EP3362590B1 - Series of electrolysis cells for the production of aluminium comprising means for balancing the magnetic fields at the end of the line - Google Patents

Description

Field of the invention

The invention relates to the production of aluminum by igneous electrolysis, namely by electrolysis of alumina in solution in a bath of molten cryolite, called an electrolyte bath, according to the well-known Hall-Héroult process. The invention particularly relates to the balancing of the magnetic field of the series of electrolysis cells, typically of rectangular shape and arranged transversely.

State of the art

The factories for the production of aluminum by igneous electrolysis contain a large number of electrolysis cells - typically several hundred - arranged in line, and electrically connected in series using bonding conductors, so as to form two or more lines. which are electrically linked together by connecting conductors. The cells, which are rectangular in shape, can be oriented either longitudinally (i.e. so that their major axis is parallel to the longitudinal axis of the rows), or transversely (i.e. say so that their major axis is perpendicular to the longitudinal axis of the lines).

A large number of arrangements of cells and connecting conductors have been proposed in order, on the one hand, to limit the losses by Joule effect and, on the other hand, to reduce the impact of the magnetic fields produced by the conductors of bond and neighboring cells on the electrolysis process. For example, the French patent application FR 2 552 782 (corresponding to the American patent US 4,592,821 ), on behalf of Aluminum Pechiney, describes a line of transversely arranged electrolysis cells capable of operating industrially at intensities greater than 300 kA. According to this patent, the magnetic stability of the cells is ensured by the configuration of the connection conductors, in particular those passing under the tank.

Also, the French patent application FR 2425 482 (corresponding to the American patent US 4169 034 ) in the name of Aluminum Pechiney, describes an aluminum smelter comprising at least two parallel parallel rows of cells in which the magnetic field generated by the current flowing in the neighboring row of cells is compensated by means of at least one independent correcting conductor passing on the side of the tanks, along all the cells of the series and crossed by a direct current of correction.

Furthermore, the French patent application FR 2 583 069 (corresponding to the American patent US 4,713,161 ), also in the name of Aluminum Pechiney, describes a file of electrolysis cells arranged transversely which can operate at intensities up to 500 to 600 kA. According to this patent, the construction and installation costs of the circuits are minimized by the use of connecting conductors as small and as direct as possible, while the magnetic stability and the Faraday efficiency are maximized by the use independent correction conductors, arranged parallel to each line and on each side thereof.

The file arrangement of the electrolysis cells has the advantage of simplifying the configuration of the connecting conductors and standardizing the map of magnetic fields. However, the presence of connecting conductors between the lines disturbs the uniformity of the map of the magnetic fields of the end cells of each line.

American patents US 3,775,280 and US 4,189,368 propose arrangements of connection conductors for series of cells arranged longitudinally intended to limit the disturbances caused by these connection conductors. In addition, the intensities of this type of cell generally do not exceed 100 kA.

European patent applications EP 0 342 033 and Chinese CN 2 477 650 describe arrangements of connection conductors applicable to the series of cells arranged transversely intended to limit the disturbances caused by these connection conductors. These documents relate to series of electrolysis cells provided with cells intended for intensities of the order of 300 kA.

The patent FR 2 868 436 (corresponding to the American patent US 7,513,979 ) in the name of Aluminum Pechiney describes a series of two rows of cells arranged transversely and provided with at least one correction conductor along the inside of the rows, with a particular arrangement of the correction conductor consisting in making a transverse section running along along its length, the first end cell of the line at a determined distance and traversed by a current flowing from the inside to the outside of the lines of cells. Such an arrangement makes it possible to satisfactorily compensate for the magnetic field generated by the connection conductors in a small number of end cells (approximately 1 to 3) while a greater number of end cells (approximately 1 to 10 ) are disturbed by the magnetic field generated by the connecting conductors. Consequently, a large number of end-of-queue cells remain unstable and difficult to operate.

The Applicant has therefore sought economically and technically satisfactory solutions for balancing the magnetic fields of the end cells of the lines, and in particular of series of cells formed from long rectangular cells, arranged transversely.

Description of the invention

• au moins une première et une deuxième files rectilignes et parallèles l'une à l'autre de cellules d'électrolyse raccordées électriquement en série,
• un conducteur de raccordement entre une première cellule d'extrémité de la première file et la première cellule d'extrémité correspondante de la deuxième file,

et caractérisée en ce que la série comprend au moins un circuit d'équilibrage magnétique des cellules d'extrémité de file comportant un premier conducteur électrique d'équilibrage magnétique des cellules d'extrémité de file s'étendant le long d'une première file de cellules uniquement en regard d'une portion d'extrémité de la première file de cellules.To this end, the subject of the invention is a series of electrolysis cells intended for the production of aluminum by igneous electrolysis according to the Hall-Héroult process, comprising:

• at least first and second straight and parallel rows of electrolysis cells parallel to each other, electrically connected in series,
• a connection conductor between a first end cell of the first file and the corresponding first end cell of the second file,

and characterized in that the series comprises at least one circuit for magnetic balancing of the end-of-line cells comprising a first electrical conductor for magnetic balancing of the end-of-line cells extending along a first line of cells only next to an end portion of the first row of cells.

The Applicant has noted that, in the absence of a magnetic balancing circuit for the end-of-line cells as defined above, the end cells of the lines are especially affected by an additional mean vertical magnetic field ΔBz, when the cells in the central portion of the lines are correctly balanced magnetically. The invention thus aims to maintain the additional vertical field ΔBz within a range limited by a minimum value and a maximum value around a target value close to zero.

