Cone-shaped polycrystalline silicon reactor capable of rapidly moving particles and method

Abstract

The invention discloses a conical polycrystalline silicon reactor capable of rapidly moving particles and a method. The conical polycrystalline silicon reactor comprises a conical reaction section and a settling section, wherein the diameter of the conical reaction section is gradually reduced from top to bottom, and the settling section is arranged above the conical reaction section; the top of the settling section is provided with an exhaust pipe, and the side wall of the settling section is provided with a silicon particle feeding pipe which is used for conveying gas and is used as a seed crystal; the upper end of the conical reaction section is communicated with the lower end of the settling section, a solid product outlet pipe is arranged at the bottom of the conical reaction section, and a silicon-containing raw material gas inlet pipe is arranged on the side wall of the conical reaction section; the reaction section of the reactor is conical, the silicon particle moving speed is high, the reaction efficiency is high, silane is completely reacted, the product crystal form is complete, hydrogen is not contained, the product density is high, the yield is high, energy consumption is low, amplification is easy, meanwhile, the side face feeding and top exhaust design of the settling section is matched, tail gas entrainment is small, tail gas dust is not generated, and the product quality is good.

Description

Technical Field

[0001] The present invention relates to the technical field of polysilicon production, and particularly to a conical polysilicon reactor with rapid particle movement and a method for preparing polysilicon. Background Art

[0002] High-purity polysilicon materials have always been the basic raw materials for the semiconductor and photovoltaic industries, and the polysilicon industry has developed rapidly. The main methods for preparing polysilicon include the improved Siemens process and the silane fluidized bed process, etc.

[0003] The improved Siemens process is the mainstream process in the current polysilicon industry. Its core process is to rectify and purify the raw material trichlorosilane (SiHCl3), mix it with high-purity hydrogen, and then 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). The silicon generated by the reaction is deposited on the silicon core, gradually thickening the silicon core. The reaction tail gas contains trichlorosilane, dichlorosilane, tetrachlorosilane, hydrogen, hydrogen chloride, etc. After recovery and separation, it is rectified and recycled. After the silicon core grows into a polysilicon rod with a certain diameter, the furnace is stopped for replacement, and the silicon rod is taken out. The silicon rod is broken and then packaged. This process has a long process flow, a high reaction temperature, a low conversion rate, a low production capacity, batch operation, a low relative volatility between the raw material and the main impurities, and a large separation difficulty, resulting in a large investment, high energy consumption (especially electricity consumption), and high costs.

[0004] Therefore, the silane fluidized bed process has been further developed in this field. The process uses silane (SiH4) as the raw material. After purification, it is sent into the fluidized bed reactor (with seed crystals) at a certain ratio. Silicon is decomposed in the reactor. Theoretically, the silicon is deposited on the seed crystals, gradually growing the seed crystals to form 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 taken out from the reactor and screened to obtain the product. The particles with a smaller particle size are returned to the reactor to continue growing. In addition, a small amount of the product needs to be broken and used as seed crystals to be supplemented into the reactor to maintain continuous production. This process theoretically has the advantages of a short process flow, a low reaction temperature, a high conversion rate, a high reactor production capacity, continuous operation, a low silane separation difficulty, and no need to break 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, resulting in a large amount of dust. Some of the dust is carried out of the system, leading to a decrease in the product yield. Since a large number of dangling bonds are generated by the homogeneous reaction, the product contains hydrogen, the product structure is loose, and fine powder is easily generated during transportation and use. All of the above lead to low product quality and difficulties 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 concentration of silane, otherwise more dust will be generated. In addition, due to the generation of the above bubbles, a small amount of silane is carried out of the reactor without being heated to the reaction temperature, and a separation and recovery process needs to be added subsequently. While the yield is reduced, the energy consumption and investment are increased. Moreover, due to the problem of the heating method, wall deposition is easily caused, the production cycle is short, and the production capacity is low.

[0006] In addition, CN11853400A also discloses a silane moving bed reaction system, including a heater, a reactor, and a stripper. The outlet of the heater is communicated with the inlet of the reactor, and the outlet of the reactor is communicated with the inlet of the stripper. Polysilicon enters the heater and is heated to the reaction temperature. The heated polysilicon enters the reactor from top to bottom for crystal growth. The reaction gas enters the reactor from bottom to top and contacts the polysilicon in the reactor reversely and reacts. The tail gas after the reaction is discharged from the upper part of the reactor. The polysilicon after the reaction enters the stripper for stripping. However, due to the design problems of its heating method and feeding method, it is easy to cause uneven bed temperature, incomplete reaction of silane, and the problem of powder entrainment in the tail gas. For this reason, a filtering element is also provided at the tail gas outlet of the reactor, which increases the system complexity and pollution risk. In addition, a head design is adopted at the lower end of the reactor, resulting in an additional supporting force on the bed layer, thereby reducing the pressure head of the bed layer. The particle flow rate of the entire bed layer above the supporting surface is slow, the particle flow rate is greatly reduced, a central flow is easily formed, and the materials near the wall stay for a long time, with poor fluidity and a risk of caking.

