EP3256623A1

EP3256623A1 - Aluminium smelter and method to compensate for a magnetic field created by the circulation of the electrolysis current of said aluminium smelter

Info

Publication number: EP3256623A1
Application number: EP16748782.6A
Authority: EP
Inventors: Benoit BARDET; Steeve RENAUDIER
Original assignee: Rio Tinto Alcan International Ltd
Current assignee: Rio Tinto Alcan International Ltd
Priority date: 2015-02-09
Filing date: 2016-02-05
Publication date: 2017-12-20
Anticipated expiration: 2036-02-05
Also published as: CA2975962C; CA2975962A1; CN107250439B; EP3256623B1; AU2016217610A1; ZA201705498B; DK201770671A1; CN107250439A; EP3256623A4; WO2016128824A1; AR103789A1; AU2016217610B2; BR112017015161A2; US10358733B2; MY183698A; US20180023207A1; FR3032459B1; FR3032459A1; EA201791722A1; DK179924B1

Abstract

The invention relates to an aluminium smelter (1) which comprises a row (2) of electrolysis cells arranged transversely relative to the row (2), one of the cells comprising anode assemblies and electrical conductors for raising and connecting to the anode assemblies. The raising and connection conductors extend upwards along two opposing longitudinal edges of the cell. In addition, the aluminium smelter (1) comprises a first electrical compensation circuit (4) extending under the cells and capable of carrying a first compensation current (IC1) in the opposite direction to the electrolysis current (IE), and a second electrical compensation circuit (6) extending on one side of the row (2) and being capable of carrying a second compensation current (IC2) in the same direction as the electrolysis current (IE).

Description

Smelter and method of compensation of a magnetic field created by the flow of electrolysis current of this smelter

The present invention relates to an aluminum smelter for the production of aluminum by electrolysis, and a method of compensating the vertical and horizontal components of a magnetic field generated by the circulation of an electrolysis current in this smelter.

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

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

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

These MHD instabilities are known to degrade the efficiency of the process. The more unstable a vessel is, the higher the interpolar distance between the anode and the metal web. However, the greater the interpolar distance, the higher the energy consumption of the process is dissipated by Joule effect in the interpolar space. On the other hand, the horizontal components of the magnetic field, generated by the entire path of the electric current, both in the conductors inside the tank and those located outside, interact with the electric current flowing through. liquids, which generates a stationary deformation of the metal sheet. The unevenness of the metal sheet caused must remain low enough so that the anodes are consumed uniformly with little waste. To obtain a small difference in level, it is necessary that the horizontal components of the magnetic field are the most antisymmetric possible in liquids (electrolytic bath and metal sheet). For the longitudinal and transverse components of the magnetic field that constitute the horizontal components, by antisymmetric means that when we move perpendicular to the central axis of the tank, parallel to the relevant component of the field, and when we go located at equal distance on either side of this central axis, the value of the component considered is opposite. The antisymmetry of the horizontal components of the magnetic field is the configuration providing the most symmetrical interface interface and as flat as possible in the tank.

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

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

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

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

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

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

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

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

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

The external loop compensation solution significantly reduces the length, mass and electrical losses of the routing conductors, but requires an additional power station and additional independent secondary electrical circuit.

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

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

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

Also, the present invention aims to overcome all or part of these disadvantages by providing an aluminum smelter with a magnetic configuration for having very magnetically stable tanks, and offering improved compactness. The present invention also relates to a method of compensating a magnetic field created by the circulation of an electrolysis current in this aluminum smelter.

For this purpose, the subject of the present invention is an aluminum plant comprising at least one row of electrolysis cells arranged transversely with respect to the length of said at least one line, one of the electrolytic cells comprising anode assemblies and electrical conductors. mounting and connecting to the anode assemblies, characterized in that the rising and connecting electrical conductors extend upwardly along two opposite longitudinal edges of the electrolytic cell to conduct the electrolysis current to the assemblies anodic, and in that the smelter includes

at least one first compensation electric circuit extending under the electrolytic cells, said at least one first compensation electric circuit being traversed by a first compensation current intended to flow under the electrolysis cells in the opposite direction of the direction overall circulation of the electrolysis current,

at least one second compensation electric circuit extending over at least one side of said at least one electrolysis cell line, said at least one second compensation electric circuit that can be traversed by a second compensation current for circulating in the same direction as the overall flow direction of the electrolysis current.

Thus, the aluminum plant according to the invention offers the advantage of having vessels that are very stable magnetically, since they compensate both the horizontal and vertical components of the magnetic field generated by the circulation of the electrolysis current, which makes it possible to improve the overall efficiency, and this without negative impact on the size of the smelter according to the invention since the first compensation electric circuit extends under the electrolysis tanks.

According to a preferred embodiment, the rising and connecting electrical conductors comprise upstream and upstream electrical connection conductors, adjacent to the upstream longitudinal edge of the electrolytic cell, and adjacent upstream and downstream electrical connection conductors. at the downstream longitudinal edge of the electrolytic cell, and the aluminum smelter is configured so that the distribution of the electrolysis current is asymmetrical between the upstream and downstream electrical up and down conductors, the intensity of the upstream electrolysis current intended to cover all the upstream electrical conductors and upstream connection of the electrolysis cell being equal to 50-100 [% of the intensity of the electrolysis current, and the intensity of the downstream electrolysis current intended to traverse all the electrical conductors of upstream and downstream connection of the electrolytic cell being equal to] 0-50 [% of the intensity of the current electrolysis, the sum of the intensities of the upstream and downstream electrolysis currents being equal to the intensity of the electrolysis current.

An advantage of these characteristics is to enable the magnetic field to be effectively compensated for a large electrolytic cell, in particular of large width, without any additional cost of raw materials.

Indeed, if the distribution of the downstream upstream electrolysis current is symmetrical, that is to say if this distribution is 50% upstream and 50% downstream, and that the width of the tanks of electrolysis is increased, for better performance, it is created, because of the increase in the path traveled by the electrical conductors routing under the electrolysis tank to supply the electrical conductors upstream and downstream connection, an imbalance detrimental to the proper functioning of the electrolysis cell. To restore a balance, it would be necessary to increase the section of these electrical conductors of routing under the electrolysis cell. However, this increase in section involves a significant additional cost of raw materials. On the other hand, the applicant has observed that the aluminum plant according to the present invention makes it possible to introduce an asymmetry in the distribution of the electrolysis current between the upstream and the downstream of the electrolytic cells without detrimental increase of the section of the electrical conductors of routing, while having electrolysis cells very stable magnetically.

The choice of the distribution between intensities of upstream and downstream electrolysis currents is made by economic study. This choice depends mainly on the distance between two vats and the height of the vats. This distribution is carried out by adjusting the sections of the electrical conductors of the upstream and downstream electrical circuits, taking into account their length.

According to a preferred embodiment, the smelter comprises a feed station configured to circulate through said at least one first compensation electric circuit a first intensity compensation current equal to twice the current intensity of downstream electrolysis, within plus or minus 20%, and preferably within plus or minus 10%.

An advantage of this characteristic is that for this value of the intensity of the first compensation current, which is a direct function of the distribution of the electrolysis current between the upstream and the downstream of the electrolysis cells, the applicant has observed that the horizontal magnetic field generated by the first compensation electric circuit precisely corrects the asymmetry of the horizontal magnetic field resulting from the dissymmetry between the upstream and downstream electrolysis current, and this, in order to have an antisymmetric distribution of the horizontal components of the field This first compensating current also makes it possible to partially correct the vertical magnetic field, as a function of the distribution between the upstream and downstream electrolysis current of the tank, in order to reduce the MHD instabilities in the tank.

According to a preferred embodiment, the smelter comprises a feed station configured to circulate through said at least one second compensation electric circuit a second intensity compensation current of between 50% and 100% of the difference between intensity between the upstream and downstream electrolysis currents, and preferably between 80% and 100% of the difference in intensity between the upstream and downstream electrolysis currents.

By intensity of the second compensation current is meant the sum of the currents flowing in the conductors forming the second compensation circuit, especially when the second compensation circuit consists of two conductors (or loops) arranged on either side of the electrolysis tank.

The applicant has observed that for this intensity value of the second compensation current, which is also directly a function of the distribution of the electrolysis current between the upstream and downstream electrolytic cells, the vertical magnetic field generated by the second compensation electric circuit corrects the vertical magnetic field generated by the electrolysis current flowing in the main electrical circuit (tank-to-tank circuit) and already partly corrected by the current flowing in the first compensation circuit.

