A method for producing granular silicon

Abstract

The present invention discloses a method for producing granular silicon. By adjusting the concentration of feed raw material gas, a concentration layer is formed on the inner wall of a 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 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 deposited silicon on the surface of the inner wall of the fluidized bed is dispersed through the formation of the concentration layer, which is conducive to extending the continuous operation time of the fluidized bed, avoiding reduction in product quality and / or production suspension for maintenance and overhaul due to rupture of 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 present invention belongs to the field of solar photovoltaic material preparation, in particular to a method for producing 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 sources. This method is called chemical vapor deposition (CVD) in this field. The current mainstream methods for preparing high-purity polysilicon are the modified Siemens method and the fluidized bed method, which are prepared by depositing silicon-containing gas on a silicon core or seed crystal through hydrogen reduction or thermal decomposition. 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 requires that the harvesting must be interrupted once the silicon rod grows to a certain diameter. It operates in an intermittent manner rather than continuously. 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, which then continue to grow on the surface of the seed crystals to form granular polysilicon products. Granular polysilicon products are usually also called granular silicon. Granular silicon can be continuously taken out of 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 source gases used to prepare granular silicon include silane, dichlorosilane, trichlorosilane, tribromosilane, etc. Currently, the commonly used silicon source gases for preparing granular silicon are silane gas, dichlorosilane and trichlorosilane. Different silicon source gases have different reaction temperatures for preparing granular polysilicon. Currently, silane gas and trichlorosilane are the main ones. In the production process of granular silicon by fluidized bed method, the fluidized bed reactor is the core equipment of the fluidized bed method.

[0003] Typical fluidized bed structures for granular silicon production are shown in patents US005260538A, CN107364869A, CN110770167A, CN108698008A, and CN105658577A. During the fluidized bed process for producing granular silicon, heat is provided by an induction heater or a graphite resistance heater. When a graphite resistance heater is used to provide heat, the inner wall temperature of the fluidized bed is higher, resulting in more silicon deposition on the inner walls of the fluidized bed reactor. To reduce the problem of silicon deposition on the reactor walls, US2012 / 230903A1 discloses a fluidized bed reactor having a gas distributor for distributing gas within the reactor's reaction chamber. The distributor includes multiple distributor openings that provide fluid communication between a first gas source, a second gas source, and the reaction chamber. Each distributor opening has at least one central opening and one non-central opening, wherein the non-central opening is fluidically connected only to the first gas source and not to the second gas source. This reactor is intended to prevent silicon deposition on the reactor walls. 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 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 be accelerated, 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 may 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 by the reactor tubes, inside which deposition occurs. For example, nickel from nickel-containing steel has been found to diffuse into the fluidized bed and contaminate the granular silicon. Other stainless steel components with a high potential for contamination are iron and chromium. In order to prevent or at least minimize such contamination, for example, a ceramic lining or coating may be employed. Thus, WO2015 / 197498A1 describes a fluidized bed reactor having a reactor tube having a matrix consisting of at least 60 wt% of silicon carbide and a coating consisting of at least 99.99 wt% of silicon carbide on its inside. The problem is that the ceramic lining is subjected to thermal and mechanical stresses over its entire length, which may lead to mechanical defects.

[0008] The internal stress, thermal stress and mechanical stress of the silicon deposited on the inner wall of the fluidized bed will cause damage to the reaction tube, especially since 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 action of the above internal stress, thermal stress and mechanical stress causes the fluidized bed reaction tube to rupture or the coating to rupture. For example, when the silicon deposited on the inner wall of the fluidized bed, the graphite inner wall and the coating rupture together, the boron, phosphorus and metal impurities on the graphite inner wall will escape and then enter the granular silicon, thereby causing the granular silicon product to be contaminated, reducing the quality of the granular silicon product, and causing the fluidized bed reactor to have to stop operating for maintenance and overhaul, which not only increases the cost of the internal materials of the fluidized bed, but also causes downtime losses, increases the unit maintenance cost and depreciation cost of the granular silicon product, and thus reduces the economic efficiency of the fluidized bed process.

