Erosion Research Of Exhaust System Of Polysilicon Reduction Furnace

Polysilicon production is the basic industry of Photovoltaic Energy and the Microelectronic; it plays an important role in chemical industry. Modified Siemens method is the mainstream technology of the polysilicon production, which is chemical cogeneration process involving Toxic, flammable, explosive media. So, industry usually pays much attention to its production safety. In actual polysilicon production, exhaust which carries a lot of hard silicon particles is discharged from reduction furnace, which leads to sustainable erosion of flow passage components in exhaust system and threats to the safety of polysilicon production seriously. However, the pipeline of exhaust system is prolixity and has complex structure; production field is a lack of the understanding of erosion of flow passage components in exhaust system as well. Therefore, it is difficult to carry out the work of anti-wear protections in exhaust system.Based on the theory of gas-solid flow and erosion, viewed from the safety of chemical industry, the article forecasted the wear conditions of flow passage components and researched on how working conditions effect on erosion by numerical simulation. On the basis of erosion research, combined with production characteristics of the reduction furnace exhaust system, the paper proposed the treatment of erosion of flow passage components in exhaust system from the perspective of active and passive protections, which guides production practices and eliminates the potential safety hazard of erosion in exhaust system of polysilicon reduction furnace.Analysis of physicochemical properties of exhaust and particles indicated that silicon particle component is almost all of amorphous silicon, but trace crystalline silicon mixed with it. Objectively, it is the result of body reaction of silicon vapor-phase epitaxial, thermal decomposition reaction of Si HCl3 and Si H2Cl2, temperature fluctuation, unstable operation of production system.The research of erosion expanded with the exhaust outlet pipe.8 areas at the bottom of the annular pipe which correspond to branch pipe, 2 areas located in 0-22.5°range at the outside of the up azimuth on both sides of annular pipe export, 4 areas lie on the upper and lower wall of single furnace main channel were defined as the serious wear regions. Meanwhile, research shows that the former 8 regions erosion was caused by silicon particles colliding with high angle. While, impacted by silicon particles with low angle and high velocity result in the erosion of latter 6 regions. Through comparative analysis, the erosion of upper wall of single furnace main channel is the most serious. The laws of work conditions influence on erosion of the exhaust outlet pipe show as follows: As the increase of exhaust velocity, the max erosion of each local region rises with the exponential law. By the growth of silicon particles diameter, the regions of erosion change and the phenomena of the granularity effect appear, the increasing extent of the max erosion of each local region decreases gradually. With the adding of silicon particles concentration, the increasing extent of the max erosion of local region rises gradually. However, the phenomena of shielding effect appear in 2 regions, the increase range of which decreases gradually.A further research of erosion focused on exhaust collecting pipe. The erosion of collecting pipe was caused by silicon particles impacting with low angle, which occurs on tee downstream wall where branch pipe connects to the main channel. On the local characteristics, the erosion of lower wall is more serious then the upper, erosion of the inside wall is much slighter than the outer, branch pipe and the upstream wall of main channel almost do not wear. The laws of work conditions influence on erosion of the exhaust collecting pipe show as follows: As the increase of exhaust velocity, the local wear regions move to both sides, the max erosion of which rises under the exponential law. By the growth of silicon particles diameter, cross-orientation changes occur in erosion zones, the max erosion of the whole tee unit appears linear growth. With the adding of silicon particles concentration, the max erosion of each local region develops under linear law nearly. Enlarging the flow proportion of main duct to branch pipe, the wear regions move from the opposite side of branch pipe to downstream, the increasing extent of the max erosion of the whole tee unit rises gradually.Besides, in terms of active protections, in order to reduce the production of silicon particles, some practical optimization of process was proposed. To achieve particles purification, tooling of exhaust was used to intercept larger particles in the reduction furnace; the smaller was captured by the metal filtration-dust collector outside of the reduction furnace. Measure of pneumatic rib anti-wear was conducted to defense the erosion of single furnace main channel as well. On the passive protections aspect, coating anti-wear by high manganese steel electrode surfacing was chose; local thickness compensation for collecting pipe by adding wear-resisting external pads was used, either. At the same time, monitoring scheme of wall thickness for erosion zones which got from numerical simulation forecast was established.