KR20070021923A - Process and apparatus for comminuting silicon - Google Patents

Abstract

The present invention is a vertically mounted jet chamber (8) having a cylindrical cross section and having a jet nozzle (4) at the base, a countercurrent gravity separator (9) directly connected to the jet chamber (8), and a silicone granule (2). An injection inlet 6, through which the mill nozzle can introduce a milling gas stream 1 into the jet chamber 8, in which the milling gas stream is connected to the jet chamber. It has a length which extends sufficiently to the cross section, and the flow cross section of the jet chamber 8 is smaller than the flow cross section of the countercurrent gravity separator 9.

Silicone granules, silicone seed particles, fluidized bed, jet chamber, grain size distribution, countercurrent gravity separator

Description

Silicon grinding method and apparatus {PROCESS AND APPARATUS FOR COMMINUTING SILICON}

1 is a schematic view showing the structure of a conventional fluidized bed jet mill.

2 is a schematic diagram showing the structure of a device according to the invention.

3 shows a preferred embodiment of the device according to the invention.

The thick arrows shown in FIGS. 1-3 show the gas flow paths in the apparatus.

4, 5 and 6 illustrate flow guidance and preferred lining concepts of the device.

7 is a graph showing the overall path distribution by mass of feed material and milled product.

8 is a graph showing the mass-based distribution density of feed materials and milled products.

The present invention relates to a method and apparatus for grinding silicon granules.

Fluidized bed deposition methods for producing high purity silicon granules for the electronics or photovoltaics industry have been described in many publications. In these methods, the silicon particles in the fluidized bed are fluidized by gas and heated to high temperature. The introduction of silicon containing gas (eg silane, tetrachlorosilane or trichlorosilane) into the fluidized bed results in pyrolysis reaction at the surface of the particles, which leads to particle growth by depositing elemental silicon on the surface of the particles. In the continuous operation of this process, relatively large "grown" particles must be extracted from the fluidized bed as a product and fine particles known as silicon seed particles must be supplied on an ongoing basis. This type of method is described, for example, in US Pat. No. 3,963,838.

Several criteria are important for the use of the silicon seed particles in the fluidized bed process described in the reference: The silicon seed particles must have high purity so that the silicon granules produced can also meet the requirements of the electronics industry and the photovoltaic industry. Generally, the contamination by metals should be less than 100 ppbw, preferably less than 10 ppbw, the contamination by dopants boron and phosphorus should be less than 1,000 pptw, preferably less than 250 pptw, and the contamination by carbon less than 1,000 ppbw. , Preferably less than 250 ppbw. The size of the silicon seed particles should be smaller than the silicone granules, but not too small. This is because excessively fine particles exit the fluidized bed with an exhaust gas stream and are therefore not suitable for use as silicon seed particles. The limits for the emissions range from about 50 μm to 250 μm, depending on the operating conditions and the process. Particle fractions below this limit in the silicon seed particles result in dust accompanying the exhaust gas system from loss of silicon and fluid bed deposition. Finally, the grain size distribution of the silicon seed particles affects the particle population balance of the fluidized bed deposition and therefore also the grain size distribution of the silicone granules. In order to obtain a steady-state grain size distribution of silicone granules that are not overly wide, it is important to be able to produce silicon seed particles reproducibly with a defined narrow grain size distribution.

In addition to the aforementioned uses, silicon seed particles are also needed as starting materials in the photovoltaic industry and the electronics industry. Examples of the use of fine grain, high purity silicon powders include the production of silicon carbide powders as a base material for high resistance substrate materials for electronic devices, described in German Patent Publication No. DE 19842078A1, and is disclosed in US Pat. No. 5,496,416. Melting the fine grain silicon powder described on the substrate material and then cooling and solidifying to produce a wafer for use in photovoltaic applications. Until now, by classification from fluidized bed deposition or from fluidized bed deposition products, it has been common that it is impossible, very difficult or expensive to obtain the corresponding grain size distribution directly.

Various techniques are known for producing silicon seed particles.

According to US Pat. No. 4,207,360, silicon particles fluidized with an inert gas are easily comminuted in a hot fluidized bed (about 1,000 ° C.). In this process, the desired silicon seed particles are formed. The document also mentions a variant in which this fluidized bed is combined with a fluidized bed for the deposition of silicon to form an integral and a process. Both variants have the drawback that tremendous high energy is consumed in heating the fluidized bed and it is very difficult to control the grain size distribution and production rate of the silicon seed particles.

U.S. Patent No. 4,314,525 describes a more integrated method of heating a silicon containing gas, in particular silane, above a decomposition temperature. In this method, the silicon containing gas decomposes to form very fine silicon particles. Particles formed during this homogeneous deposition process are called nuclei and can be used as silicon seed particles. One drawback is that the nucleus is nanometer in size, and even a few micrometers of silicon seed particles can be produced by the coagulation effect. The use of such particles as silicon seed particles in a fluidized bed for the production of silicon granules, typically having a grain size of 50 μm, results in a large portion of these fine silicon seed particles being discharged with the gas stream from the reactor. . To prevent this, additional equipment is needed.

