DESULFURIZATION OF HOT COAL-GAS IN FLUIDIZED-BED WITH REGENERABLE ZINC TITANATE SORBENTS

Integrated gasification combined cycle (IGCC) power generation process es are considered to be among the most attractive technologies for the 21st century. In such processes, solid fuels such as coal are gasifie d at pressure and the fuel gas is cleaned and combusted in the gas tur bine. The gas cleanup is necessary not only for the protection of the gas turbine hardware, but also to comply with environmental regulation s. In the so-called ''simplified'' IGCC process, the fuel gas is clean ed at high temperature and pressure to improve the overall cycle effic iency. The hot gas cleanup system being developed by Enviropower Inc., a joint venture of Tampella Power, Inc. (a leading Finnish boiler man ufacturer) and Vattenfall AB (a major Swedish utility), includes a hig h-temperature, high-pressure desulfurization unit and a particulate re moval system. The former comprises two fluidized bed reactors utilizin g regenerable zinc titanate sorbents capable of removing the sulfur ga ses (primarily H2S) to below 50 ppmv. The latter employs rigid ceramic filter elements operating at up to 700-degrees-C and 20 bar and is ca pable of reducing the ''fines'' concentration to an acceptable level f or a gas turbine. Novel regenerable zinc titanate sorbents suitable fo r fluidized-bed application have been tested. The sulfur capture and a ttrition characteristics of these sorbents have been evaluated in exte nsive testing in a bench-scale fluidized-bed reactor operating at high pressure and temperature conditions expected in IGCC operation. Two d ifferent gas mixtures representing air-blown gasifier exit gas with an d without in-situ desulfurization with Ca-based sorbents have been use d. H2S removal efficiencies of higher than 99% at acceptable levels of sorbent conversion have been achieved in all these experiments with m inimal sorbent deterioration.