EP3030695B1 - Aluminium smelter comprising a compensating electric circuit - Google Patents

Description

The present invention relates to an aluminum smelter, a method of using this smelter and a method for stirring alumina in the electrolysis tanks of this smelter.

It is known to produce aluminum industrially from alumina by electrolysis according to the Hall-Héroult process. For this purpose, there is provided an electrolytic cell comprising a steel box inside which is arranged a coating of refractory materials, a cathode of carbon material, crossed by cathode conductors for collecting the electrolysis current at the cathode to lead to cathode outlets through the bottom or sides of the box, routing conductors extending substantially horizontally to the next vessel from the cathode outlets, an electrolytic bath in which is dissolved alumina at least one anode assembly comprising at least one anode immersed in said electrolytic bath, an anode frame to which the anode assembly is suspended, and electrolysis current rise conductors extending from bottom to top connected to the conductors for routing the preceding electrolytic cell to convey the electrolysis current from the cathode outlets to the anodic frame e and the anode assembly and the anode of the next vat. The anodes are more particularly of anode type precooked with precooked carbon blocks, that is to say cooked before introduction into the electrolytic cell.

Aluminum production plants, or aluminum smelters, traditionally comprise several hundred electrolytic cells, aligned transversely in parallel queues and connected in series.

These electrolysis tanks are traversed by an electrolysis current of the order of several hundreds of thousands of amperes, which creates a large magnetic field. The vertical component of this magnetic field, generated mainly by the conductors carrying the current from one electrolysis cell to the next, is known to cause instabilities called magnetohydrodynamic instabilities (MHD).

These MHD instabilities are known to degrade the efficiency of the process. The more unstable a vessel is, the higher the interpolar distance between the anode and the metal web. However, the greater the interpolar distance, the higher the energy consumption of the process is dissipated by Joule effect in the interpolar space.

On the other hand, the horizontal component of the magnetic field, generated by the whole the path of the electric current, both in the conductors located inside the tank and those located outside, interacts with the electrical current flowing through the liquids, which generates a stationary deformation of the metal sheet. The unevenness of the metal sheet caused must remain low enough so that the anodes are consumed uniformly with little waste. To obtain a small difference in level, it is necessary that the horizontal components of the magnetic field are the most antisymmetric possible in liquids (electrolytic bath and metal sheet). For the longitudinal or transverse component of the magnetic field that constitute the horizontal components, antisymmetric means that when we move perpendicular to the central axis of the tank, parallel to the relevant component of the field, and when we go located at equal distance on either side of this central axis, the value of the component considered is opposite. The antisymmetry of the horizontal components of the magnetic field is the configuration providing the most symmetrical interface interface and as flat as possible in the tank.

It is known, including patent documents FR1079131 and FR2469475 to combat MHD instabilities by compensating the magnetic field created by the circulation of the electrolysis current, thanks to a particular arrangement of the conductors conducting the electrolysis current. For example, according to the patent document FR2469475 , the routing conductors laterally bypass the ends or heads of each electrolysis tank. We are talking about self-compensation. This principle is based on a local balancing of the magnetic field, on the scale of an electrolysis cell.

The main advantage of self-compensation is the use of the electrolysis current itself to compensate for MHD instabilities.

However, self-compensation can create significant lateral bulk since the electrical conductors bypass the heads of electrolysis cells.

Above all, the large length of the routing conductors for the implementation of this solution generates online electrical loss by resistive effect of the drivers, thus an increase in operating costs, and requires a lot of raw material, so costs of high manufacturing. These disadvantages are all the more marked that the electrolysis tanks have large dimensions and operate with high intensities.

Also, the design of an aluminum smelter with a self-compensated electric circuit is frozen. However, during the course of life, it may become necessary to increase the intensity of the electrolysis current, beyond the intensity expected during the design. This also modifies the distribution of the magnetic field of the self-compensated electrical circuit, not designed for this new distribution, which no longer allows to optimally compensate this magnetic field. There are solutions to overcome this lack of scalability and find magnetic compensation close to the optimum, but these solutions are particularly complex and expensive to implement.

Another solution for reducing MHD instabilities, known in particular from the patent document FR2425482 is to use a secondary electrical circuit, or external loop, along the rows of electrolysis tanks, on the sides. This secondary electrical circuit is traversed by a current whose intensity equals a predetermined percentage of the intensity of the electrolysis current. Thus, the outer loop generates a magnetic field that compensates for the effects of the magnetic field created by the electrolysis current of the next row of electrolysis cells.

It is also known from the patent document EP0204647 the use of a secondary circuit along the electrolysis cell lines on the sides to reduce the effect of the magnetic field generated by the routing conductors, the intensity of the current flowing through the electrical conductors of this secondary circuit being the order of 5 to 80% of the intensity of the electrolysis current, and this current flowing in the same direction as the electrolysis current.

The external loop compensation solution has the advantage of having a secondary circuit independent of the main circuit traversed by the electrolysis current.

The arrangement of the secondary circuit, located on the sides of the tank lines near the short sides of the boxes, at the height of the bath-metal interface, allows compensation of the vertical component without impacting the horizontal component of the magnetic field.

The external loop compensation solution significantly reduces the length, mass and electrical losses of the routing conductors, but requires an additional power station and additional independent secondary electrical circuit,
It should also be noted that the external loop compensation solution involves a combination of magnetic fields, with the current of the series, creating a very strong total ambient field, so that it implies constraints on operations and equipment (for example shielding necessary vehicles), and so that the magnetic field of a queue impacts the stability of the tanks of the next file. To limit the influence of a queue on the neighboring queue, it is necessary to move them away from each other, which constitutes a significant spatial constraint and therefore involves housing each row of electrolysis cells in a separate shed.

Furthermore, the junction portion of the electrolysis circuit and the secondary circuit joining the ends of two adjacent rows of electrolytic cells tends to destabilize the end of the tank. To avoid having unstable end tanks, it is possible to configure this portion of the secondary circuit according to a predetermined path, as known from the patent. FR2868436 , in order to correct the magnetic field so that the impact on the end tanks becomes acceptable. However, this path lengthens the length of the secondary circuit, therefore the material cost. It should be noted that the usual solution is to move the junction portion of the secondary circuit and the electrolysis circuit of the tanks located at the end of the line, but this increases the space requirement in addition to increasing the length of the electrical conductors so the material and energy cost.

It should therefore be noted that the known solutions of external loop compensation generate relatively high structural costs.

Also, the present invention aims to overcome all or part of these disadvantages by providing an aluminum smelter with a magnetic configuration for improved performance and a small footprint.

