RU2550683C1 - Electrolysis unit for aluminium making - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: electrolysis unit consists of the following: cathode device with a pool with carbon bottom, the pool is formed by carbon blocks enclosed in metallic casing with flame proof and heat-insulating materials arranged between metallic casing and carbon blocks; anode device including carbon anodes connected to anode bus, the anodes are arranged in upper part of bath and absorbed in fused electrolyte; on the carbon hearth along the anode perimeter the pedestals, or the floats resistant to destruction in cryolite aluminous fusions and liquid aluminium are located. The top surface of a pedestal or a float acts higher than a level of cathodic aluminium and a pedestal or floats can be moved and/or replaced if necessary. Pedestals or floats are made of carbon, carbide of silicon, their combination. The top surface of the pedestal or the float is flat, convex, concave, or inclined to the horizon.

EFFECT: decrease of specific power consumption due to reduction of interpolar gap, ohmic resistance and voltage drop in interpolar gap, increase of current output due to increase of hydrodynamic resistance to movement of fusion near the aluminium-electrolyte interface along the anode perimeter and decrease of mixing of fusion and counter reactions of metal with anode gases.

6 cl, 6 dwg

Description

The invention relates to non-ferrous metallurgy, in particular to the electrolytic production of aluminum, and in particular to the design of electrolytic cells for producing aluminum.

Known electrolyzer [X. Chang, W. de Nora and J.A. Sekhar "Materials used in the production of aluminum by the Eru-Hall method." - Publishing House: KSU, Krasnoyarsk. - 1998], comprising a cathode device and an anode device. The cathode device comprises a bath with a coal bottom, laid out of coal blocks with mounted current leads enclosed in a metal casing. Between the metal casing and the coal blocks are placed refractory and heat-insulating materials. The anode device comprises carbon anodes connected to the anode bus. Anodes are placed at the top of the bath and immersed in molten electrolyte.

A disadvantage of the known design of the electrolyzer is that the technologies developed for it are characterized by a very high specific energy consumption W, defined by the equation

, где V - напряжение на ванне, В; η - выход по току, k - электрохимический эквивалент [кг/кА*ч]. $$W=\frac{v}{k\eta }$$

where V is the voltage on the bath, V; η - current output, k - electrochemical equivalent [kg / kA * h].

Usually in aluminum production technologies W = 13-15 kWh / kg of metal. However, this energy consumption is approximately 2 times greater than theoretically predicted. There are two reasons for this:

1. In voltage V, a large part is occupied by the ohmic voltage drop in the electrolyte, determined by the magnitude of the interelectrode (interpolar) gap (MPZ). Usually this distance is about 5 cm.

2. The current efficiency η decreases with a sharp increase in the interaction (the so-called "reverse interaction") of the anode products (carbon dioxide) and cathode products (dissolved aluminum) with increasing hydrodynamic mixing (circulation) of the electrolyte and / or metal.

Thus, one of the most important drawbacks of the above design is the relatively high ohmic resistance of the MPZ and high energy consumption.

Known electrolyzer for the production of aluminum [US 4405433, C25C 3/08, publ. 09/20/1983], consisting of an anode current lead, carbon anode, carbon cathode with additional elements located under the anode - “mushrooms” made of titanium diboride, insulation, electrolyte, liquid aluminum, blooms.

A disadvantage of the known design of the electrolyzer is the insufficient thermomechanical and chemical resistance of the “mushrooms” made of titanium diboride, especially at the metal-electrolyte boundaries; the difficulty of attaching the “mushrooms” to the bottom and the impossibility of such attachment in the existing electrolytic cells, the small contact area of the “mushroom” with the coal bottom, as well as the relatively high cost and the inability to quickly remove the “mushrooms” from the interelectrode gap if necessary, for example, lowering the anode onto cathode.

The closest technical solution, selected as a prototype, is an electrolyzer for aluminum production [RU No. 111540, C25C 3/06, publ. 12.20.2011], including a cathode device containing a bath with a carbon bottom, laid out of coal blocks with mounted cathode current leads, enclosed in a metal casing, with refractory and heat-insulating materials placed between the metal casing and the coal blocks, an anode device containing carbon anodes connected with an anode busbar located in the upper part of the bath and immersed in molten electrolyte, characterized in that on the coal hearth under each of the anodes there are cabinets with a higher specific electrical conductivity than electrolyte, resistant to destruction in cryolite-alumina melts and liquid aluminum, with the upper surface of the cabinet protruding above the level of cathode aluminum, and the cabinets are made with the possibility of movement and / or replacement if necessary.