In addition to these thermal-mechanical or chemical methods, purely mechanical grinding methods for producing silicon seed particles are also known. According to the summary of patent document JP 57-067019 (Shin-Etsu Hondatai), the silicon granules are pulverized in a double roll crusher and then fractionated by sieving to obtain silicon seed particles from the silicone granules. . Contamination of the silicon seed particles with other elements is prevented by providing a silicon layer on the roll surface. However, the silicon-silicon material pairing between the roll and the finely divided material causes significant wear on the silicon layer on the roll surface, resulting in short machine uptime until the roll needs to be replaced.

Significantly improved with respect to roll wear and at the same time lowering the level of contamination on the finely divided material is achieved by using rolls with hard metal surfaces and roll nips of deformed shape, as described in patent document DE 102004048948. .

In the summary of patent document JP 08-109013, another grinding method is described. According to this document, silicon in pre-pulverized lump state can be ground in a pinned disk mill to form silicon seed particles. This type of design has the disadvantage that it is almost impossible to manufacture from materials that are free or low pollution. Significant contamination is likely to occur in the finely divided products. Therefore, if the product of this method is to be used for the production of high purity silicon, it is essential to wet chemically clean the finely ground product surface downstream.

US Pat. No. 4,691,866 describes a method of accelerating silicone granules using a gas jet to inject onto a stationary obstacle in accordance with the injector principle. The impact pulverizes the particles to form the desired silicon seed particles. In order to keep the contamination level low in this method, the obstacle is preferably made of silicon. However, as mentioned previously in connection with the roll grinding method, the encounter of silicon-silicon material results in significant wear to the obstacles.

For jet mills for grinding materials of very high purity, see Fokin, A.P .; Melnikov, V.D .: Grinding Mills In The Production Of Ultrapure Substances-Zhurnal Vses. Khim. Ob-va im. D. I. Mendeleeva; Vol. 33, No. 4, pp. 62.70, 1988. In a jet mill, the granular feed material is accelerated by the high velocity fluid jet. When such accelerated particles collide with the particles at low speed, impact stress is generated, and the particles are pulverized according to the impact energy.

Counter-jet mills for preparing silicon seed particles are disclosed in Rohatgi, Naresh K .; Silicon Production in a Fluidized Bed Reactor: Final Report-JPL Publication; No. 86-17, known through 1980. In this method, the particles are accelerated by two gas jets facing each other and pulverized by being sprayed toward each other. However, the yields mentioned by the authors of the above documents are low and the silicone granules must be finely divided several times.

US 4,424 199 describes a method of using a single high velocity gas jet in a fluidized bed for silicon deposition so that some of the silicon granules in the fluidized bed are pulverized to form silicon seed particles. The advantage of this method is that it is not necessary to take out the silicon granules from the deposition reactor, finely powder and transport them, but the disadvantage is that even in this case, it is difficult to control the production rate and the grain size distribution of the obtained silicon seed particles. However, this is a requirement for controlled operation of fluidized bed deposition. Gas jets can also adversely affect the deposition process in the fluidized bed. The idea of jet milling in a fluidized bed for silicon deposition is also disclosed by S. Lord in US Pat. No. 5,798,137.

The simplest type of jet mill is a fluidized bed jet mill with the gas jet pointing vertically upwards. In this jet mill, the gas jet accelerates the particles while ensuring that the particles remain suspended, ie fluidized, in the milling chamber. This type of mill is typically equipped with a classifier that classifies the particles exiting the gas stream and recycles the coarse particles that are filtered to the fluidized bed. Corresponding devices are described, for example, in US Pat. No. 4,602,743.

1 shows the structure of a conventional fluidized bed jet mill. In this form of arrangement, the milling gas 1 or the milling gas stream is fed through a jet nozzle 4 (denoted as a simple nozzle or a Laval nozzle) installed at the base of the milling chamber 5. The feed material 2 is fed to the milling chamber 5 from the side via the inlet 6. The fluidized bed 7 in which the particles accelerated by the gas jet collide with other particles and pulverize is formed in the milling chamber by the milling gas 1 and the particles. The ground particles are discharged from the milling chamber upwards as a common stream 3 together with the milling gas stream 1. Gas jets are primarily used for acceleration of the particles and subsequent grinding. Secondly, however, the milling gas stream 1 also produces a classification effect in the milling chamber. The gas jet flows locally in the chamber at high speed, but because the jet diffuses and interacts with the particles, the gas stream is distributed evenly across the cross section of the milling chamber. If the rate at which particles fall out of the milling chamber is lower than the average gas velocity in the milling chamber (volume flow of milling gas relative to the cross section of flow of the milling chamber), the particles are milled together with the milling gas stream 1. It is carried out from the chamber 5.

