RU2424343C2 - Procedure for melting refined ferro-chromium - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: according to procedure at products of melt teeming part of boron-containing slag is left in bath of furnace. Siliceous reducer and ore-lime part of charge is loaded on part of boron-containing slag left in a bath of the furnace. 10-20 minutes prior to products of melt teeming mixture of material containing boron oxide with siliceous reducer and lime is charged into slag melt under electrodes. Also, material containing boron oxide in terms of B₂O₃ is introduced at amount of 0.20-0.30% of weight of slag melt.

EFFECT: reduced losses of chromium with slag, improved performance characteristics and production of slag resistant to silicate decomposition.

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Description

The invention relates to the metallurgical industry and can be used in the production of ferroalloys.

A known method of smelting low-carbon ferrochrome [1], based on the reduction of chromium and iron oxide of chromium ore by silicon ferrosilicon in the presence of calcium oxide.

Signs that match the features of the invention are:

- charge loading;

- slag guidance;

- joint reduction of chromium and iron oxides by silicon ferrosilicochrome in the presence of calcium oxide;

- increased content of magnesium oxide in the composition of chromium ore;

- lowering the temperature of the recovery processes due to the introduction of additives into the mixture;

- release of smelting products.

Reasons that hinder the achievement of the technical result:

- deficiency and high cost of added additives;

- the absence of an effect that ensures the stabilization of high-temperature forms of dicalcium silicate of slag after cooling and obtaining a melting product with new technological properties.

The slag obtained by this method mainly contains dicalcium silicate, which, when cooled, passes into the γ-form with an increase in volume by 10-12%, as a result of which the slag is crushed into powder. The latter circumstance limits the scope of application of slag and negatively affects the environment.

The closest in technical essence and the achieved result is a method of smelting refined ferrochrome [2], in which the following features are common with the inventive method:

- loading the mixture, consisting of ferrosilicochrome and ore-calcareous part;

- increased content of magnesium oxide in the composition of chromium ore;

- the introduction of boron oxide into the furnace, which ensures stabilization of the slag from silicate decomposition during cooling;

- slag guidance;

- recovery smelting;

- release of smelting products;

- obtaining a slag with a stable structure.

The achievement of the expected technical result is hindered by the following circumstances.

The introduction of boron oxide into the furnace as a part of the mixture in order to stabilize the slag from silicate decomposition during cooling leads to an excessive decrease in the process temperature due to the early formation of a fusible boron-containing slag melt, which contributes to the cold running of the furnace, a decrease in the completeness of reduction reactions and, as a result, an increase loss of oxide chromium with slag and the deterioration of the technical and economic indicators of smelting ferrochrome.

The basis of the invention is the task to limit the decrease in temperature of the process at the stage of early slag formation and to ensure the completeness of the reactions of reduction of chromium from ore-lime melt with high intensity.

The expected technical result is:

- reduction of chromium losses with slag;

- improvement of technical and economic indicators of smelting refined ferrochrome.

This object is achieved by the fact that in the process of smelting refined ferrochrome, including the loading of a siliceous reducing agent, the ore-lime part of the charge and the material containing boron oxide, slag guidance, reduction smelting and the release of melting products, the release of melting products is carried out leaving part of the boron-containing in the furnace bath slag, and the siliceous reducing agent and the ore-lime part of the charge are loaded onto the part of the boron-containing slag remaining in the furnace bath, and 10-20 minutes before the release of melting products for electric ktrody charged into the slag melt blend material comprising boron oxide with a reducing agent siliceous and lime, the material comprising boron oxide by weight of the B ₂ O ₃ is introduced in an amount of 0.20-0.30% by weight of the slag melt.

A causal relationship between the set of essential features of the claimed invention and the achieved technical result is as follows.

1. Release of smelting products, leaving part of the boron-containing slag in the furnace bath, loading the siliceous reducing agent and the ore-lime part of the charge onto the part of the boron-containing slag remaining in the furnace, while 10-20 minutes before the melting products from the furnace are released under the electrodes into the slag melt loading a mixture of a material containing boron oxide with a siliceous reducing agent and lime allows one to transfer the main emphasis of the effect of boron oxide directly to slag, and not to ore-lime melt. In this case, the process of melting the mixture and the reduction of chromium from the ore-lime melt are carried out with a minimum content of boron oxide stored in the furnace bath (in the skull and the residual amount of slag melt) after the release of melting products, since the residual boron oxide in the furnace provides the necessary fluidity and temperature a melt with a high content of magnesium oxide to undergo reduction reactions with sufficient completeness and intensity, if introduced in a mixture with siliceous, it will restore oil and lime for electrodes.

2. The introduction of a material containing boron oxide into the furnace before release, when converted to B ₂ O ₃ in an amount of 0.20-0.30% by weight of the slag melt, allows slag to provide the necessary rheological properties that improve the conditions of hydrodynamic fusion (coagulation) and deposition of reduced particles from slag to metal. This ensures the stabilization of the slag after cooling from silicate decomposition.

