3 4,500^ H - i [30] 

f O ) 

The calorie is the heat unit of the metric system, and when used as a measure of the heating value of 
fuel, it is the number of units of weight of water which may be heated one degree Centigrade by the com- 
bustion of one unit weight of coal. The unit of weight may be either a kilogram, gram or pound. When 
thus used a calorie is equivalent to 1.8 B. T. U. 



132 



THE STIRLING WATER-TUBE SAFETY BOILER 



C,H,0, and 5 are the proportional content ot 
carbon, hydrogen, oxygen, and sulphur, 



formula gives results nearly identical with 
those obtained from calorimetric tests, and 



respectively. This formula is generally ac- may safely be applied to all solid fuels ex- 



cepted by all American Engineers. The 
last term represents the heating value of 



cept cannel coal, lignite, turf and wood, when- 
ever a correct ultimate analysis is available. 



100 




0610 

PERCENTAGE OF HYDROGEN 

FIG. 25 CHART ILLUSTRATING MAHLER'S FUEL FORMULA 

sulphur, based on determinations made by Mahler's Formula* is based upon the 

Lord. The method of using the formula has content of carbon and hydrogen only. It 

already been shown on page: 06. is simpler than Dulong's, and sufficiently 

The investigations of Mahler in France, accurate for many practical purposes. It is: 

Lord and Haas in this country, and Bunte B. T. U. per pound of fuel= 

in Germany, all show that the Dulong 201 C + 676 #-5540 [31] 

*For derivation of this formula see The Locomotive, November, 1903. 



WEIGHT AND CALORIFIC VALUE OF GASES 



133 



in which 6" and H are the percentages by 
weight, of carbon and hydrogen in the 
fuel. An advantage of this formula is that the 
results may, without calculation, be obtained 
from the diagram, Fig. 25. Example: To 
find the calorific value of a fuel containing 
four per cent, hydrogen, eighty-four per- 
cent, carbon, and twelve per cent, of ash, 
water, etc., locate on the hydrogen scale at 
the bottom the line under four; pass ver- 
tically upward along this line until it inter- 
sects the horizontal line passing through 
eighty-four on the carbon scale. The point 
of intersection is on the line marked 14,000, 
hence the fuel contains 14,000 B. T. U. per 
pound. 



Heat Values of Gaseous Fuels The 
method of computing calorific values from 
ultimate analyses is particularly adapted to 
solid fuels, with the exceptions already noted. 
In the case of gaseous fuels, it is better to 
separate trfem into their elementary con- 
stituent gases, and to compute the heating 
values of these gases separately. Usually 
only hydrogen, carbon monoxide (CO) and 
certain hydrocarbons will be found constitut- 
ing the combustible portion of the gas. 
Table 47 gives calorific value of the com- 
monest combustible gases. 

Application of the table. As gas analyses 
may be reported either by weight or by vol- 
ume, an example of each will be given: 



TABLE 47 

WEIGHTS AND CALORIFIC VALUE OF GASES AT 32 F. 
AND ATMOSPHERIC PRESSURE 



GAS. 


Chemical 
Symbol 


Cubic Feet 
per Pound 
of Gas. 


B. T. U. 
per Pound 
of Gas. 


Cu. Ft. of Air* 
Required per 
Pound 


B. T. U. 
per Cubic Foot 
of Gas. 


Cu. Ft. of Air 
Required per 
Cubic Foot 










of Gas. 




of Gas. 


Hydrogen . 


H 178.93 


62,000 


428.25 


346 


2 -39 


Carbon Monoxide 


CO 12. 81 


4,35 


30.60 


339 


2-39 


Marsh Gas 


CH 4 22.43 


23>5 6 4 


214 . oo 


1050 


9-54 


Acetylene . 


C 2 H 2 


13-79 


21,465 


164.87 


!55 6 


11 -93 


Olefiant Gas . 


C 2 H, 


I 2. 80 


21,440 


183.60 


1675 


14.33 


Ethane . . . 


C 2 H 6 


11.96 


22,230 


199.88 


1859 


16.72 



*To reduce volumes of air to pounds of air multiply by 12.39. 



Correction for Hydrogen, Moisture 
and Nitrogen If the fuel contains water,' the 
heat necessary to evaporate it and to super- 
heat the steam thus formed produces no 
useful result and should be deducted from 
the amount given by the above formulas. 
The same thing applies to the water formed 
from the hydrogen present. The nitrogen 
in the fuel absorbs heat without producing 
any benefit. The total losses due to these 
causes can be computed by the formula 

B. T. U. Lost= 

(9 H + W) [212.9 -* + 9 6 5-8 + 0.48 (t c -2i 2)] 

[32] 



In which H, W, and N are the proportional 
content of hydrogen, water and nitrogen, 
/ c the temperature of breeching, and / the 
temperature of air supply. 



(1) A blast furnace gas, analysis by 
weight being, oxygen (O)= 2.7; carbon mon- 
oxide (CO) = 19. 5; carbon dioxide (CO 2 ) 
= 18.7; nitrogen (N) = 59 . i ; all in per cents. 
The only combustible present is carbon 
monoxide, hence the heating value per pound 
of the gas is 0.195X4350=848.25 B. T. U. 
The net volume of air needed to burn a pound 
of the gas is 0.195X30.6=5.967 cu. ft. 

(2) A natural gas, analysis by volume 
being, oxygen (0)=o.4o; carbon monoxide 
(CO)=o.95; carbon dioxide (CO 2 )=o.34; ole- 
fiant gas (C 2 H 4 )=o.66; ethane (C 2 H 6 )= 
3.55; marsh gas (CH 4 ) = 72.i5; hydrogen 
(H)=2i.95, a U m P er cents. All but the 
and CO 3 are combustibles, hence the heat 
developed and net air required per pound 
of gas will be as worked out in detail in the 
following table: 



ANALYSIS OF ALABAMA COALS 



135 



Heat from CO =0.0095X339 = 3.22 

C 2 H =0.0066X1675= 11.05 

" C'H, =o. 0355X1859 = 65.99 

C H.=o. 7215X1050=757. 58 

H =0.2195 X 346 = 75.95 



B. T. U. 



Total, 



9 J 3-79 



B. T. U 



Air needed for CO =o.oo95X 2.39 = 0.022705^. ft. 
" C 2 H., =0.0066 X 14.33 =0.094578 Cu. ft. 
' C,H G -0.0355 X 16.72 =o.59356oCu. ft. 
" C H 4 =0.7215 X 9.54=6.883iioCu.ft. 
" H =o.2i95X 2.39 =0.524605 Cu.ft. 



Total air needed, 



8.118558 Cu. ft. 



Proximate Analysis The proximate 
analysis of fuel gives its proportions of fixed 
carbon, volatile combustible matter, moisture 
and ash. It is made by subjecting a sample 
to a temperature of 250 to 300 to expel 
the moisture, then to a red heat which expels 
the volatile matter; then to a white heat 
which causes the carbon to pass off as dioxide, 
leaving the ash as a residue. By weighing 
the residue at end of each operation the 
various percentages can be computed. See 
Article XV of Code, in chapter on Rules for 
Conducting Boiler Trials, page 204. 

Table 48 gives ultimate and proximate 
analyses of Alabama coals, and illustrates 
the relationship between the two. 

The proximate analysis is easy to make, 
it affords information as to the general 
characteristics of a fuel , and its relative heat- 
ing value, but from it the heating value can- 
not be directly computed. The reason is 
that the volatile content varies widely in 
composition and heating value. 



Comparison of many experiments has 
resulted in production of some methods of 
estimating the calorific value of coals from 
proximate analyses. Kent* deduced from 
Mahler's tests on European coals the ap- 
proximate heating values of coal dependent 
upon the content of fixed carbon in the 
combustiblef as given in the following table. 

TABLE 49 

APPROXIMATE HEATING VALUE OF COALS 
(Kent.) 



Percentage 
Fixed Carbon 
in Coal Dry 
and Free from 
Ash. 


Heating Value 
B. T. U. 
per Pound 
Combustible. 


Percentage 
Fixed Carbon 
in Coal, Dry and 
Free from Ash. 


Heating Value 
B. T. U. 
per Pound 
Combustible. 


IOO 


14,600 


68 


I5'48o 


97 


14.940 


63 


15,120 


94 


15,210 


60 


14,580 


9 


15,480 


57 


14,040 


8? 


i 5,660 


55 


13.320 


So 


15,840 


53 


12,600 


72 


15,660 


5 1 


12,240 



Example: Given a coal whose proximate 
analysis is, fixed carbon 6 1 %, volatile matter 
29%, ash 8%, moisture 2%. The com- 
bustible portion amounts to 61 + 29=90% 
of which the fixed carbon is 61^-90=68%. 
From Table 49 the combustible portion of 
such a coal has a heat value of 15,480 B. 
T. U.; hence the correct heating value, per 
pound of coal, is 

i5,48oX. 90=13, 932 B. T. U. 



TABLE 48 
PROXIMATE AND ULTIMATE ANALYSES OF ALABAMA COALS 











Common to Proxi- 






Proximate Analyses. 


Ultimate Analyses. 


mate and Ultimate 










Analyses. 


Name of Seam, 


Location. 


Volatile 






















and Com- 
bustioie 


Fixed 
Carbon. 


Carbon. 


Hydrogen 


Oxygen. 


Nitrogen. 


Sulphur. 


Ash. 


Moist- 
ure. 






Matter. 


















Wadsworth 


Helene 


34-3 


60.50 


73-23 


7.98 


11.92 


.07 


0. 60 


3-5 


.70 


Pratt 


Pratt 


33-45 


63.20 


75.82 


10.52 


7-51 


-73 


1.07 


2 . 00 


35 


Brookwood 


Brookwood 


27.80 


58.70 


72-47 


10.38 


I . 60 


0.40 


1.65 


I I .90 


.60 


Woodstock 


Bloc ton 


34.80 


60 . 60 


72-75 


8.61 


11.12 


.48 


1.44 


2.65 


95 


Underwood 


Blocton 


35-65 


57-3 


70.82 


10.19 


9-95 


3 1 


0.68 


5- 2 5 


.80 


Pratt 


Pratt 


3 x -55 


64-95 


75-05 


9.91 


8-95 


.62 


0.97 


2 -35 


J 5 


Milldale 


Brookwood 


3 -5 


66.30 


73-9 6 


10.50 


'9-57 


.62 


I - I 5 


2 . 2O 


. 00 




Blue Creek 


25.80 


69 . 90 


72.68 


10.77 


9-83 


!-39 


i .03 


2.80 


5 




Coalburg 


32-55 


65-57 


74-59 


10.58 


9.48 


i-3i 


1.32 


I . 90 


.82 


Cahaba 




3- T 5 


52.90 


60.37 


10.70 


9.00 


i . 26 


1.72 


16.30 


65 



* Steam Boiler Economy, First Edition, p. 47. 



fSee foot-note, page 112. 



28,000 



27,000 



26,000 



25,000 



24,000 



23,000 



22,000 



21 ,000 



20,000 



19,000 



18,000 



17,000 



16,000 



15,000 



14,000 



10 15 20 26 30 36 40 45 50 

PER CENT OF VOLATILE IN THE COMBUSTIBLE. 
FIG. 26. GOUTAL'S VALUES FOR "A" IN B. T. U.= 1 4.76O C +aV 



GOUTAL'S FORMULA FOR CALORIFIC VALUE OF COAL 



137 



To facilitate the use of Kent's method, 
Fig. 27 has been prepared; the per cent, of 
fixed carbon in the combustible having been 
located on the abscissa, the B. T. U. per 
pound of combustible can be determined 
from the corresponding ordinate. 

Goutal* gives carbon a fixed value, and 
considers the heat value of the volatile 
matter a function of its percentage referred 
to combustible. Goutal's formula, in Brit- 
ish units, is, 



v+c 



05 

. 10 



2 5 
30 
35 
38 
.40 



2 6 , 1 OO 

23.400 

21 ,060 
19,620 
18,540 
17,640 
16,920 

15.300 
I4,4OO 



16,000 



15,500 



i5,OOO 



14,500 



14,000 



13,500 



13,000 



12,500 



55 60 65 70 75 80 85 

PER CENT OF FIXED CARBON IN COMBUSTIBLE. 



90 



95 



FIG. 27. GRAPHICAL REPRESENTATION OF THE RELATION BETWEEN PERCENTAGE OF FIXED CARBON 
IN COMBUSTIBLE, AND THE CALORIFIC VALUE PER POUND OF COMBUSTIBLE 



B. T. U. per Ib. of coal= i4,j6oC-\-aV [33] 
In which 

C= the proportional content of fixed car- 
bon in the coal. 

V= the proportional content of volatile 
matter in the coal. 

a= a variable depending on the ratio V 
of volatile matter to combustible, 
per following table, or from Fig. 26. 



Applying the formula to the same coal as 
in preceding example, 6"=o.6i; ^=0.29; 

o . 29 

V'= = .3 2, hence from the figure" a " = 

.6i+.29 

17,300, hence B. T. U. per pound of coal = 
14,760X0.61 + 17,300 Xo. 29 = 14, 020, which 
is only about six-tenths of one per cent, 
different from the value found by Kent's 
method. 



*Comptes rendus de V Academie des Sciences, Vol. cxxxv, p. 477. 



138 



THE STIRLING WATER-TUBE SAFETY BOILER 



Illinois Coals From calorimetric de- 
terminations and chemical analyses of over 
a thousand samples of coal, R. W. Hunt 
& Co., deduced the formula, 

B. T. U. per pound of coal= 

14, 544 C+i6, 515^ io,ooo.4 [34] 

which is correct within narrow limits for Illi : 
nois coals in which the content of fixed carbon 
and volatile matter ranges from 40 to 45 per 
cent.; when the ash lies between 10 to 15 




FIG. 28 FIG. 29 

PARR'S FUEL CALORIMETER 

per cent, the formula will be more accurate 
if written. 

B. T. U. per pound of coal= 
14,544(^+16,515^+354/1-1635 [35] 

In both cases C, V, and A are the pro- 
portional content of fixed carbon, volatile 
matter, and ash. 

Range of Accuracy of Fuel Formulas- 
Mr. Kent states that for coals containing sixty 
per cent, or more of fixed carbon in the com- 
bustible, the values in Table 49 are prac- 
tically correct, but for coals containing less 



than sixty per cent, of fixed carbon the 
tabular values are liable to an error of four 
per cent, in either direction 

M. Goutal states that his formula proved 
very accurate over a wide range of exper- 
iments, six hundred different coals being 
used, and that the error rarely exceeded one 
per cent. ; it was found to give values two per 
cent, high for some anthracites and lignites. 

So far as the present writer has been 
able to test these two methods, they give 
results which are accurate enough for all 
ordinary work, when applied to eastern 
coals whose percentage of fixed carbon and 
volatile matter fall within their range, but 
they apply with less accuracy in propor- 
tion as the coals are mined in the fields far- 
ther to the west, and for fuels mined in 
Wyoming, Colorado and farther west and 
north the formulas are of little use. Con- 
sequently, while fuel formulas are of great 
value where approximate results only are 
necessary, a calorimetric determination of 
the heating value of the fuel is necessary 
whenever exact results are required. 

Calorimetry The ultimate or proximate 
analysis of a fuel is useful in determining 
its general character, and in making a close 
approximation to its heating value; but 
for a practical determination of heating 
value the calorimeter method is more sat- 
isfactory. In this a sample of the fuel 
is actually burned, and the heat of com- 
bustion is measured. 

Calorimeters are composed of a com- 
bustion chamber and a calorimeter bath, 
the latter consisting of a vessel surrounding 
the combustion chamber, and containing 
a known quantity of water. The elevation 
of the temperature of the water, when 
accurately measured and multiplied by suit- 
able constants peculiar to the apparatus, 
determines the heating power of the fuel. 

Mahler's Calorimeter is very popular' 
and much used, but its operation is very 
complicated, and requires an expert. Both 
the instrument and method of operating 
it are described in Kent's Steam Boiler 
Economy. 

Parr Calorimeter A very reliable, in- 
expensive, and simple calorimeter is that in- 
vented by Prof. S. W. Parr, of the University 
of Illinois. This apparatus does not require 



PARR'S FUEL CALORIMETER 



139 



the services of an expert operator. Oxygen 
is not used, no high pressures are employed, 
and the total time consumed in conducting 
a test on a weighed and dried sample should 
not exceed 15 or 20 minutes. 

Fig. 28 shows the relative position of parts. 
The can A is filled with two litres of water. 
The combustion takes place within the car- 
tridge D. The resulting heat is imparted to 
the water. The rise in temperature is in- 
dicated by the finely graduated thermometer 
T. Fig. 29 shows the cartridge in which is 



Extraction of the heat is complete in from 
four to five minutes. The maximum reading 
is taken and the rise in temperature, multi- 
plied by a simple factor, gives the heat in 
British thermal units per pound of coal. By 
a slight modification of the apparatus, igni- 
tion may also be effected by an electric fuse, 
and where current is available this method 
is preferred by some users. 

The instrument is well adapted to the de- 
termination of sulphur in coal, pyrites, pe- 
troleum, etc. Upon dissolving out the 




ST. CLAIR STEEL COMPANY, CLAIRTON, PA., OPERATING 6.50O H. P. OF STIRLING BOILERS 



placed a weighed quantity of coal, previously 
ground to pass through a 100 mesh sieve and 
dried in the usual way at 220 to 230 F. 
There is also put into the cartridge a chem- 
ical compound which is thoroughly mixed 
with the coal by shaking. The cartridge is 
then placed into a measured quantity of water 
in the insulated calorimeter can A. The 
stirrer is set in motion and operated by a 
cord about the pulley P. After a constant 
temperature has been attained ignition is 
effected by means of a short piece of hot wire 
dropped through the stem of the cartridge. 



products of combustion from the bomb the 
sulphur of the original material, being in 
the form of soluble sulphate, may very 
readily be made to indicate the percentage 
content by a simple photometric device. 

The residue from the combustion contains 
the carbon of the coal in the form of sodium 
carbonate. The volume of carbon dioxide 
may readily be measured, and from this the 
total carbon of the coal can be calculated. 
This is a result not heretofore available 
except by ultimate analysis, and enhances 
the value of the instrument. 



Fuel Burning 



The preceding chapter indicates the wide 
range of the nature and calorific value of the 
available boiler fuels ; the methods of burning 
these fuels to best advantage will now receive 
attention. 

Draft The intensity of draft required 
varies with the kind and amount of fuel to 
be burned per square foot of grate, as shown 
by Fig. 38* in the chapter on Chimneys. It 
is well known that if the draft is deficient, the 
volatile matter in the fuel escapes unburnt 
with the furnace gases, and the fire is dead and 
smoky. It is not generally recognized that 
an excess of draft causes equally large losses 
by burning holes through the fire and ad- 
mitting surplus air which reduces the furnace 
temperature. Consequently, to secure the 
most efficient results the draft should be 
regulated by the damper to just the amount 
corresponding to the desired combustion 
rate, and no more. 

Anthracite may be burned in almost any 
kind of furnace, but the grate area, and 
the intensity of draft must be sufficient to 
burn the amount of coal requisite to develop 
the desired capacity. When possible the 
coal should be at least 6 inches deep on the 
grates, because with thinner fires air holes 
are liable to form in the bed of coals. The 
smaller sizes of anthracite require more draft 
than the larger sizes, and the light weight of 
the coal particles renders it difficult to pre- 
vent the draft forcing holes through the fuel. 
If a thick fire is maintained so as to avoid an 
excess of air, the tendency of the fuel is to 
choke the interstices in the grate-bars and to 
cause a deficit of air. To keep between these 
limits and obtain just the correct amount of 
air requires considerable skill on the part of 
the fireman. The fires require frequent 
cleaning, and as the size of the coal decreases 
there is likely to be trouble from clinkers. 

The successful burning of these small sizes 
requires a grate with a large number of very 
small air openings, and usually forced draft. 
When the coal clinkers a steam jet blowing 
into the ash pit will be found beneficial. 
Shaking grates may also be used to advan- 
tage, since they make it possible to rid the 

*See page 174. , 



fires of ash without disturbing them to any 
great extent on the surface. Once anthracite 
is placed into the furnace it should not again 
be touched except when it is necessary to clean 
the fire. 

In proportion as the coal is coarser, more 
of it may be fired at each charge. The proper 
interval between charges can be determined 
by careful observation of the fire. After the 
fire reaches a white heat the lower part of the 
bed of coals will burn away, and the upper 
surface will sink; this sinking indicates- 
the proper moment for firing again be- 
cause unless fresh coal is quickly added, 
air holes will form in the fire. In one or 
two minutes after the new charge of coal is 
fired, flame will appear over this coal in 
in spots which indicate uneven flow of air 
through the fuel. These spots should im- 
mediately be covered with additional fresh 
coal so spread as to compel the air to pass 
at a uniform rate through the entire bed of 
fuel. No further coal should be thrown 
upon the fire until it sinks again, otherwise the 
formation of clinkers will be considerably 
increased. 

The Stirling furnace is perfectly adapted 
to anthracite, and the incandescent arch 
supplies the heat necessary to ignite the car- 
bon monoxide distilled from the fresh coal, 

Volatile Matter All coals except anthra- 
cite contain a considerable portion of volatile 
matter which must be burned to develop 
the full heating power of the fuel. How 
to do this has always been a most trouble- 
some problem which is seldom solved in 
boiler furnaces. The per cent, of volatile 
matter steadily increases in the progression 
from anthracite to lignite; accordingly, as- 
the coal is of poorer grade not only is its 
calorific power less, but it becomes more 
difficult to develop what it has. The reason 
for this lies principally in the failure to adapt 
the furnace to the peculiarities of the coal. 

When fresh bituminous coal is thrown 
upon the fire "the first thing that the fine 
fresh coal does is to choke the air spaces 
existing through the bed of coke, thus shut- 
ting off the air supply which is needed 



142 



THE STIRLING WATER-TUBE SAFETY BOILER 



to burn the gases produced from the fresh 
coal. The next thing is a very rapid evap- 
oration of moisture from the coal, a chilling 
process, which robs the furnace of heat. 
Next is the formation of water-gas by the 
chemical reaction, C+H 2 O=CO+2H, the steam 
being decomposed, its oxygen burning the 
carbon of the coal to carbonic oxide, and 
the hydrogen being liberated. This reaction 
takes place when steam is brought in contact 
with highly heated carbon. This also is a 
chilling process, absorbing heat from the 
furnace. The two valuable fuel-gases thus 
generated would give back all the heat ab- 
sorbed in their formation if they could be 
burned, but there is not enough air in the 
furnace to burn them. Admitting extra air 
through the fire-door at this time will be 
of no service, for the gases being compara- 
tively cool cannot be burned unless the air 
is highly heated. After all the moisture has 
been driven off from the coal, the distillation 
of hydrocarbons begins, and a considerable 
portion of them escapes unburned, owing to 
the deficiency of hot air, and to their being 
chilled by the relatively cool heating sur- 
faces of the boiler. During all this time great 
volumes of smoke are escaping from the 
chimney, together with unburned hydrogen, 
hydrocarbons, and carbonic oxide, all fuel- 
gases, while at the same time soot is being 
deposited on the heating surface, diminish- 
ing its efficiency in transmitting heat to 
water.' '* 

To burn these gases it is necessary that 
they be brought into contact with a supply 
of air hot enough to cause ignition, and that 
they have ample space in which to mix with 
the air and burn completely before coming 
into contact with the boiler surfaces which are 
comparatively cool and extinguish the flame. 

Inefficient Furnaces Few boiler fur- 
naces comply with these requirements. In the 
internally-fired boiler the furnace is surround- 
ed with water so that the gases are liberated 
in a space which is too restricted to permit 
proper mixture with air, and too cold to 
cause ignition. In the return tubular boiler 
there is more space available for mixing the 
gases and air but the flame is extinguished 
by the cool boiler shell which forms the top 
of the furnace. In the horizontal water-tube 
boiler the roof of the furnace is a nest of 



water- tubes, and any flame not extinguished 
by first contact with them is extinguished by 
being drawn between them and surrounded 
by water-cooled surfaces. Complete com- 
.bustion of volatile matter in such boiler 
furnaces is therefore impossible. 

The Stirling Furnace has already been 
described, and its adaptation to burning 
volatile matter set forth, f An abundant 
supply of air can be admitted to the gases at 
all times, and as the furnace is surrounded by 
incandescent fire-brick the heat necessary for 
complete ignition of the gases is available and 
at the right place. The distinguishing feature 
of the Stirling furnace is the fire-arch. That 
this is an indispensable part of any furnace 
efficient for burning volatile matter is recog- 
nized by engineers. Many opinions in sup- 
port of this statement might be quoted, but 
the following must here suffice. 

"Chilling the gases before combustion is 
complete, should be carefully prevented; 
and comparatively cold surfaces, as those 
of a steam boiler, should not be placed too 
near the burning fuel. A large combus- 
tion chamber should, where possible, be 
provided, and more complete combustion 
may be expected in furnaces of large size, 
lined 'with fire-brick, and with arches of 
the same material, than in a furnace of small 
size where the fire is surrounded by chilling 
surfaces, as in a 'fire-box steam boiler'." 
(R. H. Thurston, A Manual of Steam Boil- 
ers, yth ed., p. 188.) 

"The change required in the furnace is the 

roofing of it with fire-brick " (Kent, 

Steam Boiler Economy, 1901, p. 159.) 

"Of all the different kinds of furnaces 
designed for various purposes, the most 
persistent smoker is that of the steam 
boiler. The reason is obvious, for there 
are not hot walls to radiate back the heat 
and thus aid combustion. In some designs 
of boilers the furnace is enclosed in a fire- 
brick combustion chamber, and the products 
are not admitted to the heating surfaces 
until after combustion has become more or 
less perfect. This arrangement has met with 

success in many instances " (H. 

De B. Parsons, Steam Boilers, 1903, p. 15.) 

Bituminous Coals and Lignites The 
difficulties encountered in burning bitu- 
minous coal with economy and without 



*Kent; Steam Boiler Economy, p. 155. fSee pages 10 and n. 



THE COKING METHOD OF FIRING COAL 



143" 



smoke increase as the content of fixed carbon 
grows less; the coals requiring the greatest 
skill in handling are those of the bituminous 
variety from Illinois, Iowa, Missouri and 
the West. To burn the volatile matter 
the furnace must be large, to permit the air 
and gases to mingle; hot, to ignite the mix- 
ture and complete the combustion before 
he boiler surface is reached; and provided 
with ample grate surface to burn the requi- 
site quantity of fuel requirements pre- 
fectly met in the Stirling furnace. 

The fire needs more attention than in 
case of anthracite. The fixed carbon will 
usually take care of itself if the fire is so 
handled as to burn the volatile matter. 
The depth of coal to be carried on the grates 
to produce the best results varies through wide 
limits according to the nature of the coal. 
Coa's from the same locality may require 
different depths, hence it is impossible 
to give any general rule applicable to all 
cases. The fireman must, by careful trials 
with each coal, determine the proper depth; 
the following information may serve as a 
suggestion when making such trials. 

Semi-bitumious coals, such as Pocahontas, 
New River, Clearfield, etc., require fires 
from 12 to 14 inches thick; fresh coal should 
be charged at intervals of 10 to 20 minutes, 
and the quantity should be sufficient to 
maintain the thicknecs above given. Bi- 
tuminous coals from the Pittsburg district 
require fires 4 to 6 inches deep, and should 
be fired often and in comparatively small 
charges. The coals mined in Kentucky, 
Tennessee, Ohio, and Illinois require a 
depth of 3 to 4 inches. Free-burning coals 
from Rock Springs, Wyoming, require 6 to 
8 inches, while the poorer coals of Montana, 
Utah and Washington require a depth of 
about 4 inches. Colorado lignites require 
a depth of 4 to 6 inches, and grates with 
air spaces only \ to -j^-inch wide. Nova 
Scotia coals require a large supply of air, 
and the bed of coals must be so thin as 
barely to cover the grates. 

In general, the coals mined in the western 
part of the United States require thinner 
fires than the eastern coals. If thicker 
fires are carried the tendency to clinker 
is increased. When burning these, fresh fuel 
should be fired often and in small amounts. 



With hand firing there are three methods 
of feeding the coal: 

(1) The Alternate, in which the fresh- 
coal is fired on one side of the grate at a 
time. The volatile matter distilled from 
the fresh charge can be effectively burned 
by the air which is heated when passing 
through the other side; thus the two im- 
portant stages of coal burning are made 
to occur at once, the combustion of the- 
volatile matter, and the burning of carbon _ 
This obviates the necessity of continually 
altering the air supply to correspond first 
with one stage, and then the other. The- 
alternate method gives excellent results 
when properly carried out. 

In this method, and in the spread-firing 
method next to be described, the coal should 
be thrown exactly where it is wanted, and 
not be further disturbed by poker or slice 
bar, except when absolutely necessary to' 
clean fires or break up clinkers. 

(2) In Spread=firing very little fuel is 
charged at one time, and this is either deftly 
spread over the entire fuel bed, or in patches. 
Firing "lightly and often" is spread-firing 
practically. Where the fuel is laid in patches- 
some of the advantages of the alternate 
method are obtained, but it has the disad- 
vantage that the entire grate must be cleaned 
at one time. This method is fairly successful 
with small sizes of free-burning coals in fur- 
naces where the gases rise vertically. 

(3) The Coking Method consists of firing 
the fresh coal to a considerable depth directly 
in front of the firing doors, and pushing it 
back into the furnace as soon as it has coked. 
This results in a very hot fire in the rear of the 
furnace, due to burning carbon, and if the 
volatile matter from the fresh coal passes, 
over this highly heated portion the combustion 
will be perfect provided the air supply is> 
correct. This method is not particularly 
successful where the volatile matter rises 
vertically in the boiler, as is the case in hori- 
zontal water-tube boilers employing vertical 
baffles. In the Stirling the arched furnace 
directs the gases horizontally for a considerable 
distance, and the coking method has given 
very satisfactory results with coals containing 
a large amount of volatile matter. This 
method of firing was once very extensively 
employed, but is now going out of use. A- 



METHODS OF BURNING WOOD 



145 



disadvantage is that air passes much more 
easily through the coked coal than through 
the fresh coal, hence it is necessary to main- 
tain a considerably greater depth of fuel on 
the rear of the grates than on the front. The 
fuel is also stirred up when it is pushed 
toward the rear of the grates, and it is now 
recognized that the less the coal is disturbed 
after it is fired, the more efficiently it can be 
burned. To use the coking method success- 
fully the fireman must not only possess con- 
siderable skill, but must also give his undivided 
attention to the work. 

The best method to adopt will depend upon 
the character of the fuel, and like all other 
work done by manual labor, on the "per- 
sonal equation" of the fireman, but there 
should be some method followed, and the fir- 
ing not be done haphazardly. A careful trial 
of the three methods will show which one is 
best adapted to the conditions, and that one 
should be adhered to. There may be a dif- 
ference of from 10 to 20 per cent., between 
the results obtained from careless and skilled 
firing. Few boiler owners realize the saving 
to be effected by employing skilled and con- 
scientious firemen. 

Mechanical Stokers Of these there are 
two general classes: 

(a) Over-feed. (b) Under-feed. 

The first spreads the fresh coal over the 
fuel bed, and the second feeds it below the 
grates, then upward, until it overflows out 
over the grates. 

There are three kinds of over-feed stokers 
in use. In one the coal is carried on horizontal 
or slightly inclined grate bars, and the in- 
dividual bars are given a mechanical motion 
by which the coal is gradually advanced 
along the grates toward the bridge wall. In 
another the grates are steeply inclined, and 
the fuel is pushed on to the upper ends, 
whence it slides down slowly toward the ash- 
pit, burning in transit. The third kind 
includes "chain grates," in which the entire 
grate is an endless chain of short bars. The 
motion is from the fuel hopper in front of the 
boiler, back toward the bridge wall, at which 
point the grate passes over a sprocket, then 
returns through the ash pit. The Stirling 
Chain Grate is typical of this class. 

Underfeed stokers feed into a receptacle 
below the grates, and the fuel gradually over- 



flows out onto the grates. It undergoes a 
coking process in the receptacle, and should 
be free from all volatile matter when the 
grates are reached. Some of these stokers 
operate intermittently, by means of a plunger; 
others feed continuously through a screw mo- 
tion and forced draft is used. 

In favor of mechanical stokers it is urged 
that they reduce the cost of fire-room labor, 
cause a slightly increased evaporation per 
pound of coal, permit of the use of coal-con- 
veying apparatus, and lessen if not wholly 
prevent smoke. With the chain grate type 
of mechanical stoker, instead of a higher rate 
of evaporation per pound of coal, a positive 
loss over hand-firing may result unless the 
stoker design prevents large excess quantities 
of air. If an analysis of the flue-gases shows 
100 per cent, or more excess air, steps should 
be taken to prevent this air from entering the 
furnace, otherwise the economy will be greatly 
reduced. 

Any type of mechanical stoker purporting 
to feed the fuel regularly into a properly 
designed furnace should furnish a solution to 
the problem of smokeless combustion, since, 
with uniform fuel supply, and the air under 
control, it ought to be possible to attain just 
that proportion between the two which is 
necessary for perfect combustion; and once 
having attained it, to maintain it. Practic- 
ally this degree of perfection is not always 
realized, although mechanical stokers properly 
managed will often give results superior to 
ordinary hand-firing both in point of smoke- 
lessness and fuel economy, and permit use of 
lower grades of fuel than would be profitable 
with hand-firing. 

WOOD. 

The efficient burning of wood requires a 
large combustion chamber, and grates ar- 
ranged to prevent admission of surplus air. 
The Stirling furnace perfectly meets these 
requirements, and is easily modified to suit 
any kind of wood fuel. 

For the burning of shavings and sawdust, 
chutes are arranged in the boiler front, and 
feed the fuel directly upon the grates. Where 
sawmill refuse is conveyed to the boilers by 
carriers, a simple extension of the furnace pro- 
vides a roof containing an opening through 



GRATES FOR BAGASSE FURNACE 



147 



which the refuse can be dropped automat- 
ically into the furnace. 

For ordinary air-dried cord wood the grates 
are placed at firing floor level, their area is 
reduced to about two-fifths the amount 
required for coal, and the furnace walls, 
beginning under the arch, are battered to 
form a V, with the grates at the bottom. 
Cord wood to a depth of 30 to 36 inches can 
be carried on the grates, and the freshly fired 
wood crowds down that which has been partly 
burned, thus filling the large interstices at the 
bottom with burning coals, hence leakage of 
air past the fire is prevented. When other 
considerations prevent battering the furnace 
walls, the grates may be lowered as before, to 
secure the requisite thickness of fire, and the 
rear part of the grates may be blocked off, 
leaving in front the area that is desired. 

For burning green cord wood and wet slabs, 
the conditions closely approximate those for 
burning green bagasse, as described in the 
following article, and a similar furnace may 
be used for both. 

The Stirling Company has worked out 
many special arrangements of furnace for 
burning wood fuel in various degrees of dry- 
ness, and forms in which it is delivered as 
refuse from factories and mills, and is pre- 
pared to submit a design to fit any special 
conditions which may arise. 

Tan Bark, or mixtures of tan bark, sawdust 
and slabs, are burned perfectly in the Stirling 
bagasse furnaces. In many cases such material 
containing as high as 55 per cent, of moisture 
is handled in this furnace with entire success, 
and the full rating of the boiler is developed 
notwithstanding the high content of moisture 
in the fuel. 

BAGASSE. 

Effect of Moisture Though it has been 
shown in the chapter on Fuels that bagasse 
has practically a constant heat value per ton 
of the original cane, irrespective of the degree 
of juice extraction, it does not follow that 
bagasse of the low extractions will produce 
as much useful steam. To make this more 
clear, consider 2500 pounds of dry diffusion 
bagasse burned beneath a boiler, and assume 
that all of the heat of the bagasse (25ooX 
8325 = 20,812,500 B. T. U.) is generated and 
made available for evaporating water in the 

10 



boiler ; then with a boiler efficiency as low as 
50% this heat would evaporate 10,773 pounds 
of water from and at 212. But if to the 
2500 pounds of dry bagasse, 7500 pounds of 
water be added, the mixture will not even 
burn unless dried or mixed with large quan- 
tities of dry fuel, notwithstanding the fact 
that the heat in the 2500 pounds of dry 
matter is sufficient to evaporate nearly three 
times the 7500 pounds of water present. 
Hence it is all important how the water is 
present. When mixed with the bagasse (and 
assuming that ignition is started) its evapora- 
tion results in the absorption of so much of the 
heat generated that the surrounding tem- 
perature is lowered to a point at which further 
combustion cannot take place, and the fire is 
extinguished. If this evaporation can be 
made to occur apart from the combustion of 
the bagasse, there will be sufficient heat 
generated to evaporate the water content 
and leave an excess for useful work. 

Furnace Requirements A high furnace 
temperature must be maintained, and this 
is best accomplished by making the furnace 
entirely of fire-brick and locating it away from 
the boiler heating surfaces, so that combustion 
may be complete before the boiler surfaces 
are reached. Consequently an extension fur- 
nace, in conjunction with the Stirling boiler, 
as shown in Fig. 30, proves eminently satis- 
factory, and is a combination widely used 
in the cane-sugar countries. 

Stirling Green Bagasse Furnace The 
Stirling furnace for green bagasse is a greatly 
improved form of the Burt patent. It is 
rectangular in shape, and is made in various 
widths and depths according to the capacity 
of the boiler and the quality of the bagasse. 
The roof is arched and the entire interior of 
the furnace is lined with fire-brick. The 
fresh fuel is admitted through an opening at 
the top, being conveyed by a carrier to be 
later described. See Fig. 31. 

Grates -The grate surface is composed 
of Hollow Blast Grate Bars, alternating with 
plain herring-bone or straight ribbed bars. 
The hollow blast bar is a rectangular casting, 
provided with openings on its upper face 
which are covered with a sliding plate known 
as the "blast- valve," by means of which the 
air is discharged into the furnace in nearly 
horizontal jets, and so directed that those of 



148 



THE STIRLING WATER-TUBE SAFETY BOILER 



one bar cross those of the bars adjacent. 
Thus the air supply not only is under perfect 
control, but the manner of its admission in- 
sures an excellent distribution throughout the 
mass of fuel. The alternate arrangement of 
hollow and ordinary grate bars renders the 
furnace capable of burning coal or wood very 
advantageously, either with or without forced 
draft. 

Air from the blower is led to a cast iron 
pipe in the ash-pit, and from this connections 
are made to the hollow bars from below; 
where there are several boilers the air supply 
of each is under separate control, permitting 
any boiler to be operated independently. 

Advantages The fire-brick walls and the 
arch become white hot, thus storing heat, 
which radiates upon and dries the fresh charge 



plete shut down of the plant one or two hours 
daily. (2) The air supply can be so regu- 
lated that no excess over that actually required 
need be admitted. This greatly increases the 
efficiency of combustion. 

Stoking Arrangements An important 
feature where there are several furnaces is the 
bagasse conveyor, the automatic features of 
which contribute materially to the economy 
of the plant. See Fig. 31. 

The conveyor is supported on a structural 
steel framework, and runs in a trough made 
of steel plate. The carrier is composed of 
endless chains fitted with bars which engage 
the bagasse and convey it from the mill to the 
boilers. In the bottom of the trough are 
adjustable openings through which any 
desired charge of bagasse is automatically 




FIG. 31. FRONT ELEVATION OF STIRLING GREEN BAGASSE CONVEYOR AND AUTOMATIC FURNACE FEEDER 



of bagasse. The moisture thus evaporated 
mingles with the highly heated gases from 
the bagasse already in the furnace, and the 
actual burning of the fresh charge does not 
begin until all of its moisture has passed off. 
The air supplied is dry and the volatile 
matter is burned at the high temperature 
necessary for proper combustion, the whole 
operation taking place before the boiler 
heating surface is reached 

The superior points of this arrangement 
are : ( i ) The discharge of the air into the fuel 
insures the combustion of the sugar and 
molasses contained in it, and prevents forma- 
tion of clinker. Where the air is admitted 
in any other manner, incomplete combustion 
occurs, and the sugar and silica form a hard 
clinker which is an endless source of trouble 
frequently requiring for its removal a corn- 



dropped into hoppers set over each furnace. 
The hoppers are fitted with valves operated 
automatically by means of cams on a shaft 
along the boiler fronts. Periodically each 
valve opens, then closes when a charge of fuel 
has passed into the furnace, very little free 
air being admitted. 

Excess Bagasse Frequently more bagasse 
is discharged from the mill than is required 
at the time for steam-making; the conveyor 
provides for this by carrying the excess 
beyond the boilers, where it is stored until 
such times as it is needed. It is then con- 
veyed back to the furnace by the same 
carrier. With this system of handling and 
burning green bagasse the fuel problem is 
greatly simplified, and a sugar-house can be 
operated with excellent economy. The ap- 
paratus is practically automatic, reducing 




TEST OF BAGASSE FURNACE UNDER WORKING CONDITIONS 149 

TEST OF STIRLING BOILERS BURNING GREEN BAGASSE 

GENERAL DATA. 

Date of test December 26, 1896. 

Duration of test Six (6) hours. 

Grate area, square feet 160 

Heating surf ace, sq. ft 5>75 

Steam pressure ( gauge ) 98.1 

Feed water 150.5 F. 

FUEL. 

Kind of fuel Bagasse 

Per cent, moisture 42.21 

Total fuel consumed 6 7.343 Ibs. 

Total dry fuel consumed f 37577 

Total refuse 566 

Total combustible ." 37. 011 

Fuel burned per hour 11,224 

WATER. 

