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AMERICAN 
SULPHtJRIC ACID PRACTICE 



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rUBllSUtRS OF »OOKS FOR^ 

Coat Age « Electric Railway Journal 
Electrical Vltorld ▼ Ei^lneering News-Jtecord 
American Machinist ^ Ingenleria Intemadoial 
Engineering 8 Mining Journal " Power 
Chemical Metallurgical Engineering 
Electncal Merchandising 



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AMERICAN 

SULPHURIC ACID 

PRACTICE 



PHILIP DbWOLF 

AND 



E. L. LARISON 

AxtooHsA CoFnts MiHiHa CoHrAiti 



WITH A SPECIAL CHAPTER 



W. M. LbCLEAR 



FtR9T Edition 



McGEAW-HILL BOOK COMPANY, IHC. 

NEW YORK: 370 SEVENTH AVENUE 

LONDON: A a BOUVEBIE BT., E. C. 4 

1921 



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COFTBIOHT, 1921, BY THl 

McGraw-Hill Boos Coupant, Inc. 



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During a period of several years in close contact with the 
manufacture of Sulphuric Acid the writers have a great many 
times been asked to recommend Bome published work upon the 
subject from which a knowledge of the practical essentials of 
modern American acid making could be obtained. This inquiry 
has come from men working in association with, and under the 
supervision of, the writers, and also from men in allied lines who 
wished to acquaint themselves quickly with this information. 

So far as the writers know, such a work in English does not 
exist. Lunge's "Sulphuric Acid and Alkali" is admirable in 
many ways, and certainly every one permanently connected with 
the manufacture of acid should have it for reference: it does not, 
however, cover modern American practice, nor is it suitable to 
present to a new chamber operator as a source of information. 
Besides Lunge, there are several books which include a few 
chapters on sulphuric acid, but none is satisfying. 

The writers' purpose in preparing this volume has been to 
provide some fundamental information for the man with little 
preliminary knowledge of the subject. It does not in any way 
pretend to cover acid manufacture with the thoroughness of 
Lunge. History, chemical and physical theory, and many other 
things are treated from the technical, not the scientific, view-point, 
in an effort to avoid the error, so common in "Handbooks," of 
not devoting much time to Why, while very thoroughly covering 
How. 

Note. — "Sullivan's Handbook" so thoroughly covers the 
laboratory end that we have not included laboratory practice, 
and recommend his methods. 

The writers are much indebted to several manufacturers of 
acid plant equipment for photographs and drawings of machinery 
and apparatus. 

Philip DbWolp. 
E. L. Larison. 

Anaconda, Montana, 
April, 1921. 



381911 , , 

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CONTENTS 

Preface '. . . . v 

I. AiiCHEtn, HisTORT, Development, Status 1 

IL Elementary Cheuibtrz of Suli>buric Acid 7 

III. Cbaracteristicb and Uses ' 16. 

IV. Raw Materiau 44 

t Prodcction OF SO, 49 

iTI. A Brief Debcriftion OF THB Chaubbr Process 82 

VII. IhjsT Settlimo Apparatus 86 

VIII. The Glover Tower 94 

IX. The Chambers 101 

X. Gat Ldssac Towers 113 

XI. Acid Circdlation 118 

XII. Introduction OF NiTEB 136 

XIII. Draft 159 

XrV. Tbbtino 166 

XV. Operation 180 

^VI. Concentration 189 

(^XVII. Odtlinb or the Contact Process 207 

XVIII. Purification op Gases 217 

XIX. CONVEETINO 228 

XX. Abbobbtion 238 

XXI. Convbhteb Mas8 243 

XXII. AccocNTiNa 247 

Appendix 260 

Indse 265 



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AMERICAN 
SULPHURIC ACID PRACTICE 

CHAPTER I 
ALCHEMY, HISTORY, DEVELOPMENT, STATUS 

When the old and bewhiskered alchemist mentally planned bis 
transmutations from lead to gold, he no doubt considered his 
reagent "spiritus vitroli" second only to his trusty Philosopher's 
Stone in power and usefulness; for we read of sulphuric acid back 
through Alchemical times, but the name of the true discoverer 
will probably always remain unknown. 

The Arabian, Geber (A.D. 960), was formerly thoi^ht to 
have been the first to describe the "spirit of alum" and its 
solvent powers, in the mythical literature of the time, but there 
is a question now whether this did not creep in during the Latin 
"translations" of the same. The Persian Alchemist, Abn-Bekr- 
Alrhases (A.D. 930), and also DeBeauvais (A.D. 1240) are con- 
ceeded probable discovers, but direct evidence is woefully lacking. 

Basil Valentine (A.D. 1425), in that landmark of Alchemical 
lore, "The Triumphal Car of Antimony," is the first- to refer to 
any method of manufacture, and therein describes the burning 
of sulphur with saltpeter in glass vessels. This method was 
adopted by the apothecaries of the time, for the manufacture of 
sulphuric acid on a small scale for pharmaceutical use. From 
the apothecaries' laboratory to an industrial installation was the 
logical sequence, and about 1746, at Richmond, near London, we 
find what was then considered a large plant, operated by a quack 
doctor named Ward. 

From this point the manufacture branches off from alchemy 
and quackery, and its development is aloi^ scientific and me- 
chanical lines. The development and introduction of lead 
chambers instead of glass, took place about 1746, when Dr. 
Roebuck, and later a Mr. Garbet, erected plants with lead 
chambers six feet square. Later factories were built at Worces- 
tershire, London, and Glasgow. 



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2 AMERICAN SULPHURIC ACID PRACTICE 

FIRST AMBKICAN ACID PLAITT 

The house now known as HarriBon Btds. & Co., Inc. was 
founded in 1793 by Mr. John Harrison of Philadelphia. Mr. 
Harrison received his early education in Philadelphia, and then 
spent two years in Europe inveatigating the arts and processes 
of the manufacture of chemicals and in studying under the 
celebrated chemist, Dr. Joseph Priestley, Mr. Harrison became 
deeply impressed with the belief that many staples were imported 
which coiUd be produced to advantage in the United States, 
thereby rendering the citizens independent of foreign producers 
and aiding the industrial development of the youthful Republic. 
Following this thought, in 1793 he began in Philadelphia the 
manufacture of chemicals, notably Sulphuric Acid, of which he 
was the first maker in the United States. 

In that year, he had a lead chamber capable of producing 300 
carboys per annum. The competition of foreign makers was so 
overwhelming at first, that his enterprise was confined to manu- 
facturing for his own use and filling orders on a small but very 
remunerative scale for a few of his patrons, his investment at the 
start not exceeding (5,000. In 1807 he built what was for that 
time quite a large lead chamber; it was 50 ft. long, 18 ft. wide and 
18 ft. high and capable of making nearly half a million pounds of 
Sulphuric Acid annually, the price of the staple being then aa ' 
high as 15c. per pound. According to a letter addressed by Mr. 
Harrison to President Jefferson, dated November 1, 180S, and 
now in the archives of the State Department at Washington, it is 
learned that he bad then developed his Sulphuric Acid Plant to 
such an extent as to have a possible annual output of 3,500 
carboys and he had also extended the line of products in his 
laboratory by adding the various preparations of mercury, 
antimony, copper, etc., used in the arts and medicines at an 
investment of some $40,000. This waa at his establishment on 
Green Street, west of Third. 

As is well known, acid produced in lead chambers is not the 
Oil of Vitriol of commerce and the only method known at that 
time to concentrate it to the required strength was by boilii^; it 
in glass retorts — a very precarious and dangerous process. The 
constant breakage of the ^as largely increased the cost of the 
concentrated acid and the dangers of the work. To obviate this 
great trouble Mr. Harrison, in 1814, introduced the use of Plati- 



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ALCHEMY, HISTORY, DEVELOPMENT, STATUS 3 

num for the manufacture of Sulphuric Acid, for the first time, at 
least in this country. In the previous year, 1813, Dr. Eiic 
BoUman, a Dane, had come to Philadelphia. Dr. Bollman was 
familiar with the metallurgy of platinum and a highly scientific 
man. He brought with him from France Dr. Wollaston's 
method for converting the crude grains of platinum into bars 
and sheets. About the first use that Dr. Bollman made of these 
platinum sheets was the construction, early in 1814, of a still for 
the concentration of Sulphuric Acid for the Harrison Works. It 
weighed 700 oz., had a capacity of 25 gal., and was in continuous 
use for 15 years. This early application of platinum for such 
purposes was highly characteristic of the sagacity and ingenuity 
of the American manufacturer. At the time the use of this rare 
metal was a novelty in Europe and known only to a few persons 
and certainly entirely unknown in this country. It follows, 
therefore, that Mr. John Harrison was not only the earliest 
successful manufacturer of Sulphuric Acid in America, but the 
first in this country to concentrate it in platinum. Too great 
praise cannot be given him for, as Liebig has said, " The quantity 
of Sulphuric Acid made in a country is a sure index to its wealth 
and prosperity." 

In 1806, Mr. Harrison began the manufacture of white lead 
and he and his successors have continuously marketed their 
product since that date. In fact, with one exception, the "Harri- 
son" lead is the oldest established brand of white lead in the 
United States. In later years, he introduced into his works 
apparatus for making pyroligneous and acetic acids and their 
dependent products, white and brown sugar of lead, also oxides 
of lead, colors, alum, coppers, iron liquors, etc. Mr. Harrison 
may be credited with doing more to infiuence the establishment 
and development of the chemical industries than almost any 
man of his time. 

The Green Street Works soon grew too small for such large 
operations as Mr. Harrison had undertaken and an eligible loca- 
tion was secured in Kensii^ton, now the Eighteenth Ward of 
this city, where extensive buildings were erected and lai^ manu- 
facturing facilities provided. In 1831 he admitted his sons to 
partnership, under the title of John Harrison & Sons. He died 
in 1333 and in that year the firm name was changed to Harrison 
Brothers. In 1859, by the admission of the founder's grandsons, 
John Harrison, George L. Harrison and Thomas 8. Harrison, the 



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4 AMERICAN SULPHURIC ACID PRACTICE 

finn name became Harrison Bros. & Company and in 18^ waa 
incorporated. In 1917 the Greys Ferry plant was taken over 
by the Du Font Company and is now known aa the Harrison 
Works. 

Holker, in 1766, introduced the firet lead chambers into France, 
and at his Rouen plant the two important ideas of introducing 
steam into the chambers during combustion, and continuous air 
feed, were mechanically developed. In Germany the first lead 
chambers were probably those at Ringkuhl, near Cassel. Dr. 
Richard's plant near Dresden (1820) was one of the oldest, and 
although it was erected some time after the idea of continuous 
air feed had been perfected, it represented the old intermittent 
type. 

The last 150 years has seen little or no chai^ in the funda- 
mental idea of the English, or chamber process. True, the 
chambers have been increased tremendously in size, the genera- 
tion of SOt has undei^ne marvelous mechanical development, 
and the utilization of valuable waste products has become of 
great importance; methods of handling the product have been 
rendered many times more efficient: but for the original idea 
we are indebted to the pseudo-Bcientists of the Alchemical period. 

One of the promoters of the Contact Process once said, "The 
alchemists and the early English chemists could hardly have 
helped stumbling onto the discovery and manufacture of oil of 
vitriol by the Chamber Process, but it remained for a nation of 
real scientists to discover and develop the Contact Process." For 
nowhere in the field of industrial chemistry can the chemical 
engineer see so clearly the result of systematic, painstaking 
research, experiment, and accurate interpretation of observation. 

Up to the close of the e^hteenth century the little fuming acid 
demanded by the arts had been produced almost exclusively by 
the firm of Joseph Starck, in Bohemia, by the distillation of dry 
ferrous sulphate and the absorption of the evolved S0| in a high 
strength pan concentrated acid. From the place where it was 
stored it was called Nordhausen acid. 

About 1875, CI. Winkler, and later Squire and Wessel, showed 
that SOg is easily formed by the interaction of SOj and Oi, in the 
presence of a number of substances in a finely divided state, with 
certain other requirements as to temperature, humidity, and 
pressure. Although the oxides of iron and cobalt, and metallic 
gold, iridium, and silicon produce this result, none of them 



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ALCHEMY. HISTORY, DEVELOPMENT, STATUS .5 

approach the efficiency of conversion obtained with small per- 
centages of metallic platinum. The platinum itself is unacted 
upon and termed a catalyzer, after the si^geBtion of Berzilius, 
in 1835. 

The commercialization of Winkler's idea has been rapid during 
the last forty years, owing to the increased demands of the dye 
makers and oil refiners, so that today the old distillation process 
is obsolete. 

About 1875, the promoters of the process that later became 
known as the Hanish and Schroder, using Winkler's ideas, 
secretly tried out the catalysis of SOg, using first pure SOj and 
oxygen, and later dilute SOi from pyrites, with platinized asbestos 
as the catalytic a^ent, and a heateU entrance gas, under a pressure 
of three atmospheres. 

But the great obstacles in the way of the development of the 
process were the failure to get a dry and arsenic free entrance gas, 
the false idea that SOj and oxygen must be present in stoichi- 
ometrical proportions, and that nitrogen was detrimental. These 
three difficulties alone must be considered the causes of the failures 
of the pioneers, and the financial losses through semi-commercial 
experiments were startling. 

Through the disloyalty of a workman at the Badische works 
CLudwigshaven) the important secrets of their process were ob- 
tained by their competitors, and simultaneously, 1898, patents 
were issued to three different companies: The Badische Anilin 

DND SODAFABHIK OF LuDWIGBHAVEN; ThB FaRBEWERKE VOKM 

Meistek, Ltrcitrs & Bruning, of Hochst; and The Vbbein 
Cheuischer Fabriken of Manhbiu. 

These three companies at once set about the commercial per- 
fection of the process, as aecretely as possible, the only important 
variation being in the catalytic agent. To trace the foreign 
development would indeed be interestii^, but we are limited by 
title to American practice, 

American manufacturers, due to their lack of appreciation of 
the results of organized research and experiment, refused to 
finance any work Eilong these lines, and followed the usual course 
of importing the developed process and trained men for install- 
ations in this country. The Schroder process, employit^ 
platinized magnesium sulphate, and the Badische, with platinized 
asbestos, have been the most favored in America. 

An eminent chemical engineer has called sulphuric acid the 



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6 AMERICAN SULPHURIC ACID PRACTICE 

back bone of the chemical industry, for like soda, ita uses are eo 
diversified and its production so great, that in any country it is 
a true barometer of chemical and industrial progress. It finds 
its greatest use in fertilizer manufacture (80 per cent), and is 
indispensable in the manufacture of coal tar dye stuffs, petroleum 
products, paper, stearine, oleine, sodium sulphate, soda; hydro- 
chloric, nitric, citric, and tartaric acids; sulphates of iron and 
copper; alums, shoe blackings, coke plant by-products, electro- 
lytic refining of metals, mostly copper; it enters, directly or 
indirectly, into almost every chemical procese. In some of the 
more important branches of the chemical industry it is a raw 
material costing millions. The amounts used in the manufacture 
of explosives, during the late War, wereenormous. This huge war 
increase was of course only temporary, and there are many plants, 
paid for by the War, that should make very cheap acid. 

While the Contact process has many advant^es over the 
Chamber process, such as no bulky chambers of concentration 
pans, it is very doubtful if it will ever completely replace the 
chambers. It cannot make 50° and 60° B£. acids to compete, 
and requires some method of producing weak acid to keep it 
going. But on the production of higher strength acids it is 
supreme, and statistics show that it is gaining in the United States 
today. The cost of platinum for concentrating pans is excessive 
and increasing, and that required for contact mass is negligible 
in comparison. Both processes are being improved steadily, 
and the patent rights are costing less each year, and in a few years 
will become public property. Supervision, regulation and yield 
are all better on the contact process, while depreciation and 
maintainance are less. 

In April, 1920, the Department of Commerce had no figures for 
production since 1915. They show a 25 per cent increase in 
production during 1915 over the previous year, and one war time 
plant alone, completed in 1916, produced a qtiarter of a million 
tons of fuming acid a year, against 49,000 tons for the whole 
country in 1914. 

A few figures on the world's production will give an idea of the 
rate of development: 

1880 1,850,000 tons 

1892 2,818,000 tons 

1902 4,450,000 tona 

)9W 8,000,000 tons 



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CHAPTER II 
ELEMENTARY CHEMISTRY OF SULPHURIC ACH) 

When Bulphur, either brimBtone or a metallic sulphide, is 
burned in air, sulphur dioxide, SOa, is produced. This is the 
starting point of the sulphuric acid industry. 

SOi is a colorless gas of a suffocating odor, and will not bum 
nor support combustion directly, under ordinaiy conditions. It 
is very injurious to plants. It contains 50.05 per cent sulphur, 
and 49.95 per cent oxygen. Molecular weight, 64.04 per cent. 
Specific gravity, 2,2136. A liter of SOj at 0°C. and 760 mm. 
pressure weighs 2.8608 g. Its heat of formation is given 
(Richards) as 69,260 as a gas, or 77,600 in dilute solution. 

Anhydrous sulphur dioxide will not act upon iron, up to 100°C., 
but the commercial product, containing up to the 1 per cent 
HjO that it carries at saturation, does act slightly. 

Owing to the catalytic action of the hot iron of the bumers, 
some 8O3 is formed when brimstone is burned but not enough to 
influence the process. With pyrites, however, the 8O3 formed is 
considerable, as the catalytic action of the red hot iron oxides is very 
marked; in fact the oxides of iron, copper and chromium are the 
only catalytic (?) agents that have been seriously experimented 
with, outside of platinum. The generally accepted theory for 
the action of the metallic oxides is that they are more oxygen, 
carriers than actual catalyzers: doing their work more as the 
nitrogen oxides do theirs, than as platinum does its work. 

The yields, when ferric oxide is used, are not high enough to 
permit it to seriously compete with platinum as the catalytic 
agent used in this industry, in the present state of our knowledge. 

The reactions are probably two, both takii^ place at very 
nearly the same temperature, viz. : 

2FesOa + 30i + 6SO1 = 2Fes(SO0i 

which splits up into 

FeiOa + 3S0, 

the FejOa being ready to repeat the cycle 
7 



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8 AMERICAN SULPHURIC ACID PRACTICE 

*"** 3Fe,0, + 80, = 2Fe,04 + SO. 

"^ 4Fe,04 + Oi - 6Fe,0, 

when the FetOa is agato ready to repeat. 

SOi is pretty soluble in water, one volume of water, at atmoB- 
pheric preaeure, and 32''F., disai^!viug about 80 volumes SOj. 
However, this does not appear to be a chemical compound, 
HiSOi, sulphurous acid, because SOi evaporates trom it even at 
ordinary temperatures. 

Bunsen and Schonfeld published the following table, in 1905, 
of the solubility of SOi in water, at 760 mm. pressure: 

Tablb 1 

TaiiriKATnKi, I litbb 

79.8 

6 57,5 

10 56.6 



Solutions of SOj slowly oxidize in the pr^ence of air. 

Sulphuric acid is a compound, in varying proportions, of 
sulphur trioxide and water. Several different compounds exist, 
showing all the properties of definite chemical compounds. The 
mono- and the duo-hydrates have been the most frequently 
studied. Acid of a concentration of 98.3 per cent or better 
seems to hold the 1.7 per cent or leas of water present chemically, 
and this is the absolute limit to which a concentration by distilla- 
tion can go. In practice, 98 per cent is rarely reached, however. 

Sulphuric acid has a tremendous affinity for water, combining 
with it violently, with evolution of great heat. Of the entire 
molecular heat of formation, 192,200 calories, 100,300 calories, 
or 53.5 per cent, results from the combination of the anhydrous 
SO* with the water. A very common manifestation of this 
affinity is the charring of carbo-hydrates by sulphuric acid, the 
water in the combination being removed, leaving the carbon 
behind. 

Another familiar result of this affinity is the dense white 
cloud that forms when SOj escapes into the air. Air at all times 
contains moisture-humidity and the SOt combining with this 
moisture forms H^SO* m minute particles. These particles are 



\ 

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ELEMENTARY CHEMISTRY OF SULPHURIC ACID 9 

small enough tfl remain suspended in the air for a long time, form- 
ing a white cloud, or "fume" not properly a fume at all, because 
it is not a gas, but a mass of small liquid particles. 

As there is always some moisture in the air we always have an 
indicator as to whether S0| is going through our system and 
beti^ lost out our stacks. While "fumes" come from other 
causes, if there is no "fume" there is no SOj escaping. 
• The moisture in the air has a very direct effect upon the contact 
process in keeping down the strength of the acid that' can be 
made. The air introduced into the system carries with it its 
own share of humidity, which must be absorbed, and thus dilute 
the acid made. In the Middle Atlantic States this will average 
60 lb. of water per ton of 100 per cent acid made, or 3 per cent: 
less in winter, and more in summer, for the saturation point of 
air increases rapidly with the temperature. Consequently, if it 
is desired to make very high concentration fumii^ the location 
must be in the driest climate possible. 

There are three distinct steps in the evolution of sulphur into 
sulphuric acid, either naturally, or directed by man. They are 
the burning of the sulphur to SOi, the oxidation of the dioxide 
to the trioxide, and the hydrating of this trioxide. 

In the chamber process the last two steps proceed simultane- 
ously, the water acting both as an assistant to the catalyser, 
various oxides of nitrogen, and as the hydrator. The oxidation 
will not proceed at a commercially practicable rate unless water 
is present in excess, consequently the acid produced is dilute, 
and to make strong acid must be concentrated. 

We know what results may be attained by different methods 
of handling the process, but the intermediate changes that occur 
are the subjects of very heated controversy. There b no doubt 
that nitrososulphuric acid, SOi(OH)(ONO) is formed, which 
breaks up into HiSO* and NO. The NO becomes oxidized to 
N0«, NiOa, and N1O4, probably a mixture of all three, and HNOj, 
derivii^ the oxygen from the excess of air present, and the HjSOj 
immediately takes up an excess of water and condenses. 

In a work of this character, written as an operating handbook, 
not as a treatise, it would not serve any useful purpose to go into 
the theories of Weber, Winkler, Raschig, and Lunge, regarding 
changes withm the chambers. 

The saving of the nitn^en oxides is of the uttermost import- 
ance, as without this saving the process would not be corn- 



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10 AMERICAN SULPHURIC ACID PRACTICE 

mercially practicable. The Gay-Lussac tower was the first 
nitrate saver, and now, in conjunction with the Glover tower, 
reduces the nitrate from 11 per cent to 4 per cent. 

Strong sulphuric acid absorbs nitrous acid, forming nitroso- 
sulphuric acid as follows: 

2H^0« + NiOa = 2S0s(0H)(0N0) + H,0 
it absorbs nitric pero}dde, forming nitrososulpburic acid and 
nitric acid: 

HiSO* + NiO* = SO,(OH)(ONO) + HNO, 

Nitrososulpburic acid is decomposed by water alone, (1) or 
by water and SOj, (2) : 

(1) 2S0b(0H)(0NO) + H,0 = 2H,S04 + NjO, 

(2) 2S0,(0H)(0N0) + SO, + 2H,0 = 3H,S0« + 2N0 
and the nitric oxides are ready to repeat. 

The recovery of the nitrogen gases is accomplished by taking 
advantage of two of the reactions that proceed within the 
chamber — the absorbtion of NjOj and N1O4, in the Gay-Lussac 
tower, by strong sulphuric acid, and the decomposition of the 
product, at a point where it is available, by burner gas, (S0»), 
to H,SO, and NO. 

NjOj and 'S^^0^ are absorbed by strong sulphuric acid, forming 
nitrososulpburic acid, as shown in the reactions of the chamber. 
This prevents the escape of the nitrogen gases into the atmos- 
phere, with the attendant loss of nitre and the damage done, but 
the nitrososulpburic acid is of little value, and must be made 
into a useful product. 

The Glover tower accomplishes this. As shown in the chamber 
reactions, water and SO, decompose SO,(OH)(ONO) — nitroso- 
sulpburic acid — to HjSO* aod NO, so by bringing the hot burner 
gases, rich in SO2, in contact with the nitrososulpburic acid that 
reaction is brought about, and in addition the heat present effects 
a considerable concentration, the water from the concentrated 
acid going on with the burner gas and the NO back to the 
chambers, thus being used over and over again. 

CONTACT PROCESS 

In the contact process SOs is produced by the same means that 

are employed to make it for chambers. The last two steps are 

separate and distinct, however, and instead of an excess of water. 



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ELEMENTARY CHEMISTRY OF SULPHURIC ACID 11 

givii^ a dilute acid, there is an excess of SOt, producing fuming 
acid. 

Burner gaees must be cleaned of certain impurities, before 
touchii^ the catalytic agent, which in this country is always 
finely divided platinum, on either asbestos or roasted magnesium 
sulphate. 

The following is from a paper by Dr. Charles L. Reese, Journal 
of the Society of Chemical Industry, March 31, 1906: 

"Water — it was thought at one time to be essential that the gases 
be dried by sulphuric acid not weaker than 60°B^., but this was found 
to be an error, in that the gases could be saturated with moisture, by 
passing them through water before introduction into the contact msss, 
without affecting the conversion in any way. Fuming sulphuric add 
was produced, but, of course, such a procedure could not be carried 
out on a manufacturing scale, where it is necessary to use iron pipes. 

"Carbon dioxide had no effect whatever, whenever introduced into 
the gas, as was to be expected, but I was surprised to find that caihonic 
oxide had no deleterious effect, in spite of its reducing qualities. On 
one occasion the conversion in a certain plant ceased altogether, and 
we were at a loss to know the cause. We, however, soon found that 
some coal had got mixed with the pyrites in the burners. In this case 
there was carbon dioxide, and possibly carbonic oxide, present, but 
there was also evidently a lack of oxygen, and when the coal was con- 
sumed, conversion began again. 

"Sulphur will at times find its way through two or three scrubbing 
towers, and, before the filtering system was adopted, it became neces- 
sary te determine whether the presence of sulphur in the gas would 
affect the catalytic action of the contact material. Experiments were 
carried out to determine this point. It was desirable to introduce sul- 
phur into the gas in as finely divided condition as possible. This was 
accomplished by introducing hydrogen sulphide into the gas. When 
hydrogen sulphide ia mixed with sulphur dioxide the reaction between 
these two gases takes place, producing sulj^ur and water, and thus 
sulphur was introduced into the mass. It was found, on discontinuing 
the introduction of hydrogen sulphide, the conversion continued to be 
normal, and the sulphur was simply carried through the tube. This 
experiment waa repeated a number of times with the same result, show- 
ing that the presence of sulphur does not affect the reaction. Of course, 
hydrogen sulphide would affect it, in that it would reduce the sulphur 
dioxide. 

"The above substancesdo not aSect the reaction of the contect mass, 
but hydrochloric acid, chlorine, silicon tetra-fiuoride, arsenic, and lead 
do seem to affect it in two distinct ways: first, by their presence in 



^dbvGooglc 



12 AMERICAN SULPHURIC ACID PRACTICE 

the gaa, and only when present in the gas; and second, affecting the 
catalytic property of the contact material. In the fint case we have 
hydrochloric acid, chlorine, and silicon tetra-fluoride. In the second we 
have areenic and lead. 

"When Hydrochloric Add gas is introduced, theeffect is instantaneous, 
reducing the conversion from 98.5 per cent to 42 per cent, but when the 
hydrochloric acid gas is discontiaued and air passed through fot a while 
to displace it, the conversion becomes normal in a short time. 

"The presence of Chlorine in the gas seems to have an effect similar 
to that of hydrochloric acid, although not so intense. In both cases 
the dry chlorine or the hydrochloric acid was introduced, until a mini- 
mum yield was obtained, which in the case of HCl was about 42 per 
cent, and that of the CI was 57 per cent. After discontinuing the HCl 
and the CI, air was passed through and the operation was continued at 
the same temperature. As will be seen by the curve the percentage 
conversion gradually arose again to the normal. Although at one point 
the gas showed a trace of HCl, the conversion amounted to 94 per cent. 
"The introduction of a small quantity of silicon tetra-fluoride caused 
the conversion to drop immediately, but on discontinuing, the conver- 
sion rose in a few minutes to normal. In each case some silica was un- 
doubtedly deposited upon the contact mass, but most of it passed 
through the tube, as was made evident by the fact that the silica sepa- 
rated out niien the gas came in contact with the water solution used in 
testing the exit gas. Of course a minute quantity of silicon tetra- 
fluoride in the gas would gradually deposit silica on the contact mass, 
and would eventually cover the contact agent, so as to render it inactive; 
but when contact mass is so affected it can be easily rendered active by 
simply removing it from the converter and putting it back again. The 
handUng will be sufficient to expose surfaces. 

"The injurious effect of arsenic upon the contact mass is extremely 
marked. Areenious acid was placed in the front end of the tube, heated, 
and carried into the contact tube by the flow of gas. The effect of the 
arsenic was to reduce the conversion absolutely to zero, owing to the 
large amount introduced, but after 40 min. it rose again to 40 per cent. 
At this time HCl was introduced for 50 min. to remove the arsenic, and 
then air drawn through for 15 min. more. The process was then con- 
tinued, and the conversion then rose to 96.6 per cent. Several attempts 
were made to find a simple means of removing As from the contact 
mass, and at firat CI was used for this purpose. The mass was placed 
in a tube, heated, and CI passed throu^. This did remove some of 
the As, but did not regenerate the mass sufficiently. A very interest- 
ing observation was made, however, during this experiment. It was 
found the CI carried over platinum to the exit end of the tube, and 
deposited it in the form of a chloride. This was done at a temperature 
of 400°-i50''C. 



^dbvGooglc 



ELBMENTARY CHEMISTRY OF SULPHURIC ACID 13 

"It was found in attempting to regenerate or remove arsenic, that 
HCI mixed with the reduced sulphurous gas was much more effectire, 
as is shown by the curve referred to, ail arsenic having been removed. 

"It is w^ known that when platinum is heated in the presence of 
lead or lead salts, lead combines wiUi the platinum either to form an 
alloy or a compound, and this oombination of lead with platinum un- 
doubtedly destroys the catalytic property of the platinum. The effect 
of lead, however, was not determined in the regular way, but can be 
shown very readily by one or two experiments. 

" It is well known that when a platinum spiral is heated in a gas flame, 
tbe gas turned off for a few minutes, and on again, the spiral will reignite 
tiie gaa. A small piece of contact mass will do the same, but if either 
is moistened with a small quantity of lead acetate and then ignited, it 
will lose this property of leigniting gaa, unless it is heated sufficiently 
loi^ to volatilize the lead. A similar experiment will show in a tou^ 
way the effect of arsenic on contact mass or a platinum spiral." 

The above quotation shows very clearly the necessity for 
very careful scrubbing. The loss of sulphur, and consequently 
of acid, from unconverted SO* that passes on out the stacks 
is anywhere from 60 per cent to 80 per cent of the entire loss, 
and anything that throws the mass off at all will enormously 
increase that loss. The operation costs the same, with the 
exception of the small item of handling the finished acid, with 
a low as with a high conversion and the yield, and consequently 
the income, is cut down in the proportion that the conversion falls 
off. 

Arsenic is by all odds the worst of the contact "poisons" with 
which we have to deal. 

Opl's theory is that the destruction t£ the activity of the 
contact mass is caused by the deposition of a glass-Uke coating 
over the platinum, thus mechanically preventing ita contact 
with the gas. This coating is, he says, a deposition product of 
AstOi and SOj, with a formula SAsgO*, 2S0a. Lunge says this 
product has actually been loimd in dust chambers. 

Dr. KrauBS holds that the arsenic is oxidized to a non-volatile 
oxide, which combines with platinum. 

In a plant on the Pacific coast, operating on the Schroeder- 
GriUo process, using pyrites, it is necessary to regenerate the 
mass about every four weeks, and an astonishing fact has been 
noted — that while the platinum recovers its activity, the arsenic 
remains in the mass. It appears to exist after the regeneration 
in the form of Realgar, arsenic disulphide, AsiSt, and in that 



^dbvGooglc 



14 AMERICAN SULPHURIC ACID PRACTICE 

form is apparently not a contact poison. I have been infonned 
that after 3 years the quantity of arsenic in the mass is actually 
greater than the amount of platinum, but the old arsenic seems 
to be perfectly inert, having no effect, good or bad, and it is not 
until fresh arsenic compoimds are introduced that the mass again 
loses it« activity. 

Of course there is a loss of the efficiency of the mass in regen- 
erating, because the platinum becomes distributed through the 
grains of magnesium sulphate, instead of all being on the outside, 
thus reducing the area that can come in contact with the gas. 
' The absorbtion system requires conditions proper for the 
combination of SOi and HiO. The principal interferences with 
these conditions are vapor pressures, as follows: 

(a) Vapor pressure due to HjO, 

(fc) Vapor pressure due to SO*, and 

(c) Vapor pressure due to foreign acids, as HNOi or HCl. 

Heat increases vapor pressures, so temperature control is 



The vapor pressure due to HjO exists when the strength of 
the absorbii^ acid drops below 98.3 per cent HiSOt. Above 
that ^;ure the HjO seems to be chemically combined with the 
HiSOi and no water vapor exists. SOg coming in contact with 
water vapor forms very small drops of sulphuric acid, almost 
impossible to condense, and any SOi used in this way may be 
considered as lost beyond any reasonable hope of recovery, aa 
even a very long condensation and absorbtion apparatus will 
catch very little of it. 

The second vapor, that of SOs, is only met with in making 
fimiii^ acid. A glance at the absorbtion curve will show how 
rapidly the absorbtion drops, as the strength <A the absorbing 
acid increases. But SOi passing through fuming acid unab- 
sorbed is in no way changed, and is caught perfectly by the 
close to 100 per cent acid in the back of the system. 

The vapor pressure of foreign acids comes of course from 
impure materials. Sometimes it is necessary to clean out the 
system after foreign acids have gotten in; but frequently any 
trouble of this character can be cured by letting the system get 
as hot as possible and simply "boiling out" the foreign substance. 
It is necessary to watch weak acid from chamber plants closely, 
to prevent nitric acid getting in. 



^dbvGooglc 



ELEMENTARY CHEMISTRY OF SULPHURIC ACID 15 

As fuming acid has h^h meltii^ points, the exact varying with 
the strength, the temperature must be kept up sufficiently high 
to prevent freezii^. In shipping fuming acid it is general 
practice to add a little nitric, if the intended use will not be 
interfered with by nitric acid. Five per cent of nitric aeid wUl 
drop the freezing point of fuming acid to — 10.5°F. 



^dbvGooglc 



' CHAPTER III 
CHARACTERISTICS AND USES 

Sulphuric acid is a viscous, colorless (when pure) liquid, 
composed, by weight, of 2.04 per cent hydrogen, 32.64 per cent 
sulphur, and 65.28 per cent oxygen. It is very strongly acid. 

Its most outstanding characteristic is its affinity for water, 
either free or combined, and violent combination, with evolution 
of much heat, with it. 

The, sulphuric acid industry is a business barometer, as the 
acid enters into most other industries, and general trade condi- 
tions are very soon re&ected in both sales and prices. 

Sulphuric acid forms sulphates with all the metals, replacing 
any other acid radical, and freeing the other acid. Its affinity 
for water makes it the most important desiccating agent known. 
It readily forms bisulphates (acid sulphates) and double sul- 
phates. Most of its combinations are characterized by extreme 
stability. Below 65 per cent HtSOi it attacks iron vigorously; 
above that, very little. Below 92 per cent HiSO« its action 
upon lead is sl^ht — it increases fast with strength. Hot acid 
acts more vigorously than cold. The water in sulphuric acid 
of 98.3 per cent concentration seems to be, not a diluent, but an 
actual part of the acid, exerting none of the characteristics of 
water in the less high concentrations. 

Upon these main characteristics depends the important place 
of sijlphuric acid in modem life. A list of the industries using 
it would be a catalogue of the industry of the world. 

The LeBlanc process for soda ash, datii^ from the end of the 
eighteenth century, took the manufacture of sulphuric acid out 
of the drug business, and made it a major industry. 

Common salt, treated with sulphuric acid, gives off hydrochloric 
acid, with the formation of sodium sulphate, after the formula 
2Naa + H^04 = 2Ha + NajSO* 

The sodium sulphate, roasted with coal and slaked lime, gives 
soda ash (sodium carbonate), oxide and sulphide of calcium, and 
carbon dioxide. 

There are other methods of making sodium carbonate from the 
sulphate, with by-products of sulphur and hyposulphites, but 
the LeBlanc process is still a tremendous producer. 

Nitric acid is made from its natural sodium aait, Chile saltpeter, 
16 



iiz^dbvCoOglc 



CHARACTERISTICS AND USES 17 

by treatment with sulphuric acid, the result being nitric acid and 
sodium sulphate, or salt cake. By the use of twice the theoretical 
amount of sulphuric acid a bisulphite is formed, which is fusible, 
and easily removed from the stills. This bi-, or acid, sulphate, 
has many of the characteristics of the acid itself, and is fre^ 
quently used for pickling iron castings, its 31 per cent of free 
HsSO* being sufficient to accomplish this purpose. 

Petroleum refining consumes large quantities of sulphuric acid. 

Without sulphuric acid and its product, nitric acid, the coal tar 
dye industry could not exist. 

The fertilizer industry depends upon sulphuric acid for its 
sulphate of lime, or land plaster; and even more, as a means of 
converting cheap phosphate rock into a soluble form, from which 
phosphoric acid is made. 

The medical profession uses it in many ways. The quinine we 
are brought up on is the sulphate of that alkaloid. The manu- 
facture of "sulphuric" ether from ethel alcohol uses sulphuric 
acid as a catalytic agent. 

In all nitrating processes, whether for celluloid, nitro-cellulose, 
either for ammunition or some form of soluble cotton, the action 
of sulphuric is a desiccating one, removii^, and holding fast to 
the OH radical released, preventing its doing any harm. 

Fuming Sulphuric Acid is a solution of SOt in HjSOi — it is 

~ lai^y used in the manufacture of coal tar dye stuffs. Its most 

important use is the "butting up" the 96 per cent to 97.5 per 

cent acid of the best concentrators to the 100 per cent that is 

needed in many industries. 

The popularity of the sulphate method of pulping wood is 

growing, and with it the use of HiSOi. It is not necessary to 

' pick the wood so carefully, as in the sulphite or caustic methods, 

as resinous parts, such as knot« or sappy wood, are pulped by 

it to an extent impossible by any other method. 

An extensive use for sulphuric acid is (was) in the preparation 
of the mash for distilling. 

The large number of alums, used especially in the textile 
industry, are double sulphates. Originally sulphate of alumina 
was invariably one of the sulphates, chromium, iron, sodium, 
potassium and ammonium being the usual others, and from the 
aluminum it took its name — but today other pairs of sulphates 
go under the name of alum. Sulphate of alumina, free from 
iron, is used as a mordant and dyeing agent, to escape the injurious 
iron that alum frequently carries. 



^dbvGooglc 



18 



AMERICAN SULPHURIC ACID PRACTICE 



Both alum and sulphate of alumina have wide application for 
clarifying drinking water, and in coagulating and settling sewage. 

Sulphate of zinc is used as a drier for painta, a disinfectant, and 
a mordant in dyeing. 

Much erf the electroplating industry, including the electrolytic 
refining of copper and other metals, uses the suphate of the metal 
as the electrolyte. 

Copper sulphate, or blue vitriol, and iron sulphate, or green vit- 
riol, have large application in the dyeing industry, also in recovering 
silver by the amalgamation process. Green vitriol, perhaps better 
known as copperas, is very largely used in ink manufacturing. 

The leaching of low grade copper ores with weak solutions of sul- 
phuric acid has become a great industry within the last few years. 

"Shoddy" wool is freed from cotton by "carbonizing" the 
goods with sulphuric acid, which consists in lettii^ a solution of 
acid dry on, when the cotton or other vegetable fibre gives up its 
OH radical, only the carbon remaining, and that in the form of a 
powder, which is easily shaken off. 

.The foregoing is only a brief list of some of the most important 
uses to which sulphuric acid may be put, and is not intended to 
do more than show how dependent modem civilization is upon 
this industry. 

The Bureau of Mines BvlleHn No. 184 reports for the period 
June to August, 1918, the following distribution of sulphuric 
acid among the industries: 

Table 2 



tDdutTT 


Too. Hdd <lHd 


^^ariisr- 


Per Bent of 
toUUcid 




140,000 
111,000 
35,000 

38,600 
36,500 
S,200 
6,300 

15,200 
3,800 


2,700,000 

2,130,000 

671,000 

740,000 
700,000 
100,000 
104,000 

202,000 
73,000 


36.0 
28 






4. Chemicals, drugs, aad ammonium 






9.3 
I 3 




1.4 












390,500 


7,610,000 









idb,Go(5glc 



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^d by Google 



28 AMERICAN SULPHURIC ACID PRACTICE 

This table shows, eliminating the acid used for munitions and 
explosives, and allowing about 10,000 tons per month for domestic 
explosives, an indicated requirement for normal peace purposes 
of possibly 260,000 tons per month (basis, 100 per cent HtSOt), 
or about 5,000,000 tons per year (basis, 50°B4.}. 

There is no question that the use of phosphate fertilizer will 
increase all over the country for many years. And as acid is 
expensive to transport, it will have to be made near the place it 
is used. 

Sulphur, the primary raw material, either as pjrrites or brim- 
stone has recently been described by Drs. Raymond F. Bacoa 
and Harold S. Davis before the American Institute of Chemical 
Ei^neers. The following extracts have been taken from their 
paper.* 

America now dominates the sulphur industry and virtually all the 
American sulphur is produced by three companies— viz., the Union 
Sulphur Co., the Freeport Bulphur Co. and the Texas Gulf Sulphur Co. 
These three companies produce not only virtually all the sulphur used 
in the United States but also a considerable surplus vhioh is exported. 
The only other sulidiur which normally enters the American market in 
quantity cornea from Japan and its percentage calculated on the con- 
sumption of the United States is small and is not likely to increase. 
Riaii^ costs of living have meant much higher wages in Japan, as well 
as in other parts of the world; in fact, the percentage increase has prob- 
ably been greatest in Japan, due not only to world conditions affecting all 
countries but to the rising standards of living of the Japanese. These 
facte, together with present higher transportation costs, will make it 
increasingly difficult for Japanese sulphur to compete on our Pacific 
coast with the American product. 

Expansion of Indostrt Ddeino War 

During the World War, and especially after America's entry into it, 
the demand for sulphur grew enormously. Some time previous to our 
declaration of war consideration had been given by a certain group of 
New York capitalists to the opening up of the sulphur deposit (known 
as the "Big Dome") located near Matagorda, Tex. These plans were 
hastened to realization by our Government's need and demand during 
the war for the maximum production from every possible source of sul- 
I^ur. The plana eventuated in the formation of the Texas Gulf Sul- 
phur Co., which, however, did not get its plants into operation until 
after the armistice. Production has been practically continuous since 

Chem. & Met. Eng., January 12, 1921. 



^dbvGooglc 



CHARACTERISTICS AND USES 





Fio. 1.— Views of lie Texas GuH Sulphur Co. 
General Views Showing Topography, Figa. I, 2, S, 8. 



n,i,io,n,Go(5glc 



AMERICAN SULPHUI 



Fio. 2.— Views of the 1 
Houses, Pavilion and Hospital, 
Method of Loading for Shipmet 
Exterior and Interior Views ot ! 



i,io,n,Go(5glc 



CHARACTERISTICS AND USES 31 

the company first mined sulphur on March 19, 1919. The plant of 
this company, which has been described elsewhere,' was designed to 
have a capacity of 1,000 tons of sulphur per day, but for montiis at a 
time during the past year it has produced on an average 2,000 tons per 
day. The total production for the year 1920 exceeds 800,000 long tons, 
while in all probability the production for 1921 will be the largest of 
any sulphur company in the world. The possible daily production 
with the present plant, under favorable conditions, could be forced to 
3,000 or 4,000 tons per day. The deposit contoins upward of ten 
million tons of sulphur; and a brief description of its character is a^ 
follows; 

DESCBipnoN OF Bio Domb at Matagorda 

The main deposit has a diameter of about 4,000 ft. and is situated 
800 to 1,000 ft. below the surface of the ground. The sulphur occurs 
in an almost flat stratum, whose general shape is like that of a flat- 
topped umbrella. Above the sulphur stratum is an unconsolidated 
sediment consisting of bands of shale, gumbo and boulders. Below is 
a layer of salt and gypsum, and then a layer of salt of undetermined 
but very considerable thickness. The sulj^ur content of the deposit 
runs quite uniform with a slightly higher percentage of sulphur on one 
side of the dome. The mining operations are carefully checked, and a 
large-sized model of the deposit enables the engineers constantly to 
visualize what is taking place underground. 

Production and Stocks Exceed Post-war Normal Demand 

At the time the Texas Gulf Sulphur Co. entered the market the situa- 
tion was about as follows: The Union Sulphur Co. had on top of the 
ground, in unsold stock of sulphur, upward of one miUion tons and the 
Freeport Sul[4iur Co. had several hundred thousand tons. The normal 
consumption of sulphur in the United States had been between four and 
five hundred thousand tons per annum, which quantity could be readily 
supplied by the two older companies.* A new sulphur company enter- 
ing the market with a large production of sulphur was therefore com- 
pelled to pursue one of two policies — either to attempt to obtain a share 

Read before the American Institute of Chemical Engineeia, New Orleans, 
December 6, 1920. By Ratuond F. Bacon and Harold S. Davis. 

' Ckem. a- Met. Bng., vol. 20, No. 4, pp. 186-188. Eng. Min. J., vol. 107 
(1919), pp. 555-557. 

* It may be stated, in passing, that any economic data given regarding 
either the Union Sulphur Co. or the Freeport Sulphur Co, are subject to 
the usual statement on advertisements of bond sales; that is, "they are 
gathered from sources we believe to be reliable, but are not guoruiteed by 



^dbvGooglc 



32 AMERICAN SULPHURIC ACID PRACTICE 

of the buBiness by cuttiog prices or to place the sulphur in markets 
which hsd not hitherto used sulphur; in other worde, to increase the 
sulphur consumption of the country. 

With reference to the first possibility, competition based on cut- 
throat slashing of prices always has proved disastrous to the whole 
industry. Moreover, the mining of sulphur by the Frnsch process, to 
be carried out economically, must be conducted on a very large scale, 
80 that even if a company under the conditions outlined above had 
obtained a third of a possible 600,000-toa consumption, this would not 
have insured profitable operation. The company has chosen what is 
surely the wiser course, in attempting to place its sul|Aur by increaang 
the total consumption in the industries. 

It was possible to do this owing to the prevailing economic conditions. 
The United States had in recent years consumed annually, for the manu- 
facture of sulphuric acid, upward of 600,000 tons of sulfdiur in the form 
of pyrites, most of which came from Spain. The older sulphur com- 
panies, either because of some agreement with the pyrites iroportets or 
because of a desire to hold the price of sulphur at a certain level, had 
not attempted seriously in past years to substitute sulphur for pyrites 
as the raw material of sulphuric acid manufacture. Importetion of 
Spanish pyrites, due to war transportation conditions, fell off very 
seriously during the war years. This caused many producers of sul- 
phuric acid to discard the pyrites roasters and to install sulphur-burning 
equipment, while new producers in this field erected plants which were 
almost entirely so equipped. The new company was able to obtain its 
fair proportion of the new business and the net result has been that 
the total consumption of sulphur of the United States during the past 
year has been upward of 1,000,000 tons, as compared with a normal 
consumption in recent years of about half that figure. 

Ptbiteb vebbus Sulphdr as a Sodrcb of so* 

It is interesting, in this connection, to give just a little history, for if 
the subject is examined it is found that in the early days of sulphuric 
acid manufacture all the sulphuric 'add of Europe, excepting Nord- 
bausen acid, was made from brimstone. This includes the period from 
about 1750 to 1839, when pyrites first was used commercially for the 
manufacture of sulphuric acid in England. This use of pyrites was 
due to the fact that the Neapolitan Government in 1838 granted a 
monopoly for the exportation of sulphur to Taix & Co., of Marseilles, 
which film immediately raised the price of sulphur from $25 to $70 per 
ton. By so doing, it killed the goose that laid the golden egg, for 
I^tes was substituted immediately for sulphur in most European 
countries and the era of high-priced sulphur was but short lived. The 
loss of this market was a permanent setback to Sicilian sulphur. 



^dbvGoot^lc 



CHARACTERISTICS AND USES 33 

The subsequent history of the sulphur industry is one of violent ups 
and downs. If one considers this history up until some time after 
FrBBch made America a factor in the business, it will be noted that it 
has been characterized at all times by short periods of prosperity, 
followed by a short-sighted, selfish, destructive competition on the part 
of certain interests. Following this would come a period of such marked 
depression as to threaten the life of the entire industry, and it would 
be necessary for some governmental or other outside agency to exercise 
pressure to get the producers together on a common-sense basis and 
thus gradually put the industry again on its feet.' Since the time when 
Fraach made possible America's sulphur industry the stabiUty of the 
whole industry has been much greater. While at the present time there 
is an extremely lively competition among the companies for business, 
there is every reason to believe that American common sense, spirit of 
fair play, and co-operation will prevent this competition going to the 
extent of threatening the industry itself, as has happened many times 
in the past. Present indications are that all the sulphur companies are 
pursuing an enlightened policy, in that all are doing more or less research 
and development work having aa its ultimate object the opening up of 
broader markets for sulphur, of which sulphuric acid manufacture 
affords but one. 
Advantaobs op Sulphur over Ptoiteb 

For sulphuric acid manufacture sulphur has many very marked ad- 
vantages over pyrites. Using pyrites means handling into the works a 
comparatively large quantity of material, its slow combustion in expen- 
sive roasters, a certain inevitable dust nuisance and the disposal of a ,' 
large tonnage of cinder. As against this, sulphur of less than one-half. V'^ 
the weight of pyrites for a given tonnage of acid produced is handled' 
into the works, is humed cleanly in inexpensive equipment and leaves 
no residues to be taken care of. Sulphur ia constant in composition, 
and its freedom from arsenic and other impurities allows the production 
of a purer acid. It is also claimed that, in practice, the burnii^ of 
sulplfur means a higher rate of production for a given size of lead cham- 
ber space. 

These acknowledged advantages of the use of sulphur over pyrites 
for sulphuric-acid manufacture have been demonstrated by the willing- 
ness of acid producers to pay a higher price per unit for elementary 
sulphur than for combined sulphur in the form of pyrites. An example 
of this is the fact that one of our largest and best organized chemical 
companies, in making a large contract, chose sulphur over pyrites for 
Bulphuric acid manufacture, where the differential in offered prices was 
8c. per unit of sulphur. 

■ In this oonneetlon, see Frabch, Perkin Medal Address, Met. &■ Chtm. 
Bng.. vol. XO, No. 2, pp. 73-82, and J. Ind. Eng. Chem., vol. 4 (1912), p. 139. 



^dbvGoOgfc 



34 AMERICAN SULPHURIC ACID PRACTICE 

When one considers the present high prices of labor, the uncertainty 
of the copper market and the fact that sulphur may be purchased in a 
competing market, from concerns which have large stocks on hand, so 
that delivery is certain, it would seem to be a vise business policy to 
use sulphur rather than pyrites for Bul[^urtc acid manufacture even 
with a very large differential in price. This is especially true when one 
considers the other side of the situation — namely, that in buying im- 
ported pyrites the consumer is putting himself at the mercy of one large 
set of interests which, while it may at the present time ofFer pyrites at 
low prices and even below actual cost, will almost certainly at some time 
JD the future reap its profit by much higher prices. It is said that 
imported pyrites has been offered for lai^ contracts in this country at 
about 10c. per unit of sulphur, ex-vessel, Atlantic seaboard, while at the 
same time pyrites was selling in England, much nearer the base of 
supplies, at 20c. to 22c. per unit of sulphur. It reminds one somewhat 
of the tactics of Standard Oil in the old days before "trust-busting" 
became fashbnable with politicians; and everyone knows that those 
who bou^it cheaply when the company was extii^uishii^ a competitor 
never reaped any peimanent advantage, but later more than paid for 
temporary reductions in price. 

Sulphur is today one of the few substances which have not risen in 
price since pre-war days. In fact, sulphur is cheaper today than at any 
other time in the history of the industry. The price for large contracts 
is about $20 per ton, Atlantic seaboard. Tbia makes sulphur one of 
the cheapest raw materials available and should, it would seem, greatly 
extend its usefulness. Sulphur as mined and sold by all three com- 
panies is of remarkably high grade. In fact, many so-called C.F. chem- 
icals do not possess the purity of crude sulphur, as sold by these 
companies. The sulphur is free from arsenic, seleaium and tellurium, 
and often for days at a time wells will yield a product running higher than 
99.9 per cent sulphur, as calculated on b moisture-free basis; in fact, 
sulphur companies selling the crude sulphur on contracts guarantee the 
purity to be over 99 or 99H psr cent. 

Effect of Tracbs op Petroleum on Combustion 

One impurity occurring in traces in the sulphur of all three companies 
is oil. liere is a dearth of information in the technical literature 
respecting the subject of oil in sulphur. Since tlie effect of this im- 
purity is very interesting, it is appropriate to discuss it here. The 
peculiar effect of oil is its influence on the burning qualities and also on 
the color and odor of sul[riiur. A priori, one would not assume that 
mere traces of a combustible substance like petroleum oil could affect 
adversely the combustion of another combustible substance like sulphur, 
but such is indeed the case. 



^dbvGooglc 



CHARACTERISTICS AND USES 35 

If one will make a simple experiment by attempting to bum two small 
lots of sulphur, one being chemically pure and the other containing 0.2 
per cent of petroleum oil, he will note the following phenomena: The 
pure sulphur will bum quietly until it is b^tally consumed; the sulphur 
containing the oil will bum for a very short time, when it will be ob- 
served that a thin, elastic film is being formed over its surface. Very 
soon combustion is taking place only in spots, and within an exceedingly 
flhort time the flame goes out, although only a small percentage of the 
sulphur has been consumed. The explanation is quite simple. Sulphur 
and oil at a moderate temperature react together to form asphalt, and 
if the reaction is carried to completion the final result is carbon. 

In the burning of sulphur containing oil the oil reacts mth the sulphur 
to form an asphaltic nmterial, which quickly spreads as a film over the 
surface. The result, as combustion proceeds, is a film of carbon over 
tlie surface of the sulphur. The ignition temperature of carbon, or of 
the intermediate asphaltic material, is so much higher than that of 
sulphur itself or than the temperature developed during the burning 
of the sulphur that this film is not ignited and consequently the whole 
flame is extii^^ished. 

The remedy for burning such sulphur is also quite obvious. If the 
devices for sulphur combustion are such as to agitate the surface of the 
burning sulphur or in any other way break this film of asphaltic mate- 
rial, no difficulty will be experienced. Acid manufacturere who use 
mostly modem tyi)eB of sulphur burners, such as the rotary or cascade 
type, which allow the sulphur to drop from one level to another, have 
at^lutely no difliculty in burning sulphur containing 0.2 per cent of 
oil, which figure represents more oil than any of the. commercial sul- 
phurs contain at the present time. On the other hand, many of the 
small paper-pulp manufacturers still adhere to types of burners in 
which the burnii^; sulphur is more or less quiescent. With such a type 
there is no agitation of the burning liquid surface, so that some of these 
paper-pulp manufacturers have had difficulty in burning sulphur when 
they happened to obtain a shipment comparatively high in oil. 

The sulphur deposits of all three operatiug companies are located in 
chwe proximity to oil fields. When a sulphur deposit is first opened 
some of the product may be high in oil, running as much as 0.2 per cent, 
but as production proceeds the oil becomes progressively lower until 
finally, for days at a time, it may amount to only 0.04 per cent, which ia 
totally negligible, even for bumers which provide no agitation of the 
surface. We have assumed that hot water carried this small quantity 
of oil from small crevices in the oil-sand formation to the sulphur below 
when the well was first opened. After a region has become heated up 
by the hot water, these traces of oil are pretty well watdied out ; conse- 
quently, Buli^ur mined later in the same area is virtually free from it. 
Examination of drill cores of native sulphur showed such in aitu sul- 



^dbvGooglc 



36 AMERICAN SULPHURIC ACID PRACTICE 

phur to be oil-free. We are informed by ex-employeee of die UnioD 
Sulphur Co. th&t this con«8pond8 with tiie experiences of that organ- 
isation in heating up any new area of sulphur ground. The examina- 
tion of a very lai^ number of samples of sulphur, representing the 
production of all three companies, has shown quite positively that none 
of their sulphur contains enou^ oil to cause any difficulty in its com- 
bustion with rotary burners or other burpers which agitate the surface of - 
the burning sulphur during combustion. It is only very exceptionally 
that one will find a car of sulphur whose oil content is high enough to 
make difficulties in its combustion in a stationary type of burner. 
Properties and Uses of Sulphur 

Sulphur is now and is likdy to be for some time one of our cheapest 
raw materials, and accordingly should and undoubtedly will find a 
much wider range of usefulness. It is by studying the physical and 
chemical properties of a substance that one first obtains ideas as to 
possible new uses therefor. The chief physical properties of sulphur 
are tabulated in Table 4. The present tonnage uses of sulphur are 
presented in the chart. Those properties which suggest certain possible 
tonnage uses for sulphur are its very poor conductivity of heat and 
electricity, its resistance to being wetted by water and its inertness 
toward most acids, all of this combined with a, fair d^ree of physical 
strength. These properties suggest heat-insulating materials, electrical 
insulators of various types, water- and acid-proof cements, and acid- 
proof construction materials. 

