Sulfur melter

Earlier designs used a circular shape for the submerged coils. It was difficult to take out these coils for maintenance or for complete cleaning of the pit during annual shutdowns due to the settled sludge. 

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The rate of thiosulfate formation also increased with increasing temperature and pH. Many Stretford plants employ a sulfur melter to separate the elemental sulfur from Stretford solution. This subjects the solution to 150°C temperatures, which enhance generation of thiosulfate. 

U.3.2.5 Use of Filter Instead of Melter. Significant thiosulfate formation can occur due to the high temperatures in a sulfur melter. Replacing the melter with a filter can eliminate this problem, and also provide a way of efficiently removing commercially salable sulfur from the solution (Lorton 1988). 

Construction Materials. Carbon steel is used for most of the plants in some areas it is protected against rusting by a coal tar epoxy coating. The water outlet fine of the sulfur melter is stainless steel. No notable corrosion has occurred. 

Steam pressure regulator for sulfur melter, sulfur pumps, and feeding system to furnace... 

Maintenance cost of sulfur melter and steam coils. 

CJeneration of HP superheated steam and use in various units in the plant such as turbo-blower/turbo-generator, sulfur melter, filter, and feeding section, as well as excess steam available and used in own premises or actually sold to external clients nearby. 

Hydrocarbon solubility in the circulating LO-CAT solution is about the same as in water. Some hydrocarbons end up in the sulfur product and cause the sulfur product to darken. This problem can often be corrected by use of a coalescing filter on the feed gas upstream of the LO-CAT absorber and by keeping the LO-CAT solution temperature above the feed gas temperature. A sulfur product that is dark in appearance can also be an indication of excessive residence time and/or high operating temperature in the sulfur melter (Eaton, 1992). 

The Mivida SulFerox unit is designed for about 2 LT/day sulfur production and includes a sulfur melter to process the SulFerox sulfur filtercake for sale as a high quality molten product. A flow diagram of the sulfur melter is shown in Figure 9-44. A summary of the projected operating conditions at the Mivida SulFerox plant, which includes a mix of SulFerox pilot plant and design data, is provided in Table 9-22 (Iversen et al., 1990 Allen, 1995). 

Hgura 9-44. Process flow diagram of sulfur melter processing resluirled SulFerox sulfur filtercake. (Iverson et al.. 19901... 

The iron, now in a reduced ferrous form, is not consumed instead, it is continuously regenerated by bubbling air through the solution. The sulfur precipitates out of the solution and is removed from the reactor with a portion of the reagent. The sulfur slurry is pumped to a melter requiring a small amount of heat and then to a sulfur separator where the reagent in the vapor phase is recovered, condensed, and recycled back to the reactor. 

LOCAT units can be used for tail-gas clean-up from chemical or physical solvent processes. They can also be used directly as a gas sweetening unit by separating the absorber/oxidizer into two vessels. The regenerated solution is pumped to a high-pres.sure absorber to contact the gas. A light slurry of rich solution comes off the bottom of the absorber and flows to an atmospheric oxidizer tank where it is regenerated. A dense slurry is pumped off the base of the oxidizer to the melter and sulfur separator. 

A 200 tonne/day contact sulfuric acid plant burning elemental sulfur costs 1.5 million to build. melter by-product sulfur dioxide is available as an alternate feed at no raw material cost, but for the same capacity requires a total investment of 3.75 million to utilize this feed. Assuming continuous operation, what would the breakeven price for sulfur have to be to make the utilization of smelter sulfur dioxide attractive if the company has to pay 10% interest on capital borrowed to build either plant Use estimates based on the first year of operation only. Assume the same labor costs. 

Solid sulfur is dumped on the grids of the melter and is melted by means of the heat provided through steam coils in the melter. An agitator installed in the melter helps to melt the sulfur at a faster rate. Liquified sulfur is pumped to the pressure leaf filter and the purified sulfur stored in a separate compartment equipped with steam coils. Sulfur pumps are used to feed the liquid sulfur to the sulfur burner at a... 

