WO2015110905A1

WO2015110905A1 - Electrolysis tank casing

Info

Publication number: WO2015110905A1
Application number: PCT/IB2015/000073
Authority: WO
Inventors: Frédéric BRUN; Yves Rochet; Patrice VERDU; Steeve RENAUDIER; Didier OUILLON
Original assignee: Rio Tinto Alcan International Limited
Priority date: 2014-01-27
Filing date: 2015-01-23
Publication date: 2015-07-30
Also published as: EP3099842B1; CA2935484A1; RU2016134823A3; AU2015208859A1; RU2016134823A; EP3099842A1; DK201670544A1; RU2682729C2; DK179169B1; FR3016896A1; CA2935484C; CN105940147A; EP3099842A4; CN105940147B; FR3016896B1; BR112016015534B1; AU2015208859B2; BR112016015534A2

Abstract

The invention relates to an electrolysis tank comprising a casing (1) covered with an inner coating and including a base (10) and side walls (11, 12), the casing (1) being intended to receive a cryolite bath, and a containment enclosure on the casing, the enclosure comprising side walls, at least one of the side walls of the enclosure being offset towards the exterior of the casing relative to a side wall thereof, the tank comprising at least one peripheral shoulder (16, 17) extending between the offset side walls of the casing and of the enclosure, each shoulder comprising at least one window (18a) through each of which passes a tank component moving in translation along a translation axis T-T'.

Description

ELECTROLYTIC TANK HOUSING

Technical area

The present invention relates to the general technical field of aluminum production by electrolysis in an electrolysis cell containing a cryolite bath (hereinafter referred to as "cryolite bath").

It relates more specifically to an electrolytic cell box for containing such a cryolite bath. The anodes are more particularly carbon type precooked.

Presentation of the prior art

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

Currently, aluminum production on an industrial scale is carried out in an electrolytic cell composed in particular:

a parallelepipedic steel box including a bottom and side walls, the box being open in its upper part,

a refractory lining covering the bottom and the side walls of the box,

a cathode based on cathode blocks made of carbonaceous material disposed in the box and connected to electrical conductors for the routing of the electrolysis current.

The electrolysis cell also comprises a cryolite bath contained in the box and consisting in particular of cryolite and dissolved alumina.

A precooked carbon block constituting the anode of an anode assembly is immersed in the cryolite bath and consumed as the electrolysis reaction producing the aluminum progresses.

A through superstructure is mounted on the chamber of the electrolysis cell. This superstructure is for example placed on the box and extends to the right above the opening of the box. The superstructure makes it possible to support various elements of the electrolytic cell arranged at right above the opening of the box such as:

lifting means provided for lowering the anode in the electrolytic cell as it is consumed,

reagent feed means provided to allow the introduction into the cryolite bath of reagents consumed during the electrolysis reaction, a device for collecting polluting gases designed to prevent the emission into the atmosphere of the polluting gases generated during the electrolysis reaction - such as carbon dioxide, carbon monoxide, sulfur dioxide and fluoride; hydrogen gas.

Finally, the tank generally comprises a cowling consisting of a series of hoods placed between the upper edges of the box and the superstructure. The cowling is intended to cap the open upper part between the box and the superstructure to contain the pollutant gases inside the tank.

At the bottom of the electrolytic cell is formed a layer of liquid aluminum discharged periodically by suction or siphoning.

A disadvantage of this type of electrolysis cell concerns the risks of exhausting polluting gases to the outside. These risks of gas escape can have different origins.

In particular, various products used in the electrolysis reaction - such as the cover product - can accumulate on the edges of the box against which the covers are supported. This accumulation of products can prevent the correct positioning of the covers. This induces the appearance of leaks of polluting gases at the upper edge of the box and between the covers disposed on each side of the tank.

Also, anode rods of the anode assemblies pass through the cowling. These anode rods are associated with dynamic sealing means provided to prevent the escape of gas through the junctions between the cowling and the anode rods. However, the dynamic sealing means can be damaged, especially when handling the anode rods to change an anode used by a new anode. The damage of the dynamic sealing means induces the appearance of leaks of polluting gases at the junctions between the cowling and the anode rods.

