JPS596391A - Electrolytic reduction tank and operation thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a monopolar or multipolar electrolytic reduction tank for producing molten metal products by electrolysis of a molten electrolyte.

In such a tank, electrolyte 1. The J tJ is enclosed within a rectangular fire-retardant shell and the vessel is equipped with one or more suspended anodes. For economical reasons, the area occupied by the anode or cathode occupies a large proportion of the total tank floor area occupied by the electrolyte.

In this general type of conventional electrolytic reduction tank J3, the tank cathode is a liquid cathode formed by a pool of molten metal on the floor of the tank.
fi'C-There is. The depth of this pool increases progressively during the normal cycle of tank operation, reducing tank removal intermittently. The active surface of the anode gradually rises to keep the nominal anode/cathode distance approximately constant, and the height of the molten electrolyte in the bath rises and falls above and below each other in steps as the height of the molten metal in the metal pool moves up and down. do exercise.

Many proposals have been made to use drain cathode structures in electrolytic reduction vessels, where the main body of product metal is gradually drained from the active cathode surface. In such cases, the active cathode surface is configured by any of the following means.

1) Solid drains (horizontal, vertical or slope).

2) Pedestals as described for example in P CT W P 01899 or EP 81 300382.9.

3) Metal holding containers, such as those described in US Pat. No. 4,071,420 or British Patent No. 8217711.

4) Mushroom-shaped projections, such as those described in U.S. Pat. No. 4,177,128.

5) Metal held by the surface tension of the cuts in a metal cavitated packed bed or a ceramic shaped vessel, as described for example in PCT, WP 8102170 or French Patent No. 2,500,408. The generally preferred material of construction is refractory cemented carbide.

In drain cathode type vessels, the product metal is collected in a collecting sump from which it is conventionally withdrawn, usually by siphon, at long intervals, for example 24 hour intervals. Alternatively, metal is accumulated between the cathode members or under the pedestal.

During normal operation of the cell, in a drain cathode type or other similar type where there is little or no movement of the active cathode surface down to the cell floor, the electrolyte displaced by the product metal surrounds the anode or cathode. As it is pushed upwards into the restricted chamber, there is considerable variation in the height of the electrolyte surface.

Large variations in the height of the electrolyte surface can lead to significant operational problems, making it difficult to increase the ratio of the total anode area to the area of the top surface of the molten electrolyte. Particularly large fluctuations in the electrolyte height can greatly disturb the thermal balance of the cell, destabilizing the layer of frozen electrolyte and the frozen electrolyte crust on the wall of the cell. Intermittent impregnation of the crust with molten electrolyte tends to lead to an uncontrolled increase in crust thickness.

It is an object of the present invention to provide a means for operating an electrolytic reduction cell, in particular an electrolytic reduction cell of the drain cathode type, in such a way that variations in the height of the electrolyte surface are considerably reduced with respect to the rate at which product metal is produced and withdrawn in conventional manner. It is intended to provide the following.

In principle, the method of the invention requires only a small amount of space available for the liquid in the tank (
(for a given level). This is accomplished by moving a solid block up and down in conjunction with the melting bath, increasing and decreasing liquid space in accordance with the increase and decrease of liquid metal during conventional withdrawal cycles.

One way to practice the invention is to configure one or more of the tank anodes to be vertically adjustable independently of the rest of the tank anodes. Immediately after removal, such an anode is set at the same height as the remaining anodes, but as the circulation of the bath progresses, such an anode is upturned to compensate for the increase in the liquid content of the bath.

The current introduced by the raised anode decreases as a result of increasing the anode/cathode distance compared to the rest of the anode.

Other variant structures are explained with reference to the accompanying figures.

In FIG. 1, the reduction tank includes an insulating sidewall 1 and a floor 2.

The side walls 1 (and end walls 2) are conventionally coated with a layer 3 of frozen sliding electrolyte.
protected by. A row of brebake-type anodes 4 are installed on each side of the cell and project into the molten sliding electrolyte 7 to a predetermined depth. The drain cathode is formed of titanium diboride or other hard metal form 13, which is supported on the N-base cathode block 5 and has a slightly sloping top surface sloping downward from the center 1 to the rough or υ pump 6; The molten metal product accumulates in a trough and is periodically removed.

