WO2017064547A1

WO2017064547A1 - Series of electrolysis cells for the production of aluminium comprising means for balancing the magnetic fields at the end of the line

Info

Publication number: WO2017064547A1
Application number: PCT/IB2016/001437
Authority: WO
Inventors: Benoit BARDET; Olivier Martin
Original assignee: Rio Tinto Alcan International Limited
Priority date: 2015-10-15
Filing date: 2016-10-03
Publication date: 2017-04-20
Also published as: AU2016339054A1; EP3362590A4; CN108368624B; CN108368624A; RU2018117703A; CA3000482A1; FR3042509A1; ZA201801921B; RU2722026C2; FR3042509B1; CA3000482C; AU2016339054B2; RU2018117703A3; EP3362590B1; EP3362590A1

Abstract

The invention relates to a series (1) of electrolysis cells (100) intended for the production of aluminium, comprising: two rectilinear and parallel lines (F, F') of electrolysis cells electrically connected in series, a connecting conductor (20) between a first end cell (100') of one line and the corresponding first end cell (100') of the other line, and at least one magnetic balancing circuit (21) for balancing the end of line cells, comprising a first electrical conductor (22) for magnetic balancing of the end cells extending along one of the lines of cells, only opposite an end portion (P) of the first line of cells.

Description

SERIES OF ELECTROLYSIS CELLS FOR THE PRODUCTION OF ALUMINUM COMPRISING MEANS FOR BALANCING THE MAGNETIC FIELDS

IN END OF FILE

Field of the invention

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

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

A large number of arrangements of cells and connecting conductors have been proposed in order to limit Joule losses and to reduce the impact of magnetic fields produced by drivers. bonding and neighboring cells on the electrolysis process. For example, the French patent application FR 2,552,782 (corresponding to US Pat. No. 4,592,821), in the name of Aluminum Pechiney, describes a line of electrolysis cells arranged transversely and 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 connecting conductors, in particular those passing under the tank.

Also, the French patent application FR 2,425,482 (corresponding to US Pat. No. 4,169,034) 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 flowing current in the neighboring queue of cells is compensated by means of at least one independent correction conductor passing on the side of the tanks, along all the cells of the series and traversed by a continuous correction current. Moreover, the French patent application FR 2,583,069 (corresponding to US Pat. No. 4,713,161), also in the name of Aluminum Pechiney, describes a line of electrolysis cells arranged transversely and capable of operating at intensities of up to 500.degree. 600 kA. According to this patent, the costs of construction and installation of the circuits are minimized through the use of connecting conductors as small and as direct as possible, while the magnetic stability and Faraday efficiency are maximized through the use independent correction conductors, arranged parallel to each line and on each side thereof.

The row arrangement of the electrolysis cells has the advantage of simplifying the configuration of the connecting conductors and of standardizing the magnetic field map. However, the presence of connecting conductors between the queues disturbs the uniformity of the magnetic field map of the end cells of each queue.

US Pat. Nos. 3,775,280 and 4,189,368 provide connection lead arrangements for longitudinally arranged cell series for limiting disturbances caused by these connecting conductors. In addition, the intensities of this type of cell do not generally exceed 100 kA.

European Patent Applications EP 0 342 033 and Chinese Patent No. 2 477 650 describe connection lead arrangements applicable to transversely arranged series of cells for limiting the disturbances caused by these connecting conductors. These documents relate to series of electrolysis cells equipped with tanks for intensities of the order of 300 kA.

Patent FR 2,868,436 (corresponding to US Pat. No. 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 lines, with a particular arrangement of the correction conductor consisting in making a transverse section along its length the first end cell of the queue at a determined distance and traversed by a current flowing from the inner side to the outer side of the rows of cells. Such an arrangement satisfactorily compensates for the magnetic field generated by the connecting conductors in a small number of end cells (about 1 to 3) while a larger number of end cells (about 1 to 10 ) are disturbed by the magnetic field generated by the connecting conductors. As a result, a large number of queue end cells remain unstable and difficult to operate. The Applicant has therefore sought economically and technically satisfactory solutions to balance the magnetic fields of the end cells of the queues, and in particular of the series of cells formed of long rectangular cells arranged transversely. Description of the invention

For this purpose, 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 rectilinear rows parallel to each other of electrolytic cells electrically connected in series,

a connecting conductor between a first end cell of the first line and the first corresponding end cell of the second line, and characterized in that the series comprises at least one magnetic balancing circuit of the end cells of the second line; file comprising a first electrical conductor for magnetic balancing of the end-of-queue cells extending along a first row of cells facing an end portion of the first row of cells only.

