Polysilicon is not unfamiliar to many people in daily life, and solar panels, integrated circuit chips, etc. are all produced from it. However, for the production process of polysilicon, many people still remain in the impression of “high energy consumption and high pollution”. “Without technology, the problem of pollution and energy consumption is unavoidable. However, through independent technology research and development, we have achieved clean production many years ago. The comprehensive energy consumption of polysilicon has been reduced by more than 80%, and the pollution problem has been effectively solved.” China Yan Dazhou, deputy chief engineer of ENFI Engineering Technology Co., Ltd. (hereinafter referred to as China ENFI) and director of the National Engineering Laboratory for Polysilicon Material Preparation Technology, said.
The development of China’s polysilicon industry chain has not been smooth sailing. According to reports, before the birth of China’s self-developed polysilicon production technology, the United States, Japan, Germany and other countries imposed technical blockades on China, and could only import polysilicon raw materials from abroad. 2007 was called the “first year of polysilicon” in China. In that year, the output of polysilicon in China exceeded 1,000 tons for the first time. In 2008, foreign media made false reports on the pollution caused by China’s polysilicon production, and public opinion suppressed the newly emerging Chinese polysilicon industry. In 2010, my country’s photovoltaic industry suffered from low-price dumping of polysilicon from the United States and South Korea. In 2012, it was sanctioned by Europe and the United States on photovoltaic terminal products. After years of hard work, today, in terms of the photovoltaic industry alone, China’s current market size has reached 360 billion yuan, and many Chinese companies’ photovoltaic power generation products are exported overseas.
In the industry, polysilicon has the reputation of “the gem that God gave to mankind”. Silicon ore resources are non-toxic and harmless. China is particularly rich in silicon resources. The production of silicon metal accounts for 2/3 of the world’s total, only 1/4 is used for personal use, and all the rest are exported. Today, polysilicon has become an important raw material for the information industry and new energy industry.
Although China has abundant mineral resources, before 2005, the United States, Japan, Germany and other countries used polysilicon as a strategic material, imposed technological blockade and market monopoly on my country, and almost all demand for polysilicon depended on imports. Under the circumstance that technology is controlled by others, the production level, scale, cost, energy consumption, pollution and other issues of the domestic polysilicon industry have been criticized.
With the expectation of the huge development potential of the photovoltaic industry, after years of technical research, ENFI’s researchers finally broke the foreign monopoly and formed a technical route with Chinese characteristics. According to Yan Dazhou, in 2005, China ENFI built the first domestic demonstration line of polysilicon industrialization with an annual output of 300 tons in its subsidiary China Silicon Hi-Tech Co., Ltd. In 2007, the domestic output of polysilicon exceeded 1,000 tons. Although the related technologies and raw materials had to be imported at that time, the output of China’s photovoltaic panels ranked first in the world. In 2011, the production of domestic polysilicon further increased, which led to a significant drop in the cost of silicon downstream of the solar panel industry chain, and promoted the development of the entire industry chain.
Just as China’s polysilicon industry is developing rapidly, in 2012, European and American countries conducted “double-anti” investigations on China’s photovoltaic industry, which made China’s photovoltaic products be blocked from European and American countries. According to Yan Dazhou, polysilicon companies in Europe and the United States lock in a large number of customers by signing long-term contracts to ensure long-term profits, and then suppress emerging industries in China at low prices by signing short-term contracts. After several measures, in 2012, the whole industry of my country’s polysilicon industry lost money, more than 40 enterprises stopped production, and a large number of equipment imported from abroad with billions of yuan was lost.
The obstruction of overseas markets stimulated the rapid development of the domestic PV market, which in turn promoted the adjustment of China’s energy structure. With the rapid start of the domestic photovoltaic market, my country’s polysilicon industry has shouldered the important task of developing new energy.
In order to solve the problem of high energy consumption in polysilicon production, researchers at ENFI China have made great efforts in the research and development of large-scale energy-saving reduction furnace systems. “Energy-saving reduction furnace system is one of the key technologies to realize large-scale production of polysilicon products. It is the fundamental way to solve large-scale production of polysilicon, reduce costs and improve product quality.” Yan Dazhou introduced that the design optimization of energy-saving reduction furnace system has greatly improved the The annual output of a single furnace of polysilicon energy-saving reduction furnace provides technical support for 10,000-ton polysilicon production line and energy-saving technology. He said that at present, the gas processing capacity of a single unit in the reduction reaction process reaches 45,000Nm3/h, the comprehensive power consumption of polysilicon production is less than 75 kWh per kilogram, and the steam consumption per kilogram of polysilicon production is less than 30 kilograms. These comprehensive energy consumption data represent that China’s polysilicon production technology has reached the world’s advanced level.
In the process of polysilicon production, by-products such as silicon tetrachloride will be produced, and it is difficult to effectively treat the by-products by the previous recycling technology, which is easy to cause pollution to the environment. “In fact, if the technology is appropriate and handled well, the relevant by-products will continue to be put into the production process for use. Through the internal circulation of materials, the utilization efficiency can be further improved and the pollution problem can be solved.” Yan Dazhou introduced, “China ENFI creatively The technology of cascade separation and purification of reaction process gas is proposed, and the process of ‘pressurized separation-absorption-analysis-adsorption-regeneration’ is adopted to realize the material circulation purification, which subverts the technical route of treating the reaction process gas as tail gas in the traditional polysilicon production technology. The separation, purification, reprocessing and recycling rate of gas in the polysilicon production process has increased from 25% to 99.9%, the single-line exhaust gas treatment capacity has reached 45,000 cubic meters per hour, and the energy consumption has been further reduced by 30% compared with foreign imported technologies. Cleaner production, greatly reducing material consumption and production costs.”
The purity of polysilicon is a key indicator for measuring product quality. For this reason, China ENFI started from improving the purity of raw material trichlorosilane, overcame the problem of purifying high-quality polysilicon raw materials, and invented trichlorosilane synthesis, high-efficiency sieve plate and filler. The combined pressurized rectification and purification technology rectifies the purity of the raw material trichlorosilane to more than 9N, and studies dozens of trace components and treatment measures that affect the quality of polysilicon.
Continuous research and development and improvement of polysilicon process technology and equipment level, further energy saving, consumption reduction and cost reduction are the only choices for the survival and development of the polysilicon industry, and the only way to independently develop China’s photovoltaic industry. Yan Dazhou said that after 8 years of unremitting efforts and technology research and development, the comprehensive energy consumption of polysilicon in my country has been greatly reduced, and the market price has dropped from 3.25 million yuan per ton 10 years ago to 90,000 to 120,000 yuan per ton today. Intellectual property rights have laid the foundation for the development of my country’s photovoltaic industry.
Today, photovoltaic power generation made of polysilicon has achieved rapid development in rural electrification, communication industry, large-scale ground power stations, and photovoltaic precision poverty alleviation. For example, Yan Dazhou said that among many polysilicon applications, it is impressive that there is a 60MW photovoltaic power station on the edge of the Tengger Desert in my country. When the station was first built, there was still a desert beneath these solar panels. Gradually, as the solar panels blocked the sunlight, the evaporation of water on the ground was reduced, and grass gradually grew on the severely desertified land. Later, the power station management department raised more than 20 sheep to graze, and now the flock has grown to hundreds. In addition to generating electricity, the construction of photovoltaic power plants also helps the local area to achieve ecological restoration and green farming.