Effect of oxidation and other treatments on hydrogasification rate of coal char

Abstract

Hydrogasification of coal and other chars is a much slower process than steam or carbon dioxide gasification; moreover, the rate of gasification in pure hydrogen decreases sharply with conversion for most carbons. To better understand and overcome this rate behaviour, the effects of oxidation (partial burnoff in air at 375 °C), demineralization, heat treatment at 1000 °C, and K 2CO 3 addition on hydrogasification rate of Illinois No. 6 coal char and Saran char are investigated. Oxidation of partially hydrogasified or heat-treated chars results in up to a threefold increase in subsequent hydrogasification rate; the enhancement propagates for 5–10% conversion following oxidation. Partial burnoff prior to hydrogasification enhances the rate by only about 30% for 1–2% additional conversion. Addition of potassium carbonate catalyst eliminates the decay in rate for mineral-free chars. Oxidation and addition of catalyst enhance the rate of hydrogasification either by removing strongly chemisorbed hydrogen or by generating surface structure active in hydrogasification.