Diffusion effect and evolution of kinetic parameters during coal char-CO2 gasification

Abstract

Large coal char particle (LCC, 12 mm and 20 mm cube) and small coal char particle (SCC, less than 50 μm) were gasified under different temperatures in fixed bed reactor and thermogravimetric analyzer, respectively. The effectiveness factor and kinetic parameters (apparent activation energy and apparent pre-exponential factor) were also calculated to investigate the diffusion effect and the evolution of kinetic parameters during coal char-CO2 gasification. It was found that the internal effectiveness factor was not constant during the conversion process of coal char. In the intermediate and later stage of gasification reaction, there was a remarkable increase for the effectiveness factor. The effectiveness factor of LCC and SCC in the higher temperature range were all much less than 1, this indicated that the gasification of LCC and SCC at high temperature was limited by pore diffusion. Apparent activation energy and apparent pre-exponential factor evolved gradually during the whole conversion process, the existence of diffusion effect would lead to a certain change for the evolution law. A kinetic compensation effect was observed between the apparent activation energy and apparent pre-exponential factor during the conversion process of coal char. When the diffusion effect was very significant, it would have a certain weakening effect on the compensation effect.