Experimental investigation of some metal oxides for chemical looping combustion in a fluidized bed reactor

Chemical looping combustion (CLC) is the process in which metal oxides, rather than air or pure oxygen, supply the oxygen required for combustion. In this process, different gaseous fuels can be burnt with the inherent separation of CO2. The feasibility of the CLC system depends greatly on the selection of appropriate metal oxides as oxygen carriers (OC). In this study, NiO–NiAl2O4, Cu0.95Fe1.05AlO4, and CuO–Cu0.95Fe1.05AlO4 were tested experimentally in a fluidized bed reactor as a function of oxidation–reduction cycles, temperature, bed inventory and superficial gas velocity. The results showed that flue gases with a CO2 concentration as high as 97% can be obtained. The flue gases should be suitable for transport and storage after clean-up and purification. With an increase in the bed inventory or a decrease in superficial gas velocity, the flue gas characteristics improved i.e. more CO2 and fewer secondary components or less unreacted fuel were obtained. Carbon formation could occur during the reduction phase but it decreased with an increase in temperature and inventory and could be completely avoided by mixing steam with the fuel. The reactivity of NiO/NiAl2O4 was higher than the Cu- and Fe-based oxygen carriers. Increasing the CuO fraction in the oxygen carrier led to defluidization of the bed during the reduction and oxidation phases.