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from inaccuracies in the equilibrium data is not surprising because all equilibrium data, even though inaccurate, are always a smooth function of temperature and would thus result in a small translation of the derived curve in temperature range but not affect the degree of fractionation to a great extent.
Acknowledgment The authors wish to acknowledge the valuable assistance of Fred A. Deering of the Kanotex Refining Company in conducting plant-scale experimental work.
Nomenclature V 0 R
= moles vapor = moles overflow = moles internal (or hot) heat-balance reflux at top of tower
D
= moles overhead product
(7)
= composition of vapor, mole fraction Y = composition of vapor, liquid-volume percentage x = composition of liquid, mole fraction X = composition of liquid, liquid-volume percentage a = number of theoretical plates in tower n = plate number, counting from top c = excess vaporization or reflux as a fraction of R eR = total moles internal (or hot) reflux at top b = reflux ratio, total internal reflux divided by overhead product y
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equilibrium constant, or vapor pressure divided by total tower pressure J = a constant mp = mol. weight of overhead roduct q = mol. weight of vapor f e e l d, = density of overhead product df = density of vapor feed Subscripts: n, 1, 2, 3, etc. = plake numbers n - 1 = plate above nth plate n 1 = plate below nth plate
K
=
+
Literature Cited (1) Beale, E. L., J . Inst. Petroleum Tech., 23, 211 (May, 1937). (2) Brown and Souders, Refiner Natural Gasoline M f r . , 11, No. 6, 376 (June, 1932). (3) Brown, Souders, and Nyland, IND.ENG.CHEM.,24, 522 (1932). (4) Brown, Souders, Nyland, and Hesler, Refiner Natural Gasoline Mfr., 14, No. 4, 187 (April, 1935); 14, No. 5, 227 (May, 1935). (5) Garton and Huntington, Ibid., 14, No. 2, 60 (Feb., 1935); Cannon and Huntington, Ibid., 14, No. 10, 490 (Oct., 1935). (6) Kremser, A., Natl. Petroleum News, 43 (May 21, 1930); Proc. Calif, Natural Gasoline Assoc., 5, No. 2 (1930). (7) McCabe and Thiele, IND.ENQ.CREM.,17, 605 (1925). (8) Nelson, “Petroleum Refinery Engineering,” Chap. XXI and p. 57, New York, McGraw-Hill Book Co., 1936. (9) Peters and Baker, IND.ENQ.CHEM.,18, 69 (1926). R ~ C E I V ENovember D 15, 1937.
THE SULFUR INDUSTRY History and Development DONALD B. MASON a b l e p a r t of t h e m a r k e t f o r HE great interest accorded Sicilian sulfur in the early days, sulfur in the United States Freeport Sulphur Company, New York, N. Y. b u t s u c h use p r o b a b l y debecause of its technically clined with the fall of the Roman unisue Drocess of production and Empire and it was not until some time after crusaders brought its high’ state of purity has perhaps obscured the fact, in the back the knowledge of such uses from the East that the sulfur public mind, that the sulfur industry is world-wide, not only in industry again flourished. The use of pyrotechnical powder respect to markets but also to production. began in Europe about the twelfth century, and the demand The sulfur industry is sometimes thought of as a recent defor sulfur started the steady rise which has made i t one of the velopment, coincident with the development of the chemical basic materials of all industry. industry. There has always been a sulfur industry, and the The earliest mention of sulfur mining in original documents production of this valuable element has kept pace with the is contained in grants of mining rights in northern Italy about increasing number of uses for it which have been developed. the year 1000. I n some of these old documents the right to Not only has the quantity produced been adequate but, exmine sulfur is specifically granted. Mining methods of that cept for a few short periods, this raw material has been availtime undoubtedly differed little from those carried out by the able a t remarkably low prices, considering the extreme difancients and consisted mainly in driving inclined shafts into ficulty of production. the lenses of sulfur-bearing rock which occur in bedded limeThe few exceptions have dramatically proved the rule, for stone. As most of the mines were carried deeper and deeper the one or two attempts made by European producers to into the deposit, water became a problem, and for many years establish unwarranted prices ended in costly failure. Presthe only pumps used consisted of pails or buckets carried up sure of competition by other producers and other nations has the incline on the shoulders of boys. The sulfur was removed been, in the sulfur industry as elsewhere, the prime factor in from the ore by piling the ore in large conical heaps which adjusting prices. were then ignited. The heat from the burning sulfur melted The very early literature of the race contains sufficient menthe sulfur in the rock, and the liquid sulfur was collected in tion of the use of sulfur to indicate that it has been in general trenches where it solidified (1). w e a t all times. Archeological investigation of the Etruscan mines in northern Italy shows that these workings have always provided the production for part of the world commerce in Early Chaotic Conditions this commodity. The use of sulfur for Greek fire in war and for pyrotechnical The mines both in Italy and Sicily were operated in very small units with little consideration for efficiency in either the displays in the Roman circus probably constituted a consider-
