Quick-circulation polycrystalline silicon preparation system and process

Abstract

The invention discloses a rapid-circulation polycrystalline silicon preparation system and process. The polycrystalline silicon preparation system comprises a polycrystalline silicon reactor, a circulation lifting pipe and a heater, an exhaust pipe and a silicon particle feeding pipe are arranged at the upper part of the polycrystalline silicon reactor, and a solid product outlet pipe and a silicon-containing raw material gas inlet pipe are arranged at the lower part of the polycrystalline silicon reactor; the circulating lifting pipe is longitudinally arranged, the other end of the solid product outlet pipe is connected to the middle part of the circulating lifting pipe, the upper end of the circulating lifting pipe is directly or indirectly connected to the silicon particle feeding pipe, and the lower part of the circulating lifting pipe is connected with a hot air pipe; the heater is used for heating airflow to enter the hot air pipe to obtain hot air. Silicon particles are directly heated outside the reactor, high-temperature hot air is used for enabling the silicon particles to rapidly circulate in the circulating lifting pipe, heating and grading of the silicon particles are completed at the same time, the problem of wall surface deposition is solved, long-period operation can be achieved, and the production capacity is greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of polysilicon production, and in particular relates to a rapid-cycle polysilicon preparation system and process. Background Art

[0002] High-purity polysilicon materials have always been the basic raw materials for the semiconductor and photovoltaic industries. The main methods for preparing polysilicon include the modified Siemens method and the silane fluidized bed method.

[0003] The modified Siemens method is the mainstream process in the current polysilicon industry. Its core process is to purify the raw material trichlorosilane (SiHCl3) by distillation, mix it with high-purity hydrogen and send it into the reduction furnace reactor. A chemical vapor deposition reaction occurs on the surface of the silicon core in the reactor (temperature 1000-1150°C), and the silicon generated by the reaction is deposited on the silicon core, making the silicon core gradually thicker. The reaction tail gas contains trichlorosilane, dichlorosilane, silicon tetrachloride, hydrogen, hydrogen chloride, etc., which are recovered and separated and then distilled for recycling. After the silicon core grows into a polysilicon rod of a certain diameter, the furnace is stopped for replacement and the silicon rod is taken out. The silicon rod is crushed and packaged. The process has a long process, high reaction temperature, low conversion rate, low production capacity, intermittent operation, low relative volatility of raw materials and major impurities, and great difficulty in separation, resulting in large investment, high energy consumption (especially electricity consumption), and high cost.

[0004] To this end, the silane fluidized bed process has been further developed in this field. The process uses silane (SiH4) as raw material, which is sent to a fluidized bed reactor (with seed crystals) in a certain proportion after purification, and decomposed in the reactor to generate silicon. In theory, silicon is deposited on the seed crystals, causing the seed crystals to gradually grow and generate granular silicon of the required size. The by-product tail gas is a single hydrogen gas, which is sent to the front-end process for recycling to produce silane. The grown granular silicon is continuously extracted from the reactor, and the product is obtained by screening. The particles with smaller particle size are returned to the reactor to continue growing. In addition, a small amount of product needs to be crushed and added to the reactor as seed crystals to maintain continuous production. In theory, this process has the advantages of short process, low reaction temperature, high conversion rate, high reactor capacity, continuous operation, low difficulty in silane separation, and no need to crush the product.

[0005] In actual production, a large number of bubbles are generated in the reactor under the fluidized state, and a large number of homogeneous reactions occur in the bubbles, thereby generating a large amount of dust, part of which is taken out of the system, resulting in a decrease in product yield; a large number of dangling bonds are generated due to the homogeneous reaction, resulting in hydrogen in the product, a loose product structure, and easy generation of fine powder during transportation and use. All of the above lead to low product quality and difficulty in downstream use. Due to the existence of the above homogeneous reaction, production can only be carried out at a lower pressure and a lower silane concentration, otherwise more dust will be generated. In addition, due to the generation of the above bubbles, a small amount of silane is taken out of the reactor before being heated to the reaction temperature, and a separation and recovery process needs to be added later. While the yield is reduced, energy consumption and investment are increased; and due to the problem of the heating method, it is easy to cause wall deposition, short production cycle, and low production capacity.

[0006] CN105819449A discloses a silane moving bed reactor and a method for producing granular polysilicon using the reactor. It adopts a moving bed solution and mentions the circulation and heating of solid materials, but the two are separate, that is, low-temperature particles are circulated to a preheating system, and heating is completed in the preheating system, and the implementation method of the circulation is not specifically described.

[0007] CN104803386A discloses a fluidized bed riser reactor and method for preparing high-purity polysilicon particles, which adopts a circulating fluidized bed reactor. This reactor itself uses gas to transport particles and then achieves particle circulation by gas-solid separation. Its heat supply adopts a method of heating the partition wall outside the system, including a riser or a solid particle collection mechanism, using the riser as a reactor, a cyclone as a gas-solid separation device, and fluidizing gas for particle classification, but the effect is poor.

[0008] In addition, CN11853400A also discloses a silane moving bed reaction system, including a heater, a reactor and a stripper, and the outlet of the heater is connected to the inlet of the reactor, and the outlet of the reactor is connected to the inlet of the stripper; polycrystalline silicon enters the heater and is heated to the reaction temperature, the heated polycrystalline silicon enters the reactor from top to bottom to undergo crystal growth, the reaction gas enters the reactor from bottom to top and contacts and reacts with the polycrystalline silicon in the reactor in reverse, and the exhaust gas after the reaction is discharged from the upper part of the reactor; the polycrystalline after the reaction enters the stripper for stripping. Although its products are screened in vitro and unqualified materials are fed into the seed preparation unit, the design problems of its heating method and feeding method can easily lead to uneven bed temperature, incomplete reaction of silane, and powder entrainment in the exhaust gas. For this reason, a filter element is also set at the exhaust gas outlet of the reactor, which increases the complexity of the system and the risk of pollution. In addition, the head design is adopted at the lower end of the reactor, which leads to an additional support force for the bed, thereby reducing the pressure head of the bed. The particle flow rate of the entire bed above the support surface is slow, and the particle flow rate is greatly reduced, which is easy to form a central flow and the material close to the wall is retained for a long time, with poor fluidity and the risk of agglomeration.

[0009] CN103787336A discloses a method for producing high-purity granular silicon, in which auxiliary gas needs to be added to maintain the bed state. However, the addition of auxiliary gas increases energy consumption, and its distribution plate is prone to clogging; the auxiliary gas and the reaction gas are both dispersed in the reaction chamber, which easily causes the reaction gas to diffuse to the wall and there is a risk of wall deposition. For this reason, an air curtain device is added, making the overall structure very complicated and the operability poor; in addition, although it adopts an external screening method of the reactor and unqualified materials are transported to the preheating system, the circulation and heating are also separated, but the particles in the bed itself move slowly and the heat transfer efficiency is poor, which easily leads to uneven bed temperature and incomplete reaction of silane. For this reason, an exhaust gas separation mechanism is added, which makes the surface of the particles loose and easy to produce fine powder. For this reason, a surface treatment mechanism is added, which is inefficient and the system is more complicated. Summary of the invention

[0010] The object of the present invention is to provide a fast-cycle polysilicon preparation system and process to efficiently prepare granular polysilicon products.

