Investigation of the reaction mechanism for supercritical H2O/CO2 gasification of coal

Under the dual background that oxidation reaction is used as internal heat source for supercritical water gasification and CO2 utilization, the exploration of supercritical H2O/CO2 gasification reaction mechanism is conducive to the promotion of new gasification technology. Based on the active site mechanism and pore structure, the reaction mechanism of the supercritical H2O/CO2 gasification of coal at 550–650 °C is revealed. The results showed that CO2 and H2O were competition mechanism in the supercritical H2O/CO2 gasification process, in which the addition of CO2 would lead to the decrease of carbon gasification efficiency from 25.7 % to 20 %, but the appropriate amount of CO2 (initial CO2 coefficient N = 0.5) would increase the CH4 yield to 10.64 mol/kg. Therefore, the moderate amount of CO2 (N = 0.5) will promote the transfer of hydrogen element from the water phase to the gas phase, but the addition of excessive CO2 (N = 1) will lead to the transfer of hydrogen element from the gas phase to the water phase, oil phase and solid phase; the addition of CO2 will inhibit the aromatization process of coal, lead to the aggravation of the disorder degree of gasification residue, and CO2 is not conducive to pore development, which will reduce the pore surface roughness and enhance the homogeneity of pore structure. When the high-pressure pyrolysis temperature is 500 °C, the hydrogen yield of Char500 is higher and the maturity of organic matter in the gasification residue is higher.