RU2151738C1 - Charge for production of silicon and method of preparing molding material for production of silicon - Google Patents

Abstract

FIELD: industrial inorganic synthesis. SUBSTANCE: charge is composed, wt. %: quartzite, 35-45; wood cuttings, 19-26; oil coke, 11-15; charcoal, 7-10; gas-purification electrofilter dust from silicon production process, 4.5-11; alkaline binder, 0.5-1.3. Part from 10 to 30% of silica-carbon-containing charge is in the form of preliminarily molded material. The latter is prepared by mixing above- mentioned fine silica-containing material, 25-50%, with carbon- containing reducing agent, oil coke containing at least 70% of fraction up to 8 mm, 55-70%, and alkaline binder, 1-15% aqueous solution of sodium alkali, 3-5%. followed by molding into material with fineness 6 to 50 mm and drying to moisture content 6-8%. Process can be used in semiconductor engineering area. EFFECT: reduced cost due to lower content of expensive charge components and more efficient utilization of the charge. 5 cl, 3 tbl

Description

 The present invention relates to the preparation of charge materials and the production of silicon in electrothermal furnaces.

 Currently, the production of silicon produces a significant amount of both silica-containing and carbon-containing waste, which are particles with a size of 1 μm-10 mm. Wastes are represented by small fractions of quartzite, dust from gas purification and small fractions of reducing agents. The presence of these wastes in the process increases consumption ratios, energy consumption, loading of sludge fields, increases the cost of the product, and pollutes the environment.

 The most important tasks in a market economy are: the involvement (full or partial) of waste in the production process; replacing expensive charge components with cheaper ones; increasing the reactivity of materials and the mixture as a whole.

 The solution to these problems will improve the technical and economic indicators of silicon production, improve the environmental situation.

 The main direction for reducing the amount of waste is returning it back to the process in the form of charge materials.

Known technical solutions aimed at processing waste silicon production:
- finely dispersed silicon wastes (<5 mm) by feeding them into the furnace after stopping the supply of the mixture to it while reducing the furnace power by 1.4-1.5 times the original power (A.s.SSSR N 1518300, С 01 В 33 / 02, 1989, [1]);
- coating a carbonaceous material with a layer of fine dust of a gas treatment fraction of not more than 0.1 mm (A. s. USSR N 1479415, C 01 B 33/02, 1989, [2]).

 The disadvantages of the known solutions are that a significant part of these recyclable waste, due to its small size, does not take part in the technological process, because it is either taken out of the furnace by a gas stream or evaporates at a high temperature without being able to react, i.e. again turns into waste, in addition, significant loss of material and dust during loading.

 To reduce the loss of fine wastes, it is necessary to bring them into a compact form.

The following solutions are known in this direction:
- a method for producing silicon, in which briquettes made from a mixture of dust from a gas-treatment fraction of -8 + 0.04 with sulfite-alcohol liquor are introduced into the charge in an amount of 3-14 wt.% (A.C. USSR, N 1344735, С 01 In 33/02, 1987, [3]), but the disadvantages of this solution are the low reactivity and strength of the briquettes;
- adding to the composition of the mixture of briquetted dust gas purification fraction -8 + 0.04 mm in the amount of 14.5 - 32 wt.%, and before briquetting a fraction of -4 + 0.04 mm is isolated from it, subjected to magnetic separation and the non-magnetic component is combined with the remaining dust (AS USSR N 1535825, С 01 В 33/02, 1990, [4]), although the known solution allows to reduce the supply of iron with a charge, but at the same time requires two additional stages - screening and magnetic separation, which increases the cost of silicon. The strength of dust briquettes is not high enough, significant losses of material in the process;
- a method of preparing a carbon reducing agent in which petroleum coke (pitch coke) -8 mm calcined to 1200 ^° C for 12 minutes is mixed with liquid coal tar in an amount of 28-30 wt.%, agglomerated and heat treated at 950 ^° C for 50 min (Pat. RF N 2032616, 01 B 31/00, 1995, [5]), while achieving an increase in the reactivity of the carbon part of the charge, reducing the coefficient of excess carbon in the charge, but the method requires significant energy consumption for crushing, grinding and heat treatment ;
- a method for producing silicon, in which silicon-containing raw materials (quartzite fines, quartz sand) are mixed with carbon-containing reducing agents (lignin, poorly sintering coals or products of their coking, semi-coking), briquetted, heat treated and used in the technological process, in addition, they can be used as part of the charge briquetted waste from the woodworking industry (AS USSR N 190356, C 01 B 33/02, 1967, [6]);
- molded raw materials for the production of silicon, containing, wt.%: sand-40, neftekoks-50, oil binder with a softening temperature of 87 ^o C-9, amorphous powder of silicon dioxide with a specific internal surface of 800 m ² / g, (Pat. USSR N 1524806, C 01 B 33/02, 1989, [7]);
- briquetted mixture to obtain technical silicon, containing, wt.%:
Quartz sand - 30-50
Hydrolysis lignin - 45 - 60
Petroleum Coke - 5 - 10
petroleum coke is pre-crushed to a particle size of less than 3 mm, dehydrated lignin to a moisture content of 12-15%, briquetted under pressure of 80-95 MPa (Pat. RF N 2049057, С 01 В 33/025, 1995, [8]);
- a method of preparing a charge for smelting silicon, comprising mixing silica-carbon-containing materials and coal tar pitch in an amount of 19-33 wt. %, heating the mixture to 180-245 ^o C with a speed of 18-27 deg / min and briquetting (A. S. USSR N 1666443, 01 01 33/02, 1991, [9]).

