Study On The Thermal State Experiment And CFD Simulation Of Bubbling Fluidized Bed Of Synthesis Of Si₃N₄

As one kind of high-temperature structural material, silicon nitride obtains moreand more emphasis in recent years, especially under high-temperature, high-speed andstrong-cauterization condition provided by new technology areas, which acceleratesits development. Currently, the direct nitridation of silicon is the most prevalentpreparation method of silicon nitride. In the course of direct nitridation of silicon, thetime of silicon complete conversion is different owing to the difference of siliconthinness and purity and reactor. The traditional silicon direct nitridation method is thestatic and batch method, namely intermittent production way. This method makes thesilicon inner have high temperature because silicon powder is in the state of stack,which makes the quality of silicon nitride powder decrease. Meanwhile, thenitridation time of this method is long, which causes production efficiency low andenergy consumption high. All those shortcomings of this method get the silicon nitrideproduced by this method not satisfy a great deal of demand. Owing to many strongpoints, especially having the ability to produce successively, Fluidized bed reactorcould be as one kind of promising reactor to produce silicon nitride.High temperature fluidized bed reactor, preheating system, material feedingapparatus, material drawing apparatus and corresponding experiment flow have beendesigned and rebuilt; meanwhile, brainpower turbine flowmeter has been adjusted,and preheating apparatus and high temperature fluidized bed reactor's calefactiveperformance has been studied by experiment.The research shows that the measurement of the brainpower turbine flowmeter iscredible and the calefactive and temperature-control performance of preheatingapparatus and high temperature reactor is all right and this system can satisfy theexperiment requirement of silicon direct nitridation; at the same time, material feedingand drawing apparatuses can meet the requirement of experiment. The proportion,granularity and element constitution of silicon have been measured and analyzed.The fluidization performance, the influence of temperature on silicon fluidization iperformance of high temperature reactor in cold and thermal states have been studied,which gives this apparatus's the required condition of achieving fine fluidization incold and thermal states and silicon typical conversion curve.The high temperature reaction area in this apparatus has been simulated withCFX-4.4, and compared with the experimental results. The results show that themultiple phase model used by computation is right. At the same time, the temperaturefield and fluidization circumstances of this reactor have been simulated, givingparticle movement circumstances at high temperature.Research results give the basis of future research of high temperature fluidizationof silicon.