T
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production or marketing end of producers, but a t the same time the industry. The progress of the old cycle of rising prices, inThe American sulfur inchemistry in t h e s e v e n t e e n t h creasing production, i n c r e a s e d century initiated the chemical instocks, and final collapse began dustry, supplying nearly a dustry and gave rise to a rapid inalso (8). third of all world sulfur crease in the use of sulfur. The Two events in the technical needs, dates back to the manufacture of sulfuric acid was world further increased the seriturn of the century, when begun about the year 1736, and ousness of the predicament in Herman Frasch was perfectthe first lead chambers were emwhich the sulfur producers found ployed ten years later. themselves. One was the invening the unique hot water Sulfur, which had long been a tion of the MacDougal pyrites mining method that has rather commonplace commodity, burner in 1870. As early as 1835 made salt domes along the suddenly began to acquire great a pyrites burner had been deLouisiana and Texas coast importance, and as a result the veloped by Michel Perret; althe ideal sulfur source. price went up. So much attenthough it was fairly practical and tion was given to it that producefficient, it was difficult to operate Sulfur has played an imtion was forced and stocks were in a constant and satisfactory portant part in all periods of accumulated by consumers, both manner. Increasing demand for civilization, and sulfur minfor use and for reserves as protecacid and price uncertainties in ing was a matter of official tion against the rising prices. Sicilian sulfur soon gave pyrites governmental attention i n In 1833 the inflationary boom and the new types of burners a collapsed. The Sicilian producers dominant position. The second Italy as early as the year 1000. were hard hit and, in the hope of event was the development beThe chemical industry’s detween 1870 and 1880 of sulfur rescuing the c h a o t i c m a r k e t , velopment during the sevenclamored for some sort of control. recovery from the residues of the teenth century gave rise to The proposal of the Frenchmen Le Blanc soda process by the the rapid increase in the inTaix and Aycard that they be conChance-Claus method. stituted sole sales agents for the Competition from pyrites and dustrial use of sulfur, and Sicilian industry was accepted in Chance-Claus process sulfur, comthe manufacture of sulfuric bined with the world-wide de1838. The Sicilians thought that acid was begun about 1736. this a r r a n g e m e n t would bring flationary m o v e m e n t in comThis review of the indusgreat benefits to consumers as modity prices of the eighteentry, from the world-wide well as producers, since it made nineties and overproduction in for s t a b i l i t y a n d i n c r e a s e d Sicily, brought about an extreme standpoint, traces its ecoefficiency. price decline and consequent prosnomic ups and downs, and Provision was made for adetration among the miners. Insistshows the various sources quate compensation to producers, ent demand upon the government and the development of the and for limitation of production on the part of the miners finally American industry, describes to amounts which could be abcaused the formation of the Anglosorbed by market requirements Sicilian Sulphur Company which the hot water process and its began operations in 1896. and for istandard grades of prodrefinements, and appraises uct. The French company, howIn this company the Sicilian inthe role of sulfur in world ever, refused to share the benefits dustry was associated with English economy. with the customers on whom the manufacturers who produced reprosperity of the industry decovered sulfur and who had conpended, and adopted a shortsequently an equal interest in sighted price and profit policy. the maintenance of an orderlv The cost of sulfur to the consumer marketing program. This cokpany handled the sale of about two-thirds of the production in was rapidly raised to about 75 dollars per ton. French and English consumers immediately protested, the Sicily and helped to maintain the industry in a fairly stable question was raised in the House of Commons, British incondition by adopting an adequately low price policy. The very large number of small and entirely independent produstry was losing a thousand pounds a day, and diplomatic pressure was brought to bear. A naval demonstration in the ducers, however, continued to present a problem because their Mediterranean almost provoked war which was only averted production was not keyed to market conditions, and the industry began to be faced with increasing stock carry-over each by the intervention of the French king. The Taix contract was rescinded, and the Sicilian industry went back to its year. former methods of unrestricted production and sale