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UNITED STATES DEPARTMENT OF AGRICULTURE

Washington, D.C. - November 30, 1923

EXPERIMENTAL PRODUCTICN OF STRAW GAS.

By Harry E. RoetHe, Associate Development Engineer, Bureau of Chemistry.

CONTENTS.
Page Page
iBMtGHHeHOt. = = ielieuse fer baled: strawe 2 6
Straw-gas producing plant________~_ 1 | Value and utilization of by-products_ 6
Operation of experimental plant____ 4 | Impracticability of experimental *
Results of experimental work______ 4 [Ut a a = r
Probable annual consumption of gas improvement of experimental equip-
on average northern farm_______ s J Se ee 9
Liquefying and compressing straw Impracticability of destructive dis-
ee ee a 7G tillation of straw and similar ma-
Straw gas fer automotive power____ 6 PETIA ON TAMS = =~ 2 ee 10
INTRODUCTION.

In 1921 the Bureau of Chemistry of the United States Department
of Agriculture undertook a study of the production of gas from straw
and similar material now often wasted on American farms.?

Only one of the types of equipment available for straw-gas produc-
tion, and that not the most improved one, and only a few of the many
kinds of material which may be carbonized were used in these tests.
The experiments, however, were extensive enough to show that the
type of equipment employed in these tests is not practicable as a farm
unit, even though the gas produced can be satisfactorily used for
heating, hghting, and stationary power purposes.

STRAW-GAS PRODUCING PLANT.

Straw-gas equipment was installed at the Arlington Experimental
Farm, Va. It consisted of a cylindrical steel retort, a steel scrubber
and condenser combined, and a steel water-seal gasometer (figs.
1, 2,3).

The retort, 3 feet in diameter and 8 feet in length, with a volu-
metric capacity of approximately 50 cubic feet, was equipped with a
central return flue and rested on its horizontal axis. Walls and an
arch of brick retained the heat produced in the fire box beneath the
retort. Eight gas burners (1-inch pipes, each equipped with a single
row of holes, and a mixing valve), arranged transversely in the fire

1Roethe, H. E. The Production of Gas by the Destructive Distillation of Straw.
Power, vol: 52 (1920), pp. 853—854.

61633°—23

2 BULLETIN 1203, U. S. DEPARTMENT OF AGRICULTURE.

box to burn gas from the gasometer, were later removed. A set of
slotted bar grates was installed, so that straw, wood, etc., could be
effectively burned as fuel for carbonizing the charge.

Fic. 2.—Retort, scrubber, and gasometer.

The upright scrubber and condenser, 7 feet high and 2 feet in
diameter, contained a quantity of water, above which were placed

several fine-mesh screens and charcoal or coke. The cleaning cham-

NTAL PRODUCTION OF STRAW GAS.

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4 BULLETIN 1203, U. S. DEPARTMENT OF AGRICULTURE.

ber proper was water jacketed, with connections for the continuous
flow of water therein, in order that the gas and scrubber might be
properly cooled.

The gasometer had a volumetric capacity of about 100 cubic feet.
The upper bell; supported by three uprights, had at its top an ex-
tended rim in which water could be placed as ballast, thereby in-
creasing the pressure and quantity of the gas stored.

This “equipment was at all times considered to be a strictly de-

monstrational and experimental unit. When obtained it had some
unnecessary and undesirable features, such as heavy 6-inch wrought-
iron pipe for the main line, a small expensive gasometer, a retort not
readily accessible, and a bulky, inconvenient scrubber.

Miscellaneous equipment for the utilization of the gas produced
consisted of several gas-mantle lamps and hot plates, a reflector stove,
a 14-horsepower stationary gasoline engine, and a gas meter.

OPERATION OF EXPERIMENTAL PLANT.

In making an experimental run, about 50 pounds of unbaled, sun-
dried straw or similar material was placed in the retort through the
two oval openings, and the two cover plates, equipped with gaskets,
were tightly clamped in place. Heat was applied to the retort by
burning suitable fuel, generally straw, in the fire box. The charge
could be carbonized in from 30 to 45 minutes.

