Fragmentation behavior of single coal particles in a fluidized bed

Abstract

The fragmentation behavior of single coal particles has been studied in a small scale fluidized bed for a Kentucky No. 9 bituminous coal. A typical coal particle fragments and swells slightly during devolatilization, producing particles in two distinct size regimes. Although the fragmentation pattern varies from particle to particle, the bimodal mass-based char size distribution obtained for the pyrolysis of a collection of coal particles was found to be little influenced by changes in bed temperature (1023–1123 K), oxygen concentration (0–10%), and coal particle size (2.2–6.2 mm). During oxidation of single coal particles, the dramatic increases in burning rate following particle breakup made it possible to infer fragmentation from the carbon dioxide concentration variation with time of the gas effluent. The number and size of the coal fragments were determined by fitting the CO 2 data with the predictions of a char combustion model. Swelling and fragmentation contribute to an approximately twofold reduction in the average burning time at the experimental conditions studied.