Numerical Simulation On Characteristics Of Flow Behavior In Liquid-solid Spouted Bed With A Draft Tube

The spouted bed with a draft tube is widely used in two-phase flow,such as coal gasification and steam cracking of oil and other fields.Compared with the traditional spouted bed,it has certain advantages in structure.By adding a vertical draft tube inside the spouted bed,the spouted zone and the annulus zone can be divided in space,and the operation is more flexible and stable.Based on the kinetic theory of granular flow,this paper uses the liquid-solid two-phase Eulerian-Eulerian two-fluid model to simulate the particle flow behavior in a two-dimensional spouted bed with a draft tube numerically.In the simulation process,the standard k-ε turbulence model was used to calculate the liquid turbulence,and the Gidaspow drag model was used to solve the force between liquid and solid particles.The effects of structural parameters including installation height of the draft tube and the cone bottom angle of spouted bed with a draft tube on liquid-solid two-phase flow characteristics was analyzed.At the same time,the effects of physical parameters including particle size,the granular pile height,spouting liquid velocity,auxiliary liquid velocity,liquid density and liquid viscosity on liquid-solid two-phase flow were studied.The results show that,the circulation rate of the particles is significantly improved by adding eight auxiliary inlets at the bottom of the conical zone in spouted bed with a draft tube,and it is easier to reach a stable fluidization state,and the time is shortened by about 21%,compared to without auxiliary inlets.During the process of spouting,there are four obvious regions,which namely the spouting region,the annulus region,the fountain region and the entrainment region.With the increase of the installation height of the draft tube,the height of the bed increases,and the pseudo-temperature of the particles increases.The axial velocity of the particles increases first and then decreases,and more liquid flows into the annulus,which is not conducive to the circulation of the particles in the spouted bed with a draft tube.Increasing the cone bottom angle of spouted bed with a draft tube can significantly reduce the cross-sectional area of the cone area,but there will be local accumulation of particles.With the increase of particle size,the mass and volume of particles also increase,and the static pressure and dynamic pressure curves decrease.Therefore,the particles will accumulate in the spouting process,which the fluidization state in the spouted bed with a draft tube is poor.With the increase of the granular pile height,the fountain structure is more clear and complete,and the spouting efficiency is higher.With the increase of the spouting liquid velocity,the particles are symmetrically distributed,and the bed height is significantly increased to 1.4 times that of the original.With the increase of auxiliary liquid velocity in a certain range,the contact between particles and liquid is more sufficient.With the increase of liquid density,the suspension ability of particles is enhanced,which is helpful for the movement of particles and the spray effect is better.High viscosity of liquid increases the carrying capacity of particles and weakens their activity.Considering the structural parameters and physical parameters,the accumulation of particles can be reduced,and the optimal fluidization of particles can be realized in the spouted bed with a draft tube.