The combustible gases began to come off when a temperature of
about 200° C. (% 392° F.) was reached. Maximum production was
obtained when a temperature of about 500° C. prevailed.

Entering the scrubber at its base, the gas bubbled up through water.
then passed through fine-mesh screens and a quantity of coke or char-
coal. From the scrubber the gas passed through a gate valve into the
gasometer for storage.

RESULTS OF EXPERIMENTAL WORK.

A very satisfactory gas was secured from wheat and oat straw
and from corn stalks.?

Most of the experiments were conducted on wheat straw. <A ton of
sun-dried wheat straw gave approximately 10,000 cubic feet of
purified gas, 625 pounds of carbon residue, 10 gallons of tar, and a
large qui untity of ammoniacal liquors.

Table 1 gives an average analysis of this gas which has a heating

‘alue of about 400 British thermal units per cubic foot.

TABLE 1.—Composition of gas from sun-dried wheat straw?

Per cent.

Cathon Utextdit COs) 3 a ee 30. 0
CADDO IMONOSUd: COO i ae se re ale pea eee Foe ey ae 26. 0
Fry drogen ( Ha) 2233 Fe ee ee 26. 0
Metianes. (CB eye Fs! 2 8 ee ee 15. 0
Diluminants. (ethylene, etc.) (Cos ete) 2 22 ee y
Nitrogen:.(N:) "(Dy : difference) 2 sees 1.0
Oxygen }(O.) |S he Sieh

100. 0

2 Other investigators have reported the production of a satisfactory gas from flax,
barley, rye, rice, and other straws, from corncobs, and from wood waste and other

cellulose material. -
This table was prepared from analyses obtained from Prof. R. D. McLaurin, formerly

of the University of Saskatchewan, Saskatoon, Canada.

EXPERIMENTAL PRODUCTION OF STRAW GAS. 5

Straw gas burns with a beautiful blue flame in a Bunsen burner,
hot plate, reflector stove, etc. It produces a very satisfactory light
in a mantle lamp and has good heating value. It is also very
satisfactory for operating stationary internal-combustion engines,
giving the best results when admitted to the explosion chamber
with the addition of but little air and ignited under a compres-
sion greater than that found in the ordinary type of farm engine.
The gas is practically colorless, but has a shght odor. The presence
of a fairly high percentage of carbon monoxid (highly poisonous)
in the gas makes advisable some care in its production and utilization.

PROBABLE ANNUAL CONSUMPTION OF GAS ON AVERAGE NORTH-
ERN FARM.

As fuel for cooking and lighting purposes in the home, for heating
the house, and for heating water, about 300,000 cubic feet of straw
gas would be consumed yearly.on the average northern farm. This
computation is made on the basis that 150 cubic feet of gas is re-
quired for the daily preparation of three meals, each mantle lamp
consuming 4, each heating stove 20, and a water heater 50 cubic feet
of gas per hour. Of these 300,000 cubic feet of gas, about 55,000
cubic feet would be utilized for cooking, 17,000 cubic feet for light-
ing, 201,000 cubic feet for heating the home, and 27,000 cubic feet
for heating water. With the quantity used for cooking and water
heating remaining practically constant throughout the year and
that for lighting and home heating being greatest during the winter,
about 235 cubic feet of gas would be used daily during the summer
months and 1,750 cubic feet daily during the winter months. In case
the gas is to be used for ironing and for stationary power purposes
or for heating and lighting several buildings, the yearly requirement
would be greater than 300,000 cubic feet.

From 45 to 50 tons of dry straw would be needed for the produc-
tion of 300,000 cubic feet of purified gas, allowing 30 tons as the
ageregate charge to be carbonized, and 15 to 20 tons as fuel for sup-
plying the necessary heat for the destructive distillation of that
quantity. Approximately one-half ton of straw when burned in the
fire box will produce enough heat to carbonize 1 ton of straw in the
retort. Assuming that small grains yield on the average 1.14 tons
of straw an acre, each farm would need from 40 to 45 acres in small
grains for the production of gas alone, or 19 to 21 acres of corn, al-
lowing an average of about 2.4 tons of stover an acre.

