WO2018016989A1

WO2018016989A1 - Cathode current-conducting rod of an aluminum electrolysis cell

Info

Publication number: WO2018016989A1
Application number: PCT/RU2017/000369
Authority: WO
Inventors: Алексей Геннадьевич БУРЦЕВ; Александр Олегович ГУСЕВ; Евгений Рашидович ШАЙДУЛИН; Андрей Васильевич ЗАВАДЯК; Евгений Яковлевич ГИБЕРТ
Original assignee: Общество с ограниченной ответственностью "Объединенная Компания РУСАЛ Инженерно-технологический центр"
Priority date: 2016-07-19
Filing date: 2017-05-30
Publication date: 2018-01-25
Also published as: RU2657682C2; RU2016129595A

Abstract

The invention relates to non-ferrous metallurgy, and specifically to the design of a cathode current-conducting rod used in creating a cathode device of an aluminum electrolysis cell. Proposed is a cathode current-conducting rod comprising a metal base with an inner cavity, and an insert, made of a material having high specific electrical conductivity, installed in the inner cavity so as to be able to come into electrical contact with the metal base. The cathode current-conducting rod is made of one or of two or more rigidly-interconnected metal bases, and the insert is rigidly connected to a metal base via a connecting layer and is disposed on one or a plurality of lateral faces of the metal base. As a result, the invention provides for reduced drops in voltage in a cathode section by means of increasing the conductivity of a current-conducting rod, thus providing an acceptable electrical contact between an insert and a steel cathode rod for the entire service life of an electrolyzer, and a significant balancing of horizontal currents along the length of the cathode section.

Description

Cathode current-carrying rod

ALUMINUM ELECTROLYZER

FIELD OF THE INVENTION

The invention relates to the field of non-ferrous metallurgy, in particular, to the production of aluminum by electrolysis of molten salts, in particular to a device for a cathode current-conducting rod used in the construction of a cathode device of an aluminum electrolyzer.

State of the art

The cathode current-conducting rod, usually made of steel, is fixed in the groove of the carbon-containing cathode block using an electrically conductive material (cast iron, carbon paste or carbon glue). Carbon-containing cathode blocks with installed cathode current-carrying rods are called cathode sections, which are installed in the cathode casing of the electrolyzer and form the cathode device (cathode) of the aluminum electrolyzer.

The purpose of the cathode current-supplying rod is to remove electric current from the cathode, and transfer it to the external busbar, through which it enters the next cell. Current is transferred from the external busbar to aluminum busbar stacks (risers) connected to the anode busbar, then through the anodes, passes through the layers of electrolyte and metal, and then enters the cathode of the aluminum electrolyzer.

Known cathode section of an aluminum electrolyzer, including a cathode carbon block with a cathode current-supplying rod fixed in it using cast iron, which is made in the form two elements of the same cross section are rigidly interconnected, and the part of the rod located under the anode is made of copper, and the outer part is made of steel (patent SU 1260412 - С 25 С 3/08 А 1, 09/30/1986) One of the main disadvantages of this technical The solution is that the copper part of the cathode current-conducting rod does not have a continuous protective sheath that prevents air from entering and oxidizing copper at high temperatures, in addition, with increasing temperature, the strength of copper decreases significantly. All of the above leads to an increase in the contact resistance of the carbon block - the current-conducting rod and, accordingly, will lead to an increase in the voltage drop in the cathode of the electrolyzer.

Another disadvantage of the invention is the difficulty encountered in creating the connection of the copper part - the steel part of the current-supplying rod with an acceptable level of voltage drop in it. Since the problems associated with the difference in the thermal expansion coefficients of copper and steel, the high oxidizability and low strength of copper at temperatures close to the electrolysis temperature and the high temperature of the region of the connection of copper and steel do not allow to obtain a good connection.

These shortcomings explain the relatively low performance obtained by testing the proposed cathode section.

Blooms and a cathode block are used in an electrolyzer for aluminum production. The blooms are installed in the groove of the cathode block and sealed with an electrically conductive sealing material such as cast iron. To increase the effective electrical conductivity, a copper plate having a variable width along the length of the bloom is welded to the steel bloom by explosion welding. Explosion welding provides good electrical contact of copper and steel, and a variable width allows you to provide a given profile of the effective conductivity of the bloom. To prevent burnout, the copper plate is protected by a steel sheet welded on top of the copper plate and steel bloom.

