RU107579U1 - SILICON FURNACE LINING FOR SILICON PRODUCTION - Google Patents

Abstract

 Lining of an electric arc furnace for the production of silicon, containing a metal casing, a layer of heat-insulating material, brickwork, a filler layer of carbon material, side and hearth carbon blocks, characterized in that the layer of heat-insulating material is made of asbestos sheet, the brickwork is made of layers of heat-insulating and refractory brick, and a layer of carbon material between the layer of refractory brick and carbon blocks is made of a soot layer with a thickness of not less than 1.4 the thickness of the side angle native block.

Description

The proposed technical solution relates to metallurgy and can be used in the production of silicon by carbothermic reduction in electric arc furnaces.

The lining of the furnace is one of the determining factors in the technological process for producing silicon, which ensures the high quality of the product and long-term trouble-free operation of the equipment.

A known lining of a bath of an ore-thermal electric furnace, which includes a metal case, a heat-insulating layer of granular material, refractory masonry of walls made of bricks and coal blocks, in which the vertical seams between the coal blocks and brickwork along the entire perimeter of the walls are made of finely divided alumina (RF patent No. 21115874 , F27D 1/00, 1998, [1]). The use of a layer of finely dispersed alumina prevents the oxidation of coal blocks and increases the service life of the lining. However, this structural design of the lining does not fully provide the heat-insulating properties and safety requirements for the operation of the furnace, in particular, the temperature on the outer surface of the metal casing is not more than 60 ° C.

A lining of an ore reduction furnace is known, comprising a metal casing, a heat-insulating backfill, brickwork, coal side and hearth blocks, which is additionally provided with vertical layers of fillers of carbon mass and coke with a grain size of 15-25 mm, placed between the brickwork and the side coal blocks (A. S. USSR No. 1504476, F27D 1/00, 1989, [2]).

By purpose, technical nature, the presence of similar features, this solution is selected as the closest analogue.

A disadvantage of the known solution is the instability of the composition of the aggregates at high temperature loads, the provision of incompletely insulating properties, the prevention of the penetration of impurities from the lining into the melt and the safety requirements for the temperature of the outer surface of the casing.

The objective of the proposed technical solution is to improve the quality of the obtained silicon, increase the service life of the furnace lining and comply with safety requirements for the temperature of the outer surface of the metal casing.

Technical results include increasing the insulating properties of the lining, preventing the diffusion of impurities of elements from the lining into liquid silicon, and preventing the violation of the integrity of coal blocks.

Technical results are achieved in that in the lining of an electric arc furnace for the production of silicon, containing a metal casing, a layer of heat-insulating material, brickwork, a filler layer of carbon material, side and hearth carbon blocks, a layer of heat-insulating material is made of asbestos sheet, brickwork is made of layers heat-insulating and refractory bricks, and the layer of carbon material between the layer of refractory bricks and carbon blocks is made of a soot layer not less than e 1.4 thickness of the side carbon block.

A comparative analysis of the proposed technical solution with the solution selected as the closest analogue shows the following.

The proposed lining and lining according to the closest analogue are characterized by similar features:

- metal casing;

- a layer of insulating material;

- brickwork;

- a filler layer of carbon material;

- side and hearth carbon blocks.

The proposed lining is also characterized by signs that are different from the signs characterizing the lining according to the closest analogue:

- a layer of thermal insulation material is made of sheet asbestos;

- brickwork is made of layers of heat-insulating and refractory bricks;

- a layer of carbon material between the layer of refractory bricks and carbon blocks is made of a layer of soot;

- the carbon black layer is made with a thickness of at least 1.4 thicknesses of the side carbon block.

The presence in the proposed solution of signs that are different from the signs that characterize the solution according to the closest analogue allows us to conclude that it meets the condition of patentability of the useful model of "novelty."

The technical essence of the proposed solution is as follows.

