Modeling on High-Flux Circulating Fluidized Bed with Geldart Group B Particles by Kinetic Theory of Granular Flow

摘要

Modeling of the hydrodynamic behaviors of high-flux circulating fluidized beds (HFCFBs) with Geldart group B particles has been performed using a Eulerian multiphase model with the kinetic theory of granular flow (KTGF). The essential models involved are the dispersed k-ε turbulence model, the Gidaspow shear viscosity model, and the Syamlal -O'Brien drag model, and the boundary condition is the Johnson and Jackson wall boundary condition. The sensitivities of key model parameters (i.e., particle-particle restitution coefficient (e), particle-wall restitution coefficient (e_w), and specularity coefficient (φ)) on the predicted gas velocity, solids velocity, and solids volume fraction were tested. It was found that e has remarkable dependence on the particle diameter. Large-sized particles experience a more sensitive effect of e on predictions. The particle-wall restitution coefficient e_w has somewhat of an effect on the simulated values of gas velocity, solids velocity, and solids volume fraction; however, no critical changes in the trends of their radial distributions have been found. The specularity coefficient cp has a slight effect on the gas velocity and solids velocity distributions but a pronounced effect on the solids volume fraction distribution. An increase in specularity coefficient results in a reduction in the solids volume fraction near the wall. Based on the comparisons of simulated results with experiments, a group of suitable model parameters for modeling the flow of Geldart group B particles in HFCFB risers by a Eulerian multiphase model with KTGF was determined and verified. Besides, some interesting simulated results that are difficult to measure experimentally were presented under the suggested model parameters.