through individuals and brokers. Early Methods and Equipment I n the meantime, however, the market situation had been This small unit production characteristic also made for exceedingly favorable to the new development of the manufacture of sulfuric acid from pyrites. This new factor enslow progress in the development of mining methods. The tered the picture and the use of pyrites began to spread, parnumber of producers varied between five hundred and a ticularly in Germany. thousand, depending upon conditions of demand and price in About this time a disease of the grapevines in European the industry. At the beginning of the nineteenth century all vineyards spread a t an alarming rate, and the industry was work was performed by manual labor. Not only were pick stimulated anew when it was discovered that sulfur afforded and shovel used exclusively, but ore was raised from the mines the most effective means for control of the disease. by carrying sacks up long inclined ramps or up series of steps The French grinding and refining business made rapid cut into the inclined shafts. By this time the earlier methods strides, and a period of renewed prosperity began for sulfur of removing water from the mines by carrying in pails had
’
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INDUSTRIAL AND ENGINEERING CHEMISTRY
been displaced by crude wooden and later by metal hand pumps, but it was not until 1838 that the first power-driven pump was installed. As the market for sulfur expanded, the larger and more profitable mines were able to install mechanical hoisting equipment and underground tramways, and in general the industry slowly perfected its methods and equipment. For a long time the only method employed for winning the sulfur was to pile the ore in conical heaps, cover it with earth, and ignite the pile. By this method from 30 to 50 per cent of the sulfur contained i n the ore was consumed and less than 50 per cent of the sulfur originally contained in the ore became available for commerce. I n a few instances, where mines had been accidentally ignited and efforts to extinguish them proved hopeless, a considerable production for a number of years was obtained by collecting the molten sulfur which ran out from higher levels into lower levels in the mine. About the year 1880 the first Gill furnace was installed. This furnace originally consisted of two chambers, so built that the heat from the burning ore in one would pass through the ore in the other and melt out a considerable portion of the ore in the second chamber. When the ore in the first chamber was spent, the chamber was refilled and the partially extracted ore from the other chamber was then ignited. In this way a better utilization of the heat of combustion was obtained. This general scheme of melting sulfur has been improved until a t the present time Gill furnaces of five and six chambers are generally employed, and the recovery of sulfur has been raised to about 80 per cent. Most of the production a t the present time in Sicily is now obtained from such furnaces. More or less extensive experimentation has been carried out on numerous other methods for extracting the sulfur, including autoclaving with superheated water, solution in carbon disulfide, and extraction with high-boiling salt solutions. None of these methods have proved entirely successful; here again it is probable that the small size of the individual operations has made it difficult to secure adequate investment of capital to effect the economies that might be expected from the application of extensive plant and chemical engineering principles. The crude methods employed for recovering the sulfur have resulted in the production of a number of grades. The first grade contains 99.5 per cent sulfur and is the customary canary yellow color; the least pure grade contains not more than about 96 per cent sulfur.
Developments in America About the time the Sicilian sulfur producers thought they had solved their major difficulties by the formation of the Anglo-Sicilian Sulphur Company, important developments were taking place in the New World. While the effects of sulfur production in America did not begin to be felt until the present century, the industry really had its beginning years before. Probably the first modern production and use of sulfur in the Western World occurred a t the time of the conquest of hlexico by Cortez shortly after the landing of this expedition in 1519. In leading his military expedition to the gates of Mexico City, he had to pass by the base of the volcano, Mount Popocatepetl; judging from the letters of Cortez to his sovereign, it must have been in an unusual state of activity. Prompted possibly by the natural scientific curiosity of such an energetic mind and possibly by a desire to impress the natives with the superiority of the “white gods” over the gods supposed to exercise a protective influence over the native people, a party of the invaders ascended to the summit. This exploratory expedition was to be turned to excellent account not long after when Cortez found himself cut off from armament supplies with which to carry on his conquests ( 3 ) .
