EP1733075B1 - Cathode element for an electrolysis cell for the production of aluminium - Google Patents

Cathode element for an electrolysis cell for the production of aluminium Download PDF

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Publication number
EP1733075B1
EP1733075B1 EP05744310.3A EP05744310A EP1733075B1 EP 1733075 B1 EP1733075 B1 EP 1733075B1 EP 05744310 A EP05744310 A EP 05744310A EP 1733075 B1 EP1733075 B1 EP 1733075B1
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EP
European Patent Office
Prior art keywords
bar
insert
cathode element
block
cathode
Prior art date
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EP05744310.3A
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German (de)
French (fr)
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EP1733075A2 (en
Inventor
Delphine Bonnafous
Jean-Luc Basquin
Claude Vanvoren
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Rio Tinto France SAS
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Aluminium Pechiney SA
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Priority to SI200532251T priority Critical patent/SI1733075T1/en
Priority to PL05744310T priority patent/PL1733075T3/en
Publication of EP1733075A2 publication Critical patent/EP1733075A2/en
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Publication of EP1733075B1 publication Critical patent/EP1733075B1/en
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
    • C25C3/16—Electric current supply devices, e.g. bus bars
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
    • C25C3/08—Cell construction, e.g. bottoms, walls, cathodes

Definitions

  • the present invention relates to the production of aluminum by igneous electrolysis. It relates more particularly to the cathode elements used in the electrolysis cells intended for the production of aluminum.
  • the cost of energy is an important item in the operating costs of the electrolysis plants. Therefore, reducing the specific consumption of electrolysis cells becomes a major issue for these plants.
  • the specific consumption of a cell corresponds to the energy consumed by the cell to produce one ton of aluminum. It is expressed in kWh / t and, with constant Faraday efficiency, it is directly proportional to the electrical voltage across the electrolysis cell.
  • the voltage of an electrolysis cell can be subdivided into several voltage drops: the anode voltage drop, the voltage drop in the bath, the electrochemical voltage, the cathodic voltage drop and the line losses.
  • the present invention relates to the reduction of the cathodic voltage drop in order to reduce the specific consumption of the electrolysis cells.
  • the cathodic voltage drop depends on the electrical resistance of the cathode element, which comprises a cathode block of carbon material and one or more metal connection bars.
  • the materials constituting the cathode blocks have evolved over time to become less and less resistive at the passage of the current. This allowed to increase the intensities through the cells, while maintaining a constant cathodic voltage drop.
  • the cathodic blocks were in anthracite (amorphous carbon). This material provided a fairly strong electrical resistance.
  • these blocks were gradually replaced, from the 1980s, by so-called “semi-graphitic” blocks (containing graphite quantities ranging from 30% to 50%) then by so-called “graphitic” blocks containing 100% of graphite grains but whose binder joining these grains remains amorphous.
  • the graphite grains of these blocks since they are not very resistive, the blocks offer a lower resistance to current flow and consequently, at constant intensity, the drop in cathodic voltage drops.
  • cathode blocks have led to the emergence of new problems such as, for example, the erosion of cathodes.
  • new problems such as, for example, the erosion of cathodes.
  • the more graphite blocks contain graphite the more susceptible they are to erosion problems at the top of the block.
  • the current density is not distributed homogeneously over the entire width of the tank and there is, on the surface of the cathode, a peak current density located at each end of the block. This current density peak causes localized erosion of the cathode, erosion all the more marked that the block is rich in graphite.
  • the insert is flush - with a given tolerance - the surface of the end of said outer portion.
  • the or each insert is made of copper or copper-based alloy.
  • an insert according to the invention makes it possible simultaneously to obtain a very large reduction in the overall cathodic voltage drop (for example 0.2 V for a bar with a copper insert against 0.3 V for a bar totally in steel) and a very strong reduction in the current density at the top of the block (at least of the order of 20%).
  • the applicant has had the idea of combining a zone of non-sealing near the head of the cathode block and at least one insert in each outer portion of the connecting bar which preferably extends over substantially the entire length of the section. It has been found that, unexpectedly, the combined effect of these characteristics makes it possible to very significantly reduce the peak of density of the current existing at the head of the block, that is to say near the ends of the block, while significantly reducing the cathodic voltage drop. In particular, she noted that the non-sealing zone makes it possible to substantially reduce the impact of the slope foot on the peak of current density.
  • the invention is particularly interesting when said carbon material contains graphite.
  • a method of manufacturing a connecting bar which can be used in a cathode element according to the invention, advantageously comprises the formation of a longitudinal cavity - typically a blind hole - in a steel bar from one end thereof, the manufacture of an insert of more conductive material than the steel constituting the bar, of length and section corresponding to those of the cavity, and then the introduction of the insert into the cavity.
  • the invention also relates to an electrolysis cell comprising at least one cathode element according to the invention.
  • an electrolysis cell 1 comprises a tank 10 and at least one anode 4.
  • the tank 10 comprises a box 2 whose bottom and the side walls are covered with elements of refractory material 3 and 3 '.
  • Cathodic blocks 5 rest on the bottom refractory elements 3.
  • Connection bars 6, generally made of steel, are sealed in the lower part of the cathode blocks 5.
  • the seal between the connection bar (s) 6 and the cathode block 5 is typically produced by means of cast iron or conductive paste 7.
  • the cathode blocks 5 have a substantially parallelepipedal shape, of length Lo, one of the side faces 21 has one or more longitudinal grooves 15 for housing the connecting bars 6.
  • the grooves 15 open at the head of the block and generally extend from one end to the other of the block.
  • the so-called "off-block" portion 22 of the bar 6 which emerges from the cathode block 5 has a length E.
  • the cathode blocks 5 and the connecting bars 6 form cathode elements 20 which are generally assembled out of the tank and added thereto during the formation of its lining.
  • An electrolytic cell 10 typically comprises more than a dozen cathode elements 20 arranged side by side.
  • a cathode element 20 may comprise one or more connecting bars, which pass through the block from one side, or one or more pairs of half-bars, typically aligned, which extend only over a portion of the block.
  • connection bars 6 The purpose of the connection bars 6 is to collect the current that has passed through each cathode block 5 and to return it to the network of conductors outside the tank. As illustrated in figure 1 , the connecting bars 6 pass through the tank 10 and are typically connected to a connecting conductor 13, generally made of aluminum, by a flexible aluminum connector 14 connected to the (x) section (s) 19 of the bars which come out of the tank 10.
  • the tank 10 contains a sheet of liquid aluminum 8 and an electrolyte bath 9, above the cathode blocks 5, and the anodes 4 dive into the bath 9.
  • a solidified bath slope 12 is generally formed on the side coatings 3 '.
  • a portion 12 ' of this embankment 12, called “foot of slope”, can encroach on the upper lateral surface 28 of the cathode block 5.
  • the foot of the embankment electrically isolates the cathode and increases the peak of current density at the top of the block.
  • the figure 2 represents an electrolysis cell 1 for aluminum production, in which the same elements are designated by the same references as previously.
  • each end of connecting bar 6 is equipped with a metal insert 16, preferably copper or copper alloy, which extends over a length Lc, typically from substantially the or each outer end of the bar 6 .
  • the insert 16 is located, at least partly, in the or each outer segment 19 of the connecting rod 6 which is intended to be located outside of vessel 10.
  • the or each insert 16 is preferably housed in a cavity forming a blind hole inside the bar 6. This variant avoids the exposure of the insert to the possible infiltrations bath or liquid metal.
  • the cavity may optionally be a groove on a lateral face of the bar, as illustrated in FIG. figure 7 .
  • the insert preferably covers at least 90% of the length of the or each outer portion 19 of the connecting bar 6 in which it is housed in order to optimize the voltage drop reduction obtained using the 'invention.
  • the end surface 24, which is intended to be outside the tank 10, is generally substantially vertical when the cathode element 20 is installed in a tank.
  • the or each insert 16 is substantially flush, that is to say with a given tolerance, the surface 24 of the end of the outer portion 19 of the bar 6.
  • Said determined tolerance is preferably less than or equal to ⁇ 1 cm.
  • each insert 16 is recessed, by a determined distance, with respect to the surface 24 of the end of the outer section 19 of the bar 6. Said determined distance is preferably less than or equal to 4 cm.
  • the cavity formed by the removal of the insert may advantageously contain a refractory material to prevent heat loss by radiation and / or convection.
  • the length Lc of the insert 16 is typically between 10 and 300%, preferably between 20 and 300%, and more preferably between 110 and 270%, of the length E of the so-called "off-block" part 22 of the bar 6 which emerges from the cathode block 5 and in which the insert is housed.
  • At least one zone 17 situated between the bar 6 and the cathode block 5 does not contain any sealing material.
  • This so-called “non-sealing” zone is advantageously filled, in whole or in part, with an electrically insulating material, such as a refractory material, typically in the form of fibers or fabrics; this material is interposed between the bar 6 and the cathode block 5, in the non-sealing zone 17, as illustrated in FIG. figure 5 .
  • the or each non-sealing zone 17 is located near the end 25 of the cathode block 5, called “pack header", which emerges from the bar and covers a given surface S.
  • the or each zone non-sealing 17 is flush with the surface 27 of the block head 25 from which the bar 6 emerges .
  • the cathode element comprises two parallel connecting bars which pass through the cathode block from one side to the other. Each bar then comprises two out-of-block portions 22 and two outer portions 19.
  • the cathode element comprises four connecting bars (also called "half-bars") which each open at one end of the block. Each bar then comprises a single out-of-block portion 22 and a single outer portion 19.
  • a conductive sealing material 7 is interposed between the block 5 and each bar 6, except in the zones at the ends of the block 5 where there are non-sealing zones 17, which can be filled with refractory materials.
  • the total area A of the determined surface (s) S of the non-sealing zone (s) 17 of each connecting bar 6 is typically between 0.5 and 25%, preferably between 2 and 20%, more preferably between 3 and 15%, of the area Ao the surface So of the bar 6 which is likely to be sealed, called "sealable surface".
  • the sealable surface So corresponds to the surfaces of the portion 23 of the bar 6 which are opposite the internal surfaces of the groove 15 in the block 5.
  • each half-connecting bar 6 has a non-sealing zone 17 at one end only 25, the total area A is equal to the area of the determined surface S of this non-sealing zone.
  • the Applicant has found that when the discontinuity of the bar near the center of the block is relatively short, which is generally the case, it hardly changed the current distribution and the voltage drop, so that the area A could be determined as if the bars were continuous from one end to the other.
  • the determined surface S is typically of simple shape in order to facilitate the formation of the non-sealing zone 17.
  • the area of the determined surface S is typically equal to Ls ⁇ ( 2H + W).
  • the length Ls of each non-sealing zone 17 is preferably between 0.5 and 25%, preferably between 2 and 20%, more preferably between 3 and 15%, of the half-length Lo. / 2 of the block.
  • the section of the insert 16 also influences the reduction of the cathodic voltage drop.
  • the cross section of each insert is between 1 and 50%, and preferably between 5 and 30%, of the cross section of the bar 6. In fact, beyond 30% of total insert section, the additional amount of driver provides a significant additional cost for a small increase in performance.
  • the insert 16 typically takes the form of a bar.
  • the shape of the cross section of the insert 16 is free, this shape being able to be rectangular (as illustrated in FIG. figure 5 ), circular (as illustrated in figure 6 or 7 ), ovoid or polygonal ... It is, however, advantageously circular to facilitate the manufacture of the connecting bar, including the realization of the cavity for housing the insert.
  • the Applicant has carried out numerical calculations intended to evaluate the distribution of the cathodic current at the surface 28 of the cathode block obtained with configurations according to the prior art and according to the invention.
  • the figure 8 presents the results of a calculation corresponding to connection bar dimensions and a current intensity typical of existing electrolysis cells.
  • the curves correspond to the current density J at the upper surface 28 of the block, expressed in kA / m 2 , as a function of the distance D from the end of the block.
  • the cell has 20 cathode elements arranged side by side and each having two connection bars, as illustrated in FIG. figure 3 .
  • the total intensity is 314 kA.
  • the connecting bars have a length L equal to 4.3 m, a height H equal to 160 mm and a width W equal to 110 mm.
  • the length E of the connecting bars leaving the cathode blocks is 0.50 m.
  • Curve A relating to the prior art, corresponds to a connection bar made entirely of steel.
  • the cathodic voltage drop is 283 mV (between the center of the liquid metal sheet and the anode frame of the downstream tank).
  • Curve B corresponds to a steel bar having the same dimensions as in case A, but having a cylindrical copper insert with a length equal to 1.53 m, the diameter of which is equal to 4.13 cm.
  • the insert is placed along the longitudinal axis of symmetry of the bar and extends approximately from the center of the bar (i.e. approximately from the central plane P of the vessel) to about half the thickness of the side coating 3 ' of the cell.
  • the cathode voltage drop is 229 mV.
  • the The reduction in cathodic drop is about 19% and the reduction in current density peak is about 18%.
  • Curve C corresponds to a steel bar having the same dimensions as in case A, but comprising a cylindrical copper insert with a length Lc equal to 1.30 m, the diameter of which is equal to 4.5 cm (corresponding to a volume of copper identical to that of case B).
  • the insert is placed along the longitudinal axis of symmetry of the bar and extends, as in the figure 2 from the outer end of the bar to the inside of the cell.
  • the non-sealing zone is 0.18 m long and covers the three normally sealed sides of the bar.
  • the cathodic voltage drop is 190 mV. With respect to case A, the reduction of the cathode drop is about 32% and the reduction of the current density peak is about 37%.
  • the distribution of cathodic current is much more homogeneous than in cases A and B.

