A method for producing high-purity granular silicon

Abstract

The present invention discloses a method for producing high-purity granular silicon. By adjusting the reaction deposition temperature of a fluidized bed and the concentration of silicon-containing gas, a temperature layer and a concentration layer are formed on the inner wall of the fluidized bed. When silicon is deposited on the inner wall of a graphite inner component to a certain thickness, resulting in a temperature difference, the stress is reduced or weakened by the temperature layer and the concentration layer, thereby preventing the graphite inner component on the inner wall of the fluidized bed from being directly damaged when the stress is released. The stress of the silicon deposited on the surface of the inner wall of the fluidized bed is dispersed through the formation of the temperature layer and the concentration layer, which is conducive to extending the continuous operation time of the fluidized bed, avoiding reduction in product quality and / or shutdown for maintenance and overhaul due to rupture of the graphite components, thereby achieving long-term stable operation of the fluidized bed and extending the operation cycle of the fluidized bed.

Description

Technical Field

[0001] The invention belongs to the field of solar photovoltaic material preparation, in particular to a method for producing high-purity granular silicon. Background Art

[0002] High-purity polysilicon is the basic raw material for integrated circuits and silicon-based solar cells. The preparation of high-purity polysilicon is mainly through the preparation of high-purity elemental silicon by thermal decomposition or hydrogen reduction of silicon-containing gas. This method is called chemical vapor deposition (CVD) in this field, and silicon-containing gas is also called silicon source. The current mainstream methods for preparing high-purity polysilicon are the modified Siemens method and the fluidized bed method, which are to deposit silicon-containing gas on the silicon core or seed crystal through hydrogen reduction or thermal decomposition reaction. The modified Siemens method is to heat the silicon core to a certain temperature with electric current in a metal bell-shaped reactor, and then introduce hydrogen and silicon-containing gas. When the diameter of the silicon core grows to a certain diameter to form a large-diameter silicon rod, the application of electric current heating and the introduction of hydrogen and silicon-containing gas are stopped. After the temperature drops to below 50-100°C, the silicon rod is harvested. This method is that once the silicon rod grows to a certain diameter, the harvesting must be interrupted. It is an intermittent operation rather than a continuous operation. Through this method, The high-purity polysilicon produced by the fluidized bed method is also commonly referred to as rod-shaped polysilicon; while the fluidized bed method is to introduce silicon-containing gas and hydrogen into a fluidized bed filled with seed crystals in a fluidized bed reactor at 600-1200°C. The silicon-containing gas is thermally decomposed in the fluidized bed and deposited on the seed crystals, and then continues to grow on the surface of the seed crystals to form granular polysilicon products. Usually, granular polysilicon products are also called high-purity granular silicon or granular silicon or high-purity granular silicon. High-purity granular silicon can be continuously taken out from the fluidized bed, and silicon-containing gas and hydrogen can be continuously introduced from the bottom of the fluidized bed, and seed crystals can be continuously added from the top of the fluidized bed to continuously produce polysilicon. It is a continuous operation. The silicon-containing gases used to prepare rod-shaped polysilicon and high-purity granular silicon include silane, dichlorosilane, trichlorosilane, tribromosilane, etc. The silicon-containing gases commonly used to prepare rod-shaped polysilicon and high-purity granular silicon are silane gas, dichlorosilane and trichlorosilane. Different silicon-containing gases have different reaction temperatures for preparing rod-shaped polysilicon and high-purity granular silicon. Currently, silane gas and trichlorosilane are the main ones. In the production process of rod-shaped polysilicon by the modified Siemens process, the metal bell-shaped reactor or simply the reduction furnace is the core equipment of the modified Siemens process. In the production process of high-purity granular silicon by the fluidized bed process, the fluidized bed reactor is the core equipment of the fluidized bed process.

[0003] Typical fluidized bed structures for high-purity granular silicon production are shown in patents US005260538A, CN107364869A, CN110770167A, CN108698008A, and CN105658577A. During the fluidized bed process for producing high-purity granular silicon, heat is provided by either an induction heater or a graphite resistance heater. When using a graphite resistance heater, the inner wall temperature of the fluidized bed is higher, resulting in more silicon deposition on the inner wall of the fluidized bed reactor. In order to reduce the problem of silicon deposition on the inner wall of the reactor, US2012 / 230903A1 discloses a fluidized bed reactor, which has a gas distributor for distributing gas in the reaction chamber of the reactor, including a plurality of distributor openings connected to provide fluid communication between a first gas source, a second gas source and the reaction chamber, wherein the distributor openings each have at least one central opening and one non-central opening, wherein the non-central opening is connected only to the first gas source in a fluid-connected manner, and not to the second gas source. The reactor should be able to avoid silicon deposition on the reactor wall. Patent CN107364869A uses an induction heating device to provide heat, and places the induction heating device in a hollow cavity formed by inner and outer tubes. The hollow cavity is filled with hydrogen, nitrogen or inert gas for protection and maintains a pressure of 0.01 to 5 MPa. The fluidized bed reactor of patent CN107364869A uses induction heating to directly heat the silicon particles inside the reaction chamber, so that the temperature of the reaction tube is lower than the temperature inside the reaction chamber, thereby avoiding tube wall deposition. At the same time, the heating is more uniform, which is suitable for large-diameter fluidized bed reactors. The production capacity of a single reactor is greatly improved. However, even with induction heating, the tube wall temperature is still high. Although patent CN107364869A can significantly reduce tube wall deposition, tube wall deposition is still inevitable, and the thickness of the silicon deposited on the tube wall gradually increases with the extension of operation time.

