EP0169152B1 - Modular cathodic block and cathode with a low-voltage drop for hall-heroult electrolysis vats - Google Patents

Modular cathodic block and cathode with a low-voltage drop for hall-heroult electrolysis vats Download PDF

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Publication number
EP0169152B1
EP0169152B1 EP85420107A EP85420107A EP0169152B1 EP 0169152 B1 EP0169152 B1 EP 0169152B1 EP 85420107 A EP85420107 A EP 85420107A EP 85420107 A EP85420107 A EP 85420107A EP 0169152 B1 EP0169152 B1 EP 0169152B1
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Prior art keywords
cathode
blocks
electrolysis tank
block
tank according
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German (de)
French (fr)
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EP0169152A1 (en
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Bernard Langon
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Rio Tinto France SAS
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Aluminium Pechiney SA
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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
    • C25C3/08—Cell construction, e.g. bottoms, walls, cathodes

Definitions

  • the present invention relates to a tank for the production of aluminum by electrolysis of alumina dissolved in molten cryolite, according to the Hall-Héroult process, the cathode of which consists of modular carbonaceous cathode blocks, with low voltage drop.
  • the cathode of a Hall-Héroult electrolysis tank is formed by the juxtaposition of a set of carbonaceous blocks, provided, at their lower base, with one (or sometimes two) open groove (s) in which are sealed, generally by casting, steel bars of square, rectangular or circular section, on which are connected the connecting conductors between the successive tanks forming a series.
  • These blocks are generally joined by a carbonaceous paste known as pot lining paste, not very conductive of the current, and the thickness of which is several centimeters.
  • carbon blocks with two narrow grooves are also used which have the advantage of increasing the contact surface for sealing without weakening the block too much when it is subjected to the thermal stresses of the electrolyser. A minimum distance must then be observed between the edge of the block and the nearest groove, which limits the possible cross-section of the steel bars.
  • the construction of the cathode is always carried out by placing the blocks parallel to the short side of the metal box, so that the cathode outlets (ends of the iron bars which protrude outside the box, and on which the connecting conductors between tanks are connected), are always on the long side of the tank, that the tanks are arranged lengthwise or crosswise with respect to the axis of the series.
  • the present invention is based on a new design of cathodes which can be described as “modular”, because it adapts, by varying the number of modules, to any size of tank which is an integer multiple of the dimensions of the module .
  • this tank comprising a parallelepiped metal box supporting a cathode on which the sheet of liquid aluminum is formed, this cathode being constituted by the juxtaposition of parallelepipedal carbonaceous blocks, of elongated shape, having a ratio of the length of the major axis to width at least equal to two, and in which is cut at least one groove in which is sealed a steel bar arranged parallel to the short side of the box and which is connected to at least one cathode collector, characterized in that the sealing grooves are cut in the direction perpendicular to the long axis of the block, which is itself arranged parallel to the long side of the box.
  • a cathode half-module By associating, by gluing on a large lateral face, a first cathode block, with at least a second block, a cathode half-module is formed, the width of which corresponds to the half width of the cathode.
  • a cathode module By combining two half-modules, by a means such as bonding, a cathode module is formed, the width of which corresponds to the width of the cathode.
  • Figure 1 is a reminder of the prior art.
  • FIGS 2 to 5 illustrate the implementation of the invention itself.
  • FIG. 1 shows schematically and partially in plan the cathode of an electrolytic cell according to the current technique.
  • the cathode blocks (1) are arranged parallel to the short side (2) of the metal box which supports the cathode of the electrolysis tank.
  • These blocks are of elongated parallelepiped shape with a long axis AA ′, the height h and the width I generally being of the order of 300 to 700 mm, and the length of the order of 2 meters and beyond.
  • the length to width ratio is, in most cases, greater than 2 and can reach 4 to 8.
  • the height and width are often in a ratio little different from 1.
  • each block (1) comprises two bars (3) often each constituted, in practice, by two half-bars (3A) and (3B) which may - or may not - be joined in their central part. (4). At their end (5), on the outside, the cathode bars are connected to one or more lateral conductors such as (6) connected to the anode frame of the next tank in the series. The bars are most often sealed with cast iron in one or two longitudinal grooves (7) of the block (1).
  • the successive cathode blocks are sealed by a hot-grouted pot lining joint (8), which seals the entire cathode against infiltration of liquid aluminum and molten electrolyte , tightness on which the life of the tank closely depends.
  • the cathode blocks (10) are arranged so that their major axis AA 'is parallel to the long side (11) of the box and to its major axis XX'.
  • the cathode bars (3) and the outlets (5), as well as the collector (6) keep the same arrangement, but the grooves (12) are now cut across the cathode block, parallel to its short side, therefore perpendicular to its major axis AA '.
  • Each “cathode half-module is constituted by the association of two blocks (10A) and (10B) previously assembled by a means such as bonding (9), the positioning and sealing of the cathode bars being effected by the usual processes such as sealing with cast iron or, more rarely, carbonaceous paste.
  • the two half-modules (10A-10B) and (10C-10D) are grouted in the usual way, by pot lining (13), or preferably by gluing. This jointing can be carried out before or after installation in the box.
  • This first module cathodic is then completed by n identical modules grouted with pot lining (8), depending on the type of tank.
  • a cathode for a 180,000 amp cell for example, can be constructed from three successive modules. Although half modules have been described, each consisting of two blocks, this example does not constitute a limitation of the invention.
  • Each of the two blocks constituting a cathode half-module (10A) and (10B) can be of identical composition, that is to say obtained from the same carbonaceous paste, or of different composition, so as to give one of them has special properties, for example a different thermal or electrical conductivity.
  • the external block (10A) can, for example, be of the conventional type (pitch + anthracite grains), having at 900 ° C. an electrical resistivity of the order of 4.4 - 10 -3 ⁇ cm and a thermal conductivity At the order of 0.03 W / cm / ° C, while the inner block (10B) can be of the “semi-graphite” type, having at 900 ° C, an electrical resistivity of 2.8 ⁇ 10 - 3 ⁇ cm and a thermal conductivity ⁇ of 0.23 W / cm / ° C.
  • the external block (10A) can itself be made up of two parts, the external part (10E) being made of material with relatively low thermal conductivity, so as to reduce the heat flow drained towards the outside by the carbon blocks and thus improve the thermal balance of the electrolyser.
  • sections of the sealing grooves (12) may all be of equal width, or some, in particular those of the ends, may be different, for example in order to have a constant spacing between the holes provided in the side wall of the box. , through which the cathode bars come out.
  • the cathode blocks constituting the cathode it is possible, on at least part of the surface of the cathode blocks constituting the cathode, to incorporate a substance which makes them wettable by liquid aluminum. This incorporation can be superficial or concern all or part of the cathode blocks.
  • the useful cathode surface is increased due to the replacement of the pot lining joints 30 to 40 mm wide - electrically not very conductive - by glued joints of very small thickness, of the order of a millimeter.
  • FIG. 5 which represents, on a scale of approximately 1/20 °, vertical sections of cathode blocks according to the prior art (5A) and (5B), and according to the invention (5C), it can be seen that the we go, for a given vertical section, from 36.8 dm of sealing contact length and 17.16 dm2 of steel and cast iron section for case 5A, to 29.2 dm of contact length and 26.4 dm2 of section for case 5B, and at 41.6 dm of contact length and 25.08 dm 2 of section for case 5C.
  • the invention is compatible with the use of cathode surfaces wettable by liquid aluminum.
  • the invention has been implemented on several tanks of a series operating at 180,000 amperes, by constituting the cathode from half-modules made up of two “semi-graphite” blocks in accordance with the drawing in FIG. 5C.
  • the maximum gain obtained is 61 mV, which corresponds to almost 200 kWh less per tonne of aluminum produced. This gain was obtained for half by the use of “semi-graphite blocks with lower resistivity, and for half by the implementation of the invention of modular cathode block.

