DK201670544A1 - Electrolysis tank casing - Google Patents

Abstract

The present invention relates to an electrolytic cell comprising a pot shell (1) covered with a liner and including a base (10) and side walls (11,12), pot shell (1) being designed to receive a cryolite bath and a confinement chamber on the pot shell, the confinement chamber having side walls, at least one of the side walls of the confinement chamber being offset towards the outside of the pot shell with respect to a side wall of the pot shell, the cell including at least one peripheral shoulder (16, 17) extending between the offset side walls of the pot shell and of the confinement chamber, each shoulder including at least one window (18a) through which passes a respective cell compo-nent moving translationally along a translational axis T-T'.

Description

ELECTROLYSIS TANK CASING

Technical field

The present invention relates to the general technical field of the production of aluminum by electrolysis in an electrolytic cell containing a cryolite bath.

It relates more specifically to a pot shell for an electrolytic cell designed to contain such a cryolite bath. The anodes are particularly made of carbon of the pre-baked type.

Presentation of prior art

Aluminum is mostly produced by electrolysis of alumina dissolved in a cryolite bath.

Currently, aluminum is produced on an industrial scale in an electrolytic cell comprising in particular: a parallelepiped steel pot shell including a base and side walls, the pot shell being open in its upper part, a refractory lining covering the base and side walls of the pot shell, a cathode based on carbonaceous cathode blocks arranged in the pot shell and connected to electrical conductors used to route the electrolysis current.

The electrolytic cell also includes a cryolite bath contained in the pot shell and consisting particularly of cryolite and dissolved alumina.

A pre-baked carbon block constituting the anode of an anode assembly is immersed in the cryolite bath and is consumed as the electrolysis reaction proceeds to produce aluminum.

A crossing superstructure is mounted on the pot shell of the electrolytic cell. This superstructure is for example placed on the pot shell and extends in line above the opening of the pot shell. The superstructure is used to support different components of the electrolytic cell arranged in line above the opening of the pot shell such as: lifting means to lower the anode into the electrolytic cell as it is consumed, reagent supply means to allow reagents consumed during the electrolysis reaction to be introduced into the cryolite bath, a pollutant gas collection device designed to prevent polluting gases generated during the electrolysis reaction - such as carbon dioxide, carbon monoxide, sulfur dioxide and gaseous hydrogen fluoride - from being released into the atmosphere.

Finally, the cell generally has a cover means comprising a series of hoods placed between the upper edges of the pot shell and the superstructure. The cover means is designed to cover the open top part between the pot shell and the superstructure in order to confine the gaseous pollutants within the cell.

At the bottom of the electrolytic cell a layer of liquid aluminum forms that is periodically removed by suction or siphoning.

A disadvantage of this type of electrolytic cell is the risks of gaseous pollutants escaping to the outside. These risks of gases escaping may have different causes.

In particular, various products used in the electrolysis reaction - such as covering products- can build up at the edges of the pot shell against which the hoods bear. This accumulation of products may prevent the correct positioning of the hoods. This causes the appearance of polluting gas leaks at the upper edge of the pot shell and between the hoods arranged on each side of the cell.

Also, the anode rods of the anode assemblies pass through the cover means. These anode rods are associated with dynamic sealing means provided to prevent gas escaping through the junctions between the cover means and the anode rods. However, the dynamic sealing means may be damaged, especially during handling of the anode rods to replace a spent anode with a new anode. Damage to the dynamic sealing means leads to the appearance of polluting gas leaks at the junctions between the cover means and the anode rods.

Another disadvantage of this type of electrolytic cell relates to the movement kinematics of the anode assemblies when replacing a spent anode with a new anode. The presence of the superstructure above the pot shell opening impedes the vertical movement of the anode assemblies. It is therefore necessary to use complex movement kinematics for the anode assemblies around this superstructure to allow them to be withdrawn from the electrolytic cell.

One object of the present invention is to propose an electrolytic cell which overcomes at least one of the aforementioned disadvantages. In particular, an object of the present invention is to propose an electrolytic cell having an improved seal against gaseous pollutants and in which the extraction of anode assemblies is facilitated.