Air-dried wheat straw has a heating value of about 6,000 British
thermal units per pound. Therefore, when this straw is burned in
the fire box as fuel for carrying on the process, approximately
6,000,000 British thermal units are used in carbonizing 1 ton of
straw.

Using gas already stored in the gasometer as a fuel for continuing
the process, 3,000 cubic feet of it (representing 1,200,000 British
thermal units) burned in the gas burners of the fire box will car-
bonize 1 ton of straw. Reduced to terms of straw, this 3,000 cubic
feet of gas is equivalent to 600 pounds of straw. Therefore, the
continuation of the carbonizing process by means of gas already
produced results in a material saving in straw and at the same time
conserves by-products which otherwise would be lost. Also, it is

61633 °—23——2

6 BULLETIN 1203, U. S. DEPARTMENT OF AGRICULTURE.

more convenient and requires less labor than the burning of straw.
However, burning straw apparently gives a greater yield of the de-
sired gases, owing to tue fact that a high temperature can be obtained
in a shorter time, the length of time for carbonization is shortened,
and the added expense for piping, burners, and mixers is made un-
necessary. On the other hand, a greater quantity of heat is lost when
straw is burned as fuel than when gas is used.

LIQUEFYING AND COMPRESSING STRAW GAS.

The liquefaction of straw gas (as a simple gas) by means of com-
pression and a very low temperature is not successful in the labora-
tory on account of the different gases involved. Hydrogen must be
liquefied separately, and several of the other gases freeze during the
process. Obviously, the lhquefying of straw gas, as either a simple
or a complex gas, is not feasible, least of all on the farm. |

Straw gas can be compressed at ordinary temperatures for storage
as a gas in suitable tanks. The compression of this gas on the farm’
is not practicable, however, on account of the added expense and the
necessity of securing the services of a person thoroughly familiar
with the technique of compressing operations and with the many
precautions which must be observed. For example, care must be

taken to compress the gas to its ultimate pressure only in a suitable
number of operations, to properly cool the gas and compressors, and
to maintain the proper lubrication of the compressor.

STRAW GAS FOR AUTOMOTIVE POWER.

Straw gas has possibilities as a fuel for propelling automotive
vehicles, but under present conditions it is improbable that it
will be used to any extent in such a manner. Automobiles have
been operated on this gas carried in a flexible, impervious bag at-
tached to the car. A bag containing 300 cubic feet of gas held a
supply sufficient to run the car for 15 miles. This method, however,
is unsatisfactory .and impracticable.

USE OF BALED STRAW.

Charging the retort with baled straw would facilitate its handling,
expedite several operations, and make possible a more compact
retort. On the other hand, baling would doubtless cost from $2 to
$3.50 per ton of straw, more time would be required to completely
earbonize baled straw, and the quality of the gas produced would
probably be lower, owing to the fact that the heat penetration would
not be as uniform as when loose straw was carbonized. The maxi-
mum production of the desired inflammable gases seems to prevail
when the temperature of distillation is rapidly raised.

VALUE AND UTILIZATION OF BY-PRODUCTS.

At present the by-products from the destructive distillation of
straw and similar material apparently have no commercial value.

Although the carbon residue, which can be readily powdered to
a fine consistency, can be used satisfactorily in the manufacture of

EXPERIMENTAL PRODUCTION OF STRAW GAS. Ks

lampblack, it is doubtful whether a market for this residue or the
other by-products would yield a profit to the farmer. The cost of
collecting, hauling, and shipping, as compared with the prices these
products command, would make such a procedure unprofitable.
The most advantageous utilization of the by-products probably
is on the farm where the grain is produced. As a fuel the carbon
residue has a heating value of approximately 10,000 British thermal
units per pound, while as a fertilizer its average composition is
about 5 per cent potassium oxid (K,O), 1.5 per cent aramonia (NH,),
and 0.3 per cent phosphoric acid (H,PO,). The tar can be used
satisfactorily as a wood preservative and disinfectant.