Another disadvantage of this type of electrolytic cell concerns the movement kinematics of the anode assemblies when replacing a spent anode with a new anode. Indeed, the presence of the superstructure above the opening of the box generates an obstacle to the vertical displacement of the anode assemblies. It is therefore necessary to implement a kinematics complex displacement of anode assemblies around this superstructure to allow their extraction from the electrolytic cell.

An object of the present invention is to provide an electrolytic cell to overcome at least one of the aforementioned drawbacks. In particular, a purpose of this The invention is to provide an electrolytic cell having improved sealing to polluting gases and in which the extraction of the anode assemblies is facilitated.

Summary of the invention

For this purpose, the invention proposes an electrolytic cell that can be used for the production of aluminum, comprising a box covered with an inner lining and including a bottom and side walls, the box being intended to receive a cryolite bath, characterized in that the vessel further comprises a confinement enclosure including lateral walls extending above the side walls of the box, at least one of the side walls of the chamber being shifted outwardly of the box with respect to one of the side walls of the box, and in that the side walls offset from the box and the chamber are mechanically connected by a shoulder including at least one window through which passes a respective member of vessel moving in translation along a TT 'axis traversing the window.

In the context of the present invention, a side wall of the chamber is considered to be offset relative to a side wall of the box when the lower edge of the side wall of the chamber is offset horizontally with respect to the upper edge of the wall. side of the box. To the outside of the box means the opposite side inside the box with respect to the side wall.

The shoulder advantageously extends between the lower edge of the side wall offset from the containment chamber and the upper edge of the side wall of the box. The shoulder is more particularly a physical wall sealing between the offset side walls of the containment chamber and the box that connects mechanically. The shoulder may further advantageously support and ensure the mechanical strength of the containment enclosure.

The tank comprises one (or more) shoulder (s) between the box and the enclosure. Each shoulder comprises one (or more) window (s) through which (which) passes (s) a member (elements) movable (s) in translation along a translation axis TT 'through the (the) window (s) , in particular perpendicular to the plane in which (said) window (s) extend.

This particular arrangement (ie shoulder / window assembly for the passage of a respective vessel member moving in translation along an axis TT 'passing through the window) makes it possible to limit the dimensions of the window (s) so as to avoid exhausting pollutant gases to the outside of the electrolytic cell through that (s). This particular arrangement also makes it possible to arrange the moving elements of an electrolysis cell - such as lifting or drilling devices - at the periphery of the box, unlike the electrolysis cells of the prior art where the devices of lifting and / or mobile drilling devices are generally positioned to the right of an opening defined by the walls of the box. Positioning the lifting devices and / or the drilling devices at the periphery of the box allows the absence of obstacle to a vertical stroke of the anode assemblies. This makes it possible to facilitate the production of a sealed containment enclosure and a replacement of the anode assemblies by the top of the electrolytic cell without requiring the implementation of a kinematics of complex displacement of the anode assemblies.

The containment chamber makes it possible to confine the tank gases to facilitate their capture and treatment. The containment enclosure advantageously comprises a removable cowling system closing an opening formed by the upper portions of the side walls of the containment chamber so as to achieve without embarrassment a change of anode assembly from the top of the electrolytic cell. . An opening is made in the removable cowling system for extracting or inserting an anode assembly into the containment.

Preferred but non-limiting aspects of the electrolytic cell according to the invention are as follows.

Preferably, the box includes first and second transverse side walls and first and second longitudinal side walls, the containment enclosure includes first and second transverse side walls extending above the first and second transverse side walls of the box. , and first and second longitudinal side walls extending above the first and second longitudinal side walls of the box, the first longitudinal side wall of the chamber being shifted outwardly of the box relative to the first longitudinal side wall of the box and the first longitudinal side walls of the box and the chamber being mechanically connected by a shoulder including at least one window through which passes a respective member of vessel moving in translation along an axis TT through the window.

The shoulder is advantageously provided on at least one longitudinal side of the electrolysis cell along which lifting devices and / or piercing devices can then be distributed.

