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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
AIRPLANE VIEWOF POWERPLANT AND SULFUR STORAGE, TEXAB GULFSULPHURCOMPANY,INC.
been forced up into the sand and clay strata from the deepseated salt beds below. They lie a t depths of several hundred feet and are generally topped with a cap rock of anhydrite or of layers of calcite and anhydrite. They are circular or elliptical in cross section, and the area may vary from a few to several thousand acres. Although many domes have been discovered, in only a few has sufficient rhombic sulfur been found intermixed with the calcite of the cap rock to justify commercial mining. Only in certain tones has the structure been such that the flow of water under pressure can be controlled. Although the extraction of sulfur by the hot water process is concerned theoretically only with the efficient transfer of heat, the process cannot be carried out as smoothly and efficiently as it would be in a carefully designed chemical plant. Certain natural difficulties must be overcome, and the operation must be conducted in such a manner as to utilize the peculiarities of particular deposits. The operation must also be performed in accordance with the risks encountered in all minihg ventures. Therefore, in order to safeguard customers against the unforeseen, most producers of sulfur maintain large stocks of the mined element and make every effort to apply the best engineering technic so that, when the production of sulfur from a given deposit has been started, it will not be interrupted. The recovery of sulfur from certain subsurface deposits depends on the fact that hot water under pressure can be pumped into them. The hot water penetrates the porous limestone, calcite, and anhydrite formation containing sulfur and passes out into the dome, transferring its heat to the regions encountered. There is a gradual temperature drop between the point a t which water is injected and its advancing front. By the continuous injection of hot water under pressure, considerable areas are heated and any inefficiency in the system lies in the fact that barren areas as well as those containing sulfur are heated. The heat remaining in these barren areas is, however, not entirely wasted, for the porous rock is weakened by the extraction of sulfur, by the solution of minerals, and by expansion from increased temperatures. This causes the ground above to subside and fill cavities which would otherwise have to be maintained full of water. As a result the fresh water introduced is forced out into the ore. An artificial method of directing the flow of water is to introduce mud or chopped straw to plug porous formations. Since the mining of sulfur by the hot water process consists essentially in the transfer of heat to subsurface deposits and since the visible evidence of this operation is manifested only by the presence of large water-heating plants, the casual
visitor to this type of mining property comes away with the impression that the mining of sulfur is comparatively simple. He may be tempted to liken the operations to those of an efficient processing industry. He sees a modern heating plant drawing water from a reservcir, heating it, and sending it through a set of pipes on a mysterious journey out into the surrounding plains and marshes. He sees a second set of pipes, leading from these same plains and marshes, discharge a yellow flood of sulfur into large storage vats. He can, however, have no conception of the skill and experience required in the exploration and manipulation of underground factors in order that the maximum amount of sulfur may be extracted from a given subterranean area.
Sulfur mining by the Frasch process involves the transfer of heat. The operation is briefly discussed from this viewpoint. Sulfur mining is further concerned with the efficient and economical handling of large quantities of water, fuel, sulfur, and bleed water. Water must be softened, molten sulfur transported long distances, and bleed water treated to avoid stream pollution. The factors entering into these operations are described. Interesting data are supplied regarding the type of equipment and metals which can successfully be used in combination with sulfur or certain sulfur compounds.
Boilers In the Newgulf, Texas, water-heating plant of this company, steam is generated a t 100 and 125 pounds gage pressure in ten Babcock and Wilcox, Stirling type, 250 pound per square inch boilers operated at 150 to 225 per cent of their rated capacity. Blowdown from the boilers is continuous into the mining water softeners. Air for combustion is used for cooling the boiler settings. It is circulated around the 747
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settings by fans and is finally discharged into the boiler furnaces as preheated forced draft. Operating efficiency is under constant visual control through the medium of the usual gages, meters, and thermometers. Flue gases may be vented with natural draft through two 330-foot chimneys, but, when natural gas is burned, the flue gases are exhausted to economizers instead of being passed to the chimneys. Most of the sensible and latent heat is recovered from the flue gases in the economizers. These economizers are of rather unusual design in that the flue gases are brought into direct countercurrent contact with the raw feed water. This is possible because the natural gas burned is practically pure methane, and the productssof combustion do not offer a source of contamination. Some carbon dioxide may be dissolved, but it is eliminated in the water softeners through the vent condensers and partly by the addition of milk of lime. The scrubbed flue gases are discharged from the economizers a t the temperature of the incoming feed water.