[0007] CN103787336A discloses a method for producing high-purity granular silicon, in which auxiliary gas needs to be added to maintain the bed layer state. However, the addition of auxiliary gas increases the energy consumption, and its distribution plate is easily blocked. Both the auxiliary gas and the reaction gas are dispersed in the reaction cavity, which easily leads to the diffusion of the reaction gas to the wall surface and the risk of wall deposition. For this reason, an air curtain device is added, making the overall structure very complex and the operability poor. In addition, the particles in its bed layer move slowly by themselves, the heat transfer efficiency is poor, it is easy to cause uneven bed temperature, and the silane cannot react completely. For this reason, a tail gas separation mechanism is added, and the surface of the particles is loose, and fine powder is easily generated. For this reason, a surface treatment mechanism is added, and the system becomes more complex. Summary of the Invention

[0008] In view of this, the purpose of the present invention is to provide a conical polysilicon reactor and method for rapid movement of particles to efficiently prepare granular polysilicon.

[0009] To achieve one aspect of the above object, the present invention adopts the following technical solutions:

[0010] A conical polysilicon reactor for rapid movement of particles, characterized in that:

[0011] The conical polysilicon reactor includes a conical reaction section with a gradually decreasing diameter from top to bottom and a settling section provided above the conical reaction section;

[0012] Among them, an exhaust pipe is provided at the top of the settling section, and a silicon particle feed pipe for gas transportation as seed crystals is provided on the side wall; the settling section is used for sedimentation separation of 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;

[0013] The upper end of the conical reaction section is communicated with the lower end of the settling section, a solid product outlet pipe is provided at the bottom of the conical reaction section, and a silicon-containing raw material gas inlet pipe is provided on the side wall; the conical reaction section is used for the rising silicon-containing raw material gas to contact and react with the downward silicon particle bed layer, so that the silicon produced by the decomposition of the silicon-containing raw material gas introduced from the silicon-containing raw material gas inlet pipe deposits and grows on the surface of the silicon particles as seed crystals, and the produced granular polysilicon is discharged from the solid product outlet pipe.

[0014] Preferably, the outlet of the silicon-containing raw material gas inlet pipe extends radially and approaches the radial middle part of the conical reaction section.

[0015] 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; where 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.

[0016] Preferably, the silicon-containing raw material gas inlet pipe is provided with one group or multiple groups at different heights, and each group includes multiple silicon-containing raw material gas inlet pipes evenly distributed along the circumferential direction of the conical reaction section on the same plane.

[0017] Preferably, the outlet of the silicon-containing raw material gas inlet pipe is arranged at a height of 1 / 6 - 2 / 3 from the bottom to the top of the conical reaction section, preferably 1 / 5 - 1 / 2 height.

[0018] Preferably, the solid product outlet pipe is in an L shape and includes a stuffing section arranged vertically and a conveying section connected to the lower end of the stuffing section. The upper end of the stuffing section is directly connected to the bottom of the conical reaction section to convey the solid product descending from the conical reaction section.

[0019] Preferably, the included angle between the conveying section and the stuffing section is 90 - 150°, preferably 110 - 130°.

[0020] Preferably, a conveying air pipe is further arranged on the stuffing section. The conveying air pipe is horizontally connected to the lower part of the stuffing section, such as at a position 2D - 5D higher than the conveying section (D is the inner diameter of the pipeline of the conveying section).

[0021] Preferably, the cone angle of the conical reaction section is 15 - 50°, preferably 20 - 40°; the conical reaction section of the present invention is in an overall conical shape, and the cone angle remains unchanged from top to bottom.

[0022] Preferably, the lower end diameter of the settling section is larger than the upper end diameter 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 ring. The outer ring of the ring is connected to the lower end of the settling section, and the inner ring of the ring is connected to the upper end of the conical reaction section, so as to form an annular platform for carrying the silicon particle layer at the bottom of the settling section to block the impact of the silicon particles fed from the silicon particle feed pipe on the reactor wall surface.

[0023] Preferably, the silicon particle feed pipe is horizontally arranged towards the central axis of the settling section.

[0024] Preferably, the conical polysilicon reactor further includes a heating part for heating the silicon particles in the gas - solid mixture to be fed into the settling section so as to carry out a reaction in the conical reaction section.