In gas / particle systems, in particular gas classification processes, the particle size whose drop speed in the milling chamber closely matches, for example, the dominant average gas velocity in the classifier, is referred to as separation grain size. The rate of drop of the particles in the milling chamber depends directly on the grain size and increases significantly as the grain size increases, which can be calculated for example by the formula:

_{^{18Re ws + 3Re ws 1 .5 +}} 0.3Re ws 2 - Ar = 0

In the above formula

이고,

ego,

Where

u _ws is the rate of drop of each particle in the milling chamber,

d _p is the particle diameter,

ν is the kinematic velosity of the fluid,

ρ _s , ρ _f are the densities of solids or fluids,

g is the acceleration of gravity.

Thus, defining the milling gas stream and milling chamber cross-section also defines the separation grain size, thereby defining an upper limit on the grain size distribution of the milled product. Thus, increasing the energy introduced into the milling chamber by a larger gas throughput increases the separation grain size, thus increasing the upper limit, and consequently the average grain size of the milled particles exiting the milling chamber. At the same time, the solid concentration in the fluidized bed is lowered. The energy introduced and the grain size obtainable are directly related to each other.

Since the grinding is substantially the result of the silicon particles colliding with each other, the jet mill is very suitable for grinding the high-purity silicon granules. The importance of the stress of the components in contact with the particles is secondary. In addition, the corresponding components may be lined with a noncontaminated material or a low contaminant material or made entirely of such material. The supply of energy required for grinding is only by means of a gas jet. If high purity gas is used for this purpose, the gas jet is also not a source of contamination. The main disadvantage of conventional jet mills for the production of silicon seed particles is due to the fact that the optimum operating range of these devices according to the prior art is a milled product grain size of about 2 μm to 10 μm, i.e. a range known as ultrafine grinding. do. In this range, gas consumption is less than 10 kg of gas per kg of solid [Perry, Robert H .; Green, Don W .: Perry's Chemical Engineers' Handbook, 7th Edition, McGraw-Hill; 1997, Section 20-47]. The larger the grain size of the feed material and the milled product, the lower the operating efficiency of the mill, the higher the gas consumption, and therefore the less economic the process. Thus, for example, it is common to switch to another grinding process such as the roll grinding process mentioned above.

U. S. Patent No. 5,346, 141 describes that an important factor in the efficiency of fluid bed jet milling for the production of silicon seed particles is the solid concentration in the fluid bed; It is to be understood here that the solid concentration means the volume concentration of solid particles: high solids concentration at the jet nozzle area significantly degrades milling performance, and therefore the patent teaches that it preferably has a solids concentration of less than 10% by volume. It is a method of milling in a very thin fluidized bed. However, the milling performance achievable with this configuration is still very low, which is associated with high energy consumption and / or gas consumption. According to Example 2 of US Pat. No. 5,346,141, the nitrogen consumption required to grind the silicon granules to an average grain size of 445 μm is 48 kg of nitrogen per kg of solid (Example 2: 200 liters / min of nitrogen; 5.2 g / silicone). Min), and this gas consumption is about five times the typical consumption for ultra-fine jet milling. In addition, the space-time yield is very low. According to this document, increasing the solids concentration further degrades milling performance.

It is an object of the present invention to provide an apparatus capable of producing silicon seed particles having a particle diameter of 50 μm to 1,000 μm from silicon granules having a particle size of 300 μm to 5,000 μm in an economical manner, ie, low cost and pure form.

The object is a vertically mounted jet chamber 8 having a cylindrical cross section and having a jet nozzle 4 at the base, a countercurrent gravity separator 9 directly connected to the jet chamber 8, and a silicone granule 2 ) An injection inlet 6, through which the milling gas stream 1 can be introduced into the jet chamber 8, in which the milling gas stream is connected to the jet chamber. It has a length that is sufficiently diffused up to the cross section of, and the flow cross section of the jet chamber 8 is achieved by a device which is smaller than the flow cross section of the countercurrent gravity separator 9.

2 shows a corresponding device.

In order to successfully accelerate each particle in the jet mill, it is important to successfully form a gas jet. As already described in US Pat. No. 5,346,141, formation of good gas jets is possible only at low solids concentrations, since high solids concentrations at the jet nozzle portion interfere with the formation of the jets. However, low solids concentrations are disadvantageous because in the milling the accelerated particles are unlikely to collide with other particles. The device according to the invention is adapted to accelerate the particles using a gas stream in a region of low solid concentration, and then to cause the grinding by scattering into the region of solid concentration where these particles are likely to collide with other particles. have.

