The Simulation And Optimization Research In Polycrystalline Silicon Reduction And Tail Gas Recovery Of Siemens Process

In recent years,the large exploitation and utilization of the traditional fossil energy have caused serious environmental pollutions.Therefore the development of novel clean energy is urgently needed to replace the traditional energy.As a clean and renewable energy development to that is very urge.As a clean and renewable energy of solar energy,the key conversion and utilization technology of solar energy,i.e.the polysilicon production technology,has received great attention by many countries.The main technology that used in our country is the Improved Siemens method,however,the shortage of laggard process,outdated equipment and high cost have seriously restricted the utilization and development of domestic solar energy.So reducing the polysilicon production costs by optimizing the process is of great significance for the utilization of solar energy.At first,this paper introduced the process of Improved Siemens method,especially analyzed the basic situation of the reduction and tail gas recovery process of polysilicon production.For the reduction process,thermodynamic function and equilibrium constant of each reaction in the reducing furnace were calculated by using the thermodynamics theory respectively.The correlation plots of ArHm/T and ArGm/T of each reaction were obtained,as well as the basic reaction rule of polycrystalline silicon reduction process.Besides,the energy consumption of theoretical calculation provides theoretical support for the energy saving of production.After the research of reduction reaction mechanism in polycrystalline reducing furnace,simulations and optimizations of the Siemens process and the new process join dichlorosilane were performed within the Gibbs reactor of Aspen-Plus software based on the Gibbs principle of minimum free energy.By virtue of the optimization of traditional process parameters,the simulation results indicated that the best operational conditions of pressure,temperature and the ratio of hydrogen and trichlorosilane were 0.1MPa,1200?and 3/1,respectively,at which the production efficiency of polysilicon andadata(the amount of substance of Si by per mole feedstock)were increased,and the energy consumption per kilogram and yields of by-products were decreased.In addition,through the optimization of new process parameters,it can be found that the best operational conditions of the proportion of dichlorosilane in chlorosilane,pressure,temperature and the ratio of hydrogen and trichlorosilane were 20%,0.1MPa,1200? and 3/1 respectively.The simulated results were compared to that of the conventional process,at which the production efficiency of polysilicon andadata were increased by 20.33%and 0.0413 respectively;while the energy consumption per kilogram and yields of by-products were decreased by 0.0152 GJ/h,3.19%,and hydrogen saved about 16.7%.Energy saving and consumption reducing were very obvious.It is significant for reducing steam consumption of alumina production.In addition,simulations and optimizations of the reduction tail gas recovery process in domestic were performed by chemical process simulation software(i.e.Aspen-Plus software)based on the tail gas of 3000 tons polysilicon plant.The overall process was simulated after the optimization of absorber in process under higiner recycling purity and recovery rate of H2 and HCl,the network were improved and optimized through analyzation.The results indicated that cold consumption saved-3.0423MW(about 42.11%)and heat consumption saved 3.2749MW(decreased 66.79%).The energy saving is obvious.The result can provide a theoretical guidance for the current domestic Improved Siemens process control optimization,process improvement and cost reduction of recovery and tail gas recycling technology optimization through the simulation and optimization of polysilicon reduction and the recovery of reduction tail gas.