[0025] For another aspect of achieving the above - mentioned invention purpose, the present invention adopts the following technical solutions:

[0026] A method for preparing granular polysilicon, which is to prepare granular polysilicon by using the above - mentioned conical polysilicon reactor, and includes:

[0027] (1) The silicon particles in the gas - solid mixture from the silicon particle inlet are settled and separated in the settling section, so that the silicon particles settle to the conical reaction section to form a silicon particle bed layer;

[0028] (2) The silicon - containing raw material gas fed from the silicon - containing raw material gas inlet 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 deposits and grows on the surface of the silicon particles as seeds to obtain granular polysilicon.

[0029] (3) The prepared granular polysilicon is discharged from the solid product outlet, and the tail gas is discharged from the exhaust pipe. The tail gas is the gas rising from the conical reaction section into the settling section and the gas in the gas-solid mixture.

[0030] Preferably, the temperature of the silicon particle bed layer is 650 - 850 °C.

[0031] Preferably, the hourly circulation ratio of the silicon particles in the conical reaction section is 5 - 20.

[0032] Preferably, the silicon-containing feed gas is a mixture of silane and hydrogen, wherein the volume content of silane is 5 - 100%, preferably 50 - 100%.

[0033] Preferably, the mass ratio of the silicon-containing feed gas to the silicon particle feed entering from the silicon particle inlet pipe is (0.05 - 0.25):1.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] (1) In the present invention, the particles are directly heated outside the reactor, so that the silicon-containing feed gas is heated on the particles, greatly increasing the heating area. At the same time, the problems of wall deposition and lining damage are greatly improved, and long-term operation can be achieved; the size of the reactor of the present invention can be not limited by the heating conditions, so it can be greatly enlarged to expand the production capacity;

[0036] (2) The reaction section adopts an overall conical design, which is conducive to the rapid movement of the particles in the reaction bed layer. And when moving downward, the relative movement between the particles can effectively avoid particle caking;

[0037] (3) The reaction section of the present invention can operate without 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, thus avoiding the occurrence of homogeneous reaction, greatly reducing dust generation, and improving the product yield; and due to the absence of bubbles, silane can react 100% and there is no silane in the tail gas, which is conducive to reducing the tail gas separation process in the subsequent process;

[0038] (4) By feeding the raw material gas to the radial middle part of the reaction section in the present invention, it is conducive to heat exchange in the reactor and the concentration of the reaction area. The product deposition area is large, the product structure is dense, and it is also conducive to reducing wall deposition;

[0039] (5) By arranging a ring at the lower end of the settling section to form an annular platform in the present invention, it can effectively prevent the direct impact of the feed on the inner wall of the reactor while realizing horizontal feeding. At the same time, the accumulated silicon particles can reach a dynamic balance among the particle slippage caused by the impact of horizontal feeding, the silicon particles brought in by the feed gas flow, and the particles deposited in the settling section;

[0040] (6) In the present invention, the air conveying pipe at the lower part of the material seal section can cooperate with the material seal 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.

[0041] In summary, the present invention can realize the large-scale of equipment, greatly improve the production capacity, improve the product quality, reduce the cost, shorten the process, reduce the investment, reduce the carbon emission, and the economic benefit is very obvious. Description of the Drawings

[0042] Figure 1 It is a schematic diagram of an embodiment of the conical polysilicon reactor of the present invention. Detailed Embodiments

[0043] 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 conjunction with the embodiments and drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

[0044] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values, such as values within ±10% of the endpoint values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein. Without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other.

[0045] It should be noted that the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0046] Such as Figure 1As shown in the figure, the conical polysilicon reactor of the present invention includes a conical reaction section 14 with a gradually decreasing diameter from top to bottom and a settling section 11 provided above the conical reaction section. Among them, an exhaust pipe 13 is provided at the top of the settling section 11, and a silicon particle feed pipe 12 for gas transportation and serving as seeds is provided on the side wall; 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 layer; those skilled in the art understand that when the gas-solid mixture carrying particulate matter suddenly enters a larger space, the flow rate decreases sharply. On the basis of ensuring sufficient space in the settling section, the particulate matter will settle and separate from the carrier gas.

[0047] The upper end of the conical reaction section 14 is communicated with the lower end of the settling section 11. A solid product outlet pipe 16 is provided at the bottom of the conical reaction section 14, and a silicon-containing raw material gas inlet pipe 15 is provided on the side wall; the conical reaction section 14 is used to make the rising silicon-containing raw material gas contact and react with the downward silicon particle bed layer, so that the silicon produced by the decomposition of the silicon-containing raw material gas introduced from the silicon-containing raw material gas inlet pipe 15 deposits and grows on the surface of the silicon particles serving as seeds, and the produced granular polysilicon is discharged from the solid product outlet pipe 16.