Description

La présente invention concerne la production d'aluminium par électrolyse ignée. Elle concerne plus particulièrement les éléments cathodiques utilisés dans les cellules d'électrolyse destinées à la production d'aluminium.The present invention relates to the production of aluminum by igneous electrolysis. It relates more particularly to the cathode elements used in the electrolysis cells intended for the production of aluminum.

Le coût de l'énergie est un poste important dans les coûts de fonctionnement des usines d'électrolyse. Par conséquent, la réduction de la consommation spécifique des cellules d'électrolyse devient un enjeu majeur pour ces usines. La consommation spécifique d'une cellule correspond à l'énergie consommée par la cellule pour produire une tonne d'aluminium. Elle s'exprime en kWh/t et, à rendement Faraday constant, elle est directement proportionnelle à la tension électrique aux bornes de la cellule d'électrolyse.The cost of energy is an important item in the operating costs of the electrolysis plants. Therefore, reducing the specific consumption of electrolysis cells becomes a major issue for these plants. The specific consumption of a cell corresponds to the energy consumed by the cell to produce one ton of aluminum. It is expressed in kWh / t and, with constant Faraday efficiency, it is directly proportional to the electrical voltage across the electrolysis cell.

La tension électrique d'une cellule d'électrolyse peut se sous-diviser en plusieurs chutes de tension: la chute de tension anodique, la chute de tension dans le bain, la tension électrochimique, la chute de tension cathodique et les pertes en lignes. La présente invention se rapporte à la réduction de la chute de tension cathodique en vue de réduire la consommation spécifique des cellules d'électrolyse.The voltage of an electrolysis cell can be subdivided into several voltage drops: the anode voltage drop, the voltage drop in the bath, the electrochemical voltage, the cathodic voltage drop and the line losses. The present invention relates to the reduction of the cathodic voltage drop in order to reduce the specific consumption of the electrolysis cells.

La chute de tension cathodique dépend de la résistance électrique de l'élément cathodique, qui comporte un bloc cathodique en matériau carboné et une ou plusieurs barres de raccordement en métal.The cathodic voltage drop depends on the electrical resistance of the cathode element, which comprises a cathode block of carbon material and one or more metal connection bars.

Les matériaux constituant les blocs cathodiques ont évolué dans le temps pour devenir de moins en moins résistifs au passage du courant. Ceci a permis d'augmenter les intensités traversant les cellules, tout en conservant une chute de tension cathodique constante.The materials constituting the cathode blocks have evolved over time to become less and less resistive at the passage of the current. This allowed to increase the intensities through the cells, while maintaining a constant cathodic voltage drop.

