EP3546620B1 - Cathode assembly having a cathode block having a slot with varying depth and a securing system - Google Patents

Description

The present invention relates to a cathode arrangement for an aluminum electrolytic cell and its use.

Electrolysis cells are used, for example, for the electrolytic production of aluminum, which is usually carried out industrially according to the Hall-Heroult process. In the Hall-Heroult process, a melt composed of aluminum oxide and cryolite is electrolyzed. In this case, Na ₃ [AIF _6], the cryolite is used, tends to lower the melting point of 2,045 ° C for pure aluminum at about 950 ° C for a cryolite, alumina and additives such as aluminum fluoride and calcium fluoride-containing mixture.

The electrolysis cell used in this process has a cathode base which is composed of a large number of, for example, up to 28 adjoining cathode blocks forming the cathode. The spaces between the cathode blocks are usually filled with a carbon-containing ramming mass in order to seal the cathode against molten components of the electrolytic cell and to compensate for mechanical stresses that occur during the start-up of the electrolytic cell. In order to withstand the thermal and chemical conditions prevailing during the operation of the cell, the cathode blocks are usually composed of a carbon-containing material such as graphite. On the undersides of the cathode blocks, grooves are usually provided in each case, in each of which at least one or two busbars are arranged, through which the current supplied via the anodes is carried away. The gaps between the individual walls of the cathode blocks that delimit the grooves and the busbars are often filled with cast iron to connect the busbars electrically and mechanically to the cathode blocks through the cast iron sheathing of the busbars. About 3 to 5 cm above the layer of liquid aluminum, usually 15 to 50 cm high, located on the top of the cathode, an anode, in particular formed from individual anode blocks, is arranged, between which and the surface of the aluminum is the electrolyte, i.e. the aluminum oxide and Melt containing cryolite. During the electrolysis carried out at around 1,000 ° C, the aluminum formed settles below the electrolyte layer due to its greater density than that of the electrolyte, i.e. as an intermediate layer between the top of the cathode and the electrolyte layer. During electrolysis, the aluminum oxide dissolved in the melt is split into aluminum and oxygen by the flow of electrical current. From an electrochemical point of view, the layer of liquid aluminum is the actual cathode, since aluminum ions are reduced to elemental aluminum on its surface. Nevertheless, the term cathode in the following is not understood to mean the cathode from an electrochemical point of view, that is to say the layer of liquid aluminum, but rather the component forming the electrolytic cell base, for example composed of one or more cathode blocks.

A major disadvantage of the cathode arrangements used in the Hall-Heroult process is their comparatively low wear resistance, which manifests itself in the erosion of the cathode block surfaces during electrolysis. Due to an inhomogeneous current distribution within the cathode blocks, the abrasion of the cathode block surfaces does not take place uniformly over the length of the cathode blocks, but to a greater extent at the cathode block ends, so that the surfaces of the cathode blocks change to a W-shaped profile after a certain period of electrolysis. Due to the uneven removal of the cathode block surfaces, the useful life of the cathode blocks is limited by the areas with the greatest removal.

To counter this problem, the WO 2007/118510 A2 a cathode block has been proposed whose groove intended to accommodate one or more busbar (s), based on the length of the cathode block, has a greater depth in the middle than at the ends of the cathode block. As a result, when the electrolytic cell is operated, an essentially homogeneous vertical current distribution is achieved over the length of the cathode block, as a result of which the increased wear on the ends of the cathode block is reduced and the service life of the cathode is thus increased. The busbar (s) is or are encased in a conventional manner with cast iron, this encasing being effected by pouring liquid cast iron into the space between the groove and the busbar (s). However, such a cathode block has disadvantages. The cathode block is comparatively large during and after the pouring of the liquid cast iron into the space between the groove and the busbar (s), during and after the start-up of the electrolytic cell comprising the cathode block, and during and after the electrolytic cell is switched off and then started up again later Subject to temperature changes which lead to an expansion or a shrinkage of the cast iron and the busbar (s) relative to the cathode block. This expansion or shrinkage effect can be intensified by the temperature gradients that occur. In the following, when “large temperature change (s)” is spoken of, it is understood that one or both of the effects mentioned, ie expansion / shrinkage or temperature gradient, is / are present. Because of the higher coefficient of thermal expansion of cast iron and the material of the busbar (s) than the coefficient of thermal expansion of the cathode block material, the cast iron and the busbar (s) expand relative to the cathode block when the temperature rises, whereas they shrink when the temperature drops relative to the cathode block. This deteriorates particularly in the case of conventional grooves with a rectangular cross-sectional shape the electrical contact between busbar, cast iron and cathode block, which leads to an increased electrical resistance of the arrangement and thus to poor energy efficiency of the electrolysis process. Apart from this, the busbar or busbars are movable both in the vertical and in the horizontal direction before the liquid cast iron is poured into the space between the groove and the busbar (s), so that they move during pouring of the liquid cast iron and during the subsequent cooling and solidification of the cast iron can move uncontrollably in the groove, which can also lead to an uneven electrical contact between the busbar, cast iron and cathode block. This also leads to an increased electrical resistance of the arrangement and thus to poor energy efficiency of the electrolysis process. Ramming paste can also be used instead of cast iron. Ramming mixes based on anthracite, graphite and any mixtures thereof can be used as ramming mix. A ramming compound based on graphite is preferably used.