As against the properties of sulphur which might make it very de«r- 
able for certain construction purposes are certain objectionable ones, 
such OS its brittlenesB and its flammability. The brittleness can be 
overcome sufficiently for many purposes by making mixtures of sulphur 
with other materials, such as sand, asbestos, or paper pulp, or by rein- 
forcing with wire screen. In many cases the flammabiUty is not a 
serious objection. 

A survey of the literature, especially the patents, on the subject of 
sulphur mixtures reveals that almost every conceivable thing has been 
suggested as a perfective admixture for sulphur to obtain a material 
which has all the air- and acid-resistant properties one could desire or 
to get a completely resistant kind of concrete useful in building. We 
have tested out most of the recipes which appeared to be promising and 
find as usual that the claims have been much overstated. However, 
the ordinary mixture of sand and sulphur which has been repeatedly 
mentioned in the literature has merits which should make it better 
known. The mixture which has seemed to us the best for most uses is 
that of 40 of sulphur and 60 of sand (parts by weight). The tensile 
strengths of sulphur-sand mixtures as measured in the usual manner for 
testing cement were as follows: 



^dbvGooglc 



CHARACTBttlSTICS AND USES 37 

Tabi^ 3. — Tensilh Strenoths of Sulphur-band MixTDBEa 



100 ■ 250 

We have also used other fillers which have given tensile strengths of 
800 and even 1,100 lb. measured in the same manner and have to a 
large extent overcome the brittlenesB of the sulphur in some of these 
mixtures. Sulphur-sand briquets kept on hand for one year show no 
deterioration in strength. It is evident that the 40:60 sulphur-sand 
mixture can be used as an acid-resistant concrete, for making acid- 
resistjng pipe, tanks, gutters, launders, etc. The manipulation of such 
a mixture is much like that of pourii^ concrete and is as follows: 

Practical M amputation. — It is evident that the sand should contain 
no constituent which wilt be attacked by any material which is to come 
in contact with the finished product; for instance. In the case of acid 
tanks it should be free from limestone or other acid-soluble constituente. 
If necessary, it should be washed and dried. The sulphur may be 
melted in a kettle with constant stirring, and the sand, which has been 
heated separately, poured into it while the stirring is continued. Un- 
less the sand is heated, it will lump when poured into the sulj^ur. 
When the material is thick enou^ (40 per cent sulphur and 60 per cent 
sand) it is ladled into the molds. 

Considerable flexibility is possible in handling this material. For 
instance, a small tank was made which was 2 ft. square, IS in. deep, 
and 2 in. thick. The mixture was poured into a wooden mold in twelve 
different lots. Although several of these lots had solidified before the 
next was poured upon them, nevertheless the resulting joints were 
Btrong. Apparently the hot mixture melts sufficient of the solidified 
part to form a sohd joint. There was no contraction of the tank ae a 
whole and no tendency to split in the mold. This mixture can be 
worked with a trowel, tike mortar. It can also be reinforced by wire 
netting placed in the mold before it is poured. The specific gravity of 
a sulphur^eand mixture (40 :60) was found te be 2.46. 

Weight of! cu. ft 154 lb. 

Weiglit of Bulphur required per aubic feet 62 lb. 

Weight of Hulphur required per cubic yard — 1,670 lb. 

Taking the value of sand as SI per cu. yd. and of sulphur as $20 per 
ton, the price of the materials per cubic yard will be about $18. It may 
be possible to decrease appreciably the amount of sulphur necessary and 



^dbvGooglc 



38 AMERICAN SULPHURIC ACID PRACTICE 

hence the cost by imbedding latter pieces of crushed rock or some such 
substance in the mass. Teets of the material in sea water are being 
made, but it is too early to give results. It is apparently standing up 
well to date. 

Pipes cast of this sulphur-sand mixture show no deterioration aft«r 
one year in 5 per cent hydrochloric or 5 per cent sulphuric acid. The 
ordinary organic acids have no effect on such a mixture. 

Tabu; 4. — -The Physicochemical PaoFERTiEa op Sdlphub 



Vapor Presbcbe Curve' 
Forms of sulphar: 

CTyHtalline a». or. 

(fl) Rhmlnc. Ordinary form stable below Oe'C. (205"?.) , . 2 . 07" 

(6) Monodinic Stable above %&°C. (205°F.) 1 .96' 

(c) MiUt o} SidfkvT. Formed, e.g., by action of diluted 
acids on polysulphides. Generally called amorphous, 
but shown by Smith and Brownlee to be crystalline.' 
There are several other modifications of crystalline sul- 
phur of scientific interest but not of general importance. 

Liquid. At lia'C. (235°?.) 1.81» 

Contains: 

SvlpkuT (liquid, soluble), 8\. 

S^dphuT (liquid, insoluble or amorphous), Sfi. 

The proportion of S(i to 8\ increases with the temperature. 
Ainorphotia. S(i (sohd) 1.89' 

Flaatic Sutpkw. Formed by heating sulphur above viscous 

stage, 162°C. or 324°F., and cooling quickly 1,88' 

Elaatie S^dphur. Formed by heating sulphur above 400''C. 
or 752°F. and pouring in a thin stream into liquid air. 
Its elastic properties arc soon lost. 

Blaek S^djAur, " When sulphur mixed with very Uttle oil is 
thrown into a hot platinum dish, a black substance is 
obtained which has been looked on as a modification 
of sulphur. The product contains 55 per cent of 
sulphur and 33 per cent carbonaceous material." — 
Watts, Du^ionary of ChemiatTy. 



^dbvGoogle 



CHARACTERISTICS AND USES 



a ranges of temperatuieB a. 



Electrical CoNDUcxiviTr' 
Moaeured aa reciprocal value of rcBistivity in ohms of 1 o: 



22 72 IX 10-" 

69 156 0.254 X 10-" 

116 239 0.105 X 10-" 

130 266 O.S X 10-" 

430 806 0.1 X 10-" 

Comp&re; 

Foroelwn 1 X 10-" 

Mica 1 X 10-'» 

Ebonite 1.6 X 10-" 



Feictional Elbi 



When rubbed with practically any other aubstance, e.g., glass, fur, silk, 
wool or hard rubber — sulphur becomes charged with negative electricity. 



CiBPFiciENT OP Linear Expanbion' 



Surface Tbnsioi 



Temp. 


Ex. ooeff. 


Temp. 


Surface tension, 


C. 


F. 


C. 


F. 


mg./mm. 


0-13 


32-56 


0. 000046 


120 


248.0 


6.71 


13-50 


56-122 


0.00007 


131 


267.8 


6.12 


50-78 


122-173 


0.00009 


146 


294-8 


6.05 


78-97 


173-207 


0.0002 


195 


383.0 


6.62 


97-110 


207-230 


0.001 









idb,Go(5glc 



AMERICAN SULPHURIC ACID PRACTICE 



re 



APPROXIMATE CURVE OF SURFACE TENSION 
COMPEESSIBILtTX ' 

Average fractional change ot volume caused by 1 megabar change in 
presaure between 100-500 megabara 0.0000125. 

1 megabar ^ 0.987 atmoBphera 

CoNDOCTiviTV OF Hbat' 
Measured as the numbet of gram-caloFJes transmitted in 1 sec. throi^h 
a plate 1 cm. thick and having surfacee 1 eq. cm. id area when opposite 
faces differ in temperature by I'X?. 

20°-100°C. (68''-2l2°F.) 0. 0006 

Compare: 

Ice 0.002 

Copper 1 . 00 

InteniBtional Atomic Weight, 1920 - 32.06 
Vapor Denaity: 
At boiling point corre^mnds ^)proximate]y to formula Sg". 
At 1,000°C. (1,832°^) corresponds approximately to formula St. 
EcoNouicB DP Natural Sclpevr 
Until 1900, 96 per cent of world's supply from Sicily 
Iq 1912, 60 per cent of world's supply from Sicily 
In 1917, 14 per cent of world's supply from Sicily 
In 1917, 80 per cent of world's supply from U. S. A. 

United States f^ports and Imports 

1909 exports 37, U2 long tons 

1909 unports 30,589 long tons 

1918 exports 131 ,092 long tons 

191S imports 82 long tons 

United States Production 

1894 494 long tons 1909 303,000 long tons 

1899 1,590 long tons 1914 347,491 long tons 

1904 196,888 long tons 

1919 Texas Gulf Sulphur Co. 
Only 9 months production after start, 348,380 long tons. 

Properties of Commercial Solphuk 
Insoluble in Water 
Insoluble in Most Acids 
Tensile strength, 200 lb. per square inch (apprra.). 
Heat conduotivity, low: H that of cork, ^ that of ice. 



^dbvGooglc 



CHARACTERISTICS AND USES 41 

Electrical conductivity lower than that of practically any other solid sub- 
stance. 
Melting point, depending on conditions, 1I0.2°-119.26°C. (230.4°-24e. 

rr.). 

Ignition temperature, 248°C. (478^.).' 
Boiling point, 444.6''C. {832.3°F.).* 

Melting Point' 

Temp. ■ 

Type of sulphur C. F. 

Rhombic 112. 8 235 

Monoclinic 109 , 25 246 . 7 

Natural freezing point S\ and %i in equilibrium (96.3 per cent SX, 3.7 
per cent S^), 110.2'C. (230.4°F.). 

Specific Heat' 

Temp. . 

Type of sulphur C. F. Sp. ht 

Rhombic 0-96° 32-203° 0. 1761 

Liquid 160-201 320-393 0.279 

201-233 393-451 0.331 

Heat of Combuation' 

G. cal. per g. S B.t.u. per Ih. 

8 -I- Oi ^ SO, 2 , 200 3 ,960 

8-. HiSO. (dilute) 2,450 4,410 

S-. H.SO. (dilute) 4,460 8,010 

Heat of Vaporization* 

Temp. G. Cal. B.t.u. 

C. F. per g. per lb. 

444.6° 832.3'' 70 126 

(Approx.) 

Transition Temperature' 
S Monoclinic ^ 8 Rhombic 

I^esBure, Temp. ■ 

kg./eq. cm. Lb./in. C. F. 

10.6 16 96° 204,8° 

123 17B 100 212.2 



1,350 1,920 



TBIPLB POIHT 
Sulphur 
Uquld 



♦ Monoclinfc. 
ISZO 18TT ISI* S04* 



.dby,QQ,Qgie 



42 



AMERICAN SULPHURIC ACID PRACTICE 



Hbatb or Solution in CSi* 
G. cal. per g. 

Dilute solution -11,89 

Saturated solution —11.65 

Heats of FnaiON" 

G. cal. per g. 

Rhombic at lOO-C. (212°^) 14.9 

Monoclinicat 100°C. (212°^) 11.5 

To form pure liquid sulphur (Sx): 

From rhombic 14.6 

From monoolinio 11.1 



B.t.u. per lb. 
-21.4 
-20.9 



CHANGE IN VISCOSITY WITH TEMPERATURE' 
Solubilities in Various Solvents" 



Solubility, 
G. in 100-g. 
solution 



Carbon dimilphide. . 



Carbon tetrachloride 

Chloroform 

Coal-tar oil, sp. gr. 0.87 



^dbvGooglc 



CHARACTERISTICS AND USES 













I^naeedoU 




15 


59 


0.4 






160 


320 


9.0 


Olive oil (sp. gr. 












130 


266 


30 


Sulphur chloride 












65.2 


131.4 


43 






86 


186.8 


89 


Phenol 




175 


346 


26.7 


Toluene 




23 


73.4 


1. 48 


Turpentme (oil of) 


16 


60.8 


1.33 



Chamgd or MsLTiNa Point With Pbebsukb* 

References Cited 
> liANDOLT-BoBNarKiN-RoTH's "Physikalisch-Chemische Tabellen" (4th 
•d.). 

• R. H. Brownlbb, J. Am. Chem. Soc., vol. 29, pp. 1032-1062 <1907). 
' A. WiBOAND, Ann. Phynik, vol, 22, pp. 64-98 (1907). 

*H. ZicKENDSAHT, Ann. Phj/nk, vol. 21, p. 141 (1906). 

' T, W. Richards and others, Carnegie Inst. Pub. No. 76, May, 1907. 

■ MuELLEB AND BnnoEsB, J. Am. Cbtm. Soc., vol. 41, pp. 745-63 (1919). 
' J. R. Hill, Chem. News, vol. 95, p. 169 (1907). 

■ Calculated from vapor pressure curve. See also J. W. RiCHABns, 
"Metallurgical Calculations" (2d ed.). 

• M. BBU.ATI AND L. FiNAzii, Aui. r. Intl. Veneto, vol, 72, II, pp. 
1303-14 (1913). 

'* Lkwib and Randall, J. Am. Chem. Soe., vol. 33, pp. 476-88 (1911). 
>i Seioeli^ "Solubilities of Inorganic and Organic Compounds" (2d ed.J. 
'* MorrEseiEB, Mem. Acad, de MontepeUier, vol. 6, p. 107 (1S64). 
" Oiibi.in-Kbaut, "Handbuch der anorgonishen Chemie." 



^dbvGooglc 



CHAPTER IV 
RAW MATERIALS 

The raw materiala for Sulphuric Acid are sulphur, oxygen 
(supplied from the air), and water. The oxides of nitrogen, 
either as Chile saltpeter or nitric acid, might be called indirect 
raw materials. 

Wat^F and air need no introduction nor description, so this 
chapter will be devoted to the description of the sources of 
sulphur and the nitric oxides. The amount of acid produced by 
distillation from natural sulphates is practically nothing, leaving 
brimstone and the metallic sulphides as our commercial sources. 

Sulphur occurs native, as brimstone, in all parte of the world, 
particularly rich deposits existing in Iceland and Sicily; but the 
enormous deposits of Calca^iou Parish, south-western Louisiana, 
furnish the United States. A small amount is mined in Utah and 
Wyoming for local use, and the Pacific Coast is supplied from 
Japan. 

The Louisiana beds, worked by the Frasch process, were 
discovered in boring for oil, and a most interesting and ingenious 
method of recovering the sulphur was devised by Herinan Frasch, 
for which he was awarded the Perkin medal. 

The sulphur ore, containing up to 90 per cent sulphur, occurs 
450 ft. down, under quicksands that make usual mining methods 
impossible. The Umit^ of the bed have never been determined, 
although 40,000,000 tons have been locked out. 

The Frasch process, described in United States patents, 
No. 799,642 and No. 800,127, is as follows: A 13-in. hole is drilled 
to a depth of 800 ft., cased, and inside, concentrically, a 10-in., 
a 3-in., and a 1-in. pipe is placed. Between the 3-in. and the 
10-in,, and the 10-in. and the 13-in. pipes superheated water, 
heated by superheated steam to a temperature where sulphur 
begins to darken, is forced by its own expansive force, and by 
steam pressing, into the deposit. The hot water, after melting 
the sulphur, passes into the crevices of the rock, the molten 
sulphur separating from the water by gravity, and being forced 
up the inner pipe by steam pressure. The steam pressure is 
kept less than the head of a column of molten sulphur reaching 



^dbvGooglc 



RAW MATERIALS 45 

to the ground, and the sulphur is lifted the last part of the way 
by compressed air. 

The molten sulphur is run into huge spaces fenced in with 
boards, where it solidifies and is then blasted down for shipment. 
It will run over 99.6 per cent S, and praeticaHy no As. 

Louisiana sulphur is shipped from Sabine Pass, Texas, to 
supply all the eastern United States. It was quoted (1916) at 
$22 a ton, and was reported to cost, f.o.b. mines, under $3. 

The Japanese sulphur, greyish in color, comes in large blocks, 
about 3 by 2 by 1 ft., wrapped in matting. It supplies the 
Pacific coast demand. 

PTRITES 

Iron pyrites, FeSi, bisulphide of iron, is one of the most widely 
distributed of ores, and has been, since about 1840, a material 
of prime importance in the manufacture of sulphuric acid. 

Pyrites crystallizes in the regular system, as a cube, octohedron, 
and pyrihedron, and often as twin crystals. The crystals are 
frequently well developed, and become very large. It is greenish 
yellow in color, its popular name, "Fool's Gold," describing it 
well. Small crystals show darker colors, and the powder is 
greenish black. Fracture is concboidal or irregular. Hardness 
6 to 6.55; Bp. gr., 4.83 to 5.2; it contains 46.58 per cent of iron, 
and 53.42 per cent of sulphur. 

Volcanic pyrites contains no water, while sedimentary deposits 
do. Some of the pyrites containing water bursts upon roasting. 

The principal North American deposits of pyrit^ are at 
Tilt's Cove; New Foundland; Capleton, Quebec; Ely, Vermont; 
and Pulaski, Virginia. Cuba is becoming a large producer. 

Pyrrhotite, magnetic iron sulphide, FeySg, is not a practicable 
source of sulphur: first, because of its low sidphur content 
(39.5 per cent sulphur, 60.5 per cent iron), but even more impor- 
tant, the sulphur that it does contain is not readily given up, the 
lumps crusting with oxide of iron, and extinguishing whatever 
flame is started. It has been successfuly roasted in powdered 
form in a Herreshoff roaster. E. D. Peters speaks, in "Principles 
of Copper Smelting" (p. 169), of $200,000 thrown away on an 
acid from pyrrhotite proposition. 

Copper-bearing pyrites, of the general form of chalcoperite, 
CujS, Fe»S), is a valuable source of sulphur, either when the ore 
is roasted and the SOi given off used for acid making, and the 



^dbvGooglc 



46 AMERICAN SULPHURIC ACID PRACTICE 

cinder for copper; or aa at the Tennessee Copper Co., the gases 
from semi-pyritic emelting are used direct to the chambers. 

Zinc blende, ZnS, the principal ore of zinc, is an important raw 
material, the SOi derived from its being roasted to ZnO being 
used. Blende contains 32.9 per cent sulphur when pure — ores 
usually contain some FbS and other impurities, so that the 
sulphur content may drop as low as 20 per cent. Very little 
arsenic occurs with blende, and the acid produced from it is in 
demand for that reason. 

The SOj produced by the roasting of zinc blende would prob- 
ably never be used to make sulphuric acid if the gases were not 
injurious to v^etation, for the gas from a material so low in 
sulphur is very dilute. And in addition, sufficient air must be 
introduced, not only to bum tlie sulphur, but to oxidize the zinc 
as well: 

2ZnS + 30, = 2ZnO + 2S0j. 

As is shown, 50 per cent more oxygen than is required to bum 
the sulphur is required, and the nitrt^n from that air serves to 
dUute the gas formed. So sulphuric acid from blende is less 
a by-product than a means of taking care of the hannful gases, 
that otherwise, if let free, destroy all vegetation near the plant. 
Consequently, while an important source of acid in this country, 
the burning of blende is properiy a part of zinc metallurgy, and 
for thorough treatment the reader is referred to works on that 
subject. 

Zinc ores must be well roasted, so 'the cinder should contain 
under 0.75 per cent sulphur, either as ZnS or as ZnSOi- If the 
furnace temperature is too low the sulphate will form, and that 
must be specially treated to get it into the form of ZnO, for 
distillation. 

The muffle type of furnace, with a mechanical stirrer, is in use 
in all modem works. 

Lead ores are too low in sulphur to be used for a raw material 
for sulphuric acid, pure galena only containing 13.4 per cent 
sulphur. 

I cannot find that spent oxide of iron is used in this country as 
a raw material, although it is used abroad. Gas works remove 
the HtS from gas by a mixture of hydrated iron oxide and 
sawdust, according to the formula; 

Fe,(OH) ,-|- 3H,S - 2FeS + 6H,0 + S, 



^dbvCooglc 



RAW MATERIALS 47 

and upon exposure to the air precipitates more sulphur, as 
follows: 

4FeS + 30, + 6HtO = 2Fe,(0H), + 28, 

This regeneration is repeated perhaps thirty times, before the 
quantity of sulphur is sufficient to interfere with the use of the 
oxide as a purifier. It contains as high as 60 per cent sulphur 
then, and is used as acid material. 

KITRATB OF SODA 

Nitrate of Soda, usually called Nitre, or Chile saltpeter, has 
been the source of practically all our nitric acid, and still accounts 
for the largest part of it, although the various fixation processes 
are making the nitrogen of the air available in ever increasing 
quantities , 

Formula— NaNO,; hardness, IH to 2; sp. gr., 2.09 to 2.39; 
the large crystals are colorless, transparent, and brilliant; small 
crystals white and opaque; crystallizes in rhombohedra; has a 
bitter, cooling taste; upon heating it first melts and then decom- 
poses, at a red heat, into sodium nitrite and oxygen; fuses at 
316°C.; and it dissolves very readily in water, with absorption of 
heat. 

There are many known deposits of nitre, but the world's 
supply comes from northern Chile. There it is found under a 
cap, up to 7 ft. thick, of "costra," a hard conglomerate. The 
actual nitrate bearing ore, called "caliche," occurs in horizontal 
beds, up to 5 ft. thick, containing 45 per cent to 85 per cent 
of sodium nitrate, 20 per cent to 40 per cent sodium chloride, 
and sodium, potassium, and magnesium nitrates, sulphates, 
iodates, and chlorates, and guano. It is an old ocean bed. 

The caliche is crushed and the soluble salts leached out; then 
the sodium nitrate crystallized out in a very pure form, carrying 
the chlorates and iodates, which are recovered during the nitric 
acid manufacture. The mother liquor retains most of the sodium 
chloride. 

An average analysis of commercial Chile saltpeter is: 

96.00 per cent NaNOj (including nitrate, iodate, etc.), 
0.05 per cent NaCI, 

0.75 per cent sulphates (calculated as NaaSO*), 
2 , 75 per cent moisture. 



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48 AMERICAN SULPHURIC ACID PRACTICE 

The imports of this material into the United States have grown 
steadily, from 125,000 tons in 1898, to 519,000 tons in 1910. 
About 80 per cent of this goes into commercial fertilizers, the 
remaining 20 per cent into our chemical industry. 

Being deliquescent, the salt becomes damp and adheres to the 
bags it is shipped in, not only causit^ loss of nitre, but danger of 
fire, as the bags will ignite spontaneously. The bags are therefore 
usually washed out with hot water, and dried, the saltpeter being 
crystallized out of the water. The mother liquors from this 
crystallization contain NaNOj, KNO„ I, Nal, KI, KCIO,, 20per 
cent to 30 per cent insoluble, water, and small quantities of borates 
and chromatea. 

The mother liquor is run into a wooden vat, equipped with a 
mechanical stirrer, and is slightly acidulated with sulphuric acid; 
the result is NaHSOt and I, from the iodates — now NaNOj is 
added, reacting as follows: 

(1) NaNO, + H^O, = PNO, + NaHSO*, 

(2) 2HN0, + 2HI = 21 + 2N0 f 2H,0, 
Bubbling air through gives 

(3) 2N0 + O, = N,0„ 
which reacts with HI m 

(4) N»0» + 4HI = 41 + 2N0 + 2H,0, 

and the reaction repeats. 

Agitation is then stopped, and the liquor is allowed to settle 
over night, decanted, filtered, and washed with soda-ash. The 
product is a paste, running 75 per cent iodine and 25 per cent 
water. 

The decanted Uquor contains 0.02 per cent I, which is treated 
with sodium sulphite, to fix the iodine, so it will not pass off as a 
fume, and goes back to the bag house to be reconcentrated. The 
proper amount of sulphite is known to have been added when the 
color of the liquor changes from black to dark brown. 



^dbvGooglc 



CHAPTER V 
PRODUCTION OF SO2 

By far the largest part of the sulphuric made is from SOj pro- 
duced especially for that purpose. A very considerable tonnage, 
however, is made from gases which are by-products of certain 
metallurgical operations. 

High grade brimstone is the ideal material for niaking SO2 for 
acid manufacture. The equipment for burning it is compara- 
tively small and inexpensive, and as it ail bums, there is no ex- 
pense for handling cinder. Moreover, a verj- rich and uniform 
gas can be obtained. Several very satisfactory brimstone 
burners are made and regularly marketed in the United States. 
The two most used and perhaps best suited for burning large 
quantities of sulphur, are the cet'i'^_tyi>s and the^^helf type. 

The rotary type is shown in Fig. 3. This burner b sunilar in 
appearance to the Bruckner or White-Howell roasters, except 
that no fire box is required. 

Brimstone melts at a temperature below its combustion point, 
Bo whether it is in lumps or in powder or is run into the burner 
molten, is not important to the actual burning, although the 
condition in which it is to be fed will determine the nature of the 
feeding apparatus if it be a mechanical one. 

If a pile is made of lump sulphur and a fire started at the 
bottom of the pile, the sulphur melting and running down will 
smother the flame; so a small depression is made in the top of the 
pile, a piece of oily waste lighted and thrown in, the sulphur 
begins to melt and run down to the bottom of the cavity and to 
take fire. The pool enlarges itself rapidly by melting down new 
sulphur, and soon the entire mass is burning but all on the top. 

The molten sulphur is sticky, and this property is taken advan- 
tage of in rotary burners, of which the Glenn Falls Machine Co. 
makes the best known. This burner is a plate iron cylinder with 
east iron truncated cone-shaped ends, mounted upon trunnions, 
horizontally, the sulphur and air going in at one end, the SOj 
and partly comsumed air, with a little vaporized sulphur, passing 
out at the other into a large fire-brick lined vertical cylindrical 



^dbvGooglc 



50 AMERICAN SULPHURIC ACID PRACTICE 

combustion chamber. In the combustion chamber entrance 
further air is admitted and the vapor of sulphur is completely 
burned. (See Fig. 3.) 

The advantage of the rotating burner is that the molten sulphur 
sticks to the inside of the cylinder as it revolves and bums all 
the way around, which, with the dripping sulphur adds in small 
compass very largely to the combustion area and so increases the 
capacity. The burner revolves slowly, being adjusted to have 
the sticky film almost burned up when that portion of the side 
of the cylinder dips into the molten sulphur again. 



The labor of attending these furnaces is very light. One man 
can easily feed two of them with a shovel in addition to looking 
after oiling, adjusting dampers, and all other operation. If the 
sulphur is supplied to the burners by mechanical means they 
require very little attention. The sulphur may be fed, in either 
the solid or molten state. If solid, the material is carried into 
the burner from a small hopper by a short screw. If molten, an 
iron tank containing a steam coil b placed somewhat above the 
burner, the molten sulphur is carried to the burner through a 
steam-heated pipe, and the flow controlled by a steam-jacketed 
valve. Either method works well if properly handled. 



^dbvGooglc 



PRODUCTION OP 50, 51 

Control of the quality of gas and its volume lies in the handling 
of dampers at the feed end and the entrance to the combustion 
chamber, and in the quantity of sulphur fed. The production 
of gas of the grade most desirable for making sulphuric acid, i.e., 
not over 10 per cent SOi is not at all difficult. The chief trouble 
which occurs in the operation of sulphur burners, especially in 
producing high strei^h gas, is that if dampers are not properly 
adjusted some sulphur vapor may go through the combustion 
chamber without being burned. This sulphur on being cooled 
in the flues or in the towers becomes soUd and chokes the 



Rotary burners are regularly made in sizes with capacities 
ranging from 200 to 300 lb., to 15 tons per 24 hours. Floor space 
12 ft. by 40 ft. will accommodate even the largest size mentioned. 
The power consumed in driving them is very small. 

Rotary type burners have been Ukened to Bruckner roasters, and 
the shelf type may properly be said to resemble the McDougall 
roaster. It employs the superimposed tray or hearth construo- 
tion. Of course a stirrii^ mechanism is unnecessary because the 
sulphur is molten and simply overflows one tray and drops to the 
nextandsoon. A burner of this type is shown in Fig. 4. It consists 
essentially of a cylindrical cast-iron or steel, brick-lined chamber 
containing severai cast-iron hearths or trays. At the top is a 
chamber or reservoir into which the sulphur is chaiged and in 
which it melta. A valve in the bottom of this chamber controls 
the flow of molten sulphur into the burner proper. 

In operation a charge of sulphur is put into the top reservoir, a 
fire is started in the tray immediately below and allowed to burn 
until the sulphur starts to melt. The valve is then opened and 
the molten sulphur trickles in and ignites. Any part not burned 
on the first tray overflows to the second, and so on. Most of the 
ash and dirt is carried by the flow to the bottom pan. Doors 
are provided however to give access to any hearth. 

In capacity range these burners are regularly made to bum 
up to 10 or 12 tons of sulphur per 24 hours. The manufacturers 
point out the following advantages for this type of burner: 

1. No moving parts or power required. 

2. Small floor space. A 9-ft. diameter cyhnder burns 10 to 12 
tons per 24 hours. 

3. Better heat conservation than any other type. 

As mentioned before, brimstone burning allows the production 



^dbvGooglc 



52 AMERICAN SULPHURIC ACID PRACTICE 

of very rich and uniform gas. The percentage of SOi is limited 
by the fact that for either chamber or contact- work a certain 
minimum oxygen percentage must be maintained. This oxygen 
percentage should be at least per cent -„ — t- i, since one volume 



of SOi requires ^4 of one volume of oxygen to form SOj, and about 
4 per cent excess is desirable. Since air contains about 20.8 per 
cent oxygen, the sum of SOj and oxygen in the gas from the 
burner will be 20.8 per cent. The maximum SOi then should 



^dbyGoogle 



PRODUCTION OF SO, 53 

be, in ftccordance with the above proportion, 11.2 per cent and 
oxygen 9.6 per cent. 

BDRKING PYRITES 

Iron pyrites, when pore, has the formula FeSi, and contains 
46.7 per cent iron and 53.3 per cent sulphur. It is never obtained 
entirely pure, although material containing over 50 per cent sul- 
phur is sometimes found. The general range is from 40 per cent 
to 50 per cent aulphur. 

Sulphides of the metals burn in air, with the production of the 
metallic oxides and SOi; and if the operation, called roasting, is 
not complete, intermediate sulphates and bisulphates. 

Iron pyrites when roasted gives off of its FeSi nearly one atom 
of sulphur very easily. At comparatively low temperatures the 
sulphur bums at once to S0» leaving behind FcySg. At higher 
temperatures it is at first volatilized as a dense cloud of yellow 
smoke, and then bums to SOt. At the second stage of the process 
begins the oxidation of the iron in the ore along with that of the 
remaining sulphur. This is much slower and less vigorous than 
the burning of the primary atom of sulphur, and as the various 
iron oxides formed are fairly active catalytic agents or "contact 
Bubstances," a considerable quantity of SOg is formed at this 
Btage. For purposes of calculation the net result of these 
reactions may be written: 

4FeSt + 110, = 2Fe,0j + 8S0, 

Pyrites is obtained and burned in two different forms, viz., 
as lump pyrites and as fines. The former is material in pieces 
from the size of the fist down to about 3^ in. Fines is material 
under ^^ in. These two classes are burned in distinctly different 
forms of burners. 

The lump burners used in this country are quite simple. The 
general scheme is similar to the burning of lump coal on grates 
except that the bed of fire is carried much deeper, i.e., around 2 
ft. Fines in any appreciable amount are not permissible as they 
prevent free draught. In brief, a single burner consists of a 
brick box up to 6 ft. long from front to back, and 4 or 5 ft. wide. 
It is divided by a grate into an upper or burner compartment, 
and a lower or ash pit compartment. A charging door is placed 
at such a level above the grate as to allow a bed of ore about 2 
ft. deep. A small door at the grate level allows the grates to be 



^dbvGooglc 



54 AMERICAN SULPHURIC ACID PRACTICE 

shaken. A door in the ash pit provides for removal of dnder. 
Orate bus made of cast iron, of square section about 2 in, on a 
side are used. They are supported by cast^ron bearers at two 
or three points. The bars are made with circular section at the 
pointo of support in order that they may be turned. When 
their diagonals are set vertical and horizontal a considerably 
smaller space exists between them than when they are turned 
with their diagonals 45° from horizontal. By turning the bars 
from one position to the other with a wrench the lumps are 
crushed and the shaking out of the spent cinder is accomplished. 
F^ure 5 shows the general features of a lump burner and grates. 
Most of the modem plants using the lump burner have im- 
proved its details making it tighter and more convenient to 
operate. Burners are now made practically encased in steel or 



tB * 




cast-iron plates. Door frames and doors are planed to give 
tight joints without using putty. In scHne cases the ash pits 
discharge into cars in a tunnel below the burner set. These 
improvements have made labor less and gas more uniform, but 
the nature of this form of burner demands a considerable amount 
of hand labor which cannot well be eliminated. 

The capacity of a burner depends somewhat upon the sulphur 
tenor of the ore and its melting point. High grade pyrites con- 
taining little copper can be burned to give much more SOi per 
unit of grate area than low grade ore high in copper or which 
contains pyrrhotite; in other words ore of low fusing point. We 
cannot in any event expect to get much more than one ton of 
QO" acid from one good sized burner. Driving a burner too fast 
causes fusing and stickit^ and much hot laborious effort to clean. 

It will be seen that to provide gas for a large set of chambers 
the ground area and buildings required for lump burners is very 
great. Lump burners are built in blocks back to back and 
consisting of almost any number desired. Sets of 24 to 30 are 



^dbvGoO^lc 



PRODUCTION OF SO, 55 

common, and some up to 40 are to be Been. To decrease ground 
area the obvious thii^ to do would be to carry greater depth of 
ore on the grates. This presents several difficulties however. 
Heat would get too high if rate of burning per square foot were 
increased. Shaking out cinder uniformly would be uncertain. 
If fusing occurred, cleaning would be difficult. Burning of 
lump pyrites is practiced almost entirely on acid unitB of not 
over 50 tons OCBS. acid daily capacity. 

mSTRnCTIOHS P0« STARTING LUMP BDRHERS 

Be sure the brickwork is not too green upon starting. The 
moisture should be dried out of the bricks by means of a very 
light fire in the bottom before starting up. 

Uniformity otsize of charge is important and money spent on 
this will pay well. 

First clean out the furnaces thoroughly; see that the top fiues 
are clean; put in the grate bars. See that all doors are in place. 
Manhole doors should have a thin joint of tar and fireclay. 

The top buckstay rods should not be too tight, which is readily 
seen by striking them with a hammer, so as to allow for expan- 
sion as the furnace heats up. This must be watched carefully. 

Before putting a fire in the ftu'nace provision should be made 
for taking oS the smoke, wMch is best done by means of a tempo- 
rary stack on the uptake to the Glover tower, over the opening 
in one of the top plates. This stack should have a t^ht damper 
in it so it will not be necessary to remove it when its use is dis- 
continued. 

The damper in the Glover fiue must be closed to prevent smoke 
from gettii^ into the system. It is necessary to cover the grate 
bars with something like pyrites cinder to protect them from 
warping. If cinder is not to be had, broken stone or brick will 
do. Spread out this protector a foot thick except in the corners, 
where it should be 15 in. A wood fire is then started in each 
furnace on top of the cinder. The fire is kept burning until the 
whole interior is well warmed up and there is a bed of red ashes 
over the entire area of the furnaces. The fire is then increased 
until the interior of the furnaces is red hot, including the top of 
the bed of cinders. 

The best material for firing is oak or hickory as these make little 
smoke. Broken coke and coal are used but as these make a very 



^dbvGooglc 



56 AMERICAN SULPHURIC ACID PRACTICE 

hot fire, care must be taken that no clinkers are formed with 
the cinder. If any are formed they must be removed before 
changing ore. 

As the ^ass of brickwork and iron is bound to expand as it 
heats up, the buekstay rods must be loosened from time to time. 
A tap with a hammer shows if they are too tight, a hard nietalhc 
ring indicating that they should be slacked off. Do not loosen 
tbera too much as it is hard to tighten them again owing to the 
great pressure of the arches, which may crack in consequence. 
Care must be taken that a furnace does not get hot too quickly. 
Firii^ should take 30 to 36 hours for a new furnace, less time 
being required for an old one being restarted. 

After the final heating the wood should be burned ofE about the 
same time in each furnace, leaving a bed of hot embers. Before 
ore is charged withdraw any unbumed fuel, at the time making 
sure there is no matte where the main fire was. Distribute the 
hot embers evenly then charge sufficient pyrites to cover the 
whole grate. The pyrites should be placed in front of the fur- 
naces beforehand so that no time is lost in charging, for it is 
very important that they go in quickly before the furnaces lose 
heat. This is best done by having several men charging at the 
same time. When the charges are in, the gas can be turned 
into the system. When the first fharge is burning well, the 
furnaces should receive a second charge so as to insure a suffi- 
cient quantity of ore in the furnace to prevent any possibUity 
of running low and losing its heat. 

The gases leaving the furnace contain for a time some carbon 
dioxide in addition to SOj, due to the residual fuel. It is highly 
important to charge the furnaces with clock-like regularity. For 
example, if there are 24 furnaces one will be charged every hour or 
every half hour as desired. A regular schedule is followed in 
any event. The charging time of each furnace should be marked 
upon it. 

FUTES BURNERS 

Fines burners are by far the most used and most important 
of the apparatus for producing SO3 for making sulphuric acid. 
The main reasons for this are: 

1. I^t^ capacity with small ground area. 

2. Charging ore and dischai^ing cinder are continuous and are aoconi' 
ptiahed without opening the furnace, and the gas ia in consequence uniform. 



^dbvGooglc 



PRODUCTION OF 50, 57 

3. Handling of ore and cinder ore done by mooliiner}', practically elimi- 
nating hand labor, 

4. Several well-designod and satisfactory fumacfts are on the market and 
can be bought practically from stock. 

In the early days of acid making pyrites fines were bumed in 
the crudest way. The favorite method was on a brick heaxtb, 
the pyrites being fed by hand with shovels, and rabbled by hand. 
ThiB method produced cinder high in sulphur and most untini- 
form, besides being very costly in labor. 

The first improvements over the hand method in rabbling 
were along the line of mechanical rabbles in the form of plows 
which were dragged through the furnace on a chain, pulling 
the ore aloi^. with it and turning it over, giving a much better 
roast with lower labor costs. But to get a complete roast the 
temperature had to be high and maintenance costs were heavy. 
Also the plows were heavy and the wear on the hearths consider- 
able. 

The next step was an annular furnace with arms branching 
out from a revolving central axis, the arms carrying rakes for 
stirring the ore). The roof of the furnace had to be supported 
from the outside as the arms entered the furnace through a 
slot in the inner wall. A great deal of air entered through this 
slot so it was often covered by an iron apron revolving with 
the arms. 

In 1868, McDougall introduced his circular multiple hearth 
furnace. The McDougall furnace consists essentially of a 
cylindrical steel shell lined with about 9 in. of brick and 
containing several self-supporting arched brick hearths. Through 
the center of the furnace runs a vertical iron shaft or column. 
To it are fastened horizontal iron arms, one, two, or even three 
to each hearth, and these bear iron rabble teeth. This shaft 
with its arms is supported on a bearing beneath the furnace 
and in operation is revolved slowly. Alternate hearths have 
drop-holes near the central column and near the outside waU. 
The rabble teeth stir the burning ore and move it across the 
hearths so that it passes uniformly down through the furnace, 
crossing each hearth and falling to the one below. 

The original McDougall furnaces did not include any provision 
for keeping the shaft and arms and rabbles cool, and this was 
probably the chief reason that the furnace gave trouble and was 
not more widely used for many years. Mr. J. B. F. Herreshoff 



^dbvGooglc 



58 AMERICAN SULPHURIC ACID PRACTICE 

of the Nichola Chemical Co. on investigating the problem built 
a furnace with a hollow iron shaft and hollow armg, and blew 
cold air throi^h them, in that way keeping the temperature of 
the metal at such a point that ite strength was not impaired. 
HerreshofF also arranged to admit controUed amounts of the heated 
air issuing from the shaft and arms, into the hearths at any 
desirable points. Frasch also applied water cooling to the hollow 
shaft and arms. 

Other improvements and refinements have been made on the 
McDougall furnace and we find to-day that the name McDot^all 
has largely disappeared, and these furnaces are known by the 
names of those who have made the modifications. 

The chief differences in the furnaces of this type now on the 
market are in the shafts and arms, and the following claasification 
is made on that basis : 

1. Furnaces having water-cooled ghafta and anna. 

2. Furnaces having airnjooled ahafta and arms. 

3. &naU shaft fumacee, t.e., shafts into which a man cannot enter. 

4. Large shaft furnacea, i.e., shafts large enough to allow a man to enter 
and work. 

In roasting any of the pyritic materials suitable for acid makii^ 
it should be understood that furnace temperatures, i.e., temperar- 
tures of gas, ore, and brickwork, are influenced only to a small 
extent by either the air or water which may be circulated through 
the shaft and arms. This statement applies in greater degree 
to large than to small furnaces. The prime function of the air or 
the water is to regulate the temperature of the iron parts them- 
selves. A rough heat balance sheet of a roaster burning a pyritic 
ore of moderate sulphur tenor is interesting in showing the dis- 
posal of the heat units. 

As this balance is intended to show only the relative amounts 
of heat going to the various products, etc., rather than acutal 
heat units, only the iron sulphid is considered. 

This ore contains 34.7 per cent S as FeSi. 

The calcine contains 7.0 per cent S. 

The calcine weight is 80 per cent of that of the ore from which it is made. 

For each 100 parts of ore there is burned 34.7-80 per cent of 7 or 29.1 
parts of sulphur 

Assume that one half this is "volatile atom" and its dissociation heat 
requirement is negligible. The heat evolvera are then: 



^dbvGooglc 



PRODUCTION OF SO^ 59 

29.1 parta S to SO, @ 2,170 caloriea = 63,200 

29.7 X 1.76 parts Fe to Fe,Oi @ 1,750 calories - 44,500 
Total calories per 100 parts ore = 107,700 

Heat is absorbed by dissociation of FeS. 

40 FeS @ 273 calories - 10.920 

Net calories evolved per 100 parta ore = 96,780 

Assume that the furnace roasts 100 lb. ore per minute and that 
the gas issuing from it contains 9 per cent SOi, 8 per cent 
oxygen and 83 per cent nitrogen. 

29.1 lb. S make 320.6 cu. ft. SOi. Total gas per minute then = 
3,562 cu. ft. Assume the air enters the furnace at 20''C. and the 
gas leaves it at 620''C. Then the heat carried away by the gas is : 

SOi 09 X 3,562 (.0226 X 600 X .0000187; = 10.80 

O OS X 3,662 (.0189 X 600 X .0000017) = 6.65 

N .83 X 3,662 (.0189 X 600 X 0000017) - 59.80 



Calories per degree 75 . 3 



The ore enters the furnace at 20''C. and the calcine is discharged 
at 420''C. Heat carried away by calcine is 80 (.1456 X 400 X 
.000188) = 17.664 pound calories per degree. Calories for 
400" = 7,066. 

This furnace is assumed to be air cooled. There are 1,000 
cu. ft. per minure of air at 20°C. blown in through the arms, and 
this air issued at 220°C. Calories carried away by this air = 
3,848. 

RBCAPITUL4TION 

Total heat envolved - 96,780 caloriea 

Heat to gas 45,210 

Heat to calcine 7,066 

Heat to air ■. . 3,848 

Total accounted tor 56,124 

Balance for radiation 40,650 

Badiation surface of the furnace, 2,200 sq. ft. 

Loss per square foot per minute -> 18.4 lb. calories. 

This calculation shows that the two chief ways in which the 
heat is carried off from a roasting furnace are by the gas and by 
iBdiation. The heat units carried away by the cooling medium 
circulated through the shaft and arms, and by the calcine, are 



^dbvGooglc 



60 AMERICAN SULPHURIC ACID PRACTICE 

ins^ificant. As the radiating capacity of a furnace once built 
is not variable at will, it is apparent that control of furnace 
temperature must lie in feed of ore and volume of air admitted. 
When air cooling of the iron parts can properly be used it is to 
be preferred over water cooling for several reasons. When water 
is used for cooling, the temperature of the arms is so low that the 
iron becomes sulphated and the rabbles soon become cemented to 
the arms and can often be removed only by breaking. With 
air cooling, the temperature of the metal is usually so h^h that 
this sulpbating does not occur. Another advantage is that slight 
leaks at joints or chaplet plugs do no harm if air cooling is em- 
ployed, while with water even slight leaks cannot be tolerated. 
Often a water-cooled arm must be removed on account of a 
persistent small water leak where an air leak of the same size 
would scarcely be noticed. 




WatOT<ooled Arm Htedge Type Arm Eno 
Fia. 6. 

Air-cooled arms and shaft must have much larger p 
them than necessary when water ia tised for cooling. Indeed the 
success or failure of air cooling depends much upon whether or 
not the passages are of ample area. The thickness of metal in 
air-cooled arms is less than in water-cooled arms. 

Figure 6 shows the essential features of an air-cooled arm with 
Hanged end for bolting to shaft, and a water-cooled arm with 
end-detail as used in the Wedge furnace. 

The other major difference in the McDougall types is in the 
large and small central columns. Until the advent of the Wedge 
furnace all the McDougall furnaces had small central columns, 
i.e., not above 18 or 20 in. diameter, and hence too small foraman 
to enter. When, any thii^ became wrong with an arm which 
necessitated replacing it, it was necessary to stop the furnace and 



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PRODUCTION OF SOt 61 

allow it to cool down enough to permit men to enter the hearth, 
unfasten the bad arm from the shaft and fasten on a new one. 
This always required several days and meant that the furnace 
had to be restarted with fuel. Such a loss of time is a serious 
thing to an acid plant, especially if a single furnace is being 
depended upon. 

Many attempts have been made to devise arrangements 
whereby arms could be replaced without cooling and entering the 
hearths. It is not difficult to do this if air cooling or no cooling 
is sufficient. If water cooling is necessary and water-tight con- 
nections have to be made it seems impossible unless one can get 
at the inner end of the arm, which with the small column furnace 
means getting into the hearth. While this feature of the small 
shaft furnaces is disagreeable, it should not be overestimated. 
Well made arms properly taken care of last for long periods, and 
there are other things beside failure of arms which demand 
cooling down a furnace at times, failure of brickwork for example. 
It is often possible to get along with a sick arm for a time until a 
genera! overhauling is desirable. 

Small column furnaces of which the Herreshoff is an example 
have their columns made up of cast-iron sections flanged together. 
When water cooling is used a water supply pipe extends down 
the middle. It is provided with a tee fitting corresponding to 
each arm, into which is screwed a pipe which extends well out 
toward the end of the arm. The water enters the arm through 
this pipe and returns around it into the annular space in the 
column. Usually the arm itself has a flanged end which is 
bolted to a corresponding flange on the column casting. There 
are variations in this method of fastening but the flange is most 
used. 

For air cooling a partitioned arm, as shown in Fig. 6, is used 
and an interior column construction as shown in Fig, 5. 

The Wedge furnace, shown in Fig. 6B, is the only furnace made 
with the large column. This column is 4 or 5 ft, in internal 
diameter, built of steel plates riveted together, and covered on 
the fire side with fire brick and insulating material. The arms 
project through the wall of this column and are fastened inside. 
The air or water connections are hkewise inside the column. 
It is a simple matter in case of the failure of an arm for a man to 
enter the column immediately, disconnect the pipes, and loosen 
the latch. The arm can then be pulled out and a new one in- 



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62 AMERICAN SULPHURIC ACID PRACTICE 



Fio. 6A,- — Herreahoff furnacoB. 



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PRODUCTION OF SOt 



63 



serted and connected. It is not a pleaeant job because the inside 
of the column is decidedly warm, but it can be readily and safely 
done by any men who are reasonably accustomed to furnace 
work. There are certainly many more aevere tasks about metal- 
lurgical furnaces. If proper arrangements are made an arm 
may be removed and a new one inserted and connected ready to 
go in 4 hours. 



One feature of the large column which has given some trouble 
u) the carrying of the great rotating weight in a satisfactory way. 
The customary design for the larger sizes provides a set of six 
large beveled rollers upon which the cast spider carrying the 
column revolves. In the middle is a small guide bearing. The 
trouble with this arrangement is in maintaining the shaft plumb, 
and the load equally distributed upon the rollers. The side 



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64 AMERICAN SULPHURIC ACID PRACTICE 

thrust causes some wear of the rollers and their thrust bearings, 
whidh is not equal all the way around. As soon as one roller ia 
further away from the center than the others it ceases to carry its 
proper share of the load, or else the shaft goes out of plumb. 
This cannot be said to be a very serious fault, but it makes the 
arrangement less satisfactory than the old step bearing. 

In the 25-ft. furnaces of this type erected at Anaconda a few 
years ago, the columns are supported on 9-in, step bearings of 
very rugged construction. The coliunn is held plumb by a set 
of vertical rollers beorii^ against a ring fastened around the- top 
of the column. 

Fines bumeis are started by bedding the upper floore with ore 
then heating with wood, coal, oil, gas, or powdered coal, with the 
mechanism stationery. When sufficiently heated the floors are 
cleared and the mechanism started with a hght feed of ore. It 
is usually necessary to use a Httle fuel for a time after starting 
feed. The variables used in the control of a furnace are amount 
of ore fed, and voliune of air admitted, also sometimes the rate 
of revolution of the arms. The usual speed of revolution is from 
1 to 2 R,P,M. The operation is watched through peep-holes. 
A 15-ft (diameter) furnace requires one horse power. 

BT-PRODUCT GAS FROM COPPER REDUCTION WORKS 

About one-half million tons per year of acid is made from gases 
evolved from the reduction of copper ore. The only two sources 
of such gases at present are roasting furnaces and blast furnaces. 
The roasting furnaces used at copper reduction works in con- 
nection with acid making are all of theMcDougall type, and of 
several different miJces, embracing all the types described above. 
The materials roasted show wide range and are all materially 
difEerent from the pyrites ores regularly bought for acid making. 
However as the gas used is really a waste product and no chaige 
for sulphur is made against the acid, these acid plants can well 
afford to work with less favorable ores. 

The chief difference between the materials available at copper 
reduction works and the ordinary ores is that the former are 
lower in sulphur and higher in copper, are of irregular analysis, 
and are often exceedingly fine. While pyrites ores range from 
40 per cent to 50 per cent sulphur afld contain little copper, the 
ores and concentrates used at copper works rai^e from 25 per 



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PRODUCTION OF SOt 65 

cent to 40 per cent Bulphur, and contain up to 12 per cent or 15 
per cent copper. Moreover at eome plants the sulphur content 
of the material varies 5 tolO per cent from day to day. 

The copper-iron sulfide, and the copper sulfide minerals fuse 
at a considerably lower temperature than does straight pyrites, 
so in roasting copper ores and concentrates accretions arc found 
to form on the brickwork and on the shaft of the furnace much 
more than they do when roasting pyrites. This fact makes it 
necessary to watch the furnace temperatures carefully or serious 
formations of matte may occur. A good deal of barring and 
plowing of the hearths is necessary even with the most careful 
attention. 

As the cinder from the roasted copper ore is usually treated in 
a reverberatory furnace to make a copper matte, some sulphur 
should be left in the cinder. For example at Anaconda where 
the copper content of the cinder is about 10 per cent, it is desirable 
to leave about 7 per cent sulphur in the cinder to make matte. 

THE BLAST FURNACE 
The blast furnace is a very unusual source of SOi for acid mak- 
ing. The only place in this country where it has been used is 
at the reduction works of the Tennessee Copper Co. and the 
Ducktown Sulphur, Copper, and Iron Co., in the Ducktown 
district in southeastern Tennessee. There exists a peculiar set 
of conditions there which will rarely be duplicated, but the ton- 
nage of acid produced is so large, and the plants themselves 
present so much of interest in their construction and operation, 
that some description of the operations is in order. 

The ore treated at these works is a heavy sulfide carrying 
substantially : 

Pbh cbkt 

.Coppar 2.5 

Iron 30.0 

Sulphur 20.0 

luBoluble 30.0 

CaO, MgO 10.0 

Zinc 3.0 

Al,Oi 3.0 

This ore is treated directly in blast furnaces with no prelimi- 
nary dressing or concentration whatever. It is very near self- 
fluxing when making a 15 per cent copper matte, and it can be 
smelted with about 5 per cent coke. This permits the production 



^dbvGooglc 



66 AMERICAS SULPHURIC ACID PRACTICE 

of a gas containing 7 per cent to 8 per cent SOi, 5 per cent to 6 per 
cent COi, and about 3 per cent to 4 per cent oxygen. 

At the time the first acid plants were built, about 1907, no 
experience was available to say what could be done with such 
gas. However it was neceesaTy to undertake the manufacture 
of acid because the United States Supreme Court had enjoined 
the smelteries from allowing to escape more SOi than the state 
of Georgia deemed reasonable. The redeeming feature of the 
situation lay in the fact that Ducktown basin ts in the heart of 
that portion of the country which consumes the greater part of 
all the acid phosphate fertilizer made in the United States, that 
is to say there is an excellent market for sulphuric acid. 

For some time after the completion of the plants troubles of 
various kinds were experienced and many curious phenomena 
arose. The chief differences between this blast furnace gas 
and the gases usually used for making sulphuric acid are t-he 
high CO] content and the low oxygen. It was necessary to 
revise ideas about the oxygen content of exit gases, or else if 
the customary 6 per cent were maintained there, to take a gas 
entering at about 2 per cent to 3 per cent SOi. One solution of 
this devised at the Ducktown plant, was to adjust the gas enter- 
ing to contain about 3 per cent oxygen, and to introduce air into 
each chamber sufficient to maintain 3 to 4 per cent oxygen at all 
stages of the process. Working without this arrangement the 
best way seemed to keep the oxygen in the exit gases above 2 per 
cent and get as good SOi entering as that would allow. 

It should perhaps be explained that in near-pyritic smelting 
the gases issuing from the cbat^ contain almost no oxygen and 
if the furnace top and flues are tight the gas entering the acid 
plant contains only such oxygen as may be voluntarily admitted. 

The high percentage of COi in this gas along with the unusually 
low oxygen makes the reactions in the chambers very sluggish. 
In order to get reasonable tonnage from the plant is is necessary 
to use much more than the normal nitre circulation and this in 
turn tends to make high nitre loss. 

A very serious feature of the blast furnace work is the irregu- 
larity of the gas due to the mode of operating the furnace. It 
is necessary to open the furnace top several times an hour to 
charge and barring and cleaning are necessary every day. If 
the fines are dampered so as to cause some pressure at the 
furnace top, the working conditions on the charge floor are 



^dbvGooglc 



PRODUCTION OF SOt 67 

almost impossible. If Buction is maintained, every time the 
furnace is opened false air rushes in and dilutes the gas. In 
spite of these difficult conditions these acid plants must be 
considered very successful both technically and financially. 

COPPER CONVERTERS 

It has many times been au^ested that the gases from copper 
converters m^;ht be used for making acid, but as yet this has 
not been attempted. 

Taken without modification the gas from a single converter 
ranges in a period of a few hours from almost no SOj to perhaps 
20 per cent. As a reasonable approach to uniformity is a neces- 
sity in the chamber process, such a gas would not do. It may 
be possible with a battery of several converters working on a 
schedule and equipped with tight hoods and dampers to get a 
workable gas. It must be said that the converter is not an 
attractive source of gas for acid making, although perhaps a not 
impossible one. 

SO) FROM ROASTmO ZINC ORES 

In the reduction of the sulfide ores of zinc it is necessary to 
roast off sulphur, and the gas so produced is utilized in making 
sulphuric acid. The zinc reduction works in this country are 
usually BO located geographically that the sulphuric acid produced 
is readily marketed. 

In roastii^ zinc sulfide ores preliminary to distillation for 
metal it is necessary to convert, as nearly as possible, all the 
zinc to zinc oxide. In order to do this certain temperature and 
oxygen percentage figures must be observed which make the 
roasting operation more difficult and the gas less favorable for 
acid making than in roasting pyrites. 

The essentials of this are that in roasting zinc sulfide some 
sulphates of zinc form; these are not broken up completely at 
temperatures much below 900°C.; after the sulphur content of 
the roasting ore is down to about 8 per cent it no longer burns 
with sufficient vigor to maintain a roasting temperature, much 
less a temperature sufficient to break up the sulphates. It is 
therefore necessary at the later stages of the roast to add heat by 
means of the hot gases from burning carbonaceous fuel. As 
this fire gas would be a serious diluent of the roaster gases going 
to the chambers, it is kept separate from the latter. 



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68 AMERICAN SULPHURIC ACID PRACTICE 

The roasting furnace most used in this country for zinc roastii^ 
in connection mth acid chambers, is the Hegler furnace, first 
used at the Matthieeson and Hegler works, LaSalle, 111. The 
Hegler furnace is a multiple hearth, rectangular furnace, with 
the lower hearths of muffle construction. The ore is moved 
longitudinally over each hearth falling to the one below. The 
rabbles mounted on frames of steel shapes are drawn through 
the hearths by means of long rods. After each passage through, 
the rabbles are drawn clear out of the furnace and allowed to 
cool for a short time. Their temperature therefore never 
becomes high enough to impair their strength and rigidity. 
The latest Hegler furnaces have seven hearths, and producer 
gas is used to heat the muffled hearths in the lower parts of the 
furnace. 