Dans les années 1970, les blocs cathodiques étaient en anthracite (carbone amorphe). Ce matériau offrait une résistance électrique assez forte. Devant les besoins des usines d'augmenter leur intensité afin d'augmenter leur production, ces blocs ont été progressivement remplacés, à partir des années 1980, par des blocs dits "semi-graphitiques" (contenant des quantités de graphite allant de 30 % à 50 %) puis par des blocs dits "graphitiques" contenant 100 % de grains de graphite mais dont le liant joignant ces grains reste amorphe. Les grains de graphite de ces blocs étant peu résistifs, les blocs offrent une plus faible résistance au passage du courant et en conséquence, à intensité constante, la chute de tension cathodique baisse.In the 1970s, the cathodic blocks were in anthracite (amorphous carbon). This material provided a fairly strong electrical resistance. In view of the need of factories to increase their intensity in order to increase their production, these blocks were gradually replaced, from the 1980s, by so-called "semi-graphitic" blocks (containing graphite quantities ranging from 30% to 50%) then by so-called "graphitic" blocks containing 100% of graphite grains but whose binder joining these grains remains amorphous. The graphite grains of these blocks since they are not very resistive, the blocks offer a lower resistance to current flow and consequently, at constant intensity, the drop in cathodic voltage drops.

Enfin, les dernières générations de blocs sont des blocs dits "graphitisés". Ces blocs subissent un traitement thermique de graphitisation à haute température permettant d'augmenter la conductivité électrique du bloc par graphitisation du carbone.Finally, the last generations of blocks are so-called "graphitized" blocks. These blocks undergo a heat treatment graphitization at high temperature to increase the electrical conductivity of the block by carbon graphitization.

Parallèlement à ces avancées visant à réduire la résistance électrique des matériaux, les usines d'électrolyse pour la production d'aluminium ont augmenté leur intensité afin d'augmenter leur production (à rendement Faraday constant, le nombre de tonnes de métal produit par une cellule est proportionnel à l'intensité du courant qui la traverse). En conséquence, comme la chute de tension cathodique Uc est égale au produit de la résistance cathodique Rc et de l'intensité I du courant circulant dans la cathode (Uc = Rc × I), les chutes de tension cathodique restent de nos jours élevées, soit typiquement autour de 300 mV.In parallel with these advances to reduce the electrical resistance of materials, aluminum smelters have increased their intensity in order to increase their production (at constant Faraday yield, the number of tons of metal produced by a cell is proportional to the intensity of the current flowing through it). Consequently, since the cathodic voltage drop Uc is equal to the product of the cathodic resistance Rc and the intensity I of the current flowing in the cathode (Uc = Rc × I), the drop in cathodic voltage remains high today, typically around 300 mV.

En outre, l'évolution des propriétés des blocs cathodiques a conduit à l'apparition de nouveaux problèmes comme, par exemple, l'érosion des cathodes. On constate par exemple que plus les blocs cathodiques contiennent de graphite, plus ils sont sensibles à des problèmes d'érosion en tête de bloc. En effet, la densité de courant ne se répartit pas de façon homogène sur toute la largeur de la cuve et il existe, à la surface de la cathode, un pic de densité de courant situé à chaque extrémité du bloc. Ce pic de densité de courant engendre une érosion localisée de la cathode, érosion d'autant plus marquée que le bloc est riche en graphite. Ces zones de très forte érosion peuvent limiter la durée de vie de la cuve, ce qui est économiquement très pénalisant pour une usine d'électrolyse.In addition, the evolution of the properties of cathode blocks has led to the emergence of new problems such as, for example, the erosion of cathodes. For example, the more graphite blocks contain graphite, the more susceptible they are to erosion problems at the top of the block. Indeed, the current density is not distributed homogeneously over the entire width of the tank and there is, on the surface of the cathode, a peak current density located at each end of the block. This current density peak causes localized erosion of the cathode, erosion all the more marked that the block is rich in graphite. These areas of very strong erosion can limit the life of the tank, which is economically very disadvantageous for an electrolysis plant.

Il est connu de réduire la chute de tension cathodique Uc par l'utilisation de barres de raccordement composites comprenant une partie en acier et une partie en un métal de conductivité électrique supérieure à celle de l'acier, généralement du cuivre. On peut citer, par exemple, la demande de brevet français FR 1 161 632 (Pechiney ), les brevets américains US 2 846 388 (Pechiney ) et US 3 551 319 (Kaiser ) et la demande internationale WO 02/42525 (Servico ).It is known to reduce the cathodic voltage drop Uc by the use of composite connecting bars comprising a steel part and a part made of a metal of electrical conductivity greater than that of steel, generally copper. We can cite, for example, the French patent application FR 1 161 632 (Pechiney ), US patents US 2,846,388 (Pechiney ) and US 3,551,319 (Kaiser ) and the international application WO 02/42525 (Servico ).

Il est par ailleurs connu des demandes US 5,976,333 (Pate) et US2004/0050714 (Servico A.S.) et des demandes internationales WO 01/63014 (Comalco) et WO 01/27353 (Alcoa) que l'utilisation d'inserts en cuivre permet de mieux répartir le courant le long du bloc cathodique. Ces documents enseignent d'enfermer un insert en cuivre dans la barre de raccordement en acier et de confiner l'insert à l'intérieur de la cellule afin de réduire la conduction thermique vers l'extérieur de la cellule. Le brevet US 6, 294, 067 (Alcoa) propose d'ajouter une barre de raccordement secondaire dans une rainure distincte située en tête du bloc cathodique.It is also known US 5,976,333 (Pate) and US2004 / 0050714 (Servico AS) and international requests WO 01/63014 (Comalco) and WO 01/27353 (Alcoa) that the use of copper inserts makes it possible to better distribute the current along the cathode block. These documents teach to enclose a copper insert in the steel connecting bar and to confine the insert inside the cell to reduce heat conduction to the outside of the cell. The patent US 6,294,067 (Alcoa) proposes to add a secondary splice bar in a separate groove at the top of the cathode block.

Toutefois, d'un point de vue économique, ces solutions sont a priori onéreuses car le cuivre est plus cher que l'acier et les quantités de cuivre mises en oeuvre peuvent être importantes. En effet, dans les technologies les plus courantes, le nombre de barres par cuve d'électrolyse est généralement compris entre 50 et 100. Le surcoût global dû à la présence de composants en cuivre peut donc augmenter très rapidement.However, from an economic point of view, these solutions are a priori expensive because copper is more expensive than steel and the quantities of copper used can be significant. Indeed, in the most common technologies, the number of bars per electrolytic cell is generally between 50 and 100. The overall additional cost due to the presence of copper components can therefore increase very rapidly.

En outre, les configurations connues de l'art antérieur ne donnent pas entière satisfaction. En effet, ces configurations conduisent à des diminutions de la chute de tension cathodique globale (c'est-à-dire incluant la chute de tension dans la barre) de l'ordre de 50 mV, qui est une valeur trop faible pour que les surcoûts d'investissement soient rentables, et à des pics de densité de courant en tête de bloc qui restent relativement importants, à savoir plus de 12 kA/m2 environ.In addition, the known configurations of the prior art are not entirely satisfactory. Indeed, these configurations lead to decreases in the overall cathodic voltage drop (that is to say including the voltage drop in the bar) of the order of 50 mV, which is a value too low for the additional investment costs are cost-effective, and peaks of current density at the head of the block that remain relatively large, namely more than 12 kA / m 2 approximately.

La demanderesse a donc recherché des solutions satisfaisantes aux inconvénients de l'art antérieur, et notamment au problème de la consommation spécifique.The applicant has therefore sought satisfactory solutions to the disadvantages of the prior art, and in particular to the problem of specific consumption.