For this purpose, the subject of the present invention is an aluminum smelter, comprising at least one row of electrolysis cells arranged transversely with respect to the length of the line, one of the electrolytic cells comprising a box, and anode assemblies comprising a support and at least one anode, and a cathode crossed by cathode conductors for collecting the electrolysis current I ₁ at the cathode to lead it to cathode outlets outside the box, characterized in that the tank of electrolysis comprises electrical conductors for mounting and connecting to the anode assemblies extending upwardly along two opposite longitudinal edges of the electrolytic cell to conduct the electrolysis current I ₁ to the anode assemblies, and connected to the cathode outlets and intended to conduct the electrolysis current from the cathode outlets to the electrical conductors of the mount e and connecting the next electrolytic cell, and in that the aluminum comprises at least one electrical compensation circuit extending under the electrolytic cells, said compensation circuit being traversed by a current I ₂ of compensation circulating under the electrolysis tanks in the opposite direction of the overall circulation direction of the electrolysis current I ₁ passing through the electrolysis cells situated above.

Thus, the aluminum plant according to the invention has a small footprint and offers the advantage of having very magnetically stable tanks, so that the overall yield is improved.

According to a method of using this aluminum smelter, the compensation circuit is traversed by a compensation current I ₂ flowing under the electrolytic cells in the opposite direction to the overall flow direction of the electrolysis current I ₁ flowing through the tanks. electrolysis located above.

Advantageously, the intensity of the compensation current I ₂ is of the order of 50% to 150% of the intensity of the electrolysis current I ₁ .

The electrical conductors of rise and connection are arranged in the inter-tank spaces, at the two longitudinal sides of the electrolytic cell, on either side of the tank to compensate each other and obtain a substantially antisymmetric distribution of the horizontal components of the magnetic field of the tank providing a small difference in elevation of the aluminum sheet without impacting the vertical component of the magnetic field, so that the electrical conductors of the tank, among the conductors routing, mounting and connection , causing an unfavorable vertical and horizontal magnetic field to be compensated are in practice only the tank-bottom conductors circulating horizontally below the box, that is to say more specifically the routing conductors. The compensation of this unfavorable magnetic field is then obtained by means of the compensation electric circuit, which can advantageously be traversed by a current I ₂ of intensity compensation of the order of 50% to 150% of the intensity of the current. I ₁ electrolysis, and circulating under the electrolysis tanks in the opposite direction of the overall flow direction of the current I ₁ electrolysis in the electrolysis tanks above.

Thus, it is possible to reduce or even virtually cancel the vertical component of the magnetic field in the tank and to maintain a substantially antisymmetric horizontal magnetic field distribution in the liquids. The proposed solution therefore makes it possible to obtain a tank with very few instabilities, thus an improved yield, while maintaining a slight difference in level of the bath / metal interface which is also necessary for the proper functioning of the process.

The magnetic field is weak or virtually canceled near the tanks and rows of tanks and the aluminum plant according to the invention, so that the constraints related to strong magnetic fields on the operations and equipment used in the aluminum smelter are deleted. Also, the magnetic field of a queue no longer affects the stability of the tanks of the neighboring queue so that neighboring tank lines can be brought together and two rows of neighboring tanks can in particular be placed in the same building of reduced width, so that significant savings in structural costs can be realized even when a compensation circuit is used.

In spite of the dissuasive teachings of the state of the art, the compensation circuit passes under the electrolytic cells, and not on the sides of the electrolysis cell line or rows. Thus, a space is clear on both sides of the row or rows of electrolysis tanks. This allows to consider a lateral clearance of each electrolysis tank, and more particularly the box, which is less expensive than lifting. The absence of heavy and expensive lifting solutions offers significant structural savings.

According to a preferred embodiment, the compensation electric circuit is a secondary electrical compensation circuit distinct from the electrical circuit traversed by the current I ₁ electrolysis. Separate means that the two circuits are not electrically connected.

If, in case of drilling of one of the electrolysis tanks by the liquids contained in one of the electrolysis tanks, whose temperature is close to 1000 ° C, the compensation circuit is damaged and cut or can not no longer operate normally, this affects the efficiency, because the compensation circuit can no longer compensate the magnetic field generated by the circulation of the electrolysis current, but the smelter can continue to operate in degraded mode with a lower yield without suffering from detrimental stop, since the current flowing in the compensation circuit is intended for magnetic field compensation only and not for the production of aluminum.

The use of a separate secondary compensation circuit also offers the possibility of changing over time the compensation magnetic field created by this compensation circuit. It is necessary for this purpose to vary the intensity of the current flowing in the secondary electrical compensation circuit. This is of paramount importance in terms of scalability and adaptability. Firstly because it allows, in case of increase of the intensity of the electrolysis current during the life of the smelter, to adapt the magnetic compensation to this evolution, by variation of the intensity of the current compensation according to needs. On the other hand because it makes it possible to adapt the amperage of the compensation current to the characteristics and the quality of the available alumina. This makes it possible to control the speed of MHD flows to promote or limit the mixing of liquids and the dissolution of alumina in the bath. depending on the characteristics of the available alumina, which ultimately contributes to the best possible yield given the supply of alumina.

The secondary electrical compensation circuit may be more particularly powered by a clean power station, different from the station supplying the electrolysis cells with electrolysis current.

According to a preferred embodiment, the aluminum plant comprises two rows of tanks arranged parallel to one another, fed by the same station, and electrically connected in series so that the electrolysis current flowing in the first two rows of tanks then circulates in the second of the two rows of tanks in a direction generally opposite to that in which it circulated in the first of the two rows, and in that the compensation circuit forms a loop under these two rows of parallel tanks.

This makes it possible to bring two adjacent rows of electrolytic cells closer together in order to place them in the same building, taking into account the magnetic compensation obtained simultaneously by the compensation circuit and the routing conductors crossed by opposite electric currents. In the end, what is gained in terms of space and structural costs outweighs what is lost in the costs of achieving and operating the compensation circuit.

Since the secondary electrical compensation circuit forms a loop under the tanks, it becomes advantageous to use an electrical conductor made of a superconducting material in order to achieve it, and it is above all possible to carry out several turns in series, as described in the application for patent WO2013007893 in the name of the plaintiff.

Advantageously, the electrolytic cell comprises for each of its two longitudinal edges a plurality of electrical conductors rise and connect distributed at predetermined intervals over substantially the entire length of the corresponding longitudinal edge.

For each longitudinal edge, the rise and connection conductors may be arranged at regular intervals in the longitudinal direction of the electrolytic cell.

This improves the balance of the horizontal longitudinal component (that is to say, parallel to the length of the vessel) of the magnetic field.

A tank operating with an intensity of 400 to 1000k amps can for example preferably comprise from 4 to 40 distributed rise and connection conductors. regularly over the entire length of each of its two longitudinal edges.

