DE102015203654A1 - Promotion and fractionation of polysilicon granules in a conveyor trough - Google Patents

Abstract

The invention relates to a process for the promotion and fractionation of polysilicon granules by means of horizontal and / or vertical movement of a conveyor trough, wherein the conveyor trough is completely encapsulated to the outside and the forward movement of the polysilicon granules by a tumbling motion of the conveyor trough by means of the excitation of at least one attached to the conveyor trough Permanent magnet is generated by an electromagnetic field, wherein the electromagnetic field is applied from the outside to the encapsulated conveyor trough, characterized in that the polysilicon granulate is divided by the conveyor trough into two or more fractions, wherein the conveyor trough comprises at least two outlets, through the two or more fractions of the polysilicon granules are deducted.

Description

The invention relates to the promotion and fractionation of polysilicon granules in a conveyor trough.

Polycrystalline silicon granules or polysilicon granulate in short is produced in a fluidized bed reactor. This is done by fluidization of silicon particles by means of a gas flow in a fluidized bed, which is heated by a heater to high temperatures. By adding a silicon-containing reaction gas, a pyrolysis reaction takes place on the hot particle surface. Here, elemental silicon is deposited on the silicon particles and the individual particles grow in diameter. By the regular withdrawal of grown particles and addition of smaller silicon particles as seed particles, the process can be operated continuously with all the associated advantages. Silicon-containing compounds (for example chlorosilanes or bromosilanes), monosilane (SiH4) and mixtures of these gases with hydrogen can be used as the silicon-containing educt gas.

In the production of polycrystalline silicon granules in a fluidized bed reactor, it is necessary in the current process to meter silicon material into the reactor at regular intervals or continuously and to remove ready-grown granules from the reactor elsewhere.

US 2011/0024266 A1 discloses a method for conveying polysilicon granules by means of horizontal and / or vertical movement of the conveying device, characterized in that the conveying device is completely encapsulated outwardly and the forward movement of the granules by a wobbling movement of the conveying device by the excitation of at least one mounted on the conveyor permanent magnets an electromagnetic field is generated, wherein the electromagnetic field is applied from the outside to the encapsulated device.

Compared with conveyor troughs, which are excited by means of vibration motors, the shaking movement of the encapsulated conveying device is effected by the tumbling movement of a permanent magnet, which is excited by an external alternating electromagnetic field. As a result, the conveying device can be completely encapsulated in a housing to the outside and requires no feedthroughs for electrical leads or compressed air lines.

The conveyor has outwardly at least two connection options, preferably one on each side of the conveyor trough as an inlet and outlet. These connections are preferably designed as nozzles or flange connections in order to connect the delivery device in a pressure-tight manner to a pipeline, a reactor or a container for the storage of polysilicon granules.

Usually, polysilicon granules are first transported to the fluidized-bed reactor in a broad particle size distribution through such an encapsulated conveyor trough to the withdrawal section where they are filled into a transport container.

In the transport container, the polysilicon granules are then transported to a screening machine, divided by it into two or more fractions. The smallest sieve fraction (Siebunterkorn) can then be processed in a grinding plant to seed particles and added to the reactor. The screening target fraction is usually packaged and transported to the customer.

A screening machine is generally a machine for screening, ie the separation (separation) of solid mixtures to particle sizes.

According to the movement characteristics, a distinction is made between planing vibrating screens and throwing machines.

The drive of the screening machines is usually electromagnetic or by unbalance motors or gearbox.

The movement of the Siebbelags serves the further transport of the feed material in Sieblängsrichtung and the passage of the fine fraction, z. B. of Siebunterkorns, through the mesh openings.

In contrast to Planschwangsiebmaschinen occurs in throwing machines in addition to the horizontal and a vertical Siebbeschleunigung.

In the litter screening machines, vertical throwing motions overlap with slight turning movements. As a result, the sample material spreads over the entire surface of the sieve bottom and at the same time the particles experience an acceleration in a vertical direction (thrown up). In the air they can make free turns and are compared with the mesh of the screen fabric when falling back on the screen. If the particles are smaller than these, they pass through the sieve, they are larger, they are thrown up again. The rotational movement ensures that they have a different orientation on the next sieve on the mesh and so maybe pass through a mesh opening.

In planing sifters, the sieve tower completes a horizontal circular movement in one plane. This keeps the particles on the Siebgewebe largely their orientation. Planeting machines are preferably used for needle-shaped, platelet-shaped, elongated or fibrous screening goods, in which a throwing up of the sample is not necessarily beneficial.

A special type is the Mehrdecksiebmaschine, which can fractionate several grain sizes simultaneously. They are designed for a variety of sharp separations in the medium to ultra-fine grain range.