[0004] Even if induction heating is used, the temperature of the inner wall of the fluidized bed reactor is still high, which will inevitably lead to silicon deposition. This deposited silicon occurs not only on the internal tube wall of the fluidized bed, but sometimes also at the nozzle position of the fluidized bed air inlet. To address these issues, US Patent No. 2002 / 0102850A1 discloses a method for preventing or removing silicon deposits on the feed gas nozzle by continuously, discontinuously, or controlledly metering HCl + inert gas (H2, N2, He, Ar) or inert gas H2. US Patent No. 4868013A describes a method for cooling the surface of the reactor tube by injecting cold inert gas (e.g., H2), thereby reducing deposition on the wall. US Patent No. 2002 / 0081250A1 uses a halogen-containing gaseous etchant, such as hydrogen chloride, chlorine, or silicon tetrachloride, at or near the operating temperature of a fluidized bed reactor to etch away or partially etch away deposits on the reactor tube wall. Patent No. CN217490804U improves the gas distributor by providing an inner ring distributor and an outer ring distributor to improve the mixing uniformity of the raw gas, thereby improving reaction efficiency and product quality. It can also reduce the concentration of the raw gas in the reactor wall area, which helps reduce the rate of silicon deposition on the reactor wall.

[0005] Silicon deposition on the inner wall of the fluidized bed is detrimental to the continuous operation of the high-purity granular silicon fluidized bed. On the one hand, the expansion coefficients of the inner wall of the fluidized bed and the silicon deposited on the internal surface are inconsistent. The difference in expansion coefficients will increase the risk of cracking inside the fluidized bed, which is not conducive to the long-term operation of the fluidized bed. On the other hand, silicon deposited on the inner wall of the fluidized bed will hinder the transfer of external heat. In order to maintain the temperature required for the reaction, it is necessary to increase the power of the electric heater for induction heating or resistance heating, which will increase power consumption and operating costs. At the same time, increasing the power of the electric heater will cause the furnace wall temperature to rise, and the speed of silicon deposition on the inner wall of the fluidized bed will accelerate, forming a vicious circle.

[0006] Patent CN1088444C points out that during the modified Siemens process for polysilicon production, as the diameter of the polysilicon rod increases, the temperature difference between the inside and outside of the polysilicon rod increases, resulting in large residual stresses within the rod. Patent CN108698008A also points out that silicon deposition on hot reactor components, such as the inner wall of the reactor tube, leads to heat accumulation and, consequently, thermomechanical loading of the reactor tube, until mechanical failure or melting of the wall deposits occurs when the wall deposits reach a certain thickness. Furthermore, because the wall deposits cause the flow cross-section to shrink, seed crystals can only enter the fluidized bed to a limited extent from above, leading to reactor failure. Minimizing the problem of silicon deposition on hot reactor surfaces is crucial for the economic operation of the fluidized bed process.

[0007] Furthermore, CN110770167B also points out that a general problem affecting fluidized bed reactors can be contamination of the fluidized bed, and therefore of the granular polysilicon, at the operating temperature of the reactor. Such contamination is caused in particular by the materials of construction of the reactor, in particular the reactor tubes, inside which deposition occurs. For example, nickel from nickel-containing steels has been found to diffuse into the fluidized bed and contaminate the high-purity granular silicon. Other stainless steel components with a high potential for contamination are iron and chromium. To prevent or at least minimize such contamination, ceramic linings or coatings can be used, for example. Thus, WO2015 / 197498A1 describes a fluidized bed reactor having a reactor tube having a matrix consisting of at least 60 wt% silicon carbide and a coating consisting of at least 99.99 wt% silicon carbide on its inside. The problem is that the ceramic lining is subjected to thermal and mechanical stresses over its entire length, which can lead to mechanical defects.

[0008] Furthermore, CN108138992B states that the compressive, flexural, and tensile strengths of known liners are insufficient to allow for the construction of liners for large-scale FBRs capable of increasing polysilicon production and productivity compared to reactors known in the prior art. Specifically, tensile stresses acting on the exterior of the cylindrical graphite liner in a silicon FBR reactor can cause axial fracture of the cylindrical graphite segment that lines the reactor and serves as the process lining. Axial pressure required to maintain a seal and radial pressure required to maintain process purity can create axial cracks or cause existing graphite cracks to propagate axially, leading to liner fracture or breakage and operational failure. To address this, CN108138992B employs an annular liner that also includes at least one layer of wrapping wrapped around the outer surface. The wrapping is configured to prevent radial expansion of the tube, thereby preventing or eliminating fractures in the liner of an FBR used to produce polysilicon with high purity and productivity.