 The disadvantages of the known solutions [6-9]: significant costs for the preparation of briquetted mixture [7,8,9], insufficiently high reactivity, incomplete processing of waste from silicon production.

 Known agglomerated charge for smelting silicon, containing, wt.%: Finely divided silica-containing material 45-55, finely dispersed carbon-containing material 30-35, sodium alkali 5-8, powdered silicon 0.5-2, silica fume 7.5-2 (Pat. RF N 2049057, C 01 B 33/025, 1995, [10]).

 Obtained by a well-known solution, the agglomerated mixture has high porosity, mechanical strength and reactivity, but at the same time, significant labor and energy costs for the production of briquettes, because all charge is briquetted. The high cost of the charge, because to increase the reactivity it is necessary to add silica fume 1-150 microns.

 Closest to the proposed solutions in terms of technical nature and the achieved result is a method for producing silicon, which includes feeding a furnace charge containing quartzite and a carbon-containing reducing agent to the furnace top, briquetting with a gas-cleaning dust binder, introducing briquettes into the charge and reducing smelting, in which briquetting is additionally fed quartzite fractions -5 + 0 mm, quartz sand, carbon-containing reducing agent fractions -6 + 0 mm in quantities that provide a mass ratio in the briquette carbon and silicon dioxide (0.3-0.9): 1 (Pat. USSR N 1655900, С 01 В 33/02, 1991, [11]).

 In the well-known solution, the materials supplied for briquetting require additional part-time work (screening of fine fractions of the reducing agent and quartzite, crushing of quartzite) and equipment.

 The charge loaded together with briquettes is heterogeneous, which reduces the efficiency of its application.

 The objective of the proposed technical solutions is to reduce the cost of a commercial product.

 The technical result is to reduce the content of expensive components in the composition of the mixture and the use of production waste, as well as more efficient use of the mixture (increasing the reactivity of the mixture as a whole, reducing the waste content in the process).

The technical result is achieved in that the mixture for the production of silicon, including quartzite, wood chips, petroleum coke, charcoal and material molded from dust of a gas purification, carbon reducing agent and an alkaline binder, additionally contains finely divided silica in the form of dust from gas-purifying electrostatic precipitators of silicon production and a binder for the following ratio of components, wt.%:
Quartzite - 35 - 45
Wood chips - 19 - 26
Petroleum Coke - 11 - 15
Charcoal - 7 - 10
Silicon production gas purification electrostatic dust - 4.5 - 11
Alkaline binder - 0.5 - 1.3
and the molded material contains in an amount of 10-30% by weight of the mixture.

The technical result is also achieved by the fact that in the method of preparing a molded material for silicon production, comprising mixing a finely divided silica-containing material in the form of dust of gas purification of silicon production with a carbon-containing reducing agent and an alkaline binder, molding and drying, petroleum coke is used as the carbon-containing reducing agent, and fed to the molding the mixture of the following composition, wt.%:
Petroleum Coke - 55 - 70
Silicon production gas purification electrostatic dust - 25-50
Alkaline Binder - 3 - 5
with obtaining material with a particle size of 6-50 mm and a moisture content of 6-8%, and petroleum coke containing a fraction of not more than 8 mm in an amount of not less than 70 wt. %, and for mixing as an alkaline binder serves 10-15% aqueous solution of sodium alkali.

