Chamber Process Manufacture
of Sulfuric Acid EDWARD M.JONES Tennessee Copper Company, Copper Hill, Tenn. T h e chamber process will continue to decline in importance in the sulfuric acid industry. The design of chamber plants is still a highly empirical and rule-ofthumb procedure, and their operation continues to be more of an art than a science. The fundamental advantage lies with the contact process generally. For any specific case the two processes must be evaluated under the prevailing circumstances, taking into consideration use
of the product, freight rates, operating costs, and over-all capital costs. The small chamber plants, operating in conjunction with superphosphate fertilizer plants, have a peculiarly competitive position, and will undoubtedly continue in that position for some years to come. The passing of the chamber process has been predicted before, but it has perversely refused to expire. Its full possibilities have not been realized.
A
In the attempt to devise means for heat disposal and to increase reaction rates, many kinds of intermediate towers were used b e tween chambers. As the acid produced in these towers was usually measured as acid collected or condensed in them, and not ~ t reduc9 tion in sulfur dioxide content of the gas through them, their performance was generally very much overrated. The Pratt system found some favor ( 5 ) ,but has now been abandoned. Its essential feature was the recirculation of the chamber gas mixture through the main chamber. Larkon (6) achieved high production rate in his packed-cell process, wherein all the chamber space was packed with checkerwork brick and this packing was irrigated with chamber acid. In addition to the original installation in Anaconda, a second larger unit was built in Chile. The tower process of Petersen (8) and Opl represents a fundamental change in the nitration process, in that it largely depends upon the oxidation of sulfur dioxide in the liquid phase to sulfuric acid. The reaction takes place in a series of packed towers, with the gas in contact with weak nitrous vitriol. The process achieved
T THE time the Frasch process for mining sulfur was dcveloped at the beginning of the century, all the sulfuric acid made in this country was manufactured by the chamber process. The principal source of sulfur was Spanish pyrites, and the use of brimstone m raw material did not develop materially until World War I curtailed the importation of foreign pyrites. The subsequent adoption of brimstone, however, has materially affected the progrese of the chamber process, in that ita use has enabled small plants to operate economically at the point of use of the acid. This is shown by the number and location of such small plants at superphosphate fertilizer plants. The chamber process has had a long and honorable career since Roebuck built the first chamber in 1746 in Birmingham, England, and since 1793 in the United States, when John Harrison built his first chamber in Philadelphia. The introduction of the contact processshortlyafter 1900 brought competition that has steadily and rapidly decreased the importance of the chamber process in the chemical industry. This trend is shown in the annual production figures, given in Figure 1. In 1949 the chamber process accounted for 25.6% of the total sulfuric acid production.
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EVOLUTION OF CHAMBER DESIGN The most notable and persistent development in the chamber profess has been the increased rate of production in relation to chamber volume. The literature is full of ideas and means for obtaining increased rates of production, and attests the efforts made to improve that situation. Early plants were designed and operated at a rating of 20 cubic feet of chamber space per pound of sulfur burned per day, but with a demand for greater production it was found that the plants would operate satisfactorily at increased rates, and, with the use of fans or blowers for gas handling, space rates of 10 cubic feet per pound of sulfur were achieved. This prartice was designated as the "intensive process" and emphasized the necessity of heat dissipation as one of the primary functions of the chambers. The rating of chamber plants on the basis of chamber volume per unit of production is not a good criterion ( d , 6 ) and the capacc ity should be related to the chamber surface mea or heat-radiating Burface. The rate of production may be greatly increased by increasing the proportion of nitrogen oxides to sulfur dioxide, but heat disposal must be provided for by cooling surface. Of the many early chamber designs, the tangential chamber of Myers should be noted for the relative high space rate of which it was capable. This cylindrical chamber was the forerunner of several similar designs.
