LES-DEM investigation of an internally circulating fluidized bed: Effects of gas and solid properties

Gas-solid flow dynamics of a three-dimensional baffle-type internally circulating fluidized bed (ICFB) is numerically investigated in this paper. Detailed multiphase flow characteristics are illustrated using a computational fluid dynamics-discrete element method (CFD-DEM) in which the gas flow field is modeled using large eddy simulation (LES) while solid kinematics is handled by soft-sphere model. The mechanisms of the internal circulation are addressed together with instantaneous and time-averaged results and solid rotation plays an important role as that of its translational motion. Simulations are also carried out to examine the influences of gas-solid properties (bed pressure, solid friction coefficient, restitution coefficient, Young modulus, diameter and density) on the bed circulation performance, which is quantified by the solid circulation flux (SCF) and gas bypassing flux (GBF). The results indicate that the behaviors of solid circulation and the corresponding gas bypassing exhibit great resemblance, especially when the solid properties change. The gas property, bed pressure, seems to show significant influence on the gas bypassing flux. Meanwhile, both solid circulation and gas bypassing are affected by the solid properties to a larger extent. They are enhanced with increasing solid density, restitution coefficient and gas pressure, while weaken as the solid friction coefficient, diameter and gas temperature increases. However, solid Young modulus shows inconspicuous influence on the circulation performances of the bed. Furthermore, additional normalization of the simulation data finds that the minimum fluidization velocity (Umf) of the system is a key parameter to the operational control of the ICFB.