In order to properly roast zinc ores a plentiful supply of air 
must be allowed to pass over the roasting ore, i.e. the oxygen 
percentile must be kept well up. Observing this requirement 
then, the gas going to the chambers contains only 4 to 5 per cent 
SOi. There is of course some dilution due to rabbles entering 
and leaving the furnace and to the doors leaking air. 

BURNING P7RITE CINDER 

Even with the most careful handling some where about 2 to 
3 per cent of sulphur will remain in the cinder from roasting 
pyrites. This causes two losses, that of the sulphur, and that of 
the market for the cinder as iron blast furnace material, as 
with so high a sulphur content good iron is an impossibihty, and 
many acid plants have a potential market for their iron "ore." 
The Dwight & Lloyd sintering machine, as sold by the American 
Ore Reclamation Co., 71 Broadway, New York City, overcomes 
the twin difflculties of high sulphur content and fineness, and is 
best described by the company as follows : 

"Sintering is a comparatively recent art in the iron industry. It is 
the process of agglomerating fine ore material into a mass that is suit- 
able for blast furnace use. Sintering may be illustrated aa the making 
of flour into biscuits. With the use of the fine ores from the Mesaba 
Range in Minnesota and the resulting makii^ of flue dust at blast 
furnaces, many attempts were made to recover the valuable iron in the 
flue dust by briquetting. This means of treatment has not proven very 
satisfactory, since, to secure a firm bond, the proeess is expensive, and 
when the bond is fickle the briquettes quickly return to dust. 



^dbvGooglc 



PRODUCTION OF 50, 69 

"The briquette is a porous mass and the spaces are filled witli air, bo 
that the mass must be heated first to expel the air to allow the reducing 
mass of the furnace to Come in contact with the ore particles, which 
delays the reduction and the mass is easily disintegrated into dust. 
Sinter made by the continuous down draft process is cellular in struo- 
ture, providing an open and large area of contact between ore and reduc- 
ing gases; and as the cell walls are quickly heated to the temperature 
required for reduction, an economy in coke consumption results from 
the use of sinter. 

"To quote Shinz's law (in his "Action of the Blast Furnace"): 'A 
chemical action can only take place between two bodies, however great 
then- affinity, if they are in intimate contact with each other and the 
rapidity of this action will be much greater the more numerous the 
points of contact are.' The material which provides the greatest area 
of contact is more readily and economically reduced in the furnace. 

"The iron-bearing materials treated by sinterii^ include blast-furnace 
flue dust, roll-^cale, magnetite concentrates, magnetic sands, high sul- 
phur ore, pyrites cinder, etc. Any finely divided ore or ores, containing 
high sulphur or high moisture and combined water, can be converted 
into ideal material for use in the blast furnace. Flue dust sludge from 
blast-furnace gas washers may be sintered by adding the sludge to a 
dry sintering mixture instead of moistening the charge with water. 

"Sintering was first applied in the iron industry to the reclamation 
of flue dust, but it has since widened out into other fields and demon- 
strated its adaptability for treating pyrites cinder, magnetic ore con- 
centrates, and other fine ores or hydrated ores. 

"A plant installation is made up of two main parts, the sintering 
machine proper, and the raw materials plant, both forming a unit, of 
which the former is more or less standardized, but the latter made to 
conform to local conditions and materials. The following is a descrip- 
tion of a typical plant. 

"The materials to be sintered are delivered to a peries of bins, the 
number and size of which depend on the kind and quantity of materials 
to be treated ; or the raw materials may be dumped from the cars into 
a pit and transferred to the bins by a grab bucket. 

"In the case of fine dust the screening of it is necessary, and a con- 
siderable quantity of coke is recovered for furnace use. 

"The bins are fitted with feeders of a special type which are driven 
as a group in synchronism with the sintering machine. The required 
composition of the sintering mixture is made up by adjustii^ the feeder 
gates and the total amount of sinterii^ mixture delivered by the feeders 
is adjusted to suit the needs of the sintering machine at various speeds. 
The sintering mixture is carried to, and thoroughly mixed and moistened 
in, a pug miU or other mixing device, and is delivered onto the grates of 
the sintering machine in a continuous layer of desired thickness and 



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70 



AMERICAN SULPHURIC ACID PRACTICE 



unifonn penneability. This contiouous layer is moved under an igni- 
tion burner where the fue! in the upper surface of the layer is ignited 
and the charge then continues its movement over a wind bos connected 
to a auction fan which draws air down through all parts of the charge 
and the sintering action is progressive through the whole depth of the 
layer down to the grates. At the end of the sintering machine the 
sinter is discharged over a grizzly screem which thorouhly separates 
all fines from the sintered material and the fine sinter is returned to the 
siQtering machine to increase the permeability and thereby the rate of 
sintering is increased." 

The whole operation of regulating the feeding of material and 
speed of sintering ie controlled by a sinj^e lever. 
SINTERING MACHINBS 

Capacities of the three machines made by the Dwight & Lloyd 
people are as follows, all in tons per 24 hours: 



Material 


Type A 


1>peB 


TypeC 
(two strand) 


Elue dust 


126-160 
150-176 
175-200 


260-310 
300-375 
350-400 




Pvritea cinder 













Pyrites cinder and high sulphur ores are sintered and desul- 
phurized in one operation. The cinder contains from 1.5 per 
cent to 5 per cent sulphur, and is reduced to 0.10 per cent to 
0.15 per cent in the sintered product. About 8 to 10 per cent 
fuel is required. 

CoHTiHTS PrniTca cihdbr, Sintib, 

Iron 56.28 61.00 

Sulphur 4.41 0.07 

Mktuke of Pthites Cindee and Floe Ddbt 



Contents 


Pyrites 
ciader, 
per cent 


Hue dust, 
per cent 


Average 
mixture, 
per cent 


Smter 




56.28 
4.41 


33,00 
0.18 
24.00 


46.97 
2.72 
0.60 




Sulphur 




C&rhon 









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PRODUCTION OF SOt 



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AMERICAN SULPHURIC ACID PRACTICE 



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PRODUCTION OF SOt 73 



DplizsdbvGoOglC 



74 AMERICAN SULPHURIC ACID PRACTICE 



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PRODUCTION OF SOj 75 

Sintering machines of this type are also used to treat lead ores 
aa a preparation for blast furnacing. 

The gas from a sintering machine is not only low in SOt,but 
as it is high in COjand CO, it is not good acid material. SOthas 
been hard to concentrate up to recent years, but a new process 
is now on the market which makes available very weak gases. 

Silica gel is put out by the Davison Chemical Co. at Baltimore. 
While this material has been known for years, its commercial 
production was not possible until the researches of Prof. W. A. 
Patrick of Johns Hopkins, on gas mask absorbers during the war. 
Apparently any condensible gas is adsorbed by this material, 
the capacity of which is very great, and a small rise in temperar 
turo serves to drive out the adsorbed gaa. This is so much the 
case that the additional gas pressure produced by the slight 
increase in temperature caused by laying ones hand on the 
apparatus is easily measured. 

The action is unquestionably surface condensation, the small 
drops of "gel" being full of sub-microscopic cracks, so that Prof. 
Patrick says, "if you consider the measure of the 'gel' drop in 
centimeters, you must measiu'e the area of the cracks in acres." 

This plant consists of three towers in series, each capable of 
being cut out. Only one is used at a time, one being discharged 
and the third in reserve. The temperature is raised or lowered 
by forcing steam or brine through horizontal pipes laid in the gel 
mass. Vertical pipes were tried, but the channeling action of 
the gas was too -great. This opens up a new type of contact 
plant where the concentration of SO3 in the gas can be very high, 
thus cutting down plant and particularly mass, very greatly. 
The advantage of being able to mix air and 80^ instead of air 
and sulphur, is at once apparent. When sulphur is burned in air 
and that mixture taken into the system, the nitrogen that was 
in the air, the oxygen of which helped form the SOi goes along 
and dilutes the gas, whereas by having the S0» ready burned, 
that dead gas is avoided. 

If there is sufficient oxygen present, the contact mass is more 
efficient as the concentration of the gafi increases. By sufficient 
oxygen is meant the excess that ia needed to give good results. 
So the use of a gas mixture made from SO3 direct works out as 
follows: In a gas made by burning sulphur in the air and contain- 
ing 7 per cent SOs, 12.3 per cent of the total is the nitrogen that 
accompanied the 3.5 per cent oxygen necessary to make the 



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76 AMERICAN SULPHURIC ACID PRACTICE 

SOi. This concentration process reduces the amount of gas 
to be handled, raises the concentration of the gas, and leaves 
just as much oxygen to form SOa and furnish the excess necessary 
for this formation. 

Silica gel should be tried out along the following lines, as the 
concentration of platinum in the mass drops the conversion 
drops, also, but not in the same proportion. Therefore, there 
is a point, to be determined, to which it will pay to drop the 
conversion, catching the unconverted SOi with silica gel, and 
returning it to the gas stream. 

The saving will be in plant cost of platinum. Suppose that 
with 10 per cent of the amount of platinum required for a 97 
per cent conversion you are able to get a 60 per cent conversion 
and recover the SOi at reasonable expense. At the standard 
rate of platinum used, for a plant burning one ton of brimstone 
an hour, 90 pounds avoirdupois, of platinum would be required. 
At S95 an ounce, troy, that is $1,385 a pound avoirdupois or, 
$124,650 for platinum. Ten per cent of that would be $12,465, 
quite a difference. 

Without anywhere near sufBcient research work done upon 
this subject, I do not state the above as either an accomplished 
fact, nor as a certainty— it is simply a possible lead. The 
Davison Chemical Co., Baltimore, Maryland, hold the basic 
patents on silica gel, and will furnish the most complete informa- 
tion upon this subject that exists. 

Water is an obstacle to the adsorption by silica gel, as it is a 
great moisture adsorber, and the moistiu^ would be given up, 
under certain conditions, along with the SO*, which would have 
to be dried again before conversion. Of course there would 
be no moisture in the gas just leaving the strong acid of the 
absorption towers. 

When the contact process first became an accomplished fact 
many people looked for it to displace chambers entirely, but the 
cost of the platinum required has prevented the fulfilment of 
their hopes. Is it too much to hope that silica gel may bring 
this about? 

OTHER USES OF SO. 

Liquid S0» was first made commercially from zinc smelter 
gases in this country by the Davison Chemical Co. in Baltimore 
ftroimd 1870. It is interesting to note that the first sulphite 



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PBODVCTION OF SOi 77 

paper pulp in this country was made with liquid SOj by the 
Mitcherlich process, then the pulp mills began to bum their own 
sulphur, and now the pendulum has swung back again. 

For liquid SOi the aormal boiling point is — 11°C. 

For liquid SOi the lat«nt he&t of vaporization, at — lO'C. (dimin- 

iabes as the temperature rises) 03 . 4 cal. 

Vapor pressure temp. C..,. -10 10 20 30 40 60 
Pressure (atmospheres) 1.0 1.63 2,26 3,24 4.51 6.15 8.18 

Critical temperature = 156°C. Critical pressure = 78.9 atmospheres. 
Specific heat, between - 20° and + ISCC. - 0.31712 + 0.0003507( + 
0.00000672P 

ACTION OF METALS 

The commercial product, containing 0.07 per cent HiO, attacks 
iron above VCC, forming a solid crust of ferrous sulphate and 
thio-sulpbate, but the metal is not further attacked. Anhydrous 
SOi does not attack either iron or steel. 

USES 

For refrigeration, because of its cheapness, ease of handling, 
and the fact that it is neither acid nor alk^in in its action. 

In the manufacture of sulphite pulp. 

For petroleum refining. 

As a solvent for organic fats and resins. 

As a sewage disposal agent. 

So far as I know, there are three plants in this country making 
liquid SO). The Tacoma Smelter, of the American Smelting 
and Kefining Co., Tacoma, Wash., has a plant that has been in 
operation about5years, — operating as follows: The gas from the 
converters, containing 2.5 per cent to 3 per cent SOi, and at about 
300°C.| is lead to a scrubber tower,' brick lined and loose brick 
packed, into the top of which is fed a small amount of water, just 
enough to prevent it all vaporizing. TherunofEcleans thegas, but 
because of ite temperature contains practically no SOj. The 
gas then goes to another tower, of the same construction, but 
larger in diameter, to which water is admitted through spray 
nozzles at the top, the water being in sufficient quantity to cool 
down and absorb practically all the SOt, the scrubbed gases 
going out the stack. See Fig. 11. 

The liquor flows by gravity to a heat exchanger, made of 
lead pipe, outside of which flows the desulphurized Uquors, 



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78 



AMERICAN SULPHURIC ACID PRACTICE 



hot, from the following process. Then to 12hui. lead pipes, 
horizontal, into the bottom of which is blown steam, which 
vaporizes the SOi, which comes off through a gas outlet on top, 
and thence to the compressor. The water, aft«r the SOt has 
been blown off, flows down to heat the heat exchanger. 

Before the compressor is a scrubber, fed with 66°B^. acid, to 
remove moisture from the S0». This 66° acid drops to 60° in a 
week, and has to be renewed. 

The compressor is a bronze, singte^tage, direct-driven one, 
compressing to about 60 lb., although under perfect conditions 
45 lb. will do it. The liquid SOi then goes to lead cooling coils, 
over which water drops, and thence to a tank car. 

An iron cylinder for the compressor only lasts six weeks. 




Fta. II. 

The stor^^ tank, built to stand 300 lb., has a safety v^ve 
with a pipe running to the absorber tower, where any SOi will 
be caught and the non-condensiblc gases will escape to the stack. 

This plant started to produce in 1917, making 10 tons of Uquid 
SOj per day. In 1920 the production was increased to 30 tons 
per day, and in 1921 it will be 50 tons. The product is shipped 
partly to Crown Willimette, where it is combined with SOi 
produced on the ground, to make a 25 per cent gas to make a 
strong cooking liquor for making sulphite pulp. The rest of the 
production goes to Los Angeles for oil refining. 

At Tacoma, with coal at $8, SOj from a 3 per cent gas, includ- 
ing overhead, but with no charge for the gas, is (1920) {8 per ton. 

The plant of the Virginia Smelting Co., at Norfolk, Va., has 

Without steam or pover plant, a 10-ton per day plant coeta (1920) S30,000. 
Vnthout Bteom or power plant, a 30-toa pei day plant coats (1920) $45,000. 



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PRODUCTION OF 50, . 79 

been leased to Beer, Sondheimer, & Co., who are recovering the 
SOj in a process very Bimilar to the one at Tacoma, except 
that it is much smaller, and the Hquid SOj is shipped in cylinders. 

There is a small plant in Wisconsin which produces SOi from 
brimstone directly for the purpose of compressing and selling. 
I have been unable to get any details. 

Dr. Ralph McKee, head of the Department of Chemical 
Engineering at Columbia, is a world's authority on liquid SOi. 
He has furnished some of the information contained in this 
section, and sees a great future for the industry^ some of the 
reasons for which are given below. 

Liquid SOi will not bum nor explode, will not attack steel , 
containers, and costs H^ a pound, F.O.B. point of manufacture, 
against 7ff for gasoline and I6i for carbon-tetrachloride (1920). 

The U. S. Bureau of Chemistry does not like the use of liquid 
SOi for the extraction of oils to be used for food, if any other 
solvent can be used. 

Mr. James E. Steely, of the West Virginia Pulp and Paper 
Company, Inc., haa furnished some notes on the production and 
use of 30i in the pulp industry. 

In the manufacture of bi-sulphate liquor, it is desirable to have 
SO] gas at as high a percentage as possible, as the solubility of the 
gas in water increases in the per cent of SOj in the gas. This 
solubility also increases with a reduction in temperature ; there- 
fore the gas is cooled as low as possible, usually in some form of 
lead-pipe cooler. 

It is also necessary to keep the SOa in the gas as low as possible, 
SOs being a very undesirable component of gas for sulphite pulp 
manufacture. 

A 15 per cent to 18 per cent SOi gas meets the above requirements. 
Liquid SOi is a most desirable material to work with, and if it could 
be delivered at the mill at sightly above the cost per pound of 
sulphur, as compared to elemental sulphur, it would be in very 
wide demand. However, under present (1920) conditions, the 
cost of producing liquid SOj together with increased cost of 
fre^ht and containers for handling would make the proposition 
prohibitive in ordinary times. The efficiency of operation in a 
sulphite acid plant is very high, and maintainance cost of first- 
class equipment comparatively low ; therefore it would seem that 
only in special cases would liquid SO3 be attractive to sulphite 
pulp manufacturers. 



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80 . AMERICAN SVLPHVRIC ACID PRACTICE 

' The chief source of SOj for sulphite pulp manufacture is ele- 
mental Bulphur, burned in the same types of burner that are used 
in acid manufacture. Very little SOj is produced by any of these 
machines, but to make assurance doubly sure, at some plants a 
pyrometer is installed in the combustion chamber and the tem- 
perature maintained around ISOCF., at which point 80i disso- 
ciates into SOi and 0. Other plants depend solely upon gas 
analyses. 

Pyrites, particularly from Spain, used to be the chief source of 
SOi for pulp making, but the Louisiana sulphur discoveries, and 
the interruption to Spanish deliveries by the War, cut down its 
use so that today (1920) Mr. Steely does not know a single plant 
in this country running on pyrites. The market price of Spanish 
pyrites has not gone low enough to justify plants that used to use 
it returning, and also most important, the bumeiB, usually of the 
Herreshoff or Wedge type, must be operated with the greatest 
care to prevent formation of SOj, due to the catalytic action of the 
hot iron oxides in the cindeiB. 

There are two general schemes for makihg bi-sulphite liquor. 
In each case the SOj is cooled as low as possible. The first 
scheme is to use a'tall tower filled with lumps of lime stone, over 
which a slow stream of water is passing. The gas is admitted to 
the bottom of the tower, and is absorbed by the water, fonning 
sulphurous acid, which in turn dissolves the stone to make 
calcium-bi-sulphate liquor. 

The second scheme consists of passing the gas through towers 
containing a solution of milk of lime. The two are brought 
together in such a way that they combine and form a clear 
solution of bi-sulphite. 

When rosin is extracted from yellow pme waste, enough SOa 
remains in the wood to cook the pulp. Both United States and 
Canadian patents on this process are applied for by R^pb 
McKee and A. A. Holmes. 

The city of New Haven has experimented with hquid SO* 
on sewage disposal. The sewage \^as going into the bay ; if an 
acid was added the colloidal sludge was precipitated. HiSO« 
was first used, then SOj. If this sludge is dried and extracted, 
considerable amounts of fats and oils are recovered, gasoline 
being used as the solvent. The report says the recovery will 
pay costs, including bond interest. 

Liquid SOx is a solvent for di-ethylamine, analine, di-pbenyl- 



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PRODUCTION OF SOt 81 

amine, benzylamine, P-toIuidine, A-napbtbylamiue, B-naphthyl- 
aminc, phenyl, B-naphthylamine, benzidine, chrysaniline, 
carbazol, quinolin, pyridine, acetanilide, acetnapbtalid, benzene, 
toluene, tri-phenyl-methane, di-phenyl-flouren, phenantbren, 
naphtbalene, nitrobenzene, limonen, pinene, anthracene, B-di- 
bromnapbthalene. All fatty alcohols from methyl to capryl, 
benzyl alcohol, menthol, borneol, 0-creaol, B-naphthol, hydro- 
quinone, picric acid, phenol-chloro (and di-chloro) acetic acid, 
A-brom-butyric acid, benzoic acid, sahcyhc acid, M-oxybenzoic 
acid, B-naphthoic acid, acetic-ethyl-ester, succionic-acid-di- 
ethyl-ester, aeopropyl-aceto-acetic-ester, fumaric-acid-di-ethyl- 
ester, cinnamic-acid-di-etbyl-eater, malic-acid-di-metbyl-estet, 
mandelic-acid-di-ethyl-ester, acetic-acid-bomyl-ester, ricanelic- 
acid-propyl-ester. 

The following are also soluble — KI, Nal, NH»I, Rul, tri-methyl- 
sulphoneum-iodide, tri-methyl-ammonium,-iodide, KBr, ammo- 
nium-thio-cyanate, methyl-ammonium-chloride, di-, tri, and 
tetra-methyl-ammonium-bromide, sublimed ferric chloride, co- 
balt-thio-cyanate. More compounds for which liquid SOj is a 
solvent are continually beii^ discovered. 

CANADIAN SITUATION 

Dr. McKee shows a picture of the smelter of the International 
Nickel Co., with clouds of SOb coming out of the stack — 1,000 tons 
a day. There are numerous copper, nickel, and zinc smelters 
in the Dominion, and the lai^e pulp mills near at hand are import- 
ing sulphur from Louisiana and Japan, while this SO2 is worse 
than thrown away — it is acutally hurting the nearby farms. 

The Tennessee Copper Co. showed that the production of acid 
from smelter fume was not an impracticable dream, and when the 
acid was produced a market was found for it. The method of 
producing liquid SO2 from smelter, fum^ is already in successful 
operation, and the market for the product is ready and waiting 
at the door. 



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CHAPTER VI 
A BRIEF DESCRIPTIOIT OF THE CHAMBER PROCESS 

The Chamber Procese for the manufacture of sulphuric acid 
takes its name from the lead chambers which constitute the 
chief essential part of the apparatus. It differs from the other 
important process of making sulphuric acid, the contact process, 
both in nature of the plant proper and in the chemical reactions 
involved. The purpose of each is to oxidize SOj up to H1SO4. 
The chamber process does this by means of the reactions between 
SOs, the higher oxides of nitrogen, oxygen, and water, at low tem- 
peratures, while the oxidation in the contact process is accom- 
plished by a catalyzer, usually finely divided platinum, at a 
comparatively high temperature. 

The normal product of chamber plants is sulphuric acid of 50° 
to WB^.' Contact plants normally produce acid of 98 per cent 
HaS04 or higher strengths. The chamber process makes 50° to 
60° acid more cheaply than the contact process can make acid 
of that grade. The chamber process cannot, however, make high- 
strength acid. Each process therefore has its distinct field. 

The essential parts of a modem chamber plant are: 

1. BurnerH of some kind for the production of SOi. 

2. DuHt settling apparatus, except in those cases where brimstone is 
burned to make SOj. 

3. Glover Tower. 

4. Chambers. 

5. Gay Lussac Towers. 

6. Acid Circulating Apparatus. 

7. Fans and flues. 

S. Apparatus for introducing the oxides of nitrogen. 

The gas produced in the burners is derived from the oxidation 
of elemental sulphur, iron sulfide, iron-copper sulfides, zinc sulfide 
or mixed sulfides. It contains from 5 per cent to 10 per cent 
SOa, depending on the material burned, 8 per cent to 12 per cent 
oxygen, and nitrogen, with, in special cases some COi or possibly 
CO. 



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A BRIEF DESCRIPTION OF THE CHAMBER PROCESS 83 

When necessary this gas is drawn through some form of dust- 
settHng apparatus to remove the greater part of the dust which 
would otherwise contaminate the acid. • 

If nitre potting is practiced, the gas next passes around the 
nitre pots. These are cast iron vessels set in the gas flue, into 
which are introduced nitrate of eoda and sulphuric acid. The 
hot gases cause these compounds to react to form nitric acid 
vapor, and a mixture of sodium sulphate and sodium bisulphate. 
The latter is tapped off molten, at intervals. The nitric acid 
vapor is reduced to NO by the hot SOi and is carried along with 
the gas. 

The gas mixture next enters the Glover tower at a temperature 
of aWF. to l,000°f . It is in this tower brought into intimate 
contact with a mixture of 60°B^. sulphuric acid carrying iii 
solution NiOg, and chamber acid of about 50° B^. The hot gas 
with its considerable SOi content, reacts with the acid and de- 
nitrates it or removes from it ite NtOi, forming some HiSOi and 
converting practically all the NjOj into NO, a gas, which goes 
on with the main gas stream. Bteam and some weak sulphuric 
acid vapor are alao formed and go on with the gas. Leaving the 
Glover tower the gas mixture contains then a somewhat reduced 
percentage of SOi, nitric oxide (NO), oxygen, nitrogen and steam 
or weak acid vapor. Its temperature has been reduced to 
about 200''F. . 

If nitre potting is not practiced it is customary to introduce 
some fresh nitric acid into the Glover tower top. 

The acid issuing ffom the Glover tower at the bottom is 
mMntained at a gravity of about 60° B4. It has a temperature 
of 200°P.-300°F. and is passed through a cooling system con- 
sisting of a tank containing lead pipe coils through which cold 
water is circulated. The acid should leave this 6ooler at as low 
a temperature as possible, certainly not over 80°F. A part 
of this acid is elevated and introduced into the Gay Lussac towers, 
and the remainder is shipped. 

The gas mixture from the Glover tower is conducted into the 
chambers, usually from 3 to 10 in number, in series. From 1 to 
2 hrs. is occupied by any given portion of the gas in passing 
through the set of chambers. Steam or atomized water is 
introduced at various points. By the reactions between S0», 
oxygen, the oxides of nitrc^en and water, sulphuric acid is 
formed. This collects in the bottoms or pans of the chambers. 



^dbvGooglc 



84 



AMERICAN SULPHURIC ACID PRACTICE 



When these reactions have gone on for the proper period of 
time and the gas finally reaches the end of the last chamber the 
SOa percentage has been reduced to less than }^q of 1 per cent, 
and the nitrogen oxides are practically all in the form of NiOj. 
It is highly important that the SOj percentage be reduced below 
Ho "f 1 per <^*iit or else the recovery of the nitrogen compounds 










OtN fi?y^maif>h9iv 



Lvsiac Tor^eri 



H^Oas sprciy or sham /5 
iniroduccd in to chambers 
af mcny points 



2H0*tS(k *iO*HiO = ZHShlOs 
ZHSHOs i-UsO - 2Ms504 ^NgOj 
Fio. 12.— Flow Sheet of Chamber Process. 

will be incomplete. It is almost as essential that the SOi per- 
centage be not less than Jloo of 1 per cent for the same reason, 
and also because of increased corrosion of the lead. These 
points will be taken up in more detail later on. 

By properly regulating the amount of water or steam intro- 
duced the acid made in the chambers is kept at approximately 
SO^Bfi. It is not permissible to allow the continued formation of 
acid of much greater concentration because of the tendency of 



^dbvGooglc 



A BRIEF DESCRIPTION OF THE CHAMBER PROCESS 85 

such acid to take into solution some of the oxides of nitrogen, in 
which case they are no longer available for reaction with SOj. 

The acid-making reaetions generate a large amount of heat 
which is carried off mostly by radiation from the lead chamber 
walls. The chambers should therefore be housed in a well- 
ventilated building. 

From the chambeiB the gases pass into the Gay Luseac towers. 
Their function is to recover the NjOj. This is accomplished by 
brii^ng the gas into intimate contact with cold 60° B4. sulphuric, 
acid, which takes 86 per cent to 90 per cent of the N2O1 into 
solution, forming what is known as nitrous vitriol. Perfect 
recovery of the NjOi is never attained because the cost of appara- 
tus to accomplish it is prohibitive. 

The gas which leaves the Gay Lussac towers consists of 94 to 
96 per cent nitrogen, 4 to 6 per cent oxygen with traces of other 
things. It is discharged into the atmosphere through a stack. 

The acid issuing from the Gay Lussacs, carrying usually from 
1 per cent to 2 per cent NjOj, is elevated to the top of the Glover 
tower and the NiOs there reintroduced into the system. 

Figure 12 shows a conventional plan of a chamber plant and 
indicates the reactions which occur in the various parts of the 
apparatus. 



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CHAPTER VII 
DUST SETTLING APPARATUS 

A chamber acid plant will usually require some provision for 
removing dust from the burner gases. This varies from almost 
nothing in the case of brimstone burners, to rather large and 
elaborate chambers for use when very fine sulphide ore is burned. 
It is highly important in order to insure uninterrupted operation 
to provide suitable and adequate means for dust removal. If 
any considerable amount of dust is carried into the Glover tower 
by the gas it causes the following disagreeable and serious results : 
The packing of the Glover tower will become obstructed, inter- 
fering with passage of the gas. The acid will be contaminated 
and rendered impure. Even though this may not be of impor- 
tance to the consumer of the acid, it will cause gradual fouling and 
obstruction of pipes, valves, tanks etc., in the acid plant and will 
make uniform running impossible. 

There are two general principles applied in dust removal, which 
are: decreasing gas velocity, and causing change of direction of 
the gas stream. It is hardly necessary to consider some of the 
older proposals for washing the gas by water or acid, ae these 
involve cooling the gas so much that the Glover tower will not 
function properly. In general, it is necessary to retain the tem- 
perature of the gases as high as possible from the furnaces to the 
Glover tower. Dust chambers for acid plants should therefore 
be compact and well insulated. 

The Cottrell apparatus has been used in a few acid plants 
with considerable success. It probably has a distinct place 
in acid plant design when the sulphur bearing material burned 
produces very fine dust. This form of treater is hardly justi- 
fied otherwise, as it is expensive to install, and involves some 
operating expense. The following information is furnished by 
the Research Corporation, 31 West 43rd St., New York: 

Cottrell Precipitatorb for Cleaning Roaster Gases 

The problem of satisfactorily cleaning the sulphur dioxide gases prior 
to their oxidation and conversion into sulphuric acid has long been a 



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DUST SETTLING APPARATUS 87 

troublesome one for acid makers to solve. In contact acid plants it is 
of course esaential that the gasee be completely freed from suspended 
particles of dust or fume prior to their passage through the catalyst 
and it is almost equally desirable in the caee of chamber plants that the 
sulphur dioxide gases be thoroughly cleaned if the plant is to operate 
at high eflicieDcy and produce a clean acid of good quality. In the 
latter case, however, the problem is complicated by the fact that the 
sulphur dioxide gases must be cleaned at a very high temperature 
whereas in contact plants the gases may be cooled during the cleaning 
process or may be cooled first and then purified. 



In both cases the Cottrell Processes of Electrical Precipitation offer 

a very satisfactory method of cleaning the gases, and several Precipita- 
tion Installations are today in use for such purposes. 

In designing Cottrell Precipitators for cleaning roaster gases the 
temperature at which the gases must be cleaned and tbe character of 
the suspended matter to be removed from such gases are governing 
factors. Of course the size of tiie installation depends directly upon 
the volume of gas to be cleaned and this in turn is fixed by the quantity 
of material being roasted per unit of time and by its sulphur content 
as well as by the percentage of sulphur dioxide in the gases leaving the 



iiz^dbvCoOglc 



88 AMERICAS' SULPHURIC ACID PRACTICE 

furnaces. These factors must therefore be known or approximated in 
order that a precipitation plant of suitable capacity may be provided. 
Two types of precipitators are today being installed for cleaning the 
hot furnace gases in sulphuric acid plants. These types differ widely 
from each other and the decision as to which type should be installed 
is based largely upon the t«mperature and fume or dust conditions in 
the particular plant under consideration. In cases where the gases 
must be cleaned at temperatures of 1,000°F. and over and where the 
suspended matter to be removed is mostly dust rather than fume, pre- 



cipitators of the so-called plate type, in which the gases pass horizontally 
between the collecting and discharge electrodes, have proven highly 
Batbfactory, On the other hand, where the gases can be cooled to a 
temperature of about 600°F. or under before cleaning and where the 
suspended matter to be removed is fume rather than dust, precipitators 
of the pipe type, in which the gases pass upwards between the collecting 
and discharge electrodes, would in general be the more suitable. 

Figure 14 is a photograph of a Cottrell Precipitator of the pipe type 
which was recently installed under the supervision of the Research 
Corporation at a plant in Wisconsin, Here 17,500 cubic feet of gas 



iiz^dbvCoo^lc 



DUST SETTLING APPARATUS 89 

per minute at a temperature of 500°F. are cleaned. These gases come 
from three Mathey rotary kilns roasting Wisconsin zinc ore concentrates, 
and after being cleaned are used for the manufacture of sulphuric acid 
by the contact method. The precipitator as installed consists of two 
units, each having 36 collecting electrode tubes or pipes. These pipes 
are of steel, 12 in. in diameter and 15 ft. in height. Means are provided 
for rapping both the discha^e and the collecting electrodes in order to 
remove from time to time any dust which may have adhered to them. 
The levers for operating the pipe rappers may be clearly seen in the 
photograph. The bottom header is a reinforced concrete chamber into 
which the collecting electrode pipes project and. in which the collected 
material is deposited. This is later removed by hand through doors 
which are provided for this purpose. Should it be desirable similar 
installations could be readily provided with hoppers and screw conveyors 



Fia. 15. 

SO that the collected dust could be taken out of the precipitator con- 
tinuously and automatically. This precipitator occupies a space ap- 
proximately 17 ft. wide by 28 ft. long and has an overall height of 
about 35 ft. The amount of power required to operate the installation 
is about 18 KW. 

Figure 15 is a drawing giving the general arrangement and overall 
dimensions of a precipitator of the horizontal flow or plate type, designed 
and installed by the ReBeareh Corporation, and Fig. 13 is a view looking 
in a lengthwise direction through a precipitator of this kind which was 
installed in a chamber acid plant near Baltimore, Maryland, and f^ch 
is particularly designed to withstand the high temperatures at which 
the gases must be cleaned in such a plant. This installation operates 
at a gas temperature of 1,100°F., while occasionally temperatures as 
high as 1,400°F. have been recorded in the precipitator. 

A precipitator of the size shown in Fig. 14 will clean the hot gases 
produced by the roasting of 40 to 45 tons of fines pyrites per twenty- 



^dbvGooglc 



90 AMERICAN SULPHURIC ACID PRACTICE 

four hours. With a sulphur dioxide concentration of 7H per cent to 
8 per cent this means that the volume of gas passing through th^ in- 
stallation is about 17,500 cu. ft. per minute at a temperature of 1,100°F. 

As will be noted from an inspection of Fig. 15, the precijatator is 
divided into two sections, each of which is provided with a damper at 
both inlet and outlet ends. This makes it possible to shut off either 
section from the system when inspection or repair is required or when 
it 18 desired to clean the electrodes. Such cleaning may be necessary 
every few days if a very dusty ore is being roasted in the furnaces. 
For the above reason it is desirable to so design the plant that each sec- 
tion will have sufficient capacity to handle all the gas for short periods 
of time and in this way continuity of operation with clean gas is prac- 
tically assured. 

Among the more important benefits obtained by the use of the Cot- 
trell Processes for cleaning roaster gases in sulphuric acid manufacturit^ 
plants the following may be mentioned: 

1. The quality of the acid is improved, due to the removal of the 
dust carried by the furnace gases. 

2. More efficient operation of the nitrating pots can be obtained due 
to the absence of dust in the gas at this point in the system. 

3. Plant shutdowns for cleaning the Glover towers, wifh the atten- 
dant loss of acid and Umttation of production, are avoided. 

4. The life of the lead chambers is increased, due in part to elimination 
of dust deposition. 

5. A material is collected usually having more than sufficient value 
to carry the operating cost of the installation. 

The simplest dust settler is an enlargement of the gas Sue to 
reduce the gas velocity. A considerable amount of valuable data 
has been gathered on this method of dust settling, and it is pos- 
sible to design a dust chamber of this kind with assurance as to 
its performance. 

It seems to be well established that reduction of the velocity 
of the gas stream to not over 5 ft. per second is necessary to 
allow proper settling within a reasonable distance of travel. 
Even at this rate of speed a flue of moderate height, say 10 ft., 
will have to be 60 ft. or more long to allow the dust particles "to 
settle out. It will be readily seen that for a large acid unit a 
dust chamber of this type requires a great deal of ground space. 

Baffle walls to make the gas take a tortuous course are, in 
this form of dust chamber, of doubtful value. One baffle 
immediately in front of the inlet opening is good to spread the 
gas stream, but if a large number of baffles are put in they impede 



^dbvGooglc 



DUST SETTLING APPARATUS 91 

the draft, raise the gas velocity, and often give poorer net results 
than empty chambers. 

Wires or chains hung in a dust chamber of this type have a 
very good efEect. Their virtue of course Ues in the fact that dust 
particles impinge on them and lose their velocity and fall or else 
cling to the wires or chains. They do not interfere with draft to 
any serious extebt. It is well to provide some means of shaking 
suspended wires or chains as dust clings to them to some extent. 

An interesting account of the performance of dust chambers 
hung with wires at the Copper Queen smeltery is given in an 
article by Geo. B. Lee in the Engineering and Mining Journal of 
September 10, 1910. Two tests described showed that in a 
100 ft. loi^ chamber with gas velocity about 4J^ ft, per sec., 



62.8 per cent of the total dust was deposited with the chamber 
empty, and 77 per cent when h\in^ with wires. 

Several interesting proposals have been made along the lines 
of inserting shelves into the chambers, the idea being that by 
using them the distance which a dust particle must fall before it 
finds a resting place is greatly reduced. The Howard dust 
chamber which provides horizontal metal shelves a few inches 
ap&rt is one example of this. The Wedge dust chamber does the 
same thing except that the shelves slope sharply toward the 
outside walls and in that way the dust all slides down against the 
walls and can be more easily drawn. This principle is a good one 
so far as setthng dust is concerned, but the structural difficulties 
are considerable for large units or where the gases are very hot. 

Figure 16 shows a longitudinal section which applies to either 
the Howard or the Wedge chambers described, while the trans- 
verse sections show the horizontal position of the Howard 
shelves and the inclined position of the Wedge shelves. The 
Howard chamber has been installed in several plants with 



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92 



AMERICAN SULPHURIC ACID PRACTICE 



satiBfactory results. I do not know whether any chambers 
fotlowing the Wedge phin have been built. 

Dust chambers employing the centrifugal principle have been 
used in ^me places for acid work. They have not been as 
popular as their merits warrant. A. P. O'Brien many years 
ago used such a dust chamber at Richmond, Va. This is de- 
scribed in the Mineral Industry, Volume 9, as retaining 75 per 
cent of the dust entering, which is very good. More modem 
applications of this plan have been made at the American Steel 
and Wire Company's acid plants at Donora, Pa., in connection 
with Hegler roasters, and at the Garfield Chemical and Manu- 
facturii^ Company's plant at Garfield, Utah, where fine copper 
concentrate is roasted in Herreshoff furnaces. 




Chambers of this type are cylindrical with gas inlet tai^ential 
and near the top, and with gas outlet through a central pipe lead- 
ing from a point near the bottom. Figure 17 shows the essential 
features. The velocity of the entering gas should be as high as 
possible without too much impeding the draught. Good clearance 
requires entering gas velocity not under 25 t. per second. 

Centrifugal dust chambers are very small and compact for the 
work they accomplish and have much to recommend them for 
acid plants for that reason. In cases where it is desirable to 
hold up the temperature of the furnace gases so that the Glover 
tower will concentrate well, the small radiating surface of the 
centrifugal chamber is an advantage. 

The Anaconda Copper Mining Co. has in its acid plants 
two dust chambers of a unique design which has probably not 
been used elsewhere. These chambers have given excellent 
results and are so compact that they deserve description. They 



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DUST SETTLING APPARATUS 93 

use both the principles of decreased velocity and change of 
direction to accomplish clearance. The form of this chamber is 
a cylinder with inverted conical bottom, and in general appearance 
resembles the centrifugal chambers. 

Referring to Fig, 18, the gas enters through flues 1-1 into 
space 2, distributes radially, passes through the 4-in. vertical 
slots, and rises into space 3. Space 2 is separated from space 3 
by reinforced concrete cone 5-5, From space 3 the gas leaves 
the chamber through passage 4 which does not communicate 




sTof!..4'-Wiav . 



-"^a^ 



Section * -A 



with space 2. The dust which drops in space 3 falls through the 
vertical cast iron pipe 6 and is drawn off with the dust which falls 
in space 2, at gate 7. This chamber is entirely self cleaning. 

The original chamber at Anaconda cleans the gases from 
roasting 150 tons of copper concentrate per 24 hours, all of which 
passes J^-in. screens. It is 32 ft. in diameter and 43 ft. high 
outside. It offers very little resistance to the passage of the 
gas and in this respect is better than the centrifugal chambers. 
Its cost of construction is somewhat higher than that of a centrifu- 
gal chamber, but it is a very satisfactory apparatus from an 
operating point of view. 



^dbvGooglc 



CHAPTER VIII 
THE GLOVER TOWER 

The Glover tower is the firat division of the acid plant proper. 
It receives through a flue entering it near its bottom the gaa 
from the burners. This gas contains essentially SOj, oxygen, 
nitr(^en and — if nitre ia potted in the flue — a small amount of 
NO. Its temperature may be up to 1,000''F. or liZWF. Into 
the top of the Glover tower are fed nitrous vitriol {60" sulphuric 
containing NaOg in solution), and chamber acid about 50°B£. 
The purpose of the tower is to produce an intimate contact 
between the gas and the acid. 

With this statement of the duties of the Glover tower in 
view, it is clear that the tower must be constructed in such a way 
as to be acid and gas tight against pressures of a few ounces, 
and it must be of such materials and buUt in such a way as to 
withstand the action of gas at 1,000°F. and sulphuric acid of 
60° or erB^. at SOOT. 

A modem Glover Tower consists of a lead shell supported 
by steel or wood framework, a lining of acid- and heat-resisting 
brick, and a packing of acid- and heat-resisting material placed 
in such a way that gas may ascend through' it freely and acid 
descend over its surfaces. The structure is built in a lead, 
briek-lined pan which may be integral with the tower or fairly 
distinct from it. A brick-lined flue enters near the bottom to 
deliver the hot furnace gases into the tower, and another flue of 
bare lead leaves the top of the tower and carries the gases to the 
chambers. 

As it is desirable that the acid which issues from the Glover 
tower shall flow by gravity to coolers and tanks, the tower 
proper is built on a suitable foundation from 10 to 20 ft. high. 

The weight of the tower is very great and the stability of the 
foundation must be beyond question. In modem plants rein- 
forced concrete, or structural steel on a heavy concrete base or 
piers, are the forms of construction used. A smooth level floor 
at the desired height is obtained by one of these methods, and 
on it is laid down a sheet of Ught lead — 6 or 8 lb. per square foot 



^dbvGpO^^lc 



THE aWVER TOWER 95 

— aa a protection against leakage or overflow of acid. This lead 
extends out beyond the edge of the foundation a few inches, or 
i3 turned up to form a shallow pan which is drained by pipes. 

The pan of the Glover tower is frequently made of lead weigh- 
ing 60 lb, per square foot i.e., about 1 in. thick. It may be 
made somewhat lighter with safety if the masonry lining is well 
done. 

The sides and top of the Glover tower are of lead not less than 
10 lb. per square foot and better 15 or 20 lb. 

A sturdy framework of wood or steel or a combination of the 
two, supports the lead, and, above the top of the tower, a plat- 
form carrying acid tanks. This frame consists usually of 4 
posts or columns with horizontal members between them which 

J^^-Lsad Loop& JUL ToMTtTap^ 



T LevdSfraM L 

"'..♦Y turned ipyer-.,,^ 



'Anghlrvns 



Fia. 19. 

suppwrt the lead, or which carry small vertical pieces which 
support the lead. Horizontal or vertical straps are burned to the 
lead sheetfi and nailed or bolted to the supporting members of 
the framework. As the lead sheets are supported inside by close 
contact with the lining wall, the outside straps on the side sheets 
need not be very close together. 

The top lead is supported by straps nailed to wooden joists 
or by loops of lead passing over iron pipes, or by small iron hooks 
supporting rods burned to the lead. Several of these schemes 
are shown in Fig. 19. 

As mentioned earUer the pan of the Glover tower is often 
quite distinct from the tower proper which sits in it, though 
sometimes the upper edge of the pan and the lower edge of the 
side sheets are burned together, in which case the pan is not very 



^abvGooglc 



96 AMERICAN SULPHURIC ACID PRACTICE 

clearly defined. It cannot be said that either plan is very dis- 
tinctly better than the other though it is eaey to get into trouble 
with the latter method if the details are not carefully designed. 

The pan and the sides of the Glover tower are lined with brick, 
usually in recent years laid up in acid pixiof mortar, thou^ 
formerly and sometimes now, laid dry. So much stress has been 
put upon the quality of the brick used for this purpose that it 
seems to be a rather common idea that very exceptional clays, 
and methods of manufacture are necessary. It is difficult to 
lay down any analysis figures which show the fitness of brick 
for this purpose. Of course the higher the sum of siUca and 
alumina the better. The sum of CaO and MgO should not be 
over 3 or 4 per cent. Very satisfactory acid resisting brick may 
contain up to 6 or 7 j>er cent FeO. As a matter of fact in almost 
any part of the United States one can find within two or three 
hundred miles entirely satisfactory brick for making tower lininp. 
As a test if the brick is mechanically sound and strong, it should 
be soaked for a week or more in sulphuric acid and then allowed 
to stand in the weather for several weeks or as long as one can 
wait. If no spalling or cracking or swelling occurs after a long 
period of weathering, the brick will stand up well in the tower. 

The mortar used in laying the brick consists of silicate of soda 
and finely ground silica with a small percentage of barium sul- 
phate if desired. This mortar seta up very slowly as the set is 
due to evaporation of water only. After this initial set has taken 
place, sulphuric acid is nm over the brickwork. This reacts 
with the siHcate of soda and gives the mortar a permanent set. 
The bottom of the pan is lined with 4 or 6 in. of brick. H the 
pan is open, the sides are lined with 4 in. of brick. The lining 
wall of the tower proper is 18 to 24 in. thick in the lower part 
where the heat is high. A few feet above the top of the gas inlet 
flue the thickness can be decreased and after the middle of the 
tower is reached 9 to 12 in. thickness is correct. 

Figure 20 shows the lining and packing of a Glover tower. The 
packing of Glover towers is essentially acid-resisting solid mate- 
rial which shall present a large amount of surface to the gas 
and acid passing through it, thereby causing intimate and thor- 
ough contact between them. Many materials have been used 
for packing. Coke was formerly well thought of because it 
offered much surface and was light. It is rarely used now be- 
cause it is not so permanent or satisfactory as other things. In 



^dbvGooglc 



THE GLOVER TOWER 



97 



the courae of months or a few years coke breaks up and impedes 
the passage of the gas and has to be renewed — an expensive and 
dangerous job. Like any other non-symmetrical packing, coke 
exerts some lateral pressure on the walls of the tower, which is 
undesirable. 




Another class of material used formerly but not much now, is 
rough fragments of quartz or other natural or artificial silicious 
material. This is better than coke in that it does not break down 
readily, but it is open to the objection of creating lateral thrust. 
In using these rough unsymmctrical packings one cannot fore- 
tell very accurately what resistance to gas passage will be 
encountered, and sometimes very unexpected things in this way 
are encountered. 



^dbvGooglc 



98 AMERICAN SULPHURIC ACID PRACTICE 

Much the moBt satisfactory kind of packing ia acid-resisting 
brick or shaped pieces of symmetrical form, hud up 80 that all 
the thruat is downward and none on the walls. With such 
packing one can accurately determine how much area for gas 
passage exists and how much wetted surface for gas acid contact. 
In using unsymmetrical packing these things are very indefinite. 
With symmetrical packings also there is no thrust on the walls 
of the tower. 

There are many kinds of symmetrical packings, some patented 
and some for which very exclusively superior virtues sre^laimed. 
In deciding between the various kinds available one should con- 
sider that the most elaborately designed shapes do not as a matter 
of hard practical fact give much better results than plain rec- 
tangular brick of standard dimensions. If packing is to be used 
at a point near to the factories which make the special shapes it 
is well enough to take advantage of the fact and use them. It 
does not pay however to ship fancy packing? many hundreds of 
miles if good standard brick can be obtained locally. 

Above the top of the Glover tower are located two tanks, 
one to receive nitrous vitriol and the other chamber acid. These 
aci<k are fed into the tower through suitable ilistributors which 
should uniformly spread the acids over the entire top surface 
of the packing. The nitrous vitriol and chamber acid are best 
kept separate until they are inside the tower, because on mijdng 
them some fuming off of the nitrogen oxids occurs. 

The chief function of the Glover tower is to denitrate the 
nitrous vitriol, the solution of N^i in sulphuric acid, which 
comes from the Gay Lussac towers. This nitrous vitricJ is 
broken up by the hot SOi, the acid is freed from its nitn^en 
compounds, which are mostly reduced to the form NO, a gas, 
which proceeds with the gas stream into the chambers. 

In order that this action may be complete and the acid issuing 
from the Glover tower be entirely free from nitrogen-oxides it 
is necessary that the nitrous vitriol be diluted with water or weak 
acid at the top of the tower. It is necessary however that the 
acid issuii^ from the tower be not less than SO'Sg. as that is 
what the Gay Lussacs require. This requirement limits the 
amount of weak acid which may be introduced. Fortunately 
the usual roaster or burner gas has a sufHciently high tempera- 
ture to allow the introduction of much more weak acid that the 
amount necessary to accomplish complete denitration, and the 



^dbvGooglc 



THE GLOVER TOtVER 99 

Glover tower becomes a means of concentrating almost all of 
the chamber acid to 59° or 60° acid. This is its second (unction. 

A third function though an incidental one is that the roaster 
gas is cooled to a temperature at which it will not harm bare 
lead. 

Of course the concentrating capacity of a Glover tower depends 
largely upon the temperature of the roaster gases. If they enter 
the tower at l.OOOT. all the chamber acid can be concentrated 
to 60° or even 61". If their temperature be two or three hundred 
degrees lower not 'all the chamber acid can be concentrated. 

In the- matter of dimensions and of cubic contents there seems 
to be a surprising difference of opinion, shown by modem 
designers. Varying SOa percentages and temperatures account 
for some of the difference but by no means all. 

Lunge states that the net packed volume of a Glover tower 
should be in the neighborhood of 320 cu. ft. per ton of sulphur 
or about 80 cu. ft. per ton of 60° acid made. This refers to 
European practice and small units. 

A large American plant recently erected has a Glover tower 
whose net packed volume amounts to 33 cu, ft. per ton of 60° 
acid. 

Many American plants erected within the last few years have 
around 50 cu. ft. per ton of 60° acid produced, and that figure 
probably approaches modem opinion of ttus point. 

The vertical dimension of the packing is usually from 20 to 30 
ft. There is some possibility of makit^ this dimension too great 
to be good for the concentrating capacity of a tower in that the 
gas temperature may fall so low that condensation will take place. 
If gases entering the tower are hot, say over 1,000°F., a 30 ft. 
dimension is quite proper, but if the gas temperature is below 
800° it is well to hold the vertical dimension of the packii^ lower. 

The horizontal area of the packing will of course be fixed by 
the cubic contents and the height, and will, from the above, vary 
between 1.66 and 2.5 sq. ft. per ton 60° acid produced. The 
overall he^ht of the Glover tower is usually from 10 to 15 ft. 
more than the height of the packing proper to allow for the gas 
distribution chamber below and the acid distribution space above . 
the packing. 

The outside horizontal dimensions are greater than the hori- 
zontal dimensions of the packing by 3 or 4 ft. to allow for. the 
lining walls. ■ Jf" 



^dbvGooglc 



100 AMERICAN SULPHURIC ACID PRACTICE 

As an eicample of the above observations a Glover tower for 
a unit to produce 100 tons of 60° acid per day would assume 
dimensions as follows: 

Cubic contents of packing @ 50 cu. ft. per ton 60° acid 5,000 cu. ft. 
Vertical dimenBion of packing 25 ft. 
Area of packing 5,000 -I- 25 - 200 sq. ft. 

Assume that the tower has square section, than the horizontal 
dimensions of the poking will be 14 ft. 2 in. 

The overall height of the tower will be 25 + 15 - 40 ft. 

The outside horizontal dimensions will be about 17 ft. X 17 ft. 



^dbvGooglc 



CHAPTER IX 
THE CHAMBERS 

The gas mixture coming from the Glover tower consists of 
SOj, NO, 0, N, and water and weak acid vapor, A period of 
from 1 to 2 hours is required for reaction between them sufficient 
to convert substantially all of the SOg into aulphurie acid. 

A place in which the gases may react, a chamber or series of 
chambers then, will be required of such volume that each portion 
of gas mixture will occupy from 1 to 2 hours in its passage from 
entrance to exit of the series. Liquid sulphuric acid forms and 
condenses within the chambers, which must therefore be con- 
structed of such material and in such fashion as to retain liquid 
sulphuric acid. 

The acid-forming reactions are, taken collectively, exothermic. 
It is essential for the proper progre^ of the reactions that the 
temperature of the gas mixture shall not rise much above the 
boUing point of water. It is therefore necessary that the cham- 
bers be constructed of such material and in such fashion that the 
heat of reaction can be readily carried away by radiation. '- 

These considerations together with the experience of many 
years dictate the volume, the materials, and the method of 
construction of the chambers. 

Sheet lead possesses a desirable combination of the essential 
characteristics so predominantly that it is universally used as the 
basic material for chamber construction. It is cheap, it resists 
acid well, it can be readily shaped, and its pieces can be burned 
together to make gas- and acid-tight joints. Furthermore it 
conducts heat well. Other materials have been tried from time 
to time but none so well meets the requirements. 

It has been found best to provide instead of one single lat^e 
chamber several smaller ones, usually three or more. Several 
good reasons for this exist. Mixing and stirring up the gas mix- 
ture accomplished by passing through flues from one chamber to 
another has been found to accelerate the reactions. By dividing 
the space into several small chambers more radiating surface is 
101 



^dbvGooglc 



102 AMERICAN SULPHURIC ACID PRACTICE 

provided than if a single chamber were used. It is more con- 
venient structurally to build several small chambers than one 
large one. A modem chamber set therefore consists of from 
three to ten chambers in series. 

The individual chamber consists of three parts, pan, side or 
"curtain" walls, and top, all of sheet lead. The pan is ordi- 
narily of lead weighing 8 or 10 lb. per square foot — i.e. >^ to Ka 
in. thick — with the bottom horizontal and the sides from 18 to SO 
in. high. The pan is designed to be a reservoir for the acid made 
in the chamber and is supported strongly so that it will safely 
carry acid to within an inch or two of its top edge. 

The side or curtain walls extend from the upper edge of the pan 
to the top of the chamber. They are of sheet lead of 6 to JO 
lbs. per sq. ft. in weight. They are supported by lead straps 
burned to the sheets and fastened to a wood or steel framework 
surrounding the chamber. It was formerly common to allow 
the bottoms of the curtain sheets to extend down into the pan 
to within about 2 in. of the bottom. The acid in the pan then, 
80 long as it was maintained more than 2 in. in depth, made a seal 
which retained the gas. This plan though followed for years and 
still used sometimes is not a sensible one. It wastes lead on 
original construction and after about two years that part of the 
lead which is Immersed in the acid becomes so corroded that holes 
appear and much repair work or even reskirting becomes neces- 
sary. The usual plan of recent years is to bum together the top 
edge of the pan and the bottom edge of the curtain walls. Figure 
21 shows the two methods. 

The top of the chamber is usually of lead of the same weight as 
the curtain walls. It ia ordinarily horizontal and the sheets are 
supported by frequent straps fastened to rafters of wood or 
steel. The sheets of the top and the curtain walls are burned 
together when they meet. 

The bottoms of fRe chambers should always be far enough 
above ground to allow convenient inspection for leakage, say 6 
or 7 ft. minimum, so that a man may walk about. This is im- 
portant because leaks invariably develop and if the chamber pans 
were laid on the ground much loss of acid and damage to founda- 
tions and pans would result before the trouble was detected. 

Concrete piers properly placed in the ground to carry the 
weight of the chamber structure and the pan full of acid are first 
Bet. On these are fixed wood or steel posts surmounted by wood 



^dbvGooglc 



THE CHAMBERS 103 

or Bteel sills. On the sills is laid down a wood floor to carry the 
chamber pans. Between and around the pans the floor is of wood 
slats well apart, or perforated steel, a construction in any event 
which wUl allow free circulation of air up the sides of the cham- 
bers. It is well to build the floor on which the pans are to rest 
of plain boards, not matched — tongue and grooved — in order that 
leaks may be readQy located. If the floor is too tight it may be 
difficult to decide just where the hole in the lead is, as the acid 
may travel some distance before it finds a crack or crevice through 
which it can issue. 

The lead walls and tops of the chambers are supported by 
wood or steel framework or a combination of the two. For very 
large chambers steel is necessary because of the long spans and 
great height of columns. For small chambers wood is more 



Fio. 21. 

economical and perhaps better adapts itself to fastening to the 
lead. Certainly it is not so fireproof though there is not any 
unusual fire hazard about chambers inherent in the process 
itself. 

Two somewhat different general plans of wood framing for 
supporting the curtain walls have been used. The first, which is 
probably most used, provides posts of rather large section spaced 
perhaps 6 or 8 ft. apart. Secured to these are l^hter horizontal 
rails 3 of 4 ft. apart vertically. Horizontal lead straps to corre- 
spond to these rails are burned to the lead curtain walls and nailed 
or cleated to the rails. On the top of the posts rests a heavy cap 
or crown timber. The curtain sheets are turned back over the 
top of this crown piece and part way down its outside and there 
nailed. The theory of this method of support is that almost all 
of the weight of the curtain sheets ia carried by the crown piece, 
and the straps on the sides simply prevent lateral movement. 



^dbvGooglc 



104 



AMERICAN SULPHURIC ACID PRACTICE 



Tliere are of course many variations of detail in this acheme. 
Figure 22 shows the essential features. 

