In times of economic downturn and poor profits, polysilicon companies have begun to focus more on product technology upgrades and quality improvements. The reporter learned from the 2009 Polysilicon and Photovoltaic Industry (Huinan) Summit hosted by the China Chemical Information Center that the improvement of Siemens production of polysilicon as a monopoly will soon change. The polysilicon production process will form an improved Siemens method and new methods like the silane method, the fluidized bed method, the metallurgical method, the chlorine-free method, the carbon-thermal reduction method, and many others using cold rolled steel strip and silicon steel. An expert from the Chinese Academy of Engineering and a researcher at the Institute of Metal Research of the Chinese Academy of Sciences, Wen Lishi, said in an interview with reporters that a number of emerging technologies are also receiving attention while improving existing Siemens methods to reduce energy consumption and costs. The fluidized bed method can be modified to improve the Siemens method. The chlorine-free method is in its infancy, and the metallurgical method has also emerged. The new polysilicon technology will appear with less energy consumption, lower cost, and better environmental protection. Improved Siemens method: energy consumption and cost are the key. Wen Shi introduced the current mainstream process of polysilicon production in the world is to improve the Siemens method. China's polysilicon projects have basically adopted this method. In 2008, the production capacity has reached 80,000 tons and will increase to 100,000 tons this year. The modified Siemens method uses a thermochemical gas-phase reaction route, which is the fundamental reason for its high energy consumption and high production costs. In addition, domestic enterprises adopting the improved Siemens method still have a large gap between the technology and the international advanced level. Although technical improvements have been made, it is still relatively difficult to reduce energy consumption below 200 kWh/kg. At the same time, there are still safety and environmental protection issues in the improvement of the Siemens process. It is understood that its one-way effective conversion rate is only more than 20%, a large number of by-product silicon tetrachloride. It is estimated that for each ton of polysilicon produced, about 10 tons of silicon tetrachloride will be produced as a by-product, and the amount of material circulation will be large, and environmental pressure will also be great. To solve this problem, we must increase the efficiency of primary conversion in the production process, and continue the hydrogenation of by-product silicon tetrachloride to form a closed-circuit cycle, which is the key to reducing the production cost of polysilicon. Cold rolled oriented electrical steel: easy docking with existing equipment. The fluidized bed method is a new technology for producing polysilicon. According to Dr. Chu Yun, deputy general manager of Sunnyside Technology, USA, the production of granular polysilicon by the fluidized bed method has obvious comprehensive advantages. Using silicon tetrachloride, hydrogen, hydrogen chloride, and industrial silicon as raw materials, trichlorosilane is generated in a fluidized bed under high temperature and pressure conditions, and then the trichlorosilane is subjected to disproportionation hydrogenation to form dichlorodihydrosilane, followed by Silane gas is generated. The resulting silane gas is passed through a fluidized bed reactor with small particles of silica fume for continuous thermal decomposition to produce a granular polysilicon product. Because of the large surface area of silicon involved in the reaction in the fluidized bed reactor, high production efficiency, low power consumption, and low cost, it is suitable for large-scale production of solar-grade polysilicon. Low cost, reduce environmental risks. The experimental results show that the power consumption of polysilicon produced by this method is only 27.3 kWh/kg. The intermediate product of this process is a special electronic gas that is in short supply in the market, one of which is to invest in two revenues. Even the Siemens law projects and projects under construction can be connected with the fluidized bed method to reduce costs. However, there are few examples of fluidized bed engineering applications. The alkoxysilane process: basic open communication in all aspects In order to avoid the improvement of the Siemens environmental issues, the use of chlorine-free media alkoxysilane technology system has caused great concern in the industry. According to Liao Jun, general manager of Hubei Wuda Organosilicon New Material Co., Ltd., the system is a new method for the production of environment-friendly polysilicon, using alcohol instead of chlorine as a recycling material, and replacing it with lower-cost, non-corrosive trialkoxysilanes. Trichlorosilane is used as the basic raw material to produce the intermediate monosilane through the chlorine-free method, which avoids equipment corrosion problems and greatly reduces the investment cost. At the same time, the system also adopts a more efficient and lower-cost fluidized bed reduction technology to replace the high-energy and difficult-to-control vapor deposition process in the Siemens process, which greatly reduces the energy consumption of the system. Due to the short process, high conversion rate, and high productivity, the process energy consumption is very low, generally less than 30 kWh/kg. In the treatment of by-products, the new alkoxysilane system also broke through: After the by-product tetraalkoxysilane was de-alcoholized, high-purity polysilicon with extremely low boron and phosphorus content was obtained through char-thermal reduction. Compared with common physical polysilicon, its raw material impurity levels are extremely low and controllable, thus greatly improving the quality of the product; alcohols recovered in subsequent processes can be returned to the starting point as raw materials to achieve "zero emissions" while improving the efficiency of raw material use. This fundamentally reduces the cost of polycrystalline silicon raw materials and solves the silicon tetrachloride treatment problem. Liao Jun said that Wuda Organic Silicon New Material Co., Ltd. has made some progress in the development of polysilicon-based alkoxysilane synthesis. A 6,000 tons/year direct trimethoxysilane plant has been in operation for many years, and a 10,000 tons/year direct triethoxysilane plant was successfully launched in October; the process for producing high-purity silica from alkoxysilane has been completed, Enter the industrialization stage; the last step of the high-purity quartz reduction polysilicon production process is in the pilot stage. He hopes to further speed up its industrialization through comprehensive strategic cooperation in upstream and downstream product markets, technological processes, and capital. Metallurgical Law: Strive to Realize Industrialization in 3 Years Metallurgical production of polysilicon has also shown good signs. Dr. Shi B, president of Shanghai Pronew Energy Co., Ltd., said that the metallurgical process is a method of purifying polysilicon by physical processes. It uses a plasma melting furnace to remove boron impurities from silicon ingots, and after coarse crushing and cleaning, The electron beam melting furnace removes phosphorus and carbon impurities and generates solar grade polysilicon directly. Metallurgical polysilicon production costs are low, about 10 to 20 US dollars / kg, power consumption 50 kwh / kg, is a technology worth the wait. The current problems are mainly due to the fact that the equipment and technology are still relatively backward, dragging on the hind legs of industrialization. In September of this year, the metallurgical technology strategic alliance for solar polysilicon industry technology innovation was established. Its goal is to study the technology, processes, and equipment for the preparation of low-cost solar-grade crystalline silicon and its solar cells on the basis of the existing metallurgical method, and strive to achieve within three years. Large-scale industrialization.