The Applicant has had the idea of placing said first electrical conductor near the notoriously unstable end cells of the row of cells so as to be able to circulate in said first electrical conductor an electric current making it possible to compensate for the magnetic field produced in particular connecting conductors between the lines, and balancing the magnetic fields at the level of the cells of the end electrolysis cells.

The first electrical conductor extending along the row of cells extends parallel or substantially parallel to the longitudinal axis of the row of cells. By the terms "along the cell line", the applicant understands that the conductor extends in the immediate vicinity of the cell line, so that its impact on the magnetic field in nearby cells is maximized, and typically has a distance of less than 5 meters and advantageously less than 3 meters.

This configuration makes it possible in particular to substantially limit the vertical magnetic field Bz in these end cells. The use of such a magnetic balancing circuit of the end-of-queue cells also allows fine adjustment of the magnetic balancing thanks to the additional adjustable parameters which it provides.

The first electrical conductor is traversed during the operation of the series by a direct current for magnetic balancing of the end-of-line cells.

The first electrical conductor extends continuously along a plurality of adjacent cells of the end portion for which an imbalance of the vertical magnetic field due to the presence of the connecting conductor is observed.

Such an end portion of the first row of cells typically comprises from 3 to 10 cells, and preferably from 6 to 8 cells.

In order for the stabilizing impact on the magnetic field of the end-of-line cells to be adequate and economically viable, the first electrical magnetic balancing conductor advantageously extends over a length at least equal to three times the distance between two cells (the distance between two cells being the distance between the median longitudinal axes of two adjacent electrolysis cells, typically correspond to 5 to 10 meters).

The connection conductor no longer constitutes a destabilizing element for the electrolysis cells arranged beyond the tenth cell starting from the first end cell, due to the large distance between these cells and the connection conductor.

For the case of existing series of electrolysis cells, magnetic balancing means of the known end cells may have already been installed and correctly balance the first end cell. In which case, the first magnetic balancing electrical conductor may not extend along this first end cell.

• circulant dans le même sens que le courant d'électrolyse circulant dans la première file de cellules si le premier conducteur électrique d'équilibrage magnétique se situe le long de la première file de cellules du côté de la deuxième file de cellules d'électrolyse;
• circulant dans le sens opposé par rapport au courant d'électrolyse circulant dans la première file de cellules si le premier conducteur électrique d'équilibrage magnétique se situe le long de la première file de cellules du côté opposé à la deuxième file de cellules d'électrolyse.

The invention also relates to a method of using a series of electrolysis cells. In operation, the rows of electrolysis cells and the connection conductor are traversed by an electrolysis current and the first magnetic balancing electrical conductor is traversed by an electrical balancing current:

• flowing in the same direction as the electrolysis current flowing in the first row of cells if the first electric magnetic balancing conductor is located along the first row of cells on the side of the second row of electrolysis cells;
• running in the opposite direction with respect to the electrolysis current flowing in the first row of cells if the first magnetic balancing electric conductor is located along the first row of cells on the side opposite to the second row of electrolysis cells .

Thus, at the end-of-line cells along which the first electrical conductor extends, the balancing electric current generated by passing a vertical magnetic field opposite the vertical magnetic field generated by the current d through the first electric conductor. electrolysis passing through the connection conductor.

According to one embodiment, the magnetic balancing circuit of the end of line cells comprises a second electrical conductor parallel to the first electrical conductor of magnetic balancing of the end of line cells. This second parallel electrical conductor participates in the closure of the magnetic balancing circuit and potentially in the production of a magnetic balancing circuit comprising a plurality of loops in series. Also, this second electrical conductor is traversed by the electric balancing current flowing in the opposite direction with respect to the electric balancing current flowing in the first electric conductor. This second electrical conductor is advantageously arranged so as to improve the magnetic configuration of the end cells of the first row or of the second row, and at a minimum so that its possible negative impact on the magnetic balancing of the cells end is minimized and less than the positive impact of the first electrical conductor.

According to a particular embodiment, the second electrical conductor extends along the first row of cells only opposite the end portion of the first row of cells, the first and the second electrical conductor extending along opposite sides of the first row of cells. The vertical magnetic field generated by the circulation of the same electric balancing current, in the opposite direction, on the other side of the cell line, in the second electrical conductor then adds to the vertical magnetic field generated by the circulation of an electric balancing current in the first conductor electric to counter the destabilizing vertical magnetic field generated by the current flowing in the connection conductor.

According to another particular embodiment, the second electrical conductor extends on the same side of the first row of cells as the first electrical conductor, the distance between the first electrical conductor and the first row of cells being less than a distance between the second electrical conductor and the first row of cells. Thus, as the second electrical conductor is on the same side but further from the first row of electrolysis cells than the first electrical conductor, the vertical magnetic fields generated by the circulation of the balancing electric current in the opposite direction in the first and second electrical conductors oppose each other, but with less intensity for the vertical magnetic field generated by the circulation of the balancing electric current in the second electrical conductor than in the first electrical conductor, at the level of the end-of-line cells along from which the first electrical conductor extends.

Advantageously, the second electrical conductor is further from the electrolysis cells of the first row than the first electrical conductor so that the ratio of the values of the vertical magnetic field generated by the same balancing current flowing in the second electrical conductor and in the first electrical conductor is less than 0.5 to preferably less than 0.3, at the end-of-queue cells along which the first electrical conductor extends.