The other system, shown in Fig. 23 provides vertical posts or 
studs of comparatively small cross section, much closer together, 




say 20 to 30 in. No horizontal rails are used. The straps are 
burned to the curtain walls vertically, a row to correspond to 
each vertical stud, and cleated to the studs. A light cap at the 
top of the studs serves merely to hold them in position. The 



TTTT" 




curtain sheets are not turned over it but are curved in toward 
the center Une of the chamber. The studs are appropriately 
braced and held in position by horizontal and diagonal members 
spiked to their outside faces. When the sides of the chamber pan 



^dbvGooglc 



THE CHAMBERS 105 

are of 10 lb, lead and the studs are not more than 24 in. apart 
it is not necessary to support the pan sides with planks. The 
theory of support by tnis method is that each vertical strap 
supports its particular small sectJon^perhapa four square 
feet — of the curtain sheet, and the whole load is uniformly 
distributed. 

There is some difference of opinion as to which is the better of 
•these two general systems of support. The first described plan 
has been more generally used, but the second plan has some very 
important advantages in practice as well as in theory. Lead is 
a metal which has practically no elasticity. Under stress, par- 
ticularly when warm, it flows. When a sheet 20 or 30 ft. long is 
suspended from a crown piece as described, with light horizontal 
straps at rather large intervals to prevent sway, it unfortunately 
does not all remain just where it was placed. When the chamber 
is heated up to 200^. a considerable expansion occurs. When a 
stop and cooling takes place, it does not go back up again. On 
again heating, downward expansion again takes place. Further- 
more there is some creep caused by stretching or fiow. The net 
result of these influences in the course of a year or two, is that 
much of the load is transferred to the straps where it does not 
belong, and distortion of the curtain sheets results, or straps are 
pulled off, usually both. Another weak feature of this support 
plan is in the fact that behind the crown piece just where the 
strain is greatest on the lead, and where radiation is most ob- 
structed, the lead is inaccessible for repair. 

In the vertical-stud system each small rectangle of the lead is 
supported by its strap and the expansion of the lead with heat- 
ing shows itself in very slight curves between straps. Nolai^e 
unsightly and damping distortions occur. At the line where the 
side turns to the top, the lead is entirely accessible. From an 
erection point of view this framing plan is excellent also. 

Steel framing for supporting chamber lead has been increas- 
ingly used of late years. Its use has been necessary in some of 
the large units in which individual chamber dimensions are so 
great as to make timber construction out of the question, or at 
least very awkward. In some modern plants of small dimensions 
.the desire for permanency and fireproof construction has dictated 
the use of steel. 

The construction is simple and usually follows the idea de- 
scribed first above under wood framing, i.e., vertical posts or 



^dbvGooglc 



106 AMERICAN SULPHURIC ACID PRACTICE 

columns 8 to 12 ft. apart are used with horizontal memberB 3 
OF 4 ft. apart to which the lead is attached with straps. Angles 
are probably most used for both vertical and horizontal members 
though BometiiQj^ I beams for columns and channels for hori- 
zontal pieces are B«en. The chamber top is supported by I beams 
or pairs of channels across the short dimension of the chamber, 
with pairs of small tngles between them running longitudinally 
of the chamber to which the lead straps are fastened. 

Chambeis should always be protected by a building. The 
chief reason for this is to prevent wind pressure from reaching the 
lead Less important consideratiooB are protection from sun, 
rain and snow, and facihty of proper control of the process in 
bad weather. The chamber framing should be in no way con- 
nected with the framing or walls of the building as it is essential 
thtft movement of the building due to wind be not transmitted 
to the chambers. Ample openings in the walls below the 
chamber fioor, and roomy ventilators in the roof are necessary to 
assure free circulation of cool air along the side walls of the cham- 
bers. Modem chamber plants are housed in steel or brick 
buildings. 

It has been mentioned that one prime object of dividing the 
chamber space into several small chambers instead of using a 
single large one is to cause mixing and invigorating reaction by 
passing through connecting Sues. Much thought and experi- 
mentation has been spent upon this subject of connections be- 
tween chambers. 

The most simple plan is to run a Que from the centre of the end 
of one chamber to the centre of the end of the following one. 
Another similar method is to use two or four direct horizontal 
fiues between the ends of the adjoining chamber. Sometimes 
the gas is taken from near the bottom of one chamber and led to 
a point in or near the top of the following one. Or a flue will 
leave the lower left hand comer of the end of a chamber and enter 
the upper right hand corner of the nest or vice versa, the object 
being apparently to have entrance to and exit from a given cham- 
ber at pointfi most extremely distant from each other. The 
purpose of all these latter designs is to avoid having dead comers 
or wedges in the chamberB in which the gas moves sluggishly 
or not at all, or in a word to avoid short circuiting. An arrange- 
ment sometimes used which is intended to introduce the gas 
into a chamber in such a way that it will conform to the natural 



^dbvGooglc 



■THE CHAMBERS 



107 



movement of the reacting gases in the chamber is shown in 
Fig. 24. 

This is based on the idea that any given portion of gas mixture 
will proceed through the chamber in a spiral course. Radiation 
at the walls causes the gas nearby to cool and descend. On 
reaching the bottom it is forced in toward the centre and reaction 
heat there causes it to rise again toward the top where it is drawn 
toward the side again by the descending stream. There is 
meanwhile a forward movement. This movement of course 
takes place on each side of the central vertical plane. Tlifi flue 
connections shown inject the gas on each side near the bottom 
and direct it toward the centre where it rises and immediately 
and natiu-ally begins its double spiral progress. 




Many designers have used special structures between the 
chambers to insure thorough mixing of the gases and - often 
cooling as well. These often accomplish the work for which 
they are designed. Sometimes they coat more money than an 
additional pliun chamber which would give the same net result 
in tons of acid made and the intricacy of their lead work some- 
times makes for heavy repair costs after they are a few years old. 

In the 1918 "Transactions of the American Institute of Chemical 
Engineers" Dr. L. A. Thiele describes his Multiple Tangent 
System of introducing gases to the chambers. 

His idea is to avoid the large amount of waste space, particu- 
larly in the comers, where the circulation in the chambers ia 
sluggish. An additional advantage is a very considerable saving 
in area. 

Gas is introduced from the top of the Glover tower, through 
flues, which vary in area and length, the largest in area being the 
shortest; this makes for varying rates of cooling, thus varying 
pressures and rates of flow-all of which results in more rapid circu- 



^dbvGooglc 



108 



AMERICAN SULPHURIC ACID PRACTICE 



lation and better mixing. The flues are arranged as shown in 
the accompanying sketch, 'around the circumference of the top, 
Fig. 25. 

If the outlet should be in the centre of the bottom, the gas 
would be a spiral cone, the outside parts of the bottom being 
dead space. Thus the outlets are arranged on a circle in the 
bottom, concentric with the reaction chamber, and with a 
diameter half that of the reaction chamber. 

This arrangement is reported to save floor space and lead, and 
start remarkably easily. 

Such an arrangement is in service at the plant of the Fairmount 
Chemical Co., Fairmount, W. V. It is running on coal brasses, 
which of course produce a large amount of COj, so the figures are 




not of the value that they would be if the conditions were more 
nearly standard, but Dr. Thiele expresses himself as well pleased 
with results. 

To briefly cover a few of the best known arrangements of this 
kind, the Lunge Plate Column ia one of the early proposals. 
This is essentially a comparatively small lead tower packed with 
stoneware plates spaced a few inches apart. These plates have 
numerous small holes in them so arranged that holes in one do not 
occur directly below those in the next above. The plates have 
slightly raised circumferences and the rims of the holes are 
also riused so that some acid always Ues on each plate and drips 
down through the holes and splashes about as fresh acid forms 
or is fed in. This apparatus is not for big plants for size of 
plates is necessarily limited. 

The Gilchrist Pipe Column is a lead tower with many hori- 
zontal lead pipes extending through from side to side, both ends 



^dbvGoo^lc 



THE CHAMBERS 109 

being open to the air. CirculatioD of air through the pipes gives 
some cooling effect and the mixing is attained by the gas forcing 
through between them. 

Lead towers packed with brick or coke, or quartz, similar in 
construction to Gay Luseac towers are sometimes used between 
chambers. These may be used dry or may have cool acid circu- 
lated over the packing. 

A series of two or three open towers with neither packii^ nor 
circulation of acid has been used. 

Chambers are fitted with steam or water connections or both, 
for introducing the necessary water to make acid of proper 
Eitrength.' Steam is usually put into each chamber at two or 
three places only, as it spreads well. These are usually in the 
top, sometimes in the front end wall. Water must be introduced 
at several points and in a very finely divided condition for 
otherwise drops would go quickly down to the bottom without 
entering into the reaction. Special atomizing nozzles of glass 
or stoneware or platinum are made for the purpose. The water 
for this purpose mtist be filtered and delivered to the nozzles at 
uniform pressure usually about 60 lb. 

Steam distributes through the reacting gases better than 
water spray unless the apparatus for introducing the latter is 
carefully taken care of. Water of course is much cheaper to use 
if live steam has to be used. If a uniform supply of waste steam 
is available it is quite acceptable. Water has the advantage 
over steam in that it exerts a considerable cooling action on the 
gas mixture which in summer particularly is valuable. 

In order that the operator may know the gravity of the acid 
being made in any given chamber at any time, small gutters 
are burned to the inside of the chamber walls at one or two 
convenient points. A portion of the acid running down the 
walls is diverted by them to an opening in the curtain through 
which it Sows over a sealing lip into a small jar in which is kept 
a hydrometer. By observing and recording the hydrometer 
readings from time to time the operator is enabled to control 
properly the admission of steam or water to the individual 
chamber. 

One or two thermometers are inserted into each chamber. 
If one only is used it is placed in a side wall at the centre and 
about 5 ft. above the workit^ floor. If two are used one is 
placed near each end. These thermometers are made with a 



^dbvGooglc 



110 AMERICAN SULPHURIC ACID PRACTICE 

long stem, usually about 12 in., below the graduated portion. 
This stem is turned 45° or 90° from the graduated part and is 
inserted through a rubber stopper inside the chamber wall, the 
graduated part being vertical and conveniently read. Such 
thermometers are stock articles with the large supply houses. 

The last one or two chambers of a set are frequently equipped 
with bell jars or s^ht glasses in order that the color of the gas 
may be observed. 

For drawing off the acid from the chamber pans and for 
communication between them, pipes are led from the bottom of 
the pan to a boot near the end or between the chambers, or small 
alcoves are made on the pan ends which are joined beneath the 




l^ 




fioor by pipes. In any case at least one end of each such pipe 
should be accessible for blowing out accumulations of mud. 
Figure 26 shows details. 

CHAMBER VOLUME 

The number of cu. ft. of chamber volume which must be 
provided for making a given tonnage of acid depends upon 
several factors. It may first be well to note that it is customary 
to speak of the performance of chambers as using a certain 
number of cu. ft. per pound of sulphur per 24 hours. This 
expression of rating was broi^ht into use to do away with the 
uncertainty that existed when one spoke of volume per unit of 
acid. It was found that the manufacturer whose product was 
50° acid often spoke of his production in terms of 50° acid while 
he whose product was 60° used that as a basis, and yet others 
had in mind 66° or even 100% HjSO*. 

In order to make common ground of comparison the idea of 
using sulphur itself as a basis has come into general use. Even 
this ia not always common ground as one man will reckon on 
sulphur contained in the ore burned, another on sulphur burned 



^dbvGooglc 



THE CHAMBERS 111 

out of the ore, and a third on sulphur in the acid made. Of 
course only the last is correct. 

There is a divergence in claims of performance and a divergence 
in performajice of modem acid plants, in respect of cu. ft. of 
chamber space per pound of sulphur in acid made per 24 hours, 
of from about 8 to 20. An averse of these two extremes, say 
14, ifl probably not far from the volume actually used in most 
plants. The plants which run on 8 or 10 cu. ft. per pound ot 
sulphur have special arrangemenl^ such as towers fans, etc., in 
connection with their chambers. Some plants having small 
plain chambers in which the ratio of radiation surface to volume 
is comparatively high run on 10 to 12 cu. ft. Some few plants 
have been constructed in recent years in which large units — 100 
to 300 tons 60° acid — contained only 4 or 6 enormous chambers. 
The ratio of surface to volume is very low — mixing, cooling, and 
impingment are largely sacrificed, but construction cost per 
cu. ft. of chamber space is very low. In these plants around 
20 cu. ft. per pound of sulphur was provided and is used. 

These observations bring out the fact that merely to say that 
a plant is working on so many cu. ft. of chamber space does not 
determine whether its performance is all that should be expected 
or not. If two plants of different design are built and each 
costs $500,000, each produces 100 tons of acid a day with the 
same operating costs, and one operates on 8 cu. ft. and the other 
on 20 cu. ft. the performance of the latter is just as creditable as 
that of the former. 

It is the opinion of many designers that plain chambers of 
moderate size and simple design give the most satisfactory 
results all things being considered- 

LEAD SPECIFICATIONS 

One of the largest Chamber Acid plants in the country answers our 
inquiry as follows: 

"It has not been our practice to make any other specification except 
that lead ^all be what is known to the trade as 'chemical lead.' 

"We have always purchased this from the same company and the 
quality has been uniform. It must be free from other metab, and 
SufBciently ductile to permit of rolling out into thin sheets. The 
addition of small percentages of copper has been advocated by some 
engineera, but we have had no experience with this alloy. For the 
construction of acid valves, fans and other apparatus that requite 



^dbvGooglc 



112 AMERICAN SULPHURIC ACID PRACTICE 

structural strength, we use a mixture of chemical lead with 7 per 
cent to 10 per cent antimony. 

Life of Lead 

"The exact life of lead in chamber plants cannot be accurately stated, 
as it depends too much on local conditions. I would say that the life 
ia influenced chiefiy by the temperature and whether or not scouring 
action obtains. We have had chambers to run without interruption 
for nearly 10 years, but repairs were made to various parte during the 
interval." 



^dbvGooglc 



CHAPTER X 
GAY LUSSAC TOWERS 

The Gay Lussac towers follow the chambers in the course 
of the gas. They receive from the chamberB normally a gas 
mixture consistit^ essentially of nitrogen about 92 to 96 parts 
by volume, oxygen about 4 to S parts by volume and the oxids 
of nitrogen NO and NOi from ^o to 1 per cent by volume. 
Of course small amounts of CO^ and other gases are present 
but ordinarily have no bearing on the subject. There are a few 
special cases where carbonaceous fuel is used in the furnaces 
from which the SOi is derived, in which CO* must be reckoned 
with. These are unusual and need not be considered in a 
general discussion. The temperature of this gas entering the 
Gay Lussacs is only slightly above that of the atmosphere. 
The result desired from the Gay Lussacs is the recovery of the 
oxides of nitrogen by absorption in 60° sulphuric acid which is 
fed into them. 

The Gay Lussac towers then should be built of such material 
as to resist the action of comparatively cool 60° acid and gas. 
They should be designed in such a way as to bring the gas and 
acid into as intimate contact as possible and yet allow reasonably 
free passage for the gas. They must be of such height as to allow 
a sufficient degree of contact between gas and acid to accomplish 
substantially a 90 per cent recovery of the nitrogen oxides. 

These requirements differ from those of the Glover tower in 
Jrhe matter of temperature of gas and volume. In the Glover 
tower the gases enter at temperatures so high as to be injurious 
to bare lead and it is therefore necessary in constructing a Glover 
tower to provide & heavymasonry lining wall to protect the lead 
shell. No such protection is required in the Gay Lussac towers 
wherein the gas temperature rarely reaches ISOT. The Gay 
Lussac tower therefore need be simply a well supported lead 
shell completely filled with packing, excepting of course the gas 
chambers above and below. This statement does not apply in 
those cases where non-symmetrical packing such as coke or 
quartz is used because such material, in a column 20 to 40 ft. 
8 113 



^dbvGooglc 



114 AMERICAN SULPHURIC ACID PRACTICE 

high, exerts so much lateral thrust as to bu%e and cut the lead, 
and masonry supporting walls are necessary. It is unusual to 
use such packii^ now. With the symmetrical packings, bricks, 
rings or other shapes, the weight is all carried on the bottom. 

Some designers still build Gay Lussac towers with lining 
walls even though symmetrical packing is used, but it is a waste 
of material and a waste of good absorption space. Also it is 
actually bad for the lead shell to have an interior wall, in that 
gas gets in between the masonry and the lead, circulates sli^- 
^hly, and the nitrogen compounds oxidize up to nitric acid 
which often corrodes the lead badly. ^ 

With this exception the general construction of the Gay 
Lussac towers is much like that of the Glover. A massive 
foundation is put down of sufficient height that the acid issuing 
from the tower pans may run by gravity to circulation tanks. 
This usually means on a level site that the top of the foundation 
will be about 10 ft. above the ground. The top suriace of this 
foundation is carefully levelled and made smooth by trowelling. 
A sheet of light lead 4 to 6 lb. per square foot is next laid. The 
edges of this sheet may be turned up a few inches to make 
a shallow pan and a drain pipe put in, or else the edges are 
projected a few inches beyond the concrete and turned down 
sightly to throw any acid leakage away from the foundation. 
This lead is also turned up around the footings of the columns 
of the framework. 

The tower pans are made of 15 or 20 lb. lead and are usually 
24 in. high. False bottoms of 10 lb. lead are placed inside over 
those portions of the bottom on which the brickwork is to rest. 
The side sheets trf the tower are hung, fastened to the frame and 
burned together. They may be burned to the pan or extend 
down inside it. The latter method is not so bad here as in th^ 
chambers as the acid is cold. However it wastes lead and has 
no particular advantages. The side walls are usually of 10-lb. 
lead. 

Ordinarily the top is not put on the tower till the brickwork is 
in. Through the open top the brick and packing material 
is introduced. It is perhaps easier and safer to open three or 
four holes in one side and put in the packing through them. 
When the packing is finished these holes are closed by the lead- 
burners. All danger of bricks falling and injuring the workmen 
is done away with if this plan is followed. The top lead is of the 



^dbyGooglc 



GAY LUSSAC TOWERS 115 

same weight as the side sheets. A chamber 4 or 5 ft. high is left 
without packing at the top to provide for the [nvper acid dis- 
tribution and leave the exit flue free. 

The base structure for supportii^ the packing and the packing 
proper are substantially as described under the Glover Tower. 

There should be on each Gay Lussac tower a carefully designed 
acid distribution system with suitable tanks for feeding it. This 
apparatus is described under Acid Circulation. 

As to volume, dimensions and number of Gay Lussac towers 
suitable for a unit of given size a considerable difference of opinion 
seems to exist if one may judge by an examination of different 
plants. Reverting first to the classic Lunge we find Gay Lussac 
towers compared in volume to the total chamber space which 
they serve. Lunge states that the packed volume of the Gay 
Lussacs should be not less than 1 per cent of the chamber space 
and better between 2 per cent and 3 per cent. This method of 
proportioning would be satisfactory if all chamber space did the 
same work but such is not the case. As mentioned before some 
chamber sets use 20 cu. ft. of apace per pound of sulphur and 
others less than 10 cu. ft. Lunge of course refers to continental 
practice of several years ago in which the larger amounts of 
chamber space were used. It is more pithy in this day to pro- 
portion and speak of Gay Lussac volumes in terms of sulphur 
made into acid of 60°B£. On this basis Lunge advocates not 
less than 100 cu. ft. of packed volume per ton 60° acid produced 
and for really good nitre recovery up to 200 cu, ft. 

This range from 100 to 200 cu. ft. of packed volume per ton 
60° acid is about what is found in modem American plants. 
Certainly the upper figure should be approached but this is not 
always done. With Gay Lussacs well proportioned and skill- 
fully operated whose packed volume amounts to 200 cu. ft. per 
ton of 60° acid made in the plant, a recovery of about 90 per cent 
of the nitre can be made. The total nitre introduced into the 
modern plant amounts to 25 to 30 per cent of the sulphur. 
The loss of nitre then on the above basis amounts to 2.5 to 3 
per cent of the sulphur. 

The absorption of nitre in the Gay Lussac towers is of course 
much more rapid in the earUer part than the late parte. Without 
attempting to formulate or to give exact figures it may be said 
that in a case where the Gay Lussac space was divided into three 
towers in series it was found that the first tower retained about^ 



^dbvGooglc 



116 AMERICAN SULPHURIC ACID PRACTICE 

65 per cent of the nitre in the gas entering it, the second tower 
about 60 per cent of the remainder and the third tower about 60 
per cent of that yet remaining. It muBt be considered that prob- 
ably about 5 per cent of the nitre is not recoverable by solution 
in Sulphuric acid. The above will then work out as follows: 

9S per cent total recoverable. 
1st Toirer 65 per cent of 95 percent — 61.7S 
2d Tower 60 per cent of (95 - 61.75) = 10.96 
3d Tower 60 per cent of (95 - 81.70) = 7.98 
Total 89.68 

As explained these figures are intended simply to give a rough 
idea of the relative recovery accomplished by the different zones 
of Gay LuBsac space. 

Having decided upon the volume of Gay Lussac towers the 
number of towers and their dimensions are next calculated. In 
order to secure uniform distribution of gas and acid throughout 
the packing, it is well to make the horizontal section not too 
large and consequently the vertical dimension long. A high 
tower with small horizontal section makes a much better nitre 
recovery than a low tower with large horizontal section, the 
packed volume in botli cases being identical. This is to some 
extent due to more uniform distribution of gas and acid through 
the packing, but in larger measure to higher gas velocity and 
consequently more thorough breaking up and mixing of the gas 
with the acid. The minimum amount of horizontal section will 
be dictated by the pressure necessary to force the gas through the 
packing. It is not desirable to use high pressures because the 
leadwork of the flues, fans and towers will not stand them. Cer- 
tainly the pressure at the entrance of the first Gay Lussac should 
be not over ^o or %o of an inch of water or say 12 to 15 mm. 
For ordinary packing a gross horizontal sectional area of 2 sq, ft. 
per ton of 60° acid made should be provided to accomplish the 
above result. The total vertical dimension of the tower packing 
should then be 100 ft. if we wish to provide 200 cu. ft. packed 
volume per ton of 60° acid made. It is not practical to use a 
single tower 100 feet high because of the difficulty of pumping 
acid of 1.7 sp. g. to such an elevation, and so it is customary to 
use two or three towers in series. If two towers be used the 
height of each will be 50 to 60 ft. allowing 10 ft. in each for the 
spaces above and below the packing. Likewise if three be used 



^dbvGooglc 



QAY LUSSAC TOWERS 117 

the height of each will be 43 ft. As the tower bases will be at the 
leaBt 10 ft. above the ground and the feed tanks about 12 ft. 
above the top of the tower it is seen that to the above figures 
some 22 ft. must be added to get the vertical distance of the 
acid lift. 

It should be remarked that many planbs will be found in which 
the. Gay Lussac tower scheme does not check up at all closely 
with the line of reaaoning presented above. Unquestionably 
somewhat wide variations can be made from it without sacrificing 
good work. The figures presented are however quite certain to 
yield excellent nitre recoveries. 

To give a concrete example of Gay Lussac towers for a plant " 
to produce 100 tons of 60° acid: 

Total packed volume @ 200 cu. ft. per ton 20,000 cu. ft. 

Sectional area @ 2.25 225 sq. ft. 

Vertical diinension „'„- = 89 ft. 

Using 3 towers packed height each say 30 ft. Total height each 
allowing 10 ft, for spaces above and below packing 40 ft. 

If the section be made square the horizontal dimensions will 
be 15 X 15. In the writer's opinion it would be better to make 
the section rectangular say 9 ft. X25 ft. and to admit the gas at 
three points on the long side. Such a plan probably more fully 
utiUzes the packing than the square section. 

The course of the gas should be upward in all the towers as 
it has been demonstrated that a given tower performs better 
absorption with the gas going upward, than downward. The 
Sues between the towers then will leave the top of the first, 
descend and enter the bottom of the next. 



^dbvGooglc 



CHAPTER XI 
ACID CIRCULATION 

The acid circulating syBtem will be in this discussion taken 
to include tanks, coolers, pumps, pipe lines and distribution 
apparatus. 

Tanks are almost always provided at the top and bottom of 
each tower. They are certainly indispensable when intermittent 
pumping is used, i.e., by acid e^s or montejus. The Sow of acid 
into and out of each tower must of course, be uniform and con- 
tinuous and during the periods when the eggs are filling there 
must be a stock <^ acid at the top to feed the towers and there 
must be a place at the bottom to accommodate the acid issuing. 
Even when continuous pumping apparatus such as centrifugal 
pumps or air lifts is used, it is advisable to have tanks both above 
and below, although in this case they need not be so large. 

Three kinds of tanks are used for this service, viz., lead-lined 
wood tanks, lead tanks supported by skeleton iron framework, 
and iron tanks. The lead-lined wood tanks are most used and 
the iron tanks least. 

Wood tanks are always of rectangular section for conven- 
ience of framing. Usually they consist of rather heavy sills and 
caps with upright posts, strongly put together with bolts and 
dowels. Inside this frame, 2 or 3 in. plauks are spiked, making 
a smooth and solid wall all round. Lead usually 10 lb. per square 
foot is then put in and turned over the top caps and an inch or 
two down outeide. The burned seams should be some little dis- 
tance from the comers as they are the places most likely to break 
open. 

A neat way of making a wood tank frame, particularly for 
small tanks is to build up a crib of 2 X 4 or 2 X 6 material as 
shown in Fig. 27, This of course, leaves 2-in. strips of the lead 
open for the air, but no bulging of any moment occurs. 

Lead tanks with iron frames are always made circular. The 

iron frames consist of four or more upright angle iron pieces with 

flat circular bands or hoops riveted inside. The number of hoops 

for a tank 4 ft. 6 in, or 5 ft. high is usually four, one at the top, 

118 



^dbvGooglc 



ACID CIRCULATION 



119 



one near the middle and two below the middle where the presBure 
is greatest. The dimensions of the iron parts vary with the sise 
c^ the tank. For a 10 ft. diameter X 5 ft. deep tank, the angles 
would be about 4 X 4 X M and the bands i X H- Ten- or 12- 
Ib. lead is used in tanks of this type. They are very satisfactory 
if the details of design are correct, and very neat in appearance. 
Iron tanks have come into use to some extent in the last few 
years for 60° acid. There is no particular reason why they should 
not be as satisfactory as are iron tank cars or storage tanks. 
They cannot be so readily repaired in case of leakage as can lead 
tanks but on the other hand, for several years at least theysre 
not so likely to leak They should not of course, he used for 
acids much under 60°B^. 




Circulation tanks of any construction are usually made from 
4 ft. 6 in. to 5 ft. high. This makes them easy to look into and 
allows light construction as no great pressures are produced. 

The capacities of cireulation tanks vary widely for plants of a 
given size. It is not desirable to tie up too great a tonnage of 
acid in circulation and yet reasonable capacities should be pro- 
vided to carry over periods in which minor repairs to lines, valves, 
etc., may be necessary. It would seem that tanks large enough 
to contain at least two hours' normal Sow should be provided 
at the top and bottom of each tower. At the bottom of the Gay 
Lussac tower which produces finished nitrous vitriol, somewhat 
more space is desirable, up to six or e^ht hours' flow, say. This 
allows a stock of nitrous vitriol to be held which is highly desirable 
in restarting the acid process in case of a shut down. 

It is a very good plan to have two small tanks at each point 
instead of one lar^ one. If this is done one tank may be cut 
out to clean or repair without disturbing operations. The pipe 
lines leaving a circulation tank should have machined seats of 
hard lead (or iron, if iron tanks are used) at their points of exit 



^dbvGooglc 



120 AMERICAN SULPHURIC ACID PRACTICE 

from the tanks, and plugs or stems to correspond. In case 
valves in any line have to be changed or the line opened for any 
reason, the plugs can be set and the flow of acid stopped. It is 
convenient to have a washout pipe of generous size in the bottom 
of each tank as well as the service line. This washout is ordi- 
narily closed with a blind Sange. 

Stor^e tanks for sulphuric acid are made of mild steel plate 
with riveted joints. They are of circular section, have flat 
bottoms and dome or conical tops. They are similar in general 
features to large tanks used for stor^e of oil, except that as the 
liquid they contain has a high specific gravity they are heavier 
metal. It is highly important that all seams shall be perfectly 
tight because any leakage, however sl^ht, causes serious outside 
corrosion in a short time. The bottom of the tank shoidd be 
supported on masonry walls or piers a short distance above the 
ground in order that the bottom seams can be inspected. The 
pipe for drawii^ off the acid is equipped with a seat and plug 
or a long stem or with an inside swing pipe so that the flow of 
acid from the tank may be stopped in case of a failure of a valve 
or pipe. Every storage tank should have one or two manhole 
castings with blind flanges bolted on in its side near the bottom 
in order that the mud may be cleaned out of it from time to time. 
If such cleaning is necessary only at long intervals, say over 
one or two years, the mud may be flushed out with a strong 
stream of water. There will be produced during the time of such 
washing acid solutions of a strength which attacks iron, but the 
injury done Jhe tank during the few hours required for washing 
out is negligible. Removal of mud from a storage tank by 
hand is a serious and dangerous task. 

The acid issuing from the Glover tower is so hot as to be injuri- 
ous to pipes etc., and far too hot to absorb nitre when it is put 
over the Gay Lussacs, hence coolers are necessary at the base of 
the Glover tower. These are open-top tanks containing leftd- 
pipe coils through which cold water is circulated. 

This is sometimes augmented by spraying water on the outside 
of the tank or by making it with double walls and circulating 
cold water between them. The hot acid is discharged into the 
top of the tank and leaves it at the bottom through a pipe which 
rises up almost to the top again. In this way the cooler is 
always kept full and the acid takes its natural course, i.e., as it is 
cooled it sinks to the bottom and runs off. 



^dbvGooglc 



ACID CIRCULATION 



121 



The tanks are made with wood boxes lined with lead or with 
iron framework, as described above. Some times a brick lining 
is put inside the lead. If the tank is jacketed it is made with the 
shells heavy enough to be self sustaining. The coils are made of 
Ij^-in. or l}^-in. lead pipe. They may be made fiat spirals or 
upright spirals. If flat, several are placed superimposed. If 
vertical, they may be of different diameters and set concentric- 
ally or may be of the same size and set side by side. The cold 
water enters at the bottom and circulates upward and leaves the 








1 





Detail of Acid Di&chorg* 



top, in this way the cold water is brought into contact with the 
cooler acid, and. the warmed water with the hot acid. Superim- 
posed flat coils are not to be recommended on account of the 
inconvenience of repairing or replacing them. Uniform upr^ht 
coils are best in this respect and give fully as good results as 
regards cooling. A sketch of a cooler with this type of coils is 
shown in Fig. 28. 

Between 1 and 2 sq. ft. of coil surface should be provided 
per ton of acid per 24 hours going through a cooler tank. The 



^dbvGooglc 



122 AMERICAN SULPHURIC ACID PRACTICE 

cooler tanks should have an acid capacity such that the acid 
will be in contact with the coils from 1 hour to IJ^ hours. For 
example, if the tower is discharging 300 tons of 60° acid per 24 
hours, the total surface of the pipe coils should be perhaps 450 
sq. ft. and the acid capacity of the coolers should total around 15 
tons or 285 cu. ft. These proportions may be varied properly 
with the temperature of the acid issuing from the Glover and the 
temperature of the cooling water. They work well if the former 
is 275°F. and the water 60'*F., i.e. the acid will issue from the 
cooler at a temperature around 70°. 

There should always be at least two coolers with the inlet 
launders and discharge pipes so arrai^ed and of such size that 
any one cooler may be cut out, emptied and washed while the 
entire acid stream goes temporarUy through the others. A 
generous washout pipe leading to the sewer should be provided 
on each cooler tank. 

Pumping sulphuric acid presents difficulties which are not 
encountered in pumpii^ water, oil and other familiar liquids. 
It is corrosive to many metals and it quickly destroys any packing 
material. Hence, any pmnp which depends upon a flexible 
packing for tightness is out of the question. Reciprocating, or 
plunger pumps cannot be used at all and even centrifugal pumps 
which involve glands packed with flexible material are trouble- 
some. These facts have led to the almost universal use of an 
apparatus known vdriously as the acid egg or blow case, or monte- 
juB. The air lift or pulsometer is also widely used and to an 
increasing extent, the vertical submerged centifugal pump. 

The acid egg is a cast- or wrpught-iron vessel provided with 
three openings for pipe connections. One of them which just 
enters the egg is connected to the supply tank and through it the 
acid enters the egg by gravity flow. The second which also 
just enters the egg, serves alternately for the admission of com- 
pressed air and the biow-off. The third pipe extends almost to 
the bottom of the egg and through it the acid is forced out of the 
e^ and up through the discharge line to a tank on top of the 
towers. To operate this device, the blow-off valve is opened to 
atmospheric pressure and the compressed-air valve is closed. 
T^e valve in the feed line is opened and the egg allowed to flll 
with acid. Next the valve in the feed line is closed, the blow- 
off valve is closed and the compressed-air valve is opened. The 
compressed air flows into the egg and forces out the acid through 



^dbvGooglc 



ACID CIRCULATION 



123 



the discharge line. When the egg is empty or near^ so, the 
compressed air is shut off and the blow-off valve is opened. When 
the pressure is relieved, the feed line is once more opened and the 
cycle begins again. Figure 29 shows a typical layout. It is 
important that the blow-off pipe be carried up above the level 
of the top of the feed tank in order that acid may not run out 
through the blow-off line when the egg is filled. The blow-off 
valve is of acid proof construction. The arrai^ment shown is 
operated by hand. A convenient modification is to have a check 
valve in the feed line instead of a hand-operated valve. There 
have been many clever automatic devices developed for operating 
the compressed air blow-off valves. Almost all of them depend 
upon the action of a float within the ^g to open and close the 




Fio. 29. 

valves or ports. The Kestner Automatic Egg was an early and 
much used apparatus of this type but is probably not being in- 
stalled in this country now. Descriptions of it can be found in 
Lui^ and other publications of several years ago. Simpler and 
more satisfactory automatic valves are now being made by the 
Schulte and Koertit^ Co. and the Monarch Manufacturii^ 
Works, both of Philadelphia. Both of these consist essentially 
of a small lead casing in which a fioat works. When the egg is 
empty the lower part of this float, which ia conical^ seats in a 
depression whose sides are pierced by ports connected with high- 
pressure air, and closes them. When the acid rises up about the 
float it rises off these ports and its upper surface seats against 
the orifice of the blow-off pipe, thus admitting air to the egg and 
closing the blow off. The acid is blown out through the usual 
discharge pipe and when all out the air also escapes and the 



^dbvGooglc 



124 AMERICAN SULPHURIC ACID PRACTICE 

pressure within the egg decreases to such an extent that the float 
drops and closes the air inlet and opens the blow off. 

It is to be considered that any automatic apparatus requires a 
certain amount of attention to keep it in order. Also that the 
flows of acid into and out of tanks must be kept under observa- 
tion. One man can easily operate a lai^ battery of hand- 
operated eggs and the latter are almost trouble proof. It is a 
question therefore, whether or not, everything considered, auto- 
matic apparatus is more satisfactory than hand-operated. As 
regards economy of air and power, the matter is largely one of the 
care- with which the apparatus is operated and maintained. To 
be sure, a careless pumpman can waste a great deal of air. On 
the other hand an automatic valve which is not working properly 
can do the same. Air pumping at best, is a very inefficient 
method of using power. 






Eggs for pumping sulphuric acid were formerly almost always 
made of cast iron, but as the size of chamber units increased and 
the volumes of acid to be raised correspondingly increased, it 
became desirable to make very large eggs. In cast-iron, these 
would be enormously heavy and expensive and so the egg made 
of wrought-iron plates, riveted together was evolved. Such 
e^s are now in use of a capacity up to 250 cu. ft. 

Cast-iron eggs are made in several different shapes, one of 
which is shown in Fig. 30. Usually only two pieces are necessary 
to make up the complete egg, i.e., there is just one flanged joint 
to be made. This joint is made tight with a gasket of 10- or 
12-lb. sheet lead. Three flailed nipples are cast integral with 
the egg body. In some cases a depression, or well, is made 
below the nipple designed for the discharge pipe and the latter 
dips into it, the idea being to get all the acid out of the egg at each 
pumping. This is a rather unnecessary refinement as in a short 
time the bottom of the egg accumulates some sediment and the 
end of the discharge pipe is in a " welt " in this sediment anyway. 



^dbvGooglc 



ACID CIRCULATION 125 

It is unwise to line iron eggs witb lead as some minute opening 
in the latter is sure to develop. When this occurs the lead is 
very soon blown away from the iron by the action of the air and 
soon the iron is exposed to the action of the acid anyway. Cast 
iron eggs of ample thickness, up to 2 in. last for many years if 
only acids near M^B^. are bandied in them. 

Wrought-iron eggs should be made of as high grade wrought- 
iron plate as can reasonably be obtained. The usual design is 
shown in Fig. 29. A ca8l>-iron saddle is riveted on one side and 
this covered with a plate on which are cast the usual nipples. 
This plate is bolted to the saddle which also serves as a manhole. 
As mentioned, eg®s of this type are especially suitable in the 
large sizes. 

For elevating acid of 50° or less, iron eggs are not suitable as 
too much corrosion results. For this service the air lift is much 
used. It is a satisfactory device but it uses a very large amount 
of power and has some other disadvanta^ies which make it less 
suitable than eggs for pumping 60° acid. 

In its simplest form, the air lift is a U-ehaped pipe with one 
limb longer than the other and with a pipe for carrying com- 
pressed air entering the long limb just above the turn at the 
bottom. The acid to be elevated is fed into the short limb and 
the long limb discharges into an elevated tank. To operate, 
acid is allowed to flow into the pipe until the acid is level in both 
limbs, then the compressed air line is opened somewhat. The 
' air produces an emulsion or mixture of acid and air bubbles. 
When sufficient air has become mixed with the acid that the 
column of mixture filling the long limb is lighter than the colunm 
of solid acid in the short limb, a flow is established. To get good 
results with an air lift the long limb should be not more than 
two times the length of the short limb and it is preferable to 
make the ratio 1}4 to 1 when elevations permit. 

Ordinarily, as in elevating acid from the chambers to the top 
of the Glover tower, the elevations are such that a single air lift 
cannot be arranged above ground, i^,, the he^ht of the chambers 
above the ground is very much less than one half the height of 
the Glover tower top above ground. In order to get a sufficient 
length of the short limb of the Uft a pit or well is sunk into the 
ground and the pipe extended down into it. While this is a very 
common procedure, it sometimes leads to considerable trouble 
and serious loss of acid in case of leakage. In a well particularly. 



^dbvGooglc 



126 



AMERICAN SULPHURIC ACID PRACTICE 



inspection is impossible and a leak may exist for some time 
before it is suspected. To repair, it is necessary to draw the 
pipes out. 

In order to do away with the well, or pit, the multi-eta^ 
lift was developed. This simply amounts to putting together 



-€]I^) 



^ZD 




&^ yy> 



FlO. 31. 



Fio. 32 



several simple lifts of increasing he^ht until the final elevation 
is reached. It has the advantage of being all above ground and 
in sight. It is necessary of course, to so adjust the admission 
of air to each lift that it will take away all the acid which the 
preceding lift delivers to it. Once properly set, an air lift goes 




on elevating acid without supervision. It would seem from 
the theory of this method of lif tit^ acid that the air should be 
forced in through many small orifices rather than a single larger 
one. We find in practice both arrangements and from the ' 
author's experience, it must be said that there does not appear 



^dbvGooglc 



ACID CIRCULATION 127 

to be any great difference in general results. Details of two 
common schemes are shown in Figs. 31 and 32. At the top of 
the long limb it is necessary to provide a box, or pot, to receive 
the mixture of acid and air, in which the two can separate and 
from which the acid can run into a tank or another lift and the 
air escape. A baffle of some kind prevents acid from splashing 
out of the air exit. Figure 33 shows such an arrangement. 

From the standpoint of economy of 
power and supervision, the centrifugal 
pump would appear to be the best way 
of elevating acid. Concerning power, 
there has never been any question as 
to the economy over air pumping. 
Maintenance of centrifugal pumps has 
for years been the thing that has pre- 
vented their general use and the stuffing 
box where the shaft enters the case the 
particular point of trouble. Sixty de- 
gree acid rapidly destroys rubber, or 
flax, or any of the ordinary flexible ma- 
terials used for packing. Many metallic 
packings and combinations of metals 
with the flexible materials have been 
tried with indifferent success. Special, 
and often highly ingenious glands have 
been devised but so far as the author 
knows, all of these leave much to be 
desired. 

A centrifugal pump which approaches 
the problem from a different angle has 
been put into use during the past three 
or four years and appears to be very 
satisfactory. This is a pump with a 
vertical shaft. The whole pump is Fro. 34. 

placed in the tank from which the 

acid is to be pumped or in a boot connected with it. The 
shaft extends a short distance up above the top of the tank or 
boot and is driven by a belt or direct connected motor. The 
stuffing box trouble is entirely sidestepped. This pump is 
shown in Fig. 34. One of these pumps working in 60° acid has 
been under the author's personal observation for more than 



^dbvGooglc 



128 AMERICAN SULPHURIC ACID PRACTICE 

a year, during which time not a cent has been expended for 
repairs. To give an idea of power consumption, it may be said 
that one of these pumps equipped with a 5 H.P. motor elevates 
about 250 tons 60° acid per 24 hours to a height of about 90 ft. 
The vertical pump has no particular advanta|;e of course, over 
the horizontal pumps in the matter of power. 

The pipes used for conveying acid from one part of the appa- 
ratus to another are mostly of lead. They are joined together 
and to lead tanks by burning. When lead pipes are joined to 
iron apparatus or when the joints are not permanent as in case 
of valves, iron flanges are used. The method of making a flanged 
joint is shown in Fig. 35. Oval flanges with two bolts are 
suitable for small pipe, but for larger sizes, 2-, 3-, 4-in. or larger, 
the 4- and 6-hole circular flanges are better. 




Iron pipe is very successfully used in certain places in an 
acid plant. For example, the lines carrying 60°B4. acid from the 
eggs or centrifugal pumps to the tanks at the tower tops can 
much better be of iron than of lead. These lines often have to 
sustain pressures of 75 to 90 lb. per sq, in. If they are of lead, 
they gradually swell and grow thin and sometimes suddenly 
split open and deluge a large area with acid. Iron pipes, partic- 
ularly extra heavy iron pipes, last for years in this service and 
when they do fail they give ample warning by first showing 
minor leaks. They are best made up with flanged joints using 
lead gaskets, so that any piece may be replaced without taking 
down a long run of pipe. Turns should be made by bending the 
pipe in fairly long radius arcs instead of using fittings. Another 
advantage which iron pipe possesses is its superior rigidity. 
Lead pipe is likely to be badly shaken and eventually cracked by 
the blow off of eggs, while iron pipe can be very securely bolted 
to framework to prevent such shaking. 



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ACID CIRCULATION 



129 



As the dischai^ lines from eggs or centrifugal pumpe deliver 
acid at rather high velocity, provision must be made at the 
points of delivery to prevent splashii^. This is done by nmnii^ 
the pipes into splash eggs or covered boots as shown in Fig. 36. 
If the form shown in sketch A is used, it can well be made of cast 
iron. 

It is necessary to have some method of knowii^ how much 
acid each top tank has in it, in order that the pumping may be 
done at proper times and the flows maintained. Three schemes 
of merit are in use, viz., floats, pneumatic indicators and electrical 
indicators. 

In the float system a hollow lead float rests on the acid in 
the tank and has fastened to it a chain or cable or wire which 
runs over pulleys to a convenient point near the pumps where 






r ' Tank 



HJ 



it is fastened to a weight running on a graduated board. As 
the acid rises and falls the float moves the we^ht up and down 
and indicates the level. This works well enough but it is rather 
cumbersome. 

In the pneumatic scheme a bell or pot is set on the bottom of 
the tank. A small bore metal tube is connected to it and runs to 
a mercury gauge at the desired point. A compressed air line 
or a small air pump communicates with this tube. Air is admits 
ted to the tube until all the acid is blown out of the latter and 
out of the bell in the tank and then shut off. The head of acid 
in the tank then compresses the air in the bell and the tube 
and the pressure exerted is indicated in the mercury gai^ which 
ifi graduated to show the stage of acid in the tank. Absolute 
tightness of this apparatus is imperative as the most minute' 
leak renders it unreliable. 

Electrical indicators are simplest and best. An ordinary direct 
or alternating light circuit is employed. Lead rods of varying 
lengths are hung in the tank to be indicated. An incandescent 
lamp on a board is provided at the desired point of observation 



^dbvGooglc 



130 



AMERICAN SULPHURIC ACID PRACTICE 



to corrcBpond to each. One side of the light circuit is connected 
to one socket terminal and the other side to the lead rod. The 
metal of the tank is connected with the other socket terminal. 
When the acid in the tank is in contact with the lead rod the 
current flows through the acid and lights the lamp. When the 
acid falls below the rod, the circuit is opened and the light goes 
out. It is customary to use at least two rods and lights to each 
tank or as nutny levels as desired can be shown by usii^ more. 
It is a good plan to provide a bell or horn connected to all the 
tanks to call attention to any tank which is in danger of 
overflowing. Figure 37. 



HOVUghi-ari 




DISTRIBnTIOIl 

The fundamental purpose of the towers, both Glover and Gay 
Lussac, is to bring acid and gas into as intimate contact as 
possible. This makes it necessary to distribute or sprinkle the 
acid over the entire area of the tower packing as uniformly as 
possible so that in flowing down through the tower the surfaces of 
the packing material may be covered with a constantly changing 
film of the acid- There are two general methods of doing this. 
One of these divides the total acid stream into many small 
streams before entermg the tower tops and introduces each 
stream through a small pipe, or opening. The other plan is to 
divide the total acid stream into a few comparatively large 
portions which are further broken up and distributed inside 
the tower by spray nozzles or splash plates. The former method 



^dbvGooglc 



ACID CIRCULATION 



131 



is older and probably more used than the latter. It works 
very well if the acid ia clean and the tower small. In some 
of the large imite built in this country in recent years, the towers 
have such great areas that the first described plan involves a 
tremendous number of feed pipes and the second method is more 
suitable. 

There are many ways in which the division of the acid and 
introduction into the tower can be accomplished. Two of these 
are shown in Figs. 38 and 39. In Fig. 38 the acid is delivered 
into a central compartment A. Around A are small compart- 




Fios. 38 and 



ments B, from each of which a luted pipe runs to some point in 
the tower top. Acid overflows from A into B over lips on the 
partition. These lips are all dressed to the same level so that 
equal volumes of acid Sow over all. This apparatus is made of 
lead and may of course, be square or rectangular or any desired 
shape. 

In Fig. 39 the internal compartment is omitted, the acid 
being delivered into the shallow pan from which the small pipes 
run directly to the top of the tower. These pipes project up 
into the pan an inch or two and are covered by cups whose lower 
edges are notched. The equal distribution of the acid depends 
upon having each of these upstands precisely level and exactly 



^dbvGooglc 



132 



AMERICAN SULPHURIC ACID PRACTICE 



the same height. This is a difficult thii^ to determine and 
maintain and this apparatus is consequently not to be recom- 
mended. In any form of distributor box the individual streams 
should be in s^ht at all times and any inequalities 
easUy corrected. 

With either of these arrangements or any similar 
ones, the small streiuns of acid simply trickle down 
into the tower and on to the packing. Some de- 
signers consider it essential to provide one of these 
small streams for each square foot of packii^ area, 
i.e., for a tower 10 ft. X 10 ft. there would be 100 
small streams. Other designers consider one strefuu 
sufBcient for 6 or 7 sq. ft. It can be appreciated 
that if one pursues a middle course in the matter, 
the number of individual pipes required for a lai^ 
tower of say 250 or 300 sq. ft. area, is very great, costly to 
install, and rather troublesome to keep in 'order, especially if 
the acid carries some sediment. 

The second described general method of distribution, i.e., 
by introducing a few comparatively large streams which are 
sprayed out inside the tower, has much to recommend it. The 
original division of the main stream of acid can be carried out in 



(* 


■^ 


f\J 








-T^S- 


Jl. 


^■-'■"^ ^^«.^ 












"••-...••••A 






II II y g II n II 1 II 

Etcvdtion 




Co0e Ploh! A-A 



much the same way as shown in Fig. 3S. The secondary com- 
partments are much fewer in number. Each pipe enters the 
tower top through a luted opening and has burned to its end a 



^dbvGooglc 



ACID CIRCULATION 133 

spraying device. The simplest of these devices is the splash 
plate as shown in Fig. 40. This is a casting of hard lead. Other ~ 
more elaborate spray nozzles of acid resisting material are also 
suitable. Such sprayers can be depended upon to quite uni- 
formly distribute acid over a 4- or 5-ft. circle, at a distance of 
4 ft. below the nozzle. At 6 ft. below the nozzle they will spray 
a 6- ft. circle. It is important that each pipe should or^nate 
in an individual compartment so that if an obstruction occurs 
in any sprayer it will be immediately known by the correspond- 
ing compartment filling up. The nozzle can than be withdrawn 
through the luted hole and cleaned. The distribution' afforded 
by such an arrangement is even better than that given by the 
multiple pipe scheme, and it is obviously much simpler, and 
cheaper to build and less trouble to keep in order. Figure 41 
shows a convenient layout embracing the described features and 
including a gauging compartment. 

INTRODUCTION OF WATER INTO THE CHAMBERS 

While this subject does not properly come under acid circula- 
tion, it may well be discussed at this point. 

Water is put into the chambers as steam or as finely divided 
liquid. If there is available to the plant an unused supply of 
e^aust or by-product steam, or if there is no fairly pure water 
available, it is proper to use steam in the chambers. Otherwise 
atomized water should be used becai^e it is better for the acid- 
making process and it involves no fuel expense. The only cost 
is for driving a very small pressure pump. 

When steam is used it is ordinarily introduced at two or three 
points in the top of each chamber, more rarely at a point in the 
front end wall. A convenient arrangement is to run the steam 
main under the floor of the working aisles and to carry up one or 
two risers alongside each chamber to the top where they run in to 
the points of introduction. A cock or throttle valve is placed in 
each riser 4 ft. above the working floor. A pointer mounted on 
the wrench or handle swin^ in front of a graduated arc and 
enables the operator to judge how much of a change he is making 
when it is necessary to change the flow. Iron pipe is used to 
carry the steam to within 2 or 3 ft. of the point of admission to 
the chamber then a lead pipe is flanged to it, bent to form a trap 
and its end burned into the chamber. Low pressure steam even 



i,z.dJvCo(>glc 



134 



AMERICAN SULPHURIC ACID PRACTICE 



BO low as 2 or 3 lb, can be used, but the pressure should be 
uniform at all times. 

In using liquid water, the introduction is done through many 
small nozzles rather than through two or three large ones. There 
are two reasons for this. One is that control of the amount of 
water admitted into a chamber is accomplished by completely 
opening, or completely closing a number of the supply pipes. 
The other that even well atomized water does not spread out 
into a very large voiiune of the reacting gas and so the sprays 
must be numerous to assure each portion of the chamber of its 
proper amount of water. 

The spray nozzles used in this country are made of hard 
lead with platinum liners, or of stoneware or glass. The former 




are much more expensive than the latter thoi^h they usually 
last much longer. With platinum prices where they now are, 
one can buy eight or ten stoneware or glass nozzles for the price 
of one platinum nozzle. The principle used in all nozzles is to 
produce a swiri in the water stream just before it leaves the 
orifice. This is done in several ways, two of which are illustrated. 
When working properly the water issues in a cone shaped sheet 
which breaks into innumerable small drops. Figure 42. 

As all the passages in these nozzles are small, the areas rang- 
ing up to 1 sq, m.ra., it is essential that the water entering the 
nozzles be very free from solid impurities or they soon become 
plugged up. The water should not carry more than small 
quantities of salts in solution because when a nozzle is not used 
for some hours the water remaining in it evaporates and salts 
deposit and choke it. 



^dbvGooglc 



ACID CIRCULATION 



135 



Pressures used on this equipment are usually around 60 lb. 
per sq. in. at the nozzle. It ie important that the pressure 
what-ever it may be shall be kept uniform within a few pounds. 

There are two or three manufacturers in this country who have 
made up excellent combinationB of apparatus for filtering and 
pumping water for chamber sprays. Figure 43showB the arrange- 
ment of an individual spray nozzle with cock and strainer, lute, 




etc. The water is filtered through sponges and uniform pressure 
maintained in the Unes by an electric plunger pump with relief 
valve. In addition to this it is advisable to use a strainer as 
shown just proceeding each individual nozzle to catch any pipe 
scale or anything that escapes the main filter. In cold weather 
when there is danger of the small spray lines freezing, a steam 
pipe leading into the supply tank wanm the water. 



^dbvGooglc 



CHAPTER XII 
INTRODUCTION OF ITTTRE 

The recovery of the nitre in the chamber process is never 
complet«. The average loss is probably from 3 per cent to 
4 per cent (96 per cent NaNOs) of the sulphur in the acid actually 
produced. It is necessary then to introduce into the plant 
per 24 hours from 15 to 20 lb. of new nitre for each ton of 60° 
acid produced. 

While it is the custom to speak of introducing "nitre," the 
thing actually wanted and done is to introduce into the gas 
mixture the gaseous oxides of nitrogen. This is done in two ways. 
The first and probably most frequent is to decompose sodium 
nitrate by sulphuric acid and heat in cast iron pois placed in a 
flue between the furnaces and the Glover Tower, The heat of 
the furnace gases is depended on to produce the reaction. Some- 
times the nitre pots are placed in brick settings alongside the 
gas flue and heat is supplied by means of coal fires beneath them. 
The nitric acid vapor is led immediately into the gas Sue however. 

The other plan is to make liquid nitric acid in a separate 
plant and introduce it into the top of the Glover tower. 

In either case the chemical reactions and the end results are 
the same. The reactions which take place in the nitre pot 
whether it is in the gas flue, in a separate setting or in the nitric 
acid plant are these: 

NaNO. + HtSO* = NaHSO* + HNOi 
2NaN03 + HjSO* = NajSO* + 2HN0j 

The nitric acid comes oS as a vajwr. The acid sodiimi sulphate 
and normal sodium sulphate remain in the pot as a liquid mass 
and are tapped off from time to time. If the pot is in or near 
the gas flue the nitric acid vapor mingles with the hot burner 
gas and reacts with it substantially as follows : 

2HN0, + 3S0, + 2H»0 = mSO* + 2NO 

In the nitric acid plant the nitric acid vapor is cooled suffi- 
ciently to condense it to hquid HNOg. This when introduced 



^d by Google 



INTRODUCTION OF NITRE 



137 



into the Glover tower is reacted upon In the same way, i.e., 
HtSOt and NO are formed. 

Nitre pots are used in the gas Que and are of very simple design. 
They are generally of rectangular shape, open at the top and 
have a spout at one end for tapping off the nitre cake. Figure 
44 shows a conventional dee^. These potB have capacities 
ran^ng from about 3 to 4 cu. ft. up to 20 cu. ft. Larger sizes 
become difficult to handle when they break and have to be re- 
placed'. The small sizes accommodate 25 to 50 lb. chaises and 
the larger up to 200 lb. The thickness of metal is from 2 to 4 
in. The matter of materiid is somewhat puzzling. Some foun- 
dries claim great superiority for their special cast iron formulas. 



JEL 



=£ 



. n n. 




I have seen pots of these special irons, which also cost a special 
price, give very poor service, and some have very long lives. 
The same can be said of pots made of good ordinary cast iron by 
local foundries. Probably design and care in pouring have aa 
much to do with the life of a pot as special metals. Pots usually 
fail by cracking or goii^ through flaws rather than by actual 
corrosion. 

The number of pots which should be provided varies with the 
size of the unit somewhat, but should be never less than two and 
preferably more. 

This on account of the desirability of having as nearly uniform 
evolution of nitric acid vapor as possible, and to carry over the 
periods of changing a broken pot for a new one. If the unit is of 
50 tons 60° capacity, the normal amount of nitre introduced per 



^dbvGooglc 



138 AMERICAN SULPHURIC ACID PRACTICE 

24 hours will be from 750 to 1,000 lb. There will be timee when 
more than that will have to be potted for a few hours so it will 
be well to have pot capacity to introduce at the rate of 2,000 
lb. per 24 hours. Two hours per charge is the minimum 
time which should be allowed for the decomposition of the size 
charges ordinarily used. If therefore two pots are provided each 
should be able to handle 1,000 lb. per 24 hours in 12 chains or 
83)^ lb. per charge and should have a volume of about 10 cu. 
ft. If three pots are provided they should be of 7 cu. ft. volume 
or if four pots of 5 cu. ft. volume. 

The pots are supported well above the bottom of the flue on 
beams, in order that the hot gas may play freely around them. 
The spout extends out through the wall a short distance. If the 
pots are small and the span for the beams is not long ordinary I 
beams are used for support and last very well. In case large 
pots are used and the flue is 10 or 15 ft. wide, deep cast channels 
filled with reinforced concrete stand up splendidly. 

