Experiment And Numerical Study On Gas-solid Flow In A 3D Integral Multi-jet Spout-fluidized Bed

Spouted bed technology is an important branch of fluidization.The application field has gradually evolved from the initial process for coarse screening of narrow particles to drying,coating,granulation,pharmaceutical,chemical reaction,coal gasification,pyrolysis,flue gas desulfurization and catalytic polymerization.With the continuous application of spouted bed technology and the in-depth study of researchers,many different types of spouted bed are proposed.such as multi-jet spouted bed,spout-fluidized bed,pilot tube spouted bed and internal circulation spouted bed.The traditional spouted bed has internal and external stratified flow,lack of lateral mixing,particle accumulation and flow dead zone,agglomeration,which adversely affect the heat and mass transfer of the bed structure.Therefore,in order to solve this problem,combined the advantages of spouted bed and fluidized bed and overcame their respective disadvantages,in a 3D integral multi-jet spout-fluidized bed structure is proposed in this paper.The advantage of this bed structure is that on the basis of no need of other auxiliary gas supply equipment,the particle accumulation and the flow dead zone in the annulus region of the spouted bed is reduced,effectively strengthen the mass and heat transfer process between gas-solid two phases.In this paper,experiments and numerical simulations are carried out for a three-dimensional multi-jet spout-fluidized bed.By designing a three-dimensional spatially distributed circular-hole-type side jet on the bed cone side,a three-dimensional integrated multi-jet spout-fluidized bed is formed.Compared with the two-dimensional model,the spouting law and operating performance of the spouted bed reactor can be more realistic,so as to provide necessary references for industrial production applications.The research content of the paper is summarized as follows:(1)The particle image velocimetry(PIV)was used to study the motion of the static bed height and particle diameter on the particle trajectory in a multi-jet spout-fluidized bed,and compared with the conventional spouted bed.The results show that the inlet gas splitting effect of the multi-jet structure effectively enhances the radial movement of the particle phase in the spouted bed,thereby enhancing the radical mixing of gas and particles in the spray zone and the annulus zone.The smaller the diameter of the particles,the multi-jet structure can effectively eliminate the accumulation of particles in the annulus zone.The optimal particle treatment amount can optimize the uniformity of the particle phase flow field distribution in the spout-fluidized bed.(2)The gas-solid two phases flow characteristics in a three-dimensional multi-jet spout-fluidized bed were studied.The main research is to analyze the effects of different jet diameters,distribution modes and number of openings on the gas-solid two phases flow in a three dimensional multi-jet spout-fluidized bed.The results indicate that the volume fraction and the radial velocity distribution of the particles in the bed,and the uniformity of radial distribution are obtained.When the number of openings is 24 apertures,the cross-sectional area of the dimensionless intake is A_i/A_z=0.67,the uniformity of the flow field of the whole particle in the chemical bed is optimal,that is the multi-jet has the best fluidization effect on the whole particle in the spout-fluidized bed.At the low cross-section bed height,the distribution of the side jet Case D is the most important,and the damage of the bottom layer is the most significant,effectively fluidizing the accumulation between the particle layers in the annulus region,and the flow field uniformity is the best.When the jet diameter is 4 mm and the number of multi-jet is 24 holes,the relative standard deviation CV value is the smallest in the beds,the particles formed under this working condition have the best spouting effect.(3)The effects of particle diameter and particle processing capacity were compared.It turns out that the smaller the particle diameter,the smaller the volume fraction of the particles in the annulus region,indicating that the local fluidization of the side jet gas is particularly significant for particles with smaller particle size,which can effectively reduce the accumulation of particles in the annulus region.Under the influence of the multi-jet structure,the smaller the processing amount of the particles,the upper layer particles bear less pressure on the particles in the cone region is at the low bed height,the accumulation damage of the particles is obvious,and the gas is more likely to break through the bed,the speed of the particles was increased.