EP0204647B1 - Connection device between very high intensity electrolytic pots for aluminium production, comprising a current supply circuit and an independent circuit for correcting the magnetic field - Google Patents

Abstract

The invention relates to a circuit for electrical connection between two successive cells of a series or row, designed for the production of aluminium by electrolysis of alumina dissolved in molten cryolite by the Hall-Heroult process at an intensity of at least 150 kA and possibly attaining from 500 to 600 kA. The circuit for the electrical supply of the cells comprises, in addition to the circuit 8 for the supply of electrolysis current, a distinct circuit 17 for correcting and balancing the magnetic fields which is formed by conductors which are substantially parallel to the axis of the series and are traversed by a direct current in the same direction as the electrolysis current which creates, in the cells, a vertical correcting magnetic field directed downwards close to the left-hand heads of the cells and directed upwards close to the right-hand heads of the cells. The total current J2 traversing the magnetic correcting circuit is at most equal to the electrolysis current J1 and is preferably between 4 and 80% of J1.

Description

1. Purpose of Inventlon

The invention relates to a method of electrical connection between successive tanks of a series for the production of aluminum by electrolysis of alumina dissolved in molten cryolite, according to the Hall-Héroult process and comprising. An independent circuit for the correction of undesirable effects due to magnetic fields. It applies to series of tanks arranged transversely to the axis of the series, operating at an intensity greater than 150,000 amperes, up to 500 to 600 kA, without this value constituting a limit of the field of application of the invention.

2. Technical field of the invention

For a good understanding of the invention, it is recalled first of all that the industrial production of aluminum takes place by igneous electrolysis in tanks electrically connected in series, of an alumina solution in molten cryolite carried at a temperature of the order of 950 to 1000 ° C by the Joule effect of the current passing through the tank.

Each tank is constituted by a parallelepipedal metallic box, heat-insulated, supporting a cathode constituted by carbon blocks in which are sealed steel bars, called cathode bars, which serve to evacuate the current from the cathodes to the anodes of the next tank. . The anode system, also made of carbon, is fixed on an anode bar called "cross" or "anode frame" adjustable in height, electrically connected to the cathode bars of the previous tank.

Between the anode system and the cathode is the electrolysis bath, that is to say the solution of alumina in cryolite melted at 930 - 960 ° C. The alumina produced is deposited on the cathode; a layer of liquid aluminum is permanently maintained at the bottom of the cathode crucible.

The crucible being rectangular, the anode frame supporting the anodes is, in general, parallel to its long sides, while the cathode bars are parallel to its short sides, called tank heads.

The tanks are arranged in rows and arranged lengthwise or, most often at present, crosswise, depending on whether their long side or their short side is parallel to the axis of the row. The tanks are electrically connected in series, the ends of the series being connected to the positive and negative outputs of an electrical rectification and regulation substation. Each series of tanks comprises a certain number of lines connected in series, the number of lines being preferably even in order to minimize the lengths of the conductors.

The electric current, which runs through them. different conductive elements: anode, electrolyte, liquid metal, cathodes, connecting conductors, creates strong magnetic fields. These fields induce, in the electrolysis bath and in the liquid metal contained in the crucible, so-called Laplace forces which, by the deformation of the upper surface of the molten metal and the movements which they generate, are detrimental to the smooth running of the tank. The design of the tank and its connecting conductors is studied so that the effects of the magnetic fields created by the different parts of the tank and the connecting conductors compensate each other.

Numerous patents have been filed concerning the arrangement of connecting conductors from one tank to the next. We can cite, in particular, our French patent application FR-A-2 505 368 which describes connection conductors for tanks operating at 280 kA.

Statement of the problem

Arrangements are chosen by a person skilled in the art to more or less perfectly cancel the vertical component of the magnetic fields in the liquid metal, and to symmetrize and reduce as much as possible the circulation of the liquid metal and the liquid bath in the crucible.

The more or less perfect cancellation of the vertical component of the magnetic field is necessary for the following reasons:

The passage of electric current in the supply conductors and in the conductive parts of the cell produces magnetic fields which cause movements in the liquid bath and metal and a deformation of the metal-electrolysis bath interface. These metal movements which agitate the electrolytic bath placed under the anodes can, when they are too large, short-circuit this bath blade by contact of the liquid metal with the anode. The efficiency of electrolysis deteriorates sharply and energy consumption increases.

Those skilled in the art know that the shape of the metal-bath interface and the movements of the liquid metal are closely dependent on the values of the vertical component of the magnetic field and on the more or less perfect symmetrization of the horizontal components; reducing as much as possible the values of the vertical component of the field makes it possible to reduce the height between the highest points and the lowest points of the sheet of metal, and makes it possible to reduce the magnetic forces creating disturbances of this sheet.

• 1. L'érosion mécanique par le métal du talus de cryolithe figée étant directement reliée à la vitesse de circulation du métal, une dissymétrie de ces vitesses de circulation entraînerait une érosion différente des talus sur les deux grands côtés de la cuve.
• 2. Les échanges thermiques entre le métal et le talus de cryolithe figée sont directement reliés aux vitesses de circulation de métal: une dissymétrie de ces vitesses de circulation entraînerait des échanges thermiques différents avec les deux grands côtés de la cuve et aurait pour conséquence, gênante pour l'exploitation des cuves, une différence de forme des talus d'un grand côté à l'autre.
  Plus les intensités des cuves augmentent, plus leurs dimensions augmentent et plus le dessin des conducteurs de liaison se complique, car la sensibilité d'une nappe de métal aux champs magnétiques s'accroît avec la dimension de la nappe. Généralement, une partie plus ou moins grande du courant issu de l'amont d'une cuve est amené à la cuve suivante après avoir contourné une tête de cuve, ce qui rallonge d'autant plus le circuit électrique que la cuve a des dimensions importantes.

