DD207534A5 - METHOD FOR PRODUCING SILICON FROM POWDER-FORMED SILICON DIOXIDE-DYING MATERIAL - Google Patents

Abstract

The present invention relates to a process for the production of silicon from a pulverulent silicondioxide-containing material. This material is optionally injected together with a reducing agent by means of a carrier gas in a gas plasma. Thereafter, the thus-heated silicon dioxide-containing material is introduced together with the optional reducing agent and the high-energy plasma gas in a reaction chamber, which is surrounded by a solid stückfoermigen reducing agent, whereby the mentioned silicon dioxide is melted and reduced to liquid silicon. The gas plasma is preferably generated by an electric arc in a plasma generator. With this method one can produce in a single stage high-purity silicon with a contamination content, which amounts to at the most 110 ppm.

Description

Berlin, July 25, 1983

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Process for producing silicon from pulverulent material

Field of application of the invention

The present invention relates to a method for the production of silicon from powdered silicon dioxide-containing material.

The world's annual production at the time of the present application is on the order of 2 million tons / year of silicon, of which about 5 % is for the production of pure silicon and the rest is used in the iron and aluminum industry · 10 % of pure silicon is used in the semiconductor industry used, that is about 10 000 t.

It is expected that the consumption of silicon in the next decades will increase drastically, which is mainly due to the fact that the interest in the utilization of solar energy for the production of electrical energy is very high. In the solar cells, pure silicon is preferably used, ie a quality which is called "solar grade" and means a purity of at least 99.99 % · The type of impurities, however, is also of great importance, so that the choice of raw materials is critical «

Characteristic of the known technical solutions

The largest amount of pure silicon is produced by direct reduction in an electric arc furnace, obtaining a quality called metallurgical grade · Purity

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is about 98 %. In order to be used in solar cells, this silicon must be purified by dissolving and segregating the impurities. The high purity siliaium material becomes so expensive that generation of electric energy with solar cells made of this silicon , becomes uneconomical ·

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Intensive development work is underway to develop methods that allow cheaper production of high purity silicon. One way is to use cleaner raw materials. However, this alone is not enough to make the procedures profitable. Thus, the arc furnaces require piece-shaped starting material, which limits the raw material base and makes it difficult to use high-purity raw materials. In addition, for this purpose, the silica particles must be agglomerated by a form of binder in order to be applicable. This makes the process even more expensive.

Furthermore, the arc technique is sensitive to electrical properties of the raw materials, which makes it difficult to use reducing agents with a low content of impurities. The fact that you have to use lumpy Good as the starting material, obtained during the process locally a poorer contact between silicon dioxide and reducing agent, causing the escape of SiO. In addition, this escape increases by the fact that locally very high temperatures occur in this process. Furthermore, it is difficult to maintain absolutely reducing conditions in the gas space of an electric arc furnace, which therefore causes SiO formed to reoxidize to SiO 2

becomes. ^K. '

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The circumstances described above cause most of the losses incurred in this process, which can also be seen from the consumption of electrical energy measured in this known method, which is 25-45 MWh / t compared to a calculated theoretical consumption of 9 MWh / t , Finally, the escape of SiO and the above-mentioned reoxidation from SiO to SiO _{2 result} in severe operational disturbances because

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-3, the gas ducts enforce · Zie de l r invention

The object of the present invention is to eliminate the above-mentioned disadvantages and to prevent the process from undergoing a process which permits the production of high-purity silicon in a single stage and permits the use of pulverulent raw materials.

presentation; the essence of the invention

The invention has for its object to find a new production technology for pure silicon ·

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- 3a -

This object is achieved in that the powdered siliziumdioxydhaltige material optionally together with a reducing agent by means of carrier gas is injected into a gas plasma generated by a plasma generator, after which the so heated silica together with the optionally present reducing agent and the high-energy plasma gas into a reaction chamber which is surrounded by substantially solid sides by a solid piece-shaped reducing agent.

According to the invention, the oasplasma is produced by allowing the plasma gas to pass through an electric arc in a so-called plasma generator. The arc in the plasma generator is generated inductively.

This process design allows concentrating the entire course of the reaction to a very limited reaction zone immediately following the blow opening, whereby the high temperature volume in the process can be kept very limited. This is a great advantage over previously known processes where the reduction reactions spread over a large furnace volume gradually happen · .._. ''.

Characterized in that the method is designed so that all reactions take place in a reaction zone in the coke column immediately before the plasma generator, the reaction zone can be maintained at a very high and controllable temperature level, whereby the reaction

SiO ₂ +20 - * - Si + 2 CO is favored.

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All reactants (SiO _2, SiO, SiC, Si, C, CO) are simultaneously in the reaction zone, which is why the products of SiO and SiC formed in lesser amounts ^t respond immediately as follows:

SiO + C ->-> Si + CO SiO + SiC -> 2Si + CO 2 SiC + SiO ₂ -> 3Si + 2CO

The final products leaving the reaction zone are therefore in all cases liquid Si and gaseous CO.

The use of pulverulent raw materials proposed according to the present invention makes the choice of high-purity silicon dioxide raw material easier and cheaper. The proposed method according to the invention is also insensitive to electrical properties of the 'raw material, which facilitates the choice of the reducing agent.