[0048] In the present invention, the gas-solid mixture fed from the silicon particle feed pipe 12 undergoes 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 contact the silicon-containing raw material gas countercurrently, so that the decomposed silicon deposits and grows on the surface of the silicon particles. Finally, it is discharged from the bottom. Those skilled in the art understand that among the products discharged from the solid product outlet pipe 16, the unfully grown granular silicon can be separated subsequently and recycled as seeds back to the reactor for continued growth, which is well known in the art and will not be elaborated here.

[0049] In the present invention, the settling section 11 is used to provide a gas-solid separation and settling space, and its diameter can gradually expand or remain unchanged from bottom to top, such as a cylindrical shape or a frustum shape 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 settle sufficiently, such as being sufficient to allow the silicon particles with a particle size greater than 0.01 mm to settle sufficiently. For example, the settling rate can reach 99.99%; those skilled in the art understand that the silicon dust directly decomposed from the silicon-containing raw material gas and not deposited on the surface of the silicon particles is difficult to settle naturally in the rising tail 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, being collected in the silicon particle bed layer, and reducing collision, friction and pulverization.

[0050] In the present invention, it can be understood in the art that the lower end of the sedimentation section 11 can be directly connected to or connected to the upper end of the conical reaction section 14 through other transition sections. For example, in a conventional embodiment, the sedimentation section 11 can usually be transitionally connected through a reduced-diameter section with a larger upper part and a smaller lower part, such as being connected to the upper end of the conical reaction section 14. Among them, the cone angle (the angle between two generatrices 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, for example 20 - 40°.

[0051] In the present invention, a plurality of outlets of the silicon-containing raw material gas inlet pipe 15 can usually be arranged along the circumferential direction and / or the longitudinal direction of the conical reaction section 14 so as to feed the silicon-containing raw material gas more evenly. In one embodiment, the outlet of the silicon-containing raw material gas inlet pipe 15 extends radially to be close to the radial middle part (i.e., the central part of the horizontal circular section of the conical reaction section) inside the conical reaction section 14, so that the silicon-containing raw material gas is fed into the middle area around the central axis of the conical reaction section 14; 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, where R is the radius of the circular section of the conical reaction section on the horizontal plane where the silicon-containing raw material gas inlet pipe is located.

[0052] It is understood in the art that in order to prevent premature decomposition of the raw material gas, the raw material gas fed into the reactor is usually a cold gas with a relatively low temperature (such as a temperature not higher than 400 °C, for example, 25, 50, 100, 200 or 300 °C). In order to achieve uniform distribution of the inlet gas, the fed raw material gas is usually distributed as much as possible on the inner wall of the reactor. However, in the present invention, for the design of the overall conical reaction section, the cone angle remains unchanged or changes very little from top to bottom, such as not exceeding 10° or not exceeding 5°. It has been found that by concentrating the raw material gas at the middle of the conical reaction section 14 for feeding, the fed raw material gas can preferentially contact the silicon particles with the fastest downward velocity in the conical reaction section 14 (and thus is more likely to maintain its feeding heat), resulting in high reaction efficiency. At the same time, after the gas contacts, the temperature rises and the volume of the reaction-generated gas expands several times. The conical design is also beneficial to the rapid upward diffusion of the remaining gas to the entire bed cross-section for reaction. Since the low-temperature gas contacts the particles with a high flow velocity in the middle first, the Reynolds number is high and the heat transfer coefficient is also high, and the main heat exchange is completed instantaneously. The gas temperature reaches the decomposition temperature and the reaction is basically completed. During the radial diffusion process, when contacting the particles with a lower flow velocity, the gas temperature and the particle temperature will be made consistent, and the temperature of the entire cross-section is relatively balanced, which is beneficial 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 velocity of the silicon particles near the inner wall of the conical reaction section 14 is lower than that of the middle silicon particles, the absolute and relative movement velocities are still high. Therefore, although a small amount of remaining gas reacts efficiently after diffusion, it is still possible to effectively avoid caking of the silicon particles near the inner wall of the conical reaction section 14. In addition, due to the overall conical design of the reaction section of the present invention, it is also beneficial to the upward gas flow to decelerate due to heat and reaction-induced volume expansion, ensuring the stability of the bed without fluidization and without generating bubbles, and through the settling section and the cross-mixing with the lateral gas flow in the settling section, the gas velocity can be reduced and the solid phase entrainment can be reduced.

