Simulation of multiphase reacting flows in fluidized beds

Abstract

Recent growing interest to utilize fluidized beds for conversion of coal and biomass into fuel calls for detailed investigations to gain a better understanding of interactions between mass and heat transport and heterogeneous chemical reactions in gas-solid flows. The traditional approach to design a fluidized bed reactor involves comprehensive experimentations, progressing from laboratory bench-scale units, to pilot devices and finally, to full-scale reactors. However, there are many uncertainties in such scale-up procedure that often result in decrease in performance of the full-scale reactor. Computational fluid dynamics (CFD) has proven to be a promising alternative to analyze gas-solid flows in realistic fluidized bed configurations. Detailed understanding obtained from CFD can facilitate development and optimization of fluidized bed gasifiers by reducing the time and cost associated with design sequences. A major challenge in quantitative prediction of fluidized beds is, however, associated with realistic and affordable consideration of heterogeneous finite-rate chemical kinetics. In this study, a systematic approach is taken to efficiently implement heterogeneous reaction mechanisms in multiphase flows. A time-splitting scheme is employed to handle the chemistry calculations separately via an efficient custom chemistry solver. The accuracy and efficiency of this approach is assessed by numerical simulation of silane pyrolysis and coal combustion in a fluidized bed reactor. Results show good agreements with those generated in previous studies. After establishing the efficiency and performance of the solver, it will be employed to study catalytic gasification of coal-biomass in fluidized bed gasifiers.