Volatilisation of alkali and alkaline earth metallic species during the gasification of a Victorian brown coal in CO2

A Victorian brown coal was gasified in a bench-scale quartz fluidised-bed/fixed-bed reactor in order to study the volatilisation of Na, Ca, and Mg during devolatilisation and gasification and their roles in the reactivity of chars. It was found that the majority of Na was volatilised at 900 °C under all conditions and that a Na retention limit was achieved in the char with the progress of CO2 gasification. In some cases, the presence of CO2 during devolatilisation enhanced the Na retention in the char. In contrast, the retention of Ca (and Mg) was unaffected by CO2 during devolatilisation at 900 °C but decreased drastically upon nascent char gasification. The fundamental differences in volatilisation between the alkali and alkaline earth metallic species are discussed in this paper.