EP2459777B1 - Grooved anode for an electrolysis tank - Google Patents

Description

Field of the invention

The invention relates to the production of aluminum by igneous electrolysis according to the Hall-Héroult process and more particularly to the precooked anodes used in aluminum production plants and comprising a carbon anode block, a method of manufacturing such anode blocks. and a device for manufacturing such anode blocks.

State of the art

Aluminum metal is produced industrially by igneous electrolysis, namely by electrolysis of alumina in solution in a bath of molten cryolite, called electrolysis bath, according to the well-known Hall-Héroult process. The electrolysis bath is contained in tanks comprising a steel box, which is lined internally with refractory and / or insulating materials, and cathode elements located at the bottom of the tank. Anode blocks of carbonaceous material are partially immersed in the electrolysis bath. Each vat and the corresponding anodes form what is often called an electrolysis cell. The electrolysis current, which circulates in the electrolysis bath and possibly a sheet of liquid aluminum through the anodes and cathode elements, operates the alumina reduction reactions and also allows to maintain the bath of electrolysis. electrolysis at a temperature of the order of 950 ° C by Joule effect.

The French patent application FR 2,806,742 (corresponding to the US patent US 6,409,894 ) describes installations of an electrolysis plant for the production of aluminum.

According to the most widespread technology, the electrolysis cells comprise a plurality of so-called "precooked" anodes of carbonaceous material which are consumed during the electrolytic reduction reactions of aluminum.

Gases, and more particularly carbon dioxide, are generated during the electrolysis reactions and naturally accumulate in the form of gas bubbles under the lower, generally substantially flat, horizontal face of the anode, which influences the overall stability of the tank.

• des variations et instabilités électriques,
• une fréquence élevée et une durée importante des effets d'anode,
• une possibilité accrue de réaction inverse et donc une perte de rendement du fait de la faible distance entre la couche d'aluminium produite et les bulles de CO₂,
• une consommation accrue de carbone et la formation de gaz nocifs du fait de la transformation du CO₂ en CO au contact du carbone.

It results indeed from the accumulation of these gas bubbles:

• electrical variations and instabilities,
• a high frequency and a long duration of anode effects,
• an increased possibility of reverse reaction and therefore a loss of efficiency due to the small distance between the aluminum layer produced and the CO ₂ bubbles,
• increased carbon consumption and the formation of harmful gases due to the transformation of CO ₂ into CO in contact with carbon.

It is known to use prebaked anodes with carbonaceous anodic blocks having one or more grooves in their lower part so as to facilitate the evacuation of the gas bubbles and prevent their accumulation in order to solve the problems mentioned above and to reduce the energy consumption as shown in Light Metals 2005 "Energy Saving in Aluminum Hindalco Smelter", SC Tandon & RN Prasad . The grooves make it possible to reduce the average free path of the gas bubbles under the anode to leave the space between the electrodes and thus reduce the size of the bubbles that form under the anode.

The interest of the use of grooves has already been studied and proved, for example in Light metals 2007 p.305-310 "The impact of slots on reducing cell individual anode current variation", Geoff Bearne, Dereck Gadd , Simon Lix or Light metals 2007 p.299-304 "Development and deployment of slotted anode technology at Alcoa", Xiangwen Wang et al..

• WO 2006/137739 d'utiliser des rainures plus fines (de l'ordre de 2 à 8 mm) que celles communément utilisées (de l'ordre de 8 à 20 mm) de manière à optimiser la masse carbonée utile et la surface d'échange;
• US 7 179 353 d'utiliser un bloc anodique comportant des rainures débouchant sur un unique coté ou face latérale du bloc anodique, et plus particulièrement vers le centre de la cellule d'électrolyse de manière à améliorer la dissolution de l'alumine.

It is also known from the following documents:

• WO 2006/137739 to use thinner grooves (of the order of 2 to 8 mm) than those commonly used (of the order of 8 to 20 mm) so as to optimize the useful carbon mass and the exchange surface;
• US 7,179,353 to use an anode block having grooves opening on a single side or side face of the anode block, and more particularly towards the center of the electrolysis cell so as to improve the dissolution of the alumina.

