97/02020 A financial analysis of using sawmill residues for cogeneration in Northern Ontario

Abstract

Integrated gasification combined cycle (IGCC) power generation processes are considered to be among the most attractive technologies for the 21st century. In such processes, solid fuels such as coal are gasified at pressure and the fuel gas is cleaned and combusted in the gas turbine. The gas cleanup is necessary not only for the protection of the gas turbine hardware, but also to comply with environmental regulations. In the so-called “simplified” IGCC process, the fuel gas is cleaned at high temperature and pressure to improve the overall cycle efficiency. The hot gas cleanup system being developed by Enviropower Inc., a joint venture of Tampella Power, Inc. (a leading Finnish boiler manufacturer) and Vattenfall AB (a major Swedish utility), includes a high-temperature, high-pressure desulfurization unit and a particulate removal system. The former comprises two fluidized bed reactors utilizing regenerable zinc titanate sorbents capable of removing the sulfur gases (primarily H2S) to below 50 ppmv. The latter employs rigid ceramic filter elements operating at up to 700°C and 20 bar and is capable of reducing the “fines” concentration to an acceptable level for a gas turbine. Novel regenerable zinc titanate sorbents suitable for fluidized-bed application have been tested. The sulfur capture and attrition characteristics of these sorbents have been evaluated in extensive testing in a bench-scale fluidized-bed reactor operating at high pressure and temperature conditions expected in IGCC operation. Two different gas mixtures representing air-blown gasifier exit gas with and without in-situ desulfurization with Ca-based sorbents have been used. H2S removal efficiencies of higher than 99% at acceptable levels of sorbent conversion have been achieved in all these experiments with minimal sorbent deterioration.