The upstream and upstream electrical conductors and the upstream and downstream electrical conductors may be arranged equidistant from a longitudinal median plane of the electrolytic cell, that is to say a plane substantially perpendicular to a transverse direction of the vessel and separating it into two substantially equal portions.

By electrical conductor upstream and upstream connection and electrical conductor upstream and downstream connection is meant electrical conductors rise and connect arranged respectively next to the longitudinal edge upstream or downstream of the electrolytic cell, the upstream longitudinal edge corresponding to the one that is closest to the beginning of the electrolysis cell line and the downstream longitudinal edge corresponding to the longitudinal edge of the electrolysis cell farthest from the beginning of the electrolysis cell line, taking into account the meaning overall flow of electrolysis current at the scale of the electrolysis cell line.

According to a preferred embodiment, the electrical conductors for mounting and connection are arranged substantially symmetrically with respect to a longitudinal median plane of the electrolytic cell.

In other words, the rising and connecting electrical conductors extending along one of the two longitudinal edges of the electrolytic cell are arranged substantially symmetrically with respect to the electrical conductors for mounting and connection. extending along the opposite longitudinal edge of the electrolytic cell, with respect to a longitudinal median plane of the electrolytic cell, that is to say a plane substantially perpendicular to a transverse direction of the vessel and separating it from ci in two substantially equal parts.

This further enhances the advantageous antisymmetric characteristic of the horizontal magnetic field distribution in liquids.

According to a preferred method of use, the current distribution between the rising and connecting electrical conductors arranged upstream of the electrolytic cell and the electrical conductors for rising and connecting arranged downstream of the reactor vessel. electrolysis is of the order 30-70% upstream and 30-70% downstream, and preferably 40-60% upstream and 40-60% downstream, respectively.

This method of use makes it possible to improve the advantageous antisymmetric characteristic of the distribution of the horizontal magnetic field in liquids. Preferably, the current distribution between the electrical conductors of rise and connection arranged upstream of the electrolytic cell and the electrical conductors of rise and connection arranged downstream of the electrolytic cell is 45-55% upstream and 45-55% downstream respectively.

This further enhances the advantageous antisymmetric characteristic of the horizontal magnetic field distribution in liquids.

According to a preferred embodiment, the routing conductors extend under the electrolytic cell substantially straight, and only in a direction transverse to the electrolysis cell.

This limits the length and cost of the electrical conductors by minimizing the length of the conductors extending in the longitudinal direction of the vessel. The magnetic fields generated by such longitudinal electrical conductors are also limited in embodiments of the prior art, especially with regard to self-compensated tanks. Also, the space is clear on both sides of the row or rows of electrolytic cells, which limits at least the longitudinal dimension of the entire tanks / electrical conductors and allows to consider a release side of each electrolysis tank, and more particularly the box, which is less expensive than lifting.

The compensation electric circuit may comprise electrical conductors extending substantially parallel to a transverse axis of the electrolysis cells.

According to one embodiment, the compensation electric circuit comprises electrical conductors forming a plurality of secondary electrical secondary compensation sub-circuits independent of each other.

Each of these secondary electrical compensation sub-circuits is traversed by an intensity compensation current that can be variable independently of the intensity of the electrolysis current.

By independent secondary electrical sub-circuit compensation is meant subcircuit not electrically connected to the other secondary electrical sub-circuits compensation, and can be powered by a separate power station from that of other secondary electrical sub-circuits compensation.

Thus, in case of problems, for example piercing a tank, causing damage and / or the cutting of one or more secondary electrical compensation sub-circuits, this offers the possibility of continuing to produce according to a method of "Degraded" operation, wherein the intensity of the compensation current flowing in each of the other undamaged secondary compensation electrical sub-circuits is adjusted to compensate for the magnetic field created by the circulation of the electrolysis current. Thus, the efficiency can remain high despite a possible malfunction of one of the secondary electrical compensation sub-circuits.

The compensation electric circuit may comprise electrical conductors forming several turns in parallel and / or in series under the electrolysis cells.

According to one possibility, the compensation electric circuit comprises electrical conductors extending parallel under the electrolysis cells.

The electrical conductors of the compensation electric circuit may be arranged substantially symmetrically with respect to a transverse median plane of the electrolysis cells, that is to say a plane substantially perpendicular to a longitudinal direction of the electrolysis cells and separating the tank in two substantially equal parts.

According to one possibility, the electrical conductors forming the compensation electric circuit or, where appropriate, the secondary electrical compensation sub-circuits extend under the electrolysis cells together forming a layer of two to twelve, preferably three to ten , parallel electrical conductors.

Advantageously, said electrical conductors are substantially equidistant and distributed substantially symmetrically with respect to a transverse center axis of the electrolysis cells.

This further improves the compensation of the adverse magnetic field.

The principle of compensation or magnetic balancing of the aluminum smelter and the method of use of the smelter according to the invention makes it possible for the smelter to obtain a conductor circuit that can be produced in a perfectly modular manner. Each module may comprise, for example, an electrical conductor of the compensation electric circuit and a number of routing conductors and associated risers and connection conductors for each electrolysis cell. The conductor circuit, and therefore each tank, can be composed of a number of modules, determining the length of the tanks and the intensity of the current flowing through the tanks. The choice of the number of modules per tank during the design or an extension of the length of the tanks by the addition of such modules does not disturb the magnetic equilibrium of the tanks, unlike the lengthening of tanks of the self-compensated or compensated type by of the magnetic compensation circuits arranged on the sides of known prior art tanks for which the conductor circuits must be completely redrawn. Also, the ratio of the amount of material forming the conductor circuit brought to the production surface of the tanks does not deteriorate when extending the tanks, it increases proportionally to the number of modules and the intensity through the tanks. Thus, the tanks can be elongated simply according to the needs and the intensity of the current passing through them is not limited. It then becomes possible to increase the intensity of the current passing through the tanks above 1000 k amperes, or even 2000 k amperes.

According to one embodiment, the rising and connecting electrical conductors extending along one of the two longitudinal edges of the electrolytic cell are arranged in staggered relation to electrical conductors for mounting and connecting arranged on the adjacent longitudinal edge of a previous or next separate electrolytic cell.

In other words, the electrical conductors upstream and upstream connection of an electrolysis vessel N are arranged in staggered relation to the electrical conductors of upstream and downstream connection of the electrolytic cell N-1, that is to say say of the electrolysis tank preceding it.

Thus, this makes it possible to bring the electrolytic cells as close as possible to one another, either to place more electrolytic cells in series over the same distance, which increases the efficiency, or to reduce the length of a line of electrolysis cells. Electrolysis tanks, so save space and achieve even greater structural savings.