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  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
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  • Organic Chemistry (AREA)
  • Electrolytic Production Of Metals (AREA)
  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
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Abstract

The invention relates to a carbonaceous cathodic block having a low voltage drop, which is intended for tanks for the production of aluminium by electrolysis using the Hall-Heroult process, said tanks comprising a parallelepipedic metal casing supporting a cathode on which the layer of liquid aluminium is formed, said cathode being formed by the juxtaposition of parallelepipedic carbonaceous blocks of elongate shape wherein the ratio of the length of the major axis to the width is at least equal to two and in which there is cut at least one groove into which is sealed a steel bar which is disposed in parallel relationship to the short side of the casing and which connects to at least one cathodic collector, characterized in that the sealing grooves are cut in the direction perpendicular to the major axis of the block which is itself disposed in parallel relationship to the long side of the casing.

Description

La présente invention concerne une cuve pour la production d'aluminium par électrolyse d'alumine dissoute dans la cryolithe fondue, selon le procédé Hall-Héroult, dont la cathode est constituée de blocs cathodiques carbonés modulaires, à faible chute de tension.The present invention relates to a tank for the production of aluminum by electrolysis of alumina dissolved in molten cryolite, according to the Hall-Héroult process, the cathode of which consists of modular carbonaceous cathode blocks, with low voltage drop.

Exposé de l'art antérieurPresentation of the prior art

La cathode d'une cuve d'électrolyse Hall-Héroult est constituée par la juxtaposition d'un ensemble de blocs carbonés, munis, à leur base inférieure, d'une (ou parfois deux) rainure(s) ouverte(s) dans lesquelles sont scellées, généralement par coulée de fonte, des barres d'acier de section carrée, rectangulaire ou circulaire, sur lesquelles sont raccordés les conducteurs de liaison entre les cuves successives formant une série. Ces blocs sont généralement jointoyés par une pâte carbonée dite pâte de brasque, peu conductrice du courant, et dont l'épaisseur est de plusieurs centimètres.The cathode of a Hall-Héroult electrolysis tank is formed by the juxtaposition of a set of carbonaceous blocks, provided, at their lower base, with one (or sometimes two) open groove (s) in which are sealed, generally by casting, steel bars of square, rectangular or circular section, on which are connected the connecting conductors between the successive tanks forming a series. These blocks are generally joined by a carbonaceous paste known as pot lining paste, not very conductive of the current, and the thickness of which is several centimeters.

Celle-ci doit être étanche à l'aluminium liquide qui se dépose par électrolyse au-dessus des blocs carbonés. Le courant électrique traverse donc dans l'ordre une couche d'aluminium liquide, une partie carbonée, les scellements barre-bloc, les barres en acier et passe dans les conducteurs de liaison à la cuve suivante.This must be impermeable to liquid aluminum which is deposited by electrolysis on top of the carbon blocks. The electric current therefore passes in order through a layer of liquid aluminum, a carbonaceous part, the bar-block seals, the steel bars and passes through the connecting conductors to the next tank.

Chaque changement de matériau se traduit par une surtension de contact qui dépend des conditions d'assemblage et des surfaces sollicitées. Ceci est particulièrement vrai pour le contact carbone- scellement appelé contact de scellement.Each change of material results in a contact overvoltage which depends on the assembly conditions and the surfaces requested. This is particularly true for the carbon-sealing contact called sealing contact.