Description de l'inventionDescription of the invention

L'invention a pour objet un élément cathodique, pour l'équipement d'une cuve de cellule d'électrolyse destinée à la production d'aluminium, comportant :

  • un bloc cathodique en matériau carboné ayant au moins une rainure longitudinale sur une de ses faces latérales ;
  • au moins une barre de racco rdement en acier, dont au moins une partie dite "tronçon extérieur" est destinée à se situer à l'extérieur de la cuve, qui est logée dans ladite rainure de façon à ce qu'une partie de la barre dite "partie hors bloc" émerge d'au moins une extrémité du bloc dite "tête de bloc", et qui est scellée dans la rainure par interposition d'un matériau de scellement conducteur, tel que de la fonte ou de la pâte conductrice, entre la barre et le bloc.
The subject of the invention is a cathode element for the equipment of an electrolysis cell tank intended for the production of aluminum, comprising:
  • a cathode block of carbonaceous material having at least one longitudinal groove on one of its lateral faces;
  • at least one steel connection bar, of which at least one part called "outer section" is intended to be located outside the tank, which is housed in said groove so that part of the bar said "off-block portion" emerges from at least one end of the so-called "block head" block, and which is sealed in the groove by interposition of a conductive sealing material, such as cast iron or conductive paste, between the bar and the block.

L'élément cathodique selon l'invention est caractérisé en ce que, pour chaque tronçon extérieur :

  • la barre de raccordement comprend au moins un insert métallique, de longueur Lc, dont la conductivité électrique est supérieure à celle dudit acier, qui est disposé longitudinalement à l'intérieur de la barre et qui se situe, au moins en partie, dans ledit tronçon ;
  • la barre de raccordement n'est pas scellée au bloc cathodique dans au moins une zone dite de "non-scell ement" de surface déterminée S située à l'extrémité de la rainure en tête de bloc.
The cathode element according to the invention is characterized in that, for each outer section:
  • the connection bar comprises at least one metal insert, of length Lc, whose electrical conductivity is greater than that of said steel, which is disposed longitudinally inside the bar and which is located, at least in part, in said section ;
  • the connection bar is not sealed to the cathode block in at least one so-called "non-sealed" area of determined area S located at the end of the groove at the top of the block.

De préférence, l'insert affleure - avec une tolérance déterminée - la surface de l'extrémité dudit tronçon extérieur.Preferably, the insert is flush - with a given tolerance - the surface of the end of said outer portion.

Avantageusement, le ou chaque insert est réalisé en cuivre ou en alliage à base de cuivre.Advantageously, the or each insert is made of copper or copper-based alloy.

La présence d'un insert selon l'invention permet d'obtenir simultanément une très forte réduction de la chute de tension cathodique globale (par exemple 0,2 V pour une barre avec un insert en cuivre contre 0,3 V pour une barre totalement en acier) et une très forte réduction de la densité de courant en tête de bloc (au moins de l'ordre de 20 %).The presence of an insert according to the invention makes it possible simultaneously to obtain a very large reduction in the overall cathodic voltage drop (for example 0.2 V for a bar with a copper insert against 0.3 V for a bar totally in steel) and a very strong reduction in the current density at the top of the block (at least of the order of 20%).

Dans ses recherches, la demanderesse a noté qu'une partie importante de la chute de tension cathodique (environ un tiers) se situe dans la partie dite "hors bloc" de la barre qui sort du bloc. En effet, plus on se rapproche de la partie hors bloc de la barre, plus la densité de courant dans celle-ci augmente pour atteindre sa valeur maximale dans la partie hors bloc. Par conséquent, sur toute la partie hors bloc de la barre, une faible section assure la transmission d'une importante quantité de courant, ce qui engendre une forte chute de tension.In her research, the Applicant has noted that a significant portion of the cathodic voltage drop (about one-third) lies in the so-called "off-block" portion of the bar that leaves the block. Indeed, the closer we get to the out-of-block portion of the bar, the higher the current density in it increases to reach its maximum value in the out-of-block portion. Therefore, on all the out-of-block portion of the bar, a small section ensures the transmission of a large amount of current, which causes a large voltage drop.

La demanderesse a eu l'idée de combiner une zone de non-scellement à proximité de la tête du bloc cathodique et au moins un insert dans chaque tronçon extérieur de la barre de raccordement qui s'étend, de préférence, sur sensiblement toute la longueur du tronçon. Elle a constaté que, de manière inattendue, l'effet combiné de ces caractéristiques permet de réduire de manière très significative le pic de densité du courant existant en tête de bloc, c'est-à-dire près des extrémités du bloc, tout en réduisant de manière très significative la chute de tension cathodique. En particulier, elle a noté que la zone de non-scellement permet de diminuer sensiblement l'impact du pied de talus sur le pic de densité de courant.The applicant has had the idea of combining a zone of non-sealing near the head of the cathode block and at least one insert in each outer portion of the connecting bar which preferably extends over substantially the entire length of the section. It has been found that, unexpectedly, the combined effect of these characteristics makes it possible to very significantly reduce the peak of density of the current existing at the head of the block, that is to say near the ends of the block, while significantly reducing the cathodic voltage drop. In particular, she noted that the non-sealing zone makes it possible to substantially reduce the impact of the slope foot on the peak of current density.

L'invention est particulièrement intéressante lorsque ledit matériau carboné contient du graphite.The invention is particularly interesting when said carbon material contains graphite.

Un procédé de fabrication d'une barre de raccordement, qui est susceptible d'être utilisée dans un élément cathodique selon l'invention, comprend avantageusement la formation d'une cavité longitudinale - typiquement un trou borgne - dans une barre en acier à partir d'une extrémité de celle-ci, la fabrication d'un insert en matériau plus conducteur que l'acier constituant la barre, de longueur et de section correspondant à celles de la cavité, puis l'introduction de l'insert dans la cavité.A method of manufacturing a connecting bar, which can be used in a cathode element according to the invention, advantageously comprises the formation of a longitudinal cavity - typically a blind hole - in a steel bar from one end thereof, the manufacture of an insert of more conductive material than the steel constituting the bar, of length and section corresponding to those of the cavity, and then the introduction of the insert into the cavity.

Un contact intime entre l'insert et la barre est généralement obtenu lors de la montée en température de la cuve, grâce à la dilatation thermique différentielle entre l'insert et la barre (car l'acier se dilate relativement peu par rapport à d'autres métaux).An intimate contact between the insert and the bar is generally obtained during the temperature rise of the tank, thanks to the differential thermal expansion between the insert and the bar (because the steel expands relatively little compared to other metals).

L'invention concerne également une cellule d'électrolyse comprenant au moins un élément cathodique selon l'invention.The invention also relates to an electrolysis cell comprising at least one cathode element according to the invention.

L'invention est décrite en détail ci-dessous à l'aide des figures annexées.

  • La figure 1 est une vue en coupe transversale d'une demi-cuve traditionnelle.
  • La figure 2 est une vue similaire à figure 1 dans le cas d'une cellule comprenant un élément cathodique selon l'invention.
  • La figure 3 est une vue de dessous d'un élément cathodique selon un mode de réalisation de l'invention.
  • La figure 4 est une vue de dessous d'un élément cathodique selon un autre mode de réalisation de l'invention.
  • La figure 5 est une vue en perspective d'une extrémité du bloc cathodique des figures 3 ou 4.
  • La figure 6 représente un tronçon de barre de raccordement équipée d'un insert de section circulaire.
  • La figure 7 représente un tronçon de barre de raccordement équipée d'une insert de section circulaire dans une rainure latérale.
  • La figure 8 présente des courbes de répartition du courant cathodique le long d'un bloc cathodique.
The invention is described in detail below with the help of the appended figures.
  • The figure 1 is a cross-sectional view of a traditional half-tank.
  • The figure 2 is a view similar to figure 1 in the case of a cell comprising a cathode element according to the invention.
  • The figure 3 is a bottom view of a cathode element according to one embodiment of the invention.
  • The figure 4 is a bottom view of a cathode element according to another embodiment of the invention.
  • The figure 5 is a perspective view of one end of the cathode block of Figures 3 or 4 .
  • The figure 6 represents a section of connecting bar equipped with a circular section insert.
  • The figure 7 represents a section of connecting bar equipped with a circular section insert in a lateral groove.
  • The figure 8 presents distribution curves of the cathodic current along a cathode block.

