January, 1923
INDUSTRIAL A N D ENGINEERING GHZMISTRY
settling devices for juices and parts of the evaporation have markedly improved in the past ten years. A grinding capacity of 2500 tons of cane per 24 hours per train of mills was thought to be near the maximum with high efficiency, in 1912. There are now single trains of mills that will grind 3600 tons of cane with even higher efficiency. There has been great
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progress in factory output. I n 1912 there was but one factory with an annual capacity of 85,000 tons of sugar; in the present year, several factories have largely exceeded this output and one has produced 170,000 tons of raw sugar. These increases are largely due to progress in mill design and construction.
The Manufacture of Sulfuric Acid By L. A. Pratt MERRIMAC CHEMICAL Co , BOSTON,MASS.
CHAMBER PROCESS URING the last ten years there has been a determined effort to intensify the production of acid by the chamber process, and to this end numerous improvements have been made in the methods of chemical control and in the design of “sets” and their accessories. During the war the production of chamber plants was greatly enlarged by increasing the proportion of nitrogen oxides to sulfur dioxide in circulation. This leads to higher niter losses and larger repair charges, and is therefore not applicable to these times. As a result, chemical engineers are devoting their efforts to changes in design which will afford a better mixing of the gases and a more efficient removal of the heat of reaction, with a view to minimum unit cost of investment, operation, and maintenance. The Faldingll* high chambers are built to utilize the mixing of gases by convection currents caused by the heat of the chamber reactions. The saving in cost of lead and ground space is, however, offset by the extra cost of construction of the high chambers. There is no adequate provision made for the condensation of the acid mist. Gaillard2 uses, in place of the usual chambers, lead towers built in a slightly conical form, truncated, and having the larger diameter at the top. A hollow shaft extending inside the tower through the closed top serves for the introduction of a small stream of cold, dilute sulfuric acid which falls onto a revolving channeled disk located on the lower end of the shaft. The cool acid is projected against the upper part of tower, down which it flows in a cooling and protective film. The speed of the disk is sufficiently great to cause some of the acid to rebound and fall in a fine, heavy rain to the bottom. It is claimed that this rain serves to thoroughly mix the gases and t o condense the acid formed in the tower. It is further claimed that the temperature. throughout the tower is readily controlled, thus increasing the efficiency as well as the life of the apparatus. The Mills-Packard3 system, which was developed in England, has as its object the water cooling of the lead surface of the reaction chambers. The chambers are built in the form of truncated cones down the outside of which runs a continuous stream of cooling water. Plants of this design have been erected by 23 companies, in England, France, Italy, and New Zealand. The first two chambers were erected in 1914 and the number has increased to 112 at the present time. The results of actual operation have shown that a set of this type can be successfully operated on 3.66 cu. ft. of chamber space per pound of sulfur burned per 24 hrs., with a niter consumption of 3.62 per cent. The cost of construction is materially lower than in old style sets, and the life o€ the lead should be longer because of the efficient
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* T h e numbers in the text refer t o patent references a t end of the article.
