EP0047246B1 - Process and device for suppressing magnetic disturbances in electrolytic cells - Google Patents

Abstract

Process and device for the suppression of magnetic disturbances in series of igneous electrolysis cells, for the production of aluminum, arranged transversally with respect to the axis of the series, operating with currents ranging from 200000 to 300000 amperes. It comprises the removal of the cathode current by a plurality of conductor elements (20) sealed in the cathode block and coming out vertically through the bottom of the vat, and the tapping off from 30 to 54% of the total cathode current in the connection conductor (8) arranged, at least on one portion of their path, outside the two vertical planes passing by the extremities of the anode system.

Description

The present invention relates to a new device and a new method for eliminating magnetic disturbances harmful to the proper functioning of very high intensity electrolysis cells placed across. These tanks are intended for the production of aluminum by electrolysis of the alumina dissolved in the aluminum and sodium fluoride baths. The invention applies to the reduction of the magnetic forces applied to the liquid metal contained in these tanks. These forces are due to the combined action of the horizontal currents appearing in the metal and the magnetic field created by the conductors of a tank and its neighbors in the same line, as well as by the conductors of the tanks of adjacent lines. The tanks are, in fact, arranged in series according to a certain number of adjacent rows, so as to ensure the return of the current to its source.

The invention only applies to the balancing of the magnetic field created by the conductors of the tank and of its neighbors in the same line. The influence of one or more adjacent lines, when these are at a distance relatively close to the line in question, is the subject of separate patents: French patent 2,333,060 and its certificate of addition 2,343,826 and French patent application filed on May 11, 1978 and published under number 2425482.

Expose the problem

We know that to reduce investment and reduce operating costs, the trend is to increase the size of production units, which leads to an increase in the intensity passing through each tank. The intensity range of the new tanks, which was recently below 200,000 A, is currently in the range 200,000 to 300,000 A.

At these intensities, the magnetic effects take on such an amplitude that, if no special measures were taken to attenuate their effects, the efficiency of the electrolysis cells would be greatly reduced and, ultimately, all functioning normal might become impossible.

• - déformation permanente de la nappe de métal avec, d'une part, une dénivellation globale, pente pouvant atteindre, dans certains cas, une valeur supérieure à la distance anode-métal et, d'autre part, une déformation en dôme symétrique;
• - existence de mouvements permanents du bain et du métal dont la configuration peut être plus ou moins favorable au bon déroulement de l'électrolyse;
• - existence de mouvements périodiques de l'interface bain/métal, néfastes au rendement de l'électrolyse (instabilités), et pouvant aller, dans certains cas, jusqu'à l'expulsion de métal liquide hors de la cuve.

These disturbances are manifested by several effects:

• - permanent deformation of the metal sheet with, on the one hand, a global drop, slope which can reach, in certain cases, a value greater than the anode-metal distance and, on the other hand, a symmetrical dome deformation;
• - Existence of permanent movements of the bath and of the metal, the configuration of which may be more or less favorable for the smooth running of the electrolysis;
• - existence of periodic movements of the bath / metal interface, detrimental to the efficiency of electrolysis (instabilities), and which can go, in certain cases, until the expulsion of liquid metal out of the tank.

To suppress magnetic disturbances, one can either act on the horizontal currents, or act on the magnetic field, or both; the present invention is based on the latter case.

Exhibition of the invention

By convention, in all that follows, we denote by Bx, By and Bz the components of the magnetic field along the axes Ox, Oy and Oz, in a direct trihedron whose origin 0 is the center of the cathode plane of the tank, Ox being the transverse axis of the tank directed in the direction of current flow in the queue of tanks, Oy the longitudinal axis of the tank and Oz the vertical axis directed upwards.

The sides of the tank are called "short sides" and "long sides", the latter being, in the case of series of tanks across, perpendicular to the axis of the series; the expression "head" is used to designate the ends, on the short sides, of both the tank and the anode system. In the usual way, we will speak for each tank upstream side and downstream side by reference to the conventional direction of the current in the series. In the following figures, the direction of the current will go from the bottom to the top of each drawing and will be indicated by an arrow.

