Production Frasch process

Fluid deposits are defined as those which can be recovered in fluid form by pumping, in solution, or as particles in a slurry. Petroleum products and Frasch process sulfur are special cases. At this time no vaUd distinction is made between resources on the continental shelf and in the deep oceans. However, deep seabed deposits of minerals which can be separated by differential solution are expected to be amenable to fluid mining methods in either environment. 

Sulfuric acid is the most important sulfur-containing intermediate product. More than 85% of the sulfur consumed in the world is either converted to sulfuric acid or produced direcdy as such (see Sulfuric acid and sulfur trioxide). Worldwide, well over half of the sulfuric acid is used in the manufacture of phosphatic fertilizers and ammonium sulfate for fertilizers. The sulfur source may be voluntary elemental, such as from the Frasch process recovered elemental from natural gas or petroleum or sulfur dioxide from smelter operations. 

The sulfiu can be piped long distances in liquid form or transported molten in ships, barges or rail cars. Alternatively it can be prilled or bandied as nuggets or chunks. Despite the vast bulk of liquid sulfur mined by the Frasch process it is obtained in very pure form. There is virtually no selenium, tellurium or arsenic impurity, and the product is usually 99.5-99.9% pure. ... 

Sulfur is widely distributed as sulfide ores, which include galena, PbS cinnabar, HgS iron pyrite, FeS, and sphalerite, ZnS (Fig. 15.11). Because these ores are so common, sulfur is a by-product of the extraction of a number of metals, especially copper. Sulfur is also found as deposits of the native element (called brimstone), which are formed by bacterial action on H,S. The low melting point of sulfur (115°C) is utilized in the Frasch process, in which superheated water is used to melt solid sulfur underground and compressed air pushes the resulting slurry to the surface. Sulfur is also commonly found in petroleum, and extracting it chemically has been made inexpensive and safe by the use of heterogeneous catalysts, particularly zeolites (see Section 13.14). One method used to remove sulfur in the form of H2S from petroleum and natural gas is the Claus process, in which some of the H2S is first oxidized to sulfur dioxide ... 

Sulfur for commercial purposes is derived mainly from native elemental sulfur mined by the Frasch process. Large quantities of sulfur are also recovered from the roasting of metal sulfides and the refining of crude oil, i.e., from the sulfur by-products of purified sour natural gas and petroleum (the designation sour is generally associated with high-sulfur petroleum products). Reserves of elemental sulfur in evaporite and volcanic deposits and of sulfur associated with natural gas,... 

Elemental sulfur1-4 occurs naturally in association with volcanic vents and, in Texas and Louisiana, as underground deposits. The latter are mined by injecting air and superheated water, which melts the sulfur and carries it to the surface in the return flow (the Frasch process). Most of the sulfur used in industry, however, comes as a by-product of the desulfurization of fossil fuels. For example, Albertan sour natural gas, which often contains over 30% (90%, in some cases) hydrogen sulfide (H2S), as well as hydrocarbons (mainly methane) and small amounts of C02, carbonyl sulfide (COS), and water, is sweetened by scrubbing out the H2S and then converting it to elemental S in the Claus process.5 The Claus process is applicable in any industrial operation that produces H2S (see Section 8.5) it converts this highly toxic gas to nontoxic, relatively unreactive, and easily transportable solid sulfur. 

Pyrite is the most abundant of the metal sulfides. For many years, until the Frasch process was developed, pyrite was the main source of sulfur and, for much of the first half of the twentieth century, comprised over 50% of world sulfur production. Pyrite reserves are distributed throughout the world and known deposits have been mined in about 30 countries. Possibly the largest pyrite reserves in the world are located in southern Spain, Portugal, and the CIS. Large deposits are also in Canada, Cyprus, Finland, Italy, Japan, Norway, South Africa, Sweden, Turkey, the United States, and Yugoslavia. However, the three main regional producers of pyrites continue to be Western Europe Eastern Europe, including the CIS and China. 

Sulfur is a very important industrial chemical. Current consumption ranks sulfur with the top five inorganic and organic chemicals produced in the U.S. The U.S. is the largest producer and consumer of sulfur in the world. The U.S. position in sulfur production resulted from the development of the Frasch process toward the end of the 19th century for mining the large sulfur deposits associated with salt domes in Texas and Louisiana. 