The drive principle is based on two-deck planer on two counter-rotating unbalance motors that produce a linear vibration. The screen material moves in a straight line over the horizontal separating surface. The machine works with low vibration acceleration.

Through a modular system, a variety of screening decks can be assembled into a stack of sieves. Thus, if necessary, different grain sizes can be produced in a single machine, without having to change screen coverings. By repeated repetition of the same Siebdeckfolgen the screening material can be offered much screen area.

US 8021483 B2 discloses such an apparatus for sorting polycrystalline silicon pieces including a vibratory motor assembly and a step bottom classifier attached to the vibratory motor assembly. The vibratory motor assembly causes the pieces of silicon to move over a first bottom containing grooves. In a fluidized bed area, dust is removed by a stream of air through a perforated plate. In a profiled area of the first floor, the pieces of silicon settle in holes of grooves or remain on ridges of the grooves. At the end of the first bottom, pieces of silicon smaller than a gap fall through it onto a conveyor belt. Larger pieces of silicon move across the gap and fall to the second floor.

US 7959008 B2 claims a method for sifting out first particles of granules comprising first and second particles by conveying the granules along a first screen surface, preferably starting from a vibration device, wherein the first particles have an aspect ratio a1 with a1> n: 1 and n = 2, 3, > 3, in particular with a1> 3: 1, and the second particles have a dimensioning which allows them to pass through the meshes of the first screen surface, characterized in that the granules are conveyed along the screen surface between this and a cover extending along the screen surface and that due to the cover the first particles are aligned with their longitudinal axes running along the screen surface, wherein the longitudinal extent of each first particle is greater than the mesh size of the screen forming the first screen surface and the longitudinal extent of the second particles is equal to or smaller than the mesh size.

The disadvantage is that the polysilicon granules must be transported and transferred before it is divided into two or more fractions. This is associated with a large handling effort for the operating staff. Furthermore, the transport and Umfüllvorgänge also represent a significant source of contamination for the polysilicon granules. In addition, the cost of the required screening plants, transfer stations and transport containers, especially for the required redundancies in large production plants, relatively high.

From the problem described, the problem of the invention resulted.

The object of the invention is achieved by a method for conveying and fractionating polysilicon granules by means of horizontal and / or vertical movement of a conveyor trough, wherein the conveyor trough is completely encapsulated to the outside and the forward movement of the polysilicon granules by a tumbling motion of the conveyor trough by the excitation of at least one the permanent magnet attached to the conveyor trough is generated by an electromagnetic field, wherein the electromagnetic field is applied from the outside to the encapsulated conveyor trough, characterized in that the polysilicon granules are divided by means of the conveyor trough into two or more fractions, wherein the conveyor trough comprises at least two outlets the two or more fractions of the polysilicon granules are withdrawn.

The invention also relates to a polysilicon granule conveying and fractionating device comprising
a pressure-resistant basic body,
a movable in the base body, movably mounted conveyor trough, which is completely encapsulated to the outside,
a permanent magnet attached to the conveyor trough,
a coil for generating an electromagnetic field, which is arranged outside the conveyor trough and is adapted to excite the permanent magnet connected to the conveyor trough and thereby to tumble the permanent magnet and the conveyor trough, characterized in that the device comprises elements to the polysilicon granules into two or more fractions, with at least two outlets to extract the two or more fractions of polysilicon granules.

In contrast to the prior art, the polysilicon granules withdrawn from a fluidized-bed reactor are already classified within the conveying trough into the desired fractions.

For fractionation of the polysilicon granules, one or more screening decks may be introduced into the conveyor trough. A fraction of polysilicon granules is screened through the screen deck and reaches a first outlet through which it is withdrawn. The second fraction is not screened off, remains on the screen deck and reaches a second outlet through which it is withdrawn, or a second screen deck over which further fractionation takes place.

In another embodiment, the conveyor trough comprises a plurality of apertures proximate an outlet, wherein a fraction of the polysilicon granules is screened through the apertures and withdrawn through the outlet. The second fraction remains on the conveyor trough and reaches a second outlet, over which it is pulled off. Alternatively, the conveyor trough comprises a further region which also locally near a second outlet has a plurality of openings through which the second fraction is screened and withdrawn via the second outlet leaving a third fraction on the conveyor trough and e.g. B. is moved to a third outlet, over which it is deducted.

Those local areas with a multiplicity of openings can be introduced into the conveyor trough by means of mechanical or laser processing.

By the method according to the invention, the disadvantages of the prior art were overcome. An additional screening outside the conveyor is no longer necessary, which also eliminates the need to transport to an external screening plant. This significantly reduces the handling effort and avoids sources of contamination on the product route. In addition, the invention contributes to significant savings in the procurement of new production facilities for polysilicon granules, since the cost of the external screening machine for transfer stations and transport containers account for all or at least partially.