The introduction of boron oxide-containing material into the furnace before the release of melting products in the specified amount ensures that the required content of boron oxide is kept constant and adjustable in the required limits in the furnace bath (due to the skull and residual slag mass), ensuring optimal conditions for the refining ferrochrome smelting process with the best technical and economic indicators (TEP).

Thus, the claimed invention meets the criterion of "novelty."

When analyzing the compliance with the criterion of "inventive step", no information sources were found that indicate the popularity of the proposed technological solutions for their functional purpose and the task of the invention.

The inventive technological solutions can be implemented in industry, and the expected technical result follows from the combination of essential features of the invention, which indicates compliance with the criterion of "industrial applicability".

The method of smelting refined ferrochrome is implemented as follows. The mixture is charged in the usual manner and melted and reduced. 10-20 minutes before the release of melting products under the electrodes, material containing boron oxide is loaded into the slag melt, in terms of B ₂ O ₃ , in an amount of 0.20-0.30% by weight of the slag melt. As a material containing boron oxide, for example, calcium borate can be used. For better absorption by the melt, calcium borate is introduced together with siliceous reducing agent and lime. The amount of reducing agent in the composition of the mixture is determined depending on the state of operation of the furnace, the melting period, the silicon content in the metal, the smelted grade of ferrochrome, etc. The amount of lime in the composition of the mixture is determined from the calculation of the binding of silica to dicalcium silicate formed by the reduction of chromium oxides from the slag melt with silicon reducing agent introduced into the mixture. If a siliceous reducing agent and lime are introduced into the composition of the mixture together with calcium borate, the used amount of these materials is removed first from the composition of the charge loaded into the furnace at the beginning of melting. 10-20 minutes before the release of the melting products, a cross is broken between the electrodes (if it has formed), and a mixture of calcium borate with a siliceous reducing agent and lime is gradually loaded into the slag melt through a central tube to prevent boiling and slagging of the electrodes and sides of the bath, achieving full assimilation of the mixture materials by the melt. Within 5-10 minutes after the introduction of the mixture, it is absorbed by the melt with slight stirring due to the interaction of silicon reducing agent with chromium and iron oxides. After ~ 10 minutes after loading the mixture, a metal sample is taken from the furnace bath for silicon content, if necessary, additional metal refining is carried out and the melting products are released.

During processing of the slag melt by calcium borate, the rheological properties of the slag change, its viscosity decreases, the conditions of hydrodynamic fusion (coagulation) and deposition of reduced metal particles improve. As a result, metal loss with slag is reduced, yield is increased, and the use of chromium is increased.

After the release of the smelting products, a certain part of the slag containing boron oxide remains in the furnace bath. Boron oxide is also contained in the skull of the furnace bath. After loading the next charge of the charge and the beginning of the next melting, the boron-containing slag remaining in the furnace bath helps to accelerate the melting of this charge and the earlier start of reduction reactions. Under the conditions of using high-magnesium chromium ores for smelting refined ferrochrome, which has been taking place in Russia and Kazakhstan in recent years, the presence of a small (see below) content of boron oxide in the charge has a positive technological effect on the process of smelting refined ferrochrome. The value of this “useful” (or “favorable”) content of boron oxide in the ore-lime melt depends on the composition of the charge filling (mainly on the weight and quality of lime, as well as on the MgO content in the chromium ore) and the grade of the alloy to be smelted. On average, it is 0.10-0.20% In ₂ About ₃ . The maintenance of this content of B ₂ O ₃ in the furnace bath during smelting can be controlled by the amount of boron oxide introduced before release into the slag melt.

The minimum amount of boron oxide (0.20% of the mass of the slag melt) is determined by the minimum required final content of B ₂ O ₃ in the slag (0.30% B ₂ O ₃ ), which guarantees the stability of the slag structure from silicate decomposition after cooling.

The maximum amount of boron oxide introduced (0.30% by weight of the slag melt) is determined by the upper limit of the “useful” (favorable) content of B ₂ O ₃ in the ore-lime melt. When the content in the ore-lime melt is more than 0.20%, the process temperature decreases, as a result, the so-called “cold” course of the furnace occurs, at which the completeness of the reactions of the reduction of chromium oxides from the melt decreases. As a result, the residual Cr ₂ O ₃ content in the slag increases, and the loss of chromium with dump slag increases. To correct the “cold” course of the furnace, a portion of lime in the charge filling is increased, which, in turn, leads to an increase in the slag rate and further to an increase in the energy consumption and the deterioration of other technical and economic indicators.

The justification of the amount of boron oxide introduced into the furnace into the melt before the release of the melting products was carried out according to the results of pilot tests. Boron oxide was introduced in the form of calcium borate (В ₂ О ₃ ≤43%) in the mixture with ferrosilicochrome and lime in a weight ratio of 1: 2: 2, respectively. The mass of slag melt was determined by the amount of CaO introduced with lime and CaO content,%, in the slag. The results of the influence of the content of boron oxide in the slag on some technical and economic indicators of the smelting of low-carbon ferrochrome are shown in table 1.

