CFD Simulation of the Coal Pyrolysis in a Fluidized-Bed Reactor

The coal topping process in circulating fluidized beds (CFBs) is beneficial for efficient conversion and utilization of high-volatile solid fuels, such as biomass and low-rank coal. The hydrodynamics and pyrolysis behavior of coal are explored by experimental measurement and computational fluid dynamic (CFD) simulation in this study. A fluidized bed system is built to explore the effect of drag model on the CFD simulation of gas-solids flow. The distribution of solids velocity and pressure are obtained by the wire-mesh electrodes and pressure transducers, respectively. A hydrodynamic model of the fluidized bed is established based on the Eulerian-Eulerian two-fluid model with the kinetic theory of granular flow. Effect of the drag model, including the empirical correlation based on experiment, the correlation based on direct numerical simulation and the correlation based on energy minimization multi-scale method, on the computational results is investigated and validated by the experimental data. Both qualitative and quantitative results indicated that the drag model had a significant effect on the flow behavior. Furthermore, a comprehensive CFD model, involving continuity equations, momentum equations, energy equations, species transport equations and related constitutive equations, is established to predict the hydrodynamics and pyrolysis behavior of low-rank coal in the fluidized bed.