According to a particular embodiment, the second electrical conductor extends along the second row of cells only opposite an end portion of the second row of cells. Thus, the magnetic balancing circuit makes it possible to magnetically balance both the end cells of the first row of cells and the corresponding end cells of the second row of cells.

According to a preferred embodiment, the magnetic balancing circuit is connected to a specific electrical supply station. The intensity of the current flowing in the magnetic balancing circuit can advantageously be easily controlled and adjusted. By specific electrical supply station, it is meant that this electrical supply station does not supply current to the electrolysis circuit (connecting conductors), or correction conductors intended to carry out magnetic correction on all of the series cells.

According to a preferred embodiment, the magnetic balancing circuit of the end of line cells has two ends which are connected to conductors electrically connecting electrolysis cells to each other. The magnetic balancing circuit of the end-of-line cells is then supplied by at least part of the electrolysis current flowing in the cells and forms part of the electrolysis circuit through which the electrolysis current of the series.

According to a preferred embodiment, the magnetic balancing circuit is connected to the conductors electrically connecting electrolysis cells to one another in parallel with one or more so-called parallel electrical conductors. Thus only part of the electrolysis current flows in the magnetic balancing circuit. Advantageously, the magnetic balancing circuit of the end-of-line cells forms part of the connection conductor. The electrical balancing between the so-called parallel electrical conductors and the magnetic balancing circuit is thus facilitated.

According to a preferred embodiment, the series of electrolysis cells comprises a correction circuit comprising at least a first correction conductor, extending along the first line, a second correction conductor extending along the second line, and at least one correction conductor for connection between the first and second correction conductors, and in which the magnetic balancing circuit of the end of line cells has two ends which are connected to the correction circuit.

As presented in the preamble, certain series include one or more correction circuits extending along all of the electrolysis cells of the series to correct the destabilizing magnetic fields generated by the high intensity currents flowing in the circuits. conductors from cell to cell or in the neighboring cell queue. The correction circuit is an integral part of the series and is supplied with electric current. This solution is therefore particularly advantageous since it does not require the installation of a specific supply station which represents a significant equipment cost and can also prove to be difficult to install due to the space required.

Advantageously, the magnetic balancing circuit of the line end cells is connected in series between two portions of the correction circuit. As the first and second correction conductors extend along all of the electrolysis cells, it suffices to connect the magnetic balancing circuit of the end of line cells in series at an intermediate point of the correction circuit. at a suitable location along the cell lines. The correction current flowing in the correction circuit also passes through the magnetic balancing circuit and becomes in this magnetic balancing circuit the magnetic balancing current. According to a preferred embodiment, the first correction conductor extends along the first row on the side of the second row, and the second correction conductor extends along the second row on the side of the first row cells. The first conductor and the second conductor of the magnetic balancing circuit connected to the correction circuit are advantageously arranged outside the two rows of cells. The outside of the rows of cells, opposite the correction circuit, is less crowded than the inside and the installation of the magnetic balancing circuit facilitated. Such a magnetic balancing circuit can in particular be implemented on an existing series already comprising a correction circuit disposed inside the two rows of cells.

According to a particular embodiment, the connection conductor comprises a magnetic balancing conductor of the first end cell running along the first end cell perpendicular to the longitudinal axis of the row of cells, and the first electrical conductor not extend along the first end cell. The first end cell is already magnetically balanced via the magnetic balancing conductor of the first end cell, so that changing its magnetic field using the first electrical conductor would destabilize it.

According to a particular embodiment, the magnetic balancing circuit of the end of line cells comprises a transverse conductor electrically connecting the correction circuit to the first electrical conductor, the transverse conductor extending under the cell line.

According to one embodiment, the magnetic balancing circuit of the end-of-line cells forms a plurality of loops and the first magnetic balancing electric conductor is formed by a plurality of loop strands extending side by side along of the first row of cells only opposite the end portion of the first row of cells. The current flows in the same direction in each of the loop strands of the first electrical conductor and the impact on the magnetic field of the current flowing in the first electrical conductor is the sum of the impact on the magnetic field of the current flowing in each of the loop strands forming the first electrical conductor.

According to a preferred embodiment, the cells are arranged transversely with respect to the rows of cells.

The electrolysis cells are typically electrically connected in series by means of electrical connecting conductors connecting the cathode of an electrolysis cell to the anode of the next electrolysis cell.

• La figure 1 représente, de manière simplifiée et en coupe transversale, deux cellules d'électrolyse successives (n ; n+1) typiques d'une file de cellules.
• Les figures 2 à 4 illustrent, de manière schématique, différents modes de réalisation d'une série de cellules d'électrolyse selon l'invention comportant deux files et des circuits d'équilibrage magnétique des cellules d'extrémité.
• La figure 5 illustre, de manière schématique, un mode de réalisation de l'invention dans lequel une partie du courant d'électrolyse de la série est utilisée pour alimenter des circuits d'équilibrage magnétique des cellules d'extrémité.
• La figure 6 illustre, de manière schématique, une série de cellules d'électrolyse selon l'état de l'art comportant deux files et un circuit de correction.
• La figure 7 illustre, de manière schématique, une extrémité de série de cellules d'électrolyse selon l'invention comportant deux files et des circuits d'équilibrage magnétique des cellules d'extrémité connectés à un circuit de correction.
• La figure 8 illustre, de manière schématique, une extrémité de série dans laquelle chaque circuit d'équilibrage magnétique forme deux boucles.
• La figure 9 illustre, de manière schématique, une extrémité de série de cellules d'électrolyse selon l'invention comportant deux files, un agencement particulier du conducteur de raccordement permettant d'équilibrer magnétiquement la première cellule d'extrémité et des circuits d'équilibrage magnétique des cellules d'extrémité connectés à un circuit de correction.