In addition, more particularly, the first and second longitudinal side walls of the enclosure are shifted outwardly of the box relative to the first and second respective longitudinal sidewalls of the box, the respective first and second longitudinal sidewalls of the box and the chamber being mechanically connected by shoulders, each shoulder including at least one window through which a respective bowl member moving through is passed. translation along a TT axis through the window.

The first and second longitudinal side walls of the box extend between and below the first and second longitudinal side walls of the enclosure.

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

The tank may further comprise four peripheral shoulders extending between the upper edges of the side walls of the box and the lower edges of the side walls of the enclosure. This allows in particular to have movable elements in translation between the four side walls of the box and the four side walls of the enclosure.

Each shoulder may be part of the box and / or enclosure. For example :

the box may comprise two peripheral shoulders extending outwardly of the volume defined by the box, along the upper edges of the first and second longitudinal side walls of the box, the enclosure being devoid of shoulder and being placed on the shoulders the box,

the enclosure may comprise two peripheral shoulders extending inwardly of the volume defined by the enclosure, along the lower edges of the first and second longitudinal side walls of the enclosure, the housing being devoid of shoulder, and enclosure being placed on the upper edges of the side walls of the box,

the box and the enclosure may comprise respectively two peripheral shoulders, the shoulders of the box extending outwardly of the volume defined by the box along the upper edges of the first and second longitudinal side walls of the box, and the shoulders of the box; enclosure extending inwardly of the volume defined by the enclosure along the lower edges of the first and second longitudinal side walls of the enclosure; the fact that the box and the chamber each comprise shoulders facilitates the support of the chamber on the box and improves the stability of the stack composed of the box and the chamber, the box and the enclosure may still be one and the same monobloc element also including the shoulder or shoulders.

The box and the confinement chamber are each preferably of parallelepipedal shape. The tank then advantageously has the shape of two parallelepipeds placed one on top of the other, the upper parallelepiped (confinement chamber) being slightly wider than the lower parallelepiped (caisson).

Preferably, each window extends in a plane perpendicular to the translation axis T-T '. The translation axis T-T 'can 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 window of the shoulder and the translational cell element is then facilitated.

In an alternative embodiment, each window is of complementary shape to the sectional shape of the respective vessel member passing through said window, more particularly of homothetic shape. This makes it possible to minimize the dimensions of the gap between the window and the displaceable element so as to limit the risks of exhausting polluting gases through said gap. In certain embodiments, each element passes through a respective window through a dynamic seal, including annular. Each seal is for example mounted at the periphery of a window, around the element in translation. This makes it possible to further improve the tightness of the tank. Preferably, each window is electrically insulated from the element passing through it.

According to an alternative embodiment, the shoulder comprises at least one slot protruding in a direction opposite to the bottom of the box, a window being formed in the at least one slot.

The window made in the upper part of the crenel is thus raised relative to the height of the cryolite bath so as to limit the exposure of the elements moving in translation through the window to the heat released by the cryolite bath, gas and air. cover product.

Different types of translatable element can be associated with a window. For example, when the tank comprises at least one anode assembly supported by anodic receivers displaceable in translation along the axis TT to plunge or extract the anode assembly from the cryolite bath, windows of the shoulder can be associated with said anode receivers, each window allowing the passage of a respective anode receiver.

According to a preferred embodiment, the anode assembly passes through the vessel of a wall lateral longitudinal to the other of the containment and rests on two anode receivers crossing windows of two shoulders arranged on opposite longitudinal sides of the electrolysis cell. The anode assembly then rests on support means and translational perfectly stable and without impact on the tightness of the containment.

Of course, the windows (or other windows) may be associated with other types of elements moving in translation such as an electric current conduction device for supplying the anode with electric current, or a device for drilling.

In particular, in one embodiment, the vessel comprises a piercing device intended to create a hole in a crust forming on the surface of the cryolite bath to allow a supply, in particular of alumina of the cryolite bath, the shoulder comprising at least one window through which the drilling device passes, more particularly a part (a bar) of the drilling device moving in translation.