A well known limit to the use of these grooves results from the fact that the depth of the grooves from the lower surface of the anode blocks is limited so as not to disturb the mechanical and physical integrity of the carbonaceous anode blocks. However, the carbonaceous anode blocks are progressively consumed during the electrolysis reaction over a height greater than the depth of the grooves so that the lifetime of the grooves of an anode is less than the lifetime of the anode. . Therefore, for a certain period of time during the life of the anodes, the lower part of the anode blocks no longer has a groove. The problems mentioned above for anodes without grooves are then felt.

Indeed, as mentioned in Light metals 2007 p.299-304 "Development and deployment of slotted anode technology at Alcoa" the depth of the grooves is limited for reasons of integrity mainly in the case of grooves formed by molding on green anode blocks so that the beneficial effects resulting from the presence of the grooves are only observable over a part of the service life anodes. The grooves create weaknesses in the raw anodic blocks which then crack during their transport, storage or cooking.

In practice, it also proves to be difficult and expensive to reliably obtain anode bores with grooves as deep as the anodic block height to be consumed by sawing anode blocks. The mechanical stresses and the vibrations exerted by the saw blades provoke the crumbling, the cracking then the bursting of the blocks of carbons. Sawing anodes is also an expensive exercise, particularly because of the high cost of sawing, the high energy demand, and the collection and treatment of powders caused by sawing.

The dimensions of the anode blocks of the commonly used anodes are of the order of 1200 to 1700 mm for the length, 500 to 1000 mm for the width and 550 to 700 mm in height, with one to three grooves of depth generally between 150 and 350 mm.

Also for an anodic block of 600 mm height with a consumable carbon height of 400 mm and a groove of 250 mm depth, the groove produces a beneficial effect for only 62.5% of the life of the anode.

A first object of the invention is to provide another type of anode remedying the evacuation problems of gases accumulating under the anodes without compromising the integrity of the anode blocks during their manufacture, storage, transport or use .

Another object of the invention is to provide anodes to overcome the disadvantages mentioned above, that is to say to propose anodes producing a beneficial effect for a longer period without compromising the integrity of the blocks anodic during their manufacture, storage, transportation or use.

Description of the invention

For this purpose, the subject of the invention is an anode carbon block for anode precooked for use in a metal electrolysis cell comprising an upper face, a lower face, intended to be arranged facing an upper face of a cathode, and four lateral faces, and comprising at least one first groove opening on at least one of the lateral faces, in which the first groove has a maximum length L _max in a plane parallel to the lower face, and characterized in that the first groove does not open on the faces lower or upper, or opens on said lower or upper faces for a length L _o less than half the maximum length L _max .

In other words, the first groove according to the invention forms a recess in the core of the constituent material of the anode block which is not open on the lower or upper faces for a portion of the length of said groove.

The upper face of the anode block further comprises at least one fixing recess and the lower face of the anode block is intended in use to be immersed in an electrolysis bath. Groove means, as is known from the prior art, a substantially vertical recessed recess of depth between 50 and 500 mm and width between 5 and 40 mm.

Such a first groove has the effect of reducing the turbulence of the electrolysis bath and the kinetic energy of turbulence for the volume located below the lower face of the anode block, when it opens over a long length on the lower face, that is to say after some wear of the anode block. The reduction of turbulence is particularly beneficial in the region below the anode block because it reduces the reoxidation of the dissolved metal in the electrolysis bath.

Such a first groove preserves the structural integrity of the anodic block and therefore its physical resistance because most of the first groove is formed in the core of the material. The outer casing, which has more propensity to withstand stress and to crack than the core of the material, is then weakened to a lesser extent with such a first groove which has less surface opening on the outer faces of the anode block by relative to a groove known from the prior art.

The groove opens on a single lateral side or on two opposite lateral sides of the anode block to facilitate the evacuation of gases accumulating under the anode block.

