Ash and slag qualities of Australian bituminous coals for use in slagging gasifiers

The suitability of Australian bituminous coals from an ash and slagging vie wpoint, has been examined for use in entrained-flow slagging gasifiers whic h form the basis for more efficient power generation technologies based on integrated gasification-combined cycle (IGCC). Several coal deposits in bot h NSW and Queensland appear suitable for slag tapping without the addition of any flux, Many more thermal coals are shown to require a limestone flux addition of <3% CaCO3 by weight of coal and there could well be opportuniti es to reduce costs of flux addition by blending with other coals with lower ash fusion temperatures. Coal blending to yield a SiO2/Al2O3 ratio of 1.6- 2.0 can minimise limestone flux requirements and avoid some limitations whi ch arise from slag crystallisation. Limestone flux requirements can also be reduced by slag tapping at 1500 degrees C rather than 1400 degrees C, but this should be balanced against increased operating costs and losses in col d gas efficiency at higher gasification temperatures. Australian export coa ls with very low iron contents, after limestone flux addition, appear to ha ve the potential advantage that slag viscosities (and hence slag tapping pe rformance) are essentially independent of variability in coal ash compositi on. This should lower gasifier operating and maintenance costs, offsetting the costs of flux addition. Ash and slag characteristics and possible strat egies for optimum coal use in entrained-flow slagging gasifiers are discuss ed. (C) 2000 Elsevier Science Ltd. All rights reserved.