The windows associated with the piercing devices are thus raised relative to the height of the cryolite bath so as to limit the exposure of the piercing devices to the heat released by the cryolite bath, gases and the roofing product.

Preferably, each shoulder comprises at least one attachment device on one side of the shoulder opposite the bottom, for example a plate having a through hole and forming a hooked point, for handling the box. This facilitates the movement of the vessel using a handling unit typically comprising a crane, a carriage adapted to be moved on the crane removably connectable to the box using for example pedals.

Each shoulder may extend over the entire length of the longitudinal side wall (respectively transverse) of the box and / or the enclosure. This makes it possible to arrange the elements displaceable in translation along the T-T axis over the entire length (respectively the width) of the tank.

Advantageously, the side walls of the containment enclosure and the box can serve as a point of attachment to the periphery of the electrolytic cell for equipment generally fixed above the opening of the box in the prior art. Thus, the tank may comprise anode assembly lifting means, piercing device, a gas collection system and an alumina supply device which are fixed on the side walls of the containment enclosure and / or on the side walls of the box. Preferably, the box, the shoulder (s) and the enclosure are in one piece. This limits the risk of leakage at the junction between the box, the shoulder or shoulders and the enclosure that could be related to thermal expansion problems. Alternatively, the box, the or the shoulders and the enclosure may be in two (or more) parts.

Brief description of the figures

Other advantages and characteristics of the electrolysis cell will emerge from the following description of several alternative embodiments, given by way of non-limiting examples, from the appended drawings in which:

FIG. 1 is a longitudinal sectional view of an electrolytic cell,

FIG. 2 is a cross-sectional view of two adjacent electrolysis cells, FIG. 3 is a partial view of an electrolysis cell comprising a piercing device,

FIG. 4 is a schematic representation in perspective of a box of an electrolytic cell,

Figure 5 is a perspective view of an electrolytic cell. detailed description

An example of an electrolytic cell according to the invention will now be described. In these different figures, the equivalent elements bear the same numerical references.

In the rest of the text, the terms "side wall", "bottom" and "top opening" will be used, with reference to a rectangular parallelepiped.

The reader will appreciate that in the context of the present invention, the following is meant:

'Bottom' means a horizontal wall of a rectangular parallelepiped situated close to the ground,

'Upper opening' means an opening in a horizontal wall of a rectangular parallelepiped opposite to the bottom,

'Face / side wall' means a face / vertical wall of a rectangular parallelepiped extending in a plane perpendicular to the bottom,

'Longitudinal faces / walls' means the vertical faces / walls of a rectangular parallelepiped of which at least one dimension is greater than the dimensions of the other faces / side walls,

"Transverse faces / walls" means vertical faces / walls extending perpendicular to the longitudinal faces / walls. With reference to FIGS. 1 to 3, an example of an electrolytic cell according to the invention is illustrated.

The electrolysis tank of substantially rectangular parallelepiped shape comprises a box 1, a containment chamber 2, a plurality of anode assemblies 3, a cathode 4, a gas collection device 5, one (or more) device (s) drilling device 6, and several lifting devices 7.

This tank is used for the production of aluminum. It may be associated with a plurality of other electrolysis cells, possibly identical, the different tanks being arranged one after the other, two successive electrolytic cells being adjacent at one of their longitudinal side walls. .

With reference to FIG. 4, the casing 1 is of generally parallelepipedal shape. It comprises a bottom 10, first and second transverse side walls 11, and first and second longitudinal side walls 12. The caisson 1 also comprises cradles 13 extending on the outer faces of the bottom 10 and the side walls 11, 12 These cradles 13 make it possible to mechanically reinforce the casing 1.

The casing 1 may be metallic, for example steel. The internal faces of the bottom 10 and the side walls 11, 12 of the box 1 are covered with refractory blocks 14 for heat insulating the box 1. The blocks 14 may comprise for example refractory bricks and / or carbon blocks.

The enclosure 2 defines a closed volume of confinement of the gases above the cryolite bath 19 in which the anode assemblies 3 are displaced.