Tel qu'illustré à la figure 1, une cellule d'électrolyse 1 comporte une cuve 10 et au moins une anode 4. La cuve 10 comporte un caisson 2 dont le fond et les parois latérales sont recouvertes d'éléments en matériau réfractaire 3 et 3'. Des blocs cathodiques 5 reposent sur les éléments réfractaires de fond 3. Des barres de raccordement 6, généralement en acier, sont scellées dans la partie inférieure des blocs cathodiques 5. Le scellement entre la ou les barres de raccordement 6 et le bloc cathodique 5 est typiquement réalisé par l'intermédiaire de fonte ou de pâte conductrice 7. As illustrated in figure 1 , an electrolysis cell 1 comprises a tank 10 and at least one anode 4. The tank 10 comprises a box 2 whose bottom and the side walls are covered with elements of refractory material 3 and 3 '. Cathodic blocks 5 rest on the bottom refractory elements 3. Connection bars 6, generally made of steel, are sealed in the lower part of the cathode blocks 5. The seal between the connection bar (s) 6 and the cathode block 5 is typically produced by means of cast iron or conductive paste 7.

Tel qu'illustré aux figures 3 à 5, les blocs cathodiques 5 ont une forme sensiblement parallélépipédique, de longueur Lo, dont une des faces latérales 21 possède une ou plusieurs rainures longitudinales 15 destinées à loger les barres de raccordement 6. Les rainures 15 débouchent en tête de bloc et s'étendent généralement d'une extrémité à l'autre du bloc. La partie dite "hors bloc" 22 de la barre 6 qui émerge du bloc cathodique 5 a une la longueur E.As illustrated in Figures 3 to 5 , the cathode blocks 5 have a substantially parallelepipedal shape, of length Lo, one of the side faces 21 has one or more longitudinal grooves 15 for housing the connecting bars 6. The grooves 15 open at the head of the block and generally extend from one end to the other of the block. The so-called "off-block" portion 22 of the bar 6 which emerges from the cathode block 5 has a length E.

Les blocs cathodiques 5 et les barres de raccordement 6 forment des éléments cathodiques 20 qui sont généralement assemblés hors de la cuve et ajoutés à celle-ci lors de la formation de son revêtement intérieur. Une cuve d'électrolyse 10 comporte typiquement plus d'une dizaine d'éléments cathodiques 20 disposés côte à côte. Un élément cathodique 20 peut comporter une ou plusieurs barres de raccordement, qui traversent le bloc de part en part, ou une ou plusieurs paires de demi-barres, typiquement alignées, qui ne s'étendent que sur une partie du bloc.The cathode blocks 5 and the connecting bars 6 form cathode elements 20 which are generally assembled out of the tank and added thereto during the formation of its lining. An electrolytic cell 10 typically comprises more than a dozen cathode elements 20 arranged side by side. A cathode element 20 may comprise one or more connecting bars, which pass through the block from one side, or one or more pairs of half-bars, typically aligned, which extend only over a portion of the block.

Les barres de raccordement 6 ont pour fonction de collecter le courant ayant traversé chaque bloc cathodique 5 et le renvoyer dans le réseau de conducteurs se trouvant à l'extérieur de la cuve. Comme illustré à la figure 1, les barres de raccordement 6 traversent la cuve 10 et sont typiquement reliées à un conducteur de liaison 13, généralement en aluminium, par un raccord souple en aluminium 14 raccordé au(x) tronçon(s) 19 des barres qui sort(ent) de la cuve 10. The purpose of the connection bars 6 is to collect the current that has passed through each cathode block 5 and to return it to the network of conductors outside the tank. As illustrated in figure 1 , the connecting bars 6 pass through the tank 10 and are typically connected to a connecting conductor 13, generally made of aluminum, by a flexible aluminum connector 14 connected to the (x) section (s) 19 of the bars which come out of the tank 10.

En fonctionnement, la cuve 10 contient une nappe d'aluminium liquide 8 et un bain d'électrolyte 9, au-dessus des blocs cathodiques 5, et les anodes 4 plongent dans le bain 9. Un talus 12 de bain solidifié se forme généralement sur les revêtements de côté 3'. Une partie 12' de ce talus 12, appelée "pied de talus", peut empiéter sur la surface latérale supérieure 28 du bloc cathodique 5. Le pied de talus isole électriquement la cathode et augmente le pic de densité de courant en tête de bloc.In operation, the tank 10 contains a sheet of liquid aluminum 8 and an electrolyte bath 9, above the cathode blocks 5, and the anodes 4 dive into the bath 9. A solidified bath slope 12 is generally formed on the side coatings 3 '. A portion 12 ' of this embankment 12, called "foot of slope", can encroach on the upper lateral surface 28 of the cathode block 5. The foot of the embankment electrically isolates the cathode and increases the peak of current density at the top of the block.

La figure 2 représente une cellule d'électrolyse 1 pour fabrication d'aluminium, dans laquelle les mêmes éléments sont désignés par les mêmes références que précédemment.The figure 2 represents an electrolysis cell 1 for aluminum production, in which the same elements are designated by the same references as previously.

Tel qu'illustré à la figure 2, chaque extrémité de barre de raccordement 6 est équipée d'un insert métallique 16, de préférence en cuivre ou en alliage de cuivre, qui s'étend sur une longueur Lc, typiquement à partir sensiblement de la ou chaque extrémité extérieure de la barre 6. L'insert 16 se situe, au moins en partie, dans le ou chaque tronçon extérieur 19 de la barre de raccordement 6 qui est destiné à se situer à l'extérieur de la cuve 10. As illustrated in figure 2 each end of connecting bar 6 is equipped with a metal insert 16, preferably copper or copper alloy, which extends over a length Lc, typically from substantially the or each outer end of the bar 6 . the insert 16 is located, at least partly, in the or each outer segment 19 of the connecting rod 6 which is intended to be located outside of vessel 10.

Le ou chaque insert 16 est de préférence logé dans une cavité formant un trou borgne à l'intérieur de la barre 6. Cette variante permet d'éviter l'exposition de l'insert aux infiltrations éventuelles de bain ou de métal liquides. La cavité peut éventuellement être une rainure sur une face latérale de la barre, tel qu'illustré à la figure 7.The or each insert 16 is preferably housed in a cavity forming a blind hole inside the bar 6. This variant avoids the exposure of the insert to the possible infiltrations bath or liquid metal. The cavity may optionally be a groove on a lateral face of the bar, as illustrated in FIG. figure 7 .

L'insert couvre de préférence au moins 90 % de la longu eur Le du ou de chaque tronçon extérieur 19 de la barre de raccordement 6 dans lequel il est logé afin d'optimiser la diminution de chute de tension obtenue à l'aide de l'invention.The insert preferably covers at least 90% of the length of the or each outer portion 19 of the connecting bar 6 in which it is housed in order to optimize the voltage drop reduction obtained using the 'invention.

La surface d'extrémité 24, qui est destinée à être à l'extérieur de la cuve 10, est généralement sensiblement verticale lorsque l'élément cathodique 20 est installé dans une cuve.The end surface 24, which is intended to be outside the tank 10, is generally substantially vertical when the cathode element 20 is installed in a tank.

Selon une variante avantageuse de l'invention, le ou chaque insert 16 affleure sensiblement, c'est-à-dire avec une tolérance déterminée, la surface 24 de l'extrémité du tronçon extérieur 19 de la barre 6. Ladite tolérance déterminée est de préférence inférieure ou égale à ± 1 cm.According to an advantageous variant of the invention, the or each insert 16 is substantially flush, that is to say with a given tolerance, the surface 24 of the end of the outer portion 19 of the bar 6. Said determined tolerance is preferably less than or equal to ± 1 cm.

Selon une autre variante avantageuse de l'invention, l'extrémité extérieure de chaque insert 16 est en retrait, d'une distance déterminée, par rapport à la surface 24 de l'extrémité du tronçon extérieur 19 de la barre 6. Ladite distance déterminée est de préférence inférieure ou égale à 4 cm. La cavité formée par le retrait de l'insert peut avantageusement contenir un matériau réfractaire afin d'éviter la perte de chaleur par rayonnement et/ou convection.According to another advantageous variant of the invention, the outer end of each insert 16 is recessed, by a determined distance, with respect to the surface 24 of the end of the outer section 19 of the bar 6. Said determined distance is preferably less than or equal to 4 cm. The cavity formed by the removal of the insert may advantageously contain a refractory material to prevent heat loss by radiation and / or convection.