According to a preferred method of use of the aluminum plant according to the invention, the electric compensation circuit is traversed by an intensity compensation current of the order of 70% to 130% of the intensity of the current I ₁ d electrolysis, and preferably of the order of 80% to 120% of the intensity of the current I ₁ electrolysis.

Thus, if the smelter comprises an electrical compensation circuit formed by a single-turn electrical conductor under the electrolysis vessels, then the intensity of the compensation current flowing through this compensation circuit can be of the order of 70% at 130% of the intensity of the electrolysis current.

Also, if the smelter comprises an electrical compensation circuit formed by an electrical conductor of superconducting material making three turns in series under the electrolytic cells, the intensity of the compensation current flowing through the electrical conductor may be of the order of one third from 70% to 130% of the intensity of the current electrolysis.

According to another example, if the compensation electric circuit is formed by three secondary electrical compensation sub-circuits each making twenty turns in series and each made with electrical conductors of superconducting material, then the intensity of the compensation current, each traveling through these three secondary electrical compensation sub-circuits can be of the order of one sixtieth of 70% to 130% of the intensity of the electrolysis current.

According to one embodiment, each cathodic output leaves the box only in a vertical plane perpendicular to the longitudinal direction of the electrolytic cell.

The cathode outlets pass through the bottom of the chamber of the electrolytic cell. Having outlets at the bottom instead of at the sides of the electrolytic cell decreases the length of the feed conductors, as well as the horizontal currents in the liquids, resulting in better MHD stability.

The electrical conductors for routing may extend in a straight line, substantially parallel to a transverse direction of the electrolytic cell to the electrical conductors for mounting and connecting the next electrolytic cell.

As indicated above, the principle of compensation or magnetic balancing of the aluminum smelter and the method of using the smelter according to the invention makes it possible to increase the intensity of the current flowing through the electrolytic cells as a function of the needs. without magnetohydrodynamic problems, by lengthening the electrolysis tanks. However, a electrolysis tank of the state of the art comprises a superstructure longitudinally crossing the electrolytic cell, above the box and anodes. The superstructure includes a beam resting on feet at each of its longitudinal ends. It supports an anode frame, also extending longitudinally over the box and anodes, which supports the anode assemblies and to which the anode assemblies are connected. An elongation of a electrolysis tank of the state of the art therefore leads to an extension of the superstructure, therefore the span of the beam between the feet supporting the beam and the weight to be supported by this superstructure. The limited extension of the superstructure of a state-of-the-art electrolytic cell thus limits the possibilities offered by the principle of compensation or magnetic balancing of the smelter and the method of use of the smelter according to the invention. There are superstructures with one or more intermediate support arches of the beam, but such intermediate arches, extending transversely above the box and the anodes, are cumbersome and complexify the operations on tanks, including changes of anodes.

According to a particularly advantageous embodiment of the invention, the support of the anode assembly comprises a cross member extending transversely to the electrolytic cell being supported and electrically connected at each of the two longitudinal edges of the and other of the electrolysis cell.

It is at the longitudinal edges of the electrolysis tank that the electrical connection between the rising and connecting conductors and the anode assembly is thus performed and that the mechanical support of the anode assembly is carried out.

The anode assembly is no longer supported and electrically connected by means of a superstructure longitudinally crossing the electrolytic cell, above the box and anodes so that the electrolysis cells can be elongated to take full advantage of the possibilities offered by the principle of compensation or magnetic balancing of the method of use of the aluminum smelter according to the invention.

According to another embodiment, the rising and connecting conductors extend on either side of the box without extending to the right of the or anodes.

By "the right of the anode" or means in a volume formed by vertical translation of the surface obtained by projection of the anode or in a horizontal plane XY.

Such an embodiment makes it possible to advantageously replace the anode by pulling it vertically upwards, since the anode towed upward does not encounter any elements having served at its connection. From this simplification of the placement and the anode removal there also arise savings in the management and operation of the aluminum plant according to the invention.

Thus, the length of the rising and connecting conductors is reduced with respect to the use of conventional type rise and connection conductors which typically extend above the vessel into the longitudinal central portion of the vessel. This helps to reduce manufacturing costs.

The rising and connecting conductors are more particularly connected to the anode assemblies at the edges of the box.

By the right of the edges of the box is meant in a volume formed by vertical translation of the surface obtained by projecting the edges of the box in a plane horizontal XY.

Advantageously, the rising and connecting electrical conductors extend at a height h between 0 and 1.5 meters above a substantially horizontal plane including the surface of the liquids contained in the electrolytic cell.

The length of these rising and connecting conductors is thus greatly reduced with respect to conventional type rise and connection conductors which extend to heights greater than two meters.

• l'analyse d'au moins une caractéristique de l'alumine,
• la détermination d'une valeur d'intensité du courant de compensation à faire circuler dans le circuit électrique de compensation en fonction de ladite au moins une caractéristique analysée,
• la modification de l'intensité du courant I₂ de compensation jusqu'à la valeur d'intensité déterminée à l'étape précédente si l'intensité du courant I₂ de compensation diffère de ladite valeur.

The invention also relates to a method for stirring the alumina contained in the electrolysis cells of an aluminum smelter having the aforementioned characteristics, and using the method having the aforementioned characteristics, the method comprising:

• analyzing at least one characteristic of alumina,
• determining a value of intensity of the compensation current to be circulated in the compensation electric circuit according to said at least one analyzed characteristic,
• modifying the intensity of the compensation current I ₂ up to the intensity value determined in the preceding step if the intensity of the compensation current I ₂ differs from said value.

Thus, the method according to the invention makes it possible to modify the magnetic compensation, by increasing or decreasing the intensity of the compensation current I ₂ , to induce controlled MHD instabilities, these instabilities contributing to stir the alumina for a better yield. Such a method is particularly interesting with the configuration of the electrical conductors described above which makes the tanks magnetically very stable.

The characteristics of the alumina analyzed can notably be the ability of the alumina to dissolve in the bath, the fluidity of the alumina, its solubility, its fluorine content, its humidity, etc.

The determination of a value of intensity of the compensation current required according to the characteristics of the analyzed alumina can be carried out in particular by use of an abacus, for example made by a person skilled in the art by experimentation and recording of the optimal correspondences intensity. compensation current I ₂ / characteristics of the alumina. This is to quantify the desired MHD instabilities.

It may happen that the alumina available for continuous operation of the smelter is of different quality, more or less pasty, and therefore having different abilities to dissolve in the electrolysis bath. In this case, the movements of liquids in the electrolysis tanks are an asset, because they allow to stir this alumina to promote its dissolution. However, in the case of self-compensation in particular, the magnetic field at the origin of the movements of the liquids is directly compensated via the electrolysis current itself, with a distribution of the magnetic field imposed and frozen by the course of the routing conductors. It is therefore not possible in aluminum smelters with self-compensation to voluntarily and temporarily introduce an imbalance in the compensation of the magnetic field in order to increase the intensity of stirring of the alumina in the tanks, in order to increase the effectiveness of the dissolution. Thus, when the available alumina is only alumina more difficult to dissolve than usual, the efficiency of aluminum smelters with self-compensation can be substantially affected.