La chute de tension totale peut donc se décomposer en trois éléments prépondérants :

  • - la chute dans le carbone
  • - la chute au scellement
  • - la chute dans la barre en acier.
The total voltage drop can therefore be broken down into three main elements:
  • - the fall in carbon
  • - drop in sealing
  • - the fall into the steel bar.

Pour réduire cette chute de tension, il est connu d'utiliser des blocs carbonés de basse résistivité électrique.To reduce this voltage drop, it is known to use carbon blocks of low electrical resistivity.

A l'heure actuelle, la plupart des producteurs de blocs cathodiques proposent des blocs dits « semi-graphite obtenus à partir d'une pâte carbonée dans laquelle les grains d'anthracite ont été remplacés par des grains de graphite, et des blocs « semi-graphités •, obtenus à partir d'une pâte carbonée classique, mais avec cuisson à température élevée (> 2 000 °C) de façon à graphiter partiellement le bloc dans la masse. On augmente ainsi sensiblement la conductivité électrique des blocs. Mais ce type de bloc présente le défaut d'augmenter les distorsions de courant électrique dans la nappe d'aluminium liquide supérieure par suite d'une plus grande inclinaison des lignes de courant dans l'aluminium liquide, et de ce fait, d'augmenter les turbulences magnétiques de cette nappe ce qui dégrade la stabilité hydrodynamique de l'électrolyseur.At present, most producers of cathode blocks offer so-called “semi-graphite” blocks obtained from a carbonaceous paste in which the anthracite grains have been replaced by graphite grains, and “semi-graphite” blocks. - graphics •, obtained from a conventional carbon paste, but with baking at high temperature (> 2000 ° C) so as to partially graphitize the block in the mass. This substantially increases the electrical conductivity of the blocks. However, this type of block has the defect of increasing the distortions of electric current in the upper layer of liquid aluminum as a result of a greater inclination of the current lines in the liquid aluminum, and therefore of increasing the magnetic turbulence of this layer which degrades the hydrodynamic stability of the electrolyser.

On peut, pour corriger ce défaut, utiliser la technique des « blocs Sandwich , dont une partie est constituée, par exemple, à partir de pâte carbonée avec grains d'anthracite, et une autre partie de pâte carbonée semi-graphite ou semi-graphitée, de conductivité électrique plus élevée.We can, to correct this defect, use the technique of “Sandwich blocks, part of which is made, for example, from carbonaceous paste with grains of anthracite, and another part of semi-graphite or semi-graphite carbonaceous paste , higher electrical conductivity.

On a également proposé, pour augmenter la surface active de la cathode de substituer au jointoiement des blocs à la pâte de brasque (peu conductrice du courant), un collage au moyen d'une colle conductrice à base de graphite et de résines thermodurcissables. Cela a le quadruple avantage d'augmenter la surface totale conductrice, de permettre des transferts électriques entre deux blocs adjacents, de réduire les émissions de goudrons à la mise en place du jointoiement carboné et d'améliorer l'étanchéité.It has also been proposed, in order to increase the active surface of the cathode, to replace the jointing of the blocks with the pot lining (not very conductive of the current), bonding by means of a conductive adhesive based on graphite and thermosetting resins. This has the quadruple advantage of increasing the total conductive surface, of allowing electrical transfers between two adjacent blocks, of reducing the tar emissions when the carbonaceous joint is put in place and of improving the sealing.

Pour réduire la chute de tension totale, il est également connu d'augmenter la section de la barre d'acier, au moins dans la zone scellée dans le carbone, tout en gardant une section normale ou rétrécie à la traversée de la partie extérieure du calorifugeage de la cuve, de façon à éviter des fuites thermiques trop importantes.To reduce the total voltage drop, it is also known to increase the section of the steel bar, at least in the area sealed in carbon, while keeping a normal or narrowed section at the crossing of the external part of the insulation of the tank, so as to avoid excessive thermal leakage.

Cependant, une telle action est forcément limitée, car l'épaisseur de carbone des ailes de la rainure doit être suffisante pour résister mécaniquement aux contraintes dues à la dilatation thermique de la barre cathodique, et de son scellement, lors de la mise en régime de la cuve. La forme de la section de la partie scellée peut être indifféremment circulaire ou rectangulaire.However, such an action is necessarily limited, since the carbon thickness of the wings of the groove must be sufficient to mechanically resist the stresses due to the thermal expansion of the cathode bar, and of its sealing, when the system is brought into operation. tank. The shape of the section of the sealed part can be either circular or rectangular.

Pour réduire la chute de tension, on utilise également des blocs carbonés à deux rainures étroites qui ont l'avantage de multiplier la surface de contact au scellement sans trop fragiliser le bloc lorsqu'il est soumis aux contraintes thermiques de marche de l'électrolyseur. On doit alors respecter un minimum de distance entre le bord du bloc et la rainure la plus proche, ce qui limite la section possible des barres d'acier.To reduce the voltage drop, carbon blocks with two narrow grooves are also used which have the advantage of increasing the contact surface for sealing without weakening the block too much when it is subjected to the thermal stresses of the electrolyser. A minimum distance must then be observed between the edge of the block and the nearest groove, which limits the possible cross-section of the steel bars.

Quelle que soit la solution adoptée et quelles que soient la forme et la dimension des blocs et des barres de fer qui sont scellées dans ces blocs, la construction de la cathode est toujours effectuée en disposant les blocs parallèlement au petit côté du caisson métallique, de telle sorte que les sorties cathodiques (extrémités des barres de fer qui dépassent à l'extérieur du caisson, et sur lesquelles sont raccordés les conducteurs de liaison entre cuves), se trouvent toujours sur le grand côté de la cuve, que les cuves soient disposées en long ou en travers par rapport à l'axe de la série.Whatever solution is adopted and whatever the shape and size of the blocks and iron bars which are sealed in these blocks, the construction of the cathode is always carried out by placing the blocks parallel to the short side of the metal box, so that the cathode outlets (ends of the iron bars which protrude outside the box, and on which the connecting conductors between tanks are connected), are always on the long side of the tank, that the tanks are arranged lengthwise or crosswise with respect to the axis of the series.