US 2009/050474 A1 describes a cathode for an aluminum electrolytic cell, which has a cathode block and a busbar, the busbar being arranged in a groove in the cathode block. The groove has a greater depth at the lateral end than in the center of the cathode block.

DE 26 31 673 A1 discloses a carbon and / or graphite cathode block for an aluminum electrolytic cell, which has a groove extending in the longitudinal direction of the cathode block for receiving a busbar, this groove being delimited by a wall on which a projection extending into the groove is provided is.

CN 102 181 883 A discloses a cathode block for the aluminum electrolytic cell based on carbon and / or graphite, which has a groove extending in the longitudinal direction of the cathode block for receiving a busbar, the groove having a depth that varies over the length of the cathode block and this groove is limited by a wall. A projection extending into the groove is provided on this wall.

In order to prevent or at least make more difficult a displacement of a busbar in the groove of a cathode block, it is in the WO 2012/107412 A2 It has been proposed to provide at least one recess in the wall delimiting the graphite foil-lined groove of a cathode block and, after inserting the busbar (s) into the groove, the space formed between the groove and the busbar (s) so with liquid Fill cast iron so that the solidified cast iron engages in the at least one recess. If the groove has a depth that varies over the length of the cathode block, the at least one recess should run parallel to the groove bottom - that is, obliquely with respect to the horizontal direction - that is, have a constant distance from the bottom wall of the groove in order to be displaceable to ensure the busbar (s) parallel to the groove bottom. However, this is disadvantageous because due to the higher coefficient of thermal expansion of cast iron and the material of the busbar (s) compared to that of the cathode block during and after pouring the liquid cast iron into the space between the groove and the busbar (s) of the Cathode block occurring temperature changes as well as the temperature changes occurring during commissioning and switching off, and possibly restarting the electrolytic cell comprising the cathode block, between the cast iron and the busbar (s) on the one hand and the cathode block on the other hand, shear stresses occur which contribute to the functioning of the Damage to the cathode block impairing the cathode block in the form of, for example, cracking in the cathode block or can even lead to breakage of the cathode block. Such damage leads to a reduced electrical conductivity between the busbar or the cast iron and the cathode block and to a lower stability of the arrangement or even leads to failure of the entire arrangement. Instead of cast iron, ramming material can also be used here - as described above.

If cast iron is mentioned in the following, it should be understood that the cast iron can be replaced by ramming mass without it being explicitly described each time.

The object of the present invention is therefore to provide a cathode arrangement that is particularly suitable for use in an aluminum electrolytic cell, with which, when the electrolytic cell is operated, a substantially homogeneous vertical current distribution is achieved over the length of the cathode block, which is also achieved with an inserted busbar covered with cast iron ( n) has a low and, in particular, permanently low specific electrical resistance and low contact resistance between the cast iron-coated busbar and the cathode block, even with large temperature changes, and which, in the case of large temperature changes, also with the cast-iron-coated busbar (s) inserted is stable to mechanical damage such as cracking. Instead of cast iron, ramming mass can also be used.

According to the invention, this object is achieved by a cathode arrangement according to claim 1.

