Experiment and CFD simulation of gas-solid flow in the riser of dense fluidized bed at high gas velocity

The drag coefficient model plays a vital role in simulating dense gas-solid flow. By analyzing the heterogeneous characteristics of the dense gas-solid flow, a new drag force coefficient model based on the Energy-Minimization Multi-Scale (EMMS) model is presented. The revised drag model is embedded into an Eulerian description of gas-solid flow for inter-phase drag force, and the hydrodynamics of heterogeneous of two-phase flow can be well simulated. In addition, an experimental study is performed to investigate the gas-solid two phase flow behaviors in the dense circulating fluidized bed (CFB) reactor. The overall and local flow characteristics are determined by using the axial pressure profiles and solid concentration profiles. The cold experimental results indicate that the axial solids concentration distributions contain a dilute region towards the up-middle zone and a dense region near the bottom and the top exit zones. The typical core-annulus structure and the back-mixing phenomenon near the wall of the riser can be observed. Furthermore, in the cases of operation conditions considered in this work, the numerical results from this revised drag force model show a better agreement with the experimental axial average pressure drop and the apparent solid volume fraction when compared with the other models. The assembly and fragmentation processes of clusters can be captured. The relative motion between the gas and solid phase, and axial heterogeneity in the three sub-zones of the riser can also be investigated, which indicates that this revised drag force coefficient is appropriate for the simulation of dense CFB's riser. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.