[0011] To achieve one aspect of the above invention objectives, the present invention adopts the following technical solutions:

[0012] A fast-cycle polysilicon preparation system, the polysilicon preparation system comprising:

[0013] A polysilicon reactor, wherein an exhaust pipe and a silicon particle feed pipe for inputting high-temperature silicon particles are provided at the upper part of the polysilicon reactor, and a solid product outlet pipe and a silicon-containing raw material gas inlet pipe for introducing silicon-containing raw material gas are provided at the lower part, wherein the polysilicon reactor is used to make the silicon-containing raw material gas contact and react with the high-temperature silicon particles as crystal seeds, so that the silicon generated by the decomposition of the silicon-containing raw material gas is deposited and grown on the surface of the silicon particles, and the grown silicon particles are discharged from the solid product outlet pipe, and the tail gas after the reaction is discharged from the exhaust pipe;

[0014] A circulation riser, the circulation riser is arranged in the longitudinal direction, the other end of the solid product outlet pipe is connected to the middle part of the circulation riser, so as to feed the grown silicon particles discharged from the polysilicon reactor into the circulation riser; the upper end of the circulation riser is directly or indirectly connected to the silicon particle feed pipe, and the lower part of the circulation riser is connected with a hot air pipe, which is used to feed hot air into the circulation riser and perform airflow classification on the grown silicon particles, and heat the sorted particles with smaller particle size to a temperature sufficient to decompose the silicon-containing raw material gas and feed them upward into the silicon particle feed pipe as the high-temperature silicon particles, and the remaining particles with larger particle size flow downward and are discharged as polysilicon products;

[0015] The heater is used for heating the airflow to be introduced into the hot air pipe to obtain the hot air.

[0016] To achieve another aspect of the above invention object, the present invention adopts the following technical solution:

[0017] A process for preparing polycrystalline silicon using the above-mentioned polycrystalline silicon preparation system comprises:

[0018] (1) The silicon-containing raw material gas introduced from the silicon-containing raw material gas inlet pipe rises and contacts and reacts with the high-temperature silicon particles introduced from the silicon particle inlet pipe in the polysilicon reactor, so that the silicon produced by the decomposition of the silicon-containing raw material gas is deposited and grown on the surface of the silicon particles serving as seed crystals;

[0019] (2) sending the grown silicon particles into the circulation riser from the solid product outlet pipe, and discharging the tail gas from the exhaust pipe;

[0020] (3) The hot air heated by the heater is sent from the hot air pipe into the circulation riser, and the grown silicon particles are subjected to airflow classification. The separated particles with smaller particle sizes are heated to a temperature sufficient to decompose the silicon-containing raw gas and are sent upward into the silicon particle feed pipe as the high-temperature silicon particles, and the remaining particles with larger particle sizes are discharged downward as polysilicon products.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) The present invention directly heats silicon particles outside the reactor, uses high-temperature hot air to quickly circulate the silicon particles in the circulation riser, and simultaneously completes the heating and classification of the silicon particles; in addition, since the silicon-containing raw gas is directly heated on the silicon particles, the heating area is greatly increased, and the wall deposition problem and the lining damage problem are greatly improved, and long-term operation is possible; and since it is easy to add sufficient heat (the amount of hot particles), the size of the reactor of the present invention is not limited by the heating conditions, so it can be greatly enlarged, expanding the production capacity, and facilitating the high-speed movement of particles to prevent agglomeration.

[0023] (2) The present invention uses a circulating riser, which is not used as a reactor. Instead, the circulating riser is used to achieve classification, circulation and heating of silicon particles by taking advantage of its fast circulation, large conveying capacity and high heat transfer intensity. At the same time, the silicon particles are repeatedly heated by hot air at a higher temperature, rather than the reaction temperature in the existing fluidized bed, which is conducive to the complete breaking of silicon-hydrogen bonds, making the product crystal form complete and the structure dense.

[0024] (3) The present invention can enhance the particle classification and heat transfer effects by providing a variable diameter section on the circulation riser; through multiple variable diameter sections, the gas velocity of the hot gas can be continuously changed, the silicon particles can be separated multiple times, the separation effect can be enhanced, and the heat transfer effect can be enhanced.

[0025] (4) The present invention adopts a conical polysilicon reactor, and the reaction section adopts an overall conical design, which is conducive to the rapid movement of particles in the reaction bed, and the relative movement between particles during the downward movement can effectively avoid the agglomeration of particles; in addition, the reaction section of the present invention does not require additional auxiliary gas intake, and the conical design is conducive to the expansion and diffusion of gas reaction, which is conducive to preventing the generation of bubbles in the reactor, thereby avoiding the occurrence of homogeneous reaction, greatly reducing dust generation, and improving product yield; and because there are no bubbles, silane is 100% reacted and there is no silane in the tail gas, which is conducive to reducing the tail gas separation process in the subsequent stage; and the present invention feeds the raw gas to the radial middle of the reaction section, which is conducive to The heat exchange and reaction areas in the reactor are concentrated, the product deposition area is large, the product structure is dense, and it is also beneficial to reduce wall deposition; in addition, the present invention arranges a ring at the lower end of the sedimentation section to form an annular platform, which can effectively prevent the feed from directly impacting the inner wall of the reactor while realizing lateral feeding, and at the same time, the accumulated silicon particles can achieve a dynamic balance between the particle sliding caused by the impact of lateral feeding and the silicon particles brought in by the feed airflow and the particles in the sedimentation section. The present invention finally, by conveying the air duct at the lower part of the material sealing section, it can cooperate with the material sealing section and the conveying section, which is beneficial to the rapid conveying of solid materials in the conveying section, so as to better cooperate with the rapid movement of particles in the reactor;

[0026] In summary, the present invention can realize large-scale equipment, greatly improve production capacity, improve product quality, reduce costs, shorten processes, reduce investment, and reduce carbon emissions, with obvious economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of an embodiment of a polysilicon preparation system of the present invention;

[0028] Figure 2 is a schematic diagram of another embodiment of a polysilicon preparation system of the present invention;

[0029] Figure 3 for Figure 1 Schematic diagram of one embodiment of a tapered polysilicon reactor in FIG. DETAILED DESCRIPTION

[0030] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solution of the present invention will be clearly and completely described below in combination with the embodiments of the present invention and the accompanying drawings. Obviously, the described embodiments are only embodiments of a part of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0031] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values, such as values ​​of ±10% of the endpoint values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article. In the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other.

[0032] It should be noted that the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or apparatus.

[0033] like Figure 1As shown, the polysilicon preparation system of the present invention includes a polysilicon reactor 1, a circulation riser 2 and a heater 3; wherein, the upper part of the polysilicon reactor is provided with an exhaust pipe 13 and a silicon particle feed pipe 12 for inputting high-temperature silicon particles, and the lower part is provided with a solid product outlet pipe 16 and a silicon-containing raw material gas inlet pipe 15 for introducing silicon-containing raw material gas, wherein the polysilicon reactor 1 is used to make the silicon-containing raw material gas contact and react with the high-temperature silicon particles as crystal seeds, so that the silicon generated from the decomposition of the silicon-containing raw material gas is deposited and grown on the surface of the silicon particles, and the grown silicon particles are discharged from the solid product outlet pipe 16, and the tail gas after the reaction is discharged from the exhaust pipe 13.

