DK201670537A1 - Electrolytic cell with an anode assembly lifting device - Google Patents

Abstract

The present invention relates to an electrolytic cell comprising a pot shell (1) including a base (10) and transverse and longitudinal side walls (11, 12), the pot shell (1) and a plurality of anode assemblies (3) each including an anode structure (32) and at least one anode (31), the cell comprising a plurality of lifting devices (6) extending along the longitudinal side walls of the pot shell (1) for moving the anode assemblies (3) the lifting devices comprising a jack (61) comprising a body (611) and a jack rod (612) extending along a longitudinal axis (B- B'), and an anode receiver (62) designed to receive one end of the anode structure (32), the jack (61) being coupled to the anode receiver (62) to drive it with a translational motion along a translation axis (T - T'), characterized in that the longitudinal axis (B -B') of the jack (61) is parallel and separate from the translation axis (T -T') of the anodic receiver (62).

Description

ELECTROLYTIC CELL WITH AN ANODE ASSEMBLY LIFTING DEVICE Technical field

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

It relates more specifically to an electrolytic cell comprising a plurality of lifting devices for anode assemblies contained in the electrolytic cell, each anode assembly having at least one carbon anode of the pre-baked type.

Presentation of prior art

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

Currently, the production of aluminum on an industrial scale is carried out in an electrolytic cell composed of a steel pot shell open in its upper part, and whose base is covered with refractory material over which extends a cathode surmounted by a plurality of anode assemblies immersed in cryolite bath at a temperature between 930 and 980°C.

Each anode assembly comprises an anode structure - consisting of an anode rod and fixing means - attached to at least one anode, in particular a pre-baked carbon block.

The application of an electric current between the anode assemblies and the cathode is used to initiate the electrolytic reaction.

As the usual operating temperature of a cell is between 930 and 980°C, the aluminum produced is liquid. It is deposited by gravity on the cathode which is sealed. Regularly, the aluminum produced, or part of the aluminum produced, is sucked up by a casting ladle, and transferred to the casting furnaces.

The carbon anodes are gradually consumed during the electrolysis reaction. Once one of the anode assemblies is spent, it is replaced by a new anode assembly.

As even a current distribution as possible between the anode assemblies is essential to obtain a good aluminum production yield. This is why the position of an anode plane -defined by the lower faces of the anodes in the anode assemblies - must be accurately controlled.

However, the position of the anode plane facing the cathode layer of liquid aluminum must be periodically adjusted to take account of the variation in parameters such as: the height of the layer of aluminum, which increases steadily then declines sharply when the metal is run off, the progressive wear of the anode plane.

Positioning the anode plane is typically achieved by means of a jack and connecting rod assembly system which moves an anode frame and the plurality of anode assemblies which are fixed and connected to this anode frame.

Such a jack and connecting rod system moving an anode frame placed above the cell has the disadvantage of generating a large bulk above the cell. The height, and therefore the cost, of the building in which the cells are arranged depend on the height of the cell so that this solution is not satisfactory.

Furthermore, the movement of an anode frame to which is attached a plurality of anode assemblies does not allow fine, individual adjustment of the position of the anode assemblies which may make it possible to counter: racing of the cell linked to anode effects, detecting these as soon as they appear by recording the anode voltages and correcting them directly, raising only the anode assembly under which the anode effect is beginning, unequal current distribution between anode assemblies, local heterogeneous features of temperature or bath composition, shape changes of the metal - bath interface due to variations of the map of electrical currents in the bath and in the metal.

From patent document US3575827 a lifting device comprising a jack formed by a body and a rod, is known, the jack body being arranged against a longitudinal side wall of the pot shell of the cell and the free end of the rod serving as a support structure for the anode assemblies. A disadvantage of such a device is that the longitudinal side wall of the pot shell, particularly at the level of the liquid, is very hot and radiates so that operation of the jack and its lifetime may be degraded. Also, the positioning of the jack hinders thermal exchanges at the level of the longitudinal side wall of the pot shell, which must be regulated to control the size of the slope formed in the cell, for example by blowing air as known from patent publication W099/54526. In addition, as the height of wear of the carbon anode blocks is great in current cells, the stroke of the jack must be large so that the overall size, especially the longitudinal size, of the jack is problematic for positioning it against the wall, in particular because of the limited space left between cells by the various electrical conductors of the electrolysis current. The lifting device is also not involved in supplying the electrolysis current to the anode assembly so that when an anode assembly is changed, the electrical supply conductor must be handled in addition in order to be reconnected to the new anode assembly.

