K2CO3-catalyzed steam gasification of ash-free coal char in a pressurized and vertically blown reactor. Influence of pressure on gasification rate and gas composition

Abstract

The K2CO3-catalyzed steam gasification of ash-free coal char was conducted in a pressurized and vertically blown reactor which was also characterized as a differential reactor. At a typical condition (total pressure, 0.5MPa; steam partial pressure, 0.15MPa; temperature, 750°C; catalyst loading, 10%; superficial gas velocity, 55cms−1), the gasification proceeded so fast that it was completed within 5min. The dependence of either instantaneous gasification rate or average gasification rate on pressure was found to follow the Langmuir-Hinshelwood rate equation and the nth order rate equation, but the parameters for either rate equation varied with the carbon conversion. For a given coal char with a fixed catalyst loading, an overall kinetic model with the constancy of parameters is proposed to predict the gasification rate as a function of steam partial pressure, temperature and carbon conversion. While the elevation of steam partial pressure promoted the methanation mainly via the gas-char reaction, the yield of CH4 was negligible. The gas composition was not in the equilibrium of water gas shift reaction.