The applicant has noted that, in the absence of a magnetic balance circuit of the end-of-queue cells as defined above, the end cells of the queues are mainly affected by an additional mean vertical magnetic field ΔΒζ, when the cells of the central portion of the files are correctly magnetically balanced. The aim of the invention is thus to maintain the additional vertical field ΔΒζ within a limited range by a minimum value and a maximum value around a targeted value close to zero.

The Applicant had the idea of disposing said first electrical conductor near the notoriously unstable end cells of the queue of cells in order 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 by the connecting conductors between the queues, and balance the magnetic fields at the tanks of the end electrolysis cells.

The first electrical conductor extending along the queue of cells extends parallel or substantially parallel to the longitudinal axis of the queue of cells.

By the words "along the queue of cells", the plaintiff hears that the driver extends in the direct vicinity of the queue of cells, so that its impact on the Magnetic field in nearby cells is maximized, and typically at a distance of less than 5 meters and preferably 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 balance circuit of the queue end cells further allows a fine adjustment of the magnetic balance through the complementary adjustable parameters it provides.

The first electrical conductor is traversed during the operation of the series by a continuous magnetic balancing current of the end 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 found.

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-queue cells to be adequate and economically viable, the first magnetic balancing electrical conductor advantageously extends over a length at least equal to three times the spacing between two cells. (The spacing between two cells being the distance between the median longitudinal axes of two adjacent electrolysis cells, typically corresponding to 5 to 10 meters).

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

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

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 electric balance current: flowing in the same direction as the electrolysis current flowing in the first row of cells if the first magnetic balancing electrical conductor is along the first row of cells on the side of the second row of electrolysis cells;

circulating in the opposite direction with respect to the electrolysis current flowing in the first row of cells if the first magnetic balancing electrical conductor is located along the first row of cells on the opposite side to the second row of cells; electrolysis.

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

According to one embodiment, the magnetic balance circuit of the end-of-line cells comprises a second electrical conductor parallel to the first electrical conductor for magnetic balancing of the end-of-queue cells. This second parallel electrical conductor participates in the closing 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 counterbalancing electric current flowing in the opposite direction relative to the balancing electric current flowing in the first electrical conductor. This second electrical conductor is advantageously arranged so as to improve the magnetic configuration of the end cells of the first line or the second line, and at least so that its possible negative impact on the magnetic balancing of the cells of 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 facing the end portion of the first row of cells, the first and second electrical conductors extending along opposite sides of the first row of cells. The vertical magnetic field generated by the circulation of the same counterbalancing electric current, 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 a balancing electric current in the first electrical conductor to counter the destabilizing vertical magnetic field generated by the current flowing in the connecting 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 smaller than the distance between the second electrical conductor and the first row of cells. Thus, since the second electrical conductor is on the same side but farther from the first line 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 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 end-end cells along the which the first electrical conductor extends.

Advantageously, the second electrical conductor is further away from the electrolysis cells of the first line 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 and preferably less than 0.3 at the end-of-line 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 facing 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 power supply station. The intensity of the current flowing in the magnetic balancing circuit can advantageously be easily controlled and adjusted. By specific power supply station is meant that this power supply station does not supply current to the electrolysis circuit (connecting conductors), or correction conductors intended to perform a magnetic correction on all the cells of the series.

According to a preferred embodiment, the magnetic balance circuit of the queue end cells comprises two ends which are connected to conductors electrically connecting the electrolysis cells to each other. The magnetic balance circuit of the end-of-queue cells is then powered by at least a part electrolysis current circulating in the cells and forms a part of the electrolysis circuit through which circulates the electrolysis current of the series.

According to a preferred embodiment, the magnetic balancing circuit is connected to the conductors electrically connecting electrolysis cells with each other in parallel with one or more so-called parallel electrical conductors. Thus only a part of the electrolysis current flows in the magnetic balancing circuit.

Advantageously, the magnetic balance circuit of the queue end cells forms part of the connecting 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 queue, and at least one correction correction conductor between the first and second correction conductors, and wherein the magnetic balance circuit of the queue end cells comprises two ends which are connected to the correction circuit.