Finally, it will be appropriate to call "tank considered" that from which the current is extracted by the cathode, "previous tank" that which feeds, from its cathode outputs, the anode system of the tank considered, and "next tank" that whose anode spider is supplied with current from the cathode outputs of the tank in question.

All the values of the magnetic fields are given in 'Tesla "(T) (1 T = 10 ⁴ Gauss).

The object of the invention is a device for the suppression of magnetic disturbances in the series of igneous electrolysis cells intended for the production of aluminum, from alumina dissolved in the molten cryolite, operating at a very high intensity. , being able to reach from 200,000 to 300,000 amperes, said tanks comprising a parallelepipedic box supporting cathode blocks in which the cathode current outputs, called "cathode outputs", are sealed, and an anode system (which may be of the self-cooking Soderberg type, or of the prebaked multiple anode type) - suspended from a spider, the tanks being electrically connected in series by connecting conductors and arranged transversely with respect to the axis Ox of the series, so that the short side of the box and of the anode system are parallel to the axis of the series, the cathode outputs being constituted by a plurality conductive elements sealed in the cathode blocks and emerging vertically from the bottom of the box, device in which part of the connecting conductors connecting the cathode outputs of a tank to the cross of the next tank are arranged, on at least part of their path outside the two vertical planes passing through the ends of the anode system on the short side.

Another object of the invention is a method for the suppression of magnetic disturbances in the series of igneous electrolysis cells intended for the production of aluminum from alumina dissolved in the molten cryolite, operating at an intensity of up to 200 000 to 300,000 amperes, said tanks comprising a parallelepipedic box supporting cathode carbon blocks in which the cathode current outputs are sealed, and an anode system suspended from a cross, the tanks being electrically connected in series by conductors connecting the outputs cathodics of a tank at the cross of the next tank, and being arranged transversely with respect to the axis Ox of the series, so that the short side of the box and of the anode system are parallel to the axis of the series , the cathode current being extracted by a plurality of conductive elements sealed in the cathode blocks and exiting vertically through the bottom of the caisso n, method according to which a fraction of the total current of between 30 and 54%, flowing in the connecting conductors between the tanks, is derived in conductors arranged, on at least part of their path, outside the two planes vertical passing through the ends of the anode system on the short side. The distribution of this derivative current may be symmetrical with respect to the axis of the series, and be equally distributed on each side of the tanks, or be asymmetrical, and distributed unevenly on each side of the tanks.

• La figure 1 représente les deux systèmes de sorties cathodiques dessinées, par simplification, sur la même cuve: sorties latérales et sorties par le fond.
• La figure 2 représente schématiquement la coupe d'une cuve, sur laquelle apparaissent les trois axes de coordonnées utilisés pour définir la direction des composantes du champ magnétique.
• La figure 3 représente la répartition de la moyenne de la composante verticale Bz du champ magnétique sur les quatre quadrants de la cuve.
• La figure 4 schématise la position des conducteurs de liaison, selon l'invention, par rapport au plan vertical zz' passant par l'extrémité du système anodique.
• Les figures 5, 6, 7 indiquent, de façon schématique, les diverses variantes des trajets que peuvent suivre les conducteurs de liaison, dans le cadre de l'invention.
• La figure 8 indique comment seraient constituées les liaisons entre cuve, en mettant en oeuvre les connaissances de l'art antérieur.
• Les figures 9 à 13 représentent la mise en oeuvre de l'invention sous cinq variantes différences, qui font chacune l'objet d'exemple de mise en oeuvre.
• La figure 14 est le schéma d'une réalisation pratique et la figure 15, une coupe, dans le sens de l'axe de la série, de cette même réalisation, indiquant la position réelle des conducteurs.

