OA18402A - Aluminum smelter and process for compensating a magnetic field created by the circulation of electrolysis current from this smelter. - Google Patents

Abstract

This aluminum smelter (1) comprises a row (2) of electrolysis cells arranged transversely with respect to the row (2), one of the cells comprising anode assemblies and electrical conductors for rising and connecting to the anode assemblies. The rising and connecting conductors extend upwards along two opposite longitudinal edges of the cell. In addition, the aluminum 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), a second electrical compensation circuit (6) extending on one side of the row (2) and capable of carrying a second compensation current (IC2) in the same direction as the electrolysis current (IE).

Description

Aluminum smelter and process for compensating a magnetic field created by the flow of electrolysis current from this smelter

The present invention relates to an aluminum smelter, intended for the production of aluminum by electrolysis, and a method for 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, an electrolysis cell is provided comprising a steel box inside which is arranged a coating of refractory materials, a cathode of carbonaceous material, through which cathode conductors intended to collect the electrolysis current to be collected. the cathode to lead it to cathode outputs crossing the bottom or the sides of the box, routing conductors extending substantially horizontally to the next tank from the cathode outputs, an electrolytic bath in which 15 l is dissolved 'alumina, at least one anode assembly comprising at least one anode immersed in this electrolytic bath, an anode frame from which the anode assembly is suspended, and electrolysis current rise conductors, extending from bottom to top, connected to the routing conductors of the previous electrolytic cell to convey the electrolysis current from the cathode outputs to the anode frame and to the anod assembly ic and the anode of the next tank. The anodes are more particularly of the prebaked anode type with prebaked carbonaceous blocks, that is to say, cooked before introduction into the electrolytic cell.

Aluminum production plants, or smelters, traditionally include several hundred electrolytic cells, aligned transversely in parallel rows 25 and connected in series.

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These electrolysis cells carry an electrolysis current of the order of several hundred thousand Amps, which creates a strong magnetic field. The vertical component of this magnetic field, generated primarily by the routing conductors carrying current from one electrolytic 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 cell, the greater the interpolar distance between the anode and the sheet of metal must be. However, the greater the interpolar distance, the greater the energy consumption of the method, since it is dissipated by the 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 located inside the tank and those located outside, interact with the electric current passing through. liquids, which causes a stationary deformation of the metal sheet. The drop in the layer of metal caused must remain low enough so that the anodes are consumed uniformly with little waste. To obtain a small difference in level, the horizontal components of the magnetic field must be as antisymmetrical as possible in liquids (electrolytic bath and metal sheet). For the longitudinal and transverse components of the magnetic field which constitute the horizontal components, by antisymmetric is meant that when one moves perpendicular to the central axis of the vessel, parallel to the considered component of the field, and when one moves is located at an 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 15 providing the most symmetrical and flattest interface strain possible in the vessel.

It is known, in particular from patent documents FR1079131 and FR2469475, to combat MHD instabilities by compensating for the magnetic field created by the circulation of the electrolysis current, thanks to a particular arrangement of the conductors conducting the electrolysis current. For example, according to patent document FR2469475, the routing conductors laterally bypass the ends or heads of each electrolysis cell. We talk about self-compensation. This principle is based on 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 a significant lateral congestion since the electrical conductors bypass the heads of electrolytic cells.

Above all, the large length of the routing conductors for the implementation of this solution generates electrical loss in line by resistive effect of the conductors, therefore an increase in operating costs, and requires a lot of raw material, therefore costs. high workmanship. These drawbacks are all the more marked as the electrolysis cells have large dimensions and operate with high intensities.

Also, the design of an aluminum smelter with a self-compensating electrical circuit is fixed. 35 However, during life, it may become necessary to increase the intensity of the electrolysis current, beyond the intensity foreseen in the design. This also modifies in fact the distribution of the magnetic field of the self-compensating electric circuit, not designed for this new distribution, which no longer allows this magnetic field to be optimally compensated. There are solutions to overcome this lack of scalability and to 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, running alongside the rows of electrolytic cells, on the sides. This secondary electrical circuit is traversed by a current the intensity of which 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 from the neighboring row of electrolytic cells.

It is also known from patent document EP0204647 the use of a secondary circuit running along the lines of electrolytic cells on the sides to reduce the effect of the magnetic field generated by the routing conductors, the intensity of the current. flowing through the electrical conductors of this secondary circuit being 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 through which the electrolysis current flows.

The arrangement of the secondary circuit, located on the sides of the cell lines near the short sides of the caissons, 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 supply station and an additional independent secondary electrical circuit.

It should also be noted that the external loop compensation solution involves an accumulation of magnetic fields, with the series current, creating a very strong total ambient field, so that this implies constraints on the operations and the material (for example shielding necessary vehicles), and so that the magnetic field of one row impacts the stability of the tanks of the neighboring row. To limit the influence of a row 35 on the neighboring row, it is necessary to move them away from one another, which constitutes a significant spatial constraint and consequently involves sheltering each row of electrolytic cells. in a separate hangar.

Furthermore, the junction portion of the electrolysis circuit and of the secondary circuit joining the ends of two adjacent rows of electrolysis cells tends to destabilize the 5 end of row cells. To avoid having unstable end-of-line tanks, it is possible to configure this portion of the secondary circuit according to a predetermined path, as is known from patent FR2868436, in order to correct the magnetic field so that the impact on the tanks end of line becomes acceptable. However, this path lengthens in particular the length of the secondary circuit, and therefore the material cost. It should be noted that the usual solution consists in moving the junction portion of the secondary circuit and of the electrolysis circuit away from the cells located at the end of the line, but this increases the bulk in addition to increasing the length of the electrical conductors. material and energy cost.

It will therefore be remembered that the known solutions for compensation by external loop 15 generate relatively high structural costs.

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

To this end, the present invention relates to an aluminum smelter comprising at least one row of electrolysis cells arranged transversely with respect to the length of said at least one row, one of the electrolysis cells comprising anode assemblies and electrical conductors. of rise and connection to the anode assemblies, characterized in that the electrical rise and connection conductors extend upwardly along two opposite longitudinal edges of the electrolytic cell to conduct the electrolysis current to them. anode assemblies, and in that the aluminum smelter comprises

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

- at least one second electrical compensation circuit extending on at least one side of said at least one row of electrolytic cells, said at least one second electrical compensation circuit capable of being traversed by a second compensation current intended to flow in the same direction as the overall direction of flow of the electrolysis current.