The enclosure 2 is supported on the upper edges of the caisson 1. It comprises first and second transverse side walls 21 and first and second longitudinal side walls 22 fixed to the caisson 1.

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

The enclosure 2 also includes a removable cover 23 to cover the upper opening defined by the four side walls 21, 22 of the enclosure 2. The cover 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 enclosure 2, and more particularly on gas collection ducts extending at the upper edges of the enclosure 2.

The box 1 is open in its upper part 15. The tank comprises one (or more) peripheral shoulder (s) 16, 17 between the upper edges of the side walls of the box and the lower edges of the side walls of the enclosure .

Each peripheral shoulder 16, 17 extends outwardly from the box 1 (respectively towards the inside of the enclosure), parallel to the bottom 10 of the box 1. The shoulders may be part of the box 1 and / or the enclosure 2.

Each shoulder 16, 17 is associated with a side wall January 1, 12 (respectively 21, 22) of the box 1 (respectively of the enclosure).

More precisely in the embodiment illustrated in Figure 4, the box comprises four peripheral shoulders 16, 17 extending along one of the upper edges of the side walls 1 1, 12 of the box 1:

two longitudinal peripheral shoulders 16, each longitudinal peripheral shoulder 16 extending along an upper edge of a respective longitudinal lateral wall 12 of the casing 1,

two transverse peripheral shoulders 17, each transverse peripheral shoulder 17 extending along an upper edge of a respective transverse lateral wall 1 1 of the caisson 1.

In a variant, the caisson 1 (and / or the enclosure) may (may each) comprise:

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 an element of the vessel moving in translation along a translation axis T-T 'during the operation of the vessel. This element of the tank may be a part of a lifting device 7 moving in translation along the translation axis TT 'such as an anode receiver 72 of a lifting device 7 which will be described in more detail in FIG. after.

Thus, each window 18a is associated with a respective tank member therethrough, said bowl member being movable in translation along the translation axis T-T 'between two extreme positions.

Advantageously, each window 18a extends in a plane perpendicular to the axis of translation Τ-Τ '. This makes it possible to reduce the dimensions of the windows 18a by making them independent of the movement of the elements moving in translation along the translation 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 translation axis T-T '. In this case, the windows 18a extend in a horizontal plane. The same goes for each shoulder 16, 17.

The shape of each window 18a may be complementary to the sectional shape (in a plane perpendicular to the translation axis T-T ') of the element passing through said window. This makes it possible to minimize the dimensions of the window so as to limit the risks of exhausting polluting gases to the outside of the electrolytic cell. Referring to Figure 4, each window 18a is of rectangular shape complementary to the rectangular sectional shape of their associated anode receivers 72.

Advantageously, each window 18a of the box 1 may comprise a seal extending on its edges, so that the seal surrounds the translationally displaceable member associated with the window. This improves the sealing of the tank so as to limit the risk of exhausting polluting gases through the windows.

The seal may be adapted to cooperate with a sealing portion arranged on the sliding element. In this case, the sealing portion extends along the region of the sliding member through the seal during translational movement of the element between its extreme positions. Thus, the tightness of the tank is ensured despite the translational movement of the element.

The dynamic seal, typically annular around the sealing portion, may also serve as an electrical insulator if the sliding element is not at the same electrical potential as the edges of the window through.

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

The shape of each window 18b may be complementary to the sectional shape (in a plane perpendicular to the translation axis T-T ') of the part passing through said window18b to limit the risk of exhausting gaseous pollutants to the atmosphere. outside the electrolysis cell. Referring to Figure 5, each window 18b is circular in shape complementary to the cylindrical shape of the piercing device part 6 associated therewith. A seal may be provided on the edges of each window 18b, so that the seal surrounds the displaceably movable part of the piercing device 6.

The seal may be adapted to cooperate with a sealing portion arranged on the part of the piercing device 6, this portion extending over the entire region of the sliding part through the seal during the displacement. translation of the part between its extreme positions.

The windows 18a and 18b can extend in the combined planes.

Alternatively and as illustrated in Figure 5, the windows 18a and 18b may extend in separate planes.