According to a particular embodiment of the invention, the groove may comprise a slightly inclined bottom of an angle less than 10 ° relative to the horizontal to improve the evacuation of gases and to direct this evacuation towards a predetermined location of the tank, for example to the alumina loading points so as to facilitate stirring and dissolution of the alumina, more particularly to a central corridor in the electrolysis cell.

The particular and innovative shape of the first groove according to the invention gives it a period of full efficiency offset from grooves of the prior art formed from the underside. Since the first groove does not open on the underside or opens on the underside over a reduced length, it is inefficient or of reduced efficiency for the evacuation of gases in the first instants of immersion of the anode block in the tank. electrolysis. The first groove on the other hand finds full effectiveness after some wear of the anode block, when the groove length opening on the underside increases.

The combination of at least one first groove with at least one second groove of the prior art in anode anode block is therefore particularly advantageous. A second groove, a maximum length of groove means L _max in a plane parallel to the bottom face and opening on the bottom face over a length L _'0 equal or substantially equal to L _max, such as when the lower edge anode block is chamfered.

Thus, when a new anode is placed in an electrolytic cell, the second groove allows the evacuation of gases accumulating under the anode and when the second groove disappears under the effect of the wear of the block anodic, the first groove takes the relay for the evacuation of gases accumulating under the anode. The periods of effectiveness of the first and second grooves may overlap, that is to say that there is coexistence of the first and second grooves at the same depth relative to the underside, or be slightly disjoint.

The anode block may include one or more first grooves and one or more second grooves. The orientation of the various grooves may vary, first grooves may for example be oriented perpendicular to second grooves.

Also, with respect to an anode block of the prior art for which, from carbon consumption or wear, an effective groove to an absence of a groove was used, the anode blocks according to the invention comprising at least one first groove and at least one second groove, a passage from a second groove to a first groove, which avoids disturbances and abrupt changes in the kinetics of the fluids with the associated electrical equilibrium problems and facilitates for example adaptive adjustments.

According to a particularly advantageous exemplary embodiment of the invention, the anode block comprises two second grooves and a first groove, the first and the second grooves extending parallel in the longitudinal direction of the anode block and the first groove being disposed halfway. distance between the two second grooves. The offset, in a plane parallel to the lower face, of the first groove with respect to the two second grooves thus allows optimum preservation of the physical integrity of the anode block.

• on introduit une lame à l'intérieur d'un moule d'une vibro-tasseuse ;
• on charge le moule de la vibrotasseuse avec des matériaux carbonés constitutifs du bloc anodique ;
• on effectue un vibro-tassage des matériaux carbonés ; et
• on décharge du moule le bloc anodique ainsi formé, notamment par glissement par rapport à la lame.

According to an advantageous embodiment, the length L _o on which opens the first groove on the lower face is less than 25% of the maximum length L _max and preferably less than 10% of the maximum length L _max . The smaller the length L ₀ on which the first groove on the lower face opens, the greater the physical integrity of the anode block will be. Thus, a preferred embodiment will correspond to the case where the groove does not open on the underside. The fact that the first groove opens on the underside results mainly from a particularly advantageous manufacturing process since it is simple to implement in which:

• a blade is introduced inside a mold of a vibro-packer;
• the mold of the vibrotasseuse is loaded with carbonaceous materials constituting the anodic block;
• vibro-packing of the carbonaceous materials is carried out; and
• the anode block thus formed is discharged from the mold, in particular by sliding relative to the blade.

According to another embodiment, the anode block is discharged from the mold after removing the blade from the mold.

According to an advantageous embodiment of the invention, the blade is fixed to the bottom of the mold before loading.

According to another advantageous embodiment of the invention, the blade is fixed on a side wall or two opposite side walls of the mold before loading.

The invention extends to the anodes having at least one anode block as described above and a fixing rod.