In the device according to the invention less wear occurs than known devices for producing silicon seed particles. According to the apparatus, since the product contamination is low without further purification, a silicon seed particle is particularly suitable for use as a silicon seed particle in a fluidized bed process for producing high purity silicon granules as a feed material for the electronics industry and the photovoltaic industry. can do.

In the device according to the invention, the fluidized bed, which is locally defined at the top and bottom, ie the milling zone 10, is a transition zone from the jet chamber 8 to the countercurrent gravity separator 9. Is formed. The milling zone 10 preferably has a high solids concentration of more than 20% by volume, while in the jet chamber 8 it is preferably less than 10% by volume, particularly preferably less than 5% by volume but more than 0.1% by volume. Low solids concentration is present.

Fluidized beds with locally high solids concentrations are characterized by a jet chamber defined at the top by a countercurrent gravity separator having a flow cross section greater than the flow cross section of the jet chamber, and by the fact that the milling gas stream must pass through the separator. Is formed.

The shapes of the jet chamber, countercurrent gravity separator and the milling gas flow are matched to each other such that the average gas velocity in the countercurrent gravity separator corresponds to the rate at which the largest particle of the grain size distribution of the desired silicon seed particles falls through the milling chamber. Thus, it is desirable that the grain size separated in the separator correspond to the upper limit of the grain size distribution of the desired silicon seed particles. The average gas velocity (based on cross section of the jet chamber or separator) of the milling gas stream in the jet chamber is higher than the velocity in the separator. Thus, the grain size to be separated in the jet chamber is larger than the grain size in the separator, but must not exceed the average range of the grain size distribution of the silicon particles of the feed material so that enough particles can enter the jet chamber.

Silicon particles of the feed material larger than the grain size separated in the countercurrent gravity separator but smaller than the grain size separated from the jet chamber accumulate in the milling zone, where they form a localized fluidized bed with high solid concentration. Only the silicon particles of the feed material larger than the grain size separating from the jet chamber pass through the jet chamber, where it is accelerated and pushed into a high solids fluidized bed, whereby the particles are comminuted. Silicon particles smaller than the grain size that are sufficiently comminuted and separated in the countercurrent gravity separator are discharged from the separator as milled product with the gas stream.

The advantage of this aspect is the fact that the particles are accelerated very well in the jet chamber and then propelled into the high density fluidized bed in a manner similar to that of a solid injector, where a very effective grinding is achieved. At the same time, countercurrent gravitational separation results in a finite upper limit on the grain distribution of the resulting silicon seed particles.

The apparatus according to the invention can be used to produce silicon seed particles in grain sizes of about 50 μm to 1,000 μm with other efficiency, which is typical for ultrafine grinding of particles ranging in size from 2 to 10 μm in other cases. have.

It has been found that particularly effective milling can be achieved when the flow cross section of the jet chamber is selected at least 10-30%, preferably 20-30% less than the flow cross section of the countercurrent gravity separator.

The length of the jet chamber 8 is preferably at least 2 times, preferably 2 to 8 times the distance required until the milling gas stream reaches a point starting from the nozzle and extending to the cross section of the jet chamber. It is easy to design a jet chamber with a jet enlargement angle of about 18-20 degrees (half-angle), which is typical for free gas jets.

The structure of the jet chamber and separator according to the invention induces the introduction of energy by the milling gas stream and the desired grain size decoupled from each other. The separation grain size of the countercurrent gravity separator alone defines the upper limit of the grain size distribution of the milled product.

In a preferred embodiment, the silicone granules are not added to the jet chamber but to the separator. As a result, the silicone granules are classified even before they enter the milling zone. Particles of feed material initially smaller than the separation grain size of the separator are discharged with the gas stream and do not enter the milling zone, which pulverization contributes to the formation of undesirable fine dust.

In a particularly preferred embodiment, the silicone granules are fed to the separator at the top of the jet chamber, the weight of the silicon particles in the jet chamber and the separator is measured on a progress basis using a weighing unit, and the weighing of the silicone granules is Controllable by the control unit to optimally achieve efficient milling.

The efficiency of milling mainly depends on the loading in the mill / separator unit. If enough silicone granules are metered into the first separator, the solid concentration in the milling zone is lowered and the energy of the gas jet is not fully utilized. If too much silicon granules are metered and fed, the milling zone and the first separator are overloaded with particles, lowering the separation capacity of the first separator. By the loading level of about 0.30 kg / h of solids per kg / h of gas, the weight of the silicone granules in the mill / separator unit can be kept constant, with more than 75% of the silicon seed particles within the target grain size range. Proved to be obtained. As the load increases, the milling efficiency also increases. If the load exceeds about 0.30 kg / h of solids per kg / h of gas, the weight of the silicone granules in the mill / separator unit is increased on a run-by-step basis, and the plant is overcharged to contain the unpulverized particles in the product.