The disadvantages of the known design of the electrolyzer are: the relatively large amount of space in the MPZ occupied by the stands, the weight and cost of the stands, the difficulty of moving and / or replacing the stands, if necessary. If it is necessary to use weighting agents located inside the cabinet, for example, cast-iron “weight” or pouring, this can reduce the reliability of the structure due to the difference in the coefficients of thermal expansion of materials, as well as the penetration of electrolyte through the pores of the cabinet to the material of the weighting agent, leading to its premature corrosion and contamination of the cathode metal . It is practically difficult to automatically control the vertical movement of the cabinet when the thickness of the cathode metal layer changes.

In addition to the above, a known drawback of the existing electrolytic cells with a horizontal arrangement of electrodes (Fig. 3, anode 1 and cathode 2) is the fact that the gases formed on the anode 1 rush to the edges of the anode, driving melt 4. Along the perimeter of the anode 1, where the anode gases 7 rush up, forming a hydrodynamic rarefaction at the aluminum-electrolyte interface, an aluminum wave 9 rising upward forms. At the top of the wave, aluminum particles can detach and, being trapped by gas bubbles 7, rush I up in the electrolyte 4 and the anode 1, wherein oxidized, i.e. a reverse reaction occurs, which reduces the current efficiency of the cell. As a result of this phenomenon, the current efficiency can decrease by approximately 0.3%.

The technical result of the invention is to reduce the specific energy consumption due to a decrease in the magnetic resistance, ohmic resistance and voltage drop in the magnetic resistance, an increase in current efficiency due to an increase in hydrodynamic resistance for the movement of the melt near the aluminum-electrolyte boundary along the perimeter of the anode, and, therefore, to reduce the mixing of the melt and reverse "reactions of the metal with anode gases.

The technical result is achieved in that in an electrolyzer for aluminum production, comprising a cathode device containing a bath with a carbon bottom, laid out of coal blocks with mounted cathode current leads, enclosed in a metal casing, with refractory and heat-insulating materials placed between the metal casing and the coal blocks, the anode a device containing carbon anodes connected to the anode bus, placed in the upper part of the bath and immersed in molten electrolyte, is a new Xia that it is provided with pedestals or floats, placed at the perimeter of the anode in the interpolar gap on the boundary surfaces of the aluminum cathode-electrolyte, the upper surface which protrudes above the cathodic aluminum, movable and / or replacement of stone or the float if necessary. Also new is the fact that the cabinets or floats are made of carbon blocks, in particular waste from the battle of standard hearth blocks, calcined anodes and / or electrodes, silicon carbide or a combination of carbon and silicon carbide located and / or floating on the boundary of the cathode metal / electrolyte due to the difference in density of materials. The outer surfaces of the cabinet or float are pre-coated or impregnated with protective inhibitory substances; from 1 to 240 curbstones or floats can be installed under each anode, which (floats) can be of any shape, for example parallelepiped, prism, cube, hexagonal, orthogonal, spherical, ellipsoid, hemispherical, cylindrical, as well as combinations of shapes, etc. . The upper surface of the cabinet or float is made flat, or convex, or concave, or inclined to the horizontal.

The invention is complemented by private distinguishing features, also aimed at solving the problem:

1. The floats have a density lower than that of the cathode metal, but greater than that of the electrolyte, float at the cathode metal / electrolyte interface due to the difference in density of materials, with the upper surface of the float protruding above the level of cathode aluminum.

2. Curbstones or floats can be made of carbon blocks, blocks of silicon carbide, or a combination thereof, in particular waste in the form of a battle of standard blocks, calcined anodes and / or electrodes located at the cathode metal / electrolyte interface due to the difference in material densities.

3. The cabinets or floats, before being placed in the MPZ space, are wrapped in a vacuum package of cathode metal foil and heated to a temperature as close as possible to the electrolysis temperature, but lower than the melting temperature of the cathode metal. Then the cabinet or float is placed in the space of the MPZ.