Mining Water Heaters Mining water, the principal product of the plant, is heated in jet-type heaters through the condensation of steam at a suitable pressure for the temperature to which the water is to be heated. Five such heaters are installed, capable of delivering 9,000,000gallons of water a day a t 160" C. (320" F,). Steam is also used in turbines to drive pumps, generators, and fans, and is exhausted a t 5 pounds gage pressure to heat water in the hot process softeners. Sixty-five centrifugal pumps are required to handle water into the plant and from the heaters to the mine. Al€essential pipe lines in the plant are parallel with stand-by lines and are so crossconnected that any section may be by-passed and repairs made without disturbing the continuous supply of mining water. Besides providing energy and heat for all mining operations, the power plant acts in a municipal capacity in the supply and treatment of water for town site consumption
Pipe Lines Mining water, cold water, steam, and high-pressure air lines lead from the plant to all parts of the surface area overlying the ore body. All of these lines are welded and rest on rollers fastened to concrete blocks. Expansion loops are placed a t 1000-foot intervals. The mining water and steam lines are insulated with a 4-inch layer of rock wool which is supported and protected from the weather by a sheet metal covering. Metal spacers, placed between the pipe and the sheet metal, keep the insulating layer a t constant thickness and distribute the weight of the pipe to curved steel plates placed on the outside of the sheet metal and over the supporting rollers. The mining water temperature drop from the heaters to the mine is less than 3" C. (5.4" F.). As a result of oxygen elimination in the water softeners, there is no corrosion in the mining water lines. Corrosion in the air lines is prevented by cooling the air and removing the condensed water from it.
Fuel Adequate supplies of fuel are a primary requirement for mining sulfur with hot water. All of the deposits mined by the method are favorably located, however, near to Gulf Coast oil and gas fields and within a reasonable distance from lignite or coal beds. Oil was the only fuel used in the early days of the sulfur industry, but about 1925 natural gas was made available and since that time has been used as fuel by most producers. Its heating value is relatively constant, and little burner regulation is required. It is clean and contains no solids to form slag with the furnace brick.
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A continuous supply of hot water is necessary for mining sulfur. If the supply is stopped, wells used to introduce the water into the mine may become plugged with frozen sulfur and seriously interfere with mining operations. For this reason the larger water heating plants are equipped to utilize oil if the supply of gas is interrupted. Combination gas-oil burners are used, and changes from one fuel to the other are made so quickly that little fluctuation in boiler output is noticed. As a further provision for fuel economy, the boiler furnaces at Newgulf are designed so that powdered lignite can be used as a fuel.
Water Supplies Since the smallest producers use more than a million gallons of water per day, a dependable supply of water is another primary requirement for mining sulfur. Unlike a chemical plant, the location of a sulfur mine is predetermined. If the mine is near a river, it is by chance rather than by choice. As a result all local sources of water supply are developed to their fullest extent. Both surface and well water are used. Smaller operations, however, often depend entirely upon well water, particularly in the case of relatively short-lived deposits, where increased charges for treating well water would be more than offset by the cost of obtaining, transporting, and storing surface water. In the larger operations it is the usual practice to utilize both well and surface water. I n some cases the well water is merely a stand-by supply for periods of drought. In other cases where the water contains sodium bicarbonate, it is mixed with surface water to decrease over-all softening costs. At Newgulf the well water has a total hardness of 5 to 10 grains per gallon (as calcium carbonate) and a negative hardness of from 3 to 10 grains per gallon. As water of this type is low in sulfates, care must be taken to avoid embrittlement of boiler steel. Since there are few large rivers along the Gulf Coast, it is often necessary to impound a sufficient supply of surface water during the wet winter months to carry over the dry periods. At Newgulf water is stored in a reservoir which covers several hundred acres of ground and holds over a billion gallons. It is located on the banks of the San Bernard River from whioh water is taken by four 10,000 gallon per minute, motor-driven centrifugal pumps. Pumping periods are limited when possible to those times when the river is between its very high and very low states in order to obtain a relatively soft water which contains a minimum of suspended solids. Such water will average about 10 grains per gallon total hardness, 1 to 2 grains noncarbonate hardness, and from 2 to 3 grains suspended solids. It is much easier to treat water of this kind than to treat the softer and more turbid water obtained when the river is at higher stages. Much of the turbid water must be used, however, for the reservoir is kept well filled when water is available. The reservoir is connected to the heating plant by two 24-inch concrete conduits through which water flows to the plant by gravity.
