Elemental sulfur markets

Sulfuric acid demand surged ahead at astronomic rates, but no new plants in Europe were using elemental sulfur. All new plants were on pyrites, and the established facilities switched in the following decades. By 1880, the elemental sulfur market in Europe for the manufacture of sulfuric acid had disappeared The resilient demand for sulfur, though, was almost oblivious to these changes and continued to surge ahead. By the mid-1880 s, Sicilian exports had double in two decades to 350,000 tonnes. 

Process Alternatives. Process alternatives for sulfur recovery are shown schematically in Figure 2. The choice of either elemental sulfur or sulfuric acid will depend on economics and markets related to each plant location. Elemental sulfur may be produced by gas-phase oxidation (the Claus process) or liquid-phase oxidation (e.g., the Stretford process). Stretford units were described in Section 1 and are well discussed in the literature (1, 2> 5) Claus sulfur recovery efficiency is usually less than required by current air emission standards. Therefore, some form of tail-gas treating is required. Sulfuric acid may be produced by the well-known contact process (6). This process is licensed by a number of firms, each of which has its own... 

Sulfuric acid production is one alternative to the manufacture of elemental sulfur from acid gas streams. If a market for the product acid can be found, sulfuric acid may be economically attractive relative to elemental sulfur (14,15). 

Both of these processes direct the SO2 absorbed from the FCCU flue gas to the refinery SRU, where it is converted to elemental sulfur and added to the marketable sulfur that is generated by the SRU from H2S. Alternately, the SO2 can be converted to sulfuric acid in a dedicated sulfuric acid plant, or in combination with an existing refinery spent acid regeneration unit. When the SO2 is directed to the SRU, 1 ton of SO2 captured in the scrubber is converted to 0.5 tons of marketable elemental sulfur and less than 0.1 ton of sodium sulfate waste is generated per ton of SO2 absorbed. In an acid plant, 1 ton of SO2 generates 1.5 tons of 98% sulfuric acid. Steam is also generated from the conversion of SO2 in both the SRU and the acid plant, which moderates somewhat the steam consumption rate of the solvent regenerator for both the LABSORB and CANSOLV systems. 

The present paper is based on the author s study (1) funded by the U. S. Bureau of Mines which, however, is not responsible for the views expressed or the conclusions reached. The time element has been subdivided into three discrete points and a period. The points include current output levels, for use as a base line, 1985 and 1990. The period encompasses the decade from 1990. This reflects the increasing unreliability of the estimates as the projection is extended. Because sulfur markets tend to be discrete and sulfur sources tend to be geographically differentiated regional supply projections are required. The definition chosen here is the Petroleum Administration for Defense districts. [These are defined as I - Connecticut, Delaware, District of Columbia, Florida, Georgia, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, North Carolina, Pennsylvania, Rhode Island, South Carolina, Vermont, Virginia, and West Virginia. II - Illinois, Indiana, Iowa, Kansas, Kentucky, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, Oklahoma, South Dakota, Tennessee, and Wisconsin. 

Smelter Acid. If acid is produced involuntarily, as in a smelter operation, it is possible to estimate the cost of acid production in the same manner as that for an elemental sulfur acid plant. To the smelter, however, acid output is simply a mandated concomitant of the process required to produce the metal. Depending on the location of the smelter, the sources of demand, the size of the market, and competition from other producers, the acid sale price may or may not be sufficiently high even to yield a positive net-back, much less a desired rate of return on investment for the acid portion of the operation. This situation does not necessarily lead to closure. Positive or negative, the effect should be registered only in the overall profitability of the entire smelter operation. 

Recovered elemental sulfur is one of the purest bulk commodities available on the market today. Typical analyses quoted for bulk shipments are 99.95% purity with ash, carbon and other contaminant levels in the 10 - 100 ppm range. This is a remarkably pure bulk commodity for a 5d/lb price. What them remains to be developed by way of improvement of product quality ... 

The acid gas from the Sul find regenerator must be disposed of in an environmentally acceptable manner. The Claus process offers an effective means for converting nearly all of the sulfur in the acid gas to saleable elemental sulfur. The tail gas from the Claus plant still contains some sulfur compounds. To minimize sulfur emissions from the plant, the Claus tail gas can be fed to a Shell Claus ff-gas Jreating (SCOT) unit where most of this sulfur is recovered and recycled to the Claus plant. With use of the SCOT Process, additional marketable sulfur is recovered within the Claus plant while tail gas sulfur emissions are substantially reduced, to typically less than 250 ppmv. 