An object of the present invention is to propose a cell comprising a lifting system the configuration of which makes it possible to at least partly counter the disadvantages mentioned above.

Summary of the invention

To this end, the invention proposes an electrolytic cell used for producing aluminum, comprising a pot shell including a base and transverse and longitudinal side walls, the pot shell being covered with a liner to receive a cryolite bath and a plurality of anode assemblies each including an anode structure and at least one anode immersed in the cryolite bath, the cell further comprising a plurality of lifting devices extending along the longitudinal side walls of the pot shell to move the anode assemblies, the lifting devices comprising a jack made up of a body and a jack rod extending along a longitudinal axis B-B', and an anode receiver designed to receive one end of the anode structure, the jack being coupled to the anode receiver to drive it with translational motion along a translation axis T- Τ' between a retracted position and a deployed position, characterized in that the longitudinal axis B-B' of the jack is parallel and separate from the translation axis T- Τ' of the anode receiver.

The fact of positioning the lifting devices on the edge of the electrolytic cell - and more specifically along its longitudinal side walls - means that there is no obstruction to a vertical stroke of the anode assemblies. This allows anode assemblies to be replaced from the top of the electrolytic cell, without requiring the anode assemblies to undergo complex motion kinematics. The lifting devices do not extend above the anodes, preferably not above the cryolite bath and even more preferably not above the pot shell. The term "above" should be understood as above the component to which it relates, and in a volume formed by vertical translation of the surface obtained by projecting this component in a horizontal plane. In this way, the lifting devices do not obstruct vertical travel of the anode assemblies.

The lifting devices are used to move the anode assemblies in the electrolytic cell vertically in translation, so as to adjust the position of the anode plane during operation of the electrolytic cell and form an integral part of the electrolytic cell.

The anode assemblies are of the pre-baked kind intended to be changed periodically after wear of the anodes constituting them. The anode structure makes it possible to mechanically support the anodes which are pre-baked carbon blocks and ensure electrical connection of the anode assembly each time the anode assembly is changed. Within the context of the present invention, "parallel and separate axes" is understood to mean two parallel and non-coincident axes, i.e. spaced apart by a nonzero distance.

The fact that the longitudinal axis B- B' of the jack is parallel to and distinct from the translation axis T-Τ' makes it possible to offset the anode receiver relative to the jack. This gives a lifting device which may firstly have a minimum height (i.e. the size of the device along the longitudinal axis of the jack), and secondly can be better and more easily arranged in the small space left available between two adjacent cells for a position at the edge of an electrolytic cell. This improved layout, made possible by offsetting the anode receiver relative to the jack, limits the height of the electrolytic cells and / or decreases the space between two adjacent cells.

To enable the anode receiver to be offset relative to the jack, the lifting devices may comprise a transverse connecting beam between the rod of the jack and the anode receiver, said connecting beam preferably extending along a transverse axis perpendicular to the longitudinal axis B- B' of the jack and to the translation axis T- Τ'.

The assembly composed of the jack rod, the connecting beam and the anode receiver may form a U-shaped structure so that the jack body extends facing the anode receiver. "Facing" is understood to mean that at least one plane perpendicular to the longitudinal axis of the jack passes through the jack body and the anode receiver. This makes it possible to limit the height of the lifting devices.

Advantageously, the connecting beam is mounted interdependent with the jack rod and the connecting beam is mounted interdependent with the anode receiver. This makes it possible to transmit the movements from the rod to the anode receiver.

In one embodiment, the anode receiver may comprise a bar extending along the translation axis T- Τ'. Advantageously, this bar comprises a housing at one of its ends, said housing being designed to receive the end of the anode structure. This rod allows the anode structure to be mechanically held above the cryolite bath. It can also allow the conduction of electric current for powering the anode assemblies. To do this, a portion of the rod is electrically connected to flexible electrical conducting means. The anode assembly is in particular powered electrically via the housing, and more particularly the contact surfaces of the anode structure and the housing. A fixing system may be provided to secure the anode structure to the housing. This is to prevent the anode structure moving outside the housing during the translational movements of the anode structure. This fixing system may include means for holding the anode structure against the housing to ensure current conduction between the housing and the anode structure.

