A Novel Ancillary Utilization of Ventilation Air Methane as the Substitute of Air in Chemical Looping Combustion

摘要

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).A novel ancillary utilization of VAM was thereby proposed.In this proposal,the VAM was utilised instead of air as a feedstock to a chemical looping based process for combustion of coal.In this process Fe2O3/Fe3O4 particles were shuttled between two interconnected reactors for combustion of syngas produced by an imbedded coal gasifier.The effect of substituting air with VAM in chemical looping combustion was evaluated thermodynamically in this study.Especially the effect of VAM flow rate and methane concentration on the air reactor temperature,overall efficiency and CO2 capture rate was analyzed using Aspen Plus software.Results indicate that the air reactor temperature was decreasing quickly with the VAM flow rate while increasing slowly with the methane concentration as expected.The overall efficiency increased dramatically with the flow rate of VAM and decreased slightly with the methane concentration.It was also realized that an increase in either the flow rate or methane concentration led to a decline in the CO2 capture rate.The combustion of VAM in the presence of oxygen carriers(i.e.Fe2O3/Al2O3)was studied experimentally in a fixed bed reactor.The particles of Fe2O3/Al2O3 were made by the method of dry impregnation.The effect of temperature and inlet methane concentration on the conversion of CH4 was examined.Not surprisingly,the reaction temperature put a significant influence on the conversion of CH4.The conversion started at the temperature about 300oC and the temperature to achieve full conversion was around 500oC,while the combustion of VAM in empty reactor was at temperatures of between 665oC and 840oC.This is due to the catalytic effect of the oxygen carriers(i.e.Fe2O3/Al2O3).Moreover,it was observed that the methane conversion rate was decreasing with the increase in inlet methane concentration while it is increasing with Fe2O3 loading content.