A l'heure actuelle, les producteurs d'aluminium cherchent à accroître la puissance unitaire des cuves d'électrolyse, en vue, notamment d'augmenter les rendements, de diminuer les coûts d'investissement et de faciliter l'automatisation intégrale de l'exploitation. Le niveau de 200 000 ampères est déjà largement dépassé, et il est très probable que les 400 000 ampères seront atteints avant la fin des années 80.At present, aluminum producers are seeking to increase the unit power of electrolytic cells, with a view, in particular, to increasing yields, reducing investment costs and facilitating full automation of the exploitation. The level of 200,000 amps has already been largely exceeded, and it is very likely that the 400,000 amps will be reached before the end of the 1980s.

Parallèlement, un effort important est fait pour diminuer les consommations énergétiques de la cuve, en particulier en réduisant les chutes ohmiques dans la cathode.At the same time, a significant effort is made to reduce the energy consumption of the tank, in particular by reducing the ohmic drops in the cathode.

La construction de cathodes à basse chute de tension pour des cuves de cette puissance exige de nouvelles solutions qui ne peuvent pas être une simple extrapolation des solutions actuelles. On sait en effet, que la durée de vie d'une cuve est étroitement dépendante de la qualité de sa cathode car la plupart des mises hors-service prématurées sont dues à des infiltrations de métal et d'électrolyte dans l'espace sous-cathodique.The construction of low voltage drop cathodes for vessels of this power requires new solutions which cannot be a simple extrapolation of current solutions. We know, in fact, that the life of a tank is closely dependent on the quality of its cathode because most premature decommissioning are due to infiltration of metal and electrolyte in the sub-cathodic space .

Exposé de l'inventionStatement of the invention

La présente invention est basée sur une conception nouvelle des cathodes que l'on peut qualifier de « modulaire •, car elle s'adapte, en jouant sur le nombre de modules, à toutes dimensions de cuve qui soit un multiple entier des dimensions du module.The present invention is based on a new design of cathodes which can be described as “modular”, because it adapts, by varying the number of modules, to any size of tank which is an integer multiple of the dimensions of the module .

Elle a pour objet une cuve d'électrolyse pour la production d'aluminium selon le procédé Hall-Héroult, cette cuve comportant un caisson métallique parallélépipédique supportant une cathode sur laquelle se forme la nappe d'aluminium liquide, cette cathode étant constituée par la juxtaposition de blocs carbonés parallélépipédiques, de forme allongée, ayant un rapport longueur du grand axe sur largeur au moins égal à deux, et dans lesquels est taillée au moins une rainure dans laquelle est scellée une barre d'acier disposée parallèlement au petit côté du caisson et qui se raccorde à au moins un collecteur cathodique, caractérisée en ce que les rainures de scellement sont taillées dans le sens perpendiculaire au grand axe du bloc, qui est lui-même disposé parallèlement au grand côté du caisson.It relates to an electrolysis tank for the production of aluminum according to the Hall-Héroult process, this tank comprising a parallelepiped metal box supporting a cathode on which the sheet of liquid aluminum is formed, this cathode being constituted by the juxtaposition of parallelepipedal carbonaceous blocks, of elongated shape, having a ratio of the length of the major axis to width at least equal to two, and in which is cut at least one groove in which is sealed a steel bar arranged parallel to the short side of the box and which is connected to at least one cathode collector, characterized in that the sealing grooves are cut in the direction perpendicular to the long axis of the block, which is itself arranged parallel to the long side of the box.

En associant, par collage sur une grande face latérale, un premier bloc cathodique, à au moins un deuxième bloc, on constitue un demi-module cathodique dont la largeur correspond à la demi-largeur de la cathode.By associating, by gluing on a large lateral face, a first cathode block, with at least a second block, a cathode half-module is formed, the width of which corresponds to the half width of the cathode.

En associant deux demi-modules, par un moyen tel que le collage, on constitue un module cathodique dont la largeur correspond à la largeur de la cathode.By combining two half-modules, by a means such as bonding, a cathode module is formed, the width of which corresponds to the width of the cathode.

D'autres modes de réalisation de l'invention ressortiront des revendications 4 à 10 et de la description des figures.Other embodiments of the invention will emerge from claims 4 to 10 and from the description of the figures.

Description des figuresDescription of the figures

La figure 1 est un rappel de l'art antérieur.Figure 1 is a reminder of the prior art.

Les figures 2 à 5 illustrent la mise en oeuvre de l'invention proprement dite.Figures 2 to 5 illustrate the implementation of the invention itself.

La figure 1 représente schématiquement et partiellement en plan la cathode d'une cuve d'électrolyse selon la technique actuelle. Les blocs cathodiques (1) sont disposés parallèlement au petit côté (2) du caisson métallique qui supporte la cathode de la cuve d'électrolyse. Ces blocs sont de forme parallélépipédique allongée de grand axe AA', la hauteur h et la largeur I étant généralement de l'ordre de 300 à 700 mm, et la longueur de l'ordre de 2 mètres et au-delà. Le rapport longueur sur largeur est, dans la plupart des cas, supérieur à 2 et peut atteindre 4 à 8. La hauteur et la largeur sont souvent dans un rapport peu différent de 1.Figure 1 shows schematically and partially in plan the cathode of an electrolytic cell according to the current technique. The cathode blocks (1) are arranged parallel to the short side (2) of the metal box which supports the cathode of the electrolysis tank. These blocks are of elongated parallelepiped shape with a long axis AA ′, the height h and the width I generally being of the order of 300 to 700 mm, and the length of the order of 2 meters and beyond. The length to width ratio is, in most cases, greater than 2 and can reach 4 to 8. The height and width are often in a ratio little different from 1.

