The Research Of Narrow Screening Large Particle Size Characteristics Of Fluidization

Using gas-solid fluidized bed for polysilicon synthesis has become a hot research recently. At the beginning of the polysilicon generated in the process, silicon particle size in fluidized bed is very small, as the reaction progresses going, size of silicon particles increases gradually,the fluidization process also changes gradually.Therefore,it is questionable about the size of the particles that can be removed from the reactor. In this paper, we study the narrow screening fluidization process of large size particles in order to solve this kind of problem. Besides, in this paper, the author also avoid the wall deposition in the process of reaction and joining the inner component of heater. Experiments show that the particulate fluidization has relatively obvious reinforcement effect. This article is mainly based on numerical simulation and experimental research to study the flow of large particles, in order to find the difference of flowing between big particles and small particles, thus strengthen the fluidization process of the larger particles.Experiment part:Experiment material is small glass beads, select 1~4 narrow diameter section sieving big size particles of glass beads as samples, studied the narrow screening large size particles in the process of fluidization of bubble motion,axial solids distribution, concentration distribution and the change of bed void fraction,etc.The results show that: along the direction of the fluidized bed height, particle axial solid content is "under thick thin" distribution; Bubble aggregation and broken frequency, the size of the bubble; Grain density decreased by increasing the height of the axial, dense-phase area will become the center of radial solid phase volume fraction curve is low, the tendency of the high side, in bed dilute phase zone, solid content, the largest,of the central region of side wall at the least,and with the increase of inlet gas velocity is more pronounced; Internals heater for particulate fluidization have more obvious reinforcement effect.Numerical simulation part : In this part, by using CFD(computational fluid dynamics)tools software, using Eulerian gas-solid multiphase flow model and SIMPLE algorithm in small size particles and the big size particles for the bed of fluidized bed for studying the simulation. Particles are based on the following aspects: the instantaneous volume fraction distribution of instantaneous flow field distribution, the solid particles, particles are changes of high volume fraction along the bed, both theradial and axial velocity distribution, fluidizing gas velocity of particles in the bed and the influence law of concentration and particle size of particles in the bed and the influence law of volume fraction, the changing rule of the bed pressure drop, etc to reach the flow pattern of particles. Contrast experiment is to analyze the narrow screening of large size particles fluidized state.