Evaluation of Australian Bituminous Coals for Advanced Power Generation: Slagging Characteristics for Integrated Gasification

The suitability of Australian bituminous coals from an ash and slagging viewpoint, has been examined for use in entrained-flow slagging gasifiers which form the basis for more efficient power generation technologies based on integrated gasification - combined cycle (IGCC). Several coal deposits in both NSW and Queensland appear suitable for slag tapping without the addition of any flux. Many more thermal coal deposits are shown to require a limestone flux addition of <3% CaCO3 by weight of coal. This should not be economically prohibitive and there could well be opportunities to reduce costs of flux addition by blending with other coals with low ash fusion temperatures. Iron oxides and industrial calcium and iron based fluxes have been shown to be as, or more, effective than limestone and may be more economic in particular locations. The rates of dissolution of CaO and SiO2 have been determined and do not appear to pose operating limitations or problems. Australian very low iron containing export thermal coals, after limestone flux addition, appear to have the unique advantage that slag viscosities (and hence slag tapping performance) are essentially independent of coal ash composition. From the data accumulated during the work a number of empirical viscosity models, which give improved agreement with experimental viscosities, have been developed for Australian bituminous coals. It remains to extend the present work to cover high iron containing coals, to examine coal blending, to cover the full compositional ranges of Australian coal ash slags, and to overcome slag crystallisation problems found for a number of coals.