It will be noted that this characteristic is particularly advantageous when it is used in combination with the previous one.

According to a preferred embodiment, the electrical conductors of rise and connection are distributed at regular intervals along the longitudinal edge of the electrolysis cell to which these electrical conductors of rise and connection are adjacent.

An advantage of this characteristic is to have a uniform distribution over the entire length of the vessel of the horizontal longitudinal component of the magnetic field (that is to say, parallel to the length of the electrolytic cell), which allows to facilitate its compensation via the first compensation circuit.

The rising and connecting electrical conductors are advantageously arranged symmetrically with respect to the transverse median plane XZ of the electrolysis cells, which makes it possible to obtain an antisymmetric distribution of the transverse component of the magnetic field along X.

According to a preferred embodiment, the upstream electrical connection and upstream connection conductors and the downstream electrical connection and connection conductors are located equidistant from a longitudinal median plane YZ of the electrolysis cell.

According to a preferred embodiment, the upstream electrical connection and upstream connection conductors and the upstream electrical connection and connection conductors are arranged substantially symmetrically with respect to said longitudinal median plane YZ of the electrolysis cell.

This configuration, combined with the first compensation circuit, ensures perfect antisymmetry of the longitudinal component of the magnetic field along Y.

According to a preferred embodiment, said at least one first compensation electric circuit comprises electrical conductors extending under the electrolytic cells together forming a sheet consisting of a plurality of parallel electrical conductors, typically from two to twelve, and preferably from three to ten parallel electrical conductors. The number of parallel conductors required depends in part on the distance between the liquids and the same conductors. The greater the distance, the smaller the number of drivers, the shorter the distance, the higher the number of drivers.

An advantage of this feature is distributed compensation over the entire length of the electrolysis cell, thus producing better results. It will be noted that the first compensation electric circuit is configured so that the first compensation current flows in the same direction through all the electrical conductors of the sheet.

The intensity of the first compensation current corresponds to the sum of the intensities of the currents flowing in each of the parallel electrical conductors of the sheet extending under the tanks.

According to a preferred embodiment, the electrical conductors of said sheet are arranged at regular intervals from each other in a longitudinal direction Y of the electrolysis cells.

According to a preferred embodiment, the electrical conductors of said ply are arranged substantially symmetrically with respect to a transverse median plane XZ of the electrolysis cells.

According to a preferred embodiment, the electrical conductors of said sheet are arranged in the same horizontal plane XY.

An advantage of these features is to further improve the unfavorable magnetic field compensation.

According to a preferred embodiment, said at least one second compensation electric circuit comprises electrical conductors extending on each side of said at least one row of electrolysis cells, and the second compensation current flows in the same direction as the direction of overall circulation of the electrolysis current on each side of the electrolysis cells.

Thus, the electrical conductors of said at least one second compensation electric circuit form an inner loop and an outer loop, and thus provide improved compensation of the magnetic field. By internal loop is meant the loop being closest to the neighboring queue and external loop, the loop being the furthest.

According to a preferred embodiment, the intensity of a second compensation current flowing in an internal loop of said at least one second compensation circuit differs from the intensity of a second compensation current flowing in an external loop of said at least one second compensation circuit.

This characteristic makes it possible to compensate for the residual vertical magnetic field of the neighboring queue.

The intensity of the second compensation current corresponds to the sum of the intensities of the currents flowing in each of the loops.

According to a preferred embodiment, the intensity of the second compensation current flowing in the inner loop is greater than the intensity of the second compensation current flowing in the outer loop.

This makes it possible to correct the magnetic field created by the neighboring queue. This neighboring queue creates a magnetic field proportional to a stream of the series to which the downstream electrolysis current is subtracted twice, whereas a series of "conventional" electrolysis will undergo a magnetic field directly proportional to the totality of the current. electrolysis. Thus, thanks to the first compensation circuit, the disturbing field created by the neighboring queue is much smaller and requires a much smaller correction. Therefore, regarding the second compensation circuit, the difference between the intensity of the inner loop and that of the outer loop will be much smaller than in the case of patent EP0204647 and the gap between the two rows of tanks can be minimized.

According to a preferred embodiment, the electrical conductors forming the second electrical compensation circuit are substantially symmetrical with respect to a median transverse plane XZ of the electrolysis cells.

This improves the compensation of the deleterious magnetic field.

According to a preferred embodiment, the electrical conductors of the second compensation electric circuit extend in the same horizontal plane XY, preferably up to a sheet of liquid aluminum formed inside the electrolysis cells during of the electrolysis reaction.

This arrangement improves the compensation of the vertical magnetic field without impacting the horizontal component of the field already compensated by the first compensation circuit.

Preferably, the aluminum plant comprises two consecutive and parallel rows of electrolysis cells, and the circuit of the inner loop forms at the end of the line means of compensation for "end of line" effects caused by the connecting conductors between the queues, which provides more magnetic stability and thus improves the performance of the end tanks.

According to a preferred embodiment, said at least one first compensation electric circuit is independent of the main electrical circuit traversed by the electrolysis current.

This characteristic has the advantage of limiting the consequences of a damage such as an electrolysis cell piercing by the liquids contained in this electrolytic cell. In addition, this characteristic is advantageous in terms of scalability since it makes it possible to vary the intensity of the first compensation current to adjust the magnetic compensation. An adjustment of the magnetic compensation is useful when the electrolysis vessels are modified, because the magnetic configuration of these electrolysis cells is modified, or to adapt the stirring of the alumina to the quality of this alumina (which allows to maintain optimal performance despite the different quality of alumina).

According to a preferred embodiment, said at least one second compensation electric circuit is independent of the main electrical circuit traversed by the electrolysis current.

As explained above, this has an advantage in terms of scalability since it makes it possible to vary the intensity of the first compensation current to adjust the magnetic compensation.

According to a preferred embodiment, the electrolysis cell has a modular electrical construction in N modules repeated in the direction of its length, each module comprising electrical conductors configured to generate the same predetermined magnetic configuration.

This characteristic is advantageous in terms of scalability: it allows modifications of the electrolytic cell, for example an enlargement by adding one or more modules, without modifying the principle of magnetic equilibration of the electrolytic cell.

To obtain the same magnetic configuration, each electrical module has the same arrangement of electrical conductors, each electrical conductor of an electrical module being traversed by the same intensity and the same direction of current as the corresponding electrical conductor of an adjacent electrical module. The electrical conductors of each module include electrical risers and connectors, anode assemblies, cathodes, cathode conductors, cathode outlets, electrical conductors, and conductors. electrically of the electrical conductor ply of the first compensation electric circuit. These electrical conductors are arranged relative to each other in the same way from one module to another. In particular, each electrical module comprises the same number of electrical conductors of the electrical conductor ply of the first compensation electric circuit.

It is specified that the electrolysis cells of the smelter comprise all or part of the aforementioned characteristics of the electrolytic cell.

The invention also relates to a method for compensating a magnetic field created by the circulation of an electrolysis current in a plurality of electrolysis cells of an aluminum smelter having the aforementioned characteristics, the method comprising:

the flow, in the direction opposite to the direction of overall circulation of the electrolysis current, of a first compensation current through said at least one first compensation electric circuit,

circulating, in the same direction as the overall flow direction of the electrolysis current, a second compensation current through said at least one second compensation electric circuit.

Thus, this method provides effective magnetic compensation of the magnetic field generated by the circulation of the electrolysis current in the series of electrolysis cells of the aluminum plant, by limiting the bulk.

According to a preferred embodiment, the process comprises an asymmetrical distribution of the electrolysis current between the upstream and downstream electrolysis cells, the set of electrical conductors upstream and connection upstream of the electrolysis tanks. electrolysis being traversed by an upstream electrolysis current of intensity of between 50-100 [% of the intensity of the electrolysis current, and all of the electrical conductors for rising and connecting downstream of the tanks electrolysis being traversed by a downstream electrolysis current of intensity between 0-50 [% of the intensity of the electrolysis current, the sum of the intensities of the upstream and downstream electrolysis currents being equal to intensity of the electrolysis current.

This method makes it possible to obtain magnetically stable electrolytic cells, even when the electrolysis cells are large, in particular of great width. The yield can thus be substantially increased.