Total water apparently evaporated 153,178 Ibs. 

Total water actually evaporated 150,115 

Equivalent actually evaporated from and at 212 F 165,682 

ECONOMIC EVAPORATION. 

Water evaporated per pound of bagasse from actual temperature and pressure 2.23 Ibs. 
Water evaporated per pound of combustible from actual temperature and pressure 4.05 

Water evaporated per pound of bagasse from and at 212 F. 2.46 " 

Water evaporated per pound of dry bagasse from and at2i2F 4 41 

Water evaporated per pound of combustible from and at 212 F 4-5 

RATE OF COMBUSTION. 

Fuel actually burned per sq. ft. of grate surface per hour 70 . 2 

Dry fuel actually burned per sq. ft. of grate surface per hour 39.1" 

Combustible burned per sq. ft. of grate surface per hour 38.5 

Fuel combustible burned per sq. ft. of heating surface per hour 1.95 " 

Dry fuel burned per sq. ft. of heating surf ace per hour 1.09 " 

Combustible burned per sq. ft. of heating surface per hour 1.07 " 

RATE OF EVAPORATION. 

Water evaporated from and at 212 F. per sq. ft. of heating surface per hour . 4 . 80 " 

Water evaporated from and at 212 F. per sq. ft. of grate surface per hour . . I 7 2 -S " 

Water evaporated from 100 F. and 70 Ibs. gauge pressure 144,121 " 

Water evaporated from 100 F. and 70 Ibs. gauge pressure per hour . . . 24,020 " 

COMMERCIAL HORSE-POWER. 
H. P. rated at 30 pounds water per hour evaporation from 100 F. and 70 Ibs 

gauge pressure 800 

Builders rating in horse-power 500 

Per cent, developed above rating 60 

Mr. Pharr referring to this test, said: "The results will probably be considered extra 
good, but this test was made during an ordinary run and no precautions were taken to 
obtain favorable results." 



150 



THE STIRLING WATER-TUBE SAFETY BOILER 



labor costs to a minimum, and one man can 
operate six boilers, where ordinarily five or 
six men would be required. 

Success of the Stirling System The 
extensive application of the improved Burt 
furnace is evidenced by the fact that about 
four-fifths of the sugar plantations of Louis- 
iana are equipped with it, and in almost 
every case in connection with Stirling boilers. 
The Stirling Company has installed many 
bagasse-burning outfits in the West Indies 
and Hawaiian Islands, and wherever sugar 
cane is grown Stirling boilers and Burt 
Bagasse Furnaces are the combination giving 
uniformly satisfactory results. 

Test with Bagasse Fuel The preceding 
test on Stirling boilers burning green bagasse, 
made by Mr. J. N. Pharr, shows an evapora- 
tion probably never before equaled with this 
fuel in this country. With the longer lived 
tropical bagasse even better results may be 
obtained. It is worthy of note that during 
the test the boilers were working at sixty per 
cent, in excess of their rating. 

BURNING PETROLEUM 

The requirements for the perfect com- 
bustion of petroleum are: it must be thor- 
oughly atomized and mixed with the requisite 
quantity of air; the mixture must be burned 
in a furnace constructed of refractory material, 
which will be durable under the high tem- 
perature developed, and radiate heat to assist 
in the combustion; and the combustion must 
be completed before the gases come into 
contact with the boiler tubes. 

The first requirement is met by selection 
of a proper burner. The other requirements 
are so perfectly met in the Stirling furnace 
that the changes necessary from the design 
for coal are so few that'in an hour after shut- 
ting off the oil burner the furnace may be 
made ready to fire with coal. 

Fig. 32 shows the usual arrangement for 
oil burning. The rear half of the grate is 
covered with fire-brick laid close. In the 
front half of the furnace the bricks are laid 
with air spaces between them varying from 
l-m. wide directly under the burner tip, to 
f-in. wide at the line where the close brick 
begins. In the front half of the grate those 
portions not directly under the flame are 



covered with fire bricks laid about ^-in. apart, 
hence the wider air spaces cover an area of 
V shape under the flame. A space f-in. wide 
is left at each side wall to admit air to cool 
the wall and promote combustion. 

At the rear of the grate, or on the bridge 
wall, a checkerwork of fire-brick, from 14 to 
1 8 inches high is usually introduced to break 
up the heat, and prevent it from striking 
directly upon the tubes. Owing to the 
recoil of the gases, and necessity for ample 
space in which they can expand, the fire 
arches terminate at a point about 24 inches 
from the nearest tube, measured at right 
angles to the tube. The spandrels of the 
arch should also be filled level so as to leave 
a throat of even width across the furnace. 
See Fig. 59, page 236. 

In many cases the grates are omitted, and 
the ash-pit is filled with ashes or refuse 
fire-brick, up to a line connecting the top of 
the bridge wall and bottom of the ash-pit door, 
and this arrangement has given very satis- 
factory results. 

When the grates are covered with fire- 
brick the burner is introduced through either 
the fire door, or a hole in the pier between 
doors ; the burner tip is placed about 6 inches 
above the fire-brick over the grate, and 
projects the flame practically parallel with 
the grate. The air for combustion passes 
from the ash-pit up through the grates, 
absorbs heat in its passage through the layer 
of fire-brick, mixes with the atomized oil, 
and complete combustion ensues. 

When the grates are omitted the burner 
is either placed as before, in which case it 
is directed downward slightly, or it is inserted 
on a level with top of ash-pit doors. 

In either case the air supply is regulated 
by the ash-pit doors. 

Direction of the Jet If the proper 
quantity of air is supplied, the location or 
direction of the jet has no influence upon the 
combustion, but it has considerable influence 
on the efficient utilization of the heat. The 
experiments thus far made indicate that the 
nearly horizontal jet introduced from the 
boiler front, according to the methods above 
described, gives the best results. As soon 
as the heat is generated it is essential that 
it be absorbed by the boiler as rapidly as 
possible, without admixture of colder gases 



STIRLING BOILERS FOR BURNING PETROLEUM 



151 



which reduce the furnace temperature. In 
some cases burners have been inserted through 
an opening five to six feet above the floor 
line, and so pointed as to direct the flame 
downward; it then crosses the grates, reverses 



meets the gases which have already been 
cooled by contact with lower part of the 
tubes, and the mixture of the two causes 
a reduction in temperature. 

Heating the Air assists in the combustion, 



direction and travels up the front bank of but usually the complication and expense 










FIG. 32. SECTIONAL SIDE ELEVATION OF STIRLING BOILER FOR BURNING PETROLEUM OR NATURAL GAS 



tubes. The fire arch is omitted. Experi- 
ments show that the efficiency is lowered by 
this arrangement, because it exposes a larger 
wall surface to the intense heat, thus causing 
greater loss by radiation; further, that part 
of the heat which rises from the front part 
of the flame directly to the top of the furnace, 



of doing it offset the advantage when steam 
spray burners are used. A simple and com- 
paratively inexpensive method of heating 
the air is to provide the boiler with hollow 
walls; the air is drawn from the rear of the 
boiler, absorbs heat from the inner walls, 
and is admitted through ports in the side 



152 



THE STIRLING WATER-TUBE SAFETY BOILER 



walls, both above and below the grates. 
Installations of Stirling boilers thus arranged 
have proved entirely satisfactory. 

Whatever arrangement be used the ad- 
vantages of the Stirling furnace as described 
for coal apply with equal force to oil. 




FIG 33 THE WARREN HYDROCARBON BURNER 

Oil Burners The function of the burner 
is to pulverize or atomize the oil to a con- 
dition approaching as far as possible that 
of gas, thus permitting the oil to be burned 
like a gas flame. Of the many hundred 
burners invented those in use may be reduced 
to two classes; (i) Spray burners, in which 
the spray is made by a jet of steam or com- 
pressed air; (2) Vapor burners, in which the 
oil is converted into vapor, then passed into 
the furnace. 

While the vapor burner possesses merit, it 
has not come into general use. In spray 
burners the atomizing agent may be either 
steam, compressed air, or air and steam 
together. The steam spray burners are 
almost universally used; they are simple, 
require no blowers, compressors or other 
apparatus occupying space or demanding 
attention, and in the better types now ob- 
tainable at reasonable cost the steam used 
is so little as to be of less value than the 
expense of saving it. 



Spray burners of the older types usually 
consist of two nozzles, one within the other; 
oil is fed through the inner and steam through 
the outer nozzle; the two currents meet and 
mingle and atomization is then effected. 
The disadvantage of the general arrangement 
is that the nozzles occasionally get clogged 
by dirt or formation of coke due to the heat, 
and the openings wear to a larger size than 
wanted. Accordingly the later types of 
burner dispense with the arrangement of one 
nozzle within another. 

Steam spray burners are divisible into two 
classes: (i) Outside-mixers. (2) Inside- 
mixers. In the former the oil and steam 
meet outside the apparatus; the steam flows 
out through a flat slit or through a series of 
small holes in a horizontal row; the oil flows 
through similar slits or holes, and falls into the 
steam which seizes and atomizes it. Fig. 33 
represents a burner of this type, in vented by 
Mr. James W. Warren, of Los Angeles, Cal. 
Its construction is evident. The adjustment 
of the flame is easily made by filing the tip of 
the central washer, and wear is taken up by 
renewal of the washer. 





FIG. 34. HAMMEL OIL BURNER 

In the inside-mixers the oil and steam 
mingle inside the apparatus and the mixture 
is atomized by passing through the nozzle 
Fig. 34 represents a burner of this type, in- 
vented by Mr. Chas. A. Hammel, of Los 
Angeles, Cal. The usual inner and outer 
nozzles are eliminated, and wear is provided 



EFFICIENCIES OBTAINABLE FROM OIL FUEL 



153 



for by the removable plates K-K. The oil 
passing through the hole D is atomized by 
steam jets through the slots G, H, and /. In 
burners of this type the oil requires only 
sufficient heating to enable it to be pumped 
through the oil supply system, and oils or 
even tar, as low as 8 Beaume can be success- 
fully handled owing to the large oil channels. 

In burners of the outside-mixer type the oil 
should be heated. This is usually done by 
passing the oil through an exhaust steam 
heater. The action of the burner is improved 
as the temperature of the oil is increased, up 
to about 210 F. If raised higher the water 
in the oil will vaporize and cause the flame to 
sputter. The steam supply is also frequently 
superheated by passing the steam pipe either 
into the furnace or the boiler breeching. 
When this is not done adequate provision 
should be made to drain out entrained water 
before the steam reaches the burner. A 
by-pass between steam and oil supply pipes 
should be provided to enable the oil ducts to 
be occasionally blown out with steam. See 
Figs. 33 and 34. 

Regulation of Oil and Steam When 
starting, the oil should first be turned on and 
ignited by some burning waste; then the 
steam should be turned on ; the valves con- 
trolling the oil and steam should next be 
regulated so as to get the proper mixture. 
This regulation can best be accomplished by 
observing the top of the smoke stack, and the 
color of the fire. If the supply of steam is too 
great, steam will be seen surrounding the 
burning spray and issuing from the smoke 
stack; if the steam supply is deficient the 
atomization will not be completed; if the air 
supply is deficient the color of the flame will 
become red, and smoke will issue from the 
stack, indicating incomplete combustion. 
When the burner valves and the air supply are 
correctly adjusted the flame is a bright white in 
color and there is no smoke. Scintillating 
sparks indicate imperfect atomization. 

Number of Burners Required This 
varies with the type of burner. With either of 
the two burners already described, a furnace 8 
feet wide can be served by one burner, a fur- 
nace 14 to 1 6 feet wide by three burners and 
intermediate sizes by two burners. The 
essential point is to distribute the heat evenly 
throughout the furnace, and evidently the 



more perfectly the burner forms a wide fan- 
tail flame, the fewer the number of burners 
needed. 

Oil Pressure This varies from a few 
pounds up to 60 pounds or over depending 
upon the type of burner. The oil system is usu- 
ally fed by an ordinary duplex steam pump, 
with a relief valve between the suction and 
discharge sides. This is set at the desired 
pressure, and that pressure is always kept 
on the oil line to insure uniform supply 
through the burner. The oil passes from the 
pump through the heater then to the burner. 
The oil system should be provided with an 
air chamber to neutralize pulsations of the 
pump. In cold weather steam is circulated 
through pipes in the oil tanks, to keep the 
oil in condition to flow freely. 

Per Cent, of Steam Used In a series of 
tests made by the Bureau of SteamEngineer- 
ing,U. S. Navy,* it was found that with a 
burner using air as an atomizing agent, the 
amount of steam required to compress the 
air varied from 1.06 to 7.45% of the total 
steam generated, the mean of eight tests 
being 3.18%. Four tests on steam spray 
burners varied from 3. 98% to 5.77%, the 
average being 4.8%. Two tests on burners 
using steam and air together showed 8.54% 
and 6.09% respectively. In a series of most 
careful tests made for The Stirling Company 
on latest type of steam spray burner the 
results ran from 2.10% to 3.42% averaging 
2.69% for four tests. It therefore does not 
seem that any saving of steam is to be made 
by employing air as the atomizing agent, and 
the use of steam obviates complication, and 
risk of interrupted service. 

Boiler Efficiencies obtainable with Oil 
Fuel Since oilcan be burned with admission 
of but little more than the amount of air neces- 
sary to furnish the actual oxygen necessary for 
the combustion, and the furnace doors need 
never be opened while the boiler is under 
steam, and the boiler heating surf ace does not 
get quickly fouled by soot, it follows that with 
proper burners and careful attention higher 
boiler efficiencies may be expected with oil 
than with coal. It is highly important to 
keep down the content of water in the oil. 
The following tests on the Stirling boiler 
indicate the efficiencies obtainable with oil 
fuel. It should be noted that the per cent. 



*Report of the Hohenstein Boiler and Liquid Fuel Boards. U. S. Government Printing Office, 1903. 




PART OF 3.0OO H. P. OF STIRLING BOILERS BURNING OIL, THE LOS ANGELES GAS AND ELECTRIC 

COMPANY'S PLANTS, LOS ANGELES, CAL. 



TEST OF STIRLING BOILER BURNING OIL 



155 



of water in the oil was large, hence with a 
smaller content of water even higher effi- 
ciencies would have been developed, illustrat- 
ing the importance of sufficient tankage to 
allow the water to settle out. 

Such high efficiencies cannot, however, be 
obtained with boilers that are not particularly 
adapted to use of oil fuel. This is well 
shown by the tests made by U. S. Bureau of 



BURNING NATURAL GAS. 

Practically the only difference between 
burning petroleum and natural gas is that 
ihe former, being liquid, must be atomized 
before it is mixed with the air requisite for 
combustion, while the latter, without any 
change of state, is ready to be mixed with 
the air and ignited. Consequently the burners 



TESTS OF A STIRLING BOILER OF 500 HORSE-POWER 

AT PLANT OF THE LOS ANGELES GAS AND ELECTRIC COMPANY, LOS ANGELES, CAL. 



2 


. * . square feet, 


5,020 
Nov i ^ 


3y gauge 
eed water 
ation 


. hours, 
.... Ibs. 
. . . . Fahr. 


7i 

120 

143 



Ibs. per square in. 

. . . . Fahr. 

Fahr. 



Name of boiler 

Heating surface 

Date of test, 1902 

Duration of test 

Steam pressure, 

Temperature of 

Factor of evaporation 

Pressure of oil 

Temperature of oil 

Temperature of escaping gases . 

Per cent, moisture in steam 

Total water apparently evaporated Ibs. 

Total water evaporated to dry steam Ibs. 

Equivalent total water into dry steam, from and at 2 1 2 . Ibs. 

Kind of burner used 

Kind of oil burned 

Per cent, of water in the oil 

Heat value of oil as fired, per Ib B. T. U. 

Heat value of oil, freed of all water . . . . B. T. U. 

Total oil as fired Ibs. 

Horse-power developed 

Horse-power, builders' rating 

Per cent, developed above builders' rating 

Water evaporated from and at 21 2 per Ib. of oil as fired, Ibs. 
Water evaporated from and at 212 per Ib. of oil freed of 

water Ibs. 

Efficiency of boiler 

Average per cent, above rating 

Average efficiency of boiler 



24.7 

198 

5i8 

0-54 

117,960 



Warren 

Los Angeles 

9.87 

17,122 

18,997 

9,i54 

5 2 3-9 

500 

4.78 



16 



15.81 
80.76 



53 
81.95 



Stirling. 
5,020 
Nov. 15 
5 



123 
I - I 359 



o-54 
97,872 

97,343 
1 10,697 
Warren 
Los Angeles 
9 . 16 
17,241 
18,979 
7,460 
641.4 
500 
28.28 



16,335 
83-14 



Steam Engineering already referred to. There 
were four tests at rates of evaporation per 
square foot of heating surface equal to 3.91 
5.18; 5.52; and 5.82 pounds of water from 
and at 212. The corresponding boiler effi- 
ciencies were only 68.9; 71.5 ; 69.9, and 66.7% 
The boiler was of the water-tube type con- 
taining 2130 square feet of heating surface, 
and operated at about 274 pounds pressure. 



will differ, but in other respects the form 
of furnace, length of fire-arches, location of 
the checkerwork wall in rear of the furnace, 
location and height of the burner above the 
fire-bricks covering the grates, and the air 
spaces between these bricks, will be the same 
for natural gas as for petroleum, hence the 
design of furnace shown in Fig. 3 2 will apply 
equally well to both. 




NORTHERN TEXAS TRACTION CO., HANDLEY, TEXAS, OPERATING 1,200 H. P. OF STIRLING BOILERS BURNING OIL 



TEST OF BOILER BURNING NATURAL GAS 



157 



The most efficient gas burner will be that 
one which most intimately mingles the gas 
and air. A crude form of burner often used 
consists of a piece of one-half inch gas pipe 
placed inside of a piece of 2^-inch pipe which 
is bricked in the fire door opening. The suc- 



are all designed for the purpose of effecting 
a more intimate mixture of the gas and air 
than can be accomplished by the simple 
arrangement just described. The quantity 
of gas fed to the burner is regulated by an 
automatic reducing valve which is controlled 



TEST OF A STIRLING BOILER BURNING NATURAL GAS 

COLUMBUS, BUCKEYE LAKE, AND NEWARK TRACTION COMPANY, HEBRON, OHIO 

Duration of test, hours 8 

Pressures: . . Steam gauge, pounds 140 

Draft in rear pass, inches of water -35 

Gas at meter, ounces 8 

Temperatures: Gas at meter 70 F 

Feed Water 116 

Escaping flue -gases 4*7 

Kind of fuel Natural Gas 

Cubic feet of gas consumed 103,900 

Cubic feet of gas consumed at 32 F. and 14.7 Ibs. absolute 99,183 

Total water used, pounds 77,826 

Per cent, moisture in steam 0.65 

Total water evaporated into dry steam, pounds 77,320 

Factor of evaporation 1.1472 

Water evaporated into dry steam from and at 212, pounds 88,700 

Water evaporated per cu. ft. of gas at standard condition, Ibs .... 78 

and from and 

at 212. Ibs 895 

Horse-power developed during the test 321 

Horse-power, builders' rating 304 

Per cent, horse-power developed above rating . . 5.6 



tion created by the gas which blows out under 
pressure draws through the annular space 
between the two pipes a portion of the air 
needed for combustion, and the additional 
air required passes up through the slots 
between the bricks which cover the grates. 
The different types of burners on the market 



by the steam pressure, and this is usually 
placed in the pipe which supplies gas to all 
or a number of the boilers, the meter being 
placed between reducing valve and burners. 
The above test indicates the high effi- 
ciency obtainable from Stirling boilers fired 
with Natural Gas. 



The Stirling Chain Grate Stoker 



Chain grate stokers are extensively used 
for burning lignites, low grades of bituminous 
coal, and small sizes of anthracite. One of 
the most perfect stokers of this type is manu- 
factured by The Stirling Company, and is 
illustrated in the photograph on the opposite 
page. 

The stoker consists of a suitable framework, 
a travelling grate; fuel hopper, and the nec- 
essary driving mechanism. 

The stoker is entirely self-contained, and 
no part of it is attached in anyway to the 
boiler framework or the brick setting; the 
entire machine rests upon four wheels which 
are supported by suitable rails which extend 
a sufficient distance into the fire-room to enable 
the stoker to be drawn completely from under 
the boiler. 

The framework is made of cast iron and so 
designed that any part of it can be easily 
renewed. In the rear of the frame is a shaft 
upon which are placed idler pulleys, and a 
similar shaft in front is equipped with sprocket 
wheels. The grate is an endless chain com- 
posed of links of narrow width and relatively 
greater depth; this chain travels over the 
above mentioned pulleys and sprockets, and 
is driven by the sprocket shaft. The chain 
is of simple construction and any link can 
be replaced without disturbing other links. 
Between the front sprocket and the rear 
pulleys the chain is supported by cast iron 
rollers of narrow width, strung side by side 
on shafts extending across the framework. 
Any shaft with its rollers can be removed 
without disturbing any other part of the 
machine. 

To provide for wear and expansion of the 
grate, the distance between centers of idler 
pulley shaft and sprocket shaft can be quickly 
adjusted even while the stoker is in operation. 
The feed gates are counterbalanced, and can 
be quickly adjusted to give any desirable 
thickness of fire. Inspection doors placed 



in the side of the furnace permit the condi- 
tion of the fire to be noted, and a bar to be 
inserted when it is necessary to break up 
clinkers or remove obstructions to the free 
passage of the grates. 

A common defect of chain grate stokers 
is the admission of excess air from the ash 
tunnel. In the Stirling chain grate this 
defect is overcome by the insertion of a 
diaphragm between the stoker and the ash- 
pit floor at a point just in front of the ash-pit 
tunnel. A suitably designed opening in the 
diaphragm permits the returning portion of 
the grate to pass through without admitting 
air, hence the air supply must come into the 
ash-pit from in front of the boiler, where it 
can be controlled in the usual manner. 

The stoker may be driven from any con- 
venient source of power, but the usual method 
is to operate it from an overhead shaft. A 
connecting rod driven from this shaft operates 
a crank on the side of the stoker framework ; 
by means of a ratchet this crank moves a 
ratchet gear which drives the sprocket shaft 
through the medium of a worm wheel and 
a worm shaft attached to the ratchet gear. 
The ratchet may be adjusted to give the 
grates four different speeds, as occasion de- 
mands. An advantage of the Stirling chain 
grate is that all these working parts are 
housed in, thereby protecting them from 
dirt and grit. The connecting rod is so^ 
designed that in case of any obstruction 
tending to impede the motion of the grate, the 
driving mechanism stops, and breakage of 
parts is wholly obviated. 

The size of air openings in the links, and 
other minor details, depend upon the character 
of fuel to be burned, and must be separately 
considered in each case. The Stirling Com- 
pany is prepared to submit designs and esti- 
mates for chain grate stokers adapted to 
any conditions under which such stokers can 
be advantageously used. 



159 




ERECTING 300 H P. OF STIRLING BOILERS, ILOILO ELECTRIC LIGHT 4 POWER CO., ILOILO, PHILIPPINE ISLANDS 



160 



Utilization of Waste Heat 



A considerable saving of fuel and labor can 
be made by utilizing waste heat from blast 
furnaces, coke ovens, reverberatories for 
smelting ores, etc. While this fact has long 
been known, the installation of equipment for 
saving waste heat has not become so common 
as would naturally be expected, because of 
the lack of a boiler perfectly adapted to the 
peculiar nature of the work to be done. 
Boilers of the shell type do not absorb the 
heat readily, the available space is often too 
small to permit sufficient capacity of such 
boilers to be installed, and when the tem- 
peratures fluctuate considerably the shell 
type boiler causes trouble from unequal 
expansion. The requirements as to space 
can generally be met by installing water-tube 
boilers, but not all boilers of that type can 
comply with the other requirements. When- 
ever the boiler is out for cleaning, the heat 
which otherwise would be utilized by the 
boiler is usually wasted, hence it is essential 
that the boiler can be cleaned in the shortest 
possible time. The character of the gases 
also may vitally affect the boiler design. For 
example, the gases from reverberatory furnaces 
smelting copper matte contain a large con- 
tent of sulphur, hence if the boiler develops 
a leak sulphuric acid is formed and the 
boiler plate is quickly destroyed. The sulphur 
fumes will penetrate each place where a 
leak occurs, therefore in those boilers using 
handhole caps the bearing surface and other 
parts affected by leakage from the caps will 
soon corrode, which explains why the cap 
type of boiler cannot be successfully used 
in connection with such furnaces. 

These disadvantages are so completely 
obviated in the Stirling boiler that its merit 
as a waste heat boiler was quickly perceived, 
and its use for such work has rapidly in- 
creased. Not only has it met all require- 
ments in a most satisfactory manner, but it 
is now operating with gratifying success under 
conditions of service which no other boiler 
has been able to meet. The perfect freedom 
from expansion obviates straining and leaks; 
the absence of caps and other complication 
eliminates the necessity of stoppage except 

*See pages 20, 21 and 31. 



for cleaning, and the time necessary lor 
cleaning is less than required by other types 
as already shown.* The manhole plates are 
the only parts needing removal, and they 
are completely outside the setting, hence are 
not reached or affected by the gases. Large 
heating surface can be installed in the small 
space usually available, yet in no case need 
the general design of the boiler be changed, 
and should occassion demand it, the boiler 
can be removed and reset in the regular way. 
The form of furnace can be modified to con- 
form to the requirements of the particular gas 
to be handled, and provision be made for 
hand firing when the supply of waste heat is 
cut off. 

Each case requires careful study of all 
the conditions in order to determine the 
best method of utilizing the heat, and The 
Stirling Company will be pleased to confer 
with prospective customers, and to submit 
designs covering their requirements. The 
following descriptions will, however, indicate 
in a general way the amount of heat which 
may be saved, and the adaptation of the 
Stirling boiler to this class of service. 

Coke Ovens The best coking coal yields 
about 65 Ibs. of coke per 100 Ibs. of coal. 
Assuming the heat value of a pound of 
coke to be 13000 B. T. U., the coke produced 
by one pound of coal will represent 8450 B. 
T. U. The heat value of the coal would.be 
about 13500 B. T. U., hence the heat loss 
during the coking process is 13500 - 8450 = 
5050 B. T. U. Experience has shown that 
about one-half of this is lost by radiation from 
the oven and flue. Of the remainder about 
70% can be utilized by a proper arrangement 
of flues and stack in connection with a boiler 
of good design and ample heating surface. 
Under these conditions the evaporation per 
pound of coal coked will be about 

5050X0.5X0.70 

-^=1.83 pounds. 
965.8 

Assuming that one oven in 60 hours will 
coke 6 tons of coal, or 1,728,000 Ibs. per year, 
and that if fired under the boiler direct one 
pound of the coal would evaporate 10 Ibs. of 
water, then the annual saving in coal per 



161 



162 



THE STIRLING WATER-TUBE SAFETY BOILER 



oven under these conditions will be 

1,728,000X1.83 

=158 tons. 
10X2000 

At fifty cents per ton at the mine this 
coal represents a saving of $79.00 peryearper 
oven, hence allowing 20% interest and depre- 
ciation, an investment of $395.00 per oven 



boiler. The stack height should be not less 
than 125 feet, or higher if the flues are long 
or crooked. The flue cross-section should 
contain .5 to .75 square feet per oven, which 
limits the number of ovens per flue to about 
40. Each oven contributes enough heat to 
develop 10 to 12 boiler horse-power. 




FIG. 35. SECTIONAL SIDE ELEVATION 
OF STIRLING BOILER 



for utilizing the waste heat would be war- 
ranted. 

The arrangement of boilers, flues, etc., for 
a waste heat installation is very simple, but 
the details require close attention. The gas 
flues should be as short and direct as possible, 
and the stack must produce ample draft to 
draw the gases through the flues and the 



WITH UNDERGROUND FLUE FOR 
BURNING COKE OVEN GASES 



The foregoing statement applies more 
particularly to the bee-hive type of oven. 
In by-product ovens the heat loss is not so 
large, but even in these the waste heat can 
be utilized at a handsome profit. 

Heating Surface Required When the 
gases reach the boiler their temperature will 
not exceed 2000 and may be less. In a 



BURNING BLAST FURNACE GASES 



163 



boiler fired with coal the furnace temperature 
ranges frojn 2500 to possibly 3000, hence 
the heating surface per boiler horse-power 
should be greater in the waste heat boiler 
than in the direct-fired boiler. From 12 to 
1 5 square feet per horse-power will be needed 
for water-tube, and from 15 to 20 feet for 
return tubular, boilers. Since the volume of 
gas is large and its temperature comparatively 
low, a long pass through which the gases 
travel at considerable velocity and are well 
broken up by baffles, is of marked advantage 
in utilizing the heat. This is well shown by 
the comparative tests on Stirling and Lan- 
cashire boilers as later given. 

Fig. 35 shows the Stirling boiler with under- 
ground flue, conveying coke oven gases to the 
furnace. The gases enter through an opening 
which extends along the whole length of the 
bridge wall. In front of the bridge wall is a 
grate for firing with coal when the gas supply 
is deficient, but it is better practise not to 
fire with coal when the boiler is utilizing 
waste heat . If the waste gases do not generate 
sufficient steam, an additional boiler should 
be installed and fired exclusively with coal, to 
attain the best results. 

Tests The following tests indicate the 
amount of heat that can be saved, and the 
advantage of the Stirling as a waste heat 
boiler. Owing to a defective damper in 



the gas flue leading to the Stirling boiler, 
the leakage into the by-pass flue was sufficient 
to produce a temperature of 1440 in that 
flue. If the heat thus lost could have been 
passed through the Stirling boiler, even 
better results would have been obtained. 
These tests corroborate the statements made 
that the heating surface for best efficiency 
with waste heat boilers should be greater 
than for coal-fired boilers. Under ordinary 
circumstances the wate -tube boiler will work 
most efficiently at a rate of evaporation 
of 3.45 Ibs. of steam from and at 212 F. per 
square foot of heating surface. In these 
tests the evaporation on the Stirling was 4.01 
Ibs. per square foot; if this had been reduced 
to 3 Ibs. it is evident that the temperature 
of the exit gases would have been reduced, 
thus increasing the efficiency. 

Blast Furnace Gases.. Each ton of iron 
produced in the blast furnace requires from 
i, 800 to 2,200 Ibs. of coke, and the weight 
of gases produced will be five to seven times 
the weight of coke used. From 25 to 30 per 
cent, by weight, of these gases will be carbon 
monoxide (CO). From Table 47 page 133, the 
calorific value of carbon monoxide at 32 F. 
and at atmospheric pressure, is 339 B. T. U. 
per cubic foot, and 4,350 B. T. U. per pound. 
By burning these gases under a boiler it is 
possible to utilize a large percent, not only 



TESTS OF ONE STIRLING, AND TWO 28 FOOT X 8 FOOT LANCASHIRE 
BOILERS BURNING COKE OVEN GASES 



VICTORIA-GARESFIELD COLLIERY, ROWLAND'S GILL, NEWCASTLE-ON-TYNE, 

i Stirling 

Boilers Class A, 

Standard. 

22 
. 1,6 1 1 sq. ft. 

73-4 " " 
. 6,465 Ibs. 

- 3> 8 " 
294 " 



Number of Beehive coke ovens 

Boiler heating surface 

Boiler heating surface per oven 

Water evaporated per hour from and at 212 F 

Coal coked by above ovens per hour 

Water evaporated from and at 2 1 2 F. per oven per hour . 
Water evaporated from and at 2 1 2 F. per Ib. of coal coked 
Water evaporated from and at 212 F. per sq. ft. of heating 

surface 

Approximate temperature of gas at point of entry to boiler . 

Approximate temperature of gas leaving boiler 

Normal evaporation of boiler if coal fired in the ordinary manner 
Percentage evaporation secured to a normal evaporation of boiler 

if coal fired 



4.01 

1,720 F. 

650 F. 

6,445 Ibs. 

100.3% 



ENGLAND 

2 Lancashire 

Type, each 

28' X 8' 

37 

1,796 sq. ft. 
48.6 " " 
8,503 Ibs. 

6,39i ' 
230 " 

i-33 " 

4-79 " 
1,700 F. 
750 F. 
12,500 Ibs. 



68% 



164 



THE STIRLING WATER-TUBE SAFETY BOILER 



of the heat produced by burning the carbon 
dioxide but also of the heat stored in the 
other gases at the high temperature at which 
they enter the boiler furnace. 

The Stirling boiler has in a most satis- 
factory manner met every requirement for 



ber which enables the gases to be thoroughly 
mixed with air, and completely burned. 
The grates can be used to assist in making 
steam when there is a short supply of gas, 
without making it necessary to burn an 
excessive amount of coal for this purpose. 




FIG. 36. SECTIONAL SIDE ELEVATION OF STIRLING BOILER FOR BURNING BLAST FURNACE GAS 



burning blast furnace gases. Fig. 36 shows 
one of many designs adapted to such work. 
The boiler is coal-fired from the front in the 
usual manner, and the gases are brought into 
the setting at a point directly under the 
incandescent arch. The dropped arch at 
the rear of the furnace provides a large cham- 



The setting is provided with cleaning doors 
so that any accumulation of dust can be 
readily removed without shutting down the 
boiler. By means of a cleaning door in the 
side of the setting in front of the middle 
bank of tubes, accumulations of lime, 
dust, etc., either on or between the tubes, 



TEST OF BOILER BURNING BLAST FURNACE GAS 165 

can be readily blown off. There is also an The following report of a test made on 

ample number of explosion doors, so that Stirling Boiler using blast furnace gases 
should there be an explosion of gas in the or fuel will prove of interest. Attention 
furnace, the setting would be immediately is directed to the very satisfactory results 
relieved of strains due to internal pressure, developed during the test. 

TEST OF A STIRLING BOILER AT BRIER HILL FURNACE, YOUNGSTOWN, O. 

USING BLAST FURNACE GAS AND COAL AS FUEL 

Date of test ...... April 18, 1899 

Duration of test, hours 7:00 

Heating surf ace, square feet 2,788 

Grate surface, square feet .' 52.64 

Pressures: .... Steam, pounds by gauge ... 80 

Barometer, inches 28.67 

Gas entering furnace, inches of water -9 I 7 

Draft at flue exit over damper, inches of water ... 0.45 

Draft at furnace, inches of water 0.25 

Temperatures: . . Gas at burners 322 F 

Escaping flue-gases 594 

Feed water 55 

Outside air . . 98 

Total gas used at burner temperature, cubic feet 1,397,907 

" " " 32 F 881,965 

" coal " pounds 245 

Heating value of gas, per pound at 32 . . . B. T. U. 1,082.63 

" " cubic foot at 32 . B. T. U. 86.52 

" coalused B. T. U. 12,592 

Total water used pounds 50,380 

Per cent, moisture in steam 0.6 

Water evaporated into dry steam pounds 50,078 

from and at 212 60,745 

per i, ooo cu. ft. of gas at 32. . 54-57 
from and at 212 per 1,000 cu. ft. 

at 32 66.19 

per sq. ft. of heating surface per 

hour 2.56 

from and at 212 per sq. ft. of 

heating surface per hour . . 3 . 1 1 

Horse-power developed 251.5 

Heat delivered to boiler per hour by combustion of gas . . . B. T. U. 10,901,000 

coal . . . 440,720 

gas and coal . 11,341,720 

" utilized in evaporation 8,382,948 

Efficiency of boiler percent. 73 .91 

Efficiency of boiler not including hydrogen in heating value of fuel . " " . 78.12 



Analysis of fuel-gas % BY VOL. %BYWT. 

CO 2 I 3-5 20.00 

O o . oo o . oo 

CO 25.20 23.62 

Hydrogen . . . . 1.43 0.097 

Nitrogen 59.87 56.25 

Specific gravity 1-032 



Analysis of flue-gas. %BY VOL. %BY WT. 

CO 2 14.00 20. 19 

O 9.20 9.59 

CO o 

Nitrogen and ) 
hydrocarbons } ' 



oo o . oo 



76.80 70.2; 



Specific gravity i . 0603 




400 H. P. OF STIRLING BOILERS BURNING GASES FROM PUDDLING FURNACES. 
BLOCK-POLLACK IRON CO., CINCINNATI, O. 



WASTE HEAT FROM PLAIN CYLINDER BOILERS 



167 



Furnaces for Smelting Copper The 

gases from reverberatory furnaces smelting 
copper matte have an exit temperature which 
may reach or even exceed 2500. The heat 
thus carried off represents a large per cent, of 
the calorific value of the fuel burned, hence 
the use of waste heat boilers at once suggests 
itself. The problem is, however, distinctly 
more difficult than when handling coke oven 
or blast furnace gases, because of the presence 
of a large content of sulphur in the gases. 
If these gases come into contact with water, 



as a waste heat boiler in connection with 
furnaces smelting copper matte. 

In Puddling and Heating Furnaces the 

metal to be heated absorbs only a small per- 
centage of the calorific value of the fuel, and 
the remainder passes off with the furnace 
gases. A considerable portion of this heat 
can be saved by a properly designed waste 
heat boiler. The saving which can be 
effected is indicated by the following tests 
on Stirling boilers installed in connection 
with heating furnaces. 



TABLE 50 

SUMMARY OF TESTS OF STIRLING BOILERS INSTALLED IN 
CONNECTION WITH HEATING FURNACES 



DATA 


OF TESTS. 


AKRON 
IRON CO. 


BLOCK-POLLACK 
IRON CO. 


Heating surface square feet 




1438 


I ?I4 


Grate surface square feet 




IQ . T. C 


16. < 


Ratio heating to grate surface 
Pounds of water evap. per hou 


r . 
from and at 212 per square foot of 
heating surface 


74 
37.60 

3.06 


92. 

26. 12 
1.89 




from and at 212 per Ib. of coal 


7.09 


9 




from and at 212 per Ib. combustible 


8.48 


7-85 



sulphuric acid is formed, and the metal of 
the boiler is quickly destroyed by corrosion. 
The temperature also varies considerably 
during different stages of the smelting. In 
consequence, not only must the waste heat 
boiler be so designed as to secure perfect 
provision for expansion, thus obviating leaks, 
but it must also be free from handholes or 
other openings, which can be reached by the 
gases, and thereby be affected by the corro- 
sion. The Stirling boiler meets these require- 
ments perfectly. The curved tubes and 
suspended mud drum provide for free expan- 
sion and contraction; there are only four 
openings one manhole in each drum, and 
these are all outside of the setting, beyond the 
reach of the gases. In consequence, the 
Stirling boiler is perfectly adapted to use 



Waste Heat from Plain Cylinder Boil= 
ers. Owing to the deficient heating surface of 
the plain cylinder boiler, the breeching tem- 
perature is excessively high when the boilers 
are forced. In consequence, this type of 
boiler is now fast going out of use, but where 
such boilers are still in good condition it has 
been found profitable to keep them in service, 
and utilize the heat they waste by passing the 
gases through a water- tube boiler, before 
turning them into the stack. The gases 
frequently leave the cylinder boilers at a 
temperature of 1500 to 1600, and under 
such conditions the waste heat absorbed by 
the water-tube boiler will increase the capa- 
city of the plant 75 to 100 per cent, without 
burning additional coal, or increasing the 
number of men employed. 



Chimneys and Draft 



The height and diameter of a chimney 
depend upon the kind and amount of the fuel 
to be burned, the design and the relative 
arrangement of the boilers and flues, and the 
altitude of the plant above sea level. Thus 
far no satisfactory formula involving all 
these factors has been produced, conse- 
quently empirical methods are used. In 
this chapter a method sufficiently compre- 
hensive and accurate to cover all practical 
cases will be developed and illustrated. 

Draft is the difference in pressure which 
causes gases to rise in a stack. If the air 
inside a stack be heated, each cubic foot of 
it will expand, hence its weight will be less 
than that of a cubic foot of colder air, there- 
fore the unit pressure at the stack base due 
to the column of heated air will be less than 



that due to a column of cold air of equal 
height. This difference in pressure, like the 
difference in head of water, causes a flow of 
cold air into the base of the stack. But if 
in its passage to the bottom of the stack the 
cold air has to pass through a fire, it in turn 
becomes heated, hence it also will rise, and 
the action will be continuous. 

The difference in pressure, or intensity of 
draft, is usually measured in inches of water. 

Assume that the atmosphere has a tem- 
perature of 62 F. and the temperature of the 
gases in the chimney is 500 F. Neglecting 
for the present the increased density of the 
flue-gases as compared to air, the difference 
between the weight of the external air and 
internal flue-gases per cubic foot is .034 Ibs., 
obtained as follows: 



TABLE 51 

THEORETICAL DRAFT PRESSURE IN INCHES OF WATER* 

IN A CHIMNEY 100 FEET HIGH 
(For other heights the draft varies directly as the height.) 



TEMP. IN 
CHIMNEY 
FAHR. 


TEMPERATURE OF EXTERNAL AIR. (BAROMETER 30 INCHES.) 





10 


20 


30 


40 


50 


60 


70 


80 


90 


100 


200 


453 


.419 


.384 


353 


.321 


. 292 


.263 


234 


. 209 


.182 


J 57 


220 


.488 


453 


.419 


.388 


355 


.326 


.298 


. 269 


.244 


.217 


. 192 


240 


.520 


.488 


45 1 


.421 


.388 


359 


33 


.301 


. 276 


.250 


.225 


260 


555 


.528 


.484 


453 


. 420 


392 


363 


334 


309 


.282 


257 


280 


584 


549 


5*5 


.482 


45 1 


. 422 


394 


365 


340 


3i3 


.288 


300 


.611 


576 


541 


5 11 


.478 


449 


.420 


392 


367 


340 


3i5 


320 


637 


.603 


.568 


538 


55 


.476 


447 


.419 


394 


367 


342 


340 


.662 


.638 


593 


563 


53 


5 01 


472 


443 


.419 


392 


367 


360 


.687 


653 


.618 


.588 


555 


.526 


497 


.468 


444 


.417 


392 


3 80 


.710 


.676 


. 641 


.611 


578 


549 


.520 


.492 


.467 


.440 


415 


400 


732 


.697 


.662 


.632 


598 


570 


541 


5 J 3 


.488 


. 461 


43 6 


420 


753 


.718 


.684 


653 


. 620 


591 


563. 