The possible asymmetry, with respect to the major axis of the tank, of the metal circulations has the following drawbacks:

• 1. The mechanical erosion by the metal of the frozen cryolite slope being directly related to the speed of circulation of the metal, an asymmetry of these speeds of circulation involves different erosion of the slopes on the two long sides of the tank.
• 2. The heat exchanges between the metal and the frozen cryolite slope are directly linked to the metal circulation speeds: an asymmetry of these circulation speeds would lead to different heat exchanges with the two long sides of the tank and would have the consequence of being troublesome for the operation of the tanks, a difference in shape of the slopes from one long side to the other.
  The more the intensities of the tanks increase, the more their dimensions increase and the more the design of the connecting conductors becomes more complicated, because the sensitivity of a sheet of metal to magnetic fields increases with the dimension of the sheet. Generally, a more or less large part of the current from upstream of a tank is brought to the next tank after having bypassed a tank head, which lengthens the electrical circuit all the more as the tank has large dimensions. .

On the other hand, the effect of the magnetic fields created by the neighboring queue can no longer be neglected and a possible asymmetry of construction or compensation loops must be added to the circuit to compensate for these "neighboring queue" effects.

We then realize that beyond 350,000 amps, it becomes difficult to design tanks economically comparable to tanks with an intensity between 250,000 and 300,000 amps, because the gains on investment expected from the effect of size of the tanks are completely erased by the additional cost due to the circuit of conductors which lengthens and becomes more complex much faster than the increase in size of the tanks.

In addition, to be able to have conductors of complex shape and large dimensions between the tanks, it is necessary to separate them, which further lengthens the electrical circuit, and increases the surface of the building to be constructed to house these tanks. One could think of simplifying the circuit by admitting a certain instability of the sheet of metal: this must be excluded because the losses on the current yield of electrolysis (which usually is between 93 and 97%) would swell the costs of operating in such a way that the metal produced would not be economically competitive.

• - coût minimal de construction et de mise en place des circuits,
• - encombrement minimal, en surface au sol des séries des cuves utilisant ces circuits,
• - stabilité magnétique maximale, donc rendement Faraday maximal, compte tenu des effets de file voisine.

The problem therefore arises of designing connection circuits between very high current tanks, up to 500 and 600 kA for example, fulfilling the following three conditions:

• - minimum cost of construction and installation of circuits,
• - minimum space requirement, on the ground surface of the series of tanks using these circuits,
• - maximum magnetic stability, therefore maximum Faraday yield, taking into account the effects of neighboring lines.

Presentation of the prior art

We have already described, previously devices for compensating for magnetic effects by conductors arranged along the series or series, and traversed by a current which is a small fraction of the electrolysis current, this is the case of the patents US-3,616,317 (assigned to Alcan), and US-4,169,034 (- FR-2,425,482), assigned to Aluminum Pechiney. But, in both cases, it is exclusively a question of compensating for the effect of neighboring file, that is to say an essentially vertical field and of a constant sign over the entire surface of the tank. , as appears without ambiguity in the description and the claims of these two patents, and the method applies to series in which the tank-to-tank connection conductors have been designed so as to ensure normal operation, without neighboring lines, the neighboring queue correction only intervenes in a quasi-marginal manner. The maximum current intensity in the compensation conductors does not exceed 25% of the total J of the series in US-3,616,317, and 17% of the total J in US-4,169,034.

Due to the objective assigned to these compensation circuits, we see that they are designed to create a compensating magnetic field which keeps a constant sign on the whole tank, this sign being opposite to that of the vertical field created by the line of neighboring tanks.

Statement of the invention

The object of the invention is a connection method, that is to say an arrangement of conductors making it possible to operate electrolytic cells, arranged crosswise, under more than 150,000 amperes and up to 500 to 600,000 amperes, with a current efficiency of 93 to 97%, while greatly reducing the weight of the connecting conductors between tanks and the spacing between tanks.

It is also a method allowing a standardization of circuits and a simplification of their design to lower their manufacturing costs.

Finally, it is a method of compensating for the magnetic fields created by neighboring lines, without significant additional cost.

• - les conducteurs de cuve à cuve, comparables aux circuits électriques salon l'art antérieur et assurant l'alimentation électrique de l'électrolyse,
• - les conducteurs indépendants d'équilibrage des champs magnétiques.

In the description which follows, we will therefore distinguish two types of conductors:

• - cell-to-cell conductors, comparable to the electrical circuits of the prior art and ensuring the electrical supply of the electrolysis,
• - independent conductors for balancing magnetic fields.

We will call the inner side the side of the electrolytic cell directed towards the axis of symmetry of the rows of cells. The exterior side will therefore on the other side of the tank.

We will call the right head of the tank "the small side of the tank located to the right of an observer placed in the axis of the queue of tanks and looking in the direction of the current flowing through this queue of tanks.

We will call the left side of the tank "the other small side of the tank.

• - moyenne quadratique de la composante verticale Bz < 10⁷³ Tesla,
• - composante horizontale Bx: antisymétrique par rapport à l'axe transversal de la cuve (petit axe),
• - composante horizontale By: en moyenne, la plus proche possible de l'antisymétrie par rapport à l'axe longitudinal de la cuve (grand axe).