World elemental sulfur production in 2003 was almost 45 million metric tons.2 Over 99 percent of the sulfur that is marketed is sold as crude sulfur. The two primary grades are bright, which is bright yellow and at least 99.8 percent pure (typically 99.9+% pure with a maximum of 0.02% carbonaceous material), and dark, which at the time of production can contain in excess of 0.25 percent carbon, is typically sold as 99.5 percent (min) sulfur with... 

Many processes release sulfur in the form of H2S, which is highly toxic and must be converted to a marketable form such as elemental sulfur or a stable disposable product such as a sulfate salt. U.S. 5,397,556 (to Regents of the University of California) describes a process for converting H2S to elemental sulfur. How does the cost of sulfur produced by this process compare with the cost of sulfur produced by the conventional modified Claus process ... 

HCN is not completely stable and is marketed as a stabilized (often with H3PO4), flammable, anhydrous material. It reacts when heated, or in the presence of base or water, and may polymerize violently in contact with strong acids (e.g., sulfuric acid). Polymerization, once initiated, can be autocatalytic and, under confined conditions, lead to an explosion. It can be removed from waste streams by conversion to ammonium thiocyanate, a process involving scmbbing the waste stream with elemental sulfur in water (http //www.chemalliance.org). 

As many types of coal contain little sulfur, but have a considerable surplus of carbon for methanol production, the H2S content of the resulting sour gases is frequently around or even less than 5 vol. %. Although the sulfur concentration can be increased in the gas purification section, this is always a costly undertaking. Certain direct treatment processes may therefore be used for such sulfur gases although they lead to sulfuric acid rather than to the more easily manageable and normally more conveniently marketable elemental sulfur. 

Research and development efforts were focused on addressing several of the problems of the day. Sulfur oxides (SOx) were becoming more stringently controlled, and stack gas scrubbers or use of hydrodesulfurized gas oil feed were expensive options, so catalyst makers developed new products that worked in conjunction with a Claus unit to first reduce the sulfur to hydrogen sulfide and then recover it as elemental sulfur. Carbon monoxide, formed at the higher regenerator temperatures resulting from improved zeolite catalysts, needed to be oxidized to improve heat recovery, and additives were developed to accomplish this. Metals tolerance and octane improvement were needed as well, and producers vied with each other to address the needs of the market (85). 

Silane, SiH, is a colorless gas. Phosphine, PHj, is also a gas it catches fire spontaneously when exposed to air, is very toxic, and has a bad odor. Hydrogen sulfide, H2S, is a toxic gas with a foul, rotten-egg odor. Natural gas contaminated with hydrogen sulfide is said to be sour, and the hydrogen sulfide must be removed before the natural gas can be used as a fuel. Fortunately, HjS is readily converted to elemental sulfur or to sulfuric acid, for which there are ready markets. Hydrogen chloride, HCl, gas has a sharp odor and is very soluble in water. Solutions of hydrogen chloride in water are called hydrochloric add. About 2.5 million tons of hydrochloric acid are produced for industrial applications in the U.S. each year. 

Thus today the technology is available to produce sulfuric acid or elemental sulfur from oxides of sulfur, instead of discharging SO into the atmosphere. This technique is being used more and more. But there is not always a market for large amounts of sulfuric acid produced by remotely situated smelters. For these industries a cost-effective alternative for reducing sulfur dioxide emissions is to remove as much as possible of the pentlandite-follower pyrrhotite (FeS to Fe Sg). 

By-product Value and Markets. Elemental sulfur is a valuable byproduct with existing markets (32). Liquid elemental sulfur is the most marketable form of sulfur, and the easiest to transport. Although most sulfur is used as sulfuric acid, it is significantly less expensive to transport liquid sulfur and convert it to sulfuric acid at the location of its use than to transport the acid. For comparison, 1 ton of sulfur could produce 2 tons SO2, 3.06 tons sulfuric acid, or 5.37 tons gypsum. 

Section 2 briefly reviews sulfur use. The marketability of liquid sulfur is much better than that of other forms of sulfur because of a large existing market, value, proximity to markets, and high quality. Elemental sulfur also offers easier handling, transportation, and storage. 