Summary of the invention

To this end, the invention proposes an electrolytic cell used for producing aluminum, comprising a pot shell covered with a liner and including a base and side walls, the pot shell being designed to receive a cryolite bath, characterized in that the cell further comprises a confinement chamber including side walls extending above the side walls of the pot shell, at least one of the side walls of the confinement chamber being offset toward the outside of the pot shell in relation to the side walls of the pot shell, and in that the side walls of the pot shell and the confinement chamber are connected mechanically by a shoulder including at least one window through which a respective cell component moves translationally along an axis T -Τ' through the window.

In the context of the present invention, a side wall of the confinement chamber is considered as offset in relation to a side wall of the pot shell when the bottom edge of the side wall of the confinement chamber is horizontally offset in relation to the upper edge of the side wall of the pot shell. In relation to the side walls of the pot shell means on the side opposite the inside the pot shell with respect to the side wall.

The shoulder advantageously extends between the lower edge of the offset side wall of the confinement chamber and the upper edge of the side wall of the pot shell. The shoulder is more particularly a physical wall providing sealing between the offset side walls of the confinement chamber and the pot shell which it connects mechanically. The shoulder may also advantageously support and ensure the mechanical integrity of the confinement chamber.

The cell consists of one (or more) shoulder(s) between the pot shell and the confinement chamber. Each shoulder includes (one or more) window(s) through which pass(es) (a) component(s) that is (are) translationally movable along a translational axis T-Τ' through the window(s), particularly perpendicular to the plane in which said window(s) extend(s).

This particular arrangement (i.e. the assembly made up of the shoulder/window for the passage of a respective cell component moving translationally along an axis T-Τ' passing through the window) serves to limit the dimensions of the window(s) to prevent polluting gases from escaping to the outside of the electrolytic cell through the latter.

This particular arrangement also makes it possible to arrange the moving parts of an electrolytic cell - such as lifting or piercing devices - on the edge of the pot shell, unlike the electrolytic cells of prior art in which mobile devices lifting devices and/or piercing devices are generally positioned in line with an opening defined by the walls of the pot shell. The fact of positioning the lifting devices and/or the piercing devices on the edge of the pot shell means that the anode assemblies are unobstructed during their vertical travel. This makes it easier to produce a sealed confinement chamber and allows anode assemblies to be replaced from the top of the electrolytic cell, without requiring the anode assemblies to undergo complex motion kinematics.

The confinement chamber helps to confine the cell gases to make it easier to capture and treat them. The confinement chamber advantageously comprises a movable cover means closing an opening formed by the upper portions of the side walls of the confinement chamber in order to change the anode assembly through the top of the electrolytic cell with no hindrance. An opening is formed in the movable cover means for the extraction or insertion of an anode assembly from/into the confinement chamber.

Preferred but not limiting aspects of the electrolytic cell according to the invention are as follows.

Preferably, the pot shell includes first and second transverse side walls and first and second longitudinal side walls, the confinement chamber includes first and second transverse side walls extending above the first and second transverse side walls of the pot shell and first and second longitudinal side walls extending above the first and second longitudinal side walls of the pot shell, the first longitudinal side wall of the confinement chamber being offset toward the outside of the pot shell relative to the first longitudinal side wall of the pot shell and the first longitudinal side walls of the pot shell and the confinement chamber being connected mechanically by a shoulder including at least one window through which passes a respective cell component moving translationally along an axis T -Τ' passing through the window.

The shoulder is preferably formed on at least one longitudinal side of the electrolytic cell along which lifting devices and/or drilling devices can then be distributed.

In addition, more particularly, the first and second longitudinal side walls of the confinement chamber are offset towards the outside of the pot shell in relation to the respective first and second longitudinal side walls of the pot shell, the respective first and second longitudinal side walls of the pot shell and the confinement chamber being mechanically connected by shoulders, each shoulder including at least one window through which passes a respective cell component moving translationally along an axis T-T' passing through the window.

The first and second longitudinal side walls of the pot shell extend between and below the first and second longitudinal side walls of the confinement chamber.

A shoulder is then advantageously made on the two opposite longitudinal sides of the electrolytic cell so as to make the lifting devices and/or drilling devices symmetrical, each conventionally associated with an alumina feed device.

The cell may further comprise four peripheral shoulders extending between the upper edges of the side walls of the pot shell and the bottom edges of the side walls of the confinement chamber. This in particular makes it possible to arrange the components that are translationally movable between the four side walls of the pot shell and the four side walls of the confinement chamber.