As presented in the preamble, certain series comprise one or more correction circuits extending along all the electrolysis cells of the series for correcting the destabilizing magnetic fields generated by the high intensity currents flowing in the circuits of the series. cell-to-cell conductors or in the neighboring cell queue. The correction circuit is an integral part of the series and is powered by electric current. This solution is particularly advantageous because it does not require the installation of a specific power station which represents a high equipment cost and may also be difficult to install because of the size required.

Advantageously, the magnetic balance circuit of the queue end cells is connected in series between two portions of the correction circuit. Since the first and second correction conductors extend along the set of electrolysis cells, it suffices to connect the magnetic balance circuit of the series end-of-line cells to an intermediate point of the correction circuit. at a suitable place along the cell lines. The correction current flowing in the correction circuit also passes into 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 file on the side of the second file, and the second correction conductor extends along the second file on the side of the first file. 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 outer side of the rows of cells, opposite to the correction circuit, is less crowded than the inner side and the introduction of the magnetic balancing circuit facilitated. Such a magnetic balancing circuit may in particular be implemented on an existing series already having a correction circuit disposed within the two rows of cells.

According to a particular embodiment, the connecting conductor comprises a magnetic balancing conductor of the first end cell along the first end cell perpendicularly to the longitudinal axis of the queue of cells, and the first electrical conductor does not does 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 modifying its magnetic field by means of the first electrical conductor would have the effect of destabilizing 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 queue of cells.

According to one embodiment, the magnetic balance circuit of the queue end cells forms a plurality of loops and the first magnetic balancing electrical conductor is formed by a plurality of loop strands extending side-by-side. the first row of cells only facing the end portion of the first queue 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.

The invention is described in detail below with the aid of the appended figures.

Figure 1 shows, in a simplified manner and in cross section, two successive electrolysis cells (n; n + 1) typical of a queue of cells.

Figures 2 to 4 illustrate, schematically, various embodiments of a series of electrolysis cells according to the invention comprising two queues and magnetic balancing circuits of the end cells.

FIG. 5 schematically illustrates an embodiment of the invention in which part of the electrolysis current of the series is used to supply magnetic balancing circuits of the end cells.

FIG. 6 schematically illustrates a series of electrolysis cells according to the state of the art comprising two queues and a correction circuit.

FIG. 7 schematically illustrates a series end of electrolysis cells according to the invention comprising two queues and circuits for magnetic balancing of the end cells connected to a correction circuit.

Figure 8 schematically illustrates a series end in which each magnetic balancing circuit forms two loops.

FIG. 9 schematically illustrates a series end of electrolysis cells according to the invention comprising two queues, a particular arrangement of the connecting conductor making it possible to magnetically balance the first end cell and balancing circuits. magnetic end cells connected to a correction circuit.

The invention relates to a series 1 of electrolysis cells comprising, as shown in Figures 2 to 5, 7 and 8, a plurality of electrolysis cells 100, 100 'of substantially rectangular shape, which are arranged to form at least two rows F, F 'of substantially straight, parallel cells 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 queues) 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 queues F, F 'are separated by a distance depending on technological choices which take into account, in particular, the intensity l ₀ of the electrolysis current of the series and 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 FIG. 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 multipode 6 and mechanically and electrically connected to a anodic frame 7 by means of connection means 8. The vessel 3 comprises a metal box, usually reinforced by stiffeners, and a crucible formed by refractory materials and cathode elements disposed inside the box. The box generally has vertical side walls. In operation, the anodes 4, typically of carbonaceous material, are partially immersed in an electrolyte bath (not shown) contained in the tank. The vessel 3 comprises a cathode assembly 9 provided with cathode bars 10, typically made of steel, one end 11 of which leaves the vessel 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 electrolysis circuit of the series of electrolysis cells. The connecting conductors typically comprise flexible conductors 12, 16, 17, upstream connecting conductors 13 and mounted assemblies 14, 15. The connecting conductors, in particular upstream, may wholly or partly pass under the tank and / or circumvent it.

FIG. 2 schematically illustrates an embodiment comprising a series composed of two rows F, F 'of electrolysis cells 100 oriented transversely with respect to the longitudinal axis A, A' of the queues. The queues are straight and arranged parallel to each other. The queues, and more particularly the first corresponding end cells 100 'of the two queues F, F', are electrically bonded to each other by connecting conductors 20. The connecting conductors 20 are formed solely of electrical conductors or electrical conductors associated with a power station.

