Pneumatic sorting device for crushed polycrystalline silicon mixtures and method for producing blocks, flakes or powders from crushed polycrystalline silicon mixtures using such device

Abstract

The purpose of the present invention is to develop a device capable of highly classifying large-weight lumps or flakes by further improving the sorting effect in a pneumatic classification device for crushed polycrystalline silicon, which is excellent in terms of suppressing surface metal contamination. A pneumatic sorting device (1) for a crushed polycrystalline silicon mixture is characterized by being provided with a first pneumatic sorting pipe part (2) which is a vertically erected pipe body and in which an input port (3) for the crushed polycrystalline silicon mixture is formed in the axial middle region of the pipe body, and the first pneumatic sorting pipe part (2) is provided with a second pneumatic sorting pipe part (3) for separating the crushed polycrystalline silicon mixture from the first pneumatic sorting pipe part (2). The polycrystalline silicon broken mixture comprises blocky objects and small-particle-size objects compared with the blocky objects, particularly flaky objects or powdery objects, the first wind power sorting pipe part is used for conducting wind power sorting on the blocky objects and the small-particle-size objects, and the upper end of the first wind power sorting pipe part (2) is connected with a small-particle-size object circulation pipeline (9). The flow pipeline is provided with a suction mechanism at the upstream, and the suction mechanism is used for applying suction force which enables lumps in the polycrystalline silicon crushing mixture fed into the pipe body to fall downwards and attracts the small-particle-size substances upwards.

Description

Technical Field

[0001] The present invention relates to a wind-powered separation device for crushed polysilicon mixtures and a method for producing blocks, flakes or powders from the crushed polysilicon mixtures using the wind-powered separation device. Background Art

[0002] The Siemens process is a well-known method for producing polycrystalline silicon, also known as polysilicon. The Siemens process involves heating a silicon core wire placed inside a bell-jar reactor to a silicon deposition temperature by applying electricity. A silane compound gas, such as trichlorosilane (SiHCl3) or monosilane (SiH4), and hydrogen are then supplied to the core wire. Polycrystalline silicon is deposited on the silicon core wire via chemical vapor deposition, resulting in high-purity polycrystalline silicon rods.

[0003] The resulting polycrystalline silicon rods are crushed and sorted into sizes suitable for use in the next process or for the production of the target product in the next process, and then transported to the above-mentioned next process. Specifically, the polycrystalline silicon rods are crushed using hammers made of hard metals such as tungsten carbide to obtain raw polycrystalline silicon chunks. The raw polycrystalline silicon chunks are then further crushed into the desired particle size using a crushing device made of hard polymers or hard metals or the above-mentioned hammers. Subsequently, if necessary, the resulting polycrystalline silicon crushed mixture is classified into the desired size using a classification device made of the same material, thereby obtaining polycrystalline silicon crushed products of the desired particle size.

[0004] Here, polycrystalline silicon fragments are generally referred to as dust, powder, flakes, or lumps, depending on their size. In this specification, fragments with a particle size of less than 500 μm are referred to as "dust," fragments with a particle size of 500 μm or more but less than 1000 μm are referred to as "powder," fragments with a particle size of 1000 μm or more but less than 1500 μm are referred to as flakes, and fragments with a particle size of 1500 μm or more are referred to as lumps. These fragments are used as raw materials for the production of single crystal silicon, which is the raw material for semiconductor wafers or solar power generation wafers. They are distinguished by their filling properties or solubility in crucibles corresponding to their particle sizes.

[0005] The classification of a mixture of polycrystalline silicon crushed materials containing these various polycrystalline silicon crushed materials of varying particle sizes is typically performed using a mechanical screening machine, such as a known vibrating screening machine that performs screening through vibration or a screening machine that performs screening through the rotation of a rotary cylinder. However, in the case of such mechanical screening machines, the polycrystalline silicon crushed materials come into excessive contact with the metal material of the screening section, leading to increased surface metal contamination. This problem can be alleviated to some extent by resin lining the areas that come into contact with the metal material of the screening section. However, even in this manner, the presence of sharp corners and protrusions on the crushed surfaces of the polycrystalline silicon crushed materials can cause the resin lining to chip away if the crushed materials are vibrated for extended periods of time or vigorously, resulting in unacceptable metal contamination. Furthermore, the chipped-off resin flakes pose a risk of carbon contamination of the polycrystalline silicon crushed materials.

