Numerical Simulation Of Flow Characteristics In Circulating Fluidized Bed

Fluid-solid two-phase flow and reaction phenomena are common in petrochemical industry,hydrometallurgy,biopharmaceuticals,new materials and other fields.With the development of industry,fluidization process has been widely used.Therefore,it is of practical significance to study the flow characteristic and mechanism in circulating fluidized bed by numerical simulation.Howevermost of the studies are two-dimensional CFB or riser and downcomer in CFB.However,a complete three-dimensional circulating fluidized bed can reveal the flow of particles in the fluidized bed accurately,so the development of a complete three-dimensional circulating fluidized bed is of great significance for the simulation of two-phase flow.The liquid-solid and gas-solid two-phase flow was studied based on Euler-Euler two-fluid model(TFM)and the Kinetic Theory of Granular Flow(KTGF),The k-? turbulence model was used to simulate the flow characteristics of liquid-solid two-phase flow in a complete three-dimensional circulating fluidized bed.The forces between solid and fluid are fully considered.While the non-slip boundary condition of cut cell between the solid and wall is adopted.The flow characteristics of particles in liquid-solid and gas-solid circulating fluidized beds were simulated by different drag models.The simulation results were compared with the experimental results,and the flow characteristics in the circulating fluidized beds were analyzed.The results show that when BVK and Wen-Yu drag model were used in the liquid-solid circulating fluidized bed,the particles fluidized uniformly in riser without obvious accumulation.The axial velocities of particles under different drag models are approximately the same.The Wen-Yu drag force model has a great influence on the granular temperature;The particle concentration increases with the increase of the first inlet velocity and decreases with the increase of the second inlet velocity.Meanwhile,the larger the particle mass is,the higher the bed is,and the higher the particle concentration in the riser is.The volume fraction of the particles in the gas-solid circulating fluidized bed shows a trend of upward dilution and downward concentration,and the axial velocity of the particles is larger when the concentration of the particles is lower.The fluidization effect of CFB with BVK traction model is the best.The drag force model has little influence on the axial velocity distribution of particles.In the radial direction of Z,the drag force model has a great influence on the axial velocity of particles,but has little influence on the radial direction of X.In addition,the granular temperature distributions has great differences under different drag models,and the maximum turbulent kinetic energy of particles is obtained by using Gidaspow drag model.The distribution of velocity and concentration in riser and downcomer is also different between liquid-solid circulating fluidized bed and gas-solid circulating fluidized bed.