The spider of a tank considered is supplied with current from the cathode outputs of the previous tank by a plurality of vertical risers which can be connected either entirely on the upstream side of said spider, or both on the upstream side and on the downstream side a part of the current which can, moreover, be brought to one and / or the other of the heads of said spider.

• FIG. 1 shows the two cathode outlet systems drawn, for simplification, on the same tank: lateral outlets and outlets from the bottom.
• Figure 2 shows schematically the section of a tank, on which appear the three coordinate axes used to define the direction of the components of the magnetic field.
• FIG. 3 represents the distribution of the average of the vertical component Bz of the magnetic field over the four quadrants of the tank.
• Figure 4 shows schematically the position of the connecting conductors, according to the invention, relative to the vertical plane zz 'passing through the end of the anode system.
• Figures 5, 6, 7 indicate, schematically, the various variants of the paths that the connecting conductors can follow, within the framework of the invention.
• FIG. 8 indicates how the connections between tanks would be made up, using the knowledge of the prior art.
• Figures 9 to 13 show the implementation of the invention under five different variations, each of which is the subject of an example of implementation.
• FIG. 14 is the diagram of a practical embodiment and FIG. 15, a section, in the direction of the axis of the series, of this same embodiment, indicating the actual position of the conductors.

In these different figures, the same elements are designated by the same reference numerals. (1) designates the lateral cathode outputs according to the prior art, (2) the cathode outputs through the bottom of the box, (3) the box, (4) the outline of the anode blocks, (5) the anode system, (6 ) the electrolysis bath, (7) the sheet of liquid aluminum formed on the cathode, (8) the bypass conductor (or group of conductors), (9) the spider.

In conventional tanks, horizontal currents are mainly generated by the cathode current collection mode. The current is extracted by lateral cathode bars (1) which have the disadvantage of concentrating the current on the two long sides of the cathode. When the size of the tank is increased, the cathode is enlarged, which has the effect of increasing the horizontal currents in the liquid metal.

In the present invention, the current is extracted from the carbon cathode by vertical outlets (2) which we will designate hereinafter by the term of bottom outlets. This process makes it possible to considerably reduce the horizontal currents in the metal while obtaining a gain of the order of 0.1 V on the. cathodic fall. This improvement in cathodic drop results in a reduction of 300 kMh / t in the specific energy consumed by the tank.

Because of the bottom outlets, we will no longer distinguish the cathode current extracted upstream from that extracted downstream, as it was customary to do in the case of tanks with lateral cathode outlets, since the all the current comes out from below the tank. The definition of the number, the position and the anchoring device in the carbon cathode of the vertical outlets from the bottom, will be considered to be known to those skilled in the art.

The idea of bottom exits has been described in several old patents; three of them only use bottom outlets, excluding any description of the connecting conductors: FR 953 374, IT 451 183 and FR 1,125,949. The first relates only to tanks with relatively low intensity, close to 100,000 A. Two other patents, also applying only to tanks with intensity close to 100,000 A, describe. costly arrangements of conductors leading to summary balancing in terms of the magnetic field: NO 83 883 and FR 1 079 131 and its additive no. 65 320. The paths of the connecting conductors are long, leading to a significant investment in conductors and drops high line voltage. The invention makes it possible to eliminate magnetic disturbances on these tanks by eliminating horizontal currents and by balancing the magnetic field.

With regard to the magnetic field, it will be appropriate to call "antisymmetric" with respect to a given plane, a component, when any pair of points symmetrical with respect to this plane correspond to two opposite values of the component.

In the transverse tanks, in the absence of the effect of neighboring lines, the components Bx and Bz are, by construction, asymmetrical with respect to the plane x o z.

• - Un critère principal appliqué à la composante verticale consistant en l'égalité des moyennes de Bz par quart de cuve. La numérotation des quadrants de cuve est définie sur la figure 3. Légalité des moyennes s'écrit:
  
  Cette égalité, compte tenu de l'antisymétrie, entraînera, en l'absence de files voisines:
  
  De plus, les valeurs ponctuelles de Bz devont être faibles. Le champ sera calculé en prenant en compte l'effet des pièces ferromagnétiques de la cuve et de son environnement.
• - Un critère secondaire consistant en la réduction de la valeur maximale de la composante horizontale Bx. La valeur maximale sera généralement située à l'extrémité du plan anodique, sur les petits côté de la cuve.

