RU2554150C1 - Method and apparatus for carbothermal production of high-purity silicon - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method includes thermal reduction of quartzites to elementary silicon through a reducing gas mixture using plasma, wherein the process is carried out in a single step in counterflow of quartzites and the reducing agent, the reducing agent being a mixture of hydrocarbons and steam, the amount of which is not more than j the amount required for a conversion reaction, and the total amount of carbon contained in the hydrocarbons is at least 1.5 times more than the stoichiometrically required amount for full reduction of quartzites. The apparatus comprises an electric arc furnace 1, a plasmatron 3, a quartzite supply system 2, means of feeding the reducing agent 6; the plasmatron 3 with means of feeding the reducing agent 6 is located under a shaft 5 in the lower part of the furnace 1; the quartzite supply system 2 is placed in the upper part of the shaft 5, wherein the lower part of the furnace 1 is separated from the shaft space by a limiter 9, which controls the descent of quartzites from the shaft 5 into said lower part.

EFFECT: obtaining high-purity polycrystalline silicon using an environmentally safe method with high percentage output of silicon and low cost thereof.

2 cl, 1 dwg, 1 ex

Description

The invention relates to the field of chemical industry to technologies and devices, in particular, to obtain crystalline silicon of high purity.

The purity of the resulting silicon is determined mainly by the purity of the starting process materials. Currently, for the production of semiconductor silicon used in various electrical devices, the chlorosilane method is used. A known method of producing silicon, which is implemented in hydrogen reduction furnaces of chlorosilanes, for which deep purification has been worked out on an industrial scale (the book "Semiconductor Silicon Technology" edited by ES Falkevich, M., Metallurgy, 1992).

 The disadvantage of this method is that the technology for producing polycrystalline silicon remains very complex, multi-stage, expensive and most importantly environmentally hazardous.

The known technology for producing silicon by carbothermal reduction from silica in ore-thermal furnaces (book "Silicon Production", authors Chernykh A.E., Zelberg B.I., publ. "MANEB", Irkutsk, 2004). But this known method for producing silicon, as a rule, does not provide a level of purity that meets the requirements of semiconductor technology.

There is a method of producing silicon from silica, in which the process is carried out in two stages: at the first, silica is carbidized to produce silicon carbide, and at the second stage, at higher temperatures - up to 1900 ° C, silica is reduced by silicon carbide (A.S. 1579014, C01B 33/02, 07/27/96).

A known method of carbothermal reduction of silicon, which includes the preliminary preparation of briquettes containing silica and a carbon-containing reducing agent, and which are fed to the furnace laced with pure silica (patent RU 2383493, СВВ 33/025, 01.2006). As a carbon-containing reducing agent, materials with a content of at least 5% by weight of hydrogen are used.

The disadvantage is that the process is complex, multi-stage, and the purity of silicon does not meet the requirements of semiconductor silicon.

The closest in technical essence to the proposed invention is a method for producing crystalline silicon of high purity (patent RU 2385291, (С01В 33/023, 03/29/2010). In this method, which is selected as a prototype, the restoration of silicon-containing compounds to elemental silicon is carried out in a plasma reactor made of silicified graphite, in which quartz grains are placed and which is installed in a closed furnace under a plasma torch. A gaseous mixture of carbon monoxide and Orod in a volume ratio of 1: 1. Restoration is conducted at a temperature of 1900-2000 ° C, however, at present it is generally accepted that the energetically more favorable process of quartzite silicon recovery is the process conducted via the formation of silicon carbide..

The disadvantage is that due to the lack of free carbon in the reducing gas mixture in the method considered in the prototype, the process for producing silicon is time-consuming and energy-intensive.

The objective of the invention is to make the process of restoring silicon from quartzite less energy intensive and more productive. Using the proposed method, a technical result is achieved: the silicon recovery process becomes simpler - one-stage, dust removal is reduced, the percentage of yield and purity of the finished product increases, and the productivity of the process increases.

The above technical result is achieved by the fact that in the proposed method, the thermal reduction of quartzite to elemental silicon using a reducing carbon-containing gas mixture is carried out in a single step in counter flows, a mixture of hydrocarbons and water vapor is used as a reducing agent, the amount of which is not more than 1/4 necessary for the conversion reaction , and the total amount of carbon contained in the hydrocarbon was not less than 1.5 times the stoichiometrically required amount to implement the process of complete recovery of quartzites.

The technical result is also achieved by the fact that in the carbothermal device for producing high-purity silicon containing an electric arc furnace, the heat source is a plasmatron located under the furnace shaft through which quartzite is supplied. Any hydrocarbon (gaseous; liquid - through the nozzle; solid in the form of fine powder) with the addition of water vapor is fed into the zone of the electric arc discharge of the plasma torch. The supply of hydrocarbons and water vapor is carried out through special devices or through the electrodes of the plasma torch (plasmatrons). The reducing atmosphere of the furnace space will mainly consist of free carbon, free hydrogen and carbon monoxide.