Thus, the aluminum smelter according to the invention offers the advantage of having very magnetically stable cells, 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 that without negative impact on the size of the aluminum smelter according to the invention since the first electrical compensation circuit extends under the electrolytic cells.

According to a preferred embodiment, the upstream and connection electrical conductors comprise upstream electrical rise and connection conductors, adjacent to the upstream longitudinal edge of the electrolytic cell, and downstream rise and connection electrical conductors, adjacent. 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 connection and upstream electrical conductors, the intensity of the upstream electrolysis current intended to run through all the upstream electrical conductors and connection of the electrolytic cell being equal to] 50-100 [% of the intensity of the electrolysis current, and the intensity of the downstream electrolysis current intended to run through all of the upstream electrical conductors and downstream connection of the electrolytic cell being equal to] 0-50 [% of the intensity of the electrolysis current, the sum of the intensities of s upstream and downstream electrolysis currents being equal to the intensity of the electrolysis current.

One advantage of these characteristics is that they allow the magnetic field to be effectively compensated for a large-size electrolysis cell, in particular a large one, without additional raw material costs.

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

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

According to a preferred embodiment, the aluminum smelter comprises a supply station 10 configured to circulate through said at least one first electrical compensation circuit a first compensation current of intensity equal to twice the intensity of the current d 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 downstream of the electrolytic cells, the applicant has observed that the horizontal magnetic field generated by the first electric compensation circuit precisely corrects the dissymmetry of the horizontal magnetic field resulting from the dissymmetry between the upstream and downstream electrolysis 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 partially correct the vertical magnetic field, as a function of the distribution between electrolysis current upstream and downstream of the cell, in order to reduce MHD instabilities in the cell.

According to a preferred embodiment, the aluminum smelter comprises a supply station 25 configured to circulate through said at least one second electrical compensation circuit a second compensation current with an intensity of between 50% and 100% of the difference. 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.

The intensity of the second compensation current is understood to mean the sum of the currents circulating in the conductors forming the second compensation circuit, in particular when the second compensation circuit consists of two conductors (or loops) arranged on either side of the electrolytic cell.

The Applicant has observed that for this value of intensity of the second compensation current, which is also directly dependent on the distribution of the electrolysis current between the upstream and downstream of the electrolytic cells, the vertical magnetic field generated by the second electrical compensation 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 preceding one.

According to a preferred embodiment, the rising and connecting electrical conductors are distributed at regular intervals along the longitudinal edge of the electrolytic cell 10 to which these rising and connecting electrical conductors are adjacent.

An advantage of this characteristic is to have a uniform distribution over the entire length of the cell of the longitudinal horizontal component of the magnetic field (i.e. 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 electrolytic 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 conductors and connection and the upstream electrical conductors and downstream connection are located equidistant from a longitudinal median plane YZ of the electrolytic cell.

According to a preferred embodiment, the upstream electrical conductors and connection and the upstream electrical conductors and downstream connection are arranged substantially symmetrically with respect to said longitudinal median plane YZ of the electrolytic 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 electrical compensation 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 these same conductors. The greater the distance, the smaller the number of drivers, the shorter the distance, the more drivers should be.

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

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 one another in a longitudinal direction Y of the 15 electrolytic cells.

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

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

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

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

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

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. a second compensation circuit.

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

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 line. This neighboring line creates a magnetic field proportional to a current of the series from which we subtract twice the downstream electrolysis current, while a series of "conventional" electrolysis will experience a magnetic field directly proportional to the total current of electrolysis. Thus, thanks to the first compensation circuit, the disturbing field created by the neighboring queue is much weaker and requires much less correction. Consequently, concerning 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 difference 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 XZ plane of the electrolytic cells.

This improves the compensation of the deleterious magnetic field.

According to a preferred embodiment, the electrical conductors of the second electrical compensation circuit extend in the same XY horizontal plane, preferably at the height of a sheet of liquid aluminum formed inside the electrolytic 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 smelter comprises two consecutive and parallel rows of electrolytic cells, and the circuit of the internal loop forms at the end of the row means for compensating for the “end of row” effects caused by the connecting conductors between them. lines, which provides more magnetic stability and therefore improves the efficiency of the end-of-line tanks.

According to a preferred embodiment, said at least one first electrical compensation circuit is independent of the main electrical circuit through which the electrolysis current flows.

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

According to a preferred embodiment, said at least one second electrical compensation circuit is independent of the main electrical circuit through which the electrolysis current flows.

As explained above, this has an advantage in terms of scalability since it allows the intensity of the first compensation current to be varied to adjust the magnetic compensation.

According to a preferred embodiment, the electrolytic 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 expansion by adding one or more modules, without modifying the principle of magnetic balancing of the electrolysis 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 are in particular the rise and connection electrical conductors, the anode assemblies, the cathodes, the cathode conductors, the cathode outputs, the electrical routing conductors, and electrical conductors of the sheet of electrical conductors. of the first electrical compensation circuit. These electrical conductors are therefore 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 sheet of electrical conductors of the first electrical compensation circuit.

It is specified that the smelter's electrolysis cells include all or part of the aforementioned characteristics of the electrolysis 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 opposite direction to the overall direction of flow of the electrolysis current, of a first compensation current through said at least one first electrical compensation circuit,

- the circulation, in the same direction as the overall direction of circulation of the electrolysis current, of a second compensation current through said at least one second electrical compensation circuit.

Thus, this process provides efficient magnetic compensation of the magnetic field generated by the flow of electrolysis current in the smelter's series of electrolytic cells, while limiting the bulk.

According to a preferred embodiment, the method comprises an asymmetric distribution of the electrolysis current between the upstream and downstream of the electrolytic cells, all of the upstream electrical conductors and connection of the upstream cells of the electrolytic cells. 'electrolysis being traversed by an upstream electrolysis current with an intensity of between] 50-100 [% of the intensity of the electrolysis current, and all the electrical conductors for raising and connecting downstream of the tanks electrolysis being traversed by a downstream electrolysis current with an 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 the intensity of electrolysis current.

This process makes it possible to obtain electrolytic cells which are magnetically stable, even when the electrolysis cells are large in size, especially large in width. The yield can thus be significantly increased.