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The richly mineralized country yielded iron, copper, and tin from which cannon and other military necessities were manufactured. Powder at first presented a grave difficulty, but carbon from charcoal and saltpeter from caves were available, if only sulfur could be obtained. A realization of the supreme importance of the role of sulfur even in those early aays is to be had from the fact that a descent into the crater of Popocatepetl was made, and sufficient sulfur for fifty casks of powder was brought up from a depth of nearly 500 feet. No further attempt to mine sulfur from this crater is recorded until about 1850. At different times over a period of 10 or 15 years sulfur was taken from the crater by means of a windlass mounted on the top of the wall. Miners were let down a t the end of a long rope, they filled bags with sulfur, bag and man were hoisted to the top of the crater, and the miners returned for another load. Part of the transportation from the top of the crater to the refinery where the sulfur was separated from rock and volcanic ash was provided by using the bags of ore as toboggans. The snow-covered slopes of the cone provided a sharp 3000-foot descent. From the bottom of the run transportation was maintained on human shoulders, and from that day to this the two problems of transporting the sulfur from the bottom of the crater to the rim and from the rim to the refinery have proved insurmountable. Since 1870 several attempts have been made to revive the production of sulfur in commercial amounts from this volcano, but each time the natural obstacles and the low price of high-grade sulfur a t the consuming centers have prevented profitable exploitation.
Difficulties in Louisiana I n 1865in Calcasieu Parish, La., a large deposit of sulfur was discovered by oil prospectors. The sulfur was found at a depth of about 500 feet below the surface and appeared to be very pure. The great quantities of sulfur apparently available quickly drove the thoughts of oil from the minds of the owners, and a company was formed for mining the sulfur. The first method adopted was to sink an outer wooden shaft which was to contain an inner cast-iron tube. Two shafts were started a t points about 150 feet apart, but neither one was carried down to more than 100 feet. The difficulties encountered with the water-bearing sand were so great that no iron tubing was used in this attempt. From time to time other companies were formed, and further efforts were made to reach the sulfur deposits. I n all cases the subsurface conditions were such as to cause failure of the project ( 5 ) . I n 1886 the National Sulphur Company was formed and, after additional drilling which satisfied them as to the extent and value of the deposit, an attempt was made to sink a shaft to the sulfur by freezing the ground with ammonia refrigeration. Unfortunately for this novel attempt the Sational Sulphur Company expended all of its available cash in prospecting and preparation work, and never reached the period of actual construction of the refrigerating equipment. I n 1889 the American Sulphur Company attempted to sink a shaft to the sulfur beds by the shield process. All went well for a time, and the shaft made progress until in some unaccountable way the shield became detached from the shaft and sank out of reach in the sand; the pit promptly filled with water. This resulted disastrously for the company, but the disaster was not complete until several attempts had been made to resume work by pumping out the shaft. During all this time hydrogen sulfide gas constituted an ever-present menace and brought injury and death to a number of the miners. All efforts to resume shaft operations failed, and the next news of importance was the announcement of acquisition of the American Sulphur Company by the Union Sulphur Company (4).
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The last of these unsuccessful efforts to mine the Louisiana sulfur deposits had attracted the attention of Herman Frasch. He was already renowned for his contributions to petroleum refining, in which his chief contributions had been processes for the removal of sulfur compounds from the kerosene, at that time the all-important product of the industry. Dr. Frasch applied for his first sulfur-mining patent in 1890. The process is so familiar that it will not be described here. The first attempts to develop the process were unsuccessful because the limits of the deposit underground were not understood and it was thought that the sulfur extended laterally over very large areas. The first wells, which were drilled on land secured adjacent to the holdings of the American Sulphur Company, did not encounter any sulfur a t all. Dr. Frasch a t this time showed that he possessed not only remarkable scientific and technical ability but a considerable degree of business judgment by effecting a merger of the American Sulphur Company, which had the sulfur, and the Union Sulphur Company, which felt sure it had the method for extracting it. As so often happens, the difficulties encountered in carrying through a new and revolutionary development were considerable. Ih. Frasch described the scene of the initiation of production and his natural excitement and great joy upon view-
743
ing the first production in his speech of acceptance of the Perkin Medal award made to him in 1911 (2). Some time was to elapse between the initial production and the operation of the mine in a consistent manner. I n 1901 sulfur-was being produced in quantity, but the wells could not be operated for any considerable time without stoppage or even loss of the well due to the extremely porous nature of the rock, the breakage of well pipe, faulty operation of sulfur pumps, and a host of perplexing problems never encountered before in any industry. The number of boilers was increased from eight to sixteen and finally to twenty. I n 1902 production became more uniform, and the stock of sulfur above ground gave some assurance that full commercial success was a t hand. Thirty-five thousand tons were produced in 1903, and the following year a shipment was made to France. As a demonstration performance six wells were operated that year simultaneously and produced 122,000 tons during a %month period.
