Combined cycles (combinations of a gas turbine and a steam bottoming cycle) are an efficient power generation technology, while coal is the lowest-cost fuel. The combination of Coal Gasifiers and Combined Cycles therefore is predicted to be the lowest-cost source of baseload electric power in the next decade. In a GCC, the sulfur and particulates are removed from the gasifier gases before they enter the turbine combustor. While H2S (and COS/CS2) can be removed effectively by cooling hot gases down to near room temperature and scrubbing them with an aqueous amine solution, removing the H2S without cooling the gases (i.e., hot gas cleanup) is more advantageous. The leading hot gas sulfur absorbent uses a regenerable zinc oxide- (ZnO) based sorbent to remove the H2S and other sulfur compounds from the hot coal gases. The zinc absorbs H2S, forming zinc sulfide (ZnS); ZnS is then regenerated with oxygen (air), releasing the sulfur as a concentrated stream of SO2. The SO2 can be converted into sulfuric acid, sulfur, or reacted with calcium carbonate to form calcium sulfate (gypsum). The sorbent may be operated in a fluidized bed reactor, transport reactor, or moving bed reactor. TDA Research, Inc. (TDA) is developing sorbents suitable for moving-bed and other types of reactors. Under one contract, TDA is evaluating 3 to 5 mm sized sorbents for moving bed reactors ('A Long Life ZnO-TiO2 Sorbent'); under a second contract ('A Novel Desulfurization Sorbent') we are evaluating 50 to 400 micron sized sorbents suitable for fluidized bed or transport reactors. In this paper we discuss the application to the Moving-Bed reactor. A schematic of a moving bed system with the production of sulfuric acid from the SO2 is shown in Figure 1. Two reactors are utilized with the sorbent moving between the absorber and regenerator. The particle size is large (i.e., 3 to 5 mm = 3000 to 5000 micron).
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