Numerical evaluation and optimization of volatiles distributors with different configurations for biomass chemical looping combustion

Abstract

The rapid devolatilization of biomass in chemical looping combustion could form a local plume of volatiles, reducing contact between volatiles and oxygen carriers and thus lowering gas conversion. Hence, a novel concept called volatiles distributor (VD) has been recently proposed to enhance the mixing between the volatiles and oxygen carriers. However, the configurations of VD have significant effects on its performance. To optimize the configurations of VD, the impact of VD with different configurations has been investigated with respect to the mixing behaviors and the pathways of volatiles in this work using computational fluid dynamics (CFD) modeling with an Eulerian-Eulerian two-fluid model coupled with a two-step EMMS/bubbling drag model. Comparison to experimental results from a cold-flow fluidized bed demonstrates that the CFD model can provide quantitative predictions for the vertical pressure profiles and reasonable trends of horizontal gas distributions of the fluidized bed under various conditions. Conditions varied were the superficial gas velocity, the percentage of the simulated volatiles, primary air distributor, and configurations of VD. The CFD simulations of both original and new designs reveal that the performance of the VD can be improved by reducing the open area of the distribution holes of the VD near the injection port and increasing it further away from the injection port. An optimal configuration is proposed to achieve an even distribution of volatiles and avoid the leakage of volatiles from the bottom of the VD.