Thus, for optimal operation of the plant, it is desirable to provide a weighing unit to the mill / separator unit (eg using a weighing cell). The unit preferably weighs the mill / separator unit continuously and from this information, for example, using a computer, determines the weight of the particles in this unit, known as hold-up. The metering in the silicone granules, preferably in a computer controlled manner, is used to adjust the flow rate of the weighed granules so that the hold-up is kept as constant as possible.

A particular advantage of this embodiment over pure control of a constant addition amount is that the grain size distribution of the silicone granules has very little effect on milling results.

In a preferred embodiment of the present invention, the countercurrent gravity separator is designed in the form of a zigzag separator having a rectangular flow cross section immediately adjacent the jet chamber, wherein the flow cross section of the separator is larger than the flow cross section of the jet chamber. Zigzag separators are known in the art and are described, for example, in German patent DE 1 135 841. Such separators offer the advantage of separating particles more clearly than separators with straight flow paths.

In this embodiment of the present invention, the milling zone is a locally densely limited region of high solids concentration in the region where the flow cross section extends from the jet chamber to the zigzag separator.

The first separator is preferably followed by a second countercurrent gravity separator, which is also a zig-zag separator with a rectangular flow cross section, in which case the flow cross section of the second separator is preferably larger than the flow cross section of the first separator. The milled particles preferably pass from the first separator to the second separator together with the milling gas stream and any additional gas injected therein, in which limited, too finely milled particles, which are generally undesirable, are separated from the separator. Depending on the grain size, it is discharged upwards with the gas stream, and the required grain size fraction of the silicon seed particles falls into the collection vessel. Too finely milled silicon particles may be separated from the exhaust gas stream, for example by cyclones and filters.

The gas inlet region of the at least one separator is preferably provided with an additional gas inlet in each case so that the separation grain size of the separator can be further controlled. Here in each case an additional gas stream can be supplied, so that the separator grain size of the separator is shifted towards the larger grain size. The classifying gas used is preferably high purity nitrogen.

The upper and lower limits of the grain size distribution of the silicon seed particles are the dimensioning of the flow cross-section and milling gas nozzle cross-section of the two countercurrent gravity separators, the nozzle allowable pressure of the milling gas nozzle and the setting of the gas flow in the additional gas inlet of the separator. Can be defined by; According to the general rule for compressible gases, nozzle allowable pressure and nozzle diameter are generally used to set gas flow and maximum jet velocity. In addition, the introduction of energy for grinding is thus fixed. The separator is dimensioned in each case such that the desired separation grain size is obtained with a given gas stream.

Unnecessarily generated fine dust can generally be obtained with little or no contamination if a unit is designed which separates the fine dust from the exhaust gas stream. For this purpose, it is particularly suitable to use lined cyclones and filters (preferably filter cloth of high purity PTFE fibers).

With the exception of the metering unit which feeds the feed material, there is no moving part in the device according to the invention. The device according to the invention also has a simple form. This is particularly advantageous for lining non-contaminating materials or materials that produce little contaminants. One example of a non-polluting lining material is single crystal silicon, the purity of which is equal to or higher than the purity of the feed material. Materials that produce little contaminants should be understood to mean materials with high purity and very low proportions of substances (especially boron, phosphorus, metals) that adversely affect the application properties. These concentrations are additives (light stabilizers). And less than 100 ppmw such as high purity plastics prepared without the use of heat stabilizers, antioxidants, process aids, modifiers, flame retardants); Such plastics include polyethylene, polypropylene, polytetrafluoroethylene, polyurethane, ethylene-tetrafluoroethylene copolymers, perfluoroalkoxy copolymers or Halar ^® and the like.

The present invention also relates to a method of pulverizing silicon granules using a jet mill according to the present invention to form silicon seed particles, the present invention relates to a grinding method that simultaneously provides the advantages and efficiency of jet milling at ultra-fine jet milling levels. .

In this method, the silicone granules are accelerated by the high mill concentration fluidized bed formed of the silicone granules in the milling zone and by the high speed milling gas stream in the cylindrical jet chamber where only the low solids concentration is present to impinge on the fluidized bed of the high solids concentration. By grinding by the individual silicon particles of the silicone granules, the grinding of the silicone granules and the silicone particles takes place.

High solids concentration is preferably understood to mean a volumetric solids concentration of 20-50% by volume.

Low solids concentration is to be understood as meaning a volumetric solids concentration of less than 10% by volume, preferably less than 5% by volume but greater than 0.1% by volume.

The size of the silicon granules to be pulverized is preferably 300 to 5,000 mu m.

The size of the silicon seed particles to be produced is preferably 50 to 1,000 μm, particularly preferably 150 to 500 μm, and the mass-based median of the grain size distribution is particularly preferably 300 to 400 μm, smaller than 150 μm and 500 μm. The mass fraction of larger particles is less than 10%.

