A theoretical investigation of CLC in packed beds. Part 1: Particle model

The characteristics of the rate of reduction and oxidation that oxygen carrier particles undergo in chemical looping combustion processes are investigated from a theoretical point of view. An advanced numerical model was developed in which the effects of reaction kinetics and internal and external mass and heat transfer processes were incorporated in detail. It was found that with traditional models describing non-catalytic gas–solid reactions, e.g. the shrinking core or the homogeneous model, several important features of the process cannot be thoroughly captured. For the oxygen carrier system studied, it was found that the effect of Knudsen diffusion will usually be far more important than that of molecular diffusion. Finally, suggestions were made for the improvement of the average reaction rate via the implementation of a non-uniform distribution of the active solid material over the particle. With these results, improved understanding of the effect of mass and heat transfer processes on the rate at which oxygen carriers are reduced and oxidized has been obtained, which is essential for predicting the performance of CLC processes at larger scales.