EFFECTS OF CALCIUM, STRONTIUM, AND BARIUM AS CATALYSTS AND SULFUR SCAVENGERS IN THE STEAM GASIFICATION OF COAL CHARS

Effects of alkaline earths on the steam gasification of two coal chars, one of low and one of high intrinsic reactivity, were evaluated gravimetrically. The chars were derived from coal powders which had been impregnated with Ca, Sr, or Ba, pelletized, and pyrolysed in nitrogen. The additives increased the gasification rates in the order Ca < Sr < Ba. It follows from reaction kinetics that catalysis is caused by a large increase in the density of reaction sites, not by a lowering of the true activation energy. As shown by electron micrographs and elemental maps obtained by X-ray analysis, the strong catalytic effect is closely associated with the ability of the alkaline-earth species to spread over the char and to preserve contact with a freshly formed carbon surface as the gasification proceeds. The alkaline-earth catalysts are severely poisoned by hydrogen sulphide or sulphur dioxide from an external source. © 1979.