• La figure 1 est une vue schématique d'une aluminerie selon l'état de la technique,
• La figure 2 est une vue schématique de côté de deux cuves d'électrolyse successives de l'état de la technique,
• La figure 3 est une vue schématique en filaire du circuit électrique parcouru par le courant d'électrolyse dans les deux cuves de la figure 2,
• La figure 4 est une vue schématique en coupe selon un plan longitudinal vertical d'une cuve d'électrolyse de l'état de la technique,
• La figure 5 est une vue schématique d'une aluminerie selon un mode de réalisation de l'invention,
• La figure 6 est une représentation filaire du circuit électrique parcouru par le courant d'électrolyse dans deux cuves successives d'une aluminerie selon l'invention,
• La figure 7 est une vue en coupe selon un plan longitudinal vertical d'une cuve d'électrolyse dans une aluminerie selon un mode de réalisation de l'invention,
• La figure 8 est une vue schématique de côté de trois cuves d'électrolyse successives dans une file de cuves d'électrolyse d'une aluminerie selon un mode de réalisation de l'invention.
• La figure 9 est une représentation filaire du circuit électrique parcouru par le courant d'électrolyse dans deux cuves successives d'une aluminerie selon l'invention,

Other features and advantages of the present invention will emerge clearly from the following description of a particular embodiment, given by way of non-limiting example, with reference to the appended drawings in which:

• The figure 1 is a schematic view of an aluminum smelter according to the state of the art,
• The figure 2 is a schematic side view of two successive electrolysis cells of the state of the art,
• The figure 3 is a schematic wired view of the electrical circuit traversed by the electrolysis current in the two tanks of the figure 2 ,
• The figure 4 is a schematic sectional view along a vertical longitudinal plane of an electrolysis cell of the state of the art,
• The figure 5 is a schematic view of an aluminum plant according to one embodiment of the invention,
• The figure 6 is a wired representation of the electric circuit traversed by the electrolysis current in two successive tanks of an aluminum smelter according to the invention,
• The figure 7 is a sectional view along a vertical longitudinal plane of an electrolysis cell in an aluminum plant according to one embodiment of the invention,
• The figure 8 is a schematic side view of three successive electrolysis cells in a row of electrolysis cells of an aluminum plant according to one embodiment of the invention.
• The figure 9 is a wired representation of the electric circuit traversed by the electrolysis current in two successive tanks of an aluminum smelter according to the invention,

The figure 1 shows an aluminum smelter 100 of the state of the art. The aluminum smelter 100 comprises electrolytic cells arranged transversely with respect to the length of the line that they form. The tanks are here aligned in two rows 101, 102 parallel and traversed by an electrolysis current I ₁₀₀ . Two secondary electric circuits 104, 106 extend on the sides of the queues 101, 102 to compensate for the magnetic field generated by the circulation of the electrolysis current I ₁₀₀ from one tank to another and in the neighboring line. The secondary electric circuits 104, 106 are respectively traversed by currents I ₁₀₄ , I ₁₀₆ flowing in the same direction as the electrolysis current I ₁₀₀ . Power supply stations 108 supply the series of electrolysis cells and the secondary electrical circuits 104, 106. According to this example, for an electrolysis current of intensity 500kA, in view of the magnetic disturbances of "end of line", the distance D ₁₀₀ between the electrolysis cells closest to the power stations 108 and the stations 108 power supply is of the order of 45m, and the distance D ₃₀₀ on which the circuits 104, 106 electrical secondary beyond the end of the queue extends is of the order of 45m, while the distance D ₂₀₀ between the two rows 101, 102 is of the order of 85m to limit magnetic disturbances from one line to the other.

It is specified that the description is made with respect to a Cartesian reference system linked to an electrolytic cell, the X axis being oriented in a transverse direction of the electrolytic cell, the Y axis being oriented in a longitudinal direction of the electrolytic cell. electrolysis cell, and the Z axis being oriented in a vertical direction of the electrolysis cell. The orientations, directions, plans and longitudinal, transverse, vertical displacements are thus defined with respect to this reference frame.

The figure 2 shows two tanks 200 of traditional electrolysis consecutive of the same line of tanks. As can be seen on the figure 2 , the electrolysis tank 200 comprises a box 201 internally lined with refractory materials 202, a cathode 204 and anodes 206 immersed in an electrolytic bath 208 at the bottom of which is formed a sheet 210 of aluminum. The cathode 204 is electrically connected to cathode conductors 205 which pass through the sides of the box 201 at cathode outlets 212. The cathode outputs 212 are connected to routing conductors 214 which convey the electrolysis current to the conductors 213. mounting and connecting a next electrolysis cell. As can be seen on the figure 2 these rising and connecting conductors 213 extend on one side only, the upstream side, of the electrolytic tank 200 and extend above the anodes 206, up to the part longitudinal center of the tank.

The figure 3 schematically illustrates the path traveled by the electrolysis current I ₁₀₀ in each of the tanks 200 and between two adjacent tanks such as those shown in FIG. figure 2 . Note in particular that the rise of the electrolysis current I ₁₀₀ to the anode assembly of a tank is asymmetrical since this rise is carried out only upstream of the tanks in the overall flow direction of the electrolysis current I ₁₀₀ in the queue (to the left of the tanks on the Figures 2 and 3 ).

The figure 4 shows a sectional view of a traditional tank 200, in which there is the arrangement on the sides of the tank 200 of the electrical conductors forming the secondary electrical circuits 104, 106 to compensate for the magnetic field generated by the current flow I ₁₀₀ electrolysis of a tank 200 to another and in the neighboring queue.

The figure 5 shows an aluminum smelter 1 according to one embodiment of the invention. The aluminum smelter 1 comprises a plurality of substantially rectangular electrolysis tanks 50 intended for the production of aluminum by electrolysis, which can be aligned along one or more queues, in this case two queues, substantially parallel, connected in series. and supplied with current I ₁ electrolysis.

It is important to note that the electrolysis tanks 50 are arranged transversely with respect to the line they form. It will be noted that per electrolysis tank 50 arranged transversely is meant electrolysis tank 50, the largest dimension of which, the length, is substantially perpendicular to the overall direction in which the electrolysis current I ₁ flows, that is to say to say to the flow direction of the electrolysis current I ₁ at the level of the rows of electrolysis tanks 50.

