RU2639199C2 - Method for producing synthetic flux for steel-making production - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method includes mixing initial charge components based on secondary aluminium production wastes and a binder, subsequent moulding of the mixture. When mixing, sodium aluminate is used as a binder, and a reinforcing component in the form of borosilicate glass fibre is additionally introduced in the amount of 0.3-3.6 wt %. The produced mixture is briquetted, the ready briquettes are placed in a sealed container with a gas-discharge path, and consumption of the binder depends on specific surface of the secondary aluminium production wastes and determined according to empirical equation.

EFFECT: invention makes it possible to produce a complex steel melting flux with low energy consumption and high strength properties of briquettes with simultaneous stabilisation of refining slags.

2 cl, 6 tbl, 1 dwg

Description

The invention relates to the metallurgical industry and can be used to obtain flux used for refining various grades of steel, guidance and liquefaction of slag in the ladle-furnace (ACP) units and vacuum cleaners for out-of-furnace steel processing.

A known method of producing a complex flux for steelmaking (RF patent No. 2202627, IPC C21C 5/36, C22B 1/00, op. 20.04.2003), including mixing by co-wet grinding of a mixture consisting of dolomite and an iron-containing material, drying, firing and high-temperature pelletizing of the charge in an oxidizing atmosphere in a rotary tube furnace, subsequent cooling of the resulting flux. Before grinding, a binder additive is introduced into the charge in an amount of 1.5-3.5% by weight of the charge and preliminary pelletizing of the charge is carried out in the low-temperature part of the furnace.

The disadvantage of this method is the high energy costs of obtaining flux, since the grinding of flux mixture is carried out in a wet environment, which leads to the need for subsequent drying of the material.

Known steelmaking flux and method for its production (RF patent No. 2296800, C21C 5/36, C21C 5/54, C22B 1/216, op.10.04.2007). The flux contains, mass. %, calcined substance: magnesium oxide base; calcium oxide 3.0-12.0; iron oxides 5.0-15.0; alumina 0.2-2.5; silica 2.0-5.0. The components of the mixture, consisting of natural magnesite, caustic magnesite and siderite ore, are mixed directly in a rotary kiln with the following content of the components of the mixture, mass. %: natural magnesite 40-65; caustic magnesite 20-55; siderite ore is 5-15 and calcined at a temperature of 1550-1700 ° C, providing a rolled product. The calcined material is cooled and classified to obtain the finished product in the form of a fraction of more than 4 mm and a fraction of less than 4 mm. Screening of calcined material fractions of less than 4 mm is used as the main starting material for the manufacture of coarse flux briquetting method.

This method of producing steelmaking flux does not contain operations in a wet environment, but the flux is fired at a sufficiently high temperature in a rotary kiln, which also leads to significant energy consumption in its production.

A steelmaking flux and a method for producing it are known (RF patent No. 2374327, IPC С21С 5/36, op. November 27, 2009), which includes mixing magnesia-containing and binder materials burned in a rotary kiln, briquetting the resulting mass with additional introduction of aluminum-containing waste from the production into the charge aluminum, as well as carbon-containing materials, or natural magnesite, and / or brucite.

In the known method, the energy consumption for the production of flux is reduced, since not the entire volume of the charge for the preparation of the flux is burned, but only the magnesia-containing part, the remaining components of the charge are introduced before briquetting. However, the energy costs for firing the magnesian part are still quite large.

The closest in technical essence and the achieved effect to the claimed invention is a method for producing synthetic flux for metallurgical processes of iron and steel smelting (RF patent No. 2465342, IPC С21С 7/00, 7/076, op. 27.10.2012), including mixing fluorocarbon-containing waste electrolytic production of aluminum with a particle size of not more than 1 mm, a calcium-containing component and water, agglomeration of the mixture to obtain material with a particle size of 10-100 mm and drying. As a calcium-containing component, a material is used containing active calcium oxide or forming it during the smelting of iron or steel. The weight ratio of Ca: F in the mixture is maintained equal to 0.8-1.3. In this case, finely dispersed fluorocarbon-containing wastes are used in the form of dust from electrostatic precipitators, or gas treatment sludge, or coal foam flotation tailings, or crushed spent coal lining, or as a waste mixture with a fluorine content of at least 9 weight. % As a calcium-containing component, solid waste generated during the production of acetylene from calcium carbide, or a material containing calcium carbonate or containing calcium hydroxide with a particle size of not more than 1 mm, is fed to the mixing.

The disadvantage of this method is the presence of the operations of introducing water before mixing and drying the agglomerated material, which complicates the technology for preparing flux and leads to additional energy costs. In addition, this flux contains a significant amount of fluoride compounds, which corrode the lining and adversely affect the environment.

A common drawback of all the examined fluxes is the absence of stabilizers in their composition, which, when using such fluxes to dilute high-calcium refining slags, give the slag stability from scattering due to polymorphic transformations of dicalcium silicate, which is part of such slags.

The technical result of the present invention is to provide a method for producing a complex steelmaking flux with low energy consumption, high strength properties of briquettes while ensuring stabilization of refining slags obtained using flux according to the proposed method.

