A mathematical model of in-bed char combustion of Australian coals in PFBC

Abstract

Thermoplasticity for coal blends of Goonyella high-coking coal and Witbank slightly coking coal was evaluated by dynamic viscoelastic technique using a temperature-variable rheometer. As the weight ratio of Witbank coal in the blend increases, the thermoplasticity at a heating rate of 3 °C/min apparently decreased, compared to that for Goonyella coking coal alone. In the case of 30 wt.% Witbank coal, it still showed a sufficient thermoplasticity to form coke. In contrast, for the 50:50 blend, its thermoplasticity significantly decreased and was almost the same as Witbank coal alone, indicating that Witbank coal has any negative effect for thermoplasticity of the blends with Goonyella coal. However, when the 50:50 blend was rapidly heated (80 °C/min), the thermoplasticity was found to be enhanced greatly, compared to calculated one. Therefore, rapid heating is suggested to be effective to convert such blends into good coke, and this measurement technique was found to be useful to evaluate thermoplasticity of coals and blends under rapid heating as well as slow heating. The dependence of heating rate on thermoplasticity of coking coal was also investigated. As the heating rate increased, the maximum fluidity greatly increased and its temperature shifted to a higher value, while no significant changes in softening temperatures were observed.