 The technical essence of the proposed invention is as follows.

 Part of the charge, supplied in the form of a preformed material, supplied in an amount of 10-30% by weight of the charge, is the active-reaction zones in the composition of the charge, which increases the reactivity of the charge as a whole.

 Downloading the molded charge in the proposed amount reduces the consumption of scarce and expensive reducing agents (charcoal), increases the reactivity of the mixture as a whole, using petroleum coke waste (fraction <8 mm) and dust from gas purification electrostatic precipitators, i.e., they are processed in the proposed solution and go into production with minimal cost and silica, and carbon-containing waste of the main production.

 In addition, according to confirmed data (Radchenko NF et al. On the optimal size of petroleum coke in the production of silicon. Non-ferrous metals N 7, 1987, [12]), in the proposed embodiment, the properties of the fine reducing agent were used to the maximum and the composition of the silica-containing finely dispersed was optimally selected raw materials in the form of dust from gas purification electrostatic precipitators of silicon production (25-50 wt.%), mixed with petroleum coke (preferably fractions of not more than 8 mm in an amount of not less than 70 wt.%), an alkaline binder (preferably an aqueous solution of sodium alkali tions 10-15%) to provide briquettes with high strength, reactivity, and ensures high reactivity of the batch as a whole. The proposed solutions reduce the cost of a marketable product by eliminating expensive reducing agents in the mixture by increasing the reactivity of the mixture (the reaction in briquettes initiates the reaction in the mixture, a more complete reduction reaction in the briquettes using silicon production waste as components). The content in the charge of the indicated silica-containing and carbon-containing components, wt.%: Quartzite 35-45, wood chips 19-26, petroleum coke 11-15, charcoal 7-10, dust of electrostatic precipitators of silicon production 4.5-11, alkaline binder ( 10-15% aqueous solution of sodium alkali) 0.5 - 1.3 provides the necessary and sufficient conditions for the high reactivity of the mixture as a whole, reducing the waste content in the process.

 In addition, loading as a part of the total charge of 10-30% of the preformed silica-carbon-containing material not only allows you to comprehensively process silicon production waste, but also increase the reactivity of the charge as a whole and reduce the cost of a commercial product due to the cost of the charge.

In the method for preparing a molded charge, comprising mixing a silica-containing material in the form of dust from a gas-purifying silicon production with a carbon-containing reducing agent and an alkaline binder, molding and drying, petroleum coke is used as a carbon-containing reducing agent, and a mixture of the following composition is used for molding, wt.%:
Petroleum Coke - 55 - 70
Silicon production gas purification electrostatic dust - 25-50
Alkaline Binder - 3 - 5
with obtaining material with a particle size of 6-50 mm and a moisture content of 6-8%.

 Moreover, neftecox is used, containing a fraction of not more than 8 mm in an amount of not less than 70 wt.%, And as a binder - 10-15% aqueous solution of sodium alkali.

 The above composition of the mixture (component, quantitative and fractional composition), the size of the resulting molded material and its moisture content provide high strength molded mixture, high reactivity.

A comparison of the proposed solutions with the prototype (AS USSR N 1655900, С 01 В 33/02, 1991) revealed:
1) the proposed mixture differs from the prototype in the following:
a) their component and quantitative composition in the charge;
b) the use of production wastes in the form of gas cleaning dust both as part of briquettes and as part of the main charge;
c) the amount of molded material used in the charge (10-30 wt.% by weight of the charge), the prototype is 20.5-22.5 wt.%.

2) the proposed method differs from the prototype in the following:
a) the component composition of the briquettes is the same as the components of the main mixture;
b) in the composition of the proposed material for molding, components are used that provide the maximum reactivity of the briquettes (neftekoks containing a fraction of not more than 8 mm in an amount of not less than 70 wt.%);
c) the optimum size of the molded material is 6-50 mm and its moisture content is 6-8%.

 The above allows us to conclude that the proposed technical solutions meet the criteria of the invention of "novelty."

A comparative analysis of the proposed technical solutions with the prototype and other known in this field revealed the following:
- it is known to use finely dispersed silicon-containing waste in the process of silicon production [1,2];
- it is known to use briquettes containing dust of gas cleaning dust from the production of silicon of the fraction -8 + 0.04 mm [3.4];
- it is known to use small carbonaceous reducing agents in the charge in a compact form [5,6,8,12];
- known use in the production of briquettes containing finely divided silica-carbon materials [9,10,11].