La longueur Lc de l'insert 16 est typiquement comprise entre 10 et 300 %, de préférence entre 20 et 300 %, et de préférence encore entre 110 et 270 %, de la longueur E de la partie dite "hors bloc" 22 de la barre 6 qui émerge du bloc cathodique 5 et dans laquelle l'insert est logé.The length Lc of the insert 16 is typically between 10 and 300%, preferably between 20 and 300%, and more preferably between 110 and 270%, of the length E of the so-called "off-block" part 22 of the bar 6 which emerges from the cathode block 5 and in which the insert is housed.

Plus l'insert est long, plus la chute de tension cathodique diminue. Toutefois, la demanderesse a constaté que, au-dessus d'une longueur d'insert de 270 % de la partie hors bloc 22 de barre, l'augmentation n'intervient que faiblement sur la valeur de la chute de tension cathodique.The longer the insert, the lower the cathodic voltage drop. However, the Applicant has found that, above an insert length of 270% of the outboard block portion 22 , the increase only slightly affects the value of the cathodic voltage drop.

Tel qu'illustré à la figure 2, au moins une zone 17 située entre la barre 6 et le bloc cathodique 5 ne contient pas de matériau de scellement. Cette zone, dite de "non-scellement", est avantageusement remplie, en tout ou partie, d'un matériau électriquement isolant, tel qu'un matériau réfractaire, typiquement sous forme de fibres ou de tissus ; ce matériau est interposé entre la barre 6 et le bloc cathodique 5, dans la zone de non-scellement 17, tel qu'illustré à la figure 5. La ou chaque zone de non-scellement 17 est située à proximité de l'extrémité 25 du bloc cathodique 5, appelée "tête de bloc", de laquelle émerge la barre et couvre une surface déterminée S. De préférence, la ou chaque zone de non-scellement 17 affleure la surface 27 de la tête de bloc 25 de laquelle émerge la barre 6. As illustrated in figure 2 at least one zone 17 situated between the bar 6 and the cathode block 5 does not contain any sealing material. This so-called "non-sealing" zone is advantageously filled, in whole or in part, with an electrically insulating material, such as a refractory material, typically in the form of fibers or fabrics; this material is interposed between the bar 6 and the cathode block 5, in the non-sealing zone 17, as illustrated in FIG. figure 5 . The or each non-sealing zone 17 is located near the end 25 of the cathode block 5, called "pack header", which emerges from the bar and covers a given surface S. Preferably, the or each zone non-sealing 17 is flush with the surface 27 of the block head 25 from which the bar 6 emerges .

Les figures 3 et 4 illustrent deux modes de réalisation particuliers de l'élément cathodique 20 selon l'invention. Dans l'exemple de la figure 3, l'élément cathodique comporte deux barres de raccordement parallèles qui traversent le bloc cathodique de part en part. Chaque barre comporte alors deux parties hors bloc 22 et deux tronçons extérieurs 19. Dans l'exemple de la figure 4, l'élément cathodique comporte quatre barres de raccordement (également appelées "demi-barres") qui débouchent chacune à une extrémité du bloc. Chaque barre comporte alors une seule partie hors bloc 22 et un seul tronçon extérieur 19. Dans les deux exemples, un matériau de scellement conducteur 7 est interposé entre le bloc 5 et chaque barre 6, sauf dans les zones situées aux extrémités du bloc 5 où il existe des zones de non-scellement 17, qui peuvent être remplies de matériaux réfractaires.The Figures 3 and 4 illustrate two particular embodiments of the cathode element 20 according to the invention. In the example of the figure 3 , the cathode element comprises two parallel connecting bars which pass through the cathode block from one side to the other. Each bar then comprises two out-of-block portions 22 and two outer portions 19. In the example of the figure 4 , the cathode element comprises four connecting bars (also called "half-bars") which each open at one end of the block. Each bar then comprises a single out-of-block portion 22 and a single outer portion 19. In both examples, a conductive sealing material 7 is interposed between the block 5 and each bar 6, except in the zones at the ends of the block 5 where there are non-sealing zones 17, which can be filled with refractory materials.

L'aire totale A de la ou des surface(s) déterminée(s) S de la ou des zone(s) de non-scellement 17 de chaque barre de raccordement 6 est typiquement comprise entre 0,5 et 25 %, de préférence entre 2 et 20 %, de préférence encore entre 3 et 15 %, de l'aire Ao la surface So de la barre 6 qui est susceptible d'être scellée, dite "surface scellable". La surface scellable So correspond aux surfaces de la partie 23 de la barre 6 qui sont en regard des surfaces internes de la rainure 15 dans le bloc 5. The total area A of the determined surface (s) S of the non-sealing zone (s) 17 of each connecting bar 6 is typically between 0.5 and 25%, preferably between 2 and 20%, more preferably between 3 and 15%, of the area Ao the surface So of the bar 6 which is likely to be sealed, called "sealable surface". The sealable surface So corresponds to the surfaces of the portion 23 of the bar 6 which are opposite the internal surfaces of the groove 15 in the block 5.

Lorsque la ou chaque barre de raccordement 6 traverse le bloc cathodique 5 de part en part, comme illustré à la figure 3, l'aire Ao de la surface scellable So est typiquement égale à Lo × (2 H + W), où H est la hauteur de la barre et W sa largeur. Dans ce cas, comme chaque barre de raccordement 6 possède une zone de non-scellement 17 à chaque extrémité 25, l'aire totale A est égale à la somme des aires de chaque surface déterminée S.When the or each connecting bar 6 passes through the cathode block 5 from one end to the other as shown in FIG. figure 3 the area Ao of the sealable surface S0 is typically equal to Lo × (2H + W), where H is the height of the bar and W is its width. In this case, since each connecting bar 6 has a non-sealing zone 17 at each end 25, the total area A is equal to the sum of the areas of each determined surface S.

Lorsque les barres de raccordement 6 s'interrompent vers le centre du bloc pour former deux demi-barres alignées, comme illustré à la figure 4, l'aire Ao de la surface scellable So de chaque demi-barre est typiquement égale à Li x (2 H + W), où H est la hauteur de la barre et W sa largeur. Dans ce cas, comme chaque demi-barre de raccordement 6 possède une zone de non-scellement 17 à une seule extrémité 25, l'aire totale A est égale à l'aire de la surface déterminée S de cette zone de non-scellement. La demanderesse a toutefois constaté que lorsque la discontinuité de la barre près du centre du bloc est relativement courte, ce qui est généralement le cas, elle modifiait peu la répartition du courant et la chute de tension, de sorte que l'aire A pouvait être déterminée comme si les barres étaient continues d'une extrémité à l'autre.When the connecting bars 6 are interrupted towards the center of the block to form two aligned half-bars, as illustrated in FIG. figure 4 the area Ao of the sealable surface S0 of each half-bar is typically equal to Li x (2H + W), where H is the height of the bar and W is its width. In this case, as each half-connecting bar 6 has a non-sealing zone 17 at one end only 25, the total area A is equal to the area of the determined surface S of this non-sealing zone. However, the Applicant has found that when the discontinuity of the bar near the center of the block is relatively short, which is generally the case, it hardly changed the current distribution and the voltage drop, so that the area A could be determined as if the bars were continuous from one end to the other.

La surface déterminée S est typiquement de forme simple afin de faciliter la formation de la zone de non-scellement 17. Dans le cas, illustré aux figures 2 à 4, où la zone de non-scellement 17 est formée par l'absence de scellement sur une longueur Ls, à partir de la surface 27 de la tête de bloc 25, l'aire de la surface déterminée S est typiquement égale à Ls × (2 H + W). Dans ce cas, la longueur Ls de chaque zone de non-scellement 17 est de préférence comprise entre 0,5 et 25 %, de préférence entre 2 et 20 %, de préférence encore entre 3 et 15 %, de la demi-longueur Lo/2 du bloc.The determined surface S is typically of simple shape in order to facilitate the formation of the non-sealing zone 17. In the case, illustrated in FIGS. Figures 2 to 4 where the non-sealing zone 17 is formed by the absence of sealing along a length Ls from the surface 27 of the block head 25, the area of the determined surface S is typically equal to Ls × ( 2H + W). In this case, the length Ls of each non-sealing zone 17 is preferably between 0.5 and 25%, preferably between 2 and 20%, more preferably between 3 and 15%, of the half-length Lo. / 2 of the block.