The specified technical result is achieved by the fact that in the method for producing synthetic flux for steelmaking, comprising mixing the components of the initial charge based on secondary aluminum production waste and a binder, subsequent molding of the mixture, according to the invention, sodium aluminate is fed as a binder for mixing and an additional reinforcing component is introduced into in the form of borosilicate glass fiber in an amount of 0.3-3.6 mass. %, the resulting mixture is briquetted, finished briquettes are placed in a sealed container with a gas outlet, and the flow rate of the binder (N,%) depends on the specific surface of the OPVA and is determined by the equation:

N = -2.28 + 0.049⋅S _beats , where S _beats are the specific surface area of OPVA, m ² / g, N is the binder consumption,%.

While briquetting the mixture is carried out at a pressure of 20-100 MPa.

When implementing the inventive method, the waste from the production of secondary aluminum (OPVA) before briquetting is mixed with sodium aluminate and borosilicate glass fiber. After briquetting, the components of the raw material mixture come together and begin to react with each other. Aluminum metal, which is part of OPVA, reacts with sodium aluminate by reaction

As a result of reaction 1, due to an increase in the concentration of Al ₂ O ₃ , the caustic module of sodium aluminate in this reaction changes from 0.6 to 0.3. Since reaction 1 is exothermic, the pressed briquettes are heated to a temperature of about 60 ° C, evaporating the excess water, causing coagulation of Al ₂ O ₃ and curing of the mixture. Thus, with low energy consumption, briquettes acquire significant strength and have low humidity.

When the reaction (1) proceeds, a significant amount of hydrogen is released. With significant production volumes, an explosive mixture can form in the workshop, so briquettes are immediately placed in a sealed container with a gas outlet immediately after pressing to prevent hydrogen from entering the workshop space.

The borosilicate glass fiber included in the briquettes is a reinforcing component and increases the strength of the resulting briquettes.

High-calcium refining steelmaking slags are subject to silicate decomposition due to the presence of a significant amount of low-temperature modification of belite (2CaO⋅SiO ₂ ) γ-C ₂ S - shennonite, resulting from complex polymorphic transformations of high-temperature modifications of belite (α-C ₂ S, α'- ₂ S and β-C ₂ S) when cooling the slag to 830 ° C, accompanied by an increase in volume and subsequent decay of the slag into dust fractions.

ионами бора

, препятствующих трансформации β-C₂S в γ-C₂S при полиморфном превращении.Stabilization of such slags is possible when processing them with the proposed flux, which includes sodium aluminate as a binder and borosilicate glass fiber as a reinforcing component. The stabilizing effect of the borates that make up the borosilicate glass fiber is based on the partial replacement of C ₂ S ions in the structure of belite

boron ions

, preventing the transformation of β-C ₂ S into γ-C ₂ S during polymorphic transformation.

в высокотемпературных модификациях белита α-C₂S, α'-C₂S и β-C₂S на родственные ионы, входящие в состав оксидов MgO, Al₂O₃, Fe₂O₃, BaO, K₂O, Р₂О₅, Cr₂O₃, Na₂O, MnO₂. Такое замещение приводит к изменению радиуса ионов и трансформации молекулы двухкальциевого силиката, препятствуя полиморфным превращениям белита. Ионы натрия и алюминия, входящие в состав алюмината натрия, стабилизируют высокотемпературную модификацию белита β-C₂S.The stabilizing effect of sodium aluminate is based on isomorphic substitution of Ca ^{2+ ions} and

in high-temperature modifications of belite α-C ₂ S, α'-C ₂ S and β-C ₂ S to related ions that are part of the oxides MgO, Al ₂ O ₃ , Fe ₂ O ₃ , BaO, K ₂ O, P ₂ O ₅ , Cr ₂ O ₃ , Na ₂ O, MnO ₂ . Such a substitution leads to a change in the radius of the ions and the transformation of the dicalcium silicate molecule, preventing polymorphic transformations of belite. The sodium and aluminum ions that are part of sodium aluminate stabilize the high-temperature modification of β-C ₂ S belite.

It was experimentally established that to ensure stability of the slag with a content of 30 mass. % C ₂ S must be entered In ₂ About ₃ in an amount of from 0.02 mass. % to 0.05 mass. % When the content of C ₂ S in the slag is 80 mass. %, you must add 0.25 mass. % B ₂ O ₃ . Since in the manufacture of borosilicate glass fiber using a raw mixture containing, by weight. %, quartz (SiO ₂ ) - 27.55, microcalcite (CaCO ₃ ) - 33.9, kaolin - 29.57%, boric acid - 8.87-8.89%, the resulting glass fiber has a chemical composition, mass. % SiO ₂ - 38.3%, CaO - 26.4%, anhydrous kaolin 35.3%, B ₂ O ₃ - 7.0%. Accordingly, to ensure stability of the slag with a minimum content of Belite in it, 30 mass. % it is necessary to introduce 0.3% borosilicate fiberglass, and when the slag content is 80% belite, the required flow rate will be 3.6%.