IMPRACTICABILITY OF EXPERIMENTAL PLANT.

The results of the tests here reported indicate that the type of
straw-gas producing plant used is not practicable as a unit for
farms, chiefly on account of its initial cost and upkeep, the length
of time required to produce suitable quantities of gas, and certain
inconvenient features of the retort and scrubber.

In conducting an average run on the production of gas, about 75
pounds of unbaled straw can be placed in the retort as a maximum
single charge. Considering the time necessary for charging the
retort, carbonizing, cooling, and removing the charge, approximately
14 hours are required for the distillation of this quantity of straw,
yielding about 375 cubic feet of purified gas. The complete cost
of the plant as installed, exclusive of building, was $1,500.

The annual cost of producing gas in this plant is shown in Table 2.

TABLE 2.—Oost of producing straw gas in experimental plant.

- Interest on investment (G- per eent-on- $1500). ke $90. 00
ep en ee nEeTE. Us ICTs (PEIN) Ps 8 8 7S ee 98 eh Ae ee 120. 00
Labor for producing gas (1,000 man-hours at $0.50 per

UTD 2s Bee Se ae 2 eee ae 2 ite ee ES Le 500. 00
oe TUDE ere ae eS Cs Re Eas Sed hee ee 710. 00

On this basis, 4.22 cubic feet of gas can be produced for 1 cent, or
1,000 cubic feet for $2.36. In terms of heating units, the gas pro-
duced for 1 cent represents 1,688 British thermal units.

In the foregoing computations no charge has been made against

the straw consumed, no monetary value has been given the by-

products, and no consideration has been given to hauling charges,
or to the cost of a building for housing the equipment. The heat
for carbonizing the charge was supplied by straw burned in the
fire box. Straw, generally wasted in many sections, has a distinct
potential value by virtue of the fertilizing constituents which it
contains. According to figures® taken from accurate analyses, with
nitrogen selling for 25 cents, phosphoric acid for 8 cents, and potash
for 15 cents a pound, oat straw has a value of $7.73, barley straw
one of $6.68, wheat straw one of $4.95, and rye straw one of $5.25
a ton. It would be necessary to pay these prices to obtain the same

quantity of fertilizing constituents in commercial fertilizers. Ac-

cordingly, straw when returned to the soil for the addition of plant
food elements is very valuable.

* Yearly production of gas, 300,000 cubic feet.
A al a Value of Straw. Farm Implement News, vol. 40, no. 46 (Noy. 13, 1919),
Dp. :

eee

8 BULLETIN 1203, U. S. DEPARTMENT OF AGRICULTURE.

A general comparison can be made with the cost of the ordinary
fuels with which the straw gas produced in this plant would have to
compete. The number of British thermal units per unit for each fuel
or source of energy considered forms the basis of comparison. The
approximate heating value (in British thermal units) of straw gas
is considered to be 400 per cubic foot; that of gasoline, 108,000 per
gallon; that of kerosene, 128,000 per gallon; that of anthracite
coal, 15,100 per pound of combustible, or 12,250 per pound of coal;
that of bituminous coal (high grade), 15,200 per pound of com-
bustible, or 13,600 per pound of coal; that of wood (air dried),
6,000 per pound; and that of electricity, 3,415 per kilowatt hour. _

On the basis of heating units produced, straw gas, as a fuel for
heating, cooking, and stationary power purposes, costs at least 1
cent per 1,690 British thermal units.° Wood selling for $10 a cord,
sawed and split, costs 1 cent per 18,000 British thermal units; anthra-
cite coal at $15 a short ton cests 1 cent per 16.335 British thermal
units; bituminous coal (high grade) at $14 a short ton costs 1 cent
per 19,430 British thermal units; gasoline at 25 cents a gallon costs
1 cent per 4,320 British thermal units; and kerosene at 18 cents a gal-
lon costs 1 cent per 7,110 British thermal units.