Aluminum is obtained by electrolytic reduction of alumina in a cryolite electrolyte. This is carried out in a Hall-Herou electrolyzer, which is usually operated at low voltages and very high values of electric currents. A large electric current enters the cell through the anode structure and then passes through a cryolite electrolyte, through a layer of molten metal aluminum, and then enters the carbon cathode block. Electric current is removed from the cell by cathode blooms, which are connected to external busbars.

The flow of electric current through the aluminum layer and the carbon cathode block flows along the paths of least resistance. The electrical resistance in a conventional cathode bloom is proportional to the length of the current path from the point at which electric current enters the cathode bloom to the nearest external bus. The lower resistance on the current path, which begins at the points on the cathode bloom closer to the outer bus, causes the current passing through the aluminum melt layer and the carbon cathode blocks to deviate in this direction.

In particular, the main reason for the unsatisfactory characteristics of the cathode blocks containing graphite is the highly localized erosion of the cathode surface, due to which the blooms are exposed to aluminum metal. It was found that there is a relationship between the rapid degree of wear, the location of the area of maximum wear and the heterogeneity of the distribution of the cathode current. Therefore, there is a constant need to develop and ensure a more uniform distribution of the cathode current so that the localized wear rates of the cathode blocks are reduced and the life of the cell increases.

It is known that the electrical conductivity has become very small compared to a layer of aluminum metal, therefore, the outer third of the blues, which is closest to the side of the cell, carries most of the load, thus creating a very uneven distribution of the cathode current within each cathode block.

One of the methods that was used to achieve a more uniform distribution of the cathode current was to increase the conductivity of the bloom. This led to a decrease in the density of the localized current and, as a consequence, a decrease in the degree of wear. One of the methods that was found to increase electrical conductivity was to use copper inserts in bloom described in Patents US 5,976,333, IPC S25SZ / 16, publ. 11/02/1999 and US 3,551,319, IPC S25SZ / 16, publ. 12/29/1970

However, in both cases, the electrical connection of the copper core with the steel shell of the bloom was ensured by mechanical contact. At high temperatures, due to oxidation, the copper-steel contact resistance increases, which leads to a significant decrease in the effective electrical conductivity.

Although the use of a copper core with higher electrical conductivity is certainly useful for achieving a more uniform distribution of the cathode current, it only serves to reduce the degree of heterogeneity of the current distribution and is still not able to provide a balanced distribution of the cathode current across the width of the cathode block.

The intermittent electrical connection of the bloom with the cathode block described in Patent WO 2004/031452 A1, IPC S25CZ / 16, publ. 04/15/2004, leads to a more uniform distribution of current across the cathode block.

The use of intermittent termination portions according to this invention is effective for controlling the distribution of cathode current. This, however, can cause an additional drop in potential in the cell, leading to an increase in operating costs.

This problem was solved in patent RU 2303654, IPC S25SZ / 08, publ. 07/27/2007 where the copper insert helps to overcome this potential drop, and this also helps to increase the total cross section of the bloom. The cross-sectional area of the copper insert is preferably 20% of the cross-sectional area of the bloom. This copper insert, in combination with an increased bloom cross-sectional area, can significantly compensate for the additional potential drop caused by a stepwise decrease in the electric contact area of the side surfaces of the groove of the cathode block and the cathode rod stepwise.

Closest to the claimed invention in technical essence and the achieved result is the cathode section of an aluminum electrolyzer according to patent RU 2285754, IPC С25СЗ / 08, publ. October 20, 2006, in which the copper insert and the internal cavity in the current-supplying rod are made of rectangular cross-section, the cavity being made under the projection of the anode array and has a height of at least a third of the height of the current-supplying rod, and the copper insert is fixed with clearance from the side of the inner end and at the bottom of the current supply rod.

The main disadvantages of the prototype include: the need for high-precision fit of the copper liner and the cavity of the current-supplying rod to create good electrical contact along the entire length of the cathode current-supplying rod; It is problematic to ensure uniform (in length) electrical contact between the copper insert and the cavity of the current-supplying rod, since the rod is heated unevenly along the length (from 950 to 700 ° C) and, accordingly, the thermal expansion of the liner will be different, which means different electrical resistance of the current-supplying rod; the insecurity of the copper liner from the effects of the oxidizing environment will lead to its rapid degradation and decrease.