Chai^ng of the pots with nitre and acid can be done from top 
of the flue or from the side. In many respects charging from 
the top is more satisfactory. It does away with the rather 
laborious handling of a heavy loaded charging ladle and it puts 
charging and tapping at different levels which is desirable. If 
both operations are done on the same floor the cake pans or 
laimders are most inconvenient to work over. The nitre is put 
into the pot through a cast iron pipe with bell top if the chai^ng 
is done from the top. If the charge opening is in the side of the 
flue a lai^ scoop or ladle with a sufficiently long handle is used. 
The acid is fed in from a measuring pot or box throi^h a heavy 
cast iron pipe. The special high silicon irons and also fused 
silica are being used for these pipes of late as even a heavy cast 
pipe does not last long. Figure 45 shows an arrangement of nitre 
pots in a flue. 

The nitre cake is usually tapped off into shallow pans, allowed 
to cool and harden, then broken up and removed. When condi- 
tions permit and there is no use for the nitre cake, a simple means 
of disposal is to tap into a launder in which a stream of water runs, 
when the molten cake dissolves and is flushed away. Several 
ways have been devised for closing the spout after the charge 
has been tapped. A plate and screw clamp is sometimes used. 
Or the end of the spout is machined out to take an iron plug. 
Sometimes wooden plugs are used. If the spout is loi^ outside 



^dbvGooglc 



INTRODUCTION OF NITRE 139 

the flue a ball of mud will be sufficient. It is well to use a scheme 
which does not depend too much on machined Biu^aces for 
tightness. 




POTTING WITH FUEL 

While the general features of the method just described, i.e., 
in placing nitric pots In the flue and utilizing the heat of the SOi 
gas to effect the decomposition of the nitre, would seem the best 
and most economical possible arrangement, it has some drawbacks 
which are so annoying that many acid plants are now equipped 
with nitre pots in independent settings and fired with fuel. 
When this plan is used the operator can have at all times just the 
degree of heat he wishes to decompose his nitre. If the process 
has become badly disturbed by some breakdown or stop he 
can decompose the extra nitre the emergency demands and get 
into normal condition quickly. The weakness of the flue potting 
lies in the fact that just at those times when an unusually lai^e 
amount of nitre should be potted the flue is eold, e.g., when start- 



ed byCoOglc 



140 AMERICAN SULPHURIC ACID PRACTICE 

iu^ up the plant after a shutdown or when any unusual occurrence 
disturbs the flow of hot furnace gas about the nitre pot«. In 
choosing between Sue pot and independent pots the source of the 
SOi must be regarded. If the sulphur supply is in the form of a 
uniform high-grade pyrites which will make a hot gas and allow 
long campaigns with the roasting furnaces, flue potting is quite 
proper. If the gas is cold or if it is an unreliable metallui^cal 
by-product gas, independent fuel fired pots probably are meet 
economical. Fuel cost is not a very important consideration as 
with well designed settings a ton of ordinary soft coal will decom- 
pose 3,000 to 4,000 lb. of nitre. 

The best form of pot for fuel fired settings is shown in Fig. 46. 
This is a modem retort such as is used in nitric acid work. It 
is simple and- strong and is a design which has been very generally 
adopted of late years. 




An ingenious plan used in connection with fuel-fired pots is 
used at the works of the Tennessee Copper Co. The retorts are 
substantially standard nitric acid casting as shown in Fig. 46. 
The nitre is fed in continuously by means of a conveyor and at the 
same time the proper amount of sulphuric acid for decomposing 
it is run in. Both nitre and acid may be varied as desired to 
meet the demands of the acid process. When a retort is filled 
up to a certain point with fused nitre cake it is tapped. There 
are several retorts in the battery and the introduction of nitric 
acid vapor into the flue is continuous. This arrangement is 
described in an article by A. M. Fairlie in Chemical and Met- 
allurgical Engineering of September 25, 1918. 

At some sulphuric acid works Uquid nitric acid is made in a 
separate plant and tile nitric acid is introduced as needed into 
the Glover tower. A comparatively recent modification of this 



^dbvGooglc 



INTRODUCTION OF NITRE 141 

scheme is to make instead of straight nitric acid, mixed acid, 
i.e., a mixture of nitric and sulphuric acids. 

In either case the nitre retorts are the same and are about aa 
shown in F^ 46. Other forms of retort and setting are to be 
found in some of the older plants, but the larger and more en- 
lightened manufacturers of nitric acid seem to have come to the 
conclusion that the form shown is most satisfactory. 

In making straight nitric acid the condensation of the vapor - 
to liquid is effected in what ia known as the Hart condenser. 
It consists essentially of a pair of upright manifolds of stoneware 
or high silicon iron with glass tubes between them. The glass 
tubes are cooled by trickling cold water over them. The final 
condensation of nitric vapor and recovery of the most of the 
lower oxides of nitrogen is done by passing the gases through 
several stoneware towers in series. A counter current stream 
of water, then weak nitric acid is advanced over the towers. The 
liquid nitric acid made is received and stored in glass or stone- 
ware vessels. It is possible to use with fair success iron or lead 
tanks if only strong nitric acid be put into them and if they are 
kept tight from air leakage. The high silicon irons can be used 
with success for containing nitric acid of any strength. 

The nitric acid made in this way is conveyed to the top of the 
Glover tower sometimes by elevating the glass carboys containing 
it, sometimes by pumping it up through stone or special iron 
pipe lines. More rarely it is mixed with sulphuric acid and the 
mixed acid then handled in any apparatus suitable for sulphuric 
scid. This mixing of nitric and sulphuric acid must be done in a 
closed vessel provided with eoolii^ coils as it fumes badly 
otherwise. 

The handling of straight nitric acid especially in lai^e quanti- 
ties is rather troublesome and this fact led to the development of 
the plMi of making mixed acid directly, which will now be de- 
scribed. Mixed acid as mentioned can be handled in lead or iron 
apparatus with very little more wear and tear than straight 
sulphuric acid causes. 

The plant for making mixed acid directly consists of retorts 
similar to those used when making stra^ht nitric acid. The 
nitric acid vapor issuing from them is conducted through pipes 
of silicon iron into a small tower of acid-proof masonry construc- 
tion paclsed with acid-proof bricks or shapes, over which cold 
sulphuric acid of 60°B& or higher strength is circulated. The 



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142 



AMERICAN 8ULPHVRTC ACID PRACTICE 



nitric acid vapor is condensed and a warm mixture of nitric and 
sulphuric acids issues into a cooler whence it is pumped up and 
&g^m introduced into the tower. The operation is exceedingly 
simple and gives a high recovery. The product containing up to 
20 per cent HNOi is contained and pumped in lead apparatus. 
Its volume is such that it is very nicely controlled in introducing 
it into the Glover tower. The Fig. 47 shows an installation in 
which 4,000 lb. of nitrate of soda is comfortably handled in an 
eight hour shift. The fuel used amounts to about 900 lb. ordi- 




nary bituminous coal per ton of nitre. The recovery is 96 per 
cent or better. Some of these plants have been operating at 
least 3 years. Except for charging the retorts the operation is 
conducted by one man. 

In the writer's opinion this last described method is the most 
satisfactory and economical way of handling the matter of getting 
the nitre into the chamber process. 

It should be mentioned that a water solution of nitrate of soda 
is used to a limited extent in the Glover tower and in the cham- 



^dbvGooglc 



INTRODUCTION OF NITRE 143 

bers as a meauB of nitre introduction. It ia a plan which has the 
serious disadvantage of fouling the acid with sodium sulphate: 
if the acid is to be used for the manufacture of fertilizer this is no 
particular drawback. If more than a small proportion of the 
total necessary nitre is put into the Glover tower as a regular 
procedure in this way it very soon makes trouble in that pipe 
lines and valves become obstructed and the tanks and coolers 
fill up with it. As an emei^ency measure to tide over a few days 
when for some reason the regular source of nitrogen oxides is out 
of commission a solution of this kind can be used in the Glover 
without serious results. Certainly though a few days is the 
limit. If the solution be Introduced into the chambers and the 
chamber acid is drawn off for use in making acid phosphate or 
some other use in which sodium sulphate is not objectionable, 
very little trouble results. In any event it is unusual to use a 
nitrate solution as anything more than as in an auxiliary, or a 
temporary way of putting nitrt^n oxides into a chamber system. 

ITO FROM AHHONIA OZIDATIOD 

About 30 per cent of the European acid plants are supplying 
the oxides of nitrogen to their chambers by oxidizing ammonia 
and introducing the gas. So far but one plant in this country, 
that of the American Cyanimid Co., at Warners, New Jersey, has 
used this process, which gave them splendid results. It is not 
in operation at the present time, as nitr<^n from Chile saltpeter 
costs less than from ammonia now. 

In January, 1919, the British Ministry of Munitions issued a 
booklet on " The Oxidation of Ammonia Applied to Vitriol Cham- 
ber Plania," This is the most complete publication on the sub- 
ject, and I will quote from it very freely. 

Mr. W. S. Landis, of the American Cyanimid Co., has furnished 
the following information regarding their New Jersey installa- 
tion. 

In their process of oxidation the platinum gauze is heated by a 
current of electricity, instead of depending upon the heat of the 
reaction entirely. Of course the current costs money, but the 
operation is so free from trouble of any kind, the labor reqviired 
practically negligible, and the product so uniform, that opinion 
differs as to the best practice. (Though it will be noted in all 
(so far as I know] reports on this subject that when results have 



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144 



AMERICAN SULPHURIC ACID PRACTICE 



been wanted electrical heating of the catalyzer was practiced.) 
At Wameis an oxidation unit was set up under each chamber, 
and the operator looked in as he went by. The gas was con- 
trolled by a 2-in. valve, and the plant ran steadUy, with no ad- 
iustment.be]n>nd change of quantity of NO made, as the condition 
of the chambers demanded it, which adjustment simply meant 
open or close the 2-in. valve. 



Bactricat Cfr>r>ejf»iti_ 




'Cataliit Unit FnarK 



Outside of the ease of operation, stronger acid may be made. 
Both denitration and nitre pottii^ absorb heat, which, if not 
required for other purposes, may be utilized in the Glover to 
concentrate. At Warners this was done. The nitric oxides from 
the converters were fed to the Glovers, all the heat that was 
B^ved from the pottii^ went to concentrating, and the result 
was a constant return of 61°B£. acid, which often, forloi^perioda. 



^dbvGooglc 



INTRODUCTION OF NITRE 145 

stayed up to 62°, and occasionally reached 62,5° — with complete 
denitratioQ — which is pretty fair chamber acid. 

A patent on this subject, TJ. S. Patent |1,173,524, was issued 
on Feb. 29, 1916. 

It is necessary to introduce the mtric acid through the roof of 
the Glover or chamber, as otherwise the acid, running down 
the side walb will quickly destroy the lead. 

The British Ministry of Munitions standard converter consists 
of an upper and a lower cone, of aluminiun, the small ends of the 
cones being flanged to the inlet and outlet pipes, the large ends 
also being flanged, but to the catalyzer frame. The internal 
section of the catalyzer frame, was about 4-in. X 6-in. (that at 
Warners was larger), and was simply a pair of aluminum flanges 
between which the platimun wire, gauze-wire being 0.065 (.003") 
in. mm., square mesh, 80 mesh per inch — was held in place and 
insulated by mica and asbestos. The English used two gauzes in 
each frame, held apart by silica rods, the lower gauze alone having 
silver terminals. When electric current is not used to heat the 
gauze, three or four gauzes are necessary. 

Ninety per cent to 95 per cent efficiency of oxidation will be 
attained without electric heating of the gauze, and 98 per cent 
with the current. 

The capacity is 1.5 tons of HNOj per square foot of converter 
cross sectioQ per 24 hours. 

The aluminum used in this construction must be very pure; 
and either mica or clear silica must be used for the peep holes. 

The catalyst container must fit tight. Any air leaks may be 
luted with a mixture of asbestos powder and thick water glass. 
Allow this paste to set before heating the catalyzer. 

The following precautions are essential in handling the catalyst : 

1. Great care should be taken that the platinum gauzes are 
absolutely clean. They are boiled in pure concentrated hydro- 
chloric acid and rinsed in distilled water before fitting, and should 
on no account be touched with the fingers afterwards or otherwise 
soiled. 

2. The box containii^ the catalyst as sent from the makers 
should not be opened except immediately before fitting. 

3. Fitting should be done in a clean room free from dust, not 
on any account in a workshop, and the fitter should have clean 
hands and clothes. 

4. It is essential that the greatest possible care be taken to 



^dbvGooglc 



146 AMERICAN SULPHURIC ACID PRACTICE 

keep the gauzes clean while the catalyst unit is being fitted to 
the converter. If the completed converter Ib not at once con- 
nected to the inlet and outlet pipes, the apertures of the lower 
cone and bend pipes at the top should be closed with corks to 
keep out dust until this is done. 

As the electrical resistance of the gauze is low, the current must 
be low voltage, but high in amperage. The maximum, or start- 
ing, current for a 4-in. X 6-iii. gauze is 12 volts, 300 amperes. 

The mixture of air and ammonia may be supphed to the con- 
verters in either of two ways: 

1. By producing air and ammonia gas separately, and mixing 
them in the proper proportions — 1 vol. NH| to 7.5 vols, air — in 
an aluminum mixii^ chamber, with tangential inlets and baffle- 
plates. 

2. By passing a stream of air throi^h aqueous ammonia in a 
suitable apparatus. 

The second method is by far the better, and will alone be 
described. 

Purified ammonia liquor, 20 to 25 per cent. NHj, "free from 
sulphur," is the source of the anmionia. It is fed at the proper 
rate to an ammonia still, and there met by low pressure steam 
blown in at the bottom, cither directly or through coils, and a 
current of air. Anmionia gas is hberated, mixed with the right 
proportion of gas for oxidation, and if the top of the column is 
kept cool, the gas is fairly dry. Moisture has no influence upon 
the oxidation, but is liable to condense in the filters and impair 
their efficiency. Iron pipe, fitted with red lead and oil, may be 
used up to the filters. 

This still should work imifonnly and with little attention, and 
not be liable to breakdowns. It should have a low steam con- 
sumption, which depends upon its being kept hot below and cool 
above. It should deliver ammonia, or air and ammonia, at a 
definite rate. 

The kind of ammonia available and the amount required will 
of course influence the design. 

Where the amount required is small the ammonia may be 
generated by boiling mnmonium sulphate or ammonium chloride 
with milk of lime in an iron boiler with a reflux cooler, with a 
small balancing gas holder between the boiler and the converter. 
This method would be useful at coke ovens or gas works, where 
such salts are by-products. It has the additional advantage 



^dbvGooglc 



INTRODUCTION OF NITRE 



147 



that the ammonia is pure, as there is no Bulphur. On a large 
scale ammoniacal liquor is more economical. Gas liquor should 
not be used directly, because of the impiuitiea. 

An ammonia still of Brunner, Mond & Co. is shown (Fig. 49). 
Purified ammonia liquor of 25 per cent is run in at such a speed 




that the top compartment is kept at 8 per cent to 9 per cent 
ammonia, and 20° to 22°C. The bottom compartment is heated 
to 95" to IWC. to exhaust the ammonia. Air is passed at the 
proper rate, and Che mixture through a slag'wool or glass-wool 



^dbvGooglc 



148 



AMERICAN SULPHURIC ACID PRACTICE 



filter. A little Bteam is neceesary in the filter before the con- 
verter to avoid condensation. 

The United AlkaU Co. replaces the bubbling tower with a tall 
coke tower. Steam and air are introduced as before, but ammo- 
nia liquor ia introduced at a point two-thirds up the tower. The 
upper portion of the tower thus act^ aa a cooler and gas filter, 
and no further filtration b necessary. This is also shown 
(Fig. 50). 

*- I Liqijorfrom 

'Armonlarank 
, — ^Ghiios 
.Iwim Nrchvl Savrv 
,ibrfr/Mrirff 




Air pressure depends upon the type of apparatus used, but 
should not f^ below 5 lb. per sq. in. The air must be pure and 
free from dust; if the plant is near sulphur burners of any kind 
the wr must be purified by passing through a lime box. There 
must be an oil trap after the blower. The air must be metered — 
the Builders' Iron Foundry, Providence, Rhode Island, furnishes 
good meters. After filtration iron pipes must twt be used — 
aluminum, stoneware, or glass. The glass-wool filtering mediiun 
will probably need renewing every month, as it fills up with dust. 
Moisture can be kept out by introducing a httle steam to prevent 
condensation. 

The apparatus is started by switching on the ciurent and heat- 
ing up the gauze to visible redness. The mixture of ur and 



^dbvGooglc 



INTRODUCTION OF NITRE 149 

ammonia is then admitted at a bIow rate, until the catalyzer ia 
uniformly dull red hot (650°C.), then the rate is increased to the 
maximum, the current being rejjuced as necessary. Very little 
further attention is required for weeks of running. If the gauze 
gets too hot the heating current, or the proportion of ammonia 
in the mixture, of both, should be reduced. 

When electric heating is not used the plant is started by heating 
the gauze to redness with a hydrogen flame, turning on the air 
and ammonia mixture full, and removing the flame, after which 
the window is bolted into place. 

New platinum gauzes are somewhat inactive, and should first 
be ' activated" by passing at a fairly slow rate a mixture with an 
excess of oxygen, say, 1 vol. NHj to ten vols, air, and putting on 
full current till the gauzes are heated BRIGHT red (800° to 
OOCC). After an hour or two the platinum becomes activated, 
and the white fumes of ammonium nitrite and nitrate leaving 
the converter (after cooling) change into clear red fumes of 
oxides of nitrogen. When this occurs the current is reduced 
and the ammonia brought up to the ratio of one to 7.5 air. 

If electrical heating is not used, start with the ordinary gas 
mixture. 

If spots show on the heated gauze and do not disappear rapidly, 
the catalyzer must be taken to pieces, the gauze boiled in pure hy- 
drochloric acid, and the catalyzer reassembled. If the gauzes heat 
up unevenly it is usually a sign that the wire is too small, and the 
unit must be replaced. If in the activation any unevenly heated 
places are left they will take a long time to finally become active. 

The gases leave the converter at about 400''C.. They consist 
of NO, steam, nitrogen, and a shght excess of air. The converter 
reaction is as follows: 

4NH, + 50, = 4N0 + 6H,0. 

At this temperature the gas is colorless, as the secondary oxida- 
tion of NO to NOj has not begun. 

The gases may be used with or without cooling. 

Without cooling, the gas is conveyed through a lagged alumi< 
num pipe, or if slightly cooled through a stone-ware pipe, to the 
Glover tower, chamber, or dust catcher of the system. The 
temperature must stay high enough to prevent water condensa- 
tion in the main. There must be no pressure poasibiUties that 
burner gas could back up, in case of breakdown. 



^dbvGooglc 



150 AMERICAN SVLPHVRtC ACID PRACTICE 

If the burner gas does back up to the gauze it will rapidly 
become poisoned, and will have to be removed and boiled in 
hydrochloric acid. Therefore it is better to have the gas enter 
at a point where there is a slight suction, as in the Glover tower. 

If the gaa is cooled it is passed to a condensing cooler, where 
about 70 per cent of the water produced in the reaction is sepa- 
rated. If the cooUng is performed sufficiently rapidly the con- 
densate will contain from 1 per cent to 5 per cent of the total 
oxides of nitrogen as nitrous and nitric acid, aad any trace of 
ammonia (0.05 per cent to 0.25 per cent) which may have escaped 
oxidation. This is the result from a very efficient cooler-up 
" to 25 per cent of the oxides of nitrogen may be in' the condensate. 
The cooler may consist of a silica spiral, connected directly with 
the bend on the converter hood, by suitable asbestos packing, 
and cooled by water. A spiral of 10 turns of fused silica S-pipes, 
the turns 2'-0" in diameter, the pipe Ke-in- thick and IJ^-in. 
in diameter, will do the work. The condensate may be collected 
in a stoneware WoulfE's bottle, and then drawn off to the Glover's; 
or it may run direct to the Glover. 

The cooled gases, at about 30° to 50''C., now brown with oxida^ 
tion from NO to NOj, pass through stoneware pipes with a 
stoneware stop cock if desired, and with down pitch towards the 
point of entry, to the chamber system. 

Remember that hot gases may cause warping at the point of 
entry, and provision must be made for it. 

An advantage of using a cooler is the better analjrtical check 
on the process. Tests on the condensate for unconverted am- 
monia should be made from time to time to cheek up the working 
of the converter. 

If there is more than one Glover to be supplied it is better to 
have a small independent converter for each, rather than have one 
larger one try to supply several, as uniform distribution is very 
difficult to get. 

The accompanying table shows the quantity of ammonia that 
must be oxidized to replace any given quantity of nitre (NaNOj). 
If the consumption of nitre varies the converter may be run 
below capacity — it may be run down to 25 per cent of capacity 
at 100 per cent efficiency, and will run well at 15 per cent. One 
of the great advantages of this system is its uniform running, 
and this should be taken advantage of if possible, by keeping the 
rest of the plant going at a imiform rate. 



^dbvGooglc 



INTRODUCTION OF NITRE 
Table 5 





Metric tone of H,80, 


Grama of ammonia required per hour, if 


Sulphur 






burned 


day of 24 hours 


of the sulphur burned, per cent 


Tons 
per day 


05% plant 
efficiency 


98% plant 
efficiency 


0.5% 


... 


2% 


2.5% 


3% 


.265 


.77 


.702 


10 


20 


40 


GO 


60 


.53 


1.65 


1.584 


20 


40 


80 


100 


120 


1,06 


3.1 


3.17 


40 


80 


160 


200 


240 


2.12 


6.2. 


6.35 


80 


160 


320 


400 


480 


6.6 


19.25 


19. S 


250 


500 


1,000 


1,250 


1,500 


15.85 


46.2 


47.5 


600 


1,200 


2,400 


3,000 


3,600 


26.4 


■77.0 


79.2 


1,000 


2,000 


4,000 


6,000 


6,000 



Up to 3,000 g. NHi per hour, use 1-4-in. X 6-in, converter. 
Above 3,000 g. NH» per hour, use 2-4-in. X 6-in, converter. 



The analj^cal control of oxidization of ammonia is of the utmost 
importance, and considerable difficulty. With the methods 
here given the efficiency of any particular converter cannot be 
determined closer than 3 per cent. This is sufficiently accurate 
for works operations. 

Determination of Ratio NHa:Air before oxidation 

The method consists in aspirating a known volume of the air- 
ammonia mixture through a sufficient quantity of standard 
sulphuric acid colored with methyl orange or cochineal, contained 
in a wash bottle connected with an aspirator. A Winchester 
bottle of water is placed between this and the aspirator, just to 
equaUze the gas pressure in the inlet tubes to the converter, so 
that no gaa bubbles through the acid until the aspirator is 
started. 

The quantity of acid is sufficient to neutralize exactly 0.1 g, of 
NHj. The indicator end point is quite sharp, and experiments 
show that the absorption of ammonia is complete with a single 
wash bottle. Each experiment should be conducted at such a 
rate as to last about 10 minutes, and be repeated every 20 
minutes. An alternative method is to use a lai^er volume of 



^dbvGooglc 



152 



AMERICAN SULPHURIC ACID PRACTICE 



standard acid in two wash bottles, to aspirate for a longer time, 
say half an hour, and titrate back with standard alkah. 

A typical experiment gave 1.13 liters of water aspirated {i.e., 
1.13 1. of air in the air-ammonia mixture) to 0.1 g. of NHj. 
This gives a ratio vol. NHiivol. air of 0.116, which is about the 
ratio for conversion of ammonia to NO* (0.114). 

Determination of ratio oxidized NHi :AiT, after oxidation. 

An aliquot part of the oxides of nitrogen and air,' from the 
converter, taken from a T-tube after the cooler (see Fig. 51) 
is aspirated through: 




FiQ. 51. 

1. A Drechflel waah-bottle containing: 

100 c.c. distilled water, 
20 c.c. N/NaiO, solution, 
20 C.C. HaOa solution {20 volumes). 

2. A Drechsel wash-bottle containing: 

50 c.c. distilled water, 

10 c.c. N/NajOs solution, 

10 C.C. HgOa solution (20 volumes). 

The N/NaiOt is prepared by adding 78 g. NaiOi to 1 kg. 
powdered ice in small quantities at a time, with stirring: then 
adding 1 Uter distilled water and filtering through glass-wool. 



^dbvGooglc 



INTRODUCTION OF NITRE 153 

It is kept in a bottle with a capillary tube through the cork to 
allow the traces of Oj to escape. 

3. A 10-bulb tube containing: 

5 C.C. N/10 potassium permanganate solu- 
tion. 
10 c.c. 50 per cent H,SO*. 

All connections are made with ground joints, a stopcock being 
inserted at the point where the gas sample is taken from the T- 
tube, as shown in the Fig. 51. The aspiration is effected by- 
means of water droppii^ slowly from an aspirator bottle (about 
1 liter per hour) into a measurii^ cylinder, and 1,500 c.c. of 
water are collected; the experiment thus lasts 90 min. 

The two drechsel wash-bottles (1) and (2) are then emptied into 
two 250 c. c. Erlenmeyer flasks, the bottles being then washed, 
out with diatilled water and the liquid in the flasks titrated 
separately with standard H2S04, using litmus as indicator, and 
boiling if necessary. The end point is taken at the change blue 
to purple, and not blue to red, on account of the hydrolysis of 
the nitrous acid. This end point is easily recognized with a 
little practice. Methyl orange is useless on account of the 
action upon it of the nitrous acid, but Sodium Alizarine Sul- 
phouate ("Alizarin Red. I. W. S., Hochst") has been used with 
very satisfactory results. The contents of the permanganate 
bubbler ar» washed out into an Erlenmeyer flask, treated with 
a slight excess of N/10 oxalic acid, warming if necessary, and 
the excess of oxalic acid titrated back with permanganate. It 
is assumed that the reduction of the permanganate is due to 
NO, and the NHg equivalent of this is calculated as follows: 

2N0 + 30 = NzOft, 
that is, 2N0 (calculated as NHj) requires 3 atoms or 6 equiva- 
lente of oxygen, i.e., 60,000 c.c. N/lOKMnO,: i.e., 34 g. NH. = 
60,000 c.c. KMnO*. 

. ■ . 1 c.c. N/lOKMnb, = 0.000566 g. NH,. 
Ebcamples of calculations. 

It was found in one experiment that the oxides of nitrogen had 
neutralized a quantity of the alkali in the two vessels correspond- 
ing to 0.159 g. NHa, reckoning equivalents in nitrogen contents. 

XT .. .- ... J HNO, HNO2 NH, „„,., 
1 C.C. N alkali neutralized = -j^ = -j^ = y^ = 0.017 g. 

NH,. 



iizcdbvGoogic 



154 AMERICAN SULPHURIC ACID PRACTICE 

The permanganate in estimation (3) was titrated with N/10 
oxalic acid. It was found that 3.5 c.c. of N/lOKMnO* had been 
used up. This corresponds with 0.0035 g. NO, and this ia 
equivalent to 0.002 g. NH|. 

After the converter and the cooler, all the unconverted NHi 
will have been removed and the oxides of nitrt^^ are then totally 
absorbed in the absorption bottles. Now in the estimation 
of the ratio of NHi to air in the gas entering the converter, we 
have determined the weight of NHt associated with a given 
volume of air (the latter being simply equal to the volume of 
the water run out of the aspirator bottle). If there were no 
change of volimie of the air after the converter, we shoidd be 
able to make a direct comparison of the weight of the oxides of 
nitrogen, corresponding with 1.5 litres aspirated (these oxides 
being calculated as NHi) with the weight of NHi associated 
with the same volume (1.5 litres) of air in the mixtiure of air and 
NHj entering the converter. 

The aspirated volume after the converter, however, does not 
represent the volume of air which was associflrted with the 
ammonia corresponding to the oxides of nitrogen collected, be- 
cause a portion of this air has been used up in the oxidation. 
This consumed oxygen consists of two parts: 

1. A portion used in burning the NHi to NO in the converter. 

2. A further portion used in oxidizing the NO to higher oxides, 
which are then absorbed. 

The first portion is the same in all cases, and is calculated as 
follows: 

4NH, + 50i = 4N0 + 6H,0 
25 volumes of air become 20 volumes of Ni : 
i.e., the contraction of the air volume is here 
(25 - 20) X 22.4 
4 X17 



= 1.647 litres per g. NH, burnt. 



(Since the NHt is completely absorbed from the gas in the 
aspirator, before the converter, and the oxides of nitrogen from 
the gas in the aspirator after the converter, it is only necessary 
to consider the volumes of air.) 

The further contraction, due to secondary oxidation, will 
depend upon the particular higher oxide of nitrogen produced. 
Of these, only two, namely, NjO» and NjO*, can possibly be 
produced by the oxidation of NO by atmospheric oxygen, and 



^dbvGooglc 



INTRODUCTION OF NITRE 155 

it is therefore, neceasary to calculate the contractions for these 
two cases only. 

(a) 4NH, becomes 4N0 + 0, = 2NiO, 
that 5 volumes air becomes 4 volumes Nj: 

that is, there is a contraction of 1 volume, i.e., 

j - ' :- litres = 0.329 litre per g. NHj 

(b) 4NH, becomes 4N0 + 20i = 2N,04 
10 volumes of air becomes S volumes Ni 
that is, a contraction of 2 volumes, i.e., 

\^y^lf litres = 0.658 litre per g. NH, 

The aspirated volume, 1.5 litres, must therefore be increased in 
the ratios: 

(a) (Weight of oxides of N expressed as NHs) X (1.647 + 
0.329) : 1, when these oxides are absorbed as NiOg; 

(b) (Weight of oxides of N expressed as NH,) X (1.647 + 
0.658) : 1, when these oxides are absorbed as N1O4. 

The volume of air so corrected is then directly comparable 
with the volume of air associated with the ammonia in the aspira- 
tion before the converter, and if equal volumes are compared, 
the we^hts of NHs in each (that after the converter being 
calculated from the titrations, as described) will give an imme- 
diate figure for the efficiency: 

wt. NH, after conversion (as oxides) „ . 

. T.TTT ■ , — — '^^ X 100 = eflSciency, 

wt. NH3 before conversion •" 

the weights beii^ referred to equal volumes, as described. 

AIR VOLUME COSKECTIOn 

In the experiment described above, the -weights of NH» 
corresponding with the oxides of nitr<:^en collected in the alkaline 
peroxide and permanganate, respectively, were 0.159 g. and 
0.002 g. Since in a good experiment the permanganate 
figure should always be very small, it is only necessary to use the 
first figure, namely, 0.159 g. in correcting the air figure. 
This correction will be as follows : 

(a) Gas assumed to be absorbed as NjO, : 
corrected volume of air = 1.5 + 0.159 X (1.647 + 0.329) litres 
= 1.5 + 0.314 = 1.814 litres. 



^dbvGooglc 



156 AMERICAN SULPHURIC ACID PRACTICE 

Now in the aspiration before the converter, it was found that 
0.1 g. Nifi was contained in 1.13 litres. 

, " . NH| in 1.814 litres before conversion = -^ — jTS — ~ "" 

0.1605 g. 
Oxidized NHg after conversion - 0.159 + 0.002 = 0.161 g. 
0^ 
"0.1( 

(b) Gas assumed to be absorbed as NjO^: 
corrected volume of air = 1.5 + 0.159 X (1.647 + 0.658) litres 
= 1.867 litres. 

1 867 X 1 
NHt in 1.867 litres air before conversion = — — j-t^ — - = 

0.1650 g. 
. „_ . 0.161 X 100 „ „ 
. . Emciency = nTpA — ~ "'■" f*'" *'*"'■ 

The difference between the two values is thus seen to be only 
about 2.5 per cent, which is within the limits of experimental 
error. The true value lies between the two, and nearer the NiOj 
^ure, since experiments have shown that about four-fifths of 
the oxides are absorbed as NaOt when no oxidizing agent is 
present in the liquid, and this ratio, therefore, represents the 
composition of the gas before absorption. 

To the amounts of oxides of nitrogen collected in the absorption 
bottles must be added that present in the condensed water 
separated from the cooler. The analysis of this condensate is of 
value in estimating the unconverted ammonia, all of which 
separates in the condensed water in the form of nitrite and nitrate. 
The condensed water is collected throughout the whole experi- 
ment and its volume measiu^d. 

An aliquot part is titrated with N alkali and litmus for acidity, 
and the acidity of the total expressed as NH, (1 c.c. N/NaOH = 
0.017 g. NH,). Another aliquot part is distilled with NaOH and 
the ammonia collected in a measured volume of N/HsSO*. This 
ammonia was combined with an equivalent amount of acid, and 
its value must therefore be added to that found in the previous 
titration, to obtain the total OXIDIZED NHg in the condensed 
water. This is divided by the total weight of NH, passed 
through the converter durii^ the run, and the result, multiplied 
by 1(H), gives the term which must be added to the efficiency 



^dbvGooglc 



INTRODUCTION OF NITRE 157 

calculated from the absorption bottles, to give the true efficiency. 
In the experiment described the values were: 

Unoxidized NHj = 0.3 per cent 

Oxidized NHs ^ 0.1 per cent 

.-. Total efficiency = 100.1 + 0.4 = 100.5 or 97.6 + 0.4 = 
98.0 

If the proportion of air and ammonia entering the converter is 
BUch as to form NO, this could not be absorbed in the alkaline 
peroxide, and in this case it is necessary to add a measured volume 
of oxygen slowly to the gases aspirated from the converter. This 
is done by connecting a graduated gas-holder containing oxygen 
to a T-piece on the connection of the first bottle, the rate of 
addition of oxygen being controlled by passing it through a small 
wash-bottle containing water. About 300 c.c, of oxygen are 
added during the whole run of 90 min. This volume (300 
c.c.) is subtracted from the volume of water collected ^nd the 
usual correction for contraction apphed to the remaining volume : 
1,500 c.c. - 300 c.c. = 1,200 c.c. = 1.2 Utres. 
GENERAL REHASKS 

In the eBtimation of the ammonia, the balancing water column 
in the Winchester bottle should be such that the gas pressure 
before the converter is just sufficient to bubble through the water. 
As soon as the aspirator is started bubbles will pass, and the rate 
should be adjusted so that the color of the indicator changes in 
about 10 min. When indications of a color change appear, the 
rate of aspiration should be reduced so that about one bubble 
per second passes, and the absorption bottle should be shaken. 
The connecting tubes and the upper part of the tube in the wash- 
bottle should, of course, be dry. 

The alkaline peroxide bottles should be carefully fitted together, 
so that on opening the tap connecting with the outlet from the 
converter, on bubbles (or at most one or two) pass before the 
aspirator is started. The rate of aspiraton must be slow, as 
stated. If white fumes appear in the second bottle, or the per- 
' manganate is discolored, or depoats much MnOt, the experi- 
ment will usually be found to give an incorrect result. 

If oxygen is added it should be let in slowly, as stated, in order 
to insure that the whole of it passes through the aspirator bottles, 
and not backwards into the converter main, 



^dbvGooglc 



158 AMERICAN SULPHURIC ACID PRACTICE 

To insure that the pressures are equalised in the aapu^tor 
bottles, these may be provided with gauges, consisting of U-tubes 
containing water. 

Hydrogen peroxide solution is usually acid, and allowance 
must be made for this in the titrations. 

(ft) Determination Without the Use of Cooler. — If the hot gases 
from the converter are utilized without previous cooling it has 
been found that a short length of aluminum tubing, inserted as a 
T-tube in the main from the converter, is generally sufficient in 
itself to cool the aliquot part of the gases which are slowly passing 
through it to the absorption system. It has been usual to neglect 
the small portion of unoxidized ammonia in this case. As alter- 
natives the following suggestions are based upon information 
from those who have had occasion to carry out control tests on 
hot converter gases: 

1. The converter gas is drawn slowly throu^ a capillary tube 
to an absorption system similar to that described above. 

2. The first absorption bottle contains N/10 alkali without 
peroxide. This, according to Fox (Journal of Industrial and 
Ertgineering Chemistry, August, 1917), retains all the unoxidized 
ammonia coming over, the amount of which is estimated after 
the titration by treatment with caustic soda and sodium hypo- 
bromite, when nitrogen is liberated and is measured (of.. Tread- 
well and Hall, Quantitative Analysis, p. 622). A correction must 
be applied to this volume of nitrc^n, since the reaction is not 
quite complete (cf., Fox). 

3. The second absorption bottle contains the same solution as 
the first bottle in the method described above. 

4. The permanganate tube is retained unchanged. 



^dbvGooglc 



CHAPTER XIII 
DRAFT 

Early chamber planta depended upon natural draft for the 
movement of gases through the apparatus, but all modern plants 
use fans. In this way larger volumes can be moved and the con- 
trol is much more positive. 

Fans are of two classes, viz., iron fans which are used at some 
point preceding the Glover Tower, and lead fans, used at some 
point following the Glover Tower. Sometimes both kinds are 
used in the same system. It must be understood that if a fan 
is placed between the sulphur burners or roasters and the Glover 
Tower, high temperature, dry gases are to be handled and iron 
is the only suitable material for the service. If the fan is placed 
at any point beyond the Glover Tower, comparatively low tem- 
perature gases laden with sulphuric acid mist are to be propelled. 
For this service lead, usually stiffened by alloying with antimony, 
is the most suitable material. Iron of course would be quickly 
destroyed by the acid. Lead fans are more often used than iron 
though the latter certainly deserve much consideration as they 
hare many advantages. 

The- arrangement most common for units of moderate size is >/ 
to use a sin^ lead fan between the Glover Tower and the first 
chamber. Very often a second lead fan is used between the last 
chamber and the Gay Lussacs. A less frequent plan is to use a 
single iron fan just in front of the Glover or an iron fan, with a 
lead fan between the last chamber and the Gay Lussacs. Any of 
these arrangements of suitable size and with the other features 
of the plant in conformity may give good results. It is well to 
consider that the fans are of very vital importance to continuous 
operation and that they have to be repaired and parts replaced at 
fames. If there are two fans in a system with proper by-passes 
Que of them may be cut out and worked on without causing a 
shutdown. To be Bure a diminished production will probably 
result but that is not nearly so serious as cooUng off furnaces and 
discontinuing the acid making process. A further important 
advantage of having a fan at each end of the system is that repairs 



^dbvGooglc 



160 AMERICAN SULPHURIC ACID PRACTICE 

may be made on the chambers more readily by producing a slight 
inward suction by varying the fan Bpeeds. Thifl is appreciated 
after chambers become several years old. 

Iron fans suitable for this work are similar in general design 
to those used for many other purposes, such as ventilation of 
mines, buildings, etc. They must of course be quite tight, able 
to stand temperatures up to 1,000°F. and be of simple construc- 
tion to avoid catching dust. The housing should be of cast iron 
as plate housings will warp badly in the heat encoxmtered. The 
shaft will be course be very hot for some distance outside the 
housing and so the bearings mi^t be water cooled. The rotor 
can be of cast iron or of steel plate with a cast hub spider. It 
may be overhung or may have a bearing on each side of the hous- 
ing. The former method is perhaps more convenient as the 
inlet flue is not complicated by having a shaft and bearing on that 
side. 

The speed of iron fans should be from 500 to 1,000 r.p.m. in 
order that they may blow the dust out and keep themselves 
clean. It must also be considered that due to its high tempera- 
ture the volume of the gas is more than twice what it is after 
it passes through the Glover Tower. Consequently, the range 
of speed specified is advisable in order to move the gas with a fan 
not unduly large. 

Several manufacturers in this country have stock designs 

which with sl^ht modifications are entirely satisfactory for acid 

plant service. These fans are very much less expensive than the 

" lead fans and over a period of years require less repairs. Why 

they are not used more is hard to understand. 

Lead fans are in general much like the iron fans in design. 
It is necessary on account of the low strength of lead to make the 
metal much thicker than corresponding parts of iron. "Die 
shaft which carries the rotor is necessarily of steel, but it is 
entirely covered by lead imtil it leaves the housing. Usually 
the lead of the spider is poured around a cast iron hub which 
latter is keyed to the shaft. This is a detail which has given 
trouble in many fans, but if the cast iron hub is generous in 
size and made with dovetail grooves so that the lead can take 
hold of it well, no slipping or working loose will occur. 

There are several lead fans specially deseed for acid plant 
work on the market, and most of the manufacturers of blowers, 
will alter their designs of iron fans and make them of lead if 



^dbvGooglc 



DHAFT 161 

desired. Two widely used specially designed fans are tlie Pratt 
and the Heinz-Skinner. 

The Pratt fan, shown in Fig. 52, is made with both bearings 
on one side, t.e., with rotor overhung. The gas enters on one side 
only. The housing is of cast hard lead made in two pieces and 
is self-supporting. It is so arranged that the top casting can be 
lifted off to allow removal of the rotor. This is a well-designed 
fan with the details perfected over a period of several years. 
This fan is designed to run at rather high speeds up to 800 or 900 ■ 
r.p.m. It is therefore small comparatively and uses more power 
than the large low speed fan. 



The Heinz-Skinner, Fig. 53, has several novel features though 
the principle upon which it works is the usual one. This fan has 
its shaft extending clear through the bousing with a bearing on 
each side. The inlet pipe branches just before it reaches the fan 
and goes to an inlet on each side of the rotor. The housing is ia 
two parts with a horizontal joint at the level of the shaft. The 
joint itself is a lute made t^ht by an acid seal. The upper part 
of the housing can be lifted off to change or work at the runner. 
This fan both as to housing and runner is largely built up by 
burning together rolled hard lead plates. It is entirely of hard 
lead excepting, of course, the shaft. This fan is also very well 



^dbvGooglc 



162 



AMERICAN SULPHURIC ACID PRACTICE 



designed and if properly handled gives good service. It runs at 
speeds up to 500 or 600 r.p.m. 

The Wedge fan which has been used in several large acid 
units built of late years is soraething of a departure from the 
above types in the matter of size and speed. This fan so far as 
I know is not made regularly by any manufacturer. The fans 




so far made have all had runners 8 ft. in diameter and 4 ft. wide. 
They run at speeds not over 200 r.p.m. They are enormously 
heavy and costly but they run with surprisingly little power and 
give very little trouble. Some of them have been in practically 
continuous use for more than 4 years without being opened. 
The housing of this fan is built up of ordinary sheet lead (15-lb.) 
supported by angle iron framework. There is a gas inlet on one 



^dbvGooglc 



DRAFT 163 

Bide only. The shaft rune in a bearing on each side of the 
housing. One fan of this size will provide draft for a properly 
designed plant to make 126 to 150 tons of 60° acid per day. It 
consumes only 12 to 15 H.P. at 200 r.p.m. 

These fans are mentioned specifically not so much because 
they are more satisfactory than many others, but because they 
represent types and because they are specially designed for acid 
plant service. 

FLtTBS 

As the parts of the chamber system are enclosed in sheet lead 
considerable areas of which are unsupported, it is essential that 
flues, tower packing, etc., be so proportioned that no very great 
resistances shall be offered to the passage of the gas. Of course, 
the towers can stand somewhat higher differences between 
internal and atmospheric pressures, than can the chambers, 
because they are of heavier lead and the internal masonry lends 
them stability. 

It is well to BO design the plant that pressures corresponding to 
1-in. of water shall not be exceeded in any tower and 0.75 in. as 
a maximum for any chamber. Of course, h^her pressures will 
be found in many plants and it should not be inferred that they 
are- particularly dai^erous; however, the fact is that lead at a 
temperature of 200''F. is not very stiff and in the course of some 
years high pressures cause distortions which make trouble. 

Calculations for flue areaa must be made for individual cases, 
but the following statements will give an idea of proper areas 
which should be provided in a simple one-fan system. If the 
gas entering the acid system contains an average of 7 per cent Sd 
by volume, it will be necessary to put through the plant about 
80,000 cu. ft. per 24 hours per ton of 60" acid made, at O^C. and 
760 m.m. This will be increased somewhat by the reaction 
temperature and decreased as SO) and go to make liquid H1SO4. 
In the early parts of the system for example, the gas temperature 
may be lOO'C. which would make 80,000 cu. ft. at 0" = 109,000 
cu. ft. = 1.26 cu. ft. per sec. If we wish the gas velocity to be 
10 ft. per sec. our flue area in this part of the system would be 
.126 eq. ft. per ton of 60° acid made. For a 100 ton unit the 
flue area should then be 12.6 sq. ft. which is almost exactly that 
of a 48-in. diameter flue. 

In the back part of the system where the gas temperature is 



^dbvGooglc 



164 



AMERICAN SULPHURIC ACID PRACTICE 



perbapB 45°C., the volume wiU have decreased od this account to 
about 86,000 cu. ft. The reaction and condensation of SOj and O 
to liquid acid will have removed about 10 per cent by volume or 
8,600 cu. ft. so that the volume of gas per ton of acid will be 
about 77,400 cu. ft. per 24 hours = .9 cu. ft. per sec. and the 
necessary fine area will be 9.0 sq. ft. which is the area of a pipe 
about 41 in. diameter. 

If several small flues are to be used instead of one large one, 
or if there are many bends or very long distances between parts 
of the apparatus which the Hues connect, some allowances to 
compensate for increased friction should be made. The basis 
of 10 ft. per sec. is a safe one however for the flue connections 
found in most plants. 




For tower packing, no very definite figure can be given as a 
minimum of necessary open area, experience and data on different 
types of packing are necessary. It is also necessary to consider 
the length of the column of packing through which the gas must 
pass. It is well in a Glover tower having a packed column 
25 or 30 ft, high to provide a gross horizontal packed area of not 
under 2 sq. ft. per ton of 60° acid made. For Gay Lussafs, 
where combined packed he^hts amount to 75 ft. or more, 2 to 
2.5 sq. ft. per ton of 60° acid made should be provided. Con- 
siderable divei^ences from these specimen figures may be made 
with entire propriety by using fans at various points of the 
system. 

Circular lead flues are to be preferred to rectangular sections. 



iizcdbvGoogIc 



DRAFT 165 

They are stronger from the nature of their section and are 
simpler to support. Sharp angles are to be avoided,. in general, 
in lead construction. Circular flues are best made of 10-lb. lead. 
The supports are flat or edge bands of iron as shown in Fig, 54. 
The edge bands are slightly more expensive to apply but are 
distinctly better in the long run. Bands should be frequent as 
in the later yeara of the life of a plant insufficient support of 
fines causes much trouble. 



^dbvGooglc 



CHAPTER XIV 

TESTING 

The control tests made about an acid plant are largely per- 
formed by men who have little knowledge of the refinements of 
" chemical and physical measurementfl and consequently no h^h 
degree of accm'acy is customary. Nor is a h:^h degree of accu- 
racy necessary. The tests and instruments to be described are 
intended only to represent such work. They are for the operator 
rather than for the chemist. 

THERHOMETBRS AND PTROHBTBRS 

It is desirable in many parts of the plant to know the tem- 
peratures of the gases and acids involved in the process and for 
obtaining these, thermometers and pyrometers are used. Every- 
one is familiar with thermometers and little need be said concern- 
ing them. In the United States the Fahrenheit scale is almost 
universally used. For taking acid temperatures, straight stem 
thermometers with inclosed paper scales reading up to 220''F. 
are best. They are tess expensive and more easily read than the 
engraved instruments. It ia well to have a few thermometers 
reading up to 400° for testing the acid issuing from the Glover 
tower. Chamber thermometers having stems bent at 45° or 
90° from the graduated portion are regularly made by the 
manufacturers of chemical apparatus. The stems are inserted 
into the chambers through rubber stoppers. In reading a 
thermometer it is important that a line from the eye to the end 
of the mercury column be at a r^ht angle to the latter. 

For ascertaining high temperatures such as those of the gases 
entering the Glover Tower, the pyrometer is used. When 
certain dissimilar metals or alloys are placed in contact with each 
other and heated, an electric current is set up which can be 
measured by a galvanometer and the corresponding degree of 
heat shown by a needle on a graduated scale. For the purposes 
of the chamber-acid plant what are known as base metal couples 
for insertion into the flue are most suitable. This form of 
couple, shown in Fig. 55 consists of a pipe or tube of one 
metal and a rod of a different metal inside it and insulated from 



^dbvGooglc 



TESTING 



167 



it except at one end where the tube and the rod are welded 
t<^ether. This welded end constitutes the couple and is inserted 
into the gas whose temperature is desired. Couples made of 
platinum, and platinum alloyed with rhodium or iridium, are 



excellent but far more expensive. The only precautions neces- 
sary to be observed in using pyrometers are to have all the wire 
connections clean and tight and to keep the couple reasonably 
free from dust. 

Several couples may lead through switches to one galvano- 
meter. Temperatures exceeding 1,200''F. are not often encoun- 
tered in flues so that an instrument graduated to 1,500" or 
l.eOOT. is suitable. 

HTDROHETERS 

The hydrometer is an instrument used for showii^ the concen- 
tration of sulphuric acid. It is made of glass and consists of a 
cylindrical fioat weighted at its lower end and with mercury, or 
shot, and surmounted by a thin stem 
containing a graduated paper scale. 

The acid to be tested is placed in a tall 
jar and the hydrometer allowed to sink in 
it until it comes to rest. On account of 
surface tension, the acid will curve up ■*— 
against the stem as shown in Fig. 56. 
The readily should be taken across the 
surface of the acid on line AA, not at the 
top of the curve line, BB. 

The hydrometer universally used in 
chamber-acid plants in this country is 
called the American Beaum^. This is an 
arbitrary scale originally devised by 
making up a solution of pure salt, NaCl, 15 parts and pure water 
85 parts by weight; immersii^ a hydrometer in it and calling the 
mark 15°, The point to which the hydrometer sunk in pure 
water was called 0°. The distance between these marks was 
divided into 15 equal parts, thus establishing the degree BeaumS. 
After many years of disagreement over the exact details of 



^dbvGooglc 



168 AMERICAN SULPHURIC ACID PRACTICE 

obtaining the degree and as to its relation to specific gravity, the 
U. 8. Bureau of Standards adopted as the oflgcial American 
standard the relation expressed thus: 

Degrees BeaumS = 145 — = — p- 

In England Twaddles Hydrometer is most used. It is based 
strictly upon a specific gravity relation. Specific gravity 1.0 = 
0° Tw — and each succeeding degree represents an increase of 
.005 in specific gravity, e.g., 5° Tw = 1.025 sp. g. This scale is 
very little used in the United States. 

Standard hydrometers are made for use io liquids at 60"P. 
If the liquid is warmer than BCF. the hydrometer will read low 
and vice versa, if the liquid is colder than GCfF, Where sulphuric 
acid is said to be so many degrees Beaum6 it is understood that 
the statement refers to the hydrometer reading at OO^F. When 
it is desired to determine what the hydrometer would read at 
fiO°F. in acid which is warmer or cooler than WF., the hydro- 
meter is read at the existiug temperature and the temperature of 
the acid taken with a thermometer. The hydrometer reading is 
then corrected, increased if the acid is warmer than 60" and 
decreased if colder. 

If the acid is near 40''B^. .031°B6. for each IT. above or below 60° 
If the acid is near 50°B*. .028''B6. for each IT. above or below 60° 
If the acid is near eCB^. .026''B^. for each I'F. above or below 60° 
V^ The Manufacturii^ Chemists Association of the 

United States has adopted the tables of Ferguson 
and Talbot as a standard for the relationships be- 
tween specific gravity, degrees Beaumd, degrees 
Twaddel and per cent H,SO«. This table is very 
generally used in the United States. It can be found 
in Chapter XXIII, Table 1. 

Hydrometers most useful in the chamber acid 

plant are the loi^ 12-in. form with a range from SO* to 

^_^ JL 70° graduated to tenths of each degree and the short 

f e-V^ \ chamber 5-in. hydrometer with a range of 40 to 60° 

^T ^r graduated in degrees. The former is used for testii^; 

the tower acids and the latter for the chamber drips. 

Hydrometer jars for control testing are made of glass or lead 

in the form shown in Fig. 57. The acid enters the main jar from 

the bottom and assures the jar being full of the current Sow. 



^dbvGooglc 



GAS TESTING 

The coDstituente of the gaaes regularly determined axe SOt and 
oxygen. The Orsat apparatus is very generally used for deter- 
mining both of these in the gases entering the aystem. In the 
latter parts of the plant where the SOi percentage of the gas is 
very low the Great is not suitable. 

The Orsat apparatus consists essentially of a measuring burette 
graduated to 100 c.c, two absorption pipettes, connecting capil- 
lary tubes with stop cocks, and a levelling bottle. One pipette 
is charged with SCB^. caustic soda solution which absorbs SOj 
and the other with a solution of pyr<^allic acid in cauetic soda, 
which absorbs oxygen. This is shown in F^. 58. To operate 
the Orsat apparatus the end of the glass capillary is connected 



J3 



with the vessel containing the gas to be analyzed by a rubber 
tube. Three-way cock E is turned to open from burette B to 
waste. Bottle A is raised to expel air from B and fill B with 
water. Cock E is turned so that B communicates with V, 
bottle A is lowered and the burette drawn full of gas. In order 
to be sure of a fresh complete gas sample the cock is turned to the 
waste position and the gas in burette expelled. A second sample 
is drawn and the bottle manipulated so that the water in the 
burette stands at O when bottle A is held so that water in A and 
B are level, with cock E closed. Cock to C is now opened, bottle 
is raised and gas all forced into C. The gas is drawn back and 
forth between B and C five times, then with level of liquor in C 
at original mark and cock closed a reading is taken in B with 
water in A and B held level. This reading is noted. The gas is 
again drawn back and forth between B and C twice and the 



^dbvGooglc 



170 AMERICAN SULPHURIC ACID PRACTICE 

reading in B taken as before. If the two readings check, all the 
S0» is considered to have been absorbed in C. If the second 
reading is greater than the first the gas is sent into C again and 
until two readings do check. The final reading in cubic centi- 
meters represents the per cent SOi by volume. Next the gas is 
manipulated into D and the same procedure gone through as 
with C. The difference between the readii^ obtained from 
absorption in C and that in D indicates the per cent of oxygen by • 
volume. It is well to keep a thin rubber bulb on the back limb 
of D so that fresh air is not drawn in on the pyrogallic acid 
solution with each test, otherwise the absorbing power of the 
solution is quickly destroyed. 

In gases free from COi and which contain several per cent of 
S0» the Orsat test will answer very well for testing in connection 
with chamber control work. The accuracy is perhaps not high, 
but the test can be reliably performed by any reasonably intelli- 
gent person and it gives a good basis for estimating necessary 
changes in nitric feed and workii^ the SOj furnaces. 

The caustic soda solution used is made by dissolvii^ about 
300 g. pure caustic soda in a litre of' Water. It is not necessary 
to have these proportions exact. 

The pyrogallic acid solution is made by dissolving about 12 to 
15 g, pyrogallic acid in 125-150 c.c. of the above caustic soda 
solution. This amount is a suitable volume for chaining the 
customary Orsat pipette. The caustic solution can be made up 
in any volume desired and kept indefinitely in a glass-stoppered 
bottle. The pyrogallic acid solution is best made up as it ia 
wanted to charge the pipettes. It is well systematically to 
change the solutions once a week or at sufficient intervals to 
assure that the solutions do not become sluggish. 

A direct test for SOi suitable for any gas found in chamber 
work is the Reich Test. This depends upon the reaction between 
iodine and SOj - 21 + SOj + 2HiO = 2HI + HSOt, and upon 
the fact that a solution of cooked starch produces a deep blue 
color in a solution containing free iodine, and that the color 
disappears as soon as all free iodine has been reduced to HI. 

The test is performed in apparatus shown in Fig. 59. Bottle 
A is charged with a definite we^ht of iodine dissolved in EI 
solution and colored with starch. Syphon tube C is opened and 
the gas under observation is drawn through the iodine solution 
until the color just disappears. The amount of water drawn 



^dbvGooglc 



TESTING 



171 



from B is noted and it represents the amount of gas drawn 
through the iodine solution, less the SOj absorbed. Knowing the 
amount of iodine used and the volume of gas drawn, the per cent ^ 
SOi by volume is readily calculated. 

As a rule tests are made in a chamber plant at a point near the 
Glover tower where the SOi percentage is from 5 to 8, and at a 
point near the Gay Lussacs where the SOi percentage is under 
^0- F*^'' the former it is convenient to use a ^o normal iodine 
solution, i.e., one which contams 12.7 g. iodine per litre. For 




Fio. 60. 

each test 10 c.c. of this solution is used and a table is made up in 
the following way. 

Ten cubic centimeters of >fo normal iodine contains .127 
g. iodine. According to the reaction above this amount of iodine 
will react with .032 g. SO*. 

21 : SO, - 10 C.C. N/10 I : wt, SO, 
2 X 127 : 64 = .127 g. : .032 g. 

.032 g. SO, =- 11.184 c.c. SO, at O'C. and 760 m.ra. 

The total volume of gas drawn into the iodine solution in any test 
ia then the amount of water syphoned from the bottle B plus 



^dbvGooglc 



172 AMERICAN SULPHTJRIC ACID PRACTICE 

11.184 c.c. which is the volume of S0» absorbed. Therefore 

per cent. SO, = — ^^\^ + 11.184 
*^ c.c. water 

and c.c. water = . „■-. — 11.184 

per cent. SOi 

From this equation Table 6 is constructed. 

In the rear of the system a 1/500 nonual iodine solution is 
suitable. This contains .254 g. per litre. Table 7 is con- 
structed for this solution in the same way as described for 6. 