The bar can be of rectangular or square section to improve its mechanical strength. It may further comprise a steel skeleton and copper portions housed in or around the skeleton to route electrical energy to the anode assemblies.

As indicated above, the lifting devices may include anode receiver guide means for guiding the movement of the anode receiver along the translation axis T- Τ'. In some embodiments, the guide means at least partially surround the anode receiver and define a sliding guide path for the anode receiver. For example, the guide means may comprise two rings spaced by a non-zero distance along the translation axis T- Τ', each ring surrounding a portion of the anode receiver. Preferably, each ring may have a slot for the passage of the connecting beam when moving the anode receiver between the retracted and extended positions. This maximizes the distance between the rings in order to avoid a possible angular gap of the bar in the guide means. This ensures a vertical translation movement of the anode receiver.

The lifting devices are attached to the electrolytic cell so that the translation axis T- Τ' of each anode receiver (and therefore the longitudinal axis of the jack) is vertical.

As today's electrolytic cells have large dimensions each electrolytic cell has a plurality of anode assemblies. Each anode structure extends transversely in the cell and is associated with a respective pair of lifting devices arranged along opposite longitudinal side walls of the pot shell and each carrying one of the ends of the anode structure. The cell preferably comprises a controller connected to the lifting devices to control the synchronous movement of the lifting devices of each pair. This ensures a vertical translation movement for each anode assembly.

In some embodiments, the electrolytic cell may include a confinement chamber bearing on the pot shell, the confinement chamber including transverse and longitudinal side walls and being designed to define a confinement volume for the gases above the cryolite bath. Each lifting device can advantageously be fixed to one of the longitudinal side walls of the confinement chamber. In particular, each lifting device can be attached to an upper edge of the confinement chamber opposite the pot shell so that the jack body of each lifting device is positioned at an elevation higher than the elevation of the cryolite bath. This limits the exposure of the jack body to the thermal radiation emanating predominantly on the pot shell opposite the cryolite bath whose operating temperature is around 1000°C, as exposing the body to such temperatures may be detrimental to operation of the jack. By placing the jack body above the cryolite bath, its reliability and durability are increased.

Preferably, each lifting device is fixed to the top edge of the confinement chamber by a free end of the jack so that said free end is further from the bottom of the pot shell than the jack rod.

Preferably, the side walls of the confinement chamber are offset outwardly relative to the side walls of the pot shell so that said side walls of the confinement chamber extend around and above the side walls of the pot shell, the side walls of the pot shell and of the confinement chamber being mechanically connected by a ring-shaped ledge, the anode receiver of the lifting devices extending through openings made in the ledge. This makes it possible to improve the sealing of the cell by reducing the dimensions of the openings to the dimensions of the anode receivers.

The translation axis T- Τ' is preferably vertical, the anode receivers being able to move in vertical translation through the openings made in the ledge. In some embodiments, the anode receivers pass through the confinement chamber via ring-shaped seals providing dynamic sealing. This makes it possible to further improve the sealing of the cell.

To maximize the useful volume for the production of aluminum within the cell and to limit the risk of damage to the lifting devices, the jacks of the lifting devices can extend to the outside of the cell.

The electrolytic cell may also include a gas collection device including at least one gas capture sleeve having suction holes for sucking gas, each lifting device being fixed to said capture sleeve. Each capture sleeve of the gas collection device can extend along the upper edge of the longitudinal side walls of the confinement chamber, each lifting device being fixed to said capture sleeve through a free end of the jack so that said free end is further from the base of the pot shell than the jack rod.

A capture sleeve is thereby formed which, apart from its primary function of routing the gases, can be used in particular as: a strapping belt for the assembly consisting of the pot shell and the confinement chamber, and as an attachment support for different components of the electrolytic cell such as the lifting devices.

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

Brief description of the figures

Other advantages and characteristics of the lifting device according to the invention will emerge from the description which follows of several alternative embodiments, given as non-limiting examples, from the appended drawings in which: figures 1 and 2 are longitudinal and cross sectional views of an example of an electrolytic cell, figures 3 and 4 are perspective views of a lifting device of the electrolytic cell.

