RU2621202C1 - Method of replacement of anode in electrolysis of melt in aluminium electrolyser - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: method involves heating the new anodes before placing it in an electrolytic cell, which before replacing the previously installed under the cover of the cell in close proximity to the working anode in the post-launch period of operation of the cell. New anodes kept under cover for 8-48 h, recovered residue anodic working anode, the anode is heated in an electrolyser is set, and to place the preheated anode set a new anode.

EFFECT: improvement of electrolysis technology.

4 cl, 1 tbl, 1 dwg

Description

Technical field

The invention relates to non-ferrous metallurgy, in particular to the electrolytic production of aluminum in electrolyzers with prebaked anodes, and can be used to improve electrolysis technology by preheating the anode, before installing it in the electrolyzer.

During the electrolysis of aluminum, the anodes gradually burn out. As combustion, the anode residue (cinder) is replaced by a new anode. The new anode is installed cold in the cell, and therefore cannot fully bear the necessary load, the anode current density of the cell increases, which requires compensation in the form of an addition of voltage to the cell.

State of the art

There is a method of replacing anodes in an electrolytic cell to produce aluminum having an anode array formed by two rows of calcined anodes, according to which the replacement of spent anodes is made according to a schedule so that the size of the cinder is minimal, and the anodes in the anode array, worn and new, would be located in a checkerboard pattern. With this arrangement of the anodes, the electrical resistance of the anode array remains almost the same along the length, which contributes to a uniform distribution of current. The normal life of the anode at its initial height of 60 cm is about 30 days (M.M. Vetyukov, A.M. Tsyplakov, S.N. Shkolnikov, "Electrometallurgy of aluminum and magnesium", M. Metallurgy, 1987, p. 120).

According to this technology, during operation, usually no more than 1 anode is changed daily with successive alternation of anodes located on opposite sides (2 rows) from the longitudinal axis of the cell. Since the rated current load on the new anode is restored 16-24 hours after replacement, due to the redistribution of current among other anodes, horizontal transverse and longitudinal currents occur in the cathode metal, causing the metal mirror to skew over the bottom area of the cell. This reduces the magnetohydrodynamic stability of the electrolyzer and prevents voltage reduction to reduce power consumption.

A known method of replacing the anodes in electrolytic cells with a baked anode for producing aluminum (patent application RU 9404065102, C25C 3/12, publ. 09/10/1996), which provides for a sequential replacement of anodes located on opposite sides of the longitudinal axis of the cell, each subsequent anode is removed from the zone of the anode array located on the opposite side from the transverse axis of the cell, and the time interval between their replacement is minimal. With this method of replacing the anodes and installing them correctly, the current loads over the areas of the anode array located on the sides of the longitudinal or transverse axis will be close in magnitude, which reduces the negative effect of horizontal currents from the uneven distribution of current over the anodes after replacement. Accordingly, the skew of the metal over the area of the cathode of the electrolyzer decreases due to a decrease in the density of horizontal currents.

The disadvantages of this method include the fact that the installed unheated new anodes take longer to reach the rated load and require voltage-voltage additions to compensate for heat losses by the electrolyzer. As a result, when replacing the electrolyzer, the current distribution worsens, the stability of the electrolyzer decreases, as a result, the current efficiency decreases, which leads to an increase in the specific energy consumption.

The closest in technical essence to the claimed invention is a method for replacing carbon anodes during electrolysis of aluminum melt according to the application for invention RU 94044352, C25C 3/12, publ. 04/20/1997, in which the carbon anodes are heated using heat of the anode residues extracted from the melt pool and / or the hot material of the bath extracted from the melt pool, and then fed to the melt pool in a heated state.

The disadvantage of the above method is that when using it, an additional container is required to accommodate cinder and new heated anodes. In the process of cooling the cinders, an intensive release of greenhouse gases occurs, therefore this container requires its own gas removal system, which is very labor-intensive.

Disclosure of invention

The task of the invention is to reduce the specific energy consumption when replacing the anode of an aluminum electrolyzer.

In this case, the technical result is to reduce the temporary volt-voltage additions to replace the anode by using the generated and dissipated heat of the electrolyzer to preheat the new anode,

The achievement of the above technical result is ensured by the fact that in the method of replacing the anodes during the electrolysis of aluminum melt in an aluminum electrolytic cell with heat recovery, including heating new anodes, according to the claimed invention, before replacing the new anodes, they are pre-installed under the shelter of the electrolyzer, in the immediate vicinity of the working anodes in the post-launch period electrolyzer operation, new anodes are kept under cover for 8-48 hours, the anode residue of the working anode is removed, the heated anode is installed ivayut in an electrolytic cell and to place the preheated anode set a new anode.