The invention is described in detail below using the attached figures.

• The figure 1 represents, in a simplified manner and in cross section, two successive electrolysis cells (n; n + 1) typical of a row of cells.
• The figures 2 to 4 schematically illustrate various embodiments of a series of electrolysis cells according to the invention comprising two rows and circuits for magnetic balancing of the end cells.
• The figure 5 illustrates schematically an embodiment of the invention in which part of the series electrolysis current is used to supply magnetic balancing circuits for the end cells.
• The figure 6 illustrates, schematically, a series of electrolysis cells according to the state of the art comprising two lines and a correction circuit.
• The figure 7 illustrates schematically a series end of electrolysis cells according to the invention comprising two lines and magnetic balancing circuits of the end cells connected to a correction circuit.
• The figure 8 illustrates schematically a series end in which each magnetic balancing circuit forms two loops.
• The figure 9 schematically illustrates a series end of electrolysis cells according to the invention comprising two rows, a particular arrangement of the connection conductor making it possible to magnetically balance the first end cell and magnetic balancing circuits of the cells end connected to a correction circuit.

The invention relates to a series 1 of electrolysis cells comprising, as shown figures 2 to 5 , 7 and 8 , a plurality of electrolysis cells 100, 100 'of substantially rectangular shape, which are arranged so as to form at least two rows F, F' of cells substantially rectilinear, parallel and each having a longitudinal axis A, A '.

The cells 100 are typically arranged transversely (that is to say so that their main axis or long side is perpendicular to the longitudinal axis A, A 'of said rows) and located at the same distance from each other . The electrolysis cells 100 typically have a long side greater than 3 times their short side.

The lines F, F ′ are separated by a distance depending on technological choices which take account in particular of the intensity I ₀ of the electrolysis current of the series and of the configuration of the conductor circuits. The distance D between the two lines is typically between 30 and 100 m for recent series.

As illustrated in the figure 1 , each electrolysis cell 100 of the series 1 typically comprises a tank 3, anodes 4 supported by the fixing means typically comprising a rod 5 and a multipod 6 and mechanically and electrically connected to an anode frame 7 using connection means 8. The tank 3 comprises a metal box, usually reinforced by stiffeners, and a crucible formed by refractory materials and cathode elements arranged inside the box. The box generally has vertical side walls. In operation, the anodes 4, typically made of carbonaceous material, are partially immersed in an electrolyte bath (not illustrated) contained in the tank. The tank 3 comprises a cathode assembly 9 provided with cathode bars 10, typically made of steel, one end of which leaves the tank 3 so as to allow electrical connection to the connecting conductors 12 to 17 between cells.

The connecting conductors 12 to 17 are connected to said cells 100 so as to form an electrical series, which constitutes the electrical electrolysis circuit of the series of electrolysis cells. The connection conductors typically comprise flexible conductors 12, 16, 17, upstream connection conductors 13 and risers 14, 15. The connection conductors, in particular upstream, can, in whole or in part, pass under the tank and / or bypass it.

The figure 2 schematically illustrates an embodiment comprising a series composed of two rows F, F 'of electrolysis cells 100 oriented transversely to the longitudinal axis A, A' of the rows. The lines are straight and arranged parallel to each other. The lines, and more particularly the first corresponding end cells 100 ′ of the two lines F, F ′, are electrically linked together by connection conductors 20. The connection conductors 20 are formed only of electrical conductors or electrical conductors associated with an electric power station.

Advantageously, the series also comprises four electric magnetic balancing circuits 21 of the end cells. Thus a magnetic balancing circuit 21 balances the magnetic field at each of the two ends of the two lines F, F '. These magnetic balancing circuits are arranged at the end cells of the lines outside the cell lines F, F ', that is to say outside the space between the two lines F, F' cells.

Each magnetic balancing circuit 21 comprises a first electrical conductor 22 for magnetic balancing of the end cells which extends along a line F, F 'of cells only opposite an end portion P of said row F, F 'of cells.

By end cells is meant the n adjacent end cells starting from the first end cell 100 ′ of a row of cells which are magnetically impacted by the circulation of the electrolysis current Io in the connection conductor 20. Typically, n is between 3 and 10. The end portion P of the row of cells opposite which extends the first electrical conductor 22 is therefore limited to a segment of the queue along the end cells .

Each magnetic balancing circuit 21 further comprises a second electrical conductor 23 substantially parallel to the first electrical conductor 22 for magnetic balancing of the end cells and disposed at a greater distance from the row of cells than the first electrical conductor 22.

The first and second electrical conductors 22, 23 are electrically connected together by means of transverse conductors 24 to form a closed electrical circuit around an electrical supply station 30 advantageously connected at a point on the second electrical conductor 23.

The first electrical conductor 22, which extends along the line F, F 'in front of the end cells, makes it possible to substantially limit the vertical magnetic field Bz in the end cells when it is traversed by a current d 'magnetic balancing of the end cells of intensity I, and of opposite direction to the electrolysis current I ₀ flowing in the end cells of the queue F, F' in front of which it extends. The second electrical conductor 23 is farther from the end cells than the first electrical conductor 22 so that the magnetic field that it generates has little impact on the stability of the end cells. Due to their distance and their short length, the transverse conductors 24 have little impact on the stability of the end cells.