[0034] The circulation riser 2 is arranged in the longitudinal direction, and the other end of the solid product outlet pipe 16 is connected to the middle part of the circulation riser 2 to feed the grown silicon particles discharged from the polysilicon reactor 1 into the circulation riser 2; the upper end of the circulation riser 2 is directly or indirectly connected to the silicon particle feed pipe 12, and the lower part of the circulation riser 2 is connected with a hot air pipe 21, which is used to feed hot air into the circulation riser 2 and perform air flow classification on the grown silicon particles, so as to heat the sorted particles with smaller particle size to a temperature sufficient to decompose the silicon-containing raw gas and feed them upward into the silicon particle feed pipe 12 as the high-temperature silicon particles, and the remaining particles with larger particle size flow downward and are discharged as polysilicon products.

[0035] The heater 3 is used to heat the airflow to be introduced into the hot air pipe 21 to obtain the hot air. The specific selection of the heater 3 is well known in the art, such as electric heating / radiation heating / electromagnetic heating, etc., which will not be described in detail here.

[0036] In some embodiments, it can be understood in the art that when the upper end of the circulation riser 2 is directly connected to the silicon particle feed pipe 12, the gas-solid mixture sent out from the upper end of the circulation riser 2 can directly enter the silicon particle feed pipe 12 and then undergo gas-solid separation in the upper part of the polysilicon reactor 1, for example, the upper part of the polysilicon reactor has sufficient space for gas-solid separation, and the silicon particles settle downward and the gas is discharged upward; when the upper end of the circulation riser 2 is indirectly connected to the silicon particle feed pipe 12, the gas-solid mixture sent out from the upper end of the circulation riser 2 can first undergo gas-solid separation and then enter the silicon particle feed pipe, for example, first perform gas-solid separation in a cyclone separation device and then feed the silicon particles at the separation point into the silicon particle feed pipe 12.

[0037] In some embodiments, the circulation riser 2 is provided with one or more diameter-enlarged reducing sections 22 at the connection portion connected to the solid product outlet pipe 16 and the pipe section of the circulation riser located between the hot blast pipe and the solid product outlet pipe. The reducing section and the diameter change between the other pipe sections enable the hot gas velocity to change continuously, which is beneficial to enhance the particle classification and heat transfer effect, and directly separate the product in the circulation riser. In particular, when the diameter is changed multiple times, the hot gas velocity can change continuously, and the silicon particles can be separated multiple times, thereby enhancing the classification and heat transfer effect. It can be understood in the art that the pipe section of the circulation riser 2 located between the hot blast pipe 21 and the solid product outlet pipe 16 does not include the connection portion of the circulation riser with the solid product outlet pipe and the connection portion of the circulation riser with the hot blast pipe. Preferably, the circulating riser is provided with a reducing section 22 at the connection portion connected to the solid product outlet pipe. An expanding section is provided here. When an airflow containing product particles of different particle sizes enters, the pipe diameter is expanded, which facilitates direct sedimentation of large particles and achieves a good classification effect. More preferably, the circulating riser is provided with a reducing section 22 at the connection portion connected to the solid product outlet pipe, and one or two or more reducing sections are provided on the pipe section of the circulating riser located between the hot air pipe and the solid product outlet pipe.

[0038] In one embodiment, if Figure 1 As shown, the polysilicon preparation system also includes a buffer tank 4 and a cooler 5; wherein the buffer tank 4 is connected to the lower end of the circulation riser 2, and is used to buffer the polysilicon product discharged from the circulation riser 2; in the present invention, the buffer tank can not only play a role in product discharge buffering, but also can isolate the hot air from the cooler, which is conducive to the upward transportation of the hot air.

[0039] The cooler 5 is connected to the buffer tank 4, and is used to cool the polysilicon product discharged from the buffer tank. In one embodiment, the cooler 5 includes a shell 51, and a gas distributor 52 is provided at the lower part of the shell, so that the shell is divided into an air intake zone located below the gas distributor 52 and a cooling zone located above the gas distributor; a polysilicon product feed pipe 56 extending downward into the cooling zone is provided at the top of the cooling zone, which is used to feed the polysilicon product into the cooling zone and accumulate it on the gas distributor 52 to form a polysilicon product bed; a cooling gas inlet is provided in the air intake zone to introduce cooling gas to cool the polysilicon product accumulated on the gas distributor 52; a cooling gas outlet is provided in the cooling zone, and the cooling gas outlet is higher than the lower end of the polysilicon product feed pipe 56 to discharge the cooling gas after heat exchange with the polysilicon product and temperature increase; the gas distributor A polysilicon product discharge pipe is provided on 52, for example, a polysilicon product discharge pipe 57 extending downward to the outside of the cooler shell is provided at the center of the gas distributor; the cooler 5 is used to cool the polysilicon products accumulated on the gas distributor using the rising cooling gas introduced from the air inlet zone, and discharge the cooled polysilicon products at the bottom of the polysilicon product bed from the polysilicon product discharge pipe 57; it can be understood in the art that during operation, the polysilicon product bed accumulates to the lower end of the polysilicon product feed pipe, and when the cooled polysilicon product is discharged and the height of the polysilicon product bed decreases, the polysilicon product feed pipe will automatically feed into the polysilicon product bed, so that the polysilicon product bed is as high as the lower end of the polysilicon product feed pipe, isolating the hot air from the cooler, which is conducive to the upward transportation of hot air.

[0040] In one embodiment, the polysilicon preparation system further includes a housing 80 for accommodating the polysilicon reactor 1, the circulation riser 2, the buffer tank 4 and the cooler 5, which serves as a system pressure-bearing part.

[0041] In one embodiment, if Figure 2 As shown, the polysilicon preparation system also includes a tail gas heat exchange unit 30, a tail gas dust removal unit 40, a circulating gas compressor 50, a product tank 60 and a seed crystal preparation unit 70; wherein, the tail gas heat exchange unit 30 is used to utilize the circulating gas to cool the tail gas from the exhaust pipe 13 of the polysilicon reactor 1 to recover heat, and send the circulating gas heated by heat exchange into the heater 3 for further heating and heating, so as to be sent into the circulating riser 2 as the hot air circulation; the tail gas heat exchange unit can be a heat exchanger, which is well known in the art and will not be repeated here.

[0042] The exhaust gas dust removal unit 40 is used to remove dust from the exhaust gas from the exhaust gas heat exchange unit 30 to obtain dust-removed exhaust gas. It is understood in the art that dust removal can be performed using a dust collector such as a bag dust collector, which is well known in the art and will not be described in detail here.

[0043] The circulating gas compressor 50 is used to pressurize the dust-removed exhaust gas so as to send it into the exhaust gas heat exchange unit as circulating gas. In some embodiments, the dust-removed exhaust gas can also be sent to an adsorption unit for gas separation before being sent into the circulating gas compressor 50, such as by pressure swing adsorption or temperature swing adsorption to separate the impurity gas and / or hydrogen (hydrogen is produced by decomposition of silane) introduced during the gas circulation process. The separated hydrogen can be further sent out as a by-product hydrogen.

[0044] The product tank 60 is used to receive the polysilicon product discharged from the polysilicon preparation system; wherein, a double product tank can be provided for intermittent operation, with one product tank receiving the material and the other product tank using pneumatic transport to the system outer packaging.

[0045] The seed crystal preparation unit 70 is used to crush the polysilicon product discharged from the polysilicon preparation system and send it back to the polysilicon reactor as fine seed crystals (seeds) to maintain the silicon particle reserves in the polysilicon reactor. Since the amount added per unit time is very small (the amount of polysilicon product is several dozen times that of the fine seed crystals), the impact is small. For example, most of the polysilicon product discharged from the cooler 5 enters the product tank 60, and a small part enters the seed crystal preparation unit 70.