When designing a new very high intensity electrolysis cell, above 350 kA, one may be tempted to apply the same methods as for the 200 to 300 kA cells existing today, c that is to say, drawing the cell-to-cell connecting conductors so that the magnetic fields induced by all the circuits in each cell compensate each other so that the resulting field B has, on average, on the entire tank, the following characteristics:

• - quadratic mean of the vertical component Bz <10 ⁷³ Tesla,
• - horizontal component Bx: asymmetric with respect to the transverse axis of the tank (minor axis),
• - horizontal component By: on average, as close as possible to the asymmetry with respect to the longitudinal axis of the tank (major axis).

(Remember that there is "antisymmetry" when the two values considered are of the same absolute value but of opposite sign).

The present invention is based on a double idea, entirely different from the conceptions of the prior art, which consists in separating the two functions "transport of the etoctrotysis current" which we will try to make as simple and as direct as possible, and "magnetic field balancing", which will be provided by independent conductors.

• a) On dessine tout d'abord les conducteurs de liaison de cuve à cuve, transportant le courant d'électrolyse, en choisissant un trajet aussi proche que possible du trajet direct de façon à minimiser le poids d'aluminium immobilisé, et la distance entre cuves (donc la surface totale occupée au sol par la ou les séries), sans trop se préoccuper des effets magnétiques.
• b) On les conçoit comme un ou plusieurs ensembles de modules sensiblement identiques, qui relieront chaque groupe de collecteurs cathodiques d'une cuve de rang n dans la file à chacune des montées anodiques de la cuve de rang n+1 dans la file, ce qui se traduit par un standardisation de la construction et de la première mise en place des conducteurs.

To perform the first function:

• a) First draw the cell-to-cell connecting conductors, carrying the electrolysis current, choosing a path as close as possible to the direct path so as to minimize the weight of immobilized aluminum, and the distance between tanks (therefore the total surface occupied on the ground by the series or series), without worrying too much about the magnetic effects.
• b) They are conceived as one or more sets of substantially identical modules, which will connect each group of cathodic collectors of a tank of rank n in the queue to each of the anode rises of the tank of rank n + 1 in the queue, this which results in a standardization of the construction and the first installation of the conductors.

• a) Le courant d'équilibrage y circule dans un sens identique à celui du courant d'électrolyse dans la file des cuves, de façon à créer un champ correcteur fortement négatif sur la demi-cuve gauche et fortement positif sur la demi-cuve droite.
• b) Leur dessin est très simplifié, puisqu'ils ne comprennent pratiquement (sauf aux changements de direction aux extrémités des files) que des longueurs droites de barres d'aluminium.
• c) Leur consommation énergétique est très faible, car, si la somme des intensités J2 passant dans les conducteurs indépendants, qui est au plus égale à J1, et qui peut se situer entre 5 et 80 % et, de préférence, entre 20 et 70 % de l'intensité J1 traversant la série, est relativement importante, la chute de tension reste faible, et elle est largement compensée par le gain de tension résultant du tracé direct des conducteurs de liaison.
• d) La somme des poids des circuits de conducteurs conduisant le courant d'électrolyse d'une part et le courant de correction des champs d'autre part, est généralement très inférieure, de 5 à 15 % et même jusqu'à 25 % (pour des J proches de 500 kA), au poids nécessaire lorsqu'on utilise un circuit unique, autocompensé magnétiquement. Cependant, même pour des cuves plus petites, pour lesquelles par exemple J est de l'ordre de 180 à 280 kA, de tels circuits indépendants sont encore intéressants, car si dans ce cas l'on gagne peu ou pas sur le poids total de conducteurs de cuve à cuve, la conception modulaire et simplifiée des circuits conduit encore à un gain sur les coûts de fabrication et de mise en place, et sur la largeur de l'espace intercu- ves - donc sur la surface du bâtiment nécessaire pour abriter les cuves.
• e) Ces conducteurs indépendants de correction permettent à la fois de rétablir une configuration favorable du champ magnétique de chaque cuve, et aussi de compenser les effets de files voisines, par une dissymétrie de l'intensité passant dans les conducteurs de correction intérieurs et extérieurs, et ceci sans surcoût important tant en investissement qu'en exploitation.

This new design of direct trace conductors results, as a general rule, for very high intensity cells, by a very unfavorable magnetic field map and even completely incompatible with normal operation of electrolytic cells. Indeed, the vertical field created by the tank-to-tank conductors with a substantially direct trace is strongly positive on average on the left half-tank, and strongly negative on average on the right half-tank (see Figure 2). This is where the second inventive idea comes in, which consists in correcting this unfavorable map of magnetic fields by a set of independent balancing conductors, arranged along the line or lines and on each side of the line concerned, and which have the following characteristics:

• a) The balancing current flows there in a direction identical to that of the electrolysis current in the cell queue, so as to create a strongly negative corrective field on the left half-cell and strongly positive on the right half-cell .
• b) Their drawing is very simplified, since they practically only include (except for changes of direction at the ends of the lines) straight lengths of aluminum bars.
• c) Their energy consumption is very low because, if the sum of the intensities J2 passing through the independent conductors, which is at most equal to J1, and which can be between 5 and 80% and, preferably, between 20 and 70 % of the intensity J1 crossing the series, is relatively large, the voltage drop remains low, and it is largely compensated by the voltage gain resulting from the direct layout of the connecting conductors.
• d) The sum of the weights of the conductor circuits conducting the electrolysis current on the one hand and the field correction current on the other hand, is generally much lower, from 5 to 15% and even up to 25% ( for J close to 500 kA), at the necessary weight when using a single circuit, magnetically self-compensated. However, even for smaller tanks, for which J for example is of the order of 180 to 280 kA, such independent circuits are still interesting, because if in this case there is little or no gain on the total weight of tank-to-tank conductors, the modular and simplified circuit design further leads to savings in manufacturing and installation costs, and in the width of the inter-chamber space - therefore on the building surface necessary to house the tanks.
• e) These independent correction conductors make it possible both to restore a favorable configuration of the magnetic field of each tank, and also to compensate for the effects of neighboring lines, by an asymmetry of the intensity passing through the internal and external correction conductors, and this without significant additional cost both in investment and in operation.

More precisely, the object of the present invention is therefore a method of electrical connection between two successive tanks of a series intended for the production of aluminum by electrolysis of alumina dissolved in molten cryolite, according to the Hall process -Hérouft, at an intensity at least equal to 150 kA and up to 500 to 600 kA, each tank being constituted by a heat-insulated parallelepipedal metal box, whose major axis is perpendicular to the axis of the series, and whose two ends are called "heads", this box supporting a cathode formed by the juxtaposition of carbon blocks in which are sealed metal bars, the ends of which come out of the box, on the two long sides, upstream and downstream (relative or direction of the current in the series), each tank further comprising an anode system formed by at least one horizontal rigid beam supporting at least one and most often two barr are horizontal conductors, called "anode frame", on which the anode suspension rods are subject, this connection circuit comprising, in particular, a circuit for transporting the electrolysis current between two successive cells, constituted by cathode collectors, connected on the one hand to the cathode outputs of the tank of rank n and on the other hand to connecting conductors which join, by means of the anode frame of the tank of rank n + 1 in the series; according to the invention, this connection device further comprises an independent circuit for correcting and balancing the magnetic fields, formed of conductors substantially parallel to the axis of the series, traversed by a direct current in the same direction as the current d electrolysis, which creates, in the tanks, a vertical correcting magnetic field, directed downwards near the left heads and directed upwards near the right heads, the terms "left" and "right" being defined by reference to a observer placed on the axis of the cell line and looking in the direction of flow of the electrolysis current.

The total current J2 flowing through the magnetic correction circuit is or more equal to the electrolysis current J1.

The term "independent" circuits means that the circuits follow separate paths and fulfill distinct functions, which does not exclude that they may be supplied by the same source of direct current, or by two branches of the same source.

• - les sorties cathodiques amont de la cuve de rang n sont reliées à des collecteurs cathodiques amont qui rejoignent, par des conducteurs dont la plus grande partie passe sous ladite cuve n, par un trajet proche du trajet direct, une première section des montées qui alimentent le cadre anodique de la cuve de rang n+1 dans la série;
• - les sorties cathodiques aval de la cuve de rang n sont reliées à des collecteurs cathodiques aval directement connectés à une seconde section des montées correspondantes;
• le circuit de correction et d'équilibrage des champs magnétiques comporte deux ensembles de conducteurs, de correction de champ, indépendants des conducteurs de liaison, disposés de part et d'autre de ta file de cuves parallèlement à l'axe de la file et alimentés par un courant total J2 circulant dans le même sens que le courant J1 qui alimente la série, sous une intensité totale J2 au plus égale J1, et, généralement comprise entre 5 et 80 % de J1 et de préférence entre 20 et 70 %.

In the electrolysis current supply circuit:

• - the upstream cathode outlets of the tank of rank n are connected to upstream cathode collectors which join, by conductors the greater part of which passes under said tank n, by a path close to the direct path, a first section of the climbs which supply the anode frame of the tank of rank n + 1 in the series;
• - the downstream cathode outputs of the tank of rank n are connected to downstream cathode collectors directly connected to a second section of the corresponding risers;
• the magnetic field correction and balancing circuit comprises two sets of field correction conductors, independent of the connecting conductors, arranged on either side of your cell line parallel to the axis of the line and supplied by a total current J2 flowing in the same direction as the current J1 which supplies the series, under a total intensity J2 at most equal to J1, and generally between 5 and 80% of J1 and preferably between 20 and 70%.

Description of the figures

• - La figure 1 rappelle la nomenclature utilisée dans la description. L'axe XOX est l'axe de la file; il indique aussi le sens de circulation du courant, et le petit axe de ta série, YOY étant le grand axe. L'axe Oz représente l'axe vertical.
• - La figure 2 représente les composantes verticales du champ magnétique sur une cuve avant et après correction selon l'invention.
• - La figure 3 représente, de façon très schématique, le tracé général des conducteurs d'alimentation et des conducteurs de correction.
• - La figure 4 représente, de façon schématique, un module de connexion amont-aval.
• - La figure 5 représente, de façon schématique, la disposition des conducteurs de correction dans une série de cuve comportant deux files parallèles A et B.
• - La figure 6 représente, en vue isométrique, un module de connexion amont-aval entre deux cuves successives d'une file. Seuls les conducteurs d'alimentation ont été dessinés. Les sorties cathodiques ont été schématisées.
• - Les figures 7 et 8 schématisent la disposition réelle des conducteurs de liaison et de correction dans une série grande puissance (p.ex. 480 kA). La figure 7 a été simplifiée (par réduction de la cuve à 9 anodes) car elle a simplement pour but de montrer la position des conducteurs (9) (sous la cuve) et la position des conducteurs (17) (22) (correction du champ). La figure 8 fait apparaître en plus un module de liaison entre deux cuves.
• - La figure 9 illustre la mise en oeuvre de l'invention sur une série de cuves à 280 kA.