Each shoulder may form part of the pot shell and/or the confinement chamber. For example: the pot shell may comprise two peripheral shoulders extending outwardly from the volume defined by the pot shell, along the upper edges of the first and second longitudinal side walls of the pot shell, the confinement chamber having no shoulder and being placed on the shoulders of the pot shell, the confinement chamber may comprise two peripheral shoulders extending inwardly from the volume defined by the confinement chamber, along the lower edges of the first and second longitudinal side walls of the confinement chamber, the pot shell having no shoulder and confinement chamber being placed on the upper edges of the side walls of the pot shell, the pot shell and the confinement chamber can each have two peripheral shoulders, the shoulders of the pot shell extending outwardly of the volume defined by the pot shell along the upper edges of the first and second longitudinal side walls of the pot shell, and the shoulders of the confinement chamber extending inwardly of the volume defined by the confinement chamber along the lower edges of the first and second longitudinal side walls of the confinement chamber; the fact that the pot shell and the confinement chamber each have shoulders makes it easier for the confinement chamber to come to bear on the pot shell and improves the stability of the pile composed of the pot shell and of the confinement chamber, the pot shell and the confinement chamber can also be a single-piece component also comprising (a) shoulder(s).

The pot shell and confinement chamber are each preferably parallelepiped in shape. The cell then advantageously has the shape of two parallelepipeds placed one on the other, the upper parallelepiped (confinement chamber) being slightly wider than the lower parallelepiped (pot shell).

Preferably each window extends in a plane perpendicular to the translational axis T-T'. The translational axis T -Τ' may be vertical (or substantially vertical). In this case, each window extends in a horizontal plane. Similarly, each shoulder may be substantially horizontal. The seal between the shoulder and the translational cell component is then facilitated.

In an alternative embodiment, each window is of complementary shape to the sectional shape of the respective cell component passing through said window, particularly of a homothetic shape. This minimizes the dimensions of the gap between the window and the movable component so as to limit the risk of polluting gases escaping through said gap. In some embodiments, each component passes through a respective window via a dynamic seal, in particular a ring-shaped one. Each seal is for example mounted on the edge of a window, around the translational component. This makes it possible to further improve the sealing of the cell. Preferably, each window is electrically insulated from the component passing through it.

According to an alternative embodiment, the shoulder comprises at least one slot projecting in a direction opposite the base of the pot shell, a window being formed in the at least one slot.

The window made in the upper part of the slot is therefore raised relative to the height of the cryolite bath so as to limit the exposure of components moving translationally through the window to the heat generated by the cryolite bath, to gases and to the covering product.

Different types of translationally movable members may be associated with a window. For example, when the cell includes at least one anode assembly supported by the anode receivers that are translationally movable along the axis T-Τ' to immerse the anode assembly in or extract it from the cryolite bath, the shoulder of the windows can be associated with said anode receivers, each window permitting a respective anode receiver to pass through.

According to a preferred embodiment, the anode assembly passes through the cell from one longitudinal side wall of the confinement chamber to the other and rests on two anode receivers passing through the windows of two shoulders arranged on opposite longitudinal sides of the electrolytic cell. The anode assembly then rests on the support and translational movement means, is perfectly stable and has no impact on the leak tightness of the confinement chamber.

Of course the windows (or other windows) can be combined with other types of component moving translationally such as an electrical current conduction device for powering the anode with electric current, or a piercing device.

In particular, in one embodiment, the cell comprises a piercing device for creating a hole in a crust forming on the surface of the cryolite bath to supply, especially with alumina from the cryolite bath, the shoulder having at least one window through which the piercing device passes, particularly a part (a bar) of the piercing device moving translationally.

The windows associated with the piercing devices are therefore raised relative to the height of the cryolite bath so as to limit the exposure of the piercing devices to the heat generated by the cryolite bath, to the gases and to the covering material.

Preferably, each shoulder comprises at least one fixing device on one side of the shoulder opposite to the base, for example a plate having a through opening and forming an attachment point for handling the pot shell. This makes it easier to move the cell with a handling unit typically comprising a traveling crane, a carriage able to be moved on the traveling crane connectable removably to the pot shell using for example hoisting beams.

Each shoulder may extend along the entire length of the longitudinal (respectively transverse) side wall of the pot shell and / or the confinement chamber. This makes it possible to arrange the translationally movable components along the axis T-Τ' over the entire length (respectively the width) of the cell.