Water Treatment Water treatment for sulfur mining purposes has been a slow evolution from partial softening with makeshift equipment to complete conditioning through the use of the most efficient equipment. This evolution has been necessary in order to keep pace with the development of modern boilers and other power plant equipment. The homemade Roftening plants first used were gradually replaced as increased boiler ratings were required; then when the Newgulf plant was built in 1928, it was equipped with the largest hot-process softening installation in the world, and provisions were made for deaeration and for final conditioning in the boilers. At
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the present time all sulfur producers use hot-process softeners, and some of them treat the boiler water in separate units so as to best condition each water for its particular use. The Xewgulf hot-process softening plant is made up of six 70,000 gallon per hour Cochrane units. Each unit consists of a milk-of-lime mixing tank, chemical pumps for pr.oportioning and lifting the milk of lime to the top of the softener, a jet heater, a condenser through which gases liberated from the water are vented, a sedimentation tank, and two calcite filters. Exhaust steam supplied to the jet heaters a t 5 pounds gage pressure raises the temperature of the water to 105" C. (221' F.) as it enters the tank and mixes with the lime. When the softeners are operated at their rated capacity, the sedimentation period is 1 hour. '
Boiler Water Treatment
Since no condensed water is available for boiler feed water in sulfur mine heating plants, the make-up is 100 per cent. Boiler water a t Newgulf is a mixture of well and surface water so proportioned that residual soda in the softened water will be 3 grains per gallon. Under these conditions hot-process softening ( 1 ) produces a water with about 0.5 grain per gallon total hardness and only a trace of dissolved oxygen. In utilizing this mixture for boiler feed, advantage is taken of the sodium bicarbonate contained in the well water, and lime costs for the mixture are considerably less than the cost of lime and soda required by the surface water alone. I n order to condition the water finally, various chemicals are added to the water in the boilers. This may be done either by introducing solutions of the chemicals directly into the boiler drums by means of auxiliary pumps or by mixing them with the water as it goes to the boiler feed pumps. These chemicals include sodium sulfate to maintain ratios required to prevent embrittlement of boiler steel, sodium sulfite to combine with the last traces of oxygen, and Hagan phosphate to prevent the formation of silicate scale. At Newgulf these chemicals are added at the boiler feed-water pumps. Sodium sulfate is added continuously and phosphate and sulfite are "slugged" a t hourly intervals.
Mining Water Treatment The mining water does not require such drastic treatment. It may be made up of surface water alone, as excess soda alkalinity is not required. Treatment with lime in the hot softeners followed by filtering through calcite has given fairly satisfactory water. Boiler blowdown water is passed through a flash tank and pumped into the mine water softeners where its heat and excess chemicals are fully utilized. Mining water leaves the softeners a t 105' C. Its temperature is raised to 160" C. (320' F.) in the high-pressure heaters, and i t is pumped through 16-inch pipe lines to the surface mine workings. As a rule it is not necessary to remove the last traces of scale-forming salts from it; for, although some scale forms in the first few thousand feet of pipe line, the rate a t which it deposits is so slow that it requires 4 or 5 years to reach a thickness of 0.25 inch. This pipe line scale is r e m m d by solution in hydrochloric acid% whsc an inhibitor k b a u I
*
Bleed Water Treatment I n addition to sulfur, a by-product, bleed water, is unavoidably produced by Frasch process mining operations. Hot water pumped into a deposit soon builds up hydrostatic pressure. I n most deposits it is safe to build up mine pressure to the point a t which water flows from the bleed wells in sufficient volume to balance the mining water input. In some cases, however, pumps are used.