Figures 1 to 9 illustrate the implementation of the invention:

• - Figure 1 recalls the nomenclature used in the description. The XOX axis is the axis of the queue; it also indicates the direction of current flow, and the minor axis of your series, YOY being the major axis. The Oz axis represents the vertical axis.
• - Figure 2 shows the vertical components of the magnetic field on a tank before and after correction according to the invention.
• - Figure 3 shows, very schematically, the general layout of the supply conductors and correction conductors.
• - Figure 4 shows, schematically, an upstream-downstream connection module.
• - Figure 5 shows, schematically, the arrangement of the correction conductors in a series of tanks comprising two parallel rows A and B.
• - Figure 6 shows, in isometric view, an upstream-downstream connection module between two successive tanks of a queue. Only the supply conductors have been drawn. The cathodic outputs were shown diagrammatically.
• - Figures 7 and 8 show schematically the actual arrangement of the connection and correction conductors in a high power series (eg 480 kA). Figure 7 has been simplified (by reducing the tank to 9 anodes) because it simply aims to show the position of the conductors (9) (under the tank) and the position of the conductors (17) (22) (correction of field). Figure 8 shows in addition a connection module between two tanks.
• - Figure 9 illustrates the implementation of the invention on a series of 280 kA tanks.

In FIG. 3, the representation of 2 successive tanks in a file has been limited to the contour (1) of the metal box.

The cathode outputs, such as (2), drawn in thick lines, are connected to upstream cathode collectors such as (3), likewise, your downstream cathode outputs, such as (4) are connected to downstream cathode collectors such as (5).

On a tank of this type, provided, for example, for an intensity of 480 kA, there are for the whole of your tank 32 upstream cathode outputs and 32 downstream cathode outputs, and two parallel lines of 32 anodes, supported by rods, symbolized by the crosses (6) on your downstream half-tank. These cathode rods are subject to the anode frame, consisting of two elements 7A and 7B connected by equipotential bars 7C.

The electrical connection between the cathode collectors of the tank of rank n in the series and the anode frame of the tank of rank n + 1 is ensured by risers (8), here 8 in number.

Each climb (8) is double; it comprises a branch (8A) directly connected to a downstream cathode collector (5) and a branch (8B), connected to an upstream cathode collector (3) by at least one connecting bar (9) passing under the tank, following a route close to the most direct route. It should be emphasized that, in the technique of very high intensity electrolysis, the notion of "direct path" is not necessarily identified with the geometric straight line, due to the size of the conductors (an aluminum bar carrying 100 kA generally has a section of the order of 3000 square centimeters and can even reach 6000 square centimeters in the case of a "long" circuit transporting current from the cathode outputs upstream of a tank (n ) up to the anode frame of the next tank (n + 1)) which involves large radii of curvature, also due to the space occupied by your tanks (metal masses, ribs for reinforcing the box, pillars d 'support of the boxes) which can lead to the separation of an overly bulky bar into two or more parallel bars and electrical insulation requirements, the voltage between the conductors and the metallic masses being able to reach several hundred volts. The shortest route which reconciles the requirements listed above will be considered as "direct route".

In this case, there are soft connecting bars (9) to supply each rise 8A, each bar (9) being connected to two upstream cathode outputs (2) by a collector (3). In addition to obtaining a minimum weight of the conductors, for a given voltage drop, this arrangement offers the advantage of being suitable for modular construction.

• - 4 sorties cathodiques aval (4) de la cuve n (schématisées, pour ne pas aloudir le dessin),
• - le collecteur cathodique aval (5) et la montée correspondante (8A), vers le cadre anodique (7A) de la cuve (n+1 ),
• - le conducteur de liaison (13) relié, d'une part deux barres (9) passant sous la cuve n et d'autre part à l'autre demi-montée (8B),
• - deux éléments de collecteur cathodique amont (3)(3') de ta cuve n+1, reliés chacun deux sorties cathodiques amont (2) de la cuve (n+1 schématisées, et à la barre (91 passant sous la cuve (n+1
• - éventuellement les cales de court-circuitage (12) pour la mise provisoire hors circuit d'une cuve.

If we isolate (fig. 6) one of these modules (14), we see that it is formed by all of:

• - 4 downstream cathode outputs (4) of the tank n (shown diagrammatically, so as not to cloud the drawing),
• - the downstream cathode collector (5) and the corresponding rise (8A), towards the anode frame (7A) of the tank (n + 1),
• the connecting conductor (13) connected, on the one hand two bars (9) passing under the tank n and on the other hand to the other half-mounted (8B),
• - two upstream cathode collector elements (3) (3 ') of your tank n + 1, each connected two cathode outputs upstream (2) of the tank (n + 1 shown diagrammatically) and to the bar (91 passing under the tank ( n + 1
• - possibly the shorting shims (12) for the temporary shutdown of a tank.

The connecting bars (9) passing under the box (1) are not part of the module. Their position can indeed vary from one module to another so as to adjust the map of magnetic fields to the most favorable configuration. It will also be noted that the modules (14) located on a half-tank are generally symmetrical, rather than identical, with respect to the modules located on the other half-tank (with respect to the axis Ox).