Detailed description

We will now describe an example of an electrolytic cell including a lifting device for moving an anode frame. 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.

Furthermore, we will use the terms "above" and "below" relative to a vertical axis.

Figure 1 illustrates an example of an electrolytic cell according to the invention. The electrolytic cell is of 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 and lifting devices 6.

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 side walls as shown in figure 2 where two successive cells C1, C2 are shown.

The pot shell 1 is of a generally right-angled parallelepiped shape. It has a base 10 and transverse 11 and longitudinal sidewalls 12. The base 10 and the four side walls 11, 12 are covered with a refractory material 13 to insulate the pot shell 1. This pot shell 1 may be metallic, for example made of steel.

Pot shell 1 is open in its upper part. It is designed to receive a cryolite bath 14 in which the anode assemblies are immersed 3.

The confinement chamber 2 defines a closed volume above the cryolite bath 14 in which the anode assemblies 3 are moved.

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

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 side walls 11, 12 of pot shell 1. In this way, the planes in which the side walls 21,22 of confinement chamber 2 extend surround the side walls 11, 12 of pot shell 1.

The top edges of pot shell 1 and/or the bottom edges of confinement chamber 2 can form a ledge to mechanically connect the side walls 11, 12, 21, 22 of pot shell 1 and confinement chamber 2, so that confinement chamber 2 defines with pot shell 1 a free volume above the cryolite bath 14.

The confinement chamber also includes a removable cover means 23 to cover the upper opening defined by the four side walls 21,22 of confinement chamber 2. The cover means 23 may be composed of an assembly of panels or hoods extending generally in a plane, and may bear on the upper edges 24 of the side walls 21,22 of the confinement chamber 2.

Each anode assembly 3 comprises at least one anode 31 and anode structure 32. During the electrolysis reaction, the anode 31 immersed in the cryolite bath 14 is consumed. The anode assemblies 3 need to be replaced periodically.

The anode 31 is of the pre-baked type, i.e. a block of carbonaceous material pre-baked before being inserted into the electrolytic cell.

The anode structure 32 firstly makes it possible to support and handle the anode 31, and secondly to supply it with electric power. Each anode structure 32 forms an independent support for its associated anode(s) 31.

As illustrated in figures 1 and 2, the anode assemblies 3 extend transversely in the cell, and the cell comprises a plurality of anode assemblies arranged side by side along the cell along a longitudinal axis of the cell.

Each anode structure 32 extends transversely in the cell between the longitudinal side edges 22 of the confinement chamber 2. In the embodiment illustrated in figures 1 and 2, each anode structure 32 comprises a beam extending transversely between the longitudinal side edges 22 of the confinement chamber 2.

The anode structure 32 may include a frame 332 formed from a metal having good mechanical strength, such as steel, and segments 331 formed from a metal with good electrical conductivity, such as copper. This frame 332 allows the anode structure 32 to maintain anodes 31 in suspension, while the segments 331 are used to ensure the flow of electric current to supply power to the anodes 31.

Cathode 4 is composed of one (or more) block(s) of carbonaceous material. The cathode blocks are electrically connected to cathode conductors leaving the electrolytic cell to route electrical current to the next electrolytic cell. Cathode 4 can be of any type known to those skilled in the art and will not be described in more detail later.

The gas collection device 5 retrieves the polluting gases generated during the electrolysis reaction.

The gas collection device 5 comprises one (or more) capture sleeve(s) on which suction holes 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 the confinement chamber 2, and possibly over the transverse side walls 21 of the confinement chamber 2. The presence of suction holes along the longitudinal walls 23 of the confinement chamber 2 makes it possible to improve the efficiency of the collection of gas pollutants 5.

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 the pot shell 1 and the confinement chamber 2, and as an attachment support for various components of the electrolytic cell such as lifting devices or drilling devices. Adding several functions to the capture sleeve makes it possible to limit the size of the cell and make structural savings.

Lifting devices 6 allow the anode structures 32, from which are suspended anodes 31, to be handled. Specifically, lifting devices 6 are used to move the anode assemblies 3 vertically in translation so as to adjust the positioning of the anode plane during operation of the electrolytic cell.