534 


59 


.482 


457 


440 


774 


739 


75 


.674 


. 641 


.612 


584 


555 


53 


53 


478 


460 


793 


758 


.724 


.694 


.660 


.632 


.603 


574 


549 


.522 


497 


480 


.810 


.776 


.741 


. 7 10 


.678 


.649 


. 620 


591 


.566 


540 


5*5 


500 


.829 


.791 


. 760 


730 


.697 


.669 


639 


.610 


.586 


559 


534 



*The available draft will be the tabular values less the amount consumed by friction in the stack. In 
stacks whose diameter is determined by Formula 40 the net draft will be 80% of the tabular values. Hence 
to obtain from the table the height of stack necessary to produce a net draft of say 0.6 inches, the the- 
oretical draft will be 0.6X1.25=0.75 inches, which can be got with a stack 100 ft. high with flue-gas 
temperature of 420 F., and air temperature of o F., or a stack 125 ft. high when the air temperature is 60 F. 

169 



LOSS OF DRAFT IN STACKS 



171 



Weight of a cubic foot of air at 

62 F =.0761 Ibs. 

Weight of a cubic foot of air at 

500 F =.0414 

Difference . . =.0347 

Therefore, a chimney 100 feet high would 
have on every square foot of its base cross- 
section an upward pressure of .0347X100 
3.47 Ibs. As a cubic foot of water at 
.62 F. weighs 62.32 Ibs., one inch of water 
will exert a pressure of = 5.193 Ibs. 
per square foot, or '"'^l 3 = 0-03607 Ibs. per 
square inch. The 100 feet stack will, there- 
fore, show a draft of 3.47 -s- 5.193 = 0.67 inch 
of water, nearly. 

For the determination of the proportions 
of stacks and flues The Stirling Company's 
procedure depends upon the principle that 
if the diameter of the stack is sufficiently 
large for the volume of gases to be handled, 
the intensity of draft will depend upon the 
height; therefore, 

Select a height of stack which will produce 
the draft required by the character and 
amount of fuel to be burned per square foot 
of grate surface, then, 

Determine for this stack the diameter 
necessary to handle the gases without undue 
frictional losses. 

The application of these rules follows. 

Draft Formula The force or intensity of 
draft is given by the formula: 

D=o. 52 HXP !-----} [36] 

*\* 

In which, 

D= draft produced, measured in inches 

of water. 
H= height of top o" stack above grate 

bars, in feet. 

P = atmospheric pressure in Ibs. per sq. in., 
T = atmospheric temperature, absolute. 
J\= absolute temperature of stack gases. 

In this formula account is not taken of 
the density of the flue-gases, it being assumed 
to be practically equivalent to that of air. 
The error is safely negligible in practise.* 
The force of draft at the sea level which 
corresponds to a pressure of 14.7 Ibs. per 
square inch produced by a chimney 100 
ft. high, when the temperature of the at- 



mosphere is 60 F., and the flue-gas tem- 
perature is 500 F., is 



^=0.52X14.7 r=- 6 7 
( 5 21 9 6 i ) 

Under the same temperature conditions 
this chimney at a pressure of 10 Ibs. per 
square inch which corresponds to an alti- 
tude of about 10,000 feet above sea level- 
would produce a draft of only 

.0=0.52 X ioo X 10 (5^7- <rlr) = -45 in ch. 

For future use it is convenient to tabulate 
values of the product. 



0.52X1.47-- -}-K 
(T Tj 

for a number of different values of 7' x and 
[36] becomes 

D=KH [37] 

For an atmospheric pressure and tem- 

perature, respectively, of 14.7 Ibs. and 60 

F., which represent average conditions, the 

results are as follows: 



TEMPERATURE OF 
STACK GASES. 

75 

70O . 

650 . . 

6OO . 

550 
500 . . 

45 
400 . 

35 



CONSTANT 
A' 

.0084 
.0081 
.0078 
.0075 
.0071 
.0067 
.0063 
.0058 
0053 



Draft Losses The force of the draft as 
determined from the above formula can never 
be observed with the draft gauge or any 
recording device, but if the ash-pit doors are 
closed and the measurements are taken at 
the base of the stack, there will be but little 
difference between the actual and the theoreti- 
cal draft. The difference existing at other 
times represents the pressure required to 
force the gases through the stack against the 
friction of the sides and against their own 
inertia, and increases witji the velocity of the 
gases. When the ash-pit doors are closed, 
the volume of gases passing is a minimum, 
hence the maximum force of draft is shown 
on the gauge. 

As the measurements are taken farther 
along the path of the gases through the boiler, 



*Some draft formulas are based upon the assumption that twenty-four pounds of air are used per pound 
of coal, hence the air will weigh 96% of the chimney gas. Table 51 gives the draft pressures in inches 
of water worked out on this hypothesis. Owing to the variation in the air supply the draft either from 
the table or from Formula [36] will be accurate enough for all practical purposes. 









B1I2 

7 


3700 IjE 

3600 ::^::::i": 
3500 - 

3400 ::S:ffi^S 


::::::::::::::: ::qq:rr7T irrr 


rt ^ : jjij ;:::::::;:; 


^r~ 

f 

! UJ J 


3200 :!.::,, Err 
3100 r 


':;:;:',; :;;;' ;; - ^ ^ 


I Em: 