La section de l'insert 16 influence également la réduction de la chute de tension cathodique. Avantageusement, la section transversale de chaque insert est comprise entre 1 et 50 %, et de préférence entre 5 et 30 %, de la section transversale de la barre 6. En effet, au-delà de 30 % de section totale en insert, la quantité supplémentaire de conducteur apporte un surcoût important pour une faible augmentation des performances.The section of the insert 16 also influences the reduction of the cathodic voltage drop. Advantageously, the cross section of each insert is between 1 and 50%, and preferably between 5 and 30%, of the cross section of the bar 6. In fact, beyond 30% of total insert section, the additional amount of driver provides a significant additional cost for a small increase in performance.

L'insert 16 prend typiquement la forme d'une barre. La forme de la section transversale de l'insert 16 est libre, cette forme pouvant être rectangulaire (tel qu'illustré à la figure 5), circulaire (tel qu'illustré à la figure 6 ou 7), ovoïde ou polygonale... Elle est toutefois avantageusement circulaire afin de faciliter la fabrication de la barre de raccordement, notamment la réalisation de la cavité destinée à loger l'insert.The insert 16 typically takes the form of a bar. The shape of the cross section of the insert 16 is free, this shape being able to be rectangular (as illustrated in FIG. figure 5 ), circular (as illustrated in figure 6 or 7 ), ovoid or polygonal ... It is, however, advantageously circular to facilitate the manufacture of the connecting bar, including the realization of the cavity for housing the insert.

La demanderesse a effectué des calculs numériques destinés à évaluer la répartition du courant cathodique à la surface 28 du bloc cathodique obtenue avec des configurations selon l'art antérieur et selon l'invention.The Applicant has carried out numerical calculations intended to evaluate the distribution of the cathodic current at the surface 28 of the cathode block obtained with configurations according to the prior art and according to the invention.

La figure 8 présente les résultats d'un calcul correspondant à des dimensions de barre de raccordement et une intensité de courant typiques des cellules d'électrolyse existantes. Les courbes correspondent à la densité de courant J à la surface supérieure 28 du bloc, exprimée en kA/m2, en fonction de la distance D de l'extrémité du bloc.The figure 8 presents the results of a calculation corresponding to connection bar dimensions and a current intensity typical of existing electrolysis cells. The curves correspond to the current density J at the upper surface 28 of the block, expressed in kA / m 2 , as a function of the distance D from the end of the block.

La cellule comporte 20 éléments cathodiques disposés côte à côte et comportant chacun deux barres de raccordement, tel qu'illustré à la figure 3. L'intensité totale est de 314 kA. Les barres de raccordement ont une longueur L égale à 4,3 m, une hauteur H égale à 160 mm et une largeur W égale à 110 mm. La longueur E des barres de raccordement sortant des blocs cathodiques est de 0,50 m.The cell has 20 cathode elements arranged side by side and each having two connection bars, as illustrated in FIG. figure 3 . The total intensity is 314 kA. The connecting bars have a length L equal to 4.3 m, a height H equal to 160 mm and a width W equal to 110 mm. The length E of the connecting bars leaving the cathode blocks is 0.50 m.

La courbe A, relative à l'art antérieur, correspond à une barre de raccordement entièrement en acier. La chute de tension cathodique est de 283 mV (entre le centre de la nappe de métal liquide et le cadre anodique de la cuve aval).Curve A, relating to the prior art, corresponds to a connection bar made entirely of steel. The cathodic voltage drop is 283 mV (between the center of the liquid metal sheet and the anode frame of the downstream tank).

La courbe B, relative à l'art antérieur, correspond à une barre en acier ayant les mêmes dimensions que dans le cas A, mais comportant un insert cylindrique en cuivre d'une longueur égale à 1,53 m dont le diamètre est égal à 4,13 cm. L'insert est placé le long de l'axe de symétrie longitudinal de la barre et s'étend approximativement du centre de la barre (c'est-à-dire approximativement du plan central P de la cuve) jusqu'à environ la moitié de l'épaisseur du revêtement de côté 3' de la cellule. La chute de tension cathodique est de 229 mV. Par rapport au cas A, la réduction de la chute cathodique est d'environ 19 % et la réduction du pic de densité de courant est d'environ 18 %.Curve B, relating to the prior art, corresponds to a steel bar having the same dimensions as in case A, but having a cylindrical copper insert with a length equal to 1.53 m, the diameter of which is equal to 4.13 cm. The insert is placed along the longitudinal axis of symmetry of the bar and extends approximately from the center of the bar (i.e. approximately from the central plane P of the vessel) to about half the thickness of the side coating 3 ' of the cell. The cathode voltage drop is 229 mV. Compared to Case A, the The reduction in cathodic drop is about 19% and the reduction in current density peak is about 18%.

La courbe C, relative à l'invention, correspond à une barre en acier ayant les mêmes dimensions que dans le cas A, mais comportant un insert cylindrique en cuivre d'une longueur Lc égale à 1,30 m dont le diamètre est égal à 4,5 cm (correspondant à un volume de cuivre identique à celui du cas B). L'insert est placé le long de l'axe de symétrie longitudinal de la barre et s'étend, comme dans la figure 2, de l'extrémité extérieure de la barre jusqu'à l'intérieur de la cellule. La zone de non-scellement a une longueur de 0,18 m et concerne les trois faces normalement scellées de la barre. La chute de tension cathodique est de 190 mV. Par rapport au cas A, la réduction de la chute cathodique est d'environ 32 % et la réduction du pic de densité de courant est d'environ 37 %. La répartition du courant cathodique est nettement plus homogène que dans les cas A et B.Curve C, relating to the invention, corresponds to a steel bar having the same dimensions as in case A, but comprising a cylindrical copper insert with a length Lc equal to 1.30 m, the diameter of which is equal to 4.5 cm (corresponding to a volume of copper identical to that of case B). The insert is placed along the longitudinal axis of symmetry of the bar and extends, as in the figure 2 from the outer end of the bar to the inside of the cell. The non-sealing zone is 0.18 m long and covers the three normally sealed sides of the bar. The cathodic voltage drop is 190 mV. With respect to case A, the reduction of the cathode drop is about 32% and the reduction of the current density peak is about 37%. The distribution of cathodic current is much more homogeneous than in cases A and B.

Claims (19)