Dans le cas particulier représenté figure 1, chaque bloc (1) comporte deux barres (3) souvent constituées chacune, en pratique, par deux demi-barres (3A) et (3B) qui peuvent - ou non - être jointives dans leur partie centrale (4). A leur extrémité (5), côté extérieur, les barres cathodiques sont raccordées à un ou plusieurs conducteurs latéraux tels que (6) reliés au cadre anodique de la cuve suivante dans la série. Les barres sont scellées, le plus souvent, à la fonte dans une ou deux rainures longitudinales (7) du bloc (1).In the particular case represented in FIG. 1, each block (1) comprises two bars (3) often each constituted, in practice, by two half-bars (3A) and (3B) which may - or may not - be joined in their central part. (4). At their end (5), on the outside, the cathode bars are connected to one or more lateral conductors such as (6) connected to the anode frame of the next tank in the series. The bars are most often sealed with cast iron in one or two longitudinal grooves (7) of the block (1).

Les blocs cathodiques successifs sont scellés par un joint de pâte de brasque (8), damé à chaud, qui assure l'étanchéité de l'ensemble de la cathode vis-à-vis des infiltrations d'aluminium liquide et de l'électrolyte fondu, étanchéité dont dépend étroitement la durée de vie de la cuve.The successive cathode blocks are sealed by a hot-grouted pot lining joint (8), which seals the entire cathode against infiltration of liquid aluminum and molten electrolyte , tightness on which the life of the tank closely depends.

Selon l'invention (figure 2 et suivantes), les blocs cathodiques (10) sont disposés de façon que leur grand axe AA' soit parallèle au grand côté (11) du caisson et à son grand axe XX'. Les barres cathodiques (3) et les sorties (5), ainsi que le collecteur (6) conservent la même disposition, mais les rainures (12) sont maintenant taillées en travers du bloc cathodique, parallèlement à son petit côté, donc perpendiculairement à son grand axe AA'.According to the invention (FIG. 2 et seq.), The cathode blocks (10) are arranged so that their major axis AA 'is parallel to the long side (11) of the box and to its major axis XX'. The cathode bars (3) and the outlets (5), as well as the collector (6) keep the same arrangement, but the grooves (12) are now cut across the cathode block, parallel to its short side, therefore perpendicular to its major axis AA '.

Chaque « demi-module cathodique est constitué par l'association de deux blocs (10A) et (10B) préalablement assemblés par un moyen tel que le collage (9), la mise en place et le scellement des barres cathodiques s'effectuant par les procédés habituels tel que le scellement à la fonte ou, plus rarement, à la pâte carbonée. La juxtaposition de deux demi-modules identiques, symétriquement par rapport au grand axe de la cuve, constitue un premier module cathodique. Les deux demi-modules (10A-10B) et (10C-10D) sont jointoyés de façon habituelle, par de la pâte de brasque (13), ou de préférence par collage. Ce jointoiement peut être effectué avant ou après mise en place dans le caisson. Ce premier module cathodique est ensuite complété par n modules identiques jointoyés par de la pâte de brasque (8), selon le type de cuve. Une cathode pour cuve à 180 000 ampères, par exemple, peut être constituée à partir de trois modules successifs. Bien que l'on ait décrit des demi-modules constitués chacun de deux blocs, cet exemple ne constitue pas une limitation de l'invention. On peut concevoir des demi-produits constitués de deux blocs inégaux en largeur, ou de trois blocs égaux ou inégaux en largeur, la hauteur et la longueur devant, par contre, être égales dans tous les cas.Each “cathode half-module is constituted by the association of two blocks (10A) and (10B) previously assembled by a means such as bonding (9), the positioning and sealing of the cathode bars being effected by the usual processes such as sealing with cast iron or, more rarely, carbonaceous paste. The juxtaposition of two identical half-modules, symmetrically with respect to the major axis of the tank, constitutes a first cathode module. The two half-modules (10A-10B) and (10C-10D) are grouted in the usual way, by pot lining (13), or preferably by gluing. This jointing can be carried out before or after installation in the box. This first module cathodic is then completed by n identical modules grouted with pot lining (8), depending on the type of tank. A cathode for a 180,000 amp cell, for example, can be constructed from three successive modules. Although half modules have been described, each consisting of two blocks, this example does not constitute a limitation of the invention. One can conceive of semi-finished products made up of two unequal blocks in width, or three equal or unequal blocks in width, the height and the length having, on the other hand, to be equal in all cases.

A partir de ce principe de base, plusieurs modes de mise en oeuvre de l'invention sont possibles. Chacun des deux blocs constituant un demi-module cathodique (10A) et (10B) peut être de composition identique, c'est-à-dire obtenu à partir d'une même pâte carbonée, ou de composition différente, de façon à conférer à l'un d'eux des propriétés particulières, par exemple une conductivité thermique ou électrique différente.From this basic principle, several modes of implementing the invention are possible. Each of the two blocks constituting a cathode half-module (10A) and (10B) can be of identical composition, that is to say obtained from the same carbonaceous paste, or of different composition, so as to give one of them has special properties, for example a different thermal or electrical conductivity.