Advantageously, the series further comprises four 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 rows F, F '. These magnetic balancing circuits are arranged at the end cells of the rows outside the rows F, F 'of cells, that is to say out of the space between the two rows F, F' of 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 facing an end portion P of said file F, F 'of cells.

By end cells is meant the n adjacent end cells starting from the first end cell 100 'of a queue of cells which are magnetically impacted by the circulation of the electrolysis current I ₀ in the driver of the connection 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 cells of the end.

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 line 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 a power supply station 30 advantageously connected to a point of 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. Magnetic balancing of the end cells of intensity h and of opposite direction to the electrolysis current ₁₀ flowing in the end cells of the line F, F 'in front of which it extends. The second electrical conductor 23 is further away from the end cells than the first electrical conductor 22 so that the magnetic field it generates has little impact on the stability of the end cells. Because of their remoteness and their short length, the transverse conductors 24 have little impact on the stability of the end cells.

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

the first electrical conductor 22 along the line of cells extends at a distance from the edge of the end cells less than 5 meters, advantageously less than 3 meters; the second electrical conductor 23 is disposed at a distance from the edge of the upper end cells to 7 meters, preferably greater than 10 meters;

the balancing current of the end cells is between 30 and 150 kA.

The intensity of the balancing current and thus the resulting magnetic balance can be easily controlled and adjusted by the use of a specific power station.

Figure 3 schematically illustrates another embodiment in which each magnetic balancing circuit 21 surrounds the end cells of the queue of cells. Each magnetic balancing circuit comprises:

a first electrical conductor 22 for magnetic balancing of the end cells which extends along a queue F, F 'of cells only facing an end portion P of said file F, F' of cells outside of the two rows of cells;

a second electrical conductor 23 'for magnetic balancing of the end cells and extending along the same line F, F' of cells as the first electrical conductor 22 only facing an end portion P of the file F, F 'of cells, inner side 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 a power 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 ^, in the opposite direction to the electrolysis current ₁₀ flowing in the end cells of the queue F, F 'in front of which it extends to the first electrical conductor 22 and of identical direction to the electrolysis current ₁₀ circulating in the end cells of the line 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 may in particular pass under the rows F, F 'of cells. Because of their short length, the transverse conductors 24 have little impact on the stability of the end cells.

the first and second electrical conductors 22, 23 'along the line of cells' extend at a distance from the edge of the end cells less than 5 meters, advantageously less than 3 meters;

the balancing current h of the end cells is between 15 and 75 kA.

FIG. 4 schematically illustrates another embodiment of a series of two rows F, F of cells comprising two magnetic balancing circuits 21 of the end cells, in which each magnetic balancing circuit 21 is arranged. between the two rows F, F 'of cells. Each magnetic balancing circuit comprises:

a first electrical conductor 22 for magnetic balancing of the end cells which extends along the first row F of cells only facing an end portion P of said file F of cells, inner side with respect to 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 file 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 a power 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 queue in front of the which they extend when they are traversed by a magnetic balancing current of the end cells of the same intensity intensity of the electrolysis current ₁₀ flowing in the end cells of the queue F, F ' 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 that they respectively follow.

The transverse conductors 24 with consequent length between the two lines F, F 'only slightly negatively impact the stability of the cells, since the current h flowing in the transverse conductors 24 is less intense that the electrolysis current I ₀ circulating in the connecting conductors 20. The negative impact of these transverse conductors 24 is much lower than the positive impact of the first and second conductors which are positioned closer to the end cells.

the first and second electrical conductors 22, 23 "extend at a distance from the edge of the end cells less than 5 meters, advantageously less than 3 meters;

the balancing current h of the end cells is between 30 and 150 kA.

FIG. 5 schematically illustrates an end of a series comprising electric magnetic balancing circuits 21 of the end cells using the same principles of magnetic balancing as those presented with reference to FIG. in electric current this magnetic balancing circuit differs. Instead of being supplied with electric current by at least one specific power station, each magnetic balancing circuit 21 is supplied from the electrolysis current ₁₀ 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 together. 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 electrolytic cells together. The magnetic balancing circuit of the end cells forms a part of the electrolysis circuit, and more particularly of the connecting conductor 20, through which circulates the electrolysis current of the series. The magnetic balancing circuit is connected to the conductors electrically connecting the end electrolysis cells 100 'in parallel with a so-called parallel electrical conductor 25. Thus, in operation, a part of the electrolysis current I ₀ corresponding to the Magnetic balancing current \ _u flows in the magnetic balancing circuit. Another part of the electrolysis current ₁₀ , of intensity equal to ₁₀ -11, flows in the so-called parallel electrical conductor 25.