Disclosure of invention

The objective of the invention is to increase the technical and economic performance of the electrolyzer by increasing the service life (by reducing the wear of the cathode blocks), the stability of the electrolyzer and, accordingly, the production of metal (by aligning horizontal currents along the length of the cathode section) and reducing energy consumption per ton of aluminum produced (by reducing the voltage drop in the cathode section).

The technical result is to reduce the voltage drop in the cathode section by increasing the conductivity of the current-supplying rod, providing an acceptable electrical contact between the insert and the steel cathode rod throughout the life of the electrolyzer, substantially aligning the horizontal currents along the length of the cathode section. The problem is solved, and the technical result is achieved by the fact that in the cathode current-supplying rod used in the construction of the cathode device of an aluminum electrolyzer, including a metal base with an internal cavity and a liner made of a material with high electrical conductivity, installed in the internal cavity with the possibility of electrical contact with metal basis, the cathode conductive rod is made of one or two or more metal bases rigidly fixed to each other, while Adyshev fixedly connected to the metal substrate through a bonding layer and is arranged on one or several lateral faces of the metal substrate.

The liner may be made of copper or an alloy based on copper. It is advisable that the cross-sectional area of the liner is from 8 to 30% of the cross section of the rod. It is also preferred that the outside of the liner be covered with a steel plate that is rigidly fixed to the surface of the metal base. The connecting layer can be made by welding, for example, by explosion. The connection of a metal base with a liner of metal with high electrical conductivity can be carried out by hot rolling (rolling) - a form of metal forming.

The connecting layer is formed by itself during the welding process, and is a transition layer between the surface atomic layers of each of the joined materials (base and liner) exposed to a plasma jet (as a result of welding). Plasma causes the formation of a metal bond, in which metals are divided among themselves by valence electrons. The metal interface (connecting layer) is usually pronounced and has the appearance of regular sinusoidal waves. In the design of aluminum electrolyzers, rods of various cross-sectional shapes are used - square, rectangular, round or oval. In our case, the shape of the rod can be any.

The rod is usually made of steel, as a replacement option can be cast iron. The liner may be made of copper, an alloy based on copper, aluminum, an alloy based on aluminum.

The indicated cross-sectional area of the liner from 8 to 30% of the cross section of the rod allows you to adjust the effective electrical conductivity of the cathode current-carrying rod.

A steel plate that is rigidly fixed to the surface of the metal base helps protect the liner and the connecting layer from oxidation.

The connection of a metal base with a liner of metal with high electrical conductivity can be carried out by explosion welding. Welding method based on the use of explosion energy (a variety of metal processing by explosion). Based on the use of kinetic energy of the collision of the moving part (liner) with the surface of the fixed part (base), it is expended on the work of joint plastic deformation of the contacting layers of the metal, leading to the formation of a welded joint (connecting layer between them).

The proposed design of the cathode current-supplying rod allows to significantly reduce the voltage drop in the cathode current-supplying rod and significant alignment of horizontal currents along the length of the cathode section due to the presence of a high-quality connecting layer between the metal base and the liner. This layer provides reliable electrical contact between the metal base and the liner, regardless of temperature gradient along the length of the cathode rod.

Brief Description of the Drawings

The invention is illustrated by the following drawings:

figure 1 shows the cathode section of an aluminum electrolyzer in figure 2 - cathode current-supplying rod in disassembled and assembled condition;

in FIG. 3. shows the proposed cathodic current-supplying rod, assembled from two metal bases;

in FIG. 4 shows the proposed cathodic current-supplying rod with a steel plate covering the liner from the outside.

The implementation of the invention

The proposed cathode current-supplying rod 1 is intended for installation in a carbon-containing cathode block 2 made with a groove 3 by fixing the rod 1 with an electrically conductive material 4 (cast iron, carbon paste or carbon glue).

A cathode current-supplying rod 1, including a metal base 5, with an internal cavity 6 made by machining, an insert 7 made of a material with high electrical conductivity, installed in the inner cavity 6 and rigidly connected to the metal base 5 through a connecting layer 8, a steel plate 9 mounted on the outer side of the liner 7 and is rigidly fixed to the surface of the metal base 5 by electric arc welding around the perimeter of the plate.

The insert 7 is fixed inside the cavity 6 of the metal base 5 by explosion welding, the soft metal insert 7 "rushes" onto the surface of the metal base 5 as a result of collision, plastic deformation occurs, causing local heating surface layers of metal of a throwable insert 7 and the base of the metal base 5. As a result of deformation and heating, physical contact develops, activation of the surfaces to be welded and a joint forms - a connecting layer 8.

