Investigation into kinetic compensation effects for the production of hydrogen-rich gas during gasification of sub-bituminous coal char in varying gas environments

Abstract

This study has focused on the evolution of kinetic parameters, i.e., Eapp and lnAapp and kinetic compensation effects (KCE) of char consumption and CO, CO₂, and H₂ formation during gasification of Collie coal char in varying gas environments (15%H₂O–Ar, 8%H₂O–Ar, and 0.4%O₂+8%H₂O–Ar). The instantaneous rate was obtained continuously during experiments by measuring the product gas composition using a quadrupole mass spectrometer. Observed variations of Eapp, lnAapp, and the extent of KCE suggest that the decrease in steam partial pressure from 15%H₂O to 8%H₂O surrounding the coal char particles appears to affect the path of CO₂ and H₂ formation from surface water-gas shift (WGS) reaction in 15%H₂O–Ar to char-H₂O heterogeneous reaction in 8%H₂O–Ar, at higher conversion (conversion >0.5). However, H₂ formation displays strong KCE and increased H₂ molar flux in 0.4%O₂+8%H₂O–Ar when compared to gasification of char with steam only (8%H₂O–Ar and 15%H₂O–Ar). In contrast, the introduction of 0.4%O₂ to 8%H₂O–Ar dominates the char gasification with only consumption of carbon active sites present on the char surface. That resulted in weak KCE for char consumption and decreased CO/CO₂ (molar flux ratio) compared to the gasification of char in 15%H₂O–Ar and 8%H₂O–Ar. Furthermore, the results indicate that the residual char obtained from the faster diffusion-controlled char-O₂ heterogeneous reaction in the 0.4%O₂+8%H₂O–Ar acts as an activated char precursor for subsequent kinetics-controlled char-H₂O heterogeneous reactions. This enhances the migration of H radicals generated from the H₂O molecule to the inner char matrix in 0.4%O₂+8%H₂O–Ar with an increased H₂ formation rate than gasification of char with steam only.