According to a preferred embodiment, the intensity of the first compensation current is equal to twice the intensity of the downstream electrolysis current, within plus or minus 20%, and preferably within plus or minus 10%. An advantage of this characteristic is that for this value of the intensity of the first compensation current, which is a direct function of the distribution of the electrolysis current between the upstream and the downstream of the electrolysis cells, the applicant has observed that the horizontal magnetic field generated by the first compensation electric circuit precisely corrects the asymmetry between the upstream and downstream current, in order to have an antisymmetric distribution of the horizontal components of the magnetic field. This first compensation current also makes it possible to correct all or part of the vertical magnetic field, according to the distribution between the upstream and downstream electrolysis current of the tank, and this, in order to reduce the MHD instabilities in the tank. The entire vertical magnetic field is corrected if the distribution between upstream and downstream is 50%.

According to a preferred embodiment, the intensity of the second compensation current is between 50% and 100% of the difference in intensity between the upstream and downstream electrolysis currents, and preferably between 80% and 100% of the difference in intensity between the upstream and downstream electrolysis currents.

In the same way, the applicant has observed that for this intensity value of the second compensation current, which is also directly a function of the distribution of the electrolysis current between the upstream and the downstream of the electrolysis cells, the vertical magnetic field generated by the second compensation electric circuit precisely corrects the remaining vertical magnetic field, resulting from the sum of the vertical magnetic field of the electrolysis current (tank-to-tank circuit) and the first compensation circuit.

According to a preferred embodiment, said at least one second compensation electric circuit comprises an inner loop and an outer loop, and wherein the intensity of a second compensation current flowing in the inner loop differs from the intensity of a second compensation current flowing in the outer loop.

According to a preferred embodiment, the method comprises a step of analyzing at least one characteristic of the alumina in at least one of the electrolysis cells of said aluminum smelter, and the determination of the intensity values of the first flow of compensation and the second compensation current to be circulated according to said at least one analyzed characteristic.

Thus, the method makes it possible to modify the magnetic compensation, to deliberately induce, in particular cases, a modification of the flow in the liquid and flow velocities while controlling (weakly degrading) the MHD instabilities of the bath / metal interface. The flow of liquids (bath + aluminum) contributes to stir the alumina, which, depending on the speed and shape of the flow as well as the quality of the alumina, can improve the yield. This preferred embodiment therefore makes it possible to improve the yield by optimizing the flow to dissolve the alumina while controlling the level of "degradation" of the MHD stability of the bath / metal interface.

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

FIG. 1 is a schematic view of an aluminum smelter according to the state of the art,

FIG. 2 is a schematic side view of two successive electrolysis cells of the state of the art,

FIG. 3 is a diagrammatic wired view of the electrical circuit traversed by the electrolysis current in the two electrolysis cells of FIG. 2,

FIG. 4 is a diagrammatic sectional view along a vertical longitudinal plane of an electrolysis cell of the state of the art,

FIG. 5 is a schematic view of an aluminum plant according to one embodiment of the invention,

FIG. 6 is a schematic side view of two successive electrolysis cells of an aluminum plant according to one embodiment of the invention,

FIG. 7 is a diagrammatic view in section along a longitudinal plane YZ of an electrolysis cell of an aluminum plant according to one embodiment of the invention,

FIG. 8 is a wired schematic view of the electrical circuit traversed by the electrolysis current in an electrolysis cell of an aluminum plant according to one embodiment of the invention,

FIG. 9 is a table showing the intensity of the electrolysis current flowing through each segment of FIG. 8,

FIGS. 10 to 12 are schematic wire-plane views of the electrical circuit traversed by the electrolysis current in an electrolysis cell of an aluminum smelter according to one embodiment of the invention, showing for this electrolytic cell the zones generating a significant magnetic field, FIG. 13 is a table showing the contribution of each segment of FIGS. 10 to 12 in the calculation of the vertical component of the magnetic field generated by the circulation of the electrolysis current,

FIG. 14 is a table showing the contribution of each segment of FIGS. 10 to 12 in the calculation of the longitudinal horizontal component of the magnetic field generated by the circulation of the electrolysis current.

Figure 1 shows an aluminum smelter 100 of the state of the art. The aluminum smelter 100 comprises electrolysis tanks arranged transversely to the length of the line they form. The electrolysis tanks are here aligned in two rows 101, 102 parallel. These electrolytic cells are traversed by a current electrolysis l ₀ o- Two circuits 104, 106 electrical compensation extend on the sides of the lines 101, 102 to compensate for the magnetic field generated by the current flow ₁₀ l o electrolysis of one electrolysis cell to another and in the neighboring queue. The circuits 104, power compensation 106 are respectively driven by the currents ₁₀ 4 l ₀ 6 flowing in the same direction as the electrolysis current l ₁₀ o Stations 108 power supply series of electrolysis tanks and the electrical compensation circuits 104, 106. According to this example, for an electrolysis current of intensity 500kA, and in view of the magnetic disturbances of "end of line", the distance D ₁₀ o between the electrolysis cells closest to the power stations 108 and the power supply stations 108 is of the order of 45m, and the distance D ₃₀₀ on which the electrical circuits 104, 106 extend beyond the ends of the line is of the order of 45m, while the distance D ₂₀ o between the two rows 101, 102 is of the order of 85 m to limit the magnetic disturbances from one line to the other.

Figure 2 shows two tanks 110 of traditional electrolysis consecutive of the same row of electrolytic cells. As can be seen in FIG. 2, the electrolysis tank 110 comprises a box 112 lined internally with refractory materials 114, a cathode 116 and anodes 118 immersed in an electrolytic bath 120 at the bottom of which a layer 122 of metal is formed. 'aluminum. The cathode 116 is electrically connected to cathode conductors 124 which pass through the sides of the caisson 1 12 at cathode outlets 126. The cathode outlets 126 are connected to routing conductors 128 which convey the electrolysis current to the conductors. 130 rise and connection of a next electrolysis cell. As can be seen in FIG. 2, these rising and connecting conductors 130 extend obliquely on one side, the upstream side, of the electrolytic cells 1 and extend over the anodes 118, to the longitudinal central portion of the electrolytic cells 1 10. The electrolysis tank comprises a superstructure 132 which passes through it longitudinally, above the box 112 and the anodes 118. The superstructure 132 comprises in particular a beam resting on feet (not shown) at each of its longitudinal ends. The beam supports an anode frame 134, this anode frame 134 also extending longitudinally over the well 1 12 and the anodes 118. The anode frame 134 supports the anode assemblies, the latter being electrically connected to the anode frame 134.

FIG. 3 schematically illustrates the path traveled by the electrolysis current ₁₀ o in each of the electrolytic cells 110 and between two adjacent electrolysis cells 10 such as those represented in FIG. 2. It is notably noted that the rise of electrolysis current l ₁₀₀ to the anode assembly of an electrolytic tank 1 10 is asymmetrical since this rise is carried out only upstream of the electrolytic cells 110 in the direction of global circulation of the current. electrolysis l ₁₀ o in the queue (to the left of the tanks in Figures 2 and 3).

FIG. 4 shows the arrangement on the sides of the tanks 1 10 of the state of the art of electrical conductors forming the electrical compensation circuits 104, 106, these electrical conductors being traversed respectively by the compensating currents l ₀ 4, oe flowing in the same direction as the current I ₁₀ o electrolysis browsing here drivers 128 routing positioned below the vessel.

Figure 5 shows an aluminum smelter 1 according to one embodiment of the invention. The aluminum smelter 1 is intended for the production of aluminum by electrolysis according to the Hall-Héroult process.

The aluminum smelter 1 comprises a plurality of substantially rectangular electrolysis cells intended for the production of aluminum by electrolysis, these electrolytic cells being able to be aligned in one or more queues 2 which may be substantially parallel. Where appropriate, the queues 2 are connected electrically in series and supplied with IE electrolysis current. The aluminum smelter 1 also comprises a first compensation electric circuit 4, which extends under the lane or queues of electrolysis tanks, and a second electric compensation circuit 6, which extends over at least one side of the or 2 rows of electrolysis tanks. According to the example of FIG. 5, the second electrical compensation circuit 6 extends on both sides of each row 2 of electrolysis cells. Still according to the example of FIG. 5, the aluminum plant comprises two rows of tanks arranged parallel to one another, fed by the same supply station 8, and electrically connected in series so that the current IE electrolysis circulating in the first of two rows of electrolysis 2 then circulates in the second of the two rows 2 of electrolysis cells. Electrolysis tanks are arranged transversely with respect to each row 2 that these electrolysis tanks form. It will be noted that per electrolysis tank 2 arranged transversely is meant electrolysis tank 2, the largest dimension of which, the length, is substantially perpendicular to the overall direction in which the electrolysis current IE flows.