Each anode structure 32 is associated with two respective lifting devices on each of which rests one of its ends. In this way, the movement of each anode structure 32 is independent of the movement of the other anode structures 32 and anode assemblies contained in the cell. It is therefore possible to move the anode assemblies 3 vertically independently of each other.

Each lifting device 6 is in contact with a respective end of the anode structure 32. Two lifting devices 6 associated with an anode structure 32 are connected to a controller (not shown) to control their operation synchronously. This ensures simultaneous movement of the ends of the anode structure 32 in order to keep it substantially horizontal while it is moving. The controller can also be programmed to control the speed and direction of movement of the anode structure 32. This makes it possible to vary the speed of movement of the anode structure 32 depending on the type of operation in progress. For example, in the case of a replacement of a spent anode assembly 3 by a new anode assembly, the speed of movement of the anode structure 32 may be greater than the speed of movement of the anode structure 32 when adjusting the anode plane during electrolysis, as such an adjustment requires fine settings.

Each lifting device 6 comprises a jack 61 and an anode 62 receiver.

The jack 61 is used to move the anode receiver 62 vertically in translation along a translation axis T- Τ'. The jack 61 includes a body 611 and a rod 612 extending along a longitudinal axis B- B'. Advantageously, the jack 61 may be pneumatic or electrical to withstand the high temperatures prevailing in the vicinity of the cell.

The anode receiver 62 includes a bar 621 of rectangular section extending along a longitudinal axis coinciding with the translation axis T- Τ'. The upper end of bar 621 includes a housing 622 designed to receive the end of the anode structure 32, its shape being complementary to that of the latter.

In particular, housing 622 may be a U-shaped structure composed of a base 6221 extending in a plane perpendicular to the translation axis T- Τ' and two vertical panels 6222 extending perpendicularly to the base 6221, the end of the anode structure 32 being adapted so as to bear on the base 6221, between the vertical panels 6222.

The lifting device may also comprise a fixing system. This fixing system is used to secure the anode structure 32 to housing 622. The fixing system comprises for example an optionally threaded rod to be inserted into bores in the vertical panels 6222, the bores being arranged in the vertical panels 6222 so that the rod extends above the anode structure 32, transversely thereto when the rod is mounted on the housing 622.

The fixing system may include means for holding the anode structure 32 up against a surface of the housing 622, preferably against the base 6221 of the housing 622. For example, the fixing system may include a bolt designed to be screwed through a hole and an internal thread provided respectively in the anode structure 32 and in the base 6221 of the housing 622. The head of the bolt abutting against the anode structure 32 ensures that it is held against the base 6221 of the housing 622.

This fixing system prevents the anode structure 32 from emerging from the housing 622 when the anode structure 32 is moved vertically towards the base 10 of the pot shell 1. The production of aluminum by electrolysis results in the formation of a solidified crust on the surface of the cryolite bath 14. The anodes 31 are set in this solidified crust.

During vertical movement of the anode structure 32 towards the base 10 of the pot shell 1 in order to lower the anodes 31, the stresses - in particular the frictional forces - exerted by the crust on the anodes 31 may be greater than gravity, resulting in a risk of the anode structure leaving the housing.

The presence of a fixing system can limit this risk, particularly by the application of tensile forces on the anode structure 32 tending to keep it inside the housing 622 during the vertical movement of the anodes 31 towards the bottom 10 of the pot shell 1.

Advantageously, as can be seen in figures 2 and 4, a portion 6211 (e.g., the end closest to the bottom of the pot shell 12, or the upper end or housing 622) of the bar is electrically connected to flexible electrical conduction means 7 to supply power to anode assemblies 3 via the housing 622.

Advantageously, the anode receiver 62 is arranged so that the translation axis T- Τ' is separate (i.e., not the same) and parallel to a longitudinal axis B- B' of the jack 61.

This makes it possible to offset the anode receiver 62 relative to jack 61 so as to limit the height of the lifting device 6. This gives a lifting device 6 which may firstly have a minimum height (i.e. the size of the device along the longitudinal axis of the jack), and secondly can be better and more easily arranged in the small space left available between two adjacent cells for a position at the edge of an electrolytic cell.