According to a preferred embodiment, the intensity of the first compensation current is equal to twice the intensity of the downstream electrolysis current, to within plus or minus 20%, and preferably to 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 downstream of the electrolytic cells, the applicant has observed that the horizontal magnetic field generated by the first electrical compensation 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, depending on the distribution between electrolysis current upstream and downstream of the vessel, in order to reduce MHD instabilities in the vessel.

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.

Likewise, the Applicant has observed that for this intensity value of the second compensation current, which is also a direct function of the distribution of the electrolysis current between the upstream and downstream of the electrolytic cells, the vertical magnetic field generated by the second electrical compensation circuit precisely corrects the remaining vertical magnetic field, resulting from the sum of the vertical magnetic field of the electrolysis current (cell-to-cell circuit) and the first compensation circuit.

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

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.

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 determining the intensity values of the first current. compensation and the second compensation current to be circulated as a function of said at least one analyzed characteristic.

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

Other characteristics 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 accompanying drawings in which:

- Figure 1 is a schematic view of an aluminum smelter according to the state of the art,

- Figure 2 is a schematic side view of two successive electrolysis cells of the state of the art,

- Figure 3 is a schematic wired view of the electrical circuit through which the electrolysis current flows in the two electrolysis tanks of Figure 2,

- Figure 4 is a schematic sectional view along a vertical longitudinal plane of an electrolysis cell of the state of the art,

- Figure 5 is a schematic view of an aluminum smelter according to one embodiment of the invention,

- Figure 6 is a schematic side view of two successive electrolytic cells of an aluminum smelter according to one embodiment of the invention,

- Figure 7 is a schematic sectional view along a longitudinal plane YZ of an electrolysis cell of an aluminum smelter according to one embodiment of the invention,

- Figure 8 is a wireframe schematic view of the electrical circuit through which the electrolysis current flows in an electrolytic cell of an aluminum smelter according to one embodiment of the invention,

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

- Figures 10 to 12 are wire diagrammatic views of the electrical circuit through which the electrolysis current flows in an electrolysis cell of an aluminum smelter according to one embodiment of the invention, showing for this electrolysis cell the areas generating a significant magnetic field,

- Figure 13 is a table showing the contribution of each segment of Figures 10 to 12 in the calculation of the vertical component of the magnetic field generated by the flow of electrolysis current,

- Figure 14 is a table showing the contribution of each segment of Figures 10 to 12 in the calculation of the longitudinal horizontal component of the magnetic field generated by the flow of electrolysis current.

FIG. 1 shows an aluminum smelter 100 of the state of the art. The aluminum plant 100 comprises electrolytic cells arranged transversely with respect to the length of the line which they form. The electrolysis cells are here aligned along two rows 101, 102 parallel. These electrolysis cells are traversed by an electrolysis current hoo Two circuits 104, 106 electrical compensation extend on the sides of the lines 101, 102 to compensate for the magnetic field generated by the circulation of the current hoo of electrolysis of a electrolysis cell to another and in the neighboring row. The electrical circuits 104, 106 for compensation are respectively traversed by currents hw, hoe flowing in the same direction as the electrolysis current hoo. Power stations 108 supply the series of electrolysis cells and the electrical circuits 104, 106 for compensation. According to this example, for an electrolysis current of intensity 500kA, and taking into account the magnetic disturbances at the “end of the line”, the distance D100 between the electrolysis cells closest to the supply stations 108 and the stations 108 power supply is of the order of 45m, and the distance D ₃ oo over which the electrical circuits 104, 106 of compensation extend beyond the ends of the line is of the order of 45m, while the distance D ₂ oo between the two lines 101, 102 is of the order of 85m in order to limit the magnetic disturbances from one line to the other.

Figure 2 shows two consecutive traditional electrolysis cells 110 from a single row of electrolysis cells. As can be seen in FIG. 2, the electrolytic cell 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 is formed a sheet 122 d 'aluminum. Cathode 116 is electrically connected to cathode conductors 124 which pass through the sides of well 112 at cathode outputs 126. Cathode outputs 126 are connected to routing conductors 128 which carry electrolysis current to conductors 130. for raising and connecting a subsequent electrolysis cell. As can be seen in Figure 2, these rise and connection conductors 130 extend obliquely on one side, the upstream side, of the electrolysis cells 110 and extend above the anodes. 118, up to the longitudinal central part of the electrolysis cells 110.

The electrolytic cell comprises a superstructure 132 which crosses it longitudinally, above the box 112 and the anodes 118. The superstructure 132 in particular comprises 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 above the box 112 and the anodes 118. The anode frame 134 supports the anode assemblies, the latter being electrically connected to the anode frame 134.

FIG. 3 diagrammatically illustrates the path traveled by the electrolysis current Iwo in each of the electrolysis cells 110 and between two adjacent electrolysis cells 10 like those represented in FIG. 2. It is noted in particular that the rise in the current d 'Iwo electrolysis up to the anode assembly of an electrolysis cell 110 is asymmetrical since this rise is carried out only upstream of the electrolysis cells 110 in the direction of the overall flow of the electrolysis current Iwo in the row (to the left of the tanks in Figures 2 and 3).

FIG. 4 shows the arrangement on the sides of the tanks 110 of the state of the art of electrical conductors forming the electrical compensation circuits 104, 106, these electrical conductors being respectively traversed by the compensation currents Iio4, Iwe circulating in the same direction as the electrolysis current Iwo flowing here through the routing conductors 128 positioned below the tank.

Figure 5 shows an aluminum smelter 1 according to one embodiment of the invention.

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 electrolytic cells, substantially rectangular, intended for the production of aluminum by electrolysis, these electrolysis cells 25 being able to be aligned in one or more rows 2 which may be substantially parallel. If necessary, the lines 2 are electrically connected in series and supplied with electrolysis current IE. The aluminum plant 1 also comprises a first electrical compensation circuit 4, which extends under the row (s) of electrolytic cells, and a second electrical compensation circuit 6, which extends on at least one side of the cell. or rows 2 of electrolysis cells. According to the example of Figure 5, the second electrical compensation circuit 6 extends on both sides of each row 2 of electrolytic cells. Still according to the example of FIG. 5, the aluminum smelter comprises two rows of tanks arranged parallel to each other, supplied by the same supply station 8, and electrically connected in series so that the current 35 electrolysis IE circulating in the first of the two rows 2 of electrolytic cells then circulates in the second of the two rows 2 of electrolysis cells. The electrolysis cells are arranged transversely to each row 2 that these electrolysis cells form. It will be noted that by transversely arranged electrolysis cell 2 means electrolysis cell 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 relative to the overall direction of flow of the electrolysis current IE, that is to say the direction of flow of the electrolysis current IE on the scale of row 2 of electrolysis tanks.