In the present description, upstream and downstream are defined with respect to the global flow direction of the electrolysis current IE, that is to say the flow direction of the electrolysis current IE at the scale of the line 2 of electrolysis tanks.

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

It should be noted that the electrolysis tanks of the aluminum smelter are preferably large electrolysis cells, the use of large electrolysis cells being made possible by the particular configuration of the electrolysis cells of the smelter. aluminum plant according to the invention, as described in more detail below. The dimensions of an electrolytic cell are defined by the ground surface that this electrolytic cell represents. For this we consider that the dimensions of the tank are defined by the external dimensions of its box. By large electrolysis tank is meant electrolytic cell having a width greater than 4 m, preferably greater than or equal to 5 m, and in particular greater than or equal to 6 m, and / or having a length greater than 15 m. m, preferably greater than or equal to 20 m, and in particular greater than or equal to 25 m.

Figure 6 shows in more detail the electrolysis tanks of the aluminum plant 1 according to one embodiment. As illustrated in this figure, the electrolysis tanks 10 of the aluminum plant 1 comprise a box 12, anode assemblies 14, a cathode 16 crossed by cathodic electrical conductors 18 intended to collect the electrolysis current IE at the cathode 16 to drive it to other electrical conductors called cathode outlets 20 out of the box 12, electrical conductors rise and connect 22 to the anode assemblies 14 to conduct the electrolysis current IE to the anode assemblies 14, and conductors routing electrodes 24 connected to the cathode outlets 20 and intended to conduct the electrolysis current IE from the cathode outlets 20 to the electrical conductors of rise and connection 22 of the next electrolytic cell 10. The casing 12 comprises an inner lining 26 made of refractory materials. As illustrated in Figures 6 and 7, the housing 12 preferably comprises cradles 28 of reinforcements. The box 12 may be metallic, for example steel.

The anode assemblies 14 comprise a support 30 and at least one anode 32. The anode (s) 32 are in particular made of carbonaceous material and more particularly of precooked type. The support 30 comprises, for its part, a first electrically conductive part 34, for example a cross-member, extending essentially in a transverse direction X of the electrolytic cells 10, and a second part 36 electrically conducting, formed of several electrically conductive elements be called "logs", the logs comprising a distal end electrically connected to the first portion 34 of the support 30 and a proximal end electrically connected to the anode or 32 to conduct the IE electrolysis current from the first portion 34 of the support 30 to this or these anodes 32. The anode assemblies 14 are intended to be removed and replaced periodically when the anode or 32 are worn.

The cathode 16 may be formed of several cathode blocks of carbonaceous material. The cathode 16 is crossed by the cathode conductors 18 intended to collect the electrolysis current IE at the cathode 16 to lead it to the cathode outlets 20 advantageously leaving the bottom of the box 12, as illustrated in FIG.

The rising and connecting electrical conductors 22 extend upwards along two opposite longitudinal edges 38 of each electrolytic cell 10, to conduct the electrolysis current IE to the anode assemblies 14. It is specified that the edges The lengths of the electrolysis cells 38 correspond to the larger edges, ie the edges of the electrolytic cells 10 which are substantially parallel to the longitudinal Y direction. By way of example, an electrolytic cell 10 operating at an intensity of 400 to 1000 k amps may for example preferably comprise from 4 to 40 rise and connection conductors 22 distributed regularly over the entire length of each of its two edges. The electrical rising and connecting conductors 22 comprise upstream and upstream electrical connection conductors 22A, ie adjacent to the upstream longitudinal edge 38 of the electrolytic cell 10, and electrical conductors 22A. mounted and downstream connection 22B, that is to say adjacent the longitudinal edge 38 downstream of the electrolytic tank 10. The upstream and upstream electrical connection conductors 22A are electrically connected to an upstream end of the first portion 34 of the support 30, and the upstream and downstream electrical connection conductors 22B are electrically connected to a downstream end of this first portion 34 of the support 30. The electrical routing conductors 24 are connected to the cathode outlets 20 and are intended to conduct the electrolysis current IE from these cathode outputs 20 to the electrical connection and rise conductors 22 of the next electrolytic cell 10 of the series.

The cathode conductors 18, the cathode outputs 20 and / or the routing conductors 24 may be metal bars, possibly composite, for example aluminum, copper and / or steel.

A liquid aluminum web 40 is formed during the electrolysis reaction.

It should be noted that the electrolysis tanks of the aluminum plant 1 according to the invention are preferably vertical anode-type electrolysis cells with vertical pulling of the anode assemblies 14 above the tank 10. electrolysis, as represented by the electrolysis tank 10 on the right in FIG. 6. The rise and connection conductors 22 extend on either side of the box 12 without extending to the right anodes 32, that is to say without extending in a volume obtained by vertically projecting the area of the anodes 32 projected in a horizontal plane. In addition to the interest that this represents to allow an anode change 32 by vertical upward traction, this also makes it possible to reduce the length of the rising and connecting conductors 22 with respect to a use of rise and connection conductors 130 of the following type. conventional, visible in Figure 2, which typically extend above the tank 1 10 electrolysis into the longitudinal central portion of the tank 1 10 electrolysis. This helps to reduce manufacturing costs. It is also noted that the horizontal portion 34 of the support 30 is supported and connected at each of the two longitudinal edges 38 of each electrolysis tank 10.

Thus, the anode assembly is no longer supported and electrically connected above the box and the anodes by means of a superstructure 132, as is the case for the electrolysis tanks of the state of the art illustrated on Figure 2. The electrolysis tanks 10 of the aluminum plant 1 according to this embodiment of the invention are therefore free of superstructure. The absence of superstructure makes it possible to widen and / or lengthen the electrolytic cells, in order to benefit from large electrolytic cells 10, as mentioned above. Such widening or elongation of the electrolysis cells 110 of the state of the art is not possible because of the superstructure 132, because this enlargement and / or elongation would result in an enlargement and / or elongation of the superstructure 132 itself. same, therefore the scope of the beam between the feet supporting the beam and the weight to be supported by this superstructure 132. There are superstructures comprising one or more intermediate arches of support of the beam, but such intermediate arches, extending transversely above the box 1 12 and anodes 1 18, are cumbersome and complexify operations on tanks, including changes of anodes.

The fact of being able to increase the dimensions of the electrolysis cells, combined with an increase in the intensity of the electrolysis current IE, without creating HD instabilities because of the particular magnetic configuration of the aluminum smelter 1 according to the invention. The invention described in more detail below, substantially improves the performance of the aluminum smelter 1 in comparison with the state of the art.

The electrical conductors of the aluminum smelter 1 (in particular electrical rising and connecting conductors 22, support 30, cathodic outputs 20, routing conductors 24, electrical conductors of the first and second compensating electrical circuits 4, 6) are indeed configured to obtain effective compensation of the horizontal and vertical components of the magnetic field generated by the flow of electrolysis current IE and, in so doing, a limitation of MHD instabilities, thus an improved efficiency.

More particularly, the distribution of the electrolysis current IE traversing the electrical conductors of rise and connection 22 is asymmetrical between the upstream electrical conductors and connection upstream 22A and downstream 22B. The electrolysis current IE is distributed in an upstream electrolysis current IEA, which traverses all the electrical conductors for upstream and upstream connection 22A of the electrolytic cells, and a downstream electrolysis current IEB, which runs through all of the electrical conductors for upstream and downstream connection 22B of the electrolytic cells. The intensity of the upstream electrolysis current IEA is equal to 50-100 [% of the intensity of the electrolysis current IE, while the intensity of the downstream electrolysis current IEB is equal to] 0-50 [ % of the intensity of the electrolysis current IE, it being specified that the upstream electrolysis currents IEA and downstream IEB are complementary, that is to say that the sum of the intensities of the upstream electrolysis currents IEA and downstream IEB is equal to the intensity of the electrolysis current IE.

This asymmetrical distribution with preponderance of the upstream relative to the downstream is particularly advantageous when the electrolysis cells 10 of the aluminum smelter are large electrolysis cells. In fact, the upstream / downstream asymmetry of the electrolysis current IE makes it possible to avoid resorting to an excessive increase in the cross-section of the routing conductors 24 under the electrolytic cell 10, so that savings in materials and Space are achieved, without prejudice to the magnetic stability of the electrolytic cell. The choice of the distribution between intensities of upstream and downstream electrolysis currents IEA, IEB is carried out by economic study. This choice depends mainly on the distance between two vats and the height of the vats. This distribution is carried out by adjusting the sections of the electrical conductors of the upstream and downstream electrical circuits, taking into account their length.