[0006] On the other hand, the main use of polysilicon fragments is as raw materials for semiconductors or solar power generation wafers. In this case, reducing metal impurities is the most stringent quality requirement. Therefore, in order to avoid contact between polysilicon fragments and metal materials as much as possible, a solution for performing the above classification by wind classification has been proposed (for example, see Patent Document 1 [ Figure 1 〕 and paragraph 〔0064〕 of Patent Document 2). Specifically, Patent Document 1 discloses that semiconductor fragments such as polycrystalline silicon are caused to fall downward by gravity, and during this process, an air flow is blown from a nozzle directed horizontally from an ejection port to blow smaller particles contained in the semiconductor fragments horizontally, thereby classifying the semiconductor fragments based on particle size according to the distance they travel. Furthermore, Patent Document 2 discloses that, unlike Patent Document 1, while also causing the polycrystalline silicon fragments to fall by gravity, suction is applied horizontally to remove and remove smaller dust particles.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 2000-070859

[0010] Patent Document 2: Japanese Patent Application Laid-Open No. 2016-079053 Summary of the Invention

[0011] Problems to be solved by the invention

[0012] However, this conventional air classification method has an insufficient sorting effect, resulting in the following problem: Large, heavy lumps and flakes in the polycrystalline silicon crushed mixture cannot be accurately classified. For example, in Patent Document 2, which horizontally suctions the polycrystalline silicon crushed mixture as it falls by gravity, only dust and powder are removed, while flakes and lumps are sorted in the next step using a sieving machine or grading rollers.

[0013] Based on this background, the purpose of the present invention is to further improve the sorting effect of the wind classification device (wind sorting device) that is excellent in suppressing the surface metal contamination of the polysilicon crushed products obtained above, and to develop a device that can highly classify the above-mentioned heavy blocks or flakes.

[0014] Means for solving problems

[0015] In view of the above problems, the present inventors have conducted intensive research and have found that the above problems can be solved by providing a device with a specific structure that applies suction from above to a polycrystalline silicon crushed mixture falling by gravity, thereby completing the present invention.

[0016] That is, the present invention is a wind-forced sorting device for a polysilicon crushed mixture, characterized in that it is provided with a first wind-forced sorting pipe portion, the first wind-forced sorting pipe portion having a vertically erected pipe body, an inlet for the polysilicon crushed mixture being formed in the axial middle region of the pipe body, the polysilicon crushed mixture including lumps and small particles having a particle size smaller than the lumps, the first wind-forced sorting pipe portion being used for wind-forced sorting of the lumps and small particles, the lumps in the polysilicon crushed mixture put into the pipe body falling downward, the upper end of the above-mentioned first wind-forced sorting pipe portion being connected to a circulation conduit for small particles, the circulation conduit being provided with an attraction mechanism upstream for applying attraction to draw the small particles upward.

[0017] In addition, the present invention also provides a wind-forced sorting device for a polysilicon crushed mixture, wherein a second wind-forced sorting pipe portion is interposed in the middle of the above-mentioned circulation pipeline in the wind-forced sorting device for the polysilicon crushed mixture, and the second wind-forced sorting pipe portion has a vertically erected pipe body, and an inlet for small-particle-sized objects from the above-mentioned circulation pipeline is formed in the axial middle area of ​​the pipe body. The diameter of the pipe body is adjusted to a size that exerts the following attraction, which causes the flakes in the above-mentioned small-particle-sized objects flowing into the pipe body to fall downward, and on the other hand, attracts powders with a particle size smaller than the flakes upward. The second wind-forced sorting pipe portion is used to perform wind-forced sorting on the flakes and powders.

[0018] In addition, the present invention also provides a method for manufacturing lumps from a polysilicon crushed mixture, wherein a wind sorting device for the polysilicon crushed mixture is used, the polysilicon crushed mixture is put into the tube body of the above-mentioned first wind sorting tube part, the polysilicon crushed mixture is wind sorted, and lumps are collected from the lower end of its tube body.

[0019] In addition, the present invention also provides a method for manufacturing flakes from a polysilicon crushed mixture, wherein a wind sorting device for the above-mentioned polysilicon crushed mixture is used to wind-sort the above-mentioned small-particle materials flowing into the tube body of the above-mentioned second wind sorting tube part, and the flakes are collected from the lower end of the tube body.

[0020] Similarly, a method for producing a powder from a polysilicon crushed mixture is also provided, wherein a wind sorting device for the polysilicon crushed mixture is used to wind sort the above-mentioned small-particle material flowing into the tube body of the above-mentioned second wind sorting tube part, and the powder is collected and discharged into the above-mentioned circulation pipeline from the upper end of the tube body.

