Kinetic analysis and model evaluation for steam co-gasification of coal-biomass blended chars using macro-TGA

Abstract

A macro-thermobalance (macro-TGA) was applied to investigate the steam co-gasification characteristics of the chars produced from Huainan coal (HN), two types of biomasses, sawdust (SD) and wheat straw (WS), and coal-biomass blends at 900–1200 °C under rapid heating conditions. The gasification reaction kinetics were determined by the homogeneous reaction model (VM), shrinking core model (SCM) and random pore model (RPM), and the optimal model was selected by deviation calculation. The results show that the char gasification reactivity increased with the increase of temperature. The promotion effect of biomass semi-coke on coal char mainly occurred in the stage when the carbon conversion rate was greater than 0.5, which is mainly attributed to the migration of active AAEMs to the surface of coal char to catalyze the gasification reaction in the later stage. However, with the increase in temperature, this promoting effect is weakened due to the increasing influence of mass transfer effects over chemical rate control, and increased volatilization of the inorganic species. The RPM model is suitable for describing the coal char gasification process, while the SCM was the model that best fitted the biomass semi-coke and coal/biomass blends, which elucidates the kinetic mechanisms governing the gasification process.