The rise and connection conductors 22 extend substantially vertically, and preferably only vertically, so that the flow of the electrolysis current IE through the rise and connect conductors 22 generates a magnetic field with only horizontal components, but no vertical component.

Similarly, the second portion 36 of the support 30 of the anode assembly 14, and / or the cathode outputs 20, advantageously extend in a vertical direction, and preferably only vertically, so that the current flow of electrolysis IE through this second portion 36 and / or through the cathode outputs 20 generates a magnetic field having only horizontal components, but no vertical component.

It will be noted that the cathode outlets 20 advantageously cross the bottom of the box 12. The fact of having cathode outlets 20 at the bottom instead of cathode outlets on the sides of the electrolytic cell as in the state of the art ( 2), makes it possible to reduce the length of the routing conductors 24. The reduction in length of the routing conductors 24 makes it possible, in addition to a saving of raw materials, a substantial decrease in the horizontal currents in the liquids and thus a better MHD stability.

Moreover, still in order to effectively compensate for the magnetic field created by the flow of the electrolysis current IE, the first portion 34 of the support 30 of the anode assembly 14 preferably extends only substantially horizontally and parallel to the transverse direction X of the electrolytic cells.

Likewise, the routing conductors 24 advantageously extend substantially rectilinear and parallel to the transverse direction X of the electrolytic cells 10 up to the rising and connecting conductors 22 of the next electrolytic cell 10. This limits the cost of electrical conductors 24, minimizing their length. The magnetic fields generated by these electrical conductors 24 for routing are also limited in relation to the state of the art, and in particular compared with self-compensated electrolysis cells of the state of the art. The rising and connecting electrical conductors 22 are preferably distributed at regular intervals over substantially the entire length of the longitudinal edge 38 to which they are adjacent. In other words, the same distance separates two consecutive electrical conductors 22 and connection in the longitudinal direction Y. This improves the balance of the longitudinal horizontal component of the magnetic field (that is to say, parallel to the length of the electrolytic tank).

The upstream and upstream electrical connection conductors 22A and the upstream and downstream electrical connection conductors 22B may be arranged equidistant from a longitudinal median plane YZ of each electrolytic cell 10, that is to say a plane substantially perpendicular to the transverse direction X and separating each electrolytic cell 10 into two substantially equal portions. In other words, the upstream and upstream electrical connection conductors 22A are at the same distance from this longitudinal median plane YZ as the upstream and downstream electrical connection conductors 22B. In addition, the upstream electrical conductors and upstream connection 22A are advantageously disposed substantially symmetrically to the upstream electrical conductors and downstream connection 22B, with respect to this longitudinal median plane YZ. This further enhances the advantageous antisymmetric characteristic of the horizontal magnetic field distribution in liquids.

To limit the magnetic field generated by the circulation of the electrolysis current through the electrical conductors of rise and connection 22, these electrical conductors rise and connect advantageously extend above the liquids (electrolytic bath) to a height h between 0 and 1.5 meters. The length of the rising and connecting conductors 22 is thus greatly reduced with respect to the rise and connection conductors 130 of conventional type which extend to heights greater than two meters for the electrolysis tanks 130 of the state of the technique.

In order to improve the compactness of the aluminum smelter 1 and to limit the raw material costs, the upstream and upstream connecting conductors 22A of the electrolytic cells 10 may be arranged in staggered relation with the upstream and downstream connection conductors 22B of the electrolysis tank 10 preceding it in line 2. This makes it possible to bring the electrolytic cells as close as possible to one another, or to place more electrolytic cells in series over the same distance, which increases the efficiency, that is to reduce the length of a row 2 of electrolysis tanks, thus saving space and achieving structural savings.

For an efficient compensation of the horizontal components of the magnetic field generated by the circulation of the electrolysis current IE, that is to say in order to have antisymmetric horizontal components, the first portion 34 of the support 30 of the anode assembly 14 and the second portion 36 of the support 30 of the anode assembly 14 are configured so that the intensity of the electrolysis current fraction traversing an upstream half of this second portion 36 is substantially equal to the intensity of the fraction of electrolysis current flowing through a downstream half of this second portion 36. In other words, and as shown in FIG. 8, the intensity of the fraction of electrolysis current passing through all the logs located upstream of a longitudinal median plane YZ of the electrolytic cell 10 is substantially equal to the intensity of the fraction of electrolysis current passing through all the logs located on the side downstream of this longitudinal median plane YZ. In particular, as is apparent from the segment S9 of FIG. 8 read in combination with the table of FIG. 9, part of the upstream electrolysis stream IEA reaches the logs located downstream of the median plane YZ of the tank 10d. 'electrolysis. This is achieved through overall electrical balancing of the different conductor sections.

The principle of compensation or magnetic balancing of the aluminum smelter 1 according to the invention makes it possible for the smelter 1 to obtain a conductor circuit that can be made in a modular manner, as illustrated in FIG. 7. Each module M can comprise for example, an electrical conductor of the first compensation electric circuit 4 and a number of routing conductors 24 and associated rising and connecting conductors 22 for each electrolytic cell 10. The fact is that the electrical conductors included in each module M (rising and connecting conductors 22, anode assembly 14, cathode 16, cathode conductors 18, cathodic outputs 20, routing conductors 24, electrical conductors of the first compensation circuit 4 ) are configured to generate the same predetermined magnetic configuration. In other words, the electrical conductors of each module M are arranged and traversed by currents such that each module M generates the same vertical and horizontal components of the magnetic field.

The conductor circuit, and therefore each electrolysis cell, may be composed of a number N of modules M, determining the length of the electrolytic cells and the intensity of the current flowing through the electrolytic cells ( the intensity of the electrolysis current IE flowing in the series of electrolysis cells being equal to the intensity of the fraction of electrolysis current passing through each module M multiplied by the number N of modules M).

It is important to specify that, given the magnetic configuration of each module M, the choice of the number N of modules M per electrolytic cell 10, compensated by the secondary compensation circuit 6 on the tank ends, does not disturb that little the magnetic equilibrium of the electrolytic cells. This makes it possible to obtain an optimal magnetic configuration for amperages above 1000 kA or even 2000 kA when designing or extending the length of the electrolytic cells 10 by the addition of such modules. In contrast, the elongation of autocompensated type of electrolysis tanks or compensated by magnetic compensation circuits arranged on the sides of known tanks of the prior art require complete redrawing of the conductor circuits. Also, the ratio of the amount of material forming the conductor circuit brought back to the production surface of the electrolytic cells does not deteriorate when the electrolysis cells are extended, it increases proportionally to the number N of modules. M and the intensity through the electrolytic tanks. Thus, the electrolysis cells can be elongated simply according to the needs and the intensity of the current passing through them is not limited. The modular construction of the electrical conductors of the electrolytic cells therefore offers an advantage in terms of scalability, since this modular construction, combined with a simple adjustment of the amperage of the secondary compensation circuit, makes it possible to modify the tanks 10 electrolysis without compromising their magnetic and electrical balance.

The table of FIG. 9, read in conjunction with FIG. 8, shows for a module the intensity values going through the various electrically conductive elements of the electrolytic cells, these conductive elements being symbolized by segments: S1 for the drivers rising and upstream connection 22A; S2, S5 and S8 for the first portion 34 of the support 30; S3 and S9 for the second part 36 of the support 30, the anode (s) 32, the electrolytic bath, the aluminum sheet 40, the cathode 16, the cathode conductors 18 and the cathode outlets 20; S4, S6 and S10 for the routing conductors 24; S7 for upstream and downstream conductors 22 B.

It is specified that the sum of intensities i and ia indicated in the table of FIGS. 9, 13 and 14 is equal to the intensity of the upstream electrolysis current IEA divided by the number N of modules of the electrolytic cell; the intensity ib is equal to the intensity of the downstream electrolysis current IEB divided by the number N of modules of the electrolytic cell; the sum of ia and ib is equal to i; the sum of the upstream and downstream electrolysis currents IEA, IEB is therefore equal to 2i multiplied by the number N of modules; and the intensity of the electrolysis current IE flowing through the series of electrolysis cells is equal to the sum of the intensity of the upstream electrolysis current IEA traversing the entire upstream part of the electrolysis cell and the electrolysis cell. intensity of the IEB downstream electrolysis current passing through the entire downstream part of the electrolysis tank, that is to say the product of 2i and the number N of modules of the electrolytic cell. FIGS. 10 to 12 are wired schematic views of the electrical circuit traversed by the electrolysis current in a module of an electrolysis cell 10 of the aluminum plant 1, and showing for this electrolytic cell 10 the three main zones P1, P2, P3 generating a significant disturbing magnetic field: an upstream zone P1, a central intermediate zone P2, and a downstream zone P3 symmetrical to the upstream zone P1 with respect to a longitudinal median plane YZ of the electrolysis cells.