[0021] Effects of the Invention

[0022] According to the present invention, in the wind-force sorting device which excels in suppressing surface metal contamination of the obtained polycrystalline silicon fragments, its sorting function can be further improved, and even heavy blocks or flakes can be sorted at a high level. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic cross-sectional view of an apparatus for wind-force separation of a crushed polycrystalline silicon mixture according to one embodiment of the present invention. DETAILED DESCRIPTION

[0024] The polycrystalline silicon crushed mixture classified by the apparatus of the present invention comprises at least one selected from lumps and small particles smaller than the lumps, i.e., powders, flakes, etc. While the polycrystalline silicon crushed mixture may be of any origin, it is typically obtained by crushing raw polycrystalline silicon lumps. Typically, raw polycrystalline silicon lumps are obtained by crushing polycrystalline silicon rods obtained by the Siemens process using hammers made of hard metals such as tungsten carbide.

[0025] In such a polycrystalline silicon crushed mixture, the content of the agglomerates having a particle size of 1500 μm or greater is preferably 80% by mass to 98.5% by mass, particularly preferably 85% by mass to 98% by mass.

[0026] On the other hand, the content of small particles smaller than the agglomerates in the polycrystalline silicon crushed mixture is preferably 1.5% to 20% by mass, excluding the preferred content of the agglomerates. Specifically, the content of flakes with a particle size of 1000 μm or more and less than 1500 μm is preferably 0.5% to 10% by mass, and particularly preferably 1% to 9% by mass, based on the polycrystalline silicon crushed mixture. Furthermore, the content of powders with a particle size of 500 μm or more and less than 1000 μm is preferably 0.5% to 10% by mass, and particularly preferably 1% to 9% by mass, based on the polycrystalline silicon crushed mixture.

[0027] Furthermore, as described above, the polycrystalline silicon crushed mixture contains, in addition to lumps, flakes, and powder, dust (generally less than 1% by mass based on the polycrystalline silicon crushed mixture) having a particle size smaller than that of the powder (less than 500 μm). However, this dust composed of fine particles tends to have more significant surface metal contamination than other forms with larger particle sizes, and its utilization value is generally low. Moreover, since this dust is light in weight, it is relatively easy to remove from the polycrystalline silicon crushed mixture. As described in the aforementioned Patent Document 2, it can be effectively removed by applying an appropriate suction force in the horizontal direction during the gravity drop within the crushing device after crushing. Furthermore, even during the above-mentioned conveyor transportation process after crushing, the dust can be effectively removed by applying an appropriate suction force from above the polycrystalline silicon crushed mixture. Therefore, it is also a preferred method to remove most of the dust in the polycrystalline silicon crushed mixture by these methods before providing it to the wind separation device of the present invention.

[0028] The surface metal concentration of these polycrystalline silicon crushed mixtures is preferably 0.3 ppbw to 10 ppbw, particularly preferably 0.4 ppbw to 9 ppbw. In addition, in the present invention, the surface metal concentration of the polycrystalline silicon crushed material refers to the value measured by the following method. That is, for the polycrystalline silicon crushed material as the measurement object, its surface is decomposed and removed, and each metal element in the obtained sample liquid is analyzed and quantified using inductively coupled plasma mass spectrometry (ICP-MS). Specifically, about 400 g of polycrystalline silicon crushed material is transferred to a 500 ml clean polytetrafluoroethylene beaker, 100 ml of a dissolving solution (50 mass% HF: 10 ml, 70 mass% nitric acid: 90 ml) is added, and extraction is performed at 25°C for 15 minutes. The liquid component in the polytetrafluoroethylene beaker and the cleaning liquid obtained by washing the surface of the polycrystalline silicon crushed material with 100 ml of ultrapure water are transferred to a clean polytetrafluoroethylene beaker to prepare a surface extract of the polycrystalline silicon crushed material. The surface extract of the polysilicon crushed material was evaporated to dry and solidify, and a 3.5% by mass nitric acid aqueous solution was added to make the volume to 20.0 ml. ICP-MS measurement was performed to determine the metal concentrations of Na, Mg, Al, K, Ca, Cr, Fe, Ni, Co, Cu, Zn, W, Ti, and Mo, which were calculated as concentration values ​​per unit total mass of the polysilicon crushed mixture.

[0029] The wind-force separation device according to the present invention is a device for accurately separating the polycrystalline silicon crushed mixture described above into large-sized lumps and small-sized particles having a smaller particle size than the lumps. The device is characterized by comprising a first wind-force separation pipe section having a vertically erected pipe body, with an inlet for the polycrystalline silicon crushed mixture formed in an axially intermediate region of the pipe body. The first wind-force separation pipe section is used to separate the lumps from the small-sized particles by wind force, and the lumps introduced into the polycrystalline silicon crushed mixture into the pipe body fall downward. The upper end of the first wind-force separation pipe section is connected to a flow conduit for the small-sized particles, and a suction mechanism is provided upstream of the flow conduit section for applying a suction force to draw the small-sized particles upward.