The conveying and fractionating device comprises a pressure-resistant base body and a conveyor trough.

The conveyor trough is preferably firmly connected to the main body and stored in this movable. The storage can be done by springs or flexible retaining rings.

By means of a coil, an electromagnetic field is generated, whereby the permanent magnet, which is preferably located in a directly coupled to the conveyor chute housing, set in tumbling movements, whereby the conveyor trough is vibrated.

With respect to the preferred embodiment of the conveying device is fully on US 2011/0024266 A1 Referenced.

The throughput of polysilicon granules through the conveyor trough is preferably as an analog size on the modulation of amplitude (coil current) and frequency of the alternating electromagnetic field of the coil z. B. set by means of a frequency converter. The frequency is adjusted to the natural frequency of the conveyor trough in the respective installation situation. By selecting the appropriate magnetic material, the dimensioning of the cavity diameter, the inclination of the inner conveyor trough and the size of the permanent magnet working areas can be defined for different applications.

For excitation of the magnet, a single-phase magnetic field is preferably used. Preference is given to a variable frequency of 0.1 to 1000 Hz, more preferably 5 to 100 Hz. The frequency is preferably tuned to resonance according to the installation conditions. For example, a frequency converter can be used for tuning. The frequency of the tumbling motion corresponds to the frequency of the exciter field.

To set the required throughput of the conveyor trough, the current amplitude can be controlled continuously. This is preferably carried out in a range of 0.1 to 100 A, more preferably in a range of 0.1 to 5 A. The field strength results from the ampere-turn number used and varies with the set for the required flow rate of current.

The polysilicon granulate particles in the conveyor trough are transported to outlets, with separation into two or more fractions. There are at least two outlets available. The first fraction of polysilicon granules is withdrawn from the conveyor via a first outlet and the second fraction of polysilicon granules via a second outlet. In one embodiment, one or more screen decks are introduced into the conveyor trough.

The screen decks can be used as sieve mesh made of plastic materials such. As polyethylene, polyamide or polyurethane, which are based on screen frame made of plastic materials such. As polypropylene, polyurethane, polyethylene or Polyamide or uncoated and coated metals are spanned. Alternative materials for screen frames are also high-purity materials such. As quartz or silicon.

In one embodiment, the screen decks as a massive plate made of plastic materials such. As polypropylene, polyethylene, polyurethane or polyamide or made of uncoated as coated metals with mechanical holes or laser bores according to the required separation fractions. Alternatively, the massive plate can also be made of high-purity materials such. As quartz or silicon.

The fixation of the screen decks within the conveyor trough can be done via insertion gaps or insertion strips on the sides of the conveyor trough, by welding points or by fitting by means of thermal or mechanical pressure.

In a further embodiment, the underside of the conveyor trough comprises locally in the region of an outlet a multiplicity of holes or bores corresponding to the desired separation fractions. Through the holes and holes a fraction of Polysilicumgranulats is screened and reaches a first outlet. As materials for the conveyor trough plastic materials such. As polypropylene, polyethylene, polyurethane or polyamide, uncoated or coated metallic materials and high purity materials such. As quartz or silicon possible.

By using more than two screen decks and a corresponding number of additional outlets, the polysilicon granules can be separated into more than two fractions.

Likewise, the conveyor trough on the outlet side may comprise a plurality of local areas with different hole sizes, so that by providing a corresponding number of additional outlets even after this embodiment, a separation of the polysilicon granulate into more than two fractions is possible.

For example, if a separation into four fractions to take place, the device comprises three decks and four outlets or a conveyor trough with three hole areas and four outlets.

The features specified with regard to the above-mentioned embodiments of the method according to the invention can be correspondingly transferred to the device according to the invention. Conversely, the features specified with regard to the embodiments of the device according to the invention described above can be correspondingly transferred to the method according to the invention. These and other features of the embodiments according to the invention are explained in the description of the figures and in the claims. The individual features can be realized either separately or in combination as embodiments of the invention. Furthermore, they can describe advantageous embodiments that are independently protectable.

Brief description of the figures

1 shows a conveying and fractionating device with a sieve deck within the conveyor trough.

2 shows a conveying and fractionating device in which the conveyor trough comprises openings through which a fraction of the polysilicon granules is sieved.

LIST OF REFERENCE NUMBERS

1

body

2

conveyor trough

3

compensator

4

permanent magnet

5

housing

6

excitation coil

7

feather

8th

particle inlet

9

First particle outlet

10

Second particle outlet

11

Screendeck

12

openings

1 shows a conveying and fractionating device of a pressure-resistant body 1 (For example, made of metal) and a conveyor trough 2 that have compensators 3 firmly with the main body 1 is connected and elastic over springs 7 movable in the body 1 is stored.

