| Abstract |
Combined cycles (combinations of a gas turbine and a steam bottoming cycle) are the most efficient power generation technology, while coal is the lowest cost fuel. Therefore, the combination of Coal Gasifiers and Combined Cycles 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 combuster. While H(sub 2)S (and COS/CS(sub 2)) can be removed effectively by cooling hot gases down to near room temperature and scrubbing them with an aqueous amine solution, removing the H(sub 2)S 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, zinc titanate (Zn(sub 2)TiO(sub 4) and/or ZnTiO(sub 3)), to remove the H(sub 2)S and other sulfur compounds from the hot coal gases. The zinc absorbs H(sub 2)S, forming zinc sulfide (ZnS); ZnS is then regenerated with oxygen (air), releasing the sulfur as a concentrated stream of SO(sub 2). The SO(sub 2) 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. Both the fluidized-bed and the transport reactor use two separate reactors; one absorbs H(sub 2)S COS and CS(sub 2) and converts the ZnO to ZnS; the second bed regenerates the sorbent with air converting the ZnS back to ZnO and producing SO(sub 2); the sorbent moves between the two reactors to carry sulfur out of the absorber and return regenerated sorbent. Fluidized bed and transport reactors circulate very small particles at high gas velocity. The high gas-solid contact area of very small particles rapidly transfers both heat and mass within the reactor. The fluidized bed and transport reactor hot gas cleanup desulfurization systems are very similar and the sorbent particles are also of the same size (i.e., 50 to 400 micron). While there are several differences between the two reactors, the one which most affects the sorbent is the operation of the regenerator: fluidized bed reactors operate with diluted air while transport reactors operate with undiluted air. |