[0053] In the present invention, one set or multiple sets (such as 2-4 sets) of silicon-containing raw material gas inlet pipes 15 located at different heights can be provided. Each set includes multiple (such as 2-6) silicon-containing raw material gas inlet pipes 15 evenly distributed along the circumferential direction 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 set at 1 / 6-2 / 3 (such as 1 / 5-1 / 2, for example, 1 / 4 or 1 / 3) of the height of the conical reaction section from bottom to top, which is more conducive to full contact 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 some raw material gas to flow downward or even generate bubbles, resulting in a decrease in yield, while if the height is too high, it is easy to cause the reaction section to become shorter and the conversion rate to decrease.

[0054] In the present invention, the silicon particle feed pipe 12 introduces silicon particles into the reactor by gas transportation. Preferably, the silicon particle feed pipe is horizontally arranged towards the central axis of the settling section 11 so that the gas-solid mixture is fed in a substantially horizontal direction, thereby avoiding the problems that are not conducive to settling caused by being too inclined upwards and the problems that affect the upward airflow from the conical reaction section 14 and cause greater impact force due to the acceleration of particles in the feed by gravity when being too inclined downwards. If the feed is horizontally tangential, it is easy to cause abrasion of the silicon particles and the reactor wall of the settling section.

[0055] However, those skilled in the art understand that since the silicon particle feed pipe is arranged on the side wall of the settling section, its feed (especially horizontal lateral feed) will still impact the side wall of the settling section 11, which will not only cause the silicon particles in the feed to be crushed, but also easily lead to an increase in the impurity content of the product.

[0056] In one embodiment, the lower end diameter of the settling section 11 is larger than the upper end diameter 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 for carrying the 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 impact of the silicon particles fed from the silicon particle feed pipe 12 on the wall surface of the settling section of the reactor; it is found that since it is in the settling section 11, such an arrangement is beneficial to the natural settlement and accumulation of silicon particles on the annular platform and will not cause the natural downward movement depending 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 settling section 11, the accumulated silicon particle layer can, on the one hand, effectively block the direct collision of the feed on the inner wall of the reactor while realizing horizontal feed, and on the other hand, the accumulated silicon particles can reach a dynamic balance between the reduction of particles caused by the impact of the horizontal feed airflow and the deposition of particles in the settling section 11, realizing a balance of a certain material replacement and continuous protection.

[0057] In the present invention, the silicon particles in the conical reaction section 14 are sent out from the solid product outlet pipe 16 after descending. Those skilled in the art understand that the solid product sent out can be classified subsequently, and the silicon particles with unqualified sizes will be separated, for example, recycled back to the reactor through the silicon particle inlet to continue growing.

[0058] In one embodiment, the solid product outlet pipe 16 is in an L shape, including a material seal section 17 arranged vertically and a conveying section 18 connected to the lower end of the material seal section 17. The upper end of the material seal section 17 is directly connected to the bottom of the conical reaction section 14, so that the solid product leaving the conical reaction section 14 directly enters the material seal section 17 of the solid product outlet pipe 16, reducing resistance and facilitating the conveyance of the solid product descending from the solid product outlet. Of course, those skilled in the art can understand that the "L" shape of the solid product outlet pipe 16 does not represent a strict right-angle connection between the material seal section 17 and the conveying section 18 or a strict length ratio between the material seal section 17 and the conveying section 18. In the present invention, the "L" shape mainly means that the solid product outlet pipe 16 is designed in a bent shape. For example, the material seal section 17 and the conveying section 18 can be connected through an arc-shaped elbow and the included angle between the material seal section 17 and the conveying section 18 can be not 90°. Those skilled in the art understand that the conveying section can also convey when it is inclined downward. For example, the included angle between the conveying section 18 and the material seal section 17 can be 90 - 150°, such as 100, 120, 140° or 110 - 130°.

[0059] In one embodiment, a conveying air pipe 19 is further provided on the material seal section 17. The conveying air pipe 19 is horizontally connected to the lower part of the material seal section 17, such as at a position 2D - 5D, such as 3D or 4D (D is the inner diameter of the pipe of the conveying section) higher than the conveying section. It is found that through the combined setting of the conveying air pipe 19 and the material seal section 17, it is more beneficial for solid material conveyance. Among them, through the setting of the material seal section 17, a material seal with a certain height can be formed, and the conveying air horizontally fed by the conveying air pipe 19, due to being perpendicular to the feeding of the material seal section, can appropriately increase the particle gap in the material seal section, reduce the internal friction force between particles, and play a role in loosening the material. And the material seal formed by the material seal section 17 can well prevent the air flow from rising into the conical reaction section 14. Finally, the conveying air descends to convey the solid product, so it is also beneficial for the rapid conveyance of the solid material in the conveying section 18 to better cooperate with the rapid movement of the particles in the reactor.