With regard to the balancing of the magnetic field, which governs the choice of the arrangement of the conductors of links, we adopted the following two criteria:

• - A main criterion applied to the vertical component consisting of the equality of the means of Bz per quarter of tank. The numbering of the tank quadrants is defined in Figure 3. Legality of the means is written:
  
  This equality, taking into account the asymmetry, will lead, in the absence of neighboring lines:
  
  In addition, the point values of Bz should be small. The field strength will be calculated taking into account the effect of the ferromagnetic parts of the tank and its environment.
• - A secondary criterion consisting in the reduction of the maximum value of the horizontal component Bx. The maximum value will generally be located at the end of the anode plane, on the short sides of the tank.

The invention consists, for tanks across an intensity between 200,000 A and 300,000 A, in a combination of the outputs from the bottom and a bypass of part of the current in conductors arranged outside the two vertical planes passing through the ends of the anode system.

In reality, this definition of the location of the branch conductors must be clarified, because it includes part of the box, and it is obvious that the connecting conductors cannot pass inside the box.

In practice, the branch conductors are therefore placed in the hatched area ABCDEF of FIG. 4. This area is delimited on the box side, by the vertical walls AB on the short side of the box, and, below the box, by the bottom up to 'plumb with the end of the anode system (BC). However, the conductor will be slightly moved away from the wall of the box, at a distance compatible with the requirements of electrical safety. On the side opposite to the wall of the box, there is no theoretical limit of the area. However, in order not to inconsiderately lengthen the path of the conductors, we will not deviate beyond an EF plane located about one meter from the wall of the box. The height of the zone is theoretically unlimited, but, for reasons of economy of journey and so that the bypass conductor does not interfere with operations on the tank, the height of the zone will be delimited, in its upper part, by the top of the box (FA) and, in its lower part, by a border ED located about one meter below the bottom of the box.

Figures 5, 6 and 7 provide a better definition of the term "branch conductor".

In FIG. 5, the cathodic current collected under the tank considered, circulates in the conductor (10) and is derived by the heads of the tank considered (outside the vertical plane passing through the end of the anode system (4) by the bypass conductor (11) which bypasses the two upstream and downstream angles of the end (12) of the anode plane). The bypass conductor (11) passes under the box (3) of the tank in question and is connected to the crosspiece of the next tank by the rise (13).

In FIG. 6, the cathodic current collected under the tank in question circulates in the conductor (14) and is derived by the heads of the next tank by the bypass conductor (15) which bypasses the two angles upstream and downstream of the end (12) of the anodic plane of the next tank (outside the vertical plane passing through the end of said anodic system). The bypass conductor (15) runs along its side of the next tank on its short side.

In FIG. 7, part of the cathode current collected under the tank in question, circulates in the conductor (16) and is derived by the heads of the tank considered by the bypass conductor (17) which bypasses the two angles upstream and downstream of the end (12) of the anode plane of the tank considered. The bypass conductor (17) runs along the box (3) of the tank considered on its short side. Another part of the cathode current, collected under the tank in question, circulates in the conductor (18) and is derived by the heads of the next tank by the same conductor. bypass (19) which bypasses the two upstream and downstream angles of the end (12) of the anode plane of the next tank. The bypass conductor (19) runs along the box (3) of the next tank on its short side.

• - dans le cas où le conducteur de dérivation alimente le croisillon de la cuve suivante par une montée positive située sur le grand côté amont de la cuve suivante, la fraction de courant dérivé par chacune des têtes de la cuve considérée sera comprise entre 15% et 27% de l'intensité totale;
• - dans le cas où le conducteur de dérivation alimente le croisillon de la cuve suivante par une montée positive située sur le grand côté aval de la cuve suivante, la fraction de courant dérivé par chacune des têtes de la cuve suivante sera comprise entre 15% et 27% de l'intensité totale.

