JPS6230611A - Manufacture of silicon or silicon iron in low axis electric furnace and raw material molding therefor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for producing silicon or silicon iron using a low-axis electric furnace, and more specifically, the present invention relates to a method for producing silicon or silicon iron using a low-axis electric furnace. The containing raw material is first formed, then the raw material is mixed and integrated with silicon dioxide and introduced into a low shaft electric furnace, and the silicon dioxide in the raw material molding is carbonized at the top of the low shaft electric furnace at a temperature below 1600 ° C. A coke-structured agglomerate is formed from the raw molding carbon that was not used during the reduction reaction, and the above-mentioned integrated and doped molded silicon difluoride is reduced from the coke-structured agglomerate to silicon. of silicon carbide and carbon at the bottom of a low shaft electric furnace.
It is reduced to silicon at a temperature of 1800 to 2000°C or above, preferably 1800 to 2000°C. The present invention relates to a method for producing silicon or silicon iron in a low-axis electric furnace.

(Definitions of various terms) Silicon dioxide is the usual silicon carrier for all.

Specifically meant quartzite or quartz sand. The term "fine grains" refers to sand-fine grains, such as from 0.5 to 5 mm, preferably about 1 mm. The term "excess" means that the carbon not used in the raw molding to reduce silicon dioxide to silicon carbide is sufficient in quantity to form a coke-structured agglomerate. Reduction is generally carried out in two stages as follows.

+30 to 81 = SiG + 200S102 +
2SiO=3Si+200 In the second stage -silicon oxide is formed.

5i02 + O = SiO + CO Gaseous silicon monoxide reaches the top of the low axis electric furnace.

(Prior Art) In DE 34 11 371 A1, raw material moldings are produced by blocking. Although cold blocking with the addition of a bituminous binder has also been employed, carbon that can be reblocked in sufficient quantities by warm blocking is preferably employed. The raw material molding contains carbon in the form of a carbon carrier, such as petroleum coke, anthracite, graphite, which is inert to blocking.

Includes lignite cox 1 petroleum coke and similar materials. Of course, it is possible to produce silicon iron and metallic silicon from silicon by introducing suitable materials such as cut iron, granulated iron or iron oxide into a low-axis electric furnace. These known steps were fully satisfactory. In other words, silicon can be obtained in a low-axis electric furnace at a considerably high yield with low power consumption.

Therefore, the consumption of electrodes is also low. This is due to the fact that the coke-structured agglomerates are formed from the raw material molding in the first reduction step to silicon carbide and have a larger surface, i.e., the coke-structured surface, compared to the silicon dioxide and carbon in the carbon filling. This is due to the fact of the announcement. The internal specific surface area is usually less than 5rn'/g. The enlarged surface makes coke-structured agglomerates particularly reactive [7. and the agglomerates are characterized in terms of carbon reactivity within a certain range. However, gaseous silicon oxide is still liberated, and this fact has an adverse effect on silicon yield and current consumption.

OBJECTS OF THE INVENTION The object of the invention is to improve the process in such a way that it provides improvements in terms of current consumption and silicon yield, and in order to obtain very pure gold-4-silicon.

According to the invention, this object is achieved by forming coke-structured agglomerates having a total internal specific surface area of 5 m'/g or more, preferably 10 rrf/g or more during the reduction of silicon to silicon carbide in the molding. In such quantity as is formed,
A raw material molding doped with finely divided silicon dioxide having an internal specific surface area of at least 3 rn'/g is formed with a bituminous binder.

Furthermore, the reduction by coke structure agglomerates having an internal specific surface area of 5 rIf/g or more is achieved by performing the reduction at the bottom of the low-axis electric furnace.

Additional internal surface area is created in the coke-structured agglomerates by finely divided silicon dioxide powder which is first reduced to silicon carbide in a low axis electric furnace. During the process silicon monoxide is reduced. of course.

Particulate silicon dioxide also contributes to the formation of internal surface area. The term bituminous binder refers to all suitable bitumens, especially bituminous binders.
For example, it refers to a binder commonly used in road construction and blocking. The melting point is desirably 60°C or higher as much as possible.

It is of course necessary that the two individual finely divided silicon dioxide powders be as directly wetted as possible and mixed as homogeneously as possible with the bituminous binder. This is possible without difficulty by heating the bituminous binder and then liquefying it thoroughly by mixing it thoroughly with silicon dioxide, for example using the jet mixing principle. The term powdered silicon dioxide refers to very fine particles of silicon dioxide [highly dispersed amorphous silicon dioxide,
The Degus Manufacturers
(see data on Aerosil by Sa Manufacturers), but also relates to other very fine powders of silicon dioxide. In other words, according to the invention, the reactivity of the carbon surface is additionally induced in the coke-structured agglomerates by adding silicon dioxide to the raw molding, which is similar to the addition of silicon dioxide to the bituminous binder. This becomes possible. Reactivity-induced internal surface area is formed within the virgin carbon in the reduction of distined silicon powder to silicon carbide in the first stage reduction.

