EP2989235A1

EP2989235A1 - Cathode block having a slot with varying depth and a securing system

Info

Publication number: EP2989235A1
Application number: EP14721300.3A
Authority: EP
Inventors: Frank Hiltmann; Markus Pfeffer
Original assignee: SGL Carbon SE
Current assignee: Tokai Cobex GmbH
Priority date: 2013-04-26
Filing date: 2014-04-25
Publication date: 2016-03-02
Anticipated expiration: 2034-04-25
Also published as: EP3546620B1; RU2015150375A; PL3546620T3; RU2727621C2; CN105247109B; EP2989235B1; JP2016516905A; DE102013207737A1; UA117481C2; RU2020114123A3; EP2989235B9; RU2020114123A; WO2014174089A1; CA2910233C; CN105247109A; CA2910233A1; EP3546620A1; PL2989235T3; JP6808485B2

Abstract

A cathode block for an aluminum electrolysis cell based on carbon and/or graphite has at least one slot for receiving at least one bus bar, said slot extending in the longitudinal direction of the cathode block, wherein at least one of the at least one slot has a depth that varies when viewed over the length of the cathode block, and wherein at least one recess which extends horizontally in the longitudinal direction of the cathode block is provided in the cathode block wall bordering the at least one slot. According to another embodiment, a cathode block for an aluminum electrolysis cell based on carbon and/or graphite has at least one slot for receiving at least one bus bar, said slot extending in the longitudinal direction of the cathode block, wherein at least one of the at least one slot has a depth that varies when viewed over the length of the cathode block, and wherein this slot is bordered by a wall, at least one projection that projects into the slot being provided on said wall.

Description

Cathode block with a groove of varying depth and

a fixing device

The present invention relates to a cathode block for an aluminum electrolysis cell, its use and a cathode comprising this.

Electrolysis cells are used, for example, for the electrolytic production of aluminum, which is usually carried out industrially by the Hall-Heroult process. In the Hall-Heroult process, a melt composed of alumina and cryolite is electrolyzed. The cryolite, Na 3 [AIF ₆ ], serves to lower the melting point from 2045 ° C. for pure aluminum oxide to approximately 950 ° C. for a mixture containing cryolite, aluminum oxide and additives such as aluminum fluoride and calcium fluoride.

The electrolytic cell used in this method has a cathode bottom, which is composed of a plurality of, for example, up to 28 adjacent cathode blocks forming the cathode. The spaces between the cathode blocks are usually filled with a carbon-containing ramming mass to seal the cathode against molten components of the electrolytic cell, and to compensate for mechanical stresses that occur during commissioning of the electrolysis cell. In order to withstand the thermal and chemical conditions prevailing in the operation of the cell, the cathode blocks are usually composed of a carbonaceous material, such as graphite. On the undersides of the cathode blocks are usually provided in each case grooves, in each of which at least one or two bus bars are arranged, through which the current supplied via the anodes is dissipated. The gaps between the individual walls delimiting the grooves of the cathode blocks and the busbars are often poured with cast iron to to thereby electrically and mechanically connect the bus bars to the cathode blocks by the covering of the bus bars with cast iron produced thereby. About 3 to 5 cm above the top of the cathode, usually 15 to 50 cm high, layer of liquid aluminum is arranged, in particular of individual anode blocks, anode, between the and the surface of the aluminum, the electrolyte, ie Alumina and cryolite-containing melt is located. During the electrolysis carried out at about 1000 ° C., the aluminum formed is deposited below the electrolyte layer due to its greater density compared to that of the electrolyte, ie as an intermediate layer between the upper side of the cathode and the electrolyte layer. In the electrolysis, the dissolved in the melt aluminum oxide is split by electric current flow to aluminum and oxygen. From an electrochemical point of view, the layer of liquid aluminum is the actual cathode because aluminum ions are reduced to elemental aluminum on its surface. Nevertheless, the term cathode will not be understood below to mean the cathode from an electrochemical point of view, ie the layer of liquid aluminum, but rather the component forming the base of the electrolytic cell, for example composed of one or more cathode blocks.