[0009] The combined effects of the internal stress, thermal stress, and mechanical stress of the silicon deposited on the inner wall of the fluidized bed can cause damage to the reaction tubes. In particular, the expansion coefficient of the silicon deposited on the inner wall of the fluidized bed is inconsistent with the expansion coefficient of the inner wall lining and coating of the fluidized bed. As the thickness of the silicon deposited on the inner wall of the fluidized bed increases, the internal stress, thermal stress, and mechanical stress of the silicon deposited on the inner wall of the fluidized bed are aggravated. The combined effects of the above-mentioned internal stress, thermal stress, and mechanical stress can cause the fluidized bed reaction tubes or the coating to rupture. For example, when the silicon deposited on the inner wall of the fluidized bed, the inner graphite wall, and the coating rupture together, boron, phosphorus, and metal impurities on the inner graphite wall will escape and then enter the high-purity granular silicon, thereby causing contamination of the high-purity granular silicon product and reducing the quality of the high-purity granular silicon product. The fluidized bed reactor has to be stopped for maintenance and overhaul, which not only increases the cost of the internal materials of the fluidized bed, but also causes downtime losses, resulting in increased unit maintenance and depreciation costs of the high-purity granular silicon product, thereby reducing the economic efficiency of the fluidized bed process.

[0010] In order to solve the impact of silicon deposited on the inner wall of the fluidized bed on the inner wall of the graphite, while reducing the silicon deposited on the inner wall of the fluidized bed, reducing silicon loss, and extending the fluidized bed reaction time, patent CN102083522B provides a fluidized bed reactor system and a method for reducing silicon deposition on the reactor wall. Its reactor system and distribution unit are particularly well suited to reducing the deposition rate of thermally decomposable compounds on the reactor wall (for example, the deposition of silicon from silane). The distributor of the reaction system is configured to direct the thermally decomposable compound toward the central part of the reactor and away from the reactor wall to prevent material (for example, silicon) from being deposited on the reactor wall. Although patent CN102083522B minimizes silicon deposition on the inner wall of the fluidized bed, silicon deposition on the inner wall of the fluidized bed reactor is still difficult to avoid and affects the process of producing granular silicon.

[0011] Therefore, on the basis of the existing situation, it is necessary to develop a method for producing high-purity granular silicon. When the fluidized bed is running, silicon is deposited on the inner wall of the fluidized bed, which is unavoidable. The internal stress of the deposited silicon on the inner wall of the fluidized bed is reduced or / and weakened, and the impact on the inner wall of the fluidized bed reactor or / and the lining and coating of the inner wall of the fluidized bed is reduced or / and weakened, and the rupture of the reaction tube inside the fluidized bed and / or the rupture of the coating on the surface of the internal reaction tube is avoided, thereby extending the continuous operation time of the fluidized bed. Summary of the Invention

[0012] The object of the present invention is to overcome the deficiencies in the prior art and to provide a method for producing high-purity granular silicon, which can reduce the influence of the internal stress of silicon formed on the surface of the inner wall of a fluidized bed reactor on the inner wall of the fluidized bed reactor and / or the lining and coating of the inner wall of the fluidized bed, thereby avoiding the rupture of the reaction tubes inside the fluidized bed and / or the rupture of the coating on the surface of the internal reaction tubes, thereby extending the continuous operation time of the fluidized bed.

[0013] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0014] The present invention provides a method for producing high-purity granular silicon, comprising the following steps:

[0015] The process of preparing high-purity granular silicon by depositing silicon-containing gas in the feed gas into the fluidized bed reaction zone at a reaction deposition temperature of 650°C to 1200°C includes:

[0016] Adjusting the reaction deposition temperature at least once to form at least one temperature ring on the inner wall of the fluidized bed reactor; and

[0017] The concentration of the silicon-containing gas is adjusted at least once to form at least one concentration ring layer on the inner wall of the fluidized bed reactor.

[0018] Furthermore, the silicon-containing gas is at least one of silane, dichlorosilane, trichlorosilane, and tribromosilane.

[0019] Furthermore, the temperature circle layers are 2-50 layers, preferably 5-30 layers.

[0020] Furthermore, the concentration circle layers are 2-50 layers, preferably 5-30 layers.

[0021] Furthermore, the difference in the reaction deposition temperature before and after adjusting the reaction deposition temperature is 30-200°C, preferably 50-150°C.

[0022] Furthermore, when adjusting the concentration of the silicon-containing gas, the volume concentration of the silicon-containing gas in the feed gas is controlled at 2-50%; and the difference in the volume concentration of the silicon-containing gas in the feed gas before and after the adjustment is 2-20%, preferably 5-15%.

[0023] Furthermore, at the beginning of the reaction, the initial volume concentration of the silicon-containing gas in the feed gas is 5%-30%, preferably 10%-20%.

[0024] Furthermore, the thickness of the temperature circle is 0.2-3 cm, preferably 0.5-1 cm;

[0025] And / or, the concentration circle layer has a thickness of 0.2-3 cm, preferably 0.5-1.5 cm.

[0026] Furthermore, adjusting the reaction deposition temperature at least once to form at least one temperature layer on the inner wall of the fluidized bed reactor; and adjusting the concentration of the silicon-containing gas at least once to form at least one concentration layer on the inner wall of the fluidized bed reactor, including:

[0027] To set the interval time, proceed in the following order:

[0028] Adjust the reaction deposition temperature first and then adjust the silicon-containing gas concentration, or adjust the reaction deposition temperature first and then adjust the silicon-containing gas concentration, or continuously adjust the reaction deposition temperature and then adjust the silicon-containing gas concentration, or continuously adjust the silicon-containing gas concentration and then adjust the reaction deposition temperature. Preferably, adjusting the reaction deposition temperature and adjusting the silicon-containing gas concentration are performed alternately in sequence.