[0046] In one embodiment, if Figure 2 As shown, the polysilicon preparation system also includes a first cold air pipe 53 and a second cold air pipe 55; wherein the first cold air pipe 53 is connected to the cooling air inlet of the cooler 5, and is used to send the cooling air into the cooler to cool the incoming polysilicon product; the second cold air pipe 55 is respectively connected to the cooling air outlet of the cooler 5 and the exhaust gas dust removal unit 40, and is used to send the heated cooling air from the cooler as part of the exhaust gas into the exhaust gas dust removal unit.

[0047] In some embodiments, the polysilicon reactor 1 may be a fluidized bed reactor or a moving bed reactor; in other embodiments, such as Figure 3 As shown, the polysilicon reactor is a conical polysilicon reactor, and the conical polysilicon reactor includes a conical reaction section 14 whose diameter gradually decreases from top to bottom and a settling section 11 arranged above the conical reaction section. Among them, the top of the settling section 11 is provided with an exhaust pipe 13, and the side wall is provided with a silicon particle feed pipe 12 for gas transportation as a seed; the settling section 11 is used to settle and separate the silicon particles in the gas-solid mixture from the silicon particle feed pipe 12, so that the silicon particles settle to the conical reaction section 14 to form a silicon particle bed; those skilled in the art understand that the gas-solid mixture carrying particulate matter suddenly decreases in flow rate after entering a larger space, and on the basis of ensuring sufficient space in the settling section, the particulate matter will settle and separate from the carrier gas.

[0048] The upper end of the conical reaction section 14 is connected to the lower end of the sedimentation section 11, and a solid product outlet pipe 16 is provided at the bottom of the conical reaction section 14, and a silicon-containing raw gas inlet pipe 15 is provided on the side wall; the conical reaction section 14 is used to make the rising silicon-containing raw gas contact and react with the descending silicon particle bed, so that the silicon produced by the decomposition of the silicon-containing raw gas introduced from the silicon-containing raw gas inlet pipe 15 is deposited and grown on the surface of the silicon particles serving as seed crystals, and the grown silicon particles are discharged from the solid product outlet pipe 16.

[0049] In the present invention, the gas-solid mixture fed from the silicon particle feed pipe 12 is subjected to gas-solid separation in the settling section 11, the tail gas is discharged from the top, and the silicon particles sink into the conical reaction section 14 to form a bed layer, and are countercurrently contacted with the silicon-containing raw gas, so that the decomposed silicon is deposited and grown on the surface of the silicon particles, and finally discharged from the bottom. It is understood by those skilled in the art that the undergrown granular silicon in the product discharged from the solid product outlet pipe 16 can be subsequently separated and circulated back to the reactor as a seed crystal for continued growth, which is well known in the art and will not be described in detail here.

[0050] In the present invention, the sedimentation section 11 is used to provide a gas-solid separation sedimentation space, and its diameter can be gradually expanded from bottom to top or remain unchanged, such as a cylindrical shape or a truncated cone with a larger diameter at the top and a smaller diameter at the bottom; in addition, its height should be sufficient to allow the silicon particles in the gas-solid mixture to fully settle, such as sufficient to allow silicon particles with a particle size greater than 0.01 mm to fully settle, for example, the sedimentation rate can reach 99.99%; it is understood in the art that silicon dust that is directly decomposed by the silicon-containing raw gas and not deposited on the surface of the silicon particles is difficult to settle naturally in the rising exhaust gas, and it is necessary to optimize from other aspects to reduce the generation of silicon dust, such as the full conversion of silane in the present invention, collection in the silicon particle bed, and reduction of collision, friction and crushing.

[0051] In the present invention, it is understood in the art that the lower end of the settling section 11 can be directly connected to the upper end of the conical reaction section 14 or connected through other transition sections. For example, in conventional embodiments, the settling section 11 can usually be transitionally connected through a reduced diameter section with a larger upper portion and a smaller lower portion, such as being connected to the upper end of the conical reaction section 14. The cone angle (the angle between the two generatrixes of the axial section of the cone) of the conical reaction section 14 can be 15-50°, such as 20, 25, 30, 35, 40 or 45, such as 20-40°.

[0052] In the present invention, the outlet of the silicon-containing raw material gas inlet pipe 15 can generally be arranged in multiple numbers along the circumference and / or longitudinal direction of the conical reaction section 14, so as to more evenly feed the silicon-containing raw material gas. In one embodiment, the outlet of the silicon-containing raw material gas inlet pipe 15 extends radially to the radial middle part of the conical reaction section 14 (i.e., the central part of the horizontal circular cross section of the conical reaction section), so that the silicon-containing raw material gas is fed into the middle area of ​​the conical reaction section 14 around its central axis; preferably, the distance between the outlet of the silicon-containing raw material gas inlet pipe 15 and the central axis of the conical reaction section 14 is (1 / 10-2 / 3)R, preferably (1 / 8-1 / 2)R, such as 1 / 6R, 1 / 4R or 1 / 3R, so that the silicon-containing raw material gas can be fed into the radial middle part of the conical reaction section 14, wherein R is the radius of the circular cross section of the conical reaction section on the horizontal plane where the silicon-containing raw material gas inlet pipe is located.

[0053] It is understood in the art that in order to prevent the premature decomposition of the raw gas, the raw gas fed into the reactor is usually a relatively low temperature cold gas (for example, the temperature is not higher than 400°C, such as 25, 50, 100, 200 or 300°C). In order to evenly distribute the intake gas, the feed raw gas is usually distributed as much as possible on the inner wall of the reactor. However, in the present invention, for the overall conical reaction section design, the cone angle remains unchanged or changes very little from top to bottom, such as not more than 10° or not more than 5°. Studies have found that by concentrating the feed gas in the middle of the conical reaction section 14, the feed raw gas can be preferentially contacted with the silicon particles with the fastest downward speed in the conical reaction section 14 (therefore, it is also easier to maintain its feed heat), and the reaction efficiency is high; at the same time, the temperature of the gas rises after contact and the volume of the gas generated by the reaction expands exponentially. The conical design is also conducive to the rapid diffusion of the remaining gas upward to the entire bed cross-section for reaction. Since the low-temperature gas first contacts the particles with high flow rate in the middle, the Reynolds number is high and the heat transfer coefficient is also high. The main heat exchange is completed instantly, the gas temperature reaches the decomposition temperature, and the reaction is basically completed. In the process of radial diffusion, contact with particles with a lower flow rate will make the gas temperature consistent with the particle temperature, and the temperature of the entire cross section is relatively balanced, which is conducive to gas reaction deposition and further improves the reactor conversion rate; in addition, due to the overall conical design of the reaction section of the present invention, although the downward speed of the silicon particles close to the inner wall of the conical reaction section 14 is lower than that of the silicon particles in the middle, the absolute movement speed and relative movement speed are still high. Therefore, although a small amount of residual gas reacts efficiently after diffusion, the agglomeration of silicon particles close to the inner wall of the conical reaction section 14 can still be effectively avoided. In addition, due to the overall conical design of the reaction section of the present invention, it is also conducive to the deceleration of the rising airflow after the volume expansion caused by heat and reaction, ensuring that the bed is stable and non-fluidized, and no bubbles are generated, and through the sedimentation section and the cross-mixing with the lateral airflow in the sedimentation section, the gas velocity can be reduced and the solid phase entrainment can be reduced.