The milling gas used is preferably a high purity gas; High purity here is to be understood to mean that the impurity ratio is 5 ppm or less. For example, purified air, argon or nitrogen can be used, preferably purified nitrogen with a purity higher than 99.9995% by volume.

The milling gas jet is preferably directed upward in the vertical direction. For effective acceleration of the particles, the inlet velocity at the nozzle should exceed 300 m / s and it is desirable to set the velocity at 400-800 m / s. In the preset jet chamber shape and gas throughput, the speed can be set by the nozzle diameter. The throughput can be easily adjusted by setting the gas pressure upstream of the nozzle.

The milling gas flow and the flow cross section of the jet chamber are designed such that the separation grain size in the jet chamber is larger than the largest particle of the targeted grain size distribution of the silicon seed particles and smaller than the average grain size of the silicon particles of the feed material.

According to the process according to the invention, it is preferred that the gas consumption is low, with less than 10 kg of gas per kg of milled product, and at the same time silicon seed particles can be obtained in high yield.

According to the method according to the invention, it is possible to produce silicon seed particles with a defined, narrow grain size distribution, which is capable of contamination-free grinding of the silicone granules and which does not require subsequent sieving of the milled product. Additional sieving steps will involve additional work and potential contamination. In addition, the yield of silicon particles expressed by the amount of silicon particles produced relative to the unit amount of the feed material is also lowered.

Silicon seed particles having a size of 50 to 1,000 μm, particularly preferably most of 150 to 500 μm, are prepared, and the mass-based median of the grain size distribution is particularly preferably 300 to 400 μm, smaller than 150 μm and larger than 500 μm. The mass proportion of the particles is less than 10%.

This limited, narrow grain size distribution of high purity silicon seed particles is preferred because, while metering the silicon seed particles into the fluidized bed deposition reactor, finer materials than those ranges will be discharged immediately with the exhaust gas stream. Silicon seed particles coarse than this range will grow further in the fluidized bed, resulting in disturbing the overall grain distribution in the fluidized bed.

The process according to the invention can be used for milling not only silicon seed particles for fluid bed deposition, but also other silicon grain fractions targeted for particular applications. This field of application is a special field of application which requires very fine grain distribution and very high purity, for example, silicon particles, which are required as base materials in the photovoltaic and electronics industries.

3 shows a particularly preferred embodiment of the device according to the invention. A preferred embodiment of the method according to the invention is described below on the basis of an example of this apparatus.

The silicone granules 2 are metered from the storage container 11 using the metering device 12 and supplied to the first zigzag separator 9 through the supply line 6. The jet chamber 8 is located just below the first separator 9. The milling gas stream 1 is injected into the jet chamber 8 via a Laval nozzle 4. A throttle member 13 is used to establish the milling gas flow. The milling zone 10 in the fluidized bed is formed in the transition between the jet chamber 8 and the first separator 9. An additional gas stream 15 to control the separation may be supplied through the gas inlet 14. The jet chamber 8 and the first separator 9 are separated from the rest of the installation by compensators 16, 17, 18 with respect to the force applied. The weighing device 19 measures the weight of the jet chamber 80, the first separator 9 and the particles present therein. From the information on the weight, the computer unit 20 determines the weight of the particles in the milling chamber / separator unit. Determine the weight This value is used as a guide parameter for controlling the metering of the feedstock Particles with a diameter smaller than the separating grain of the first separator 9 are obtained from the milling gas stream and any additional classifying gas. And enter the second zigzag separator 22 from the first separator 9 through the connection line 21. Particles falling in the target grain size range fall down. A gas inlet 24 may be used to feed an additional gas stream 25 to the second separator 22 to control the second separation process. All of the additional classifying gas is discharged upwards from the second separator 22. These particles are separated from the gas stream in a cyclone 26 and a filter 27 installed downstream. The silver is discharged from the plant, overly finely milled particles fall downward from the cyclone and the filter, and streams 29 and 30 of the particles following the drop can be collected again in the vessel.

In the device according to the invention, it is particularly preferred that the part which comes into contact with the silicon particles comprises an outer metal casing with an inner wall provided with a lining. The linings used are silicone or plastic materials in monocrystalline or polycrystalline form, with preferred plastic materials being polyethylene, polypropylene, polytetrafluoroethylene, polyurethane, ethylene-tetrafluoroethylene copolymers, perfluoroalkoxy copolymers or Halar ^® and the like. The materials are preferably used in high purity form.

It is particularly preferred that an inliner, preferably made of polycrystalline or monocrystalline silicon or quartz, is installed in a positive locking manner in a jet chamber lined in this way or in a separator lined in this way. The lining material is preferably used in high purity form. No sealing is necessary between the inliners or between the linings and the inliners.

When carrying out the method according to the invention, fine silicon dust fills the gaps between the inliners or between the linings and the inliners so that these gaps are gradually blocked as the operating time is streamed.