Le bloc extérieur (10A) peut, par exemple, être du type classique (brai + grains d'anthracite), ayant à 900 °C une résistivité électrique de l'ordre de 4,4 - 10-3 Ω cm et une conductivité thermique À de l'ordre de 0,03 W/cm/°C, alors que le bloc intérieur (10B) peut être du type « semi-graphite • , ayant à 900 °C, une résistivité électrique de 2,8 · 10-3 Ω cm et une conductivité thermique λ de 0,23 W/cm/°C.The external block (10A) can, for example, be of the conventional type (pitch + anthracite grains), having at 900 ° C. an electrical resistivity of the order of 4.4 - 10 -3 Ω cm and a thermal conductivity At the order of 0.03 W / cm / ° C, while the inner block (10B) can be of the “semi-graphite” type, having at 900 ° C, an electrical resistivity of 2.8 · 10 - 3 Ω cm and a thermal conductivity λ of 0.23 W / cm / ° C.

Dans une variante représentée figure 3, le bloc extérieur (10A) peut lui-même être constitué en deux parties, la partie externe (10E) étant en matériau à conductivité thermique relativement faible, de façon à réduire le flux de chaleur drainé vers l'extérieur par les blocs carbonés et à améliorer ainsi le bilan thermique de l'électrolyseur.In a variant shown in FIG. 3, the external block (10A) can itself be made up of two parts, the external part (10E) being made of material with relatively low thermal conductivity, so as to reduce the heat flow drained towards the outside by the carbon blocks and thus improve the thermal balance of the electrolyser.

Enfin, les sections des rainures de scellement (12) peuvent être toutes de largeur égale, ou certaines, notamment celles des extrémités, peuvent être différentes, par exemple en vue d'avoir un écartement constant entre les trous prévus dans la paroi latérale du caisson, par lesquels sortent les barres cathodiques.Finally, the sections of the sealing grooves (12) may all be of equal width, or some, in particular those of the ends, may be different, for example in order to have a constant spacing between the holes provided in the side wall of the box. , through which the cathode bars come out.

Par ailleurs, on peut, sur une partie au moins de la surface des blocs cathodiques constituant la cathode, incorporer une substance qui les rende mouillables par l'aluminium liquide. Cette incorporation peut être superficielle ou intéresser tout ou partie des blocs cathodiques.Furthermore, it is possible, on at least part of the surface of the cathode blocks constituting the cathode, to incorporate a substance which makes them wettable by liquid aluminum. This incorporation can be superficial or concern all or part of the cathode blocks.

Il est connu, notamment par la publication de K. Billehaug et H. A. Oye, « ALUMINIUM 56, 1980, pages 642 à 648 (avril 1980) et pages 713 à 718 (nov. 1980) que les composés réfractaires dits « RHM (Refractory Hard Metals), et plus particulièrement le diborure de titane TiB2, sont à la fois mouillés par l'aluminium liquide et relativement très peu attaqués par ce métal à 930-960 °C.It is known, in particular by the publication of K. Billehaug and HA Oye, "ALUMINUM 56, 1980, pages 642 to 648 (April 1980) and pages 713 to 718 (Nov. 1980) that the refractory compounds known as" RHM (Refractory Hard Metals), and more particularly the titanium diboride TiB2, are both wetted by liquid aluminum and relatively little attacked by this metal at 930-960 ° C.

On peut ainsi soit revêtir totalement ou partiellement la surface des blocs cathodiques, de plaques ou autres éléments en TiB2 pur ou en composite titrant au moins 30 en TiB2, soit effectuer, par tous moyens connus, un dépôt de TiB2, ou de composite à base de TiB2, sur tout ou partie de la surface cathodique, soit introduire dans la pâte carbonée constituant les blocs cathodiques, ou tout au moins la partie supérieure des blocs cathodiques en contact avec l'aluminium liquide, du TiB2 et/ou un composé RHM, à une teneur au moins égale à 30 %, qui est le minimum reconnu pour assurer l'effet de mouillabilité. On peut ainsi stabiliser la nappe d'aluminium liquide et réduire sensiblement la distance anode-cathode, donc la chute de tension dans le bain d'électrolyse, ce qui entraîne une réduction corrélative de l'énergie spécifique en kilowatts heure par tonne d'aluminium produit.It is thus possible either to completely or partially coat the surface of the cathode blocks, of plates or other elements in pure TiB2 or in composite titrating at least 30 in TiB2, or to carry out, by any known means, a deposition of TiB2, or of composite based TiB2, over all or part of the cathode surface, either introduce into the carbonaceous paste constituting the cathode blocks, or at least the upper part of the cathode blocks in contact with liquid aluminum, TiB2 and / or an RHM compound, at a content at least equal to 30%, which is the minimum recognized for ensuring the wettability effect. We can thus stabilize the sheet of liquid aluminum and significantly reduce the anode-cathode distance, therefore the voltage drop in the electrolysis bath, which results in a corresponding reduction in specific energy in kilowatt hours per ton of aluminum product.

Avantages procurés par l'inventionBenefits of the invention

La mise en oeuvre de l'invention procure de très nombreux avantages, que l'on peut présenter de la façon suivante :The implementation of the invention provides numerous advantages, which can be presented as follows:

1. La surface cathodique utile est augmentée du fait du remplacement des joints en pâte de brasque de 30 à 40 mm de largeur - électriquement peu conducteurs - par des joints collés de très faible épaisseur, de l'ordre du millimètre.1. The useful cathode surface is increased due to the replacement of the pot lining joints 30 to 40 mm wide - electrically not very conductive - by glued joints of very small thickness, of the order of a millimeter.

2. On peut maintenant concilier une section d'acier importante avec une surface de contact carbone- acier importante, ce qui n'était pas le cas selon l'art antérieur.2. It is now possible to reconcile a large section of steel with a large carbon-steel contact surface, which was not the case according to the prior art.