[0054] In the present invention, the silicon-containing raw material gas inlet pipe 15 can be provided in one group or multiple groups such as 2-4 groups at different heights, each group comprising multiple (such as 2-6) silicon-containing raw material gas inlet pipes 15 uniformly distributed along the circumference of the conical reaction section 14 on the same plane, so as to feed from multiple positions to the radial middle of the conical reaction section 14. In some embodiments, the outlet of the silicon-containing raw material gas inlet pipe 15 can be provided at 1 / 6-2 / 3, such as 1 / 5-1 / 2, such as 1 / 4 or 1 / 3 of the height from bottom to top of the conical reaction section, which is more conducive to sufficient contact and reaction with the silicon particles in the conical reaction section 14; it can be understood in the art that if the height is too low, it is easy to cause part of the raw material gas to flow downward or even generate bubbles, and the yield is reduced, while if the height is too high, it is easy to cause the reaction section to become shorter and the conversion rate to decrease.

[0055] In the present invention, the silicon particle feed pipe 12 introduces silicon particles into the reactor through gas transportation. Preferably, the silicon particle feed pipe is horizontally arranged toward the central axis of the sedimentation section 11 so that the gas-solid mixture is fed in a substantially horizontal direction, thereby avoiding the problem of being too inclined upward and causing unfavorable sedimentation, and the problem of being too inclined downward and affecting the rising airflow from the conical reaction section 14 and causing the particles in the feed to have a greater impact force due to gravity acceleration. If the feeding is horizontally tangential, it is easy to cause wear between the silicon particles and the wall of the sedimentation section reactor.

[0056] However, it is understood in the art that since a silicon particle feed pipe is provided on the side wall of the sedimentation section, the feed (especially horizontal lateral feed) will still impact the side wall of the sedimentation section 11, which will not only cause the silicon particle feed to be crushed, but also easily lead to an increase in the impurity content of the product.

[0057] In one embodiment, the diameter of the lower end of the settling section 11 is greater than the diameter of the upper end of the conical reaction section 14 and is flush with the upper end of the conical reaction section 14; the lower end of the settling section 11 is connected to the upper end of the conical reaction section 14 through a horizontally arranged ring 10, wherein the outer ring of the ring 10 is connected to the lower end of the settling section 11, and the inner ring of the ring 10 is connected to the upper end of the conical reaction section 14, thereby forming an annular platform carrying a silicon particle layer at the bottom of the settling section 11, so that the silicon particle layer accumulated thereon can be used to block the silicon particles fed from the silicon particle feeding pipe 12 from contacting the reaction The research found that, because it is in the sedimentation section 11, such a setting is conducive to the natural sedimentation and accumulation of silicon particles on the annular platform and will not cause the natural descent relying on gravity as usually expected; in addition, due to the feed impact of the gas-solid mixture introduced by the silicon particle feed pipe 12 and the particle deposition in the sedimentation section 11, the accumulated silicon particle layer can, on the one hand, effectively hinder the direct impact of the feed on the inner wall of the reactor while realizing lateral feeding, and on the other hand, the accumulated silicon particles can reach a dynamic balance between the particle reduction caused by the impact of the lateral feed airflow and the deposition of the particles in the sedimentation section 11, thereby achieving a certain balance between material replacement and continuous protection.

[0058] In one embodiment, the solid product outlet pipe 16 is L-shaped, including a vertically arranged material sealing section 17 and a conveying section 18 connected to the lower end of the material sealing section 17, wherein the upper end of the material sealing section 17 is directly connected to the bottom of the conical reaction section 14, so that the grown silicon particles leaving the conical reaction section 14 directly enter the material sealing section 17 of the solid product outlet pipe 16 to reduce resistance and facilitate the conveying of the product descending from the solid product outlet pipe; of course, it can be understood in the art that the solid product outlet pipe 16 is "L"-shaped and does not limit the material sealing section 17. A strict right-angle connection with the conveying section 18 or a strict length ratio between the sealing section 17 and the conveying section 18; in the present invention, the "L" shape mainly refers to the solid product outlet pipe 16 being designed in a bent shape, for example, the sealing section 17 and the conveying section 18 can be connected by an arc elbow and the angle between the sealing section 17 and the conveying section 18 may not be 90°. It is understood in the art that the conveying section can also be transported by being tilted downward. For example, the angle between the conveying section 18 and the sealing section 17 can be 90-150°, such as 100, 120, 140° or 110-130°.

[0059] In one embodiment, the material sealing section 17 is also provided with a conveying air duct 19, and the conveying air duct 19 is horizontally connected to the lower part of the material sealing section 17, such as a position higher than the conveying section 2D to 5D, such as 3D or 4D (D is the inner diameter of the pipeline of the conveying section). Studies have found that the coordinated arrangement of the conveying air duct 19 and the material sealing section 17 can be more conducive to the transportation of solid materials, wherein a material seal of a certain height can be formed by the arrangement of the material sealing section 17, and the conveying air horizontally fed into the conveying air duct 19 can appropriately increase the gap between the particles in the material sealing section due to the vertical feeding of the material sealing section, reduce the internal friction between the particles, and play a role in loosening the material, and the material sealing section 17 can form a material seal well to prevent the airflow from rising into the conical reaction section 14, and finally the conveying air flows downward to transport the product, so it is also conducive to the rapid transportation of solid materials in the conveying section 18, so as to better cooperate with the rapid movement of particles in the reactor.

[0060] In addition, a feeding pipe may be provided at an appropriate position of the conical polysilicon reactor to add the fine seed crystals (a small amount added per unit time, with a small impact) to maintain the bed layer in the reactor, for example, it may be provided in the sedimentation section or on the silicon particle feed pipe.

[0061] The process of preparing granular polysilicon using the polysilicon preparation system of the present invention includes:

[0062] (1) The silicon-containing raw material gas introduced from the silicon-containing raw material gas inlet pipe and the high-temperature silicon particles introduced from the silicon particle inlet pipe are contacted and reacted in the polysilicon reactor, so that the silicon produced by the decomposition of the silicon-containing raw material gas is deposited and grown on the surface of the silicon particles serving as seed crystals;

[0063] (2) sending the grown silicon particles into the circulation riser from the solid product outlet pipe, and discharging the tail gas from the exhaust pipe;

[0064] (3) sending the hot air heated by the heater into the circulation riser from the hot air pipe, and performing airflow classification on the grown silicon particles, and heating the selected particles with smaller particle sizes to a temperature sufficient to decompose the silicon-containing raw gas and sending them upward into the silicon particle feed pipe as the high-temperature silicon particles, and the remaining particles with larger particle sizes are discharged downward as polycrystalline silicon products;

[0065] In the present invention, the silicon-containing raw gas can be a mixture of an effective silicon-containing gas and a diluent gas, wherein the effective silicon-containing gas is a gas that can be decomposed to produce silicon when heated, which is well known in the art, such as silane or disilane, and the diluent gas can be hydrogen, nitrogen, helium or argon (it can be understood in the art that they can also be used as gases for transporting silicon particles). For example, the silicon-containing raw gas can be a mixture of silane and hydrogen, wherein the volume content of silane can be 5-100%, such as 20%, 40%, 60% or 80%, preferably 50-100%; it can be understood in the art that when the silane content is 100%, the silicon-containing raw gas is pure silane gas rather than a mixed gas.

