Abstract
Burning rates for pulverized coal chars prepared by a variety of thermal and chemical pretreatments from three US low-rank coals are reported for gas temperatures from 760 to 1270 K. The combustion of individual particles was observed in a laminar flow reactor with very dilute suspension loadings. Overall combustion rates were inferred from measured temperatures of individual particles (1329 to 1825 K), and were found to exceed the diffusion-limited rates based on conversion to CO at oxygen concentrations below 12%. The extreme reactivity is rationalized by diffusion-limited conversion of carbon to both CO and CO 2. Model predictions satisfactorily depict changes with size, ambient gas temperature and oxygen concentration, and yield an activation energy difference for CO CO 2 selectivity of 271 KJ mol −1. It is suggested that conversion to CO 2 at the char surface arises from catalytic impurities in the char.
Published Version
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