Hydrogen production from coal using coal direct chemical looping and syngas chemical looping combustion systems: Assessment of system operation and resource requirements

Coal direct chemical looping (CDCL) substitutes the gasification process in syngas chemical looping (SCL), thus eliminating the need for higher oxygen consumption. In this study, operating conditions are assessed for CDCL and SCL, directed towards hydrogen production from coal. The main objective is to increase the overall H₂/CO₂ ratio for a given amount of coal, based on the various conditions. The operating variables considered as part of a resource optimization analysis include: (i) inlet conditions to the primary reactors, (ii) minimum resource requirements (air, steam and iron oxide), (iii) hydrogen-to-component ratios, and (iv) effect of coal carrier gas. The results suggest that CDCL has a higher hydrogen-to-CO₂ ratio than SCL along with advantages such as low overall resource requirements (steam and air) and fewer intermediate processes. The coal carrier gas affects the hydrogen production only in the SCL system by altering the composition of syngas induced by gasifier temperature variation.