While the importance of wear is secondary when compared to other grinding methods, the component jet chamber, jet chamber / separator transition part and the first separator have been found to have a greater degree of wear than the rest of the product transport element. Higher wear by about 10 to 100). Thus, in another preferred embodiment, the constituent jet chamber, jet chamber / separator transition part and the first separator are internally lined with polyurethane alone, since the polyurethane has proved to be particularly wear resistant.

Comparing the analysis of the feed material and the silicon seed particles produced, it has been demonstrated that this type of device can perform milling virtually without contamination.

4 shows a cross section of a jet chamber 32 perpendicular to the milling gas flow direction. The flow cross section for the milling gas flow 31 is circular. The metal body of the jet chamber 32 is provided with a lining of high purity plastic 33 inside. The flow passage is delimited by the silicon inliner 34.

5 shows a cross section of one of the zigzag separators perpendicular to the flow direction of the milling gas. The flow cross section for the milling gas flow 35 is rectangular. The metallic body 36 is provided with a lining of high purity plastic 37 inside. The flow passage is delimited by the silicon inliner 38.

The flow cross section for the gas flow is larger in the first separator than in the jet chamber. The flow cross section for the gas flow is larger in the second separator than in the first separator.

Fig. 6 is a longitudinal cross section of the part of the jet chamber in the flow direction of the milling gas, showing that silicon inliners 34a and 34b are provided. The inliners 34a and 34b are installed in a positive locking manner in the metal body of the jet chamber 32, and the jet chamber 32 is provided with a lining of high purity plastic 33. No special attachments or adhesive bonds are necessary. Each inliner 34a, 34b is connected to each other by a protrusion and a recess. The formed gap 39 is filled with very fine dust while the plant is running, providing additional stability to the inliner. Since the plastic lining is installed, the milled product cannot be contaminated by being moved behind the inliner.

The following examples are intended to illustrate the present invention in more detail.

Example  One

High purity silicon granules were ground in a milling facility as shown in FIG. 3. The purpose of milling is from a silicon granule having a grain size distribution of about 250 to 4,000 μm, an average diameter (mass basis) of 711 μm, a grain size distribution of about 150 to 500 μm, and an average diameter (mass basis) of 300 Silicon seed particles having a size of ˜400 μm were prepared.

The flow cross section of the jet chamber was 3,020 mm 2, the flow cross section of the first zig-zag separator was 4,200 mm 2, and the flow cross section of the second zig-zag separator was 19,600 mm 2. The Laval nozzle, a milling flow nozzle, had the narrowest circular cross section with a diameter of 4 mm. The length of the jet chamber was 550 mm.

The milling plant was run for 14.5 hours. In this case the average metering of the feed material was 17.83 kg / h. Laval nozzles were used to set the milling gas flow to purified nitrogen 52 m 3 / n (s.t.p.) of quality grade 5.5 (purity> 99.9995%), ie to set the loading to an average of 0.274. No further classified gas stream was metered into the first separator. 4 m < 3 > / n (s.t.p.) of purified nitrogen was metered in as an additional classified gas stream.

The pressure in the jet chamber / separator combination was maintained at approximately atmospheric pressure levels (1,013 hPa ± 100 hPa) using suction devices in the exhaust stream of the facility.

In the milling operation, the amount of silicone granules in the jet chamber and the first separator was constantly controlled to 2.5 kg by weight measurement as described above.

Given the dimensions and gas stream, the result in the jet chamber is 516 μm of separation grain size for the first separator separation grain size of 516 μm and for the second separator of separation grain size of 140 μm.

Overall, 258.5 kg of silicone granules were milled, of which 235 kg were collected as milled product under the first separator. 20.7 kg of fine particles were collected at the bottom of the cyclone and an additional 2.8 kg of ultrafine particles were removed from the gas stream in the filter.

7 is a graph showing the overall path distribution by mass of feed material (silicone granules) and milled product (silicon seed particles). 8 is a graph showing the mass-based distribution density of feed material (silicone granules) and milled product (silicon seed particles). The silicon seed particles had an average diameter (mass basis) of 337 μm. The ratio of unnecessary coarse fraction to fine fraction (fractions larger than 500 μm or smaller than 150 μm) was about 8%.

The consumption of nitrogen was 3.93 kg of gas per kg of feed material or 4.32 kg of gas per kg of milled product. The yield of milled products was 90.9% based on the feed material, and the yield of milled products included in the target grain size range of 150 μm to 500 μm was 83.6% based on the feed material.

For metal contamination, feed materials and milled products were tested using mass spectrometry (ICP-MS: inductively coupled plasma mass spectrometry) according to ASTM F1724-01. The results for metal iron, chromium and nickel in the feed material and milled product were in each case below the detection limit of the method. The detection limit was 2100 pptw for iron, 170 pptw for chromium and 400 pptw for nickel. Therefore, metal contamination of the silicone granules during milling is within or below the detection limit of the above method.