This arrangement of the conductors, as just described, gives, for the intensities considered, a map of the magnetic field, completely unacceptable and incompatible with stable operation of the tank. For example, it may be that, for a vessel 480 made according to this method, one obtains a Bz max exceeding 120-10- ⁴ Tesla (120 gauss).

The correction and balancing of the magnetic field is entrusted to an independent equilibration circuit, shown diagrammatically in FIGS. 3 and 5, where the arrows indicate the direction of the current in the rows of tanks proper, and in the balancing circuit . FIG. 2 shows your distribution of the vertical components of the magnetic field on the long axis of the tank, before and after correction by the balancing circuit, object of the invention; the By values without correction are such that normal operation of the tanks would be impossible. Note that these values are taken at the level of the electrolysis-metal interface and in the vertical plane containing the largest axis of the cell.

In FIG. 5, we have taken the case of a series composed of two parallel rows A and B, comprising a number of tanks which may be any (one hundred for example). These tanks are symbolized by a simple rectangle (11). The parallel axes X1, X1 and X2, X2 are located a distance which can be of the order of a hundred meters.

The connections between each tank are made according to the diagrams in Figures 3,4 and 6.

According to the invention, there is arranged along the tanks, on either side of each series, a set of independent correction conductors, distinct from the connecting conductors between the tanks, located substantially at the level of the sheet of liquid aluminum. , and at a short distance from the external side walls of the tanks (of the order of 0.5 to 2 meters for example), each conductor or bundle of conductors grouped, being traversed by a current in the same direction as the direction of the current in the series.

The first correction conductor (16) has a first section (17) on the outside of the A series, traversed by a current in the same direction as the current which feeds this series A, then a connection section (18) which bypasses the head of series A and the free space between series A and B, then a section (19), on the side outside of series B, the current in this section (19) being in the same direction as that which supplies the series.

The second correction conductor (21) comprises a first branch (22), which runs along the interior side of the A series, then a connection section (23) which bypasses the free space between the A and B series, and a section (24) which runs along the inside of series B, the current in sections 17 and 22 on the one hand and 19 and 24 on the other hand, being in the same direction as that of the current which feeds the corresponding line.

The total intensity J2 is adjusted in the correction conductors (16) and (21) so as to re-establish a map of the magnetic fields ensuring normal operation, stability and optimal performance of all the series. This intensity is at most equal J1 and is normally between at least 5% and up to 80% of the total intensity J1 supplying the series proper, and preferably between 20 and 70% of J1.

For example, for a series supplied with J1 - 480 kA, the correction current could be fixed for example between 100 and 150 kA, in each external and internal branch of the correction circuit, the value of J2 equal to twice 135 kA being generally close to the optimal for an isolated series, without taking into account the effect of neighboring file, the correction conductor being arranged 1.5 meters from the external wall of the metal boxes of the tanks. This is an order of magnitude, and the exact optimum value depends on the position with respect to the box and at the level of the bath + metal interface, of the independent correction conductors.

In the case of multiple queues (at least 2) those skilled in the art know that it is necessary to take into account the "neighboring queue effect", that is to say the induced magnetic field, on a file, by the neighboring file or files, and whose magnetic effects are added to those created on each tank by the current flowing through it.

The present invention also makes it possible to compensate for the neighboring queue effect. For this, the current is distributed in each of the sets of internal and external correction conductors (16) and (21) in a different manner from that which provided magnetic balancing in the absence of a neighboring line: this is how that, for two series A and B, whose axes are 130 meters apart, the intensity J will be reduced from 135 to 120 kA in the external correction conductor (16) and increased from 135 to 150 kA in the correction conductor (21), the total intensity J2 remaining equal to 270 kA, or 56% of J1. If the center distance of the lines is reduced to 65 meters, the intensity will be lowered to 105 kA in (16) and increased to 180 kA in (21), the total intensity J2 being thus only increased by 15 kA , to settle at 285 kA, or 60% of J1.

There is a way to bring your different lines or series built on the same site, without compromising their overall stability, and the resulting reduction in floor space has many advantages: reduced investment (purchase of land, area of buildings to be constructed), length of conductors and pipelines of all types, and reduction of travel journeys for operating personnel, transport of raw materials and finished products, etc.

Finally, it should be noted that your compensation for the neighboring line effect by asymmetry of the intensity in the correction conductors, as just described, could also be obtained or refined by other known means, in particular by moving the upstream-downstream connecting bars (9) which pass under the tank, and by modifying the intensity in these different bars. The latter method can be used as the only means of compensating for the effect of a neighboring file or in addition to the method of the invention, by asymmetry of the intensity in the correction conductors.

Example of realization Example 1

The invention was applied to a small experimental series of electrolytic cells, arranged transversely to the axis of the series, and operating at 480 kA. The arrangement of the connection conductors between tanks is in accordance with that of FIGS. 3 and 4, each of the mounted (8) (-8A + 8B) carrying 60 kA.

There are 32 + 32 cathode outputs upstream (2) and downstream (4). On the large upstream side, two adjacent cathode outputs (2) are connected by a collector (3), connected to a bar (9) passing under the tank. There are therefore, in all, 16 bars (9) passing under the tank, each carrying 15 kA. Each group of two adjacent bars (9) joins, upstream, a connecting conductor (13) which is itself connected to the half-rise 8A.