In particular in the embodiment illustrated in FIG. 5, each shoulder 16, 17 comprises slots projecting in a direction opposite to the bottom 10 of the box 1.

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

Advantageously, the side walls 21, 22 of the enclosure 2 may be in abutment with the upper edges of the caisson 1 at the free ends of the shoulders 16, 17. As a result, the surface of the opening defined by the lower edges lateral walls 21, 22 of the enclosure 2 are substantially equal to the sum of:

the surface of the shoulders 16, 17 and

the surface of the upper opening defined by the upper edges of the side walls 11, 2 of the box 1.

Preferably, the casing 1 or the shoulders 16, 17 and the enclosure 2 are monobloc. This limits the risk of leakage at the junction between the box and the enclosure. These risks are otherwise significant because the chamber 1 and the enclosure will have a different behavior compared to the expansion caused by the high operating temperatures of an electrolysis cell.

Alternatively, the box or the shoulders 16, 17 and the enclosure may be in two (or more) parts. In one embodiment, the caisson 1 and the enclosure 2 each comprise shoulders extending:

for the shoulders of the box 1, on one (or more) edge (s) of the upper (or) side wall (s) longitudinal (s) (and transverse) of the box,

for the shoulders of the chamber 2, on a lower edge (s) of one (or more) side wall (s) longitudinal (s) (and transverse) of the enclosure.

The shoulder (s) extend (s) preferably perpendicular to the walls the side of the chamber 1 and the chamber 2, each shoulder of the chamber 2 can come into contact with a respective peripheral shoulder of the box.

The presence of shoulders both on the side walls of the chamber 1 and the chamber 2 facilitates the support of the chamber 2 on the chamber 1 and improves the stability of the stack composed of box 1 and enclosure 2.

As indicated above, each shoulder may extend over the entire length of the side wall of the enclosure 2 (respectively of box 1), the shoulders of the enclosure 2 and the box 1 each comprising one (or more) window ( s) at coinciding positions when the enclosure 2 is placed on the caisson 1.

Each anode assembly 3 comprises an anode 31 and an anode structure 32. The anode structure 32 on the one hand manipulates the anode 31, and on the other hand to supply the electric current. During the electrolysis reaction, the anode 31 immersed in the cryolite bath is consumed. Anode assemblies 3 must therefore be replaced periodically.

The anode 31 is preferably a block of precooked carbonaceous material.

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

The anode structure may comprise an armature made of a metal having good mechanical strength, such as steel. This allows the anode structure to maintain the anode assemblies in suspension. It may also comprise sections made of a metal having a good electrical conductivity such as copper or aluminum. This allows the anode structure to provide electrical power routing for the power supply of the anode assemblies.

The cathode 4 may comprise a plurality of cathode blocks of carbonaceous material.

The cathode 4 is connected in its lower part to electrical conduction means of the electrolysis current 41 formed in particular of one or more conductors. More particularly, each cathode block comprises at least one recess in its lower part inside which is disposed an electrical conduction means 41.

A good physical and electrical connection is made in the recess between the cathode block 4 and the electrical conduction means 41 using cast iron. The driver passes through the box 1 at the openings in the housing 1, more particularly the bottom 10 or the longitudinal side walls 12.

The conductor collects electrical current at the cathode to allow it to be routed from one electrolysis cell to another.

The gas collection device 5 can recover for treatment the pollutant gases generated during the electrolysis reaction.

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

The capture sheath (s) is (are) associated with one (or more) suction device (s) (not shown). It (s) extends (ent) on the longitudinal side walls 22 of the chamber 2, and possibly on the transverse side walls 21 of the enclosure 2. The presence of openings along the longitudinal walls 22 of the enclosure 2 improves the efficiency of collection of gaseous pollutants.

Advantageously, the number of openings of the collection device 5 may 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 drilling device 6 and be positioned close to it.

Advantageously, each capture sheath 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 the strength of the suction duct. A collection sheath is thus formed which, in addition to its primary function of conveying gases, can be used in particular as a strapping belt for the assembly composed of the box 1 and the chamber 2, and as a support for fixing for different elements of the electrolysis cell such as drilling devices 6 or lifting devices 7.