It is also specified that the description is carried out with respect to a Cartesian frame of reference linked to an electrolytic cell, the X axis being oriented in a transverse direction of the electrolysis cell 10, 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 electrolytic cell.

The orientations, directions, planes and longitudinal, transverse and vertical displacements are thus defined in relation to this reference frame.

It will be noted that the electrolysis cells of the aluminum smelter are preferably electrolysis cells of large dimensions, the use of electrolysis cells of large dimensions being made possible by the particular configuration of the electrolysis cells of the aluminum plant. aluminum smelter according to the invention, as described in more detail below. The dimensions of an electrolytic cell are defined by the floor area that this electrolytic cell represents. For this it is considered that the dimensions of the tank are defined by the external dimensions of its casing. By large-size electrolysis cell is meant electrolysis 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 cells 10 of the aluminum smelter 1 according to one embodiment. As illustrated in this figure, the electrolysis cells 10 of the aluminum smelter 1 comprise a box 12, anode assemblies 14, a cathode 16 traversed by cathodic electrical conductors 18 intended to collect the electrolysis current IE at the cathode 16 to lead it to other electrical conductors 30 called cathode outputs 20 outside the box 12, upward and connecting electrical conductors 22 to the anode assemblies 14 to conduct the electrolysis current IE to the anode assemblies 14, and electrical routing conductors 24 connected to the cathode outputs 20 and intended to conduct the electrolysis current IE from the cathode outputs 20 to the electrical conductors 35 for rising and connecting 22 of the next electrolysis cell 10.

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The box 12 comprises an inner lining 26 of refractory materials. As illustrated in Figures 6 and 7, the box 12 preferably comprises reinforcing cradles 28. The box 12 can be metallic, for example steel.

The anode assemblies 14 comprise a support 30 and at least one anode 32. The anode or anodes 32 are in particular made of carbonaceous material and more particularly of the prebaked type. The support 30 comprises 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 electrically conductive part 36, formed of several electrically conductive elements may be called "logs", the logs comprising a distal end electrically connected to the first part 34 of the holder 30 and a proximal end electrically connected to the anode (s) 32 in order to conduct the electrolysis current IE from the first part 34 from 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 anodes 32 are worn.

Cathode 16 can be formed from several cathode blocks made of carbonaceous material. Cathode 16 is crossed by cathode conductors 18 intended to collect the electrolysis current IE at cathode 16 to conduct it to the cathode outputs 20, advantageously exiting through the bottom of well 12, as illustrated in FIG. 6.

The electrical rise and connection conductors 22 extend upwards along two opposite longitudinal edges 38 of each electrolysis cell 10, to conduct the electrolysis current IE to the anode assemblies 14. It is specified that the Longitudinal edges 38 of the electrolytic cells 10 correspond to the edges of greater dimension, that is to say the edges of the electrolytic cells 10 which are substantially parallel to the longitudinal Y direction. By way of example, an electrolysis cell 10 operating with an intensity of 400 to 1000k Amperes may for example preferably comprise 4 to 40 rise and connection conductors 22 distributed regularly over the entire length of each of its two. longitudinal edges 38. The upstream and connection electrical conductors 22 comprise upstream electrical connection and rise conductors 22A, that is to say adjacent to the upstream longitudinal edge 38 of the electrolytic cell 10, and conductors electrical rise and downstream connection 22B, that is to say adjacent to the longitudinal edge 38 downstream of the cell 10 of electrolysis. The upstream and upstream connection electrical conductors 22A are electrically connected to an upstream end of the first part 34 of the support 30, and the downstream rise and connection electrical conductors 22B are electrically connected to a downstream end of this first part 34 support 30.

λ

The electrical routing conductors 24 are connected to the cathode outputs 20 and are intended to conduct the electrolysis current IE from these cathode outputs 20 to the upward and connecting electrical conductors 22 of the next electrolysis cell 10 of the series.

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

A sheet of liquid aluminum 40 is formed during the electrolysis reaction.

It will be noted that the electrolysis cells 10 of the aluminum smelter 1 according to the invention are preferably 10 electrolysis cells 10 of the anode replacement type by ascending vertical traction of the anode assemblies 14 above the cell 10 d. 'electrolysis, as represented by the intermediary of the electrolysis cell 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 straight anodes 32, that is to say without extending 15 in a volume obtained by vertical projection of the area of the anodes 32 projected in a horizontal plane. In addition to the advantage that this represents in allowing a change of anode 32 by ascending vertical traction, it also makes it possible to reduce the length of the rise and connection conductors 22 compared to a use of rise and connection conductors 130 of the type conventional, visible in Figure 2, 20 which typically extend above the cell 110 electrolysis into the longitudinal central part of the cell 110 electrolysis. This helps to reduce manufacturing costs. It is also noted that the horizontal part 34 of the support 30 is supported and connected at each of the two longitudinal edges 38 of each electrolysis cell 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 cells of the state of the art illustrated on FIG. 2. The electrolysis cells 10 of the aluminum smelter 1 according to this embodiment of the invention are therefore free of superstructure. The absence of a superstructure makes it possible to widen and / or lengthen the electrolysis cells 10, in order to benefit from electrolysis cells 10 of large dimensions, as mentioned previously. Such a widening or lengthening of the electrolysis cells 110 of the state of the art is not possible because of the superstructure 132, because this widening and / or lengthening would cause a widening and / or lengthening of the superstructure 132 itself. same, therefore of the span of the beam 35 between the legs supporting the beam and of the weight to be supported by this superstructure 132. There are superstructures comprising one or more intermediate arches supporting the beam, but such intermediate arches, s' extending transversely above the box 112 and the anodes 118, are bulky and complicate the operations on tanks, in particular the 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, this without creating MHD instabilities due to the particular magnetic configuration of the aluminum smelter 1 according to the The invention described in more detail below makes it possible to substantially improve the efficiency of the aluminum smelter 1 in comparison with the state of the art.