water cooling. None of these chambers has been built in this country as yet, so far as the writer knows. According t o the published results, this system is one of the important developments in chamber acid manufacture. There is no special provision for thorough mixing of the gas in this design, but it is reported that modifications are being considered which may further increase the efficiency of this system. Several types of “intermediate” or “reaction” towers have been brought forth, the purpose of which is to both COOI and mix the reacting gases. These are inserted between the chambers and offer a large amount of contact surface. One of the most successful types is designed by the Chemical Construction Company and consists of a lead-lined tower packed with spiral rings. Results of careful tests in a set where the tower space is equal to 7 per cent of the total chamber space, have shown that 33.5 per cent of the “make” of the plant was produced in the intermediate towers. The efficiency of the chambers alone was 10.7 CU. ft. per lb. of sulfur, and of the chambers plus the tower capacity was 7.6 cu. ft. per lb. sulfur. Larger intermediate towers are now being designed with a view of cutting down the chamber space proportionately. A patent was recently taken out by C. H. MacDowell* which covers the spraying of a large amount of dilute sulfuric acid (in place of water) into a chamber set for cooling purposes. The necessary amount of sulfuric acid is continuously drawn from the chamber pans, diluted, cooled, and re-sprayed into the chambers. It is reported that the capacity of the plant where this process was tested over a period of 6 mo. was increased 46 per cent, making it possible to operate the set on 6’/2 cu. ft. of chamber space per pound of sulfur burned with a 3 per cent niter consumption. A radical departure frofn the use of large reaction chambers is embodied in a process patented by 0pl6in 1908, and in two processes vhich have recently been patented and are now being tested in this country. The Opl process is carried out in a series of six towers. I n the first three towers the sulfur dioxide gas comes in contact with a descending stream of nitrosylsulfuric acid dissdved in concentrated sulfuric acid. Denitration of the acid takes place just as in the ordinary Glover tower and simultaneously the sulfur dioxide is oxidized. The last three toivers are for the absorption of the oxides of nitrogen evolved in Towers 1, 2, and 3. By this arrangement it is claimed that 1 lb. of sulfur may be burned per 2.1 CU. ft. of tower space per 24 hrs. About of these systems are in operation in Europe. A recent British patent by P. Farrish0 and The Sou Metropolitan Gas Company claims to double the efficiency of the Opl process by passidg the ng gases through a 4-in. layer of nitrosylsulfurio acid,
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
The tower process developed by E. L. LarisonT of the Angconda Copper Mining Company is known as the “packed cell” process. The gaees from the Glover tower are passed through a set of towers constructed of acid-proof brick and filled with a checkerwork of the same material. Cold acid of 48” to 50” BB., in which neither sulfur dioxide nor oxides of nitrogen will dissolve, is run down the checkerwork, thus effectively controlling the temperature at the points of reaction. The thorough mixing and cooling, together with the extremely high. niter circulation (equivalent to 70 pts. sodium nitrate per 100pts. sulfur), causes very rapid reaction. A large Gay-Lussac space is necessary for recovery of the oxides of nitrogen. It is claimed that the cost of construction of the packed cell plant is only 50 to 60 per cent of a wellconstructed chamber plant. It is doubtful whether there would be so great a saving in construction in most localities. The cost of maintenance and the efficiency of niter recovery are points in question. The other procedure referred to above is the “tube” system patented by Kaltenbach.* I n this development, the chambers are replaced by series of lead pipes, the pipes in each unit being connected in parallel. They are approximately 31 in. in diameter and may be packed with Raschig rings. The gases pass up around the rings while a regulated stream of cold dilute acid flows downward. The advantages claimed are: 1-Ease of temperature control. 2-Rapid dissipation of heat in close proximity to place of its gyneration. 3-Intimate contact between the reacting gases and liquids. 4-Elimination 6f water atomizers. ay be cut out to change the capacity 43esults of operation of a commercial unit are not available a6,the present time. her processes have recently been pateeted. and H. KlenckeD have covered the spraying and mechanical mixing of nitrosylsulfuric acid into sulfur dioxide gases. E. Dior*O has protected a design consisting of a series of ch&mbew each resembling an inverted funnel, the sides of more nearly vertical than those of gases are said to move through each chamber in a spiral fashion. C. J. Reed” heats a mixture of air, sulfur dioxide, and oxides of nitrogen, absorbs the gaseous reaction products in concentrated sulfuric acid, subsequently removes the oxides of nitrogen from solution and recovers concentrated sulfuric acid.. G. Mirat and P. Pipereaut12have designed a set with a series of small lead chambers and with severd special features. >METHODS OF INTRODUCING NITROGEN OXIDES-There are four methods in use for supplying nitrogen oxides in the ordinary chamber’process: (1) potting niter; (2) adding nitric acid in the Glover tower; (3) spraying sodium nitrate solution into the first chamber; (4) catalytic oxidation of ammonia. I n the potting of niter, there has been a decided tendency toward the installation of the pots outside the flues, thus necessitating %heuse of fuel to fire them. This change has come about largely because of the accumulation of niter cake in the flues by the older process. I n the opinion of the author there is little trouble from this source if the niter pots are properly designed. The use of nitric acid in the Glover tower is excellent for companies having a supply of weak nitric acid a t their disp9sal. Care should be taken to obtain a constant flow of the nitric acid and a uniform distribution over the tower.