Advantageously, the side walls of the confinement chamber and the pot shell may serve as an attachment point on the edge of the electrolytic cell for equipment generally fixed above the opening of the pot shell in prior art. In this way, the cell may comprise means for lifting the anode assemblies, piercing devices, a gas collection system and an alumina feed device which are fixed to the side walls of the confinement chamber and/or on the side walls of the pot shell.

Preferably, the pot shell, the shoulder(s) and the confinement chamber are single-piece. This limits the risk of leakage at the junction between the pot shell, the shoulder(s) and the confinement chamber that may be related to thermal expansion problems. Alternatively, the pot shell, the shoulder(s) and the confinement chamber may be in two (or more than two) parts.

Brief description of the figures

Other advantages and characteristics of the electrolytic cell will become apparent from the following description of several alternative embodiments, given by way of non-limiting examples, from the attached drawings, on which:

Figure 1 shows a longitudinal cross-sectional view of an electrolytic cell,

Figure 2 shows a transverse cross-sectional view of two adjacent electrolytic cells, Figure 3 is a partial view of an electrolytic cell comprising a piercing device.

Figure 4 is a schematic perspective view of an example of a pot shell of an electrolytic cell,

Figure 5 shows a perspective view of an electrolytic cell,

Detailed description

We will now describe an example of an electrolytic cell according to the invention. In these different figures, equivalent elements bear the same reference numerals.

The expressions "side wall", "base", and "top opening" will be used later in the text in reference to a right-angled parallelepiped.

The reader will appreciate that in the context of the present invention: "base" means a horizontal wall of a right-angled parallelepiped located near the ground, "top opening" means an opening in a horizontal wall of a right-angled parallelepiped opposite the base, "side face/wall" means a vertical face/wall of a right-angled parallelepiped extending in a plane perpendicular to the base, "longitudinal faces/walls" means vertical faces/walls of a right-angled parallelepiped of which at least one dimension is greater than the dimensions of the other sides faces/walls, "transverse faces/walls" means vertical faces/walls extending perpendicularly to the longitudinal faces/walls.

Referring to figures 1 to 3, we have illustrated an example of an electrolytic cell according to the invention.

The electrolytic cell is of substantially rectangular parallelepiped shape and comprises a pot shell 1, a confinement chamber 2, a plurality of anode assemblies 3, a cathode 4, a gas collecting device 5, one (or more) piercing device(s) 6 and several lifting devices 7.

This cell is used for the production of aluminum. It may be associated with a plurality of other electrolytic cells, possibly identical, the various cells being arranged one after the other, two successive electrolytic cells being adjacent at the level of one of their longitudinal sidewalls.

Referring to figure 4, the pot shell 1 is of generally parallelepiped shape. It comprises a base 10, first and second transverse side walls 11, and first and second longitudinal side walls 12. The pot shell 1 also has cradles 13 extending on the outer sides of the base 10 and the side walls 11, 12. These cradles 13 are used to mechanically reinforce the pot shell 1.

This pot shell 1 may be metallic, for example made of steel. The internal faces of the base 10 and side walls 11,12 of the pot shell 1 are covered with refractory blocks 14 to insulate the pot shell 1. Blocks 14 may for example include refractory bricks and/or carbon blocks.

The confinement chamber 2 defines a closed volume above the cryolite bath 19 in which the anode assemblies 3 are moved.

The confinement chamber 2 rests on the top edges of pot shell 1. It comprises first and second transverse side walls 21 and first and second longitudinal side walls 22 fixed to the pot shell 1.

Preferably, the side walls 21,22 of confinement chamber 2 are offset outwardly relative to the side walls 11, 12 of pot shell 1 so that the side walls 21,22 of confinement chamber 2 extend around and above the side walls 11, 12 of pot shell 1, the side walls 11, 12, 21,22 of pot shell 1 and confinement chamber 2 being mechanically connected by shoulders 16, 17 which will be described in more detail later.

The confinement chamber 2 also includes removable hood 23 to cover the upper opening defined by the four side walls 21, 22 of confinement chamber 2. The hood 23 may be composed of an assembly of panels extending generally in a plane, and bear on the upper edges of the side walls 21,22 of the confinement chamber 2, and more particularly on the gas collecting sleeves extending at the level of the upper edges of the confinement chamber 2.