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Bleed water is quite corrosive to steel. Various naval bronzes Are used for metal parts of equipment which come in contact with it. When possible it is transported through ditches. Redwood is preferred when pipe is required. Cement-lined steel pipe is used for certain purposes, however, and bronze pipe for others. Concrete is slowly attacked by bleed water and is usually protected by emulsified asphalt paint or by a course of acidproof brick laid in Vitrobond, a sulfur cement ( g ) , or Sulmor, a plasticized sulfur product (3). Bleed wells are usually located on the flanks of the deposit, and, as would be expected, the composition and the temperature of the bleed water vary considerably. When mining operations are started, the bleed water may contain several thousand grains per gallon of total solids as chlorides, sulfates, and soluble sulfides; the temperature is about 32O C. (89.6' F.). As mining proceeds, the bleed water is diluted with fresh mining water and its temperature rises. The p H of the water is about 7. The concentration of soluble sulfides remains relatively constant throughout the life of a mine. Hydrogen sulfide is given off in large volumes when the water reaches the surface. Because of the relatively large amount of heat left in the water that has passed through the ore and collected in the top part of the porous formation, various attempts have been made to recirculate it through the ore. When this is done, water is bled to the surface; if necessary its temperature is raised by mixing with much hotter fresh water, and it is again pumped into the ore. Until recently the method has not been used successfully, since the loss in equipment from corrosion has usually more than offset the cost of the recovered heat. Much heat has been recovered, however, by passing bleed water through corrosion-resistant heat exchangers in which its heat is transferred to fresh water as a first step in heating mining water. Thia heat recovery method is seldom used until sufficient water has been introduced into a deposit so that water bled from relatively low levels is hot enough to warrant recovering heat from it. l h e disposal of bleed water from inland mines often be- ' comes R serious problem, for obviously in such locations it cannot be wasted through fresh water streams. Two methods of disposal are in use. I n one the water is impounded and wasted through adjacent streams during the rainy season. In the other, sulfides are removed and the relatively inoffensive waste water is carried through ditches to tidewater.. At Newgulf, where sulfides are removed from the water, the disposal ditch is over 20 miles long. Large-scale treatment of bleed water to remove sulfides has been carried out either by aeration in the presence of traces of nickel salts or by scrubbing the water with flue gas. The second method is preferable from an operating standpoint because of its lower costs, although in this method hydrogen sulfide, given off by the reaction of sulfides with carbon dioxide, must be vented to the atmosphere; in the other method it is possible, by controlling the alkalinity, to remove sulfides without liberating hydrogen sulfide. Bleed water sulfides are probably present as dissolved hydrogen sulfide, calcium hydrosulfide, calcium sulfide, and calcium polysulfide. While most of these sulfides are removed as hydrogen sulfide by a few minutes of aeration, 5 t o 10 hours of aeration are required to remove the last traces of them from the water. As aeration progresses, the alkalinity of the water increases, thiosulfates are formed, and calcium carbonate and sulfur are precipitated. If the alkalinity is kept low by adding acid, much shorter periods are required. The time required for aeration a t any given alkalinity, however, can be greatly decreased by the addition of very small amounts of nickel salts. Aeration in the presence of traces of nickel salts was carried out on a large scale a t Newgulf until 1930, when the method
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was replaced by treatment with flue gas. In this method the water is scrubbed with flue gas taken from the heating plant boilers. Carbon dioxide in the gas keeps the alkalinity of the water constant (at a pH of 7), and sulfides are completely removed as hydrogen sulfide by a few minutes of scrubbing. The present plant, which was installed under the supervision of the Koppers Company, is made up of five 1750 gallon per minute units with a maximum daily capacity of over 32,000,000 gallons. Each unit consists of two redwood towers, 18 feet in diameter and 40 feet high. These towers are filled with wooden hurdles over which the water is pumped countercurrent to the flow of flue gas. The water passes down through the towers in series, and the gas passes up through them in parallel. Tobin bronze pumps and piping are used for the water, which leaves the towers through gassealed openings. The foul gas is led through downcomers into a concrete duct from which a fan exhausts it to the atmosphere through a 150-foot concrete chimney. About 4 to 5 cubic feet of flue gas are required per gallon of water treated. Very small amounts of solutions of sulfur dioxide and phosphates are added to the water before it is scrubbed to prevent the precipitation of sulfur and calcium carbonate upon the tower packing.