In the production of high-quality silicon, for example for solar cells, in a carbothermic manner, the question arises of protecting the reduced product (Si) from the influence of the furnace lining. The recovery process is carried out under the condition that the temperature of the inner wall of the shaft of the furnace from carbon blocks reaches 2000 ° C. In this case, boron actively diffuses from the refractory lining to silicon. It has been established that when the temperature of the fireclay lining is reduced to a temperature of not more than 800 ° C, boron diffusion ceases (Grabmeier, Siemens, Chernyakhovsky LV, Russia). The goal is achieved by creating a heat-insulating layer between graphite blocks and chamotte, which prevents the diffusion of boron from the lining into the melt. Such material may be carbon black, graphite felt and other carbon materials. The proposed solution uses a soot layer as a material having a high thermal resistance and is more technologically advanced when installing the lining.

The thickness of this layer is determined by calculation and depends on the thickness of the carbon lining, furnace power, process temperature. Varying the thickness of the soot layer allows you to change both the type of materials used to manufacture the lining, and to regulate their consumption, depending on the design features of the furnace, on technological needs and taking into account the reduction in the cost of the lining, simplification and reduction of installation time and increase the effective life of the lining. In addition, when using a soot layer of the required thickness, the requirement to safely conduct the process according to the temperature of the outer surface of the metal casing is not more than 60 ° C.

The results of experiments to determine the necessary and sufficient thickness of the soot layer are shown in table 1.

Table 1 №p \ p The thickness of the side carbon block, mm Soot layer thickness, mm The temperature of the inner surface of the fireclay, ° C The boron content in silicon, ppm. Outside temperature. ° C one fifty 65 826 1.30 68 2 fifty 70 800.6 1.005 60 3 fifty 78 780 1,0003 58 four fifty one hundred 732.0 1,0003 57 5 fifty 120 700,0 1,0002 56.3 6 fifty 150 650 traces 53.4

For high-power furnaces with a technological temperature of ≈2000 ° С, the thickness of the soot layer should be at least 1.4 of the thickness of the side carbon block. When the layer thickness is less than 1.4 of the thickness of the side carbon block, it is not possible to prevent the diffusion of boron into liquid silicon. The use of a carbon black layer of more than 1.4 thicknesses of the side carbon block provides the necessary degree of purity of the obtained silicon by impurities, but increasing the thickness of the carbon black layer by more than two times the thickness of the carbon side block is advisable for constructive changes in the lining: changing the thickness of the layers of materials, the use of other materials. In this case, an additional thermal calculation is required taking into account the thermophysical properties of the materials.

The lining of the electric arc furnace contains (Fig. 1) a metal casing, 1, 5 mm thick, a layer of heat-insulating material from sheet asbestos, 2, 5 mm thick, brickwork from a layer of diatomaceous brick, 3, 130 mm thick, from a layer of refractory brick, 4 , 130 mm thick, carbon black filler layer, 5, 78 mm thick, side carbon blocks, 6, 50 mm thick, and hearth carbon blocks, 7.

The lining of the electric arc furnace operates as follows. The heat flow from the working space of the furnace through the skull (not shown) formed during the operation of the furnace, through the carbon blocks 6, passes through a layer of porous carbon filler from soot 5, and then through layers of refractory brick 4, diatomite brick 3, a layer of heat-insulating material made of sheet asbestos 2 and reaches the metal casing 1. In this case, when the layers of the lining are heated, elements from the lining materials diffuse towards the silicon melt in the furnace. The presence of a layer of carbon filler from carbon black 5, 78 mm thick (1.56 thickness of the side carbon block), provides a temperature on the inner surface of the fireclay lining of ~ 780 ° C, which prevents the diffusion process. The calculation of the thicknesses of the layers of brickwork (refractory and heat-insulating), the thickness of the layer of sheet asbestos, also provides a temperature on the outer surface of the metal casing of ~ 58 ° C (according to the requirements of TB no more than 60 ° C), which ensures the safety requirements for the operation of the furnace.

INFORMATION

1. RF patent №2115874, F27D 1/00, 1998

2. A.S. USSR No. 1504476, F27D 1/00, 1989

Claims (1)

Lining of an electric arc furnace for the production of silicon, containing a metal casing, a layer of heat-insulating material, brickwork, a filler layer of carbon material, side and hearth carbon blocks, characterized in that the layer of heat-insulating material is made of sheet asbestos, the brickwork is made of layers of heat-insulating and refractory brick, and a layer of carbon material between the layer of refractory brick and carbon blocks is made of a soot layer with a thickness of not less than 1.4 the thickness of the side angle native block.