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Figure 1. Chamber Process Production Trend Fortified spent acid not inaluded Estimated figures shown by broken liner Source, 1916 to 1816, inclusive (10)
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SNDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
COURTESY hATlONAL LEA0 C W C A N Y
Figure 2. Modern Mills-Packard Chambers high space rates with relatively small towers, and is well adapted for use with metallurgical gas of fluctuating grade and low temperature. Although there were 28 plants (3) operating in 1932 in foreign countries, this procesb has not found acceptance in this aountry. Internally cooled cylindrical chambers were erected by Parriah in England, using the Gaillard Turbodisperser for spraying cooled chamber acid into the chambers. Their performance has not been outstanding. Several box-chamber plants in the United States made experimental installations of dispersera, but abandoned them. The most successful design of chamber is the Mills-Packard. This chamber is in the form of a rapidly tapering cylinder and is cooled by a film of water flowing down the outside (4). MillsPackard chambers of small size are operating successfully at 2.0 cubic feet per pound of sulfur, and large ones at 3.5 cubic feet. These rates correspond to approximately 0.5 and 0.7 square foot per pound of sulfur, and thus have but one half to one third the surface of conventional box chambers. There are now about 140 of these chambers in operation in the United States. DEVELOPMENTS OF AUXILIARY EQUIPMENT The use of ammonia oxidation for supplying nitrogen oxides in the nitration process has been an outstanding development. This was first used in England during World War I and was rapidly adopted in this country when low-cost ammonia became available. The platinum-rhodium alloy catalyst developed by Dupont-Baker contributed materially to the success of thk proceas. In addition to providing lower cost of nitrogen oxides and lower operating cost, it has the advantage over sodium nitrate of steady flow and exact control, contributing to decreased consumption of nitrogen oxides. This nitration process, using either anhydrous ammonia or ammonia liquor, has almost complebly eliminated the use of sodium nitrate for chamber nitration in this country. Today leas than a dozen small plants continue with sodium nitrate. The rotary sulfur burner, an early development, was a decided improvement in producing sulfur dioxide for the chamber proceas. Major developments and changes have been made in gas-producing and gas-cleaning equipment for plants using mineral sulfides 88 a source of sulfur dioxide. Cottrell dust precipitators and centrifugal-type dust collectors are in general use. Flash-roasting of sulfur minerals represents a great departure from earlier roasting technique. Air lifts and blow cases for pumping acid were displaced by centrifugal pumps as suitable alloys became available for that wrvice. The use of alloys, except for pumps and valves, has been small, as only in the vital spots has it been economical to use the higher type alloys required for the acid concentrations and temperatures encountered. Lead continues to be the dominant material of construction. An alloy of lead, containing lesa than
Figure 3. Falding Box Chambers
0.1Q/o tellurium and possessing increased tensile strength, has been used to a limited extent. CONSTRUCTION DEVELOPMENTS Progress has been made in improved construction of plants, particularly in the case of towers. All-masonry construction of both Glover and Gay-Lussac towers has achieved lower initial cost and decreased maintenance. Improved tower-packing materials, particularly for Gay-Lussacs, provide large effective surface and low resistance to gas flow (7), resulting in smaller and more efficient towers. There has not been a similar improvement in the corrosion resistance of these materials. The use of structural steel in place of wood has resulted in better structures and improved support for lead. Instrumentation has been adopted to a limited degree and has contributed to the mechanization and decreased use of manpower in the industry, but it is evident that further progrem can be made along this line. CHEMISTRY OF THE PROCESS Since the time of Lunge there has been but little contributed to an undentandmg of the chemistry of the chamber process. Petersen ( 8 ) convincingly showed, from studies of the tower process, that the essential oxidation reaction takes place in the liquid
Figure 4. All-Masonry G a y - h a c Towera
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
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phase, between sulfur dioxide in solution and the dissociated coniponents of nitrosyl sulfuric acid (HNOSO,). He concluded that the same reaction mechanism takes place in the more conventional chamber. Berl(1) arrived at a similar conclusion, but assigned an important role to the so-called “violet acid” (HaS04.NO) in the series of reactions. Petersen placed no importance in the violet acid, as it is found only when the p r o w is improperly operated. Berl also showed the importance of the reaction rate of oxidation of nitric oxide to nitrogen peroxide, and it is the slow speed of this react,ion with its negative temperature coefficient that is the ratedetermining step in the p r o w . He investigated the effect of presmre on the reactions involved and showed that the over-all rate could be greatly accelerated by pressure. It doea not appear that this development has much possibility for practical application, or could offer any economic advantage.
