WSA-SNOX process

The SNOX process is also known as the WSA-SNOX process when both SO2 and NO are removed or, if only SO2 is removed, as the WSA process where WSA stands for Wet Sulfuric Acid. This process catalytically reduces both the SO2 and the NO in flue gases by more than 95% and, with integration of the recovered heat from the WSA condenser, is reported to have lower operating costs than conventional technologies. No chemical or additive is required other than ammonia for optional NO reduction. Sulfuric add at 93.2% concentration is produced that is said to meet or exceed U.S. Federal Specifications. The SO2 conversion catalyst can tolerate up to 50% water vapor and several hundred ppm of chlorides. CO and hydrocarbon emissions are said to be low (Collins et al., 1991). 

HaUor Tops0e WSA-SNOX. The WSA-SNOX process was developed by Haldor Topspe A/S, Denmark, and is offered in the U.S. by ABB Combustion Engineering, Inc. The process is one of the most highly developed of the combined NOj,/S02 systems. Several industrial systems are in operation in Europe, and a demonstration unit has been operated in the U.S. (Kingston et al., 1990). 

In the WSA-SNOX process, the flue gas passes first through a conventional SCR unit where NO is reduced to N2 by ammonia. The flue gas is then heated slightly and passed through a second catalyst where SO2 is oxidixed to SO3. The SO3 is hydrated to form sulfuric acid and concentrated to 9S wt% acid in an air-cooled falling-film condenser constructed of glass. Ammonia slip from the SCR reactor is oxidized in the SO2 converter, eliminating a problem encountered in conventional SCR processes. A more detailed description of the process is given in Chapter 7 in the section titled SNOX Process. ... 

Kingston, W. H., Cunninghis, S., Evans, R. J., and Speth, C. H 1990, Demonstration of the WSA-SNOX Process Through the CCT Program, paper 90-JPGC/FACT-17 presented at the Joint ASME/IEEE Power Generation Conference, Boston, MA, October 21-25. 

WSA-SNOX A combined flue-gas treatment process which converts the sulfur dioxide to sulfuric acid and the nitrogen oxides to nitrogen. Developed by Snamprogetti and Haldor Topsoe, based on the WSA process. A large demonstration unit was under construction in 1989. 

SNOX A combined flue-gas desulfurization and denitrification process. The NOx is first removed by the SCR process, and then the S02 is catalytically oxidized to S03 and converted to sulfuric acid by the WSA process. Developed by Haldor Topsoe and first operated at a power station in Denmark in the 1990s. 

WSA [Wet gas sulphuric acid] A process for recovering sulfur from flue-gases and other gaseous effluents in the form of concentrated sulfuric acid. It can be used in conjunction with the SCR process if oxides of nitrogen are present too. The sulfur dioxide is catalytically oxidized to sulfur trioxide, and any ammonia, carbon monoxide, and carbonaceous combustibles are also oxidized. The sulfur trioxide is then hydrolyzed to sulfuric acid under conditions which produce commercial quality 95 percent acid. Developed by Haldor Topsoe 15 units were commissioned between 1980 and 1995. See also SNOX. 

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