According to the invention, it was recognized that by providing at least one projection extending into the groove, which serves as a support surface for ends of busbars or their cast iron sheathing, when configuring the Groove with varying depth in the cathode block, a cathode block is created in which the busbar inserted in the groove and - especially in the case of two adjacent busbars introduced into the groove, each with a length of half the length of the cathode block - the busbar (n) - depending on the design of the projection - are fixed in the vertical and / or horizontal direction, so that an uncontrolled movement or displacement of the busbars in the case of the cast iron-covered busbar ( n) performed pouring of liquid cast iron into the space between the groove and the busbar (s) and in particular also during the subsequent cooling and solidification of the cast iron despite the usually higher thermal expansion of cast iron and the material of the busbar (s) compared to the thermal expansion of the cathode blo ckmaterials, whereby this movement or displacement can lead to poor or uneven electrical contact between busbar, cast iron and cathode block, is reliably avoided. The at least one projection extending into the groove is therefore a support nose or a support pin on which an end piece of a busbar or two end pieces of two busbars rest. Because of this, the cathode arrangement made from cathode block with inserted or inserted busbar (s) encased in cast iron has a low specific electrical resistance and low contact resistance between the cast iron-coated busbar (s) and the cathode block and, in particular, also a permanently low specific electrical resistance and low contact resistance between the cast iron-coated busbar (s) and the cathode block, even with large temperature changes. The cathode block according to the invention of the cathode arrangement according to the invention is therefore particularly suitable for receiving two adjacent busbars introduced into the groove, each having a length of half the length of the cathode block, with in In this case, the projection is preferably provided in the center of the cathode block, so that in each case one end of both busbars can rest on the contact surface formed by the projection. Furthermore, the cathode block of the cathode arrangement according to the invention is also particularly suitable for busbars with a rectangular cross-section. In particular, in the case that a recess extending horizontally in the longitudinal direction of the cathode block is also provided in the groove wall of the cathode block, mechanical damage to the cathode block is also inserted into the groove in the wall delimiting the groove of the cathode block, even with large temperature changes Cast iron sheathed busbar, such as cracking of the cathode block, reliably avoided. By using a groove with a variable depth in the longitudinal direction of the cathode block, such a uniform current density distribution on the cathode block surface is achieved that during operation of the electrolytic cell comprising the cathode block, excessive removal of cathode block material is effectively avoided in those areas where a cathode block is used with the same groove depth in the longitudinal direction of the cathode block, there would be a high local current density. By adapting the groove depth accordingly, the current density distribution can be modified and evened out within wide limits. Overall, a control of tensile stresses, shear stresses and compressive stresses, which occur as a result of the different thermal expansion coefficients of cast iron, busbar and cathode block, is achieved even with large or strong temperature changes, which ensures excellent electrical conductivity and excellent mechanical stability of the cathode block also in the groove inserted and covered with cast iron busbar guaranteed.

In order to achieve a particularly uniform vertical current density distribution on the cathode block surface during the electrolysis operation, it is proposed in a further development of the inventive concept that at least one of the at least a groove and preferably all of the grooves with varying depths have or have a smaller depth at their longitudinal ends than in their middle (s). In this way, an even distribution of the electrical current supplied during the electrolysis operation is achieved over the entire length of the cathode block, whereby an excessive electrical current density at the longitudinal ends of the cathode block and thus premature wear at the ends of the cathode block is avoided. Such a uniform current density distribution over the length of the cathode block also avoids movements in the aluminum melt caused by the interaction of electromagnetic fields during electrolysis, which makes it possible to arrange the anode at a lower height above the surface of the aluminum melt. As a result, the electrical resistance between the anode and the aluminum melt is reduced and the energy efficiency of the melt-flow electrolysis carried out is increased. Another particular advantage of this embodiment is that in this embodiment the busbar (s) fixed by the at least one projection, possibly encased with cast iron, move in the horizontal direction during and after the temperature increase that occurs when the electrolysis cell is started up expand or expand, as a result of which the busbar (s) is or are pressed against the bottom wall of the cathode block groove (s) delimiting the groove at this point, whereby the contact resistance between the cast iron-coated busbar (s) and the cathode block is reduced .

In the above embodiment, the depth of at least one of the at least one groove with varying depth, viewed in the longitudinal direction of the cathode block, preferably increases at least substantially monotonically from one longitudinal end to the center of the cathode block and increases this from the center to the other longitudinally End of the cathode block at least substantially monotonously so that, viewed in the longitudinal section of the cathode block, an at least substantially triangular groove results. As a result, the advantages mentioned above are achieved to a greater extent.

The wall delimiting the at least one groove of varying depth comprises a bottom wall and two side walls, with at least one projection extending into the groove being provided on the bottom wall, which projection preferably extends vertically into the at least one groove. In this way, a particularly good fixation of the busbar in the groove can be achieved, while at the same time sufficiently high mobility of the busbar in the horizontal direction to reliably prevent the occurrence of shear stresses due to the different coefficients of thermal expansion of cast iron, busbar and cathode block even with large temperature changes avoid. According to a further preferred embodiment of the present invention, the at least one projection in the embodiment described above has on its side opposite the bottom wall at least one support surface for at least one busbar, which at least in sections is at least substantially parallel, preferably parallel, to the surface of the groove opposite side of the cathode block, ie perpendicular to the lower end of the side walls of the wall delimiting the groove of the cathode block. Such a support surface is particularly suitable for supporting a busbar or for supporting two busbars.

Good results are obtained in this regard, in particular, if at least one of the at least one bearing surface of the at least one projection is planar, preferably at least substantially rectangular and parallel, particularly preferably rectangular and parallel, to the surface of the side of the cathode block opposite the groove.

In order to achieve a sufficiently large support surface, especially for two adjoining end pieces of two busbars, it is proposed in a further development of the inventive concept that the side of the at least one projection opposite the bottom wall is delimited by a support surface which is completely planar, preferably at least substantially rectangular and is configured to run parallel, particularly preferably rectangular and parallel, to the surface of the side of the cathode block opposite the groove. In this embodiment, the entire surface of the projection opposite the bottom wall of the cathode block is designed as a support surface for one or two end pieces of one or two busbar (s).