The part of the current which is derived by each of the heads of the tank is between 15% and 27% of the total current of the tank. More precisely:

• - in the case where the bypass conductor feeds the spider of the next tank by a positive rise located on the large upstream side of the next tank, the fraction of current diverted by each of the heads of the tank considered will be between 15% and 27% of the total intensity;
• - in the case where the bypass conductor feeds the spider of the next tank by a positive rise located on the large downstream side of the next tank, the fraction of current diverted by each of the heads of the next tank will be between 15% and 27% of the total intensity.

In these ranges, the compensation for the effect of one or more neighboring queues adjacent to the queue in question is not taken into account.

For high intensity tanks, the number of positive rises will generally be greater than or equal to four. However, in the case where the invention is applied to tanks with an intensity of less than 200,000 A, it will be possible to settle for less than four positive rises.

• En reliant directement les sorties par le fond au plan anodique de la cuve suivante à l'aide de cinq montées positives d'égale intensité, réparties sur le grand côté d'une cuve 250.000 ampères (figure 8), comme on le ferait en appliquant les connaissances de l'art antérieur, on obtient un champ magnétique vertical croissant du centre de la cuve vers les têtes, avec des valeurs moyennes par quadrant, déduction faite de l'effet des pièces ferromagnétiques:
  
  la condition:
  
  n'est absolument pas vérifiée puisque l'on a au contraire:
  

Let us illustrate with an example the importance of a judicious choice of connection conductors for a tank with bottom outlets:

• By directly connecting the outputs from the bottom to the anode plane of the next tank using five positive rises of equal intensity, distributed on the long side of a 250,000 amp tank (Figure 8), as we would do by applying knowledge of the prior art, a vertical magnetic field is obtained increasing from the center of the tank towards the heads, with average values per quadrant, minus the effect of the ferromagnetic parts:
  
  the condition:
  
  is absolutely not verified since on the contrary we have:
  

This circuit, although having the advantage of the shortest electrical path, does not allow the magnetic field of a tank with outlets from the bottom to be balanced.

We provide below examples of application of the invention which show the improvement obtained on the balancing of the magnetic field. In FIGS. 9 and 13, for the sake of clarity, we only very schematically represent the conductors connecting the cathode outputs (2) of the tank in question to the spider (9) supplying the anodes of the next tank. In practice, the connecting conductors pass below the level of the work surface, and then join the cross braces by vertical or slightly oblique climbs.

In all the examples presented, each cathode block arranged parallel to the axis Ox has three vertical outlets. But, well heard, the actual number of outputs can be different without departing from the scope of the invention.

Example 1 Tanks with bottom outlets, with five positive ascents, the current derived by the heads of the next tank feeds the latter through the large downstream side (Figure 9)

The current drawn at the two ends of the cathode is derived by the heads of the next tank to feed its cross-bar downstream by two positive rises located at 1/4 and 3/4. The fraction of current flowing through each of the two branch conductors is 3/16, or 18.75%, of the total current. The rest of the current feeds the spider of the next tank upstream, in three positive ascents, one located along the axis Ox of the tank and the other two at the heads of the spider. The latter climbs can be placed either on the large or on the small side of the tank.

The average vertical field per quadrant of this tank at 250,000 A, and taking into account the effect of the ferromagnetic parts, is:

The maximum horizontal field Bx is 60.1 ₀ - _4.

Example 2 Tanks with outlet from the bottom, with six positive ascents, the current derived by the heads of the next tank is collected in the inter-tank space and is sent downstream of the spider of the next tank (Figure 10)

The current drawn at the two ends of the cathode is collected on either side of the tank considered in the inter-tank space. Part of this current is derived from the heads of the tank in question. The bypass conductor then goes along the heads of the next tank and feeds its spider, downstream at 1/4 and 3/4 of the long side. Each of the bypass conductors by the heads of the next tank is crossed by 1/5 of the total current. The rest of the cathode current feeds upstream the cross of the next tank by four positive ascents located at 1/8, 3/8, 5/8 and 7/8.