The trough needs to be sized to accommodate the metal produced in conventional metal extraction synchronization. Since the anode 4 itself remains in a fixed position with respect to the cathode block 5, the electrolyte displaced from the molten metal by the molten metal rises into the space surrounding the anode. To limit the width of the electrolyte height change (
This results in gradual changes in the height and shape of the protective frozen layer 3)
, a vertically movable block 8 is made to sink into the electrolyte and descend into the trough 6. As the metal gradually displaces the electrolyte from the trough, the block 8 rises, lifting an increasing portion of the block from the electrolyte and thus increasing the space available for the liquid electrolyte. This device may be used to regulate the entire or only part of the electrolyte, thus keeping the electrolyte height approximately constant or during normal operation synchronization the electrolyte height gradually increases slightly. make it possible.

A moving block 8 cooperating with the trough 6 can be provided longitudinally (as shown) or laterally of the tank or at one end (or both ends for very large tanks) of the tank. Block 8
is preferably located on the top of the sump, but may be located elsewhere.

Move the small capillary part 9 of the block 8 to the Cybon extraction position.
It is convenient to have the following. This allows the electrolyte to rise out of the bath prior to the withdrawal operation without significant disturbance of the height.

The moving block 8 may be made of carbon (or constituted by one or more of the anodes already described).

However, moving blocks are essentially electric w4. Formed from frozen matter. As shown diagrammatically in FIG.
A cold) JJ body (air or scum) is passed through it, thus maintaining a solid mass 12 of frozen electrolyte covering the fins 11.

In the variant shown in FIG. 3, the moving block is located in a container outside the electrolyte of the cell. Such containers can be tied either inside or outside the steel shell of the tank. In this case, the molten metal accumulates in a slightly smaller jump 26 at one end of the cypress, which communicates via a passage 28 with a chamber 27 of another metal bundle f11.

The height of the molten metal in the chamber 27 is determined by the vertical movable block 29.
It is formed from a pond refractory that is not susceptible to erosion by alumina or molten aluminum.

Blocks are removed at a substantially constant rate set by the metal production rate of the bath.

This maintains a constant metal height in chamber 27.

Alternatively, the drive of block 29 is controlled by a sensor that continuously senses the metal height in chamber 27. The upward movement of the block 29 is therefore automatically adjusted in order to keep the height of the metal in the chamber 27 approximately constant. room 2
By keeping the metal height approximately constant at 7, the height of the metal and the sliding electrolyte in the integrated sump 26 are also maintained approximately constant.

Although it is not necessary in all cases, especially where passage 2B leads upwards from the bottom of a fairly deep sump, in which most of the head of molten metal is maintained by actuation of block 29, European Patent No. A selective filter of the type described in US Pat.
Preferably, it is inserted between the chambers to prevent the sliding electrolyte from entering the chamber.

For this purpose, the sump 26 is small in size and filled with precisely sized balls or pieces of Ti 82 or other hard metal refractory that are resistant to attack by molten aluminum and molten sliding electrolyte.

In FIG. 3, the vessel includes a drain cathode arrangement 35, which includes a cathode current collector (not shown) and a conventional effect anode 34.

Production metal is withdrawn from chamber 27 intermittently, e.g., every 24 hours, by conventional means, such as by extraction.

Where there is a selective filter, the metal is taken from chamber 27 through port 3.
6 to the collecting crucible (not shown) by simply driving the transfer block down to the bottom of the chamber. The high resistance of fluid through the selective filter prevents any amount of metal from re-entering the cell electrolyte. narrowing 2
It is desirable to maintain an inert gas blanket on top of 7.

Alternatively, the product metal can be withdrawn from the collection chamber 27 at more frequent intervals, for example every 15 minutes.

This has several advantages. The metal accumulation chamber can be made relatively small and is preferably fitted within the steel shell of the tank. For example, if you take out a tank that produces metal from 1 ton to 21 - tons per day every 15 days, the production amount per removal is only IOK! It is 20KCI from +. Such output storage capacity is easily accommodated within the transfer tube in which the moving block moves.

Another advantage is that the metal can be removed to a molten metal pipeline such as that described in EP 68,782. Electrical insulation between vessels interconnected by molten metal pipelines can be maintained and covered by successive actuation of moving blocks to different vessels, so that only one vessel is removed and molten metal removed at any time. It is electrically connected to the pipeline. This configuration can be used as the basis for a fully automatic metal extraction device.

