Utilization of ventilation air methane as an oxidizing agent in chemical looping combustion

Abstract

Release of fugitive methane (CH4) emissions from ventilation air in coal mines is a major source of greenhouse gas (GHG) emissions. Approximately 64% of methane emissions in coal mine operations are the result of VAM (i.e. ventilation air methane) which is difficult for use as a source of energy. A novel ancillary utilization of VAM was thereby proposed. In this proposal, the VAM was utilized instead of air as a feedstock to a chemical looping combustion (CLC) process of coal. In this case, Fe2O3/Fe3O4 particles were shuttled between two interconnected reactors for combustion of syngas produced by an imbedded coal gasifier.The effect of VAM flow rate and methane concentration on the performance of CLC was analyzed thermodynamically using Aspen Plus software. Results indicated that the variations of air reactor temperature with VAM flow rate and methane concentration can be minimized as expected. The effect of temperature and inlet methane concentration on the conversion of CH4 was examined experimentally in a fixed bed reactor with the presence of particles of Fe2O3/Al2O3. Not surprisingly, the reaction temperature put a significant influence on the conversion of CH4. The conversion started at the temperature about 300°C and the temperature to achieve full conversion was around 500°C while the temperature in empty reactor between 665°C and 840°C. This is due to the catalytic effect of oxygen carriers (i.e. Fe2O3/Al2O3) on the conversion of methane. Moreover, it was observed that the methane conversion rate decreased with the increase in inlet methane concentration while increasing with Fe2O3 loading content.