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

More particularly, the distribution of the electrolysis current IE flowing through the upstream and connection electrical conductors 22 is asymmetrical between the upstream electrical conductors and connection 22A and downstream 22B. The electrolysis current IE is divided into an upstream electrolysis current IEA, which runs through all the upstream electrical connection and upstream conductors 22A of the electrolysis cells 10, and a downstream electrolysis current IEB, which runs through all the upstream electrical conductors and connection 22B of the electrolysis cells 10. 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 IEA and downstream IEB electrolysis currents are complementary, that is to say that the sum of the intensities of the upstream IEA and downstream IEB electrolysis currents is equal to the intensity of the electrolysis current IE.

This asymmetric distribution with preponderance of upstream over downstream is particularly advantageous when the electrolysis tanks 10 of the aluminum smelter are large electrolysis tanks. Indeed, the upstream / downstream asymmetry of the electrolysis current IE makes it possible to avoid having to resort to an excessively large increase in the section of the routing conductors 24 under the electrolysis cell 10, so that savings in materials and costs. 'space are achieved, and this without prejudice to the magnetic stability of the electrolytic cell 10.

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

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

Likewise, the second part 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 flow of the current of electrolysis IE through this second part 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 outputs 20 advantageously pass through the bottom of the well.

12. The fact of having cathode outputs 20 from the bottom, instead of cathode outputs on the sides of the electrolytic cell as in the state of the art (FIG. 2), makes it possible to reduce the length of the conductors of. routing 24. The reduction in the length of the routing conductors 24 allows, in addition to a saving in raw materials, a substantial reduction in horizontal currents in liquids and, thus, better MHD stability.

Furthermore, still with a view to effectively compensating for the magnetic field created by the circulation of the electrolysis current IE, the first part 34 of the support 30 of the anode assembly 14 extends, preferably only, in a substantially horizontal and parallel manner. to the transverse direction X of the electrolysis cells 10.

Likewise, the routing conductors 24 advantageously extend in a substantially rectilinear manner and parallel to the transverse direction X of the electrolysis cells 10, up to the rise and connection conductors 22 of the following electrolysis cell 10. The cost of the electrical routing conductors 24 is thus limited, while minimizing their length. The magnetic fields generated by these electrical conductors 24 are also limited in relation to the state of the art, and in particular in relation to the self-compensating electrolysis cells of the state of the art.

The electrical rise and connection 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 electrical conductors of rise and connection 22 consecutive 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 electrolysis tank 10).

The upstream and upstream connection electrical conductors 22A and the downstream rise and connection electrical 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 electrolysis cell 10 into two substantially equal parts. In other words, the upstream electrical connection and upstream conductors 22A are at the same distance from this longitudinal median plane YZ as the upstream electrical connection and connection conductors 22B. In addition, the upstream electrical connection and upstream conductors 22A are advantageously arranged substantially symmetrically to the upstream electrical connection and upstream conductors 22B, with respect to this longitudinal median plane YZ. The advantageous substantially antisymmetric characteristic of the distribution of the horizontal magnetic field in liquids is thus further improved.

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

To improve the compactness of the aluminum smelter 1 and limit raw material costs, the upstream connection and upstream conductors 22A of the electrolysis cells 10 can be staggered with respect to the upstream and downstream connection conductors 22B of the electrolytic cell. electrolysis cell 10 preceding it in line 2. This in fact makes it possible to bring the electrolysis cells 10 as close as possible to each other, or to place more electrolysis cells 10 in series over the same distance, which increases the efficiency, or to reduce the length of a row 2 of electrolysis cells 10, thus saving space and achieving structural savings.

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

The principle of magnetic compensation or balancing of the aluminum plant 1 according to the invention makes it possible to obtain, for the aluminum plant 1, a circuit of conductors which can be produced in a modular fashion, as illustrated in FIG. 7. Each module M may comprise for example an electrical conductor of the first electrical compensation circuit 4 and a certain number of routing conductors 24 and associated rise and connection conductors 22 for each electrolysis 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, cathode 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 M module are arranged and traversed by currents such that each M module generates the same vertical and horizontal magnetic field components.

The circuit of conductors, and therefore each cell 10 of electrolysis, can be composed of a certain number N of modules M, determining the length of the cells 10 of electrolysis and the intensity of the current passing through the cells 10 of electrolysis ( 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 cell ends, does not disturb the magnetic balance of the electrolysis cells 10 little. This makes it possible to obtain an optimal magnetic configuration, and this for amperages beyond 1000 kA or even 2000 kA during the design or an extension of the length of the electrolysis cells 10 by adding such modules. On the other hand, the elongation of electrolytic cells of the self-compensating type or compensated by magnetic compensation circuits arranged on the sides of the cells known from the prior art require a complete redesign of the conductor circuits. Also, the ratio of the quantity of material forming the circuit of conductors brought back to the production surface of the electrolysis cells 10 does not deteriorate when the electrolysis cells 10 are extended, it increases in proportion to the number N of modules. M and the current passing through the electrolysis cells 10. Thus, the electrolytic cells 10 can be lengthened simply as needed and the intensity of the current passing through them is not limited. The modular construction of the electrical conductors of the electrolytic cells 10 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, allows the cells 10 to be modified. electrolysis without affecting their magnetic and electric balance.

The table of FIG. 9, read in combination with FIG. 8, shows for a module the current values flowing through the various electrically conductive elements of the electrolysis cells 10, these conductive elements being symbolized by segments: S1 for the conductors rise and upstream connection 22A; S2, S5 and S8 for the first part 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 outputs 20; S4, S6 and S10 for routing conductors 24; S7 for the upstream and downstream connection conductors 22B.

It should be noted that the sum of the intensities i and ia indicated in the table of Figures 9, 13 and 14 is equal to the intensity of the upstream electrolysis current IEA divided by the number N of modules of the electrolysis cell 10; the intensity ib is equal to the intensity of the downstream electrolysis current IEB divided by the number N of modules of the electrolysis cell 10; 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 passing through the entire upstream part of the electrolysis cell and of the intensity of the downstream electrolysis current IEB passing through the entire downstream part of the electrolysis cell, that is to say the product of 2i and the number N of modules of the electrolysis cell.

FIGS. 10 to 12 are schematic wire views of the electrical circuit through which the electrolysis current flows in a module of an electrolysis cell 10 of the aluminum smelter 1, and showing for this electrolysis 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 with the upstream zone P1 with respect to a longitudinal median plane YZ of the electrolysis cells 10.