• le premier conducteur électrique 22 longeant la file de cellules s'étend à une distance du bord des cellules d'extrémité inférieure à 5 mètres, avantageusement inférieure à 3 mètres ;
• le deuxième conducteur électrique 23 est disposé à une distance du bord des cellules d'extrémité supérieure à 7 mètres, avantageusement supérieure à 10 mètres ;
• le courant d'équilibrage I₁ des cellules d'extrémité est compris entre 30 et 150kA. L'intensité du courant d'équilibrage I₁, et donc l'équilibrage magnétique résultant, peut être facilement contrôlé et ajusté du fait de l'utilisation d'une station d'alimentation électrique spécifique.

Advantageously, for a series traversed by an electrolysis current I ₀ of between 300kA and 600kA with rows of cells 30 to 80 meters apart:

• the first electrical conductor 22 running along the row of cells extends at a distance from the edge of the end cells of less than 5 meters, advantageously less than 3 meters;
• the second electrical conductor 23 is disposed at a distance from the edge of the end cells greater than 7 meters, advantageously greater than 10 meters;
• the balancing current I ₁ of the end cells is between 30 and 150kA. The intensity of the balancing current I ₁ , and therefore the resulting magnetic balancing, can be easily controlled and adjusted due to the use of a specific electrical power station.

• un premier conducteur électrique 22 d'équilibrage magnétique des cellules d'extrémité qui s'étend le long d'une file F, F' de cellules uniquement en regard d'une portion d'extrémité P de ladite file F, F' de cellules, côté extérieur par rapport aux deux files de cellules ;
• un deuxième conducteur électrique 23' d'équilibrage magnétique des cellules d'extrémité et s'étendant le long de la même file F, F' de cellules que le premier conducteur électrique 22 uniquement en regard d'une portion d'extrémité P de la file F, F' de cellules, cote intérieur par rapport aux deux files de cellules, c'est-à-dire entre les deux files F, F' de cellules ;
• des conducteurs transversaux 24 connectant électriquement les premier et deuxième conducteurs électriques 22, 23' pour former un circuit électrique fermé autour d'une station d'alimentation électrique 30 connectée en un point du deuxième conducteur électrique 23'.

The figure 3 schematically illustrates another embodiment in which each magnetic balancing circuit 21 surrounds the end cells of the row of cells. Each magnetic balancing circuit includes:

• a first electrical conductor 22 for magnetic balancing of the end cells which extends along a row F, F 'of cells only opposite an end portion P of said row F, F' of cells , outside on the two rows of cells;
• a second electrical conductor 23 ′ for magnetic balancing of the end cells and extending along the same row F, F ′ of cells as the first electrical conductor 22 only opposite an end portion P of the row F, F 'of cells, internal dimension with respect to the two rows of cells, that is to say between the two rows F, F' of cells;
• transverse conductors 24 electrically connecting the first and second electrical conductors 22, 23 'to form a closed electrical circuit around an electrical supply station 30 connected at a point of the second electrical conductor 23'.

The first and second electrical conductors 22, 23 ', which extend along the line F, F' in front of the end cells, make it possible to substantially limit the vertical magnetic field Bz in the end cells when they are traversed by a magnetic balancing current of the end cells of intensity I1, in the opposite direction to the electrolysis current Io flowing in the end cells of the queue F, F 'in front of which it extends for the first electrical conductor 22 and in the same direction as the electrolysis current I ₀ flowing in the end cells of the queue F, F 'in front of which it extends for the second electrical conductor 23'. In this embodiment, the first and second electrical conductors 22, 23 'have a cumulative beneficial magnetic impact.

The transverse conductors 24 can in particular pass under the rows F, F ′ of cells. Due to their short length, the transverse conductors 24 have little impact on the stability of the end cells.

• les premier et deuxième conducteurs électriques 22, 23' longeant la file de cellules s'étendent à une distance du bord des cellules d'extrémité inférieure à 5 mètres, avantageusement inférieure à 3 mètres ;
• le courant d'équilibrage I₁ des cellules d'extrémité est compris entre 15 et 75kA.

Advantageously, for a series traversed by an electrolysis current I ₀ of between 300kA and 600kA with rows of cells 30 to 80 meters apart:

• the first and second electrical conductors 22, 23 ′ running along the row of cells extend at a distance from the edge of the end cells of less than 5 meters, advantageously less than 3 meters;
• the balancing current I ₁ of the end cells is between 15 and 75kA.

• un premier conducteur électrique 22 d'équilibrage magnétique des cellules d'extrémité qui s'étend le long de la première file F de cellules uniquement en regard d'une portion d'extrémité P de ladite file F de cellules, côté intérieur par rapport aux deux files de cellules ;
• un deuxième conducteur électrique 23" d'équilibrage magnétique des cellules d'extrémité et qui s'étend le long de la deuxième file F' de cellules uniquement en regard d'une portion d'extrémité P' de ladite file F' de cellules, côté intérieur par rapport aux deux files de cellules ;
• des conducteurs transversaux 24 connectant électriquement les premier et deuxième conducteurs électriques 22, 23" pour former un circuit électrique fermé autour d'une station d'alimentation électrique 30 connectée en un point d'un des conducteurs transversaux 24.