Pot shell 1 is open in its upper part 15. The cell has one (or more) peripheral shoulder(s) 16, 17 extending between the upper edges of the side walls of the pot shell and the bottom edges of the side walls of the confinement chamber.

Each peripheral shoulder 16, 17 extends towards the outside of pot shell 1 (respectively towards the inside of the confinement chamber), parallel to the base 10 of pot shell 1. The shoulders may form part of pot shell 1 and/or confinement chamber 2.

Each shoulder 16, 17 is associated with a side wall 11, 12 (respectively 21, 22) of pot shell 1 (respectively the confinement chamber).

Specifically in the embodiment shown in figure 4, the pot shell comprises four peripheral shoulders 16, 17 extending along one of the upper edges of the side walls 11, 12 of pot shell 1: two longitudinal peripheral shoulders 16, each longitudinal peripheral shoulder 16 extending along an upper edge of a respective longitudinal side wall 12 of pot shell 1, two transverse peripheral shoulders 17, each transverse peripheral shoulder 17 extending along an upper edge of a respective transverse side wall 11 of pot shell 1,

Alternatively, pot shell 1 (and / or the confinement chamber) may (each) include: a single longitudinal peripheral shoulder 16, or two longitudinal peripheral shoulders 16, or one (two) longitudinal peripheral shoulder(s) 16 and a transverse peripheral shoulder 17.

Each shoulder 16, 17 may comprise one (or more) window(s) 18a, through which passes a cell component moving translationally along an axis T-Τ' when the cell is in operation. This cell component may be a part of a lifting device 7 moving translationally along the translational axis T-Τ' such as an anode receiver 72 of an anode lifting device 7 which will be described in more detail later.

In this way, each window 18a is associated with a respective cell component passing through it, said cell component being movable translationally along the translational axis T-Τ' between two extreme positions.

Advantageously, each window 18a extends in a plane perpendicular to the translational axis T-Τ'. This makes it possible to reduce the size of the windows 18a by making them independent of the travel of the components moving translationally along the translational axis T-T'.

In the embodiment illustrated in figure 2, each window 18a is associated with a respective anode receiver 72 moving in vertical translation along the translational axis T-Τ'. In this case, window 18a extend in a horizontal plane. The same is true for each shoulder 16, 17.

The shape of each window 18a can be complementary to the sectional shape (along a plane perpendicular to the translational axis T-Τ') of the component passing through said window. This makes it possible to minimize the dimensions of the window so as to limit the risk of polluting gases escaping towards the outside of the electrolytic cell. Referring to figure 4, each window 18a is rectangular in shape, complementarily to the sectional rectangular shape of their associated anode receivers 72.

Advantageously, each window 18a of pot shell 1 may include a seal extending over its edges so that the seal surrounds the translationally movable component associated with the window. This makes it possible to improve the leak tightness of the cell so as to limit the risk of polluting gases escaping through the windows.

The seal can be designed to work in conjunction with a sealing portion arranged on the sliding component. In this case, the sealing portion extends along the area of the sliding component through the seal during the translational movement of the component between its extreme positions. In this way, leak tightness of the cell is ensured in spite of the translational movement of the component.

The dynamic seal, typically ring-shaped around the sealing portion, may also serve as electrical insulation if the sliding component is not at the same electric potential as the edges of the window through which it passes.

Each (or some) shoulder(s) 16, 17 may also comprise one (or more) window(s) 18b through which a part of a piercing device 6 passes which will be described in more detail later.

The shape of each window 18b can be complementary to the sectional shape (along a plane perpendicular to the translational axis T-Τ') of the part passing through said window 18b to limit the risk of polluting gases escaping towards the outside of the electrolytic cell. Referring to figure 5, each window 18b is circular in shape, complementarily to the cylindrical shape of the part of the piercing device 6 associated with it.

A seal may be provided on the edges of each window 18b, so that the seal surrounds the translationally movable part of the piercing device 6.

The seal can be designed to work in conjunction with a sealing portion arranged on the part of the piercing device 6, this portion extending over the entire area of the part sliding through the seal when the part is moving translationally between its extreme positions.

Windows 18a and 18b may extend into non-coincident planes.

Alternatively and as shown in figure 5, windows 18a and 18b may extend in different planes.

In particular in the embodiment shown in figure 5, each shoulder 16, 17 includes slots protruding in an opposite direction to the base 10 of pot shell 1.

