CFD simulation on two-phase flow in gas-solid fluidized beds with coarse granules

Eulerian pseudo-fluid model combined with the granule kinetics model,by integrating them in a CFD code(Fluent 6.3) was used to numerically simulate the gas-solid flow patterns in fluidized beds of coarse granules.Different conditions including particle density,distributor types and drag models were taken into account for paramter study.The dependance of characteristics of fluidization and flow patterns,as well as the influences of phase fraction distribution,instantaneous pressure,radial particle velocity,expansion ratio and axial voidage distribution,on the parameters were thoroughly investigated.Simulation results show that two-phase flow characteristics in the bed with a concave distributor is rather different from that in the bed with a flat distributor.For example,bubbles will occur sooner and more particles move laterally in the concave distributor bed.It is also found that for larger solid-gas density ratio,particle velocity profile near the wall becomes much flatter in the concave distributor bed.A comparison among the Syamlal-O'Brien,Gidaspow and Arastoopour models illustrates that the predicted axial voidage distributions and pressure drops by the three models are very different.Numerical prediction based on all the three drag models underestimates the bed expansion ratio,comparing with the published experimental correlation.It can be concluded that numerical results based on Gidaspow drag model are of the least deviation in the simulation of gas-solid fluidized beds with coarse granules.