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

FIG. 6 schematically illustrates a series of electrolysis cells according to the state of the art comprising two rows F, F 'of cells and a correction circuit 26 arranged 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', of the connection correction conductors 28 between the two correction conductors 27 and a power supply station 31 of the correction circuit. Such a correction circuit makes it possible in particular to compensate, at the level of a queue, the magnetic field generated by the electrolysis current I ₀ flowing in the neighboring queue. The correction conductors are typically traversed by a correction current l ₂ flowing in the same direction as the electrolysis current ₁₀ flowing in the queue they run.

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

FIG. 7 schematically illustrates an end of a series comprising electric magnetic balancing circuits 21 of the end cells and a correction circuit as presented with reference to FIG. 6. The magnetic balancing circuits 21 of the end cells use the same principles of magnetic balancing as those presented with reference to FIGS. 2 and 5. On the other hand, the method of supplying electrical power to this magnetic balancing circuit differs. Each magnetic balancing circuit 21 is fed from the correction current I ₂ 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 connecting electrically 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 a 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 h is equal to the intensity of the correction current l ₂ .

This embodiment has the advantage of eliminating the need to use a specific power 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 queues, 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 corresponding correction conductor 27 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.

Figure 8 schematically illustrates an end of a series having magnetic balancing circuits 21 of the end cells and a correction circuit. The magnetic balancing circuit 21 of the end-of-queue cells forms two loops and the first magnetic balancing conductor 22 is formed by the two loop strands 29 of the magnetic balancing circuit extending side-by-side. the queue of cells only facing the end portion P of the queue of cells.

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.

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

FIG. 9 schematically illustrates a variant of the embodiment of FIG. 7 in which the connecting conductor 20 comprises a magnetic balancing conductor 40 of the first end cell 100 'along this first end cell 100' perpendicular to the longitudinal axis of the file F, F 'of cells. At least a part of the electrolysis current ₁₀ flows in the conductor 40 in a direction opposite to the flow direction of the electrolysis current ₁₀ in the main branch of the connecting conductor 20 extending between the two lines F, F . The negative magnetic impact generated by the connecting conductor 20 is thus counteracted at the first end cell 100 'along the lead 40. It is therefore not necessary to magnetically balance this first end cell 100 by means of the magnetic balance circuit 21 of the end-of-queue cells. The end portion P of the queue opposite which extends the first electrical conductor 22 of the magnetic balancing circuit 21 of the end of queue 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 facing an end portion P does not follow 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 below the line 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.

As shown in the figures, the electrolysis current ₁₀ runs through the queues F, F 'of electrolysis cells 100 and the connecting conductor 20 and the first electrical conductor 22 of magnetic balancing is traversed by an electric current. balancing:

circulating in the same direction as the electrolysis current I ₀ flowing in the queue F, F 'of cells that it runs if the first magnetic conductor 22 magnetic balancing is along the line F, F' on the side the other line of electrolysis cells of the series; circulating in the opposite direction with respect to the electrolysis current ₁₀ circulating in the line F, F 'of cells which it runs along if the first magnetic conductor 22 of magnetic equilibration is located along the line F, F' of cells on the opposite side to the other row of electrolysis cells in the series. The second electric magnetic balancing conductor 23 is also traversed by the balancing electric current but flowing in the opposite direction of the balancing electric current flowing in the first magnetic balancing conductor 22.

Claims

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

at least first and second rows (F, F ') that are rectilinear and parallel to each other with electrolytic cells electrically connected in series,

a connecting conductor (20) between a first end cell (100 ') of the first file and the corresponding first end cell (100') of the second file,

and characterized in that the series comprises at least one magnetic balancing circuit (21) of the queue end cells comprising a first electrical conductor (22) for magnetic balancing of the queue end cells extending along the first row of cells only facing an end portion (P) of the first queue of cells.

A series of electrolysis cells as claimed in claim 1, wherein the magnetic balancing circuit (21) of the queue end cells comprises a second electrical conductor (23, 23 ', 23 ") parallel to the first electrical conductor 22 of magnetic balance of the end cells of file.