[0029] Furthermore, each time the deposition temperature or the silicon-containing gas concentration is adjusted, the interval time ranges from 4 to 120 hours.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The method for producing high-purity granular silicon described in the present invention adjusts the reaction deposition temperature of the fluidized bed to achieve the purpose of controlled formation of temperature layers when silicon is inevitably deposited on the inner wall of the fluidized bed. When the silicon deposited on the inner wall of the fluidized bed reaches a certain thickness, resulting in excessive stress release, the released stress is weakened or reduced at the junction of the temperature layers, thereby achieving the purpose of reducing or / and weakening the released stress by the temperature layers, avoiding damage to the inner wall of the fluidized bed reactor or / and the lining and coating of the inner wall of the fluidized bed when the internal stress of the silicon deposited on the inner wall is released. The temperature layers also reduce and weaken the stress difference inside the silicon deposited on the inner wall of the fluidized bed, which is beneficial to avoiding the reduction in quality of high-purity granular silicon products or the need to stop production for maintenance due to rupture of the inner wall of the reactor or / and the lining and coating of the inner wall of the fluidized bed, thereby extending the continuous operation time of the fluidized bed, improving the operation cycle of the fluidized bed, and improving economic efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the structure of a fluidized bed reactor provided by an embodiment of the present invention;

[0033] Figure 2 、 Figure 3 、 Figure 4 It is a schematic diagram of depositing silicon on the inner surface of the liner provided by an embodiment of the present invention.

[0034] In the figure: 1. Reaction outer tube; 2. Reaction inner tube; 3. Induction heating device; 4. Gas distributor; 5. Inner lining; 6. Insulation layer; 7. Exhaust gas outlet; 9. Seed crystal feed inlet; 101. Top; 102. Expansion section; 103. First straight pipe section; 104. Second straight pipe section; 105. Bottom; 401. Product outlet; 402. Cooling fluid inlet and outlet; 403. Gas inlet; 404. Nozzle; 405. Mixed air inlet cavity; 406. Cooling fluid cavity; 12. Initial layer; 13. Concentration layer two; 14. Temperature layer three; 15. Temperature layer four. DETAILED DESCRIPTION

[0035] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. In the case described below, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0036] In this embodiment, the deposition temperature of the granular silicon deposition reaction is adjusted. Without affecting the continuous production of granular polycrystalline silicon, the problem of unavoidable silicon deposition on the inner wall of the fluidized bed reactor during granular polycrystalline silicon production is exploited. At a set deposition reaction temperature, a ring of deposited silicon layer is formed on the inner wall of the fluidized bed reactor. When the silicon deposited on the inner wall of the reactor reaches a certain thickness, the deposition reaction temperature is changed. At the new reaction deposition temperature, silicon is deposited on the inner wall of the fluidized bed reactor during normal production. Due to the temperature change, the density and crystallinity of the silicon deposited on the surface of the fluidized bed differ, and the silicon deposited on the inner surface of the fluidized bed at different temperatures forms another ring of deposited silicon layer. In this embodiment, the annular deposited silicon layers of different density and crystallinity formed at different reaction deposition temperatures are referred to as temperature rings. Similarly, in this embodiment, the feed raw gas concentration, i.e., the concentration of the silicon-containing gas in the feed gas, is adjusted. Without affecting the continuous production of granular silicon, the problem of unavoidable silicon deposition on the inner wall of the fluidized bed reactor during granular silicon production is exploited. At a set feed raw gas concentration, a ring of deposited silicon is formed on the inner wall of the fluidized bed reactor. When the silicon deposited on the reactor inner wall reaches a certain thickness, the feed raw gas concentration, i.e., the volume concentration of the silicon-containing gas in the feed gas, is adjusted. At the new volume concentration of the silicon-containing gas in the feed gas, silicon is deposited on the inner wall of the fluidized bed reactor during normal fluidized bed production. Due to the change in the concentration of the silicon-containing gas in the feed gas, the density and crystallinity of the silicon deposited on the inner wall of the fluidized bed vary. Silicon deposited on the inner surface of the fluidized bed at different concentrations of the silicon-containing gas in the feed gas forms another ring of deposited silicon. In this embodiment, the annular deposited silicon layers of varying density and crystallinity formed at different concentrations of the silicon-containing gas in the feed gas are referred to as concentration rings.