The Spanish Civil War and World War II finally ruined the Spanish pyrites industry. Shipments had been blocked during these years, and alternatives had been found. After World War II, many new sulfuric acid plants were constructed in Europe to replace those that had been destroyed, and U.S. expansion was bolstered by economic growth, especially by demand for phosphate fertilizers. These new plants all used elemental sulfur (Contact process). While Spanish pyrites production returned to pre-war levels by 1950 (see Figure 2.5 for the early history of production), their market share had seriously eroded as sulfur demand, overall, had more than doubled. Pyrites mining as a source of sulfur continued in Spain until 2002. 

The fastest growing sulfuric acid market, the U.S., remained with elemental sulfur until the end of the century. While Sicily was losing most of its sulfuric acid market in Europe, U.S. demand was racing to replace it. In 1892, Sicilian exports to the U.S. alone were 89,000 tonnes. Later, the U.S. sulfuric acid industry also switched to pyrites. There had been no American duties on elemental sulfur, but there was on pyrites, which were removed in 1890. In 1895, 75% of U.S. sulfuric acid was still being manufactured from elemental sulfur, but had dropped to only 16% in 1901. 

The luck of sulfur continued though. The loss of another major market did little to dampen the unstoppable growth of sulfur. By then, new major markets for elemental sulfur had been established, especially for the production of sulfite pulp (uses sulfur dioxide from the burning of sulfur), pesticides (for grapes) and mbber manufacturing (vulcanizing). 

Adding to their woes, the largest sulfur market, the manufacture of sulfuric acid, had disappeared in the U.S. When Frasch had filed his patent over 80% of the rapidly growing American sulfuric acid industry used elemental sulfur as its raw material. By 1901, 85% of the industry had switched to pyrites. The only major acid producers using elemental sulfur were Kalbfleisch (later purchased by Cyanamid in 1929) and Grasselli Chemical Company of Cleveland. Most of the sales of Union Sulfur had been through Petit Parsons in New York City for resale. Other shipments were made to a sulfite pulp mill in Wisconsin and fertilizer manufacturer in Meridian, MS. 

At the start of World War II, the U.S. was producing more than 75% of the world s elemental sulfur. U.S. consumption reached record levels of more than 1.8 million tonnes in 1939. By the end of the war, the U.S. market was almost three million tonnes and U.S. production hit yet another new record in 1945. As the war wound down, there was fear of a collapse as had happened after World War I. In fact, just the opposite took place as demand soared even more, especially being driven by the superphosphate fertilizer maiket. Consumption in the U.S. hit 4.3 million tonnes in 1947 Adding to the growth of elemental sulfur was the decline of the p5uites industry of Europe, especially Spain and Norway. In the late 1940 s, the strong market eontinued with demand outpacing supply, but the 18 per tonne price remained, and the export price went up to a modest 22 per torme. 

Within the sulfur world, there is a notable example of pure market pull the replacement of elemental sulfur by pyrites after the TAC incident. An unprecedented feature was the speed of the entire process, from the technical development to its penetration into a global industry. The stage had been perfectly set. The new technology was fairly easy to develop and implement. The special feature was that the customers detested the current supplier. The sulfur world had more than its fair share of these market-pull technology advances the Frasch process is another notable example. That is not to say that sulfur scientists are more market oriented than others. Quite the opposite, the driving force has often been the poor performance of the sulfur industry, which creates these rare maiket-pull opportunities. Instead of being labeled market-pull situations, fundamentally they should more properly be tagged supplier push ... 

The SO2 gas produced by many regenerable processes can be converted in an auxiliary plant into any of several byproducts, including liquid SO2, H2SO4, and elemental sulfur. The marketability of these products depends on local demand and economic factors. Transporta-... 

Commercialization of the ammonia process was pioneered by the Consolidated Mining Smelting Company, Ltd. (Cominco), which operated a 3 ton/day sulfur-producing pilot unit at their Trail plant in 1934 and placed a 40-ton/day commercial plant in operation in 1936 (King, 1950). The sulfur dioxide recovered in these early units was reduced to elemental sulfur. Later changes in the market picture made it more economical to use the concentrated sulfur dioxide streams as feed to sulfuric acid plants. Sulfur dioxide-absorption processes using both heat and acid neutralization were developed at Trail. Present operations use the neutralization process. 

---