Each slot has a horizontal plate in which is formed a respective window 18b so that windows 18b extend to a height greater than the height of windows 18a.

Advantageously, the side walls 21,22 of confinement chamber 2 can bear upon the upper edges of pot shell 1 at the free ends of the shoulders 16, 17. It follows that the surface area of the opening defined by the lower edges of the side walls 21, 22 of confinement chamber 2 is substantially equal to the sum of: the surface area of shoulders 16, 17, and the surface area of the upper opening defined by the upper edges of the side walls 11, 12 of pot shell 1.

Preferably, pot shell 1, the shoulder(s) 16, 17 and confinement chamber 2 are singlepiece. This limits the risk of leakage at the junction between the pot shell and the confinement chamber. These risks are otherwise great in that pot shell 1 and the confinement chamber will behave differently with respect to the expansion caused by the high operating temperatures of an electrolytic cell.

Alternatively, the pot shell, the shoulder(s) 16, 17 and the confinement chamber may be in two (or more than two) parts. In one embodiment, pot shell 1 and confinement chamber 2 each have shoulders, extending: for the shoulders of pot shell 1, along an (one of the) upper edge(s) of a (one of the) longitudinal (and transverse) wall(s) of the pot shell, for the shoulders of confinement chamber 2, along a (one of the) lower edge(s) of a (one of the) longitudinal (and transverse) wall(s) of the confinement chamber,

The shoulder(s) extend (s) preferably perpendicular to the side walls of pot shell 1 and confinement chamber 2, each shoulder of the confinement chamber 2 being able to come into contact with a respective peripheral shoulder of pot shell 1.

The presence of shoulders on both the side walls of pot shell 1 and confinement chamber 2 makes it easier for confinement chamber 2 to come to bear on pot shell 1 and improves the stability of the pile composed of pot shell 1 and of confinement chamber 2.

As indicated above, each shoulder may extend along the entire length of the side wall of the confinement chamber 2 (pot shell 1, respectively), the shoulders of confinement chamber 2 and pot shell 1 each comprising one (or more) window(s) at positions that coincide when confinement chamber 2 is placed on pot shell 1.

Each anode assembly 3 comprises an anode 31 and anode structure 32. The anode structure 32 firstly makes it possible to handle the anode 31, and secondly to supply it with electric power. During the electrolysis reaction, anode 31 immersed in the cryolite bath is consumed. The anode assemblies 3 need to be replaced periodically.

Anode 31 is preferably a block of carbon material of the pre-baked type.

Anode assemblies 3, and more particularly the anode structure 32 of each anode assembly 3 extend transversely in the cell between the longitudinal side edges 22 of the confinement chamber 2. The anode structure comprises in particular a transverse beam. The cell comprises a plurality of anode assemblies 3 distributed along a longitudinal axis of the cell.

The anode structure may comprise a frame made of a metal having good mechanical strength, such as steel. This allows the anode structure to keep the anode assemblies suspended. It may also comprise sections made from a metal having good electrical conductivity such as copper or aluminum. This allows the anode structure to route electrical power to power the anode assemblies.

Cathode 4 may include a plurality of cathode blocks made of carbonaceous material.

Cathode 4 is connected in its lower part to electric conduction means for the electrolysis current 41 formed, in particular, from one or more conductors. More particularly, each cathode block has at least one cavity in its lower portion within which is arranged electrical conduction means 41.

Good physical and electrical connection is made in the cavity between the cathode block 4 and the means of electrical conduction 41 using cast iron. The conductor passes through pot shell 1 at the level of holes in pot shell 1, especially the base 10 or the longitudinal side walls 12.

The conductor collects the electric current at the cathode to route it from one electrolytic cell to another.

The gas collection device 5 retrieves the polluting gases generated during the electrolysis reaction in order to treat them.

The gas collection device 5 comprises one (or more) capture sleeve(s) on which suction openings for the suction of gas are distributed.

The capture sleeve(s) is (are) associated with one (or more) suction device(s) (not shown). They (it) extend(s) over the longitudinal side walls 22 of confinement chamber 2, and possibly over the transverse side walls 21 of confinement chamber 2. The presence of openings along the longitudinal walls 22 of confinement chamber 2 makes it possible to improve the efficiency of the collection of gas pollutants.

Advantageously, the number of openings of the collection device 5 can be equal to a number of piercing devices 6 attached to the electrolytic cell. In this case, each opening may be associated with a respective piercing device 6 and be positioned close to it.