World Developments since 1900 The Anglo-Sicilian Sulphur Company, formed in 1896 and operated a t a substantial profit to the English backers and to the full satisfaction of the Sicilian miners, renewed its contract in 1901 for an additional 5-year period. These able and intensely practical business men knew of the oaerations of the Union SulDhur ComDanv a t
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organization, aided by government funds, financed the sale of the Sicilian production and managed to maintain a measure of balance between markets and production a t prices which enabled the miners to live. It was during this period that the rapid increase in the consumption of sulfur began, particularly for the production of acid. The Sicilian industry, in spite of high cost and antiquated production methods, was able to maintain its business in the face of strenuous competition from pyrites as well as from the rapidly developing American production because new markets opened up everywhere to absorb the output of expanding production. Each year, however, saw a greater and greater proportion of the new business awarded to American producers, as the American markets expanded rapidly and the high quality and low price of American crude sulfur were more and more appreciated by consumers. The expiration in 1908 of the original Frasch patents stimulated competition in the American as well as world markets, which further complicated the sulfur industry’s problems. The advent of additional American production began in 1912 with production from Bryanmound by the Freeport Sulphur Company. This entry of a new company into the industry brought about a suit for patent infringement by the Union Sulphur Company on the basis of patents granted in 1907 and 1911 for improvements on the invention as disclosed in the patents granted in 1891. The case was a most momentous one. Decision in the case was handed down in 1919. While it refused redress to the Union Sulphur Company because of invalidity of the patents in question, the Court paid an unusual tribute to Dr. Frasch for his inventive fertility and imaginative power. The decision said, in effect, that Dr. Frasch’s original invention and patents of 1891 which expired in 1908 so well foresaw the difficulties and so accurately prescribed proper remedies, that no further development that could be regarded as an invention was necessary to effect the improvements disclosed in the later patents (7). Rapidly expanding use of sulfuric acid and the restriction of pyrites imports during the World War greatly stimulated sulfur production. For a time many surface deposits in California, Colorado, Nevada, New Mexico, Texas, Utah, and Wyoming were operated. Then a new mine using the Frasch process was put in operation by the Texas Gulf Sulphur Company in 1919. The postwar depression, brought about by feverish speculation after the Armistice, demoralized and disorganized the industry in all countries. Particularly in Sicily, where production continued at a high rate and stocks accumulated, the financial position became strained and the Bank of Sicily stopped payment for production, with resultant despair, strikes, and rioting among the miners. Disastrous as it was a t the moment, this time of trial taught the industry that i t could hope to prosper only as it succeeded in effecting a higher and higher degree of efficiency, not alone in production but also in management and distribution activities which contribute so largely to world economy. I n 1924 mining operations of the Union Sulphur Company a t Sulphur Mines, near the town of Sulphur, La., ceased. This salt dome with a cap of rock and sulfur, discovered in 1865, had been a source of grief and despair until 1890, and of hope from 1890 until 1900. Commercial quantities of sulfur were first produced from it in 1903, and in the 21 years of its active life this deposit furnished more than 10,000,000 tons of sulfur which found its way into all parts of the world. Since 1924 the Union Sulphur Company has produced millions of barrels of oil from this same property. All of the Gulf Coast sulfur deposits occur in the limestone cap rock which usually is found overlying the characteristic salt plugs of Gulf Coast geology. Conditions were favorable for the formation of sulfur in only a few of the
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domes discovered by geophysical methods during the last few years. Of a total of more than three hundred salt domes in Louisiana and Texas, only eleven so far have been found suitable for the commercial production of sulfur. The process and the discovery deposit were developed by the Union Sulphur Company. Three deposits have been developed by the Freeport Sulphur Company, three by the Texas Gulf Sulphur Company, two by the Duval Texas Sulphur Company beginning in 1928, and two by the Jefferson Lake Oil Company beginning in 1929. The original deposit was discovered in Louisiana, and for many years this state was the only producer by the Frasch process. But Texas has now become known as. the sulfur state because eight of the eleven successful operations are located there. I n considering world production of sulfur from all sources, it is found that the seven domes now operating along the Gulf Coast supply nearly one-third of total world demand.
