CFD modelling of the thermal degradation of biomass in fluidized beds

Abstract

Pyrolysis is considered as a promising technology of recovering bioenergy from biomass into gas, liquid and solid fuels. A series of works have been carried out previously on the fundamentals and the decomposition mechanism of pyrolysis empirically. Based on these experimental works, numerical approaches are employed to achieve a better understanding of the pyrolysis mechanism or aid the applications in experimental and industrial area.In order to construct a systematic model of the thermochemical processes in biomass pyrolysis in a fluidized bed, the mass and heat transfer processes are investigated by two sub-subjects: modelling of the heat exchange between an immersed tube and a fluidized bed; modelling of mixing-segregation phenomena of binary mixture loaded in a fluidized bed as bed materials. Based on the finished studies, two reacting beds are represented by Eulerian approaches. The fast pyrolysis and catalytic pyrolysis of biomass is modelled by incorporating the corresponding kinetic schemes into the mass and heat transfer processes. The relevant models, coefficients and functions are tested and discussed for the sensitivity and the simulation results show qualitative consistence with the existing experimental works. The general model for thermochemical processes of biomass in the fluidised beds is built up in the present work successfully. The entire structure and methods can be introduced into other applications but not limited to biomass pyrolysis. The further optimization based on this model can be a useful tool on design of a large-scale pyrolyzor.<br/