Additional features that contribute to the achievement of the technical result

New anodes are heated using heat from the surfaces of the melt, the working anode, the casing of the electrolyzer and from the gases released during electrolysis.

New anodes are installed under the shelter of the electrolyzer located on its end and / or longitudinal sides.

The temperature of heating the anode before installing it on the workplace is 80-200 ° C.

The main differences and advantages of the claimed invention from the prototype are that the output of the preheated anode installed at the rated load is faster, the anode heating time in the electrolysis melt is shorter, the temporary voltage addition voltage for replacing the heated anode is lower, and the current distribution is much better. This allows you to achieve a more stable operation of the electrolyzer, increase the current efficiency and reduce the specific energy consumption. In addition, this invention allows the rational use of the generated heat of the electrolyzer, which contributes to even greater energy savings (up to 200 kWh / t).

This method involves pre-placing the anodes, before installing them in the electrolytic cell, under the shelter of the electrolytic cell for the purpose of pre-heating, which reduces the heating time of the anode in the molten cell, reaching its rated power, and as a result allows to increase the current efficiency and reduce the specific energy consumption.

This method can be used with existing regulated technologies for replacing the anodes and is characterized by the additional operation of preheating a new anode before installing it in the workplace.

A new anode is installed under cover in the end or longitudinal side of the cell. Heat transfer in the space under the shelter is carried out by convection - as a result of the flow of gases, as well as radiation - from heated surfaces. The installed new anode is heated in the space under the shelter of the electrolyzer until one of the working anodes burns (from 8 to 48 hours). During the replacement, the anode residue (cinder) is removed and a preheated anode is installed in its place. A new anode is installed on the vacant place under the shelter, on preheating. This operation is repeated during each cycle of replacing the anode cinders during the electrolytic production of aluminum.

The following is a calculation of energy savings (kWh per tonne of aluminum) due to preheating of the anode.

As an example, energy savings depending on the heating time of the anode were calculated using an OA-120 electrolyzer.

Energy savings (kWh per ton of aluminum) were determined by the formula

Where

E - electric power saving, kW⋅h / t Al;

W is the amount of electricity to heat the mass of the anode, kW⋅h;

Q _Al - the amount of accumulated aluminum, kg / day;

The amount of accumulated aluminum per day (Q _Al ) was determined by the formula

Where

Q _Al - the amount of accumulated aluminum, kg / day;

I is the current strength, kA;

k is the electrochemical equivalent, g / (A⋅h);

τ is the number of hours in a day;

η is the current output.

The amount of energy required to heat the mass of the anode was determined by the formula

Where

W is the amount of energy needed to heat the mass of the anode, kW⋅h;

m is the mass of the anode per day, kg;

C _V is the heat capacity of the coal part of the anode, J / (kg⋅ ° C);

T is the temperature at which the new anode is heated, ° C.

The results of the calculations of energy saving, made by formulas (1), (2) and (3), depending on the heating time of the anodes during industrial tests of the method of replacing the anode in an aluminum electrolyzer are presented in the table.

Industrial tests showed that heating the anode for 4 hours did not lead to significant energy savings and is not cost-effective, as the resulting energy savings (9 kWh / t Al) are very low in relation to labor costs regarding preheating of the anode. Heating the anode for more than 48 hours did not show an improvement in the reduction in specific energy consumption compared to heating for 48 hours or less. Thus, according to the results of industrial tests, the optimal time period of heating (8-48 hours) was selected, in which the use of the proposed method would be appropriate.

The figure shows the location of the new anode under the shelter of the cell.

When implementing the method, a new anode 1 is installed under the shelter of the cell 2 in the end of the cell (Fig. A) and / or on its longitudinal side (Fig. B) for preheating, after 8-48 hours the anode cinder 3 is removed, and installed in its place new heated anode.

Claims (4)

1. The method of replacing the anodes in the electrolysis of molten aluminum in an aluminum electrolytic cell with heat recovery, comprising heating new anodes, characterized in that in the post-start-up period of the electrolyser, the new anodes are pre-heated for heating under the electrolyzer in the immediate vicinity of the working anodes, kept under cover within 8-48 hours, the anode residue of the working anode is removed and the heated new anode is installed in the electrolyzer, and a new anode is installed in its place. 2. The method according to p. 1, characterized in that the new anodes are heated using heat from the surfaces of the melt, the working anode, the casing of the electrolyzer and from the gases released during electrolysis. 3. The method according to p. 1, characterized in that the new anodes are installed under the shelter of the cell located on its end and / or longitudinal sides. 4. The method according to p. 1, characterized in that the new anodes are heated to 80-200 ° C before being installed in the electrolyzer.

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