The internal surface area where reactivity is induced is predetermined by the amount of silicon dioxide powder and the amount of internal specific surface area. After coking the bituminous binder, the powdered silicon dioxide is heated to 1500°C.
The formation of silicon carbide, which takes place at temperatures above, is coated with a coke layer which is recognized. The surface of the powder remains transferred to the coke. Silicon carbide continues to develop its surface.

It is especially used up on the outer bounding surfaces of small crystalline silicon carbide. It is possible to control the increase in surface area very precisely by percentage in powdered silicon dioxide and binder.

In general, raw moldings weigh between 4 and 2
Formed by 0% weight blue binder.

Silicon dioxide is added to the binder in an amount of 2-20% by weight based on its weight.

According to a preferred embodiment of the invention, powdered silicon dioxide is used in the bituminous binder with an internal specific surface area of 200 to 5 oorn'/g. This is a useful point. The weight N% of the product and the internal surface area are all kept constant in relative proportions in the mixture. This means that for example, 30% by weight of silicon dioxide powder with an internal surface area of 1 orrp/g has the same effect as 0.7% by weight of silicon dioxide powder with an internal surface area of about 450rn'/g. means.

The raw molding is preheated at a temperature below the temperature that reduces silicon dioxide to silicon carbide.

During the pretreatment the bituminous binder is decomposed. The heating pre-treatment is carried out at the top of a low-axis electric furnace which can be maintained at a temperature of, for example, about 500°C. Apart from this, it is also possible to carry out the heating pretreatment as a pre-coking process by ordinary coking outside a low-axis electric furnace. In principle, various methods are possible for producing the raw moldings according to the invention. but.

The bituminous binder must be selected so that its solid form has sufficient strength for the molding body and is strong enough to maintain its shape during transport and in the low-axis electric furnace.

In the most effective embodiment of the invention, 200 to 80
Preferably, a certain amount of powdered silicon dioxide having a surface area of 0rr+'/g is used, resulting in an internal specific surface area of 5.
A coke-structured agglomerate of 0-100 rrII/g is formed in a low-axis electric furnace.

According to the invention, the raw molding can be introduced as a charge into a low-axis electric furnace in the form of a mixture of agglomerated silicon dioxide and added carbon. If metallic silicon or ferrous silicon is produced directly in a low-axis electric furnace, it can be added to the filling in the form of finely divided iron 9, for example cut iron or powdered iron, or alternatively iron oxide. Also.

In addition, raw material moldings containing finely divided iron may also be used. The raw molding always contains an excess amount of carbon with respect to the reduction of silicon dioxide to silicon carbide that takes place in the molding. Advantageously, the raw molding is formed to contain an excess of carbon of at least 50% by weight and up to 90% by weight with respect to the reduction of silicon dioxide to silicon carbide. If the teachings of the present invention are applied and very fine raw materials, especially very fine bituminous binders, are used in the form of double distilled petroleum products.

Silicon of extremely high purity is obtained.

Examples Examples illustrating the features of the invention are described in detail below, describing on the one hand the production of raw moldings and on the other hand the production of silicon.

The preparation of raw moldings with bituminous binder added with finely divided silicon dioxide is carried out by any relevant method. Flood blocking is used in the following example.

A binder produced from petroleum and having a softening point of 87° C. is heated to 170° C. and placed under vigorous stirring. The stirrer is designed in such a way that silicon dioxide powder with a high surface area (specific surface area aoorr?/g) is sucked through a conduit into the hollow shaft of the stirrer. Powdered silicon dioxide is distributed below the surface of the liquid binder and bonding is effected by vigorous stirring.

Constant circulation in the stirrer vessel ensures that the preferred 10% concentration of silicon dioxide is homogeneously distributed.

Binder foaming is kept within acceptable limits by the large agitator vessel area. The viscosity of the mixture increases as a result of the addition of powdered silicon dioxide. And the flow capacity is maintained. The mixture can be pumped, which is important for further processing.

Preheated sand and petroleum coke are added to the liquid mixture. This mixture is at a temperature of 110°C. Kneading is carried out under a steam atmosphere. The final mixture consists of powdered silicon dioxide, 40% sand and 50% petroleum coke.
% bituminous binder.

Powdered silicon dioxide is expressed at 1% of the total mixture.

This mixture is formed into blocks in a roller press at 104
Performed at °C. With this method, raw moldings are produced in the form of blocks with a volume of 18. After cooling to ambient temperature.

This molding has an average point compressive strength of 185 kg
and it meets all mechanical requirements regarding storage and transportation. Screen tests have shown that transport over relatively long distances by land and sea does not increase sieving by more than 2%.

It is important for the method according to the invention that the raw molding has the necessary flame stability. This term refers to fuels and reactants when heated or bombarded. This is a routine occurrence and occurs after each fill in a low axis electric furnace. It's a new cooling body.