[0030] pass Figure 1 To explain the details, Figure 1 is a schematic cross-sectional view of a representative embodiment. Figure 1In the embodiment, the wind-force sorting device 1 is provided with a first wind-force sorting pipe section 2, which is composed of a vertically erected pipe body and is used to sort lumps and small-sized particles. As the first wind-force sorting pipe section 2, a straight pipe of the same caliber is usually used, but a pipe with a part having a different caliber, or a conical pipe with a smaller caliber at the top or bottom can also be used. The caliber of the pipe body is also affected by the particle size distribution or the amount of the polysilicon crushed mixture fed in, and cannot be determined in general. Preferably, the caliber of the pipe body is such that the opening area of ​​the pipe body (the area of ​​the opening of the pipe body when the pipe body is cut with a plane perpendicular to the axial direction of the pipe body) reaches 25 cm 2 ~2500cm 2 More preferably, the size of the tube body diameter is such that the opening area of ​​the tube body reaches 100cm 2 ~1600cm 2 In addition, its axial length is preferably 50 cm to 200 cm, more preferably 70 cm to 180 cm.

[0031] An inlet 3 for the polycrystalline silicon crushed mixture is formed in the axially middle region of the first wind separation pipe section 2. The axially middle region of the first wind separation pipe section 2 is defined as a region extending upward from its lower end from 1 / 4 to 3 / 4 of the total axial length of the wind separation pipe section, preferably from 1 / 3 to 2 / 3. In other words, the axially middle region of the first wind separation pipe section 2 is defined as a region extending from the lower end of the first wind separation pipe section 2 from 1 / 4 to 3 / 4 of the vertical length of the first wind separation pipe section 2, preferably from 1 / 3 to 2 / 3.

[0032] Here, regarding the inlet 3 for the polycrystalline silicon crushed mixture in the first air separation pipe section 2, the polycrystalline silicon crushed mixture 4 produced by crushing the raw polycrystalline silicon blocks using a crushing device or hammer is transported by a feeder 5 and fed into the first air separation pipe section 2. The amount of polycrystalline silicon crushed mixture fed is not particularly limited, but is preferably 10 kg / min to 150 kg / min, more preferably 15 kg / min to 100 kg / min. Furthermore, the speed at which the polycrystalline silicon crushed mixture 4 is fed by the feeder 5 before being fed into the first air separation pipe section 2 is preferably 5 m / min to 20 m / min, more preferably 7 m / min to 18 m / min. Preferably, the polycrystalline silicon crushed mixture 4 is fed into the feeder 5 so that the crushed materials are evenly dispersed and overlap as little as possible.

[0033] The crushed materials composing the polycrystalline silicon crushed mixture 4 thus introduced into the first wind separation pipe 2 are subjected to the downward force of gravity acting on them. In the present invention, within the pipe 2 of the first wind separation pipe 2, the larger lumps fall directly downward due to the gravity. Meanwhile, a strong attraction force is exerted from above on the smaller particles, resisting the gravity force and drawing them upward within the pipe. Consequently, the lumps 6 and smaller particles 7 are separated from the polycrystalline silicon crushed mixture 4 introduced into the pipe. The lumps 6 fall downward and are removed and collected from the lumps discharge port 8 at the lower end of the first wind separation pipe 2. Meanwhile, the smaller particles 7 are drawn upward and flow into the smaller particle flow line 9 connected to the upper end opening of the separation pipe, flowing upstream.

[0034] A suction mechanism is connected upstream of the circulation pipe 9 for the above-mentioned small-sized objects. The suction mechanism is used to apply a suction force of appropriate strength to the tube body of the first wind-force separation pipe section 2 for separating the above-mentioned lumps 6 and small-sized objects 7. As the suction mechanism, a dust collector or a suction pump can be used without limitation. Preferably, the small-sized object collection mechanism is provided on the way to the circulation pipe 9 for the small-sized objects up to its suction port. The details will be described below. Preferably, a second wind-force separation pipe section 11 is provided on the way to the circulation pipe 9 for the small-sized objects. The second wind-force separation pipe section 11 is used to wind-force separate the small-sized objects 7 flowing therethrough into flakes and powders. In this case, the dust collector 10 is preferably used as the above-mentioned suction mechanism. The dust collector 10 generates suction force by rotating a fan with an electric motor, and fine matter contained in the inhaled air can be collected by a filter 19. Therefore, the powdery matter along with the dust flows upstream of the small particle flow duct 9 through the second air separation pipe section 11 , is sucked by the dust collector 10 , and is collected by the filter 19 .

