Numerical Simulation Of Flow Characteristics Of Binary Particles In A Liquid-Solid Fluidized Bed

Liquid-solid fluidized bed(LSFB)has been widely used in petroleum and chemical industry due to its good mixing,heat and mass transfer properties.In actual production,particles in the LSFB often have different sizes and densities,which directly affect the mixing and separation characteristics of particles,thus affecting the mass and momentum transfer efficiency of the LSFB,and further affecting its performance.Therefore,in the design of the LSFB,it is of great significance to better understand the mixing and separation characteristics of particles in the LSFB.Firstly,the Eulerian-Eulerian two-fluid model(TFM)and the Eulerian–Lagrangian Multiphase Particle in Cell(MP-PIC)method are adopted to simulate the flow behavior of particles with different densities in a LSFB,respectively.Compared with Gidaspow and Wen-Yu drag model,it is found that BVK drag model considering multi-component flow has a good applicability for the flow of binary particles in the LSFB.The dynamic separation index and the bed height are used to analyze the motion law of binary particles in the LSFB.Compared with MP-PIC method,the separation index of TFM is smaller,and the separation phenomenon simulated by TFM is more obvious.The expansion height of light particles is more significantly affected by the inlet velocity than heavy particles.The particles interaction in the liquid-solid fluidized bed was analyzed by the dispersion coefficient and the granular temperature.There are significant differences in the interaction of binary particles,and the MP-PIC method can better explain that the local interaction between particles.Furthermore,the MP-PIC method combined with BVK drag model was used to simulate the layer inversion experiments of Jean & Fan with different particle sizes and densities of glass ball(GB)and activated carbon(AC).It is found that in the layer inversion process of the two particles,as the increase of the inlet velocity,the bed height of GB particles increases gradually,the bed height of AC particles increases first and then decreases,and the bed height difference of the two particles shows a trend of decreasing first and then increasing.At this time,the two particles present from separation to mixing and then to separation.In particular,when the inlet velocity is at the layer inversion velocity,the bed height of the two particles is basically the same and the particles are fully mixed,but the separation index shows that even at the layer inversion velocity,the separation index of particles is also much smaller than that of the initial homogeneous mixing.Through the gravity of particles,the forces on particles are de-dimensioned.It is found that when two kinds of particles are in fluidization state,the total force(the sum of drag force,pressure gradient force and collision contact force)on the vertical direction of particles is basically balanced with their own gravity.Due to the larger particle size of AC particle compared with GB particle,GB particle is mainly affected by the drag force,while the AC particle is mainlyaffected by the pressure gradient force,and with the increase of inlet velocity,the influence of pressure gradient force on AC particles gradually weakened,while the influence of drag force on AC particles gradually enhanced.By analyzing the turbulent kinetic energy and the dissipation rate of turbulent kinetic energy,it is found that the movement of particles makes the turbulent kinetic energy and dissipation rate of fluid larger.The variation trend of granular temperature affected by particle mixing degree is the same as separation index.