[0037] In order to achieve the purpose of the above embodiment, this embodiment adopts the following technical solution: adjusting the feed raw material concentration and the reaction deposition temperature, without affecting the continuous production of high-purity granular silicon, utilizing the problem of inevitable wall deposition of silicon on the inner wall of the fluidized bed reactor during the production of high-purity granular silicon, so that the silicon deposited on the inner wall of the fluidized bed reactor forms a concentration layer and a temperature layer. When the internal stress of the silicon deposited on the inner wall of the fluidized bed reactor is released, the internal stress release is reduced or / and weakened at the junction of the temperature layer and / or the concentration layer, avoiding the internal stress release of the silicon deposited on the inner wall of the fluidized bed reactor, which leads to damage to the inner wall of the fluidized bed reactor or / and the lining and coating of the inner wall of the fluidized bed reactor, and avoiding boron, phosphorus and metal impurities from entering the reaction zone of the fluidized bed reactor, resulting in the quality of the high-purity granular silicon product being reduced and then stopping the operation for maintenance, thereby extending the continuous operation time of the fluidized bed and improving the economy of the fluidized bed operation.

[0038] It is particularly pointed out that in this embodiment, the inner wall of the fluidized bed refers to the wall portion that is in direct contact with the gas inside the fluidized bed, and is not limited to the inner lining without a layer of silicon carbide coating deposited on the surface or the inner lining with a layer of silicon carbide coating deposited on the surface. For example, here, the inner lining without a layer of silicon carbide coating deposited on the surface or the inner lining with a layer of silicon carbide coating deposited on the surface are collectively referred to as the inner wall of the fluidized bed.

[0039] A specific implementation method is to intermittently adjust the reaction deposition temperature in the fluidized bed and the concentration of silicon-containing gas in the feed raw material gas within a certain operating time. When adjusting the reaction deposition temperature, by adjusting the reaction deposition temperature inside the fluidized bed, different temperature zones are formed by taking advantage of the fact that a low reaction deposition temperature leads to slow deposition, which results in high density but lower crystallinity; a high reaction deposition temperature leads to fast deposition, which results in low density but higher crystallinity; and adjusting the feed raw material gas concentration, i.e., the silicon-containing gas concentration, by taking advantage of the fact that a low silicon-containing gas concentration in the feed gas leads to slow deposition, which results in higher density and higher crystallinity. The concentration of silicon-containing gas in the inlet air is high, the deposition is fast, and the corresponding density and crystallinity are lower, thereby forming different concentration layers; when the silicon deposited on the inner wall of the graphite internal reaches a certain thickness, resulting in a temperature difference, the stress is reduced or / and weakened at the junction of the temperature layer and / or the concentration layer, avoiding direct damage to the inner wall of the fluidized bed reactor or / and the lining and coating of the fluidized bed inner wall when the internal stress of the silicon deposited on the inner wall is released. The stress difference inside the silicon deposited on the inner wall of the fluidized bed is also reduced through the temperature layer and / or concentration layer, which is beneficial to extending the continuous operation time of the fluidized bed.

[0040] A method for producing high-purity granular silicon, comprising the following steps:

[0041] At 650-1200°C, the volume concentration of silicon-containing gas in the feed gas is 5%-30%, preferably 10%-20%, and is introduced into the fluidized bed reaction zone through a gas distributor. Deposition is carried out at a reaction deposition temperature of 650°C to 1200°C to produce a high-purity granular silicon product. During the operation of the fluidized bed, the reaction deposition temperature or the silicon-containing gas concentration is adjusted every 4-120 hours. The adjustment can be made 2-51 times, preferably 5-31 times, to form 5-30 temperature circles. For example, in the fluidized bed granular silicon production process, after the fluidized bed starts feeding, the first adjustment is made after 4 hours of operation. The reaction deposition temperature is adjusted during the first adjustment. The second adjustment is made after the fluidized bed has been running for 10 hours, but the silicon-containing gas concentration is adjusted at this time. By analogy, 1-50 temperature circles are formed, preferably 5-30 temperature circles. When adjusting the reaction deposition temperature and the silicon-containing gas concentration, the reaction deposition temperature and the silicon-containing gas concentration can be adjusted alternately in sequence, that is, the silicon-containing gas concentration can be adjusted after adjusting the reaction deposition temperature, or the reaction deposition temperature can be adjusted after adjusting the silicon-containing gas concentration. The reaction deposition temperature can also be adjusted continuously before adjusting the silicon-containing gas concentration, or the reaction deposition temperature can be adjusted continuously after adjusting the silicon-containing gas concentration. However, preferably, the reaction deposition temperature and the silicon-containing gas concentration are adjusted alternately in sequence.

[0042] When forming the concentration layer or the temperature layer, the volume concentration of the silicon-containing gas in the silicon-containing gas concentration raw material is 2-50%.

[0043] When forming the concentration layer or the temperature layer, the volume concentration of the silicon-containing gas in the silicon-containing gas concentration raw material is preferably 10%-30%.

[0044] When forming the temperature ring, the difference in the decomposition and deposition temperature of the silicon-containing gas is 30-200° C., preferably 50-150° C. When forming the concentration ring, the difference in the volume concentration of the silicon-containing gas is 2-20%, preferably 5-15%.

[0045] When forming the temperature layer, the thickness of the temperature layer is 0.2-3 cm, preferably the thickness of the temperature layer is 0.5-1.5 cm. When forming the concentration layer, the thickness of the concentration layer is 0.2-3 cm, preferably the thickness of the concentration layer is 0.5-1.5 cm.

[0046] The concentration of silicon-containing gas entering the fluidized bed can be expressed as volume concentration or molar concentration. However, these two expressions are essentially the same.

[0047] The following describes the contents involved in the above embodiment in conjunction with a preferred embodiment.