[0035] The suction force applied to the first wind-force separation pipe section 2 by the suction mechanism, such as the dust collector 10, is also affected by the particle size distribution of the polysilicon crushed mixture being separated or the amount of material fed into it, and cannot be determined in a general manner. Regarding the aforementioned lumps 6 and small particles 7, separation is generally successful when the upward wind speed is between 7 m / s and 20 m / s, and more preferably between 8 m / s and 17 m / s. Therefore, the suction force is set according to the diameter of the pipe section 2 so as to produce a region within the pipe section having the aforementioned wind speed. The wind speed is calculated using the following formula. Furthermore, area S represents the opening area of ​​the pipe section.

[0036] Wind speed V = air volume Q ÷ area S (cross-sectional area of ​​the pipe)

[0037] In order to implement the separation of the lumps 6 and the small-size particles 7 with higher precision, it is particularly preferred to set the suction force so that the above-mentioned wind force is achieved within the tube body of the first wind separation tube 2, from the lower end of the opening of the polysilicon crushed mixture inlet 3 toward 10 cm downward, more preferably 15 cm, to the upper end of the opening of the inlet toward 10 cm upward, more preferably 15 cm.

[0038] then, Figure 1 In the wind sorting device 1, a second wind sorting pipe section 11 is provided on the way from the small particle size circulation pipe 9 connected to the upper end of the first wind sorting pipe section 2 to the upstream portion where the above-mentioned suction mechanism is provided. The second wind sorting pipe section 11 is used to sort the small particle size 7 sorted by the above-mentioned first wind sorting pipe section 2 and flowing therethrough into flakes and powders. Similar to the above-mentioned first wind sorting pipe section 2, the second wind sorting pipe section 11 also has a vertically erected pipe body, and an inlet 12 for small particle size from the above-mentioned small particle size circulation pipe 9 is formed in the axial middle area of ​​the pipe body. The definition of the axial middle area is the same as that of the above-mentioned first wind sorting pipe section. The pipe body of the second wind sorting pipe section 11 is vertically erected on the way of the circulation pipe 9.

[0039] The second wind-force separation pipe section 11 is located in the flow pipe 9 for the small-particle material. A suction mechanism such as a dust collector 10 is provided upstream of the second wind-force separation pipe section 11, thereby applying suction force to the pipe section from above. However, the key point of the present invention is to adjust the pipe body diameter so that the suction force reaches such an intensity that, among the small-particle material 7 flowing into the pipe section, flakes fall downward, while, on the other hand, powdery material with a particle size smaller than the flakes is attracted upward. Therefore, among the small-particle material 7 flowing into the pipe section, flakes 13 and powdery material 14 are separated, and the flakes 13 (and, if there are any residual lumps that were not separated by the first wind-force separation pipe section 2 and are entrained in the flow pipe 9 for the small-particle material, the same applies to these lumps) fall downward and are removed and collected from the flake discharge port 15 at the lower end of the second wind-force separation pipe section 11. On the other hand, the powdery matter 14 (including dust) is sucked upward, flows again into the small particle flow passage 9 from the upper end opening of the separation pipe portion, and flows further upstream.

[0040] Adjustment of the diameter of the second air separation pipe section 11 is also affected by factors such as the particle size distribution of the small particles 7 being separated, the amount of inflow, and the length of the small particle flow line 9, and cannot be determined in a single, universal manner. However, for the aforementioned flakes 13 and powder 14, optimal separation is generally achieved when the upward wind speed is greater than 2 m / s and less than 7 m / s, more preferably greater than 3 m / s and less than 6 m / s. Therefore, the diameter of the first air separation pipe section 2 can be set to create a region within the pipe section with the aforementioned wind speed. To achieve more precise separation of flakes 13 and powder 14, it is particularly preferred to set the suction force within the pipe section 11, from the lower end of the opening of the small particle inlet 12, 10 cm (more preferably 15 cm) below, to the upper end of the opening of the inlet, 10 cm (more preferably 15 cm) above.

[0041] Therefore, the diameter of the tube body of the second wind-force separation tube section 11 can be adjusted to achieve the suction condition. For this purpose, the diameter of the tube body of the second wind-force separation tube section 11 must be larger than the diameter of the tube body of the first wind-force separation tube section 2. Specifically, regarding the diameter of the tube body of the second wind-force separation tube section 11, it is preferred to select a size that meets the above conditions from a range where the opening area of ​​the tube body of the second wind-force separation tube section 11 is 3 to 7 times, and particularly preferably 3.5 to 6.5 times, of the opening area of ​​the tube body of the first wind-force separation tube section 2. As the diameter of the tube body of the second wind-force separation tube section 11, it is preferred to make the opening area of ​​the tube body of the second wind-force separation tube section 11 reach 75 cm 2 ~17,500cm 2 The size of the second wind separation pipe 11 is more preferably such that the opening area of ​​the pipe body reaches 300 cm 2 ~11,200cm 2 size.