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Vol. 15, No. I
The spraying of sodium nitrate solution into the first chamber has been used successfully by certain concerns, notably fertilizer manufacturers, where the contamination of the sulfuric acid with sodium sulfate is not objectionable. The sodium nitrate solution must be carefully strained and the spray nozzles kept in good working order so that liquid nitric acid will not be formed in the pan of the chamber. Oxidized ammonia gas is being used in certain countries where the price differential of nitrogen is sufficiently in favor of ammonia. This process has been adopted in England and the details have been carefully worked out. It is doubtful whether it will gain much headway in the United States, in the near future. Two of the large companies in this country have, however, installed the process in one or two of their plants for the purpose of collecting data. The argument has been used that i t affords a saving in labor, but this is certainly not true in cases where only one man per shift is employed in operating a chamber set which includes potting the niter as well as running the sulfur burner and controlling the process. I n isolated cases, where the niter cake formed in the niter pot process is a waste product, it is possible that the ammonia oxidation process may find favor. RAW MATERIALS FOR SULFUR DIOXIDE-For nearly 20 years prior to 1914, pyrites was the great raw material for the production of sulfur dioxide. During the war it was impossible to obtain anything like the required amounts of Spanish pyrites, and American manufacturers were forced to return to the use of brimstone. New sulfur fields have been opened up ensuring a sufficient supply of excellent brimstone, and there seems to be very little desire on the part of manufacturers in this country to return to the use of pyrites. The higher purity of acid produced from brimstone, coupled with the simplicity of operation and lower labor requirements, are factors in favor of the continued use of sulfur. Large amounts of sulfuric acid are manufactured from the gases produced in the roasting of copper and zinc sulfide ores. One of the notable developments for utilization of waste gases from copper blast furnaces is the large plant of the Tennessee Copper Go., at Copperhill, Tenn. IMPROVEMENTS IN DESIGN OF SULFURBURNERS,DUST PRECIPITATORS, TOWERS, AND ACCESSORIES-since Sulfur SO largely displaced pyrites in this country, the design of a burner suitable for the combustion of the brimstone became important. The Tromblee and Paul burner, better known perhaps as the “Glen Falls” burner, has found great favor and is highly satisfactory. I n many plants employing roaster gases or pyrites as a source of sulfur dioxide, the Cottrell electrical precipitator has been installed for removing the dust. This process has been modified and improved to a high state of efficiency. It has also found valuable use in the precipitation of fume from the stacks of sulfuric acid concentrators. The development of the acid-proof masonry Glover and Gay-Lussac towers without the use of lead curtains is worthy of special mention. The use of towers of this design will be watched with considerable interest during the next few years. Water has very largely displaced steam for furnishing the necessary moisture in the chambers and several very satisfactory spray nozzles have been developed for atomizing the water into the chambers. I n the concentration of sulfuric acid, some very important steps have been made in the direction of higher efficiencies and greater stability of apparatus. Special mention may be made of the Gaillard, the Mantius, and the Gilchrist concentrators. The latter has had a very rapid development in this country, particularly for the concentration of acid from the sludge acid produced in the refining of petroleum. It
January, 1923
INDUSTRIAL A N D ENGINEERING CHEMISTRY
is well designed, embodying several new principles, and has shown excellent thermal efficiencies over long periods of operation. CONTACT PROCESS There are four contact processes in successful operation: the Badische, Mannheim, Grillo-Schroeder, and Tentelew systems. Very few improvements of recent date have been recorded in the manufacture of contact acid. H. F. Merriaml3 has patented a process which consists of drying the air used for combustion of brimstone. This procedure permits the passage of the hot burner gases to the converter after being slightly cooled to the proper temperature. The advantages claimed are: (1) conservation of heat; (2) simplicity and stability of apparatus; (3) longer life of contact mass because of the elimination of sulfuric acid mist. F. Slama and H. WolfL4have patented a catalyst consist-
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ing of vanadium oxide deposited on pumice or kieselguhr. A 96 per cent conversion of sulfur dioxide to sulfur trioxide is claimed with this catalyst. . W. A. Patrick15 proposes a process for the conversion of sulfur dioxide to sulfur trioxide catalytically by passing the gases through silica-gel previourly treated with certain metallic salts. The process has not been tried out on a commercial scale as yet but experimental work has been in progress for some time. PATENT REFERENCES 1-U S. Patent 932, 771 (1909). 2-Fr. Patent 528,080. 3-U. S. Patents 1, 112,546 (1914); 1,312,741 (1919); 1,312,742 (1919). 4-U. S. Patent 1,402, 941 (1922). 5-U. S. Patent 1,012,421 (1911). 6-Brit. Patent 156,328 (1921). 7-TJ. S. Patents 1, 334, 384 (1920); 1,342, 024 (1920).
