Steam gasification rates of 17 kinds of demineralized coals were measured at 787°C by a rapid heating method to clarify the factor controlling the gasification reaction and to present a valid reactivity index. Upon the demineralization, the gasification rates of lower-rank coals (C<ca.80%) decreased largely, whereas those of higher-rank coals (C>ca.80%) changed little. The difference in the reactivity among the demineralized coals was very small, indicating that the intrinsic reactivity changes little with the coal rank. Thus the gasification of the lower-rank coals was found to be catalyzed by the coal minerals. Ca and Na in carboxylate salts were expected to act as effective catalysts for gasification. The pore structure such as surface area and micro pore volume could not be employed as a reactivity index especially for the lower-rank coals. The amount of oxygen trapped by the char, no, which was measured by the flash desorption technique, was expected to be a valid index of gasification reactivity, because no showed fairly good correlation with the gasification rate irrespective of the rank of coals.