Storage and Shipment of Sulfur At some of the smaller mines sulfur wells discharge directly on the storage vats. This arrangement necessitates placing the vats fairly close to the producing wells. At the larger mines it has been found more economical to locate storage vats in EL common area and a t a considerable distance from the wellti. When this plan is followed, the wells discharge sulfur into sumps a t collecting stations which are so located that no well is much more than a quarter of a mile from a station. Pipe lines used to convey sulfur from the wells to the stations are heated by means of steam gut h e s . Station sumps are usually about 6 feet deep and 20 feet square, and are lined with cast-iron plates and heated with steam coils. High-pressure pumps move the sulfur to the storage vats which may be 2 to 3 miles from the stations. Multistage motor-driven centrifugal steam-jacketed pumps are usually used. Experience has proved cast iron to be the most satisfactory metal for the impellers used in these pumps. At temperatures below 150" C. (302" F.) liquid sulfur is not corrosive to steel unless it is mixed with water vapor. Cast iron is more resistant to the action of sulfur than steel and has been extensively used for handling it. both as centrifugally cast pipe for sulfur lines and as plates for sump linings. As Allegheny metal or similar chromium-nickel alloy steels are quite resistant to corrosion by this element, various valve parts and gages are made from these metals. Frasch provided barrels for storing production from the first sulfur well. When the barrels were filled, he was forced to store sulfur in a pit with earthen walls. Evidently the merits of storage in relatively large masses impressed him for he soon built wooden bins in which to freeze the sulfur into huge blocks or vats. These vats were built up by adding liquid sulfur in shallow layers and freezing each layer before more sulfur was added. When the vat reached a suitable height, the wooden retaining walls were removed and the sulfur was blasted down for shipment. While present-day equipment and pouring methods differ from those used by Frasch, vats built up layer by layer have proved to be the most satisfactory method of freezing and storing sulfur a t the mines. The largest vats a t Newgulf are 1200 feet long, 160 feet wide, and 50 feet high. The sides of the vats may be made of wood, in which case the wood cannot be re-used. Recently galvanized sheet metal has been utilized for this purpose
75 1
with marked success. As the sulfur layers solidify, they support themselves and the sheet metal is raised and used over and over. Improvements in the distribution of sulfur on the vat tops have been made to give the sulfur layers uniform thickness and plenty of time to cool and solidify between pumpings. Vat storage is ideal in many respects. It furnishes weatherproof storage in the open, with no deterioration or contamination over indefinitely long time periods. There are no upkeep costs and no fire hazards. None of these advantages can be claimed for the storage of sulfur by other methods. For shipment, sulfur is broken from the vats by blasting and loaded into open cars and into boxcar loaders by means of locomotive cranes. Open-car shipments go to Galveston where the sulfur is placed in stock piles, from which boats are loaded at the rate of about 500 tons per hour.
