The effects of fragmentation on devolatilization of large coal particles

Abstract

Spherical coal particles (5 to 12 mm diameter) from three Australian bituminous coals were devolatilized in an inert atmosphere of nitrogen at 850 °C, using a specially designed thermogravimetric rig based on an electrically heated stainless steel tubular reactor. Weight loss histories of the coal particles were recorded and the simultaneous concentrations of gases evolved were determined chromatographically. It was concluded that the particle size had no effect on the ultimate yields of gas, tar plus water and char. Tar was the major volatile component and evolved before the gaseous volatiles. Therefore, it is recommended that the devolatilization time should be measured as the time for 95% of the ultimate weight loss, rather than the time for 95% of the ultimate gaseous volatiles yield. Fragmentation of the coal particles, which varied with different coals depending on the coal plasticity, occurred early in the devolatilization process and increased the rate of devolatilization and decreased the devolatilization time. The increase in devolatilization time correlated with particle diameter by an empirical equation t v = Ad p n for each coal. Comparison of the data with previous work using a fluidized bed reactor showed that the devolatilization time was shorter in the fluidized bed because of a greater degree of fragmentation.