Quartzite recovery will proceed according to the reaction:

SiO2 + 3С = SiC + СО (one) SiO2 + SiC = 2Si + CO2 (2)

Or the total reaction:

SiO2 + C = Si + CO2 (3)

The essence of the invention is illustrated by the drawing, which shows a General diagram of a device carbothermal production of silicon of high purity.

The device comprises an electric arc furnace 1 with a shaft 5. In the upper part of the shaft there is a quartzite supply system 2, there is also an exhaust gas outlet 7. A plasma torch 3 or electrodes 4 are introduced into the lower part of the furnace below the shaft. The lower part of the furnace is separated from the shaft space by a limiter 9, regulating the flow of quartzite from the mine to the bottom of the furnace. The supply of hydrocarbons in a mixture with water vapor 6 is carried out through a plasma torch or through electrodes. To drain the melt at the bottom of the furnace there is a notch 8.

The device operates as follows. Before supplying the starting materials to the furnace, the furnace space is heated by an electric arc burning in the plasma torch 3, or between the electrodes 4, to a temperature of at least 1600 ° C. Then, quartzite is loaded into the furnace 1 into the upper part of the mine 5 through the quartzite supply system 2, and a mixture of hydrocarbons and water vapor 6 is supplied to the lower part of the furnace through special devices or plasma torch electrodes. At the same time, the temperature of the furnace space is raised to a level of at least 2200 ° C. The shaft structure of the furnace with the lower position of the plasma torch ensures the opposite direction of the starting materials (quartzites move down the shaft, and the reducing gas mixture rises from the bottom of the furnace), which contributes to the active interaction of the reagents already in the shaft space of the furnace. In the temperature range 1600–1700 ° C, active carbidization of quartzites occurs inside the mine with the formation of SiC by reaction (1). When the resulting mixture of quartzites with silicon carbide moves to a region of higher temperatures, the process of silicon reduction proceeds to the stage of reaction (2). In addition, the organization of the oncoming movement of the reacting components in the present invention contributes to a more efficient use of thermal energy introduced into the furnace, and significantly reduces dust removal from the furnace.

The free hydrogen and carbon monoxide present in the reducing gas mixture, being good heat carriers, increase the efficiency of the reduction process by reactions (1) and (2) and contribute to loosening the solid reaction components coming from above. The limiter 9 located between the shaft and the lower part of the furnace also influences the quartzite flow. Reduced silicon accumulates on the hearth of the furnace and is removed from it through the groove 8. The active form of oxygen present in the furnace space contributes to the formation of volatile oxides of undesirable impurities (including boron and phosphorus) that are carried away by the gas stream. All these measures allow obtaining silicon with a purity of not less than 99.999% at a yield of not less than 90% and with a specific energy consumption of not more than 20 kWh per 1 kg of silicon.

Example. The carbon-containing material is acetylene (C2H2). To carry out the conversion reaction:

C2H2 + 2H2O = 3H2 + 2CO (four)

1.4 mass parts of water vapor must be supplied per mass part of acetylene. When using 1/4 of the amount of water vapor required for the conversion reaction, a gas mixture of the following composition will be formed as a result of the reaction:

C2H2 + 0.5H2O = H2 + 0.5CO + 1.5C (5)

In this case, two mass parts of free pyrocarbon are formed on three mass parts of acetylene.

When recovering quartzite by the formula (3), 3.3 mass parts of quartzite and 0.8 mass parts of carbon are required per mass part of the obtained silicon, or 1.2 mass parts of acetylene for the given example. Taking into account the disequilibrium of the reduction processes occurring in the furnace, it is advisable to feed 1.5 times more stoichiometrically necessary amount of carbon into the furnace, or in this case 1.8 parts by weight of acetylene.

In other words, to obtain 1 kg of silicon by the proposed method when using acetylene as a carbon-containing material, about 3 kg of quartzite, 1.8 kg of acetylene and 0.9 kg of water vapor will be needed.

The calculation of the ratio of the starting reagents when using other hydrocarbons is carried out in a similar way.

Thus, the proposed method for producing pure silicon in comparison with the prototype allows to simplify the process of silicon recovery while maintaining the purity of the final product, reduce heat loss with exhaust gases, reduce dust removal, which increases the yield of silicon and improves the energy and environmental performance of the process of silicon recovery.

Claims (2)

1. The method of carbothermal production of high-purity silicon, including thermal reduction of quartzite to elemental silicon using a reducing gas mixture using plasma, characterized in that the process is carried out in a one-stage process in counter flows of quartzite and a reducing agent, a mixture of hydrocarbons and water vapor is used as a reducing agent, amount which is not more than ¼ necessary for the conversion reaction, and the total amount of carbon contained in hydrocarbons is not less than 1.5 p of the excess of the stoichiometric amount required for the implementation of the process of full recovery of quartzite. 2. A carbothermal device for producing high-purity silicon containing an electric arc furnace, a plasmatron, a quartzite supply system, reducing agent supply means, characterized in that the plasma torch with reducing agent supply means is located under the shaft in the lower part of the furnace, the quartzite supply system is located in the upper part of the shaft, this lower part of the furnace is separated from the shaft space by a limiter that regulates the flow of quartzite from the shaft to the lower part.