Crude Sulfur Native sulfur is found as rhombic crystals in deposits mined by the Frasch process. Vat sulfur produced from these deposits is also made up of rhombic crystals. It differs from native sulfur, however, in that its crystals are essentially pseudomorphs which are formed from liquid sulfur a t its freezing point as monoclinic prisms and changed into rhombic crystals as the sulfur cools to temperatures below 96" C. (204.8" F.). Vat sulfur varies in structure from a somewhat porous, rather soft material to a fairly dense relatively tough material. Both of these types are preferred by certain users of sulfur. Producers, however, usually try to obtain an average product more or less intermediate between the porous and dense forms. When sulfur is broken from the solid vats for shipment, it becomes the so-called crude sulfur of commerce and is sold as containing 99.5 per cent sulfur. It usually contains traces of amorphous sulfur (which is insoluble in carbon disulfide) and from 0.01 to 0.1 per cent ash. Since liquid sulfur freezes about 10" C. (18" F.) above the boiling point of water, vat sulfur contains no moisture. After the sulfur is broken from the vat, some moisture is unavoidably entrained in it through exposure to the weather. It is difficult to wet sulfur with water, however, as water runs off sulfur in much the same manner that it runs off a duck's back. Crude sulfur usually contains traces of organic matter as the result of contact with petroleum present in the deposits from which it is mined. If more than the barest trace of organic matter is present, it is apt to discolor the sulfur and may interfere with its burning freely. Sulfur burners of the rotary and spray types have proved to be the most efficient. Arsenic, selenium, and tellurium are not present in Gulf Coast crude sulfur. The production of this element at reasonable cost to American industry involves the application of the most efficient methods of handling material, the latest developments in the conservation of heat, the introduction of newest technic in water treatment, the adoption of strict methods of control to secure a uniform product of continually improved quality, and the continued drive of research to seek out better methods of maintaining the independence of American industry that there may be available a crude material of high purity.
Literature Cited (1) Butterworth, C. E., IND.ENQ.CHEM.,27, 548-55 (1935). (2) Duecker, W. W., Chem. & Met. Eng., 41, 583-6 (1934). (3) Dueoker, W. W., and Schofield, H. Z., Bull. Am. Ceram. Soc., 16, 435-8 (1937). R E C E I Y March ~D 28, 1938. Presented before the Division of Industrial and Engineering Chemistry at the 95th Meeting of the American Chemical Society., Dallas, Texas, April 18 to 22, 1938.
Re-use of Bleed Water in Sulfur '
T
Mining
HE underground-fusion or Frasch process is used ex-
clusively for the production of sulfur from the cap rock of salt domes in the Gulf coast area of the United States. A salt dome is the upward intrusion of a salt plug which may or may not have a cap rock. These salt plugs may be from a few feet to several thousand feet below the surface of the ground and do not always cause the surface formation directly above them to rise above the surrounding terrain. Only a small percentage of salt domes discovered to date have beea,found to contain sulfur in areas of the cap rock, in amounts that would justify mining on a commercial scale. I n all cases where sulfur is found disseminated through the cap rock, it exists as rhombic crystals in that portion of the cap rock which is composed mainly of porous limestone. This sulfur-bearing formation is found over salt plugs, the depths of which are usually from 500 to 2500 feet. The upper formations consist of sedimentary deposits, and in some cases there is a layer of barren limestone directly above the ore. Between the sulfur-bearing limestone and the sodium chloride plug there is an impervious layer of anhydrite that varies in thickness and does not contain elemental sulfur in commercial quantities. The sodium chloride plug beneath this anhydrite is of unknown depth.
Reclamation and Treatment D.T.McIVER, J. B. CHATELAIN, AND B. A. AXEZRAD Freeport Sulphur Company, New Orleans, La.
then equipped with a set of three concentric pipes (Figure 1). Water raised to the desired temperatures, usually from 300° to 320" F., by heating it with steam under pressure is forced down the outer pipe and through perforations into the porous sulfur-bearing limestone. This superheated water melts the sulfur which accumulates around the well and enters the outer pipe through a set of perforations below and sealed off from those through which the water is discharged. The hydraulic pressure causes the molten sulfur to rise a certain distance in the middle pipe of the concentric series; the sulfur is then raised from its static level to the surface of the ground by an air lift. The air is supplied under pressure through the inner pipe of the well equipment.
Frasch Process I n the mining of sulfur by t h e Frasch process a hole is drilled through the upper unconsolidated formation and the porous sulfur-bearing limestone, and is usually terminated in the impervious anhydrite of the cap rock. The well is 752