[0009] Therefore, on the basis of the existing situation, it is necessary to develop a method for producing 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, so as to avoid 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, thereby extending the continuous operation time of the fluidized bed. Summary of the Invention

[0010] The object of the present invention is to overcome the deficiencies in the prior art and to provide a method for producing granular silicon, which can reduce the influence of the internal stress of silicon formed on the inner wall surface 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 tube inside the fluidized bed and / or the rupture of the coating on the surface of the internal reaction tube, thereby extending the continuous operation time of the fluidized bed.

[0011] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0012] The present invention provides a method for producing granular silicon, comprising the following steps:

[0013] After the reaction starts, at 650-1200°C, when producing granular silicon in a fluidized bed, by adjusting the volume concentration of the silicon source gas in the inlet gas, at least two concentration layers are formed on the inner wall of the fluidized bed reactor, so that the density of deposited silicon between adjacent concentration layers is different.

[0014] Furthermore, the concentration ring layer is an annular deposited silicon layer with different density and crystallinity formed under different concentrations of silicon source gas in the inlet gas.

[0015] Furthermore, the silicon source gas is silane, dichlorosilane, trichlorosilane, or tribromosilane.

[0016] Furthermore, the concentration circle is 2-50 layers.

[0017] Furthermore, the concentration circle is 5-30 layers.

[0018] Furthermore, when forming the concentration ring, the volume concentration difference of the silicon source gas concentration is 2-20%.

[0019] Furthermore, when forming the concentration ring layer, the volume concentration difference of the silicon source gas concentration is 5-15%.

[0020] Furthermore, when forming the concentration ring layer, the volume concentration of the silicon source gas in the silicon source gas concentration raw material is 2-50%.

[0021] Furthermore, when forming the concentration ring layer, the volume concentration of the silicon source gas in the silicon source gas concentration raw material is 10%-30%.

[0022] Furthermore, the thickness of the concentration layer is 0.1-4 cm.

[0023] Furthermore, the thickness of the concentration circle is 0.3-1.5 cm.

[0024] Furthermore, the inner wall of the fluidized bed also includes a coating, and the concentration ring layer is deposited on the coating on the inner wall of the fluidized bed.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention discloses a method for producing granular silicon, which achieves the purpose of controlled formation of concentration layers when silicon is inevitably deposited on the inner wall of the fluidized bed by adjusting the volume concentration of the silicon source gas in the feed gas. 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 concentration layers, thereby achieving the purpose of reducing or / and weakening the released stress by the concentration 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 concentration 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 the granular silicon product or the necessity to stop production for maintenance due to the 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 the economic efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the structure of a fluidized bed reactor provided by an embodiment of the present invention;

[0028] Figure 2 、 Figure 3 It is a schematic diagram of depositing silicon on the inner surface of the liner provided by an embodiment of the present invention.

[0029] In the figure: 1. Outer wall of fluidized bed reactor; 2. Induction heating coil; 3. Insulator; 4. Sensor; 5. Inner tube of fluidized bed reactor; 6. Raw gas inlet; 7. Raw gas nozzle on gas distributor; 8. Tail gas outlet; 9. Granular silicon product outlet; 10. Gas distributor; 11. Seed crystal inlet; 12. Temperature circle one; 13. Temperature circle two; 14. Temperature circle three; 15. Temperature circle four. DETAILED DESCRIPTION

[0030] 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.

