COVER FOR AN ELECTROLYSIS CELL FOR PROCUDING ALUMINIUM

Abstract

The invention relates to non-ferrous metallurgy, more particularly to producing aluminium by electrolysis, and even more particularly to a structural element for covering the space above a melt in an electrolysis cell for producing aluminium by the electrolysis of cryolite-alumina melts. In a cover for an electrolysis cell for producing aluminium, which is in contact with a vapour-gas phase when the electrolysis cell is in operation and which is in the form of central and peripheral sections which are movably arranged relative to each other, the central and peripheral sections are made from a corrosion-resistant and erosion-resistant material which comprises 80.0-99.0 wt % of fluorophlogopite and 20.0-1.0 wt % of a refractory filler. The central sections of the cover may be permanently fixed on each anode rod, and the peripheral sections may be configured as convex panels rigidly and removably fixed on the top surface of a cathode and supported by the central section of the cover. Moreover, the refractory filler may be chosen from the following chemical substances: clay, calcium fluoride, rutile, sodium aluminosilicate, fluorapophyllite, nepheline, olivine, magnesium fluoride, and spinel. The end and side joints of the central and peripheral covers may be coated with a sealant layer in the form of a layer of alumina, and the central section of the cover may be provided with apertures. The use of this invention provides for the hermetic sealing of the cover, the reliability and safety of the structure, and a reduction in energy consumption.

Claims

1. A cover for an electrolysis cell for producing aluminium, which is in contact with a vapour-gas phase when the electrolysis cell is in operation and which is in the form of central and peripheral sections which are movably arranged relative to each other, characterized in that the central and peripheral sections are made from a corrosion-resistant and erosion-resistant material which comprises 80.0-99.0 wt % of fluorophlogopite and 20.0-1.0 wt % of a refractory filler.

2. The cover according to claim 1, characterized in that central sections of the cover are permanently fixed on each anode rod.

3. The cover according to claim 1, characterized in that peripheral sections are configured as convex panels rigidly and removably fixed on the top surface of a cathode and supported by the central section of the cover.

4. The cover according to claim 1, characterized in that the refractory filler may be chosen from the following chemical substances: clay, calcium fluoride, rutile, sodium aluminosilicate, fluorapophyllite, nepheline, olivine, magnesium fluoride, and spinel.

5. The cover according to claim 1, characterized in that the end and side joints of the central and peripheral covers are coated with a sealant layer in the form of a layer of alumina.

6. The cover according to claim 1, characterized in that the central section of the cover is provided with apertures.

Description

[0026] The object of the invention is to provide a multifunctional sectional <<artificial>> cover above electrolyte melt in electrolysis cells having an inert, backed anode and a Soderberg anode, which shows corrosion and erosion resistance to an aggressive vapour-gas environment of electrolysis cells.

[0027] The technical effect of the present invention is to provide a hermetically sealed cover, a reliable and safe structure, and a reduction in energy consumption.

[0028] Such technical result is achieved by that in a cover for an electrolysis cell for producing aluminium, which is in contact with a vapour-gas phase when the electrolysis cell is in operation and which is in the form of central and peripheral sections which are movably arranged relative to each other, the central and peripheral sections are made of a corrosion and erosion-resistant material which comprises 80.0-99.0 wt % of fluorophlogopite and 20.0-1.0 wt % of a refractory filler.

[0029] The central sections of the cover may be permanently fixed on each anode rod, and the peripheral sections may be configured as convex panels rigidly and removably fixed on the top surface of a cathode and supported by the central section of the cover. Moreover, the refractory filler may be chosen from the following chemical substances: clay, calcium fluoride, rutile, sodium aluminosilicate, fluorapophyllite, nepheline, olivine, magnesium fluoride, and spinel.

[0030] The end and side joints of the central and peripheral covers may be coated with a sealant layer in the form of a layer of alumina, and the central section of the cover may be provided with apertures.

