Swelling Behavior of a Chinese Bituminous Coal at Different Pyrolysis Temperatures

Abstract

Pyrolysis experiments were performed in a drop tube furnace at 1373, 1523, and 1673 K to investigate the swelling behavior of a Chinese bituminous coal. Particle size distributions and morphologies of chars prepared from three size-classified fractions of the coal were analyzed by laser diffraction and SEM, respectively. The results show that significant swelling occurs during pyrolysis. It is found that both heating rate and particle size have important effects on coal swelling. For each size fraction used in the present study, the swelling ratio initially increases with increasing heating rate from 5 x 10{sup 3} to 2 x 10{sup 4} K/s, but then decreases when the heating rate further increases to 4 x 10{sup 4}K/s. A maximum swelling ratio is obtained at 2 x 10{sup 4} K/s for all coal samples, indicating that coal particles swell most at this heating rate. At the same temperature, the swelling ratios of the three size fractions are markedly different. It is shown that the finer the particle size, the higher is the swelling ratio. This is considered to be the result of the enrichment of vitrinite in small particles, as observed in this study, and the high volatile yields for them atmore » elevated temperatures. It is also noted that the difference in swelling ratio diminishes with increasing particle size. The results also suggest that fragmentation observed in this study may contribute to reducing swelling ratio. Coal particles with a large size or undergoing a high heating rate have the tendency to fragment violently during pyrolysis, resulting in the decrease of their swelling ratios. 34 refs., 6 figs., 2 tabs.« less