8-Brit. Patent 9-Brit. Patent 10-Brit. Patent 11-U. S. Patent 12-Brit. Patent 13-U. S. Patent 14-U. S. Patent 15-Brit. Patent
159, 156 (1920). 149, 648 (1920). 164, 572 (1920). 1, 363,918 (1920). 163,030 (1921). 1,384, 566 (1921). 1, 371,004 (1921). 159, 508 (1921).
Stabilizing t h e Sulfur Market for Chemical Industry By Harold S. Davis ARTHURD. LITTLE, INC., CAMBRIDGE, MAPS.
HE STABILITY of any industry is
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greatly influenced by the degree of accuracy with which the prices of the raw materials it needs can be predicted, Sulfur, owing mainly to the everincreasing usefulness of sulfuric acid, has become one of the basic elements for chemical industry. Let the reader consider for a moment whether, if the price of sulfuric acid were to double in the next few yeam, the particular organization with which he is affiliated would not be adversely affected by the rising price of some necessary raw material. It is therefore a great satisfaction to be able to predict a stable sulfur market in America for a t least the next ten years, with almost complete independence of production and consumption in foreign countries. THEPAST Up to the present century, only negHAROLD S. ligible quantities of sulfur were mined in the United States and practically the world’s supply came from Sicily.- The deposits in this idand contained originally about 65 million tons of sulfur available for mining.l More than half of this has now been mined, The total sulfur recovered up to 1885 was estimated at 10 million tons and 13.6 million long tons were exported from 1885-1919.2 About one-quarter of the sulfur mined has been lost in processing, a factor which must be considered in estimating the value of the supplies that remain. In the past the methods of mining were very crude, manual labor being employed for the most part in transporting the ore from the pits to the surface. Even to-day, thousands of children still work in the Sicilian mines.3 The methods used for separating the sulfur from the ore were also very wasteful. 1 J . JOG. Chem. I n d . , 7 (1888), 140. *Mineral Ind., 1 (1892); 9 (1900); 18 (1904); 21 (1912); 38 (1919); Thorpe’s “Dictionary of Applied Chemistry,” 5 (1913), 287. 8 Eng. Mining J . , 112 (1921). 138.
It is true that scientific methods of production and conservation have been to some extent introduced into the Sicilian sulfur industry, but the cost of mining the deposits is of necessity rather heavy. The ore, containing only 10 to 20 per cent of sulfur, must all be transported to the surface before the sulfur can be recovered, The resultingproduct contains 2 to 11 per cent of impurities, and for most purposes must be further refined by distillation. To-day this sulfur must compete with the American product which, by one process, is brought to the surface nearly 100 per cent pure and which is handled a t the mines, transported to the seaboard and loaded on ships entirely by mechanical means. The plain fact seems to be that no large quantity of Italian sulfur can be mined and sold to-day in free competition with the American product, even in Europe, except at a loss. DAVIS THEPRESENT America now dominates the world’s sulfur industry. She owes the position primarily to the daring genius of Hermann Frasch, who originated and developed the method of mining which made available the vast supplies of sulfur existing in the so-called “salt domes” of the Gulf coastal plain. I n the Frasch process, the sulfur which exists in great beds about 800 to 1000 ft. below the surface is melted in situ by means of superheated water and then raised to the surface in a molten condition by means of an air lift.4 The basic Frasch patents expired in 1908 and to-day three large and well-financed companies are utilizing his methods for mining. One company is in Louisiana and two are in Texas. I n addition a new company apparently well financed has recently entered the field. All the essential features of the process as it is still used were worked out by Frasch. However, some of the companies have employed the highest 4
THISJOURNAL, 4 (1912), 134, Bacon and Davis, Chem. Met. Eng.,
24 (lQZl), 65.