[0031] In this embodiment, the feed raw gas concentration, i.e., the concentration of silicon-containing gas in the feed gas, is adjusted. Without affecting the continuous production of granular silicon, the problem of inevitable silicon deposition on the inner wall of the fluidized bed reactor during granular silicon production is utilized. At the set feed raw gas concentration, 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 feed raw gas concentration, i.e., the volume concentration of the silicon source gas in the feed gas, is adjusted. At the new volume concentration of the silicon source gas in the feed gas, silicon is deposited on the inner wall of the fluidized bed reactor during normal production of the fluidized bed. Due to the change in the concentration of the silicon source gas in the feed gas, the density and crystallinity of the silicon deposited on the surface of the fluidized bed are different. At different concentrations of the silicon source gas in the feed gas, the silicon deposited on the inner surface of the fluidized bed forms another ring of deposited silicon layer. In the present invention, the annular deposited silicon layers of different densities and crystallinities formed at different concentrations of the silicon source gas in the feed gas are referred to as concentration ring layers.

[0032] It is particularly pointed out that, in the present invention, 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.

[0033] When the internal stress of silicon deposited on the inner wall of the fluidized bed reactor is released, the internal stress release is reduced and / or weakened when it reaches the intersection of the concentration circle, thereby 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 reactor caused by the internal stress release of silicon deposited on 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 reduced quality of the granular silicon product 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. A specific implementation method is to adjust the ratio of silicon source gas and hydrogen within a certain operating time, that is, to adjust the concentration of silicon source gas entering the fluidized bed gas, and utilize the low concentration of silicon source gas in the incoming air, slow deposition, and corresponding higher density and crystallinity; high concentration of silicon source gas in the incoming air, fast deposition, and corresponding lower density and crystallinity, thereby forming different concentration layers. When the silicon deposited on the inner wall of the graphite inner component reaches a certain thickness, resulting in a temperature difference, the stress is reduced or / and weakened at the junction of the concentration layers, avoiding the internal stress of the silicon deposited on the inner wall directly damaging 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 stress difference inside the silicon deposited on the inner wall of the fluidized bed is also reduced through the concentration layer, which is beneficial to extending the continuous operation time of the fluidized bed.

[0034] A method for producing granular silicon, comprising the following steps:

[0035] At 650-1200°C, the volume concentration of silicon source gas in the feed gas is 2%-50%, preferably 10%-30%, and the feed gas is introduced into the fluidized bed reaction zone through a gas distributor, and a continuous thermal decomposition reaction is carried out at a reaction temperature of 650°C to 1200°C to produce a granular silicon product. When the fluidized bed is operated for 1-120 hours, the volume concentration of silicon source gas in the feed gas is 5-30%, and when the fluidized bed is operated for 6-240 hours, the volume concentration of silicon source gas in the feed gas is 10-35%, wherein the volume concentration of silicon source gas in the feed gas for 0.1-120 hours and the volume concentration of silicon source gas for 24-240 hours differ by 5%-10%. The concentration can be adjusted every 6-120 hours, and can be adjusted 1-50 times, preferably 5-30 times, to form 5-30 concentration circles. For example, in the fluidized bed granular silicon production process, after the fluidized bed starts feeding, the volume concentration of silane gas is adjusted for the first time after 4 hours of operation, and the volume concentration of silane gas is adjusted for the second time after the fluidized bed has been running for 10 hours, and so on, to form 1-50 concentration layers, preferably 5-30 concentration layers.

[0036] The concentration of the silicon source gas entering the fluidized bed can be expressed as a volume concentration or as a molar concentration. However, these two expressions are essentially the same.

[0037] The following describes the contents involved in the above embodiment in conjunction with a preferred embodiment.