The table of figure 13, read in combination with figures 10, 11 and 12, shows schematically the vertical component of the magnetic field generated by the electrical conductors (represented schematically by segments) of the electrolysis cell 10, respectively in the three zones P1, P2, P3 of the electrolysis cells 10, by the first and second compensation 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 is noted that the vertical component Bz of the magnetic field 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 figure 14, also read in combination with figures 10, 11 and 12, shows schematically the longitudinal horizontal component of the magnetic field generated by the flow of electrolysis current through the electrical conductors (symbolized by segments) of the electrolysis cell 10, zone by zone, and through the first and second compensation circuits 4, 6. The transverse horizontal component of the magnetic field is for its part antisymmetric because the conductors are symmetrical with respect to the plane XZ. By adding the contributions of each segment, and those of the first and second compensation circuits 4, 6, it can be seen that the longitudinal horizontal component By of the magnetic field is antisymmetric (opposite in the upstream and downstream areas P1, P3, and zero in the central P2 zone). This antisymmetry eliminates the deleterious effects linked to the horizontal components of the magnetic field.

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

The first electrical compensation circuit 4 extends under the electrolysis tanks 10. This first electrical compensation circuit 4 is intended to be traversed by a first compensation current IC1, in the opposite direction to the overall direction of flow of the electrolysis current IE, as can be seen in FIGS. 5 and 7. It is recalled that by overall direction of flow of electrolysis current IE means direction of flow of electrolysis current IE on the scale of the aluminum smelter 1 or of the row or rows 2 of electrolysis cells 10.

The first electrical compensation circuit 4 comprises electrical conductors which may be metal bars, for example made of aluminum, copper or steel, or, advantageously, electrical conductors made of superconducting material, the latter making it possible to reduce energy consumption. and, because of their lower mass than that of 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 (figure 7) or by them. burying. Advantageously, these electrical conductors of superconducting material can be arranged to make several turns in series under the row or rows of cells, as described in patent application WO2013007893 in the name of the applicant.

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

This supply station 44 may be a clean power supply station, that is to say separate from the supply station 8 supplying the electrolysis tanks 10 with electrolysis current IE. The power supply station 44 of the first compensation circuit 4 is therefore exclusively dedicated to the power supply of this first compensation circuit 4.

The first electrical compensation circuit 4 is thus also independent of the main electrical circuit through which the electrolysis current IE flows, in particular comprising the row or rows 2 of electrolysis cells 10. If the first electrical compensation circuit 4 suffers a failure, for example a piercing of one of the electrolysis tanks 10 by the liquids contained in the electrolysis tanks, the temperature of which is close to 1

000 ° C, the electrolysis reaction can continue, but with less efficiency since the magnetic compensation is affected. In addition, the intensity of the first compensation current IC1 can be changed independently of the electrolysis current IE. This is of paramount importance in terms of scalability and adaptability. On the one hand because this makes it possible, in the event of an increase in the intensity of the electrolysis current IE during the life of the aluminum smelter 1, to adapt the magnetic compensation to this change, by varying the intensity of the first compensation current IC1 according to requirements. On the other hand, because it makes it possible to adapt the amperage of the first compensation current IC1 to the characteristics and quality of the alumina available. This makes it possible to control the speed of the MHD flows to promote or limit the stirring of the liquids and the dissolution of the alumina in the bath according to the characteristics of the available alumina, which ultimately contributes to the best possible yield taking into account the alumina supplies.

The electrical conductors of the first electrical compensation circuit 4 extend under the electrolytic cells, together forming a sheet of parallel electrical conductors 5, advantageously from two to twelve, and preferably from three to ten parallel electrical conductors. In other words, in longitudinal section of an electrolysis cell 10, that is to say in a longitudinal plane YZ of the electrolysis cell 10, as shown in FIG. 7, the first circuit electrical compensation 4 extends under several places of the electrolysis cell 10. Note 10 that the first compensation current IC1 flows in the opposite direction to the overall direction of flow of the electrolysis current IE, through all the electrical conductors forming the sheet. The sheet can be formed by the same electrical circuit forming several turns or loops in series under the electrolysis tanks 10, each loop corresponding to an electrical conductor of the sheet. Alternatively, the sheet may be formed by a division into a bundle of parallel electrical conductors of the first electrical compensation circuit 4, the latter possibly forming a single loop under the electrolytic cells 10.

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 web. Preferably, the intensity of the first compensation current IC1 in each electrical conductor of the sheet is equal to the intensity of the first compensation current IC1 divided by the number of electrical conductors of this sheet.

The electrical conductors of the sheet are advantageously equidistant from each other. The same distance therefore separates two adjacent electrical conductors of the sheet. The compensation of the unfavorable magnetic field is thus further improved.

The electrical conductors of the sheet can extend parallel to each other. They preferably extend parallel to the transverse direction X of the electrolysis cells 10. Furthermore, the electrical conductors forming the sheet can all be arranged in the same horizontal XY plane. It also improves the compensation of the magnetic field generated by the flow of electrolysis current.

In addition, the electrical conductors of the sheet can extend substantially symmetrically with respect to the transverse median plane XZ of the electrolytic cells, that is to say with respect to the plane perpendicular to the longitudinal direction Y, this plane separating the cells 10 electrolysis into two substantially equal halves.

'18402

According to the example of FIG. 7, the first electrical compensation circuit 4 forms a layer of three conductors that are substantially equidistant and arranged in the same substantially horizontal XY plane. This sheet comprises as many electrical conductors as the electrolysis cell 10 comprises M modules.

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

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

The second electrical compensation circuit 6 extends on at least one side, transverse, of the electrolytic cells 10, substantially parallel to the transverse direction X of the electrolytic cells 10, that is to say parallel to the row or rows 2 of electrolysis cells 10. The second electrical compensation circuit 6 is intended to be traversed by a second compensation current IC2, in the same direction as the overall direction of flow of the electrolysis current IE.

Preferably, the second electrical compensation circuit 6 extends along the two transverse sides of the electrolysis cells 10, as illustrated in FIG. 5. In this case, the internal loop 61 denotes the electrical conductors of the second. 20 electrical compensation circuit 6 which are located between the two adjacent first rows 2 of electrolysis cells 10, and by external loop 62 the electrical conductors of the second electrical compensation circuit 6 which are located on the outside of rows 2 of cells 10 d electrolysis, that is to say which are on the other side of the electrolysis cells 10 with respect to the electrical conductors forming the internal loop 61. The internal loop 61 is traversed by a second compensation current IC21 and the external loop 62 is traversed by a second compensation current IC22. The second compensation currents IC21 and IC22 flow in the same direction. The sum of the currents IC21 and IC22 flowing respectively in the internal loop 61 and in the external 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 applicable, the intensity of the current IC21, respectively IC22, is the product of the number of revolutions in series by the intensity of the current flowing in each revolution in series.