Sur la figure 5 qui représente, à échelle d'environ 1/20°, des sections verticales de blocs cathodiques selon l'art antérieur (5A) et (5B), et selon l'invention (5C), on constate que l'on passe, pour une coupe verticale donnée, de 36,8 dm de longueur de contact de scellement et 17,16 dm2 de section acier et fonte pour le cas 5A, à 29,2 dm de longueur de contact et 26,4 dm2 de section pour le cas 5B, et à 41,6 dm de longueur de contact et 25,08 dm2 de section pour le cas 5C. Il en résulte une très forte réduction de la chute ohmique de contact de scellement, combinée à une très basse chute ohmique dans l'acier. Il est remarquable que ce gain global, qui a été trouvé égal à plusieurs dizaines de millivolts, ait été obtenu sans fragiliser le bloc de carbone, les ailes (16) des blocs c'est-à-dire les parties de carbone restant entre rainures ou entre rainure et côté des blocs, ayant conservé les mêmes dimensions. L'homme de l'art sait qu'un gain de 10 mV équivaut à une baisse de consommation de 30 à 35 kWh par tonne d'aluminium produit.In FIG. 5 which represents, on a scale of approximately 1/20 °, vertical sections of cathode blocks according to the prior art (5A) and (5B), and according to the invention (5C), it can be seen that the we go, for a given vertical section, from 36.8 dm of sealing contact length and 17.16 dm2 of steel and cast iron section for case 5A, to 29.2 dm of contact length and 26.4 dm2 of section for case 5B, and at 41.6 dm of contact length and 25.08 dm 2 of section for case 5C. This results in a very strong reduction in the ohmic drop in sealing contact, combined with a very low ohmic drop in the steel. It is remarkable that this overall gain, which has been found equal to several tens of millivolts, was obtained without weakening the carbon block, the wings (16) of the blocks, that is to say the parts of carbon remaining between grooves or between groove and side of the blocks, having kept the same dimensions. Those skilled in the art know that a gain of 10 mV is equivalent to a reduction in consumption of 30 to 35 kWh per tonne of aluminum produced.

3. La disposition nouvelle des blocs cathodiques permet la réalisation de blocs mixtes (ou « sandwiches ») de façon simple et économique. Selon l'art antérieur, il fallait découper les blocs (1) puis assembler les deux parties (anthracite et semi-graphite, par exemple) lors du montage des cathodes, alors que, selon l'invention, chaque bloc mixte tel que 10A = 10B est obtenu par simple collage de deux blocs de dimensions standards et mis en place tel quel.3. The new arrangement of cathode blocks allows the production of mixed blocks (or "sandwiches") in a simple and economical way. According to the prior art, it was necessary to cut the blocks (1) and then assemble the two parts (anthracite and semi-graphite, for example) during the mounting of the cathodes, whereas, according to the invention, each mixed block such as 10A = 10B is obtained by simple bonding of two standard size blocks and set up as is.

4. La mise en place requiert moins de main-d'oeuvre : on remplace la pose de quatre blocs (figure 1) par celle de deux demi-modules (figure 2) ou d'un seul module préassemblé par collage.4. The installation requires less labor: we replace the installation of four blocks (Figure 1) by that of two half-modules (Figure 2) or a single module pre-assembled by gluing.

5. Par rapport au collage classique de blocs (1) en travers poussés par des vérins (14) à grande course (figure 4A), difficile à pratiquer, car cette disposition cumule les erreurs de parallélisme, le montage par modules s'accommode d'imprécisions importantes que l'on compense par le joint (8) de pâte de brasque entre modules adjacents (figure 2). Il suffit, en outre, de vérins (15) de faible course, disposés contre le grand côté du caisson, pour assujettir les deux demi-modules (5C) en cours de collage pour former chaque module cathodique.5. Compared to the conventional bonding of blocks (1) across pushed by long-stroke cylinders (14) (Figure 4A), difficult to practice, because this arrangement accumulates parallelism errors, mounting by modules accommodates d 'important inaccuracies that are compensated by the seal (8) of pot lining between adjacent modules (Figure 2). It suffices, moreover, jacks (15) of short stroke, disposed against the long side of the box, to secure the two half-modules (5C) during bonding to form each cathode module.

6. En remplaçant les joints en pâte de brasque par des joints collés, on améliore l'étanchéité de la cathode aux infiltrations de métal et d'électrolyte fondus. L'importance de cette étanchéité a été signalée précédemment.6. By replacing the pot lining joints with glued joints, the sealing of the cathode is improved against infiltration of molten metal and electrolyte. The importance of this seal has been mentioned previously.

7. Enfin, l'invention est compatible avec l'utilisation de surfaces cathodiques mouillables par l'aluminium liquide.7. Finally, the invention is compatible with the use of cathode surfaces wettable by liquid aluminum.

Exemple d'applicationApplication example

L'invention a été mise en oeuvre sur plusieurs cuves d'une série fonctionnant sous 180 000 ampères, en constituant la cathode à partir de demi-modules constitués de deux blocs en « semi-graphite conformes au dessin de la figure 5C.The invention has been implemented on several tanks of a series operating at 180,000 amperes, by constituting the cathode from half-modules made up of two “semi-graphite” blocks in accordance with the drawing in FIG. 5C.