[0060] In the present invention, the conical polysilicon reactor may further include a heating part (not shown in the figure) for heating the silicon particles in the gas-solid mixture fed into the settling section 11 so as to carry out a reaction in the conical reaction section 14. The action mode of the heating part can be hot gas heating / electric tracing heating / radiation heating / electromagnetic heating, etc.

[0061] In addition, a feeding pipe may be provided at an appropriate position of the conical polysilicon reactor to add fine seed crystals (the addition amount per unit time is very small and the influence is small) for maintaining the bed layer in the reactor, for example, arranged in the settling section or on the silicon particle feeding pipe.

[0062] The method for preparing granular polysilicon using the above-mentioned conical polysilicon reactor of the present invention includes:

[0063] (1) The silicon particles in the gas-solid mixture fed from the silicon particle inlet pipe 12 are sedimentationally separated in the sedimentation section 11, so that the silicon particles settle to the conical reaction section 14 to form a silicon particle bed layer;

[0064] (2) The silicon-containing feed gas fed from the silicon-containing feed gas inlet pipe 15 rises and contacts and reacts with the downward silicon particle bed layer, so that the silicon produced by the decomposition of the silicon-containing feed gas deposits and grows on the surface of the silicon particles as seeds to obtain granular polysilicon;

[0065] (3) The prepared granular polysilicon is discharged from the solid product outlet pipe 16, and the tail gas is discharged from the exhaust pipe 13. The tail gas is the gas rising from the conical reaction section 14 into the sedimentation section 11 and the gas in the gas-solid mixture.

[0066] In the present invention, the silicon-containing feed gas can be a mixture of a silicon-containing effective gas and a diluent gas. The silicon-containing effective gas is a gas that can be decomposed by heating to produce silicon and is well-known in the art, such as silane or disilane. The diluent gas can be hydrogen, nitrogen, helium or argon (it can be understood in the art that it can also be used as the gas for transporting silicon particles). For example, the silicon-containing feed gas can be a mixture of silane and hydrogen, and 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 feed gas is pure silane gas rather than a mixture gas.

[0067] In the present invention, the temperature of the silicon particle bed layer can be 650-850 °C, such as 700, 750 or 800 °C, so as to enable the reaction to proceed.

[0068] In the present invention, the pressure inside the reactor can be 0.5-3 MPa.g, such as 1 or 2 MPa.g.

[0069] In the present invention, the hourly circulation ratio of the silicon particles in the conical reaction section 14 (that is, the ratio of the amount of silicon particles fed into the silicon particle feed pipe 12 per hour to the storage amount of silicon particles in the silicon particle bed layer in the conical reaction section) can be 5-20, such as 8, 10 or 15. It can be understood in the art that too low an hourly circulation ratio may be unfavorable for preventing particle agglomeration, and too high may cause wear of the system equipment and affect the product purity.

[0070] In the present invention, the silicon particle bed layer in the conical reaction section 14 serves both as a seed to provide a deposition surface and as a heating medium to heat the raw material gas; preferably, the mass ratio of the silicon-containing raw material 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 may result in low yield and high cost, while too high may lead to a decrease in conversion rate.

[0071] The following further illustrates the present invention in combination with specific operation examples / comparative examples.

[0072] Example 1

[0073] The used conical polysilicon reactor is as Figure 1 shown, including the conical reaction section 14 (cone angle 20°) and the settling section 11 connected thereto; an exhaust pipe 13 is provided at the top of the settling section, and a silicon particle feed pipe 12 for gas transportation and serving as a seed is provided on the side wall; the upper end of the conical reaction section is communicated with the lower end of the settling section, and a solid product outlet pipe 16 is provided at the bottom of the conical reaction section, and a silicon-containing raw material gas inlet pipe 15 is provided on the side wall.

[0074] The outlet of the silicon-containing raw material gas inlet pipe extends radially and is close to the radial middle part of the conical reaction section, and the distance from its central axis is 1 / 2R; and four silicon-containing raw material gas inlet pipes are evenly distributed circumferentially along the conical reaction section on the same plane, and their height is at the 1 / 3 height from the bottom to the top of the conical reaction section.

[0075] A horizontal ring 10 is provided at the lower end of the settling section. The outer ring of the ring is connected to the lower end of the settling section, and the inner ring of the ring is connected to the upper end of the conical reaction section, so as to form an annular platform for carrying the silicon particle layer at the bottom of the settling section to block the impact of the feed of the silicon particle feed pipe.