 The analysis did not reveal technical solutions characterized by similar identical (equivalent) features with those proposed, which allows us to conclude that they meet the criterion of "inventive step".

 Preliminary pilot tests confirmed the effectiveness of the proposed solutions and allow us to conclude that there is “industrial applicability”.

 The proposed solutions not only improve the technical and economic indicators of the process by replacing some of the expensive charge materials and involve waste in production, but also improve the environmental situation by reducing the amount of waste sent to sludge fields.

During the tests, the options were tested:
1) the preparation of the molded mixture of the proposed composition with limit and transcendent ratios of the components, as well as determining the properties of the molded material;
2) the use of the proposed composition of the charge with the limit and prohibitive ratios of the components, using the preformed material in the composition of the charge, the definition of technical and economic indicators of the process.

 Preparation of molded mixture is as follows.

Petroleum coke - 60 wt.% (Including 45 wt.% Fractions <8 mm) is mixed with dust of electrostatic precipitators of silicon production - 36 wt.%. A 15% aqueous solution of sodium alkali (4 wt.%) Is added to the resulting mixture, mixed and formed by extrusion on an OGM-1.5 A aggregate. The obtained molded material with a particle size of 20-50 mm is dried on a PL-10 (TK) metal belt conveyor for 20-30 minutes at a temperature of 200-260 ^o C, using a heat generator G2, 5A.

 Extrusion molding is preferable since It does not require significant energy costs and sophisticated equipment and, at the same time, allows to obtain pieces of material that are uniform in properties (density, porosity, strength) of a given size (6-50 mm), which, when used, increase the technical and economic indicators of the silicon production process.

 Data on the properties of the obtained molded material and the composition of the mixture are given in table. 1,2.

 The charge of the proposed compositions, including with a part of the preformed charge material, is loaded into the furnace according to the standard scheme according to the technological instruction and using standard equipment. The test results are given in table. 3.

Sources of information
1. A.S. USSR N 1518300, С 01 В 33/02, 1989.

 2. A.S. USSR N 1479415, C 01 B 33/02, 1989.

 3. A.S. USSR N 1344735, С 01 В 33/02, 1987.

 4. A.S. USSR N 1535825, С 01 В 33/02, 1990.

 5. RF patent N 2032616, C 01 B 31/00, 1995.

 6. A.s. USSR N 190356, C 01 B 33/02, 1967.

 7. USSR patent N 1524806, C 01 B 33/02, 1989.

 8. RF patent N 2036144, C 01 B 33/025, 1995.

 9. A.s. N 1666443, C 01 B 33/02, 1991.

 10. RF patent N 2049057, С 01 В 33/025, 1995.

 11. USSR patent N 1655900, С 01 В 33/02, 1991.

 12. Radchenko N. F. et al. On the optimal size of petroleum coke in the production of silicon. Tsvet.met.N 7, 1987.

Claims (5)

1. A mixture for the production of silicon, including quartzite, wood chips, petroleum coke, charcoal and material formed from dust of a gas treatment, carbon reducing agent and an alkaline binder, characterized in that it additionally contains finely divided silica in the form of dust of electrostatic precipitators of silicon production and a binder in the following ratio of components, wt.%:
Quartzite - 35 - 45
Wood chips - 19 - 26
Petroleum Coke - 11 - 15
Charcoal - 7 - 10
Silicon production gas purification electrostatic dust - 4.5 - 11
Alkaline binder - 0.5 - 1.3
and the molded material contains in an amount of 10-30% by weight of the mixture.  2. The mixture for the production of silicon according to claim 1, characterized in that as an alkaline binder it contains a 10 - 15% aqueous solution of sodium alkali. 3. A method of preparing a molded material for the production of silicon, comprising mixing a finely divided silica-containing material in the form of dust from a gas-purifying silicon production with a carbon-containing reducing agent and an alkaline binder, molding and drying, characterized in that petroleum coke is used as the carbon-containing reducing agent, and the mixture is charged with the following composition, wt.%:
Petroleum Coke - 55 - 70
Silicon production gas purification electrostatic dust - 25-50
Alkaline Binder - 3 - 5
with obtaining material with a particle size of 6 - 50 mm and a moisture content of 6 - 8%.  4. The method according to claim 3, characterized in that the petroleum coke containing a fraction of not more than 8 mm in an amount of not less than 70 wt.% Is fed to the molding.  5. The method according to claim 3, characterized in that for mixing as an alkaline binder serves 10 - 15% aqueous solution of sodium alkali.

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