Such a lifting device 6 can then be positioned at the edge of the electrolytic cell.

It offers the possibility of changing anode assemblies 3 via the top of the electrolytic cell without the lifting devices 6 hindering the vertical travel of the anode assembly 3 replacement operation, which means that major structural savings can be envisioned. Furthermore, the fact of offsetting jack 61 relative to anode receiver 62 makes it possible to position the jack 61 outside the confinement chamber while the anode receiver 62 is inside the confinement chamber. This reduces the risk of damage to jack 61 by limiting its exposure to gas and heat radiation. The jack may advantageously be housed in a free space between the reinforcement cradles of the pot shell 1 to reduce the bulk of the lifting device inside the confinement chamber.

Different solutions may be considered to make the translation axis T- Τ' not the same as, and parallel to the longitudinal axis B- B'.

For example, the jack 61 may be connected to the anode receiver 62 via a transverse connecting beam 63. This transverse connecting beam 63 preferably extends perpendicularly to the rod 612 and the bar 621. The connecting beam 63 is mounted interdependently with the bar 621 and the rod 612 of the jack 61. A bolting system arranged to secure the rod 612 to the transverse connecting beam 63 compensates for any defects of parallelism between the jack 61 and the anode receiver 62.

Guide means 64 ensure the vertical movement of the anode receiver 62 along the axis of translation T - Τ'. The guide means may comprise two rings 641, 642 spaced apart by a nonzero distance along the translation axis T- Τ', each ring partially surrounding bar 621 to allow it to slide vertically between: a retracted or low position where the housing 622 is close to the surface of the cryolite bath 14, and an extended or high position where the housing 622 is distant from the surface of the cryolite bath 14.

In the embodiment illustrated in figure 4, each ring 641,642 is split to allow passage of the transverse beam 63 during sliding of the bar 621 between the retracted and extended positions.

Jack 61 is attached to the pot shell "head-up More specifically, the body 611 of jack 61 is mounted on the pot shell 1 so that its free end 613 is further from the base 10 of pot shell 1 than the rod 612. The free end 613 of the body 611 of jack 61 is preferably fixed to the upper edge of the confinement chamber and advantageously on the capture sleeve of the gas collection device 5. In this way, the body 611 of jack 61 extends against the longitudinal side wall 22 of the confinement chamber 2, to a height greater than that of the cryolite bath. This limits the risk of damage to the jack by exposure of its body 611 to excessive temperatures. The temperature of the side walls 11, 12 of the pot shell 1 is generally higher than the temperature of the side walls 21,22 of the confinement chamber 2 due to the presence nearby of the cryolite bath 14 whose operating temperature is of the order of 1000 0 C.

The operating principle of the lifting device is as follows. Anodes 31 are assumed to be immersed in the cryolite bath.

To vertically move the anode assembly 3, the controller controls the synchronized actuation of the two lifting devices 6 on which the anode structure 32 of the anode assembly 3 rests.

Each jack 61 applies a force on its rod 612 tending to move it between: an open position where rod 612 extends mainly outside the body 611, and a compact position where the rod 612 extends mainly within the body 611 of jack 61.

Movement of the rod between the open and compact positions is transmitted to the anode receiver 62 via the transverse connecting beam 63.

The anode receiver 62 of each jack slides within the guide means 64 and moves from the retracted position to the deployed position.

The combination of anode assemblies in respective lifting devices therefore makes it possible to move the anode assemblies 3 independently of each other. Furthermore, the fact of offsetting the anode receiver relative to the jack allows the lifting devices to be positioned at the edge of the electrolytic cell without hindering the movement of the anode assemblies above the cells, and means that they can be easily inserted at the edge of the cell without constraints on the electrical conductor circuits passing under and between the cells as a result of their increased compactness.

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

Moreover, the shapes of the various component parts of the lifting device, such as the shape of the bar or housing etc., may vary.

Also, in the embodiments illustrated in figures 1 to 4, the jack 61, the anode receiver 62 and the anode structure 32 are aligned, i.e. they extend substantially in the same plane. Alternatively, the jack 61 may be offset from the plane containing the anode receiver 62 and the anode structure 32.