The aluminum smelter 1 also comprises an electric compensation circuit 6, traversed by a compensation current I ₂ . Unlike circuits 104, 106 illustrated on the figure 1 it is important to note that the electric compensation circuit 6 extends under the electrolysis tanks 50. It will also be noted that the compensation current I ₂ flows in the opposite direction of the electrolysis current I ₁ . The electric compensation circuit 6 of the figure 5 more particularly form a loop under the rows of electrolysis tanks 50.

Advantageously, a set of supply stations 8 independently feeds the electrolysis tanks 50 and the electric compensation circuit 6. In other words, the electric compensation circuit 6 is a secondary electric circuit of compensation distinct from the main electric circuit 7 traversed by the current I ₁ of electrolysis.

The intensity of the compensation current I ₂ is variable, independently of the electrolysis current I ₁ . Thus, the intensity of the compensation current I ₂ can be modified without the intensity of the electrolysis current I ₁ necessarily being so.

The figure 8 shows three consecutive electrolysis tanks 50 of the aluminum plant 1. The electrolysis tanks 50 can conventionally comprise a box 60, provided with cradles of reinforcements 61, which may be metallic, for example steel, and an inner coating 62 refractory materials.

The electrolytic cells 50 comprise a plurality of anode assemblies consisting of a support 53 (here a transverse horizontal bar) and at least one anode 52, in particular of carbon material and more particularly of precooked type, conductors 54 of mounted and connected which, unlike the electrolysis tank 200, extend on either side of each of the electrolysis tanks 50 to conduct the current I ₁ electrolysis to the anodes 52, and a cathode 56, optionally formed of several cathode blocks of carbon material, crossed by cathode conductors 55 for collecting the electrolysis current I ₁ to lead to cathode outlets 58 leaving the bottom of the box 60 and connected to conductors 57 routing in turn leading the electrolysis current to the conductors 54 for mounting and connection of the next electrolysis tank 50. The anode assemblies are intended to be removed and replaced periodically when the anodes are worn.

The cathode conductors, the cathode outputs and the routing conductors 57 may correspond to metal bars, for example aluminum, copper and / or steel.

The figure 6 schematically represents the path of the electrolysis current I ₁ in two successive electrolysis tanks 50 of the aluminum plant 1 according to the invention. In comparison with the figure 3 It will be readily seen that the rise of the electrolysis current I ₁ is here advantageously carried out on both longitudinal sides of the electrolytic cell 50. Note also the presence of the compensation circuit 6, under the electrolysis tanks 50, and traversed by the current I ₂ compensation circulating in the opposite direction of the overall flow direction of the electrolysis current I ₁ of a tank 50 to the next one.

The figure 9 represents schematically the path of the electrolysis current I ₁ in two successive electrolysis tanks 50 of the aluminum plant 1 according to the invention and differs from the figure 6 in that the cathode outputs 58 come out of the box 60 more conventionally at the sides of the box 60.

The figure 7 shows a sectional view of an electrolysis tank 50 of the aluminum plant 1. Note also the presence of the compensation circuit 6, under the electrolysis tanks 50, and traversed by the current I ₂ compensation circulating in the direction inverse of the global circulation direction of the electrolysis current I ₁ from one tank 50 to the next.

It will also be noted that the compensation circuit 6 forms, according to the example of the figure 7 a layer of three conductors substantially equidistant and arranged in the same substantially horizontal plane XY; in addition, the conductors of this layer may extend substantially symmetrically with respect to a transverse median plane XZ.

The circuit of electrical conductors of the tank, and of the smelter, can advantageously be made in a modular manner. The figure 7 shows in particular a tank formed of three identical modules M. In this example, each module comprises the routing conductors 57 disposed between three adjacent cradles 61 of the box and a conductor of the compensation circuit 6 disposed substantially under the central cradle 61 of the module. The conductor of the module compensation circuit 6 is traversed by a current of the order of 50% to 150% of the intensity of the electrolysis current corresponding to this module. As the magnetic stability of the tank is achieved by module, the stability of the tank does not depend on the number of modules forming the circuit of electrical conductors of the tank and the smelter. Thus, the length and intensity of the tanks can be adjusted simply by adding modules to meet the desired conditions of realization of the smelter.

As is visible on the figure 8 the rising and connecting conductors 54 extend upwards, for example substantially vertically, along each longitudinal edge of the electrolysis cells 50. The longitudinal edges of the electrolysis tanks 50 correspond to the edges of larger dimension, substantially perpendicular to the transverse X direction.

The rising and connecting conductors 54 upstream and downstream may also be arranged equidistant from a median YZ plane of the electrolysis tank 50.

The rising and upstream connection conductors 54 may be substantially symmetrical to the downstream electrical conductors 54 relative to the median YZ plane of the electrolysis cells 50.

Although this is not shown, the conductors 54 upstream and connecting upstream of one of the electrolysis tanks 50 may be arranged in staggered relation to the conductors 54 of upstream and downstream connection of the electrolysis tank 50 preceding it in the line.

The figure 8 also shows that the conductors 54 of rise and connection extend on either side of the box 60 without extending to the right of the anodes 52, that is to say without extending into a vertically projected volume of the area of the anodes in a horizontal plane.

Note also that the electrical conductors 54 of rise and connection extend above the liquids 63 at a height h between 0 and 1.5 meters.

Furthermore, the support 53 of the anode assembly comprises a cross member extending transversely with respect to the electrolytic cell 50 being supported and electrically connected at each of the two longitudinal edges on either side of the vessel. 50 electrolysis.

It will be noted that the distribution of electrolysis current I ₁ between the conductors 54 for upstream and upstream connection of the electrolysis tanks 50 and the conductors 54 for upstream and downstream connection of the electrolysis tanks 50 may be, for example, 30% to 70% upstream and 70% to 30% downstream respectively. Advantageously, this current distribution is 40% to 60% upstream and 60% to 40% downstream, and preferably 45% to 55% upstream and 55% to 45% respectively. 'downstream. In other words, it is of the order of 50% plus or minus 20% upstream and the remainder downstream, and preferably of the order of 50% plus or minus 10%, and more preferably of the order of 50% plus or minus 5%.

As can be seen on the figure 8 the cathode outputs 58 and the routing conductors 57 may extend only in a vertical plane XZ perpendicular to the longitudinal direction Y of the electrolysis vessels 50. In particular, the cathode outputs 58 may extend substantially vertically only.

The cathode outlets 58 may pass through the bottom of the box 60 of the electrolysis tanks 50, and the routing conductors 57 may extend under the electrolysis tanks 50, advantageously in a straight line, substantially parallel to a transverse direction. X 50 electrolytic tanks, to the conductors 54 for mounting and connection of the next electrolysis tank 50.

