The Simulation and Experimental Validation on Gas-Solid Two Phase Flow in the Riser of a Dense Fluidized Bed

Gas-solid flow in dense CFB (circulating fluidized bed)) riser under the operating condition, superficial gas 15.5m/s and solid flux 140 kg/m2s using Geldart B particles (sand) was investigated by experiments and CFD (computationalfluid dynamics) simulation. The overall and local flow characteristics are determined using the axialpressure profiles and solid concentration profiles. The cold experimental results indicate that the axial solid concentration distribution contains a dilute region towards the up-middle zone and a dense region near the bottomand the top exit zones. The typical core-annulus structure and the back-mixing phenomenon near the wall of theriser can be observed. In addition, owing to the key role of the drag force of gas-solid phase, a revised drag forcecoefficient, based on the EMMS (energy-minimization multi-scale) model which can depict the heterogeneouscharacter of gas-solid two phase flow, was proposed and coupled into the CFD control equations. In order to findan appropriate drag force model for the simulation of dense CFB riser, not only the revised drag force model butsome other kinds of drag force model were used in the CFD. The flow structure, solid concentration, clustersphenomenon, fluctuation of two phases and axial pressure drop were analyzed. By comparing the experimentwith the simulation, the results predicted by the EMMS drag model showed a better agreement with the experimentalaxial average pressure drop and apparent solid volume fraction, which proves that the revised drag forcebased on the EMMS model is an appropriate model for the dense CFB simulation.