The above embodiment can be implemented, for example, in that the at least one projection, seen cut along the length of the cathode block, is at least substantially rectangular or trapezoidal, preferably rectangular or trapezoidal, over its entire height, with the side of the at least one opposite the bottom wall Projection is limited by a bearing surface which is planar, at least substantially rectangular and parallel, preferably rectangular and parallel, to the surface of the side of the cathode block opposite the groove.

The extension of the rectangular support surface running in the longitudinal extension of the cathode block is preferably 20 to 600 mm, particularly preferably 50 to 400 mm, very particularly preferably 100 to 300 mm and most preferably 150 to 250 mm, such as about 200 mm, whereas the in the width of the cathode block, extension of the rectangular support surface is preferably at least 50%, more preferably at least 80%, particularly preferably at least 90% and very particularly preferably 100% of the width of the groove, measured in the plane of the rectangular support surface.

According to an alternative and particularly preferred embodiment of the present invention to the above embodiment, the side of the at least one projection opposite the bottom wall is delimited by a surface which, viewed in the longitudinal direction of the cathode block, comprises two outer sections and a central section arranged between them, wherein the two outer sections each form a support surface for a busbar and each are planar, preferably at least substantially rectangular and parallel, particularly preferably rectangular and parallel, to the surface of the side of the cathode block opposite the groove and are designed to run, based on the depth the groove, are located at the same height, whereas the middle section opposite the two outer sections, seen from the bottom wall, is raised into the groove. This embodiment is particularly preferred for cathode blocks which are designed to accommodate two busbars, each approximately half the length of the length of the cathode block. This is because, through the elevation provided in the middle section of the projection, the two adjacent outer sections of the projection, which form the support surface for each end piece of a busbar, are separated from one another by a partition wall extending in the depth direction of the groove, so that the end pieces of the both busbars rest on opposite sides of the partition, whereby the two busbars are not only fixed in the vertical direction, but also on these two end pieces in the horizontal direction. This ensures that the two busbars expand in a defined direction, namely in the direction of the end of the cathode block, in the event of expansion as a result of a temperature increase. As a result, the two busbars, possibly sheathed with cast iron, during and after the increase in temperature in the horizontal direction that occurs when the electrolysis cell is started up as a result of the expansion in the direction the end of the cathode block is pressed against the bottom wall of the cathode block, which delimits the groove at this point, as a result of which the contact resistance between the busbar, which is sheathed with cast iron, and the cathode block is reduced.

In order to achieve the advantages described above to a particularly high degree, it is preferred that the middle section of the projection, seen cut in the longitudinal direction of the cathode block, is rectangular - that is, in the form of a rectangular nose - so that between the two outer Sections and the middle section is each formed a step. This step can be at right angles or also rounded at the transition area from the support surface to the elevation.

Good results are obtained in particular when the height of the steps is 10 to 100 mm, preferably 40 to 80 mm and particularly preferably 50 to 70 mm, whereas the extension of the steps along the width of the cathode block is preferably at least 50% further preferably at least 80%, particularly preferably at least 90% and very particularly preferably 100% of the width of the groove.

The above embodiment can be implemented, for example, in that the at least one projection, seen in section in the longitudinal extension of the cathode block, is at least substantially rectangular or trapezoidal, preferably rectangular or trapezoidal, over 20% to 80% and preferably over 30 to 50% of its height is, wherein on the side of this section of the projection opposite the bottom wall, a raised portion or nose is provided which is centrally located in the longitudinal extent of the cathode block and extends over the remaining height of the projection.

According to the present invention it is provided that the at least one projection, based on the longitudinal extent of the cathode block, is arranged at the point at which the groove has the greatest depth, the projection itself being disregarded here. If, as set out above, the groove with varying depth has a smaller depth at its longitudinal ends than in its center and in particular the depth of the groove, seen in the longitudinal direction of the cathode block, from a longitudinal end to the center of the Cathode block increases at least substantially continuously and this decreases at least substantially monotonically from the center to the other longitudinal end of the cathode block, the at least one projection is therefore preferably arranged centrally, based on the longitudinal extent of the cathode block.

Furthermore, it has proven to be advantageous that the at least one projection extends over at least 50%, preferably over at least 80%, particularly preferably over at least 90% and very particularly preferably over the entire width of the groove. This achieves sufficient mechanical stability of the projection on the one hand and ensures that the busbar (s) rest with their end piece (s) over at least a large part or their entire width on the contact surface (s) formed by the projection .

In principle, the at least one projection can be composed of any material, such as metal. However, it is preferred that the at least one projection is composed of a material which has the same coefficient of thermal expansion as the material of the rest of the cathode block. The at least one projection is particularly preferably made of the same material as the remaining part of the cathode block.