A major disadvantage of the cathode arrangements used in the Hall-Heroult method is their comparatively low wear resistance, which manifests itself by a removal of the cathode block surfaces during the electrolysis. In this case, the removal of the cathode block surfaces due to an inhomogeneous current distribution within the cathode blocks is not uniform over the length of the cathode blocks, but to an increased extent at the cathode block ends, so that the surfaces of the cathode blocks change after a certain electrolysis time to a W-shaped profile. By the uneven removal of the cathode block surfaces, the useful life of the cathode blocks is limited by the locations with the largest removal. In order to counteract this problem, a cathode block has been proposed in WO 2007/1 18510 A2, the groove of which, in relation to the cathode block length, has a greater depth in the center than one of the cathode block ends to accommodate one or more busbars. Thereby, a substantially homogeneous vertical current distribution is achieved in the operation of the electrolysis cell over the cathode block length, whereby the increased wear on the cathode block ends is reduced and thus the life of the cathode is increased. The bus bar (s) is or are wrapped in a conventional manner with cast iron, said wrapping is done by pouring liquid cast iron in the space between the groove and the or the bus bar (s). However, such a cathode block is subject to disadvantages. During and after the pouring of the molten cast iron into the space between the groove and the busbar (s), during and after startup of the electrolysis cell comprising the cathode block, and during and after the switching off of the electrolysis cell and subsequent recommissioning, the cathode block is comparatively large Subjected to temperature changes, which lead to expansion or shrinkage of the cast iron and the bus bar (s) relative to the cathode block. This effect of expansion or shrinkage can be enhanced by occurring temperature gradients. Hereinafter, when the term "large temperature change (s)" is used, it is understood that one or both of the above effects, ie, expansion / shrinkage or temperature gradient, is present due to the higher coefficients of thermal expansion of cast iron and the material of the bus bar (FIG. n) than the coefficient of thermal expansion of the cathode block material, the cast iron and the bus bar (n) expand relative to the cathode block when the temperature increases, whereas they shrink with a decrease in temperature relative to the cathode block In particular, in conventional grooves having a rectangular cross-sectional shape, the electrical contact between the busbar, cast iron and cathode block deteriorates, which leads to an increased electrical resistance of the arrangement and thus to a poor energy efficiency of the electrolysis process. Apart from that, the bus bar (s) are movable in the space between the groove and the bus bar (s) both in the vertical and in the horizontal direction before pouring the molten cast iron so that they are poured of the molten cast iron and during the subsequent cooling and solidification of the cast iron can move uncontrollably in the groove, which can also lead to uneven electrical contact between busbar, cast iron and cathode block. This also leads to an increased electrical resistance of the arrangement and thus to a poor energy efficiency of the electrolysis process. Instead of the cast iron ramming mass can also be used. As ramming mass ramming compounds based on anthracite, graphite and any mixtures thereof can be used. Preferably, a ramming mass based on graphite is used. In order to prevent or at least make it difficult to displace a bus bar in the groove of a cathode block, it has been proposed in WO 2012/107412 A2 to provide at least one depression in the wall of a wall bounded by a graphite foil of a cathode block and, after insertion of the Bus bar (s) in the groove the forming intermediate space between the groove and the bus bar (s) (s) filled with liquid cast iron so that the solidified cast iron engages in the at least one recess. If the groove has a varying depth, as seen over the length of the cathode block, the at least one depression should run parallel to the groove bottom-that is, obliquely relative to the horizontal direction-that is to say have a constant distance from the bottom wall of the groove, in order to be displaceable - speed of the busbar (s) to ensure parallel to the groove bottom. However, this is disadvantageous because, due to the higher coefficients of thermal expansion of cast iron and the material of the busbar (s) compared to that of the cathode block during and after the pouring of the molten cast iron into the space between the groove and the busbar (s) of the Cathodes occurring changes in temperature and occurring during startup and shutdown, and possibly the recommissioning, the cathode block comprehensive electrolysis cell occurring temperature changes between the cast iron and the or the busbar (s) on the one hand and the cathode block on the other hand shear stresses, which is one of the Function of the cathode block impairing damage to the cathode block in the form of, for example, cracking in the cathode block or even a breakage of the cathode block may result. 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 the failure of the entire arrangement. Instead of the cast iron can also ramming - as described above - are used. In the following, when talking about cast iron, it is to be understood that the cast iron can be replaced by ramming mass without being explicitly described each time.

It is therefore an object of the present invention to provide a cathode block which is suitable, in particular, for use in an aluminum electrolysis cell, with which a substantially homogeneous vertical current distribution is achieved during operation of the electrolysis cell over the cathode block length, which also has an encased and cast-iron encapsulation Busbar (s) a low and especially over large temperature changes longer operating times durably low resistivity and low contact resistance between the cast iron sheathed busbar and the cathode block, and which at high temperature changes even with inserted and cast iron sheathed busbar (s) against mechanical damage, such as cracking is stable. Instead of the cast iron ramming mass can be used.

According to the invention, this object is achieved by a cathode block for an aluminum electrolytic cell based on carbon and / or graphite, wherein the cathode block has at least one extending in the longitudinal direction of the cathode block groove for receiving at least one busbar, wherein at least one of the at least one groove , seen in the length of the cathode block, varying depth, wherein in the at least one groove of varying depth bounding wall of the cathode block is provided at least one recess which extends horizontally in the longitudinal direction of the cathode block.