The combination of the electric compensation circuit 6 passing under the electrolytic cells 50, the compensation current I ₂ of which flows in the opposite direction of the electrolysis current I ₁ and the rising and connecting conductors 54 extending on two edges The longitudinal opposites of the electrolysis tanks 50 make it possible to stabilize the liquids contained in the electrolysis tanks 50 and to limit the disturbances of the electrolysis tanks 50 at the end of the line because the magnetic fields generated by the electrolytic cells 50 electrolysis current passing under the tanks and the conductors of the compensation electric circuit are canceled.

The intensity of the compensation current flowing through the compensation circuit is advantageously of the order of 50% to 150% of the intensity of the electrolysis current I ₁ , preferably of the order of 70% to 130% of the current. intensity of the electrolysis current I ₁ , and more preferably of the order of 80% to 120% of the intensity of the electrolysis current I ₁ , in order to ensure an appropriate cancellation of the magnetic fields and the stability of the tanks.

Therefore, the distances between the queues, and the lengths of the electrolysis electric circuit and the electric compensation circuit 6, can be reduced. Also, referring again to the figure 5 the distance D ₁ between the electrolysis tanks 50 closest to the supply stations 8 and / or the distance D ₃ over which the electrical compensation circuit 6 extends beyond the ends of the line is less than or equal to at 30m, for example less than or equal to 20m, and preferably less than or equal to 10m; the distance D ₂ between the two rows is less than or equal to 40m, for example less than or equal to 30m, and preferably less than or equal to 25m. So, as we can see on the figure 5 , the two rows of the aluminum smelter 1 according to the invention can be arranged in the same building 12, which allows very significant structural gains.

Preferably, the electric compensation circuit 6 extends under the tanks 50 forming a sheet of two to twelve, preferably three to ten, substantially equidistant parallel electrical conductors distributed substantially symmetrically with respect to a transverse median axis X of the tanks 50. The compensation current I ₂ traversing, for example, evenly across the conductors of this layer of parallel conductors is thus better distributed over the entire length of the tank 50. The magnetic fields generated by the routing conductors 57 traversed by the current I ₁ of electrolysis, themselves distributed under the tank 50 over its entire length, are thus better compensated.

The electrical conductor or conductors forming the electrical compensation circuit 6 extend under the rows of tanks 50 substantially parallel to a transverse axis X of the electrolysis tanks 50.

It will be noted that the compensation circuit 6 may be formed by electrical conductors forming a plurality of independent secondary secondary electric compensation sub-circuits and each traversed by a compensation current flowing in the opposite direction of the current I ₁ d 'electrolysis. The secondary electrical compensation sub-circuits can form parallel loops under the electrolysis tanks 50, for example two in the case of the figure 5 . So, in case of piercing an electrolytic tank 50, if one of the subcircuits is reached, the other secondary electrical compensation sub-circuit (s) may continue to compensate for the magnetic field.

Moreover, the electrical conductors of the compensation circuit 6, or if appropriate of one of the secondary electrical compensation sub-circuits, may perform several turns in parallel and / or in series under the electrolysis cells, in particular when these Electrical conductors are made of superconducting material.

The electrical conductors forming the compensation circuit 6 may correspond to metal bars, for example aluminum, copper or steel, or, advantageously, to electrical conductors made of superconducting material, the latter making it possible to reduce the power consumption and because of their smaller mass than the equivalent metal conductors, to reduce structural costs to support them or to protect them from possible metal pouring by means of metal baffles. Advantageously, these electrical conductors made of superconducting material can be arranged to perform several turns in series under the row or rows of tanks.

The sum of the intensities going through all the conductors of the compensation electric circuit passing under the tank is advantageously of the order of 50% to 150% of the intensity of the electrolysis current I ₁ , preferably of the order of 70%. at 130% of the intensity of the electrolysis current I ₁ , and more preferably of the order of 80% to 120% of the intensity of the electrolysis current I ₁ .

Thus, if the smelter 1 comprises a secondary electric compensation circuit 6 forming a single tower under the electrolysis tanks 50, the intensity of the compensation current flowing through this compensation electric circuit 6 may be of the order of 50%. at 150% of the intensity of the electrolysis current I ₁ . If this secondary electric compensation circuit 6 forms N turns under the electrolysis tanks 50, then the sum of the N intensities crossing each of these turns is of the order of 50% to 150% of the intensity of the electrolysis current. Also, according to the example of figure 5 , The current I ₂ corresponding to the sum of the intensities I ₂₀ and I ₂₁ passing through each of the two towers can be of the order of 50% to 150% of the intensity of the current I ₁ of electrolysis.

The invention also relates to a method for stirring alumina in the electrolysis tanks 50 of the aluminum plant 1. This method comprises a step of modulating the intensity of the compensation current flowing through the electric compensation circuit 6, or where appropriate compensation currents flowing through the subcircuits forming it. This modulation may more particularly be a function of the characteristics of alumina, varying the intensity of the electrolysis current or structural modifications of the smelter.

• d'analyse d'au moins une caractéristique de l'alumine (par exemple l'habilité de l'alumine à se dissoudre dans le bain, la fluidité de l'alumine, sa solubilité, sa teneur en fluor, son humidité...),
• de détermination d'une valeur d'intensité du courant de compensation à faire circuler dans le circuit de compensation en fonction de ladite au moins une caractéristique analysée (cette étape de détermination pouvant être réalisée au moyen d'un abaque obtenue par expérimentation présentant une relation entre la valeur d'intensité et la caractéristique analysée), dans le but de générer un seuil de vitesse des écoulements MHD adapté pour brasser efficacement l'alumine en impactant le moins possible le rendement,
• de modification de l'intensité du courant I₂ de compensation conformément à la valeur d'intensité déterminée à l'étape précédente.

The brewing process of alumina comprises the steps:

• for analyzing at least one characteristic of alumina (for example the ability of alumina to dissolve in the bath, the fluidity of alumina, its solubility, its fluorine content, its humidity, etc. )
• determining a value of intensity of the compensation current to be circulated in the compensation circuit according to said at least one analyzed characteristic (this determination step can be performed by means of an abacus obtained by experimentation having a relationship between the intensity value and the analyzed characteristic), with the aim of generating a flow threshold of the MHD flows adapted to efficiently stir the alumina with the least possible impact on the yield,
• modifying the intensity of the compensation current I ₂ according to the intensity value determined in the previous step.

Of course, the invention is not limited to the embodiment described above, this embodiment having been given as an example. Modifications are possible, especially from the point of view of the constitution of the various elements or by the substitution of technical equivalents, without departing from the scope of the invention. This invention is compatible for example with the use of "inert" type anodes at which oxygen is formed during the electrolysis reaction.