The fact of associating several functions with the capture sheath thus makes it possible to limit the bulk of the tank and to facilitate its manufacture.

The piercing devices 6 make it possible to form holes in a crust of alumina and solidified bath forming on the surface of the cryolite bath 19 during the electrolysis reaction.

These holes are formed regularly to allow the addition of various compounds - such as alumina, cryolite (Na3AIF6) or aluminum fluoride (AIF3) - to stabilize the operating parameters of the electrolysis cell. .

The piercing device comprises a jack 61 and a piercing member 62. The piercing member 62 is intended to be positioned above the crust to be pierced. The jack 61 makes it possible to animate the piercing member 62 in a vertical reciprocating movement to pierce the crust via a U-shaped structure 63 composed of first and second wings connected to a transverse core. .

The first wing is integral with a rod of the jack 61 and extends in the extension thereof along a T-T 'axis of translation of the rod. The second wing is secured to the piercing member 62.

A thermally insulating part may be fixed between the first flange and the rod to limit the risk of propagation of heat to the cylinder 61, an excessive increase in the temperature of the cylinder 61 may degrade.

Sliding guide means of the cylinder rod 61 may be provided for the window (s) associated with the drilling device (s). These guide means serve to guide the displacement. in translation of the assembly consisting of the cylinder rod 61, the piercing member 62, and the U-shaped structure 63.

For example, each window 8b associated with a piercing device 6 may comprise a channel 64 surrounding the first wing and forming the sliding guide means. This channel 64 extends on the edges of the window 18b, and protrudes, preferably perpendicularly to an outer face of the shoulder 16a, 17a opposite the bottom 10 of the box 1 (ie face of the shoulder opposite the volume closed defined by the enclosure 2), so as to minimize the height of the transverse core above the shoulder 16a, 17a.

The lifting devices 7 allow the manipulation of the anode structures 32, and consequently the anode assemblies 3. More precisely, the lifting devices 7 make it possible 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. Thus, the displacement of each anode assembly 3 is independent of the displacement of the other anode assemblies 3 contained in the tank.

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

The cylinder 71 makes it possible to move the anodic receiver 72 vertically in translation along a translation axis T-T '.

The anode receiver 72 comprises a bar of rectangular section extending along a longitudinal axis coinciding with the translation axis T-T '. A portion (for example the end closest to the bottom of the box) of the bar is electrically connected to flexible electrical conduction means to allow the power supply of the anode assemblies. The upper end of the bar comprises a housing for receiving the end of the anode structure 32 and whose shape is complementary thereto.

Guiding means for ensuring a vertical displacement along the translation axis T-T 'of the anode receiver 72 may be provided at the windows 18a associated with the anode receivers.

These guide means may comprise one (or more) ring (s) partially surrounding the bar to allow its vertical sliding between:

- A retracted position where the housing is close to the surface of the cryolite bath, and a deployed position where the housing is removed from the surface of the cryolite bath.

The lifting device is advantageously electrically isolated from the caisson 1 and the enclosure 2.

The reader will have understood that many modifications can be made to the invention described above without physically going out of the new teachings described here.

For example, in the embodiments described above, the windows 18a were associated with lifting devices 7, and the windows 18b were associated with drilling devices 6. It is obvious to those skilled in the art that the windows 18a and 18b 18b can be associated with any other bowl member moving in translation along a translation axis T-T '. Also and contrary to what is presented above, windows 18a can be associated with drilling devices 6 and windows 18b with lifting devices 7.

Moreover, in the foregoing description, the window (s) corresponded to two-dimensional openings. In the case of three-dimensional openings, the (or) window (s) correspond to the projection in a plane of said three-dimensional openings, this projection defining a passage region for the cell element associated therewith.