• fournir au moins une anode telle que définit ci-dessus ;
• installer l'anode dans une cuve d'électrolyse d'aluminium ;
• faire passer du courant dans la cuve d'électrolyse à travers l'anode ;
• récupérer l'aluminium obtenu par électrolyse dans le fond de la cuve d'électrolyse.

The invention also extends to an igneous electrolysis aluminum production cell comprising at least one anode as described above, as well as to a process for the manufacture of aluminum comprising the steps of:

• provide at least one anode as defined above;
• install the anode in an aluminum electrolysis cell;
• passing current in the electrolytic cell through the anode;
• recover the aluminum obtained by electrolysis in the bottom of the electrolysis cell.

The invention is described in more detail below with the aid of the appended figures.

Brief description of the figures

• The figure 1 illustrates, cross-sectional view, a typical electrolysis cell for the production of aluminum.
• The Figures 2A and 2B represent in front view an embodiment of anode anode block according to the invention.
• The figure 3 represents a sectional view of the anodic block of Figures 2A and 2B according to the AA cut to highlight the shape of the first groove.
• The figure 4 is a front view of a blade intended to be fixed in a mold for the formation of the first groove during the manufacture of the raw anode block of Figures 2 and 3 .
• The Figures 5 to 7 are sectional views of the type of the figure 3 , showing other particular shapes of first grooves.
• The Figure 8A and 8B show respectively in front view another embodiment of an anode block according to the invention.

Detailed description of the invention

Electrolysis plants for aluminum production include a liquid aluminum production zone that includes one or more electrolysis rooms including electrolysis cells. The electrolysis cells are normally arranged in rows or rows, each row or line typically having more than one hundred cells, and electrically connected in series using connecting conductors.

As illustrated in figure 1 an electrolysis cell 1 comprises a tank 2, a support structure 3, called a "superstructure", carrying a plurality of anodes 4, means 5 for supplying the alumina and / or AlF ₃ tank, and means 12 to recover the effluents emitted by the tank in operation. The tank 2 typically comprises a metal box 6 internally lined with refractory materials 7, 8, a cathode assembly which comprises blocks of carbonaceous material 9, called "cathode blocks" disposed in the bottom of the tank, and connecting rods metal 10 to which are attached electrical conductors 11 for the routing of the electrolysis current. The anodes 4 each comprise at least one consumable anode block 13 made of precured carbonaceous material and a metal rod 14. The anode blocks 13 typically have a substantially parallelepiped shape. The rods 14 are typically attached to the anode blocks 13 by means of fasteners 15, generally called "multipodes", having studs which are anchored in the anode blocks 13 generally via recesses 36 in the face upper part of the anode block. The anodes 4 are removably attached to a movable metal frame 16, called "anode frame", by mechanical fixing means. The anode frame 16 is carried by the superstructure 3 and attached to electrical conductors (not shown) for the routing of the electrolysis current.

The refractory materials 7, 8 and the cathode blocks 9 form, inside the tank 2, a crucible adapted to contain an electrolyte bath 17 and a sheet of liquid metal 18 when the cell 1 is in operation. In general, a cover 19 of alumina and solidified bath covers the electrolyte bath 17 and all or part of the anode blocks 13.

The anodes 4, and more precisely the anode blocks 13, are partially immersed in the electrolyte bath 17, which contains dissolved alumina. The anode blocks 13 initially each have a bottom face that is typically substantially planar and parallel to the upper surface of the cathode blocks 9, which is generally horizontal. The distance between the lower face of the anode blocks 13 and the upper surface of the cathode blocks 9, called the "interpolar distance", is an important parameter in the regulation of the electrolysis cells 1. The interpolar distance is generally controlled with great precision.

The anodic carbonaceous blocks are gradually consumed in use. In order to compensate for this wear, it is common practice to gradually lower the anodes by regularly moving the anode frame downwards. In addition, as illustrated in figure 1 , the anode blocks are generally at degrees of wear different, advantageously to avoid having to change all the anodes at the same time.