Vol. 42. No. 11
LITERATURE CITED (1) Berl, Ernst, Tram. Am. Inat. C h a . Engrs., 31, 193 (1935). (2) Fairlie, A. M., “Sulfuric Acid,” A.C.S. Monograph 69, p. 191, New York, Reinhold Publishing Corp., 1938. (3) Ibid., p. 214. (4) Fairlie, A. M., TTans. Am. Inst. C h a . Engra., 33, 563 (1937). (5) Harney, T. R., C h a . Met. Eng., 36, 402 (1929). (6) Larison, E. L., Ibid.,26,830 (1922). (7) Molstad, M. C., Abbey, R. G., Thompson, A. R., and McKinney, J. F., TTans. Am. Inst. Chem. Engrs., 38, 387 (1942); 39, 605 (1943). (8) Petersen, Hugo, C h a . - Z l u . , 55,493 (1911). (9) Peteraen, Hugo, 16me. Congr. chim. id.(Brussels, 6eptember 1935), 1936,80-7. (10) Wells and Fogg, Bur. Mines Bull. I84 (1918). RECEIVED April 13,SB50.
OFFSHORE SULFUR PRODUCTION JAMES M. TODD Jefferson Lake Sulphur Company, New Orleans, Lis.
Sulfur mining in offshore operations in the Gulf of Mexico can be considered at the present time, only as research activities to extend known reserves. The cost of offshore construction makes sulfur mining uneconomical on the present competitive sulfur market. It is entirely feasible: in fact, overwater production of sulfur has elready been accomplished in protected areas. However,
the extension of this expeFience to gulf offshore operations. at the present time, would be costly. Pipe lines from offshore oil locations on the gulf ffoorto land-based tankage are in daily use, and the pumping of mxlfur through such facilitiee can be accomplished. The special problems to be encountered in offshore sulfur production are discussed in this article.
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If one assumes that permanent platform serving only a limited area, and hence a limited number of production wells, can be economical in Frasch process mining, it is definite that the area to be mined must be extremely rich in sulfur deposit to pay the construction costs of such platforms. Cappel (I) has pointed out that the considerations affecting the design of stationary-type platforms include depth of water, fetch and exposure, bottom characterktics, normal wave action, hurricane wave action, hurricane winds, littoral currents, load concentrations, possible and probable cumulation of forces, rigidity under drilling conditions, areas required for machinery and supply layout, and crew quarters. Experience shows that 30-pound-per-square-foot wind velocity loads are not sufficient design stresses for offshore permanently fixed structures, but that structures designed on a 50-pound-persquare-foot basis have withstood gulf hurricane winds. “The height of hurricane waves as well as the horizontal forces exerted by them is directly related to the depth of water and the fetch-that distance over which the wind has free play on the water.” (1). The generally accepted maximum wave height is two thirds of the depth of the water.
HE mining of sulfur by the Frasch procem in water which is relatively shallow and reasonably protected from high wave and tide action presents no particularly difficult problem. This lias been done succeasfully and competitively by two sulfur operat ing companies. Jefferson Lake Sulphur Company a t its Lake Piegneur operations in Louisiana, mined sulfur by using permanent wharves with drilling equipment mounted on submersible barges. When fivst approached, the problem of submersible barge-mounted rigs offered some interesting prospects. The e84e with which refloating and moving of the rigs to new locations waa accomplished, was not only surprising but contributed substantially to the economy of the whole operation. The Freeport Sulphur Company, in its operations a t Grande I?caille, La., uses wharves and land-fill rig locations. They have riot found the problem of overwater operation too difficult or too costly for competitive production. The offsbre prospect, of aourse, presents many new conoiderations which as yet have not been dealt with economically or competitively in sulfur production. Of course, as long as sulfur can be produced from land-based operations and the competitive selling price of the product is a t its present level, prospective operations for sulfur on the continental shelf would seem only a remote possibility. However, i t does have the advantage of outlining additions to the present rapidly diminishing reserves. PLATFORM CONSTRUCTION ON OFFSHORE LOCATIONS The oil companies have demonstrabd the feasibility and the
costa of platform construction on offshore locations in the Gulf of Mexico.
DATA ON FIRBT PLATFORM IN GULF AREA
The original platform in the gulf area was built in 1937. It was erected in 13 feet of water, 6000 feet offshore, and was constructed of creosoted piling and timber. The lost time during construction because of weather was roughly 75% and considerable equipment was lost. Today the permanent platforms are built of steel. Owing to improvement in technique, the lost time during construction because of weather, over a %year period, has been considerably less than 10%. The minimum cost of platforms or permanent structures of