On a procédé sur les cuves classiques à blocs anthracitiques et sur les cuves modifiées selon l'invention, à la mesure de la chute de potentiel dans le système cathodique, au contact de scellement et dans la barre cathodique ; on a obtenu les résultats suivants :

Figure imgb0001
The standard tanks with anthracite blocks and the tanks modified according to the invention were measured to measure the potential drop in the cathode system, in contact with the seal and in the cathode bar; the following results were obtained:
Figure imgb0001

Le gain maximum obtenu est de 61 mV, ce qui correspond à près de 200 kWh en moins par tonne d'aluminium produit. Ce gain a été obtenu pour moitié par l'utilisation de blocs « semi-graphite à résistivité plus basse, et pour moitié par la mise en oeuvre de l'invention de bloc cathodique modulaire.The maximum gain obtained is 61 mV, which corresponds to almost 200 kWh less per tonne of aluminum produced. This gain was obtained for half by the use of “semi-graphite blocks with lower resistivity, and for half by the implementation of the invention of modular cathode block.

Claims (10)

1. An electrolysis tank for producing aluminium according to the Hall-Heroult process, comprising cathodic blocks having a low voltage drop, said tank comprising a parallelepipedic metal casing supporting a cathode on which the layer of liquid aluminium is formed, said cathode being formed by the juxtaposition of parallelepipedic carbonaceous blocks of elongate shape, having a ratio of the length of the major axis to the width which is at least equal to two, and in which there is cut at lest one groove into which is sealed a steel bar disposed in parallel relationship to the short side of the casing and the end of which issues at the long side of the casing and connects to at least one cathodic collector, characterised in that the sealing grooves (12) are cut in the direction which is perpendicular to the major axis AA' of the block which is itself disposed in parallel relationship to the long side (11) of the casing.
2. An electrolysis tank according to claim 1 characterised in that a block 10 is associated by glucing on a large side face with at least one second block thereby to form a cathodic demi-module whose width corresponds to half the width of the cathode.
3. An electrolysis tank according to claim 2 characterised in that it comprises at least one cathodic module whose width corresponds to the width of the cathode, formed by the association of two demi-modules (10A, 10B), (10C, 10D).
4. An electrolysis tank according to claim 2 characterised in that each demi-module is formed by blocks produced from the same carbonaceous paste and having substantially identical thermal and/or electrical properties.
5. An electrolysis tank according to claim 2 characterised in that each demi-module is formed by blocks having thermal and/or electrical properties which are different from each other.
6. An electrolysis tank according to claim 1 characterised in that all the sealing grooves (12) are of equal width.
7. An electrolysis tank according to claim 1 characterised in that some of the sealing grooves (12) of a same block 10 are different in width from the others.
8. An electrolysis tank according to claim 3 characterised in that its cathode is formed by the juxtaposition in the same plane of at least two modules (10A, 10B), 10C, 10D).
9. An electrolysis tank according to claim 2 or 3 characterised in that the demi-modules (10A, 10B) and the modules (10A, 10B, 10C, 10D) are connected together by a means choosen between glucing and joining by lining paste.
10. An electrolysis tank according to any of claims 1 to 9 characterised in that each cathodic block (10) is provided with a surface coating comprising at least 30% of titanium diboride.
EP85420107A 1984-06-13 1985-06-11 Modular cathodic block and cathode with a low-voltage drop for hall-heroult electrolysis vats Expired EP0169152B1 (en)

Priority Applications (1)

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AT85420107T ATE30746T1 (en) 1984-06-13 1985-06-11 MODULAR CATHODE BLOCK AND LOW VOLTAGE LOSS CATHODE FOR HALL-HEROUL ELECTROLYTIC FURNACES.

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FR8410557 1984-06-13
FR8410557A FR2566002B1 (en) 1984-06-13 1984-06-13 MODULAR CATHODE BLOCK AND LOW VOLTAGE DROP CATHODE FOR HALL-HEROULT ELECTROLYSIS TANKS

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FR2606428B1 (en) * 1986-11-10 1989-02-03 Pechiney Aluminium METHOD AND DEVICE FOR SEALING, UNDER PRESSURE, CATHODE RATES
US5286359A (en) * 1991-05-20 1994-02-15 Reynolds Metals Company Alumina reduction cell
NO20053072D0 (en) * 2005-06-22 2005-06-22 Norsk Hydro As Method and apparatus for aluminum production.
DE102010041081B4 (en) * 2010-09-20 2015-10-29 Sgl Carbon Se Cathode for electrolysis cells
DE102011004014A1 (en) * 2011-02-11 2012-08-16 Sgl Carbon Se Cathode block with a covering layer containing hard material
DE102011004013A1 (en) * 2011-02-11 2012-08-16 Sgl Carbon Se Graphitized cathode block with an abrasion resistant surface
NO2650404T3 (en) 2012-04-12 2018-06-09
JP6457397B2 (en) * 2012-12-13 2019-01-23 エスジーエル・シーエフエル・シーイー・ゲーエムベーハーＳＧＬ ＣＦＬ ＣＥ ＧｍｂＨ Side wall bricks for electrolytic cell walls for reducing aluminum
CN110760887B (en) * 2019-11-27 2020-07-31 镇江慧诚新材料科技有限公司 Electrode structure for combined production and electrolysis of oxygen and aluminum
CN111390065B (en) * 2020-03-24 2021-05-18 陈思涵 Equal-length cutting equipment for mechanical reinforcing steel bars

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US2728109A (en) * 1952-06-06 1955-12-27 Savoie Electrodes Refract Method of making cathodic electrodes for electrolysis furnaces
CA968744A (en) * 1970-12-12 1975-06-03 Kurt Lauer Cathode for the winning of aluminum
DE2105247C3 (en) * 1971-02-04 1980-06-12 Schweizerische Aluminium Ag, Zuerich (Schweiz) Furnace for the fused aluminum electrolysis
US4076610A (en) * 1975-07-10 1978-02-28 Elettrocarbonium S.P.A. Cathode in cells for producing aluminium by electrolysis of smelted salts thereof

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