When wood and coal are burned for home-heating purposes a large
quantity of heat is lost and wasted. It has been estimated that in the
neighborhood of 30 per cent of the heating units pass up the chimney
with the flue gases. The aggregate loss is still greater when these
fuels are used for cooking purposes, since much heat is also wasted
during the preparation of a hot fire and after the completion of the
cooking. These losses do not occur when gas is burned. Considering
these heat losses, wood selling at $10 per cord would cost 1 cent per
12,600 British thermal units, anthracite coal at $15 a ton; 1 cent per
11,485 British thermal units, and bituminous coal at $14 a ton, 1 cent
per 138,600 British thermal units, when used for heating the home.
These figures would be somewhat higher when these fuels were used
for cooking purposes. The cost of straw gas produced in the experi-
mental plant, then, is very high as compared with the cost of ordi-
nary fuels.

The cost of straw gas as a source of light for farms is about half
again as great as that of electricity supplied by an individual electric
lighting plant. Assuming the yearly consumption to be 432 kilowatt
hours, the cost of electricity produced by a good farm eléctric plant
of approximately one kilowatt output for the average farm varies
from $0.36 to $0.46 per kilowatt hour.’ For the sake of comparison,
a cost of $0.40 per kilowatt hour will be taken. When burned in an
inverted gas-mantle lamp at the rate of 4 cubic feet per hour, straw
gas produces a light of about 14.4 candlepower. Considering a
tungsten incandescent (vacuum) electric lamp to average about 1
candlepower for each watt, and allowing appropriate charges for
the necessary gas pipe and gas-lighting fixtures, straw gas would
cost about 67 cents per 1,000 candlepower hours, or 1 kilowatt hour.

6 Round numbers are used in all these calculations. s
7 Fogle, F. E. The Farm Electric Plant. Michigan Agricultural College Quarterly
3ulletin 4 (1921), pp. 119-121.

-

aa

EXPERIMENTAL PRODUCTION OF STRAW GAS. g
IMPROVEMENT OF EXPERIMENTAL EQUIPMENT.

Much could be done to lower the cost of, simplify, and improve
the experimental equipment used.

The brick arch and walls incasing the retort are effective in con-
serving heat, but their initial cost is high, as well as their cost of
upkeep in case it is necessary to repair or replace the retort. The
retort would probably last for four or five years when used to produce
300,000 cubic feet of gas per year and subjected to the heat of straw
burned in the fire box. ‘The retort is very inaccessible under the
present arrangement. A _ sheet-iron casing, similarly shaped and
covered with heavy layers of asbestos, inclosing a readily replaceable
retort or baking chamber, would be more practicable from every
standpoint. The main gas line could be 2-inch piping, with attach-
ment to the retort on top at its center.

The front end of the retort should be equipped at the top with a
single large gas-tight charging door which can be readily opened
and closed. A similar door should be placed at. the bottom to permit
easy and rapid removal of the carbon residue after the charge has been
carbonized. For the exclusive burning of straw, the fire box should
be equipped with a regular straw-firing door.

The return flue, while increasing the cost of the retort, slightly
decreasing its volumetric capacity, and making the charging opera-
tion more laborious, permits a more even and rapid carbonization of
the charge.

Everything considered, the gas burners, as arranged in the fire box,

were not entirely successful, and the burning of straw in the fire box
seemed to be more satisfactory.
_ While effective, the scrubber is bulky and expensive, with an in-
terior not readily accessible. A better arrangement would be a se-
parate, compact water-cooled condenser, and a separate scrubber
which could be much smaller than the one used. Such equipment
would cost less and at the same time result in a more effective and
satisfactory recovery of tar, heavy oils, and ammoniacal liquors. On
account of the size and thickness of the main gas line, there is a
tendency for the tar to condense and collect in the gas outlet and
elbow at the front of the retort.

