Meco-scale Structure Based Multi-scale Flow And Reaction Simulation Of The Polysilicon Process From Silane In Fluidized Bed

Compared with conventional processes of poly-silicon production,fluidized bed process using silane has attracted more and more attentions due to its advantages of low energy consumption,high conversion efficiency and ability of continuous operation.Despite its advantages,there are still some difficulties to handle silane in fluidized bed process because of its combustible and explosive nature,which needs strict safety management rules and reaction monitoring strategies during experiment.Moreover,the gas-solid flow,heat/mass transfer and chemical reactions in fluidized bed reactors are coupled with multi-scale structures inherently and now there is still a lack of thorough understanding of these complex behaviors.Therefore further developments of fluidized bed processes for polycrystalline materials production from silane were hindered.With CFD(Computational Fluid Dynamic)numerical simulation methods,such difficult-to-measure flow behavior and reactions in reactors can be studied in depth.However,it has been shown that the traditional simulation method based on uniform assumption is difficult to simulate such complex systems accurately,calling for establishing meso-scale models.In this paper,the multi-scale flow and reaction simulation of polysilicon production in silane fluidized bed is carried out based on the EMMS(Energy Minimization Multi Scale),which provides a theoretical guidance for the optimization,design and scale-up of silane fluidized bed reactors.The main works are as follows:In the second chapter,the flow simulation of gas-solid bubbling fluidized bed is carried out using DDPM(Dense Discrete Phase Model)coupled with EMMS drag,and the influence of the parcel parameters in the DDPM on the simulation results is studied.The results show that grid size and parcel have a great influence on the simulation results.Considering calculation accuracy and calculation speed,the number of the parcels in the grid cell Vcell/Vparcel= 100 is the best choose.Further,the simulation result of gas-solid fluidized bed using TFM(Two Fluid Model)and DDPM,with different drag models(Gidaspow and EMMS)and particle size treatment methods(uniform particle size and particle size distribution),were compared and verified with experimental data in the third chapter.The comparison shows that in order to describe the state of the fluidized bed accurately,the influence of the meso-scale structure must be considered in both TFM and DDPM.And the more obvious the heterogeneous structure of fluidized bed shows,the better the effect of EMMS drag is.Compared to TFM,DDPM can consider particle size distribution.After the particle size distribution is adopted in DDPM,the change of bed fluidization height with different gas velocity is predicted accurately,and the phenomenon of particle stratification in the experiment is captured,indicating the importance of the particle size distribution on hydrodynamics.Based on the above flow study,the fourth chapter uses Euler-Euler TFM coupled with EMMS flow and mass transfer reaction models to simulate polysilicon production in a silane fluidized bed.The simulation results show reasonable agreement with experimental data,which further verifies the key role of EMMS model in the simulation of reaction.