Three-dimensional numerical simulation of a lab-scale pressurized fluidized bed using a soft-sphere DEM-CFD approach

The present work is dedicated to the numerical study of the hydrodynamics of a pressurized fluidized-bed using an Euler-Lagrange approach. The gas phase is modeled by filtered Navier-Stokes equations, and the solid particles are tracked using a Discrete Element Method (DEM). Collisions are handled using a soft-sphere model. Numerical predictions of the mean (timeaveraged) vertical particle velocity are compared with experimental measurements available from the literature, obtained from a Positron Emission Particle Tracking (PEPT) technique. In addition, Discrete Element Method (DEM)-Computational Fluid Dynamics (CFD) results are extensively compared with predictions from Two-Fluid Model (TFM) numerical simulations. Results accounting for inelastic frictionless particle-particle collisions show a very good agreement with the experimental data and Two-Fluid Model (TFM) results in the central zone of the reactor. In the near wall region the numerical simulation overestimates the downward particle velocity with respect to the experimental measurements, especially when the particle-wall friction is neglected. The influence of the friction at the wall is therefore further investigated and a local analysis of the particle-wall interactions is carried out. It is demonstrated that the long sustained contacts of particle clusters with the wall in such a dense regime play a crucial role on the overall bed behavior. Therefore, this effect should be taken into account in the boundary conditions of a TFM approach when it is used to predict bubbling fluidized beds