  1. Cathode element (20), for use in a pot (10) of an electrolytic cell (1) intended for production of aluminium, comprising:
    - a cathode block (5) made of a carbonaceous material with at least one longitudinal groove (15) along one of its side faces (21);
    - at least one steel connection bar (6), of which at least one part called the "external segment" (19) will be located outside the pot (10), which is housed in the said groove (15) such that a part (22) of the bar called the "part outside the block" emerges at least at one end (25) of the block called "block head", and which is sealed in the groove (15) by insertion of a conducting sealing material (7) such as cast iron or conducting paste between the bar and the block,
    and characterised in that for each external segment (19):
    - the connection bar (6) includes at least a metal insert (16) with length Lc, whose electrical conductivity is higher than the electrical conductivity of the said steel, which is arranged longitudinally inside the bar and which is at least partly located in the said segment (19);
    - the connection bar (6) is not sealed to the cathode block (5) in at least a zone called the "unsealed" zone (17) with a determined surface area S located at the end of the groove (15) at the head of the block, the total area A of the determined surface(s) S of the unsealed zone(s) (17) of each connection bar (6) is between 0.5 and 25% of the area Ao of the surface So of the bar (6) that may be sealed.
  2. Cathode element (20) according to claim 1, characterised in that each insert (16) is made of copper or a copper based alloy.
  3. Cathode element (20) according to either of claim 1 or 2, characterised in that the length Lc of each insert (16) is between 10 and 300% of the length E of the "part outside the block" (22) of the bar (6) in which the insert is housed.
  4. Cathode element (20) according to either of claim 1 or 2, characterised in that the length Lc of each insert (16) is between 20 and 300% of the length E of the "part outside the block" (22) of the bar (6) in which the insert is housed.
  5. Cathode element (20) according to either of claim 1 or 2, characterised in that the length Lc of each insert (16) is between 110 and 270% of the length E of the "part outside the block" (22) of the bar (6) in which the insert is housed.
  6. Cathode element (20) according to any one of claims 1 to 5, characterised in that the cross section of each insert (16) is between 1 and 50% of the cross section of the bar (6).
  7. Cathode element (20) according to any one of claims 1 to 5, characterised in that the cross section of each insert (16) is between 5 and 30% of the cross section of the bar (6).
  8. Cathode element (20) according to any one of claims 1 to 7, characterised in that the total area A of the determined surface(s) S of the unsealed zone(s) (17) of each connection bar (6) is between 2 and 20% of the area Ao of the surface So of the bar (6) that may be sealed.
  9. Cathode element (20) according to any one of claims 1 to 8, characterised in that the total area A of the determined surface(s) S of the unsealed zone(s) (17) of each connection bar (6) is between 3 and 15% of the area Ao of the surface So of the bar (6) that may be sealed.
  10. Cathode element (20) according to any one of claims 1 to 9, characterised in that an electrically insulating material is inserted between the connection bar (6) and the cathode block (5) in the unsealed zone or each unsealed zone (17).
  11. Cathode element (20) according to any one of claims 1 to 10, characterised in that each insert (16) is flush, with a defined tolerance, with the surface (24) of the end of the external segment (19) of the bar (6).
  12. Cathode element (20) according to claim 11, characterised in that the said determined tolerance is less than or equal to ± 1 cm.
  13. Cathode element (20) according to any one of claims 1 to 10, characterised in that the external end of each insert (16) is set back by a determined distance from the surface (24) of the end of the external segment (19) of the bar (6).
  14. Cathode element (20) according to claim 13, characterised in that the said determined distance is less than or equal to 4 cm.
  15. Cathode element (20) according to claim 14, characterised in that the cavity formed by setting back the insert contains a refractory material.
  16. Cathode element (20) according to any one of claims 1 to 15, characterised in that the cross section of each insert (16) is circular.
  17. Cathode element (20) according to any one of claims 1 to 16, characterised in that each insert (16) is housed in a cavity forming a blind hole inside the bar (6).
  18. Cathode element (20) according to any one of claims 1 to 17, characterised in that the said carbonaceous material contains graphite.
  19. Electrolytic cell (1) intended for the production of aluminium, characterised in that it comprises at least a cathode element (20) according to any one of claims 1 to 18.
EP05744310.3A 2004-04-02 2005-03-30 Cathode element for an electrolysis cell for the production of aluminium Active EP1733075B1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
SI200532251T SI1733075T1 (en) 2004-04-02 2005-03-30 Cathode element for an electrolysis cell for the production of aluminium
PL05744310T PL1733075T3 (en) 2004-04-02 2005-03-30 Cathode element for an electrolysis cell for the production of aluminium

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR0403497A FR2868435B1 (en) 2004-04-02 2004-04-02 CATHODIC ELEMENT FOR THE EQUIPMENT OF AN ELECTROLYSIS CELL INTENDED FOR THE PRODUCTION OF ALUMINUM
PCT/FR2005/000757 WO2005098093A2 (en) 2004-04-02 2005-03-30 Cathode element for an electrolysis cell for the production of aluminium

Publications (2)

Publication Number Publication Date
EP1733075A2 EP1733075A2 (en) 2006-12-20
EP1733075B1 true EP1733075B1 (en) 2019-03-13

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EP05744310.3A Active EP1733075B1 (en) 2004-04-02 2005-03-30 Cathode element for an electrolysis cell for the production of aluminium

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US (1) US7618519B2 (en)
EP (1) EP1733075B1 (en)
CN (1) CN1938454B (en)
AR (1) AR051433A1 (en)
AU (1) AU2005232010B2 (en)
BR (1) BRPI0509509B1 (en)
CA (1) CA2559372C (en)
EG (1) EG24808A (en)
FR (1) FR2868435B1 (en)
NO (1) NO343609B1 (en)
PL (1) PL1733075T3 (en)
RU (1) RU2364663C2 (en)
SI (1) SI1733075T1 (en)
TR (1) TR201906708T4 (en)
WO (1) WO2005098093A2 (en)
ZA (1) ZA200608183B (en)

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TW200925328A (en) 2007-10-29 2009-06-16 Bhp Billiton Aluminium Technologies Ltd Composite collector bar
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CN102234820B (en) * 2011-08-04 2013-03-20 中国铝业股份有限公司 Method for reducing horizontal current in molten aluminum of aluminum electrolysis bath
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CN103014765B (en) * 2011-09-24 2016-07-06 沈阳铝镁设计研究院有限公司 Cathode structure for reducing horizontal current in aluminum liquid
CA2878424C (en) 2012-08-09 2020-03-24 Mid Mountain Materials, Inc. Seal assemblies for cathode collector bars
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CN103233245B (en) * 2013-05-23 2015-04-29 黄河鑫业有限公司 Method for monitoring and accurately judging damages of online electrolytic cell cathode lining
AU2015348020B2 (en) 2014-11-18 2018-05-17 Novalum Sa Cathode current collector for a hall-heroult cell
GB2542150A (en) * 2015-09-09 2017-03-15 Dubai Aluminium Pjsc Cathode assembly for electrolytic cell suitable for the Hall-Héroult process
GB2548830A (en) * 2016-03-29 2017-10-04 Dubai Aluminium Pjsc Cathode block with copper-aluminium insert for electrolytic cell suitable for the Hall-Héroult process
RU2657682C2 (en) * 2016-07-19 2018-06-14 Общество с ограниченной ответственностью "Объединенная Компания РУСАЛ Инженерно-технологический центр" Cathode current conducting rod of aluminum reduction cell
EP3491175A1 (en) * 2016-07-26 2019-06-05 COBEX GmbH Cathode assembly for the production of aluminum
JP2019527462A (en) * 2016-07-26 2019-09-26 コベックス・ゲーエムベーハー Hall Elsell cathode current collector / connector
BR112019004699B1 (en) * 2016-09-09 2022-08-16 Glencore Technology Pty Ltd SUSPENSION BAR FOR AN ELECTRODEPOSITION CELL OR AN ELECTROLYTE REFINING CELL AND ELECTRODEPOSITION CATHODE ASSEMBLY
GB2554702A (en) * 2016-10-05 2018-04-11 Dubai Aluminium Pjsc Cathode assembly for electrolytic cell suitable for the Hall-Héroult process
CN109666953A (en) * 2017-10-16 2019-04-23 沈阳铝镁设计研究院有限公司 A kind of compound, highly conductive cathode steel bar
CN110605677B (en) * 2019-09-16 2024-02-06 中冶天工集团有限公司 Detachable cathode carbon block assembling and fixing device and use method
CN115103931A (en) * 2019-12-24 2022-09-23 阿迪特亚比拉科技私人有限公司 Device for improving performance of aluminum reduction cell in smelting process
NO20201415A1 (en) * 2020-12-21 2022-06-22 Storvik As Method for producing a cathode steel bar with copper insert, and method for removing a copper insert from a used cathode bar
BR112023023545A2 (en) * 2021-05-10 2024-02-06 Novalum S A CATHODIC CURRENT COLLECTION BAR OF AN ALUMINUM PRODUCTION CELL

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RU2364663C2 (en) 2009-08-20
TR201906708T4 (en) 2019-05-21
NO20064798L (en) 2006-12-21
NO343609B1 (en) 2019-04-15
SI1733075T1 (en) 2019-06-28
BRPI0509509A (en) 2007-09-11
WO2005098093A2 (en) 2005-10-20
WO2005098093A3 (en) 2006-07-20
AR051433A1 (en) 2007-01-17
AU2005232010B2 (en) 2009-11-19
FR2868435B1 (en) 2006-05-26
BRPI0509509B1 (en) 2015-10-27
PL1733075T3 (en) 2019-08-30
AU2005232010A1 (en) 2005-10-20
FR2868435A1 (en) 2005-10-07
CA2559372C (en) 2012-09-04
CN1938454A (en) 2007-03-28
RU2006138619A (en) 2008-05-10
CN1938454B (en) 2011-12-28
CA2559372A1 (en) 2005-10-20
EG24808A (en) 2010-09-19
US7618519B2 (en) 2009-11-17
ZA200608183B (en) 2008-07-30
EP1733075A2 (en) 2006-12-20
US20050218006A1 (en) 2005-10-06

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