The table of FIG. 13, read in conjunction with FIGS. 10, 11 and 12, schematically shows the vertical component of the magnetic field generated by the electrical conductors (schematically represented by segments) of the electrolytic cell 10, respectively in the three zones P1, P2, P3 of the electrolytic cells 10, by the first and second compensating circuits 4, 6. By adding the contributions of each of these electrical conductors, and that of the first and second compensation circuits 4, 6 it can be seen that the vertical magnetic field component Bz generated by the circulation of the electrolysis current is zero, that is to say perfectly compensated. Thus, MHD instabilities are reduced to a minimum; this offers the possibility of substantially improving the yield.

In addition, the table of FIG. 14, also read in conjunction with FIGS. 10, 11 and 12, schematically shows the horizontal longitudinal component of the magnetic field generated by the circulation of the electrolysis current through the electrical conductors (symbolized by FIG. segments) of the electrolysis cell 10, zone by zone, and through the first and second compensation circuits 4, 6. The horizontal transverse component of the magnetic field is itself antisymmetric because the conductors are symmetrical with respect to XZ plane. By summing the contributions of each segment, and those of the first and second compensating circuits 4, 6, it is found that the horizontal longitudinal component By of the magnetic field is antisymmetric (opposite in the upstream and downstream zones P1, P3, and zero in the central P2 zone). This antisymmetry suppresses the deleterious effects associated with the horizontal components of the magnetic field.

The first compensation electric circuit 4 is described in more detail below.

The first compensation electric circuit 4 extends below the electrolytic cells. This first compensation electric circuit 4 is intended to be traversed by a first compensation current IC1, in the opposite direction of the overall flow direction of the electrolysis current IE, as can be seen in FIGS. 5 and 7. It will be recalled that by IEC 60050 - International Electrotechnical Vocabulary - Details for IEV number 511-21-21 flow direction of the electrolysis current IE is understood to mean the flow direction of the electrolysis current IE on the scale of the aluminum smelter 1 or the lane 2 or queues 10 of electrolysis cells. The first compensation electric circuit 4 comprises electrical conductors which may be metal bars, for example made of aluminum, copper or steel, or, advantageously, electrical conductors of superconducting material, the latter making it possible to reduce the power consumption. and, because of their lower mass than that of the equivalent metal conductors, to reduce the structural costs to support them or to protect them from possible metal flows by means of metal baffles 42 (FIG. 7) or by burying them . Advantageously, these electrical conductors of superconducting material may be arranged to perform several turns in series under the row or rows of tanks, as described in the patent application WO2013007893 in the name of the applicant.

The smelter 1 comprises a feed station 44 configured to circulate through the first compensation electric circuit 4 a current intensity IC1 equal to twice the intensity of the downstream electrolysis current IEB, plus or minus 20% near, and preferably within plus or minus 10%.

This supply station 44 may be a clean power station, that is to say distinct from the supply station 8 supplying electrolysis tanks IE electrolysis current. The power supply station 44 of the first compensation circuit 4 is therefore exclusively dedicated to supplying this first compensation circuit 4.

The first electrical compensation circuit 4 is thus also independent of the main electric circuit traversed by the electrolysis current IE comprising in particular the row or rows 2 of electrolytic cells. If the first compensating electrical circuit 4 is damaged, for example a piercing of one of the electrolytic tanks 10 by the liquids contained in the electrolytic cells, whose temperature is close to 1000.degree. Electrolysis can continue, with less efficiency, however, since the magnetic compensation is impacted. In addition, the intensity of the first compensation current IC1 is modifiable independently of the electrolysis current IE. This is of paramount importance in terms of scalability and adaptability. On the one hand because, in the event of an increase in the intensity of the electrolysis current IE during the lifetime of the aluminum smelter 1, this makes it possible to adapt the magnetic compensation to this evolution, by varying the intensity of the first compensation current IC1 as needed. On the other hand because it makes it possible to adapt the amperage of the first compensation current IC1 to the characteristics and the quality of the available alumina. This makes it possible to control the speed of the MHD flows to promote or limit the mixing of the liquids and the dissolution of the alumina in the bath according to the characteristics of the available alumina, which in fine contributes to the best possible yield considering the supply of alumina.

The electrical conductors of the first compensation electric circuit 4 extend under the electrolysis cells together forming a sheet of parallel electrical conductors, preferably from two to twelve, and preferably from three to ten parallel electrical conductors. In other words, in longitudinal section of an electrolytic cell 10, that is to say in a longitudinal plane YZ of the electrolytic cell 10, as shown in FIG. 7, the first circuit Electrical compensation 4 extends under several places of the electrolytic tank 10. It will be noted that the first compensation current IC1 flows in the opposite direction of the overall flow direction of the electrolysis current IE, through all the electrical conductors forming the layer. The web may be formed by the same electrical circuit forming several turns or loops in series under the electrolytic cells, each loop corresponding to an electrical conductor of the web. Alternatively, the sheet may be formed by dividing into a parallel electrical conductor bundle of the first compensation electric circuit 4, the latter possibly forming a single loop under the electrolysis cells.

The intensity of the first compensation current IC1 is equal to the sum of the intensities of the compensation current flowing through each electrical conductor of the sheet. Preferably, the intensity of the first compensation current IC1 in each electrical conductor of the ply is equal to the intensity of the first compensation current IC1 divided by the number of electrical conductors of this ply.

The electrical conductors of the web are advantageously equidistant from each other. The same distance separates two adjacent electrical conductors from the web. This further improves the compensation of the adverse magnetic field.

The electrical conductors of the web can extend parallel to each other. They extend preferably parallel to the transverse direction X of the electrolytic cells. Moreover, the electrical conductors forming the web may be all arranged in the same horizontal plane XY. This also makes it possible to improve the compensation of the magnetic field generated by the circulation of the electrolysis current.

In addition, the electrical conductors of the ply may extend substantially symmetrically with respect to the transverse median plane XZ of the electrolysis cells, that is to say with respect to the plane perpendicular to the longitudinal direction Y, this plane separating the electrolysis tanks in two substantially equal halves. According to the example of FIG. 7, the first compensation electrical circuit 4 forms a sheet of three substantially equidistant conductors and arranged in the same substantially horizontal plane XY. This sheet comprises as many electrical conductors as the electrolytic cell 10 comprises modules M.

In fact, the sheet is advantageously configured so that each module M of the electrolytic cell 10 comprises the same number of electrical conductors of the first compensation electric circuit 4. This makes it possible to obtain a compensation of the magnetic field per module, which produces better effects and offers a significant advantage in terms of implementation and scalability.

The second compensation electric circuit 6 is described in more detail below.

The second compensation electric circuit 6 extends over at least one transverse side of the electrolytic cells 10 substantially parallel to the transverse direction X of the electrolysis cells 10, that is to say, parallel to the line (s) 2 of electrolytic cells. The second compensation electric circuit 6 is intended to be traversed by a second compensation current IC2, in the same direction as the overall flow direction of the electrolysis current IE.

Preferably, the second electric compensating circuit 6 extends along the two transverse sides of the electrolytic cells 10, as illustrated in FIG. 5. In this case, the internal conductors 61 denote the electrical conductors of the second compensation circuit 6 which are located between the first two adjacent rows 2 of electrolytic cells 10, and by external loop 62 the electrical conductors of the second electric compensation circuit 6 which are located on the outside of the lines 2 of tanks 10 of electrolysis, that is to say on the other side of the electrolytic cells 10 with respect to the electrical conductors forming the inner loop 61. The inner loop 61 is traversed by a second compensation current IC21 and the outer loop 62 is traversed by a second compensation current IC22. The second compensation currents IC21 and IC22 move in the same direction. The sum of the currents IC21 and IC22 flowing respectively in the inner loop 61 and in the outer loop 62 is equal to the compensation current IC2. The inner loop 61 and / or the outer loop 62 may optionally make several turns in series; if necessary, the intensity of the current IC21, respectively IC22, is the product of the number of turns in series by the intensity of the current flowing in each series tower.

