An Improved Form of Shrinking Core Model for Prediction of the Conversion during Reduction Process in Chemical Looping Combustion

The chemical looping combustion (CLC) process involves the combustion of gaseous fuel through heterogeneous chemical reaction with the oxygen carriers, usually granular metal oxides, in the fluidized bed fuel reactor. It has been recognized that the reaction kinetics of granular metal oxide in the fuel reactor affects the gas-solid flow behavior significantly. This work explores the improvement in one of the most widely adopted kinetic models describing the reduction kinetics, the "chemical control shrinking core model", in which oxide oxygen carriers are assumed to consist of spherical particles. In the analysis, the effects of gas diffusion in the product layer and geometrical irregularity of the oxygen carrier particles on the reaction kinetics are negligible. The work presented in this paper attempts to account for the effects of the gaseous reactant diffusion and particle shape on reaction kinetics by modifying the kinetic model so as to achieve better prediction of the conversion rate in the reduction for the oxygen carriers. The nondimensional form of the derived kinetic model is also discussed. A semiempirical relation is proposed to account for the effect of diffusion changes on the conversion during the reaction. The modeling results have clearly shown that inclusion of the gas diffusion in porous particles can provide better prediction of the reaction kinetics, especially the time for the complete conversion. The shape factor also has a noticeable influence on the conversion rate of oxygen carriers and the time for complete conversion.