According to the invention, the cathode block is composed on the basis of carbon and / or graphite. Good results with regard to a sufficiently high electrical conductivity and a sufficiently high wear resistance are obtained in particular if the at least one projection and the remaining part of the cathode block are composed of amorphous, graphitic and / or graphitized carbon.

In a further development of the inventive concept, it is proposed that the at least one projection and the rest of the cathode block are monolithic, i.e. in one piece. This achieves a particularly high mechanical stability of the connection between the projection and the remaining part of the cathode block.

Alternatively, the at least one projection on the bottom wall of the cathode block can also be connected to a connecting means. This can be achieved, for example, in that the at least one projection is glued to the remaining part of the cathode block via an adhesive such as synthetic resin, putty, tar or similar substances or any mixture of the above substances or mechanically to the remaining part of the cathode block with a fastening means Cathode block is connected.

The cathode arrangement according to the invention contains at least one cathode block described above, with at least one busbar being provided in at least one of the at least one groove with varying depths of the at least one cathode block, which is preferably at least partially encased of cast iron, the busbar possibly encased with cast iron at least rests on a portion of the at least one projection.

The cathode arrangement preferably comprises at least one cathode block, two preferably at least one in at least one of the at least one groove with a varying depth of the at least one cathode block Sheath made of cast iron having busbars are provided which each rest with one of their end pieces at least on a portion of the at least one projection.

According to a further preferred embodiment of the present invention, the at least one busbar is at least partially and particularly preferably completely encased with cast iron.

The present invention also relates to the use of a cathode arrangement described above for carrying out a fused-salt electrolysis for the production of metal, specifically preferably for the production of aluminum. The present invention is described below purely by way of example using advantageous embodiments and with reference to the accompanying drawings.

Fig. 1

einen Querschnitt eines Ausschnitts einer Aluminium-Elektrolysezelle mit einer Kathodenanordnung gemäß eines ersten nicht erfindungsgemäßen Ausführungsbeispiels der vorliegenden Erfindung,

Fig. 2

einen Längsschnitt der Kathodenanordnung der in der Fig. 1 gezeigten Aluminium-Elektrolysezelle,

Fig. 3

einen Querschnitt eines Ausschnitts einer Aluminium-Elektrolysezelle mit einer Kathodenanordnung gemäß eines zweiten nicht erfindungsgemäßen Ausführungsbeispiels der vorliegenden Erfindung,

Fig. 4

einen Längsschnitt der Kathodenanordnung der in der Fig. 3 gezeigten Aluminium-Elektrolysezelle,

Fig. 5a-d

beispielhafte Querschnitte von Vertiefungen, die in einer Nut eines nicht erfindungsgemäßen Kathodenblocks vorgesehen sind,

Fig. 6

einen Längsschnitt einer Kathodenanordnung gemäß eines ersten Ausführungsbeispiels der vorliegenden Erfindung und

Fig. 7

einen Längsschnitt einer Kathodenanordnung gemäß eines zweiten

Show:

Fig. 1

a cross section of a section of an aluminum electrolysis cell with a cathode arrangement according to a first exemplary embodiment of the present invention, not according to the invention,

Fig. 2

a longitudinal section of the cathode assembly in FIG Fig. 1 shown aluminum electrolysis cell,

Fig. 3

a cross section of a section of an aluminum electrolysis cell with a cathode arrangement according to a second exemplary embodiment of the present invention, not according to the invention,

Fig. 4

a longitudinal section of the cathode assembly in FIG Fig. 3 shown aluminum electrolysis cell,

Figures 5a-d

exemplary cross-sections of depressions which are provided in a groove of a cathode block not according to the invention,

Fig. 6

a longitudinal section of a cathode arrangement according to a first embodiment of the present invention and

Fig. 7

a longitudinal section of a cathode arrangement according to a second

Embodiment of the present invention. In the Fig. 1 A section of an aluminum electrolysis cell 10 with a cathode arrangement 12 is shown in cross section, which at the same time forms the bottom of a trough for an aluminum melt 14 generated during operation of the electrolysis cell 10 and for a cryolite-aluminum oxide melt 16 located above the aluminum melt 14. An anode 18 is in contact with the cryolite-aluminum oxide melt 16. Laterally, the trough formed by the lower part of the aluminum electrolytic cell 10 by an in the Fig. 1 Lining, not shown, made of carbon and / or graphite is limited.

The cathode arrangement 12 comprises a plurality of cathode blocks 20, which are each connected to one another via a ramming compound 24 inserted into a ramming compound joint 22 arranged between the cathode blocks 20. A cathode block 20 comprises two grooves 26 arranged on its underside with a right-angled, namely essentially rectangular, cross-section, a conductor rail 28 made of steel with a likewise right-angled cross-section being received in each groove 26.