In using the Reich test, at any point in the chamber system 
following the Glover tower, a modification is necessary. The 
nitrc^n oxids contained in the gaa mixture render the test as 
described above worthless in that they reoxidize the HI formed 
and prevent decolorization of the solution. This can be pre- 
vented and the test made fairly accurate by adding to the iodine 
solution just before making the test, 10 or 15 c.c. of a solution 
containing 100 g. sodium acetate and 100 g. acetic acid per 
litre. 

In Fig. 59 bottle A should be a 12 oz. salt mouth bottle fitted 
with a two hole rubber stopper carrying two tubes. One of these 
extends to within a short distance of the bottom. Its end is 
drawn down so that the opening is only 1 or 1^ mm. in diameter 
in order that the gas bubbles shall be small. The second tube 
goes barely through the stopper. This arrangement is for all 
practical purposes ae good as the expensive and elaborate absorp- 
tion bottles and when it is broken, it is quickly and cheaply 
replaced. The syphon bottle B should be at least two or three 
litres. Two graduated cylinders, a 500 c.c. and a 1000 c.c. should 
be provided. 

The yio normal iodine solution is made by dissolving 15 
or 20 c.c. of potassium iodide crystals in 25 c.c. of water. Into 
this solution dissolve 12.7 g. iodine crystals. It is important 
that the KI solution be very concentrated or else the iodine will 
be slow to dissolve. When solution is perfect, make up to one 
litre with water. 

The J-^oo normal solution is made by making up 20 c.c. of the 
}io normal solution to one litre with water. 

Starch solution is made by mixii^ 5 or 6 g. soluble starch to a 
thin paste and pouring into 500 c.c. of boiling water and allowing 
to boil for 5 min. The addition of a few drops of chloroform or 



iiz^dbvCooglc 



Table fl. — Standard SOi Tabi/b 
10 C.C. N/10 Iodine. O'C.-VeO mm. 



Percent 
SO. 


C.e. water 


Fercent 
80. 


Cc. water 


Percent 
80. 


Cc. water 


.1 


11,173 


4.1 


262 


8.1 


127 


.2 


6,581 


4.2 


255 


8.2 


125 


.3 


3,717 


4.3 


249 


8.3 


124 


.4 


2,788 


4.4 


243 


8.4 


122 


.8 


2,226 


4.6 


237 


8.5 


120 


.6 


1,863 


4.6 


232 


8.6 


119 


.7 


1,587 


4.7 


227 


8.7 


117 


.8 


1,387 


4.8 


222 


8.8 


116 . 


.0 


1,231 


4,9 


217 


8,9 


114 


1.0 


1,107 


5.0 


212 


9.0 


113 


1.1 


1,006 


5.1 


208 


9-1 


112 


1.2 


921 


5.2 


204 


9-2 


no 


1.3 


849 


6.3 


200 


9,3 


109 


1.4 


788 


5.4 


196 


9.4 


108 


1.5 


734 


6.6 


192 


9.5 


107 


1.6 


688 


5.6 


189 


9.6 


105 


1.7 


647 


5.7 


,185 


9-7 


104 


1.8 


610 


5.8 


182 


9-8 


103 


l.fl 


677 


5.9 


178 


9-9 


102 


2.0 


548 


6.0 


175 


10.0 


101 


2.1 


521 


6.1 


172 


10,1 


. 99.5 


2.2 


497 


6.2 


169 


10.2 


98,5 


2.3 


476 


6.3 


166 


10,3 


97-4 


2.4 


466 


6.4 


104 


10,4 


96.4 


2.8 


436 


6.5 


161 


10,5 


95.3 


2.6 


419 


6.6 


158 


10 6 


94.3 


2.7 


403 


6.7 


166 


10,7 


93,3 


2.8 


388 


6.8 


153 


10,8 


92.3 


2.9 


374 


6.9 


161 


10,9 


91.4 


3.0 


362 


7.0 


149 


11,0 


90.6 


3.1 


350 


7.1 


146 


11. 1 


80.6 


3.2 


338 


7.2 


144 


11.2 


88.7 


3.3 


328 


7.3 


142 


11.3 


87.8 


3.4 


318 


7.4 


140 


11.4 


86.9 


3.6 


308 


7.5 


138 


11.5 


86.1 


3.6 


299 


7.6 


136 


11.6 


85,2 


3.7 


291 


7.7 


134 


11,7 


84.4 


3.8 


283 


7,8 


132 


11,8 


83.6 


3-9 


276 


7.9 


130 


n,9 


82.8 


4.0 


268 


8.0 


129 


12.0 


82.0 



This table is calculated using 2.86tl g. aa the weight of the litre of SO.. 



^d by Google 



AMERICAN SULPHURIC ACID-PRACTICE 

Table 7. — SO, by Reich Test 
10 C.c. N/500 Iodine 



Per cent SO, ■ 


C.C. water 


Per cent SO, 


C.c. water 


.010 


2,236 


.060 


373 


.OlS 


1,491 


.065 


343 


.020 


1,118 


.070 


319 


.025 


894 


.075 


298 


.030 


745 


.080 


279 


.036 


639 


.085 


263 


.040 


659 


.090 


248 


.046 


497 


,095 


235 


.050 


447 


.100 


224 


.055 


406 







oil of cinnamon to the cooled solution prevents souring. Only a 
few drops are used for each test. 

The acetate solution is made by dissolvii^ about 100 g. 
sodium acetate crystals in water, adding 100 c.c. acetic acid and 
making up to one litre with water. About 10 c.c. of this is used 
for each test. 

TESTING FOR HITROGEH OXIDES 

There are several materials about a chamber plant to be tested 
tor their content of nitrogen oxides. The nitrometer method is 
suitable for any of them and every plant should have one in use. 
This instrument can be had in several different forms with com- 



^^ 



Plain invArff Tu 



Z\ 



^=iac 



pensating attachments but for the control work about a chamber 
plant the simplest form, consisting of a simple graduated burette 
with thistle top and two-way stop cock, and a plain levelling tube, 
is quite satisfactory. Figure 60 illustrates this. 

The nitrometer method depends upon the fact that in the pres- 



^dbvGooglc 



TESTING 175 

ence of sulphuric acid mercury will react with nitric acid or any of 
the nitrogen oxides above NjO, to f own HgiSO* and NO, a colorleea 
gaB. By observing the volume of gas derived from a known weight 
of the compound to be examined,!^ nitric acid or sodium nitrate 
content, or equivalent, can be calculated at 0°C. and 760 mm. 
1 c.c. NO = .00281 g. HNOs 
1 C.C. NO = .00379 g. NaNOj 

In performing a nitrometer test one should know in a general 
way the amount of nitrogen oxides contained in the material 
under examination and should figure out a suitable quantity for 
introduction into the nitrometer. If the graduated tube is of 60 
c.c. capacity, a quantity of material should be used which will 
evolve a volume of gas preferably between 25 and 50 c.c. of NO. 

The nitrometer is prepared by opening the stop cock into the 
reservoir A and raising the levelling tube until the mercury barely 
appears in the bottom of A. An accurately we^hed or measured 
amount of the material under examination (in solution if a solid) 
is put into A. The cock is slightly opened and A is almost but not 
quite drained. Next about 10 c.c. of concentrated pure sulphuric 
acid is put into A, the cock opened slightly and the acid drawn 
into B as completely as possible without drawing in air. Tube B 
is now well shaken for about two minutes to bring the mercury and 
the solution into thorough contact. When one is assured that 
complete reac Jon has taken place a reading is taken of the volume 
of NO which has been evolved. The acid in B has a specific 
gravity about J^ that of mercury so to observe the gas volume 
under atmospheric pressure the readii^ is taken with the mercury 
surface in C held at a point above the mercury surface in B equal 
to 3^ (rf the length of the acid column. For example, if the acid 
column is 14 c.c. the mercury in C will be held 2 c.c. above the 
mercury surface in B when the reading of gas volume is taken. 
A correction for temperature and pressure must be made in most 
cases. It is sufficient for the class of work under discussion 
to determine a correction factor for the usual room temperature 
and the normal barometer and to use this factor in all cases. This 
factor is determined by the following formula: 
B ^ 273 
Factor = 760^ T+273 

B = Normal barometer in m.m. 

T = Normal temperature in degrees Centigrade. 



^dbvGooglc 



176 AMERICAN SULPHURIC ACID PRACTICE 

The observed gas volume is multiplied'by this factor and the 
rcBult is the gas volume at 0°C. and 760 mm. pressure. The 
mateiialfi about a chamber plant to which the nitrometer test 
will be applied aie nitrate of soda, nitre cake, nitrous vitriol and 
mixed acids. 

To test nitrate of soda, dissolve 50 g. in water and make 
up to one htre. With a pipette introduce 2 c.c. into the nitro- 
meter and perform the test as described. 

Per cent NaNO, = c.c. NO X 3.79 
To test nitre cake, dissolve 5 g. in water and make up to 25 c.c- 
With a pipette introduce 5 c.c. into nitrometer and perform 
test as described. 

Per cent NaNO, = c.c. NO X .379 
To teat nitrous vitriol containing not over 70 oz. NaNOj 
per cu. ft., introduce 2 c.c. with a pipette into nitrometer and 
proceed as described. 

Oz. NaNOi per cu. ft. = c.c. NO X 1.91 

To test mixed nitric-sulphuric acids, it is usually necessary 
to dilute with concentrated sulphuric acid in order to avoid 
having to measure an exceedingly small quantity for use in the 
nitrometer. It is not well to try to use less than 2 c.c. of a solu- 
tion for test as pipettes smaller than that are not very accurate. 

A quick method of estimating the amount of nitrogen oxides 
in nitrous vitriol is by a titration with potassium permanganate 
solution. This assumes that all the nitrogen oxide existe as 
N^i and reacts thus: 

5N,0j + 4KMn04 + 6H^0, = 2K,S04 + 4MnS0* 
+ lOHNO, + H,0 

Lunge and other writers on this subject recommend perform- 
ing this test by measuring a known amount of permanganate into 
a dish and nmning in nitrous vitriol from a burette until the 
permanganate is decolorized. This is perhaps slightly more 
accurate than the way which will now be described. 

Fill a 50 c.c. burette with standard permai^anate. solution. 
Draw a little water into a porcelain evaporating dish or casserole 
and run into it, from the burette, an amount of permanganate 
slightly less than needed. Now measure into the dish with a 



^dbvGooglc 



TESTING 177 

pipette 5 c.c. of nitrous vitriol. This ehould decolorize the 
permanganate. If it does not, repeat, using less permanganate. 
Next add permanganate from the burette until a faint color, 
which remains on stirring, appears in the dish. 

This plan is much more convenient than the first described 
in that it is not necessary to fill, empty and clean a burette for 
nitrous vitriol for each test. It very closely checks the first 
method also. It is convenient to use a permanganate solution 
of such strength that 1 c.c. indicates 2 oz. NaNOs per cu. ft. 
of nitrouB vitriol when using 5 c.c, nitrous vitriol for each t-est. 
In this, if the nitrous vitriol carries 50 to 60 oz. per cu. ft., 
there will be drawn 25 or 30 c.c. of permanganate tor each test 
and a 50 c.c. burette is suitable for measuring it. SucK a per- 
manganate solution is made by dissolving 7.44 g. KMnO* crystals 
in water and making up to one litre. 

EXIT GAS 

A useful thot^ rather rough test to determine if the Gay 
Lussac towers are functioning well mechanically is made by 
drawing several cubic feet of exit stack gas through a bulb tube, 
partly filled with 60° sulphuric acid. The bulb tube is shown in 
Fig. 61. It is chatted with 100 c.c. of 60° sulphuric acid and the 




Fio. 61. 



gas is bubbled throi^ it for several hours. Its content of 
nitrogen oxides is then determined by the nitrometer. This 
test will show approximately how much nitre loss is being suf- 
fered by reason of insufficient contact between the gas and the 
acid in the Gay Lussac towers. Its results will often point out 
poor distribution of gas or acid or the need for further Gay 
Lussac towers. 



^dbvGooglc — 



of 



178 AMERICAN SULPHURIC ACID PRACTICE 

DRAFT MEAStlREMENTS 

It is desirable to observe daily the gas pressures at several 
points in the chamber system to be certain that fans are working 
properly and that no obetnictions exist. The following points 
certainly should be examined; entering and 
leaving the Glover tower, before and after each 
fan and entering and leaving the Gay Lussac 
towers. In some plants further observations 
may be necessary. Two instruments are most 
useful for this work, viz., the small diameter 
U tube and the Ellison gage. The U tube is 
simply a glass tube of J^ to 1 cm. bore bent to 
a U shape with the limbs about 1 in. apart. 
This need not be more than 6 in. long. Behind 
this is placed a graduated paper scale marked in 
inches and tenths or in millimeters. One limb 
of this tube is connected to the fiue or chamber 
whose pressure is to be determined, and the 
other left open to the atmosphere. The dif- 
ference between the level of water in the two 
limbs shows the difference between atmos- 
pheric pressure and that in the Sue. Figure 
62 illustrates this. 
A much more sensitive instnunent is the 
Ellison gauge, shown in Fig. 63. It is suitable for measuring 
very small differences of pressure as well as measuring considerable 
pressures with accuracy. In this instrument as shown, one limb 



Fta. 62. 




is vertical and the other at a small angle with the horizontal. 
Any movement of the Uquid in the vertical limb is accompanied 
by a movement about ten times as long in the sloping limb behind 



^dbvGooglc 



TESTING 179 

which the graduated scale is placed. The Ellison gauge is filled 
with a Bpecial oil colored red and the Bcaic with which it is 
equipped is graduated to show directly hundredths of an inch 
of water and thousandths can be fairly accurately estimated by 
the eye. There is a leveUiug tube ou the case and the base is 
equipped with levelling screws. This is a very practical and 
satisfactory instrument. 

The apphcation of the tests described will be taken up iu the 
chapter on operation. 



^dbvGooglc 



CHAPTER XV 
OPERATION 

To successfully operate a chamber acid plant one should 
get clearly in mind the chemical and physical changes undei^ne 
by the gas mixture in its course through the plant. One must 
know what the ideal attainable conditione are in each part of 
the plant and make such observations as are necessary to know 
that they are being closely approximated. 

First, to state the process briefly and simply, we have in the 
normally operating plant a steady uniform amount of SOj com- 
ing into the chambers and moving through them at such a rate 
that say 90 min. are occupied in the passage from one end to 
the other. Such an amount of nitric oxide is introduced into the 
gas by nitre pots and in the Glover tower as will oxidize sub- 
stantially all of the SOt to sulphuric acid in that 90 min . This 
amount of nitre must be very accurately proportioned or results 
will be bad. A sufficient amount of water or st«ajn must be 
introduced into the chambers at various points to make the acid 
formed therein have a concentration of approximately 50°B€. 
The Gay Lussac towers through which the residual gas from the 
chambers is passed must be fed with a suitable uniform amount of 
cold 60°B6. sulphuric acid to take into solution 85 to 90 per cent 
of the nitrogen compounds existing in the gas. This solution, 
the "nitrous vitriol,"' must be fed back uniformly into the Glover 
tower and there diluted to such an extent that the hot incoming 
gas will remove and carry on with it in gaseous form all of the 
nitrogen compounds. This is, of course, the main source of the 
nitric oxide to the process, constituting by simple inference 
85 to 90 per cent of the amount required. The other 10 to 15 
per cent is supplied by potting new nitre or adding nitric acid. 

The chemical reactions which take place in the chamber 
process have been subjects of much controversy and there is still 
much difference of opinion concerning some of them. Without 
attempting any discussion of the various theories, a brief state- 
ment of the ideas of Lunge will be given. These may or may not 



^dbvGooglc 



OPERATION 181 

be Coirectly representative of the chamber process, but they 
give a good basis for reasouiiig and are very well borne out by 
the phenomena of the chambers. 

The reactions which take place in the nitre pots or the retorts 
of the nitric acid plant are: 

(1) NaNOj + HiSO, = NaHSO, + HNO» 

(2) NaHSO* + NaNOs = Na^O* + HNO, 

The first reaction takes place at low temperatures and the 
latter at higher temperatures. Nitre cake as usually made is 
a mixture of Na»SO, and NaHSOi. 

In the Glover tower, nitric acid is reacted upon thus: 

(3) 2HN0b + 3S0, + 2Hp^= 3H^0, + 2N0 

In the Glover tower, nitrous vitriol is reacted upon thus 
"(denitration") : 

(4) 2HSN0( + SOj + 2H,0 - SH^O* + 2N0 

In the Glover tower this reaction probably also takes place: 
- (5) 2N0 + 2S0, + H,0 + 30 = 2HSN06 

In the Glover tower and the first chambers these two reactions 
4 and 5 are the predominating ones. The only oxide of nitrogen 
which exists in quantity is NO. This is a colorless gas which 
explains the fact that front chamber gases show little red 
color. 

As the gas mixture becomes leaner in SOj the following reactions 
take place: 

(6) 2HSN06 + H,0 = 2H,S04 + N,0, 

(7) N,0, + 2S0« + 20 + H,0 = 2HSN0. 

These two reactions take place more and more as the gas 
approaches the last chamber. The predominating oxide of 
nitrogen is N»0» (probably a mixture of NO and NOi), which is 
a red gas and which gives the gas mixture its red color. 

If conditions are ideal, the gas mixture entering the Gay 
LuBsac tower contains substantially all its nitrogen oxide as NiO) 
or equal parts of NO and NOi. This is absorbed by the sulphuric 
acid in the Gay Lussac packing thus: 

(8) N,0. + 2H^04 = 2HSN0» + H^ 

If an excess of NO exists it is not absorbed by the Gay Lussacs, 
This condition exists when there is a considerable amount of SO3 



^dbvGooglc 



182 AMERICAN SULPHURIC ACID PRACTICE 

in the gas mixture entering the Gay Lussacs. If an excess of 
NOi exista, it partly reacts with the sulphuric acid in the Gay 
Lussacs thus: 
(9) 2N0, + HjSO, = HNO, + HSNO* 

This reactioD is uot complete and some NO* goes through and 
shows as a red cloud at the stack. This condition exists when an 
undue amount of nitre is introduced with the entering gas and 
the SOt is completely converted to sulphuric acid sometime 
before the gas reaches the Gay Lussacs. 

The time of passage of the gas through the chambers is some- 
thing which varies in different plants and which depends upon 
the style of work done. In some chamber plants the period is as 
short as 1 hour and in others more than 2 hours. It is simple to 
calculate from the SOj analyses, the make of acid and the volume 
of the chambers what the period is. This should be known by the 
operator. The amount of nitre necessary to be introduced for 
normal work is also dependent on the individual characteristics 
of the plant and upon the style of work. In modem American 
plants, an average amount is probably 25 to 30 parts sodium 
nitrate for each 100 parts sulphur. For example, if 100 tons 60° 
acid is made per day, the sulphur in the SOi used is approximately 
25 tons or 50,000 lb. The sodium nitrate equivalent of the 
nitrous vitriol plus the new nitre will amount to 25 or 30 per cent 
of 50,000 lb., or 12,500 to 15,000 lb. 

If absolute uniformity of all the factors of the process could be 
maintained, the operation would be very simple. Involving 
as it does h^h temperature, dusty, corrosive gas and sulphuric 
and nitric acids, many irregularities occur and it is in meeting 
them properiy that the skill in operatii^ lies. It is of course, 
much simpler to operate a plant derivii^ its gas from brimstone 
burning than to operate one on blast furnace gaa or some of the 
other metallurgical by>product gases. 

In years gone by, chamber acid plants were almost entirely 
operated by rule of thumb methods. Operators by considerable 
periods of experience became often very skilled in handling the 
process, depending upon such observations aa color of the gas 
mixture in the chambers, effervescence of nitrous vitriol on dflu-' 
tion with warm water and various other equally inexact phe- 
nomena. The old hand at the business did well sometimes but 
several years were necessary to make an old hand. In recent 



^dbvGooglc 



OPERATION 183 

years, particularly since metallurgical gases have come to be 
used to a considerable extent, more exact methods are being 
employed, for control of the acid process. It is true that there 
are plants still operated by the old plan, but certainly better 
work can be done in any plant by making accurate observations 
and records. 

The thing of chief importance in the chamber process is the 
proper proportioning of nitre to SOj. The amount of nitre 
derived from the nitrous vitriol and from the nitre pots or fresh 
nitric acid must at any given time be precisely enough and not too - 
much, to convert substantially all of the SOi coming in at that 
time to sulphuric acid durii^ the period of passi^ of that gas 
through the chambets. If the amoimt of nitre is not sufficient 
all of the SOi will not be converted to sulphuric acid. The SOi 
remaining unconverted will pass out and be lost. The nitrogen 
compounds will exist as NOj and NO with NO in excess and as 
NO is not absorbed by the Gay Lussac towers, that excess will 
be lost. There will be loss of both sulphur and nitre. If the 
amount of nitre introduced be too much, there will be no loss 
of SO,. 

The SOi will all be converted to sulphuric acid some time before 
the gas mixture finishes its passage through the chambers and 
during that time, oxidation of the NO present will proceed and the 
gas entering the Gay Lussacs will contain NOi and NO with NO* 
in excess. NOi is pari,ly but not completely absorbed by the 
Gay Lussac towers and the part that is not absorbed passes out 
into the atmosphere as a red cloud. In the absorption some 
nitric acid is formed which is not particularly good for the lead. 
From these statements it can be understood that nitre loss occurs 
if the amount of nitre originally introduced be either too large 
or too small to completely convert its accompanying SO* in just 
the proper time. 

The original establishment of these conditions is done by trial. 
To maintain them, the modem acid maker depends mainly upon 
periodical observation and recording of the temperatures in the 
chambers at many points throughout the system, and upon period- 
ical determinations of SOi in the gas mixture at a point just 
preceding or following the Glover tower, and at another point 
just preceding the Gay Lussac tower. There are other indica- 
tions which are made of use to some extent such as the concen- 
tration and appearance of the chamber drips, the color of the gas. 



^dbvGooglc 



184 AMERICAN SULPHURIC ACID PRACTICE 

the appearaace of the exit stack, the nitrous vitriol determina- 
tions, etc., but these are used more to con&nn the temperature 
and SOs knowlec^ than anything else. 

To illustrate in a concrete way how these observations are used, 
we will assume that hourly observations and records are made of 

1. Temperature and °B^. of drip on each chamber, - 

2. 80s in gas entering Glover tower. 

3. SOi in gas entering Gay Lussac towers. 

4. Nitrous vitriol. 

5. Atmospheric temperature. 

The operator comes on and immediately makes a set of rec- 
or(^ as above. If the percentage of SOi in the gas entering the 
Gay Lussac towers is correct he knows that 90 min. before, the 
nitre was properly proportioned to the SOj. He looks back on 
his record sheets and observes that at that time the SO* entering 
the Glover was say 8.0 pet cent and that the temperature of the 
front chamber was 195°F. If the gas entering the Glover is still 
8.0 SO2 he can reasonably assume that the front chamber tem- 
perature should be within a degree of ISS'F. If it is much under 
ISS^F. the amount of nitre entering is deficient and if much over 
ISST. the nitre feed is more than necessary. If the SOi in the 
gas entering the Glover has decreased to say 7.6 per cent the oper- 
ator will know by experience that his front chamber temperature 
should be somewhat less than 195''F., say 190''F. If on the other 
hand, the gas entering the Glover has increased to say 8.2 per cent 
he will know that his front chamber temperature should be pei> 
haps 197° or I98'F. He will in the one case decrease the nitrous 
vitriol stream s%htly and continue such adjustments untfl the 
desired temperature is attained. The correctness of the opeiv 
ators adjustments will be shown by the SOj determination at 
the Gay Lussacs 90 min. later. This system of observation and 
adjustment is carried out constantly and if faithfully attended to, 
produces excellent results. 

A further elaboration of the plan of control by SOj tests has 
been proposed and carried out successfully by A. M. Fairlie. 
This plan is as follows: An S0| test is made at a point near the 
Glover tower. A short time later an SOs test is made at another 
point some little distance along say at the end of the leading 
chamber. The time between the tests is approximately that 
occupied by the gas in passing between the two test points. As- 



^dbvGooglc 



OPERATION 185 

Burning uniform gas velocity, for any given SOf percentage at the 
first point there is a certain proper SOa percentage at the second 
point to assure perfect conditions at the entrance to the Gay 
Lussacs. If the 80j at the second point is not correct, an adjust- 
ment in the nitre feed is made. This is a most excellent method 
of control and in certain cases where the gas supply fluctuates 
widely, its practical value is high. 

Control of the nitre feed lies in two things, the nitrous vitriol 
and the nitre pots, oi* the nitric acid. Of the total the nitre 
derived from the nitrous vitriol amounts to between 85 and 90 
per cent, and the added or new nitre to 10 to 15 per cent. It is a 
very good plan-to decide upon a suitable amount of new nitre to 
be used at the beginning of each shift and to maintain it constant 
throughout the shift, barring, of course, large irregularities. 
The minor changes necessary, such as the ones specified above are 
taken care of by changing the flow of nitrous vitriol. This can 
be accomplished readily by means of a long distance control 
arrangement. If the frequent small changes desirable are made 
by varying the amount of nitre potted, the potting schedule 
becomes very intricate. If it is done by varying the flow of new 
nitric acid, many trips to the top of the Glover tower are neces- 
sary as it is hardly feasible to make nice changes in a stream of 
liquid ranging from knitting needle to pencil size with any long 
distance methods. The nitrous vitriol, on the other hand, is a 
rather ample flow, and its nitre content is low so that its control 
is very convenient. 

To illustrate by an example, suppose a system running normally 
with 8 per cent gas ajid proper nitre feed of which 87 per cent is 
from the nitrous vitriol and 13 per cent new nitre. The gas 
decreases to 7.6 per cent, i.e., 5 per cent. The nitre feed should 
be decreased 5 per cent. This can be done by decreasing the 
nitrous vitriol flow by 5.75 per cent (since 5 per cent is 5.75 per 
cent of 87). If the change is made by varying the new nitre, this 
will have to be decreased by 38.5 per cent(8ince 5 is 38.5 per 
cent of 13). With suitable tank space for nitrous vitriol, these 
minor changes are not often reflected back to the Gay Lussac 
towers which go on running with constant flows. 

To decide upon the amount of new nitre to be used for a shift, 
the operator will observe the stock of nitrous vitriol in the tanks 
and whether the nitrous vitriol is of normal grade. If the stock 
ia right and the nitrous vitriol normal he will establish or con- 



^dbyCooglc 



186 AMERICAN SULPHURIC ACID PRACTICE 

tinue the introduction of the normal amount of new nitre. If 
the stock is low or the nitrous vitriol below normal in nitre content, 
he will establish a rate of introduction of new nitre somewhat 
above normal in order to brii^ the nitrous vitriol stock and grade 
back where it belongs. If, on the other band, stock or grade of 
nitrous vitriol are above normal, he will have an opportunity to 
run with less than the normal feed of new nitre. 

The drips on the chambers are tested hourly. They should 
be kept between 48° and SCB^ — not higher, because the nitrogen 
compounds begin to be taken into solution, and not lower, be- 
cause concentration capacity of the Glover tower will be over- 
taxed. The control of the acid strength lies in the amount of 
water or steam admitted to the chambers. Ordinarily the hy- 
drometer readings are taken without correcting for temperature, 
although for strict accuracy, corrections up to .5°B^. should be 
added. The bottom acid in a chamber is always slightly higher 
in strength than the drip. 

The acid issuing from the Glover tower coolers should be ob- 
served several times a day for strength and temperature. It 
should ordinarily be kept between 59° and 61° after applying the 
temperature correction. The minimum represents the lowest 
proper strength for Gay Lussac feed. Above 61° there exists 
danger of incomplete denitration in the Glover unless the burner 
gas is very hot. The temperature of the acid issuing from the 
cooler should be not over 80°F. and preferably less. From time 
to time, the coils in the cooler become encrusted and. when the 
acid temperature rises above 80°F. the cooler should be drained 
and washed out with a hose. It is well to test this acid from time 
to time by the nitrometer to be certain that no nitre is being 
retained by the acid. If denitration is not complete, the feed of 
weak acid on the Glover must be increased. 

The nitrous vitriol issuing from the first Gay Lussac tower is 
tested with potassium permanganate once an hour. Any great 
variation from the normal should be accounted for. This 
normal nitrous vitriol is something which will be decided upon 
for each system. It is right in one plant to run with perhaps 35 
oz. NaNO] per cubic foot and in another with 70 oz. or more. 
Several considerations enter. The amount of absorbable nitre 
entering the Gay Lussacs in a given system will be fairly con- 
stant. The nitre content of the nitrous vitriol will then depend 
uptm the amount of acid fed to the Gay Lussac tower. The 



^dbvGooglc 



OPERATION 187 

smallest permissible amount is that which can be divided and 
distributed over the packing with sufficient thoroughness to 
assure wetting the entire area. If any of the packing remains 
dry, or nearly so, the nitre laden gas will pass through that part 
of the tower without having the nitre recovered from it, A good 
safe quantity to assure wetting is one ton of acid per.square foot 
of horizontal area per 24 hours. If the tower has for example, an 
area of 200 sq. ft., about 200 tons per day should be put over it. 
This quantity may be exceeded and assurance of complete wetting 
made doubly sure, but a greater amount than that mentioned is 
not necessary. If the plant served by this tower makes 100 
tons 60" acid, the nitre entering the Gay Lussac tower will 
amount to about 12,500 lb. NaNOg and if 87 per cent recovery is 
made, the normal nitrous vitriol will be 45 to 46 oz. per cubic 
foot. 

If, as in many plants, the horizontal area of the Gay Lussac 
towers is proportionally less, a smaller acid circulation will be 
used and nitrous vitriol of higher nitre content produced. 

In any event, a proper normal will be established and any wide 
variation from it indicates an irregularity in process, or acid 
flow. 

An observation and record of drafts should be made once a day 
by the instruments already described. Any important variation 
from normal should be investigated. Sometimes in a Glover 
tower, for example, there will be a very gradual increase in the 
packing resistance indicated by an increase in the difference 
between the pressures at bottom and top. This indicates usually, 
the accumulation of sediment or dust in the packing, and when 
it reaches a certain point, flushing out is necessary. 

LABOR FORCE 

The number of men required to operate a chamber plant is 
snuill, but care and reliability are absolutely essential. In 
order to ^ve an idea of the normal labor force required, assume 
a 100-ton unit having mechanical burners, flue nitre pots and 
acid eggs for pumping. There will be, on each shift, one fumace- 
man, one nltreman, one pumpman and a chamberman who 
exercises general supervision. On the day shift will be a repair- 
man and two laborers. This force may be reduced in certain 
small plants by havii^ the furnaceman attend the nitre pottifig 



^dbvGooglc 



188 AMERICAN SULPHURIC ACID PRACTICE 

as well as the furnaces. In case a nitric-acid or mixed acid plant 
is used instead of flue pote, one man will produce enough nitric 
acid in one shift to run the plant 24 hours. 

The whole operation should be supervised by a man of experi- 
ence and judgment. It is a false economy to run even a modest 
sized plant without such a man. 



iiz^dbvCooglc 



CHAPTER XVI 
CONCENTRATION 

Sulphuric acid made in the chambers is only, at its best, 52° to 
SS^B^., and where an acid of greater concentration is required 
it is necessary to concentrate this chamber acid. There are 
various methods of doing this. 

Before the introduction of the Glover tower, chamber acid was 
concentrated in lead pans, up to 60° or 61°B£. Since the Glover's 
introduction it has been an easy matter for manufacturers to 
bring their chamber acid up to 61°B^. in the tower, as described 
under that subject. 

Lead pans are still used in old works that have no Glover 
tower, and in concentrating waste acid. 

The vapor from boiling, dilute sulphuric acid consists almost 
entirely of water vapor: therefore, the acid will become more 
and more concentrated, as the boiling proceeds, as long as 
60°B6. is not exceeded. 

In pan concentration lead pans are almost universally used for 
the concentration of acid up to dO^BS. Above this point, lead 
is acted upon, necessitating the use of other material. 

Pans may be heated by direct flame, either from the top or 
bottom, by steam, or by the waste heat from pyrites or sulphur 
burners. 

When the purity or appearance of the acid is of less importance 
than the saving in fuel, or in labor, top firing is generally used. 
The pans are generally 30 ft. long, 4 ft. 11 in. wide, with sides 
17 in. high. They are built from heavy lead, 15 to 30 lb. to the 
sq. ft., and always in one piece; the corners are never cut, but 
are folded over. 

It is necessary to protect the lead from the direct action of the 
fire. The fire box is always built separate from the pan, and is 
only connected to it by an arch which extends the length of the 
pan, and a fire-proof clay slab at the bottom. The pan inside is 
protected by acid-proof bricks or slabs. At the long side these 
extend up to the arch, while on the short, or fire side, they only 
reach to the top of the pan, and there is placed the fire-proof 



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ISO AMEniCAN SULPHURIC ACID PRACTICE 

slab to the Gre box. There are openin^^ left Id the bottotn of the 
partition slabs, so the acid can circulate freely. The pan is 
always raised 3 ft. or more above the grouod. 

The acid is introduced at the end nearest the fire box, and 
drawn out at the far end. Evaporation is very rapid, both 
because the hot gases come into direct contact with the acid, and 
because the chimney draught carries away the water formed. 
The damage to the pans is very sl^ht, as the brick lining protects 
the lead from direct heat, and up to 60°, or even fil^B^. the acid 
has very little effect upon lead. But above that degree of con- 
centration not only does the acid act upon lead, but its boiling 
point gets close to the temperature at which lead begins to 
soften. 

Keeping the acid at a constant level also protects the pans. 
Except for repairs the acid is never drawn off entirely, but as 
the concentrated acid sinks and is drawn off from the bottom 
fresh weak acid is added at the top. Efforts at water coolii^; 
have not been successful, as Ifiari PJIT' "*" jackets start leaking 
easily, and cause trouble. 

The greatest destructive effect is at the fire end of the pan, and 
to keep it as cool as possible the weak acid is added here, through 
a pipe throt^h the arch. The syphon to withdraw concentrated 
acid is at the cool end of the pan, but even then the acid is too 
hot to use, and is run into shallow lead cooling pans, stayed with 
wood or iron frames. 

If the pans need staying it should be done by cast-iron or 
pressed-steel grids, as their large radiatli^ surface will help keep 
the lead cool. 

Coal used will vary from 2 per cent to 10 per cent by weight of 
the acid concentrated, varying with quality of coal and size of 
pan. A long pan is most economical. 

One square foot of pan surface will concentrate 150 lb. of 
chamber acid to 61°B4. per 24 hours. 

The strength of concentrate is regulated by the fire and the 
weak acid fed. 

No data ia available as to the loss of acid in this method of 
concentration, but it is probably more than for bottom-heated 
pans, as the stream of hot gases carries away acid in minute 
drops, that are very hard to condense. We meet this same mist 
in the contact process, and it gives us the same trouble. 

The spray of acid from the stacks is not only a loss, but a 



iiz^dbvCoOglc 



CONCENTRATION 



191 



nuisance, and sometimes the basis . of suits by neighboring 
property owners. Gas, instead of coal, firing has been tried aa 
a remedy, without much success, and the only relief has come 
from the use of higher stacks, causii^; a better diffusion in the air. 

Lead pans heated from below are always smaller than those 
usii^ "top fire," and are built in seta. The reason for this is 
that the-pans nearer the fire are worn out first, and it is cheaper 
to have a small pan to replace. The concentration is very regular, 
the weak acid Sowing in at one end, and running from one pan 
to the next, until it runs off sufEciently stroi^ at the other end. 

The pans are rectangular, 5 to 7 ft. on a side, and about 15 in. 
deep. There are four to six in a set. The acid is carried from 
pan to pan by overfiow pipes, so that it takes the acid from the 
bottom of one pan to the top of the next, as the acid is stronger 
at the bottom. The Sow of weak acid is so regulated that the 
proper concentration of acid is obtained at the last pan. 

The pan bottoms are protected from the fire by iron plates, 
these plates being heavier at the fire end. The iron, being a 
good conductor of heat, also assists the heat distribution. Some- 
times copper plates are placed between the pan bottom and the 
iron plate to prevent, by their good conducting qualities, local 
overheating and buckling of the pan. 

The general plan is to place the fire under the weak pan. In 
this way the strong pan does not receive much more damage 
than the others, and evaporation goes on satisfactorily as welL 
The old practice was to place the fire under the strong pan, 
because the boiling point of the strong acid is the h^hest, but 
on account of the wear on the pan it has been found more 
economical to reverse the operation. 

Bode gives the following table, where the fact that the greatest 
heating takes place at the third pan shows that the fire is badly 
utilized : 







1st 
pan 


2nd 
pan 


3rd 
pan 


4th 
pan 


5th 
pan 








pan 




25° 
110' 


112° 
113° 


150° 
120° 


160° 
128° 


148° 
134° 


145° 
140° 


U3°C. 








24' 
110° 


110° 
113° 


146° 

us- 


156° 
126° 


145° 


142° 


142°C. 











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192 AMERICAN SULPHURIC ACID PRACTICE 

He estimates, for English practice (1910), that a aet of six pans 
will cost $500, and the maintenance will be 12 per cent;. Total 
coet of concentration 55f! to 65^ per ton. 

Coal required is about 15 per cent of the weight of the acid 
concentrated, and each squae foot of pan area will produce 85 lb. 
of 60° acid every 24 hours. 

Fans for utilizing waste heat from pyrites or brimstone burners 
must be designed for each special case, the principles being the 
same as for bottom-heated pans. Sometimes the pans are 
placed over the dust flue, but protected from the direct action of 
the burner gases by brick, or often over the burners themselves. 
This method of concentrating is very cheap, requiring only part 
of a man's time, and the maintenance chaises, Bode says, 
lOf! to 18^ per ton (1910). 

Steam pans are of many forms, all dependUig upon slow 
evaporation far below the boiling point of the pan acid. Steam 
is introduced through a lead coil, which lies on the bottom of the 
pan, the condensation returning from it to the boiler. There is 
no acid mist escaping, so no injury to vegetation ia possible; 
but steam coil concentration ia so expensive that the writer does 
not know of a single installation in the United States. 

OTTALITY OF LEAD 

Lead as heavy as that used for concentratii^ pans is difficult 
to bend cold, so a light fire ctf shavings is made on the part of 
the lead plate to be bent, and the lead softened sufficiently to 
be easily manipulated. 

W. B. Hart, Journal of the Chemical Soci^, 1907, writes as 
follows: 

Lead may fail from either or both chemical or phj^ical faults: 

The effects of impurities are as follows: 

(a) With bismuth and tin, lead forms alloys of low fusibility, 
causing local perforation. Acid may concentrate in these leaks, 
and become strong enough to attack the lead itself. 

{b) Aluminum, tin, or zinc may cause sudden failure at certain 
stages of the concentration. 

(c) The physical condition of zinc will sometimes increase the 
chemical action of acid upon lead. 

(d) Electrolytic action may be set up between deposits of 
impurities and the lead. 



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CONCENT RA TION 1 93 

(e) Antimony may have a strong and harmful chemic^ effect, 
and copper, arsenic, and silver very little. Copper may even 
be helpful under certain conditions. By constant use copper 
may be entirely dissolved out, and ite corrosive effect upon other 
impuritiea lost. This will sometimes explain the sudden failure 
of a pan that has been in good condition for a long time. 

(J) Pure lead, under normal pan conditions, is undoubtedly 
less affected than the impure metal. 

Faulty physical conditions may be due to bad remelting, use 
of unsuitable castit^ temperatures, and too severe pressure in the 
rolling operation. 

(a) Production of a loose crystalline structure, by casting the 
metal at too high a temperature, causing leakf^e. 

(b) Production of a surface more susceptible to attack, by too 
severe pressure during rolling. 

(c) Strong acid action in the temporarily physically altered 
form of lead, before the annealing effect can take effect, explains 
the failure of pans that have been in use a very short time. 

(d) Altered physical condition can make unsuitable even a 
lead of exceptionally pure chemical composition. 

COMCEHTBATION PROM 60° TO 66° 

Concentration of sulphuric acid naturally resolves itself into 
three divisions — first, chamber to 60''B6.; second, 60°to66''B^., 
or "93.19" (per cent), as it is often called, and from 93.19 per 
cent HiSO* up to 97.50 or 98 per cent HjSOt. 

Ordinary pan concentration, as just described, is the usual first 
step. For the second several methods are used, and are presented 
in what the writer considers their order of merit. 

First, because very simple and efficient, comes the "heat ex- 
changer." As applied at one large works, this is a continuation 
of the lead pans. 

A series of five lead pans concentrates the acid to SZ^Bfi,, and 
the acid leaves the last lead pan at a temperature of from 285° to 
320°F., practically the temperature of the first pan. The highest 
temperature usually comes in the third pan. 

From the last lead pan the acid flows to a pulsometer, or air 
lift, which raises it to the top of the heat exchanger. The heat 
exchanger is a lead-lined steel tower, further lined with three 
courses of acid-resisting brick, and filled with broken quartz. It 



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194 AMERICAN SULPHURIC ACID PRACTICE 

is 12 ft. high, and 21 in. in diameter inside the brick. The acid 
trickles down throi^ the broken quartz packing, and meets the 
aBcending gases, rich in SOi, from the covered iron pan, which is 
Bet directly over the flame. The falling acid is cool enough to 
absorb practically all of the 80i in the ascending gas, and while 
it does take up some of the moisture driven off too, it is not 
enough to hinder the concentrating operation. The unabsorbed 
gas, now almost entirely steam, passes from the top of the heat 
exchanger to two lead-lined condensing towers, filled with coke. 




which catches any drops of acid. The passage of the gases 
through the heat exchanger and condensii^ towers is induced by 
a steam jet, attached to the exit flue of the second tower. 

From the bottom of the heat exchanger the acid, enriched by 
the SOi absorbed, flows to the iron pan, where it is concentrated 
to 66°B6., and is then syphoned off to a tant-iron box, equipped 
with cooling coils of lead, where it is cooled down to SCF, 
Thence it goes to storage. 

The temperature of the iron pan is unheeded. The first lead 
pan is kept at 285° to 310°F., and upon the fire necessary to 
accomplish this depends the d^ree of heat of the iron pan. 



^dbyGoogle 



CONCENTRATION 195 

The lead pans hold the following temperatures: 

No. 1 about 320°F 
No. 2 about 330 
No. 3 about 360 
No. 4 about 345 
No. 5 about 330 

The Eessler apparatus really covers two steps of the concen- 
trating field, as it will bring chamber acid up to 98 per cent HjSOi 
in one operation. In this apparatus hot air is used to concentrate 
the acid. The operation requires that a current of hot air shall 
be brought into contact with the liquid, to immediately reduce 
its temperature. The air must become thoroughly saturated 
with steam and acid vapor. The apparatus must be so con- 
structed that it will stand the action of hot acid, and that the 
deposits do not give any trouble. Under these conditions the 
acid may be concentrated at a temperature far below its boiling 
point, for instance, to concentrate acid to 95 per cent H^SOi, 
boiling at 280''C., the temperature needs to be only 180° to igO^C. 

The part of the apparatus where the gases are saturated with 
-acid vapors, and the temperature greatly reduced, is called the 
"saturator. " Immediately above it is placed the "recuperator," 
where the acid vapors are caught. This recuperator resembles 
the dephlegmating columns used in the rectification of spirits. 

The saturator is a trough built of acid-proof slabs, surrounded 
by a thick lead jacket, both of which must resist, hot acid and 
gases. Between the bottom and cover of the saturator there are 
placed several partitions, to force the hot gases into immediate 
contact with the acid. In this way the gases are quickly reduced 
to ISCC, and the acid as quickly gives off its water and some 
acid vapor. The acid is run off from the saturator in the con- 
Gentrat«d state, at the end furthest from the fire box. 

The recuperator consists of a tower, lined with a«id-proof 
brick, and containing 5 horizontal plates, dividing the tower up 
into 6 equal parts; each plate, however, is perforated by 100 holes 
with raised edges, so that there is always a film of acid on the 
plates. The holes are covered by inverted porcelain cups with 
jagged edges, forming an hydraulic seal, so that ascending gases 
must bubble up through the acid on the plates. The chamber 
acid runs to the top plate first, and then by overflow piping to the 
other lower ones, and finally to the saturator. The gases from 



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196 AMERICAN SULFHURW ACID PRACTICE 

the saturator are drawn up through the holes, and so through the 
descending acid, by an injector, and SO* is absorbed, and a little 
water given up, as in the tower of the just described heat 
exchanger. 

A thermometer is placed at both top and bottom of the recu- 
perator, for temperature control. The lower one should stand 
at SOOT., the upper a little under 200"^ 

After leaving the recuperator the gases pass through a coke 
tower, to recover any acid spray. 

Ninety-eight per cent HjSOj can be made in one operation, from 
chamber acid. Gas firing is most satisfactory, and requires 8 
per cent coke, on the acid concentrated. The injector requires 
2 per cent steam, also figured on the concentrate. 

The Benker system is a third modification of the heat ex- 
changer, all being based upon the principle of the Glover Tower, 
althoi^h I do not know who first applied this ^stem in this way. 
The Benker system uses a cascade instead of a pan, however, for 
the final heating. 

Two parallel rows of duriron or tantiron plates, are arranged 
in cascade form, with the flue running up between the two rows. 
On account of the great fire space, and the thin film of acid, 
evaporation is very rapid. The cascades are covered, and the 
gases are lead to a packed tower, which removes the SO*, the 
drai^ht being provided by a fan. A cooling box is necessary, 
between the cascades and the tower, as the gases, owing to the 
intimate contact with the heat, due to the thin film of acid, are 
too hot for good working of the tower. The gas passes through 
a coke tower after the tower. 

The acid leaves the tower at the bottom, at a concentration of 
61° to 62°B^., and a temperature of 300°F., running direct to the 



Such a plant, to cost, in 1916, S3,500, will furnish 9 to 10 tons 
of 92 to 93 per cent HiSOj, clear as water, in 24 hours, with a 
coke (for gas) consumption of 12 to 15 per cent on the acid made. 
At this concentration losses will run about 3 per cent, and higher 
on 98 per cent acid. 

Because of the thin film of acid on the plates, the temperature 
of the acid will get higher than in either of the two previously 
mentioned systems, giving this method greater capacity, but 
driving off more SO*: and as the tower acid is less efficient, the 
higher the SOi content of the ascending gases, the losses are consid- 



^dbvGooglc 



CONCENTRATION 197 

erably greater. Of the three, the writer prefers the "heat 
exchai^r," 

The objection to the use of direct heat in all concentrating 
systems is that at the high temperatures, up to 800°C., from direct 
flame there is considerable dissociation of the acid into HjO and 
SOg, requiring very large spaces, usually coke boxes, to give 
room and thus time to assist in reassociation. For instance, in 
a Kessler system, concentrating 5 tons of 66°6£. acid per 24 hours, 
a coke boic 24 ft. long, 8 ft. wide and 6 ft. high is needed: and this 
coke box, with its supports, constitutes a large proportion of the 
cost of plant. 

The Buffalo Foxmdry and Machine Co. system gets away from 
this by combining outside and direct heatii^, as follows: 

The hot gases pass from the fire around the acid pot at a 
temperature of approximately 800°C.; thence to a heat exchanger, 
where they heat air that is under 5 lb. pressure and then pass into 
the tee that is at the bottom of the concentrating tower, at a tem- 
perature of approximately SOO^C, This tower, of four 2-ft. 6-in. 
sections of cast iron, 36 in. in diameter inside of lining, is lined 
with sheet lead and acid-resisting brick, discharges the vapors, 
now well cooled down, through a 12-in. I.D. lead pipe, to a 6-ft. X 
6-ft._^ X 3-ft. scrubber, where any acid carried over is condensed. 
There is very little dissociation at the temperatures employed, 
and this small scrubber, is ample in size. 

The weak acid feed is to the heat exchanger, which is heated 
by the concentrated acid, hot from the pot. From the heat 
exchai^r the weak acid goes to the top of the tower, trickling 
down over the tower packing meeting the ascending gase^ from 
the tee, and runs off into the acid pot. The final concentration 
takes place in this pot, and the overflow from it is 66°B€. and plus 
acid, which is cooled for storage by heating the feed acid. 

This pot, in addition to its acid feed from the tower, receives 
the heated air under pressure, from the heat exchanger, near the 
bottom. A small removable liner is placed to receive the im- 
pingment of the air and protects the pot. A collar of high-silicon 
iron, carried on lugs, and outside of which is the outlet, pre- 
vents the weaker acid from reaching and attacking the pot itself. 
The arrows in the sketch show the course of the acid within 
the pot. 

The an* introduces heat and agitation, furnishing, in effect, 
"direct flame," but at a low enoi^h temperature to avoid acid 



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198 AMERICAN SULPHURIC ACID PRACTICE 



^dbyGoOglc 



CONCENTRATION 199 

disBocktioD and, of course the heat outside the pot is ^milar 
to that applied to the bottom of a pan. 

The vapors rising from the pot pass to one leg of the tee, the 
other one of which receives the gases from the heat exchanger, 
and up through the tower. 

The same number of heat units is applied as sometimes give a 
dissociation up to 25 per cent, at a concentration to 97.5 per cent 
in a direct heated [>an system, but the distribution is better. 

Tubes and small castings are made of high-silicon iroc-lat^r 
ones, such as the pot and tower sections, are close grained 
semi-steel. 

This system uses 8 per cent to 10 per cent of coke on the acid 
made depending upon the strength of the feed, and finaJ concen- ' 
tratioQ of the acid. 

PLATmnii snLLS 

The concentration of sulphuric acid in platinum dishes is still 
carried on to a small extent in this country, when very pure acid 
is required, as for laboratory use. But with platinum at $145 
an ounce (1920), the contact process can use it more economically. 

In the platinum still of today only the pan is platinum, the bell 
being a lead water jacket. The size of the still depends upon the 
production — roughly 75 oz. of platinum per ton of 95 per cent acid 
produced per 24 hours. A dish to turn out seven tons of 95 per 
cent acid daily would weigh 45 lb., be 33>^ ft. in diameter, and 
cost $78,300. The rim of the dish has a groove in which the lead 
bell sets loosely, condensation forming an hydraulic seal. There 
is an overflow pipe from this seal, to remove the weak acid 
condensed. 

A lai^e pipe runs over from the top of the bell, and dips down 
into a condenser, through which the vapors pass, the weak 
condensate frora here and the seal being added to the feed. Two 
or three stills make up a set, the acid from the first one going by 
gravity to the next, for further concentration. 

The still is carried upon a cast-iron frame. 

Acid fed to platinum stills is first concentrated in bottom-fired 
lead pans, to furnish it as pure and clean as possible. Glover 
tower acid contains too much dissolved iron sulphate, which 
settles out to form "crusts" in the platinum stills. The stills 
are cleaned by running them as nearly dry as possible, and wash- 
ing them out with hot Water or weak acid, which dissolves tiie 



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200 AMERICAN SULPHURIC ACID PRACTICE 

crusts. The frequency of cleaning depends entirely upon 
the acid fed, it may be every day, it may be every three 
months. 

The acid is kept very shallow in the still, from 2 to 3 in. only, 
and even comparatively small heat fluctuations cause large varia- 
tions in the concentration of acid produced. Coal firing is not 
sufficiently steady, so gas, usually from a producer, is used, and 
gives excellent results. 

The lead work on such a set of stills has to be renewed in two 
years. The platinum is also slowly dissolved, losses running 
from .2 to .3 g. per ton of 98 per cent acid made. 

TITREOSn, CASCADE COHCENTRATORS 

The continuous cascade concentrator was originated in Eng- 
land, and at first consisted of four or five glass retorts arranged 
in cascade over a coal- or a gas-fired furnace. Porcelain dishes 
set in an acid-proof brick chamber were later substituted for 
glass retorts. One of the most serious drawbacks to this system, 
whether using glass or porcelain, was the heavy breakage of the 
pans and the difficulty of getting high fuel efficiency; hence the 
system was not generally adopted. 

With the development of vitreoeil (fused silica) in 1906, there 
was a more general adoption of the use of cascade systems, and 
several were installed in this country. The largest is at the plant 
of the Davison Chemical Co., at Baltimore, Md. 

Plant for full range of concentration (50° to 66''B6.) is com- 
posed of rectangular trays and circular basins. The trays mea- . 
sure 24 X 12 X 6 in. and are used only in the operation of the 
plant covering the rai^ from 50° to WB^. This portion of the 
plant is uncovered, as the fume from acid below 60°B^. is practi- 
cally acid free. The basins are used on the range 60° to 66°B6. 
and may be either 12 in. or 16 in. in diameter. This portionof 
the plant must be covered, as the fiunes from acid of higher 
strength than 60°B£. carry sulphuric acid and it is essential 
that these fumes be scrubbed of their acid content before allowing 
them to pass out into the air. If higher strengths than 66°B£. 
are required, the aeid from the cascade may be run directly into 
iron pans, which would be so set up as to be fired from the same 
firebox as the basin cascade, and the fumes from this acid re- 
covered by one of the systems previously described. 



^dbvGooglc 



CONCENTRATION 201 

In the full range plant, the tray and basin cascades are set 
up so as to allow a continuous flow from one to the other and to 
allow a fire from a single firebox. 

There is but slight loss of acid in the concentration up to 66°B^., 
this usually amounting to about 2 per cent, based on the weight 
of finished acid, and usually running in strei^h from 10° to 12°B^. 
for the entire distillate. For the fuel efficiency of the cascade 
concentrator, it is usual practice to concentrate over the range 60° 
to 66°B^. with a fuel consumption of about 14 per cent, while 
over the range 50° to 66°B6., the fuel consumption is usually 
about 17 per cent. The above percent^e figures are based on 
the weight of finished acid and figuring oa soft coal as a fuel 
running about 13,000 B.T.TJ. Breakage in usual operation 
amounts to about 5 per cent on the basins and about 1 per cent 
on the trays per annum. 

The cascade concentrator is appficable to the concentration 
of sulphuric acid from either a brimstone or pyrites set. Sludge 
acid may be recovered in the cascade plant if free from high per- 
centages of mineral or organic matter, which will cause excessive 
frothing due to evolution of SOj. Sludge acids carrying only 
small amounts of oi^anic matter, and in which the frothing would 
not be excessive, may be readily carried on in this type of plant 
by using a specially designed basin. 

The cascade type of concentrator, using vitreosil dishes is 
especially recommended where freedom from contamination 
during concentration is desired. 

Vitreosil is imaffected by sulphuric acid of any strength or at 
any temperature. Its melting point is about 1,750''C., although 
there is slight softening around a temperature of 1,400°C. Vit- 
reosil due to its extremely low coefficient of expansion .00000054 
per degree centigrade, over the range 0° to 1,000°C., about }i^ 
that of glass, is applicable to high temperature operations. 

The process of the Kalbperry Corporation, worked out from 
the tower developed at the plants of the Franklin H. Kalbfieisch 
Co., cannot be described, aa it is a trade secret, unpatented, 
licenses being issued for its use. One important feature is that 
it will give a high degree of efficiency on concentrating very 
dirty acid, the concentrate being perfectly clean. Operating cost 
is low, in 1916, it being 50 cts. per ton of 97 per cent acid pro- 
duced. Exclusive of buildir^ and license, this tower cost, in 
1916, about $4,000. 



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202 AMERICAN SULPHURIC ACID PRACTICE 

The license charge is a flat fe« of $3,500, in return for which the 
client receives complete detail working drawings, bills of material, 
flow sheets, and can obtain the service of a skilled operator for 
a time to demonstrate and put the tower on a working basis. 



Nitric acid alone cannot be handled in steel or iron containers, 
because of its corrosive action, unless it is sufficiently dilute. As 
in most nitrating operations water is liberated, and must be 
cared for, sulphuric acid fulfills the double function of diluting 
nitric acid to a point where it will not attack iron containers too 
energetically, and of absorbing the water liberated. 

It is impracticable to remove this water without separating 
the two acids and reconcentrating them, and a brief description 
of the most successful method of separation is in order. 

Nitric acid boils at 188°F., water at 212''F., but a mixture below 
91 per centacjd boils at a higher point still. 68.5 per cent HNOs 
boils air251.5°f% which is the highest boiling point of nitric acid 
of any concentration, and i^tric acid of any concentration, if 
boiled alone, wUl approach that concentration, by the loss of 
HNOj if above that concentration, of water if below 68.5 per 
cent. It will then evaporate to dryness, remaining at 68.5 
per cent. 

So it is necessary to use something to retain the water, letting 
the HNO) fumes pass to the condensers, and sulphuric acid is an 
ideal substance. 

A tower 21 ft. high, 3 ft. in diameter, packed with quartz, with 
openings for steam. at the bottom and for the concentrating 
mixture at the top, with sulphuric acid opening at the bottom and 
fume (HNOj), outlet at the top, is the apparatus required. 

The concentratng mixture, strong HjSO* and weak HNOj, is 

J.J. ,, , , per cent HiSOi „ 

denved from the formula , „ „„ , — uTLrr^ = S 

per cent HjSO* + per cent HNOi 

H = per cent HNOj in mixture, 
* . h = per cent HjSOi in mixture, 

then, S = IqqZT^ 

S is therefore directly proportional to HiSO*, and inversely 
proportional to HiO, and is a direct measure of the heat-develop- 

D,pl,zsdbvG0(>glC 



CONCENTRATION 203 

ing capacity of the mixture: and since a definite amount of HNOi 
requires a definite amount of heat to volatilize it, it must be high 
for high HNOi, low for low. 