A retort the size of that in the experimental unit would require a
gasometer having a capacity of at, least 400 cubic feet. It could be
constructed of lighter material than that used and could be made
more compact by making the lower bell upright instead of inverted:
Gasometers are expensive, bulky, and somewhat troublesome, especi-
ally during the winter when antifreezing solution must be kept in the:
water compartment. The question arises as to the most satisfactory
method of storing the gas, for which several other devices suggest
themselves. <A steel tank in which the gas could be stored at a pres-
sure of, say, 75 to 100 pounds per square inch, or an impervious can-
vas-rubber bag, similar to those used in England during the* World
War on motor busses driven by coal gas, might be more practicable.

10 BULLETIN 1203, U. S. DEPARTMENT OF AGRICULTURE

IMPRACTICABILITY OF DESTRUCTIVE DISTILLATION OF STRAW
AND SIMILAR MATERIAL ON FARMS.

Gas produced from straw may be used successfully for lighting
and heating and as a motor fuel. The question of the feasibility
of a straw-gas plant on the farm, then, depends primarily upon the
cost of production and ease of operation. The estimated cost of the
gas as produced under the conditions here outlined is prohibitive.
This cost is dependent upon a number of factors, the most important
of which are the initial cost of the equipment, cost of upkeep,
length of time necessary for carbonizing individual charges, and
the total quantity of gas required. Any conditions which tend to
decrease the expense of manufacture or enhance the value of the
main product and by-products would, of course, increase the attrac-
tiveness of the proposition, but that such conditions would be of a
magnitude to make it a financial success is doubtful. On the
other hand, the use of this gas would afford many advantages and
conveniences which can not be measured in dollars and cents.

Considering the proposition impartially from every angle, it ap-
pears that the destructive distillation of straw and similar material
for the production of gas on the farm is not practicable.

ee i lO lll

ORGANIZATION OF THE

UNITED STATES DEPARTMENT OF AGRICULTURE.
October 3, 1923.

eerematy OF AQTICULLUTC.. 2 Hengy C. WALLACE.

aSsist SCcreLary___._ -— __~ es . Howard M. Gore.

PeererOre Gp SClenti fic Works = BD ALT,

Director of Regulatory Work=____________. WALTER G. CAMPBELL.
eee be rrension Work. C. W. WARBURTON.

Weather Bureau________ ioe eet ee ee CHARLES FF. Marvin, Chief.
Bureau of Agricultural Economics_______ Henrzy C. Taytor, Chief.
Bureau of Animal Industry _______ _ JOHN R. MOHLER, Chief.
Bureau of Plant Industry_~—_~__—~ ==> WIEETAM . A. Paytor, Chief.
pare errno 20h __. W. B. GREELEY, Chief.
eerremsre Or ONCIUISITY 9 C. A. BRowneE, Chief.

CEE NE a MILtton WHIrTNEy, Chief.
Bureau of Entomology_____-_—- PG Fi te ¥ L. O. Howarp, Chief.

Bureau of Biological Survey_____—— Pe EK. W. NELSON, Chief.

ere ae Fanic koedgds--. = THoMAS H. MacDonaLp, Chief.
Bureau of Home Hconomics_______-____ + LOUISE STANLEY, Chief.

Fized Nitrogen Research Laboratory______ F. G. Corrreiy, Director.
Division of Accounts and Disbursements____. A. ZAPPONE, Chief.

we a a CLARIBEL R. BARNETT, Librariai.
Federal -Horticultural Board__ pee ot by ARLATT "CHAITHIOR.
Insecticide and Fungicide Board________ J. K. Haywoop, Chairman.
Packers and Stockyards se tn chase ee CHESTER MorriL., Assistant to the
Grain Future Trading Act Administration __ Secretary.

mie geet LIGIIOT = R. W. WixiaMs, Solicitor.

This bulletin is a contribution from

Bureau Of Chemistry $8. C. A. Browne, Chief.
Office of Development Work__________- Davip J. Pricr, Engineer in Charge.

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