The aluminum plant 1 comprises a supply station 46 which is advantageously configured to circulate through the second electrical compensation circuit 6 35 (internal loop 61 and / or external loop 62) a total current (if applicable internal loop 61 plus external loop 62) of 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 asymmetric distribution 5 of the electrolysis current IE in each electrolysis cell 10, offers, in synergy with the choice of the asymmetric distribution value IEA, IEB and the intensity of the first compensation current IC1, the best magnetic field compensation results, effectively applicable to large electrolysis cells 10.

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

The current flowing through the inner loop 61 may be increased in order to compensate for the impact of the neighboring line 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 tank and D61 is the distance from the internal loop 61 to the center of the tank. For a conventional electrolysis series 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 which allows the approach of the neighboring line because the creation of the magnetic field by the neighboring line is much lower at no additional cost compared to what is known to those skilled in the art.

The power supply station 46 supplying the second compensation circuit 6 can be a clean electrical supply station, that is to say separate from the supply station 8 supplying the electrolysis cells 10 with current of electrolysis IE and separate from the supply station 44 supplying the first electrical compensation circuit 4.

The electrical supply station 46 of the second compensation circuit 6 is therefore exclusively dedicated to the supply of this second compensation circuit 6. The second electrical compensation circuit 6 is thus also independent of the main electrical circuit through which the current d. 'IE electrolysis. 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 previously concerning the first electrical compensation circuit 4 Advantageously, the second compensation circuit 6 can also be distinct from the first compensation circuit 4.

'4 L

When the second electrical 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 compensation for the deleterious magnetic field.

Furthermore, still with the aim of effectively compensating for this magnetic field, created by the flow of electrolysis current IE, the electrical conductors of the second electrical compensation circuit 6 advantageously extend in the same horizontal plane XY. Preferably, this horizontal XY plane is located at the height of the sheet of liquid aluminum 40 formed inside the electrolysis cells 10 during the electrolysis reaction.

It will be noted that the electrical conductors forming the second electrical compensation circuit 6 can advantageously be configured so as to limit the “end of row” effects, as shown in FIG. 5.

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

The invention also relates to a method of compensating for the magnetic field created by the circulation of an electrolysis current IE in the electrolysis cells 10 of the aluminum smelter 1 described above. This process includes:

- the fact of circulating, in the opposite direction to the overall direction of flow of the electrolysis current IE, the first compensation current IC1 through the first electrical compensation circuit 4,

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

The method also advantageously comprises distributing the electrolysis current IE asymmetrically between the upstream upstream electrical connection conductors 22A and the upstream connection and downstream electrical conductors 22B.

This step of asymmetric distribution of the electrolysis current between the upstream and downstream of the electrolysis cells 10 comprises the separation of the electrolysis current IE into an upstream electrolysis current IEA, which circulates through all of the electrolysis cells. upstream electrical conductors and connection 22A of each electrolysis cell 10, so that the intensity of the upstream electrolysis current IEA is between J50-100 [% of the intensity of the electrolysis current IE, and in a downstream electrolysis current IEB, which flows through the set of upstream electrical conductors and downstream connection 22B of each electrolysis 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 10 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 double the intensity of the downstream electrolysis current IEB, to 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 electrolysis currents IEA and downstream IEB, and preferably between 80% and 100% of the difference in intensity between the upstream and downstream electrolysis currents.

For these intensity values of the upstream electrolysis current IEA, of the downstream electrolysis current IEB, of the first compensation current IC1 and of the second compensation current IC2, the Applicant has observed 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 internal 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 internal loop 61 is advantageously greater than the intensity of the current IC22 flowing in the external loop 62.

Furthermore, the method can advantageously comprise a step of analyzing at least one characteristic of the alumina in at least one of the electrolysis tanks 10 of the aluminum smelter 1 described above, and the determination of a distribution of intensity values of the upstream and downstream electrolysis currents IEA, IEB to be circulated as a function of this analyzed characteristic, which also defines, where appropriate, the intensity values of the first and second compensation currents IC1, IC2 and the case appropriate upstream and downstream electrolysis streams IEA, IEB. The intensity values of the first and second compensation currents IC1, IC2, and where appropriate of the upstream and downstream electrolysis currents IEA, IEB, can then be modified up to the values determined previously if the intensity values of the first and second compensation currents IC1, IC2 and the initial upstream and downstream electrolysis currents IEA, IEB 5 differ from the values thus determined. Thus, the method allows the magnetic compensation to be modified, in order to increase or reduce the mixing of liquids while controlling MHD instabilities. In general, the stronger the stirring (or flow) of liquids, the more effective the alumina dissolution will be, but the more unstable the bath / metal interface will be (= MHD instability), which can degrade the efficiency of 10 tanks. Such a method is particularly interesting with the configuration of the electrical conductors described above because it makes the electrolysis cells magnetically very stable and therefore offers a greater range to modulate / optimize the stirring depending on the quality of the alumina. . The characteristics of the alumina analyzed can in particular 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 of intensity values of the first and second compensation currents IC1, IC2 as a function of the characteristics of the alumina analyzed can be in particular carried out by use of an abacus, for example produced by a person skilled in the art by calculating, experimenting and recording the optimum correspondences between the intensities of the upstream and downstream electrolysis currents IEA, IEB / characteristics of the alumina. The aim here is to quantify the intensity of the desired liquid stirring with regard to the level of MHD instabilities.

It may happen that the alumina available for continuous operation of the aluminum smelter 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 electrolysis tanks 10 constitute an advantage, because they allow this alumina to be stirred 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 of the liquid. magnetic field imposed and frozen by the route of the routing conductors. It is therefore not possible in aluminum smelters with self-compensation to deliberately and temporarily introduce an imbalance in the compensation of the magnetic field in order to increase the intensity of the stirring of the alumina in the tanks, in order to increase the effectiveness of dissolution. Thus, when the available alumina is only alumina more difficult to dissolve than usual, the performance of self-compensating smelters can be significantly affected.