Also, the insert 7 can be fixed inside the cavity 6 of the metal base 5 using joint hot rolling (knurling). In this case, the metal base 5 and the insert 7 are heated and jointly rolled between the rollers, as a result, the insert is soldered to the metal base and a strong connecting layer 8 appears.

In the case of making the cathode current-supplying rod 1 composite, consisting of two metal bases 5, they are connected rigidly to each other by the sides on which the insert 7 is mounted. The connection of two metal bases 5 is carried out by perimeter arc welding.

In the design of the cathode current-conducting rod, the liner with high electrical conductivity is made of copper or an alloy based on copper.

In the design of the cathode current-supplying rod for more radical alignment of the vertical current on the surface of the cathode section, it is proposed to perform a section of the insert from 8 to 30% of the section of the rod.

The operation of the device is as follows

The general layout of the cathode section of an aluminum electrolyzer is related to the global conversion of the vertical current entering from the side of the molten metal (on top of the cathode section) into horizontal current along the cathode current-supplying rods. This leads to uneven vertical current on the surface of the hearth, especially when the use of cathode blocks with a high content of graphite (materials with high electrical conductivity), an increased voltage drop in the cathode section, uneven wear of the cathode block (since in places with a high current density on the surface intense erosion of the material of the cathode block occurs) and, accordingly, to reduce the life of the electrolyzer .

The cathode current supply rod with an insert 7 installed in the cavity 6 can significantly increase the conductivity of the cathode current supply rod 1, which in turn leads to a decrease in voltage drop in the cathode section, a significant alignment of horizontal currents along the length of the cathode section, thereby reducing the uneven wear of the cathode section and, accordingly to increase the service life and stability of the cell.

A relatively small addition of copper (from 8%) as a liner leads to a noticeable improvement in the current distribution. Depending on the technological conditions, the copper insert allows to reduce the voltage drop in the cathode section by 50-100 mV.

Examples

A cathode current-supply rod, of arbitrary length, consisting of a steel base with a cross-section of 230x110 mm and a cavity with a cross-section of 155x20 mm and a copper insert with a cross-section of 150x20 mm, which is thrown onto a steel base, then, on the outside of the insert, a steel plate with a cross-section of 180x10 mm is welded, which protects the copper insert from oxidation by atmospheric oxygen and exposure to aggressive electrolyte vapors. The cathode current-supplying rod is obtained with a cross section of 230x120 mm. Cathodic current-supplying rod, of arbitrary length, consisting of two identical steel substrates with a section of 230x60 mm and a cavity with a section of 155x10 mm and a copper insert with a section of 150x10 mm that is thrown onto a steel base. Then, the two bases (halves) are deployed with a copper liner to each other and welded together. This results in a cathode current-supplying rod with a cross section of 230x120 mm which forms an integral steel protective sheath with a copper insert inside.

This leads to a decrease in voltage drop in the cathode section by 50-80 mV, to a significant equalization of horizontal currents along the length of the cathode section, so the delta between the maximum and minimum values of current density decreases by 50%. The service life is increased by 6 months. (It is confirmed by full-scale tests on electrolyzers of high power> 300 kA).

The above particular embodiments of the invention are not the only ones possible. Various modifications and improvements are allowed without departing from the scope of the invention defined by the first claim.

Claims

CLAIM

1. The cathode current-conducting rod used in the design of the cathode device of an aluminum electrolyzer, comprising a metal base with an internal cavity and an insert made of a material with high electrical conductivity, installed in the inner cavity with the possibility of electrical contact with the metal base, characterized in that the cathode conductive rod made of one or two or more rigidly fixed to each other metal bases, while the liner is rigidly connected to a metal again through the connecting layer and placed on one or more side faces of the metal base.

2. The cathode current supply rod according to claim 1, characterized in that the liner is made of copper or an alloy based on copper.

3. The cathode current supply rod according to claim 1, characterized in that the liner is made of aluminum or an aluminum-based alloy.

4. The cathode current-supplying rod according to claim 1, characterized in that the cross-sectional area of the liner is from 8 to 30% of the cross-section of the rod.

5. The cathode current supply rod according to claim 1, characterized in that the outer side of the liner is closed by a steel plate, which is rigidly fixed to the surface of the metal base.

6. The cathode current supply rod according to claim 1, characterized in that the connecting layer is made by explosion welding.

7. The cathode current-supplying rod according to claim 1, characterized in that the connecting layer is made by rolling (rolling).