CFD modelling of biomass catalytic fast pyrolysis in bubbling fluidized reactor: effects of catalyst parameters on process performance

Abstract

In this study, a CFD mathematical model has been developed for catalytic fast pyrolysis (CFP) of biomass based on multi-phase flow, transfer process and biomass pyrolysis reactions in a bubbling fluidized bed reactor. The multi-phase fluid flow, and the inter-phase momentum and energy transfer processes are modelled with Eulerian multi-phase formulas, representing the flows of gases and solids (catalyst and biomass) within the reactor. The biomass catalytic fast pyrolysis reactions are described by using a two-stage, semi-global model. Specified secondary tar catalytic cracking process, which considers both intrinsic reaction rates and mass transfer process, is embedded to the developed model by user-defined function (UDF). The model simulation results of pyrolysis product yield and distribution are compared with the experimental data with close agreement. The model is then employed to investigate the effects of structural properties of catalyst, such as specific internal area, average size of active sites, pore diameter, and tortuosity, on products yields and composition. The tar cracking process by the selected catalyst is proposed and the influences of adsorption capability of tar molecule on catalyst surface and external film mass transfer are also analyzed. The developed model can be solved with short computational time and thus it can be employed for further research and engineering designs of the catalytic pyrolysis of carbonaceous materials.