Table 1 The dependence of technical and economic indicators of the smelting of low-carbon ferrochrome on the amount of B ₂ O ₃ introduced into the slag melt in the furnace before the release of melting products No. p / p Indicator Units rev. The amount of ₂ About ₃ introduced into the furnace,% by weight of the slag melt base 0.15 0.20 0.25 0.30 0.35 0.40 one The content of ₂ About ₃ in the slag melt in the furnace before the introduction of calcium borate (residual content in the bath of the furnace) % - 0.05 0.10 0.15 0.20 0.25 0.28 2 The content of ₂ About ₃ in the final slag % - 0.18 0.28 0.37 0.45 0.52 0.60 3 Stability of the structure of slag from silicate decomposition, degree of decomposition % 100.0 30,0 0,03 0,0 0,0 0,0 0,0 four Slag rate hl / me 3.31 3.26 3.16 3.10 3.23 3.41 3.60 5 The content of Cr ₂ About ₃ in the final slag % 5.30 5.25 4.83 4.67 4.97 5.73 6.30 6 Loss of oxide chromium with slag % of the set chrome 12.41 12.11 10.80 10.24 11.35 13.82 16.04 7 Specific consumption per 1 t of Cr: Lime bases kg 2513 2480 2400 2350 2450 2590 2730 Chrome ore bases kg 3348 3357 3310 3229 3325 3410 3490 Ferrosilicochrome (48% Si) bases kg 1217 1218 1187 1120 1210 1232 1267 Electric power kWh 5052 4975 4830 4735 4930 5205 5495

From the above data it follows that the introduction of a material containing boron oxide into the slag melt in the furnace contributes to the improvement of technical and economic indicators of refined ferrochrome smelting. This is especially evident in the specific consumption of lime. The slag ratio and power consumption directly depend on this indicator. With an increase in the amount of boron oxide introduced in excess of 0.30% by weight of the slag melt, the conditions for the reduction of chromium significantly worsen, as a result, the loss of oxide chromium with slag and the consumption of chromium ore increase. An increase in the consumption of lime leads to an increase in the oxidizing ability of the slag and, as a consequence, an increase in the consumption of ferrosilicochrome. Recommended limits on the amount of input In ₂ About ₃ are 0.20-0.30% by weight of the slag melt. The optimal value is 0.25%.

During industrial tests, the optimal time was determined for the introduction of boron oxide into the slag melt before the release of slag. When introduced into the melt less than 10 minutes before the release, boron oxide was not completely assimilated by slag, as evidenced by the spread in the content of В ₂ О ₃ in the final slag and the residual content of В ₂ О ₃ in the furnace bath (table 2). The introduction of boron oxide over a period of more than 20 minutes before the release led to overheating of the fluid-borne boron-containing slag due to the exit of the electrodes to the “open” arc and the useless consumption of electricity. In addition, the prolonged operation of the furnace at the end of the smelting with superheated liquid slag led to intensive erosion of the upper layers of the furnace lining, especially in the notch area. The time limits for introducing boron oxide into the furnace into the slag melt to solve the problem are 10-20 minutes before the release of melting products. The optimal time for introducing boron oxide into the melt is 15 minutes before the release of melting products.

table 2 Dependence of the content of В ₂ О ₃ in the slag on the time of introduction of boron oxide into the furnace into the slag melt (average values are given for 5 melts) Indicator Units rev. The input time In ₂ About ₃ before the release of the heat *) 5 10 fifteen twenty 25 thirty The content of ₂ About ₃ in the final slag % 0.22 **) 0.30 0.35 0.37 0.37 0.37 The content of ₂ About ₃ in the bath of the furnace before the introduction of boron oxide into the melt in the next heat % 0.28 0.20 0.15 0.13 0.13 0.13 *) The amount of introduced In ₂ About ₃ in all experiments 0.25% by weight of the slag melt **) Slag partially crumbled

Information sources

1. A.G. Kucher, N.V. Novikov, N.T. Tadzhibaev and others. Improving the silicothermal process of smelting low-carbon ferrochrome. Steel, No. 4, 1995, pp. 31-33.

2. Patent of the Republic of Kazakhstan No. 12434 dated January 18, 2002

3. RF patent No. 2222629 of 03/18/2002

Claims (1)

A method for smelting refined ferrochrome, comprising loading a siliceous reducing agent, an ore-lime portion of a charge and a material containing boron oxide, inducing slag, reducing melting and releasing melting products, characterized in that the melting products are released with a part of boron-containing slag leaving in the furnace bath, siliceous the reducing agent and the ore-lime part of the charge are loaded onto the part of the boron-containing slag remaining in the furnace bath, and 10–20 minutes before the release of melting products under the electrodes into the slag melt The downloaded material mixture comprising a boron oxide with a reducing agent siliceous and lime, the material comprising boron oxide is charged in an amount providing a content of 0.20-0.30% B ₂ O ₃ by weight of the slag melt.