[0066] In the present invention, the temperature of the silicon particle bed can be 650-850°C, such as 700, 750 or 800°C, to facilitate the reaction; it is understood in the art that the temperature of the hot air should be higher to be sufficient to heat the silicon particles to the desired temperature.

[0067] In the present invention, the pressure in the reactor may be 0.5-3 MPa.g, such as 1 or 2 MPa.g.

[0068] In the present invention, the hourly circulation rate of the silicon particles in the polysilicon reactor (i.e., the ratio of the amount of silicon particles fed into the silicon particle feed pipe 12 per hour to the amount of silicon particles stored in the polysilicon reactor) can be 5-20, such as 8, 10 or 15. It can be understood in the art that too low an hourly circulation rate may be detrimental to preventing particle agglomeration, while too high an hourly circulation rate may cause wear of system equipment and affect product purity.

[0069] In the present invention, the silicon particles in the polysilicon reactor serve as seeds to provide a deposition surface and also as a heating medium to heat the raw gas; preferably, the mass ratio of the silicon-containing raw gas to the silicon particle feed entering from the silicon particle inlet pipe 12 is (0.05-0.25):1, such as 0.1:1, 0.15:1 or 0.2:1; it can be understood in the art that too low a ratio may result in low yield and high cost, while too high a ratio may result in reduced conversion rate.

[0070] The present invention is further described below with reference to specific operating examples / comparative examples.

[0071] Example 1

[0072] like Figure 1 As shown, the polysilicon preparation system of the present invention comprises a polysilicon reactor 1, a circulation riser 2, a heater 3, a buffer tank 4 and a cooler 5; wherein the polysilicon reactor 1 is a conical polysilicon reactor, such as Figure 3As shown, it includes the conical reaction section 14 (cone angle 20°) and the sedimentation section 11 connected thereto; an exhaust pipe 13 is provided at the top of the sedimentation section, and a silicon particle feed pipe 12 for gas transportation as a seed is provided on the side wall; the upper end of the conical reaction section is connected to the lower end of the sedimentation section, and a solid product outlet pipe 16 is provided at the bottom of the conical reaction section, and a silicon-containing raw gas inlet pipe 15 is provided on the side wall.

[0073] The outlet of the silicon-containing raw gas inlet pipe 15 extends radially close to the radial middle of the conical reaction section, and is at a distance of 1 / 2R from its central axis; and four silicon-containing raw gas inlet pipes are evenly distributed along the circumference of the conical reaction section on the same plane, and their height is at 1 / 3 of the height of the conical reaction section from bottom to top.

[0074] A horizontal ring 10 is arranged at the lower end of the sedimentation section, the outer ring of the ring is connected to the lower end of the sedimentation section, and the inner ring of the ring is connected to the upper end of the conical reaction section, so that an annular platform carrying a silicon particle layer is formed at the bottom of the sedimentation section to block the feed impact of the silicon particle feed pipe.

[0075] The solid product outlet pipe 16 is L-shaped, including a vertically arranged material sealing section 17 and a conveying section 18 horizontally connected to the lower end of the material sealing section, wherein the upper end of the material sealing section is directly connected to the bottom of the conical reaction section, and the horizontally connected conveying air duct 19 is connected at a position higher than the conveying section 3D at the lower part of the material sealing section.

[0076] The other end of the conveying section is connected to the middle part of the vertically arranged circulation riser, the upper end of the circulation riser is connected to the silicon particle feeding pipe, and the hot air (hydrogen) heated by the heater enters from the lower part of the circulation riser through the hot air pipe; wherein, the circulation riser is provided with a reducing section at the connection part connected to the solid product outlet pipe, and two reducing sections are provided on the pipe section of the circulation riser located between the hot air pipe and the solid product outlet pipe.

[0077] In addition, a feeding pipe is provided at an appropriate position of the polysilicon reactor 1 to add fine seed crystals (the amount added per unit time is very small and the impact is small) to maintain the bed layer in the reactor, for example, it is set in the sedimentation section or the circulation riser between the conveying section and the silicon particle feed pipe.

[0078] During operation, (1) the silicon particles in the gas-solid mixture introduced from the silicon particle inlet pipe are subjected to sedimentation separation in the sedimentation section, so that the silicon particles are settled to the conical reaction section to form a silicon particle bed layer; (2) the silicon-containing raw material gas (100% silane) introduced from the silicon-containing raw material gas inlet pipe rises and contacts and reacts with the descending silicon particle bed layer, so that the silicon produced by the decomposition of the silicon-containing raw material gas is deposited and grown on the surface of the silicon particles serving as seed crystals, thereby obtaining granular polycrystalline silicon; (3) the grown silicon particles are introduced from the solid product outlet pipe into the conical reaction section to form a silicon particle bed layer; The hot air (850°C) heated by the heater is sent from the hot air pipe to the circulation riser, and the grown silicon particles are subjected to airflow classification, and the selected particles with smaller particle size are heated to a temperature sufficient to decompose the silicon-containing raw gas and sent upward into the silicon particle feed pipe as the high-temperature silicon particles, and the remaining particles with larger particle size are sent downward as polysilicon products and discharged; (6) The discharged polysilicon products are sent downward into the buffer tank for buffering, and then enter the cooler from the buffer tank for cooling.

[0079] Among them, the reactor pressure is about 5 bar.g, the average temperature of the silicon particle bed is about 700°C, the mass ratio of the silicon-containing raw gas to the silicon particle feed entering from the silicon particle inlet pipe is about 0.15:1, the circulation ratio of the silicon particles is about 17.5, and the raw gas inlet temperature is 250°C.

[0080] Reaction result description: silane conversion rate 100%, tail gas dust content (ratio to product weight) 0.03%wt, the apparent density of the product silicon particles was measured to be 2.05g / cm 3 The hydrogen content was not detected, the product had complete crystal form and dense structure; the lining of the sedimentation section was intact without wear, there was no deposition on the reactor wall, and the product had no agglomeration.

[0081] Example 2

[0082] The difference from Example 1 is that the conical polysilicon reactor is replaced by a fluidized bed reactor. The rest is the same as Example 1.

[0083] Description of reaction results: Due to the use of circulating riser heating, there is no obvious deposition on the inner wall of the reactor after operation. However, due to the existence of bubbles in the reactor, there is still a large amount of fine powder in the tail gas.

[0084] Example 3

[0085] The difference from Example 1 is that no diameter-changing section is provided on the circulating feed pipe. The rest is the same as Example 1.

[0086] Description of reaction results: The content of fine particles (particle size below 1 mm) in the product polycrystalline silicon increased by 3wt% compared with Example 1.

[0087] Example 4

[0088] The difference from Example 1 is that: the cone angle of the reaction section is 40°; the distance between the outlet of the highly conical reaction section of the silicon-containing raw material gas inlet pipe and the central axis is 1 / 4R at 1 / 5 of the height from bottom to top; the inlet silane content is 50% (the silicon-containing raw material gas is 50 vol% silane + 50 vol% hydrogen). The rest is the same as Example 1.

[0089] Reaction result description: silane conversion rate 100%, tail gas dust content (ratio to product weight) 0.05%wt, the apparent density of the product silicon particles was measured to be 2.04g / cm 3 The hydrogen content was not detected, the lining of the sedimentation section was intact, there was no wear, there was no deposition on the reactor wall, and there was no agglomeration in the product.