The aluminum smelter 1 comprises a feed station 46 which is advantageously configured to circulate through the second compensation electric circuit 6 (internal loop 61 and / or external loop 62) a total intensity (where appropriate, loop internal 61 plus outer loop 62) compensation current IC2 between 50% and 100% of the difference in intensity between the upstream and downstream electrolysis currents, and preferably between 80% and 100% of the difference in intensity between the upstream and downstream electrolysis currents. This intensity value, set as a function of the asymmetrical distribution of the electrolysis current IE in each electrolytic cell, offers, in synergy with the choice of the asymmetrical distribution value IEA, IEB and the intensity of the first one. IC1 compensation current, the best compensation results of the magnetic field, effectively applicable to large electrolytic cells.

Preferably, the intensity of the current IC21 flowing in the inner loop 61 differs from the intensity of the current IC22 flowing in the outer loop 62. More particularly, the intensity of the current IC21 flowing in the inner loop 61 is advantageously greater than 1 intensity of current IC22 flowing in external loop 62.

The current flowing through the inner loop 61 can be increased to compensate for the impact of the neighboring queue on the vertical magnetic field. This increase will have a typical value close to (within 50%) IE2xD61 / DP2, where IE2 = IE- IC1 + IC2 = IE + IEA - 3 IEB and DP2 is the distance from the neighboring queue to the center of the vessel and D61 is the distance of the inner loop 61 in the center of the tank. For a series of conventional electrolysis IE2 is greater than or equal to IE. It can be noted that IE + IEA - 3 IEB is much lower than IE. This is a gain of this design that allows the approximation of the neighboring queue because the creation of the magnetic field by the neighboring queue is much lower at no extra cost compared to what is known to those skilled in the art.

The supply station 46 supplying the second compensation circuit 6 may be a clean power station, that is to say distinct from the supply station 8 supplying the electrolysis cells with electrolysis current. IE and distinct from the power supply station 44 supplying the first compensation electric circuit 4. The power supply station 46 of the second compensation circuit 6 is therefore exclusively dedicated to supplying this second compensation circuit 6. The second The compensation electric circuit 6 is thus also independent of the main electrical circuit traversed by the electrolysis current IE. The intensity of the second compensation current IC2 can be modified independently of the electrolysis current IE, thus offering substantial advantages in terms of scalability and adaptability of the aluminum smelter 1, as explained above with regard to the first compensation electric circuit 4 Advantageously, the second compensation circuit 6 may also be distinct from the first compensation circuit 4. When the second electric compensation circuit 6 extends on both sides of the electrolytic cells 10, the electrical conductors forming this second electrical compensation circuit 6 can advantageously be symmetrical with respect to a median transverse plane XZ of the electrolysis cells 10. . This improves the compensation of the deleterious magnetic field.

Moreover, still with a view to effectively compensating for this magnetic field created by the flow of the electrolysis current IE, the electrical conductors of the second compensation electric circuit 6 advantageously extend in the same horizontal plane XY. Preferably, this XY horizontal plane is located at the height of the liquid aluminum sheet 40 formed inside the electrolytic cells during the electrolysis reaction.

It will be noted that the electrical conductors forming the second compensation electric circuit 6 may advantageously be configured so as to limit the "end of line" effects, as shown in FIG. 5.

The electrical conductors forming the second electric compensation circuit 6 can be metal bars, for example made of aluminum, copper or steel, or, advantageously, electrical conductors of superconducting material, the latter making it possible to reduce the energy consumption. and because of their lower mass than the equivalent metal conductors, reduce the structural costs to support them. Advantageously, these electrical conductors of superconducting material may be arranged to perform several turns in series on the side or sides of the rows 2 of electrolytic cells 10, as described in the patent application WO2013007893 in the name of the applicant.

The invention also relates to a method for compensating the magnetic field created by the circulation of an electrolysis current IE in the electrolysis cells of the aluminum smelter 1 described above. This process comprises:

circulating the first compensation current IC1 through the first compensation electric circuit 4 in the opposite direction of the overall circulation direction of the electrolysis current IE,

circulating, in the same direction of flow as the overall flow direction of the electrolysis current IE, the second compensation current IC2 through the second compensation electric circuit 6.

The method also advantageously comprises the fact of asymmetrically distributing the electrolysis current IE between the upstream and upstream electrical connection conductors 22A and the upstream and downstream electrical connection conductors 22B. This step of asymmetrically distributing the electrolysis current between the upstream and the downstream of the electrolysis cells comprises separating the electrolysis current IE into an upstream electrolysis current IEA, which circulates through all the electrolysis streams. upstream electrical connection and upstream connection conductors 22A of each electrolytic cell, such that the intensity of the upstream electrolysis current IEA is between 50-100 [% of the intensity of the electrolysis current IE, and in a downstream electrolysis current IEB, which circulates through all of the upstream and downstream electrical connection conductors 22B of each electrolytic cell 10, so that the intensity of the downstream electrolysis current IEB is included between 0-50 [% of the intensity of the electrolysis current IE, the sum of the intensities of the upstream and downstream electrolysis currents IEA, IEB being equal to the intensity of the electrolysis current IE.

The step of circulating the first compensation current IC1 is advantageously such that the intensity of the first compensation current IC1 is equal to twice the intensity of the downstream electrolysis current IEB, within plus or minus 20%, and preferably within plus or minus 10%.

The step of circulating the second compensation current IC2 is advantageously such that the total intensity (internal loop 61 + external 62) of the second compensation current IC2 is between 50% and 100% of the difference in intensity between the upstream IEA and downstream IEB electrolysis currents, and preferably between 80% and 100% of the difference in intensity between the upstream and downstream electrolysis currents.

For these values of intensities of the upstream electrolysis current IEA, the downstream electrolysis current IEB, the first compensation current IC1 and the second compensation current IC2, the Applicant has found that the magnetic field generated by the flow of current electrolysis is most effectively compensated.

In addition, the intensity of the current IC21 flowing in the inner loop 61 may differ from the intensity of the current IC22 flowing in the outer loop 62. More particularly, the intensity of the current IC21 flowing in the inner loop 61 is advantageously greater than the intensity of the current IC22 flowing in the outer loop 62.

Furthermore, the process may advantageously comprise a step of analyzing at least one characteristic of the alumina in at least one of the electrolysis tanks of the aluminum smelter 1 described above, and the determination of a distribution of values. the intensity of the upstream and downstream electrolysis currents IEA, IEB to be circulated as a function of this analyzed characteristic, which also defines, if appropriate, the intensity values of the first and second compensation currents IC1, IC2 and, where appropriate upstream and downstream electrolysis currents IEA, IEB. The intensity values of the first and second compensation currents IC1, IC2, and possibly upstream and downstream electrolysis currents IEA, IEB, can then be modified up to the values determined above if the intensity values of the first and second compensation currents IC1, IC2 and upstream and downstream electrolysis currents IEA, IEB initials differ from the values thus determined. Thus, the method makes it possible to modify the magnetic compensation, in order to increase or reduce the stirring of the liquids while controlling the MHD instabilities. In general, the higher the mixing (or the flow) of the liquids, the more effective the dissolution of alumina, but the more the bath / metal interface will be unstable (= instability MHD), which can degrade the yield of the liquids. tanks. Such a method is particularly advantageous with the configuration of the electrical conductors described above because it renders the electrolytic cells 10 magnetically very stable and therefore offers a greater range for modulating / optimizing the stirring depending on the quality of the alumina . The characteristics of the alumina analyzed can notably be the ability of the alumina to dissolve in the bath, the fluidity of the alumina, its solubility, its fluorine content, its humidity, etc.

The determination of a distribution of intensity values of the upstream and downstream compensation currents IEA, IEB and / or intensity values of the first and second compensation currents IC1, IC2 as a function of the characteristics of the analyzed alumina may be in particular carried out using an abacus, for example made by a person skilled in the art by calculation, experimentation and recording of the optimum correspondences intensities of upstream and downstream electrolysis currents IEA, IEB / characteristics of alumina. It is a question here of quantifying the intensity of the mixing of the desired liquid with regard to the level of instabilities MHD.