Technical Improvements No summary of the sulfur industry would be complete without a brief resum6 of the technical progress which has been made in the Frasch process since its first successful application. When Dr. Frasch started, nothing was known about the geologic formations which subsequently proved t o b e rock-capped pillars of salt, and the porous limestone containing the sulfur was supposed to extend great distances in all directions. Single wells were drilled more or less a t random, and the concentric pipes were lowered without the protection of outer casing. Each well required a complete operating unit of twenty locomotive-type oil-fired boilers, water heater, pump, well, and wooden bin for collecting the molten sulfur. The molten sulfur was pumped from the bottom of the well with a plunger-type pump. Every conceivable difficulty was encountered; chief among them was the corrosion of metals strong enough to stand the service, since aluminum and zinc which are corrosion-resistant cannot stand the mechanical shocks. The adoption of the air-lift principle solved this. problem and permitted the building of higher vats since the. discharge point could be elevated. Individual vats for each well permitted easy measurement of that well’s production but caused high vat costs, high shipping costs, and occasional annoyance when a vat encountered difficulties due to the subsidence of the surface. To overcome these difficulties, vats were built a t greater distances from the wells, and two or three wells were made to discharge into a single vat. This method of collecting the sulfur caused craters to form around the discharge pipes, and men broke holes in the sides to allow the molten sulfur to flow out. These men were called “sulfur punchers,” and the designation is still given to those whose duty is to supervise the elaborate equipment used to transport sulfur from well to vat. The final form which this development has taken consists of vats as large as 200 feet wide, 1200 feet long, and 50 feet high, holding as much as 600,000 tons of sulfur in one piece. These vats are located a t some distance from the wells, and the sulfur is collected from several wells in steam-heated tanks and pumped through steam-heated lines by means of steam-jacketed multistage centrifugal pumps capable of pumping 100 tons per hour at pressures up to 150 pounds per square inch. Careful provision is made at the vat for securing even distribution of the liquid over the top of the vat so that no crater shall form. The latest type distributor deposits an eighthinch layer every 15 minutes. The layer solidifies within a few minutes so that the top of the vat is safe at all times. Not so long ago large volumes of still liquid sulfur were occasionally released from apparently solid vats during ship-
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ment operations, and serious injury sometimes resulted when so that 10 minutes later the well blows into a “blow box” men were caught without warning by streams of liquid sulfur. instead of into the relay tank. Although variation in the Not long after commercial production had begun, it was quantity of compressed air introduced into a well will vary realized that the formation containing the sulfur was waterthe amount of sulfur pumped from that well, this adjustment tight in the sense that continual pumping of water into the is not sufficiently exact, and fine adjustment is secured by deposit caused an increase in underground pressure with the viscosity changes due to slight changes in the temDerature of result that a broken well t6e water passing down the pipe resulted in a manouter pipe. As new deposits were created geyser of water opened, it was found that heavily charged with hyno two were alike and that d r o g e n sulfide. Wells each had to be treated in were drilled a t a distance accordance with its own from the zone of operacharacteristics and temtions, and water was alperament. The first mine lowed to flow out to reoperated subsided so badly lieve the p r e s s u r e . In that the hole which was order to avoid blowouts, formed had to be filled to it has been found neceskeep the operations above sary to remove water from ground-water l e v e 1. A the deposit equal i n deposit operated later was volume to the water inso porous and cavernous troduced. I n some dethat the water flowed away posits the rock formation from t h e well b o t t o m is such that superheated through c h a n n e l s , and water accumulates a t the millions of cubic yards of top of the dome. mud had .to be pumped The re-use of this water down the wells b e f o r e has always been the dream efficient o p e r a t i o n w a s of mining engineers, but secured. The problems the extremely corrosive involved in securing an nature of the hot water adequate understanding of has foiled all attempts. the characteristics of an Chemical treatment of the ore deposit are sufficiently water proved too expengreat where the ore can be sive and resulted in the seen in place and the geoloss of too much heat. I n logical features can be inthe last few years a soluspected underground. tion h a s f i n a l l y b e e n Samples of rock 6 to 8 worked out whereby a protective coating is laid inches in diameter are reFIELD RELAY STATIONWHERE LINES FROM INDIVIDUAL WELLSPOURMOLTENSULFURINTO A HEATEDTANKAND covered by core drilling; down in the pipe system THENCE INTO A MASTERLINE TO STORAGE V A T 6 such information as can be by the water itself (6). The use of temporary obtained is accumulated Water, air and sulfur flow, and temperature are all measured here. b o i 1c:r i n s t a1 1a t i o n s through geophysical and a t each well soon