Multi-scale CFD Simulation Of Organosilicon Fluidized-bed Reactor

Silicone is a kind of important new chemical material products,which has been widely applied to chemical industry,light industry,textile,military industry,construction and many other downstream industries.The fluidized bed reactor is the core device for the synthesis of organosilicate monomer.The process of multiphase flow,heat/mass transfer and reaction in the bed is extremely complicated.Therefore,in-depth understanding of these complex processes is the basis for structural optimization and amplification of the reactor,and has important guiding significance for improving the level of organic silicon synthesis technology.Computational fluid dynamics(CFD)model based on the assumption of uniform distribution is often used in the simulation of organosilicon fluidized bed.However,this assumption cannot truly reveal the complex multi-scale structure in the bed,especially the non-uniform drag force between gas and solid phases.In the second chapter,a set of multiscale CFD model equations,including the basic governing equation and the constitutive equation,were constructed for the typical bubble characteristic structure in the fluidized bed of organic silicon.Then,the gas-solid phase drag model based on bubbles was analyzed and reconstructed,and the model was extended to silica powder system with wide screening,which ensured that the drag model was consistent with the physical intrinsic structure from the root of the model.Finally,a multi-scale model of organosilicon fluidized bed is proposed by coupling the multi-fluid model with the bubble drag force.In the third chapter,two-dimensional simulation of cold organosilicon fluidized bed was carried out by using the above multi-scale CFD model.The process of coalesce and breakage of bubbles,the distribution of transient concentration of silica powder,the distribution of time-average concentration/velocity,the wide sifting of silica powder system and the influence of different gas velocities were systematically investigated.The results show that the multi-scale CFD model can accurately capture the bubbling fluidization characteristics in the fluidized bed of organosilicon.Compared with quantitative experimental data such as expansion void ratio,the errors of the multi-scale CFD simulation results are generally less than 10%,which indicates that the model can predict the experimental phenomenon more accurately.However,the simulation results of the traditional uniform distribution hypothesis are greatly distorted.On the basis of the above preliminary verification,the fourth chapter further uses the multi-scale CFD model for three-dimensional simulation and structural optimization design.In the three-dimensional simulation,the phenomenon of coalescence and fragmentation during the bubble rising process is analyzed,and the typical "ring-core" non-uniform structure on the cross section of the bed is reproduced,which is consistent with the structural characteristics reported in the literature.Then,the influence of cone Angle,finger type heat conduction tube and other structures on flow field distribution was emphatically investigated.It was found that the smaller cone Angle could make the flow field distribution more uniform when the cone Angle was 65°,75° and 85° were designed.After adding the inner components of the finger-shaped tube,the larger bubbles and particle clusters can be broken effectively,and the gas-solid contact in the bed can be promoted more fully.Finally,this paper summarizes the research content and gives the future research direction.