Bimetallic Chemical Looping Gasification with Oxygen Uncoupling –Feasibility Study and Process Analysis

In a typical chemical looping gasification (CLG) process, an iron oxide based oxygen carrier is used to indirectly convert carbonaceous fuels into separate streams of sequestrable CO₂, hydrogen, and heat/electricity. Although the novel process concept has the potential to be both clean and efficient, the reactions between the oxygen carrier particles and fuels are often kinetically limited, especially when solid fuels such as coal and/or biomass are used. In order to enhance the rates of the aforementioned reactions, it is proposed that a secondary metal oxide be incorporated to the iron oxide based oxygen carrier. For instance, when copper (II) or manganese (III/IV) oxide is used as the secondary metal oxide, molecular oxygen can be released from the bimetallic oxygen carrier through “oxygen uncoupling”, i.e. decomposition of the secondary metal oxide at high temperature. As a result, both the in-situ solid fuel gasification and iron oxide reduction reactions can be kinetically promoted. The present study explores the technical feasibility of this novel bimetallic CLG process concept. A potential configuration for the bimetallic CLG process is first proposed. This is followed by thermodynamic analysis of key reactors to arrive at the maximum fuel and oxygen carrier conversions considering thermodynamic equilibrium limitations. Finally, ASPEN Plus® simulation is carried out to evaluate the energy conversion efficiency of the bimetallic CLG process. Preliminary kinetic data for coal char conversion with bimetallic oxygen carrier are also presented. The present study indicates that the incorporation of the oxygen uncoupling metal oxide has the potential to enhance the fuel and oxygen carrier conversions without adversely affecting the overall efficiency of the CLG process.