[0076] The solid product outlet pipe 16 is in an L shape, including a stuffing section 17 arranged vertically and a conveying section 18 horizontally connected to the lower end of the stuffing section. The upper end of the stuffing section is directly connected to the bottom of the conical reaction section, and the horizontally connected conveying air pipe 19 is higher than the conveying section 3D at the connection position below the stuffing section.

[0077] The other end of the conveying section is connected to the middle of a vertically arranged heating circulation pipe (not shown in the figure). The upper end of the heating circulation pipe is connected to the silicon particle feed pipe. The hot air (hydrogen) heated by the heating section enters from the lower part of the heating circulation pipe. After the small particles in the solid product from the conveying section 18 are separated by pneumatic separation and heated together with the silicon particles from the make-up pipe, they are sent upward into the silicon particle feed pipe. In addition, a make-up pipe is provided at an appropriate position in the reactor to add fine seed crystals (the addition amount per unit time is very small and the influence is small) to maintain the bed layer in the reactor. For example, it is arranged in the settling section or at the position of the heating circulation pipe between the conveying section and the silicon particle feed pipe.

[0078] During operation, (1) the silicon particles in the gas-solid mixture fed from the silicon particle inlet pipe are sedimentationally separated in the settling section so that the silicon particles settle to the conical reaction section to form a silicon particle bed layer; (2) the silicon-containing raw material gas (100% silane) fed from the silicon-containing raw material gas inlet pipe rises and contacts and reacts with the downward silicon particle bed layer so that the silicon produced by the decomposition of the silicon-containing raw material gas deposits and grows on the surface of the silicon particles as seeds to obtain granular polysilicon; (3) the produced granular polysilicon is discharged from the solid product outlet pipe, and the tail gas is discharged from the exhaust port.

[0079] Among them, the reactor pressure is about 5 bar.g, the average temperature of the silicon particle bed layer is about 700 °C, the mass ratio of the silicon-containing raw material 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 inlet temperature of the raw material gas is 250 °C.

[0080] Reaction result description: The silane conversion rate is 100%, the tail gas dust content (the ratio to the product weight) is 0.03% wt, and the apparent density of the measured product silicon particles is 2.05 g / cm 3 , the hydrogen content is not detected, the inner lining of the settling section is intact without wear, there is no deposition on the reactor wall, and the product has no caking situation.

[0081] Example 2

[0082] The difference from Example 1 is that the cone angle of the reaction section is 40°; the height of the silicon-containing raw material gas inlet pipe is at the 1 / 5 height from the bottom to the top of the conical reaction section, and the distance between its outlet and the central axis is 1 / 4R; 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.

[0083] Reaction result description: The silane conversion rate is 100%, the tail gas dust content (the ratio to the product weight) is 0.05% wt, and the apparent density of the measured product silicon particles is 2.04 g / cm 3, the hydrogen content was not detected, the inner lining of the sedimentation section was intact without wear, there was no deposition on the reactor wall, and the product did not form lumps.

[0084] Example 3

[0085] The difference from Example 1 is that the circular ring 10 used to form the annular platform in the reactor is replaced by a frustum-shaped transition section with a larger upper diameter and a smaller lower diameter and a 45° inclined side wall. The upper end of this transition section is connected to the lower end of the sedimentation 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.

[0086] Reaction result description: Compared with Example 1, on the opposite side of the inlet of the solid-gas mixture in the sedimentation section, obvious scratches appeared on the inner lining after long-term operation, and the components of the inner lining material were detected in the silicon particle product; in addition, the tail gas dust content (the ratio to the product weight) was 0.05% wt.

[0087] Example 4

[0088] The difference from Example 1 is that the outlets of the four silicon raw material gas inlet pipes are retracted to the inner wall of the conical reaction section. The rest is the same as Example 1.

[0089] Reaction result description: Compared with Example 1, the tail gas dust content (the ratio to the product weight) is relatively high, reaching 0.22% wt, and a small amount of deposition appears on the reactor wall surface.

[0090] Example 5

[0091] The difference from Example 1 is that the connection position of the conveying air duct 19 is moved downward to align with the conveying section 18, so that an inverted T-shaped connection is formed between the material sealing section, the conveying section and the conveying air duct. The rest is the same as Example 1.

[0092] Reaction result description: Compared with Example 1, due to the deterioration of the material conveying effect, the hourly circulation ratio drops to 5. Due to the decrease of the circulation ratio, the number of hot silicon particles entering the reactor decreases significantly, the temperature in the reactor begins to decrease, the conversion rate decreases, and when the inlet gas mass decreases to 20% of that in Example 1, the reactor temperature reaches the requirement and the conversion rate recovers to 100%, which has a great impact on the entire output.

[0093] Comparative Example 1

[0094] The difference from Example 1 is that the lowermost section of the conical reaction section 14 (i.e., the part 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 this head. The rest is the same as Example 1.