The grooves 26 are each delimited by two side walls 32 and a bottom wall 34 of the cathode block 20, a recess 36 with an approximately semicircular cross-section extending essentially perpendicularly into the side wall 32 being provided in each of the side walls 32. Each depression 36 is delimited in each case by an upper and a lower transition area 37 of the cathode block 20. In the present exemplary embodiment not according to the invention, the transition areas 37 are formed at an angle with an angle α between the adjoining section of the groove wall and the wall of the recess of 90 degrees. The space between the busbar 28 and the groove 26 is filled with cast iron 38 in each case. The cast iron 38 forms a casing 39 for the busbar 28 and is in a materially bonded connection with the busbar 28.

In addition, the cast iron 38 received in the recesses 36 forms a positive connection with the material of the cathode block 20 delimiting the recess 36, which prevents the busbar 28 connected to the cast iron 38 from moving in the direction of the arrow 40.

In the Fig. 1 Specifically, the cross section of the cathode arrangement 12 at a longitudinal end of the cathode block 20 is shown. The depth of the groove 26 of the cathode block 20 varies over the length of the groove 26. The groove cross-section in the region of the center of the groove 26, based on the longitudinal direction of the cathode block, is in the Fig. 1 indicated by a dashed line 42. The difference between the groove depth at the longitudinal ends of the groove 26 and in the middle of the groove 26 - based on the longitudinal direction of the cathode block - is approximately 5 cm in the present exemplary embodiment. The depth of the groove 26 at the two longitudinal ends of the groove 26 is about 16 cm, whereas the depth of the groove 26 in the middle of the groove 26 - based on the longitudinal direction of the cathode block - is about 21 cm. The width 44 of each groove 26 is over the entire length of the groove Essentially constant and is approximately 15 cm, whereas the width 46 of the cathode blocks 20 is approximately 42 cm in each case.

In the present exemplary embodiment not according to the invention, several anodes 18 and several cathode blocks 20 are arranged one above the other in such a way that each anode 18 covers two cathode blocks 20 arranged next to one another in width and covers half of a cathode block 20 in length, with two anodes 18 arranged next to one another in each case Cover the length of a cathode block 20.

the Fig. 2 shows the in the Fig. 1 shown cathode block 20 in longitudinal section. As from the Fig. 2 As can be seen, the groove 26 viewed in its longitudinal section tapers towards the center of the cathode block 20 in the shape of a triangle, whereby an essentially uniform electrical vertical current density is ensured over the entire length of the cathode. The recess 36 runs as in FIG Fig. 2 indicated by the correspondingly marked line parallel to the horizontal direction, ie parallel to the surface of the side of the cathode block 20 opposite the groove 26 Fig. 2 for the sake of clarity, busbar 28, not shown, is bar-shaped in the present exemplary embodiment and has a right-angled longitudinal section, so that between the busbar and the groove bottom 34 there is an interspace that increases towards the center of the groove 26, either through cast iron 38 or through additional metal plates connected to the busbar 28 can be filled.

The ones in the Fig. 3 and 4th The cathode arrangement and cathode block shown in longitudinal section and cross section according to a second exemplary embodiment of the present invention not according to the invention differs from that in FIG Fig. 1 and 2 shown in that only one groove 26 is provided in the cathode block 20, which groove has two depressions 36, 36 '.

Also show the Figures 5a to d exemplary recesses 36 which are provided in a groove 26 of a cathode block 20 according to the invention, in cross section. The depressions 36 each have an essentially semicircular cross-section ( Figure 5a ), a substantially trapezoidal cross-section ( Figure 5b ) or a substantially triangular cross-section ( Figure 5c ) on. The angle α of the transition areas 37 between the wall of the recess 36 and the adjoining section of the groove wall 32, seen from the inside of the cathode block 20, is in this case in Figure 5a about 90 degrees in which Figure 5b about 120 degrees and in the Figure 5c about 125 degrees. the Fig. 5d shows an embodiment in which several as in Figure 5c Depressions 36 shown with a triangular cross-section are arranged one after the other in the depth direction of the groove 26 in order to effect a particularly reliable retention of an inserted busbar 28. The transition areas 48 between two adjoining depressions 36 have an angle β of approximately 70 degrees between the walls of two adjoining depressions 36, as seen from the inside of the cathode block 20. The ones in the Figures 5a to d Depressions 36 shown each extend perpendicularly into the side wall 32 of the cathode block 20 delimiting the groove 26, so that they form a fixation with the cast iron received in the depressions 36, which is effective in the depth direction of the groove 26 and an undesired movement of the busbar 28 parallel to it the depth direction of the groove 26 after the busbar 28 has been cast with cast iron 38, but allows horizontal movement of the cast iron-covered busbar - for example as a result of expansion of the cast-iron-covered busbar as a result of a large temperature change.