[0042] The second air separation pipe section 11 is also typically a straight pipe of uniform diameter. However, a pipe with a partially different diameter or a tapered pipe with a diameter that tapers at the top or bottom may also be used. The axial length is preferably selected from 50 cm to 250 cm, more preferably from 60 cm to 200 cm.

[0043] In the front half of the small-particle flow conduit 9 connecting the second air separation conduit 11 and the first air separation conduit 2, the wind speed is preferably 7 m / s to 20 m / s, more preferably 8 m / s to 17 m / s, to prevent the flowing small-particles from stagnating en route. This wind speed is similar to that in the first air separation conduit 2 for separating the agglomerates 6 and small-particles 7. Specifically, the conduit diameter is preferably adjusted to achieve this wind speed.

[0044] As mentioned above, a dust collector 10 is provided in the rear half of the small-particle flow duct 9, upstream of the portion where the second air-force separation duct 11 is located. Therefore, the powdery matter separated by the second air-force separation duct 11 and flowing into the duct is captured by the dust collector 10 and removed from its powdery matter discharge port 17. An exhaust port 18 is formed in the upper portion of the dust collector 10, and air separated from the powdery matter by the filter 19 is exhausted through the exhaust port 18.

[0045] Furthermore, as described above, the polycrystalline silicon crushed mixture 4 produced by crushing using a polycrystalline silicon block crusher or hammer generally contains a certain amount of dust in addition to the lumps, flakes, and powder. If this dust is not removed in advance and is supplied to the wind separation device 1, due to its small particle size, it will be entrained in the powder and sorted, mixed with the powder and discharged from the powder discharge port 17. The powder obtained in this dust-containing state can be used directly as a raw material for semiconductor wafers or solar power generation wafers, but it is preferably subjected to a gentler suction treatment to remove as much of this mixed dust as possible.

[0046] In the wind-powered sorting device described above, there are no particular restrictions on the material used. Specifically, for areas requiring structural strength, metals such as iron and nickel, and alloys such as stainless steel and Ni-based alloys (Hastelloy, Inconel, etc.) are preferred. To prevent surface metal contamination of the polysilicon crushed material, lining the inner surface with a resin or the like is a preferred method. Furthermore, for areas not requiring structural strength, resins such as polyvinyl chloride, polyvinylidene fluoride, polypropylene, and polyetheretherketone are more preferred.

[0047] By using this wind-powered sorting device for sorting, a polycrystalline silicon crushed mixture can be sorted into chunks, flakes, and powder with high precision. Furthermore, this wind-powered sorting minimizes contact with metal materials, allowing the sorted crushed materials of various particle sizes to be produced with minimal surface metal contamination. Consequently, the resulting crushed materials are highly suitable for use as raw materials for semiconductor wafers or solar power generation wafers.

[0048] Example

[0049] The present invention will be further described below based on detailed examples, but the present invention is not limited to these examples. In each example and comparative example, the physical properties were measured by the following methods.

[0050] [Contents of lumps, flakes, powder, and dust in the polysilicon crushed mixture]

[0051] The polycrystalline silicon crushed mixture was sieved using sieves with mesh sizes of 500μm, 1,000μm, and 1,500μm, starting with the larger mesh size. The weights of the oversize and final undersize were measured using an electronic balance, and their weight ratios were calculated. The weight ratio of the oversize on the 1,500μm sieve was calculated as the content of lumps, the weight ratio of the 1,000μm sieve was calculated as the content of flakes, the weight ratio of the oversize on the 500μm sieve was calculated as the content of powders, and the weight ratio of the undersize on the 500μm sieve was calculated as the content of dust.

[0052] [Surface Metal Concentration of Polysilicon Crushed Mixture]

[0053] Approximately 400 g of polycrystalline silicon crushed material was transferred to a clean 500 ml polytetrafluoroethylene beaker, 100 ml of a dissolving solution (50 mass% HF: 10 ml, 70 mass% nitric acid: 90 ml) was added, and extraction was performed at 25°C for 15 minutes. The liquid content in the polytetrafluoroethylene beaker and the cleaning solution obtained by washing the surface of the polycrystalline silicon crushed material with 100 ml of ultrapure water were transferred to a clean polytetrafluoroethylene beaker to prepare a surface extract of the polycrystalline silicon crushed material. The surface extract of the polycrystalline silicon crushed material was evaporated to dryness and solidified, and a 3.5 mass% nitric acid aqueous solution was added to adjust the volume to 20.0 ml. ICP-MS analysis was performed to determine the metal concentrations of Na, Mg, Al, K, Ca, Cr, Fe, Ni, Co, Cu, Zn, W, Ti, and Mo, and calculated as the concentration value per unit mass of the polycrystalline silicon crushed material mixture.