-/- I 
/ 

~~~l 


sooo j[T|i f mt 






J 







. '. '. - '.- \ \ '. '. | ; ". '.'. i '.'.'.'. '. '. '. '. 1 '. ' ' ' '. '. \ 




2800 






4 








/ 
i 




''.'', '.'.".'. '.''* '.'-'. \ ''. y. ' '. \ ' \ - ~ '. '. 


":: " \ ll : : : . :::! ^j^ -: 


j 


2600 .{:. . . 

:;:: : : :: ;:;: 


;: : ;; : :; : :; :: :;!.: , : : | ; ;; : 




~T ;;---| 
/ 


2500 r 






7- 






:; : iHMm Hi 




w 

2200 ~ " 




iiiiiliiiiii 





O ^ uu 4 . | i 1 ; fprr 

CQ 




K 





^ 2 1 00 x 

IHIIHII TH 




fit 


:~: :::_: : : :: rrEJi:: 


01 




5^ 


: : i: : ; : ::: : 


O 

Q. 




1(6 r 


::.:: :::: ' : ' : .~': : . ' 1 


CO 




It 


:::: :::::: .: ;::: : :.^ 


o I70 i 

X 




?^ 

1 i - p i / 








/ 


ffiffig^fei; 


1 500 f 


;:i: ; ::;| ; ii: |M| :;:; ; i; 


:: : ; ;;;: :::: ;;;: : \/ ;; ; : 


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1400 

j tfft 

isoo frfffr~rf^7 r 


l||i|ill 


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II II yfii iffF 


..... i . . ._ 


1200 j-- -Fir Trfr: 

i i nn -^ 












::/::: 
::: ::./:: 


: . 


1000 -+-4-T- iji! . ;;;i 

jEiiMffi 




m 


! : 


900 :|tir trrr 




\/ ;i - 




soo SttTtrrr-r 
700 -r 


tin ijt ( H 1 1 ) j I i j 1 1 1 1 1 I j 1 1 1 1 1 1 1 - 


iipiiiiiil 


1 












llpif^ yj 


Z 




: : : ! : : : : 
+----- 




/;' 





400 n~ 


i / 






... 


.:[/: 


i 




300 :d 


fflSlMll 








^>^: 




: : : ::;!:. i- ; . 




^^-^ 




. . . . . . i 


- g. - <- 


-^ SHll - : 




:t - 



20 30 40 50 60 70 80 90 

DIAMETER OF STACK IN INCHES 



100 



130 



FIG. 37. CURVE SHOWING DIAMETER OF CHIMNEY STACKS AT SEA LEVEL 

COMPUTED FROM FORMULA NO. 40. FOR BRICK OR BRICK-LINED STACKS, INCREASE THE DIAMETER 6 PER CENT 
ONE-FIFTH OF THE THEORETICAL DRAFT IS LOST IN THE STACKS 

172 



FORMULAS FOR DIAMETER OF CHIMNEYS 



173 



from the stack toward the grate, the readings 
grow gradually less, until in the ash-pit hardly 
a perceptible rise takes place in the water 
of the gauge. The breeching, the boiler 
damper, baffles and tubes, and the coal in 
the grate, all retard the passage of the gases, 
and in each case the draft from the chimney 
is required to overcome their resistance. 
The draft at the rear of the setting, where 
the connection is made to the flue or stack, 
might be o. 5 inch, while in the furnace over 
the fire it might not be more than 0.15 inch, 
the difference, 0.35 inch, being the draft 
required to force the gases between the tubes 
and around the baffling. 

An important factor in chimney design is 
the pressure required to force the air through 
the bed of coals. In many instances this will 
be a large percentage of the total draft. Its 
measure is found directly, in the case of 
natural draft, by noting the draft in the 
furnace, for it is evident with ash-pit doors 
of ample size the pressure under the grates 
will not differ sensibly from the atmospheric 
pressure. 

Loss In Stack The difference between 
the theoretical draft as determined by 
formula [37] and the amount lost by friction, 
etc., in the stack proper, is the available draft, 
or that which the draft gauge indicates when 
connected to the base of the stack. The sum 
of the draft lost in the flue, boiler, and furnace, 
must be exactly equal to the available draft, 
and as these quantities can be determined 
from records of experiments, the proportion- 
ing of a stack resolves itself into finding a 
stack which will produce a given available 
draft. 

The loss in the stack and flue by friction 
and inertia can be calculated from the fol- 
lowing formula: 

A0-2f* [3 8] 

where AD =draft lost in inches of water. 

W / =weight, in pounds, of gases 

passing per second. 
C ==circumf erence of a stack or flue 

in feet . 

^4=area of passage in square feet. 
H =height of stack in feet ; or when 

used for flues, length of flue. 
/ =a constant with the following 

values, for sea level: 



.0015 for steel stack, temperature of gases 600 F 
.0011 for steel stack, temperature of gases 350 F. 
.0020 for brick or brick-lined stack, temperature of 

gases 600 F. 
.0015 for brick or brick-lined stack, temperature of 

gases 350 F. 

The available draft is equal to the difference 
between the theoretical draft from Formula 
[37], and the loss from Formula [38], hence 

fW 2 CH 



d'= available draft =K H - 



[39] 



Height and Diameter of Stack It fol- 
lows from this formula that a stack of a 
certain diameter, by increasing its height, 
can be made to produce the same available 
draft as one of a larger diameter, the ad- 
ditional height being required to overcome 
the greater friction loss. Consequently, 
among the various stacks which could meet 
the requirements there must be one which 
can be constructed cheaper than the others. 
By deducing an equation connecting the 
cost of stacks with their height and diameter, 
and using it in connection with the formula 
for available draft, it has been found that 
the minimum-cost stack has -a diameter de- 
pending solely upcn the horse-power of the 
boilers it serves, and a height proportional 
to the available draft required. 

Assuming 120 Ibs. of flue-gas per hour 
for each boiler horse-power, which provides 
for allowable overload and use of poor coal, 
the method above stated gives : 

For an unlined steel stack, 

Dia. in inches = 4. 68 (H.P.f [40] 
For stacks lined with masonry, 

Dia. in inches = 4.92 (H. P.y [41] 

In both of these formulas H. P. = rated 
horse-power of boilers. 

From this formula the curve in Fig. 37 has 
been calculated, and from it the stack di- 
ameter for any boiler horse-power can be 
taken. 

Stacks with diameters determined as above 
have an available draft which bears a con- 
stant ratio to the theoretical draft, and, 
allowing for the cooling of the gases in their 
passage up through the shaft, this ratio is 
.80. Using this correction in Formula [37], 
and transposing, the height of the chimney 
becomes 




(U3J.VM dO S3HONI) 'Xld HSV QNV POVNUOd N33MX38 O3ain&3a 



dO 3OHOd 



DRAFT REQUIRED FOR DIFFERENT FUELS 



175 



H = 



d' 
.8/C 



[42] 



H= height of stack in feet, measured from 

the point where the flue enters, 
d' = available draft required, 
K = constant as in formula [37]. 

Losses in Flues The loss of draftsuction 
in passing through a straight flue can be 
calculated approximately from Formula [38], 
which was given for the loss in a stack. 
It must be borne in mind that C in this 
formula is the actual perimeter of the 
flue, and is least compared to the area when 
the section is a circle, is greater for a square, 
and still larger for a rectangle. The re- 
tarding effect of the square flue is 12% greater 
than of a circular one of the same area. 
The greater resistance of the more or less 
uneven brick flue is provided for in the values 
given to the constants. Both steel and 
brick flues should be short, and as near to a 
circular or square section as is possible. 
Abrupt turns are to be avoided, but long, 
easy sweeps take up valuable space, and it is 
often desirable to add to the height of a 
stack, rather than take up additional room 
below. Short right-angled turns reduce the 
draft by an amount which can be roughly 
approximated as equal to 0.05 inch for 
each turn. The turns which the gases make 
in leaving the damper box of a boiler and 
entering a horizontal flue, must always 
be considered. 

The sectional area of the passage leading 
from the boilers to the stack is determined 
largely by considerations of cost, and the 
subject resolves itself into whether it is 
cheaper to add to the height of the stack 
or to increase the flue area. The general 
practise is to make the area of the flue the 
same as, or slightly larger than, that of the 
stack ; its area should preferably be at least 
20% greater. It is unnecessary to maintain 
the same size of flue the entire distance 
behind a row of boilers, and the area may 
be reduced as connections with the various 
boilers are passed. 

With circular steel flues of the same size 
as the stack or reduced proportionately 
to the volume of the gases, a convenient 
rule is to allow o . i inch draft loss per 
each hundred feet length of flue, and 
0.05 inch for each right-angle turn. For 



square or rectangular brick flues, these 
values should be doubled. 

Loss in Boiler In calculating the avail- 
able draft of a chimney, 120 Ibs. per hour 
has been used as the weight of the gases per 
boiler horse-power. This covers an over- 
load of the boilers to an extent of 50%,, 
which provides for all practical requirements, 
Stirling boilers require comparatively little 
draft in the boiler proper, o . 2 inch being 
all that is lost when working at rated ca- 
pacity. At 50% overload, 0.4 inch should 
be allowed, and this figure is the one to be 
used when summing up the available draft 
the stack must furnish. 

Loss in Furnace The draft loss in the 
furnace varies between wide limits. The 
air necessary for combustion must come 
through the interstices of the coal on the 
grate, and when these are large, as with a 
broken lump coal, but little pressure is re- 
quired to force air through; but if they are 
small, as with slack or anthracite culm, a 
much greater pressure is required. If the 
draft is insufficient the coal will accumulate 
on the grate and a dead, smoky fire will 
result, causing imperfect combustion; if the 
draft is too great the coal is rapidly con- 
sumed, leaving a thin fire and portions of 
the grate bars uncovered. 

Draft Required for Different Fuels 
For every kind of fuel and rate of combustion 
there is a certain draft with which the best 
general results are obtained. It is com- 
paratively small with the free-burning 
bituminous coal, and increases in amount as 
the percentage of volatile matter diminishes 
and the fixed carbon increases, being highest 
for the anthracites. Other things, such 
as the percentage of ash and the air spaces 
in the grates, etc., exert an influence, but 
like other factors, their effect can be found 
only by experiment. 

The curves in Fig. 38 give the furnace 
draft necessary to burn various kinds of 
coal at the combustion rates indicated as 
abscissas. These have been plotted from 
the records of numerous tests in the files 
of The Stirling Company, and they allow 
a safe margin for economically burning 
coals of the kind noted. One curve is given 
for the draft required with Stirling chain 
grates burning bituminous slack. The greater 



176 



THE STIRLING WATER-TUBE SAFETY BOILER 



draft than that required for hand firing is 
due to the fact that in the chain grates the 
fire is not broken up and cleaned. As the 
amount of fixed carbon in coal increases, 
the differences in the draft required by a 
chain grate and for hand firing grow less, 
and for culm they are about the same ; in both, 
however, the draft is so great as to neces- 
sitate very high stacks or forced draft. 

Rate of Combustion The amount of 
coal which can be burned per hour per 
square foot of grate is controlled by the 
character of the coal and the ratio of grate 
surface to boiler heating surface. When 
this ratio is properly proportioned the 
efficiency of boiler and furnace will be 
practically the same for different rates of 
combustion (unless they are either unduly 
large or small) , provided the draft is adjusted 
to suit the particular rate of combustion 
desired. Hence the area of the grate can be 
fixed and the stack be designed to suit, or 
the stack may be decided upon, and the 
grate area be adjusted to burn the necessary 
quantity of coal at a rate per square foot 
of grate corresponding to the draft the 
stack can provide. 

Solution of a Problem The stack di- 
ameter can be determined from the curve, 
Fig. 37. The height is determined by 
adding the draft required in furnace, boiler, 
and flue, and computing from formula [37] 
the height necessary to give this draft. 
Example: proportion a stack for 1000 H. P. 
of boilers, using chain grates, burning fuel 
that will evaporate 8 pounds of water from 
and at 212 per pound of coal; ratio of 
heating surface to grate surface being 40 to 
i; the flue being 100 feet long, with two 
right-angled turns; the chimney to be able 
to handle boiler overloads of 50%. 

The atmospheric temperature may be 
assumed as 60 F., and the flue-gas tem- 
perature at the stated boiler overload as 
550 F. 

The combustion rate at boiler rating is 

40 X si 

- = 17-5 pounds. 

o 

For 50% above rating, the combustion 
rate will be about 60% more than this, or 

1.60X17.5 = 28 Ibs. of coal per sq. ft. of 
grate surface per hour. The furnace draft re- 
quired for this combustion rate, from the 



curve, Fig. 38, is 0.4 inch. The loss in the 
boiler also will be 0.4 inch, the loss in the 
flue o.i inch, and in the turns 2X0.05=0.1 
inch. The available draft required at the 
chimney where the flue enters is therefore: 



Boiler 

Furnace . 

Flue . . 

Turns . 

Total . 



0.4 inch 
0.4 
o.i 
o.i " 



i.o inch 

Since the available draft is 80% of the 
theoretical, the theoretical draft due to the 
height required is I.OOH-. 8 = 1.25 inch. 

The chimney constant for temperatures of 
60 and 550 F. is .0071, formula [37], hence 
the height of the stack above the point where 
the flue enters is, by the same formula 



. 0071 

Its diameter, from the curve in Fig. 37, 
is 75 inches if unlined, and 80 inches inside 
if lined with masonry. The greatest diameter 
of the breeching, if circular, for 20% greater 
area than the stack, would be 82 inches, and 
would taper down to about 42 inches where the 
last boiler connects, if four units were used. 

Correction for Altitude From formula 
[36] it follows that the draft is proportional to 
the atmospheric pressure, hence for a stack 
of given height the draft will decrease when 
the altitude is increased, consequently to 
secure at high altitudes the draft necessary 
for the rates of combustion in Fig. 38 the 
dimensions of a stack as determined for sea 
level must be altered. 

Let p be the atmospheric pressure at sea 
level, and p v the pressure at any other alti- 
tude; H the height of a chimney which at 
sea level produces a given draft, and H^, the 
height of a stack which will give at the as- 
sumed altitude the same draft that H gives 

P 
at sea level. Put =r, then from formula 

ft 

[36], H^=rH. It therefore remains only to 
determine the increased diameter needed. 
Formula [18], page 87, shows that the 
weight of gas per minute flowing through a 
pipe is 

r pod* i* 

w=a constant X < ( 




SIZES OF CHIMNEYS BY KENT'S FORMULA 



177 



Let d=diameter of the stack H deter- 
mined for sea level; d^ the diameter of H^ 
determined for the altitude; D the density 
of gases at sea level, and D t the density at 
the given altitude. In the formula P will 
evidently be the quantity AD, in formula 
[38] page 173, which will be the same in both 
stacks H and //,; regardless of the altitudes 
the same weight of oxygen will be needed 
to burn a pound of a given coal, hence the 
diameter of stack H 1 must be such as to pass 
the same weight of gas at the altitude that 
stack H passes at sea level. To apply the 
formula, H and //, , will be the lengths de- 
noted by L; also, as previously shown, H^ = 
rH and D=rD^, hence since both stacks 
deliver the same quantity of gas, it follows, 

!i!{ 

d' 



neglecting the small term 



.that 



PDd 5 PDjl* D^rtf 
or 



H H l H rH 

Whence d t **dr*, hence the following rule 
to determine stack dimensions for any 
altitude: Divide the barometric pressure at 
sea level (=30") by the barometric pressure 
at the given altitude, and call the quotient r. 
Determine the stack height and diameter 
required at sea level, then multiply the 



height so determined by r, and the diameter 
by r% and the resulting dimensions apply 
at the given altitude. The flue area can be 
determined in the same way. 

Table 52 gives values of r and rl com- 
puted from data in Table 12.* These show 
that altitude affects the height more than 
the area, and that practically no increase 
of area is needed for altitudes up to 3,000 
feet. The grate areas should be increased 
in the same proportion as the stack areas 

TABLE 52 



Altitude 


Atmospheric 




9 


in Feet above 


Pressure. 


r 


rl 


Sea Level. 


Lbs.per Sq.In. 






5,221 


8. 19 




.80 




27 


4,075 


8.56 




.72 




24 


2,934 


8. 9 4 




.65 




22 


1,799 


9-33 




ss 




20 


0,1 27 


9-95 




.48 




17 


9.031 




0.38 




42 




15 


7,932 




0.82 




.36 




13 


6,843 




i .28 




.3 




1 1 


5-764 




i . 76 




25 




09 


5,225 




2 .01 




. 22 




08 


4,160 




2-51 




.18 




07 


3,115 




3-03 




- 13 




05 


2,063 




3-57 




.08 




03 


1,539 




3.8 4 




.06 




, 02 



Kent's Table Mr. William Kent has 
prepared a table giving the size of boiler 
chimneys that has met with much approval. 



TABLE 53 
DIMENSIONS OF CHIMNEYS BY KENT'S FORMULA 



Diameter in 
Inches. 


1 
t| 
1 


HEIOHT OP CHIMNEV IN KEET. 


200 


I 

hi. 

nil 

lg|| 

1 1 


Diameter in 

Inches 


80 


86 





16 


too 


106 


110 


116 


120 


126 


ISO 


136 


140 


146 160 


165 


160 


166 


170 


176 


180 


186 


190 


196 


COMMERCIAL HORSE POWER 


30 


4.91 


107 

its 


110 
























E 




























E 







17 


80 


3* 


S.U1 


1S7 


178 
























80 


88 


M 


7.0; 


Id 

196 


IKS 


























82 


88 


M 


8.80 


202 


20t> 


214 













86 


m 


48 
48 


9.62 

li.67 


Ml 
111 


288 
820 


24* 

880 


261 

aim 


858 
S48 


286 
866 


871 

806 


878 


881 


888 


S'.Mi 




























88 
48 


48 

48 


(4 


16.90 

~l9.64~ 





416 


427 


488 
661 


44 
686 

4 


481 


472 


482 


498 


608 
882 


618 
844 


628 


682 


642 


692 

849 


704 

"4 




















48 


64 
0~ 


60 





M 


67* 


6 

728 


HIM! 


81* 


667 


66 


680 
886 


716 

877 




918 


64 


M 


88.76 






78 


711 


744 


780 


776 


781 


806 


821 


8!)1 


904 
1 089 

1291 








6 


88 


11 

78 


28.27 

8.1. IS 













886 


868 
1014 


878 

1088 
1214 


*>(! 

1082 
1241 


818 
1084 


084 
1107 


862 
1128 


70 

1160 
1846 


HUN 

1171 


100U 
1ID2 


1028 

1218 
1418 


1040 
12K2 


1068 
1262 


107S 
1272 


1106 
1810 


1120 

1828 
1668 


1186 

1846 
1674 


1161 

1864 
1696 


1882 


1400 
1S7 


84 
70 


72 

78 

84~~ 


84 


(8.48 




1268 


1294 


1820 


1870 


1884 


1441 


1404 


1487 


1609 


1581 


1616 


76 


M 


44.18 
















1486 


1486 


1486 


1626 


1656 


1684 


1612 


lSi> 


1BO 


KllllI 


1719 


1746 


1771 


17M5 


1820 


1846 


1869 


1888 


80 


80 


8t 


511.27 












1848 


1678 


1718 


1747 


1780 


1818 


1846 


1876 


1907 
2166 

2481) 


1988 


196H 


1998 


2027 


205 


2084 


2112 


2140 


2167 


88 





108 

108 


5B.75 
flil.llS 


















1806 


1*44 

2100 


18H8 
22S4 


2021 
2276 


2068 
2818 


2084 
2869 


2180 
2899 


2200 

2478 


2284 
2516 


2268 
2654 


2:1111 
2592 


2888 
2628 


2888 

2664 
2982 
8816 


2897 
2700 


2429 
2786 


8469 
8771 


1 

88 


lOt 

108 


114 


70.KN 































249 


2647 


2694 

2886 


2640 
2988 


2686 


272 


2778 
8084 


2816 


2868 


2900 


2941 


8022 


8081 
8406 


X100 


101 


114 


190 


7N.61 




2888 


2986 


8086 


8182 


8179 


8226 


8271 


8861 


8448 


107 


ito 


IN 


96.08 

























8460 


8614 


8676 
4279 


8687 


S697 


8766 


8816 


8872 


829 


8984 


4089 


4098 


4147 


4200 


117 


182 


144 


111.10 
























4206 


4862 


4424 


4496 


4666 


4682 


4701 


4768 


4884 


4899 


4988 


6026 


128 


144 



*See page 58. 



178 



THE STIRLING WATER-TUBE SAFETY BOILER 



For ordinary rates of combustion of bitu- 
minous coals it is reliable, provided no 
unusual conditions are encountered. For 
ready reference in cases where approximate 
dimensions of a chimney based on boiler 
horse-power are required Mr. Kent's table 
is extremely convenient. In this the figures 
correspond to a coal consumption of 5 Ibs. 
of coal per H. P. per hour. Mr. Kent says: 
"This liberal allowance is made to cover 
the contingencies of poor coal being used, 
and of the boilers being driven beyond 
their rated capacity. In large plants with 
economical boilers and engines, good fuel 
and other favorable conditions, which will 
reduce the maximum rate of coal consump- 
tion at any one time to less than 5 Ibs. per 
H. P. per hour, the figures in the table 
may be multiplied by the ratio of 5 to tne 
maximum expected coal consumption per 
H. P. per hour. Thus, with conditions 
which made the maximum coal consumption 
only 2 . 5 Ibs. per hour, the chimney 300 ft. 
high X 12 ft. diameter should be sufficient 
for 6155X2 = 12,310 horse power. 

STACKS FOR BOILERS USING OIL FUEL 

The requirements for stacks attached to 
boilers burning oil are entirely different 
from those required when burning coal. 
The loss of draft caused by a bed of coals 
is eliminated, the volume of flue-gas will 
be less than for an equal weight of coal 
if the air supply is properly adjusted, and 
the action of the burner is in a measure 
equivalent to a forced draft. Experimental 
data such as are available for coal have not 
been gathered for oil, hence no such elaborate 
methods of determining proportions of stacks 
for oil as have been worked out for coal, 
are at present available, but the method 
to be given has been found entirely satis- 
factory for a large number of cases, and 
may be used without hesitation. 

A stack 75 to 80 feet high above a boiler 
damper plate furnishes ample draft to burn 
oil, if there are no long flues or turns in the 
breeching, hence the only other requirement 
is to determine the diameter. Owing to 
the smaller volume of gas formed as com- 
pared with coal, and the forced draft action 
of the burner, it has been found by ex- 



perience that when oil is burned, a stack 
having 60 per cent, of the cross section re- 
quired by the same boiler if bituminous 
coal were used, will be amply large to enable 
the boiler to be fired at 50 per cent, above 
rating with oil. Example: required the 
dimensions of a stack for 500 H. P. of boilers 
burning oil. 500 X. 60 = 300. Kent's Table 
may be used with facility in this case, hence 
referring to this it will be found that a 
stack 48 inches in diameter and 80 feet 
high will develop 311 H. P. with bituminous 
coal, hence a 48-inch stack will meet the 
requirements of this case. Many plants 
are operating successfully with stack areas 
equal to only 50 per cent, of the coal area, but 
this allowance is too scant to provide prop- 
erly for overloads. 

Correction for Flues It has already 
been shown that a flue 100 feet long loses 
o.i inch of draft, and that a right-angled 
turn loses .05 inch. But Table No. 51 
shows that for a stack temperature of 450 
and external air temperature of 80 the 
draft in a loo-foot stack will be o. 549 inches, 
hence the draft due to one foot of height 
will be practically 0.0055 inches, conse- 
quently for each elbow in the breeching an 
addition of 10 feet to the height of the 
stack will be needed, and for a length of flue 
100 feet long, an addition of o.i -H 0.0055, 
= 18.1 feet, will be sufficient. 

Where local conditions, such as buildings, 
etc., necessitate use of stacks exceeding 80 
feet in height the corresponding diameter 
may be found in the same way. Example: 
if for 1000 H. P. a stack 140 feet high were 
assumed, and the breeching were 50 feet 
long and contained two right-angled turns, 
the part of the height required to give the 
additional draft for flue and turns would 
be 2X10 + 9 = 29 feet. 14029 = 111 feet. 
ioooX.6o=6oo H. P. From Table 53 a 
stack 60 inches diameter, and no feet high, 
the nearest tabular value to 1 1 1 , is equal to 
593 H. P., hence a 6o-inch stack would 
be suitable for the given conditions. 

DRAFT GAUGES 

The ordinary form of draft gauge consist- 
ing of the U-tube, Fig. 39, containing water, 
lacks sensitiveness when used for measuring 



ELLISON'S DRAFT GAUGE 



179 



such slight pressure differences as exist in 
a chimney, hence gauges which multiply the 
draft indications are more convenient, and 
are much used. 

Barrus 5 Gauge Mr. G. H. Barms for a 
number of years has used with excellent 
results an instrument which multiplies the 
ordinary indications as many times as is de. 
sired. It is illustrated in Fig. 40, and consists 
of a U-tubemade of ^-inch glass, surmounted 
by two larger tubes, or chambers, each having 
a diameter of 2^-inch. Two different liquids 
which will not mix, and which are of differ- 
ent color, are used. The movement of the 
line of demarcation is proportional to the dif- 
ference in the areas of the chambers and of 
the U-tube connecting them below. The 
liquids generally employed are alcohol colored 





FIG. 39 
U-TUBE DRAFT GAUGE 



FIG. 40 
BARRUS' DRAFT GAUGE 



red and a certain grade of lubricating oil. A 
multiplication varying from eight to ten times 
is obtained under these circumstances; in 
other words, with ^-inch draft the movement 
of the line of demarcation is some 2 inches. 



The instrument is calibrated by referring it 
to the ordinary U-tube gauge. 

Ellison's Gauge In this form of gauge 
the lower portion of the ordinary U-tube 
has been replaced by a tube slightly inclined 
to the horizontal, as shown in Fig 41. By 
this arrangement any vertical motion in 
the left hand upright tube causes a very much 
greater travel of the liquid in the inclined 
tube, thus permitting extremely small va- 
riation in the draft pressure to be read with 
facility. 




FIG. 41. ELLISON'S DRAFT GAUGE 

The gauge is first leveled by means of 
the small level attached to it, both legs 
being open to the atmosphere. The liquid 
is then adjusted (by adding to or taking 
from it) until its meniscus rests at the zero 
point on the right. The left hand leg is 
then connected to the source of draft by 
means of a piece of rubber tubing. Under 
these circumstances, a rise of level of one inch 
in the left hand vertical tube causes the 
meniscus in the inclined tube to pass from 
the point o to i.o. The scale is divided 
into tenths of an inch, and the subdivisions 
are hundredths of an inch. 

The right hand leg of the instrument 
bears two marks. By filling the tube to 
the lower of these the range of the instru- 
ment is increased one-half inch, i. e. it will 
record draft pressures from o to i^ inches. 
Similarly, by filling to the upper mark, the 
range is increased to 2 inches. When so 
used the observed readings in the scale are 
to be increased by one-half or one-inch, 
as the case may be. 

The makers recommend the use of a non- 
drying oil for the liquid, usually a 300 
test refined petroleum, but water suffices 
for all practical purposes. 



Analysis of Flue-Gases 



In the chapter on Combustion* the effect 
of excess air in cooling the fire is set 
forth. This excess air would not reduce the 
boiler efficiency if the gases of combustion, 
when sweeping over the heating surface, 
were cooled to the initial temperature of 
the air supply, since before their exit they 
would give up the heat they absorbed after 
entering the furnace. Such abstraction of 
the heat is not possible in a boiler because 
the flue-gases cannot be reduced to a tem- 
perature below 50 to 100 above the tem- 
perature of the steam. With a fixed tem- 
perature of discharge the loss in the waste 
gases is proportional to the weight of the 
gases, hence excess air not only reduces the 
temperature of the furnace, which causes 
a decrease in the boiler capacity and efficiency 
but it causes still further loss by serving as 
a vehicle to convey heat to the stack. 

An insufficient air supply causes formation 
of carbon monoxide (CO) instead of carbon 
dioxide (CO 2 ), and if this passes away un- 
burned the heat derived from a pound of 
carbon will be only 4450 B. T. U. instead of 
the 14600 B. T. U. obtainable when carbon 
dioxide is formed. 

If the combustion were perfect and no 
excess air were admitted, the resulting gases 
would be carbon dioxide, and steam, to- 
gether with the nitrogen from the air. The 
amount of carbon dioxide and nitrogen 
would bear a fixed ratio to the carbon burned. 
Consequently, since some excess air is un- 
avoidable, the nitrogen in the flue-gases fur- 
nishes an index to the amount of that 
excess, and the presence of carbon dioxide 
indicates incomplete combustion of carbon. 

Object of the Analysis The object of 
the flue-gas analysis is to determine from a 
sample of the gas the amount of excess air 
admitted, the degree of completeness of the 
combustion of the carbon, and the amount 
and distribution of the heat losses due to 
the excess air and incomplete combustion. 
The quantities actually determined by the 
analysis are the relative proportions of 
carbon dioxide (CO 2 ), carbon monoxide 
(CO), and oxygen (0) in the gases. Although 

* Article "Temperature of the Fire," page 107. 



the analysis does not directly. determine the 
amount of nitrogen present in the flue-gases, 
yet its actual amount, as well as that of the 
air supply, may readily be ascertained by 
calculation. When air is drawn through 
an opening, like an ash-pit door, sometimes 
an anemometer can be used for ascertain- 
ing the velocity through the area, and the 
air supply be determined by these means. 

Before describing in detail the apparatus 
and methods used for analyzing flue-gases, 
the application of the results obtainable 
from the analysis will be illustrated. 

A pound of carbon requires for complete 
combustion, 2.67 pounds of oxygen, or a 
volume of 32 cubic feet at 60 F., and the 
gaseous product, carbon dioxide (CO 2 ), 
when cooled, occupies precisely the same 
volume as the oxygen, viz., 32 cubic feet. 
If the oxygen is mixed with nitrogen in the 
same proportion as it is found in air (20.91 O 
and 79.09 N), the volume of the carbon 
dioxide (CO 2 ) after combustion, and also 
its proportion to nitrogen, is the same as 
that of the oxygen; hence, for complete 
combustion of carbon, with no excess of air, 
the volumetric analysis of the flue gases is, 
Carbon dioxide . . CO 2 =2o.9i% 
Carbon monoxide . CO =None 
Oxygen . O =None 

Nitrogen. . . . N =79.09% 
If the supply of air is in excess of that 
required to supply the oxygen needed, the 
combined volumes of the carbon dioxide 
and oxygen are still the same as that of the 
oxygen before combustion; consequently, 
for the complete combustion of pure carbon, 
the sum of the percentages by volume of the 
carbon dioxide and oxygen in the flue gases 
must always be 20.91, no matter what the 
slip ply of air may be. 

Carbon monoxide (CO) produced by im- 
perfect combustion of carbon, occupies twicQ 
the volume of the oxygen entering into its 
composition, and renders the volume of the 
flue gases greater than that of the. air supply 
in the proportion of 

hence 



i oo- i the % of CO' 



182 



THE STIRLING WATER-TUBE SAFETY BOILER 



when pure carbon is the fuel, the sum of the 
percentages of carbon dioxide, oxygen, and 
one-half the carbon monoxide , must be in the 
same ratio to the nitrogen as is oxygen in air, 
i. e., 20. 91 to 79 .09 

The action of hydrogen in coal is to increase 
the apparent percentage of nitrogen in the flue- 
gases, because the water vapor condenses 
at the temperature at which the analysis 
is made, and account of it is lost, but the 
nitrogen that accompanied the oxygen with 
which the hydrogen combined, maintains 
its gaseous form and passes into the analyz- 
ing apparatus with the other gases. 

Example Suppose an analysis of flue- 
gases shows 12.5% of carbon dioxide, 0.6% 
of carbon monoxide and 6.5% of oxygen, 
all by volume. Then nitrogen, which is the 
only other constituent in the flue-gases 
worthy of consideration, will represent a 
percentage of the total volume, 

ioo-(i2.5+o.6+6.5)=8o.4% 
Assume the unit of volume here designated 
as 100% to represent 100 cubic feet. From 
Table 54, the weights of the various gases 
per cubic foot are as follows: 

Carbon dioxide (CO 2 ) =0.12 2681 
Carbon monoxide (CO) =0.078071 
Oxygen (O) -0.088843 

Nitrogen (N) =0.078314 

The weight of the flue-gas per unit volume 
of 100 cubic feet will therefore be 



Carbon dioxide (CO2) = .12268X12.5 = 1.5534^3. 
Carbon monoxide (CO) =. 07807 X 0.6= .0468 
Oxygen . . (O) = .o8884X 6.5= .5775 
Nitrogen . . (N) = .07831 X 80.4=6. 2961 

i oo.o 8. 4738 Ibs. 

From the atomic or combining weights 
of the elements, it is known that in a unit 
of carbon dioxide, oxygen constitutes eight- 
elevenths of the weight, the remaining 
three-elevenths being carbon ; and in carbon 
monoxide four-sevenths is oxygen by weight, 
and three-sevenths carbon. Therefore, the 
weight of oxygen in 100 cubic feet of flue- 
gas in question is. 

Oxygen in COa . . = 1.5534X8/11 = 1.1297^3. 

Oxygen in CO . . =0.0468X4/7 =0.0267 

Free Oxygen = ... =0.5775 

Total weight of Oxygen . . . =1.7339 Ibs. 

The weight of carbon as determined from 
the same gas analysis is, 

Carbon in CO2 . . = 1.5534X3/11=0.4236^5. 
Carbon in CO ...."". 0468 X 3/7 =0.0201 
Total weight of Carbon . . . =0.4437 Ibs. 

As atmospheric air supplied to the fire 
contains 23.15% of oxygen by weight, then 
the weight of air which contained 1.7339 

i . 7339X100 
Ibs. of oxygen is =7.49^5; and, 

O ' D 

as this amount of air was required for the 

combustion of 0.4437 Ibs. of carbon, 

the weight of air per pound of carbon is 

7-49 



= 16.88 Ibs. 



0.4437 



TABLE 54 
DENSITY OF GASES AT ATMOSPHERIC PRESSURE 

(Adapted from Kent.*) 













Relative Density, 








Weight of One 


Cubic Feet 


Hydrogen = i 


GAS. 


SYMBOL. 


Specific Gravity 
Air=i. 


Cubic Foot 
at 32 F. 


per Pound 
at 32 F. 


Exact 
Relative 


Approximate 
Whole 












Densities 


Numbers. 


Oxygen. 


O 


I . 10521 


0.088843 


11.257 


15.96 


16 


Nitrogen 


N 


o . 9701 


0.078314 


12 . 764 


14.01 


14 


Hydrogen . . . 


H 


0.069234 


0.005589 


178.930 


I . OO 


i 


Carbon dioxide 


CO 2 


1.51968 


o . 122681 


8.158 


21-95 


22 


Carbon monoxide 


CO 


o . 96709 


0.078071 


12.818 


13-97 


14 


Methane 


CH 4 


0-55297 


o . 044640 


22.412 


7-99 


8 


Ethylene . 


C,H, 


0.96744 


0.078100 


12 . 804 


13-97 


14 


Acetylene . 


C 2 H 2 


0.89820 


O.O73OIO 


I3-697 


12.97 


13 


Sulphur dioxide 


S0 2 


2 . 21295 


o. 178646 


5-598 


31.96 


32 


Air 




I . OOOO 


0.080728 


12.383 











*Steam Boiler Economy, p. 20. 



HEAT LOST IN CARBON MONOXIDE 



183 



If the coal in the example considered con- 
tained 86% of carbon, 4% of hydrogen, and 
2 -5% f x yg en > then the air per pound 
of coal=i6.88X- 86=14. 52 Ibs., disregarding 
the hydrogen and oxygen. But the oxygen 
in fuel renders inert ^ of its weight of hy- 
drogen, and only the remainder of the hydro- 
gen is available for combustion; therefore 
the air required to burn the hydrogen is 

( . 025 ) 

] .04 ^3 4 .56=.o369X34-5 6 * =I - 2 75 Ibs. 

f 8 ) 

Thus the total air supply per pound of fuel 
becomes 14.52+1.28=15.80 Ibs. 

Air Required and Supplied When the 
ultimate analysis of a fuel is known the air 
required for complete combustion, with no 
excess, can be found as shown in chapter on 
Combustiont or from the following approx- 
imate formula: 

Pounds of air required per pound of fuel= 



[43] 



34. 56 ? 

3 



where C, H and O=per cent, by weight of 
carbon, hydrogen and oxygen in the fuel, 
divided by 100. 

When the flue-gas analysis is known, the 
total amount of air supplied is,J 

Pounds of air supplied per pound of fuel= 

3.032^ -- bet [44] 

(C0 2 +C0\ 

where N, CO and C0 2 =percentage by vol- 
ume of nitrogen , carbon monoxide and carbon 
dioxide in the flue-gases, and C the propor- 
tionate part, by weight, of carbon in the fuel. 
The weight of the flue-gases will be one 
minus the per cent, of ash (expressed in 
hundredths) more than this, i. e., it will be 
the sum of the weights of the air, and the 
combustible and moisture in the fuel, hence 
Weight of flue-gases per Ib. of fnel= 



3.032 



CO 2 + CO 
where A=proportionate 
of ash in the fuel. 



-A) [46] 

part, by weight, 



The ratio of the air actually supplied per 
pound of carbon to that theoretically re- 
quired to burn it is 

N 



3-032 



co 9 +co 



11.52 



=o. 2632 



C0 



[47] 



in which N, C0 2 and CO are the percentages 
by volume in the flue-gas. 

The ratio of the air supplied per pound 
of fuel to the amount theoretically required is 

N 
N- 3 . 7 8 2 

which is derived as follows: The N in the 
flue-gas is the content of nitrogen in the 
whole amount of air furnished. The oxygen 
in the flue-gas is due to the air supplied 
and not used. This oxygen was accom- 
panied by 3.782 times its volume of nitrogen. 
(AT- 3 . 782 0) represents the nitrogen content 
in the air actually required for combustion. 
Hence N+ (N 3 . 782 0) is the ratio of 
the air supplied to that required . The per cent . 
of excess air is this ratio minus one. Table 
55 gives the values of this ratio correspond- 
ing to various percentages of CO 2 + CO and 
CO 2 +CO + O 

The heat lost in the flue-gases is 

L, = o . 2 4 W (T t) [49] 

where 

L = B. T. U. lost per pound of fuel. 
W = Weight of flue-gases in pounds per 

pound of fuel. 

T = Temperature of flue-gases. 
t = Temperature of atmosphere. 
0.24 is the specific heat of flue-gas. 

The heat lost in the carbon monoxide in 
B. T. U. per pound of fuel is 

CO 



where, as before, CO and C0 2 are the per cent, 
by volume in the flue-gas, and C the pro- 
portion (by weight) of carbon in the fuel. 



*Weight of air required for the combustion of one pound of hydrogen, t Article, "Air Required," p. 106. 
JThe derivation of this formula may be found in Kent's Steam Boiler Economy, First Edition, page 32. 
As a check the following formula may be used: 

Pounds of air supplied per pound of fuel = n.52x p'U ,nr\ XC + 34-S6H 1 [45] 

Where H 1 is the available hydrogen (H -|O) in the fuel. This formula and that above given will not 
produce the same result unless the flue-gas and coal analyses are accurate, and the sample of the gas is 
a true one. The more accurate the work the more nearly the formulas will agree. 



184 



THE STIRLING WATER-TUBE SAFETY BOILER 



Orsat Apparatus The analysis of the 
flue-gases is best made for practical pur- 
poses by means of the Orsat apparatus, 
shown in Fig. 42. The operation is as 
follows: Exactly 100 cc of the gas sample 
are drawn into the graduated measuring 
burette, A, and then passed in succession 



tubes placed in the vessels for that purpose, 
and comes in intimate contact with the gas. 
Each vessel absorbs a different constituent. 
D is filled with a solution of potassium hy- 
droxide and takes up the carbon dioxide; 
E contains pyrogallic acid,* which re- 
moves the oxygen ; and F absorbs the carbon 



TABLE 55 

RATIO OF TOTAL AIR SUPPLIED TO THAT THEORETICALLY REQUIRED 
FOR VARIOUS ANALYSES OF FLUE-GASES 



N 



N 3.782 O 



CO2+CO 


N = 79 
CO2+CO+O 

= 21 


N = 7 Q.5 
CO2+CO+O 

= 20.5 


N = 8o 
CO2+CO + O 

= 20 


N = 8o.s 
CO2+CO+O 
= 19-5 


N=8r 
CO2+CO + O 
= IP 


N=8i. S 

CO2+CO + O 
= 18.5 


N=8 2 
CO2+CO+O 
= 18 


21 


I . OO 














20 


i. <>S 


1 .02 


1 .00 










19 


I . II 


1. 08 


J - 5 


1 . 02 


1 .00 






18 


1.17 


1.14 


I . 10 


1. 08 


I -5 


I .02 


1 .00 


17 


1.24 


I . 20 


1.17 


1-13 


I . IO 


1.07 


J -5 


16 


1.32 


1.27 


1.23 


I . 20 


i . 16 


*-I3 


I . IO 


15 


I . 40 


i-35 


I 31 


1.27 


1.23 


I . 19 


1.16 


14 


*"-5i 


i-45 


i-39 


J-35 


1.30 


I . 26 


1.23 


13 


1 .62 


i-55 


J-S 


1.44 


i-39 


!-34 


1.30 


12 


1.76 


1.68 


1.61 


1-54 


i .49 


J -43 


1.38 


II 


1 .92 


1.82 


i-74 


1.66 


i .60 


i-53 


1.48 


IO 


2 . I I 


2 OO 


i .90 


1.81 


1.73 


1.65 


i-59 


9 


2.35 


2.21 


2.08 


1.97 


1.88 


i-79 


1.71 


8 


2.65 


2.47 


2.31 


2.18 


2 .06 


1. 95 


1.86 


7 


3-3 


2.80 


2.59 


2.44 


2 . 27 


2.14 


2.03 


6 


3-55 


3-22 


2 .96 


2.74 


2-54 


2 3 8 


2 . 24 


5 


4.27 


3.81 


3-44 


3-J4 


2.89 


2.68 


2.50 


4 


5-37 


4-65 


4.11 


3.68 


3-34 


3-5 


2.8 3 


3 


7- 2 3 


5-97 


5- J o 


4-45 


3-96 


3-5 6 


3-25 


2 


ii .06 


8-34 


6.71 


5-63 


4.85 


4.27 


3.82 


I 


23-5 1 


13-83 


9-83 


7.64 


6 . 27 


6.12 


4.64 



into the U-form absorbing vessels, D, E, F, 
each time being returned to and measured 
in A. In passing into the U-shaped vessels, 
the gas displaces the liquid contained therein , 
driving it up into the other legs. A portion 
of the fluids, however, adheres to the glass 



monoxide in a solution of cuprous chloride. 
The reduction in volume measured in A 
gives the percentage of each constituent 
gas. 

The connections to A are made through 
the glass stop cocks M and the capillary 



*SOLUTIONS FOR ORSAT APPARATUS 

For absorbing CO 2 Caustic Potash. Dissolve one part by weight of caustic potash in two and one- 
half parts of water. 

For absorbing O Pyrogallol. Dissolve one part by weight of pyrogallic acid in two parts of hot water, 
and three parts of caustic potash solution, made as above directed. 

For absorbing CO Cuprous Chloride. Dissolve one part by weight of cuprous chloride in seven parts 
of hydrochloric acid, then add two parts of copper clippings and let stand for twenty-four hours, after- 
wards adding three parts of water before use. 



APPLICATION OF FORMULAS AND RULES 



185 



tube C. The movement of the gases is 
produced by lowering or raising the bottle 
L, which is connected to the lower part of 
A by the rubber tube S, and is partially 
filled with water. When a measurement 
is taken, the level of the water in A and L 
must be the same, so that all measurements 
are taken at atmospheric pressure. A con- 
stant temperature of the gas in A is main- 
tained by the water in the surrounding 
cylinder shown. 

The sample is drawn into the apparatus 
through the cock B, which also serves to 
connect the capillary tube to the atmos- 
phere, the latter connection being through 
the spindle of the cock; this permits the 
removal of any excess of gas above 100 cc 
that may have been drawn into A. Before 
the sample is drawn, the vessels D, E and F 
should have their respective liquids raised 
to the cocks M (which can then be closed, 
and the atmospheric pressure acting through 
the other leg, which is open, will keep them 
filled) ; the burette A and the capillary tubes 
should be filled with water up to the cock B. 
All this can easily and quickly be done by 
raising and lowering L, and opening and 
closing cocks M and B. The absorption 
of oxygen and carbon monoxide is very slow, 
and the gas should be passed back and forth 
a number of times until a reduction of 
volume is no longer indicated. 

As the pressure of the gases in a flue is 
less than the atmospheric pressure, they 
will not, of themselves, flow through the 
rubber or metal tubing connecting to the 
analyzing apparatus; but by filling the 
instrument two or three times and discharg- 
ing it into the atmosphere through cock B, 
the air can be removed from the connecting 
tubing and a sample of the gas be obtained. 
For rapid work, an aspirator can be used 
for drawing the gas from the tube in a con- 
stant stream. If this is used there is less 
danger of an admixture of air. It is some- 
times desirable to take a sample that repre- 
sents an average during half an hour or an 
hour, and in this case a metal or glass vessel 
with a stop -cock at both top and bottom, 
and filled with water, can be connected 
through the upper stop-cock to the flue, and 
the bottom cock then be opened. The water 
will gradually drip out, drawing the gas into 



the vessel. The time taken to fill it can 
be regulated by the lower cock. 

The result of a flue-gas analysis depends 
both on the manner and time of taking the 
sample, and to get at the average compo- 
sition of the gas, a number of determinations 
should be made on samples from different 
parts of the flue. 




FIG. 42. ORSAT APPARATUS FOR FLUE-GAS ANALYSIS 

The analysis made by the Orsat apparatus 
is volumetric; if the analysis by weight is 
required it can be .found from the volumetric 
analysis as follows: 

Multiply the percentages by volume by the 
molecular weight of the gas, and divide by the 
sum of all the products; the quotient will be 
the percentage by weight. 

The molecular weights are as follows: 
Carbon dioxide .... 44 
Carbon monoxide. . . . 28 
Oxygen ...... 32 

Nitrogen 28 

Application of Formulas and Rules 
Pocahontas coal used in a furnace was 
composed of 82.1 % Carbon 

4.25% Hydrogen 
2.6 % Oxygen 
6. % Ash 




186 



THE STIRLING WATER-TUBE SAFETY BOILER 



C0 2 =10.6% 

O = 10. 
CO = o. 

N =79.4 
analysis by 



The flue-gas analysis gave 
Carbon dioxide .... 
Oxygen ... 
Carbon monoxide 
Nitrogen (by difference) 

Determine : The flue-gas 
weight, the amount of air required for perfect 
combustion, the actual weight of air per 
pound of coal, the weight of flue-gas per pound 
of coal, the heat loss in chimney if gases are 
discharged at 500 F., and the ratio of the 
air supplied per pound of coal to that theo- 
retically required. Solution: 

Weight of air for perfect combustion= 
( .821 .026 ) 

34.56XJ * *" > = 

v O 



Weight of flue-gases per pound of coal= 
18.64+1 -.06=19.58 Ibs. (Formula 46) 

Heat lost in flue-gases per pound of coal= 
.24X19.58 X (500-60) = 2063.25 B. T. U.'s. 
(Formula 49) 

The coal contains about 14,500 B. T. U.'s, 

2 06^ 2 C 

so there is ^ =14.2% of the heat lost 

14,500 

in the flue-gases. 

Ratio of air supplied to that required= 

^^ =1.90 (Formula 48.) 

.794-. 10X3- 782 

This may also be calculated from the first two 
18.64 



.0425- 



= 10. 8 1 Ibs. 



results above, 



1.72, the difference 



(Formula 43) 

Actual weight of air per pound of coal= 
794 



3-Q32X- 
( Formula 44) 



106 .00 



X .821-18.64 Ibs. 



10.81 

between this ratio and that obtained from 
Formula [48] being due to inaccuracies in 
either the flue-gas or coal analysis, or in both. 
Table 56 shows the method of converting 
a flue-gas analysis by volume into an an- 
alysis by weight. 



TABLE 56 
ANALYSIS OF FLUE-GASES 



GAS. 


Analysis by 
Volume. 


Molecular Weight. 


Volume X 
Molecular Weight. 


Analysis by Weight. 


Carbon dioxide . . (CO 2 ) 
Carbon monoxide . . (CO) 


10. 6 
0.0 
10. 

79-4 


12 + 2 X l6 
12 + l6 
2 X l6 

2 X 14 


466 . 4 

0.0 

320 . o 

2223 . 2 


466.4 


5% 

o% 

7% 
8% 


3.009.6 
O . O 


3009 . 6 
320.0 


Nitrogen . .. . '. (N) 


3009.6 

2223 . 2 

i 


f. '3 
3009.6 


Total . . 


. 3009.6 



Steam Boiler Efficiency 



The efficiency of a boiler is the ratio be- 
tween the heat units utilized in production 
of steam, and the heat units contained in 
the fuel used. But whenever solid fuel such 
as coal is used, it is impossible to prevent 
a portion of it from falling through the 
grates, where it mixes with the ashes without 
burning, and generates no heat. The boiler 
itself cannot justly be charged with failure 
to absorb the heat value represented by the 
fuel wasted through the grates, but the boiler 
owner must pay for the fuel so wasted, and 
is justified in charging this waste to the 
combination of boiler and furnace. The heat 
supplied to the boiler is that due to the com- 
bustible actually burned, irrespective of how 
much may be dropped through the grates. 
In consequence two efficiencies may be de- 
termined, viz.: 

(1) Efficiency of the boiler= 

Heat absorbed per Ib. of combustible [51] 