This is because the gas has a temperature of 500° C. or higher and is constantly added to the surface of the thermal packing, where the gas is heated and combusted.

The raw material molding satisfies all expectations in this respect.

In the case of a wire basket mounted at the bottom in a low-axis electric furnace, the raw material mold slides under the surface of the filling after filling. The raw material molding is there at 1:11 (1tm).

It is then removed from the electric furnace using a wire basket and immediately introduced into an airtight container to form a coke-structured agglomerate. The point compressive strength of this agglomerate is measured after cooling. It was found that the compressive strength at this point had increased to 210 kg. Volatile components were reduced to less than 2%.

Some of the moldings were reheated in the laboratory. Weight loss up to 1600°C was measured, strength was tested, and internal surface area was measured. All prices were satisfactory. The internal specific surface area is 14,3 m'/
It was g. A test without the addition of powdered silicon dioxide was run in parallel, and its internal specific surface area was only 4.2 m2/g.

Silicon was produced using the raw moldings prepared as described above in a low axis electric furnace. The results were conclusive. Silicon yield is 10600 Kwh/
The current consumption of tSi was 96.6%. Parallel tests on raw material molding without the addition of powdered silicon dioxide resulted in only about 80% with an energy consumption of 12800 Kwh/tSi.

Claims (12)

[Claims] (1) In the reduction to silicon carbide, a raw material containing an excess amount of fine-grained silicon dioxide and carbon is first formed, and then the raw material is mixed with silicon dioxide, integrated, and introduced into a low-axis electric furnace to mold the raw material. 16 silicon dioxide in
Reduced to silicon carbide at the top of a low-axis electric furnace at a temperature below 00°C, a coke-structured agglomerate is formed from the raw molding carbon that was not used during the reduction reaction, and the above-mentioned integrated and additive-filled molding Silicon dioxide is
The silicon carbide and carbon from the coke-structured agglomerates are reduced to silicon in the bottom of the low-axis electric furnace at temperatures above 1600°C, preferably between 1800 and 2000°C. In the method for producing silicon iron, the total internal specific surface area of carbon is 5 m^2/g
above, preferably with an internal specific surface area of at least 3 m^2/g in such an amount that coke-structured agglomerates of not less than 10 m^2/g are formed during the reduction of silicon to silicon carbide in said molding. A raw material molding to which fine-grained silicon dioxide is added is formed with a bituminous binder, and further reduction with a coke-structured agglomerate with an internal specific surface area of 5 m^2/g or more is carried out at the bottom of a low-axis electric furnace. A method for producing silicon or silicon iron in a low-axis electric furnace, characterized by: (2) The raw molding is formed with a bituminous binder in an amount of 4 to 20% by weight relative to the total weight of the raw molding, and the binder contains silicon dioxide powder in an amount of 2 to 20% by weight relative to the bituminous binder. 2. The method according to claim 1, wherein: (3) The method according to claim 1 or 2, characterized in that fine-grained silicon dioxide powder having an internal specific surface area of 200 to 800 m^2/g is used. (4) Claims 1 to 3, characterized in that the raw molding is pretreated by heating at a temperature below the temperature at which silicon dioxide is reduced to silicon carbide, during which the bituminous binder decomposes. The method according to any one of the above. (5) The method according to claim 4, wherein the preheating treatment is performed in the upper part of a low-axis electric furnace. (6) The method according to claim 4, wherein the heating pretreatment is performed as a pre-coking process outside the low-axis electric furnace. (7) Claim 1, characterized in that coke-structured agglomerates with an internal specific surface area of 50 to 100 m^2/g are formed in the raw material molding due to the amount of silicon powder. 7. The method according to any one of items 6 to 6. (8) The raw molding is introduced as a filling into a low-axis electric furnace together with a mixture of carbon and silicon dioxide which is additionally added in integral form. The method according to any one of Item 7. (9) In the case of direct production of metallic silicon or silicon iron, iron in the form of fine iron particles, such as cut iron, iron powder, iron powder granules or iron oxide, is added to the filling. The method according to any one of items 1 to 8. (10) When directly producing metallic silicon or silicon iron,
9. The method according to claim 1, wherein the additionally used raw material molding contains, for example, cut iron, iron powder, iron powder granules or iron oxide. . (11) Producing silicon or silicon iron in a low axis electric furnace containing finely divided silicon dioxide and an excess amount of an inert carbon support such as petroleum coke, anthracite, graphite, etc. for the reduction of silicon dioxide to silicon carbide; In the raw molding for implementing the method, the raw molding is reblocked with a bituminous binder in an amount of 4 to 20% by weight based on the total weight, and the binder has an internal specific surface area of 5 m^2.
/g or more, preferably 200 to 800 m^2/g, and preferably 2 to 20% by weight of finely divided silicon dioxide. (12) The raw material molding according to claim 11, wherein the bituminous binder is decomposed by coking in the first stage of the raw material molding.