[0048] The fluidized bed reactor used in the embodiment is as described in CN107364869A. Figure 1 This is a schematic diagram of the structure of a fluidized bed reactor used in an embodiment of the present invention. 1 represents an outer reaction tube, 2 an inner reaction tube, 3 an induction heating device, 4 a gas distributor, 5 an inner liner, 6 an insulation layer, 7 an exhaust gas outlet, 9 a seed crystal feed port, 101 a top portion, 102 an expansion section, 103 a first straight tube section, 104 a second straight tube section, 105 a bottom portion, 401 a product outlet, 402 a cooling fluid inlet and outlet, 403 a gas inlet, 404 a nozzle, 405 a mixed gas inlet cavity, and 406 a cooling fluid cavity. The reaction tube consists of an inner reaction tube 2 and an outer reaction tube 1. The heating device is an induction heating device and is located in a hollow cavity formed by the inner and outer tubes. The hollow cavity is filled with hydrogen, nitrogen, or an inert gas for protection and maintained at a pressure of 0.01 to 5 MPa. The pressure in the hollow cavity is higher than the pressure inside the reaction tube. The pressure in the hollow cavity is P1, the pressure at the fluidized bed exhaust outlet 7 is P2, and the pressure in the reactor tube is P3. P1>P3>P2. The pressure P3 in the fluidized bed reactor tube cannot be measured. The pressure P2 at the fluidized bed exhaust outlet 7 can, to a certain extent, represent changes in P3. A pressure detection device is installed in the hollow cavity to maintain a constant pressure of the gas filling the hollow cavity. When the reactor tube ruptures, the pressure detection device detects a pressure fluctuation in the hollow cavity, indicating a rupture.

[0049] The silicon-containing gas is one or more of silane, dichlorosilane, trichlorosilane, and tribromosilane.

[0050] The temperature circle layer is 2-50 layers, preferably 5-30 layers. The temperature circle layer or concentration circle layer can be deposited multiple times as the continuous operation time increases, and is not limited to the number of layers shown in this embodiment.

[0051] When forming the concentration layer or the temperature layer, the volume concentration of the silicon-containing gas in the silicon-containing gas concentration raw material is 2-50%.

[0052] When forming the concentration layer or the temperature layer, the volume concentration of the silicon-containing gas in the silicon-containing gas concentration raw material is preferably 10%-30%.

[0053] When forming the temperature ring, the difference in the decomposition and deposition temperature of the silicon-containing gas is 30-200° C., preferably 50-150° C. When forming the concentration ring, the difference in the volume concentration of the silicon-containing gas is 2-20%, preferably 5-15%.

[0054] When forming the temperature layer, the thickness of the temperature layer is 0.2-3 cm, preferably the thickness of the temperature layer is 0.5-1.5 cm. When forming the concentration layer, the thickness of the concentration layer is 0.2-3 cm, preferably the thickness of the concentration layer is 0.5-1.5 cm.

[0055] Example:

[0056] Example 1:

[0057] The silicon-containing gas in the feed gas is trichlorosilane, which enters the fluidized bed reaction zone through the gas distributor 4, the gas inlet 403 and the nozzle 404, and undergoes continuous thermal decomposition reaction at a reaction deposition temperature of 1150°C to produce high-purity granular silicon products.

[0058] like Figure 2 、 Figure 3 As shown, after the reaction starts, at 1150°C, the volume concentration of trichlorosilane in the feed gas is 30%, and high-purity granular silicon is continuously produced. After 24 hours of production operation, silicon is deposited on the inner surface of the liner 5 to form an initial ring layer 12; at this time, the reaction deposition temperature remains unchanged, and the volume concentration of trichlorosilane in the feed gas is adjusted to 20% and the operation is continued, so that the volume concentration difference of trichlorosilane is 10%°C. At this time, a concentration ring layer 2 13 is formed on the surface of the initial ring layer 12; at this time, the volume concentration of trichlorosilane is kept unchanged at 20%, and the deposition temperature is adjusted to 950°C, so that the reaction deposition temperature difference of silicon-containing gas is 200°C. After 72 hours of operation, a temperature ring layer 3 14 is formed on the surface of the concentration ring layer 2 13; at this time, the volume concentration of trichlorosilane in the feed gas is adjusted to 25%, and the reaction deposition temperature is adjusted to 1100°C and no longer changes. After 85 days of continuous operation, the pressure detection device set in the hollow cavity does not detect pressure fluctuations. At this time, the vehicle was stopped for maintenance and it was found that the thickness of the initial layer 12 was 0.2 cm, the thickness of the second concentration layer 13 was 0.3 cm, and the thickness of the third temperature layer 14 was 0.3 cm.

[0059] Comparative Example 1:

[0060] The silicon-containing gas in the feed gas is trichlorosilane, which enters the fluidized bed reaction zone through the gas distributor 4, the gas inlet 403 and the nozzle 404, and undergoes continuous thermal decomposition reaction at a reaction deposition temperature of 1150°C to produce high-purity granular silicon products.