gave electrical methods: and temperature measurements provide clues to the probable‘course way t o the unit servjng a group, and this, finally, to the of underground water channels. Yet with the application of permanently located and fully equipped central power plant all the ingenuity of staffs of technicians trained in this induslocated off the dome structure and protected in this way from strains resulting from earth movement. The modern power try, the nature and character of the wide variety of underplant contains the latest type high-efficiency boilers, gas-fired ground conditions still has to be determined largely by deducand supplied with zero hardness water by chemically contive reasoning rather than by measurement or inspection. trolled water softeners. Such is the heat economy of these I n spite of all these and many more remarkable achievements which have raised sulfur mining by the Frasch process plants that it seems almost as though some B. t. u.’s must be made to work twice. I n some cases stack gases are pushed from an art to a scientifically operated industry, there still out into the atmosphere a t temperatures no higher than exists no way for determining in advance whether or not a de100” F. This is made possible by the large volumes of water posit can be mined with profit or even mined a t all. Test steaming of a well or even of a series of wells would indicate to be heated, and the last heat units are taken from the stack gases in gas cooling towers. only that that well or group of wells would produce. If the Originally the wells were operated more by instinct than by initial wells failed to produce, it would not demonstrate that scientific methods--“played by ear,” in fact, since the sound the deposit could not be mined but only that those wells could made by the air-lift discharge was an important factor. Tonot be operated a t that time. Later when underground day air and water are controlled as to volume and temperature changes have taken place due to operation of other wells, subfor each well separately from a central station governing as sidence, or mudding, they may become profitable producers. many as ten wells. Air, water, and liquid sulfur are continuThe history of the sulfur industry has always been one of ously metered and recorded. Should the level of liquid sulintense competitive effort. First the Italian and Sicilian profur at the bottom of any well fall to the point where the sulfur ducers competed among themselves for the small world pipe is no longer sealed with liquid sulfur and water about to markets of the eighteenth century. As markets grew, combe blown out by the compressed air, the slight drop in air petition in the form of pyrites and then by-product sulfur appressure causes an alarm to ring and shifts the valve positions peared. Later on, a single American competitor with a new
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and extremely ingenious process forced world prices to new low figures. About this same time the recovery of sulfur in the form of by-product acid from smelter operations began to become important, and the pyrites consumption likewise increased. Other forms of by-product sulfur recovery have appeared. Many of these were suggested and partially developed as early as 1840, and others were forced into being, regardless of cost, by the raw material shortage in Germany during the war. All have been given a stimulus by the extraordinary development of both tools and technic in the past 20 years. Under favorable conditions such as are found a t the Orkla Mine in Norway and the Trail Smelter in Canada, the recovery of elementary sulfur directly from smelter gases has been accomplished. For many years by-product sulfur from manufactured gas purification has sought with more or less success its share of the market, but in general the quality is poor and it cannot be considered a low-cost source. Elsewhere the production of sulfur is being fostered by governments in the interests of national self-sufficiency. Production in Japan, Germany, Norway, Spain, Chile, and other areas has increased. The rapid development of markets throughout the world, which has been characteristic of this industry for the past hundred years, is encouraging the expansion of production. While the growth of by-product sulfur production since its initiation in 1870 by the Chance-Claus process has been steady, the growth in consumption of sulfur in all forms has been many times as rapid. Sulfuric acid, and consequently sulfur, enters into nearly all industrial processes a t some stage. This widespread use has made it the barometer of industrial activity. From time
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to time it may recede in some one industry, as it did in petroleum refining, with the development of continuous acid treating. This process displaced batch treating methods, causing a considerable reduction in acid consumption per unit of crude oil. Unit consumption receded still farther upon the introduction of solvent treating methods. During this past year, however, the total consumption in the oil industry turned upward again. New uses are continually being developed and new consuming industries increase yearly in importance. The steel industry, with the trend towards greater use of rolled sheet in fabrication, is increasing its unit consumption of acid, and the amazing growth, of the paper, rayon, and pigment requirements continues. The production and consumption of sulfuric acid both in the United States and throughout the world in 1937 was greater than ever before, greater even than the peak year of 1929 which many thought would never be exceeded.