On the large downstream side, four cathode outputs (4) are connected to a downstream cathode collector (5), which therefore collects 30 kA, and feeds the corresponding half-rise (8B).

The spacing between bars (9) passing under the tank can be modulated according to whether they correspond to cathode outputs, located in the center of the tank or near the heads, i.e. relative to their distance from the small axis of the tank so as to refine the map of the magnetic field but while respecting the direct path "as has been defined elsewhere. As a general rule, the distance between the bars (9) located on the side of the heads of the tank is less than the distance between the bars (9) located in the center of the tank These bars (9) can also be equidistant.

• Bz maximum 69.10^-4 Tesla
• Bz (moyenne quadratique): 35.10^-4 Tesla By: écart moyen amont/aval : 2,6.10^-4 Tesla
• (N.B.- l'écart l'antisymétrie des valeurs de By entre amont et aval étant défini comme |By| amont - |By| aval).

In the absence of any corrective conductor (all normal operation of the tanks then being impossible, the values of the components of the magnetic field were estimated by very reliable calculation methods:

• Bz maximum 69.10 ^-4 Tesla
• Bz (quadratic mean): 35.10 ^-4 Tesla By: mean upstream / downstream deviation: 2.6.10 ^-4 Tesla
• (NB- the difference in asymmetry of By values between upstream and downstream being defined as | By | upstream - | By | downstream).

• Bz maximum: 14.10^-4 Tesla
• Bz (moyenne quadratique): 5.10-⁴ Tesla
• By: écart moyen amont/aval: 1.10^.3 Tesla

Then the series being in operation and the internal and external correction conductors each being supplied at an intensity of 135 kA, these conductors being disposed at about 1.5 meters from the external wall of the metal boxes of the tanks and the direction of the current in the two conductors being the same as that of the electrolysis current supplying the series, (i.e. a total correction current J2 - 270 kA 56% J1), we measured:

• Bz maximum: 14.10 ^-4 Tesla
• Bz (quadratic mean): 5.10- ⁴ Tesla
• By: mean upstream / downstream deviation: 1.10 ^.3 Tesla

Finally, a neighboring line was simulated by a bundle of conductors arranged parallel to the axis OX, considering that the axes of the real series and of the simulated series were distant from 65 meters.

To compensate for the effects of this simulated neighboring queue, the correction conductor (16), placed on the opposite side of the simulated neighboring line, is supplied at 105 kA and the correction conductor (21) placed on the side of the simulated neighboring queue, under 180 kA, i.e. a total correction current J2 - 285 kA (60% of J1).

• Bz maximum: 23.10'⁴ Tesla
• Bz (moyenne quadratique): 5.3.10^-4 Tesla By: écart moyen amont/aval: 6,9.10^-4 Tesla

The measurements of the components of the magnetic field gave the following results:

• Bz maximum: 23.10 ' ⁴ Tesla
• Bz (quadratic mean): 5.3.10 ^-4 Tesla By: mean upstream / downstream deviation: 6.9.10 ^-4 Tesla

The experimental series, with or without neighboring simulated and compensated line, showed a perfect stabilization of the sheet of liquid aluminum, an absence of any asymmetrical erosion of the slopes and a Faraday yield of between 93 and 97%.

Finally, compared to a conventional solution, without correction conductors, the weight gain on all of the conductors can be estimated at around 14,000 kg of aluminum per cell, for this series having an electrolysis intensity of 480 kA. Added to this is a gain of 350 mm on the center-to-center of tank to tank, which represents a saving of 84 meters of building for a complete series of 240 tanks.

The implementation of the invention therefore opens the way to a new generation of electrolysis cells operating at an intensity which can reach and greatly exceed 500 kA. with remarkable stability and a Faraday yield at least equal to that of previous generations A 250 - 300 kA.

Example 2

To show that the invention is not limited to very high power electrolysis cells, in the range of 500 kA, the invention has also been applied to cells operating at 280 kA. As already explained to you in the description of the invention, the implementation of the independent correction circuit and of the modular design of the tank-to-tank connection conductors further leads to a significant gain in manufacturing costs, of installation and surface occupied by buildings.

FIG. 9 represents two successive half-tanks in a series operating at 280 kA, with 5 modular rises (8) each carrying 56 kA from tank n to the anode frame of tank n + 1 in the series.

Each independent correction conductor (17) (27) is supplied at 90 kA in the absence of a neighboring line, this current flowing in the same direction as that which supplies the series proper for carrying out the electrolysis, ie a total current of correction J2 equal to 180 kA, therefore 64% of J1.

• Bz maximum: 18.10-⁴
• Bz en moyenne quadratique: 4,6.10^-4
• Ecart à l'antisymétrie By: 2.10^-4

The following values were noted (in Tesla), in normal operation at 280 kA, the two compensation conductors each being supplied at 90 kA:

• Bz maximum: 18.10- ⁴
• Bz as quadratic mean: 4.6.10 ^-4
• Difference in antisymmetry By: 2.10 ^-4

We then simulated, in a known manner, a neighboring line located 65 meters from the line considered, and we compensated for the magnetic disturbance due to this line by increasing the compensation current in the internal independent conductor (27) located on the side of the neighboring line, from 90 to 120 kA, and by reducing the current from 90 to 75 kA in the independent external conductor (17) located on the side opposite to the neighboring line (fig. 5). The total correction current is therefore brought to D2 - 195 kA, i.e. 70% of D1.