The average vertical field per quadrant of this tank at 250,000 A, and taking into account the effect of the ferromagnetic parts, is:

The maximum horizontal field Bx is 25.10- ⁴ _T.

Example 3 Tank with outputs from the bottom, with five positive ascents, the current derived by the heads of the tank in question is taken at 1/4 and 3/4 of the cathode (Figure 11)

The current drawn at 1/4 and 3/4 of the cathode joins along the large upstream side of the tank considered the bypass conductor circulating on the heads of the tank considered before supplying upstream the heads of the spider of the next tank by a positive rise on both sides of the tank. The climbs can be indifferently placed on the long side or on the short side of the tank.

Each of the bypass conductors through the heads of the tank in question is traversed by 3/16, or 18.75%, of the total intensity. The rest of the cathode current feeds directly upstream, as shown in Figure 11, the cross of the next tank by three positive rises located 1/4, 1/2 and 3/4 of the large. side.

Le champ horizontal Bx maximum est de 40.10-⁴ T.The average vertical field per quadrant of this tank at 250,000 A, and taking into account the effect of the ferromagnetic parts is:

The maximum horizontal field Bx is 40.10- ⁴ T.

Example 4 Tank with outputs from the bottom, with five positive ascents, the current derived by the heads of the tank in question is taken at both ends of the cathode (Figure 12)

The current drawn at the two ends of the cathode joins along the large upstream side of the tank considered the bypass conductor circulating on the heads of the tank considered before supplying the upstream end of the crosspiece of the next tank by a positive rise on either side of the tank. The climbs can be placed either on the long side or on the short side. Each of the bypass conductors by the heads of the tank in question is traversed by 1/4 of the total intensity. The rest of the cathode current feeds directly upstream the cross of the next tank by three positive rises located at 1/4, 1/2 and 3/4 of the long side.

The average vertical field per quadrant of this tank at 250,000 A and taking into account the effect of the ferromagnetic parts is:

The maximum horizontal field Bx is 48.10- ⁴ _T.

Example 5 Tank with outlets from the bottom, with four positive ascents, the current derived by the heads of the tank considered is collected in the inter-tank space upstream of the tank considered (Figure 13)

This collector supplies the bypass conductor through the heads of the tank in question. The bypass current then feeds the upstream crosspiece of the next tank by two positive ascents located 1/8 and 7/8 of the long side. Each of the bypass conductors by the heads of the tank in question is traversed by 1/4 of the total intensity. The rest of the cathode current feeds upstream the cross of the next tank by two positive ascents located 3/8 and 5/8 of the long side.

The average vertical field per quadrant of this 250,000 A tank, and taking into account the effect of the ferromagnetic parts is:

The maximum horizontal field Bx is 22.10- ⁴ _T.

Implementation of the invention

We have produced a series of tanks according to the invention, the operating intensity of which has been set at 250,000 A.

Figure 14 schematically gives the arrangement of all the connecting conductors between the tank considered and the next tank.

Figure 15 is a cross section along an axis parallel to Ox of the tank considered and the next tank. The numbering of the elements is common to the two figures. In FIG. 15, the alumina supply device, the superstructure, the anodes and their suspension system have either been omitted, or shown very schematically for clarity of the drawing. They are, in reality, in accordance with the prior art.

The cathodic outputs through the bottoms (20) are connected to several negative collectors (21). The current collected at the two ends of the cathode is connected by the conductors (22) to the bypass conductors (8) by the heads of the next tank and then feeds the crosspiece (9) of this tank by the risers (23) located ' on the downstream side at 1/4 and 3/4.