With HjSO* about 84 per cent the mixture automatically falls 
about right for complete denitration. 

The addition of water, in the form of steam, is the one weak 
point. It takes about a pound of steam to distill a pound of 
HNO>. 

The concentratit^ mixture is fed in at the top and tricklesdown 
over the quartz, meeting the steam blowing in at the bottom. 
The heat from the steam, and that from its reaction with the 
HjSO*, volatihze all the HNOj, which rises, being pulled throu^ 
by suction. 

As it approaches the top the steam begins to condense, and 
havii^ greater affinity for the HiSOt than for the HNO», unites 
with it, leaving the vapors practically water free. The reverse 
of this process takes place in the decending mixtures, more and 
more HNOt is driven oS in its downward passage, until at the 
bottom there is no HNOt, the mixture being only HjSOi and 
HiO. A top temperature of under 200°F, is excellent operation, 
and that at the bottom should run 300 to 330°F. 

The rate of feed mixture and steam must be correct, or imme- 
diate trouble insues. Too httle mixture means too Uttle HjSO* 
to unite with the steam, the excess of which escapes at the top, 
raising the top temperature, and giving weak nitric acid. Also, 
too much steam may first Uberate, and then condense and 
reabsorb HNO». 

If too much concentrating mixture is used, there will not be 
heat enough to vaporize all the HNOt. 

The weak sulphuric acid is then concentrated in lead and iron 
pans and the heat exchanger, up to 66°B6. 

The vapors from the concentrating towers are almost entirely 
HNO,, with a little H»0, NO and NO,, and traces of Na, NjO, 
and CO). All the water, and practically all the HNOt, are con- 
densed, a httle HNOj going over as a spray into the absorbtion 
towers, where it condenses. The NO is oxidized to NOj by the 
air present, and then reacts as follows with water: 
2N0i + H,0 = HNO, + HNO, 

The HNOi is absorbed, and the HNOi reacts as follows: 
3HN0i = 2N0 + H,0 + HNO,, 



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204 AMERICAN SULPHURIC ACID PRACTICE 

the NO being oxidized and the product decompoBed over and 
over again, until it is practically all acid. 

Spent acids from the nitration of nitro-cellulose, nitro-glycerine, 
or ftimilftr substances contain so small an amount of low oxides 
of Nitrogen actually in chemical combination with HiSOt, that 
whilst dilution of the spent acid in the denitrating tower is neces- 
sary, such dilution need not be carried to anythii^ like the extent 
that is necessary when handlii^ spent acid from nitration of 
hydrocarbons: and in the case of spent acid from glycerine it 
may be regarded as more of a distilling process than dinitration; 
the principal function of the tower in this case (nitro-glycerine) 
is to remove the nitric acid as such from S/A in a most highly 
concentrated state, and decompose traces of N.G. in S/A. 

But "spent" from the nitration of hydrocarbons, in the manu- 
facture of T.N.T., picric acid, etc., usually contains about 2 per 
cent nitric acid and 4 per cent of the lower oxides : in the case of 
one lai^ T.N.T. plant in Canada it was the equivalent of 7 per 
cent of 100 per cent HNO» — certainly well worth recovering. 

These lower oxides are in large part not free, but are combined 
as definite compounds with sulpbiuic acid, and the Buffalo 
Foundry & Machine Co. has worked out a plant which will 
make a 98 per cent recovery at low cost. 

Their process for handhng S/A from nitro-^ycerine or nitro- 
cellulose is based upon careful heat control : and this includes the 
superheating of the steam introduced, furnishing the amount of 
heat required with the minimum of water, thus keeping down the 
amount of water which must be removed by, and later from, the 
sulphuric acid. 

A X2-in. column of high siUcon metal If^ged with 4 in. of 
asbestos, or acid proof lined C.I., 35 ft. high, is fed at the top with 
heated acid, the temperature being controlled within approxi- 
mately 1°C.,. automatically. This top temperature is kept under 
lOO'C, the exact point depending upon local conditions (Fig. 66). 

If it is at 100°C., the recovery wUl be in 93% HNO,v 
If it is at 95''C., the recovery will be in 97% HNO»'' 

The steam, carrying 100° of super-heat, is introduced through 
high-silicon iron tubes, full of small holes, 6 in. below the surface 
of the liquid in the bottom. The bottom temperature is main- 
. t^ned at approximately SOO'C, The amount of steam intro- 
duced being kept down, the H1SO4, absolutely denitrated, runs 



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CONCENTRATION 



205 



out 78 per ceiit-80 per cent, instead of the customary 60 per cent 
that obtains from the ordinary denitrating system. At this 
strength iroD paus may be used for concentrating, eliminating 
lead pans entirely. 

The fume leaves the tower at the top, and is carried down 
through a condenser, from which the condensate Sows to a re- 
ceiver. From this receiver the non-condensible gases are sucked 
throt^h oxidizing towers, in series, similar in construction to the 
denitrating tower, but of greater diajneter and less height. In 
th^e towers good construction, low velocity, plenty of air, and 




good atomizing of the absorber make the oxidation good enough 
to make a 98 per cent recovery. 

The absorbing liquid fed to each tower is from the base of the 
succeeding tower, raised to a receiving tank above the tower, and 
fed through an atomizer, with valve control. The fume is fed 
at the bottom of each tower, and drawn off at the top. 

Mr Authur Hough, the designer of the apparatus, stated that 
the increased operating efficiency of a modem dynamite plant, of 
10 tons per day capacity, using the improved acid recovery 
system, amounts to many thousands of dollars per year. 

Corrosive liquids, like strong mineral acids, cannot be handled 
by pumps, bo the pulsometer has been developed. It is shown 
in section in Fig. 64; is made of chemical stone ware, and operates 



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206 AMERICAN SULPHURIC ACID PRACTICE 

as follows: Up from the three openings shown lead tubes, not 
over an inch and a quarter in diameter. The inlet, indicated by 
"acid" comes from a raised supply, which, flowing in, of course 
rises to an equal height in the two other tubes. Sufficient pres- 
sure of air is then blown in at the appropriate opening, to over- 
come the head of hquid. This air blows all the liquid out of the 
air inlet, blows down and under the partition, and of course rises 
through the hquid, up throtigh the "out" tube. It is kept from 
entering the incoming tube by that tube being extended near to 
the bottom of the pulsometer than the bottom of the partition. 

The air, rising through the outgoing tube, carries up with it 
bubbles and regular "slugs " of Uquid, these slugs being sometimes 
two inches thick. If the tubes are too lai^ in diameter the slugs 
will not form, the air just blowing up through, and agitating the 
liquid. 

The heigbth to which a Uquid can be raised by this apparattis 
depends upon the hydrostatic head of the entering liquid, air 
pressure, diameter of tubes, and Uquid itself— nitric acid can be 
raised to four times the hydrostatic head. 

BATTERY ACID 

Battery acid is pure sidphuric acid, from 1.118 sp. g. to 1.125 
sp. g. 

As the fume from the concentration of acid from 60° to 66°B^. 
runs about 1.1 sp. g., and is usuaUy clean, and of good purity, it 
is an easy matter to condense this fume, and concentrate it, using 
Vitreosil, as platinum is not necessary for this work. 



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CHAPTER XVII 
OUlXUfE OF THE CONTACT PROCESS 

The^l^Contact^Proc^^ tt^M^its name from the fact upon 
which~it~3^e5as — thatSOt i md O^wiircomb mno^form SOa . 
"iiriflpr prjippr wiT^rfi^.in ne of temperatuTe, c oncentrat ion, aim* 
purity of gas, In C^n^H^tBqaMa^ WlWlLtJviHoatiijL 

Catalytic action has been known since 1834, when Mitsnerlicii 
concluded that the formation of ethyl ether and water from 
ethyl alcohol, in the presence of sulphuric acid did not depend 
upon the dehydrating power of the acid, nor upon any inter- 
mediate product being formed, but that the mere presence of 
the acid facilitated the reaction, although it did not in any wi^ 
^nter into it. 

Miteherlich suggested calling this contact action, but the 
next year Berzilius called it catalysis, and the latter name, 
while certainly no better nor more descriptive, is the better 
known. 

SCOPE 

While from its great affinity for sulphur tri-oxide, water 
would seem the l<^cal "absorber" in this process, thus rendering 
possible by this one method the production of any and all degrees 
of concentration, with practically no change of apparatus for 
different concentrations, from the very weakest to 100 per cent 
SOj, we are practically limited to the making of fuming acid, 
because water will aoL^o. 

When S0» comes into contact with water vapor a white misH^ 
is formed. As to its character, two opposing views are held. 
One is that it is minute drops of HjSO*, the other is that in the 
presence of the water vapor a double molecule, SjOi, is formed, 
and that this molecule is not easily absorbed. 

Whatever the actual reason for, or character of, this mist, 
it resists all attempts to condense it, passing through as many 
as six scrubbers, with sulphuric acid as the scrubbing agent. 
It is, however, partly removed by condensation, when filtered 
through fine coke or asbestos fibre. It causes trouble when 
present before the conversion by ite activity as an arsenic or 
207 



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208 



AMERICAN SUWHVRIC ACID PRACTICE 



lead carrier, and in the absorber house, because it passes, iu 
apparently undiminished volume, right through the absorbers 
and out of the fume stacks, simply throwing away that much 
goodSOs. 

This mist is, of course, what limits our product. 

Sulphuric acid of 98.3 per cent concentration, or more, holds 
very firmly to its small percentage of water, but as concentration 
drops below that point the space above the acid contains water 
vapor, aod especially where the temperatures are at all high, 
as in the first scrubber or absorber tower. 

So we are in practice limited to sulphuric acid of not less than 
98.3 per cent concentration as an absorbing medium, which in 
turn means that we must make an acid of higher concentration 
than that: in other words, "fuming." For this reason the 
hopes of the pioneers in the industry, that this process, requiring 
a smaller, more compact plant, would ultimately entirely super- 
cede the older process, have not been realized. It has, however, 
entirely eliminated the Starck process of distillation of Bohemian 
shales, and the "cracking" of sulphuric acid into SO* and HtO, 
the sulphur tri-oxide being absorbed as in our process. 

TECHNOLOOT 

There are three steps in the production of sulphurio acid by 
the contact process. 




FiQ. 67. — Layout for contact plant. 

(a) Production of SOj from some sulphur bearing material, 
as pyrites or brimstone. (While this process has not yet been 
adapted to the utilization of metallui^ical gases, as the Anaconda 
Company, for instance, is doing with the chamber process, the 



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OUTLINE OF THE CONTACT PROCESS 209 

Davison Chemical Co. silica gel promises great things in this 
direction.) 

(b) Oxidation of the SOi to SO,. 

(c) Absorbtion of the SO3 formed by a weaker acid, until the 
desired concentration is reached. 

There are two processes used extensively in this country, the 
Badische, the rights for which are controlled by the General 
Shemical Co., and the Sehroder-Grillo, controlled by the New 
Jersey Zinc Co. The methods of cooling the burner gas, the 
contact mass, and the means of bringing the purified gas up to 
the temperature necessary for conversion are fundamentally 
different in the two processes. 

But they are alike in that both require a clean gas for the 
conversion of SO; into SOs, and that the same underlying 
principles control their absorbtion systems. 

The production of SO2 has already been covered in Chapter V, 
the methods in use being common to both the chamber and 
contact processes. After this the gas must be 

Cooled; 

Freed from dust, moisture, small quantities of SO3 formed in 
the burners, and other impurities; 

Freed from any mechanically carried sulphuric acid; 

Filtered to remove any last traces of liquids, which at this 
point is usually a sulphuric acid mist; 

Heated to the conversion temperature; 

Converted; 

Cooled; 

Absorbed ; 

The acid weighed and delivered. 

LuQge says, ironically, in his "Sulphuric Acid and Alkali:" 
"There, are 279 sulphuric acid plants in the United States today,' 
of which 44 employ chemists." Working within the compara- 
tively narrow limits that we must in this process, a well equipped 
laboratory is a necessity — even more than in the chamber 
process — for this must be controlled all the way through by 
analysis. If the acid in either the scrubbers or absorbers gets 
too low in concentration we will soon be face to face with a badly 
corroded system; if the absorber acid gets too high, its absorbing 
properties fall off very fsist, and we loose SOj out of the stacks. 
Acid is bought and sold on analysis, both as to concentration and 
purity. 



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210 AMERICAN SULPHURIC ACID PRACTICE 

The "strength" of the gas is detennined at regular (every 
two-hour) intervals, by the Reich Btarch-iodine test: it is most 
important that this test be made frequently and regularly, 
because in a well conducted plant the loss due to imperfect 
conversion is the largest loss, and the gas strei^hs, both relative 
and absolute, give us all our information upon this important 
point. 

The method used is that of Reich for the estimation of 
sulphurous acid in gas, and while of no higher degree of accuracy 
than any other color test, is sufficiently accurate to control the 



process. This test, and the pyrometers for reading the converter 
temperatures are our only guides, but with a properly made mass 
and clean gas, are enough to insure a satisfactory conversion- 

Thia is of course occasionally checked by the laboratory, 
using the KjCOj method. 

The early investigators worked along serenely at this process 
in the belief that SOs and must be present in stoichometrical 
proportions, and many believed that nitrogen had a distinctly 
bad effect, aside from its diluting the gas; which means, of 
course, more gas to move, heat, and cool. Those who were 



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I 



OUTLINE OF THE CONTACT PROCESS 211 

Workmg to put it upon a commercial basis, and bbw in the air 
the natural supply of oxygen, tried to get a burner gas that ran 
20.3 per cent SOi, which left just enough oxygen to oxidize the 
SOj to SOj. But the rate of conversion was low; the process 
would not become a success. 

In 1878 Winkler, reaUzing that reactions do not go to con- 
clusion but rather to a state of equiUbrium, showed that there 
must be an excess of air to get a good rate of conversion, and 
while he never reached 100 per cent efficiency, he frequently was 
able to get up to 99 per cent. This is high for general practice, 
as the production suffers when conditions that wiU] allow so 
high a conversion are maintained. 

This discovery of Winkler's put the contact process upon a 
commercial basis. 

Suppose that the plant is burning 1,000 lb. of sulphur an hour, 
with an 8 per cent entrance gas. If the SOi content is increased 
to 9 per cent the amount of sulphur must be 1,130 lb. per hour 
and correspondingly more acid made, without any increase of 
expense except in the one item of raw material-less than 50 per 
cent of the cost anyway. The same labor and overhead pay for 
the increased production. 

Acid production may be figured as follows: 

Let a — available S0| = sulphur burned X 2.5 X per cent yield, 
h ~ pounds water made per 1,000 lb. fuming acid, 
X " weight of weak acid used per day, 
tf = weight of fuming acid produced per day, 
e = per cent strength of weak acid, 
rf = per cent strength of fuming acid. 



y 

But as the SOj content of the gas goes up, above a certain 
point, the rate of conversion goes down. This point is not the 
same for all plants, nor is it a constant for any one plant, varying 
with the contact mass and the purity of the gas, which in itself 
varies with the weather, etc. Seven per cent may be taken as a 
safe starting point, however, and the best working conditions for 
the individual plant then determined. It is impossible to draw a 
curve showing per cent conversion plotted against per cent SOs 



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212 AMERICAN SULPHURIC ACID PRACTICE 

in the gaa — and it is equally impossible to show, except for the 
individual plant, at what point the decreased conversion ceases 
to be overbalanced by the increased production. 

Gases leave the converters around 3S0°C.; much too hot to 
make possible any high degree of abaorbtion, which should be 
conducted not far from 40''C. (KMT.). The methods of remov- 
ing this heat used by the Badische and the Schroder processes 
are fundamentally different — the former uses it to heat the incom- 
ing gases, the latter wastes it by radiation. The net result is a 
gas of the proper temperature, which is brought into intimate 
contact with sulphuric acid, not less than 98.3 per cent, by towers 
and tanks, such as are described in the chapter on absorbtion, 
the SOa absorbed, and the remaining gases passed out through 
the stack. This remainder consists of N, 0, the minor gases 
contained in the air, and practically all the unconverted SOi 
— this latter constituting by far the greater part of the loss in 
the system. The S0» absorbed by the acid, either in the scrub- 
bers or absorbers, and slowly oxidized to S0», thus becoming part 
of the acid, is not only inconsiderable, but is not a loss. 

The degree of concentration of the finished product must 
depend upon the market to which it goes. Higher acid ia made 
more slowly, as the absorbing power of any acid varies directly 
as its vapor pressure, and reference to the curve trf vapor pres- 
sures in Chapter XXIII will show the very rapid increase in 
vapor pressure with concentration, of "fuming." While acid 
of 80.5 per cent S0» will absorb practically 100 per cent of the 
SOi in any gas passed through it, at 88 per cent SO, it will only 
take up 23 per cent. 

The freezing point must be considered very carefully in decid- 
ing what concentration of acid to make. A glance of the curve 
of freezing points, Chapter XXIII, shows a wide range of choice. 
Eighty-four and five tenth per cent SOa will remain liquid at 
the lowest temperature of any really concentrated acid. The 
addition of a few per cent of nitric acid drops the freezing point 
many degrees, but spoils the acid for some purposes. 

COSTS 

A thousand pounds of 100 per cent sulphuric acid made by the 
contact process cost, in 1914, from $7.50 to S8.50. A plant to 
bum 1000 lb. of brimstone an hour cost then $150,000. This 



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OUTLINE OF THE CONTACT PROCESS 213 

does not include power house, sulphur storage, ehops, office, 
laboratory, or any auxiliary buOdings. Operating labor will 
be 134 to 1}4 ^°^B hours per 1000 lb. acid. Capital expense 
must of course be figured for each case. 

Where depreciation leaves off and maintenance begins is a 
difficult question to answer. The usual practice is to take a figure 
gained by experience for depreciation, and all renewals above 
that are chai^d to maintenance. Maintenance will vary so with 
the management that it is not possible to give any figure that 
could serve as a guide. 

An industry handling corrosive material expects very rapid 
depreciation. Weak sulphuric acid, and nitric acid, even in small 
quantities, destroy iron and steel very rapidly. The usual 
method of handling sulphuric acid, by compressed air, puts 
serious strains upon parts of the apparatus. When acid mixtures 
are made a great deal of heat is evolved and high temperatures 
result, producing expansion that will have serious results unless 
the design of the plant {)rovideB for expansion bends as liberally 
as on steam lines. Expansion joints are not practicable for pipe 
work to handle corrosive liquors. 

Fuming sulphuric acid does not destroy cast iron by dissolving 
it, but by bursting. Cracks appear, in no particular direction, 
and sometimes the fitting actually suddenly explodes with a 
considerable report. Examination of the broken pieces rarely 
shows a Saw. Dr. Kneitsch suggests that the acid enters into 
the pores of the iron and becomes vaporized, producing sufficient 
pressure to burst it. At any rate, steel castings are far less 
liable to rupture, and as the pores are smaller would seem to 
bear out this theory. 

Acid is moved by "blow cases" — horizontal air tight tanks of 
stee! — with the acid outlet pipe running down almost to the bot- 
tom of the tank. When air pressure is put on the tank the acid 
rises in the pipe, and is thus forced around without the use of 
pumps, upon which acid is very hard. 

All iron gate valves should be used. The writer prefers sheet 
asbestos packing, although sheet lead is widely used; this is open 
tb two objections — the direct action of the acid upon lead, and 
the additional corrosive effect of the electrolytic action, between 
two metals, in the presence of an acid. Brass valves have a very 
short life where there are any acid fumes in the air, in spite of 
which they are frequently used on air lines. Any valve that ia 



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214 AMERICAN SULPHURIC ACID PRACTICE 

exposed to sulphuiic acid and is not frequently eased by opening 
and closing will soon become useless. 

The use of rising spindle valves is not to be thought of. A 
valve left open by mistake can be attended with very serious 
consequences, and the only safe way is to try each valve each 
time : any type of valve that indicates whether it is open or shut 
without actual trial tends to promote carelessness in this respect. 

Shower baths, where the full stream is released by one turn of 
the handle, frequently inspected, should be placed at convenient 
intervals. When a man gets any acid on himself he wants water, 
and he wants it in a hurry. 

The first aid boxes should contain a bottle of a solution of bi- 
carbonate of soda, boracic acid, an eye cup, vasoline, absorbent 
cotton, and sui^cal tape. This will care for any probable injury 
until medical aid can arrive. 

LABOR 

Such a plant requires on each shift a foreman, bimier man, 
engineer, fireman, and absorber-house man, wfio also attends to 
the scrubbers. Three men, a millwright, a pipe fitter, and an 
electrician, can attend to all maintenance, and the outside help, 
tmskilled labor, will bring in sulphur or ore, coal, pack filters, 
remove ashes and cinder, help the maintenance crew, and keep 
the outside clean. The flize of this crew depends upon local 
conditions. 

The operation of a well-designed contact plant is easy and 
ple^ant, and it is always possible to get a good grade of labor. 
The writer prefers Americans, and likes them young enough to 
be easily trained. 

In any continuous process codperation between the shifts is an 
absolute essential. Eivalry is to be discouraged, as it tends to- 
wards evils such as trying to bum more sulphur on one shift than 
the condition of the burners warrant, leaving the following shift 
to pull the plant out of the hole. Try above everything else to 
make the men realize that the DAY, not the SHIFT, is the unit 
of time, and that to gain an apparent temporary advantage, such 
as the burning of a couple of thousand pounds more sulphur than 
the shift before, and leaving the plant in such condition that the 
following shift cannot come within four thousand pounds of the 
required amount, is not a victory at all. Have a meeting that 
all three foremen MUST attend, every week. Post your monthly 



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OUTLINE OF THE CONTACT PROCESS 216 

yields OQ a plant bulle.tiD board. Let all the men know what 
the results are. Success of all kinds appeals to all men, and when 
the figures are posted the men will forget all about the Athletics 
or the White Sox, while they digest — and more important-, dis- 
cuss — the comparisons. Where there are few men employed 
they come to know each other well, and as friends will get along 
better together than enemies, ao unpopular man has no place 
in such an organization. 

SUUTDOWH 

Because of the corrosive effect of sulphuric acid upon iron, a 
plant making or handling it must be very carefully prepared for 
a shutdown, either temporary or permanent. If the work is 
done as outlined below the plant will be in good condition to 
start up at any time on short notice, and at small expense. 

It is a good plan to start in at the burners and work through, as 
in this way nothing is likely to be overlooked, 

All traces of sulphur must be burned, the burners thoroughly 
cleaned, and then painted, inside and out. The outlobk will 
dictate the extent of repairs and replacementa of arms, etc. All 
bearings must be well greased. 

Get the preheaters going, and run the blowers for several hours, 
thus forcing ho,t air through the converters and absorbers, which 
will remove n^oet of the SO*. 

All gas lines must be washed out thoroughly with a little soda 
ash and water, then rinsed out with water and allowed to dry, 
and then blanked off into convenient sections, the blanks being 
air tight. Fittings at low points in the lines must be removed, 
putting on the blanks there. 

Pump tanks are filled up with soda ash and water, rinsed, and 
allowed to drain. The pumps should be washed, greased, assem- 
bled, and painted, and put back into the tank again. 

The soda solution from the tanks should be pumped over the 
towers for 2 hours, when the interior will be neutral. If the shut- 
down is to be long, the packing and lining should be removed, the 
inside of the tower washed, dried, and painted, and then the 
tower sealed tight. , 

The acid-soaked, coke in the coke filters may disintegrate in 
time — it does not always do so. The most thorough way is to 
remove the coke, neutralize it with lime water, wash it, wash the 
filters, paint them, and replace the same coke. Then seat up 



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216 AMERICAN SULPHURIC ACID PRACTICE 

the filters tight. Or the filters may be simply sealed up, taking 
a chance od the coke standing up. 

The blower must be washed out with soda water, dried, and 
painted. All bearings must be greased. The cylinder head of 
the engines must be removed, and the inside of the cylinder 
greased. 

The converter mass ia safer inside the converter than anywhere 
else, and as there ahould be no S0» nor S0» nor moisture left 
inside after the blowing out with hot air, simply blanking off the 
preheaters and converters is the best thing to do. 

The absorber house can be treated as was the Bcrubber house, 
with the addition that the brick linings of the pump tanks should 
be removed. 

All acid lines should be washed out with soda, dried, and 
blanked off in sections, all valves being greased. 

All iron work, such as on the buildings, should be carefully 
painted. 



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CHAPTER XVIII 
PORIFICATIOIf OF GASES 

In the Contact Procesa, to get any reasooable degree of con- 
vereion, the gas must be of a certain concentration, certain tem- 
perature, and CLEAN. 

Impurities in the gas are both mechanical and chemical, and 
each class of treatment is necessary. 

A distinction must be drawn between an impurity that is 
merely a diluant, and one that has in it»elf a bad effect upon the 
result, either from its effects upon the system or upon the contact 
mass. 

The first class is well represented by atmospheric nitrc^n, 
present to the ejttent of 77 per cent (by weight) in the air drawn 
into the system. This means that about four-fifths of the gas 
handled, cooled, and heated, is worthless; but this handling is 
more economical than the use of pure oxygen would be. The 
nitn^en, also the minor gases of the atmosphere, have no effect 
upon the contact mass nor upon the life of the system, and leave 
the stacks as inert as they were upon entering the burners. 

Mechanically-carried dust will finally stop the contact action 
simply by covering the mass and preventing its coming in contact 
with the gas. If in sufficient quantity it might clog the system. 

Moisture dilutes acid, and the action of dilute acid is well 
shown in Table 21, Chapter XXIII, covering the action of 
sulphuric acid of various concentrations upon iron. 

Sulphur as a sublimate will crystalize out somewl^re in the 
system, possibly causing a complete block. 

Sulphur trioxide unites with water vapor to cause the mist 
spoken of in the last chapter. 

Arsenic, antimony, lead, mercury, selenium, tellurium, and 
silicon tetra-fluoride are all enemies of the contact process, 
chemically, and the greatest of these is arsenic. They destroy 
almost entirely the catalytic action of the platinum; they "poi- 
son" it; and the action cannot be reobtained in any known way, 
short of removing the mass, recovering the platinum in the form 
of platinic chloride, and making up the mass again. 
217 



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218 AMERICAN SULPHURIC ACID PRACTICE 

Arsenic can be partly, and some authorities say completely, 
removed from the mass by passing chlorine, or, better, hydro- 
chloric acid g^ through the mass, and then removing the gas by 
blowing heated air through. But at ordinary convertii^ tem- 
peratures part of the platinum is converted into chloride, carried 
off, and deposited somewhere in the system. 

Lead, mercury, and their salts form compounds, or perhaps 
alloys, with platinum, which destroy the catalytic properties 
of the platinum. It is theoretically, but not practically, possible 
to volatilize the lead. 

Nitric acid rapidly destroys iron work. 

Silicon tetra-fluoride, chlorine, and hydrochloric acid stop the 
catalytic action of platinum while actually present : but as soon 
as the impurity has passed by the action goes on without any bad 
effect. In this respect these impurities differ from arsenic and 
antimony. 

The gas, under suction, leaves the burners not far from 500°C., 
carrying with it all or any of the impurities mentioned above. 

The order usually observed in purifying the gas is to remove 
first the sulphur vapor, then dust, excess heat, SOi, arsenic and 
the other contact "poisons," moisture, and the sulphuric acid 
"mist." The arsenic may be partly removed, but a fuel contain- 
ing much of it. will soon destroy the usefulness of the mass, so 
great care must be exercised in the purchase of ores or sulphur. 

Although SOj begins to form at KWC, and sulphur melts 2° 
h^er, there is probably always some unbumed sulphur escaping 
from the burner, due to incomplete mixing with air. The tem- 
perature is high enoi^h to bum this sulphur vapor, if sufficient 
oxygen is present, as is always the case after dilution with air 
at the back end of the burner. This results in combustion in the 
combustion chamber, and in cases where very hot burners pro- 
duce large quantities of unbumed, vaporized sulphitt, even back 
into the cooling due. This of course cuts down the cooling sur- 
face, and throws an additional load upon the cooling system, 
whatever form it may take, which follows. 

Dust recovery is a mechanical problem, the dust being carried 
slowly through brick dust chambers, sometimes depending solely 
upon the very slowly moving gas to afford an opportunity for 
the dust to settle out, and sometimes equipped with baffle plates. 
These chambers have a bottom sloping to one side, and at the 
bottom of the slope iron clean-out doors. One of the many 



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PURIFICATION OF GASES 219 

advantages of brimstone over pyrites is the absence of dust; no 
provision at all need be made for it. 

As the bulk of the dust carried over comes from the iron oxides 
left after roasting pyrites, and as FejO* is an active catalytic 
agent, particularly at the temperature of the dust flue, some SOi 
is produced at this part of the line. 

This dust is so fine that without some method of agglutination 
it is practically impossible to smelt it. It is free enough from 
sulphur to be a welcome addition to a blast furnace charge, when 
properly a^lutinated — for a fair sized plant a sintering machine 
of the type described in Chapter V is the best from every angle, 
but briquetting will make a salable product, under most condi- 



Fio. 69. — Cooling coils. 

tions. Large lumps usually have "green" cores, but the dust is 
roasted through and through. I speak of iron furnaces as possible 
customers, but frequently the cinder is valuable for other metals, 
as copper or zinc, and if the pyrite carries gold or silver there is 
almost certain to be a concentration of the precious metals in 
the dust chamber, due to their votility. 

The brick walls of the dust chamber are very poor conductors 
of heat, so there is little cooling effect felt in the chamber. 

The first fundamental difference between the Badische and the 
Schroder-Grillo processes is in the method of cooling the gases. 

The Badische process effects the cooling by evaporating water. 
A large tower, usually 8 ft. in diameter, by 12 ft. high, receives 
the gas: and within that tower, where, owing to the ample space, 



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220 AMERICAN SULPHURIC ACID PRACTICE 

the gaa travels slowly, SS^B^. acid trickles down over br6ken 
quartz, making an intimate contact with the gaa. At this con- 
centration of acid, the gaa, at its temperature of 500°C., aimply 
distills off water, great clouds of steam being formed: but as there 
is no decomposition of the acid, and consequently no SOj formed, 
there is no mist. Because of the lai^ amount of water removed 
as steam, it is constantly necessary to "butt down" this coohng 
acid. 

This cooling tower must not have any exposed iron work, as 
acid of such low concentration attacks it very rapidly. The 
towers are usually lead, and the piping and tanks lead-lined. 
The pumps are hard lead, on an iron frame. Towers are some- 
times built of iron, chemical brick-hned, but any leak through the 
lining will soon let throi^h enough acid to attack the metal.' 

Pass^e through this cooling tower lowers the temperature of 
the gas to 250°C.; below the decomposition point of the real 
scrubber acid. The gaa enters the second tower, which is much 
smaller in diameter than the first, or cooling, tower, and rises 
through 99 per cent HsS04. There is so much moisture in the 
gas that the acid, in absorbing this moisture, drops 1 per cent 
in its passage down the 12 ft. of the tower. This of course 
necessitates constant "butting up," as 99 per cent is at the top 
of the curve of vapor pressures, which corresponds almost exactly 
with the absorbing properties of sulphuric acid. The gas leaving 
the tower is free from moisture. 

Experiments with the use of 88 per cent H2SO4 for cooling, 
showed that the temperature of the entering gas was sufficient to 
decompose acid of that concentration, forming a large amount 
of mist. Eighty-eight per cent was chosen, as it is the lowest 
concentration that is safe to apply hot to iron and steel. 

The Schroeder process removes heat by radiation. The gas 
is passed through a long iron flue, which is water cooled, usually 
by passing it through a tank of water, and delivered to the first 
scrubber at 250''C. This temperature is low enough so that the 
scrubber acid is not decomposed. When running on pyrites 
lead must be used in the construction of this flue, because enough 
HiSOt, formed from the moisture in the air and the SOj formed 
by the catalytic action of the iron oxides, is condensed, to destroy 
any iron work. Only if the temperature of the gas is kept up to 
400''C. is it safe to use iron, and at that temperature the scrubber 
acid ia decomposed. 



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PURIFICATION OF OASES ' 221 

After passing the scrubber towers what little acid condensee is 
cool enough and strong enough not to be harmful to cast iron. 

In the writer's experience it has been necessary to keep the 
temperature of the acid in the first scrubber down to 9^F. to 
prevent dissociation of acid, and consequent formation of mist. 
twenty cubic feet of 98 per cent acid, at 95°F., will cool a 
thousand feet of gas at 450° to SWC, to below the dissocia- 
tion temperature, and at the same time dry it thoroi^hly, leaving 
it entirely free from moisture or miet. 

It is difficult to give any figures on the amount of water neces- 
sary to cool the acid, owii^ to local conditions. Water in the 
South, particularly if from shallow rivers or ponds, gets warm 
enoi^h in summer to seriously complicate the cooling. 

It may be assumed that no fuel having over a trace arsenic 
would ever be used for the contact process, so that no company 
that makes lower concentration acid by diluting fuming with 
water need ever fear getting any arsenic into its mass, which 
should last indefinitely. So much chamber acid carries arsenic 
in relatively lai^ quantities that the plant that depends upon 
purchased acid for the weak acid it requires must exercise the 
greatest and most constant care. If the gas is properly cooled, 
so that no mist is formed, there is no need for concern, even with 
a considerable amount of arsenic in the scrubber acid : but if any 
mist forms, and there is over 0.02 per cent arsenic in the scrubber 
acid, trouble may be looked for with confidence, as that mist is 
the arsenic carrier par excellence, and it will go through any kind 
of filter or scrubber that the writer has ever seen. 

Too much stress cannot be laid upon proper cooling, for only 
by keeping the temperature down can this mist be prevented. 
Its formation must be prevented, because after once forming we 
do not know how to remove it from the gas. 

To prevent spashing of acid, and the consequent spray that 
the draught will carry over, two devises are in use. The acid 
may be introduced onto a cast iron plate, through a funnel. 
The plate, covering the entire inside diameter of the tower, is as 
shown in Fig. 79. Normally the acid goes through the many 
^-in. holes onto the filler inside the tower: the gas rises through 
the 2-in. holes, which are guarded against the entry of acid by 
the surrounding cast iron nipples, and thus the gas gets into the 
space above the plate with a minimum of splashing. When the 
small holes become do^^ed, as sometimes happens, the acid rises 



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222 AMERICAN SULPHURIC ACID PRACTICE ' 

high enough upon the plate to relieve itaelf through the large 
holes. 

The other method is to pump the acid to a reservoir, from 
which it floTTS gently through porcelaiu tubes to the surface (A 
the filler. 

The acid must be delivered at the top of the tower, as it flows 
down by gravity, but the gas may pass in either direction that 
plant convenience dictates. 

The coohng coils, filled by gravity from the tower are cast 
iron pipe, usually 6 in., laid horizontally. The a«id is admitted 
into the lower section of pipe, so that water dropping first upon 
the top pipe and then on to the tower one will reach the coolest 
acid first, and reserve its greatest cooling action, by evaporation, 
for the hot acid at the bottom. 

Figure 7S, in Chapter XIX, showii^ an absorber tower, tank, 
and equipment, illustrates equally well an ideal scrubber tower. 

As the hot gasses direct from the burner have greater volume 
than those later on, it is customary to use a lai^er tower, or two 
small ones in parallel, for the first tower. 

The amount of moisture taken out of the air drawn through it 
by the scrubber s^tem is large. I have seen a plant handhng 
150,000 cu. ft. air per hour remove 3,500 lbs. of water, in 24 hours, 
on adampdayin winter from the air, and over 6,000 lbs. insummer. 

The unit of a scrubber system is a tower, set of water cooled 
cooling pipes, and a tank with a turbine pump. For our ideal 
plant a tank holding 100,000 lbs. of acid is a good size. This 
tank should be horizontal, 6 ft. X 24 ft. of ^-in. boiler plate, 
unUned, with a cleanout hole in the bottom, turbine pump of 20 
cu. ft. a minute capacity, set through a manhole in the top, man- 
hole for cleaning out, proper connections to receive and diachai^e 
acid, and a gauge glass in the end. The acid is pumped to the 
top of the tower, and is spread by a distributer, so that in its 
passage down throi^ the tower it comes into very intimate 
contact with the gas, flows from the towers to the cooleiB by 
gravity, and thence back to the tank. 

Do not depend upon the gai^e glass reading for accurate in- 
formation about the quantity of acid in the tank. The acid that 
passes up into the gauge glass when the tank is filled is practically 
withdrawn from circulation, and retains its original specific 
gravity. So as that in the tank becomes diluted by scrubbing, 
or Btroi^er by absorbing, that in the glass will float upon, or, sink 



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PURIFICATION OF GASES 223 

into, thia acid of different Btrength, and will not stand at the level 
of that inside. The writer has found 5 in. difference between a 
gauge glass and a stick measurement. 

Each tank should have a 1-in. vent pipe, leading outside the 
buildii^, to relieve the pressure caused by incomii^ acid. For 
sampling, a 2)^-in. gate valve, or a 2^-in. nipple and cap should 
be set in the top. Do not uae a tapped hole and pli^, as plugs 
stick badly, roi^h handling with a wrench makes them loose 
their comers quickly, and then they are very hard to get out. A 
cap on a nipple is much better, and a gate valve best of all. 

Types of pumps are discussed in Chapter XIX. 

The towers of different designers vary greatly, although all have 
the same function : to bring into intimate contact the scrubber 
acid and the gas. Twelve feet high seems to be the only com- 
mon dimension. The internal diameter varies from 3 ft. 6 in. 
to 8 ft., they may be lined with lead or acid-resisting brick, set 
in Pecora or other acid-resisting cement, and filled with broken 
quartz, chemical-ware rings, or cast-iron filling pieces. 

The cooler pipes, always warm, afford excellent opportunities 
for the growth of any water plants, particularly those of a slimy 
nature, and slime and mud collect upon them very quickly. 
Any fore^ matter acte as an insulator, and should be removed 
at once. Rubbing with a piece of burlap is the best way to 
clean these pipes, although a broom will do a fine job. 

The current of gas carries some acid aloi^ with it mechani- 
cally, and some method of mechanical condensation and filtera- 
tion is necessary to remove it. A large tower filled with pea 
coke, followed by another filled with buckwheat size, each 
tower having a trapped drain in the bottom, will remove most 
c^ the spray, and a good part of the mist that forms. These 
towers ^ould be large enough (not under 10 ft. in diameter) to 
permit a slow movement of the gas, and should have a depth 
of at least 10 ft. of coke, with ample space at the top and bottom, 
for entrance and exit of gas. In practice about as many plants 
take the gas in at the top and release it at the bottom as do it the 
other way. The writer prefers to remove the gas from the top, 
believing that in the open space at the bottom, with acid dripping 
from the coke above, some new spray is formed, which is carried 
along by the suction. When a tower is newly packed there is 
undoubtedly some dust taken along from the top, but the coke 
soon becomes damp enough to prevent this. 



iiz^dbvCooglc 



'224 AMERICAN SULPHURIC ACID PRACTICE 

The quantity of spray caught will vary, but will be Bu£Bcient 
to make the installation of a small blow case to save the drip well 
worth while. It should be so piped that all the coke towers, or 
"spray catchers," run into it, and can run to a storage tank. 

While much mist is condensed by the coke, enough is still 
left in the gas to make further filtration necessary. While 
cotton is occasionally recommended as a filtering medium, I 
have never known it to last a week. The condensed acid is 
strong enough to carbonize the cotton rapidly, even in the cold, 
causing it to turn to a black dust — of course worthless 
for filtering. 

So asbestos fibre has come to be the one material used. It 
is picked over, usually by hand, to break up the lumps it packs 
into during handling and storage, and is then blown by a light 
current of air, which "fluffs" it. The apparatus required is a 
covered wooden trough, with air, controlled, by a haad valve, 
admitted at one end through a 3^-iQ. pipe. The fibre is blown 
down the trough to a lai^ box, with one side made of burlap, 
through which the air escapes. The longest staple asbestos 
possible should be procured. Grade 201A of the H. W. Johns 
Manville Co. is an excellent product. On account of the light- 
ness of the asbestos fibre it is necessary to bring the gas in at the 
top, driving it down through the filter: otherwise the strength 
of the draught will carry it away. A good form of filter is a 
set of cylindrical tanks, three or four in number, 6 ft. in diameter 
by 4 ft. high, in parallel, with a screen of %-m. boiler plate, 
punched with ^-in. holes, set on lugs 12 in. from the bottom. 
There are usually two sets of these filters, in series. 

The fibre is spread smoothly over this screen, to a depth of 
15 in.; 7,5 sq. ft. filtering surface, per hundred pounds of sulphur 
burned per hour, in each series will do good work, and will require 
a little over a pound d fibre per square foot every time they , 
are packed. 

These filters work better when moist, so moisture in itself is 
harmless. But where there is arsenic in the mist the filtSfS'jK,^ 
rapidly become impregnated with it and must be clean^ to 
prevent the arsenic from reaching the converter mass. When 
the filters are drained constantly there is less necessity for 
frequent cleaning than where the condensate is allowed to 
accumulate in the bottom, to be removed at intervals. 

Cleaning simply consists in removing the manhole cover and 



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PURIFICATION OF GASES 



225 



taking out the old asbestos with a fork, then spreading the new. 
The blower must be stopped while the work is under way. 
Only experience can tell how often it is necessary to repack 
filters — one plant may need it every 3 weeks, another every 
6 months. When the asbestos is so^y it is time to repack it, 
but being damp will do no harm at all. 

AI! attempts to regenerate the asbestos have failed, not that 
it is hard to wash out the acid, but that wet asbestos packs into a 
cement. 

Unslacked lime, nut or pea size, has been tried as a filtering 
material, and does its work well, but is hard to keep open, as the 
calcium sulphate formed crumbles, and the dust packs. Also, 
the condensed acid is lost. 




The Tetelow Chemical Co. uses, on gases that contain a little 
chlorine, a weak mOk of lime wash, where first a bisulphite is 
formed with the SOi, which reacts with and retains the chlorine. 

The Tyndall test shows any mist in the gas that is invisible to 
the naked eye. An apparatus, shown in Fig. 70, consists of C, 
a small flask with a rubber stopper, through which two glass 
tubes pass, and A, a lens, the focus of which is just beyond the 
flask: all enclosed in a wooden box, painted black inside. The 
flask is filled with the gas to be tested, either by direct pressure, 
or, if on the suction end of the system, by an aspirator bottle, 
the ends of the tubes corked, the flask replaced in the box, and 
a beam of sunlight directed through the gas in the flask, via 
the lens. If there is any mist it will show in the path of the 
beam as the motes dance in a beam of sunhght in the old dusty 



^dbvGooglc 



226 AMERICAN SULPHURIC ACID PRACTICE 

attic. But if the gas is dty a disk of light shows on the side of 
the flask where it passes through the glass, and that is all. 

If, through faulty design, it b impossible to prevent the 
formation of this mist, this arsenic carrier, the greatest efforts 
must be made to remove as much of it as possible, because 
arsenic is more hable to get into the system via the scrubber 
acid than through the fuel burned, and if there is no mist this 
arsenic will not be taken from the acid, ultimately getting to 
the converter mass. 



Fia. 71. — Roots blower. 

Without proper provision for cooling mist will form. One 
of the plants built in a hurry to respond to the demand for 
fuming acid at the beginning of the European War, in 1915, 
was not provided with sufficient cooling area, and although 
operated with great skill, and giving in all respects but this very 
satisfactory results, showed all the bad effects of insufficient 
cooling — the filters had to be cleaned very frequently, arsenic 
went through to the converter mass, and the exit stacks were 
always fogging. 

The blower is placed at the end of the scrubber system, so 
that the maximum pressure may be available to force the gas 



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PURIFICATION OF GASES 227 

through the converter mass. This blower is always a valveless, 
direct-acting blower, of the Roots type. These engines are so 
well known that any extended description is unnecessary. 
They may be built either direct connected to a steam eu^ne, 
or to be belted to shafting or a motor, and act over a very wide 
range of speeds very efficiently. The usual guarantee is that the 
slip will not exceed 15 per cent. As the rotors have K2S-iii- 
clearance, and no sliding surfaces, these engines have a very 
long life. The small clearance is not sufficient to cause much 
slip. If a sudden stop in the suction line occurs the partial 
vacuum formed will cause the blower to reverse itself for several 
. revolutions, against the steam pressure. 

If arranged this way, the pressure at the engine is almost twice 
the suction, mainly because of the resistence offered by the 
converter mass: but also because there are usually more showers 
in the absorber house than in the scrubber house. Our ideal 
unit will show, for normal runniii^, about 12 in. of water suction 
at the blowers. 



^dbvGoogle 



CHAPTER XIX 
CONVERTING 

The second step ia making Sulphuric Acid by the Contact 
Proceaa id the conversion of SOt to SOj, by bringing it into 
intimate contact, at a suitable temperature with finely divided 
platinum. 

A mixture of 80» with air will slowly oxidize to S0», but so 
slowly that this action is valueless from a commercial stand- 
point. Many substances have a catalytic action upon this 
chemical reaction, that of FeiOg and FetO*, among the common 
substances, being very marked. All the metals of the platinum 
group posses this activity, but none other to the extent that 
platinum itself, in a finely divided state, does. 

The catalyzer itself is entirely unacted upon, and its simple 
presence is oU that is necessary. The effect is without doubt 
adsorbtion, or condensation of gas upon the surface of the 
catalyzer. When glass is wet by water the water is not absorbed 
— it is held however by the force we call adsorbtion — and some 
solids have this effect upon some gases. It is probable that 
there is a concentration of gas in a condition to react, and by 
the law of Mass Action the reaction must be hastened. Reason- 
ing along these lines, the plan of the Davison Chemical Co. to 
use liquid SOi, recovered from fume stacks by their new silica 
gel process, should give high yields and capacity, because of the 
"strong" gaa used. 

Six factors enter into the conversion; catalytic agent, which 
is always finely divided platinum; sulphur dioxide; air, supplying 
oxygen; temperature; time, and impurities. 

The Badische process, worked out mainly by Rudolf Knietsch, 
uses platinized asbestos as a catalizer, a solution of platinio 
chloride being sprayed over the asbestos fibre, which is then put 
into the converters and dried. The mass then looks Uke wool 
died a lemon yellow, is soft and fluffy, and is not subjected to 
any fumacing at all. It dries out very rapidly in the converter, 
the chlorine of the platinic chloride is driven off, and metallic 
platinum left in an extreme state of division. 

The Badische conversioB unit is made up of a preheater.used 



^dbvGooglc 



CONVERTING 229 

for starting up and in emergencies, two converters and three 
transfere. The drawii^ shows the general arrangement of the 
converter — the gas enters at I, filling the space A, goes up the 
closed bottom tubes B, and down through C containing the 
converter mass, into D, and through the outlet to the absorb- 
tion system. C ia made about three inches in diameter, to 
provide for uniform cooling of the mass by the incoming stream 
of cold SOi and air. It is this form of converter that gives 
the Knietsch process its economy of fuel, and is patented in this 
country under United States patents 652,119, 688,020, and 



823,472, dated respectively, June 19, 1900, December 3, 1901, 
and June 12, 1906. Of these 652,119 is the fundamental one, 
the others being modiEcations thereof. See fig. 70. 

The Schroeder-Grillo process uses platinum deposited upon 
m^nesium sulphate for the mass. 

Pure magnesium sulphate, with the. water of crystalization 
driven off, is coated, not impregnated, with platinum to the 
extent of 0,3 per cent of its weight. This gives a very large 
surface, as the salt in this state is very porous, and the platinum 
is spread out thin over a wide area. The magnesium sulphate 
is spread out upon a flat surface, 6 in. thick, and the platinic 
chloride is sprayed on through glass nozzles connected by rubber 
tubing to the bottles of solution, the bottles being suppUed with 
air under pressure. At intervals the mass* is turned over with 



^dbvGooglc 



230 AMERICAN SULPHURIC ACID PRACTICE 

wooden ehovela, aa it is of the utmost importaJice to get the 
platimim oa evenly. 

The spriyred mass is then put into the furnace previously 
used to dry the magneeium sulphate, and heated to redness for 
half an hour. By this time all the chlorine has been driven 
off, leaving the platinum in an extreme state of division. 

The mass is then allowed to cool and is put into tight cans, 
weighed, and put away until needed, as it will keep indefiimtely. 

Usual practice is 4.5 per cent of platinum on the weight of SOi 
per hour. This will give a 97 per cent conversion with good 
handling. A smaller proportion of platinum will give a lower 
conversion, and in each case it must be determined whether it is 
better to have a smaller investment, and loose more SOt out of 
the stacks. For instance, ^ the platinum investment will about 
double the stock loss — 2)^ per cent platinum on the hourly SOi 
will give about 953^ per cent conversion, other conditions being 
equal to the 97 per cent conversion with 5 per cent platinum. 

The sulphur dioxide and air are intimately mixed in their 
passage through the burners, scrubbers, and blowing engines, 
and are freed from impurities as much as possible, so that the 
gas entering the converters contains, SOi and as active agents, 
and the nitrogen and other inert gases of the air as diluanta. 

Dr. C. L. Reese has proved experimentally that moisture 
present will not affect the mass, but as of course acid would be 
formed the plant would suffer. COi is harmless. The worst 
of the impurities liable to be encountered is arsenic, which 
"poisons" the mass by forming a glassy coatii^ of a salt of 
arsenic and platinum, as little as 2 per cent of As on the weight 
of platinum being sufficient to render the mass inert. Dr. 
C. L, B«ese says that As can be removed from the mass by 
passii^ HCl in with the gas mixture, but my advise is not to 
let any get into the mass — the action seems to be that the As 
coatii^ simply encloses the platinum so that it cannot come 
into contact with the gas mixture. 

Dust of all kinds has a purely mechameal coverii^; action, 
which is just as effective as the arsenic in preventing contact, 

HtSOt "gums up" the mass, making it difficult to penetrate. 

TEMPERATURE 

2S0, + 0, = 2{80» + 40250 B.T.U.), on the authority oS 

Prof. J. W. Richards. The reaction proceeds slowly at low 



^d by Google 



CONVERTING 



231 



temperatures, really beginning at about 200''C., and continuing 
to increase in velocity with rising temperature. However, 
the reaction is reversible and above 420''C., decomposition of 
SOs sets in, becoming more marked with further increase of 
temperature, until at 1,000°C. SOj cannot exist, in the presence 
of the catalizer. 

The best temperature to carry is entirely dependent upon the 
condition of the mass and the "strength" of the entering gas, 




and it will vary with variations in these two, and therefore is 
a purely local condition. From 375°C. to 425°C. is about right. 

The enterii^ gasea must be heated sufficiently to start the 
reaction, as they have been well cooled by the scrubbing, and 
the converted SO3 must be cooled before absorbtion. 

Here lies the fundamental difference between the Badische 
and the Schroeder-Grillo processes — the former makes its 
converber into a heat exchanger, and heats its entering gases by 
taking the excess heat from its SOj, where the latter uses fuel 
to heat up, and then wastes the heat generated in the converter. 

The Badische conversion unit has been described. The 



ncizoJ^vCoO^^lc 



232 AMERICAN SULPHURIC ACID PRACTICE 

Schroeder-Grillo unit is a vertical cylinder of cast iron, 5 to 8 ft. 
in diameter, built up in 18 in. to 2 ft, sections, flanged, joints 
packed with asbestos wicking, all held together by stay bolts 
from the top to the bottom flanges. Each section contains a 
perforated cast iron floor, upon which hes ^^-in. mesh iron wire 
screen, and upon this the mass. There are usually 5 sections 
to a converter, and 4 converters to a unit. For a converter 
7 ft. outside diameter the normal amount of mass is 7500 lbs. 
evenly divided among the 5 trays, and carrying 0.3 per cent Pt. 
That means about $190,000 worth of platinum at today's {No- 
vember, 1919) prices, of $145 per ounce. Such a plant will burn 
1000 lbs. of sulphur an hour. 



During the war, at one large plant, the quantity of mass was 
cut in half, concentration (per cent of Pt) remaining the same. 
This dropped the conversion from 97 per cent to between 94 
per cent and 95 per cent — this brings up the question of the bal- 
ance between stack losses, which represent raw material, power, 
and labor, and the investment in platinum. This will be con- 
sidered in the chapter on accounting. 

Good recording pyrometers are absolutely necessary for con- 
ducting this operation. Leeds & Northrup, Philadelphia; 
Industrial Instrument Co., Foxboro, Mass.; and the Taylor 
Instrument Co., Rochester, N. Y., can be depended upon to 
furnish good ones. 

The Schroeder-Grillo preheater is a brick box, full of 6-in. 



^dbvGooglc 



CONVERTING 233 

boiler tube pipe, vertically set, flanged, connected by return 
bends, through which the gas passes to the converters, all heated 
by coal or oil fireB, flue gases passing around the outside of the 
pipes. For a plant burning 1,000 lb. sulphur per hour, 4 con- 
verters, each 5 sections high, will be used, and the preheater to 
each one will contain 250 ft. of 6-in. pipe, plus the return bends. 
The pipe is set vertically to prevent flue dust from settling on it, 
insulating the gas inside. Such a plant will use 6 tons of steam 



coal daily in summer, 7 to 8 in winter. On 1919 coal prices, that 
is, over 50 cts. per 1,000 lb., 100 per cent acid produced — well 
worth saving. But even with this high fuel cost, the writer 
prefers this system to that of the Badische because of its 
simpler operation. 

The gases from the Schroeder-Grillo converters, consisting of 
N, SOa, unconverted SOj, and impurities (mighty few of these 
however) are at a temperature around 350''C., much too hot for 



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234 AMERICAN SULPHURIC ACID PRACTICE 

absorption; so they are cooled by passing through 250 ft. of cast 
iron pipe, set horizontally, between headers, and arranged to 
have a spray of water drip over them in warm weather. These 
pipes must be equipped with drain cocks, because upon starting 
up there is always some moisture in the mass, which will come 
from the hot converters as sidphuric acid vapor, and will condense 
here, effectually trapping the sj-stem if not removed. 

Time of contact is controlled by the blowing engine, and will 
vary so with the plant that no rule can be laid down. For the 



Fio. re. 

size of blowing engine figure the volume of gas necessary to 
provide a 7 per cent gas for the sulphur to be burned, at 80°F. 

The only pressure is that of the blowing engines, sufficient to 
overcome the friction of the system, and keep the current of gas 
moving. 

The early experimenters thought a stoicometric mixture of 
SOa and necessary to get a good conversion, but were never 
able to convert over 77 per cent of their SOi, and then only imder 
laboratory conditions. The production of pure oxygen was 
expensive, and later proved a needless expense, as air was shown 
to give excellent results, the nitrogen having no deleterious effect 
whatever, 



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CONVERTING 235 

Ferric oxide comes to it« maximum as a catalytic agent at 
STS'C, at a point where the dissociation of S0» ia very marked, 
which ehminates it as a possible contestant with platinum. 

It is necessary to use a catalytic agent that will do maximum 
work at or under 450°C., and platinum is the only one known so 
- far. 

Some experimental work along the lines of colloidal precipita- 
tion of the platiniun upon the mass have been done, notably by 
Botho Schwerin, in U. S. patent 1,098,176, owned by the Chemical 
Foundation, 81 Fulton St., New York. In view of the fact that 
the investment is the greatest part of the cost of contact acid, 
anything to increase the surface of platinum exposed will pay 
well, and should be followed up. 

Kurt Albert, in U. S. patent 1,018,402, also owned by the Chemi- 
cal foundation, claims to have reached a 94 per cent yield with 
iron and strontium oxides as a catalyzer. This with the Davison 
adsorption system on the exit stacks to prevent the loss of uncon- 
verted SOi offers a fertile field for research. 

Dr. Knietsch formulated the law of mass action as follows : 

SO, iooVko^ 
SO, ~ 1 + Vko; 

when K = concentration in volume per cent. This shows the 
conversion we may obtain, but nothing about velocity of reaction 
or proper temperature. 

Each plant rnvsi develop its own suitable working conditiona, 
and adhere as closely as possible to them. If the operator starts 
out to make a 7 per cent "gas" — 7 per cent by volume — he will 
not be far wrong. 

Although it is necessary to dry the gas as much as possible, an 
absolutely dry gas will stop the reaction. It is not possible to 
remove the last traces of moisture with our scrubbing systems, but 
they remove all that might be dangerous, as an excess would be. 

Uniformity of temperature is of the utmost importance — ^tbe 
control should be within S'C. If the mass is injured in' any way 
it is likely to require a higher temperature to get conversion, and 
that is about the only way there is of detecting mass " poisoning. " 

GAS CONTROL 

The Reich test for SO, in gas, with the pyrometer readings, is 
our guide. This test is conducted as described in Chapter XIV. 



iiz^dbvCooglc 



236 AMERICAN SULPHURIC ACID PRACTICE 

The laboratory should occasionally cheek this by the KtCO«. 
test. 

This gas test should be made not less often than every 2 hours, 
on both the entrance and exit gases. Be sure the gas passes 
through the apparatus for a minute before each test, to make 
certain that it is the gas of the present, not of 2 hours ago, that 
is being tested. Quarter inch pipes, kd off of the gas mains, 
and controlled by valves, bring the gas to the test. 