Heat value of one Ib. of combustible* 

(2) Efficiency of boiler and grate= 
Heat absorbed per pound of fuel [52] 
Heat value of one pound of fuel, 

The first is of value in comparing relative 
performances of boilers apart from the par- 
ticular kind of grate used under them; the 
second is of value in comparing performances 
of different kinds of fuels, grates, etc., under 
the same boiler. If the loss of fuel through 
the grates could be wholly obviated, then 
the two efficiencies would be identical, as 
in case of a boiler fired with oil. Thus, if a 
coal contained 90% combustible, efficiency 
( i ) would be 

Heat absorbed per Ib. of fuel X . 90 
Heat value of one Ib. of fuel X. 90 

which reduces to efficiency (2). Similarly, 
efficiency (2) will in any particular case 
figure out the same whether the fuel be taken 
as dry coal, or coal as fired with its content 
of moisture. Example: If the coal con- 
tained 3% of moisture, efficiency (2) would be 



Heat absorbed per pound of dry coal X 0.9 7 
Heat value of one Ib. of dry coal X 0.97 

Here the content of moisture cancels out, 
hence efficiency (2) may be based on either 
dry coal, or coal as actually fired. 

Assume the following data : 
Steam pressure by gauge . . . 149 Ibs. 
Temperature of feed water . . . 84 F. 
Weight of coal as fired . . . . 7152 Ibs. 
Percentage of moisture in coal . . .96 

Total ash and refuse 286 Ibs. 

Percentage of moisture in steam . 0.5 
Total water evaporated .... 68664 Ibs. 

Analysis of the coal, by weight. 

Moisture 0.96% 

Ash 2.19 

Carbon f .. . .87.76 

Hydrogen 4 . 1 1 

Oxygen , nitrogen and sulphur . .4.98 



of 



100.00% 

dry coal by 



Heat value per pound 
calorimeter 15450 B. T. U. 

The factor of evaporation for the condi- 
tions named is 1.182, hence the equivalent 
evaporation from and at 212 is 68664 X 
1.182 = 81161 Ibs., and, corrected for the 
moisture present, is .5% less, or 80755 Ibs. 
of dry steam from and at 212. This contains 
80755X966 = 78,009,330 B. T. U. 

The dry coal fired was 

7152- ( .0096X7152) = 7083 Ibs. 
The ash-pit contained 286 Ibs. of ash and 
refuse, whence the combustible, or coal dry 
and free from ash, was 7083286=6797 Ibs. 
The heat units in the steam are therefore: 

Per pound of coal as fired, 

78,009,330 = I0907 B T n (a) 



Per pound of dry coal, 
78,609,330 



7083 

Per pound of combustible, 
78.009,330 






6797 



= 11477 B.T. U. (c) 



*By combustible is here meant that part of the fuel dry and free from ash. Nitrogen and oxygen are 
thus included. Neither is combustible in strict accuracy, but custom has included them, as they form 
part of the volatile content of coal. 

187 



COMBUSTION RATE CHART 



DIAGONAL LINES REPRE- 
SENT POUNDS OF COAL 
BURNED PER SQUARE FOOT 
OF GRATE PER HOUR 



RATIO OF HEATING SURFACE TO GRATE SURFACE 




4.5 



85% 



u. 8 



BOILER EFFICIENCY CHART 



DIAGONAL LINES 

REPRESENT PERCENTAGES 

OF EFFICIENCY 




5.6 



4.5 



,000 8,000 



9,000 10, 

HEAT VALUE IN 



000 11,000 12,000 13,000 14,000 15,000 1 6,000 

B.T.U. PER POUND OF FUEL OR COMBUSTIBLE. 



DISTRIBUTION OF HEAT LOSSES 



191 



The heat value per pound of dry coal, as 
given by the calorimeter, is 15450. Since 
the moisture in the coal amounted to 0.96%, 
the heat value per pound of "coal as fired" 
is (100 .oo96)X 15450 = 15302 B. T. U. 
The analysis shows that the combustible 
portion of the coal amounts to 87. 76+4. n + 
4.98=96.85% of the original coal, and 
15302-^.9685 = 15800 nearly. Hence the heat 
values of the fuel are : 

Per pound of coal as fired 15302 B. T. U. (d) 
Per pound of dry coal . 15450 B. T. U. (e) 
Per pound of combustible 15800 B. T. U. (f) 
and the efficiencies are : 
Based on coal as 

fired .... 10907-^-15302 = 71.28% 
Based on dry coal . 11013-^15450 = 71.28% 
Based on combust- 

ble .... 11477-^-15800 = 72.64% 

Efficiency and Combustion=Rate Charts 

The charts on pages 188 and 189 illustrate 
the relation existing between heat value, 
evaporation, efficiency, heating surface, grate 
surface and combustion rate, as factors in 
steam boiler operation, and the two charts 
may be used separately or jointly, as the 
conditions of the problem may determine. 
Only one assumption is made, viz.: that 
ten square feet of heating surface represent 
one boiler horse-power, and that, in conse- 
quence, at rating a boiler evaporates 3.45 
pounds of water (from and at 212) per 
hour per square foot of heating surface. 
Given the equivalent evaporation and calor- 
ific value of the fuel in any case, the efficiency 
(of the boiler, or of boiler and grate, accord- 
ing as the evaporation and heat-value are 
referred to combustible or to coal as fired] 
is shown by the diagonal passing nearest 
the intersection of the lines corresponding 
to the other two quantities; in the right- 
hand chart the corresponding combustion 
rates, at rating and 50% above rating, are 
indicated on the diagonal nearest the in- 
tersection of the lines for the equivalent 
evaporation and ratio of heating surface to 
grate surface. 

If, on the other hand, it is desired to ob- 
tain a certain rate of evaporation with a 
boiler of known ratio of heating surface to 
grate surface, the right-hand chart will 
indicate the amount of fuel per square foot 



of grate which must be burned to obtain 
such evaporation, and by reference to the 
left-hand chart the heat value of the coal 
necessary to obtain this evaporation at any 
given efficiency may be determined. 

Distribution of Losses The efficiency of 
a boiler, whether based on the combustible 
or the dry coal, will be found to range from 
50% to 80%, and in some cases higher. The 
difference between the actual efficiency and 
1 00% is the loss occurring in the conversion 
of the heat energy of the coal into that con- 
tained in the steam. This loss is made up 
of items as follows: 

(1) Loss of fuel through the grate. 

(2) Unburned fuel carried beyond the 
bridge wall in the form of soot or small 
particles. 

(3) The heat required to raise the tem- 
perature of the moisture in the coal from 
atmospheric temperature to 212, to evapo- 
rate it at that temperature, and to superheat 
to the flue-gas temperature the steam thus 
formed. 

(4) The loss due to the presence of hydro- 
gen in the fuel, which forms water which must 
be evaporated and superheated as in Item 3. 

(5) Superheating the moisture in the air 
supplied, from the prevailing atmospheric 
temperature to that of the flue-gases. 

(6) Heating the products of combustion 
(excepting the steam) to the flue-gas tem- 
perature. 

(7) The loss due to incomplete combus- 
tion when carbon burns to carbon monoxide 
(CO) instead of to carbon dioxide (CO 2 ), 
and when the volatile gases pass out through 
the stack unburned. 

(8) The loss due to radiation of heat from 
the boiler and furnace. 

It would require an elaborate test to as- 
certain each one of those items, and in 
practise it is customary to summarize them 
as follows: 

(a) Loss due to moisture in the coal; 
this refers to the hydroscopic moisture only. 
Loss due to moisture formed by burning 
the hydrogen in the fuel. These two losses 
in B. T. U.= 

(gH+VV) [212-^ + 965. 8 +0.48(^-2 12)] 

In which H and W are the proportional 
part, referred to the combustible, of the 



192 



THE STIRLING WATER-TUBE SAFETY BOILER 



hydrogen and water; / the fire room tem- 
perature, and T the breeching temperature. 

(b) Loss due to heat carried off in chim- 
ney gases, equal in B.T U. to (T-t)Xo. 24* 
X weight of gases per pound of combustible. 

(c) Loss due to incomplete combustion 
of carbon, forming CO, equal in B. T. U. to 

10.150 CO 
(CO, + CO) 

in which CO, and CO are percentages by 
volume of the flue-gases and C is proportion- 
al part of carbon in the combustible. 

(d) Heat unaccounted for, equal to total 
heat generated, less the sum of that utilized 
and the losses (a), (b) and (c). This includes 
the losses under items (2,) (5) and (8) as 
.above, and loss from un consumed gases. 

A schedule of these losses is called a "Heat 
Balance." To make it requires an evapora- 
tive test of the boiler, an analysis of the 
flue-gases, an ultimate analysis of the coal, 
and a calorimeter determination of its heat 
value. 

Example: To illustrate the application of 
the foregoing the following data from a 
test of a 517^ H. P. Stirling boiler may be 
taken : 



Steam pressure, absolute ... 

Temperature of stack 

" fire-room 
" feed-water 

Weight of coal as fired, per hour, 

Moisture in coal 

Weight of dry coal, per hour . 

Ash arid refuse, per hour . 

Ash and refuse, per hour 

Combustible per hour 

Calorific value of combustible per 

Analysis of dry coal 



lb.. per sq. in. 
deg. F. 



175.7 

481 .o 
87. 
76.7 

153. i 

2-7 

1489.8 

113.6 

7.6 

1376. 2 
15696 



Evaporation, actual, per hour 
Moisture in steam .... 
Analysis of flue-gases . 



. . Ibs. 

per cent. 
. . Ibs. 
. . Ibs. 

percent. 
. . Ibs. 
pound B. T. U. 

C= 83 . 84% by weight. 
H= 4.72 
O= 3-77 
N= 1.65 
S= 1.07 
Ash= 4.95 

100 .00% 

. . Ibs. 14577-9 

per cent. . 7 

002=13.5% by volume 

O= 5.8 

CO= o.i 

N=8o.6 



100.0% 

Since the steam contains .75% moisture, 
the dry steam per hour amounts to 14,577 .9 
X ( ioo. oo- o. 7 5) = 1 4, 468. 6 Ibs. 



The absolute steam pressure being 157.7 
Ibs. and the temperature of the feed 76.7, 
the factor of evaporation is 1.1911; and 
the equivalent evaporation per hour from 
and at 2 12, is 14,468.6X1 .1911 = 17,233.5 Ibs. 

J 7. 233. 5-1376. 2 = 12.523 U. E.| per Ib. 
of combustible 

17.233.5-1489.8=11.568 U. E. per Ib. of 
dry coal. 

12.523X965.7 = 12093.4 B. T. U. in steam 
per Ib. of combustible 

11.568X965.7.1=11171.2 B. T. U. in steam 
per Ib. of dry coal 

The calorific value of the fuel, per pound 
of combustible, is 15696. The combustible 
amounts to 100-4. 95^=95 .05% of the dry 
coal, whence the calorific value of 'i Ib. of 
the dry coal is 9505X15696 = 14919 B. T. U. 
and the two efficiencies are, 

Efficiency of boiler - =. 7704 

15696 

= 77 .04 per cent, based on the combustible. 

Efficiency of boiler and grate= 

14919 

.7487 = 74.87 per cent., based on the dry coal. 
The heat losses are calculated as follows: 

(a) Loss due to moisture in coal. The 
content of moisture referred to combustible 
is 2.7-89.88!! =.03, and this loss is .03X1X212- 
76.7)+966J +0.48 (48i-2i2)]=36.9o B.T.U. 

From the ultimate analysis, the hydrogen 
in the coal is seen to be 4.72%, therefore the 
loss due to burning hydrogen is, 
9X^472 X [(212-76.7)+ 966+0.48 (481 - 

212)1=522.5 B. T. U. 

(b) To compute the loss of heat in the 
dry chimney gases per pound of combustible, 
the weight of the gases must first be ascer- 
tained. 

From formula [46] page 183 the weight of 
gases per pound of coal as fired is, 
3.032 XXC , 



C0 2 +CO 



3.032X80.6X0.8384 



+ (1-0.0495) 



= 16.01 Ibs. 
Hence the weight of flue-gases per pound of 



*Specific heat of chimney gas. fU. E.=Units of evaporation. See p. 72. 965. 8 would be more 
exact, but 966 is recommended in the Code of 1885. gNote that this is the real ash as determined 
from the ultimate analysis, hence is the value to use in determining the B. T U. per pound of dry coal. 
|| Combustible consumed per hour-:- coal as fired per hour. Note the difference between the combus- 
tible as a per cent, of the coal as fired, and of the dry coal. 




VARIATION OF EFFICIENCY WITH RATE OF DRIVING 



193 



combustible is 16.01-^ .8988=17.81 Ibs., 
therefore the loss of heat in stack is 

17.81X0.24 (48i-87) = i684 B. T. U. 
(c) Loss due to incomplete combustion. 
From the ultimate analysis the per cent, of 
carbon in the combustible is 

-=88 .2%, hence this loss is 



100-4.95 

o. 1X0. 882+10150 



= 65.35 B.T. U. 



I3-5+ - 1 

(d) The above determined losses amount 
to 36.90 + 522.5 + 1684+65.35=2308.75 B. 
T. U. The heat absorbed by the boiler per 
pound of combustible is 12093.4 B. T. U., 
hence the total heat accounted for is 12,093 . 4 
+ 2,308.75=14,402.15 B. T. U. But the 
calorific value of one pound of combustible 
is 15,696 B. T. U., hence 

Heat unaccounted for 

= 15.696-14,402.15 = 1293.85 B. T. U. 

The heat balance should be arranged thus: 

HEAT BALANCE 

Total heat of i Ib. of Combustible = 
15696 British Thermal Units. 



DISTRIBUTION OP THE HEAT. 


B. T. U. 


PERCENT 


i. Heat absorbed by the boiler 


I 2,093.4 


77 .04 


2. Loss clue to moisture in coal 


36.0 


2 4 


3. Loss due to moisture formed by the 






burning of hydrogen .... 
4. Loss due to heat carried away in dry 


522.5 


3-33 


chimney-gases 


1,684.0 


IO -73 


5. Loss due to incomplete combustion 








65 ^ 




6. Unaccounted for 




8 24 








Totals 


15,696 .OO 


100 .00 



Application of the Heat Balance- 
Whenever a boiler test supplies data for making 
a heat balance, it should be made, particu- 
larly if the boiler performance is considered 
unsatisfactory. The distribution of the heat 
is thus determined and any extraordinary 
loss can be detected and steps be taken to 
reduce it. 

The heat absorbed to produce steam will 
range from 50 to 80 per cent., or more, 50% 
being very poor efficiency and 80% very 
high; in judging efficiencies the character of 
fuel must always be considered, since an 
efficiency that would be regarded as high for 
one fuel might be very low for another. 



The loss due to moisture in the coal is 
small but appreciable. Therefore coal should 
be kept under roof, and should not, as in 
some plants, be wetted before using. 

The largest heat loss is due to the chimney- 
gases. The factors affecting this are the 
amount of gas and the temperature at which 
it leaves the boiler. There is a lower limit 
to the amount of gas, fixed by the minimum 
air supply with which thorough combustion 
may be obtained. This limit usually is 18 
pounds of air per pound of coal. The limit 
may be still lower when burning gas or oil. 
If the air supply is too small, the loss due 
to carbon burning to carbon monoxide will 
be increased. The stack temperature is 
limited, with natural draft, to not much less 
than 450, since a lower temperature causes 
loss of draft and a low heat transfer from 
gases to water in the boiler. Artificial draft 
and economizers may reduce these limits, and 
whether or not they can save enough to 
compensate for the extra outlay is a problem 
to be solved for each particular case. 

Variation of Efficiency with Rate of 
Driving Under any set of conditions there 
is one rate of evaporation per square foot 
at which the greatest efficiency will be 
developed, and there will be a falling off for 
both higher and lower rates of evaporation. 
The grade of fuel, skill with which it is fired, 
the air supply, condition of boiler surfaces, 
and temperature of steam and of feed water, 
are some of the factors which affect the re- 
sult, hence no exact figure for the rate of 
evaporation which will give the greatest 
efficiency can be given. Under average 
conditions it varies from 3 to 4 pounds per 
square foot of heating surface from and at 
212 per hour for water-tube boilers. As 
the rate is increased the drop in efficiency 
varies greatly for different types of boiler 
and the kind of fuel. The matter is of the 
utmost importance in plants where the boilers 
must be operated at high rates of evapora- 
tions for several hours daily to carry peak 
loads. The Stirling boiler falls off in effi- 
ciency, as the load is increased, much less 
rapidly than other types, because of the 
efficient absorption of heat in the rear tube 
bank where the feed water enters. See 
"Possibility of Driving at Both High and 
Low rates of Evaporation," page 27. 



Horse-Power Rating of Boilers 



Work, as the term is used in mechanics, is 
the overcoming of a resistance through space. 
The unit of work is the foot-pound. 

Power is the rate at which work is done, or 
is the amount of work done in one unit of 
time. The unit of power in general use 
among steam engineers is the Horse- 
power,* which is equivalent to 33,000 
foot-pounds per minute, or the work done 
in lifting 33,000 pounds i foot high, or 33 
pounds 1,000 feet high, or 1,000 pounds 33 
feet high, etc., in one minute. 

Horse=Power of Boilers Boilers for 
land use are usually rated in "horse-power," 
and few terms used in engineering are more 
often misunderstood. 

A boiler when in service does not move, 
hence*it does no work in the sense in which this 
word is used in mechanics, therefore it has 
no power. What it really does is to generate 
steam which acts as a vehicle to convey the 
energy of the fuel, in the form of heat, to 
an engine which converts that heat into 
work and develops power. If every engine 
developed precisely the same power from 
an equal amount of heat, the boiler might 
conveniently be designated as a boiler 
having the same horse-power as the engine; 
though inaccurate, the statement could 
through custom be interpreted to mean that 
the boiler is of just the capacity required 
to supply the steam necessary to generate 
the given horse-power in an engine. Un- 
fortunately, engines of different sizes and 
types require widely different amounts of 
steam to produce the same power, hence a 
boiler which could supply enough steam to 
produce 500 H. P. in one engine might be 
able to supply only enough to produce 300 
H. P. in another engine which is of less 
economical design. 



Present Meaning of (Stationary) Boil= 
er Horse=Power To obviate the confusion 
resulting from an indefinite meaning of the 
term boiler horse-power, the judges in charge 
of boiler trials at the Centennial Exposition 
ascertained that a good engine of the then 
prevailing types required about 30 Ibs. of 
steam per hour per horse-power developed. 
In order to establish a relation between the 
engine power and the size of boiler needed to 
furnish steam to develop that power, they 
recommended that an evaporation of 30 
pounds of water per hour from an initial 
feed temperature of 100 F. to steam of 
70 pounds gauge pressure be considered as 
one boiler horse-power. The standard thus 
laid down has been generally accepted by 
American engineers, and whenever in this 
countryt the term boiler horse-power is 
used in connection with stationary boilers! 
without special definition, it is to be under- 
stood as having the meaning above defined. 

To permit easy comparison of results of 
boiler trials, it is usual to reduce them all 
to a basis of equivalent evaporation from 
and at 212 F. One boiler horse-power as 
above defined is equivalent to an evapora- 
tion from and at 212 F. of 34.486 Ibs. of 
water, or practically 34. 5 Ibs., hence, 

One boiler horse-power is equal to an evapora- 
tion per hour of 30 Ibs. of water from 100 F. 
to steam at jo pounds pressure; or is equal 
to an evaporation of 34. $ pounds of water per 
hour from and at 212 F. It is, therefore, 
purely a measure of evaporation, and not 
of power. 

Selection of Boilers to Operate an En= 
gine of given Power To determine the 
rated horse-power of boiler necessary to devel- 
op a given power from an engine, it is neces- 
sary to determine the amount of steam re- 



*The French horse-power (cheval) is seventy-five kilogrammeters per second = 75X7.233 foot-pounds = 
542.5 foot-pounds per second, or somewhat less than that used by English-speaking nations, which is 
equal to 550 foot-pounds per second. Hence, 

One horse-power =1.0139 cheval 
One cheval = .9864 horse-power 

fin other countries boilers are usually rated, not in horse-powers, but by specifying the quantity of 
water they are to be capable of evaporating from and at 212, or under other conditions which can be 
reduced to equivalent evaporation from and at 212. 

JWhen the horse-power of marine boilers is stated it generally refers to and is synonymous with the 
horse-power developed by the engines which receive steam from the boilers. 

See "Equivalent evaporation from and at 212," page 69. 

13 IQ5 



196 THE STIRLING WATER-TUBE SAFETY BOILER 

TABLE 57 

INDICATED HORSE-POWER PER BOILER HORSE-POWER FOR VARIOUS 
AMOUNTS OF STEAM PER I. H. P. AXD FACTORS OF EVAPORATION 



Factor of 






















Evaporation. 


1 . 02 




I . O t 




1.07 


5 


I . 




i . i 


'-5 


Actual Water 
Consumption 
of Engines 
per I. H. P. 
per Hour. 


Equivalent 
Evaporation 
per 
I. H. P. 


Engine 
H.P. 
per 
Boiler 
H.P. 


Equivalent 
Evaporation 
per 
I. H.P. 


Engine 
H.P. 
per 
Boiler 
H.P. 


Equivalent 
Evaporation 
per 
I. H. P. 


Engine 
H.P. 
per 
Boiler 
H.P. 


Equivalent 
Evapor- 
ation per 
1. H. P. 


Engine 
H. P. 
per 
Boiler 
H. P. 


Equivalent 
Evapor- 
ation per 
I. H. P. 


Engine 
H.P. 
per 
Boiler 
H.P. 


ro. 


10. 25 


3.36 


10.5 


3-28 


10.75 


3-21 


I I . O 


3 - i 3 


ii .25 


3.06 


to. S 


10. 76 


3.20 


1 1 . 02 


3- 13 


11.30 


3.05 


11-55 


.98 


ii .81 


9 2 


ii . 


11.27 


3.06 


n-55 


.98 


11.83 


.91 


I 2 . IO 


-85 


12.37 


79 


ii. S 


11.78 


03 


12 .07 


.85 


12.38 


.78 


12 . 65 


-73 


12.94 


.67 


I 2 . 


12.30 


.80 


I 2 . 6O 


73 


12 .90 


.67 


13. 20 


.61 


13.5 


.56 


12.5 


I 2 . 8l 


.69 


13.12 


.62 


13-44 


.56 


13.75 


-50 


14.06 


45 


13- 


1 .3 - 3 2 


59 


I.i.65 


52 


13.98 


49 


14.30 


4i 


14. 62 


36 


13.25 


13.58 


54 


I3-9I 


47 


14- 25 


.42 


14.57 


37 


14.91 


31 


I3-S 


I3.8 4 


.49 


14. I? 


43 


14.52 


.38 


I4.S5 


32 


15.19 


27 


13-75 


14.09 


45 


14-43 


37 


14.72 


33 


15.12 


.28 


15-47 


23 


14. 


14-35 


40 


14. 70 


33 


15.05 


.29 


15-4 


24 


15.75 


'9 


14- 25 


14. 60 


.36 


14.96 


.29 


15.32 


25 


15 .67 


. 20 


16.03 


IS 


14-5 


14.86 


32 


15.22 


25 


15-59 


. 2 1 


15.95 


. K) 


16.31 


. 12 


14. 7. S 


15.12 


.28 


15.48 


. 2 I 


15-86 


- I 7 


l6. 22 


. 1 2 


16.59 


.08 


IS- 


15.38 


24 


15-75 


. 18 


16.13 


13 


16.5 


.09 


16.87 


OS 


IS- 25 


15-63 


. 21 


16. 01 


IS 


1 6. 40 


. IO 


10.77 


. 06 


17.16 


.01 


15-5 


15.89 


17 


16.27 


. I 2 


16.67 


.07 


17 -05 


.03 


17 -45 


.98 


15.75 


16.14 


- 13 


16.53 


.08 


16.94 


.04 


[7.32 


99 


17.72 


95 


16. 


16.40 


. IO 


16.80 


05 


17 . 20 


. OI 


17 . OO 


.96 


18.00 


92 


16. 25 


16.65 


. 06 


17 .06 


. O I 


17-47 


.98 


17-87 


94 


18.28 


.89 


16.5" 


16.91 


03 


17-32 


.98 


17-74 


94 


i 8 . i S 


-1)0 


18.56 


.86 


16.75 


17.16 


.00 


17-58 


95 


iS.OI 


.91 


18.42 


.87 


18.84 


83 


17. 


17.42 


.98 


17-85 


93 


I 8 28 


.88 


18.7 


-84 


19.12 


.80 


17-25 


17.67 


95 


i8.ii 


.91 


18-55 


.86 


18.97 


.82 


19.40 


77 


17-5 


17-93 


92 


18.37 


87 


18.81 


.83 


19- 25 


.So 


19.69 


75 


17-75 


18. 19 


.89 


18.63 


-84 


19- 13 


.80 


I9.52 


77 


19.97 


.73 


18. 


18.45 


.87 


1 8 . 90 


.81 


19-35 


77 


19.8 


74 


20 . 25 


.70 


18.25 


18.70 


.85 


19 . 16 


78 


I 9 . 6 2 


-75 


20 . 07 


71 


20.53 


67 


18.5 


18.96 


.82 


19-43 


76 


19.89 


73 


20.35 


.69 


20.81 


65 


i8-75 


19 . 22 


79 


19.69 


74 


20.15 


7i 


20. 62 


67 


2 I . 09 


63 


19. 


19.48 


.76 


19-95 


72 


30.42 


.69 


20.9 


65 


21 .37 


.61 


19- 25 


19-73 


74 


2O. 21 


.70 


20. 69 


.67 


21.17 


63 


21.65 


59 


iQ-5 


19.99 


-7i 


20.47 


.67 


2O . 96 


.64 


21 .45 


.61 


21 .93 


57 


19-75 


2O . 24 


.69 


20.73 


.65 


21 . 23 


.62 


21.72 


59 


22.22 


55 


30. 


20. 50 


-67 


21 .OO 


.63 


21 . 50 


.60 


22 . O 


57 


32. 50 


S3 


30. 25 


2O . 76 


.65 


21 . 26 


.61 


21 .77 


.58 


22 . 27 


54 


22.78 


Si 


20. S 


21 .02 


.63 


21 .52 


59 


22 . 04 


.56 


22.55 


52 


23.06 


-49 


20.75 


21.27 


.61 


21 .78 


57 


22.31 


54 


22.82 


51 


23.34 


47 


31 . 


21.52 


.60 


22.05 


.56 


22.58 


53 


23. 10 


.49 


23.62 


.46 


21.25 


21 .77 


58 


22.31 


54 


22.84 


Si 


23.37 


47 


23.91 


44 


31-5 


22 .03 


.56 


22.57 


52 


23.11 


49 


23.65 


-45 


24. 20 


42 


21.75 


22 . 29 


-54 


22.83 


50 


33.38 


47 


23.92 


43 


24.47 


40 


22. 


22.55 


52 


23. 10 


.40 


23.65 


.46 


24.2 


42 


24-75 


39 


22. S 


25 .06 


49 


23.62 


45 


24- 19 


42 


24.75 


39 


25 -31 


-36 


23- 


23.58 


.46 


24. 15 


-42 


24.73 


39 


25.3 


36 


25.87 


33 


23-5 


24.09 


43 


24.67 


.39 


25 26 


.36 


25.85 


33 


26 .43 


30 


24- 


24.60 


40 


25 . 20 


-36 


25.80 


.33 


26.4 


.30 


27 .OO 


.28 


24-S 


25.11 




25.72 


.33 


26. 34 


.30 


26.95 


27 


27.5<' 


25 


25 


25.63 


-34 


26 . 25 


. 3 I 


26.88 


. 2.S 


27 .5 


25 


28. 12 


23 


25-5 


26. 14 


32 


26.77 


29 


27 -42 


.26 


28.05 


. 23 


28.68 


. 21 


26. 


26.(, 5 


29 


27.30 


. 20 


27.95 


. 23 


28.6 


. 20 


29. 25 


.18 


26.5 


27 . l6 


27 


27.82 


24 


28.49 


. 21 


29. 15 


. i 8 


29 . 80 


.16 


27- 


27.68 


.24 


28.35 


. 22 


29.03 


19 


29.70 


. i 6 


30.37 


14 


27 - 5 


28. 10 


. 22 


28.87 


. 2O 


29. 56 


17 


30. 25 


14 


30.43 


. I 2 


28. 


28.70 


. 2O 


29.40 


. 17 


30 . 10 


14 


30.8 


. i i 


31 50 


.09 


2Q. 


29.72 


. 16 


30.45 


13 


31.18 


. I I 


3i-9 


.08 


32.62 


05 


30. 


30.75 


. I 2 


3 i . 50 


.00 


32.25 


.08 


33-0 


.05 


33 73 


.02 


31- 


31.78 


.08 


32.55 


-05 


33.32 


.03 


34- i 


.02 


34.87 


99 


32. 


32.80 


.5 


33.6o 


.02 


34.40 


.OO 


35-2 


.98 


36.0 


.96 


33- 


33.83 


.02 


34.65 


99 


35.47 


97 


36.3 


.95 


37-12 


93 


34. 


34.85 


.99 


35-70 




36.55 


.94 


37-4 


.02 


38.25 


.00 


35- 


35.87 


.96 


36.75 


93 


37-02 


.91 


38.5 


.S,, 


39-37 


.87 


36. 


36.90 


93 


37.8o 


.90 


38.70 


.89 


39-6 


.87 


40. 5 


-85 


37- 


37.92 


.90 


38.85 


.88 


39-77 


.86 


40.7 


.84 


41 .02 


.82 


38. 


38.95 


.88 


39-90 


.86 


40.85 


.84 


41 .8 


.82 


42.75 


.80 


39- 


39.98 


.86 


40.95 


.84 


41 .92 


.82 


42.9 


.80 


43-87 


79 


40. 


41 .00 


.84 


42 . oo 


.82 


43.00 


.80 


44-0 


.78 


45. 


-77 


41 


42.03 


.82 


43.05 


.80 


44-07 


-78 


45-1 


.76 


46. 12 


75 


42. 


43.05 


.80 


44- 10 


.78 


45-15 


.76 


46. 2 


74 


47 25 


73 


43- 


44.08 


.78 


45- IS 


.76 


46. 22 


.74 


47 -3 


72 


48.57 


7i 


44- 


45- 1 


.76 


46. 20 


.74 


47-30 


.72 


48.4 


70 


40 - 5 


.69 


45- 


46 . i 2 


75 


47.25 


73 


48.37 


7 1 


49-5 


.69 


50. 62 


.68 



RELATION BETWEEN INDICATED AND BOILER HORSE-POWER 

TABLE 57 CONTINUED 

INDICATED HORSE-POWER PER BOILER HORSE-POWER FOR VARIOUS 
AMOUNTS OF STEAM PER I. H. P. AND FACTORS OF EVAPORATION 



197 



Factor of 


I . I 




1.17 




I . 2 




I . 2 


25 


I . 2 


5 


Evaporation. 






















Actual Water 
Consumption 
of Engines 
p-r I. H. P. 
per Hour. 


Equivalent 
Evaporation 
per 
I. H. P. 


Engine 
H. P. 
per 
Boiler 
H. P. 


Equivalent 
Evaporation 
per 
I. H. P. 


Engine 
H. P. 
per 
Boiler 
H.P. 


Equivalent 
Evaporation 
per 
I. H.P. 


Engine 
H.P. 
per 
Boiler 
H.P. 


Equivalent 
Evapor- 
ation per 
I. H. P. 


Engine 
H.P. 
per 
Boiler 
H.P. 


Equivalent 
Evapor- 
ation per 
I. H. P. 


Engine 
H.P. 
per 
Boiler 
H. P. 


o . 


I I .5 


2-99 


H.75 


-93 


12.0 


.87 


12.25 


2.81 


12.5 


.76 


o. 5 


12.57 


2.85 


12.33 


79 


12.6 


73 


12.86 


2 . 69 


13.12 


.67 


[ . 


12. 65 


2.72 


12.92 


.67 


13- 2 


.61 


13-47 


2. 57 


13.75 


.58 


r . 5 


13-22 


2 . 60 


13.51 


55 


13-8 


SO 


14 . 08 


2-45 


14.35 


44 


2 . 


1.5.8 


2.49 


14. 10 


44 


14-4 


39 


14.7 


2.35 


15.0 


30 


2 - 5 


14.38 


2 .40 


14.69 


35 


15-0 


30 


iS-31 


2. 25 


IS .62 


. 21 


3 . 


J4-95 


2.31 


15-28 


2S 


15. 6 


. 21 


15-92 


2. l6 


16. 25 


. 12 


1 .1 2 5 


15.23 


2 . 26 


iS-57 


. 21 


15.9 


-17 


l6. 22 


2.12 


16.56 


.08 


13.5 


15.52 


2.22 


15-86 


17 


16. 2 


13 


16.53 


2.08 


16.87 


04 


i .. 7 5 


15.81 


2. l8 


16. 15 


13 


16.5 


.09 


16.84 


2 . 04 


17.19 


.01 


14- 


16 . 10 


14 


16.45 


.09 


16.8 


-05 


I7-IS 


2 . OI 


17-5 


97 


14- 25 


16. 38 


. 10 


16. 74 


05 


17.1 


.01 


17-45 


1.97 


17.81 


93 


14- 5 


16.67 


. 06 


17.04 


. O2 


17.4 


.98 


17.76 


1-94 


18.12 


.90 


I4-7S 


16.96 


. 02 


17-33 


.98 


17-7 


-94 


18.06 


I . 90 


18.44 


87 


IS- 


17 25 


-99 


17.63 


95 


18. 


-91 


18.37 


1.8 7 


18.75 


.84 


15.25 


17.53 


.96 


17.92 


.92 


18.3 


.88 


18.68 


1.84 


19 . 06 


.81 


15-5 


17.82 


93 


l8. 22 


.89 


18.6 


8s 


18.98 


1.81 


19.37 


.78 


15-75 


1 8 . 1 1 


.90 


18.51 


.86 


18.9 


.82 


19. 29 


1.78 


19 . 66 


75 


16. 


18.40 


87 


iS.So 


83 


19.2 


-79 


19 .6 


1.76 


20. 


72 


16.25 


18.68 


.84 


19.10 


.80 


19-5 


76 


19.9 


1-73 


20.31 


.69 


16.5 


18.97 


.81 


19-39 


-77 


19.8 


74 


2O . 21 


i .70 


20.62 


.67 


l6.75 


IQ . 26 


.78 


19.68 


-74 


20 . i 


7i 


20. 51 


1.67 


20.93 


65 


17- 


19.55 


76 


19.98 


72 


20 . 4 


.69 


20.82 


1.65 


21 . 25 


.62 


17 25 


19.83 


73 


20. 27 


.70 


20. 7 


.66 


21.12 


i . 62 


21 . 56 


59 


17-5 


2O . I 2 


71 


20.56 


.68 


21 . 


.64 


21 -43 


i . 60 


21.87 


57 . 


17-75 


20. 41 


.68 


20.85 


-65 


21.3 


.62 


21.74 


.1.58 


22.18 


55 


18. 


2O . 7O 


.66 


21.15 


.63 


21.6 


59 


22.05 


1.56 


22.50 


53 


18.25 


20 . g8 


.64 


21 .45 


.60 


21.9 


57 


22.35 


i -54 


22. 8l 


Si 


18.5 


21.27 


.62 


21 .74 


.58 


22 . 2 


55 


22.66 


1-52 


23. 12 


49 


18.75 


21.56 


.60 


22 .0.3 


-56 


22.5 


S3 


22 . 96 


1.50 


23-43 


47 


10 . 


ai.Ss 


59 


22.33 


-55 


22.8 


5i 


23.27 


1.48 


23-75 


45 


ig. 25 


22. 13 


5f> 


22.62 


-54 


23-1 


.40 


23-57 


i .46 


24.06 


43 


19.5 


22 .42 


54 


22.91 


-52 


23.4 


47 


23-88 


1.44 


24-37 


.41 


ig.75 


22.71 


Si 


23.21 


49 


23.7 


45 


24- 19 


1.42 


24.68 


39 


20. 


23.0 


49 


23. 5 


47 


24 . o 


43 


24. 50 


1.41 


25 .00 


^38 


20. 2S 


23.28 


47 


23. 79 


-45 


24.3 


.41 


24.81 


1.39 


25.31 


.36 


20.5 


23-57 


45 


24. 08 


43 


24.6 


-40 


25.11 


1-37 


25 .62 


34 


20. 75 


23.86 


.43 


24-37 


4i 


24.9 


39 


25-41 


1-35 


25.93 


33 


21 . 


24- 15 


.42 


24-67 


40 


25.2 




25-72 


1-34 


26. 25 


31 


21.25 


24-43 


.40 


24.96 


37 


25- 5 


35 


26.02 


1.32 


26.56 


.29 


21 . 5 


24- 72 


39 


25.26 


.36 


25.8 


34 


26.33 


I-3I 


26.87 


.28 


21.75 


25.01 


-38 


25- 56 


-35 


26.1 


32 


26.64 


1.30 


27.18 


27 


22 . 


25.3 


.36 


25-85 


33 


26.4 


3i 


26.95 


1.28 


27.5 


.26 


22.5 


25.87 


-33 


26.43 


31 


27. 


.28 


27-56 


1.25 


28. 12 


23 


23- 


26. 45 


-30 


27 .02 


.28 


27 . 6 


25 


28.17 


I . 22 


28.75 


. 20 


23-5 


27 .02 


- 27 


27 . 61 


25 


28.2 


. 22 


28.78 


I.I9 


29-37 


-17 


24- 


27.6 


-25 


28 . 20 


- 23 


28.8 


19 


29.40 


I. 17 


30. 


IS 


24. 5 


28. 17 


. 22 


28.78 


. 20 


29.4 


17 


30.01 


I. 14 


30.62 


. 12 


25. 


28.75 


. 2O 


29-37 


.17 


30. 


IS 


30.62 


I . 12 


31-25 


. IO 


25.5 


29-32 


. 18 


29.96 


- IS 


30.6 


13 


31-23 


I . IO 


31.87 


.08 


26. 


29.9 


- IS 


30.55 


. I 2 


31.2 


. I I 


31.85 


I. 08 


32.S 


.06 


26. 5 


30.48 


- 13 


31 13 


. IO 


31.8 


.09 


32.46 


I .06 


33-12 


04 


27- 


3i -5 


. 1 1 


31 .72 


.00 


32.4 


.06 


33.07 


I .04 


33-75 


.02 


27.5 


31 -62 


.00 


32.31 


07 


33. 


.04 


33.63 


I .02 


34-37 


.OO 


28. 


32.2 


.06 


32.90 


.04 


33.6 


.02 


34-30 


I .OO 


35- 


.98 


29. 


33-35 


.02 


34.07 


. oo 


34-8 


99 


35-52 


97 


36.25 


93 


30. 


34-5 


90 


35-25 


97 


36. 


.96 


36.75 


94 


37- S 


-92 


31 . 


35.65 


. Q 6 


36.42 


.94 


37-2 


.92 


37-97 


.91 


38.7S 


.89 


32. 


36.8 


93 


37-6o 


9 2 


38.4 


.89 


39-20 


.88 


40. 


.86 


33- 


37-95 


.90 


38.77 


.89 


39-6 


.87 


40.42 


.85 


41.25 


.84 


34. 


39- I 


.88 


39-9S 


.87 


40.8 


.85 


41.65 


.83 


42.5 


.8r 


35- 


40. 25 


.85 


41.12 


.84 


42. 


.82 


42.87 


.80 


43-75 


.78 


36. 


41 .4 


-83 


42.3 


.81 


43.2 


.80 


44. 10 


.78 


45- 


76 


37- 


42.55 


.80 


43-47 


.78 


44-4 


78 


45.32 


.76 


46.25 


74 


38. 


43-7 


.78 


44.65 


.76 


45-6 


76 


46.55 


74 


47-5 


72 


39- 


44.85 


77 


45.82 


75 


46.8 


74 


47.77 


72 


48.75 


.70 


40. 


46. 


75 


47-00 


73 


48. 


72 


49.0 


70 


50. 


.68 


41- 


47- iS 


73 


48.18 


-7i 


49-2 


70 


SO. 22 


.68 


51.2 


.66 


42. 


48.3 


71 


49-35 


.69 


S0.4 


.63 


51-45 


.66 


52.5 


.65 


43. 


49-45 


.69 


50-52 


.68 


51.6 


.67 


52.67 


.65 


53-75 


.64 


44. 


50.6 


-67 


Si -70 


.66 


52.8 


.65 


53.90 


.63 


S5- 


63 


45. 


51-75 


.66 


52.87 


-65 


54. 


.63 


55-12 


.62 


56.25 


.62 



198 



THE STIRLING WATER-TUBE SAFETY BOILER 



quired to produce the given power in the en- 
gine, then ascertain the size of boiler requisite 
to generate this steam. The determination 
of the amount of steam needed by engines 
of various sizes, types and conditions, can be 
done only by making actual trials, or by 
reference to trials on similar engines. 



sure, engine speed, and point of cut-off. In 
modern plants using large compound con- 
densing engines with high pressure steam 
one boiler horse-power may be sufficient to 
develop two engine horse-power, including 
the steam necessary to operate pumps and 
other auxiliaries. A simple engine of ordi- 



TABLE 58 
STEAM CONSUMPTION, POUNDS PER INDICATED HORSE POWER* 





Steady 


Loads. 


Variable Loads. 


Extreme Variations, 
Railway Work, etc., 


TYPE OF ENGINK. 






50 to 125 per cent. 


o to 150 per cent. 




Non- 
Condensing. 


Condensing. 


Non- 
Condensing. 


Condensing. 


Non- 
Condensing. 


Condensing. 


High Speed, simple . 


3 2 


28 


34 


3 


36 


3 1 


High Speed, compound . 


23 


18 


2 5 


21 


27 


22 .5 


Slow Speed, simple . 


25 


21 


28 


2 3 


31-5 


26.5 


Slow Speed, compound . 


2O 


J 5 


22-5 


18 


26 


2 3 


High Speed, triple exp. . 


J 7-5 


13 


20 


16 






Slow Speed, triple exp. . 


14-5 


I2 -5 


17 


T 5 







Table 58 gives a rough approximation 
of the steam required per indicated horse- 
power for engines of different types : 

Such performance can be expected only 
from engines of good grade. Plain slide 
valve engines may use 55 to 60 Ibs. per 
hour per H. P. All similar tables are neces- 
sarily very approximate, since the steam 
consumption will vary with the steam pres- 



nary build, operated non-condensing, will 
require more than one boiler horse-power 
per engine horse-power, while direct acting 
steam pumps will require as much as two 
or more boiler horse-power per engine horse- 
power. Consequently, when designing a 
steam plant it is necessary to determine 
from the type of engine the steam that will 
be required, and to make the necessary 



TABLE 59 

REQUIRED HOURLY EVAPORATION PER BOILER HORSE-POWER 
AT VARIOUS FEED TEMPERATURES AND STEAM PRESSURES 



STEAM PRESSURE IN POUNDS BY GAUGE. 



f 


DllaAM r^lS.C*OOU IS.C/ UN rWUi>IL/O DX VJrtUVJfO. 


o 


10 


20 


3 


40 


50 


60 


7 


80 


90 


IOO 


I IO 


I2O 


130 


140 


150 


160 


170 


180 


190 


200 


50 


19.51 


29.29 


29.14 


29.02 


28.92 


28.84 


28 77 


28.70 


28.64 


28.59 


28.54 


28.49 


28.45 


28.41 


2837 


2833 


28.29 


28.26 


28.23 


28.20 


28.17 


60 


29 77 


29 55 


29.40 


29.28 


29.18 


29.09 


29.02 


28.95 


28.89 


28.84 


28.79 


28.74 


28.69 


28.65 


28.61 


285? 


28.54 


28.51 


28.48 


28 45 


28.42. 


70 


30.04 


29.81 


29.66 


29 54 


29-44 


29 35 


29.27 


29 21 


29.15 


29.09 


29 04 


28.99 


28.94 


28.90 


28 86 


28.82 


28.78 


28.75 


28.72 


28.69 


28.66 


80 


3031 


30.08 


29-93 


29.80 


29.70 


29.61 


29 53 


29.46 


29.40 


29 34 


29.29 


29.24 


29.19 


29 15 


29.11 


29.07 


29 03 


29 oo 


28.97 


28.94 


28.91 


90 


3 59 


3 36 


30.20 


30-07 


29-97 


29.88 


29.80 


29 73 


29.67 


29.61 


29 55 


29-50 


29 45 


29.41 


29 37 


29 33 


29.29 


29.25 


29.22 


29.19 


29 16 


100 


3088 


30.64 


30-47 


3034 


3 24 


30 15 


30.07 


30.00 


29 93 


29.87 


29 82 


29 77 


29.72 


29.67 


29 63 


29 59 


29 55 


29 5' 


29.48 


29-45 


29.42 


I 10 


3' '7 


3-93 


30 76 


3063 


3 52 


30.43 


3034 


30.27 


30.20 


3 '4 


30.09 


30.04 


29.99 


29.94 


29 90 


29.86 


29.82 


29.78 


29 74 


29.71 


29.68 


I 20 


31.46 


31.22 


3' 05 


3 Qi 


30.80 


30 7' 


3 63 


30.55 


30.48 


30.42 


3036 


30 3' 


30.26 


30.21 


3 '7 


3 '3 


30.09 


3005 


30.01 


29.98 


29 95 


'3 


3' ?6 


3' S^ 


3' 34 


31.20 


3' 09 


3099 


30 9' 


3083 


30 76 


30 70 


30.65 


30.59 


30 54 


3 49 


345 


30 41 


30 37 


3033 


30.29 


30 25 


30.22 


140 


32 07 


31.82 


3' 64 


3> So 


3138 


3 r - 2 9 


31.20 


31.12 


31-05 


30 99 


30 93 


30.88 


3083 


30.78 


30 73 


30.69 


30 65 


30.61 


30.57 


30-53 


3 50 


150 


3* 39 


,52.12 


3 '-94 


31.80 


31.68 


3L58 


3> So 


3' 42 


31-35 


31.28 


31 22 


31-17 


31.12 


3' 07 


31 02 


3097 


393 


30.89 


30.85 


30.81 


3078 


1 60 


32 7' 


3 2 44 


32.26 


32.11 


3' 99 


3'8 9 


31.80 


3" 72 


3'.6s 


3i 58 


3' 52 


31.46 


3'.4> 


3' 36 


3' 3' 


3" 27 


3' 23 


3' "9 


J'-'S 


31.11 


31.08 


170 


33 3 


32-76 


32-58 


32 43 


32-31 


32.20 


32.11 


32 03 


31.96 


3'-89 


J'-83 


3'-77 


3I-7I 


31 66 


31.61 


3' 56 


3' 52 


31-48 


3'-44 


31 40 


31-37 


180 


33-37 


33 9 


32.90 


32-75 


3 2 63 


32 52 


32 43 


32.34 


32.27 


32.20 


32 M 


32.08 


32.02 


3' 97 


3" 92 


3' 87 


3' 83 


3'-79 


3'-75 


3 1 7" 


3' 67 


190 


33-7' 


33 43 


33-23 


3308 


32-95 


32.84 


32-75 


3266 


32.59 


32.52 


32 45 


32.39 


3 33 


32.28 


32 23 


32.18 


32-.M 


32.10 


32.06 


32.02 


3'98 


100 


34 06 


33-77 


33 57 


33 4i 


33 28 


33-'7 


33o8 


32 99 


32 9' 


32.84 


32 77 


32.71 


32 65 


32.60 


32 55 


32 50 


32 45 


32 41 


32 37 


32 33 


32 11 


111 


34 49 


34 18 


33.98 


32.80 


33 69 


33 58 


33.48 


33-39 


33.31 


33-24 


33-7 


33 I' 


33 05 


33 99 


32 94 


32 89 


32.84 


32.80 


32.76 


32.72 


32 68 



* See "Economy of Modern Engine Room." Engineering Magazine, Oct. 1896. 



BOILER HORSE-POWER TABLES 



199 



allowance for auxiliaries and boilers un- 
dergoing cleaning, and then determine the 
corresponding boiler capacity. 

Number of Units Required The re- 
quired boiler horse-power having been determ- 
ined, the number of units into which it should 
be divided will depend upon the character of 
the work to be done. If, for example, there 
is a day load which is about double the night 
load, the boiler units should be so propor- 
tioned that half the boiler power can be cut 



fuel, while exhibiting good economy; and 
further, the boiler should be capable of 
developing at least one-third more than its 
rated power to meet emergencies at times 
when maximum economy is not the most 
important object to be attained." 

Boiler Horse=Power Tables When the 
feed water temperature and the gauge pres- 
sure are known, the water per boiler horse- 
power hour may be taken directly from 
Table 59. When the actual weight of 




2,500 HORSE-POWER OF STIRLING BOILERS, COTTON STATES AND INTERNATIONAL EXPOSITION, 

ATLANTA, GEORGIA 



out at night. When fixing the number of 
units, provision should be made for reserve 
power to allow for repairs, cleaning boilers, 
and emergencies. 

Allowance for Overload The Commit- 
tee on Trials of Steam Boilers in their re- 
port to the American Society of Mechanical 
Engineers, said "A boiler rated at any 
stated number of horse-powers should be 
capable of developing that power with 
easy firing, moderate draft, and ordinary 



steam required by an engine per indicated 
. horse-power hour, and the steam pressure 
and boiler feed temperature are known, the 
boiler horse-power per engine horse-power 
can be taken without calculation from Table 
57. First, from Table 16 determine the 
factor of evaporation, then refer to the 
column under that factor in Table 57 and 
the tabular value opposite the water con- 
sumption of the engine is the boiler horse- 
power per engine horse-power. 



Rules for Conducting Boiler Trials 



Whenever a boiler test is made it is desirable 
that the results be recorded in such shape 
as to permit ready comparison with other 
tests. In this country boiler tests are 
usually conducted according to the latest 
code of rules formulated by a committee of 
the American Society of Mechanical Engineers, 
hence this code is here reproduced complete 
except some portions which touch upon 
matters more fully treated elsewhere in this 
book, and to which the reference is given in 
each case. 

RULES FOR CONDUCTING BOILER TRIALS 
CODE OF 1899.* 

I. Determine at the Outset the specific object 
of the proposed trial, whether it be to ascertain the 
capacity of the boiler, its efficiency as a steam 
generator, its efficiency and its defects under usual 
working conditions, the economy of some particular 
kind of fuel, or the effect of changes of design, pro- 
portion, or operation; and prepare for the trial 
accordingly. 

II. Examine the Boiler, both outside and inside; 
ascertain the dimensions of grates, heating surfaces, 
and all important parts; and make a full record, 
describing the same, and illustrating special features 
by sketches. The area of heating surface is to be 
computed from the surfaces of shells, tubes, fur- 
naces, and fire-boxes in contact with the fire or 
hot gases. The outside diameter of water- tubes 
and the inside diameter of fire-tubes are to be used 
in the computation. All surfaces below the mean 
water level which have water on one side and pro- 
ducts of combustion on the other are to be con- 
sidered as water heating surface, and all surfaces 
above the mean water level which have steam on 
one side and products of combustion on the other 
are to be considered as superheating surface. 

III. Notice the General Condition of the boiler 
and its equipment, and record such facts in relation 
thereto as bear upon the objects in view. 

If the object of the trial is to ascertain the maxi- 
mum economy or capacity of the boiler as a steam 
generator, the boiler and all its appurtenances 
should be put in first-class condition. Clean the 
heating surface inside and outside, remove clinkers 



from the grates and from the sides of the furnace. 
Remove all dust, soot, and ashes from the chambers, 
smoke connections, and flues. Close air leaks in the 
masonry and poorly fitted cleaning doors. See that 
the damper will open wide and close tight. Test 
for air leaks by firing a few shovels of smoky fuel 
and immediately closing the damper, observing 
the escape of smoke through the crevices, or by 
passing the flame of a candle over cracks in the 
brickwork. 

IV. Determine the Character of the Coal to be 
used. For tests of the efficiency or capacity of 
the boiler for comparison with other boilers, the 
coal should, if possible, be of some kind which is 
commercially regarded as a standard. For New 
England and that portion of the country east of the 
Allegheny Mountains, good anthracite egg coal, 
containing not over 10 per cent, of ash, and semi- 
bituminous Clearfield (Pa.), Cumberland (Md.), 
and Pocahontas (Va.), are thus regarded. West 
of the Allegheny Mountains, Pocahontas, (Va.), 
and New River (W. Va.) semi-bituminous, and 
Youghiogheny or Pittsburg bituminous coals are rec- 
ognized as standards. f There is no special grade 
of coal mined in the Western States which is widely 
recognized as of superior quality or considered 
as a standard coal for boiler testing. Big Muddy 
lump, an Illinois coal mined in Jackson County, 
111., is suggested as being of sufficiently high 
grade to answer these requirements in districts 
where it is more conveniently obtainable than the 
other coals mentioned above. 

For tests made to determine the performance 
of a boiler with a particular kind of coal, such as 
may be specified in a contract for the sale of a 
boiler, the coal used should not be higher in ash 
and in moisture than that specified, since increase 
in ash and moisture above a stated amount is apt 
to cause a falling off of both capacity and economy 
in greater proportion than the proportion of such 
increase. 

V. Establish the Correctness of all Apparatus 
used in the test for weighing and measuring. These 
are: 

1. Scales for weighing coal, ashes, and water. 

2. Tanks, or water-meters, for measuring water. 
Water-meters, as a rule should be used only as a 



*From Volume XXI. of the Transactions of the American Society of Mechanical Engineers. 

tThese coals are selected because they are about the only coals which possess the essentials of excellence of quality, adaptability 
to various kinds of furnaces, grates, boilers, and methods of firing, and wide distribution and general accessibility in the markets. 




202 



THE STIRLING WATER-TUBE SAFETY BOILER 



check on other measurements. For accurate work, 
the water should be weighed or measured in a tank. 

3. Thermometers and pyrometers for taking 
temperatures of air, steam, feed-water, waste gases, 
etc. 

4. Pressure gauges, draught gauges, etc. 

The kind and location of the various pieces of 
testing apparatus must be left to the judgment of 
the person conducting the test; always keeping in 
mind the main object, that is, to obtain authentic 
data. 

VI. See that the boiler is thoroughly heated to 
its usual working temperature before the trial. 
If the boiler is new and of a form provided with a 
brick setting, it should be in regular use at least 
a week before the trial, so as to dry and heat the 
walls. If it has been laid off and become cold, it 
should be worked before the trial until the walls 
are well heated. 

VII. The boiler and connections should be 
proved to be free from leaks before beginning a 
test, and all water connections, including blow 
and extra feed pipes, should be disconnected, stopped 
with blank flanges, or bled through special open- 
ings beyond the valves, except the particular pipe 
through which water is to be fed to the boiler during 
the trial. During the test the blow-off and feed 
pipes should remain exposed to view. 

If an injector is used, it should receive steam 
dirctly through a felted pipe from the boiler being 
tested.* 

If the water is metered after it passes the injector, 
its temperature should be taken at the point where 