A series of electrolysis cells according to claim 2, wherein the second electrical conductor (23 ') extends along the first line (F, F') of cells only opposite the end portion ( P) of the first row of cells, the first and second electrical conductors (22, 23) extending along opposite sides of the first row of cells.

A series of electrolysis cells according to claim 2, wherein the second electrical conductor (23) extends on the same side of the first (F, F ') cell line as the first electrical conductor (22), the distance between the first electrical conductor and the first row of cells being smaller than the distance between the second electrical conductor and the first row of cells.

A series of electrolysis cells according to claim 4, wherein the second electrical conductor (23 ") extends along the second row (F, F ') of cells facing only one end portion (Ρ ') of the second row of cells.

The electrolysis cell series according to one of the preceding claims, wherein the magnetic balancing circuit (21) of the queue end cells comprises two ends which are connected to a power station (30).

A series of electrolysis cells according to one of claims 1 to 5, wherein the magnetic balancing circuit (21) of the queue end cells has two ends which are connected to conductors electrically connecting cells of the electrolysis between them.

Electrolysis cell series according to one of claims 1 to 5, comprising a correction circuit (26) comprising at least a first correction conductor (27) extending along the first line (F, F '), a second correction conductor (27) extending along the second line (F, F'), and at least one patch correction conductor (28) between the first and second correction conductors (27). ), and wherein the magnetic balancing circuit (21) of the queue end cells has two ends which are connected to the correction circuit (26).

The series of electrolysis cells according to claim 8, wherein the magnetic balancing circuit (21) of the queue end cells is connected in series between two portions of the correction circuit (26).

10. Series of electrolysis cells according to one of claims 8 and 9, wherein the first correction conductor (27) extends along the first line (F, F ') on the side of the second file, and the second correction conductor (27) extends along the second queue (F, F ') on the side of the first row of cells.

1. A series of electrolysis cells according to one of claims 8 to 10, wherein the first conductor (22) and the second conductor (23) of the magnetic balancing circuit (21) connected to the correction circuit (26). ) are arranged outside the two rows (F, F ') of cells.

Electrolysis cell series according to one of the preceding claims, wherein the connecting conductor (20) comprises a magnetic balancing conductor (40) of the first end cell (100 ') along the first cell. end portion perpendicular to the longitudinal axis of the line (F, F ') of cells, and wherein the first electrical conductor (22) does not extend along the first end cell.

A series of electrolytic cells as claimed in claim 12 when dependent on claim 11, wherein the magnetic balance circuit (21) of the queue end cells comprises a transverse conductor (24) electrically connecting the correction circuit (26) to the first electrical conductor (22), the transverse conductor extending under the line (F, F) of cells.

Electrolytic cell series according to one of the preceding claims, in which the magnetic balancing circuit (21) of the end-of-queue cells forms a plurality of loops and the first balancing electrical conductor (22). The magnetic stripe is formed by a plurality of loop strands (29) extending side by side along the first line (F, F ') of cells facing only the end portion P of the first line of cells.

15. Electrolysis series according to one of the preceding claims, wherein the end portion (P) of the first row (F, F ') of cells comprises from 3 to 10 cells, and preferably from 6 to 8 cells. 16. A method of using a series (1) of electrolysis cells (100) according to one of the preceding claims, wherein the queues (F, F ') of electrolysis cells and the connecting conductor ( 20) are traversed by an electrolysis current (l ₀ ) and wherein the first magnetic balancing conductor (22) is traversed by a balancing electric current (h):

- flowing in the same direction as the electrolysis current (I ₀₎ flowing in the first queue (F, F ') cells if the first electric conductor (22) of magnetic balance is located along the first row of cells on the side of the second row (F, F ') of electrolysis cells;

flowing in the opposite direction with respect to the electrolysis current ( ₁₀ ) flowing in the first row of cells (F, F ') if the first magnetic balancing conductor (22) is located along the first row of cells cells on the opposite side to the second row (F, F ') of electrolysis cells.

17. Method of using a series of electrolysis cells according to the claim

16. in which the series (1) comprises a second magnetic balancing electric conductor (23, 23 ', 23 ") and in which this second magnetic balancing electrical conductor is traversed by the balancing electric current (h) but circulating in the opposite direction of the balancing electric current (l1 circulating in the first magnetic balancing electrical conductor (22).