The figure 4 schematically illustrates another embodiment of a series of two rows F, F 'of cells comprising two electric magnetic balancing circuits 21 of the end cells, in which each magnetic balancing circuit 21 is disposed between the two rows F, F 'of cells. Each magnetic balancing circuit includes:

• a first electrical conductor 22 for magnetic balancing of the end cells which extends along the first row F of cells only opposite an end portion P of said row F of cells, on the inner side with respect to the two rows of cells;
• a second electrical conductor 23 "for magnetic balancing of the end cells and which extends along the second row F 'of cells only facing an end portion P' of said row F 'of cells, inner side with respect to the two rows of cells;
• transverse conductors 24 electrically connecting the first and second electrical conductors 22, 23 "to form a closed electrical circuit around an electrical supply station 30 connected at a point of one of the transverse conductors 24.

The first and second electrical conductors 22, 23 ", which extend respectively along the lines F and F 'in front of the end cells, make it possible to substantially limit the vertical magnetic field Bz in the end cells of the line in front which they extend when they are traversed by a magnetic balancing current of the end cells of intensity I1, in the same direction as the electrolysis current Io flowing in the end cells of the queue F, F ' in front of which they extend. In this embodiment, the first and second electrical conductors 22, 23 "have a beneficial magnetic impact on the end cells of the two rows F and F 'of cells which they pass along respectively.

The transverse conductors 24, of substantial length between the two lines F, F ′ only have a slightly negative impact on the stability of the cells, because the current I ₁ flowing in the transverse conductors 24 is of less intensity than the electrolysis current I ₀ circulating in the connection conductors 20.

The negative impact of these transverse conductors 24 is much less than the positive impact of the first and second conductors which are positioned as close as possible to the end cells.

• les premier et deuxième conducteurs électriques 22, 23" s'étendent à une distance du bord des cellules d'extrémité inférieure à 5 mètres, avantageusement inférieure à 3 mètres ;
• le courant d'équilibrage I1 des cellules d'extrémité est compris entre 30 et 150kA.

Advantageously, for a series traversed by an electrolysis current I ₀ of between 300kA and 600kA with rows of cells 30 to 80 meters apart:

• the first and second electrical conductors 22, 23 "extend at a distance from the edge of the end cells of less than 5 meters, advantageously less than 3 meters;
• the balancing current I1 of the end cells is between 30 and 150kA.

The figure 5 schematically illustrates one end of a series comprising electrical magnetic balancing circuits 21 of the end cells using the same principles of magnetic balancing as those presented with reference to figure 2 . The methodology for supplying electric current to this magnetic balancing circuit differs. Instead of being supplied with electric current from at least one specific electric power station, each magnetic balancing circuit 21 is supplied from the electrolysis current I ₀ flowing in the electrolysis cells of the series.

The magnetic balancing circuit 21 comprises a first electrical conductor 22, a second electrical conductor 23 and transverse conductors 24 electrically connecting the first and second electrical conductors to each other or electrically connecting the first and second electrical conductors to conductors electrically connecting to each other the corresponding end electrolysis cells 100 ′ of the two neighboring rows.

The transverse conductors 24 form two ends of the magnetic balancing circuit which are connected to conductors electrically connecting two electrolysis cells between them. The magnetic balancing circuit of the end cells forms part of the electrolysis circuit, and more particularly of the connection conductor 20, through which the series electrolysis current flows.

The magnetic balancing circuit is connected to the conductors electrically connecting the end electrolysis cells 100 ′ in parallel with an electrical conductor called parallel 25. Thus, in operation, part of the electrolysis current I ₀ , corresponding to the magnetic balancing current I ₁ , flows in the magnetic balancing circuit. Another part of the electrolysis current I ₀ , of intensity equal to I ₀ -I ₁ , flows in the so-called parallel electrical conductor 25.

This embodiment has the advantage of eliminating the need to use a specific feeding station.

The figure 6 illustrates, schematically, a series of electrolysis cells according to the state of the art comprising two rows F, F ′ of cells and a correction circuit 26 disposed between the two rows of cells. This correction circuit 26 comprises two correction conductors 27 extending along each of the rows F, F 'of cells between the two rows F, F', connection correction conductors 28 between the two correction conductors 27 and an electric power station 31 of the correction circuit. Such a correction circuit makes it possible in particular to compensate at the level of a file the magnetic field generated by the electrolysis current I ₀ flowing in the neighboring file. The correction conductors are typically traversed by a correction current I ₂ flowing in the same direction as the electrolysis current I ₀ flowing in the line they run along.

For a series traversed by an electrolysis current I ₀ comprised between 300kA and 600kA with rows of cells 30 to 80 meters apart, the correction current I ₂ is typically comprised between 30 and 150kA.

The figure 7 schematically illustrates one end of a series comprising electrical circuits for magnetic balancing 21 of the end cells and a correction circuit as presented with reference to figure 6 . The magnetic balancing circuits 21 of the end cells use the same principles of magnetic balancing as those presented with reference to figures 2 and 5 . On the other hand, the methodology for supplying electric current to this magnetic balancing circuit differs. Each magnetic balancing circuit 21 is supplied from the correction current I2 flowing in the conductors 27, 28 of the correction circuit 26.

The magnetic balancing circuit 21 comprises a first electrical conductor 22, a second electrical conductor 23 and transverse conductors 24 electrically connecting the first and second electrical conductors to each other or electrically connecting the first and second electrical conductors to conductors 27, 28 of the correction circuit 26.