it leaves the injector. If the quantity is deter- 
mined before it goes to the injector the temperature 
should be determined on the suction side of the 
injector, and if no change of temperature occurs 
other than that due to the injector, the temperature 
thus determined is properly that of the feed water. 
When the temperature changes between the injector 
and the boiler, as by the use of a heater or by 
radiation, the temperature at which the water enters 
and leaves the injector and that at which it enters 
the boiler should all be taken. In that case the 
weight to be used is that of the water leaving the 
injector, computed from the heat units if not di- 
rectly measured, and the temperature, that of the 
water entering the boiler. 



Let w=weight of water entering the injector. 
x = " steam 

^j=heat units per pound of water entering 

injector. 
/? 2 =heat units per pound of steam entering 

injector. 
/z 3 =heat units per pound of water leaving 

injector. 
Then zy+.T=weight of water leaving injector. 



See that the steam main is so arranged that water 
of condensation cannot run back into the boiler. 

VIII. Duration of the Test For tests made to 
ascertain either the maximum economy or the 
maximum capacity of a boiler, irrespective of the 
particular class of service for which it is regularly 
used, the duration should be at least ten hours of 
continuous running. If the rate of combustion 
exceeds 25 pounds of coal per square foot of grate 
surface per hour, it may be stopped when a total 
of 250 pounds of coal has been burned per square 
foot of grate. 

In cases where the service requires continuous 
running for the whole 24 hours of the day, with 
shifts of firemen a number of times during that 
period, it is well to continue the test for at least 
34 hours. 

When it is desired to ascertain the performance 
under the working conditions of practical running, 
whether the boiler be regularly in use 24 hours a 
day or only a certain number of hours out of each 
24, the fires being banked the balance of the time, 
the duration should not be less than 24 hours. 

IX. Starting and Stopping a Test The con- 
ditions of the boiler and furnace in all respects should 
be, as nearly as possible, the same at the end as 
at the beginning of the test. The steam pressure 
should be the same; the water level the same; 
the fire upon the grates should be the same in 
quantity and condition; and the walls, flues, etc., 
should be of the same temperature. Two methods 
of obtaining the desired equality of conditions 
of the fire may be used, viz.; those which were 
called in the Code of 1885 "the standard method" 
and "the alternate method," the latter being 
employed where it is inconvenient to make use of 
the standard method. f 



*In feeding a boiler undergoing test with an injector taking steam from another boiler, or from the main steam pipe from 
several boilers, the evaporative results may be modified by a difference in the quality of the steam from such source compared with 
that supplied by the boiler being tested, and in some cases the connection to the injector may act as a drip for the main steam 
pipe. If it is known that the steam from the main pipe is of the same pressure and quality as that furnished by the boiler under- 
going the test, the steam may be taken from such main pipe. 

tThe Committee concludes that it is best to retain the designations "standard" and "alternate," since they have become widely 
known and established in the minds of engineers and in the reprints of the Code of 1885. Many engineers prefer the "alternate" 
to the "standard" method on account of its being less liable to error due to cooling of the boiler at the beginning and end of a test. 



KEEPING THE RECORDS 



203 



X. Standard Method of Starting and Stopping 
a Test Steam being raised to the working pres- 
sure, remove rapidly all the fire from the grate, close 
the damper, clean the ash-pit, and as quickly as 
possible start a new fire with weighed wood and 
coal, noting the time and the water level* while 
the water is in a quiescent state, just before 
lighting the fire. 

At the end of the test remove the whole fire, 
which has been burned low, clean the grates and 
ash-pit, and note the water level when the water 
is in a quiescent state, and record the time of 
hauling the fire. The water level should be as 
nearly as possible the same as at the beginning 
of the test. If it is not the same, a correction should 
be made by computation, and not by operating the 
pump after the test is completed. 

XI. Alternate Method of Starting and Stopping 
a Test The boiler being thoroughly heated 
by a preliminary run, the fires are to be burned 
low and well cleaned. Note the amount of coal 
left on the grate as nearly as it can be estimated; 
note the pressure of steam and the water level. 
Note the time and record it as the starting time. 
Fresh coal which has been weighed should now be 
fired. The ash-pits should be thoroughly cleaned 
at once after starting. Before the end of the test 
the fires should be burned low, just as before the 
start, and the fires cleaned in such a manner as to 
leave a bed of coal on the grates of the same depth, 
and in the same condition, as at the start. When 
this stage is reached, note the time and record it as 
the stopping time. The water level and steam 
pressures should previously be brought as nearly 
as possible to the same point as at the start. If 
the water level is not the same as at the start, a 
correction should be made by computation, and 
not be operating the pump after the test is com- 
pleted. 

XII. Uniformity of Conditions In all trials 
made to ascertain maximum economy or capacity, 
the conditions should be maintained uniformly 
constant. Arrangements should be made to dis- 
pose of the steam so that the rate of evaporation 
may be kept the same from beginning to end. 
This may be accomplished in a single boiler by 
carrying the steam through a waste-steam pipe, 
the discharge from which can be regulated as de- 
sired. In a battery of boilers, in which only one 
is tested, the draft may be regulated on the re- 
maining boilers, leaving the test boiler to work 
under a constant rate of production. 



Uniformity of conditions should prevail as to 
the pressure of steam, the height of water, the rate 
of evaporation, the thickness of fire, the times of 
firing and quantity of coal fired at one time, and as 
to the intervals between the times of cleaning the 
fires. 

The method of firing to be carried on in such tests 
should be dictated by the expert or person in 
responsible charge of the test, and the method 
adopted should be adhered to by the fireman 
throughout the test. 

XIII. Keeping the Records Take note of 
every event connected with the progress of the 
trial, however unimportant it may appear. Record 
the time of every occurrence and the time of 
taking every weight and every observation. 

The coal should be weighed and delivered to the 
fireman in equal proportions, each sufficient for 
not more than one hour's run, and a fresh portion 
should not be delivered until the previous one has 
all been fired. The time required to consume each 
portion should be noted, the time being recorded 
at the instant of firing the last of each portion. It 
is desirable that at the same time the amount of 
water fed into the boiler should be accurately 
noted and recorded, including the height of the 
water in the boiler, and the average pressure of 
steam and temperature of feed during the time. 
By thus recording the amount of water evaporated 
by successive portions of coal, the test may be 
divided into several periods if desired, and the 
degree of uniformity of combustion, evaporation, 
and economy analyzed for each period. In ad- 
dition to these records of the coal and the feed 
water, half hourly observations should be made of 
the temperature of the feed water, of the flue- 
gases, of the external air in the boiler room, of the 
temperature of the furnace when a furnace pyro- 
meter is used, also of the pressure of steam, 
and of the readings of the instruments for de- 
termining the moisture in the steam. A log 
should be kept on properly prepared blanks con- 
taining columns for record of the various observa- 
tions. 

When the "standard method" of starting and 
stopping the test is used, the hourly rate of com- 
bustion and evaporation and the horse-power 
should be computed from the records taken during 
the time when the fires are in active condition. 
This time is somewhat less than the actual time 
which elapses between the beginning and end of 
the run. The loss of time due to kindling the fire 



*The gauge-glass should not be blown out within an hour before the water level is taken at the beginning and end of test, 
otherwise an error in the reading of the water level may be caused by a change in the temperature and density of the water in 
the pipe leading from the bottom of the glass into the boiler. 



204 



THE STIRLING WATER-TUBE SAFETY BOILER 



at the beginning and burning it out at the end makes 
this course necessary. 

XIV. Quality of Steam The percentage of 
moisture in steam should be determined by the use 
of either a throttling or a separating steam calori- 
meter.* The sampling nozzle should be placed 
in the vertical steam pipe rising from the boiler. 
It should be made of J-inch pipe, and should extend 
across the diameter of the steam pipe to within 
half an inch of the opposite side, being closed at 
the end and perforated with not less than twenty 
J-inch holes equally distributed along and around 
its cylindrical surface, but none of these holes 
should be nearer than J-inch to the inner side 
of the steam pipe. The calorimeter and the 
pipe leading to it should be well covered with 
felting. Whenever the indications of the throttling 
or separating calorimeter show that the percentage 
of moisture is irregular, or occasionally in excess 
of three per cent., the results should be checked 
by a steam separator placed in the steam pipe as 
close to the boiler as convenient, with a calorimeter 
in the steam pipe just beyond the outlet from the 
separator. The drip from the separator should be 
caught and weighed, and the percentage of moisture 
computed therefrom added to that shown by the 
calorimeter. 

Superheating should be determined by means 
of a thermometer placed in a mercury-well inserted 
in the steam pipe. The degree of superheating 
should be taken as the difference between the 
reading of the thermometer for superheated steam 
and the readings of the same thermometer of 
saturated steam at the same pressure as deter- 
mined by a special experiment, and not by refer- 
ence to steam tables. 

For calculations relating to, and corrections for, 
quality of steam, see pages 79 to 85. 

XV. Sampling the Coal and Determining Its 
Moisture As each barrow load or fresh por- 
tion of coal is taken from the coal pile, a repre- 
sentative shovelful is selected from it and placed in 
a barrel or box in a cool place and kept until the end 
of the trial. The samples are then mixed and 
broken into pieces not exceeding one inch in diam- 
eter, and reduced by the processes of repeated 
quartering and crushing until a final sample weigh- 
ing about five pounds is obtained, and the size of 
the larger piece is such that they will pass through 
a sieve with J-inch meshes. From this sample 
two one-quart, air-tight glass preserving jars, or 
other air-tight vessels which will prevent the 
escape of moisture from the sample, are to be 



promptly filled, and these samples are to be kept 
for subsequent determinations of moisture and of 
heating value and for chemical analyses. During 
the process of quartering, when the sample has been 
reduced to about 100 pounds, a quarter to a half 
of it may be taken for an approximate determina- 
tion of moisture. This may be made by placing 
it in a shallow iron pan, not over three inches deep, 
carefully weighing it, and setting the pan in the 
hottest place that can be found on the brickwork 
of the boiler setting or flues keeping it there for 
at least 1 2 hours, and then weighing it. The de- 
termination of moisture thus made is believed to be 
approximately accurate for anthracite and semi- 
bituminous coals, and also for Pittsburg or Youghio- 
gheny coal; but it cannot be relied upon for coals 
mined west of Pittsburg, or for other coals con- 
taining inherent moisture. For these latter coals 
it is important that a more accurate method be 
adopted. The method recommended by the Com- 
mittee for all accurate tests, whatever the char- 
acter of the coal, is described as follows: 

Take one of the samples contained in the glass 
jars, and subject it to a thorough air-drying, by 
spreading it in a thin layer and exposing it for 
several hours to the atmosphere of a warm room, 
weighing it before and after, thereby determining 
the quantity of surface moisture it contains. Then 
crush the whole of it by running it through an 
ordinary coffee mill adjusted so as to produce some- 
what coarse grains (less than i/i 6-inch), thor- 
oughly mix the crushed sample, select from it a 
portion of from 10 to 50 grams, weigh it in a balance 
which will easily show a variation as small as i 
part in 1,000, and dry it in an air or sand bath at a 
temperature between 240 and 280 degrees Fahr. for 
one hour. Weigh it and record the loss, then heat 
and weigh it again repeatedly, at intervals of an 
hour or less, until the minimum weight has been 
reached and the weight begins to increase by oxida- 
tion of a portion of the coal. The difference be- 
tween the original and the minimum weight is 
taken as the moisture in the air-dried coal. This 
moisture test should preferably be made on dupli- 
cate samples, and the results should agree within 
0.3 to 0.4 of one per cent., the mean of the two 
determinations being taken as the correct result. 
The sum of the percentage of moisture thus found 
and the percentage of surface moisture previously 
determined is the total moisture. 

XVI. Treatment of Ashes and Refuse The 
ashes and refuse are to be weighed in a dry state. If 
it is found desirable to show the principal character- 



*See pages 79 to 83. 



THE HEAT BALANCE 



205 



istics of the ash, a sample should be subjected to 
a proximate analysis and the actual amount of in- 
combustible material determined. For elaborate 
trials a complete analysis of the ash and refuse 
should be made. 

XVII. Calorific Tests and Analysis of Coal 
The quantity of the fuel should be determined either 
by heat test or by analysis, or by both. 

The rational method of determining the total 
heat of combustion is to burn the sample of coal 
in an atmosphere of oxygen gas, the coal to be 
sampled as directed in Article XV of this code. 

The chemical analysis of the coal should be made 
only by an expert chemist. The total heat of 
combustion computed from the results of the ulti- 
mate analysis may be obtained by the use of Du- 
long's formula, pages 106 and 131. 

It is desirable that a proximate analysis should 
be made, thereby determining the relative propor- 
tions of volatile matter and fixed carbon. These 
proportions furnish an indication of the leading 
characteristics of the fuel, and serve to fix the class 
to which it belongs. As an additional indication 
of the characteristics of the fuel, the specific gravity 
should be determined. 

XVIII. Analysis of Flue=Gases The analysis 
of the flue-gases is an especially valuable method 
of determining the relative value of different 
methods of firing, or of different kinds of furnaces. 
In making these analyses great care should be taken 
to procure average samples since the composi- 
tion is apt to vary at different points of the flue. 
The composition is also apt to vary from minute 
to minute, and for this reason the drawings of gas 
should last a considerable period of time. Where 
complete determinations are desired, the analyses 
should be intrusted to an expert chemist. For 
approximate determinations the Orsat* or the 
Hempelf apparatus may be used by the engineer. 

For the continuous indication of the amount of 
carbonic acid (CO 2) present in the flue-gases, an 
instrument may be employed which shows the 
weight of the sample of gas passing through it. 

XIX. Smoke Observations It is desirable to 
have a uniform system of determining and record- 
ing the quantity of smoke produced where bi- 
tuminous coal is used. The system commonly 
employed is to express the degree of smokiness by 
means of percentages dependent upon the judg- 
ment of the observer. The Committee does not 
place much value upon a percentage method, be- 
cause it depends so largely upon the personal 
element, but if this method is used, it is desirable 



that, so far as possible, a definition be given in 
explicit terms as to the basis and method employed 
in arriving at the percentage. The actual meas- 
urement of a sample of soot and smoke by some 
form of meter is to be preferred. 

XX. Miscellaneous In tests for purposes of 
scientific research, in which the determination of 
all the variables entering into the test is desired 
certain observations should be made which are 
in general unnecessary for ordinary tests. These 
are the measurement of the air supply, the determi- 
nation of its contained moisture, the determination 
of the amount of heat lost by radiation, of the 
amount of infiltration of air through the setting, 
and (by condensation of all the steam made by 
the boiler) of the total heat imparted to the water. 

As these determinations are rarely undertaken, 
it is not deemed advisable to give directions for 
making them. 

XXI. Calculations of Efficiency Two methods 
of defining and calculating the efficiency of a boiler 
are recommended. They are: 

i. Efficiency of the boiler 

Heat absorbed per Ib. combustible 



Calorific value of i Ib. combustible 
2 . Efficiency of the boiler and grate 
Heat absorbed per Ib. coal 



[52] 



Calorific value of i Ib.coal 
The first of these is sometimes called the effi- 
ciency based on combustible, and the second effi- 
ciency based on coal. The first is recommended 
as a standard of comparison for all tests, and this 
is the one which is understood to be referred to 
when the word "efficiency" alone is used without 
qualification. The second, however, should be in- 
cluded in a report of a test, together with the first, 
whenever the object of the test is to determine the- 
efficiency of the boiler and furnace together with 
the grate (or mechanical stoker), or to compare 
different furnaces, grates, fuels, or methods of firing. 
The heat absorbed per pound of combustible 
(or per pound of coal) is to be calculated by multi- 
plying the equivalent evaporation from and at 
212 degrees per pound combustible (or coal) by 

965-74 

XXII. The Heat Balance An approximate 
"heat balance," or statement of the distribution 
of the heating value of the coal among the several 
items of heat utilized and heat lost may be included 
in the report of a test when analyses of the fuel 
and of the chimney-gases have been made. The 
methods of computing the heat balance and the 



*See page 184. tSee Hempel's Methods of Gas Analysis. (Macmillan & Co.) 965. 8 is more accurate, and is used through- 
out this book. 



206 



THE STIRLING WATER-TUBE SAFETY BOILER 



form in which it should be reported, are given in 12. Draft between damper and boiler ins. of water 

chapter on Steam Boiler Efficiency. 13. Force of draft in furnace " 

XXIII. Report of the Trial The data and 14. Force of draft or blast in ash-pit.... 
results should be reported in the manner given in Average Temperatures. 

either one of the two following tables,"!" omitting 15. Of external air deg. 

lines where the tests have not been made as elabor- 16. Of fireroom " 

ately as provided for in such tables. Additional 17. Of steam 

lines may be added for data relating to the specific 18. Of feed water entering heater " 

object of the test. The extra lines should be 19. Of feed water entering economizer " 

classified under the headings provided in the tables, 20. Of feed water entering boiler " 

and numbered as per preceding line, with sub-letters 21. Of escaping gases from boiler " 

a, b, etc. The Short Form of Report is recom- 22. Of escaping gases from economizer " 

mended for commercial tests and as a convenient Fuel. 

form of abridging the longer form for publication 23. Size and condition 

when saving of space is desirable. For elaborate 24. Weight of wood used in lighting fire Ibs. 

trials, it is recommended that the full log of the 25. Weight of coal as fired* _ " 

trial be shown graphically, by means of a chart. 26. Percentage of moisture in coal% percent. 

27. Total weight of dry coal consumed 

DATA AND RESULTS OF EVAPORATIVE 28. Total ash and refuse 

TgST 29. Quality of ash and refuse 

30. Total combustible consumed .... ..Ibs. 

Arranged in accordance with the Complete Form, ,-. , , . , . . 

31. Percentage of ash and refuse in dry coal 
Code of 1899. 

per cent. 

Made by ot boiler at to ,-, .,,... 

Proxtmate Analysis of Coal. 

determine.. 

Coal. Combustible. 
Principal conditions governing the trial .... 

32. Fixed carbon per cent, per cent. 

33. Volatile matter 

Kind of fuel ... . ^ 

. , , , 34- Moisture... 

Kind of furnace .. ,, 

State of the weather _ 

Method of starting and stopping the test ("stand- 

dard" or "alternate," Art. X and XI, Code).... 36. Sulphur, separately de- 

1 . Date of trial termined .. 

2. Duration of trial .. ....hours. Ultimate Analysis of Dry Coal. 

Dimensions and Proportions . (Art. XVII., Code.) 

(A complete description of the boiler, and draw- Coal. Combustible, 

ings of the same if of unusual type, should be given 37- Carbon (C) ....percent, percent, 

on an annexed sheet.) 38. Hydrogen (H) 

3. Grate surface width length 39- Oxygen (O) ... 

....area.... .. sq. ft. 40. Nitrogen (N) . 

4. Height of furnace .. ....ins. 4i- Sulphur (S) ... 

5. Approximate width of air spaces in grate.... in. 4 2 - Ash . 

6. Proportion of air space to whole grate sur- 100 % 100 % 

face _ percent. 43. Moisture in sample of coal 

7. Water-heating surface sq.ft. as received 

8. Superheating surface Analysis of Ash and Refuse. 

9. Ratio of water-heating surface to grate sur- 44. Carbon . per cent. 

face.... to i. 45. Earthy matter. 

10. Ratio of minimum draft area to grate sur- Fuel per Hour. 

face i to . 46. Dry coal consumed per hour Ibs. 

Average Pressures. 47. Combustible consumed per hour . 

11. Steam pressure by gauge ...Ibs. persq. in. 48. Dry coal per sq. ft. of grate surface per hour " 

tTo save space, only the table giving the "Complete Form" is here reproduced, but the items printed in italics constitute the 

"Short Form." *Including equivalent of wood used in lighting the fire, not including unburnt coal withdrawn from furnace 
at times of cleaning and at end of test. One pound of wood is taken to be equal to 0.4 pounds of coal, or, in 'case greater 
accuracy is desired, as having a heat value equivalent to the evaporation of 6 pounds of water from and at 212 degrees per pound. 
(For more complete information on this point see page up.) The term "as fired" means in its actual condition, including moist- 
ure. tThis is the total moisture in the coal as found by drying it artificially, as described in Art. XV. of Code. 



207 



49- Combustible per square foot of water heat- 
ing surface per hour Ibs. 

Calorific Value of Fuel. 
(Art. XVII., Code.) 

50. Calorific value by oxygen calorimeter, 

perlb. of dry coal B. T. U. 

51. Calorific value by oxygen calorimeter, 

per Ib. of combustible " 

52. Calorific value by analysis, per Ib. of 

dry coal* " 

53. Calorific value by analysis, per Ib. of 

combustible 

Quality of Steam. 

54. Percentage of moisture in steam ..per cent. 

55. Number of degrees of superheating deg. 

56. Quality of steam (dry steam= unity) 

Water. 

57. Total weight of water fed to boiler^ Ibs. 

58. Equivalent water fed to boiler from and at 

212 degrees " 

59. Water actually evaporated, corrected for 

quality of steam " 

60. Factor of evaporation! " 

61. Equivalent water evaporated into dry 

steam from and at 212 degrees! 

(Item 5(;X Item 60.) " 

Water per Hour. 

62. Water evaporated per hour, corrected for 

quality of steam " 

63. Equivalent evaporation per hour from and 

at 212 degrees^ " 

64. Equivalent evaporation per hour from and 

at 212 degrees per square foot of water 
heating surface^ " 

Horse-Power. 

65. Horse-Power developed (34$ Ibs. of water 

evaporated per hour into dry steam from 
and at 212 degrees, equals one horse- 
power^ . H. P. 

66. Builders' rated horse-power " 

67. Percentage of builders' rated horse-power 

developed per cent. 

Economic Results. 

68. Water apparently evaporated under actual 

conditions per pound of coal as fired. 
(Item si+Item 25.) Ibs. 

69. Equivalent evaporation from and at 212 

degrees per pound of coal as fired\. 
(Item 6i-i-Item 25.) " 



70. Equivalent evaporation from and at 212 de- 

grees per pound of dry coal\. (Item 
6i-^-Item 27.) Ibs. 

7 1 . Equivalent evaporation from and at 212 

degrees per pound of combustible^ 

(Item 6i+Item 30.) " 

(If the equivalent evaporation, Items 
69, 70 and 71, is not corrected for the 
quality of steam, the fact should be 
stated.) 

Efficiency. 
(Art. XXI, Code.) 

7 2 . Efficiency of boiler; heat absorbed by the boiler 
per Ib. of combustible divided by the heat value 
of one Ib. of combustible]] percent. 

73. Efficiency of boiler, including the grate; heat 

absorbed by the boiler, per Ib. of dry coal, 
divided by the heat value of one Ib. of dry 
coal per cent. 

Cost of Evaporation. 

74. Cost of coal per ton of Ibs. delivered in 

boiler room $ 

75. Cost of fuel for evaporating 1,000 Ibs of 

water under observed conditions $ 

76. Cost of fuel used for evaporating 1,000 Ibs 

water from and at 212 degrees ...$ 

Smoke Observations. 

77. Percentage of smoke as.observed per cent. 

78. Weight of soot per hour obtained 

from smoke meter ounces. 

79. Volume of soot per hour obtained 

from smoke meter cub. in. 

Methods of Firing. 

80. Kind of firing (spreading, alternate 

or coking).... 

81. Average thickness of fire 

82. Average intervals between firing for 

each furnace during time when 
fires are in normal condition 

83. Average interval between times of 

leveling or breaking up... 

Analyses of the Dry Gases. 

84. Carbon dioxide (CO. ; ) .per cent. 

85. Oxygen (O) ....".. " 

86. Carbon monoxide (CO) 

87. Hydrogen and hydrocarbons 

88. Nitrogen (by difference) (N) 



100 per cent 



*See Formula No. 24, page 106. tCorrected for inequality of water level and of steam pressure at beginning and end of test. 

t Factor of evaporation, see page 70. JThe symbol "U. E." meaning "Units of Evaporation," may be conveniently 
substituted for the expression "Equivalent water evaporated into dry steam from and at 212 degrees," its definition being given 
in afoot-note. See page 72. Held to be the equivalent of 30 Ibs. of water per hour evaporated from 100 degrees Fahr. into 
dry steam at 70 Ibs. gauge pressure. See page 195. Illn all eases where the word combustible is used, it means the coal 

without moisture and ash but including all other constituents. It is the same as what is called in Europe "coal dry and free 
from ash." See foot-note on page 112. 



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Mergenthaler Linotype Co. Brooklyn 
Mergenthaler Linotype Co., Brooklyn 


Midvale Colliery, Wilburton, Pa . 
Lehigh & Wilkes-Barre Coal Co. 
Lehigh ct Wilkes-Barre Coal Co. 


Blackstone Mfg. Co., Blackstono, Ma~ 
Toledo Water Works., Toledo, O. 


Portland (Me.) Street Railway Co. 
Public Works. , Bangor, Me. 

Old Colony S reet Ry. Co., Taunton, I 
Winilber Electric Co., Windber, Pa. 


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Boilers for Mining Service 



To prove satisfactory for mining service 
a boiler must be capable of meeting a wider 
range of requirements than is ordinarily 
met with in other industries. It must be 
simple in construction so that repairs can be 
quickly made with the limited equipment 
usually available; it must be safe in opera- 
tion because skilled boiler attendants are 
often unavailable; it must be easy to force 
in emergencies, and its design of fire-box 
must be such as to permit use of wood, oil, 
and high or low grade coal. The boiler 
must be reasonable in first cost, because of 
the uncertainty as to the life of many mines, 
and it must also be easy to transport into 
places difficult of access. An especially 
important requirement is that the boiler can 
be opened, cleaned and closed in the shortest 
possible time, not only because of the ex- 
pense of keeping it out of commission, but 
because of the high cost of labor. The single 
item of labor-cost of cleaning some types 
of boilers has prevented their extensive use 
for mining plants. 

A careful reading of the preceding descrip- 
tion of the Stirling boiler will demonstrate 
that it perfectly meets each of these re- 
quirements, and surpasses any competing 
type in its adaptation to varying fuel re- 
quirements, and ease and cheapness of cleaning. 
A more convincing evidence that it is justly 
regarded as the "Ideal Boiler for Mine Use" 
is found in the fact that over 200,000 horse- 
power of Stirling boilers are now in success- 
ful operation in mine and smelter plants. 

Boilers supplying Hoisting Engines are 
often blamed for insufficient capacity, wet 
steam, etc., when the fault is due not to 
the boiler, but to improper piping. The 
hoist is usually some distance from the 
boiler, and often the steam pipe is so imper- 
fectly covered that between lifts large quan- 
tities of steam condense and the water thus 
formed is swept into the cylinder when the 
engine starts. When the throttle is thrown 
open the momentary draft on the boiler may 
be many times greater than its rated capacity 
and in such cases, irrespective of the kind of 
boiler, there may be a momentary lift of 



water. To prevent this it is common prac- 
tise to provide the boiler with an auxiliary 
steam drum, but this is a makeshift and not 
a cure, as will now be shown. 

Condensation in the pipe line cannot be 
prevented, but it can be largely reduced, 
and the evident means are an efficient cover- 
ing of ample thickness, and a reduction of 
the capacity. A reliable method of extracting 
all water of condensation before the steam 
enters the engine is necessary. 

Consider the case of a tank supplied with 
water through a pipe connected to a distant 
reservoir. It is evident that if one wants 
to fill the tank say every minute, yet allow 
only one-quarter of a minute to do the .actual 
filling, and shut off the pipe the other three- 
quarters of a minute, then the column of 
water in the pipe is not only started and 
stopped at every filling, but the capacity 
of the pipe will have to be four times as 
great as would be the case if the water ran 
all the time into a storage tank from which 
the other tank could be filled at the same 
intervals as before. Provided the original 
reservoir feeding the pipe were of sufficient 
size to supply the requisite volume of water, 
any further increase in its size could not 
alter in the slightest degree the action as 
above described. 

If in the above case a boiler be substituted 
for the reservoir, and a hoisting engine for 
the tank to be periodically filled, then the 
storage tank from which it is to be filled 
corresponds exactly to the steam drum, 
hence it is evident that when the drum is 
placed on the boiler, it is at the wrong end 
of the line. Its proper place is as near to 
the engine as it can possibly be put, and its 
cubical capacity should be not less than 
one-seventh the actual volume of steam used 
per minute by the engine. It should be 
well covered, and provided with an absolutely 
reliable drainage apparatus, and a gauge glass 
to indicate when that apparatus fails to 
work. Steam traps are not always reliable, 
and an automatic drainage pump is better. 

The area of the steam pipe may next be 
figured. The maximum number of strokes 



SIZE OF STEAM PIPE FOR HOISTING ENGINES 



211 



per minute of the engine being known, dis- 
regard the cut-off and assume the cylinder 
is entirely filled with steam at each stroke, 
then compute the diameter of steam pipe 
between engine and drum based on steam 
velocity of 6,000 feet per minute. This 
velocity will actually exist during the part 
of the stroke up to cut-off, since the velocity 
of the steam at that time will be the same 
as it would be were the engine taking steam 
during: the entire stroke. 



flow in the engine supply pipe will continue 
only up to time the engine cuts off ; the steam 
being elastic and the drum acting as a re- 
ceiver and pressure steadier (like the rubber 
bag in a gas engine supply pipe) the flow of 
steam between boiler and drum will be 
practically continuous, hence its velocity 
will be less than assumed in the calculation. 
The decrease in pipe size will reduce the 
surface available for condensation. The stor- 
age drum next to the engine is preferably 




LOS ANGELES-PACIFIC RAILROAD, LOS ANGELES, CAL. OPERATING 1,300 H. P. OF STIRLING BOILERS 



To reduce the condensation, the pipe be- 
tween boiler and drum should be no larger 
than actually required, and it will be en- 
tirely safe to figure its area in exactly the 
same manner as above shown for engine 
supply pipe, except that the steam velocity 
may be assumed as 8,000 or even 9,000 feet 
per minute. The actual velocity through the 
pipe thus determined will be less than these 
figures, because the volume of steam as- 
sumed as basis of the calculation is that which 
would be required to fill the entire engine 
cylinder if there were no cut-off; actually the 



made vertical, and to assist in separating 
any water a vertical partition should extend 
from the top to within 18 inches of the 
bottom, and both steam inlet and outlet 
should be near the top. To secure the maxi- 
mum of volume with minimum of exposed 
surface, the diameter and length should not 
differ greatly. 

Regardless of the purpose for which a 
steam plant may be used, there are many 
more cases than commonly supposed where 
an arrangement of drum and piping as above 
described would be a profitable investment. 




PART OF 11 600 H P. OF STIRLING BOILERS, WASHOE SMELTER, ANACONDA COPPER MINING CO. 

ANACONDA, MONTANA 



Principles of Steam Piping 



In the design of a steam plant no detail 
merits more careful consideration than the 
steam piping. Not only is it frequently 
overlooked, but the evils resulting from de- 
fective design are usually attributed to other 
parts of the equipment. 

The nature of the material to be conveyed 
by the pipe must be considered, as the re- 
quirements for steam are entirely different 
from those of water, oil, or gas. The princi- 



ample strength, provision for expansion, 
and valves of suitable type properly located. 
No perfect heat insulator is known ; the 
loss of heat from steam pipes by radiation 
may be reduced by methods given in the 
next chapter, but it cannot be wholly pre- 
vented, hence some water of condensation 
must form. If this water as fast as it is 
formed is carried to the engine it will cause 
troubles which will later be pointed out. If 



TABLE 61 

STANDARD DIMENSIONS OF WROUGHT IRON AND STEEL STEAM, GAS 

AND WATER PIPE* 



Diameter. 




Circumference. 


Transverse Areas. 


Length of Pipe per 
Square Foot of 


Length 




v % 




C ^ 








of Pipe 




jlJSl 
























Contain- 


Nominal 


, 


11 

11 


Actual 
External 


Approxi- 
mate 
Internal 


l| 


External. 


Internal. 


External. 


Internal. 


Metal. 


External 
Surface. 


Internal 
Surface. 


ing one 
Cubic 
Foot. 


Weight 
per 
Foot. 


s" 3 

~ o 




Diameter 


Diameter 






















-Q C 


Inch. 


Inches. 


Inches. 


Inches. 


Inches. 


Inches. 


Sq. Inch. 


Sq. Inch. 


Sq. Inch. 


Feet. 


Feet. 


Feet. 


Pounds. 


! 


, 


-405 


.27 


068 


1.272 


.848 


. 129 


-0573 


.0717 


9-44 


14- 15 


2513- 


. 241 


2-7 


1 


-54 


364 


088 


i .'696 


1. 144 


. 229 


.1041 


1249 


7-075 


10.49 


1383-3 


.42 


18 


1 


.675 


494 


091 


2 . 121 


1-552 


-358 


1917 


.1663 


5-657 


7-73 


751 -2 


-559 


18 




.84 


.623 


109 


2.639 


1-957 


554 


.3048 


2492 


4-547 


6.13 


472.4 


-837 


14 


J 


1.05 


.824 


113 


3.299 


2.589 


.866 


-5333 


3327 


3.637 


4-635 


270. 


1.115 


14 


i 


I.3I5 


i .048 


i34 


4-131 


3.292 


1.358 


.8626 


4954 


2.904 


3-645 


166. 9 


1.668 


ii* 


ii 


1.66 


1.38 


14 


5-215 


4-335 


2. 164 


i .496 


.668 


2 .301 


2.768 


96.25 


2.244 


ii* 


i* 


1.9 


i .61 1 


i45 


5-969 


5.061 


2.835 


2.038 


-797 


2 .OI 


2.371 


70 .66 


2.678 


ii* 


2 


2.375 


2 .067 


i54 


7-461 


6-494 


4-43 


3-356 


1.074 


I .608 


1.848 


42.91 


3-609 


1 1* 


2* 


2.875 


2.468 


204 


9.032 


7-753 


6.492 


4.784 


1.708 


1.328 


i -547 


30. i 


5-739 


8 


3 


3-5 


3.067 


217 


10. 996 


9 . 636 


9.621 


7 . 388 


2.243 


I .09! 


i . 245 


19.5 


7.536 


8 


3* 


4- 


3.548 


226 


12 . 566 


ii . 146 


12.566 


9 . 887 


2.679 


-955 


1.077 


14-57 


9 .001 


8 


4 


4-5 


4 .026 


237 


14.137 


I 2 . 648 


15.904 


12.73 


3-174 


-849 


949 


11.31 


10 . 665 


8 


4* 


5- 


4.5o8 


246 


15.708 


14. l62 


I9-635 


15.961 


3-674 


764 


.848 


9 .02 


12.49 


8 


5 


5-563 


5-045 


259 


17-477 


15.849 


24.306 


19. qp 




.687 


757 


7.2 


14.502 


8 


6 


6. 625 


6.065 


28 


2O.8l3 


I9.O54 


34-472 


28.888 


5 '584 


-577 


63 


4.98 


18.762 


8 


7 


7-625 


7.023 


301 


23-9.55 


22.063 


45.664 


38.738 


6 . 926 


.501 


-544 


3.72 


23-271 


8 


8 


8.625 


7.982 


322 


27 .096 


25.076 


58.426 


50.04 


8.386 


-443 


.478 


2.88 


28.177 


8 


9 


9.625 


8.937 


344 


30.238 


28.076 


72.76 


62.73 


10.03 


-397 


.427 


2.29 


33-701 


8 


10 


10.75 


10.019 


366 


33-772 


31-477 


90.763 


78.839 


11.924 


355 


.382 


1.82 


40 .065 


8 


1 1 


11-75 


1 1 . 




36.914 


34.558 


108.434 


95-033 


13.401 


-325 


347 


1.51 


45 .028 


8 


I 2 


12.75 


I 2 . 




40.055 


37-7 


127 .677 


113 .098 


I4-S79 


. 290 


-319 


i . 27 


48.985 


8 



pies governing steam pipe design are: (i) 
The moment steam leaves the boiler it loses 
heat and some of it must condense. (2) 
Water of condensation is an evil, and since 
its formation cannot be wholly prevented 
a perfect pipe system must provide means 
of removing it as fast as it forms. (3) There 
can be no flow of steam without a correspond- 
ing drop of pressure. (4) Drop of pres- 
sure of steam does not cause a loss of energy. 
(5) The mechanical design must provide 

*From Crane Company's Catalog. 



the pipe contains low spots or "pockets" 
where the water can accumulate it will 
gradually decrease the effective pipe area 
until the steam velocity is increased to a 
sufficient degree to lift the water and sweep 
it along the pipe. This is especially liable 
to happen when the demand for steam is 
irregular; when the flow is small the water 
will settle into the pockets but when the 
heavy load is suddenly thrown on, the re- 
sulting rush of steam will carry the water 



214 



THE STIRLING WATER-TUBE SAFETY BOILER 



bodily with it. Since water is practically 
incompressible its effect when traveling at 
high velocity differs little from that of a 
solid body of equal weight, hence its impact 
agrinst elbows, valves, or other obstructions, 
is equivalent to a heavy hammer blow, and 
frequently the pipe is ruptured. If the quan- 
tity of water is insufficient to produce such 
serious results, it will certainly cause knock- 
ing and vibrations in the pipes, the final 
consequence of which will be leaky joints. 
When the water reaches the engine its effects 
will vary from disagreeable knocking to 
destruction of the engine. In such cases the 
usual procedure is to blame the boiler for 
producing "wet" steam, but the fallacy of 
this view can easily be shown. Assume a 
compound condensing engine which develops 
200 H. P. under 125 Ibs. gauge pressure, and 



pies governing this removal. Each sketch 
represents an elevation of a system of steam 
piping. 

M indicates the boiler and E the engines. 
Sketch .1 shows the simplest scheme of pip- 
ing. All the water of condensation will 
flow into the engines, unless removed by 
separators at 5. If all the engines are shut 
down, water will collect in the pipes, and 
unless it be drained off by "bleeders" it will 
cause trouble when an engine is started. 

In sketch B the engine connections are 
taken from the top of the main, hence most 
of the water will flow to the "dead end" or 
drop leg X; the small amount carried over 
to the 5ngine may be removed by the sepa- 
rators 5. The water which collects at A' 
must be continuously removed by a trap or 
pump, and if this be done the system will 





f 


( 


\ j 


~N 

^ r 


s 

L 




X 


< 


' s J 


s 

h r^ 


5 


I 


1 


[_ 


LI Li 


J LJ 


LJ 


r 


4 


[j 


y [_ 


y [E 


J 








A 












B 








FIG. 43. LINE DIAGRAMS SHOWING ELEVATION OF STEAM PIPE SYSTEMS 



uses 1 8 Ibs. of steam per horse-power hour. 
Assume that the air temperature is 80, 
and that the steam pipe is 6 inches dia., and 
150 feet long. The engine will use 3,600 Ibs. 
of steam per hour, and under the given con- 
ditions the steam pipe, if uncovered, will 
condense about 225 Ibs. per hour, or 6.25% 
of the total. If by proper covering 80% 
of this condensation can be prevented, the 
remainder will be i.25%of the total, and 
the boiler is in no sense responsible for this 
amount of moisture in the steam. In many 
cases where properly designed boilers are 
blamed for wet steam, a similar analysis 
would locate the trouble in the steam pipes. 
Removal of the Water It follows that 
efficient means of removing the water of 
condensation are absolutely imperative. The 
sketches in Fig. 43 will illustrate the princi- 



be drained, and the piping maintained at an 
even temperature, whether the engines are 
operating or not. 

If the trap or pump at X be replaced by a 
drain pipe which is connected below the 
boiler water-line, as in sketch C, the steam 
main is at once converted into a high pres- 
sure gravity steam-Heating system, and it will 
automatically drain itself, provided the drop 
in pressure in the main is not sufficient to 
maintain a level \)t water in the drain higher 
than the point X. If the level due to the 
drop be lower than the separators 5, then 
their drips also could be connected to the 
drainage pipe, and in that case the engine 
supply pipes will form part of the high pres- 
sure heating system, and will be self draining. 
Should it be necessary to make a dip or pocket 
in the steam main, as at Y, its lowest point 



ADVANTAGES OF AN EFFICIENT DRAINAGE SYSTEM 



215 



should also be connected to the drainage 
system. Thus arranged, the entire system 
will maintain its circulation, there will be 
no straining due to heating and cooling, 
and the system will be self-draining whether 
the engines be working or not. All such 
drainage connections should be provided 
with check valves, as shown in Fig 44. 

When boilers are situated a sufficient dis- 
tance below the engines (as in some mills), 
the installation of piping arranged as a 
gravity-return system is entirely feasible 
and the results leave nothing to be desired. 
In most cases the necessary difference of 
level cannot be obtained, and a mechanical 
equivalent for it must be installed. The 
usual method is to install either steam traps, 
which will deliver the water of condensation 
into the heater or hot well; or steam pumps, 
which will return the water directly into the 
boiler at practically steam temperature. A 
number of drain pipes are connected to each 
trap or pump. Traps are not as reliable as 
pumps, hence the latter should be preferred 
if the amount of work to be done will justify 
their greater cost. 

Branches from the mains should never 
be taken from the bottom. When possible 
they should be taken from the top, and a 
horizontal partition in the center of the 
tee will still further improve the action, 
since in case of a sudden demand for steam 
at the engine, the water flowing along the 
bottom of the main cannot be lifted into the 
outlet pipe. 

The pitch of all pipe should be in the direc- 
tion of the steam travel. Whenever a rise 
in the main is necessary, a drain, as at Y in 
sketch C, should be tapped into the lowest 
point just below the rise. The mains and 
all important branches should terminate in a 
drop-leg, as at X, and every such drop-leg 
or other low spot in the system, should be 
connected to the drainage pump. A similar 
connection should be made to every fitting 
which is of such shape that it can form a 
water pocket. An effective method of drain- 
ing the mains is to run at a suitable distance 
below them a small drainage pipe, about i^ 
to i^-inch dia., which is connected to all 
low spots in the piping or fittings, and con- 
veys the water to the drainage pump. To 
prevent this pipe from delivering steam and 



water into any section of the main from which 
steam mav have been cut off bv the regular 
valve systems, a swinging check valve should 
be inserted into each connection between 
the main and the drainage pipe. This valve 
can be placed at an angle of nearly 45, as 
in Fig. 44, so that the check valve disk 
is nearly vertical, hence requires practically 
no head of water to open it when in action. 
Each engine supply pipe should have its 
own separator placed as near the throttle 
as possible, and the drains from these sep- 
arators can be connected to a drainage 
system also. 




FIG. 44. LOCATION OF CHECK VALVE IN DRAIN PIPE 

Drain pipes which are occasionally opened 
by hand may be useful for blowing out large 
quantities of water at intervals, but their 
action must be intermittent, and they are 
usually neglected. 

It is questionable whether the small 
additional cost of providing a steam plant 
with an efficient drainage system as above 
described could be invested to better ad- 
vantage. It will insure a positive saving by 
reducing the initial condensation in the en- 
gine; it will insure better cylinder lubrica- 
tion with a reduced supply of oil; and it 
will return the water of condensation to the 
boilers at practically steam temperature. It 
will eliminate the straining of pipes due 
to cooling when engines are shut down, hence 



216 



THE STIRLING WATER-TUBE SAFETY BOILER 



obviate leaks; and it will remove all danger 
of wrecking engines by water. 

Size of Steam Pipes The larger the pipe, 
the greater the surface, hence the greater 
the amount of condensation. The usual 
practise is to limit the steam velocity in 
mains to 6,000 feet per minute, yet there are 
many cases where this figure could be in- 
creased with advantage. That this is not 
more frequently done is due to the impression 
that drop of steam pressure causes a loss of 
energy. In the explanation of the throttling 
calorimeter, page 79, it was shown that 
there is no loss, because the difference in 
energy between the steam at the higher 
and lower pressures is converted into heat 
which evaporates moisture and superheats 
the steam. But if the pressure drop is in- 
creased the steam velocity is also increased, 
hence the pipe area is decreased; but in that 
case the exposed surface is also decreased, 
hence the amount of condensation is pro- 
portionately decreased. Therefore, by in- 
creasing the drop in pressure, the condensa- 
tion is not only decreased, but the heat 
