Kinetics of steam gasification of nascent char from rapid pyrolysis of a Victorian brown coal

Steam gasification of nascent char from rapid or slow pyrolysis of a Victorian brown coal was performed at 1073-1173 K in a novel drop-tube/fixed-bed reactor, in which steam-containing gas was forced to pass through an extremely thin bed of nascent char particles at sufficiently high velocity and large flux. The nascent char underwent parallel reactions consisting of non-catalytic gasification and catalytic one. The non-catalytic gasification followed first-order kinetics with respect to the fraction of unconverted carbon, and the rate constant was hardly influenced by operating variables such as heating rate for the pyrolysis, total pressure and even period of isothermal heating between the pyrolysis and gasification. The overall activity of inherent catalysts, alkali and alkaline earth metallic species, diminished due to volatilization and intra-particle deactivation, both of which were induced by the gasification. As a result, the catalytic gasification took place within a limited range of the char conversion up to 60-80%. The initial catalyst activity and the kinetics of activity loss largely depended on the operating variables as above and also partial pressure of steam.