The transverse conductors 24 thus form two ends of the magnetic balancing circuit which are connected to the conductors 27, 28 of the correction circuit 26. The magnetic balancing circuit 21 of the end cells then forms part of the correction circuit 26 at through which the correction current flows.

The magnetic balancing circuit is more particularly connected to the conductors 27, 28 of the correction circuit in series between two portions of the correction circuit.

Thus, in operation, the entire correction current I ₂ flows in the magnetic balancing circuit. Thus, the intensity of the magnetic balancing current I ₁ is equal to the intensity of the correction current I ₂ .

This embodiment has the advantage of eliminating the need to use a specific supply station for the magnetic balancing circuit 21 of the end cells. As the conductors 27, 28 of the correction circuit extend along the lines F, F 'over the entire length of the lines, the electrical connection of the magnetic balancing circuit 21 is easy and feasible at any point considered appropriate. The positioning of the magnetic balancing circuit 21 on the opposite side of the line F, F 'with respect to the correction conductor 27 corresponding is advantageous for reasons of space and because the insertion of the end cells between the first electrical conductor 22 and the correction conductor 27 is particularly stabilizing for these end cells.

The figure 8 schematically illustrates one end of a series comprising electrical circuits for magnetic balancing 21 of the end cells and a correction circuit. The magnetic balancing circuit 21 of the end-of-line cells forms two loops and the first electrical conductor 22 of magnetic balancing is formed by the two loop strands 29 of the magnetic balancing circuit extending side by side along of the cell line only opposite the end portion P of the cell line.

The current flows in the same direction in each of the loop strands 29 extending side by side to form the first electrical conductor 22 and the impact on the magnetic field of the current flowing in the first electrical conductor is the sum of the impact on the magnetic field of the current flowing in each of the loop strands 29 forming the first electrical conductor 22.

As the magnetic balancing circuit is connected in series to the conductors 27, 28 of the correction circuit, the entire correction current I2 flows in each of the loop strands 29 of the magnetic balancing circuit 21. Thus, the intensity of the current magnetic balancing I1 'flowing in the first electrical conductor 22 is twice the intensity of the correction current' 2.

The figure 9 schematically illustrates a variant of the embodiment of the figure 7 in which the connecting conductor 20 comprises a conductor 40 for magnetic balancing of the first end cell 100 'along this first end cell 100 'perpendicular to the longitudinal axis of one of the rows F, F' of cells. At least part of the electrolysis current I ₀ flows in the conductor 40 in a direction opposite to the direction of circulation of the electrolysis current I0 in the main branch of the connecting conductor 20 extending between the two lines F, F ' . The negative magnetic impact generated by the connection conductor 20 is thus countered at the level of the first end cell 100 ′ skirted by the conductor 40. It is therefore not necessary to magnetically balance this first end cell 100 'by means of the circuit 21 for magnetic balancing of the end-of-line cells. The end portion P of the line opposite which extends the first electrical conductor 22 of the magnetic balancing circuit 21 of the line end cells then advantageously does not include the first end cell 100 '. The first electrical conductor 22 extending along the line F, F ′ of cells only opposite an end portion P does not run along the first end cell.

The transverse conductor 24 electrically connecting the conductors 27, 28 of the correction circuit 26 to the first electrical conductor 22 extends under the row F, F 'of cells and more particularly under the first end cell 100'.

It is thus possible to improve the stability of the end cells of an existing electrolysis series comprising a magnetic balancing arrangement of the first end cell of the type known from European patent applications EP 0 342 033 or Chinese CN 2 477 650 .

• circulant dans le même sens que le courant d'électrolyse I₀ circulant dans la file F, F' de cellules qu'il longe si le premier conducteur électrique 22 d'équilibrage magnétique se situe le long de la file F, F' du côté de l'autre file de cellules d'électrolyse de la série;
• circulant dans le sens opposé par rapport au courant d'électrolyse Io circulant dans la file F, F' de cellules qu'il longe si le premier conducteur électrique 22 d'équilibrage magnétique se situe le long de la file F, F' de cellules du côté opposé à l'autre file de cellules d'électrolyse de la série. Le deuxième conducteur électrique 23 d'équilibrage magnétique est également parcouru par le courant électrique d'équilibrage I₁ mais circulant dans le sens inverse du courant électrique d'équilibrage I₁ circulant dans le premier conducteur électrique 22 d'équilibrage magnétique.

As shown in the figures, the electrolysis current I ₀ flows through the rows F, F 'of electrolysis cells 100 and the connection conductor 20 and the first electric conductor 22 for magnetic balancing is traversed by an electric current of balancing I ₁ :

• flowing in the same direction as the electrolysis current I ₀ flowing in the line F, F 'of cells which it runs along if the first electrical conductor 22 for magnetic balancing is located along the line F, F' on the side from the other row of electrolysis cells in the series;
• flowing in the opposite direction with respect to the electrolysis current Io flowing in the line F, F 'of cells which it runs along if the first electrical conductor 22 for magnetic balancing is located along the line F, F' of cells on the side opposite the other row of electrolysis cells in the series. The second electric conductor 23 for magnetic balancing is also traversed by the electric balance current I ₁ but circulating in the opposite direction to the electric balance current I ₁ flowing in the first electric conductor 22 for magnetic balance.