About an excitation coil 6 an external electromagnetic field is generated, creating a strong permanent magnet 4 who is in an enclosure 5 located directly with the conveyor trough 2 coupled, is set in tumbling movements, whereby the conveyor trough 2 is vibrated and the polysilicon granulate particles contained therein from the particle inlet 8th up to the particle outlets 9 and 10 be transported.

It is a screen deck 11 into the conveyor trough 2 introduced so that the polysilicon granules in the conveyor trough 2 classified and through two particle outlets 9 and 10 is deducted.

2 is different from the execution in 1 in that there is no screen deck, but instead the underside of the conveyor trough 2 in the area of the particle outlet 9 with openings 12 is provided. The size of the openings 12 is selected according to the separation fraction to be sifted off.

Comparative example

In the exhaust system of a fluidized bed reactor for the production of polysilicon granules, the product is conveyed with a particle size distribution of 100-10,000 microns via a conveyor trough in a buffer container and filled from there into a transport container.

Subsequently, the transport takes place in a plastic container to an external screening plant.

Once there, the transport container is docked and transferred to a Siebvorlagebehälter.

In the screening plant, the product is separated into three target grain fractions (D90 values 500 μm, 2000 μm, 6000 μm) and filled into separate product containers.

These steps accommodate a high handling effort and a high risk of contamination for the high-purity polysilicon granules.

example

In the exhaust system of the fluidized bed reactor for the production of polysilicon granules, the product is introduced with a particle size distribution of 100-10,000 microns in a conveyor trough, and separated in the conveyor trough in three target grain fractions (D90 values 500 .mu.m, 2000 .mu.m, 6000 .mu.m) and filled into separate product containers ,

The handling effort is significantly reduced. By saving transfer and transport steps, the risk of contamination for the high-purity polysilicon granules is minimized.

The above description of exemplary embodiments is to be understood by way of example. The disclosure thus made makes it possible for the skilled person, on the one hand, to understand the present invention and the associated advantages, and on the other hand, in the understanding of the person skilled in the art, also encompasses obvious modifications and modifications of the structures and methods described. It is therefore intended that all such alterations and modifications as well as equivalents be covered by the scope of the claims.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2011/0024266 A1 [0004, 0033]
• US 8021483 B2 [0019]
• US 7959008 B2 [0020]

Claims (9)

A method for conveying and fractionating polysilicon granules by means of horizontal and / or vertical movement of a conveyor trough, wherein the conveyor trough is completely sealed to the outside and the forward movement of the polysilicon granules by a tumbling motion of the conveyor trough by the excitation of at least one mounted on the conveyor trough permanent magnets by an electromagnetic field wherein the electromagnetic field is applied from the outside to the encapsulated conveyor trough, characterized in that the polysilicon granules are divided into two or more fractions by means of the conveyor trough, the conveyor trough comprising at least two outlets through which two or more fractions of the polysilicon granules are withdrawn become. Process according to claim 1, wherein the fractionation of the polysilicon granules into two or more fractions takes place by means of one or more screen decks inserted into the conveyor trough. The method of claim 1, wherein the conveyor trough has a plurality of apertures proximate to an outlet, wherein a fraction of the polysilicon granules is screened through the apertures and withdrawn through the outlet. The polysilicon granulate conveying and fractionating apparatus comprising a pressure-resistant base body, a moving-type conveying trough completely encapsulated in the body, a permanent magnet attached to the conveying trough, an electromagnetic field generating coil disposed outside the conveying trough and is adapted to excite the permanent magnet associated with the conveyor trough and thereby to tumble the permanent magnet and the conveyor trough, characterized in that the apparatus comprises elements for dividing the polysilicon granules into two or more fractions, at least two outlets being present to withdraw the two or more fractions of polysilicon granules. Apparatus according to claim 5, wherein one or more screen decks are introduced into the conveyor trough for fractionating the polysilicon granules. Apparatus according to claim 5, wherein the screening decks comprise mesh screens made of plastic and sieve frames made of plastic, metal, silicon or quartz. Apparatus according to claim 5, wherein the screen deck is a solid plate of plastic, metal, silicon or quartz comprising bores. Device according to one of claims 5 to 7, wherein the fixing of the screen decks within the conveyor trough via insertion gaps or insertion strips on the sides of the conveyor trough, by welding or by fitting by means of thermal or mechanical pressure. Apparatus according to claim 4, wherein the conveyor trough has a plurality of apertures proximate to at least one outlet, and through the apertures a fraction of the polysilicon granules can be screened and withdrawn through the outlet.

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