[0095] Reaction result description: Compared with Example 1, the particles are almost stationary at the change of the cone angle, the upper particles flow slowly, and after running for a period of time, the particles agglomerate and gradually increase.

[0096] As can be seen from the above examples / comparative examples, (1) the reaction section of the reactor of the present invention adopts an overall conical design and a large change in the cone angle caused by the absence of an additional lower head, and the wall surface of the entire reaction section is straighter, which is beneficial to the rapid movement of the particles in the reaction bed, and the relative movement between the particles during the downward movement can effectively avoid particle agglomeration;

[0097] (2) By feeding the raw material gas into the radial middle of the reaction section in the present invention, compared with feeding air near the inner wall of the reaction section, it is more conducive to heat exchange in the reactor and the concentration of the reaction area, the product deposition area is large, the product structure is dense, the generation of fine powder is reduced, the entrainment of the tail gas is less, and it is also more conducive to reducing the wall reaction;

[0098] (3) By setting a ring at the lower end of the settling section to form an annular platform, it is beneficial to improve the product purity and reduce the entrainment of fine powder in the tail gas while reducing equipment wear;

[0099] (4) By arranging a conveying air pipe at the lower part of the material seal section in the present invention, it can cooperate with the material seal section and the conveying section, which is beneficial to the rapid conveying of the solid material in the conveying section, so as to better cooperate with the rapid movement of the particles in the reactor, and is beneficial to improving the circulation ratio and increasing the output.

Claims

1. A conical polysilicon reactor with rapid particle movement, characterized in that: The conical polysilicon reactor comprises a conical reaction section whose diameter gradually decreases from top to bottom and a settling section arranged above the conical reaction section; The top of the settling section is provided with an exhaust pipe, and the side wall is provided with a silicon particle feed pipe for gas transportation as a seed; 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; The upper end of the conical reaction section is connected to the lower end of the sedimentation section, and a solid product outlet pipe is provided at the bottom of the conical reaction section, and a silicon-containing raw gas inlet pipe is provided on the side wall; the conical reaction section 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 is deposited and grown on the surface of the silicon particles serving as seed crystals, and the obtained granular polysilicon is discharged from the solid product outlet pipe.

2. The conical polysilicon reactor according to claim 1, 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 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 gas inlet pipe is located.

3. The conical polysilicon reactor according to claim 2, characterized in that: The silicon-containing raw material gas inlet pipes are provided in one group or multiple groups located at different heights, each group comprising 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.

4. The conical polysilicon reactor according to any one of claims 1 to 3, 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 to convey the solid product descending from the conical reaction section; Preferably, the angle between the conveying section and the material sealing section is 90-150°, preferably 110-130°.

5. The conical polysilicon reactor according to claim 4, characterized in that: The material sealing section is also provided with a conveying air duct, and the conveying air duct is horizontally connected to the lower part of the material sealing section.

6. The conical polysilicon reactor according to claim 4 or 5, characterized in that: The cone angle of the conical reaction section is 15-50°, preferably 20-40°.

7. The conical polysilicon reactor according to any one of claims 1 to 6, characterized in that: The diameter of the lower end of the sedimentation 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 sedimentation 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 sedimentation 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 supporting a silicon particle layer at the bottom of the sedimentation section, which is used to block the impact of silicon particles fed from the silicon particle feeding pipe on the reactor wall.

8. The conical polysilicon reactor according to claim 7, characterized in that: The silicon particle feeding pipe is horizontally arranged toward the central axis of the sedimentation section.

9. The conical polysilicon reactor according to any one of claims 1 to 8, characterized in that: The conical polysilicon reactor further comprises a heating section for heating silicon particles in the gas-solid mixture to be fed into the settling section so as to react in the conical reaction section.

10. A method for preparing granular polysilicon, the method comprising preparing granular polysilicon using the conical polysilicon reactor according to any one of claims 1 to 9, comprising: (1) silicon particles in the gas-solid mixture fed from the silicon particle inlet pipe are subjected to sedimentation separation in the sedimentation section, so that the silicon particles are settled in the conical reaction section to form a silicon particle bed layer; (2) the silicon-containing raw material gas introduced from the silicon-containing raw material gas inlet pipe rises and contacts and reacts with the descending silicon particle bed, 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) discharging the produced granular polycrystalline silicon from the solid product outlet pipe and discharging tail gas from the exhaust pipe, wherein the tail gas is the gas rising from the conical reaction section into the settling section and the gas in the gas-solid mixture; Preferably, the temperature of the silicon particle bed is 650-850°C; Preferably, the hourly circulation rate of the silicon particles in the conical reaction section 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.

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