[0054] Example 1

[0055] use Figure 1 The wind-powered separator 1 shown here separates the polycrystalline silicon crushed mixture 4 into various particle sizes. The main components of the wind-powered separator 1 are made of resin-lined stainless steel to ensure structural strength, while parts not requiring structural strength are made of polypropylene or polyvinyl chloride.

[0056] Furthermore, the diameter of the first wind separation pipe 2 is such that the opening area of ​​the pipe body of the first wind separation pipe 2 reaches 450 cm 2 The axial length of the first wind separation pipe 2 is 100 cm. The diameter of the second wind separation pipe 11 is such that the opening area of ​​the pipe body of the second wind separation pipe 11 reaches 1500 cm. 2The axial length of the second wind separation pipe 11 is 100 cm. The diameter of the pipe body of the second wind separation pipe 11 is such that the opening area of ​​the pipe body of the second wind separation pipe 11 is 3.3 times the opening area of ​​the pipe body of the first wind separation pipe 2.

[0057] Polycrystalline silicon rods obtained by the Siemens process are crushed using a raw polycrystalline silicon block crushing device and tungsten carbide hammers to produce a polycrystalline silicon crushed mixture 4. This mixture is then transported by a feeder 5 to a polycrystalline silicon crushed mixture inlet 3 located at the mid-height of the first air separation pipe section 2 and fed into the inlet. The speed of transport to the polycrystalline silicon crushed mixture inlet 3 is 10 m / min.

[0058] Here, the polysilicon crushed mixture 4 contained 92% by mass of lumps, 3% by mass of flakes, 5% by mass of powders, and a certain amount of dust. The surface metal concentration of these crushed materials was 4 ppbw.

[0059] In the wind-force separation device 1, the operation of the dust collector 10 applies an attractive force to the interior of the first wind-force separation pipe 2. The load of this attractive force is such that the wind force reaches an intensity of 13 m / s within a range from 15 cm downward from the lower end of the opening of the polysilicon crushed mixture inlet 3 to 15 cm upward from the upper end of the opening of the inlet. Therefore, in the polysilicon crushed mixture 4 introduced into the first wind-force separation pipe 2, the lumps 6 and small-sized particles 7 are separated, and the lumps 6 fall downward and are removed from the lumps discharge port 8 at the lower end of the first wind-force separation pipe 2. The amount removed is equivalent to 98% by mass of the lumps 6 contained in the polysilicon crushed mixture 4 to be separated, and the recovery result is good. In addition, the surface metal concentration of the removed lumps 6 was measured and the result was a high cleanliness result of 2.5 ppbw.

[0060] Meanwhile, the small particles 7 contained in the crushed polysilicon mixture 4 are sucked upward within the first air separation pipe section 2, flow through the small particle flow conduit 9, and flow into the second air separation pipe section 11 through the small particle inlet 12. The load within the pipe body of the second air separation pipe section 11 is such that, due to the suction of the dust collector 10, the wind force reaches 5 m / s within a range from 15 cm below the lower end of the opening of the small particle inlet 12 to 15 cm above the upper end of the opening of the inlet.

[0061] Therefore, the flakes 13 and powder 14 are separated from the polycrystalline silicon crushed mixture 4 introduced into the second wind separation pipe section 11. The flakes 13 fall downward and are removed from the flake discharge port 15 at the lower end of the second wind separation pipe section 11. The amount removed is equivalent to 83% by mass of the flakes 13 contained in the polycrystalline silicon crushed mixture for separation, and the recovery result is good.

[0062] In addition, in the second wind separation pipe section 11, the residual lumps 6 that were not fully separated by the above-mentioned first wind separation pipe section 2 and were entrained in the circulation pipe 9 of small-sized particles also basically all fall downward and are taken out from the sheet discharge port 15 together with the above-mentioned sheet 13.

[0063] Furthermore, powder 14 contained in the small-sized particles 7, along with the dust, is sucked upward within the second air separation pipe section 11, flows again through the small-sized particle flow line 9, and is collected by the filter 19 of the dust collector 10. The powder (including dust) collected by the filter 19 is shaken off the filter 19, removed from the powder discharge port 17 of the dust collector 10, and recovered in a bucket located below. The amount of powder (including dust) 14 removed is equivalent to 99% by mass of the powder 14 contained in the polycrystalline silicon crushed mixture subjected to the above-described separation, resulting in a satisfactory recovery result.

