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

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