Claims

1. Electrolysis tank usable for the production of aluminum, comprising:

a box (1) covered with an interior coating (14) and including a bottom (10) and side walls (1 1, 12), the box (1) being intended to receive a cryolithic bath (19), characterized in that

the tank further comprises a confinement enclosure (2) including side walls (21,22) extending above the side walls (11,12) of the box (1),

at least one of the side walls (21,22) of the confinement enclosure (2) being offset towards the outside of the box (1) relative to one of the side walls (11,12) of the box (1), and in that the offset side walls (1 1, 12; 21, 22) of the box (1) and the confinement enclosure (2) are mechanically connected by a shoulder (16, 17) including at least one window (18a, 18b) through which passes a respective tank element moving in translation along an axis T-T' passing through the window (18a, 18b).

2. Electrolysis tank according to claim 1, in which the shoulder (16,17) extends between a lower edge of the offset side wall of the confinement enclosure (2) and an upper edge of the side wall of the box (1).

3. Electrolysis tank according to any one of claims 1 or 2, in which the box (1) includes first and second transverse side walls (11) and first and second longitudinal side walls (12), the enclosure containment (2) includes:

first and second transverse side walls (21) extending above the first and second transverse side walls (11) of the box (1), and - first and second longitudinal side walls (22) extending above first and second longitudinal side walls (12) of the box (1), the first longitudinal side wall (22) of the confinement enclosure (2) being offset towards the outside of the box (1) relative to the first wall longitudinal side (12) of the box (1) and the first longitudinal side walls (12, 22) of the box (1) and the confinement enclosure (2) being mechanically connected by a shoulder (16, 17) including at least a window (18a, 18b) through which passes a respective tank element moving in translation along an axis TT' passing through the window (18a,

4. Electrolysis tank according to claim 3, in which the first and second longitudinal side walls (22) of the enclosure (2) are offset towards the outside of the box (1) relative to the first and second longitudinal side walls (12) of the box (1), the respective first and second longitudinal side walls (12, 22) of the box (1) and the enclosure (2) being mechanically connected by shoulders (16, 17), each shoulder (16, 17) including at least one window (18a, 18b) through which passes a respective tank element moving in translation along an axis T-T' passing through the window (18a, 18b).

5. Electrolysis tank according to any one of claims 1 to 4, in which the confinement enclosure (2) comprises a removable cover system closing an opening formed by the upper portions of the side walls of the enclosure (2 ) confinement.

6. Electrolysis tank according to any one of claims 1 to 5, in which each window extends in a plane perpendicular to the translation axis T-T'

7. Electrolysis tank according to any one of claims 1 to 6, in which the translation axis T-T' is vertical, each shoulder extending substantially in a horizontal plane.

8. Electrolysis tank according to any one of claims 1 to 7, in which the box (1) and the confinement enclosure (2) are of substantially parallelepiped shape.

9. Electrolysis tank according to any one of claims 1 to 8, in which each window is of shape complementary to the sectional shape of the respective tank element passing through said window.

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

11. Electrolysis tank according to any one of claims 1 to 10, in which the shoulder comprises at least one slot projecting in a direction opposite to the bottom of the box, a window (18b) being formed in the at least one niche.

12. Electrolysis tank according to any one of claims 1 to 11, in which the tank comprises at least one anode assembly (3) supported by anodic receivers (72) movable in translation along the axis TT' to immerse or extract the anode assembly of the cryolite bath, the shoulder comprising at least one window (18a) through which a respective anode receiver passes.

13. Electrolysis tank according to claim 12, in which the anode assembly (3) passes through the tank from one longitudinal side wall (22) to the other of the confinement enclosure (2) and rests on two receivers anodes (72) passing through windows (18a) of two shoulders (16,17) arranged on opposite longitudinal sides of the electrolysis tank.

14. Electrolysis tank according to any one of claims 1 to 13, in which the tank comprises at least one drilling device intended to create a hole in a crust forming on the surface of the cryolite bath, the shoulder comprising at least minus a window through which the drilling device passes.

15. Electrolysis tank according to any one of claims 1 to 14, in which the box, the shoulder(s) and the confinement enclosure are in one piece.

16. Electrolysis tank according to any one of claims 1 to 15, comprising means for lifting anode assemblies, drilling devices, a gas collection system and an alumina supply device which are fixed on side walls (21,22) of the confinement enclosure (2) and/or on side walls (11,12) of the box (1).