Based on laboratory studies, a relationship was established between the specific surface area of the raw materials of OPVA at a pressing pressure of 20-100 MPa and the consumption of a binder, sodium aluminate, necessary for the preparation of a high-quality briquette. The specific surface of the initial OPVA ranges from 50 to 200 m ² / kg, which affects the consumption of the binder. The results of determining the specific surface area of OPVA and binder costs are presented in the figure and table 1.

The figure shows a graphical dependence of the flow rate of the binder on the specific surface of the OPVA.

The obtained empirical equation is suitable for calculating the flow rate of a binder depending on the specific surface of the OPVA. In conventional units of notation, the regression equation is as follows:

where N is the binder consumption,%; S _beats - the specific surface of the OPVA, m ² / year

To increase the strength of the flux obtained, the prepared mixture is briquetted at a pressure of 20-100 MPa, which ensures good contact between the components and allows to reduce losses during transportation and storage of the material. At a compaction pressure of less than 20 MPa, part of the flux (about 7%) disintegrates, and a force of more than 100 MPa is impractical, since energy costs increase.

An example embodiment of the invention

At the first stage, the strength characteristics of briquettes prepared by the method claimed in the present invention were studied.

The initial mixture for obtaining the proposed flux was prepared on the basis of secondary aluminum production waste (OPA) - dust (fineness less than 100 microns, humidity not more than 1.5%) and slag (fineness not more than 3-5 mm) of secondary aluminum production. The chemical composition of OPVA is shown in table 2.

The specific surface area of the OPVA determined on the PSX-4 device by the method of air permeability was 67 m ² / kg. The calculation according to equation (2) indicates that to ensure the normal strength of the briquette in the OPVA, it is necessary to introduce about 1.0 mass. % binder.

The components of the raw mix were mixed for 1-2 minutes in a rotating drum - pelletizer. Immediately after mixing, the raw material mixture was pressed at a pressure of 20 and 100 MPa. Finished briquettes, having the shape of a spheroid with a diameter of 60 mm and a thickness of 40 mm, were placed in a sealed chamber with a gas outlet for the removal of hydrogen.

After 24 hours, the briquettes were determined by the compressive strength. The test results are presented in table 3.

According to the test results, it can be seen that at a pressing pressure of 50 MPa, the minimum normative manipulative strength (1.2 MPa), briquettes reach a content of 1.0 mass in the mixture. % sodium aluminate. The introduction of reinforcing borosilicate glass fiber with a diameter of 9.2-10.2 μm and a length of 9.0 mm before pressing into the raw material mixture showed that when reinforcing glass fiber is introduced into the initial mixture simultaneously with sodium aluminate in the entire claimed range, it increases the briquette strength by an average of 25% .

At the second stage of the studies, the stabilizing effect of the flux prepared in accordance with the claimed method on the refining slag of a typical composition was determined.

The chemical composition of the refining slag is shown in table 4.

The initial mixture to obtain the proposed flux was prepared on the basis of secondary aluminum production waste (OPA) - dust and slag from the production of secondary aluminum. The binder and reinforcing components were mixed with OPVA and pressed at a pressure of 50 MPa. Obtained by the proposed method, the briquettes were introduced into the model slag in an amount of 10 mass. %, were placed in a muffle furnace and heated to a temperature of 1350 ° C. After the mixture was completely melted, the slag was kept at this temperature for 15 minutes and cooled together with the furnace.

After cooling, the degree of stability of the slag was determined, equal to the ratio of the amount of mass of the sample that did not pass through a 063 sieve, referred to the mass of the initial sample, multiplied by 100%.

The experimental design and stabilization results of the slag with the joint introduction of a binder and reinforcing components are shown in table 5.

The test results are shown in table 6.

According to the test results, it is clear that slag stabilization with the joint introduction of a binder and reinforcing components occurs when the content of sodium aluminate is more than 1.0%, and borate glass is more than 0.28%. Thus, the lower limit of the content of borate glass is taken equal to 0.28 mass. %, and the binder consumption is determined by calculation, depending on the specific surface area of the OPVA. The upper limit of the content of the binder and borate glass is taken for economic reasons, so that a slight introduction of these components does not lead to a significant increase in the cost of flux produced by the proposed method.

The use of industrial waste in the proposed method for producing synthetic flux for steelmaking provides an increase in the technical and economic indicators of the metallurgical process and the production of flux material, which has a complex effect on the phase composition of high-calcium refining slags.

Claims (5)

1. A method of producing a synthetic flux for steelmaking, comprising mixing the components of the initial charge based on secondary aluminum production waste (OPVA) and a binder, subsequent molding of the mixture, characterized in that sodium aluminate and a reinforcing component in the form of borosilicate glass fiber are used as a binder in an amount 0.3-3.6 wt. %, and the resulting mixture is briquetted, and the finished briquettes are placed in a sealed container with a gas outlet, while the flow rate of the binder N is determined depending on the specific surface of the OPVA according to the equation: N = -2.28 + 0.049⋅S _beats , where S _beats - the specific surface of the OPVA, m ² / g, N - binder consumption,%. 2. The method according to p. 1, characterized in that the briquetting of the mixture is carried out at a pressure of 20-100 MPa.

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