Claims (22)

1. An aluminum smelter (1) comprising at least one row of electrolytic cells (50) arranged transversely in relation to the length of the row, each of the electrolytic cells (50) comprising a pot shell (60), anode assemblies comprising a support (53) and at least one anode (52), and a cathode (56) through which pass cathode conductors (58) intended to collect the electrolysis current (I₁) at the cathode to route it to the cathode outputs outside the pot shell, characterized in that the electrolytic cell (50) comprises rising and connecting electrical conductors (54) to the anode assemblies running upwards along the two opposite longitudinal edges of the electrolytic cell (50) to conduct the electrolysis current (I₁) to the anode assemblies, and linking conductors (57) connected to the cathode outputs designed to route the electrolysis current from the cathode outputs to the electrical rising and connecting conductors (54) of the next electrolytic cell (50), and in that the aluminum smelter (1) comprises at least one electrical compensating circuit (6) running beneath the electrolytic cells (50), through which compensating circuit (6) may flow a compensating current (I₂) flowing beneath the electrolytic cells (50) in a direction opposite to the overall direction of flow of the electrolysis current (I₁) passing through the electrolytic cells (50) located above.
2. Aluminum smelter (1) according to claim 1, in which the compensating electrical circuit (6) is a secondary compensating electrical circuit separate from the electrical circuit through which the electrolysis current (I₁) flows.
3. Aluminum smelter (1) according to claim 1 or 2, characterized in that the aluminum smelter (1) comprises two rows of cells arranged parallel to each other, supplied from a single station and electrically connected in series in such a way that the electrolysis current flowing in the first of the two rows of cells then flows in the second of the two rows of cells in a direction which is overall opposite to that in which it flows in the first of the two rows, and in that the compensating electrical circuit (6) forms a loop beneath these two rows of parallel cells.
4. Aluminum smelter (1) according to any one of claims 1 to 3, characterized in that the electrolytic cell (50) comprises a plurality of rising and connecting electrical conductors (54) distributed at predetermined intervals over substantially the entire length of the corresponding longitudinal edge along each of its two longitudinal sides.
5. Aluminum smelter (1) according to any one of claims 1 to 4, characterized in that the rising and connecting electrical conductors (54) are arranged in a substantially symmetrical way in relation to a longitudinal median plane of the electrolytic cell (50).
6. Aluminum smelter (1) according to any one of claims 1 to 5, characterized in that the linking conductors (57) run substantially straight beneath electrolytic cell (50) in a transverse direction in relation to the electrolytic cell (50).
7. Aluminum smelter (1) according to any one of claims 1 to 6, characterized in that the compensating electrical circuit (6) comprises electrical conductors forming a plurality of secondary compensating electrical sub-circuits which are independent of each other.
8. Aluminum smelter (1) according to any one of claims 1 to 7, characterized in that the compensating electrical circuit (6) comprises electrical conductors running in parallel beneath the electrolytic cells (50).
9. Aluminum smelter (1) according to any one of claims 1 to 8, characterized in that the electrical conductors forming the compensating electrical circuit, or if applicable, secondary compensating electrical sub-circuits run beneath the electrolytic cells (50), together forming a layer of between two and twelve and preferably between three and ten parallel electrical conductors.
10. Aluminum smelter (1) according to either of claims 7 to 9, in which the said electrical conductors are substantially equally spaced and are arranged substantially symmetrically in relation to a transverse median axis of the electrolytic cells (50).
11. Aluminum smelter (1) according to any one of claims 1 to 10, characterized in that the rising and connecting electrical conductors (54) running along one of the two longitudinal edges of the electrolytic cell (50) are in a staggered arrangement in relation to the rising and connecting electrical conductors (54) located on the adjacent longitudinal edge of a separate preceding or following electrolytic cell (50).
12. Aluminum smelter (1) according to any one of claims 1 to 11, characterized in that each cathode output (58) leaves the pot shell (60) only in a vertical plane perpendicular to the longitudinal direction of the electrolytic cell (50).
13. Aluminum smelter (1) according to any one of claims 1 to 12, characterized in that the support (53) for the anode assembly comprises a cross-member extending transversely in relation to the electrolytic cell (50), being supported and electrically connected at each of the two longitudinal edges on either side of the electrolytic cell (50).
14. Aluminum smelter (1) according to any one of claims 1 to 13, characterized in that the rising and connecting conductors (54) run on either side of the pot shell (60), without running above the anode or anodes (52).
15. Aluminum smelter (1) according to any one of claims 1 to 14, characterized in that the rising and connecting electrical conductors (54) run at a height (h) of between 0 and 1.5 metres above a substantially horizontal plane, including the surface of the liquids (63) present in the electrolytic cell (50).
16. Method for using an aluminum smelter (1) according to any one of claims 1 to 15, characterized in that a compensating current (I₂) flowing beneath the electrolysis cells (50) in a direction opposite to the overall direction of flow of the electrolysis current (I₁) flowing through the electrolytic cells (50) located above passes through the compensating circuit (6).
17. Method according to claim 16, characterized in that the intensity of the compensating current (I₂) is of the order of 50% to 150% of the intensity of the electrolysis current (I₁).
18. Method according to claim 17, characterized in that the intensity of the compensating current (I₂) is of the order of 70% to 130% of the intensity of the electrolysis current (I₁) and preferably of the order of 80% to 120% of the intensity of the electrolysis current (I₁),
19. Method according to any one of claims 16 to 18, characterized in that the distribution of current between the rising and connecting electrical conductors (54) located upstream of the electrolytic cell (50) and the rising and connecting electrical conductors (54) located downstream of the electrolytic cell (50) is of the order of 30-70% upstream and 30-70% downstream respectively.
20. Method according to claim 19, characterized in that the distribution of current between the rising and connecting electrical conductors (54) located upstream of the electrolytic cell (50) and the rising and connecting electrical conductors (54) located downstream of the electrolytic cell (50) is of the order of 40-60% upstream and 40-60% downstream respectively.
21. Method according to claim 20, characterized in that the distribution of current between the rising and connecting electrical conductors (54) located upstream of the electrolytic cell (50) and the rising and connecting electrical conductors (54) located downstream of the electrolytic cell (50) is of the order of 45-55% upstream and 45-55% downstream respectively.
22. Process for stirring the alumina present in the electrolytic cells (50) of an aluminum smelter (1) according to any one of claims 1 to 15 used according to the method of use of claim 16, the process comprising:

    - analyzing of at least one characteristic of the alumina,

    - determining a value for the intensity of the compensating current which has to flow in the compensating electrical circuit (6) as a function of the said at least one characteristic analyzed,

    - changing the intensity of the compensating current I₂ to the intensity value determined in the previous stage, if the intensity of the compensating current I₂ differs from that value.

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