[0064] Comparative Example 1

[0065] The polycrystalline silicon crushed mixture 4 was sorted for each particle size using a circular vibrating screen device. The components of the circular vibrating screen device were made of resin-lined stainless steel. Screening was performed using sieves with mesh sizes of 500 μm, 1,000 μm, and 1,500 μm, with the larger mesh sizes being processed first.

[0066] After the sieving, the surface metal concentration of the agglomerates obtained as the oversize of a sieve having 1,500 μm mesh was measured to be 12.3 ppbw, which was a higher value than the result in Example 1.

[0067] Comparative Example 2

[0068] Using the same polycrystalline silicon block crushing apparatus as used in Example 1 of Patent Document 2, a polycrystalline silicon crushed mixture was caused to fall from an opening on the upper surface of the apparatus within its falling moving portion. This polycrystalline silicon crushed mixture was the same as that introduced into the inlet 3 for the polycrystalline silicon crushed mixture of the first wind separation pipe section 2 in Example 1. At this time, air was sucked horizontally from the suction removal section 40 at a suction rate of 10 m / s within the falling moving portion. This suction rate was the same as the upward suction force applied near the height of the inlet 3 for the polycrystalline silicon crushed mixture formed in the first wind separation pipe section 2 in Example 1.

[0069] However, the result is as follows: most of the materials sucked by the suction removal section are powders, and only 15% by mass of the flakes 13 contained in the polysilicon crushed mixture are separated, and most of them fall into the receiving section below together with the lumps.

[0070] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Configurations obtained by appropriately combining a plurality of technical means disclosed in the embodiments are also included in the technical scope of the present invention.

[0071] Explanation of symbols

[0072] 1: Wind sorting device

[0073] 2: The first wind separation pipe

[0074] 3: Inlet for polysilicon crushed mixture

[0075] 4: Polysilicon crushed mixture

[0076] 5: Feeder

[0077] 6: Lump

[0078] 7: Small particle size matter

[0079] 8: Lump discharge outlet

[0080] 9: Circulation pipeline for small particles

[0081] 10: Dust collector

[0082] 11: Second wind separation pipe

[0083] 12: Inlet for small particles

[0084] 13: Flakes

[0085] 14: Powder

[0086] 15: Sheet discharge outlet

[0087] 17: Powder discharge outlet

[0088] 18: Exhaust port

[0089] 19: Filter

Claims

1. A wind-powered separation device for crushed polysilicon mixture, characterized in that: The invention is provided with a first wind separation pipe part, which has a vertically erected pipe body, and an inlet for a polysilicon crushed mixture is formed in an axial middle area of ​​the pipe body. The polysilicon crushed mixture includes lumps and small particles with a particle size smaller than the lumps. The first wind separation pipe part is used to perform wind separation on the lumps and small particles. The lumps of polysilicon crushed mixture put into the tube fall downwards. A small particle flow conduit is connected to the upper end of the first wind separation pipe portion, and a suction mechanism for applying a suction force to suck the small particle upward is provided upstream of the flow conduit.

2. A wind-powered separation device for crushed polysilicon mixture, characterized in that: In the wind-force separation device for crushed polysilicon mixture according to claim 1, a second wind-force separation pipe section is provided in the middle of the flow pipe. The second wind-force separation pipe section has a vertically erected pipe body, and an inlet for small-sized particles from the flow pipe is formed in the axial middle region of the pipe body. The diameter of the tube body is adjusted to the size of applying the following attraction, which causes the flakes in the small-particle material flowing into the tube body to fall downward, and on the other hand, attracts the powder with a particle size smaller than the flakes upward. The second wind sorting tube part is used to perform wind sorting on the flakes and powders.

3. A method for producing blocks from a crushed mixture of polycrystalline silicon, wherein: Using the wind-force separation device for the polysilicon crushed mixture according to claim 1, the polysilicon crushed mixture is put into the tube body of the first wind-force separation tube part, the polysilicon crushed mixture is wind-force separated, and the lumps are collected from the lower end of the tube body.

4. A method for producing flakes from a polycrystalline silicon crushed mixture, wherein: The wind-force separation device for crushed polysilicon mixture according to claim 2 is used to separate the small-sized particles flowing into the pipe body of the second wind-force separation pipe part by wind force, and flakes are collected from the lower end of the pipe body.

5. A method for producing a powder from a crushed mixture of polycrystalline silicon, wherein: The wind-force separation device for crushed polysilicon mixture according to claim 2 is used to separate the small particles flowing into the pipe body of the second wind-force separation pipe part, and collect the powder discharged into the circulation pipe from the upper end of the pipe body.

Images