liberated by the drop will evaporate all or 
part of the water which is formed, hence the 
steam which reaches the engine will be drier 
than if it had been delivered through a larger 
pipe; consequently the drop in pressure 
causes an actual saving in heat instead of 
a loss. To deliver the steam at the engine 
at a given pressure it is necessary only to 
increase the boiler pressure by the amount 
of the drop, and if this be done it is evident 
that the size of steam mains and the resulting 
condensation will both be decreased, with 
consequent improvement in tne action of 
the engine. When steam is to be conveyed 
through long lines of piping the advantage 
of raising the boiler pressure and keeping 
the mains small will be very marked. The 
entire method is exactly parallel to standard 
practise in electrical distributing systems, 
where the generator voltage is adjusted 
to suit the loss in the feeder lines; this loss 
corresponds to the drop in pressure in the 
steam pipe, and by reason of the drop both 
feeder wire and the steam pipe can be of 
reduced size. At the electrical receiving 
station a storage battery is often installed, 
and its analogue in the steam plant is a 
receiving drum placed near the engine. The 



effect of this drum is to cause a nearly con- 
stant flow of steam through the pipe which 
connects it to the boiler or main header, 
while the engine draws out steam inter- 
mittently. The action is more fully de- 
scribed under caption "Boilers Supplying 
Hoisting Engines," page 209, and is worthy 
of careful study. To carry the analogy still 
farther, it is known that in an electrical 
distribution system covering a wide area, 
storage batteries installed at particular points 
absorb energy when there is a surplus, and 
liberate it when there is a deficiency, and 
thus steady the voltage on the entire system, 
and obviate necessity of supply mains of 
excessive size. In precisely the same way 
a steam pipe system can be designed so that 
storage drums at ends of long lines, etc., 
will receive steam during the time the engine 
cut-off is in action, and thereby steady the 
pressure, and enable the pipe sizes to be so 
reduced that the area of exposed surface 
saved in the pipe exceeds that added by the 
drum, hence not only will the pressure at 
the engine be kept more steady and the 
vibrations of the pipe be reduced, but the con- 
densation will be decreased, and the removal 
of the water which is formed will be more 
easily accomplished. There are many cases 
in all kinds of plants where a practical ap- 
plication of these principles would greatly 
improve the operation of the machinery. 

The Constructive Details of steam piping 
have been so well worked out that only the 
leading points need be touched upon. The 
defects usually noted are flanges which are 
too light, and inadequate provision for ex- 
pansion. The use of pipe bends of long 
radii, instead of cast elbows, is becoming 
more general, and they can usually be so 
placed as to take up all the expansion without 
the use of slip-joints with stuffing boxes. 
The latter almost invariably cause trouble; 
if their use is compulsory the pipe must be 
so anchored that the slip-joint cannot pull 
itself apart. 

Duplicate Pipe Systems are now seldom 
installed. They increase first cost, multiply 
the number of valves and joints, increase 
the condensation, and are of questionable 
utility. It will generally be found that the 
same or less money, if invested in a single 
pipe system properly designed and built, will 



AUTOMATIC BOILER STOP VALVES 




insure equally good service at a lower cost 
for maintenance. 

Valves should be so located that they can- 
not form water pockets when either opened or 
closed. Globe valves cause a drop of pres- 
sure, but as explained, this does not cause a 
loss of energy, but a conversion of it into heat ; 
the globe forms a water pocket unless it is set 
with its stem horizontal, while a gate valve 
may be set with spindle vertical or at an 
angle as occasion demands. Valves over 5 
to 6 inches diameter should be provided with 
by-pass, to enable them to be easily opened, 
and to permit steam to be admitted very 
slowly into the pipe which can thereby be 
gradually warmed up, and prevent water 
hammer. 

Boiler Valves The feed valve should 
always be a globe. A gate valve cannot be 
closely regulated, and often clatters owing 
to the pulsations of the feed pump. 

Boiler stop valves should be so placed that 
water cannot collect above them. Thus, 
if the pipe rises for a distance above the 
boiler nozzle before turning horizontal, the 
stop valve should be in the horizontal run. 
When a long bend leads out of the boiler 
nozzle the stop valve should be at the highest 
point of the bend. When it is impossible 
to avoid locating the valve so that water can 
accumulate above it when closed, a drain 
pipe should be provided. The best practise 
is to provide two valves, one placed as near 
the boiler as practicable, and the other at 
the junction of the boiler pipe and the main 
header, with a drain pipe placed between the 
two valves to remove any water due to 
leakage through the header valve. 

Automatic Stop Valves are coming more 
into use, and in some European countries 
their installation, when several boilers are 
operated together, is prescribed by law. 
When several boilers feed into the same 
header it is evident that if a tube ruptures 
the steam from the main will rush toward the 
disabled boiler, hence all the boilers will tend 
to discharge through the one which is dis- 
abled. The sudden rush of steam thus caused 
will lift water, which may be swept along to 
the engine and wreck it. The difficulty 
of closing the stop valve of the disabled 
boiler is evident. This can be obviated by 
selecting for position nearest the boiler an 



automatic stop valve, which will close when 
the pressure in the main slightly exceeds 
that in the boiler, and open when the boiler 
pressure rises again. Such valves cost but 
little more than ordinary stop valves, and 
should a tube fail in a boiler to which such 
a valve is attached the operation of the other 
boilers is not affected, and nothing need be 
done except to allow the disabled boiler to 
empty itself. 

TABLE 62 

DIAMETER AND DRILLING TEMPLET 

FOR EXTRA HEAVY 

PIPE FLANGES 

MASTER STEAMFITTERS' STANDARD 



Diameter 
of Pipe 
Inches 


Diameter 
of 
Flanges 
Inches 


Bolt 
Circle 
Inches 


Number 
of Bolts 


Diameter 
of Bolts 
Inches 


Length of 
Bolts 
Inches 


I 


4* 


3i 


4 


4 


2 


li 


5 


3f 


4 


i 


a* 


I* 


6 


4i 


4 


I 


'* 


2 


6* 


5 


4 


1 


J 


2* 


7* 


si 


4 


a 

4 


3 


3 


8i 


6f 


8 


f 


3 


3i 


9 


7i 


8 


5 

8 


3i 


4 


10 


7i 


8 


1 


3* 


4i 


io 


8* 


8 


3 

4 


3^ 


5 


II 


9i 


8 


3 

4 


3f 


6 


iai 


i of 


12 


a 

4 


4 


7 


14 


"I 


12 


8 


4 


8 


15 


i3 


12 


i 


4i 


9 


16 


14 


12 


8" 


4i 


10 


i7* 


'Si 


16 


1 


4l 


12 


20 


T>7 3 

J 74 


16 


1 


5 


14 


22^ 


20 


20 


1 


Si 


15 


23i 


21 


2O 


I 


Si 


16 


25 


22^ 


20 


I 


si 


18 


27 


24^ 


24 


I 


6 


20 


29^ 


26| 


24 


i* 


61 


22 


34 


28f 


28 


it 


6^ 


24 


34 


3ii 


28 


i* 


6.| 



Note Flanges, flanged fittings, valves, etc., 
are drilled in multiples of four, so that fittings may 
be made to face in any quarter and holes straddle 
center line. 




V^l^/v^l CTTT *JL "**' *a* r~?7 

/ y4 <* 'jf il ^1i ; ftfc "T^^ . 

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** X** 4*" H ' <ft Ll - * * f ; j& ! '~T~1 -*~-:.-=-r. ;r , 

x x ><?L^ 'J? 1 : -dUILJiii 



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bttl 

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tf 




FIRST NATIONAL BANK BUILDING, CHICAGO, ILL., OPERATING 1,875 H. P. OF STIRLING BOILERS 

218 



Boiler and Steam Pipe Coverings 



When saturated steam is conveyed through 
pipes a portion will condense, the amount 
depending upon the temperature of the steam, 
and the velocity and temperature of the air 
surrounding the pipe. This condensation 
causes a loss not only of volume of steam, 
but of efficiency in utilizing the remainder 
of the steam when it reaches the engine, con- 
sequently where fuel economy is an object 
all steam pipes, boiler steam drums, re- 
ceivers, etc,, should be covered with some 



For practical purposes 3 B. T. U. per hour 
may be assumed. To determine the money 
value of the loss in any particular case, de- 
termine the square feet of exposed pipe surface ; 
determine the temperature of the steam, by 
referring to Steam Table, page 74, assume 
the average temperature of the air sur- 
rounding the pipe, and then compute the 
temperature difference. Conditions of oper- 
ation of the plant will approximately de- 
termine the number of hours per annum 



TABLE 63 
EXPERIMENTS ON STEAM PIPE COVERING* 











B. T. U. per Hour 






Kind of Covering. 


Diam. of 
Test Pipe. 
Inches. 


Thickness 
of Covering 
Inches. 


Temperatures Fah. 


per Square Foot of 
Pipe Surface. 


Date of 
Test. 


Testing 
Expert. 
















Steam . 


Air. 


Total. 


Per Degree 
Difference. 






Hair Felt .... 


2 


o .96 


302.8 


71 -4 


89.6 


0.387 


1901 


Jacobus 


" " .... 


8 


0.82 


348-3 


69 . o 


117.9 


o .422 


1894 


Brill 


Remanit for intermediate p essure 


2 


0.88 


304 . 5 


73-3 


100.3 


0-434 


190 


Jacobus 


' high pressure 


2 


.30 


306.6 


76.! 


83.7 


0.363 


190 


Jacobus 


Mineral Wool ... 


& 


30 


344- 


58.3 


81.3 


o. 284 


1894 


Brill 


Champion Mineral Wool 


s 


.44 


34<3. 


74-3 


86. i 


0.317 


1894 


Brill 


Rock Wool 


8 


.60 


344 


63 . o 


72.O 


O.256 


1 89^ 


Brill 


Asbestos Sponge Felted 


2 


I2 5 


364- 


60 . 7 


145-Q 


0.477 


190 


Barrus 


" " " . 


IO 


375 


364. 


62.8 


85.0 


o . 248 


190 


Barrus 


" " . . 


2 


14 


309. 


79-4 


SQ-7 


o . 260 


190 


Jacobus 


Magnesia. .... 


4 


. I 2 


388. 


72 .0 


147.0 


0.465 


1896 


Norton 


" 


2 


9 


354 


80. I 


155-8 


o 5^7 


1896 


Paulding 


" 


8 


25 


S44 . 


66.3 


1 06 . 6 


o "?8i 


i So 


Brill 


" 


2 


.08 


310 . 


81 .6 


69^8 


^ . j.*f 
0.304 


i uy 
I9O 


Jacobus 


. 


2 


.00 


365. 


64.6 


155-0 


0.515 


1 90 


Barrus 


Asbestos, Navy Bran ! . 


IO 
2 


.19 

. 20 


365- 
309. 


66.0 
79-4 


103.0 
69.9 


0-347 
0.304 


190 
190 


. Barrus 
Jacobus 


. 


2 


125 


365- 


64.6 


176.0 


0.585 


190 


Barrus 


* ' " " , . 


IO 


375 


365. 


66.8 


I 12 .0 


o. 375 


190 


Barrus 


Manville Sectional 


8 


.70 


345- 


78.3 


93 -4 


0.394 


1894 


Brill 


. 


2 


3i 


354. 


80. I 


157-0 


0.572 


1896 


Paulding 


Asbestos Air Cell 


4 

4 


25 

. 12 


388. 
388. 


72.0 
72.0 


143.0 
1 66.0 


0-453 
0.525 


1896 
1896 


Norton 
Norton 


Asbestos Fire Felt 


2 

8 


. 9 6 
30 


303.3 
344.7 


72.3 
79.0 


165.5 
133-5 


0.716 
0.502 


1901 
1894 


Jacobus 
Brill 




2 


. oo 


354-7 


80. i 


198.0 


o. 721 


1896 


Paulding 


Fossil Meal ... 
Riley Cement ... 


2 

8 

8 


.90 

75 
75 


307.4 
347 I 
347-9 


72-5 
75-3 
74.3 


180.0 
238.0 
260.0 


0.766 
0.876 
0.950 


1901 

1894 
1894 


Jacobus 
Brill 
Brill 



efficient heat insulating material, and the 
saving thus effected will pay large interest 
on the investment. 

It has been experimentally determined that 
each square foot of bare iron pipe surface 
will radiate about 3 British thermal units 
per hour for each degree Fahr. difference 
between the temperatures of the steam and 
the outside air, the exact amount varying 
with the velocity and humidity of the air. 



during which steam will be in the pipe line, 
hence the total B. T. U's lost per annum 
can be roughly determined. This divided 
by 965.8 will give the number of pounds 
of steam from and at 212 equivalent to this 
loss; the evaporation per pound of coal and 
the cost of coal per ton (including cost of 
handling it and ashes) being known, the 
money value of the loss is at once derived. 
Or expressing the matter in a formula: 



*Arranged from data given in Paulding's Condensation of Steam in Covered and Bare Pipes. 



KINDS OF PIPE COVERING 



221 



Cost per annum of steam condensed= 
- f } 



In which .4=area of exposed pipe surface in 

square feet. 

^temperature Fah. of steam. 
^=average temperature Fah. of sur- 

rounding air. 

A/=hours per annum steam is in 
the pipe line. 

=evaporation from and at 212 
Fah. per Ib. of coal. 

C=cost of coal and handling, 
per ton. 

For long tons the constant 2,000 should 
be changed to 2,240. 

By properly applying a covering of good 
grade, as much as 90 per cent, of this may be 
saved. There are many brands of covering 
on the market, and the only practical way 
to be sure of what each will do is either to 
purchase of a firm of established integrity, 
or else make comparative tests. If the co- 
efficient of conductivity of a covering is 
known, the heat loss for any given set of 
conditions can be calculated, but the com- 
putation is tedious and the results are only 
approximate. The method of using this 
coefficient, and of determining it by experi- 
ment, may be found in Paulding's Con- 
densation of Steam in Covered and Bare Pipes, 
together with curves showing the relation 
between thickness of covering and the heat 
loss, and other interesting information on 
the transmission of heat. 

It is questionable, however, whether in- 
tricate calculations of the heat loss from 
pipes are of great practical utility, owing to 
the impossibility of assigning sufficiently 
close values to the factors which affect all 
such calculations. About all that can be 
done is to determine with a fair degree of ap- 
proximation the relative amount of heat 
lost by bare and covered pipes. Table 63 
has been compiled from tests made by various 



authorities, and for each covering the B. T. 
U.'s transmitted per square foot of pipe sur- 
face per hour per degree difference between 
the steam and air temperatures have been 
computed and entered in the table. Since 
bare pipe loses 3 B. T. U. per hour per square 
foot per degree difference in temperature, 
the per cent, of heat saved by the covering 
can be computed with sufficient accuracy for 
all practical purposes. In case of an , un- 
known covering the heat loss per degree of 
difference can be determined experimentally. 

There is a dearth of accurate data on the 
life of pipe coverings of different kinds. It 
is well known, however, that as a result of 
constant vibrations, some of them when on 
horizontal pipes lose their shape, hang loose 
on the pipe, and allow the material to shift 
so that the covering becomes thicker on the 
bottom than on the top. Only previous 
experience or careful inquiry as to the ex- 
perience of others can indicate what defects 
of this nature may develop in a covering 
after it has long been at work. 

Pipe coverings may be either "sectional" 
that is, moulded to shape, and attached to 
pipes by bands, etc., so it can be removed at 
any time, or "plastic" which is mixed in 
shape of mortar, and built up on the pipe in 
layers, so that it cannot be removed and 
replaced without working it over. The 
former has more joints, and often under 
vibration changes shape, but is more con- 
venient for work subject to future altera- 
tion. The plastic covering obviates joints, 
adheres closely to the pipe if of proper quality 
and workmanship, needs few repairs, and 
the thickness can be varied to suit. It is 
more difficult to apply than sectional cover- 
ing but more permanent when applied. 

Pipe coverings should receive the same 
care and frequent inspection as any other 
part of a plant. Their efficiency quickly 
falls off if air is allowed to circulate between 
them and the pipe, and if allowed to become 
wet they only increase the evil they are 
expected to remedy. 



Boiler Cleaning 



No boiler can maintain its efficiency un- 
less it is kept clean both inside and out. 
Deposits of solid matter on the water side of 
the heating surface interfere with the heat 
transmission, and cause the metal to burn, 
blister, or crack, thereby greatly increasing 
the repair and fuel bills. Systematic boiler 
cleaning should therefore be included as a 
regular feature of the operation of every 
steam plant, and for the purpose of assist- 
ing those who do this work the following 
suggestions are offered. 

Cutting Boilers out of Service Prepara= 
tory to Cleaning A boiler should never 
be emptied while the brickwork is hot; if 
this be done there will be danger of over- 
heating the metal, and the incrustation will 
bake to such hardness as greatly to increase 
the difficulty and expense of removing it. 

The best procedure is to allow the boiler 
to stand at least twelve hours, and more if 
possible, after the fires are drawn, then to 
empty it slowly; the manhole plates should 
then be removed, and the interior be thor- 
oughly washed out with cold water, after 
which the use of the turbine cleaner should be 
started. If this plan requires a longer time 
than is available, the next best method is to 
allow the boiler to stand three or four hours 
after the fires are drawn and the main stop 
valve is closed; the pressure should then be 
let off, the blow-off valves be opened slightly 
and water be pumped in at the same rate 
as it is escaping from the blow-off, which 
can be done by regulating the pump to the 
speed necessary to hold the water at the 
same level in the gauge glass. Pumping 
should be continued until the boiler is cooled 
to a temperature low enough to permit it to 
be opened and washed with cold water, and 
the use of the cleaner should then begin. 

To hasten the cooling of the boiler it is 
not unusual to open the fire and ash-pit doors 
and the damper, thus causing a rush of cold 
air through the setting. While this assists 
in the cooling, it is an unsuspected cause of 
the destruction of many furnace walls. A 
rush of cold air over highly heated fire-brick 
causes a rapid cooling of the exposed sur- 



faces, uneven shrinkage, and cracking or 
"spalling" of the brick and loosening of the 
joints. The degree to which these evil 
effects are caused by cold air is not generally 
recognized, and it is advisable never to throw 
open the damper and draft-doors until about 
four hours after the fires are drawn. 

Before starting to remove a manhole plate 
the operator should, by trying the gauge 
cocks, or by opening the valve on the steam 
hose connection, definitely ascertain that 
there is neither a steam pressure nor a 
vacuum inside of the boiler. A disregard of 
this simple precaution has been responsible 
for many serious accidents to those engaged 
in cleaning boilers. 

Cleaning the Interior Practically all 
waters available for boiler feeding contain 
some impurities which deposit either as 
mud or as scale. When mud is present it 
is nearly always precipitated into the lower 
drum of the Stirling boiler, whence it should 
be blown out. at regular intervals which must 
be determined by close observation in each 
case. Occasionally some mud adheres to the 
rear bank of tubes, and this should be 
regularly removed by washing down with 
water applied under a good pressure through 
a hose terminating in a rose-shaped nozzle. 

Scale varies from a porous texture which 
adheres loosely to the metal, to a hard flinty 
structure which can be removed only by 
chiseling or cutting it. Its removal is often 
tedious but the task should never be slighted 
Various ways of removing scale have been 
tried, but experience shows that the most 
satisfactory method it to use some mechani- 
cal device, operated by power, and so de- 
signed as to cut or break the scale. Such 
devices may be divided into two classes: 
(i) Those which, by very rapid hammer 
blows, detach the scale by cracking it; (2) 
those which, after the manner of an emery 
wheel dresser, cut the scale into small pieces. 
Tools of the first-named kind have the serious 
disadvantage of swaging the tubes to a larger 
or irregular diameter, producing crystalliza- 
tion in the metal, and causing leaks where the 
tubes are expanded into the sheets, hence 



223 




CANDLER INVESTMENT CO.'S BUILDING, ATLANTA, GA., OPERATING 6OO H. P. OF STIRLING BOILERS 

224 



OPERATING THE TURBINE CLEANER 



225 



their use is not to be recommended. Tools 
of the second-named class are preferable, 
and of these the most satisfactory is the 
hydraulic turbine tube-cleaner. 

Hydraulic Turbine Tube=Cleaner This 
is made in many designs, one of which is 
shown in Fig. 45. The cylindrical casing 
contains a hydraulic turbine, consisting of a 
fixed guide plate which directs the water at 
the proper angle upon the vanes of the 
rotating wheel. The water is supplied 
through a wire-wound rubber hose attached 
to the upper end of the casing, and the power 
generated in the turbine is transmitted, 
through a universal joint, to a cross-shaped 
head which carries four pivoted arms to the 
extreme end of which the cutters are at- 
tached. This construction makes the tool 
perfectly flexible, so that with equal facility 
it will pass through either a straight or curved 



into a sump or sunken tank, in which it 
can settle and be used repeatedly. 

Piping for Supplying the Water 

In many cases the turbine is operated by 
two men, one in the boiler, and another 
outside to turn the water on and off as . 
required. This method not only requires 
one man more than is necessary, but causes 
waste of time in giving orders to operate 
the water valve. A much better plan is 
to locate along the rear of the boilers a 
pipe conveying the water, and to provide 
this pipe with branches opposite the middle 
of each aisle between boilers. On these 
branches place a plug valve, upon the 
stem of which an S-shaped handle about 
1 8 inches long can be placed whenever 
cleaning is to be done. A piece of light 
rope tied to each end of this handle is ex- 
tended into the boiler drums, and by pulling 




FIG. 45. HYDRAULIC TURBINE TUBE CLEANER 



tube. The thrust on the working parts is 
taken upon ball bearings or on hardened 
steel rings, placed between the turbine wheel 
and the guide plate. 

The cutters used under normal conditions 
are hardened steel toothed disks, similar 
to those used for emery wheel dressers, as 
shown in Fig. 46. In special cases other 
forms of cutters are used, as later described. 

When the turbine is revolving at a high 
speed, the pivoted arms are thrown out, and 
the cutters, through centrifugal force, bear 
upon the surfaces to be cleaned and chip 
away the scale in small pieces. The stream 
of water flowing from the turbine envelops 
the cutters, keeps their edges cool, and 
washes away the scale as fast as it is de- 
tached. 

In arid countries, where water is scarce, 
the overflow from the turbine may be run 



these ropes the operator regulates the water 
to suit himself, wastes no time in giving 
orders, and but one man is required. The 
pipe supplying the water should be free from 
reducers, and the hose connection should 
be full size 

Operating the Cleaner Always use 
the largest size of turbine which will pass 
through the tubes. When cleaning begins 
the turbine should be inserted into the 
end of a tube, and the operator should 
have a firm grasp on the hose within 6 or 
8 inches of the tube end. When the water 
is turned on, the rotating parts begin to 
revolve, the cutter arms fly out, and the 
attack on the scale begins. The operator 
should then immediately begin moving the 
turbine alternately up and down and con- 
tinue this as long as the tool is working. 
The water should not be cut off while the 



>vT^ H 

f OF THE 

f UNIVERSITY 




HOW TO SOFTEN REFRACTORY SCALE 



227 



cleaner is in the tube, nor should the cleaner 
be permitted to remain stationary - - it 
must be kept constantly moving up and 
down. As the scale is removed, the turbine 
will gradually travel farther down the tube, 
and when it finally reaches the mud drum 
the tube will be clean, unless the tool has 
been either pushed through too fast, or 
allowed to draw itself through. Usually 
the weight of the tool and hose will tend 
to draw the turbine down, and if allowed 
to go ahead too fast, it may remove the 
scale from a spiral-shaped strip, leaving 
it in other places, hence it is important 
that the operator train himself to detect 
by the sound, and vibration of the hose, 
the character of the surface upon which 
the cleaner is working, and to regulate the 
forward motion of the cleaner accordingly. 

The toothed disk cutters give entirely sat- 
isfactory results when the scale does not 
exceed ^-inch in thickness, which covers 
all cases of normal use, since except in an 
emergency, scale exceeding | to T 3 g-inch 
thick should never be allowed to form in the 
rear bank of tubes between regular clean- 
ings, and T V-inch thickness of scale on tubes 
in the front or middle bank is prima facie 
evidence that the boiler has been neglected. 
In cases of neglect, not only will a greater 
thickness of scale form, but by long ex- 
posure to heat it bakes harder than other- 
wise, which greatly increases the difficulty 
and expense of removing it. As soon as 
a boiler is found to be heavily scaled, it 
should at once be cut out of service and 
cleaned. If it is found that the scale does 
not exceed f-inch thick, the toothed disk 
cutters should be replaced by solid conoidal 
cutters, made of tool steel, as in Fig. 47. 
Place these with the small end downward. 

Should the scale exceed f-inch in thickness, 
it is best removed by a four-lipped drill, 
made of hardened tool steel, with cutting 
edges at an angle of 45 degrees to the axis 
of the tool, as in Fig. 48. When the scale 
is excessively thick, it should first be attacked 
by using a drill head of the form shown in 
Fig 49. which should be followed by Fig. 48. 

The tools represented in Figs. 48 and 49 
are fastened to the turbine by removing 
the cross-shaped piece which carries the arms, 
and substituting the head to which the 



drill is attached. When using these tools 
on heavy scale the turbine should be handled 
with judgment, as it is evident that the 
tool cannot be advanced as rapidly as when 
the scale is thin . 

By careful observance of the foregoing 
instructions it will be possible to remove 
any deposit found in a tube, but the time 
required will of course vary according to 
the nature of the scale, and the thickness 
to which it has been allowed to accumulate. 

Care of the Turbine Cleaner Those 
who have had no experience with turbine 
cleaners are advised to take the tool apart, 
and familiarize themselves with its con- 
struction. While the tool is well built, 
it must be properly cared for if satisfactory 
results are to be obtained. When each 
boiler cleaning is finished, the turbine should 
be thoroughly washed, then stored in a 
pail of oil. 

How to Soften Refractory Scale When 
scale has been allowed to accumulate and 
bake to an excessive hardness its removal 
is difficult, The work may be expedited 
by introduction of some agent which will 
rot and soften the scale. One method 
is to introduce 40 to 80 Ibs. of carbonate 
of soda (ordinary soda-ash) according to 
size of the boiler, block the safety valves 
open, then allow the water to simmer gently; 
in a particularly bad case this may require 
several day's boiling. The scale will thus 
be softened so that it can easily be cut; the 
boiler should finally be thoroughly rinsed 
with fresh water, or foaming may result. 

Kerosene is often used for the same 
purpose. Some spray it over the surface 
with a squirt pump, or other means, while 
some fill the boiler nearly full of water, 
introduce a quantity of kerosene, then 
open the blow-off valve very slightly, so 
that as the water level slowly falls the 
kerosene is brought into contact with every 
portion of the interior surface. Before one 
enters the boiler it should be thoroughly 
ventilated to remove volatile gases from 
the oil, since they are highly explosive. 

Kerosene should never be used without 
first testing it for free acid which is liable to 
be present from the refining. Insert blue 
litmus paper, and if it turns red the oil should 
be rejected since the acid will cause corrosion. 



15 



228 



THE STIRLING WATER-TUBE SAFETY BOILER 



Oil in Boilers Scale is not the only 
cause of burned tubes. Burnt and blistered 
tubes will be the inevitable result of allowing 

011 to enter boilers. When the presence 
of oil is detected the boiler should at once 
be cut out of service, and as soon as it has 
cooled it should be emptied, and several 
pailfuls of soda-ash be placed into the 
mud drum. The boiler should then be 
filled with water, and be gently fired for 

12 to 15 hours, keeping the steam pressure 
down to 12 or 15 pounds. At intervals, 
a portion of the water may be let out, and 
be replaced by pumping in an equivalent 
amount; finally the boiler should be allowed 
to cool, then be emptied and the interior 
be thoroughly rinsed with fresh water. 

Cleaning the Fire Side of the Heating 
Surface The fire side of the heating sur- 
face should be kept clean, and under no 
circumstances should a thickness of soot 
exceeding ^V of an inch be allowed to form, 
or the boiler efficiency will be greatly de- 
creased. The surface of the tubes and 
drums should be regularly blown off with 
steam by using the hose and steam blower- 
pipe furnished with the boiler. Since the 
heating surface can be blown off in 10 to 
15 minutes, there is no reason for neglecting 
this work. The interval between such clean- 
ings will depend upon the character of the 
fuel; with smoky fuels the cleaning should 
be done at least once per day, preferably 
during the period of lightest load; the sur- 
face should also be well brushed off at reg- 
ular intervals. 

Never use the steam-blower when the boiler 
is cold, or the steam will condense, dam- 
pen the brickwork, and cause the sooty 
deposits to become gummy and adhere 
to the metal. It is advisable to have not 
less than 50 pounds pressure on the boiler 
when the steam-blower is used, and there 
should be a fire on the grates to insure the 
brickwork being hot. 

Necessity for Periodical Examinations 
No matter how excellent the feedwater 



may appear to be, every boiler should at 
regular intervals be examined, and even 
though no trace of deposit be noted the 
cleaner should be passed through the tubes, 
to ascertain their condition, and enable 
one to know that they are clean. 

The mud drum should be inspected reg- 
ularly, and all accumulation of soot, ashes, 
or dirt, be thoroughly removed. In all 
cases where coal, particularly anthracite, 
is used, the accumulations on the mud 
drum should be blown off before the boiler 
is emptied. The reason for this is that 
such deposits often contain coal which 
holds fire for many hours after the furnace 
fires are drawn, and the heat due to this 
cause may damage the drum or tube ends 
if the boiler is emptied. 

All soot, ashes and dirt should be removed 
from the top of furnace arches every time 
the boiler is cleaned. The top of the bridge 
wall should be swept clean, and any defects 
in the brickwork should be repaired. The 
asbestos rope joint between brickwork and 
ends of the mud drum should be inspected, 
and unless found perfectly air tight, it 
should be made so before the boiler goes 
into service. The opening where the blow- 
off pipe passes through the wall should be 
inspected, and if air leaks are found they 
should be stopped by caulking with asbestos 
rope. All cleaning doors should be examined, 
and if air leaks are detected they should 
be stopped. 

Whenever a boiler is off for cleaning it 
is an excellent plan to make a careful general 
inspection of it both inside and out, in- 
cluding the setting, cleaning doors, valves 
fittings, etc. Incipient defects may thus 
be discovered and corrected at a trifling 
expense, serious troubles will be obviated, 
and the general operation of the plant will 
be improved. It is doubtful whether the 
short time necessary for such inspection could 
be more profitably employed, since a boiler 
plant continually proves the truth of the 
ancient maxim," A stitch in time saves nine.' ' 



Care and Management of the Stirling Boiler 



Before starting a new Boiler Make a 
complete examination of boiler and setting. 
Inspect all valves, fittings and attachments, 
and ascertain that they are properly connected 
and in perfect order. See that nuts on all 
tie rods in frame are turned up tight, and 
at intervals during the first six months after 
the boiler is in operation, ascertain if these 
nuts are tight, and if not, make them so. 

Inspect the brickwork, and see that 
height of fire-arches and distance between 
end of fire-arches and nearest tube corre- 
sponds with drawings. Sec that the mud 
drum can expand freely; that baffle openings 
are as marked on drawings, baffle tiles all 
in place and joints sealed with fire clay, 
and that all mortar and rubbish which has 
dropped down on the mud drum while 
brickwork was in progress, has been scraped 
off and drum surface brushed clean. This 
is frequently overlooked. See that blow-off 
pipe and valve, as well as blow-off main to 
which they are connected, can move freely; 
on no account should they be cemented or 
bricked in, but should lie free in a trench or 
slot. See that space around the blow-off 
pipe where it passes through rear setting 
wall is plugged with asbestos rope until it 
is air-tight. 

When oil or gas fuel is used, take par- 
ticular care to ascertain: if the fire arches 
terminate at proper distance from the tubes; 
checkerwork walls in rear of grates are of 
proper height; openings between brick over 
grates are of proper width, and burners set 
to blow the flame parallel to the brick over 
grates and at proper distance above them; 
to minimize effect of gas explosions, turn 
back the latches of cleaning doors, so the 
doors can blow open freely and release the 
pressure due to the explosion. 

See that all dirt, waste, and tools, are re- 
moved from interior of boiler. Then place 
in boiler about a peck of soda-ash, fill to 
usual level with water, boil gently for several 
hours after boiler is finally heated up, let 
stand till cold, then empty, and finally give 
interior of boiler a thorough washing with 
cold water. This will remove all oil and 



grease and prevent foaming when the boiler 
goes into commission. 

Firing a Boiler with Green Walls will 
invariably crack the Setting, hence it is 
absolutely necessary to dry out the brickwork 
properly. If circumstances permit, it is 
advisable as soon as stack connections are 
made, to block open the damper and ash-pit 
doors, so that circulation of air will aid in 
drying the brickwork. The next step is to 
fill the boiler with water and put in a light 
fire of shavings, which may gradually be 
increased by using some wood, continuing 
until the walls are thoroughly dried inside 
and out. This will require several days, 
but by close observation the walls, if built 
according to instructions (page 233) can be 
dried out without cracking. 

When steam is available an excellent 
method of drying the brickwork is to connect 
temporarily a small steam supply pipe to 
the new boiler, and to attach a trap or other 
drainage apparatus to the blow-off pipe. 
The new boiler when filled with steam will 
then act as a large radiator, and will heat 
the air around it, hence if ash-pit doors 
and damper be left open there will be a 
steady current of warm air passing through 
the setting, and the brickwork will be grad- 
ually and effectively dried out. The steam 
supply should be very small at first, and 
be increased as the drying-out proceeds. 

Cutting Boiler into Steam Main Under 
no circumstances whatever should a boiler 
be "cut in" with other boilers unless the 
pressure within it is identical with that in 
the main. Before opening the boiler stop 
valve or the header valve, be sure that there 
is no water in the length of pipe between these 
two valves. Steam valves should always 
be opened or closed very slowly, and the 
valves should first be eased from their seats 
slightly for some moments to permit a cir- 
culation to become established before the 
valves are fully opened. 

When the boiler is in service, observe 
the following carefully and at regular in- 
tervals make an inspection so you will know 
everything is right. 




368 H. P. OF STIRLING BOILERS, DOBCROSS LOOM WORKS, DOBCROSS, ENGLAND 

230 



TROUBLES CAUSED BY OIL IN BOILERS 



231 



Steam Gauges When pressure is off 
these should stand at zero, and when safety 
valve blows off, the gauge should indicate 
the same pressure for which the valve was set 
to pop. If it does not, one is wrong, and the 
gauge should at once be compared with one 
of known accuracy, and any error be rectified. 

Safety Valves These are useless if al- 
lowed to become stuck on their seats. To 
prevent this, cause the valves to pop once 
on every shift. 

Water Level Never fire a boiler with- 
out first ascertaining that it contains the 
necessary quantity of water. When operat- 
ing, never depend on gauge glass, or water 
alarms alone, but try the gauge cocks. 

Gauge Cocks, Water Gauges, and pas- 
sages to gauge must be kept clean, and should 
be blown out frequently. Formation of 
colored rings on the glass, due to oil or other 
deposits, is misleading, and should be ob- 
viated by frequent cleaning. Automatic 
water gauges of all types and all other 
automatic appliances, need frequent in- 
spection. 

Blow=Off Valves must be kept tight, and 
should be known to be tight. Every blow- 
off pipe should be so arranged that a leak 
can be seen. This can be arranged by plac- 
ing in the pipe just beyond the blow-off 
valve, a tee with a i" outlet to which a gate 
valve is attached; this valve should be left 
open except when bio wing-off is in progress, 
so that it will act as a tell-tale in case the 
blow-off is leaking. Where boiler water 
deposits material that is liable to cut the 
blow-off valve and cause leaks, a gate or 
asbestos packed plug cock should be placed 
between boiler and regular blow-off, so it 
can be closed and permit the blow-off valve 
to be cleaned without shutting dawn the 
boiler. 

Firing The method of firing coal to be 
adopted will depend upon the kind of coal 
used; the chapter on Fuel Burning should 
therefore be carefully studied, and the most 
efficient method of firing be determined by 
close observation and experiment. The draft 
should be regulated to the least amount 
necessary to maintain the desired rate of 
combustion. 

When burning wood, carry as thick a fire 
as the draft will allow; the fresh wood on 



top tends to force down the partly burned 
wood thus covering the grate with a bed of 
coals, and reducing the air excess. 

When burning oil, see that the flame is 
white, not red, and free of sparks which 
indicate incomplete combustion. The air 
supply should be regulated to a point where 
further diminution of it will cause smoke to 
appear in the stack. Avoid squirting un- 
atoinized oil on the tubes as each spot where it 
touches is liable to develop a blister. 

Foaming If caused by excessive demand 
for steam, checking the outflow of steam will 
usually stop it. If caused by excess of dirt 
due to concentration, blowing down and 
pumping in clean water will usually stop it. 
In case of violent foaming, check the draft 
and fires. The Stirling boiler never foams 
with good water unless the water is carried 
too high, in which case lower the water-line, 
which should never be carried higher than 
two gauges when the boiler is steaming. 

Blowing Off When feed water is salty 
or muddy, blow off a portion at as frequent 
intervals as the conditions demand. Empty 
the boiler every week or two and fill up 
afresh, but never empty the boiler while brick- 
work is hot, and never feed cold water into a 
hot boiler. Always blow off all accumulations 
of soot, fuel, etc., from the mud drum before 
emptying a boiler. The fine coal, particularly 
anthracite, carried over on the drum by the 
draft, may hold fire many hours after the 
furnace fires are out. If under such con- 
ditions the boiler is emptied the mud drum 
and tube ends may be overheated, and leaks 
or broken tubes are liable to result. 

Low Water Immediately cover fire with 
ashes or earth, preferably wet; in default of 
anything else handy use fresh coal; the 
important point is to check the heat as 
quickly as possible. Draw the fire as soon 
as it can be done without increasing the heat. 
Do not turn on the feed, lift safety valve, start 
or stop engine, until boiler is cooled down. 
Before firing the boiler again, put on the cold 
water test, locate any leaks, and stop them. 

Cleaning To avoid waste of fuel and 
deterioration of the boiler, keep it clean inside 
and out, by carefully following the directions 
given in chapter on Boiler Cleaning. 

Oil in Boilers Burnt and blistered tubes 
will be the inevitable result of allowing oil 



232 



THE STIRLING WATER-TUBE SAFETY BOILER 



to enter boilers. As soon as the presence of 
oil is detected the boiler should be cut out of 
service, and be treated as directed in chapter 
on Boiler Cleaning. 

Air Leaks All air that enters boiler or 
breeching except by passing through the fire, 
causes losses which are often large and un- 
suspected. Carefully test for leaks around 
cleaning door frames, blow-off pipes, dampers, 
breeching connections, etc., and carefully 
plug each with asbestos rope or cement. 



use unless it receives proper attention as 
soon as its use is discontinued, hence the fol- 
lowing instructions must be carefully ob- 
served. Before emptying the boiler place 
in each upper drum several gallons of crude 
oil so that when the blow-off is opened the oil 
will form a light covering over the inside 
surface of all tubes and drums. (Before the 
boiler is started again, remove this oil with 
soda-ash as already directed.) Dry the 
boiler thoroughly when emptied out. 




STIRLING CHAIN GRATE STOKERS READY FOR SHIPMENT 



Steam or Water Leaks should be stopped 
without delay, and extra precaution should 
be taken to exclude water from those portions 
of the boiler covered by brickwork, other- 
wise unsuspected corrosion may occur. Leaks 
in steam pipes over the boilers should be 
located and stopped. 

Internal Corrosion of Boiler This is 
caused by some harmful agent in the water, 
and the matter should at once be referred to 
some competent chemist experienced in in- 
vestigating boiler feed water. 

Standing Unused If a boiler remains idle 
it will deteriorate much faster than when in 



If the boiler cannot be emptied, fill it quite 
full of -water, to which has been added a 
quantity of soda-ash, then boil off the air 
and close the boiler air-tight. 

Remove the baffle. tiles, thoroughly sweep 
off all accumulations of ashes and soot with 
a wire brush, and give all tube and drum 
surfaces a coat of boiled linseed oil. Smear 
all brass or finished work with vaseline slush, 
or a mixture of white lead and tallow. 

Cover the stack tops with a water tight 
hood, and see that no water can reach the 
boiler through breechings, openings in roof, 
or other sources. 



Specifications for Masonry in Stirling Boiler Settings 



To secure satisfactory service from the 
boilers, it is absolutely essential that the 
setting be constructed with utmost care, 
and of the best materials. After the setting 
is completed it should be carefully dried 
out as directed in chapter on "Care and 
Management of the Stirling Boiler" (page 229) 
and from time to time inspection should be 
made to locate any cracks or loose brick- 
work, and these should be at once repaired. 
Prompt attention to this matter will not 
only insure more efficient results from the 
boiler, but obviate unnecessary repair bills. 

The following specifications should be 
observed during progress of the work: 

Excavation Consult the drawings and 
stake off accurately according to dimensions 
given thereon. Where boilers rest upon rock, 
excavate for ash-pit and space under mud 
drum. In other cases excavate to depth 
shown upon drawing or to such additional 
depth as is requisite to insure a solid foun- 
dation. 

Concrete Cover the entire surface with 
concrete to a thickness of 8 inches, unless 
the nature of the soil should require a heavier 
bed. When found necessary do not hesitate 
to make the bed heavier. The composition 
of the concrete should be one yard of rock 
broken to pass through a 2-inch ring, \ 
yard of clean, sharp sand, and 2\ barrels 
of Portland cement. Clean gravel will an- 
swer as well as broken rock. Mix well when 
dry, then wet and mix thoroughly. Avoid 
using too much water; 40 pounds of water 
to each 100 pounds of cement will be more 
than ample. When placing the bed of con- 
crete on foundation cover only such space 
as the quantity mixed will bring to the thick- 
ness required; work rapidly; ram the con- 
crete well with a 50 Ib. rammer having a face 
8 inches in diameter, and continue to ram 
until the mass is so compacted that water 
appears on the surface. See that the bed 
of concrete is level and smooth when finished. 

When concrete does not cost more than 
brickwork, the entire foundation up to floor 
line is frequently made of concrete with 
excellent results. 



Red Brickwork Carefully follow the 
drawing in laying off the brickwork and use 
good, hard, well burned brick, uniform 
in dimensions. Wet the brick before laying. 
From the concrete bed to the floor line use 
a well mixed mortar, composed of one part 
Portland cement to two parts of clean, 
sharp sand, grouting each course thoroughly 
with slush mortar. While the drawings 
show a cap stone under each support, this 
is imperative only where the brick has not 
a crushing resistance equal to eight times the 
load to be carried. When the cap stone is 
omitted, it may be replaced by a pier made 
of concrete, or of selected hard brick care- 
fully laid in Portland cement mortar. 

From the time the work is started until 
the last brick is laid, do not forget the im- 
portance of tight walls. See that every 
brick is properly bedded, and every joint 
well and thoroughly filled with mortar. 
Air leaks through the walls ruin the draft 
and destroy the efficiency of the boiler. 

All walls must be built straight and plumb, 
and carried up simultaneously, thoroughly 
grouting each course. 

On all red brickwork, from the floor line 
up, use well mixed mortar, composed of one 
part lime to three parts clean, sharp sand. 
Mortar must not be used while hot, caused 
from the slacking of freshly burned lime. 

The brick should be laid in courses of 
four stretchers to one header, i. e., every 
fifth course should be a header course. 

As the work progresses, see that all stay 
rods and anchor bolts are properly placed; 
set and anchor all door frames as shown on 
drawing, turning over each door an arch 
extending through the thickness of the wall. 
See that there are no air leaks between the 
door frames and the brickwork. 

The mud drum must be perfectly free, to 
allow the tubes to expand and contract as 
the conditions may require, and at no place 
must the brickwork be allowed to touch 
either the mud drum or the blow-off pipe. 
This rule positively admits of no exception. 
Nothing must affect the freedom of the mud 
drum. At the manhole end of mud drum 






o - 



PROPERTIES OF FIRE-CLAY 



235 



turn a complete arch circle, the inside of 
the circle being kept i-inch clear of the 
drum. This space to be afterwards filled 
with a ring of i-inch asbestos rope. Before 
the blow-off valve is attached, slip over 
blow-off pipe a piece of 4-inch pipe 12 inches 
long, and build same into wall as a thimble 
through which blow-off pipe passes, then plug 
