Early-stage kinetics and char structural evolution during CO2 gasification of Morupule coal in a wire-mesh reactor

Abstract

Understanding the intrinsic gasification kinetics and structural evolution of char is crucial in the effective design of industrial gasifiers. This work studies the kinetics of Morupule coal gasification in atmospheric pressure CO2 at isothermal temperatures of 900–1050 °C using a rapid heating wire-mesh reactor (WMR). The gasification reaction order was determined by varying the concentration of CO2 in the reactor atmosphere. The bulk chemical structure and surface chemistry of the early-stage residual chars were characterised using Raman and X-Ray photoelectron spectroscopy, respectively. Gasification reaction rates were significantly higher than those presented in published literature with an activation energy of 320 kJ mol−1 and a pre-exponential factor in the order of 1010 s−1. In a chemical reaction controlled kinetic regime, the reaction order was found to be zero and increased to 0.6 in a mixed chemical reaction plus pore diffusion controlled kinetic regime. The bulk chemistry of the chars was largely unaffected by CO2 in the conversion range studied. However, surface chemistry analyses revealed a decrease in the carbon content, through the depletion of CC/CC bonds, resulting in the development of char surface porosity. Residual chars from gasification experiments showed a lower combustion reactivity to those produced under inert pyrolysis conditions. This study provides insights on direct gasification (i.e. no char preparation in a separate pyrolysis stage) for kinetic determinations and a concomitant extensive characterisation of char structural properties.