Numerical Simulation Of Polysilicon Deposition By Silane Pyrolysis And Internal Component Design In A Fluidized Bed

The production of solar-grade polysilicon by the silane fluidized bed method is gradually becoming the focus of research due to its advantages such as:energy saving,eco-friendly,and high efficiency.However,the flow and reaction of gas-solid phases are complex and not sufficiently studied,and the high risk factor of silane pyrolysis experiments also restricts the development of this technology.In this paper,the CFD simulation method is used to study the reaction process and structural optimization design of gas-solid two-phase flow and silane pyrolysis in the fluidized bed.The main research results are as follows:(1)Establish a calculation model suitable for gas-solid two-phase flow based on the single-equation WA turbulence model,conduct simulation research on the gas-solid two-phase flow process in the fluidized bed,and compare this with the commonly used two-equation Standard k-ε model and SST k-ω model.The results show that the WA model has the smallest relative error between the predicted value of the bed pressure drop and the theoretical value,which is only 1.6%;the predictions of the three turbulence models for the axial void ratio are all within the allowable range of error,and the WA model has the lowest relative error in the bed layer.The near middle(0.75 m)is in better agreement with the experimental value;the predictions of the three turbulence models for the radial solid holdup at different heights are also within the allowable range of error,and the prediction value of the WA model near the wall shows that it has a higher consistency with the experimental values.The reliability and applicability of the WA model are thus verified.(2)The established calculation model was coupled with the PBM model,and the reaction process of silane pyrolysis in the fluidized bed was simulated.The results show that the chemical reaction kinetic model obtained by combining the heterogeneous reaction rate proposed by Furusawa,the homogeneous decomposition rate proposed by Hogness and the redeposition rate of silicon powder proposed by Pina is the most reliable,and the relative error between the predicted value of this combination and experimental results is only-2.30%;the recommended suitable operating conditions are:the mole fraction of silane inlet is 30%～50%,and the fluidized bed reaction temperature is 923～1023 K.(3)A three-dimensional model of an industrial fluidized bed was established to investigate the effects of inlet gas velocity,different internals,and different baffle layers on the fluidization quality of the fluidized bed.The results show that the appropriate inlet gas velocity is 0.55-0.66 m/s;The average pressure drop in the bed of a mesh baffled fluidized bed is 14204 Pa,which is 4.1%higher than that of an empty tower structure.Its relative standard deviation is the smallest,which is 1.01%.The improvement of fluidization quality of the fluidized bed is the most effective;The average bed pressure drop of a six layer mesh baffled fluidized bed is 14355 Pa,which is 2.1%higher than that of the four layers.Within an acceptable range,its relative standard deviation is 0.88%,and the improvement of fluidization quality of the fluidized bed is the most effective.