In the context of the present invention, a depression extending horizontally in the longitudinal direction of the cathode block is understood to mean that the depression extends parallel to the longitudinal plane of the cathode block. Under one parallel extension is understood to mean that the recess at each of its locations an angle of less than 8 °, preferably less than 5 °, particularly preferably less than 2 °, very particularly preferably less than 1 °, most preferably less than 0.5 °, and most preferably less than 0.1 ° to the longitudinal plane of the cathode block. In this context, the term longitudinal plane is understood to mean the plane which extends in the direction of the longitudinal axis of the cathode block and runs parallel to the surface of the side of the cathode block opposite the groove.

In addition, in the context of the present invention, a recess, as opposed to a mere surface roughness, is understood to mean a recess which, based on the surface of the wall delimiting the groove, has a depth of at least 0.5 mm and preferably of at least 2 mm.

By providing at least one recess that extends horizontally in the longitudinal direction of the cathode block in the wall delimiting the groove of the cathode block, preferably in both of the side walls, in particular also when the groove is designed with varying depths in the cathode block, a cathode block is created which also with a busbar inserted into the groove and covered with cast iron, it has a low electrical resistance and low contact resistance. Apart from this, due to the provision of the recess extending horizontally in the longitudinal direction of the cathode block in the wall delimiting the groove of the cathode block, mechanical damage to the cathode block with the busbar inserted into the groove and covered with cast iron, such as cracking of the cathode block, occurs even with large temperature changes , reliably avoided. On the one hand, through the use of a groove of variable depth in the longitudinal direction of the cathode block, such a uniform current density distribution on the cathode block surface is achieved that during operation of the An electrolytic cell comprising cathode block effectively prevents excessive removal of cathode block material in those areas where a high local current density would be present when using a cathode block with the same groove depth in the longitudinal direction of the cathode block. By adapting the groove depth accordingly, the current density distribution can be modified and evened out within wide limits. Since the cathode block has a recess in its groove that extends horizontally in the longitudinal direction of the cathode block, the cast iron-coated busbar is fixed vertically in the groove of the cathode block, which however allows a certain movement in the horizontal direction of the cathode block. Due to this horizontal mobility of the cast iron-coated busbar, the occurrence of shear stresses between the cast-iron-encased busbar and the cathode block is reliably avoided, especially in the case of the rapid temperature changes that occur during and after start-up or when an electrolytic cell comprising the cathode block is switched off in the case of an obliquely arranged depression as a result of the higher expansion or shrinkage of the cast iron and the busbar relative to the cathode block, which occurs due to the higher coefficient of thermal expansion of cast iron and the material of the busbars compared to the coefficient of thermal expansion of the material of the cathode block. This reliably prevents damage to the cathode block, for example in the form of cracking or even breakage of the cathode block, even during long operating periods of the electrolytic cell, while at the same time ensuring excellent electrical conductivity between the busbar or the cast iron and the cathode block. Due to the vertical fixation of the cast iron-coated busbar in the groove of the cathode block, the cathode bar / cast iron arrangement is advantageously pressed against the groove bottom due to the thermal expansion of the bar / cast iron arrangement relative to the cathode block during commissioning. In this way, an improved electrical contact is achieved, the leads to a lower electrical resistance and thus to a higher energy efficiency. In further advantage to that from the WO 2012/107412 A2 known cathode block, these excellent properties are achieved in particular when the groove of the cathode block is not lined with an expensive graphite foil that is laborious to introduce. Overall, a control of tensile stresses, shear stresses and compressive stresses, which occur as a result of the different coefficients of thermal expansion of cast iron, busbar and cathode block, is achieved even with large temperature changes, which results in excellent electrical conductivity and excellent mechanical stability of the cathode block even with and with the groove Cast iron sheathed busbar guaranteed.

In the Fig. 6 a cathode arrangement 12 with a cathode block 20 according to a first embodiment of the present invention is shown in longitudinal section, in contrast to that in FIGS Figs. 1 to 4 shown upside down, based on the later installation in the electrolysis cell, to clarify the arrangement during pouring with liquid cast iron. This cathode block 20 differs from that in FIGS Figs. 1 to 4 represented in that it has no recess in the wall delimiting the groove 26. Instead, this cathode block 20 has in its groove 26 a projection 50 which is arranged centrally in relation to the longitudinal direction of the cathode block 20 and is trapezoidal when viewed in section in the longitudinal direction of the cathode block. The surface of the projection 50 that is opposite the bottom wall 34 of the cathode block 20 is planar, rectangular and runs parallel to the surface of the side of the cathode block opposite the groove and thereby forms a support surface for the end pieces of two busbars 28. can also have a recess on at least one or on both of the side walls of the cathode block 20 delimiting the groove 26, as in the Fig. 1 and 2 shown, or two indentations, as in the Fig. 3 and 4th shown, be provided.