[0090] Example 5

[0091] The difference from Example 1 is that the ring 10 used to form the annular platform in the reactor is replaced by a truncated cone-shaped transition section with a larger diameter at the top and a smaller diameter at the bottom and a side wall inclined at 45°, and the upper end of the transition section is connected to the lower end of the settling section 11, and the upper end is connected to the upper end of the conical reaction section 14. The rest is the same as Example 1.

[0092] Description of reaction results: Compared with Example 1, on the opposite side of the solid-gas mixture inlet in the sedimentation section, obvious scratches appeared on the lining after long-term operation, and components of the lining material were detected in the silicon particle product; in addition, the exhaust dust content (ratio to product weight) was 0.05%wt.

[0093] Example 6

[0094] The difference from Example 1 is that the outlets of the four silicon-containing raw material gas inlet pipes are retracted to the inner wall of the conical reaction section. The rest is the same as Example 1.

[0095] Description of the reaction results: Compared with Example 1, the dust content of the tail gas (ratio to the product weight) is higher, reaching 0.22%wt, and a small amount of deposition occurs on the reactor wall.

[0096] Example 7

[0097] The difference from the first embodiment is that the connection position of the conveying air duct 19 is moved down to align with the conveying section 18, so that an inverted T-shaped connection is formed between the sealing section, the conveying section and the conveying air duct. The rest is the same as the first embodiment.

[0098] Description of reaction results: Compared with Example 1, due to the poor feeding effect, the hourly circulation rate was reduced to 5. Due to the reduction in the circulation rate, the number of hot silicon particles entering the reactor decreased significantly, the temperature in the reactor began to decrease, and the conversion rate decreased. When the mass of the intake air was reduced to 20% of that in Example 1, the reactor temperature reached the requirement and the conversion rate returned to 100%, which had a great impact on the overall output.

[0099] Comparative Example 1

[0100] The difference from Example 1 is that the lowest section of the conical reaction section 14 (i.e., the section below 1 / 6 of the height of the conical reaction section from bottom to top) is replaced by a conical head with a cone angle of 60°, and the solid product outlet pipe 16 is directly connected to the bottom of the head. The rest is the same as Example 1.

[0101] Description of reaction results: Compared with Example 1, the particles are almost stationary at the point where the cone angle changes, and the particles in the upper part flow slowly. After running for a period of time, the particles clump and gradually increase in size.

[0102] It can be seen from the above embodiments / comparative examples that (1) the present invention uses a circulating riser, which is not used as a reactor, but takes advantage of the characteristics of the circulating riser, such as fast circulation, large conveying capacity, and high heat transfer intensity, to complete the classification, circulation, and heating of silicon particles, thereby reducing the deposition on the reactor wall; at the same time, the silicon particles are repeatedly heated by hot air at a higher temperature, which is conducive to the complete breaking of the silicon-hydrogen bond, so that the product has a complete crystal form and a dense structure;

[0103] (2) The present invention can enhance particle classification and heat transfer effects by providing a variable diameter section on the circulation riser; through multiple variable diameter sections, the gas velocity of the hot gas can be continuously changed, silicon particles can be separated multiple times, the separation effect can be enhanced, and the heat transfer effect can be enhanced;

[0104] (3) The reaction section of the reactor of the present invention adopts an overall conical design, and there is no additional lower head design that causes a large change in the cone angle. The wall surface of the entire reaction section is straighter, which is conducive to the rapid movement of particles in the reaction bed. In addition, the particles move relative to each other during downward movement, which can effectively avoid particle agglomeration.

[0105] (4) The present invention allows the feed gas to be fed into the radial middle of the reaction section, which is more conducive to heat exchange and reaction area concentration in the reactor than feeding gas close to the inner wall of the reaction section. The product deposition area is large, the product structure is dense, the generation of fine powder is reduced, the tail gas is less entrained, and it is also more conducive to reducing wall surface reaction;

[0106] (5) By setting a ring at the lower end of the settling section to form an annular platform, it is beneficial to reduce equipment wear, improve product purity and reduce the entrainment of fine powder in tail gas;

[0107] (6) The present invention provides a conveying air duct at the lower part of the material sealing section, which can cooperate with the material sealing section and the conveying section, thereby facilitating the rapid conveyance of solid materials in the conveying section, so as to better coordinate with the rapid movement of particles in the reactor, thereby facilitating the improvement of the circulation ratio and the increase of production.

Claims

1. A rapid cycle polysilicon preparation system, characterized in that: The polysilicon preparation system comprises: A polysilicon reactor, wherein an exhaust pipe and a silicon particle feed pipe for inputting high-temperature silicon particles are provided at the upper part of the polysilicon reactor, and a solid product outlet pipe and a silicon-containing raw material gas inlet pipe for introducing silicon-containing raw material gas are provided at the lower part, wherein the polysilicon reactor is used to make the silicon-containing raw material gas contact and react with the high-temperature silicon particles as crystal seeds, so that the silicon generated by the decomposition of the silicon-containing raw material gas is deposited and grown on the surface of the silicon particles, and the grown silicon particles are discharged from the solid product outlet pipe, and the tail gas after the reaction is discharged from the exhaust pipe; A circulation riser, the circulation riser is arranged in the longitudinal direction, the other end of the solid product outlet pipe is connected to the middle part of the circulation riser, so as to feed the grown silicon particles discharged from the polysilicon reactor into the circulation riser; the upper end of the circulation riser is directly or indirectly connected to the silicon particle feed pipe, and the lower part of the circulation riser is connected with a hot air pipe, which is used to feed hot air into the circulation riser and perform airflow classification on the grown silicon particles, and heat the sorted particles with smaller particle size to a temperature sufficient to decompose the silicon-containing raw material gas and feed them upward into the silicon particle feed pipe as the high-temperature silicon particles, and the remaining particles with larger particle size flow downward and are discharged as polysilicon products; The heater is used for heating the airflow to be introduced into the hot air pipe to obtain the hot air.

2. The polysilicon preparation system according to claim 1, characterized in that: The circulation riser is provided with one or more diameter-enlarging reducing sections at the connection portion connected to the solid product outlet pipe and at the pipe section of the circulation riser located between the hot air pipe and the solid product outlet pipe; Preferably, the circulating riser is provided with a reducing section at the connection portion connected to the solid product outlet pipe; more preferably, the circulating riser is provided with a reducing section at the connection portion connected to the solid product outlet pipe, and the circulating riser is provided with one or two reducing sections on the pipe section located between the hot air pipe and the solid product outlet pipe.

3. The polysilicon preparation system according to claim 1 or 2, characterized in that: The polysilicon preparation system further comprises: A buffer tank connected to the lower end of the circulation riser and used for buffering the polysilicon product discharged from the circulation riser; a cooler connected to the buffer tank and used to cool the polysilicon product discharged from the buffer tank; Preferably, the cooler comprises a shell, and a gas distributor is provided at the lower part of the shell, so that the shell is divided into an air intake zone located below the gas distributor and a cooling zone located above the gas distributor; The top of the cooling zone is provided with a polysilicon product feed pipe extending downward into the cooling zone, which is used to feed the polysilicon product into the cooling zone and accumulate it on the gas distributor to form a polysilicon product bed layer; The air inlet area is provided with a cooling air inlet to introduce cooling air to cool the polysilicon products accumulated on the gas distributor; the cooling area is provided with a cooling air outlet, and the cooling air outlet is higher than the lower end of the polysilicon product feed pipe to discharge the cooling air after heat exchange with the polysilicon product and temperature rise; The gas distributor is provided with a polysilicon product discharge pipe, and the cooler is used to cool the polysilicon product accumulated on the gas distributor by using the rising cooling gas introduced from the air inlet area, and discharge the cooled polysilicon product at the bottom of the polysilicon product bed from the polysilicon product discharge pipe; Preferably, the polysilicon preparation system further comprises a shell for accommodating the polysilicon reactor, the circulation riser, the buffer tank and the cooler.