FIG. 4 shows an alternative arrangement in which the metal accumulation container is located at the lower end of the sun 126, rather than simply communicating with the nozzle by a passageway 28, as shown in FIG. Similar parts are designated by like reference numerals in FIGS. 3 and 4. In FIGS.

In FIG. 4, a metal transfer port 36 communicates with a collection vessel 37, which may be a collection crucible or a molten metal pipeline.

A metal selective filter 25 is provided over the entry point at the bottom of the metal accumulation vessel. Alternatively, this filter can be used with Leanmp 2
You can also prepare it within 6 days. Although it is desirable to avoid the risk of electrolytic chambers entering metal accumulation chambers, metal selective filters are not essential for frequent or automatic withdrawals. Any type of restrictive orifice can be used at the entrance 25 to the metal accumulation chamber so that the lowering of the transfer block 29 drives molten metal into the extraction device and prevents it from returning to the tank. Preferably, one or more metal accumulation chambers are used in six vessels. Then, if one metal accumulation chamber becomes inadvertently occluded or otherwise malfunctions, it can be removed from the sump and returned after repair without the need to interrupt vessel operation.

[Brief explanation of the drawing]

Figure 1 is a schematic cross-sectional view of a tank equipped with a drain cathode, Figure 2 is a longitudinal cross-sectional view of a moving block used in the structure of Figure 1, and Figure 3 is a device for controlling the height of the sliding electrolyte. FIG. 4 is a longitudinal sectional view of an electrolytic cell with an inner electrolyte height control device and a metal extraction device. (Explanation of symbols) 1...Layer side wall 2...Calendar method 3...Frozen sliding electrolyte 4...Anode 5...Cathode block
6... Sump 7... Molten sliding electrolyte 8...
Moving block 26...Zump 27...Separate metal accumulation chamber 34...Anode 35...Drain cathode structure Patent applicant Alcan International Limited (4 others)

Claims (1)

[Claims] 1. A method for operating an electrolytic reduction tank of the type in which molten product metal is produced by electrolysis of a fusion electrolyte having a density lower than that of the molten product metal, comprising a moving block connected to the contents of the molten tank; A method characterized in that the block is raised and lowered to increase or decrease the liquid space in the bath, thereby reducing variations in the height of the surface of the electrolyte in relation to the rate of production and withdrawal of product metal. 2. The method according to claim 1, wherein the tank is of a drain cathode type. 3. The method according to claim 1 or 2, in which the moving block moves up and down in contact with the sliding electrolyte. 4. A method according to any one of claims 1 to 3, wherein the cell comprises an anode suspended in an electrolyte, one or more of the anodes being vertically adjustable; How to act as a moving block. 5. The method according to any one of claims 1 to 3, wherein the moving block comprises a hollow cooling support surrounded by a large amount of frozen electrolyte. 6. The method according to any one of claims 2 to 5, wherein the tank is equipped with a sump for accumulating product metal, and the moving blocks are located above and below one number. 7. A method according to claim 1 or 2, in which the moving block is located in a container outside the electrolytic chamber of the tank. 8. A method according to claim 7, in which the moving 10 pieces are positioned in contact with the product metal in another metal accumulation chamber. 9. The method of claim 8, wherein the metal aggregate is in communication with the cell electrolyte through a selective filter that passes the molten product metal but not the fused electrolyte. 10. The method according to claim 9,
A method of removing product metal from a metal accumulation chamber by lowering a moving block into it. 11. In an electrolytic reduction tank of the type that produces molten product metal by electrolysis of a low-density fusion electrolyte with molten metal, and which includes an electrolysis chamber and a separate metal accumulation chamber, a moving block that joins to the molten metal in the metal accumulation chamber. and a means for raising and lowering the block. 12. In the tank according to claim 11,
A vessel in which the electrolytic chamber is of the drain cathode type with a sump for the molten product metal. 13. In the tank according to claim 11,
A vessel in which the metal accumulation chamber communicates with the electrolytic chamber through a selective filter that passes molten product metal but not the fusion electrolytic chamber. 14. The tank according to any one of claims 11 to 13, wherein the product metal is taken out from the metal accumulation chamber by operating means for raising and lowering the moving block.