The injected reducing agent may e.g. consist of hydrocarbons, such as natural gas, coal dust, charcoal dust, carbon black, petroleum coke - which may possibly be purified - and coking gravel.

The temperature required for the process can be easily controlled by the amount of electrical energy supplied per unit of plasma gas, which can maintain optimum conditions for minimizing the escape of SiO.

Since the reaction chamber is surrounded by particulate reducing agent substantially from all sides, a reoxygenation of SiO is also effectively prevented.

According to a suitable embodiment of the invention

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the solid piece-shaped reducing agent according to its consumption continuously supplied to the reaction zone.

M is best used as solid particulate reducing agent coke, charcoal, petroleum coke and / or carbon blacl $ and the plasma gas used in the process can best consist of recirculated from the reaction zone process gas · ν

The solid bar-shaped reducing agent may be a powder which has been converted into pieces by means of a binder which is optionally composed of C and H, for example sucrose.

According to another embodiment of the invention, the plasma torch used consists of a so-called inductive plasma torch, whereby any impurities are reduced to an absolute minimum by the electrodes.

The method proposed according to the invention can be used to advantage for producing high-purity silicon intended as a raw material for solar cells and / or semiconductors, whereby high-purity silicon dioxide and reducing agent having very low impurity contents can be used as raw materials.

embodiment

The invention will be described in more detail below with reference to some embodiments. The reactions are preferably carried out in a shaft furnace-like reactor, the above continuously, z. B. by a gout with "moderately distributed and closed feeders or an annular feed gap" in the connection to the periphery of the shaft, is charged with a solid reducing agent.

The optionally pre-reduced silicon-containing powdery material is blown down in the reactor by means of an inert or reducing gas through blowholes in the reactor »At the same time hydrocarbons can be blown and optionally also oxygen, preferably through the same blowholes.

In the lower part of the slot-shaped reducing agent-filled shaft is a reaction chamber which is surrounded on all sides by the mentioned piece-shaped reducing agent. In this reduction zone the reduction of the silicon dioxide and the melting take place momentarily.

The escaping reactor gas, which consists of a mixture of carbon monoxide gas and hydrogen in high concentration, can be recycled and used as a carrier gas for the plasma gas.

In order to further explain the invention, two experiments carried out are reported below.

Example 1 ν

An experiment was carried out on a half-scale scale. As the silicon raw material, crushed quartz crystal of rock crystal type having an impurity content of less than 100 ppm and having a particle size of about 0.1 mm was used. The "reaction chamber" consisted of briquetted carbon black. As a reducing agent, propane (gasol) was used, and as a carrier gas and plasma gas, washed reducing gas consisting of CO and H ~ was used.

The supplied electric power was 1,000 kWh. 2.5 ₅ kg of SiO ₂ / min was supplied as a raw material, and 1.5 kg of propane / min was supplied as a reducing agent.

In the experiment, a total of 300 kg of high-purity silicon

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produces α The average consumption of electrical energy was about 15 kWh / kg of produced Si.

The experiment was carried out on a small scale, which is why the heat loss was large. With gas recovery, the consumption of electrical energy can be further reduced and the heat losses are also reduced significantly in a larger system.

Example 2

Under otherwise the same conditions as in Example 1 > high-purity silicon using powdered carbon black was prepared as a reducing agent.

1.2 kg carbon black / min was supplied.

In this experiment, 200 kg of high-purity Si were produced. The average consumption of electrical energy was about 13.5 kWh / kg of produced Si.

Claims (9)

APC 01 B / 248 46i / 3 62 033 18 846 1 3. \. '. Erfindungaanapruch A process for producing silicon from powdered siliceous material, characterized in that the powdered silicon dioxide-containing material is optionally injected together with a reducing agent by means of a carrier gas in a gas plasma, after which the thus heated silicon dioxide material together with the optionally present reducing agent and the high-energy plasma gas is introduced into a reaction chamber, which is surrounded by a solid piece-shaped reducing agent « 2 «method according to item 1, characterized in that the gas plasma is generated by allowing the plasma gas to pass through an electric arc in a so-called« plasma generator. Method according to points 1 and 2, characterized in that the arc is generated inductively in the plasma generator. 4 · Method according to points 1 to 3 _9, characterized in that the solid piece-shaped reducing agent is continuously fed to the reaction zone «» 5. The method according to points 1 to 4, characterized in that. Charcoal or coke solid particulate reductant consists of 6 · Method according to items 1 to 5, characterized in that the plaamagas from the reaction zone AP C P1 B / 248 461/3 62 033 18 24846 1 3 -V- recycled process gas böstent » 7. The method according to items 1 to 4, characterized in that for the production of high-purity silicon, which is intended as a raw material for solar cells and / or semiconductors as the silicon dioxide-containing material, a material having an impurity level of less than 0.1 wt. jS is chosen. 8. The method according to item 7, characterized in that the solid particulate reducing agent is selected from a group consisting of briquetted carbon black, briquetted petroleum coke, briquetted charcoal dust and piece-shaped charcoal. Method according to points 7 and 8, characterized in that the injected reducing agent is selected from a group consisting of powdered carbon black, wood-carbon dust, petroleum coke, hydrocarbons in gaseous form and liquid form, such as natural gas, propane, gasoline.