The Figures 2A, 2B and 3 show a first embodiment of an anode block 13a according to the invention. The anode block 13a is typically parallelepiped rectangular in shape of length L between two opposite short side faces 21 and 22 typically vertical and of height H between a bottom face 23 and a top face 24 typically horizontal. As shown on Figures 2A, 2B and 3 , the upper edges can be trimmed to limit carbon losses. The anode blocks are intended to be consumed up to a maximum wear height indicated by the arrows 25.

The anode block 13a has a first groove 31a and two second grooves 32 and 33.

The second grooves 32, 33 typically pass through the anode block from one side to the other along the length L. Figures 2A and 2B , which show the opposite short side faces 21,22 of the anode block 13a, show that these second grooves 32,33 open on the lower face 23 over its entire length and on both short side faces. Therefore the second grooves 32,33 open on the lower face 23 on lengths L ' ₀ equal to their maximum lengths L' _max respective, and also equal to L. For the case where the lower edges are trimmed, these lengths L ' _max and L ' ₀ are also substantially equal because the cropped portion is not significant.

For the sake of comprehension, the scales are not rigorously respected in the figures, especially as regards the width of the grooves, the width of the grooves being typically between 5 and 40 mm while the width of the anodic blocks, corresponding to the faces short side is usually between 550 and 700mm. Dashed lines are shown on the Figures 2A, 2B (and also Figures 8A and 8B ) the non-visible parts of faces but seen by transparency. The figure 3 is a view of the anode according to section AA at through the first groove 31 so as to more specifically show the shape of the first groove 31.

• une première portion I formant une perforation ou un évidement au coeur du matériau carboné et ne débouchant pas sur la face inférieure 23 du bloc anodique 13a ;
• une deuxième portion II débouchant sur la face inférieure 23 du bloc anodique 13a. Ainsi, lorsque le bloc anodique 13a est entier, la première rainure 31a à la forme d'un L couché et comporte sur la première portion I un fond 40 et une paroi inférieure 42 et uniquement le fond 40 sur la deuxième portion II.

The first groove 31 a has on its length:

• a first portion I forming a perforation or a recess in the heart of the carbonaceous material and not opening on the lower face 23 of the anode block 13a;
• a second portion II opening on the lower face 23 of the anode block 13a. Thus, when the anode block 13a is entire, the first groove 31a has the shape of a lying L and comprises on the first portion I a bottom 40 and a bottom wall 42 and only the bottom 40 on the second portion II.

The first groove 31a opens on the two short side faces 21, 22 of the anode block 13a for the evacuation of gases accumulating under the anode. The maximum length L _max of the first groove 31a in a plane parallel to the underside is therefore equal to the length L of the anode. The first groove 31a opens against the lower face 23 over a length L _o low relative to the maximum length. To maintain physical integrity and sufficient resistance to the anode block while maintaining significant gas drainage properties, the Applicant considers that L _o must be less than half L _max and preferably less than 25% L _max and more preferably less than 10% of L _max .

The first groove 31a extends parallel and midway between the second grooves 32,33 so as to maximize the physical integrity and strength of the anode block 13a.

As visible on Figures 2A and 2B , the second grooves 32, 33 have a bottom 44 disposed at the same height in the anode block 13a as the lower wall 42 of the first groove 31a. Thus, when the second grooves 32, 33 are worn out and disappear, the first portion I of the first groove takes the relay and allows the evacuation of gases.

The anode block 13a as well as the anode formed from this anode block 13a allows an efficient and continuous evacuation of the gases forming in the electrolytic cell.

We also observe in dotted lines on the Figure 2A, 2B recesses 51 forming locations within which can be fixed pins of "multipodes". In this example, the anode block 13a has more particularly six recesses 36 arranged in two rows. These recesses are also very shallow and therefore have little impact on the integrity of the structure of the anode block.

The existence of the second portion II of the first groove 31a, which opens on the underside of the anode intended to be disposed facing an upper face of a cathode disposed at the bottom of the electrolytic cell is dictated by an adaptation in a conventional manner of manufacturing anode blocks. As this second portion II is a source of weakening of the anode block, it attempts to reduce its length and therefore its impact so that the invention is limited to anode blocks in which the length Lo is less than half of L _max , and preferably less than 25% L _max and more preferably less than 10% L _max .