Advantageously, each capture sleeve may be of square or rectangular section, and be made of a material having a high mechanical strength, such as steel. This makes it possible to increase the rigidity and strength of the suction sleeve. A capture sleeve is thereby formed which, apart from its primary function of routing the gases, can be used in particular as a belt for strapping the assembly composed of pot shell 1 and confinement chamber 2, and as an attachment support for various components of the electrolytic cell such as piercing devices 6 or lifting devices 7.

Adding several functions to the capture sleeve makes it possible to limit the size of the cell and make manufacturing it easier.

The piercing devices 6 are used to make holes in an alumina and solidified bath crust forming on the surface of the cryolite bath 19 during the electrolysis reaction.

These holes are formed regularly to enable various compounds such as alumina, cryolite (Na3AIF6) or aluminum fluoride (AIF3) to be added in order to stabilize the operating parameters of the electrolytic cell.

The piercing device comprises a jack 61 and a piercing component 62.

The piercing component 62 is designed to be positioned on top of the crust to be pierced. Jack 61 drives the piercing component 62 with a vertical to-and-fro movement to pierce the crust by means of a U-shaped structure 63 composed of first and second wings connected to a transverse core.

The first wing is interdependent with a rod of jack 61 and extends as a prolongation thereof along a translational axis T-Τ' of the rod. The second wing is interdependent with the piercing component 62.

A thermally insulating part may be fixed between the first wing and the rod to limit the risk of heat spreading to jack 61, since an excessive increase in temperature of jack 61 may cause damage to it.

Sliding guide means for the rod of jack 61 may be provided for the window(s) associated with the piercing device(s) 6. These guide means make it possible to guide the translational movement of the assembly consisting of the rod of jack 61, the piercing component 62, and the U-shaped structure 63.

For example, each window 18b associated with a piercing device 6 may comprise a channel 64 surrounding the first wing and forming the guide means for sliding. This channel 64 extends over the edges of the window 18b, and protrudes preferably perpendicularly on an outer face of the shoulder 16a, 17a facing the base 10 of pot shell 1 (i.e. the face of the shoulder opposite the volume defined by confinement chamber 2), so as to minimize the height of the transverse core above the shoulder 16a, 17a.

Lifting devices 7 allow the anode structures 32, and consequently the anode assemblies 3, to be handled. Specifically, lifting devices 7 are used to move the anode assemblies 3 vertically in translation.

Each anode assembly 3 is associated with two respective lifting devices 7 on each of which rests one of its ends. In this way, the movement of each anode assembly 3 is independent of the movement of the other anode assemblies 3 contained in the cell.

Each lifting device 7 comprises a jack 71 and an anode receiver 72.

The jack 71 is used to move the anode receiver 72 vertically in translation along a translation axis T-T'.

The anode receiver 72 includes a bar of rectangular section extending along a longitudinal axis coinciding with the translational axis T-Τ'. A portion (e.g., the end closest to the base of the pot shell) of the bar is electrically connected to flexible electrical conducting means to enable the anode assemblies to be powered. The upper end of the bar includes a housing designed to receive the end of the anode structure 32, its shape being complementary to that of the latter.

Guide means for ensuring a vertical movement along the translational axis T-Τ' of the anode receiver 72 may be provided at the level of the windows 18a associated with the anode receptors

These guide means may comprise one (or more) ring(s) partially surrounding the bar to allow it to slide vertically between: a retracted position where the housing is close to the surface of the cryolite bath, and an extended position where the housing is far from the surface of the cryolite bath.

The lifting device is advantageously electrically isolated from the pot shell 1 and confinement chamber 2.

The reader will have understood that many modifications may be made to the invention described above without materially departing from the new information described herein.

For example in the embodiments described above, the windows 18a were associated lifting devices 7, and the windows 18b were associated with piercing devices 6. It is obvious to those skilled in the art that windows 18a and 18b can be associated with any other component of the cell moving translationally along a translational axis T-Τ'. Also, and in contrast to what is presented above, the windows 18a may be associated with piercing devices 6 and the windows 18b with lifting devices 7.

Furthermore, in the foregoing description, the window(s) corresponded to two-dimensional openings. In the case of three-dimensional openings, the window(s) correspond(s) to the projection in a plane of said three-dimensional openings, this projection defining a passage area for the cell component which is associated with it.

