Rapid devolatilisation of Yallourn brown coal at high pressures and temperatures

A pressurised drop-tube furnace was used to study the devolatilisation behaviour of Yallourn brown coal. Coal particles of 37-53 mu m size were devolatilised at pressures of 100, 500 and 1000 kPa. The experiments were carried out at temperatures of 873, 1073 and 1273 K. Residence times were varied from 0.02 to 3 s. Weight loss was calculated based on ash as a tracer. The maximum weight loss due to devolatilisation is temperature and pressure dependent. At a particular residence time and pressure, the weight loss increases with an increase in devolatilisation temperature. Increasing the pressure not only increases the residence time required to achieve a given level of weight loss, but also reduces the total weight loss attainable at a particular temperature. Weight loss due to devolatilisation was fitted by a 2-stage first-order kinetic expression. The calculated kinetic parameters are considerably lower than the reported parameters for lignites and bituminous coals. It appears that initial devolatilisation of Yallourn brown coal is mainly dominated by very low activation energy. Variation of activation energy with the level of devolatilisation was observed. This variation could be partially due to the presence of active sites in the char with different characteristic reactivities. (C) 1998 Elsevier Science Ltd. All rights reserved.