CFD simulations of a full-loop CFB reactor using coarse-grained Eulerian-Lagrangian dense discrete phase model: Effects of modeling parameters

The hydrodynamics of a 3D full-loop circulating fluidized bed (CFB) reactor were investigated using a coarse-grained dense discrete phase model (DDPM). The effects of changes in key modeling parameters such as the drag force, particle number per parcel, and particle-particle/particle-wall restitution coefficients were thoroughly investigated. Previous experimental data were used as a benchmark for validating the numerical results. In terms of the drag force, the simulation results show that the effect of mesoscale structures on drag force must be considered in the DDPM approach. Regarding the number of particles per parcel, the predictions indicate parcel-independent behavior at all of the coarse-graining ratios tested (d(cl)/d(p) = 55, 95, and 125), which is further proof that parcel-independent results can be achieved when the parcel diameter is in the size range of clusters. The effect of energy dissipation from particle-particle (e(pp)) collisions shows that better results are generated when e(pp), is in the non-ideal range (0.1-0.9) than for the ideal case (e(pp) = 1.0). However, the particle-wall restitution coefficient (e(pw)) has little effect on hydrodynamic behavior in either the ideal or non-ideal collision range. In addition, the effect of the particle size distribution on the full-loop hydrodynamics was investigated. The predicted results are similar to those from mean particle diameter simulations, but the distributions for different particles in the CFB are different. This would certainly affect the heat and mass transfer and reactions, and will be further investigated in our ongoing simulations of combustion in CFBs. (C) 2019 Elsevier B.V. All rights reserved.