[0038] The fluidized bed reactor used in the embodiment is similar to that described in patent CN106660002B. Figure 1This is a schematic diagram of the fluidized bed reactor structure used in an embodiment of the present invention; 1 represents the outer wall of the fluidized bed reactor, 2 the induction heating coil, 3 the insulator, 4 the susceptor, 5 the inner tube of the fluidized bed reactor, 6 the feed gas inlet, 7 the feed gas nozzle on the gas distributor, 8 the exhaust gas outlet, 9 the granular silicon product outlet, 10 the gas distributor, and 11 the seed crystal inlet. 12 represents temperature zone one, 13 represents temperature zone two, 14 represents temperature zone three, and 15 represents temperature zone four. The reaction chamber cavity is the area within the reactor inner wall 5, and the hollow cavity is the area between the reactor outer wall 1 and the reactor inner wall 5. This area contains the induction heating coil 2, the insulator 3, and the susceptor 4. The induction heating coil 2 generates an electromagnetic field, which generates eddy currents in the susceptor 4, rather than in the inner tube 5 of the fluidized bed reactor, which heats the reaction chamber cavity. The induction heating coil 2 and the susceptor 4 work together to generate heat to supply heat to the inner tube 5 of the fluidized bed reactor. A pressure detection device is provided in the hollow cavity. The pressure in the hollow cavity is P2. A pressure detection device is provided at the fluidized bed tail gas outlet 8. The pressure at the fluidized bed tail gas outlet is P1. The pressure in the reaction chamber cavity is P3. P2>P3>P1. The pressure in the reaction chamber cavity is P3 and cannot be directly measured. During operation, the change in P1 can be monitored instead of the change in P3. When the reactor inner wall 5 is intact, the pressure of the gas filling the hollow cavity remains unchanged. When the reactor inner wall 5 is ruptured, the pressure detection device in the hollow cavity detects a fluctuation in the pressure P2 in the hollow cavity, indicating that the reactor inner wall 5 is ruptured.

[0039] The silicon source gas is one or more of silane, dichlorosilane, trichlorosilane, and tribromosilane.

[0040] The concentration circle layer is 2-30 layers, preferably 4-20 layers. The 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.

[0041] When forming the concentration ring layer, the volume concentration difference of the silicon source gas concentration is 2-20%.

[0042] When forming the concentration ring layer, the volume concentration difference of the silicon source gas concentration is preferably 5-15%.

[0043] When forming the concentration ring layer, the volume concentration of the silicon source gas in the silicon source gas concentration raw material is 2-50%.

[0044] When forming the concentration ring layer, the volume concentration of the silicon source gas in the silicon source gas concentration raw material is preferably 10%-30%.

[0045] The thickness of the concentration circle is 0.1-4 cm.

[0046] The thickness of the concentration circle layer is preferably 0.3-1.5 cm.

[0047] Example:

[0048] Example 1:

[0049] The silicon source gas in the feed gas is trichlorosilane, which enters the reaction chamber of the fluidized bed reactor through the gas distributor 10 and the raw gas nozzle 7 on the gas distributor, and undergoes continuous thermal decomposition reaction at a reaction temperature of 1150°C to prepare granular silicon products.

[0050] like Figure 2 As shown, after the reaction commenced at 1150°C, the feed gas contained 50% trichlorosilane by volume, and granular silicon was continuously produced. After 24 hours of production, silicon deposited on the inner surface of the liner 5, forming concentration layer 12. The feed gas trichlorosilane concentration was then reduced to 10%. After 72 hours of operation at this 10% trichlorosilane concentration, concentration layer 2 13 formed on the surface of concentration layer 12. The feed gas trichlorosilane concentration was adjusted to 15% by volume, and operation continued for another 72 hours. At this point, concentration layer 3 14 formed on the surface of concentration layer 2 13. The trichlorosilane concentration was subsequently adjusted to 20% and remained constant. After 60 days of continuous operation, no pressure fluctuations were detected by the pressure detection device installed in the hollow cavity. At this point, the reactor was shut down for maintenance, and it was found that concentration layer 12 had a thickness of 0.2 cm, concentration layer 2 13 had a thickness of 0.1 cm, and concentration layer 3 14 had a thickness of 0.2 cm.

[0051] Comparative Example 1:

[0052] The silicon source gas in the feed gas is trichlorosilane, which enters the reaction chamber of the fluidized bed reactor through the gas distributor 10 and the raw gas nozzle 7 on the gas distributor, and undergoes continuous thermal decomposition reaction at a reaction temperature of 1150°C to prepare granular silicon products.