Literature Cited (1) Brunfaut, Jules, “L’exploitation des soufres en Italie,” Paris, 1874.
(2). Frasch, Herman, J. IND.ENG.CHEM.,4, 134-40 (1912). (3) Harrar, N. J., J . Chem. Education, 11, 640-5 (1934). (4) Kerr, F. N., paper presented before meeting of Assoc. of Eng. Societies. Jan. 11. 1902. ( 5 ) Koontz, N.’ J., paper presented before meeting of New Orleans Acad. Sci., April 21, 1873. (6) McIver, D. T., Chatelain, J. B., and Axelrad, B. A , , IND.EKQ. CHEM.,30,752 (1938). (7) Mock, H., and Blum, A., Chem. & Met. Eng., 20, 637-8 (1919). (8) Vanutelli, Cesare, I n d . mineraria, 1931.
RECEIVED March 28, 1938. Presented before the Division of Industrial and Engineering Chemistry a t the 95th Meeting of the American Chemical; Society, Dallas, Texas, April 18 to 22, 1938.
Sulfur Mining as a Processing Industry
A
LTHOUGH the American sulfur industry is not new, its operations are still much of a mystery to many technical men. We have here an industry that utilizes the unique physical properties of sulfur and by the adroit application of physical laws is able to recover from considerable depths an element that, together with salt, limestone, and coal, may be said to be the foundation of the American chemical industry. Until 1903 the large part of the world’s supply of sulfur came from mines in Sicily. Here the ore was mined and heated in kilns to a temperature above the melting point of sulfur, and the molten sulfur recovered from the bottom of the kiln. The heat required for the process was obtained by burning part of the sulfur. As early as 1865sulfur was known to exist in Louisiana a t depths of 500 to 1500 feet. Considerable time and money were spent trying to overcome quicksand and hydrogen sulfide while sinking shafts to this deposit. Failure followed failure. After having witnessed the failures attending the mining of sulfur by mechanical means, Herman Frasch attempted in 1890 to apply other methods. Originally he contemplated extracting the sulfur with solvents, but this idea was abandoned because of the high cost of the solvents and the difficulty attending their recovery. Subsequently he conceived the idea of heating the sulfur underground, melting it, and recovering it in
C. E. BUTTERWORTH A N D J. W.SCHWAB Texas Gulf Sulphur Company, Inc., New York, N. Y.
liquid form. The heating medium chosen for this purposewas water applied a t temperatures slightly above the meltingpoint of sulfur (114O to 120” C., or 237.2”to 248” F.).
Mining Sulfur with Hot Water The technic of mining sulfur resolves itself into the efficient transfer of heat from the hot water to the underground deposit of sulfur. The deposit to be mined, however, must possess certain characteristics. It must have a certain minimum concentration of sulfur. The strata containing sulfur must be sufficiently porous to allow the penetration of water. The structure of the deposit must be such that hot water under pressure may be maintained in contact with the sulfur for sufficient time to allow the efficient transfer of heat. At present the hot water method of mining sulfur is applied only to the removal of this element from certain domes situated on the Gulf Coast of the United States. These “salt” domes consist geologically of salt plugs which have