In addition, the Fig. 7 a cathode arrangement 12 with a cathode block 20 according to a second embodiment of the present invention shown in longitudinal section, again in contrast to that in FIG Figs. 1 to 4 depicted standing upside down. This cathode block 20 differs from that in FIG Fig. 6 represented by the fact that the projection 50 shown here hatched is not trapezoidal, seen in section in the longitudinal direction of the cathode block, but is rectangular in its lower part, with a side of this part of the projection 50 opposite the bottom wall 34 of the cathode block 20 Seen in the longitudinal extent of the cathode block 20, centrally arranged nose 54 is provided, which extends over the remaining height of the projection 50. In other words, the side of the at least one projection 50 opposite the bottom wall 34 is delimited by a surface which, viewed in the longitudinal direction of the cathode block, comprises two outer sections 52, 52 'and a middle section 54 arranged between them, the two outer sections 52, 52 'each form a support surface for a busbar 28 and are each designed to be planar, rectangular and parallel to the surface of the side of the cathode block 20 opposite the groove 26 and are at the same height, based on the depth of the groove 26, whereas the middle section 54 opposite the two outer sections 52, 52 ', viewed from the bottom wall 34, is formed so as to be raised into the groove 26. The middle section 54, seen in section in the longitudinal direction of the cathode block 20, is configured to be rectangular, so that a step is formed between the two outer sections 52, 52 'and the middle section 54. Of course, at least one or both of the Groove 26 delimiting side walls of the cathode block 20 each also have a recess, as in the Fig. 1 and 2 shown, or two indentations, as in the Fig. 3 and 4th shown, be provided.

Reference list

10

Aluminum electrolytic cell

12th

Cathode arrangement

14th

Aluminum smelting

16

Cryolite-aluminum oxide melt

18th

anode

20th

Cathode block

22nd

Rammed earth joint

24

Ramming mass

26th

Groove

28

Busbar

32

Side wall

34

Bottom wall

36.36 '

deepening

37

Transition area between the wall of the recess and the adjoining section of the groove wall

38

cast iron

39

Wrapping

40

arrow

42

dashed line

44

Width of the groove 26

46

Width of the cathode block 20

48

Transition area between two adjacent depressions

50

head Start

52, 52 '

outer portion of the protrusion

54

middle section of protrusion / nose

Claims (6)

1. A cathode assembly (12) comprising at least one cathode block (20) for an aluminium electrolysis cell based on carbon and/or graphite and which has at least one slot (26) which extends in the longitudinbusal direction of the cathode block (20) for receiving at least one current bar (28), wherein at least one of the at least one slots (26) has a variable depth when viewed over the length of the cathode block (20), wherein this slot (26) is delimited by a wall (32, 34), wherein the wall (32, 34) has a base wall (34) and two side walls (32), wherein at least one protrusion (50) which extends into the slot (26) is provided on the base wall (34), wherein at least one current bar (28) is provided in at least one of the at least one slots (26) with variable depth of the at least one cathode block (20),
   characterized in that
   the at least one current bar (28) is seated on at least one section of the at least one protrusion (50) and, with respect to the longitudinal extent of the cathode block (20), the at least one protrusion (50) is disposed at the position at which the slot (26) is at its greatest depth, so that the distance between the current bar (28) and the base wall (34) increases from both longitudinal ends of the slot to the protrusion (50).
2. The cathode assembly (12) according to claim 1,
   characterized in that
   on its side opposite to the base wall (34), the at least one protrusion (50) has at least one seating surface for at least one current bar (28) and which, at least in sections, runs substantially parallel to the surface of the side of the cathode block (20) which is opposite to the slot (26).
3. The cathode assembly (12) according to claim 2,
   characterized in that
   the side of the at least one protrusion (50) which is opposite to the base wall (34) is delimited by a face which comprises two outer sections (52, 52') and a central section (54) disposed between them when viewed in the longitudinal direction of the cathode block, wherein the two outer sections (52, 52') respectively form a seating surface for a current bar (28) and are each flat in configuration and at least substantially rectangular and run parallel to the surface of the side of the cathode block (20) which is opposite to the slot (26) and which are at the same height with respect to the depth of the slot (26), whereas the central section (54) is constructed so as to be raised into the slot (26) compared with the two outer sections (52, 52') when viewed from the base wall (34).
4. The cathode assembly (12) according to claim 3,
   characterized in that
   when viewed in section in the longitudinal direction of the cathode block (20), the central section (54) is rectangular in configuration so that a respective step is formed between the two outer sections (52, 52') and the central section (54).
5. The cathode assembly (12) according to claim 4,
   characterized in that
   the at least one protrusion (50) is composed of the same material as the remaining portion of the cathode block (20).
6. Use of a cathode assembly (12) according to one of claims 1 to 5 in order to carry out fused salt electrolysis for the production of metal, preferably for the production of aluminium.

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