Sulfur is a, relatively abundant element, occurring as an impurity in many metal ores and fossil fuels. It also occurs in relatively pure form from which it can be mined via the Frasch process. Until recently Frasch mining was the major source of supply in the world with the largest producers being the U.S., Mexico and Poland. In the late 1960 s, recovery of sulfur as a by-product from "cleaning" operations began to accelerate rapidly. Sulfur recovery from... 

The development of the Frasch process, first used successfully in 1891, has made this country substantially independent of foreign sources of sulfur. An inspection shows the growth of this country as a producer of sulfur (in relation to the world production) and the rapid decline in the quantity of sulfur imported. 

In the United States, the situation was in many ways different. With its large sulfur, natural gas, phosphate, and even potash resources, America s fertilizer industry rested on a sound base. It was an exporter of minerals and fertilizers, and did not have to worry to the same extent as Europe s industry about competing imports from Socialist countries. But reserves of sulfur extracted by the Frasch process have been depleted in Louisiana and Texas, and President Ronald Reagan s payment in kind (PIK) farm-acreage cuts reduced the fertilizer requirement of American farmers. These farmers are also much in debt and are having trouble selling their products on saturated markets. 

In 1975 world production of elemental sulfur exceeded 32.5 million tons (I). Exploitation by the Frasch process of the large deposits found in association with the salt domes of the Gulf Coast regions has made the United States the world s leading producer (5). In the U.S. a potential (although unlikely) production of 40 million tons of sulfur per year from all sources by the year 2000 has been forecast, compared with a forecast consumer demand of only 30 million tons (6). Greater use of oil sand, oil shale, and coal, again with sulfur extraction, holds further promise of increases in the supply of sulfur in western Canada, the U.S., and elsewhere. 

About 60% of the sulfur produced in the United States comes from the underground deposits of elemental sulfur found in Texas and Louisiana. This sulfur is recovered by using the Frasch process developed by Herman Frasch in the 1890s. Superheated water is pumped into the deposit to melt the sulfur (mp = 113°C), which is then forced to the surface by air pressure (see Fig. 19.16). The remaining 40% of sulfur produced in the United States either is a by-product of the purification of fossil fuels before combustion to prevent pollution or comes from the sulfur dioxide (S02) scrubbed from the exhaust gases when sulfur-containing fuels are burned. 

Over 80 percent of the world s production of sulfur is mined in Louisiana and Texas by a very clever method, the Frasch process. The sulfur, mixed with limestone, occurs at depths of about one thousand feet, under strata of sand, clay, and rock. A boring is made to the deposit, and four concentric pipes are sunk (Fig. 17-3). Superheated water (155°) under pressure is pumped down the two outer pipes. This melts the sulfur, which collects in a pool around the open end. Air is forced down the innermost pipe, and a bubbly froth of air, sulfur, and water rises through the space between the innermost pipe and the next one. This mixture is allowed to flow into a very large wooden vat, where the sulfur hardens as a product 99.5% pure. 

Elemental sulfur is mined along the U.S. Gulf Coast by the Frasch process (Figure 24-2). Most of it is used in the production of sulfuric acid, H2SO4, the most important of all industrial chemicals. Sulfur is used in the vulcanization of rubber and in the synthesis of many important sulfur-containing organic compounds. 

Traditionally, sulfur has been produced using the Frasch process, in which superheated water (440 K under pressure) is used to melt the sulfur, and compressed air then forces it to the surface. For environmental reasons, the Frasch process is in decline and many operations have been closed. Canada and the US are the largest producers of sulfur in the world, and Figure 15.2 shows the dramatic changes in methods of sulfur production in the US over the period from 1970 to 2001. The trend is being followed worldwide, and sulfur recovery from crude petroleum refining and natural gas production is now of greatest importance. In natural gas, the source of sulfur is H2S which occurs in concentrations of up to 30%. Sulfur is recovered by reaction... 

Fig. 15.2 Production of sulfur in the US from 1970 to 2001 note the increasing importance of recovery methods which have now replaced the Frasch process as a source of sulfur in the US. [Data US Geological Survey.]...

Sulfur is commercially recovered from wells sunk into the salt domes along the Gulf Coast of the U.S. Using the Frasch process, heated water is forced into the wells to melt the sulfur, which is then brought to the surface. Sulfur also occurs in natural gas and petroleum crudes and must be removed from these products. Formerly, this was done chemically, which wasted the sulfur new processes now permit recovery. Large amounts of sulfur are also recovered from Alberta gas fields. 

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