New technologies enable the green manufacturing of polysilicon

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First, multi-effect distillation is employed to make full use of energy. Multiple-effect distillation involves dividing the feedstock into N roughly equal portions, which are fed separately into N distillation columns with progressively increasing pressures; the operating temperatures of these N columns also increase in sequence. The vapor at the top of the tower with higher pressure and temperature supplies heat to the reboiler at the bottom of the lower tower, while it itself is condensed; and this process repeats, thereby saving energy consumption in the reboiler of the low-pressure tower as well as water usage in the condenser of the high-pressure tower. In this system, it is sufficient to supply heat only to the first tower with the highest pressure for the system to operate; the energy required is approximately 1/N of the energy needed for a single tower. If three towers are connected in series using triple-effect distillation technology, the energy consumption is reduced to only 1/3 of the original level, resulting in a 67% reduction in energy use – an extremely significant savings. In polysilicon production, many towers are used for purifying polysilicon; by optimizing the balance between energy and temperature differences, multi-effect distillation can be achieved, thereby achieving significant savings in energy use and emission reduction. Second, improve separation efficiency and reduce the reflux ratio to further achieve energy savings and cost reduction. During the separation process, improving separation efficiency can significantly reduce energy consumption, enhance product quality, decrease emissions, increase recovery rates, and boost corporate profitability. In the polysilicon distillation process, the use of new separation equipment such as high-efficiency guide sieve plates and novel packing materials can improve the separation efficiency and reduce the operating reflux ratio of the distillation tower. Since the energy consumption of the distillation tower is proportional to the reflux ratio, energy consumption is reduced in proportion as well. Improving separation efficiency is also the most effective way to enhance the quality of polysilicon products and reduce silicon tetrachloride emissions. Third, comprehensively optimize processes to achieve energy savings. A comprehensive material balance and energy balance is conducted for the various materials used in polysilicon production, to assess the rationality of energy consumption. Thermal integration techniques are employed to optimize the process and minimize energy use and waste. By implementing energy-saving and clean production measures throughout the production line, as well as achieving closed-loop clean production during the manufacturing process, it is possible to reduce energy consumption and the use of raw materials such as Si (silicon), H2 (hydrogen), and Cl2 (chlorine), thereby cutting costs. This approach enables the products to be competitive on the international market, with quality that meets the requirements of current and future ultra-large-scale integrated circuits and solar cells. In addition, the production of polysilicon generates large amounts of chlorosilane by-products such as SiCl4 (silicon tetrachloride), SiH2Cl2 (dichlorodihydrosilane), and SiHCl3 (trichlorohydrosilane), which keeps production costs high. Some of these chlorosilanes and hydrogen chloride end up in the exhaust gas emissions, increasing both the costs associated with exhaust gas treatment and the amount of pollutants released. The concentration of chloride ions in the wastewater ranges from 1700 to 2500 mg/L. Finding effective ways to deal with the by-products of chlorosilanes is key to reducing the production costs of polysilicon and achieving energy conservation and emission reduction; it also represents a major technical challenge for polysilicon manufacturers today. The recycling and comprehensive utilization of exhaust gases, by-products, and waste heat can reduce the environmental impact of polysilicon production projects, thereby further achieving the goals of energy conservation and emission reduction. The establishment of polysilicon plants abroad is often carried out in conjunction with chemical companies, operating under the umbrella of these chemical groups, which facilitates the implementation of a \"circular economy\" within the group, allowing for \"zero waste emissions\". For example, the German company Wacker has achieved a fully closed-loop production process for polysilicon; its annual sales from silicon products exceed 3 billion euros, of which 1 billion euros comes from silicone products derived from the further processing of polysilicon by-products. In addition to hydrogenating silicon tetrachloride to recover trichlorosilane, silicon tetrachloride and hydrogen chloride can also be used to produce materials in demand in the market today, such as vapor-phase silica, ethyl silicate, silicone products, and synthetic quartz. Improving the photoelectric conversion efficiency reduces production costs. Improving the conversion efficiency of photovoltaic materials and reducing the manufacturing costs of solar cells are two goals that the photovoltaic industry has been striving to achieve. Polysilicon wafers are the core component of solar photovoltaic cells, and the quality of these wafers plays a crucial role in the photoelectric conversion efficiency of solar energy. Under normal circumstances, the photovoltaic conversion efficiency of ordinary solar photovoltaic cells ranges from 10% to 14%, while that of solar photovoltaic cells using high-purity silicon wafers can reach 16% or even higher. Therefore, in the production process of solar cells, the production of polycrystalline silicon is even more crucial. There are two main methods for producing semiconductor-grade polysilicon from metallurgical-grade silicon: the modified Siemens method and the silane method. In its production process, multi-stage distillation technology and its associated equipment are crucial; the use of advanced chemical distillation equipment and related distillation techniques can improve the quality of the final product, ultra-pure silicon. We have observed that in recent years, driven by policy support in various countries, the downstream photovoltaic industry has grown rapidly. On the upstream side, however, due to the large-scale investments required for capacity expansion and related time constraints, the supply of polysilicon has been significantly insufficient. As a result of this imbalance between supply and demand, polysilicon prices have continued to rise. Polysilicon material represents the largest component of the overall cost of photovoltaic power generation. In most domestic photovoltaic companies, the cost of silicon materials accounts for over 56.2% of the total production cost of solar cells, and roughly 30% of the cost of grid-connected photovoltaic systems. Therefore, further reducing costs and enhancing the market competitiveness of polysilicon materials play a crucial role in promoting the development of the entire photovoltaic industry chain. The main approaches include: first, introducing new types of separation and mass transfer equipment; for example, the high-efficiency guided sieve tray towers and packed towers developed by Beijing University of Chemical Technology play a significant role in accelerating the distillation process in polysilicon production and facilitating integrated and closed-loop clean production ； II. Increase polysilicon production by introducing new distillation units, thereby enabling larger-scale polysilicon manufacturing ； III. Development and application of large-scale synthetic furnaces and reduction.