Of course, the invention is in no way limited to the embodiment described above, this embodiment having been given only by way of example. Modifications are possible, in particular from the point of view of the constitution of the various elements or by the substitution of technical equivalents, without thereby departing from the scope of protection of the invention. Thus, the present invention is for example compatible with the use of anodes of the "inert" type at which oxygen is formed during the electrolysis reaction.

Claims (18)

1. Aluminum smelter (1) comprising at least one row (2) of electrolysis cells (10) arranged transversely with respect to the length of said at least one row (2), one of the electrolysis cells (10) comprising anode assemblies (14) and up and connecting electrical conductors (22) to the anode assemblies (14), characterized in that the rising and connecting electrical conductors (22) extend upward along two edges opposing longitudinal sections (38) of the electrolysis cell (10) to conduct the electrolysis current (IE) to the anode assemblies (14), and in that the aluminum smelter (1) comprises: - at least a first electrical compensation circuit (4) extending under the electrolysis tanks (10), said at least one first electrical compensation circuit (4) capable of being traversed by a first compensation current (IC1) intended for to flow under the electrolysis tanks (10) in the opposite direction to the overall direction of flow of the electrolysis current (IE), - at least one second electrical compensation circuit (6) extending on at least one side of said at least one row (2) of electrolysis cells (10), said at least one second electrical compensation circuit (6) which can be traversed by a second compensation current (IC2) intended to flow in the same direction as the overall direction of flow of the electrolysis current (IE). 2. Aluminum smelter (1) according to claim 1, wherein the upstream electrical conductors and connection (22) comprise upstream electrical connection and rise conductors (22A), adjacent to the longitudinal edge (38) upstream of the vessel ( 10) electrolysis, and upstream electrical conductors and downstream connection (22B), adjacent to the longitudinal edge (38) downstream of the electrolytic cell (10), and the aluminum smelter (1) is configured so that the distribution of the electrolysis current (IE) is asymmetrical between the upstream (22A) and downstream (22B) upstream and connection electrical conductors, the intensity of the upstream electrolysis current (IEA) intended to flow through all the conductors electrical rise 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 run through all the upstream electrical conductors and downstream connection (22B) of the electrolysis cell (10) being equal to] 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). 9 3. Aluminum smelter (1) according to claim 2, in which the smelter comprises a supply station (44) configured to circulate through said at least one first electrical compensation circuit (4) a first compensation current (IC1). ) of an intensity equal to twice the intensity of the downstream electrolysis current (IEB), to more or 5 minus near 20%, and preferably within plus or minus 10%. 4. Aluminum smelter (1) according to claim 2 or 3, wherein the smelter (1) comprises a supply station (46) configured to circulate through said at least one second electrical compensation circuit (6) a second compensation current (IC2) with an intensity between 50% and 100% of the difference in intensity between the 10 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). 5. Aluminum smelter (1) according to one of claims 1 to 4, wherein the electrical conductors of rise and connection (22) are distributed at regular intervals along the longitudinal edge (38) of the tank (10) of electrolysis to which these electrical conductors of 15 rise and connection (22) are adjacent. 6. Aluminum smelter (1) according to one of claims 1 to 5, wherein said at least one first electrical compensation circuit (4) comprises electrical conductors extending under the cells (10) of electrolysis forming together a sheet made up of a plurality of parallel electrical conductors, typically from two to 20 twelve, and preferably three to ten parallel electrical conductors. 7. Aluminum smelter (1) according to claim 6, in which the electrical conductors of said sheet are arranged at regular intervals from one another in a longitudinal direction (Y) of the electrolysis cells (10). 8. Aluminum smelter (1) according to one of claims 6 to 7, wherein the electrical conductors of said sheet are arranged in the same horizontal plane (XY). 9. Aluminum smelter (1) according to one of claims 1 to 8, wherein said at least one second electrical compensation circuit (6) comprises electrical conductors extending on each side of said at least one row (2) of electrolysis cells (10), and the second compensation current (IC2) flows in the same direction as the direction of 30 global circulation of electrolysis current (IE) on each side of the electrolysis tanks (10). 10. Aluminum smelter (1) according to claim 9, in which the electrical conductors of the second electrical compensation circuit (6) extend in the same horizontal plane (XY), preferably at the height of a sheet of liquid aluminum ( 40) formed inside the electrolysis cells (10) during the electrolysis reaction. 11. Aluminum smelter (1) according to one of claims 1 to 10, wherein said at least one first electrical compensation circuit (4) and / or said at least one second electrical compensation circuit (6) are independent of the electrical circuit. main traversed by the electrolysis current (IE). 12. A method of compensating a magnetic field created by the circulation of an electrolysis current (IE) in a plurality of cells (10) for electrolysis of an aluminum smelter (1) according to one of claims 1 to 11, the method comprising: - the flow, in the opposite direction to the overall direction of flow of the electrolysis current (IE), of a first compensation current (IC1) through said at least one first electrical compensation circuit (4), - the flow, in the same direction as the overall direction of flow of the electrolysis current (IE), of a second compensation current (IC2) through said at least one second electrical compensation circuit (6). 13. The method of claim 12, wherein the method comprises an asymmetric distribution of the electrolysis current (IE) between the upstream and downstream of the electrolysis cells (10), all of the upward electrical conductors and connection (22) upstream of the electrolysis cells (10) being traversed by an upstream electrolysis current (IEA) of intensity between] 50-100 [% of the intensity of the electrolysis current ( IE), and all the upstream and connection electrical conductors (22) downstream of the electrolysis tanks (10) being traversed by a downstream electrolysis current (IEB) of intensity 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). 14. The method of claim 13, wherein the intensity of the first compensation current (IC1) is equal to twice the intensity of the downstream electrolysis current (IEB), to within plus or minus 20%, and preferably within plus or minus 10%. 15. The method of claim 12 or 13, wherein the intensity of the second compensation current (IC2) is between 50% and 100% of the difference 4-. * * 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 ). 16. The method according to one of claims 12 to 15, wherein said at least one second electrical compensation circuit (6) comprises an internal loop and an external 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. 17. The method of claim 16, 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. 18. Method according to one of claims 12 to 17, wherein the method comprises a step of analyzing at least one characteristic of the alumina in at least one of the electrolysis tanks (10) of said aluminum smelter (1 ), and the determination of the intensity values 15 of the first compensation current (IC1) and of the second compensation current (IC2) to be circulated as a function of said at least one analyzed characteristic.