up the annular space between the two pipes 
with asbestos rope or fiber. 

The bridge wall must be carefully laid to 
allow the mud drum freedom. There must 
be a space of i^ inches between the top of the 
bridge wall and the front row of tubes. 

In laying the red brick on top of the 
steam drums and the steam circulating 
tubes, use every precaution to have tight 
joints so as to thoroughly exclude air leaks. 
These bricks are to be laid in lime mortar, 
with the joints open at the upper edge, and, 
after all the bricks are in place, these joints 
should be slushed with cement, leaving a 
covering on top of the brick at least ^-inch 
thick. The thinner the joints between the 
bricks the longer the setting will last. 

Fitting Brickwork Around Boiler Sup= 
ports Figs. No. 50 to 57 show how this 
should be done. The red bricks should be 
laid up close against the inside flange of the 
outer columns as shown in Figs. No. 50 
and 51. Along the rear side of the front 
column, and the front side of the rear column, 
the face of the brickwork should be in line 
with the outer edge of the flanges of the 
I-beam column, with the exception that every 
fifth course of bricks should be placed into 
contact with the web of the columns, as 
marked in Fig. 51. 

When two boilers are set in battery there 
will be three angle-iron columns placed in- 
side of the party wall, and all around these 
columns a clearance of one-half inch must 
be left between them and the brickwork, 
as shown in Figs. 52, 53, and 54. 

When building the brickwork behind the 
metal front of the boiler care must be taken 
to see that it is placed in exact accordance 
with Fig. 55. The outer course of the side 
walls should be carried up to, and closely 
fitted against, the inside of the face of the 
outer columns and pilasters, so that the flange 
of the pilaster or column overlaps the side 
wall as shown in Fig. 56. The remainder 



of the brickwork behind the metal front 
should be carried up so that its forward face 
is one inch behind the panel plates, with the 
exception that each fifth course of brick 
should project forward sufficiently to come 
into contact with the metal front, thus as- 
sisting in supporting it and in holding the 
panel plates securely in place, as illustrated 
in Fig. 55. 

In order that the brickwork may be per- 
fectly tied or bonded, the header courses 
on the inside and outside faces of the wall 
should be on the same level and abut each 
other in the center of the wall; a course of 
headers must also be placed inside of the 
wall both above and below the outside 
header courses, and across their abutting 
line, as in Fig. 57. 

Lime Mortar Lime is greatly improved 
by allowing it to stand as long as possible 
between time of slacking, and using in the 
wall. In some countries lime is slacked and 
allowed to remain in pits a year before using, 
as the first slacking is not complete, and 
the mass contains small particles which slack 
only after long standing. When freshly 
slacked lime is used in a boiler setting, these 
unslacked particles finally swell, the mortar 
gets loose and "shattered," and the brick- 
work is a failure. Lime for boiler setting 
should be slacked at least six weeks, or longer 
if possible, before using. 

Fire=Clay Fire-clay is not a cement, 
and it has little or no holding power. Its 
office is therefore not to act as a binder, but 
merely to fill the voids. In consequence a 
fire-brick joint is the more perfect in pro- 
portion as the quantity of fire-clay ap- 
proaches the amount necessary to fill the 
voids, without preventing the brick from 
touching, precisely as in case of a glue joint 
between pieces of wood. Clay of consistency 
sufficient to permit use of trowel should not 
be permitted; the proper way is to mix the 
clay to requisite thinness, dip each brick 
into the clay, "rub and shove" each brick 
into final place, then drive it with mallet 
or hammer and block, until it actually 
touches the brick below it. Rigid adherence 
to these directions is absolutely essential when 
constructing -fire-arches. 

The two defects of fire-clay are its shrink- 
age during drying, and its lack of cement- 



236 



THE STIRLING WATER-TUBE SAFETY BOILER 



ing power. The former may be greatly 
diminished by adding to the clay about 20 
per cent, of its volume of fire-brick pulverized 
and sifted to fire-brick flour. This can be 
obtained in many places, but unless it is 
of the requisite fineness, avoid it, as coarse 
material will thicken the joints an amount 
which offsets the advantage. 

The cementing power of fire-clay may be 
increased by adding to and slacking . in with 
it about i^ per cent, of its volume of lime; 
measure the clay and for each cubic foot, put 
in a piece of lime not exceeding 4X2X2^ 
inches. This will have just sufficient fluxing 
power to unite with the clay and form a hard 
clinker which takes a grip on the fire-brick. 
It should always be used when building 
arches. 



measurements carefully, and lay off the 
lines of the skewback. When determining 
length of arch, be sure to consult the draw- 
ing for the particular job on which you are 
working, as the arch length varies with 
character of fuel. While laying off the skew- 
back, and while laying the brick in same, 
use a true straight edge the length of the 
arch. See particularly that the skewbacks 
have no lumps, bumps or other irregular- 
ities and the brick wall behind them is 
absolutely solid, and the red bricks laid close 
together so there will be no space filled with 
mortar or spalls. See that the two skew- 
backs are perfectly parallel, level and in 
line, the one with the other. Keep using 
the straight edge until the surfaces are smooth 
and regular. 





PLAN OF ARCHES 





SKEW BACKS TO BE ALL 
FIRE BRICK, LAID CLOSE 
AVOID SPALLS OR MORTAR 
FILLING. 

W WEDGE BRICK 
S=SQUARE BRICK 



FIG. 58 



DETAILS OF FURNACE ARCHES 



FIG. 59 



Fire=Brick Work When the point in 
the brickwork has been reached where 
the fire-brick commences, the fire and red 
brick must be carried up together, and from 
a distance 6 inches below the bottom of the 
grate bars to the skewback of the arch, every 
course must be a header course, and every 
fifth course of the fire-brick must be tied 
into the red brick. The best fire-brick 
obtainable must be used in the side walls 
of the furnaces and arches, beginning 6 inches 
below the bottom of the grate bars, and 
carried up on both side walls to the top of 
the arch, and from the front wall back to 
the front baffle-tiling. The arches must be 
constructed also of the very best grade of 
fire-brick obtainable. All fire-brick must 
be closely laid with a solution of fire-clay 
and water as above directed. 

Fire=Arches When the arch above the 
fire is reached, consult the drawing, take 



Next, set the center upon which the arch 
is to be turned and make the center as fol- 
lows : cut from i -inch plank three seg- 
ments of the proper length and radius. Let 
the distance between the two outer segments 
be 6 inches less than the length of the arch; 
place the third segment in the center of the 
two outer ones. See that they are parallel 
with each other and square, so that there 
will be no wind in the center when nailed up. 
Batten the segments with i-inch square 
strips, laid close together, said strips being 
smooth and straight. 

After the strips are well and securely 
nailed to segments, plane off to a true circle. 
When the center is completed, set in place, 
being careful that the two outside strips 
line exactly with skewbacks. If they will 
not line, either the skewbacks or center 
must be wrong, and the defective one should 
be righted before a single brick is laid. 



LOCATING THE BAFFLING TILES 



137 



When the center is set and found right, 
select smooth, straight and uniform rectan- 
gular bricks and wedge bricks (bull heads); 
have the solution of fire-clay soft and well 
mixed. Do not use a trowel; dip the bricks 
and shove up close, driving to place with a 
brick hammer, or mallet and block. 

Keep the joints as thin as possible. 

The bricks must positively not be laid in 
consecutive rings; every joint must be 
broken and have a bond equal to one-half the 
width of a brick. While laying the arch, 
alternate square brick with bull heads and 
vice versa, as may be found necessary to 



show the smallest and largest arches, the 
same general plan of procedure covers all 
intermediate sizes. 

Finally, at end of arch, run a g-inch wall 
across the spandrel openings, as at A, Fig. 59, 
to provide a parallel throat for gases as they 
pass into the tubes. 

Fire Door Arches For building the fire 
door arch The Stirling Company furnishes- 
a special skewback. Consult the draw- 
ing, and the accompanying cuts, Figure 60, 
and follow them closely, using the same 
careful methods advised in building the fire- 
arches. The bricks (bull heads) in this arch 






ELEVATION OF ARCH NO. 1 



ELEVATION 



SECTIONAL ELEVATION 






SECTIONAL PLAN 



SKEW BACK 



FIG. 60. DETAILS OF FIRE DOOR ARCHES 



maintain a true circle. Be particularly 
careful that the arch is not turning too fast. 
When the keying course is reached, try the 
bricks in dry and see that they have the 
proper taper. If not of the proper taper 
cut them nicely to fill the space. 

Do not leave any interstices to be filled 
with fire-clay, as it will only fall out when 
dry and let the arch down. 

The keying course should be a snug fit, 
driven carefully to place by laying a small 
block of wood on top of the brick, on which 
hammer lightly, being careful not to drive 
so hard as to crush or otherwise mutilate 
the brick. When properly keyed, remove 
the center. 

Figures 58 and 59 fully illustrate how 
this arch should be built. While the figures 



must be turned in consecutive rings, making 
no attempt to bond the one with the other. 

The fire bricks laid above the water circu- 
lating tubes must not be laid tight nor keyed 
like an arch. Dip the bricks in fire-clay and 
lay snugly to place; when completed grout 
with fire-clay wash, leaving a good coating 
above the bricks. 

Baffling Tile Consult the drawing and 
see that all supports and hangers for the 
baffling tiles are in proper place. If found 
wrong have them righted before laying a 
single tile. Commence at the side wall and 
lay the tiles in rows longitudinally with the 
drums, laying a single row at a time. 

See that the first tile fits smoothly and 
closely to the side wall, and that the other 
edge comes immediately back of the vertical 



238 



THE STIRLING WATER-TUBE SAFETY BOILER 



center of the tube. If found too wide, cut 
to fit. Care at this point will bring every 
seam in the row exactly back of the tube 
centers. Fit the entire row dry, and see 
that each tile lies closely and snugly to its 
companion. 



Follow all these instructions until all the 
tiles are laid, watching that the tiles fit 
closely at the joints, top, bottom and sides. 
See that there are no bumps on the portion of 
the tile face that comes into contact with the 
tubes; let it lie smoothly and evenly in place. 




PART OF 1,500 H. P. OF STIRLING BOILERS, WOLVERINE COPPER MINING CO, KEARSARGE, MICH. 



Here also, the trowel must be set to one 
side. Dip the edges of the tiles in a fire-clay 
solution, then lay them into place carefully. 

There must be no leaks in joints nor stop- 
ping up of interstices with fire-clay to fall 
out when dry, and thus divert the gases from 
their proper course, allowing them to take 
short cuts to the smokestack. 



After all is done, give the joints several 
coats of clay wash which should be made 
of a thin solution of fire-clay, and be applied 
with a whitewash brush. 

All cleaning doors are to be located in 
side and rear walls as shown on blue prints; 
fit the brick close up against the door frames 
to prevent air leakage. 



Index 



The figures refer to the pages. 



Absolute pressure, definition, 72; of steam, 

7 1 . 7 2 - 74- 

Absolute temperature, 48. 

Absolute zero, 48. 

Acids, cause pitting and corrosion, 61 ; method 
of neutralizing, 61 ; sources of in feed water, 
6 1 ; testing for in kerosene, 228. 

Acetylene, weight and calorific value, 133. 

Adaptability, the comparative of different 
types of boiler to various duties, 41. 

Air, chapter on, 55 ; composition of, 55 ; causes 
corrosion of boilers when dissolved in feed 
water, 61 ; cooling effect of excess of, table, 
1 08; filters through leaks in boiler settings, 
232; specific heat of, 55; weight of required 
for combustion, 106, table, 107; formula 
for pressure and volume of, 55; weight 
and volume of, table, 55; vapor in, 55, 56. 

Alabama coals, analyses and heating value 
of, 116; proximate and ultimate analyses 

of, i35- 

Alabama Steel and Wire Co., boilers of, 140. 

Altitude, atmospheric pressure correspond- 
ing to, 58; determination of stack dimen- 
sions according to, 176; effect of on boiling 
point of water, 58. 

American coals, analyses and calorific value 
of, 1 14. 

American Society of Mechanical Engineers' 
code of rules for boiler trials, 201. 

Anaconda Copper Mining Co., boilers of, 212. 

Analyses, caution in interpreting, 131; cal- 
culation of heat value from, 106, 131, and 
135 to 138; of flue-gases, 181; proximate, 
131, 135; ultimate, 131. 

Analysis of coal for boiler tests, 205. 

Anthracite, analyses of, in, 114; chemical 
changes from wood into, in; calorific 
value of, 112, 114; description and market 
sizes of, in; fixed carbon and volatile 
matter in, in, 112; may hold fire many 
hours, 231; methods of burning, 141. 

Atmosphere, flow of steam into, 90 and 91; 
Napier's formula for flow of steam into, 
91 ; pressure per square inch of, at different 
altitudes, 58. 

Atomic weight of elements affecting com- 
bustion, 105. 



Arch bars of the Stirling boiler, 9, 15. 
Arches, construction of for furnaces and fire 

doors, 236, 237; necessary over furnaces 

for good combustion, 142. 
Armour Institute, boilers of, 40. 
Ash, composition of, 112. 
Ashes and refuse, treatment of during boiler 

test, 204. 

Ash-pit doors of the Stirling boiler, 17. 
Automatic furnace feeder for bagasse, 148. 
Automatic stop valves for boilers, 169, 173. 
Available draft in stacks, 217. 

.Baffles, in the Stirling boiler, n; effect of 
tubes passing through, n; tiles for, and 
how they should be laid, 237. 

Bagasse, description and calorific value, 120, 
12 1 ; conveyor and automatic feeder for, 
148; effect of moisture in, 147; furnace and 
setting of Stirling boiler for burning, 146, 
147 ; test of boiler burning, 149. 

B amis' draft gauge, 179. 

Beaume's hydrometer for testing oils, 126. 

Benzine, 123. 

Bernoulli's theorem, 87. 

Berwind White Coal Mining Co., boilers 
of, 20. 

Bingham Copper and Gold Mining Co., boilers 
of, 194. 

Bituminous coal, analyses of, in, 115; 
behavior of in furnaces, 142; description 
and general properties, in; heat value of, 
112, 115; fixed carbon and volatile matter 
in, in, 112; injured by exposure to weather, 
113; methods of burning, 142. 

Block-Pollack Iron Co., boilers of, 166. 

Blast Furnace gas, boiler for utilizing, 164; 
burning of, 163; computation of heating 
value of, 133; test of boiler burning, 165. 

Bio wing-off, with salt or muddy water, 231. 

Blow-off valves, 231. 

Boilers, adaptability of different types to 
different requirements, 41 ; cleaning of, 
223; chart representing efficiencies of, 188; 
code of rules for trials of, 201 ; covering for, 
219; distribution of heat developed in fur- 
naces of, 191 ; effect of oil in, 231 ; efficiency 
of, 29, 39, 126, 127, 153, 187, 205; for min- 




MILLS BUILDING, SAN FRANCISCO, CAL., OPERATING 450 H. P. OF STIRLING BOILERS 



ur I n r 




INDEX 



241 



ing service, 209; horse-power of, 195 et seq.; 

preparation of, for standing unused, 232; 

provision for overload capacity in, 199; 

selection of, for a given engine capacity, 

195; Scotch Marine boiler, 37; the Stirling 

boiler, see Stirling boiler; water-tube versus 

fire-tube boilers, 35. 
Boiler feed water, see feed water. 
Boiling points, of water at different altitudes, 

58; of sea water, 58; table of, for various 

substances, 49. 

Bolts for steam pipe flanges, table, 217. 
Brickv/ork, specifications for, 233. 
British thermal unit, 48. 
Brownlee's table for flow of steam, 91. 
Brail's experiments on constriction of circu- 
lation in horizontal water- tube boilers, 15. 
Burners for petroleum, 152; number required 

for different furnace widths, 153; per cent. 

of steam used by, 153 ; pressure of oil needed 

for, 153. 

(Baking and non-caking coals, in. 

California oils, heat value of, 125. 

Calorimetry, of fuels, 138; as applied in 
determining specific heat of solids, 55. 

Calorimeters for fuel, Mahler's, 138; Parr's, 
138. 

Calorimeters for steam, chart for use with, 
80; compact form of, 83; formulas for, 81, 
85; limits of accuracy of throttling, 83; 
location of sampling nipple for, 85, 204; 
separating, 83; sources of error in, 81; 
taking an observation with, 85; throttling, 
and equations for, 79. 

Calorific value, see heat value. 

Calorie, 48, 131, foot-note. 

Candler building, boilers of, 224. 

Cannel coal, 112. 

Capital invested, efficiency of, 31. 

Carbon monoxide, heat loss due to incom- 
plete combustion of, 191; weight and heat 
value of, 133. 

Carbon, atomic weight of, 12; combustion 
data for, 106; fixed, 112. 

Care and management of boilers, 229. 

Cast iron, why first used in manufacturing 
water-tube boilers, 7 ; elimination of from 
the Stirling boiler, 17; is a cause of boiler 
explosions, 17; trade names under which it 
is often disguised, 17. 

Caustic potash for Orsat apparatus. 184. 

Caution in interpreting analyses, of fuels, 131. 



Chain grate stokers, effect of excess air in 
connection with, 145; the Stirling chain 
grate, 159. 

Charts, showing boiler efficiency, 188; show- 
ing combustion rate of coal, 189; showing 
ing diameter and horse-power of chimneys, 
172; showing draft required for different 
coals, 174; showing graphical representa- 
tion of Kent's heating values in terms of 
combustible, 137; for Goutal's fuel formula, 
136; for Mahler's fuel formula, 132; show- 
ing relation between gas temperature, steam 
generated, and heating surface passed over, 
94; for throttling calorimeter, 80. 

Check valve in drain pipe, 215. 

Chemical elements, combining weights of, 

105- 

Cheval, definition and value of, 195. 

Chicago Union Traction Co., boilers of, 22. 

Chimneys and draft, chapter on, 169. 

Chimneys, draft in one 100 feet high, 169; 
draft losses in, 171, 173; height and diameter, 
173; horse-power of, 172; Kent's table of, 
177; proportions of, for boilers burning oil, 
178; proportions of, for high altitudes, 176; 
solution of a typical problem in the design 
of, 176. 

Cincinnati Gas and Electric Co., boilers 
of, 14. 

Circular drum seams eliminated from the 
Stirling boiler, 8. 

Circulation of water, constriction of obviated 
in the Stirling boiler, 15; M. Brail's ex- 
periments on, 15. 

Classification of coals according to com- 
bustible, in. 

Classification of good and bad feed water, 65. 

Cleaning of boilers, chapter on, 223; com- 
parison of the difficulty of, for various 
types, 39; on fire side of heating surface, 
23, 228; on interior of heating surface, 21, 
223. 

Cleaning doors of the Stirling boiler, n. 

Coal, analyses of Alabama, 135; analyses 
and calorific value of leading American, 
114; approximate heating value of general 
grades, 112; ash in, 112; bituminous, de- 
scription of, in; behavior of in furnace, 
142; caking and non-caking, in; cannel, 
112; classification of according to com- 
bustible, in; compared with natural gas, 
129; compared with petroleum, 126; defini- 
tion of kinds, in; description and sizes 



242 



THE STIRLING WATER-TUBE SAFETY BOILER 



of anthracite, 1 1 1 ; determination of moisture 
in, 204; draft required for different kinds, 
113; dust, burning of, 113; Hunt's formula 
for heat value of Illinois, 136; Kent's table 
of approximate heat values of, 135, and 
chart, 137; methods of firing various kinds 
of, 143; sampling of, 204; semi-anthracite, 
in; semi-bituminous, in; tables, 112, 114 
to 1 1 8 ; weathering of, 113; weight of burned 
per square foot of grate at different boiler 
ratings, 191, and chart, 189. 

Coal tar, 129. 

Coke, 119. 

Coke ovens, utilization of waste heat from, 
161; boilers for burning gases from, 162; 
test of boiler burning gases from, 163. 

Colorado Fuel and Iron Co., boilers of, 12. 

Columbia Chemical Co., boilers of, 16. 

Combining weights of chemical elements, 105. 

Combustible, classification of coals according 
to, in; does not really include oxygen 
and nitrogen, 112, foot-note. 

Combustion, air required for, 106, 107, 183; 
chapter on, 105; chart showing draft re- 
quired for various rates of for various coals, 
174; hydrogen available for, 106; rates of, 
at different boiler capacities, chart, 189; 
ratio of air supplied to theoretical amount 
required for, 183, 184. 

Commercial efficiency of boilers, 29. 

Compressibility of water, 57. 

Concrete, composition and working of, 233. 

Consolidated Main Reef Mines and Estates, 
boilers of, 78. 

Constriction of circulation in boilers, causes 
steam pockets and reversal of direction of 
flow, 15; obviated in the Stirling boiler, 15. 

Construction of the Stirling boiler, advan- 
tages of, 11, 23; imitations of, 33. 

Contraction and expansion fully provided for 
in Stirling boilers, 13. 

Convection of heat, 50. 

Cooling effect of excess air in boiler fur- 
naces, 108. 

Copper Queen Consolidated Mining Co., 
boilers of, 170. 

Correction for heat values, on account of 
hydrogen, moisture and nitrogen, 133. 

Corrosion of boilers, 61, 232; Ost's theory 
of, 61. 

Cotton States and International Exposition, 
boilers of, 199. 

Counterbalanced fire doors, 31. 



Course of gases in the Stirling boiler, 1 1. 
Coverings for boilers and pipes, 219. 
Cuprous chloride for Orsat apparatus, 184. 
Curved tubes, advantages of, and unfounded 

prejudice against, 21. 
Cutters for turbine tube cleaner, 226. 
Cutting boiler into steam main, 229. 
Cylinder boilers, waste heat from, 167. 

Data and results of evaporative tests, 206; 

same worked out for a specific case, 192. 
Density, of gases at atmospheric "pressure, 

182 ; of mixtures of air and vapor, 56. 
Determination of heating value of fuels, 131. 
Detroit Edison Company, boilers of, 96. 
Diagrams of steam pipe systems, 214. 
Diffusion bagasse, 121, 122. 
Distribution of heat losses in boilers, 191. 
Dobcross Loom Works, boilers of, 238. 
Draft, available, 169, 173; for different 

fuels, 174, 175; formula and constants for, 

171; in chimney 100 feet high, 169; losses 

of in furnaces and flues, 175; losses in 

stacks, 171; must be regulated for each 

fuel and combustion rate, 141. Also see 

chimneys and draft. 
Draft gauges, 178. 
Drain pipes for steam mains, 215; check 

valve in, 215. 

Drilling templet for steam pipe flanges, 217. 
Driving boilers at high and low rates of 

evaporation, 27. 
Drums, absence of complication in, of the 

Stirling boiler, 13; for steam storage, proper 

location for, 209, 211, 216. 
Drum heads of forged steel, 9,13. 
Drum lugs of the Stirling boiler, 15. 
Dry steam, production of in the Stirling 

boiler, 27. 

Dulong's fuel formula, 106, 131. 
Duplicate steam pipe systems, 216. 
Durability of the Stirling boiler, 23. 
Dust from coal, utilization of, 113. 

rLbullition, 49. 

Economizers, 67. 

Economy of high pressure steam, 73. 

Edison Electric Co., Los Angeles, boilers 
of, 98. 

Effect of and correctives for impurities in 
feed water, 59. 

Efficiency, of boiler and grates, 187; calcula- 
tion of for boilers, 205; chart of, 188; 191; 



INDEX 



243 



of fuel, 29; of capital invested, 29; of ideal 
perfect heat engine, 73; obtainable from oil, 
153; relative, of boilers when clean and 
foul, 39; variation of, at different rates of 
driving, 193. 

Elbows in steam pipes, resistance of, 89. 

Elimination of temperature stresses from 
the Stirling boiler, 37. 

Ellison's draft gauge, 179. 

Energy stored in steam boilers, 17. 

Engines, consumption of steam for different 
types of, 198; efficiency of ideal perfect, 73; 
hoisting, and boilers for operating them, 
209; selection of boilers for operating a 
given power of, 195. 

Equivalent evaporation from and at 212 
degrees, 69. 

Ethane, weight and heat value of, 133. 

Evaporation, driving boilers at high and 
low rates of, 27; factors of, 70, 71; from 
and at 212 degrees, 69; required amount 
per hour per boiler horse-power from differ- 
ent feed temperatures, 198; total heat of, 50; 
units of, 72. 

Excess air in furnaces, effect of, 108. 

Expansion, coefficients of linear, 51; and 
contraction, fully provided for in the Stirling 
boiler, 13. 

Explosion of tubular boilers, 36, 37. 

r actors of evaporation, 70. 

Feed valve for boilers, should always be a 
globe, 217. 

Feed water, chapter on, 59; classification of 
good and bad, 65; effect of and correctives 
for impurities in, 59; heating of, 63, 67; 
operation of Stirling boilers when fed with, 
19; purification of by chemicals, 61; re- 
agents for treating after it enters boiler, 
63; scale-forming materials in, 59. 

Fire, temperature of, table, 50; computa- 
tion of temperature of, 107. 

Firing, methods of for boilers, 143, 231. 

Fire-brick, arches of over furnaces necessary 
for good combustion, 142; directions for 
laying, 236; damage to, caused by admitting 
cold air into furnaces, 223. 

Fire-clay, properties and preparation of, 235. 

Fire doors, construction of arches over, 237; 
counter balanced, 31; of the Stirling boiler, 

17- 

Fire-tube versus water-tube boilers, 35. 
First National Bank building, boilers of, 218. 



Flanges for steam pipe, dimensions and drill- 
ing templet of, 217. 

Flash point of oils, 125. 

Flow of steam, chapter on, 87; into the at- 
mosphere, 90, 91; Napier's formula for, 91; 
through pipes, 87, 89. 

Flowed steel, a trade name for cast iron, 17. 

Flues, draft losses in, 175; effect of right- 
angled turns in, 175; proper area of, 175; 
for boilers burning oil, 178. 

Flue-gas, analysis of, 181, 205; formula for 
weight of. 183; heat carried off by, 183; 
object of analysis of, 181; Orsat apparatus 
for analysis of, and solutions for, 184; 
table of results from analysis of, 186. 

Foaming in boilers, causes and remedies, 65, 
231; due to carbonates, 60; due to feeding 
cold water 68; due to grease, 64; due to 
scum, 60. 

Ford Plate Glass Co., boilers of, 38. 

Formulas in this book: 

No. PAGE No. PAGE No. PAGE 

i 53 20 89 38 173 

2 55 21 89 39 173 

3- 5 8 22. .91 40 173 

4- 67 23. ... 91 41 173 

5 7 2 j 106 42 175 

6.. . 81 ( 131 43-. -183 

7 ..... 81 25 107 44 183 

8 81 26 107 45 183 

9 85 27 121 46 183 

10 87 28 123 47. . 183 

ii 87 29. ....131 48 183 

12. . .87 30. .. .131 49. . . 183 

13- - - 87 31. . . .132 50 183 

14- 87 32 133 j 187 

15 87 33 137 | 205 

16. . . 87 34. . ..138 j 187 

17. . . 87 35. . .138 5 j 205 

18 87 36 171 53 202 

19- -89 37. . .171 54 221 

Fort Wayne Electric Co., boilers of, 220. 
Framework of Stirling boiler, 10; fitting 
brickwork around, 234, 235. 
Fuel, adaptation of Stirling boilers to dif- 
ferent kinds of, 27; additional quantity 
needed for superheating steam, 93; burn- 
ing of, chapter 141; calorific value of, 105; 
and chapter on determination of, 131 ; draft 
required for burning, 174, 175. 
Fuels, bagasse, 121 to 123, blast furnace 
gas, 163; chapter on, in; coals, in to 119; 
coal tar, 129; coke, 119; coke oven gas, 161; 



244 



THE STIRLING WATER-TUBE SAFETY BOILER 



corn, 123; gaseous, 106, 133; natural gas, 
128, 129; patent or pressed, 119; peat, 119; 
petroleum and crude oils, 123 to 127; spent 
tan, 120; straw, 120; water-gas tar, 129; 
wood, 119, 120; table of tests of boilers 
burning various kinds of, 208. 

Fuel formulas: Dulong's, 106, 131; Goutal's, 
136, 137; Kent's method, 135, 137; Hunt's 
for Illinois coals, 138; Mahler's, 132; cor- 
rection of, for hydrogen, nitrogen, and 
moisture, 133; range of accuracy of, 138. 

Furnaces, design and advantages of the 
Stirling, 10, 142; inefficient forms of, 142. 

Crases, course of in the Stirling boiler, n; 

density of at atmospheric pressure, 182; 

distinction between vapors and, 69; from 

blast furnaces, 163; from coke ovens, 161; 

natural, 128, 129; flue-, chapter on analysis 

of, 181; molecular weight of, 185; relation 

between temperature of from furnace, and 

heating surface passed over, 94; weight 

and calorific value of, 106, 133. 
Gasoline, 123; gasoline test for moisture in 

oil, 124. 
Gauge glass, fittings for, 19; level of water 

in, 203, 231. 

Gauges, 14; draft, 178; steam, 231. 
Gauge pressure of steam as distinguished 

from absolute, 72. 
General Electric Co., boilers of, 92. 
Globe valves, should always be used for 

feed valves, 217; resistance of to flow of 

steam, 89. 

Goodrich Co., The B. F., boilers of, 66. 
Goutal's fuel formula, 136, 137. 
Grates, efficiency of in connection with 

boiler, 187; for bagasse furnaces, 147; for 

oil fuel, 1 50; for wood, 147. 
Gravity of oils by Beaume hydrometer, 126. 
Grease in feed water, causes foaming, 64; 

causes overheating of plates, 64. 
Guanica Centrale, boilers of, 64. 

Hammel oil burner, 152. 

Hawaiian Brewing & Malting Co., boilers 
of, 88. 

Head of water, pressure due to, 57. 

Heat, chapter on, 47; distribution of losses 
of in boilers, 191; effects of, 47; latent, 48; 
losses of when burning anthracite with vary- 
ing supply of air, 107; loss of in flue-gases, 
183; mechanical equivalent of, 50; of liquid, 



50; specific, 48, table, 49; total, of evapora- 
tion or vaporization, 50; transfer of, 50; 
utilization of waste, 161. 

Heat balance, 193, 205. 

Heat value, of bagasse, 121, 122, 123; of 
blast furnace gas, 133, 163; of coal, tables, 
112, 114 to 118, 135; of coal tar, 129; of 
coke oven gas, 161; of corn, 123; of mis- 
cellaneous gases, 106, 133; of natural gas, 
128, 129; of oil fuel, 124, 125, 127; of spent 
tan, 120; of straw, 120; of water-gas tar, 
129; of wood, 119, 120. 

Heat value, formulas for, see fuel formulas. 

Heaters for feed water, open, closed, and 
economizers, 67. 

Heating of feed water, chapter on, 67. 

Heating furnaces, utilization of waste heat 
from, and tests of boilers installed in con- 
nection with, 73. 

Heating surface, all accessible in the Stirling 
boiler, 21; cleaning fire side of, 228; effect 
of soot in diminishing efficiency of, 23, 
foot-note; laws governing ratio of, to super- 
heating surface in boilers, 95 to 99; rela- 
tion between, and the gas temperature and 
amount of steam generated, 94. 

Hoisting engines, selecting boilers for, 211, 
steam pipes and drums for, 211. 

Horse-power, chapter on, 195; definition of, 
195; of stationary and marine boilers, 195- 
hourly evaporation corresponding to, 198; 
hourly consumption of steam per H. P. 
of engines, 198; indicated H. P. per boiler 
H. P., table, 196, 197. 

Hot-water heating, unique application of 
the Stirling boiler to, 29. 

Hunt's formulas for heat value of Illinois 
coals, 138. 

Hydraulic turbine tube cleaner, care of, 227; 
cutters for, 226; description of, 225; operat- 
ing of. 225. 

Hydrogen available for combustion, 106; 
calorific value of, 106, 133; correction for in 
fuel formulas, 133 ; weight of, 133. 

Illinois Steel Co., boilers of, 222. 

Iloilo Electric Light and Power Co., boilers 

of, 160. 

Imitations of the Stirling boiler, 33. 
Impure feed water, action of in the Stirling 

boiler, 19; effects of and correctives for, 

65; how to handle, 61. 
Impurities in water, chapter on, 57; effect 



INDEX 



245 



of, 59; solubilities of, 60; where deposited 
in boilers, 19. 

Independently-fired superheater, 102, 104. 

Indicated engine horse-power per boiler 
horse-power, 196, 197. 

Inefficient furnaces for boilers, 142. 

Injectors, in connection with boiler under- 
going test, 202. 

Inland Steel Co., boilers of, 190. 

I et, direction of for oil burners, 150. 
Joule's equivalent of heat, 50. 

Kenil worth Sugar Estate, boilers of, 144. 

Kent, Wm., statement of requirements for 
burning coal without smoke, 10; table of 
horse-powers of chimneys, 177; table of 
heat values of classes of coals, 135, 137. 

Kerosene, 123; use of for softening scale, 227. 

Kilowatt-hour, oil and coal per, table, 127. 

Kindling point of combustibles, 105. 

Kioto Electric Light Co., boilers of, 34. 

Latent heat, 48, of steam, 50, 69, 74. 

Laws defining relation between boiler heating 
surface and superheating surface, 99. 

Leaks, of air into boiler settings, 232; of 
steam and water in boiler plants, 232. 

Le Chatelier's pyrometer, 51, 52. 

Lehigh Portland Cement Co., boilers of, no. 

Level of water in gauge glass, 203, 231. 

Lignites, analyses and heat value, 118; dis- 
integration of by weathering, 113; descrip- 
tion of, 112; behavior of in furnaces, 142. 

Lime mortar, 235. 

Linear expansion of substances, table, 51. 

Liquid, heat of, 50. 

Los Angeles Gas and Electric Co. boi- 
lers of, 154. 

Los Angeles- Pacific R. R., boilers of, 211. 

Losses, of draft in stacks, 171; of draft in 
boilers, flues, and furnaces, 175; of heat in 
boilers and distribution of same, 191; of 
heat when burning anthracite with varying 
air supply, 107; of pressure in pipes con- 
veying steam, 87, 89. 

Low water in boilers, 231. 

Mahler, calorimeter, 138; fuel formula, 132. 
Management and care of boilers, chap, 229. 
Manhole plates and arch bars, 15. 
Marine boilers, as built by THE STIRLING 
COMPANY, 45; horse-power of, 195. 



Marsh gas, weight and heat value of, 133. 
Master Steamfitters Association Standard for 

pipe flanges, 217. 

McCahan Sugar Refinery, boilers of, 18. 
Measurements of high temperature, 51. 
Mechanical equivalent of heat, 50. 
Mechanical stokers, 145. 
Megass, see bagasse. 
Melting points of metals, 51, 52. 
Mercurial pyrometer, 51. 
Methane, combustion data for, 106. 
Methods of firing coal, alternate, coking, and 

spread- firing, 143. 
Mill bagasse, description and heat value of, 

122, 123. 

Mills building, boilers of, 240. 
Mining service, boilers for, 209. 
Molecular weight of gases, 185. 
Monongahela Light and Power Co., boilers 

of, 86. 
Moisture, in bagasse, 147; correction for in 

fuel formulas, 133; determination of in 

coal, 204. 

Mortar, for boiler settings, 235. 
Mud in feed water, effect of, 59. 
Mud drum, action of in precipitating im- 
purities, 19; door in wall opposite, 23; 

should be blown off on outside before 

emptying boiler, 231. 

Napier's formula for flow of steam into 
atmosphere, 91. 

Natural gas, 129; analyses and heat values, 
128; arrangement of boiler for burning, 151 ; 
burning of, 155; comparison of, with coal, 
129; computation of heat value of, 133; 
test of boiler burning, 157. 

Nipple for drawing off sample of steam for 
calorimeters, 85. 

Nitrogen, atomic weight of, 105; corrections 
for in fuel formulas, 133; dilutes furnace 
gases and causes heat loss, 105; molecular 
weight of, 185; weight and volume of, 182. 

Northern Texas Traction Co., boilers of, 156. 

Nova Scotia Steel and Coal Co., boilers of, 180. 

Nozzles for Stirling boilers, 115. 

Old Dominion Copper Mining and Smelt' 
ing Co., boilers of, 210. 

Olefiant gas, weight and heat value of, 133, 

Oil, advantages and disadvantages of, as 

fuel, 126; burners for, 152; comparison of, 

with coal, 126, 127; composition and heat 



246 



THE STIRLING WATER-TUBE SAFETY BOILER 



values of, 124, 125; effect of in boilers and 
methods of removing from, 228, 2<;i; 

\J 

efficiencies obtainable from, 153; flash point 
of, 125; gravity of by Beaume hydrometer, 
126; stacks for boilers burning, 178. 

Orsat apparatus for flue-gas analysis, 184. 

Ost's theory of corrosion of boiler plate by 
decomposition of water, 61, 

Oxygen, atomic weight and physical prop- 
erties, 105; computation of weight of for 
combustion of fuel, 106; determination of 
percentage of in flue-gases by Orsat ap- 
paratus, 182. 

Parr's fuel calorimeter, 138. 

Peat, 119. 

Peoples Railway Company, boilers of, 32. 

Petroleum, see oil. 

Philadelphia Museum's Exposition, boilers 
of, 134- 

Philadelphia and Reading R, R., boilers of, 28. 

Pioneer Iron Co., boilers of, 168. 

Pipes, covering of for steam, 219; flow of 
steam through, 87, 89; flanges for, table, 
217; for supplying steam to hoisting en- 
gines, 21 1 ; table of sizes for steam, gas, 
and water, 213. 

Piping for steam, chapter on principles of, 
213; diagrams illustrating systems of, 214; 
drainage of, 214; duplicate systems of, 
216; location of valves in , 217. 

Pitting of boilers, 61,232. 

Plain cylinder boilers, waste heat from, 167. 

Power, definition, 195 ; see horse-power. 

Pressed fuels, 119. 

Pressure, due to head of water, 57; to height 
of chimney, 169; of oil fed to burners, 153. 

Priming in boilers, causes and remedies, 65, 
231; due to carbonates, 60; due to feeding 
cold water, 68; due to grease, 64; due to 
scum, 60. 

Principles of steam piping, 213. 

Properties of saturated steam, 74. 

Proximate analysis, definition, 135; table 
of for coal, 114. 

Purification of feed water by chemicals, 61. 

Pyrogallol, for Orsat apparatus, 184. 

Pyrometer, 51; expansion, and errors of, 
52; Le Chatelier's thermo-electric, 52; mer- 
curial, 51. 

Quality of steam, 204; definition, 69, 79; 
determination of, 79 to 85. 



Quick closing gauge glass fittings, 19. 
Quick steaming, comparison of various types 
of boilers with respect to capacity for, 37. 

rvadiation of heat, 50; from steam pipes, 
213, 214, 219. 

Rapid circulation of water in the Stirling 
boiler, 13 ; advantage of, 15. 

Rate of driving, and effect on boiler effic- 
iency, 193. 

Ratio of air supplied to theoretical amount, 
for various analyses of flue-gases, 183, 184. 

Red brick, how they should be laid, 233; 
fitting of around boiler framework, 234, 235. 

Refractory scale, methods of softening, 227. 

Removal of water from steam mains, 214. 

Repairs, comparison of for different types 
of boiler at World's Columbian Exposition, 
33 ; comparison of on Stirling and shell types 
of boiler, 41 facility for making, to Stirling 
boiler, 25. 

Report of boiler trials, forms for, 206. 

Republic Iron and Steel Co., boilers at, 130. 

Resistance of elbows and globe valves to 
flow of steam, 89. 

Return tubular boilers, explosion of, 36, 37. 

Riverside Iron Works, boilers of, 84. 

Robinson's Central Deep, boilers of, 109. 

Rules for conducting boiler trials, 201. 

Ruppert Ice Co., boilers of, 82. 

Rupture of boiler tubes, causes of, 25. 

Safety, of the Stirling boiler, 17; of different 
types of boiler compared, 35. 

Safety valves, care of, 231. 

Saturated mixtures of air and vapor, 56. 

Saturated steam, table of properties of, 74. 

Saving, by covering steam pipes, 221; by 
heating feed water, 67. 

Scale, action of Stirling boiler in preventing 
formation of, on hottest tubes, 19; diffi- 
culty of removing from fire-tube boilers 
39; forms on hottest tubes of horizontal 
water-tube boilers, 21; how to soften re- 
fractory, 227; materials which form, 59, 
60; removal of, 63, 223 to 228. 

Scotch marine boilers, straining of due to 
unequal expansion, 37 ; tube renewals in, 39. 

Scum, causes, effects, and method of hand- 
ling, 60, 61. 

Sea water, boiling point and specific gravity 
of, 58- 

Selby Smelting and Lead Works, boilers of, 6. 



INDEX 



247 



Settings for boilers, causes of cracking of, 
229; how to dry them out, 229; specifica- 
tions of, 233. 

Sherry building, boilers of, 30. 

Shops of THE STIRLING COMPANY, 45; views 
from, 44, 46, 62, and frontispiece. 

Simplicity of the Stirling boiler, 13. 

Smoke, how to burn coal without, 10; elimi- 
nation of by using mechanical stokers, 145. 

Softening refractory scale, 227. 

Solids, amount deposited in boilers, 59; 
coefficients of linear expansion of, 51; 
specific heat of, 49, 53. 

Solvent power of water, 57. 

Soot, effect of in reducing boiler efficiency, 23. 

Space, comparison of that needed for various 
types of boiler, 43 ; required by Stirling 
boiler, 29. 

Spacing of tubes in Stirling boilers, 25. 

Specific heat, definition, 48; mean, for cer- 
tain solids, 53; of air, 53; table of for solids, 
liquids and gases, 49. 

Specific gravity, of fuel oils, 124, 125; of 
gases, 182; of sea water, 58. 

Specific volume of steam, 69. 

Stacks, see chimneys. 

Standing unused, preparing boilers for, 232. 

Steam, absolute and gauge pressure of, 72; 
chapter on, 69; dry, 69, and production of 
by the Stirling boiler, 27; consumption of 
by different types of engine, 198; economy 
of high pressure, 73; flow of into the atmos- 
phere, 90, 91; flow of through pipes, 87, 89; 
latent heat of, 50, 69; per cent, of used by 
oil burners, 153; principles of piping for, 
213; properties of saturated, tables, 71, 
72, 74 to 77; quality of, 69, 79, 204; re- 
lation between amount of generated, heating 
surface passed over, and temperature of hot 
gases, 94; relative volume of, 69; saturated, 
69; specific volume of, 69; superheated, 69, 
93; total heat of, 69, 74. 

Steam engine, efficiency of ideal perfect, 73; 
indicated horse-power of per boiler horse- 
power, 196, 197; steam consumption per 
hour of, 198. 

Steam gauges, care of, 231. 

Steam main, cutting boilers into, 229; drain- 
age of, 214. 

Steam nozzle pads, 15. 

Steam pockets in water- tube boilers, 15. 

Steel framework of the Stirling boiler, 10; 
fitting brickwork around, 235. 



Stirling bagasse conveyor and automatic 
furnace feeder, 148, 

Stirling water- tube safety boiler; adapta- 
tion of to different kinds of fuel, 27; ad- 
vantages of in installations for saving waste 
heat, 161 to 167 ; arch bars over manholes of, 
15; baffles and course of gases in, n; brick 
setting of, 10, 233; cleaning doors of, u; 
cleaning exterior of, 23, 228; cleaning in- 
terior of, 21, 223; colored sections illustrat- 
ing general design and setting of, 8, 9; 
constriction of circulation obviated in, 15; 
counterbalanced fire doors of, 31 ; discussion 
of efficiency of, 29 ; door and frame in setting 
opposite mud drum of, 23; driving at high 
and low rates of evaporation, 27; drum 
lugs of wrought steel, 15; durability of, 23; 
early types of, 7 ; elimination of tempera- 
ture stresses from, 37; facility of making 
repairs to, 25; forged steel drum heads of, 
9, 13; furnace of, and its advantages, 10, 
142; imitations of, 33; manner in which it 
precipitates impurities into the mud drum, 
19; produces dry steam, 27; provision for 
expansion and contraction in, 13; quick 
closing gauge glass fittings of, 19; rapid 
circulation of water in, 13; repairs of, in 
comparison with those of other types at 
World's Columbian Exposition, 33; setting 
of, 8, 9; see setting; setting for burning ba- 
gasse, 146, 147; setting for burning blast 
furnace gas, 164; setting for burning coke 
oven gas, 162; setting for burning oil or 
natural gas, 151; simplicity of design of, 
13; steel firing and ash-pit doors of, 17; 
space occupied by, 29; steam nozzle pads 
of, 15; steam space in, 25; tests of, table, 
208, see tests; tubes of, 9; tube spacing in, 
25; unique use of, for hot-water heating, 
29; water columns and connections, 19; 
water spaces in, 25. See superheater. 

Stirling chain grate stokers, 158, 159. 

STIRLING COMPANY, THE, works of, 45, and 
frontispiece. 

Stokers, mechanical, 145; chain grates, 159. 

Stoking apparatus for bagasse, 148. 

Stop valves for boilers, 217. 

Sulphur, combustion data for, 106; is des- 
structive to boiler plate, 105. 

Superheater, chapter on the Stirling, 93; 
course of steam in, 102, 103; flooding pipes 
for, 102, 103; for boilers already installed, 
104; in middle pass of boiler, 101; in rear 



248 



THE STIRLING WATER-TUBE SAFETY BOILER 



pass, 100 ; independently fired, 102, 104; 

replacing tubes of, 103. 
Superheated steam, additional heat needed 

for producing, 93; definition of, 69, 93; 

specific heat of, 93. 
Superheating surface, relation between it 

and boiler heating surface, 95 to 99. 

1 ables in this book: 

No. PAGE No. PAGE No. PAGE 



I 


33 


22 


. . . 91 


43- 


. . .125 


2 


47 


23- 


93 


44- 


. . . 126 


3- 


49 


24. . 


97 


45- 


. . .127 


4- 


.. 49 


2 S . ... 


. .105 


46... 


. .128 


5-- 


50 


26. ., 


. . 106 


47- 


-133 


6. .. 


5 1 


27. . 


. .107 


48.. 


-135 


7- 


52 


28. . 


. .107 


49- 


-135 


8. . . 


53 


29. .. 


. .108 


50... 


. . 167 


9. . . 


55 


30. .. 


in 


51. .. 


. . 169 


10 


5 6 


31. .. 


. . in 


52. . . 


-177 


ii 


57 


32. . . 


. . 112 


53- 


-177 


12 . . . 


58 


33- 


.114 


54- 


. .182 


13. .. 


. . 60 


34- 


. .119 


55--- 


. .184 


14. . . 


.. 6s 


35- 


. . I2O 


56... 


. .186 


15. . . 


7 1 


36... 


. . 120 


57- 


. . 196 


16. . . 


70 


37- 


. . 121 


58... 


. .198 


17. .. 


72 


38... 


. . 122 


59- 


. .198 


18. . . 


74 


39- 


. . 122 


60. .. 


. .208 


19. . . 


. . 87 


40. . 


-123 


61. .. 


.213 


20. .. 


.. 8q 


41 . . . 


.124 


62. .. 


. . 217 


21 


. . 90 


42. .. 


..I2 5 


63... 


. . 219 



Tar, analysis and heat value of, 129. 

Tan, heat value of, 120; burning of, 147. 

Temperature, definition, 47; of fire, 50, and 
method of computing, 107 ; elimination from 
the Stirling boiler of stresses due to, 37; 
measurement of high, 51. 

Tests of steam boilers, code of rules for, 201 ; 
forms for data and results of, 206; starting 
and stopping of, 202. 

Tests of Stirling boilers, general table, 208; 
when burning green bagasse, 149; when 
burning coke oven gas, 163; when burning 
blast furnace gas, 165 ; when burning natural 
gas, 157; when burning oil, 155; when util- 
izing gases from heating furnaces, 167. 

Texas oils, 125. 

Thermal unit, British, 48; metric, 48. 

Thermometers, 47. 

Throttling calorimeter, 79 to 85. 

Tiles for Stirling boiler baffles, n; laying of, 
237, not destroyed by tubes passing between 
them, ii. 



Time required for cleaning boilers, 31. 

Transfer of heat, 50. 

Trials of boilers, code of rules for, 201. 

Turbine tube cleaner, 223. 

Tubes, causes of rupture of, 25; description 
of those used in the Stirling boiler, 9 ; great 
advantage of curved, 13; method of ascer- 
taining whether there is any deposit in , 21; 
renewals of in Scotch marine boilers, 39; 
spacing of and ease of replacing them in the 
Stirling boiler, 25; unfounded objection to 
curved, 21. 

Union Steel Co., boilers of, 54, 200. 
Unit of evaporation, 72, 207, foot-note. 
Utilization of waste heat, 161. 
U-tube draft gauge, 179. 

Vacuum, gauges for indicating, 72; prop- 
erties of steam for various amounts of, 71. 

Valves, blow-off, 231 ; care of safety, 231 ; on 
boilers, 217 ; location of in steam mains, 217. 

Vapor, as distinguished from a gas, 69; 
amount of in air, 55, 56. 

Volatile matter in fuel, a cause of smoke 
and low boiler efficiency, 141 ; contains con- 
stituents which are not really combustible, 
112, foot-note; requirements for burning 
of, 10 ; how the Stirling furnace meets these 
requirements, 142. 

Warren hydrocarbon burner, 152. 

Waste heat, chapter on utilization of, 16 1. 

Water, chapter on, 57; boiling point at dif- 
ferent altitudes, 58; hourly evaporation of 
per boiler horse-power, 198; removal of 
from steam pipes, 214; see feed water. 

Water column of Stirling boilers, 19. 

Water space in Stirling boilers, 25, 43. 

Water-tube versus fire-tube boilers, 35. 

Water-gas tar, 129. 

Weathering of coal, 113. 

Weights, combining, of chemical elements, 
1 05; molecular, of gases, 185. 

Whitman and Barnes Co., boilers of, 42. 

Wolverine Mining Co., boilers of, 238. 

Wood, composition of, 119, 120; heat values 
of, 120; methods of burning, 145. 

Works of THE STIRLING COMPANY, 45; 
views of, 44, 46, 62, and frontispiece. 

World's Columbian Exposition, table show- 
ing causes of withdrawal from service of 
water-tube boiler operating at, 33.