[0031] The subject matter of the present invention is as follows:

[0032] a cover is manufactured in the form of large-sized products in the form of plates (FIG.1). The cover is arranged above the top surface of the anode so that it doesn't contact with the electrolyte melt and consists of sections. One complete cover section consists of a central section 1 and a peripheral section 2. The central section 1 of the cover is directly fixed on an anode rod by means of protrusions, wherein the distance from the cover surface to the electrolyte melt is selected based on the electrolysis cell type and specifications. This selected distance makes allowance for the likelihood of brief exposure to electrolyte run-ups onto the cover working surface when changing anode-to-cathode distance in the electrolysis cell. Cover central sections are provided with apertures for alumina dispensers arranged in accordance with an electrolysis cell feeding scheme. The peripheral section 2 of the cover is mounted so that one of its sides is supported by the cover central section, and another side is supported by the top surface of the cathode (such as a flange, an edge, a lining). The width of the peripheral section is equal to that of the central section and is a parabola in shape, thus enabling quick cover removal from the bath for technological operations to be performed. In this way, central and peripheral sections of the cover define a cover section for one anode on the blank or front side, and the number of cover sections corresponds to the number of anodes. Each cover section is movable together with the anode and can change own position separately from neighbor cover sections and neighbor anodes. The electrolysis cell cover permanently contacts the gas-air environment of the electrolysis cell and periodically contacts the electrolyte melt, that is why the cover is manufactured of the corrosion and erosion resistant material, proof to the aggressive vapour-gas environment of electrolysis cells having backed, self-baking, or inert anodes. The used cover material is not soaked and wetted with the cryolite-alumina melt. For cover manufacturing, fluorophlogopite or alumina slurries can be used. Independent movement of the cover allows for hermetic sealing of the operation space of the electrolysis cell having inert anodes and makes technological operations simple and mobile. Any cover section can be disassembled independently from the others and replaced with a new part.

[0033] One of the factors of variance for a fluorophlogopite cover is a chemical composition of an agglomerate in terms of the main component KMg.sub.3(Si.sub.3Al)O.sub.10F.sub.2*, because the change of material chemical purity results in the change of physical and chemical properties of the material, and consequently, its mechanical strength, heat conductivity, and corrosion and erosion resistance. When fluorophlogopite is used as the cover material, it is required to use the material containing the main component, fluorophlogopite, in the range of 80-99%, which will allow flexible usage of materials for different types of electrolysis cells. In addition to hermetic sealing, heat insulation of the operation space above a melt in an electrolysis cell, fluorophlogopite ensures melt and aluminium purity. Operational apertures in the central section of the cover allow using the cover for electrolysis cell feeding, cover installation and disassembling, and maintenance operations. To seal the joints of cover sections alumina is used, which is chemically similar to the fluorophlogopite material. Operational through-apertures in the ends of the cover central section in the electrolysis cell center provide removal of the gas-air mixture from the electrolysis cell to a gas removal system.

[0034] The procedure for preparation of the electrolysis cell having the claimed cover includes following steps:

[0035] Central and peripheral cover sections are produced from the machined blanks. Then, appropriate apertures are made in the produced sections according to location and position markings in the electrolysis cell. Next, these cover sections are placed on anodes mounted or being mounted in the following sequence: at first, the central section and then the peripheral section. The cover made of fluorophlogopite can be placed in an active electrolysis cell because this material is resistant to thermal shocks.

[0036] The electrolysis cell cover according to the suggested solution features improved reliability, provided by not only the corrosion and erosion resistance of a cover material but also by an independent structural feature of the sectional cover allowing access to any part of the electrolysis cell in a short time without significant intervention in the process. In addition, thermal expansion of the cover material is prevented due to the material properties, allowing free movement of the cover along adjacent covers.

[0037] The ease of the suggested cover manufacture process is ensured by the processability of the inventive cover material (fluorophlogopite) and the simplicity of a fastening system on an anode rod allowing for section functionality ensured by means of the product strength and the shape of fastening surface and by supporting the central cover.

[0038] Recently conducted long-term laboratory and pilot-scale tests of the claimed fluorophlogopite cover according to the suggested technical solution have shown its functional ability and efficiency.