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

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

Claims

1. Smelter (1) comprising at least one line (2) of electrolysis tanks (10) arranged transversely to the length of said at least one line (2), one of the electrolytic cells (10) comprising anode assemblies (14) and electrical conductors for mounting and connecting (22) to the anode assemblies (14), characterized in that the rising and connecting electrical conductors (22) extend upwards along two edges longitudinal members (38) of the electrolytic cell (10) for conducting the electrolysis current (IE) to the anode assemblies (14), and in that the illumination (1) comprises:

at least one first compensation electric circuit (4) extending under the electrolytic cells (10), said at least one first compensation electric circuit (4) being traversed by a first compensation current (IC1) for circulating under the electrolytic cells (10) in the opposite direction to the overall flow direction of the electrolysis current (IE),

at least one second compensation electric circuit (6) extending over at least one side of said at least one electrolysis cell line (2), said at least one second compensation electric circuit (6) being to be traversed by a second compensation current (IC2) intended to flow in the same direction as the overall flow direction of the electrolysis current (IE).

An aluminum smelter (1) according to claim 1, wherein the rise and connect electrical conductors (22) comprise upstream and upstream electrical connection conductors (22A), adjacent to the upstream longitudinal edge (38) of the vessel ( 10), and upstream and downstream electrical conductors (22B), adjacent to the downstream longitudinal edge (38) of the electrolysis cell (10), and the aluminum plant (1) is configured so that the distribution of the electrolysis current (IE) is asymmetrical between the electrical conductors upstream and upstream connection (22A) and downstream (22B), the intensity of the upstream electrolysis current (IEA) intended to travel all drivers electrical upstream and upstream connection (22A) of the electrolysis tank (10) being equal to 50-100 [% of the intensity of the electrolysis current (IE), and the intensity of the electrolysis current downstream (IEB) intended to cover all the electrical conductors of mo and downstream connection (22B) of the electrolytic tank (10) being equal to] 0-50 [% of the intensity of the electrolysis current (IE), the sum of the intensities of the upstream electrolysis currents and downstream (IEA), (IEB) being equal to the intensity of the electrolysis current (IE).

The smelter (1) according to claim 2, wherein the smelter comprises a supply station (44) configured to circulate through said at least one first compensation electric circuit (4) a first compensation current (IC1 ) of intensity equal to twice the intensity of the downstream electrolysis current (IEB), within plus or minus 20%, and preferably within plus or minus 10%.

4. Aluminerie (1) according to claim 2 or 3, wherein the aluminum smelter (1) comprises a feed station (46) configured to circulate through said at least one second compensation electric circuit (6) a second compensation current (IC2) of intensity between 50% and 100% of the difference in intensity between the upstream and downstream electrolysis currents (IEA, IEB), and preferably between 80% and 100% of the difference of intensity between the upstream and downstream electrolysis currents (IEA, IEB).

5. Aluminerie (1) according to one of claims 1 to 4, wherein the rising and connecting electrical conductors (22) are distributed at regular intervals along the longitudinal edge (38) of the tank (10) of electrolysis to which these electrical risers and connection leads (22) are adjacent.

6. Aluminerie (1) according to one of claims 1 to 5, wherein the upstream electrical conductors and upstream connection (22A) and the electrical conductors upstream and downstream connection (22B) are located equidistant from a longitudinal median plane (YZ) of the electrolytic cell (10).

7. Aluminerie (1) according to claim 6, wherein the upstream electrical conductors and connection (22) upstream (22A) and the electrical conductors upstream and downstream connection (22B) are arranged substantially symmetrically with respect to said longitudinal median plane (YZ) of the electrolytic cell (10).

8. Aluminerie (1) according to one of claims 1 to 7, wherein said at least a first compensation electric circuit (4) comprises electrical conductors extending under the cells (10) of electrolysis forming together a ply consisting of a plurality of parallel electrical conductors, typically from two to twelve, and preferably from three to ten parallel electrical conductors.

9. Aluminerie (1) according to claim 8, wherein the electrical conductors of said web are arranged at regular intervals from each other in a longitudinal direction (Y) of the electrolytic cells (10).

10. Aluminerie (1) according to claim 8 or 9 wherein the electrical conductors of said web are arranged substantially symmetrically with respect to a transverse median plane (XZ) of the electrolytic cells (10).

1 1. Aluminerie (1) according to one of claims 8 to 10, wherein the electrical conductors of said web are arranged in the same horizontal plane (XY).

12. Aluminerie (1) according to one of claims 1 to 1 1, wherein said at least one second electrical compensation circuit (6) comprises electrical conductors extending on each side of said at least one line (2) of electrolytic cells (10), and the second compensation current (IC2) flows in the same direction as the overall flow direction of the electrolysis current (IE) on each side of the electrolytic cells (10).

13. Aluminerie (1) according to claim 12, wherein the intensity of a second compensation current (IC21) flowing in an inner loop of said at least one second compensation circuit (6) differs from the intensity of a second compensation current (IC22) flowing in an external loop of said at least one second compensation circuit (6).

14. Aluminerie (1) according to claim 13, wherein the intensity of the second compensation current (IC21) flowing in the inner loop is greater than the intensity of the second compensation current (IC22) flowing in the outer loop.

15. Aluminerie (1) according to one of claims 12 to 14, wherein the electrical conductors forming the second electric compensation circuit (6) are substantially symmetrical with respect to a plane (XZ) median transverse tanks (10) d 'electrolysis.

16. Aluminerie (1) according to one of claims 12 to 15, wherein the electrical conductors of the second compensation electric circuit (6) extend in the same horizontal plane (XY), preferably up to a tablecloth liquid aluminum (40) formed inside the electrolytic cells (10) during the electrolysis reaction.

17. Aluminerie (1) according to one of claims 1 to 16, wherein said at least a first compensation electric circuit (4) is independent of the main electrical circuit traversed by the electrolysis current (IE).

18. Aluminerie (1) according to one of claims 1 to 17, wherein said at least one second compensation electric circuit (6) is independent of the main electrical circuit traversed by the electrolysis current (IE).

19. Smelter (1) according to one of claims 1 to 18, wherein the electrolysis tank (10) has a modular electrical construction in N modules (M) repeated in the direction of its length, each module (M) comprising electrical conductors configured to generate the same predetermined magnetic pattern.

Method for compensating a magnetic field created by the circulation of an electrolysis current (IE) in a plurality of electrolysis tanks (10) of an aluminum smelter (1) according to one of claims 1 to 19, the method comprising: circulating, in the opposite direction of the overall flow direction of the electrolysis current (IE), a first compensation current (IC1) through said at least one first compensation electric circuit (4) circulating, in the same direction as the overall flow direction of the electrolysis current (IE), a second compensation current (IC2) through said at least one second compensation electric circuit (6).

21. The method of claim 20, wherein the method comprises an asymmetrical distribution of the electrolysis current (IE) between the upstream and downstream electrolysis tanks (10), the set of electrical conductors rise and connection (22) upstream of the electrolysis tanks (10) is traversed by an upstream electrolysis current (IEA) of intensity of between 50-100 [% of the intensity of the electrolysis current ( IE), and all of the electrical conductors for mounting and connection (22) downstream of the electrolysis tanks (10) being traversed by a downstream electrolysis current (IEB) of intensity of between 0.degree. 50 [% of the intensity of the electrolysis current (IE), the sum of the intensities of the upstream and downstream electrolysis currents (IEA), (IEB) being equal to the intensity of the electrolysis current (IE).

22. The method of claim 21, wherein the intensity of the first compensation current (IC1) is equal to twice the intensity of the downstream electrolysis current (IEB), within plus or minus 20%, and preferably to plus or minus 10%.

23. The method of claim 21 or 22, wherein the intensity of the second compensation current (IC2) is between 50% and 100% of the difference in intensity between the upstream and downstream electrolysis currents (IEA, IEB ), and preferably between 80% and 100% of the difference in intensity between the upstream and downstream electrolysis currents (IEA, IEB).

24. Method according to one of claims 20 to 23, wherein said at least one second compensation electric circuit (6) comprises an inner loop and an outer loop, and wherein the intensity of a second compensation current ( IC21) flowing in the inner loop differs from the intensity of a second compensation current (IC22) flowing in the outer loop.

25. The method of claim 24, wherein the intensity of the second compensation current (IC21) flowing in the inner loop is greater than the intensity of the second compensation current (IC22) flowing in the outer loop.

26. Method according to one of claims 20 to 25, wherein the method comprises a step of analyzing at least one characteristic of alumina in at least one of the electrolytic cells (10) of said aluminum smelter (1). ), and determining the intensity values of the first compensation current (IC1) and the second compensation current (IC2) to be circulated as a function of the at least one analyzed characteristic.