[0053] After the reaction started, at 1150°C, the volume concentration of trichlorosilane in the feed gas was 50%, and granular silicon was produced continuously. The subsequent volume concentration of trichlorosilane remained unchanged. After 10 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.

[0054] Example 2:

[0055] The silicon source gas in the feed gas is silane gas, which enters the reaction chamber of the fluidized bed reactor through the gas distributor 10 and the raw gas nozzle 7 on the gas distributor, and undergoes continuous thermal decomposition reaction at a reaction temperature of 800°C to prepare granular silicon products.

[0056] like Figure 3As shown, after the reaction starts, at 800°C, the volume concentration of silane in the feed gas is 30%, and granular silicon is continuously produced. After 24 hours of production operation, silicon is deposited on the inner surface of the lining 5 to form a concentration layer 12; the volume concentration of silane in the feed gas is reduced to 15%, and after 72 hours of operation, a concentration layer 13 is formed on the surface of the concentration layer 12; the volume concentration of silane in the feed gas is adjusted to 10%, and the reaction is continued for 72 hours, at which time a concentration layer 14 is formed on the surface of the concentration layer 13; the volume concentration of silane in the feed gas is increased to 20%, and after 72 hours of operation, a concentration layer 15 is formed on the surface of the concentration layer 14; the subsequent volume concentration of silane is reduced to 15% and no longer changes. After 85 days of continuous operation, the pressure detection device set in the hollow cavity did not detect pressure fluctuations. At this time, the vehicle was stopped for maintenance and it was found that the thickness of concentration circle 1 12 was 0.1 cm, the thickness of concentration circle 2 13 was 0.2 cm, the thickness of concentration circle 3 14 was 0.1 cm, and the thickness of concentration circle 3 15 was 0.2 cm.

[0057] Comparative Example 2:

[0058] The silicon source gas in the feed gas is silane, which enters the reaction chamber of the fluidized bed reactor through the gas distributor 10 and the raw gas nozzle 7 on the gas distributor, and undergoes continuous thermal decomposition reaction at a reaction temperature of 800°C to prepare granular silicon products.

[0059] After the reaction started, at 800°C, the volume concentration of silane in the feed gas was 12%, and granular silicon was produced continuously. The subsequent volume concentration of silane remained unchanged. After 25 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.

[0060] 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 granular silicon, characterized in that: The method comprises the following steps: After the reaction starts, at 650-1200°C, when producing granular silicon in a fluidized bed, by adjusting the volume concentration of the silicon source gas in the inlet gas, 2-50 concentration layers are formed on the inner wall of the fluidized bed reactor, so that the density of deposited silicon is different between adjacent concentration layers; The concentration ring layer is a ring-shaped deposited silicon layer with different density and crystallinity formed under different concentrations of silicon source gas in the inlet gas; When forming the concentration layer, the volume concentration difference of the silicon source gas concentration is 2-20%; when forming the concentration layer, the volume concentration of the silicon source gas in the silicon source gas concentration raw material is 2-50%; the thickness of the concentration layer is 0.1-4 cm; the inner wall of the fluidized bed also includes a coating, and the concentration layer is deposited on the coating on the inner wall of the fluidized bed.

2. The method for producing granular silicon according to claim 1, wherein: The silicon source gas is silane, dichlorosilane, trichlorosilane, or tribromosilane.

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

4. The method for producing granular silicon according to claim 1, wherein: When forming the concentration ring layer, the volume concentration difference of the silicon source gas concentration is 5-15%.

5. The method for producing granular silicon according to claim 1, wherein: When forming the concentration ring layer, the volume concentration of the silicon source gas in the silicon source gas concentration raw material is 10%-30%.

6. The method for producing granular silicon according to claim 1, characterized in that: The thickness of the concentration circle layer is 0.3-1.5 cm.

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