Chemical looping combustion of ultra low concentration of methane with Fe2O3/Al2O3 and CuO/SiO2

Abstract

This study examines the performance of two metal oxide species in oxidizing ultra low concentration of methane (below 1% in volume). The focus on low methane concentrations are driven by its practical importance in applications such as abatement of ventilation air methane (VAM) in mining operations. Two mixed metal oxides, Fe2O3/Al2O3 and CuO/SiO2, were selected as oxygen carriers and prepared using dry impregnation method. The metal oxide loading contents are found to be 45wt% and 48wt%, respectively. The redox reactivity of the selected oxygen carriers were studied at various methane concentrations (i.e., 0.1%, 0.5% and 1% in volume) and temperatures between 873K and 1073K using a thermogravimetric analyzer. At low methane concentrations and low temperatures (below 1073K) the conversion of Fe2O3 to Fe3O4 showed higher reduction reactivity than the reduction of CuO to Cu. The redox reactivity of Fe2O3/Al2O3 was also found to be quite stable even after 60 redox cycles at 1073K. The respective weight percentages for oxidation and reduction were found to be 100% and 96.67%, corresponding to a full oxidized state Fe2O3 and a reduced state between Fe3O4 and FeO respectively. Moreover, the results for the global reactivity of reduction and oxidation (calculated at X=0.5) showed that the reduction rates were temperature and concentration dependent, varying from 0.14%/s to 2.2%/s over the range of temperatures and methane concentrations of interest. The oxidation rates were much higher than their reduction counterpart. The values varied from 8.95%/s at 873K to 10.65% at 1073K.