Claims (17)

1. Series (1) of electrolysis cells (100) for the production of aluminum by igneous electrolysis according to the Hall-Heroult process, comprising:

   - at least one first and one second row (F, F'), rectilinear and parallel to each other, of the electrolysis cells (100) electrically connected in series,

   - a connecting conductor (20) between a first end cell (100') of the first row (F) and a corresponding first end cell (100') of the second row (F'),
   characterized in that the series (1) comprises at least one magnetic-balancing circuit (21) of the end cells (100') having a magnetic-balancing first electric conductor (22) of the end cells (100') extending along the first row (F) of cells (100) solely with regard to an end portion (P) of the first row (F) of cells (100).
2. The series (1) of electrolysis cells (100) according to claim 1, wherein the magnetic-balancing circuit (21) of the end cells (100') has a second electric conductor (23, 23', 23") parallel to the magnetic-balancing first electric conductor (22) of the end cells (100').
3. The series (1) of electrolysis cells (100) according to claim 2, wherein the second electric conductor (23') extends along the first row (F, F') of cells solely with regard to the end portion (P) of the first row (F) of cells (100), the first and the second electric conductors (22, 23) extending along opposite sides of the first row (F) of cells (100).
4. The series (1) of electrolysis cells (100) according to claim 2, wherein the second electric conductor (23) extends along a same side of the first row (F) of cells (100) as the first electric conductor (22), a distance between the first electric conductor (22) and the first row (F) of cells (100) being smaller than a distance between the second electric conductor (23) and the first row (F) of cells (100).
5. The series (1) of electrolysis cells (100) according to claim 4, wherein the second electric conductor (23") extends along the second row (F') of cells (100) solely with regard to an end portion (P') of the second row (F') of cells (100).
6. The series (1) of electrolysis cells (100) according to any one of the preceding claims, wherein the magnetic-balancing circuit (21) of the end cells (100') has two ends connected to a power station (30).
7. The series (1) of electrolysis cells (100) according to any one of claims 1 to 5, wherein the magnetic-balancing circuit (21) of the end cells (100') has two ends connected to conductors electrically linking electrolysis cells (100) to each other.
8. The series (1) of electrolysis cells (100) according to any one of claims 1 to 5, comprising a correction circuit (26) having at least one first correction conductor (27) extending along the first row (F), a second correction conductor (27) extending along the second row (F'), and at least one connection correction conductor (28) between the first and second correction conductors (27, 28), the magnetic-balancing circuit (21) of the end cells (100') having two ends connected to the correction circuit (26).
9. The series (1) of electrolysis cells (100) according to claim 8, wherein the magnetic-balancing circuit (21) of the end cells (100') is connected in series between two portions of the correction circuit (26).
10. The series (1) of electrolysis cells (100) according to any one of claims 8 and 9, wherein the first correction conductor (27) extends along the first row (F) on a side by the second row (F'), and the second correction conductor (27) extends along the second row (F') on a side by the first row (F) of cells (100).
11. The series (1) of electrolysis cells (100) according to any one of claims 8 to 10, wherein the first electric conductor (22) and the second electric conductor (23) of the magnetic-balancing circuit (21) connected to the correction circuit (26) are disposed exterior to the two rows (F, F') of cells (100).
12. The series (1) of electrolysis cells (100) according to any one of the preceding claims, wherein the connecting conductor (20) has a magnetic-balancing conductor (40) of the first end cell (100') of one of the two rows (F, F') running along the first end cell (100') perpendicular to a longitudinal axis of the one of the rows (F, F') of cells (100), and the first electric conductor (22) does not extend along the first end cell (100').
13. The series (1) of electrolysis cells (100) according to claim 12 as it depends from claim 11, wherein the magnetic-balancing circuit (21) of the end cells (100') has a transverse conductor (24) electrically linking the correction circuit (26) to the first electric conductor (22), the transverse conductor (24) extending below the one of the two rows (F, F') of cells (100).
14. The series (1) of electrolysis cells (100) according to any one of the preceding claims, wherein the magnetic-balancing circuit (21) of the end cells (100') forms a plurality of loops and the first electric conductor (22) is formed by a plurality of loop strands (29) extending side by side along the first row (F) of cells (100) solely with regard to the end portion (P) of the first row (F) of cells (100).
15. The series (1) of electrolysis cells (100) according to any one of the preceding claims, wherein the end portion (P) of the first row (F) of cells (100) has from 3 to 10 of the cells (100), and preferably from 6 to 8 of the cells (100).
16. Method of using the series (1) of electrolysis cells (100) according to any one of the preceding claims, wherein the rows (F, F') of electrolysis cells (100) and the connecting conductor (20) are traversed by an electrolysis current (I₀), and the magnetic-balancing first electric conductor (22) is traversed by a balancing electric current (I₁):

    - flowing in the same direction as the electrolysis current (I₀) flowing in the first row (F, F') of cells if the magnetic-balancing first electric conductor (22) is located along the first row (F) of cells (100) on the side by the second row (F') of electrolysis cells (100);

    - flowing in the opposite direction with respect to the electrolysis current (I₀) flowing in the first row (F) of cells (100) if the magnetic-balancing first electric conductor (22) is located along the first row (F) of cells (100) on a side opposite the second (F') row of electrolysis cells (100).
17. The method of using the series (1) of electrolysis cells (100) according to claim 16, wherein the series (1) has a magnetic-balancing second electric conductor (23, 23', 23"), the magnetic-balancing second electric conductor (23, 23', 23") traversed by the balancing electric current (I₁) flowing in a direction opposite that of the balancing electric current (I₁) flowing through the magnetic-balancing first electric conductor (22).

Images