Evaluation of The Slag Flow Characteristics of Australian Bituminous Coals in Slagging Gasifiers

The suitability of Australian bituminous coals from an ash and slagging viewpoint, has been confirmed for use in entrained-flow slagging gasifiers which form the basis for more efficient power generation technologies based on integrated gasification - combined cycle (IGCC). A number of coals appear suitable for IGCC use without the addition of any flux. About half the coal samples examined are shown to require a limestone flux addition of <3% CaCO3 by weight of coal at a tapping temperature of 1450oC. Such coals would appear suitable for use in blends with other coals. Blending of Australian high ash fusion coals with other low ash fusion coals can reduce or eliminate the need to add a limestone flux. Slag viscosity versus temperature data has been obtained for the reference coals of the CRC for Black Coal Utilisation. The efficacy of coal blending has been demonstrated for reducing flux requirements and overcoming limitations which can arise from slag crystallisation. In addition two ways to reduce temperatures of critical viscosity have been demonstrated: add more fluxes (limestone, dolomite or iron oxides) or increase the SiO2/Al2O3 ratio to be >1.8-2.0. A number of empirical viscosity models have been developed for Australian coal ash slags in the range 10-15% FeO. A method of relative Coal Value Modelling is presented and applied for economic optimisation of limestone flux addition and gasification temperature. It remains to further develop this IGCC Coal Value Model, covering reactivity and slagging aspects, for the three main generic entrained-flow gasifiers. This will allow an improved economic ranking of the suitability of a particular coal for use in the different IGCC processes.