The earlier method for removal of settled muck in the melter involved manual scooping of sludge. Provision of an on-line strainer was not very efficient. Hence it was replaced by filtration of liquid sulfur by pumping it through steam jacketed filters ... 

Issue of raw sulfur from the storage yard to the plant melter. 

Solid sulfur can be stored in open yards but it is better stored in covered sheds and protected from rain to avoid formation of acid. Rain water in the sulfur powder can increase steam consumption in the melter. 

Solid elemental sulfur is non-toxic. However, persons working at the melters can inhale sulfur dust or vapor present and these can cause irritation to the eyes and mucous membranes of the respiratory tract. 

Agitators are provided in melters for faster melting of the sulfur if there are chances of the sulfur being damp. 

Hydrocarbon impurities in sulfur can generate H2S gas during melting of the sulfur and this can be very dangerous due to its highly toxic nature. It can also cause fires at the melters. 

COREX Process (26). The COREX process began as an advanced process for iron making, not for coal gasification. It uses an oxygen-blown combination coal gasifier/iron melter. Coarse-size coal and hot pre-reduced iron are fed to this gasifier/melter. This process favors coals that have a minimum of fines and are low in sulfur and volatiles. 

Broken sulfur was replaced by liquid (or liquid into prills) because of environmental and safety issues. An early attempt to melt solid sulfur in blocks was made by Freeport Sulfur at Joliet, IL, in 1964. In 1977, the first melters were utilized to recover sulfur from blocks in Canada. These devices heat the top and outside of the block, shaving layers off the yellow ice palisades. Melting capacity in Canada had reached 300,000 tonnes per month three years later. 

In. systems where the sulfur is reslurried and sent to a melter, there are no filtercake solution losses, but some blowdown is necessary to purge salts from the system. Since the required blowdown rate depends on the process tendency to form undesirable by-products, mainly thiosulfate, the selection of operating conditions that lower by-product formation will push the optimum iron content of the solution toward higher concentration values and lower circulation rates (Hardison and Ramshaw, 1990). 

Sulfur handling has also been upgraded. In the Mobil unit, which has a sulfur capacity of 1.5 LT/D. a slipstream of the external circulation stream is taken to a dual bag filter system where the sulfur is recovered and stored in 1,000 kg capacity filter bags (Hardison, 1992 Nicmiec. 199. >). LO-CAT 11 units equipped with melters have intermediate filtering devices to improve the quality of the sulfur product. 

With any LO-CAT unit having a sulfur production capacity greater than about 1.5 LTPD. it may be economical to sell molten sulfur (Quinlan, 1991). The exact breakpoint must be determined on a case by case basis. Also, in recent years, the economic justification for melters has become more difficult as the sulfur product usually demands a low price due to... 

In the older LO-CAT and Autocirculation LO-CAT process configurations, sulfur is separated from the bulk solution by primary settling, which produces a slurry of 10-15 wt% sulfur. See Figures-9-31 and 9-32. When a melter is used, this slurry is fed directly to the melter where the temperature is raised above the melting point of sulfur and a liquid/liquid separation is conducted. In both of these older processes, there is usually no intermediate filtering and prewashing step prior to melting. Table 9-20 summarizes the properties of molten sulfur produced by this technique (Kwan and Childs, 1991). 

The 50 wt% slurry of sulfur in solvent from the bottom of the sulfur settler is fed to a pusher-type centrifuge. The sulfur crystals are freed of solvent and washed with water in the centrifuge. The sulfur crystals (about 250 microns in size) arc then resluiried in water (33 wt% solids), preheated in a heat exchanger, and pumped to a melter/decanter. The pressure in the decanter is high enough to prevent the vaporization of water when the slurry is heated above the melting point of sulfur. 

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