Claims (15)

1. Electrolytic cell used for aluminum production, comprising: a pot shell (1) covered with a liner (14) and including a base (10) and side walls (11,12), the pot shell (1) being designed to receive a cryolite bath (19), characterized in that the cell further comprises a confinement chamber (2) including side walls (21,22) extending above the side walls (11,12) of the pot shell (1), at least one of the side walls (21,22) of the confinement chamber (2) being offset toward the outside of the pot shell (1) in relation to one of the side walls (11,12) of the pot shell (1), and in that the offset side walls (11,12; 21,22) of the pot shell (1) and the confinement chamber (2) are mechanically connected by a shoulder (16, 17) including at least one window (18a, 18b) through which passes a respective component of the cell moving translationally along an axis T-Τ' through the window (18a, 18b).

2. Electrolytic cell according to claim 1, wherein the shoulder (16,17) extends between the lower edge of the offset side wall of the confinement chamber (2) and the upper edge of the side wall of the pot shell (1).

3. Electrolytic cell according to any one of claims 1 or 2, wherein the pot shell (1) includes first and second transverse side walls (11) and first and second longitudinal side walls (12), the confinement chamber (2) includes: first and second transverse side walls (21) extending over the first and second transverse side walls (11) of the pot shell (1), and first and second longitudinal side walls (22) extending over the first and second longitudinal side walls (12) of the pot shell (1), the first longitudinal side wall (22) of confinement chamber (2) being offset toward the outside of pot shell (1) relative to the first longitudinal side wall (12) of pot shell (1) and the first longitudinal side walls (12, 22) of pot shell (1) and confinement chamber (2) being mechanically connected by a shoulder (16, 17) including at least one window (18a, 18b) through which passes a respective cell component moving translationally along an axis T-T' through the window (18a, 18b).

4. Electrolytic cell according to claim 3, wherein the first and second longitudinal side walls (22) of confinement chamber (2) are offset towards the outside of pot shell (1) relative to the first and second respective longitudinal side walls (12) of pot shell (1), the first and second respective longitudinal side walls (12, 22) of pot shell (1) and confinement chamber (2) being mechanically connected by shoulders (16, 17), each shoulder (16, 17) including at least one window (18a, 18b) through which passes a respective cell component moving translationally along an axis T-Τ' through the window (18a, 18b).

5. Electrolytic cell according to any one of claims 1 to 4, wherein confinement chamber (2) comprises a removable cover means closing an opening formed by the upper portions of the side walls of confinement chamber (2).

6. Electrolytic cell according to any one of claims 1 to 5, wherein each window extends in a plane perpendicular to the translational axis T-T'

7. Electrolytic cell according to any one of claims 1 to 6, wherein the translational axis T-T' is vertical, each shoulder extending substantially in a horizontal plane.

8. Electrolytic cell according to any one of claims 1 or 7, wherein pot shell (1) and confinement chamber (2) are of substantially parallelepiped shape.

9. Electrolytic cell according to any one of claims 1 to 8, wherein each window is of complementary shape to the sectional shape of the respective cell component passing through said window.

10. Electrolytic cell according to any one of claims 1 to 9, which further comprises a dynamic seal associated with each window.

11. Electrolytic cell according to any one of claims 1 to 10, wherein the shoulder comprises at least one slot projecting in a direction opposite the base of the pot shell, a window (18b) being formed in the at least one slot.

12. Electrolytic cell according to any one of claims 1 to 11, wherein the cell comprises at least one anode assembly (3) supported by anode receivers (72) that can move translationally along the axis T-Τ' to immerse the anode assembly in or extract it from the cryolite bath, the shoulder having at least one window (18a) through which passes a respective anode receiver.

13. Electrolytic cell according to claim 12, wherein the anode assembly (3) passes through the cell from one a longitudinal side wall (22) to the other of the confinement chamber (2) and rests on two anode receivers (72) passing through the windows (18a) of two shoulders (16,17) arranged on opposite longitudinal sides of the electrolytic cell.

14. Electrolytic cell according to any one of claims 1 to 13, wherein the cell comprises at least one piercing device for making a hole in a crust forming on the surface of the cryolite bath, the shoulder having at least one window through which the piercing device passes.

15. Electrolytic cell according to any one of claims 1 to 14, wherein the pot shell, the shoulder(s) and the confinement chamber are single-piece.