[0061] After the reaction started, at 1150°C, the volume concentration of trichlorosilane in the feed gas was 30%, and high-purity granular silicon was continuously produced. The subsequent volume concentration of trichlorosilane remained unchanged, and the temperature remained unchanged. After 12 days of continuous operation, the pressure detection device installed in the hollow cavity detected pressure fluctuations, indicating that the inner tube of the reaction was ruptured, causing the gas in the hollow cavity to flow into the reaction zone.

[0062] Example 2:

[0063] The silicon-containing gas in the feed gas is silane, which enters the fluidized bed reaction zone through the gas distributor 4, the gas inlet 403 and the nozzle 404, and undergoes continuous thermal decomposition reaction at a reaction deposition temperature of 800°C to produce high-purity granular silicon products.

[0064] like Figure 2 、 Figure 3 As shown, after the reaction began, at 800°C, the feed gas contained 20% silane by volume, continuously producing high-purity granular silicon. After 48 hours of production, silicon deposited on the inner surface of the liner 5 to form an initial layer 12. The silicon-containing gas concentration in the reaction gas was adjusted to 10% by volume, resulting in a 10% difference in silicon-containing gas concentration. After 72 hours of operation, a second concentration layer 13 formed on the surface of the initial layer 12. The reaction deposition temperature was then adjusted to 900°C, resulting in a 100°C difference in silicon-containing gas reaction deposition temperature. The reaction continued for another 72 hours, forming a third temperature layer 14 on the surface of the second concentration layer 13. Subsequently, the silane concentration was increased to 20% by volume, and the reaction deposition temperature was adjusted to 850°C and not changed. After 100 days of continuous operation, no pressure fluctuations were detected by the pressure detection device installed in the hollow cavity. The process was shut down for maintenance, and it was found that the thickness of the initial layer 12 was 0.2 cm, the thickness of the second concentration layer 13 was 0.3 cm, and the thickness of the third temperature layer 14 was 0.4 cm.

[0065] Comparative Example 2:

[0066] The silicon-containing gas in the feed gas is silane, which enters the fluidized bed reaction zone through the gas distributor 4, the gas inlet 403 and the nozzle 404, and undergoes continuous thermal decomposition reaction at a reaction deposition temperature of 800°C to produce high-purity granular silicon products.

[0067] After the reaction started, at 800°C, the volume concentration of silane in the feed gas was 20%, and high-purity granular silicon was continuously produced. The subsequent volume concentration of silane remained unchanged, and the temperature remained unchanged. After 20 days of continuous operation, the pressure detection device installed in the hollow cavity detected pressure fluctuations, indicating that the inner tube of the reaction was ruptured, causing the gas in the hollow cavity to flow into the reaction zone.

[0068] Example 3:

[0069] The silicon-containing gas in the feed gas is dichlorosilane, which enters the fluidized bed reaction zone through the gas distributor 4, the 403 gas inlet and the 404 nozzle, and undergoes continuous thermal decomposition reaction at a reaction deposition temperature of 850°C to produce high-purity granular silicon products.

[0070] like Figure 2 、 Figure 3As shown, after the reaction began, at 850°C, the feed gas contained 10% by volume of silicon, continuously producing high-purity granular silicon. After 48 hours of production, silicon deposited on the inner surface of the liner 5 to form an initial layer 12. The volume concentration of dichlorosilane was adjusted to 15%, resulting in a 5% volume concentration difference. The reaction continued for 48 hours, at which point a second concentration layer 13 formed on the surface of the initial layer 12. The reaction deposition temperature was then adjusted to 900°C, resulting in a 50°C temperature difference in the silicon-containing gas reaction deposition. After 72 hours of operation, a third temperature layer 14 formed on the surface of the second concentration layer 13. The reaction deposition temperature was subsequently adjusted to 850°C and the volume concentration of dichlorosilane to 20%. After 75 days of continuous operation, no pressure fluctuations were detected by the pressure detection device installed in the hollow cavity. The reactor was shut down for maintenance, revealing that the thickness of the initial layer 12 was 0.2 cm, the thickness of the second concentration layer 13 was 0.3 cm, and the thickness of the third temperature layer 14 was 0.3 cm.

[0071] Comparative Example 3:

[0072] The silicon-containing gas in the feed gas is dichlorosilane, which enters the fluidized bed reaction zone through the gas distributor 4, the 403 gas inlet and the 404 nozzle, and undergoes continuous thermal decomposition reaction at a reaction deposition temperature of 850°C to produce high-purity granular silicon products.

[0073] After the reaction started, at 850°C, the volume concentration of dichlorosilane in the feed gas was 10%, and high-purity granular silicon was continuously produced. The subsequent volume concentration of silane remained unchanged. After 15 days of continuous operation, the pressure detection device installed in the hollow cavity detected pressure fluctuations, indicating that the inner tube of the reaction was ruptured, causing the gas in the hollow cavity to flow into the reaction zone.

[0074] Example 4:

[0075] The silicon-containing gas in the feed gas is silane, which enters the fluidized bed reaction zone through the gas distributor 4, the gas inlet 403 and the nozzle 404, and undergoes continuous thermal decomposition reaction at a reaction deposition temperature of 800°C to produce high-purity granular silicon products.

