Scrubbing operation desulfurization

Howden An early flue-gas desulfurization process using a lime or chalk slurry in wooden grid-packed towers. The calcium sulfate/sulfite waste product was intended for use in cement manufacture, but this was never commercialized. The key to the process was the use of a large excess of calcium sulfate in suspension in the scrubbing circuit, which minimized the deposition of scale on the equipment. The process was developed by Imperial Chemical Industries and James Howden Company in the 1930s and operated for several years at power stations at Fulham, London, and Tir John, South Wales, being finally abandoned during World War II. British Patents 420,539 433,039. 

Walther Also called Walther Ammonia. A flue-gas desulfurization process in which the gas is scrubbed with aqueous ammonia. Two scrubbing stages are used, operating at different pH values. The by-product is suitable for use as a fertilizer. Developed and licensed by Walther Company. Two plants were operating in Germany in 1987, one of which was experiencing serious operational problems. 

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. 

Satriana (2) provides a summary of the development of flue gas treatment technology. The first commercial application of flue gas scrubbing for sulfur dioxide control was at the Battersea-A Power Station [228 MW(e)] in London, England, in 1933. The process used a packed spray tower with a tail-end alkaline wash to remove 90 percent of the sulfur dioxide and particulates. Alkaline water from the Thames River provided most of the alkali for absorption. The scrubber effluent was discharged back into the Thames River after oxidation and settling. A similar process was also operated at the Battersea-B Power Station [245 MW(e)] beginning in 1949. The Battersea-B system operated successfully until 1969, when desulfurization efforts were suspended due to adverse effects on Thames River water quality. The Battersea-A system continued until 1975, when the station was closed. 

While most commercial flue gas desulfurization processes use wet scrubbing technology, there are economic incentives to develop dry sorption-based processes. The dry processes offer potential for lower capital and operating costs, but are limited primarily by low sorbent utilization. ... 

This report describes the results of the Shawnee Lime and Limestone Wet Scrubbing Test Program conducted by EPA s Industrial Environmental Research Laboratory, Research Triangle Park, North Carolina (IERL-RTP). In this program, flue gas desulfurization (FGD) tests were conducted at the EPA 10 MW prototype Shawnee Test Facility located at the Tennessee Valley Authority (TVA) coal-fired Shawnee Power Station near Paducah, Kentucky. Bechtel Group, Inc. of San Francisco was the major contractor and test director, and TVA was the constructor and facility operator. Results of the program before July 1978 have been reported elsewhere (1.2) ... 

With the exception of one operation, all carry out some form of sulfiir capture. The majority (six) produces sulfuric acid. One smelter did not ecifically define the desulfurization plant installed, and another is scrubbing the off-gas. The average conversion efficiency of the sulfuric acid plants is claimed to be between 94% and 98.5%. Overall recovery figures of sulfur were not provided. 

Thus, the tendency is to advocate the use of dry lime scrubbing systems thereby producing a waste stream that can be handled by conventional fly ash removal procedures. There are also dry processes, such as the metal oxide processes, in which sulfur dioxide can be removed from gas streams by reaction with a metal oxide. These processes, which are able to operate at high temperatures (approximately dOO C [TSO F]), are suitable for hot gas desulfurization without an energy-wasteful cooUng step. The metal oxides can usually be regenerated by aerial oxidation to convert any metal sulfide(s) back to the oxide(s) or by the use of a mixture of hydrogen and steam. 

Hence, although these techniques are relatively inexpensive and simple to operate, they are not very effective for large organic sulfur coals. Flue gas desulfurization by scrubbing is impractical for small plants, and uneconomical and energy intensive for plants which operate intermittently. Finally, coal conversion to clean gaseous or liquid fuels is very expensive. 

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