Minimisation of calcium sulphide in gasification residues by combustion in a circulating fluidized bed

摘要

Successful development of the CFBC component of the Air Blown Gasification Cycle (ABGC) requires that residues from the partial gasification of coal are burned efficiently and with environmentally acceptabel emissions for both flue gas and solid ashes. The aim of this study was to minimise the amount of residual calcium sulphide (CaS) in the ash; this compound can release H_2S gas on exposure to moisture, which makes ash disposal more difficult. The CaS can be converted by oxidation to more stable CaSO_4. Tests have been carried out using a 100 kW CFBC test facility. The excess air level, degree of air staging and bed temperature were varied to establish the best operating conditions to minimise CaS in the ash while giving good combustion performance. Very high conversion of CaS to CaSO_4 was achieved when dolomite sulphur sorbent had been used in the pressurised gasification process. Two dolomites were tested and gave similar results. Less than 1percent of the sulphur in the CFBC ash was present in the form of CaS. The degree of conversion was not affected by the combustion conditions.