In figuring conversion after the test, it must be borne in mind 
that the volume of gas is decreased by the amount of oxygen the 
SOi has taken in its oxidation. 

Slide bule for SOa to SOi conversion* 
In general, if an equation can be written in the form 
f(x) =f(y),f(z) 
a slide rule may be so constructed that the value of any variable 
can be found if the others are known. As a simple illustration, 
consider the computation of conversion in the contact process for 
the manufacture of sulphuric acid. 
Let a = per cent by volume of SOi in entrance gas, 
b = per cent by volume of SOi in exit gas, 
c = per cent conversion = per cent SOj converted 
toSOa- 
These quantities are related by the equation 
10,000 (a - b) 

°" 10O.-?|> 

This form of equation is not suitable for the construction of 
a slide rule, but it may be rewritten as 

100 3\ . /lOO 3\ 



/lOO _ 3\ _ /: 
la 2) '■ \ 



SO; In 



0..1 '^.^vT. 



ib' ' ' Is'o' ' ' Ibb" 

ft CBnwnlon 



SOi — S0» slide rule set, 10 per cent entrance, 0.7 per cent exit 
= 94 per cent conversion. 

> From Chemical and Metallurgical Enffijuerinf, September 15, 1919. 



iiz^dbvCoOglc 



CONVERTING 237 

The Blide rule scales for the solution of this equation are in the 
accompanying figure. The upper scale is laid off proportionally 
to \ag ( nj , the slide to log (-r- — 5 1 , and the lower scale 

to log 11 — Tj^l • These scales are laid off from right to left bo 
that the marked values a, b, c will increaxe from left to right, 
as this is the most natural method of reading scales. The proper 
values of SOt in burner gas and exit gas are set together, and the 
conversion read opposite the arrow. The zero point {i.e., 1(^) 
of the lower scale is moved to the left relative to the upper one, 
to make the rule more compact, and the arrow displaced the same 
distance to give the correct reading. 



^dbvGooglc 



CHAPTER XX 
ABSOKBTION 

As stated briefly in Chf^iter XII, water is not a satisfactory 
absorbing agent for 80a, and as the water in diluted HiSO* acte 
like water, it is necessaiy to use strong (not less than 98.3 per 
cent) sulphuric acid. You might say that the gas is scrubbed 
with the absorbii^ medium, for the apparatus used is a gas 
scrubber of some type, the object beii^ to get as intimate an 
association as possible of the gas and the acid. 

If sulphuric acid of less than 98.3 per cent is heated in an open 
pan at 350°C. water will distill off until this "critical" point, 
i.e., 98.3 per cent is reached — if the original acid is of a higher 
concentration than the "critical" strength, S0» will come off 
until the strength drops to 98.3 per cent — after it has reached 
that point however it comes over at that strength until the end. 
Of course pan concentration cannot go to this point profitably, 
because the losses by entrainment increase very fast with the 
strength of the pan acid. 

At 98.3 per cent and lOO^C. sulphuric acid has a minimum 
vapor pressure in vacuo, and at this point its Bp.g. is the highest. 
At this point absorbtion of SOg is practically 100 per cent. 

The heat of combination of SOi and HiO is 180,540 B.T.U., 
according to Richard's "Metallurgical Calculations," which 
runs the temperature in the absorbing apparatus up to the point 
where cooling is always necessary. This is usually done by 
circulating the absorbing acid, keeping a large volume in service, 
and coohng the storage tank and circulating system with water. 
The first tower will require, for a unit plant of 1000 lbs. S per 
hour, not less than 250 ft. d cooling pipe, aside from necessary 
connections. 

As fuming acid is very hard on iron or steel, tanks uid towers 
must be carefully lined with an acid-resisting material. The 
writer does not think much of any of the asphalt bitumens that 
are used for this purpose, prefering a good acid-proof tile, well 
laid in acid-proof cement. The cost of towers thus protected 
is high, but worth that cost. 



^dbvGooglc 



ABSORBTION 239 

Aa the strength of the acid in the tower increases, so does the 
vapor tension, and the absorbing qualities fall : also the tempera- 
ture being high works against good absorbtion, so it is usual 
to arrange 6 towers in series, fresh acid being added in the last 
one, at intervals, the towers nearer the first one being replenished 
from those behind, and the acid made being drawn from No. 1. 
The temperature in the later towers is progressively lower than 



























































































/ 




\ 
























/ 






\ 






























\ 


















t 


^ 








'C 


\ 




















/ 








■^r 


, 




















/ 








Ico 


"s 


















/ 






^ 


^ 


I 


















// 




/' 








\ 
















/ 


/ 


^ 










\ 














/ 






7 










I \ 












/ 




/' 


/ 




jj3a 


■^ 




" 


^ 










/ 




ly 


/ 


^ 


/ 










^ 




K 




^ 






^ 














4n 




r» 






^ 


-> 


> « 


9 


r-« 


TJ 




3. 


r-A, 



PartiiJ prmuTa Fnrtial prnBure dus in SOi 

Fia. 77. 

in the first, and as the strength also gets nearer and nearer to 
that point where the vapor tension is negligable, the percentage 
absorbtion is increasingly great, and if the acid in all towers is 
above the dead line of 98.3 per cent, so that no "mist" tB formed, 
the absorbtion will be practically complete. 

The use to which the acid is to be put of course determines the 
strength to be made, but the season of the year has an influence 
also: and a look at the freezing curve, in Chapter XXIII, will 



iiz^dbvCoOglc 



240 



AMERICAN SULPHURIC ACID PRACTICE 



show why. Acid of about 103.6 per cent with a freezing point 
of 10°F. is a good winter strength to aim at. 

While anal^iis is necessary to determine the strength of acid 
in the variods toweis, experience will soon teach the operator 
how often to sample: and while this system is very flexible, and 
will stand a lot of bad handling, it is easy to handle welL 

If the Feld washer, made by the Bartlett-Hayward Co., of 
Baltimore, can be designed to stand fuming acid it will be an 
ideal piece of apparatus, and as the rotating part is hung from 
an overhead bearing, out of the acid, it seems reasonable to hope 
that it will. Of course there is bound to be some vibration, 
which in time is sure to open up the joints in the acid lining. 



Coaliivi 0>il -e Ptpffj 




It has been proposed to build the tower of stone-ware, but this 
seems impracticable to the writer, because of the h^h tempera- 
tures in the first toweis, which would be reasonably sure to 
crack the stone-ware if a draft of cold aii struck the outside. 

Apparatus of the type shown in the cut on this page 
is very satisfactory. The pump is a centrifugal, made by 
G. C. Bretting, Ashland, Wis., belt driven, 1700 R.P.M., deliver- 
i:^ 40 cu.ft. of acid a minute, and requiring 7^ H.P. It is 
built with a manhole cover, so can be hoisted into place by a 
chain block on a mono-rail, and fastened with set screws. As the 
pump is about the only part of the system that is likely to get out 
of order, this ease in changing is very important. The pump 
made by the Kutztown Foundry & Machine Co., Kutztown, Pa., 
is also a good one. 



^dbvGooglc 



ABSORBTION 



241 



Failures of the wrought iron piping come apparently not from 
corrosion, but from bursting. These bursts are alwaj-s longi- 
tudinal, and can be welded. The writer has seen many bursts, 
but never one on a welded pipe, either at the weld or anywhere 
else in that vicinity, which seems 
to show that when the internal 
strains have been relieved by the 
springing open of the pipe in the 
first burst, the acid alone cannot 
burst it. 

Failure to provide for expansion 
in pipes handUng the hot acid 
from the tanks is sure to result in 
broken fittings, as the acid is so hot 
that expansion is considerable. 

There are more likely to be tower. 

"spills" of acid in this department than in any other, so the floor 
must be one that will stand such acid. Common red brick, laid 
dry in sand, makes a splendid floor. 

The gas coming from the converters is hot. The heat is used 
in the Badische system to heat up the incoming gases, but in 




Fio. 79. — Distributor 



the Schroeder-Grillo process the heat must be removed by some 
other means. The simplest means is a cast iron or steel header, 
with 6-in. wrought-iron pipe running to another header. For our 
standard unit 450 ft. of 6-in. pipe will do the work, without 



^dbvGooglc 



242 AMERICAN SULPHURIC ACID PRACTICE 

help in wtater, but will require the help of a spray of water in the 
summer. 

Drainage must be allowed for in the bottom of the cooler, as 
no matter how well the mass is made up the magnesium sulphate 
is sure to contain some moisture, which of course will form acid 
and condense in the cooler. This blocks the system. 

The "absorber man" has little to do but sample and shift ias 
acid, as it increases in strength, and could easily handle four 
^}Borber units; so where the production is sufficient it is custom- 
ary to house two units in the same building, in parallel. Weak 
acid is usually received, and strong delivered, at this end. 



^dbvGooglc 



CHAPTER XXI 

CONVERTER MASS 

The most costly part of a contact plant is the platinum, and 
every effort is being made to find a suitable substitute, and failing 
that, to reduce the amount necessary. As the catalytic action is 
undoubtedly a surface condensation, the logical thing to do is to 
spread the platinum out as thin aa possible. Much research 
work has been done along these lines. 



As with varying conditions it is not possible to use any stand- 
ard plant, a simple laboratory converter is useful, and will be 
here described. 

Five (6) 2-in. C.I. tees, connected by close nipples, and a 
2 X 6-in. fiange at the outlet, on another close nipple, the whole 
stood upright, and a circle of 10 mesh iron wire screen resting 



243 



^dbvGooglc 



244 AMERICAN SULPHURIC ACID PRACTICE 

in the bottom of each tee, Qpon the upper end oE the close nipple. 
The maas is put in through the outlet, held from nmning out by 
a piece of screen sprung in, the companion flange, in which there is 
B%X 2-in. bushii^, put on, the thermometer put in the bushing, 
connected up with the gas supply at the lower end, and started off. 
Plastic asbestos is the beat covering, and such a system must 
be covered, as the area is large in proportion to the volume. 
(Fig. 81.) 

Sodium free magnesium sulphate is melted in its water of 
crystalization (it contains 52 per cent) in a crucible, stirring con- 
tinuously after it melts, both to prevent its sticking and to make 
it porous — the porosity depends directly upon the amount of 
stirring. In about 35 min. the mass will be free from water and 
solidifies, when it is heated to a dull red, and poured out to cool. 
After cooling it is broken to pass a ^-in. screen, but to stay on a 
3^-in. one. The platinic chloride is then sprayed on with a glass 
nozzle, from a solution made up as later described in this chapter, 
the mass put back in the furnace in the crucible and heated to a 
dull red, when the chloride is reduced to metaUic platinum and the 
mass turns black. It is then ready for use. 

Such a plant will enable the research laboratory to work out 
any. problems in connection with the gas to be used. 

PREPARATION OF MASS 

Platinum has increased in price within the last e^ht years, up 
to 1920, from $12 to $145 a Troy ounce, and as the quantity 
necessary to get a 97 per cent conversion, in a plant burning 12 
tons of sulphur a d^ of 24 hours, is about 1,300 oz. — $188,500 
— every effort must be made to spread it out very thin. 

The logical thing to do is to deposit it upon a base of such 
uneven surface that a very large area is exposed in a relatively 
small volume. This base must also be unaffected by the gases 
passing through, by the temperature, and by the chemicals used 
in depositing the platinum. It should also be of such a nature 
that the platinum can be easily recovered. 

Asbestos fibre fulfills perfectly the first four requirements, and 
is lai^ly used. It has the fault of packing under any consider- 
able weight, BO the converter must have shelves only a few inches 
apart, thus having comparitively shallow layers of platinized 
asbestos. 



^dbvGooglc 



CONVERTER MASS 245 

Dehydrated magnesium sulphate answers all five requirements, 
plus the fact that it does not pack. 

The base is coated by spraying with a solution of platinic 
chloride, made by dissolving platinum at the rate of 125 gr. Ft 
per liter beaker in twice the theoretical amount of aqua regia. 
This is heated over a sand bath. The beaker should stand in a 
porcelain dish containing water, lai^ enough to hold the entire 
contents of the beaSer, in case of accident. 

About 80 per cent of the platinum will dissolve readily. This 
solution is poured into a porcelain dish, which, for safety's sake, 
stands inside a lai^er dish, and is concentrated. More aqua 
regia is added to the imdissolved portion, until all has gone into 
solution. 

The solution is then analyzed and diluted to contain 7 gr. per 
e.c.* Because of the high at omic we i ght of sol^itiqnq^ ontaininff 
platinum, they diffuse slowly, go mixing must be very carefully , 
and thoroughly done. fThis, is diluted to 3^a before using. 

The asbestce fibre musT be very carefully "fluffed," and the 
solution sprayed on from glass bottles, through a rubber tube 
with a glass nozzle, drawn to a fine opening, using low-pressure 
air to drive the solution out. The asbestos must be turned over 
continuity, to get as even a distribution as possible: a pitchfork 
makes a good tool. 

This mass is put right into the converters, where the heat of 
starting up reduces the platinic chloride to metallic platinum 
before the first SOj arrives for conversion. 

The m^nesium sulphate used must be pure. The New Jersey 
Zinc Co. supplies a very high grade. 

A small reverberatory furnace is used for calcining the "mag. 
sulph." lots of 250 lb. to 500 lb. being a charge. Thirty-five to 
40 min. is sufficient time to melt the salt in its own water of 
crystallization and drive the water off. The furnace should be at 
a dull red heat, and the chai^ rabbled continuously, as otherwise 
it will harden and stick to the hearth. The more it is rabbled 
the more porous it becomes. 

* The Avoirdupois pound is the usual unit of weight in the sulphuric acid 
industry, but platinum ia weighed in the Troy (or Jewelers') scale. The 
following comporiHonti of the two scales are helpful: 

1 pound Avoirdupois =• 7,000 grains = 16 Avoirdupois ounces, 
1 pound Troy — 5,760 grains = 12 Troy ounces. 

I pound Troy - .8229 pounds Avoirdupois. 



^dbvGooglc 



246 AMERICAN SULPHURIC ACID PRACTICE 

After the charge is drawn it is broken and screened, pieces 
above % in. being broken, and below % in. rejected. 

Various plants use varying amounts of platinum per unit of 
mass — 0.2 per cent to 0.3 per cent are the most usual. 

The spraying is done the same as with asbestos fibre, but the 
mass is put back into the furnace for 20 or 30 min., at a dull red 
beat, and rapidly turns black, from the reduction of platinic 
chloride. 

RBGEHERATION 

Asbestos is difficult to dissolve, so when it is necessary to. 
recover the platinum it is simpler to dissolve the platinum in aqua 
regia, filter, purify the solution, and make new mass, than to try 
to dissolve the asbestos. 

A spraying with a solution containing 20 per cent HCl, 7 per 
cent HNO), and a little soluble organic matter, such as starch or 
sugar, and returning the mass to the converter, will serve for 
regeneration if the mass is not in very bad shape. The effect 
is to dissolve (partially) and redistribute the platinum, and dis- 
solve the impurities and have them carried off in the gases from 
the burning organic matter. 

If the mass from magnesium sulphate to be regenerated con- 
tains a large proportion of fines it should be put into a wooden 
tub, with a solution similar to that used for ordinary regenera- 
tion, and water added as the solution boils down from the heat 
of the reactions; and finally, after perhaps 10 to 24 hours, a 
smooth paste results. It should be more or less sloppy. The 
finer the material the less time required. 

The result is a senu-solution of crystalline magnesium sulphate, 
with platinum, which is fiunaced as was the new salt, and the 
mass is then ready for use. 

Of course this treatment results in some platinum being shut 
up within the pieces of magnesium sulphate, and the action of 
such quantities lost, so it is good practice to spray on 5 per cent 
of the original quantity, after r^eneration. After several 
regenerations the salt should be dissolved in a weak sulphurie 
acid solution, the platinum recovered, and new mass made. 



iiz^dbvCooglc 



CHAPTER XXII 

ACCOUNTING 

Bt W. M. Lb Clkab 

All well organized concerns recognize the advantages of Cost 
Sheeta which reflect the costs to a very accurate degree, and it 
is not considered necessary to dwell or argue upon this point, 
because it is a conceded fact that without these records the 
management cannot follow the destinies of its operations. 

The usual factors entering into the cost of any product are 
apprised here — i.e. 

Labor, dinct, Repftira and Maintainance, 

I^bor, indirect, Inauranoe, Taxes, etc., 

* Materials, dinot, Overhead, 

Materials, indirect, Depreciation. 

These various charges reflected in the cost sheets may come 
through sub-cost sheets, such as Power House cost sheets, or 
they may be charged direct to the Sulphuric Acid cost sheet, 
depending entirely upon what basis the managment wishes the 
cost data to be prepared. In either case the flnal result should 
be identical. 

The Direct Labor represent^ the labor actually employed in 
obtaining the product. The Indirect Labor is labor that is 
necessary to the operation, but which does not go directly into 
the product, as for instance, foremans' time, laboratory time, 
sweepers, oilers, etc., ■ 

Direct and Indirect Materiak are classifled along lines similar 
to the Direct and Indirect Labor. Direct Materials represent 
such items as sulphur, pyrites, etc., while the Indirect Materials 
would be Nitric acid in some form (usually Chile saltpeter), 
fuel etc. 

The Repair and Maintainance charges should represent the 

labor and materials expended which keep the apparatus in 

operating condition, and do not add perceptably to the life of the 

247 



^dbvGooglc 



248 AMERICAN SULPHURIC ACID PRACTICE 

equipment. Charges falling into the latter cUseification should 
be capitahzed. 

The Charges, (or Taxes, Insurance, etc., should be determined 
as nearly as is possible to estimate them. It may not be amiss 
to state that accounting authorities do not consider the United 
States. Government Income and Excess Profite Taxes to be a 
part of the manufacturing cost, and are in reality a division of 
profits with the Government. 

The charge for Depreciation should represent the diminish- 
ment in value due to wear, tear, and obsolesence, as nearly as it 
can be estimated. With proper care the buildings will last a 
long time, while the chambers, the most costly part of a chamber 
plant, should be amortized on an 8-year basis, although they 
will frequently go 10. Other parts of the plant must be taken 
care of with regard to their varying life. The thought I wish to 
bring out is that no one figure will do for a plant making corrosive 
chemicals. Buildings at 4 per cent and Power House Equipment 
at 10 per cent, will fit in very well. 

The charges for Overhead should represent General Office 
salaries, etc., which are not charged under the classifications 
previously discussed. If desired the details on the cost sheets 
may be carried out to the minute8:t details, but ordinarially 
this is not considered necessary. 

The basic feature to be borne in mind in the t>reparation of 
the Cost Sheet is, that EVERY CHARGE that has any bearing 
upon coets is reflected therein. The details of these items and 
their arrangement is of course important, but only secondarily 
so. 

It is probably unnecessary to add that the costs should be 
refiected upon the pounds of 100 per cent acid produced. 

It is difficult to lay down any specific rules or instructions 
regarding the cost information which should be furnished daily, 
as this feature depends entirely upon what the management 
considers necessary for its information. It is very important 
however that the management know the number of men, cost of 
labor and materials used, and the production daily. The 
author's opinion is that all elements of cost should be calculated 
daily, some factors must of necessity be estimated, which by 
the preparation of a monthly progressive sheet would at the 
end of each month very closely tie up with the monthly coet 
sheet. 



^dbvGooglc 



ACCOVNTINQ 

Per 1,000 lb. H,SO, 

lAbor 1.3 hr. @ 48c. 

(Production roughly 3,825,000 lb. per mo.} 

Say S275,O0O.0O investment per line. 

Interest 6 per cent 16,500 

Dep. 26 per cent 68,750 

Insurance 3 per cent 8,250 

Taxes 1.5 per cent 4,125 * 

(97,626 

Labor fl24 

Materials, 330 lb. 8 , 3.03 

Coal 50 

Superintendence 16 

Office and labor inclutting supplies 076 

Capital 2.12 

S6.500 

Repairs not included. 

Steam not included. 



^dbv-Googlc 



APPENDIX 

TAHK CAR TABLE 

The Standard Tank Car for acid is 78 in. in dianeter, and the 
length of the side is 27 ft. 6 in. The two ends are dished out- 



oU^L-i^_J L 



Hore 

Carve 'a''% OfptH va. % CenfonH Curvr for PliKnC/6'nJifr 
Ltngifuilmal^itii HoriiBntal ' 

furm 'S'-%&!pth vi.foConfmH Cvrvg for OiihtdEne/ 
TotolVolumsofCi^rmderR<fferTeettoinOjrv^'A'-a7SS4D^ 
To*al'-AjlumeQfSSndil^fsrr3tliginCurve'6''2TTh^{I>-b} 

Q'Insiels OipmefarofTBtih^aad Radius ofOiihed End 
L • Lenath of Plain CuU'ndiical H>rfof Tank 
h'TofalDmihofOishadEnd 
h - 0.134 D 



, the radius of the dish always being the same as the 
iter of the tank itselt 



^dbvGooglc 



APPENDIX , 251 

Other sizes of "tanks" are used for acid — so many in fact 
that it would be out of the question to give a gaugeing table for 
all sized tanks. However, with the tank curve a table for 
any sized tank can be quickly prepared. 

To prepare such a table, first find the area of the vertical 
section of the car in feet: then multiply this by the length of 
the straight side of the tank — this will give you the number of 
cubic feet in the cylindrical part of the tank. Then prepare a 
table giving the per cent of height for every inch of height — then 
set down opposite each inch the per cent of the capacity of the 
tank that is represented at that height — for instance, in the 
table given, at 16 in. the per cent of the total is 20.54. Then 
multiply this by 913+, which is what the cylinder holds full, 
and you get 135.55 cu. ft. Then figure from the formula given 
how much the dished ends hold full, look on the "end curve" 
to see how much the ends hold at 20.54 per cent, and you will 
find it is about 8.4 per cent. From the formula the ends hold 
about 37 cu. ft., and you get 3.08 cu. ft., which added to the 
135.55 cu. ft. of the cylinder gives you the amount of acid in 
the tank; 138.63 cu.ft. 

Because of the varying relations between the length and 
diameter, it is not possible to work it all out in one formula, 
so a table must be prepared as above. 

From a hydrometer the density of the acid is then determined, 
its weight per cu. ft. looked up, and the total weight calculated. 

While there may be some errors in the last place of decimals, 
it is not possible to read a stick to within one-hundredth of an 
inch, and after a tank car has been in service a very short time 
it will be distorted more than any error in this curve. 



^dbvGooglc 



AMERICAN SULPHURIC ACID PRACTICE 
Table fob Stamdaiid Tank Caa 



Height 






Height 






of acid 


Fteroentof 


No. of 


of acid 


Per cent of 


No. of 


in tank, 


depth 


cu. ft. 


in tank, 


depth 


cu. ft. 


inches 






inches 






1 


1.28 


2.24 


40 


51.28 


491.02 


2 


2.66 


6.09 


41 


52.56 


506.96 


3 


3.84 


11.67 


42 


53.84 


523.58 


4 


S.13 


17.88 


43 


55.13 


538.10 


fi 


6.41 


24.81 


44 


56.41 


553.65 


6 


7.69 


32.49 


45 


£7.69 


669.00 


7 


8.98 


40.93 


46 


68.98 


584.42 


8 


10.26 


40.86 


47 


60.26 


599.73 


9 


11.64 


59.36 


48 


61.64 


616.17 


10 


12.83 


68.52 


49 


62.83 


030.28 


11 


14.11 


79.23 


50 


64.11 


645.33 


12 


16.38 


90,65 


51 


65.38 


660,29 


13 


16.69 


102.32 


52 


66.69 


676.20 


14 


17.97 


114.07 


63 


67.97 


689.72 


16 


19.25 


126.24 


54 


69.25 


704.14 


16 


20.53 


138.63 


55 


70.54 


718-71 


17 


21.82 


150.97 


56 


71.82 


732.95 


18 


23.10 


163.31 


57 


73.10 


746.74 


19 


24,39 


176.43 


58 


74.39 


760.22 


20 


25.67 


189.78 


59 


75.67 


773.57 


21 


26.95 


203.26 


60 


76.96 


786.69 


22 


28.24 


217.05 


ei 


78.24 


799.03 


23 


29.52 


231,29 


62 


79.52 


811.37 


24 


30 80 


246.86 


63 


80.80 


823.76 


25 


32.09 


260.28 


64 


82.09 


835.93 


26 


33.37 


274.80 


65 


83.37 


847.68 


27 


34,65 


289.71 


66 


84,65 


859.35 


28 


35.93 


304.67 


67 


85.93 


870.77 


29 


37.21 


319.72 


68 


87.21 


881.48 


30 


38.49 


334,83 


69 


88,49 


890,64 


31 


39.77 


350.27 


70 


89.77 


000.16 


32 


41,05 


365.58 


71 


91.05 


909.07 


33 


42.33 


381.00 


72 


92.33 


917.51 


34 


43.62 


396.45 


73 


93.61 


925.19 


35 


44.89 


411.90 


74 


94.89 


932.12 


36 


46.17 


427,42 


76 


96.17 


938.33 


37 


47,45 


443.04 


76 


97.46 


943.91 


38 


48.72 


458-98 


77 


98.73 


947.46 


39 


50.00 


475.00 half full 


78 


100.00 


950.00 



idbyGoOglc 



APPENDIX 

Tables and General lofonnation 

SpBCmc Gbavitt 

Manufacturing ChemiBta Association of the United States 







Per cent 


Weight of 


Freezing 


'Bt 


%i. gr. 


1 cu. ft. in 


(melting) 






H|SO< 


pounds, av. 


point, °F. 





1.0000 


0.00 


62.37 


32.0 


1 


1.0069 


1.02 


62.80 


31.2 


2 


1.0140 


2.08 


63.24 


30.5 


3 


1.0211 


3.13 


63.69 


29.8 


4 


1,0284 


4.21 


64.14 


28.9 


5 


1.0357 


5.28 


64.60 


28.1 




1.0432 


6.37 


65.06 


27.2 


7 


1.0507 


7.45 


65.53 


26.3 


8 


1.0584 


8.55 


66.01 


25.1 


9 


1.0662 


9.86 


66.50 


24.0 


10 


1.0741 


10.77 


66.99 


22.8 


11 


1.0821 


11.89 


67.49 


21.5 


12 


1.0002 


13.01 


68.00 


20.0 


13 


1.0985 


14.13 


68.51 


18.3 


14 


1.1069 


15.25 


69.01 


16.6 


15 


1.1164 


16.38 


69.57 


14.7 


16 


1 . 1240 


17.53 


70.10 


12,6 


17 


1.1328 


18,71 


70.65 


10.2 


IS 


1.1417 


19.89 


71.21 


7.7 


10 


1.1508 


21.07 


71.78 


4.8 


20 


1.1600 


22.25 


72.35 


1.6 


21 


1.1694 


23.43 


72.94 


- 1.8 


22 


1.1789 


24 61 


73.53 


- 6.0 


23 


1,1885 


26.81 


74.13 


-11.0 


24 


1.1983 


27.03 


74.74 


-16.0 


25 


1.2083 


28.28 


75.36 


-23.0 


26 


1.2185 


29.53 


78.00 


-30.0 


27 


1.2288 


30.79 


76.64 


-39.0 


28 


1.2393 


32.05 


77.30 


-49,0 


29 


1.2500 


33.33 


77,96 


-61.0 


30 


1,2609 


34.63 


78.64 


-74.0 


31 


1.2719 


35.93 


79 33 


-82.0 


32 


1.2832 


37.26 


80.03 


-96,0 


33 


1.2946 


38.58 


80.74 


-97,0 


34 


1.3063 


39.92 


'81.47 


. -91.0 


35 


1.3182 


41.27 


82.22 


-81.0 


36 


1.3303 


42.63 


82.97 


-70.0 


37 


1.3426 


43.99 


83.74 


-60,0 



,db, Google 



AMERICAN SULPHURIC ACID PRACTICE 

SpEciric GRAvnr 

Manufacturing Chemists Association of the United States 







Percent 
H,SO, 


Weight of 


fYeesing 


-B6. 


Sp-ur. 


1 cu. ft. in 


(melting) 






poundB, »v. 


point, 'F. 


38 


1.3551 


45.35 


84.52 


-53 


3ft 


1.3679 


46.72 


85.32 


-47 


40 


1-3810 


4S.10 


86.13 


-41 


41 


1.3942 


40.47 


86.96 


-36 


42 


1.4078 


50.87 


87.80 


-31 


43 


1.4216 


52.26 


S8.67 


-27 


44 


1.4356 


63.66 


89.64 


-23 


45 


1.4600 


65.07 . 


90.44 


-20 


46 


1.4646 


56.48 


91.35 


-14 


47 


1.4796 • 


57,90 


92,28 


-15 


48 


I. 4948 


60.32 


93.23 


-18 


49 


1.5104 


60.75 


94.20 


-22 


60 


1.5263 


62.18 


95.20 


-27 


51 


1.5426 


63.66 


96.21 


-33 


52 


1.5591 


65.13 


97,24 


-39 


53 


1.5761 


66.33 


98.30 


-49 


54 


1.5934 


6S.13 


99.38 


-59 


55 


1.6111 


69.65 


100.48 


Below -40 


56 


1.6292 


71.17 


101.61 


Below -40 


57 


1.6477 


72,75 


102.77 


Bebw-40 


58 


1.6667 


74.36 


103,95 


Betow -40 


50 


1.6860 


75.99 


106.16 


- 7 


60 


1.7059 


77.67 


106.40 


+12.6 


61 


1.7262 


79.43 


107.66 


27.3 


62 


1.7470 


81.30 


108.96 


39.1 


63 


1.7683 


83.34 


110.29 


46.1 


64 


1.7901 


85,66 


111.66 


46.4 


MH 


1.7067 


86.33 


112.00 


43,6 


64 Ji 


1.8012 


87.04 


112.34 


41.1 


MH 


1.8068 


87.81 


112.69 


37.9 


65 


1.8125 


88,65 


113.05 


33.1 


65H 


1.8182 


Sd.SS 


113.40 


24.6 


65H 


1.8239 


90.60 


113.76 


+13.4 


65H 


1.8297 


91.80 


114.12 


- 1.0 


66 


1.8354 


93.1fl 


114.47 


-29.0 



idb,Go(5glc 





APPENDIX 




Allowance fob Teuferattbe 


At ICBfi., 


.039°B4. or .00023sp.gr 


= rp. 


At 20''B6., 


.036°B6 


or .00034 sp-gr 


= VF. 


At WBi., 


.035°Bfi 


or .00039Hp.gr 


= 1-F. 


At WW., 


.031°BS 


or .00041 ap. gr 


= 1°F. 


At 50°Be., 


.028'B6 


or .00045 8p. gr 


- IT. 


At 60°Be., 


.oae-K 


or .00053sp.gr 


- rF. 


At 63'Be., 


.026°Be 


or .00057 8p.gr 


-1°F. 


At 66°B6., 


.OaaS-M. or ,00054 8p.gr 


- rp. 



Afpkoximati: Boilino Points 



50°B^ 295°F. 

Wm ■.. 386°F. 

ei-Bfi 400^. 

Si-Bi 415°F. 



63°B« 432°^ 

64°B^ 451''F. 

aS°B4 485'*F. 

6a°Be 538°P. 



l^EORETICAL PKODTTCTION FlQUBE 

5H|2^ = 3.0585 Log of 3.0585 "- .485508 

Specific GaAvm (at 65°F.) and Melting Point (Freeeinq Poi 
Fuming Solfhuric Acin 

TOTAI. Soi Fun So, Bp. an. Multthq <ni)E 



2.05 1 


8300 


7.50 1 


8480 


12.95 1 


8B57 


18.38 1 


8847 


23.84 1 


9086 


29.27 1 


9258 


34.70 1 


9429 


40. 17 1 


9607 


45.63 1 


9667 



idb,Go(5glc 



AMERICAN SULPHURIC ACID PRACTICE 



Pbk CBNT TOTIL 80l « 

81.03 
81.99 



8e.40 
86.76 
87.14 
87.60 



Toni. SOi Pu CI 



iTU>80.- 


PU CBHT Tor* 


00 


87.87 


2 


88.3^ 


4 


88.60 


6 


88,97 


8 


89.33 


10 


89.70 


12 


90.07 


14 


90.44 


16 


90.81 


18 


91.18 


20 


01.66 


22 


91.91 


24 


92.28 


26 


92.65 


28 


93-02 


30 


93,38 


32 


93.76 


Specific Heat 


Swacamit 


TouL 80i Pm tn 


.3500 


92 


.3460 


94 



.4000 
.4660 
.5350 
.6500 
.7700 







Vapor Tbnbion 


Pas CBNT 


ae-F. 


104°F. 140°F. 


H,SO. 


M.M. 


M.M. M.M. 


61.7 


3 


10 25 


70.0 


2 


3 8 


81.5 


1 


1 1.5 



at all temperatures. 



^dbvGooglc 



Vapor PitBSBtrBEs of Soue Qoauties or OLBnu 
K volume oleum. H volume air. 





Pre». 


Pres- 


Pres- 


Pres- 


Pres- 


Pres- 


Pres- 


Temp. 


sure of 


Bureof 


sure of 


sure of 


sure of 


sure of 


sure of 


°C. 


oleum. 


oleum, 


oleum, 


oleum, 


oleum. 


oleum. 


oleum, 




30% 


40% 


50% 


60% 


70% 


80% 


100% 




atm. 


atm. 


atm. 


atm. 


atm. 


atm. 


atm. 


35 












0.150 


0.40 


40 




0,075 




0.22S 


0.375 


0.600 


0.65 


4fi 


o!050 


0.125 




0.350 


0.575 


0.650 


0.87 


50 


0.100 


0.175 


0.350 


0.S2S 


0.775 


0.875 


1.20 


55 


0.140 


0.225 


0.450 


0.676 


1.025 


1.200 


1.60 


60 


0.200 


0.276 


0-660 


0.825 


1.400 


1.500 


1.85 


65 


0.225 


0.350 


0.700 


1.025 


1,650 


1.900 


2.26 


70 


0-275 


0.400 


0.825 


1,275 


2,060" 


2.300 


2.76 


75 


0,340 


0.475 


1,000 


1.670 


2.625 


2.800 


3.30 


80 


0.400 


0.675 


1.150 


1.850 


3.100 


3.500 


4.00 


85 


0.450 


0.675 


1.400 


2.160 


3.700 


4.176 


4.90 


90 


0.530 


0.825 


1.700 


2.576 


4.400 


5.050 


5,90 


95 


0.625 


0.960 


2.060 


3.150 


5.000 


6.0OO 




100 


0.730 


1.100 


2.400 


3.700 


6.000 







idb,Go(5glc 



AMERICAN SULPHURIC ACID PRACTICE 

■ Heat of Solutiok. (Dh. Knkitchb} 
Determined Values 

Oi Pm CBKT 80i Fib obht Fbb> 80i Pm cint Cuaum 

fiO.32 41.07 40.46 

60.18 49.12 66.46 

63.86 62.13 79.05 

70-24 S7.33 110.05 

73.76 60 21 132.3 

76.86 62.74 151.4 

71.41 64.82 171.7 

99.88 81. K 0.0 194.06 

83.49 10.12 ' 221.4 

85.26 19.75 246.27 

87,3! 30,91 277.6 

89.08 40.66 299.05 

91.06 61.28 327.9 

- 92.67 60,10 361.4 

94.72 71.26 393.6 

96.62 81.60 433.6 

98-48 97.81 470.6 

99.64 00.48 491.1 

BtsAT or SoLnnoN or Boud Oleuu. (Db. Kneitche) 





Determined Valuea 




To**!. 80> P«B CBHT 


Fmi so, Pi« cb»t 


CjU-ORIU 


89.4 


42.3 


271.0 


90.73 


49.63 


303.2 


92,6 


59.2 


330.4 


94,6 


70,1 


369.2 


06.28 


70.76 


408,8 


98.14 


97.32 


436.1 


08.64 


99,34 


481.4 


09.84 


90.77 


486.0 



id»,Googlc 



HXAT OP SOLDTIOK O 



ScLFHCRic Acid akd Oustni. (Db. Kmbitche) 
Graphically DetermiDed 





Oleum 














Heat of 


so„% 


H,SO., 

% 


Cal. 


80,, % 


Free 
80,.% 


C&L 


solution 

ofaolid 

oleum, oaL 


60 


61.25 


39 


82 


2 


199 




51 


62.48 


41 


83 


7.5 


210 






52 


63.70 


44 


84 


12.9 


223.6 






63 


64.93 


46.6 


85 


18-3 


237.6 






84 


66,15 


49 


86 


23-8 


250 






55 


67.38 


51.5 


87 


29.2 


266 






56 


68.60 


64 


88 


34.7 


278 






57 


69.83 


67 


89 


40.1 


292 






58 


71.06 


59.5 


90 


46.6 


308 


286 


59 


72-28 


62 


91 


61.0 


325 


304 


60 


73.60 


65 


92 


56.4 


344 


322 


61 


74.73 


68 


03 


61.9 


363 


340 


62 


75.96 


72 


94 


67.3 


381 


360 


63 


77.18 


75 


06 


72.8 


401 


380 


64 


78,40 


79 


96 


78 3 


421 


402 


65 


79.63 


83.6 


97 


83.7 


442 


423 


66 


80.86 


88 


OS 


89.1 


465 


442 


67 


82.08 


93 


90 


94.6 


400 


463 


68 


83.30 


98 


100 


100 


515 


486 


69 


84,53 


103 










70 


85.75 


108 










71 


86.98 


113 










72 


88.20 


119 










73 


89.43 


126 










74 


90.65 


133 










75 


91.88 


139 










76 


93,10 


146 










77 


94.33 


152 










78 


96.66 


160 










79 


96-78 


168 










80 


98-00 


178 










81 


99-23 


188 










"■"^ 


100-00 


193 











^dbvGooglc 



AMERICAN SULPHURIC ACID PRACTICE 



ELiiOTBiCAi. Rbbistancb of Sclpburic Acid at 2S°C. 
(Dk. Kkeitche) 



«..% 


H,SO., % 


(ftm 


80., % 


H,SO<, % 


Ohm 


40.19 


49.23 


0.235 


75.19 


92.01 


0.70 


48.80 


B9.79 


0.29 


76.73 


94.00 


0.72 


S3. 27 


65,14 


0.245 


78.46 


96.11 


0.795 


57,64 


70.55 


0.345 


78.52 


96.20 


0.79 


60.28 


73.85 


0.475 


79.55 


97.46 


0,80 


61.07 


74.82 


0.525 


80.22 


98.27 


1.10 


64.00 


78.40 


0.60 


80.98 


99.21 


1.95 


65.14 


79.80 


0.67 


81.27 


99.66 


2.2 


67.04 


82.14 


0.74 


81.345 


99.64 


2.7 


68.53 


83.97 


0.75 


81 . 425 


99.74 


3.5 


69.12 


84.68 


0.76 max. 


81 . 455 


99.78 


4-2 


70.23 


86.03 


0.746 


81.53 


99.87 


5.7 


70.84 


86.79 


0.74 


81 . 535 


99.88 


6 7 


73.40 


89.92 


0.705 


81.59 


9g.95monohydrate 


7,45 man. 



Electrical Rebibtakcb of OlbuiC at 26°C. 



Total 
SO., % 


Free 
SO., % 


Ohms 


Total 
80.,% 


Free 
80., % 


Ohms 


81.695 


0.34 


6.15 


90,5 


45.0 


23,4 


81.74 


0,5 


5.35 


90.8 


50,0 


53,0 


82.4 


4,0 


2.43 


91.6 


54,0 


88,0 


83,44 


9,8 


2.20 


92.7 


60,3 


222,0 


84.2 


14,0 


-=}^„„ 


93.4 


64,0 


287.0 


84,7 


16.7 


94,6 


69.6 


759,0 


85,2 


19.4 


2.23 


95.4 


75.0 


1,265,0 


86.3 


26,5 


2.95 


96,35 


80.0 


4, 000. Oat 27 


87,06 


29.6 


4.05 


06,87 


83,0 


6, 650, Oat 32 


88.3 


36.3 


6.65 


98.16 


90.0 


61, 850, Oat 36 


89,0 


40.2 


15.2 









idb,Go(5glc 



Attacking AtmoN upon Ibon 

Decrease per squara meter per hour in grama after 72 hours action of add 
acid at I8'-20''C. (85*'-68''F.l. (Dr. Kneitche.) 



H,80fc% 


80„ % 


Cast iron 


Ingot iron 


Welding iron 


48.8 


39.9 


0,2177 






61.2 


50,0 


0.1510 




0.3032 


67.7 


55.3 


0.0847 




0.0789 


73.4 


59.9 


0.0662 




0.0623 


79.7 


65.0 


0.1560 




0.1159 


83.7 


68.4 


0.1388 




0.1052 


85.1 


69.6 


0.1306 




0.1034 


88.2 


72.0 


0.1636 




0.1417 


90.6 


73.9 


0.1750 




0. 1339 


92.0 


75.2 


0.0983 




0.1040 


93.0 


76.9 


0.0736 


0,0987 


0.0856 


94.1 


77.0 


0.0723 


0.0933 


0.0708 


95.4 


77.9 


0.1274 


0.1471 


0.1209 


96.8 


79.0 


0.1013 


0.0815 


0.0988 


98.4 


80.3 


0.0681 


0.0533 


0,0656 


98.7 


80.6 


0.0583 


0.0509 


0,0570 


99.2 


81.0 


0.0668 


0.0418 


0.0504 


99.3 


81.07 


0.057 


0.042 


0.060 


99.5 


81.25 


0.060 


0.038 


0.049 


99.77 


81.45 


0.066 


0,042 


0,049 


100.0 


81.63 


0.087 


0.088 


0.076 


Total SO. 


Free 80, 








81.8 


0.91 


0.201 


0.393 


0.323 


82.02 


2.00 


0.190 


0.285 


0.514 


82.28 


3.64 


0.132 


0.441 


0.687 


82.64 


4,73 


0.164 


0.956 


1.075 


82.80 


7.45 


0.161 


0.566 


1.321 


83.50 


10.17 


0.079 


0,768 


1.540 


&1-20 


12.89 


0.270 


1.024 


0,892 


84 62 


16.16 


0.271 


1.300 


0,758 


85.06 


18 34 


0.076 


1.988 


1.530 


86.00 


23.78 


0.070 


0.246 


0.471 


88.24 


34.67 


0.043 


0.033 


0.063 


90.07 


45.56 


0.040 


0.018 


0.019 



CovroeinoH Carbok QaAPHirs 

Oast iron 3.55 per cent, 2,787 per cent. 

Ingot iron 115 

Welding iron 0.076 



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INDEX 



Abn-Bekr-Alrhaaea, 1 
Absorption, 14, 238 

beat temperature for, 212 

heat of combinstion of SOi and 
H,0, 238 

of SOi hj weaker acid, 209 

Btrength of acid for, 212 

towera, 238 

water not satisfactory for, 238 
Accounting, 247 

Acid, proper strength to make, 239 
Acid egg (blow case), 122, 213 
Adsorbtion, 228 
Alum, 17 

epirit of, 1 
Aluminum in lead, 192 
American Cyanimid Company, 143 
American makers of liquid S0|, 77 
American Smelting & Refinii^ Com- 
pany, 77 
Ammonia as source of NO for 
chambets, 143 

analyses, 151 

oxidation-reaction, 149 

atiU, 147 
Anaconda Copper Mining Company, 

»2 ,. 

duBt chambers, 92 

large Wedge (an, 64 
Antimony, cantAct poison, 217 

in lead, 103 

the Triamphial Car of, I 

to harden lead, 112 
Arsenic, carried by mist, 207 

enemy of contact process, 217 

in entrance, effect, 11 

in entrance gas, 5 

in lead, 193 

removal from maas, 230 



Asbestos, beat packing, 213 
fluffed filter packing, 224 
platinised, 228 

Avoirdupois compared with Troy 
weights, 24S 



Bacon, Dr. Raymond P., Louisiana 

sulphur, 28 
Badische contact process, 209-228 

converter, 228 

patents bearii^ upon, 229 
Battery acid, 206 
Baum£ curve, 263 

hydrometer, 167 

tables, 253, 254, 255 
Benker system, 196 
Bismuth, efiect upon lead, 192 
Blow cases (acid eggs), 122, 213 
BoUman, Dr. Eric, 2 
Brimstone, as raw material, 44 

burning to SOi, 49 
Brunner-Mond Co., ammonia still, 

147 
Bufialo Foundry & Machine Co., 
197, 198 

apparatus for recovering acid, 
197, 198 
Builders Iron Foundry, meters, 148 



Carbon dioxide, effect upon contact 

process, 11 
Cast iron not dissolved by fuming 

acid, 213 
Catalytic action of metallic oxides, 

7,228 
taw of mass action applied to, 

236 
Catalyser, 4, 6, 228 

other than platinum, 236 



^dbvGooglc — 



Chalcopjrrite, 46 

Cb&mber plant, reactione in, 180 

operatioa, ISO 
Chamber proceaa, deacription of, 82 

flow sheet, 84 

outline, 8 ' 
CbambeTB, construotion, 101, 102 

protecting wind pressure on, 106 

volume required, 110 
Chambers, lead, 1, 2 

acid must be concentrated, 189 

control of acid strength, 186 

position in chamber process, 83 
Chemiatfl, need for, 200 
Chlorine, in the contact process, 11 
Circulation, promoting in chambera, 
106 

Gilchrist pipe column, 108, 118 

multiple tangent system, 107 
plate column, 108 
Qean gas absolutely necessary for 

conversion, 200, 217 
Cobalt, 4 
Combustion chambers, far sulphur 

burners, 218 
Concentration, Benker system, 196 

bottom firing, IM 

temperatures, lOI-lflJIi 

by cascade, 201 

by Kalbpeny system, 207 

degree of depends upon its 
market, 212 

heat exchangers, 193 

in fused silica, 200 

objection to direct heat in 
concentrating, 197 

pan, 186 

platinum stills, 109 

top firing, 100 
Conductivity of heat by sulphur, 40 
Contact mass, different for different 

methods, 209 
Contact process, 4 

early blunders, 210 

outline, 10, 207 
Conversion of SOt, slide rule for, 236 
Converter for oxidizing NHi, 145 

Badiache, 229 

Sohroeder GriQo, 232 



Converting SO. to 80^ 228 

Coolers, acid, 120 

Cooling, different methods, 209 

gases, Badische method, 219 
Schroeder, Grillo method, 220 
Copper, 2 

in lead, 193 
Costs, by contact process, 212 
Cottrell apparatus for dust settling, 

86 
Cubical expansion of sulphur, 39 



Davison Chemical Co., Silica gal, 75 
liquid SOi, 75 
saving SO^ 228 
De Beauvais, 1 

Depreciation on contact plant, 213 
Differences between Badische and 
Schroeder-Grillo contact 
processes, 209, 231 
Distillation of ferrous sulphate, 4 
Distribution of acid in Glover's and 

Gay Lussac's, 130 
Draft, 179 

measurements, 178 
Dnunage necessary for coolers, 242 
Driiddng water, clarifying, 18 
Ducktown Sulphur, Copper & Iron 

Co., SOt from blast, 65 
du Pont Co., 91 
Dust settlmg apparatus, 86 
Cottrell apparatus, 86 
chamber with hanging wires, 91 
Howard, 91 
centrifugal, 92 
Anaconda type, 92 
effect in contact process, 217 
Dwight & Uoyd sinterii^ machine. 



Electrical conductivity of sulphur, 

39 
Ellison draft gauge, 178 
Exit gas, 177 

testing, 177 
Expansion joints faihires with acid, 

213 



^dbvGooglc 



Fans, 1S9 

design of, 160 
Ferrous sulphate, dietiUatioa of, 4 
Fertiliier induBtry depends upon 

HSO,, 17 
Filtering material grade 201A as- 

beatoa, 163 
Flues, methods of supporting, 164 

size of, 163 
Foremen's meetings, 214 
Frasoh process, 33 
Freezing, acid, 15 

point of acid aa .related to 
product, 212, 240 

curve of, points, 262 

point of acid, 255 
Frictional electricity of sulphur, 39 
Fuming acid, 4 

composition and uses, 17 
Fused siUoa, for concentration, 201 



Garbet, Mr., 1 

Gas for contact process, best 
strength, 211 
control, 235 
temperaturcfl, 212 
Gauge glasses undependable, 222 
Gay Lussac tower, reactions in, 181 

deeoription of, 113 

packing, 114 

position in ohamber process, 
85 
Geber, 1 

General Chemical Co., 209 
Qlens Falls Machine Co., sulphur 

burners, 49 
Glover tower, 

as a concentrator, 99 

brick for, 96 

chief function of, 98 

construction, 94 

description, 94 

lining and packing of, 96 

position in chamber proces3,83 

reactions in, 181 

size of, 100 
Gold, 4 



Hamish & Schroeder process, 5 
Harrison Bros. A Co., 1 
Mr. John, 2 
Hart condenser, 141 
Heat exchanger for concentrating 

aoid, 193 
Heins-Skinner taa, 161 
H^h silicon irons, 141 
Holker, 4 

Hough, Arthur, 205 
Humidity combines with 80|, 8 
Hydrochloric acid in the contact 

process, 11 
Hydrometers, 167 

I 

Impurities in gas in contact process, 11 
Iridium, 4 

attacking action of sulphuric 
acid on, 261 



Jefferson, President, 2 



Kalbperry Corporation, concentrat- 
ing tower, 201 



I^iboT for chamber process, 187 

for contact process, 213, 214 
Landis, W. S., 143 
Lead, effect upon contact process, 1 1, 
217 
flowing, 105 
life of, 112 
methods of supporting, 95, 102, 

104 
quality for concentrating pans, 

192 
specifications. 111 
weight of in chambers, 102 
Lnnge, comments on American prac- 
tice, 209 
plate column, 108 
theory of chamber acid, 9, 



^dbvGooglc 



Magnesium sulphate, in tlie Scbro- 

eder process, 5, 228, 

265 
M^ufftcturera in the U. 8., 19, 27 
Maaa action, law of, applied to 

contact action, 236 
Mass contact, p eparation of in, 244 
Scbroeder-Grillo process, 229 

r^eneratioD of, 246 

tegtii^, 243 
MoKee, Dr. Ralph, on liquid SO,, 41 
Meltii^ joint of sulphur, 41 
Mercury, enemy of contact process, 

2, 217 
Metallui^ical gases for SO,, 208 
Meters, gas, 148 
Mist, arsenic carrier, 207 
Mixed acid to introduce nitric 

oxides to chambers, 141 
recovery of sulphuric from, 

201 
testily, 176 
Moisture in contact system, 217 
Dr. Reese's experiments, 230 
taken from air-quantity of, 222 
Montejus, 122 
Mortar, to stand acid, 96 

N 

New Jersey Zinc Co., 209 
Nitrate of soda, characteristics, 47 

purification, 48 

testii^, 176 
Nitre cake, disposal of, 138 

testing, 17S 
Nitre losses, 183 

absorption of, 115 

feed control of, 185 

introduction of, 136 

methods of introducing, 138 

pots, 137 

potting with fuel, 139 

reactions, 136 
Nitric acid, 16 

condensii^ the vapor, 141 

curve of boilii^ points, 262 

in mixed acids, 203. 



Nitric acid, lower freezing point of 
H,SO., 212 
production in chambers, 13S 
Nitrogen oxides — saving, 9, 10 
Nitrometer, 174 
Nitrosoeulphuric acid, 9 
Nitrous vitriol in the Glover tower, 98 
testing, 176 
O 
Oil of vitriol, 2 
Operation, chamber plant, 180 
Orsat apparatus, 169 
Oxygen, pure In contact process 
unnecessary, 217, 234 
P 
Packing for Glover towers, 98 
for piping and valves, 213 
Pan concentration, 186 
bottom firing, 191 
temperatures, 191 
top firing, 190 
Platinum, 2-S 

as SO, catalyzer, 228 
quantities for SO* oonveraion, 



246 
Poison, contact, Opl'a theory, 13 

c atalyzer for oxidizing N Hi, 150 
Dr. Krause theory, 3 
list of, 217 
Pratt fan, 161 

Preheaters, Schroeder-Grillo, 232 
Priestly, Dr. Joseph, 2 
Production to figure for contact 

plant, 211 
Fulsometer, 122 
Pump, acid, 127, 240 

makers, 240 
Purification of gases in contact 

process, 217 
Pyrites cinder, catalytic action of,219 
burning, 53, 59 
fines burners, 56 

Henerhoff furnace, 57 
MoDougal furnace, 67 
Wedge fnmace, 61 



^dbvGooglc 



Pyrites, importation of Spanish, ', 

lump burners, 55 

prices, Si 

propcrtiee, 45 
Pyrometers, 166 

dependent upon, 210 

makers of, 232 
Pyrrhotite, 46 



Raschig, theory of chamber process, 

Raw matcrisJe, 44 

brimstone, 44 

chalcopyrite, 45 

galena, 46 

nitrate of soda, 47 

pyrites, 45 

pyrrhotite, 45 

spent oxide of iron, 46 

line blende, 46 
Reactions, time of, in chamber pro, 
101 
are exothermic, 101 
Reese, Dr. Charles L., impurities in 

contact process, 11, 230 
Regeneration of contact mass, 246 
Reich test for SOi, 170 

made regularly in contact 
process, 210 

tables, 173, 174 
Roebuck, Dr., 1 
Rule of thumb methods, 182 



Safety appliances, 214 

Salt cake, 17 

Saltpeter, 1 

Scbroeder-Orillo contact process, 209' 

catalyzer, 228 
Scrubbing, need for, 13 
Shut down, preparation for, of 

contact plant, 215 
Silica gel for recovering SOi, 75, 228 
Silicon, 4 

tetrafiuoride, effect upon con- 
tact process, 11, 217 
Silver in lead, 173 



Sintering pyrites cinder, 68 
Soda ash, 16 
Sodium sulphate, 136 
Solubilities of sulphur in various 

solvents, 82 
Solution, heats of, 258, 259 
SOi, best percentage for conversion, 
211 
converting to SOj, 228 
first step in making H:SO« tem- 
perature of formation, 208 
slide rule for converaion of, 236 
SO,, oxidation of SOi to, 209 
converting SO, to, 228 
free table, 255, 256 
in burner gas causes mist, 217 
total table, 255, 256 
Specific gravity, table of, 253, 254, 

255 
Specific heat and heat of combus- 
tion, 41, 256 
Squire, 4 
Starck, Joseph, 4 

process eliminated, 208 
StMly, James E., on SO,, 79 
Stoicometric mixture of SO, & O 

won't work, 234 
Strength of acid to make, 239 
Sulphur, as in impurity in the con- 
tact process gas, 11 
impurities in, 34 
in the U. S., 28 
Japanese, 45 
Louisiana, 34 

physicochemical properties, 38 
prices, 34 
production of, 31 
statistics, 
sublimated, 217 
uses, 36 
Sulphur dioxide characteristics, 7 
production of, 49 
from brimstone, 49 

metallurgical processes, 

64 
Pyr fines, 66 

lump, 66 
pyrite cinder, 68 
zinc ores, 67 



^dbvGooglc 



270 ISl 

Sulphur dioxide abeorbtion by silica 
gel, 76 
liquid, 76 
ch&racter and uses, 77, 81 
Sulphuric acid, characteristics, 8, 16 
distributioa among indus- 

triea, 18 
makera in the U. 8., 19, 27 
uses and production, 5, 16 
Sulphuric acid, electrical resistance 
of, 260 



Tin, effect upon lead, 192 
Towers, acid, various, 223 
Troy compared with Avoirdupoia 

weights, 245 
Twaddle's hydrometer, 168 
Tyndall test for dust in gas, 226 



United Alkali Co., ammonia still. 



Tank car table, 260, 252 
Tanks, storage, 120 

circuIatiDn, 222 
Temperatures in chambers, cheeking, 

109 
Temperatures for abeorbtion, 212 
for burner gases, 218 



heat exchanger concentration, 

195 
in pan concentrating, 191 
of conversion in contact process, 

230 
Tennessee Copper Co., acid from 

met gases no dream, 61 
ohaloopyrite as of sulphur, 46 

SOi from blast furnace, 65 
Testing contact mass, 243 
exit gas, 177 
gas, 166 

instruments, 100 
mixed acids, 170 
nitrate of soda, 176 
nitre cake, 170 
nitrogen oxides, 174 
nitrous vitriol, 176 
Reich teat for SO., 170 
Tyndall test (for dust I 



225 



1 gas). 



Thennometere, 166 

Time of reaction in chamber process, 



Valves, proper ones for acid, 213 
Vapor pressure as related to abeorb- 
tion, 14, 212, 239 
curves of pressures due to 

wat«r and SO,, 239 
of sulphur, 38 
tables, 256, 257 
Virginia Smelting Co., producing 
liquid SO,, 78 

W 

Ward, Dr., 1 

Water, introducing water to cham- 
bers, 109, 133 
effect upon contact process, 11 
not satisfactory for absorbtion, 
238 

Weber, theory of chamber process, 9 

Weight of acid, curve, 263 

Weasel, 4 

White lead, 3 

Winkler, C. I., 4 

theory of chamber process, I 

Wollaston, Dr., 3 



Zinc blende, properties, 46 
ores, SO, from, 67 
effect upon lead, 192 



SFP 2 6 1921 



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