4. The polysilicon preparation system according to any one of claims 1 to 3, characterized in that: The polysilicon reactor is a fluidized bed reactor or a moving bed reactor; the gas-solid mixture sent from the upper end of the circulation riser directly enters the silicon particle feed pipe and then undergoes gas-solid separation at the upper part of the polysilicon reactor, or undergoes gas-solid separation first and then enters the silicon particle feed pipe.

5. The polysilicon preparation system according to any one of claims 1 to 4, characterized in that: The polysilicon reactor is a conical polysilicon reactor, comprising a conical reaction section whose diameter gradually decreases from top to bottom and a settling section arranged above the conical reaction section; The exhaust pipe is provided on the top of the settling section, and the silicon particle feed pipe is provided on the side wall; the settling section is used to settle and separate the silicon particles in the gas-solid mixture from the silicon particle feed pipe, so that the silicon particles settle to the conical reaction section to form a silicon particle bed layer; The upper end of the conical reaction section is connected to the lower end of the settling section, the solid product outlet pipe is provided at the bottom of the conical reaction section, and the silicon-containing raw material gas inlet pipe is provided on the side wall; the conical reaction section is used to make the rising silicon-containing raw material gas contact and react with the descending silicon particle bed layer, so that the silicon generated by the decomposition of the silicon-containing raw material gas introduced from the silicon-containing raw material gas inlet pipe is deposited and grown on the surface of the silicon particles serving as crystal seeds, and the grown silicon particles are discharged from the solid product outlet pipe; Preferably, the cone angle of the conical reaction section is 15-50°, preferably 20-40°.

6. The polysilicon preparation system according to claim 5, characterized in that: The outlet of the silicon-containing raw material gas inlet pipe extends radially close to the radial middle of the conical reaction section; Preferably, the distance between the outlet of the silicon-containing raw material gas inlet pipe and the central axis of the conical reaction section is (1 / 10-2 / 3)R, preferably (1 / 8-1 / 2)R; wherein R is the radius of the circular cross-section of the conical reaction section on the horizontal plane where the silicon-containing raw material gas inlet pipe is located; Preferably, the silicon-containing raw material gas inlet pipe is provided with one group or multiple groups located at different heights, each group comprises multiple silicon-containing raw material gas inlet pipes uniformly distributed along the circumference of the conical reaction section on the same plane; Preferably, the outlet of the silicon-containing raw gas inlet pipe is arranged at a height of 1 / 6-2 / 3, preferably 1 / 5-1 / 2, from bottom to top of the conical reaction section.

7. The polysilicon preparation system according to claim 5 or 6, characterized in that: The solid product outlet pipe is L-shaped, comprising a vertically arranged material sealing section and a conveying section connected to the lower end of the material sealing section, wherein the upper end of the material sealing section is directly connected to the bottom of the conical reaction section, and the other end of the conveying section is connected to the middle of the circulation riser, so as to convey the grown silicon particles discharged from the conical reactor into the circulation riser; preferably, the angle between the conveying section and the material sealing section is 90-150°, preferably 110-130°; The material sealing section is also provided with a conveying air duct, which is horizontally connected to the lower part of the material sealing section; preferably, the conveying air duct is horizontally connected to the lower part of the material sealing section at a position 2D-5D higher than the conveying section, wherein D is the inner diameter of the pipeline of the conveying section.

8. The polysilicon preparation system according to any one of claims 5 to 7, characterized in that: The diameter of the lower end of the settling section is greater than the diameter of the upper end of the conical reaction section and is flush with the upper end of the conical reaction section; the lower end of the settling section is connected to the upper end of the conical reaction section through a horizontally arranged circular ring, wherein the outer ring of the circular ring is connected to the lower end of the settling section, and the inner ring of the circular ring is connected to the upper end of the conical reaction section, thereby forming an annular platform carrying a silicon particle layer at the bottom of the settling section, which is used to prevent the silicon particles fed from the silicon particle feeding pipe from impacting the reactor wall; Preferably, the silicon particle feeding pipe is horizontally arranged toward the central axis of the sedimentation section.

9. The polysilicon preparation system according to any one of claims 1 to 8, characterized in that: The polysilicon preparation system further comprises: An exhaust gas heat exchange unit, used to cool the exhaust gas from the exhaust pipe of the polysilicon reactor using circulating gas to recover heat, and to send the circulating gas heated by heat exchange into the heater for further heating and heating, so as to be sent into the circulating riser as the hot air circulation; A tail gas dust removal unit, used for removing dust from the tail gas from the tail gas heat exchange unit to obtain dust-removed tail gas; A circulating gas compressor, used for pressurizing the dust removal tail gas to be sent into the tail gas heat exchange unit as circulating gas; A product tank, used for receiving the polysilicon product discharged from the polysilicon preparation system; A seed crystal preparation unit, used for crushing the polysilicon product discharged from the polysilicon preparation system and sending it back to the polysilicon reactor as seed crystals; Preferably, the polysilicon preparation system further comprises: a first cooling air pipe connected to a cooling air inlet of the cooler and used to deliver cooling air into the cooler to cool the incoming polysilicon product; The second cooling air pipe is respectively connected to the cooling air outlet of the cooler and the exhaust gas dust removal unit, and is used to send the heated cooling air from the cooler as part of the exhaust gas into the exhaust gas dust removal unit.

10. A process for preparing polycrystalline silicon using the polycrystalline silicon preparation system according to any one of claims 1 to 9, comprising: (1) The silicon-containing raw material gas introduced from the silicon-containing raw material gas inlet pipe and the high-temperature silicon particles introduced from the silicon particle inlet pipe are contacted and reacted in the polysilicon reactor, so that the silicon generated by the decomposition of the silicon-containing raw material gas is deposited and grown on the surface of the silicon particles serving as seed crystals; (2) sending the grown silicon particles into the circulation riser from the solid product outlet pipe, and discharging the tail gas from the exhaust pipe; (3) sending the hot air heated by the heater into the circulation riser from the hot air pipe, and performing airflow classification on the grown silicon particles, and heating the selected particles with smaller particle sizes to a temperature sufficient to decompose the silicon-containing raw gas and sending them upward into the silicon particle feed pipe as the high-temperature silicon particles, and the remaining particles with larger particle sizes are discharged downward as polycrystalline silicon products; Preferably, the temperature of the high-temperature silicon particles entering the polysilicon reactor is 650-850°C; Preferably, the hourly circulation rate of silicon particles in the polysilicon reactor is 5-20; Preferably, the silicon-containing raw material gas is a mixture of silane and hydrogen, wherein the volume content of silane is 5-100%, preferably 50-100%; Preferably, the mass ratio of the silicon-containing raw gas to the silicon particle feed entering from the silicon particle inlet pipe is (0.05-0.25):1.

Images