Claims (16)

1. Electrolytic cell used for producing aluminum, comprising a pot shell (1) including a base (10) and transverse and longitudinal side walls (11, 12), the pot shell (1) being covered with a liner (13) to receive a cryolite bath (14) and a plurality of anode assemblies (3) each including an anode structure (32) and at least one anode (31) immersed in the cryolite bath, the cell further comprising a plurality of lifting devices (6) extending along the longitudinal side walls of the pot shell (1) to move the anode assemblies (3), the lifting devices comprising a jack (61) made up of a body (611) and a jack rod (612) extending along a longitudinal axis (B-B’), and an anode receiver (62) designed to receive one end of the anode structure (32), the jack (61) being coupled to the anode receiver (62) to drive it with a translational motion along a translation axis (T-T) between a retracted position and a deployed position, characterized in that the longitudinal axis (B-B’) of the jack (61) is parallel and separate from the translation axis (T-Τ’) of the anode receiver (62).

2. Electrolytic cell according to claim 1, wherein the lifting devices may comprise a transverse connecting beam (63) between the rod (612) of the jack (61) and the anode receiver (62), said connecting beam (63) preferably extending along a transverse axis perpendicular to the longitudinal axis (B-B’) of the jack (61).

3. Electrolytic cell according to claim 2, wherein the assembly composed of the rod (612) of the jack, the connecting beam (63) and the anode receiver (62) form a U-shaped structure

4. Electrolytic cell according to either of claims 2 or 3, wherein the connecting beam (63) is mounted interdependently on the rod (612) of the jack (61) and the connecting beam (63) is mounted interdependently on the anode receiver (62).

5. Electrolytic cell according to any of the preceding claims, wherein the anode receiver (62) comprises a bar (621) extending along the translation axis (T - Τ'),

6. Electrolytic cell according to claim 5, wherein the anode receiver comprises a housing (622) at one end of the bar (621), said housing (622) being designed to receive the end of the anode structure (32).

7. Electrolytic cell according to claim 6, further comprising a fixing system for securing the anode structure (32) to the housing (622).

8. Electrolytic cell according to claim 7, wherein the fixing system comprises means of holding the anode structure (32) up against the housing (622).

9. Electrolytic cell according to any one of claims 5 to 7, wherein a portion of the bar (621) is electrically connected to flexible electrical conducting means to enabling power to be supplied to each anode assembly (3).

10. Electrolytic cell according to any of the preceding claims, further comprising guide means (64) for the anode receiver (62) to guide the movement of the anode receiver (62) along the translation axis (T - Τ').

11. Electrolytic cell according to any one of the preceding claims, wherein the lifting devices are attached to the electrolytic cell so that the translation axis (T- Τ') of each anode receiver (62) is vertical.

12. Electrolytic cell according to any one of the preceding claims, wherein each anode structure (32) extends transversely in the cell and is associated with a respective pair of lifting devices arranged along opposite longitudinal side walls of the pot shell (1) and each carrying one of the ends of the anode structure (32).

13. Electrolytic cell according to any one of the preceding claims, which further comprises a confinement chamber (2) bearing on the pot shell (1), the confinement chamber (2) including transverse (21) and longitudinal (22) side walls, the confinement chamber (2) being designed to define a confinement volume for gases above the cryolite bath (14), each lifting device (6) being fixed to a one of the longitudinal side walls of the confinement chamber (2).

14. Electrolytic cell according to claim 13, wherein the side walls (21, 22) of the confinement chamber (2) are offset outwardly relative to the side walls (11, 12) of the pot shell (1) so that said side walls (21, 22) of the confinement chamber (2) extend around and above the side walls (11, 12) of the pot shell (1), side walls (11, 12, 21, 22) of the pot shell (1) and of the confinement chamber (2) being mechanically connected by a ring-shaped ledge, the anode receivers (62) of the lifting devices extending through openings in the ledge.

15. Electrolytic cell according to claim 14, wherein the anode receivers (62) pass through the confinement chamber (2) through ring-shaped dynamic seals.

16. Electrolytic cell according to any one of claims 13 to 15, wherein each lifting device is fixed to an upper edge of the confinement chamber (2) opposite the pot shell (1) so that the jack body of each lifting device is positioned at an altitude higher than the altitude of the cryolite bath.