• Bz maxi: 22.10^-4
• Bz moyenne quadratique: 4,9.10^-4
• Ecart à l'antisymétrie By: 2.10^-4

The following values were noted in Tesla:

• Bz max: 22.10 ^-4
• Bz quadratic mean: 4.9.10 ^-4
• Difference in antisymmetry By: 2.10 ^-4

The tanks thus supplied showed very stable operation and a current yield (Faraday yield) of between 93 and 95%.

In the case of 280 kA tanks, the weight gain on the conductors is not significant, on the other hand, the 270 mm gain on the tank-to-tank center distance represents a saving of approximately 64 meters in length of the building for a complete series of 240 tanks.

Claims (14)

1. A method of electrical connection between two successive cells in a series intended for the production of aluminium by electrolysis of alumina dissolved in molten cryolite by the Hall-Herouft process at an intensity of at least 150 kA, which may be as high as 500 to 600 kA, each cell being constituted by an insulated parallelepiped metal box, the large axis of which is perpendicular to the axis of the series, and of which the two ends are known as "head", this box supporting a cathode formed by the juxtaposition of carbonaceous blocks in which there are sealed metal rods, the ends of which issue from the box, on its large upstream and downstream sides (relative to the direction of the current in the series), each cell also comprising an anode system formed by at least one horizontal rigid beam supporting at least one, and preferably two, horizontal conducting rods known as "anode frame", to which the anode suspension rods are connected, this connection circuit comprising, in particular, a circuit for transmitting the electrolysis current between two successive cells, constituted by cathode collectors connected, on the one hand, to the cathode outlets of the cell in row n and, on the other hand, to the linking conductors which join, via risers, the anode frame of the cell of row n+1 in the series, this method of connection comprising, in addition to the circuit for the transmission of the electrolysis current, a distinct circuit for correcting and balancing the magnetic fields which is formed by conductors which are substantially parallel to the axis of the series and are traversed by a direct current, characterised in that this current is in the same direction as the electrolysis current and creates, in the cells, a vertical correcting magnetic field which is directed downwards near the left-hand heads and is directed upwards near the right-hand heads for an observer viewing in the direction of the electrolysis current.

2. A method of electrical connection according to claim 1, characterised in that the total current J2 traversing the magnetic correcting circuit is at most equal to the electrolysis current J1.

3. A method of connection according to claim 1, characterised in that the current J2 is between 5 and 80% of J1.

4. A method of connection according to claim 1, characterised in that the current J2 is between 20 and 70 % of J1.

5. A method of connection according to claim 1, characterised in that, in the circuit for the supply of electrolysis current:

- the upstream cathode outlets (2) of the cell in row n are connected to upstream cathode collectors (3) which directly join, via conductors (9) of which the majority pass beneath said cell n, a first section (half-riser) (8A) of the risers (8) which supply the anode bus (7) of the cell in row n+1 in the series;

- the downstream cathode outlets (4) of the cell in row n are connected to downstream cathode collectors (5) directly connected to a second section (half riser) (8B) of the risers (8).

6. A method of connection according to claim 1, characterised in that, in the supply circuit:

- on the large upstream side: two adjacent cathode outlets (2) are connected by a collector (3) connected to a rod (9) passing beneath the cell; each group of two adjacent rods (9) joins, upstream, a linking conductor (13) itself connected to a half riser (8A);

- on the large downstream side: four adjacent cathode outlets (3) are connected to a downstream cathode collector (5) which is itself connected to the other corresponding half riser (8B).

7. A method of connection according to claims 5 or 6, characterised in that the linking rods (9) arranged beneath the box are equidistant.

8. A method of connection according to claims 5 or 6, characterised in that the distance between the linking rods (9) is varied as a function of their position relative to the small axis of the cell.

9. A method of connection according to claims 5 or 6, characterised in that the distance between the linking rods (9) located on the side of the heads of the cell is smaller than the distance between the linking rods located in the centre of the cell.

10. A method of connection according to claim 1, characterised in that the circuit for correcting and balancing the magnetic fields is constituted by two sets of correcting conductors (17) (22) which are independent from the supply conductors, are arranged on either side of the line of cells parallel to the axis of the line, and are supplied by a total current J2 circulating in the same direction as the current J1 supplying the line and at an intensity at most equal to J1.

11. A method of connection according to claim 1, characterised in that, when the series comprises at least two lines of cells arranged in parallel, the conductor or the set of conductors for compensation arranged on the side of the adjacent line is traversed by a current having an intensity higher than the current traversing the compensating conductor arranged on the side remote from the adjacent line.

12. A method of connection according to claim 1, characterised in that the compensating conductors are arranged at a short distance from the metal box of cells and substantially at the metallic surface level of molten aluminium.

13. A method of connection according to claim 1, characterised in that the part of the independent supply circuit providing the link between the cathode outlets (2) (4) of the cell in row n to the anode frame (7) of the cell in row n+1 in the line is made up in the form of modules (14) which are substantially identical to one another and each correspond to a riser (8).

14. A method of connection according to claim 13, characterised in that each module (14) is constituted by:

- four downstream cathode outlets (4) of the cell n;

- the downstream cathode collector (5) and the half-riser (8A) toward the anode frame (7A) of the cell n+1;

- a linking conductor (13) connected, on the one hand, to two rods (9) passing beneath the cell n and, on the other hand, to the other half-riser (8B);

- two upstream cathode collector elements (3) (3') each connected to two upstream cathode outlets of the cell n+1.

Images