Using the device according to the invention, silicon seed particles having a particle size of 50 μm to 1,000 μm can be produced economically and in pure form from silicon granules having a particle size of 300 μm to 5,000 μm.

Claims (17)

An apparatus for producing silicon seed particles from silicon granules, The silicon granules have a size of 300 μm to 5,000 μm, and the silicon seeds have a size of 50 μm to 1,000 μm, A vertically installed jet chamber 8 having a cylindrical cross section and having a jet nozzle 4 at the base, Countercurrent gravity separator 9 directly connected to the jet chamber 8, and Inlet for injection of silicone granules (2) (6) Including, Through the jet nozzle a milling gas stream 1 can be introduced into the jet chamber 8, The jet chamber 8 has a length which extends the milling gas stream sufficiently to the cross section of the jet chamber 8, the cross section of flow of the jet chamber 8 being the countercurrent gravity separator 9. Characterized by being smaller than the flow cross section of Apparatus for producing silicon seed particles. The method of claim 1, Apparatus for producing silicon seed particles, characterized in that the cross-sectional area of the jet chamber (8) is 10-30%, preferably 20-30%, smaller than the cross-sectional area of the countercurrent gravity separator. The method according to claim 1 or 2, The length of the jet chamber 8 is at least twice the distance required, preferably until the milling gas stream 1 reaches a point starting from the nozzle 4 and extending to the cross section of the jet chamber. It is 2-8 times, The manufacturing apparatus of the silicon seed particle | grains characterized by the above-mentioned. The method according to any one of claims 1 to 3, A device for producing silicon seed particles, characterized in that the inlet (6) of the silicon granules (2) is open into the separator. The method according to any one of claims 1 to 4, Apparatus for producing silicon seed particles, characterized in that a weighing unit (19) is provided for measuring the weight of silicon particles in the jet chamber (8) and the separator (9). The method of claim 5, Apparatus for producing silicon seed particles, characterized in that the weight of the silicon particles (2) can be controlled by a control unit for weighing the silicon particles (2) so that milling efficiency can be optimally achieved. The method according to any one of claims 1 to 6, Apparatus for producing silicon seed particles, characterized in that the countercurrent gravity separator (9) is a zigzag separator having a rectangular flow cross section. The method of claim 7, wherein The second countercurrent gravity separator 22, which is preferably a zig-zag type separator having a rectangular flow cross section larger than the flow cross section of the first countercurrent gravity separator 9, is installed next to the first countercurrent gravity separator 9. An apparatus for producing silicon seed particles, characterized in that. The method according to any one of claims 1 to 8, An apparatus for producing silicon seed particles, characterized in that an additional gas inlet (14, 24) for classifying gas is provided in the inlet region of the separator (9, 22). The method according to any one of claims 1 to 9, Wherein the portion which is to collide with the silicon particles comprises an outer metal casing having an inner wall provided with lining. The method of claim 10, The lining is a single crystal or polycrystalline form of silicon, or a plastic material, preferably polyethylene, polypropylene, polytetrafluoroethylene, polyurethane, ethylene-silicon oxide particles, characterized in that consisting of tetrafluoroethylene or Halar ^® by Manufacturing device. The method according to claim 10 or 11, wherein Inliner (inliner) is provided in the part provided with the lining in a positive locking (positive locking) method, the inliner is a device for producing silicon seed particles, characterized in that preferably made of polycrystalline or monocrystalline silicon, or quartz. A method of comminuting silicon granules for forming silicon seed particles using the apparatus according to any one of claims 1 to 12, A fluidized bed 7 having a high solid concentration is formed from the silicon granules in the milling zone 10, and each silicon particle of the silicon granules has a low solid concentration cylindrical jet chamber 8. Is accelerated by a high-speed milling gas stream within the shell) and impinges on the fluidized bed 7 having a high solid concentration, thereby pulverizing silicon granules and silicon particles. Grinding method of silicone granules. The method of claim 13, The solid concentration of the fluidized bed 7 having a high solid concentration is 20 to 50% by volume, and the solid concentration of the fluidized bed with a low solid concentration is less than 10% by volume, preferably less than 5% by volume, but greater than 0.1% by volume. Grinding method of silicone granules, characterized in that. The method according to claim 13 or 14, A particle size of the silicon granules to be pulverized, characterized in that the silicon granules crushing method characterized in that 300 ㎛ to 5,000 ㎛. The method according to any one of claims 13 to 15, Process for grinding silicon granules, characterized in that the milling gas (1) used is air, argon, or nitrogen, particularly purified nitrogen having a purity higher than 99.9995% by volume. The method according to any one of claims 13 to 16, The milling gas jet is introduced into the jet chamber (8) at a speed faster than 300 m / s at the nozzle.

Images