A conventional way of manufacturing a grooved anodic block is to introduce the constituent material of the anode block into a mold of generally parallelepiped shape and having one or more blades fixed in the bottom of the mold to form the grooves by complementarity. The material of the anode block is then compacted by pressurization or vibrotassage, the lateral faces of the mold raised and the anode block pushed beyond the bottom of the mold. During the thrust, the anode block is more particularly slid with respect to the blade or blades. According to one variant, the blade is removed before the thrust.

We have represented on the figure 4 a blade 46 for obtaining in a vibrotasseuse a first groove 31a according to the invention. This blade 46 more particularly comprises a means 48 for fastening the blade in the bottom of the mold. This means 48 for the attachment is more particularly constituted by screws. The portion of the blade used for this attachment corresponds more particularly to the second portion II of the first groove 31a.

As visible on the figure 4 , the blade 46 may further comprise for example a notch 50 complementary to a reversible fixing means provided in a side face of the mold. Although optional, this attachment to an end opposite to the means 48 for fastening the blade 46 in the bottom of the mold allows a good retention of the blade in the mold, in particular vertically and / or laterally. This retention of the blade makes it possible to improve the quality of the manufacture of the anodes, in particular to reduce the rate of cracking of the anodes during cooking, and to increase the duration of use of the blade which is in fact less likely to occur. veil. During demolding of the anode block 13a, the reversible fixing means are disengaged from the notch 50, the lateral faces of the mold are lifted and the anodic block is slid with respect to the blade 46.

Also, the blade can also be advantageously fixed relative to a side wall of the mold at the end of the blade near the means 48 for the attachment of the blade 46. The use of such a second means of reversible attachment, which may for example be constituted by a groove formed in the side wall of the mold and in which slides and is housed at the end of the blade, also limits movement, deformation and wear of the blade .

According to a variant of the manufacturing process, the blade 46 can be removably mounted in the mold so that the blade 46 can be removed from the anode block 13a before pushing the anode block 13a out of the mold.

We have shown on the figure 5 another anode block 13b with a first groove 31b having a bottom 40 inclined relative to the horizontal so as to improve the gas evacuation speed and to promote the evacuation of gases to a particular point of the electrolysis cell . The inclination of the bottom 40 relative to the horizontal is more particularly between 1 and 10 °.

We have shown on the figure 6 another anode block 13c with a first groove 31c having a maximum length L _max in a plane parallel to the lower face shorter than the length L of the anode block 13c and opening on a single side face 22 of the anode block 13c. The length L _o of the first groove 31c opening on the lower face 23 is less than half of L _max to maintain the physical integrity and strength of the anode block while maintaining significant drainage properties of the gases.

We have shown on the figure 7 another anode block 13d with a first groove 31d extending through the material of the anode block 13d between the two short side faces 21, 22 opposite without opening on the underside 23 of the anode block 31d. Such a first groove 31d is particularly advantageous because it does not affect the integrity of the anodic block at the lower face 23. The blade introduced into the mold of the vibrotasseuse for molding the anode block is then hooked on the side faces of the mold and not at the bottom of the mold. The opposite side walls of the mold may for example have two slot-shaped holes within which the blade is slid, held in suspension and fixed by means of locking devices. A setting and withdrawal ram associated with a blade gripping device can be used to set up the blade in the mold prior to loading the constituent materials of the anode and remove it from the raw compacted anodic block and the front mold. unloading the mold.

The invention also extends to an anode block comprising only one or more first grooves, without second grooves. The structural integrity of the anode block will then be close to an anode block without grooves and an improved evacuation of the gases will be obtained during the period when the (or) first groove will lead under the lower face over a substantial length.

The invention is not limited to the embodiments described above but extends to all embodiments accessible in a simple manner to those skilled in the art with regard to the teaching given below.

