Hot gas desulphurisation with dolomite sorbent in coal gasification

Gasification technologies are among the most promising electrical power generation options both from an environmental and efficiency point of view, as they allow efficient, environmentally-friendly use of national coal, as well as other carbonaceous materials mixed with coal, including high sulphur by-products. During gasification, sulphur is converted mainly into H2S and secondly into COS, and control of these has been researched using several H2S adsorbents. The aim of this paper was advanced removal of these compounds. Dolomite, which reacts with H2S to yield calcium sulphide, was chosen from among several earth-alkaline compounds for research due to its properties and low cost in reducing the presence of H2S in coal gasification. Tests were carried out using dolomite from Granada, Spain, with this sorbent used without blending and with amounts of 100 g and 150 g in each test. The dolomite was sulphurized using a mixture of gases that simulates the gasification gas. The influence of sulphurisation conditions such as gas velocity, bed length, grain size, gas temperature, and gas composition were investigated. The solid products obtained were characterised by X-ray diffraction and chemical analysis. The behaviour of COS that normally accompanies H2S in gasification gases was investigated and found to follow a breakthrough curve similar to H2S, With equilibrium existing between the COS destroyed due to reaction with hydrogen and by hydrolysis and the COS formed by reaction of CO2 with H2S. Hence, its content in outlet gases is a function of the composition of this gas, especially in terms of CO2, H2S and H2O. The accelerating effect of sulphurised dolomite on the rate of the reverse water-shift reaction was demonstrated. (C) 2008 Elsevier Ltd. All rights reserved.