[0076] like Figure 2 、 Figure 3 、 Figure 4As shown, after the reaction starts, at 800°C, the volume concentration of silane in the feed gas is 20%, and high-purity granular silicon is continuously produced. After 48 hours of production operation, silicon is deposited on the inner surface of the liner 5 to form an initial layer 12. At this time, the volume concentration of the silicon-containing gas in the reaction gas is adjusted to 10%, so that the volume concentration difference of the silicon-containing gas is 10%. After running for 72 hours, a concentration layer 2 13 is formed on the surface of the initial layer 12; at this time, the reaction deposition temperature is adjusted to 900°C, so that the reaction deposition temperature difference of the silicon-containing gas is 100°C. The reaction is continued for 72 hours, and a temperature layer 3 14 is formed on the surface of the concentration layer 2 13. Subsequently, the volume concentration of silane is increased to 20%, and the reaction deposition temperature is maintained at 900°C. The reaction continues for 72 hours, and a temperature layer 4 15 is formed at this time; subsequently, the volume concentration of silane is reduced to 15%, and the reaction deposition temperature is maintained at 850°C and no longer changes. After 80 days of continuous operation, the pressure detection device set in the hollow cavity does not detect pressure fluctuations. At this time, the vehicle was stopped for maintenance, and it was found that the thickness of the initial layer 12 was 0.2 cm, the thickness of the concentration layer 2 13 was 0.3 cm, the thickness of the temperature layer 3 14 was 0.4 cm, and the thickness of the temperature layer 4 15 was 0.4 cm.

[0077] Comparative Example 4:

[0078] The silicon-containing gas in the feed gas is silane, which enters the fluidized bed reaction zone through the gas distributor 4, the gas inlet 403 and the nozzle 404, and undergoes continuous thermal decomposition reaction at a reaction deposition temperature of 800°C to produce high-purity granular silicon products.

[0079] After the reaction started, at 800°C, the volume concentration of silane in the feed gas was 20%, and high-purity granular silicon was continuously produced. The subsequent volume concentration of silane remained unchanged, and the temperature remained unchanged. After 20 days of continuous operation, the pressure detection device installed in the hollow cavity detected pressure fluctuations, indicating that the inner tube of the reaction was ruptured, causing the gas in the hollow cavity to flow into the reaction zone.

[0080] The above describes in detail the preferred embodiments of the present invention. It should be understood that numerous modifications and variations based on the concepts of the present invention are possible by those skilled in the art without inventive effort. Therefore, any technical solution that can be derived by those skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. A method for producing high-purity granular silicon, characterized in that: The method comprises: The process of preparing high-purity granular silicon by depositing silicon-containing gas in the feed gas into the fluidized bed reaction zone at a reaction deposition temperature of 650°C to 1200°C includes: Adjusting the reaction deposition temperature at least once to form at least one temperature ring on the inner wall of the fluidized bed reactor; and Adjusting the concentration of the silicon-containing gas at least once to form at least one concentration ring layer on the inner wall of the fluidized bed reactor; Among them, the annular deposited silicon layers with different densities and crystallinity formed at different reaction deposition temperatures are called temperature layers; the annular deposited silicon layers with different densities and crystallinity formed at different concentrations of silicon-containing gas in the inlet gas are called concentration layers.

2. The method for producing high-purity granular silicon according to claim 1, wherein: The silicon-containing gas is at least one of silane, dichlorosilane, trichlorosilane, and tribromosilane.

3. The method for producing high-purity granular silicon according to claim 1, wherein: The temperature circle layer is 5-30 layers.

4. The method for producing high-purity granular silicon according to claim 1, wherein: The concentration circle layers are 5-30 layers.

5. The method for producing high-purity granular silicon according to claim 1, wherein: The difference in reaction deposition temperature before and after adjustment was 50-150°C.

6. The method for producing high-purity granular silicon according to claim 1, wherein: When adjusting the concentration of the silicon-containing gas, the volume concentration of the silicon-containing gas in the feed gas is controlled at 2-50%; and the difference in the volume concentration of the silicon-containing gas in the feed gas before and after the adjustment is 5-15%.

7. The method for producing high-purity granular silicon according to claim 1, wherein: At the beginning of the reaction, the initial volume concentration of silicon-containing gas in the feed gas is 10%-20%.

8. The method for producing high-purity granular silicon according to claim 1, wherein: The thickness of the temperature circle is 0.5-1 cm; And / or, the concentration layer has a thickness of 0.5-1.5 cm.

9. The method for producing high-purity granular silicon according to claim 1, wherein: Adjusting the reaction deposition temperature at least once to form at least one temperature ring on the inner wall of the fluidized bed reactor; and adjusting the concentration of the silicon-containing gas at least once to form at least one concentration ring layer on the inner wall of the fluidized bed reactor, including: To set the interval time, proceed in the following order: The reaction deposition temperature is adjusted first and then the silicon-containing gas concentration is adjusted, or the reaction deposition temperature is adjusted first and then the silicon-containing gas concentration is adjusted, or the reaction deposition temperature is adjusted continuously and then the silicon-containing gas concentration is adjusted, or the reaction deposition temperature is adjusted and the silicon-containing gas concentration is adjusted alternately.

10. The method for producing high-purity granular silicon according to claim 1, wherein: Each time the deposition temperature or the silicon-containing gas concentration is adjusted, the interval time ranges from 4 to 120 hours.

Images