The bottom of the second grooves and the lower wall of the first groove may for example be provided at slightly different heights so that the first and second grooves coexist for a period of time or on the contrary that there is a time without effective groove after the wear of the second groove and the actual appearance of the first groove. The number of first (s) and / or second (s) grooves may vary, as well as their respective positions and / or orientations.

Another 13th anode block on the Figure 8A and 8B the anodic block 13e has two second grooves 32, 33 extending longitudinally and four first grooves 31e extending laterally and not opening on the lower face 23. The first grooves 31e therefore extend transversely to the second grooves 32,33. The bottom 44 of the second grooves is advantageously disposed below the lower wall 42 of the first grooves 31e, which avoids weakening the resistance of the anode block 13e by intersecting the different grooves.

Also, according to variants of the invention, can be understood by second groove, any groove of the type known from the prior art, opening on the underside for a length equal to or substantially equal to their maximum length. The second grooves may in particular be of the known type of the patent documents WO 2006/137739 or US 7,179,353 .

Claims (16)

1. An anode block (13, 13a-13e) made of carbon for a pre-baked anode (4) for use in a metal electrolysis cell (1) comprising a higher face (24), a lower face (23), designed to be laid out opposite a higher face of a cathode (9), and four side faces (21,22,34), and including at least one first groove (31a-31e) leading onto at least one of the side faces, in which the first groove has a maximum length L_max in a plane parallel to the lower face, and characterized in that the first groove does not lead onto the lower or higher faces, or leads onto said lower or higher faces over a length L_o less than half the maximum length L_max.
2. An anode block according to claim 1, in which the first groove leads onto two opposite sides faces (21,22) of the anode block.
3. An anode block according to one of the preceding claims, comprising at least one second groove (32,33) of maximum length L'_max in a plane parallel to the lower face and leading onto the lower face over a length L'₀ substantially equal to L'_max.
4. An anode block according to one of claims 1 to 3, comprising a plurality of first grooves.
5. An anode block (13a-13d) according to claim 3, comprising two second grooves (32,33) and a first groove (31 a-31 d), in which the first and the second grooves extend in parallel in the longitudinal direction from the anode block and in which the first groove is laid out halfway between the two second grooves.
6. An anode block (13d, 13e) according to one of the preceding claims, in which the first groove (31 d, 31 e) does not lead onto said lower (23) or higher (24) faces.
7. An anode block (13a-13c) according to one of the preceding claims, in which the first groove leads onto the lower face (23) over a length L_o less than half the maximum length L_max.
8. An anode block according to claim 7, in which the length over which the first groove leads onto the lower face is less than 25% of the maximum length L_max and preferably less than 10% the maximum length L_max.
9. A pre-baked anode (4) comprising at least one anode block according to any of the preceding claims.
10. A cell (1) for the production of aluminum by igneous electrolysis comprising a plurality of anodes (4), characterized in that at least one of the anodes is an anode according to claim 9.
11. A process for the manufacture of aluminum including stages consisting in:

    - providing at least one anode according to claim 9;

    - fitting the anode in an aluminum electrolysis cell above a cathode;

    - sending current into the electrolysis cell through the anode;

    - recovering the aluminum obtained by electrolysis in the bottom of the electrolysis cell.
12. A process for the manufacture of an anode block according to one of claims 1 to 9 in which:

    - a blade (46) is inserted inside a vibrocompactor mold;

    - the vibrocompactor mold is loaded with carbonaceous materials that make up the anode block;

    - the carbonaceous materials are vibrocompacted; and

    - the anode block thus formed is removed from the mold.
13. A process according to claim 12, in which the blade is withdrawn from the mold before removing the anode block.
14. A process according to claim 12, in which the anode block is removed by slippage in relation to the blade.
15. A process according to one of claims 12 to 14, in which the blade (46) is fixed to the bottom of the mold.
16. A process according to one of claims 12 to 15, in which the blade (46) is fixed to one lateral face or two opposed lateral faces of the mold before loading

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