Each of the bypass conductors through the heads is crossed by 3/16, or 18.75%, of the total intensity. The Oz dimension of these conductors is determined so as to ensure the balance of the magnetic field. The location area of these conductors was previously defined (Figure 4).

The current collected at the center of the cathode is connected by the conductors (24) to three vertical risers, connected to the heads and in the middle of the spider, on the upstream side. Each of the conductors supplying the heads of the cross is crossed by 1/4 of the total intensity and the conductor feeding the center of the cross is crossed by 1/8 of the total intensity.

dimension intérieure 13,68x4,15 (en mêtres) du caissonThe tanks of the series built according to the invention have the following characteristics:

inner dimension 13.68x4.15 (in meters) of the box

During their operation, the following results were obtained:

The corresponding specific energy consumption is 12,690 kMh / tonne AI, which is a record value with tanks operating at such a high intensity. This gain was obtained inter alia by a lowering of the cathodic drop which was on average at 0.25 V.

Claims (7)

1. A device for eliminating magnetic disturbances in series of igneous electrolysis cells intended for the production of aluminium from alumina dissolved in molten cryolite, operating at a very high intensity capable of reaching from 200,000 to 300,000 amperes, the said cells comprising a parallelepiped box which supports the cathodic blocks (4) in which there are sealed the cathodic current outlets (2) and an anodic system (5) suspended from a bus bar (9), the cells being connected electrically in series by linking conductors and arranged transversely to the Ox axis of the series in such a manner that the small side of the box and of the anodic system are parallel to the axis of the series, the cathodic outlets being formed by more than one conducting element sealed in the cathodic blocks and projecting vertically through the base of the box, characterised in that some of the linking conductors (8) connecting the cathodic outlets (2) of one cell to the bus-bar (5) of the following cell are arranged, over at least a section of the path thereof, outside the two vertical planes passing through the ends (12) of the anodic system (5) on the small side.

2. A process for eliminating magnetic disturbances in series of igneous electrolysis cells intended for the production of aluminium from alumina dissolved in molten cryolite, operating at an intensity capable of reaching from 200,000 to 300,000 amperes, the said cells comprising a parallelepiped box which supports the carbon cathodic blocks in which there are sealed the outlets of the cathodic current, and an anodic system suspended from a bus-bar, the cells being connected electrically in series by conductors connecting the cathodic outlets of one cell to the bus-bar of the following cell and being arranged transversely to the Ox axis of the series, such that the small side of the box and of the anodic system are parallel to the axis of the series, the cathodic current being extracted by several conducting elements sealed in the cathodic blocks and projecting vertically through the base of the box, characterised in that a fraction of the total current of from 30 and 54%, circulating in the linking conductors between the cells is shunted in conductors arranged over at least part of the path thereof, outside the two vertical planes passing through the ends of the anodic system on the small side.

3. A process for eliminating magnetic disturbances in series of igneous electrolysis cells according to claim 2, characterised in that the shunted current is distributed in the shunt conductors symmetrically to the axis of the series.

4. A process for eliminating magnetic disturbances in series of igneous electrolysis cells according to claim 2, characterised in that the shunted current is distributed in the shunt conductors asymmetrically to the axis of the series.

5. A process for eliminating magnetic disturbances in series of igneous electrolysis cells according to any one of claim 3 or 4, characterised in that the bus-bar of each cell is supplied with current from the cathodic outlets of the preceding cell by several vertical risers connected to the upstream side thereof.

6. A process for eliminating magnetic disturbances in series of igneous electrolysis cells according to any one of claims 3 or 4, characterised in that the bus-bar of each cell is supplied with current from the cathodic outlets of the preceding cell, partially by several vertical risers connected to the upstream side thereof, and partially by several vertical risers connected to the downstream side thereof.

7. A process for eliminating magnetic disturbances in series of igneous electrolysis cells according to any one of claims 3 or 4, characterised in that the bus-bar of each cell is partially supplied with current from the cathodic outlets of the preceding cell by vertical risers connected to either or to both of the two ends thereof on the small side of the anodic system.

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