4. The cabinets can be made of silicon carbide and / or ANAPLAST type material.

5. The outer surfaces of the cabinet or float are pre-treated / impregnated with protective inhibitory substances.

6. Around the perimeter of the anode can be installed from 1 to 240 pedestals or floats.

7. The upper surface of the cabinets or floats is made flat, or convex, or concave, or inclined to the horizontal.

8. The floats can be of any shape, for example, parallelepiped, prism, cube, hexagonal, orthogonal, spherical, ellipsoid, hemispherical, cylindrical, combinations of various shapes, etc., but the design features and unification of the floats can be taken into account for optimal design and electrolysis process .

These differences allow us to conclude that the proposed technical solution meets the criterion of "novelty." Signs that distinguish the claimed method from the prototype are not identified in other technical solutions in the study of this and related areas of technology and, therefore, provide the claimed solution with the criterion of "inventive step".

The invention is illustrated by drawings 1-6.

The cell contains a carbon anode with an anode current lead 1, a carbon bottom (cathode) 2. The lower surface of the carbon anode is immersed in the electrolyte 3. A lining is laid inside the cell 6. The cell is equipped with a traditional device for feeding raw materials (alumina, fluorine salts, etc.) and drain exhaust gas 8, a device for supplying current 3 to the cathode 2. In the interpolar gap (MPZ) at the surface boundary of the cathode metal-electrolyte 4 along the perimeter of the anode 1, in the place where a wave of cathode metal 9 is usually formed (Fig. 3), bollards or float and in the form of a parallelepiped 10 (figure 4) or other forms or combinations thereof (figure 5), incl. a prism, cube, hexagonal, orthogonal, spherical, ellipsoid, hemispherical, cylindrical, and in the lower part of the cabinet or float there are through holes 12 for the flow of aluminum (figure 5). Unlike the pedestal, the float is attached with brackets 11 around the perimeter of the anode 1 (Fig. 6), and the brackets 1 are made of silicon carbide or a similar non-conductive material that is stable in cryolite-alumina melts and aluminum at temperatures of 950-1100 ° C.

Installation of an aluminum electrolyzer is as follows.

The cabinets or floats, before being placed in the MPZ space, can be wrapped in a vacuum package of cathode metal foil in order to close surface pores, protect the float from oxidation in air, improve heat transfer and are heated to a temperature as close as possible to the electrolysis temperature, but less than the melting point of the cathode metal. Then the float is placed in the space MPZ.

At the same time, the following TECs of aluminum electrolysis are improved: a decrease in the magnetoresistance, working voltage and specific energy consumption, an increase in current efficiency and electrolyzer productivity.

Claims (6)

1. An electrolytic cell for aluminum production, comprising a cathode device having a bath with a coal bottom, laid out of coal blocks with cathode current leads mounted in a metal casing, with refractory and heat-insulating materials placed between the metal casing and the coal blocks, an anode device containing carbon anodes connected to the anode bus, placed in the upper part of the bath and immersed in molten electrolyte, characterized in that it is provided with blocks in the form of curbstones or bench, placed on the perimeter of the anode in the interpolar gap on the boundary surfaces of the aluminum cathode-electrolyte, the upper surface which protrudes above the cathodic aluminum, adapted to move and / or replace them if necessary. 2. The electrolyzer according to claim 1, characterized in that the blocks in the form of pedestals or floats are made of carbon materials, in particular from waste in the form of a battle of standard hearth blocks, calcined anodes and / or electrodes, silicon carbide or a combination of carbon and silicon carbide, located and / or floating on the cathode metal-electrolyte boundary due to the difference in density of materials. 3. The electrolyzer according to claim 1, characterized in that the outer surfaces of the cabinet or float are pre-coated or impregnated with protective inhibitory substances. 4. The electrolyzer according to claim 1, characterized in that from 1 to 240 pedestals or floats are installed under each anode. 5. The electrolyzer according to claim 1, characterized in that the floats are made of any shape, for example in the form of a parallelepiped, prism, cube, hexagonal, orthogonal, spherical, ellipsoid, hemispherical, cylindrical, as well as in the form of combinations of the above-mentioned shapes. 6. The electrolyzer according to claim 1, characterized in that the upper surface of the cabinet or float is made flat, or convex, or concave, or inclined to the horizontal.

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