Under a horizontally extending in the longitudinal direction of the cathode block recess is understood in the present invention that the recess extends parallel to the longitudinal plane of the cathode block. A parallel extension is understood to mean that the depression at each of its points has an angle of less than 8 °, preferably less than 5 °, particularly preferably less than 2 °, very particularly preferably less than 1 °, most preferably of less than 0.5 °, and most preferably less than 0.1 ° to the longitudinal plane of the cathode block. In this context, the 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 depression, in contrast to a mere surface roughness, is understood to be a recess which has a depth of at least 0.5 mm, and preferably of at least 2 mm, relative to the surface of the wall delimiting the groove.

According to the invention, it has been recognized that by providing at least one recess extending 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 configuring the groove with varying depth in the cathode block a cathode block is provided, which also has with inserted into the groove and cast iron busbar a low electrical resistance and low contact resistance. Apart from this, due to the provision of the longitudinally extending in the longitudinal direction of the cathode block recess in the groove bounding the cathode block wall even with large temperature changes, mechanical damage to the cathode block with inserted into the groove and cast iron busbar, such as cracking of the cathode block , reliably avoided. On the one hand, the use of a groove with variable depth in the longitudinal direction of the cathode block achieves such a uniform current density distribution on the cathode block surface that the operation of the electrolysis cell comprising the cathode block effectively avoids excessive removal of cathode block material in those regions. where there would be a high local current density when using a cathode block with the same groove depth in the longitudinal direction of the cathode block. By appropriate adjustment of the groove depth, the current density distribution can be widely modified and evened out. By the cathode block has in its groove a horizontally extending in the longitudinal direction of the cathode block recess, a vertical fixation of the cast iron sheathed busbar is achieved in the groove of the cathode block, but which some movement in the horizontal direction of the Cathode blocks allowed. Because of this horizontal mobility of the busbar sheathed busbar, the occurrence of shear stresses between the busbar sheathed busbar and the cathode block is reliably avoided, especially in the rapid and temperature changes occurring during and after startup of a cathode cell comprising the electrolysis cell at an obliquely located depression due to the higher expansion or shrinkage of the cast iron and the bus bar relative to the cathode block, due to the higher coefficients of thermal expansion of cast iron and the material of the bus bars as compared to the thermal expansion coefficient of the material of the cathode block. As a result, damage to the cathode block, for example in the form of crack formation or even breakage of the cathode block, is reliably prevented even during a long service life of the electrolysis cell, while ensuring excellent electrical conductivity between the busbar or the cast iron and the cathode block. Due to the vertical fixation of the cast iron sheathed busbar in the groove of the cathode block, there is an advantageous contact pressure of the cathode bar / cast iron assembly against the groove bottom by the thermal expansion of the ingot / cast iron arrangement relative to the cathode block during commissioning. Thus, an improved electrical contact is achieved, which leads to a lower electrical resistance and thus to a higher energy efficiency. In a further advantage to the cathode block known from WO 2012/107412 A2, these outstanding properties are also achieved, in particular, when the groove of the cathode block is not lined with an expensive graphite foil which is to be introduced in a complicated manner. Overall, a control of - due to the different thermal expansion coefficients of cast iron, busbar and cathode block occurring - tensile stresses, shear stresses and compressive stresses is thus achieved even with large changes in temperature, which excellent electrical conductivity and excellent mechanical Stability of the cathode block also ensured with inserted into the groove and sheathed with cast iron busbar.

In order to achieve a particularly uniform vertical current density distribution at the cathode block surface in the electrolysis operation, it is proposed in a development of the invention that at least one of the at least one groove and preferably all of the grooves with varying depth have or have a smaller depth at their longitudinal ends than in their middle (s). In this way, a uniform distribution of the electrical current supplied in the electrolysis operation over the entire length of the cathode block is achieved, whereby an excessive electric current density at the longitudinal ends of the cathode block and thus premature wear at the ends of the cathode block is avoided. As a result of such a uniform current density distribution over the length of the cathode block, movements in the aluminum melt caused by the interaction of electromagnetic fields during electrolysis are also avoided, making it possible to arrange the anode at a lesser height above the surface of the aluminum melt. This reduces the electrical resistance between the anode and the aluminum melt and increases the energy efficiency of the fused-salt electrolysis carried out. Another particular advantage of this embodiment is that in this embodiment of the groove provided in the recess of the groove possibly sheathed with cast iron busbar (s) during and after the occurring during commissioning of the electrolytic cell increasing the temperature in the horizontal direction expands As a result, the bus bar (s) are respectively pressed against the bottom wall of the cathode block which delimits the groove at this point, thereby reducing the contact resistance between the cast iron covered bus bar and the cathode block. In the above embodiment, the depth of at least one of the at least one groove of varying depth, seen in the longitudinal direction of the cathode block, preferably at least substantially monotonically increases from one longitudinal end to the center of the cathode block and takes it from the center to the other longitudinal side End of the cathode block at least substantially monotonically, so that, as seen in the longitudinal section of the cathode block, results in an at least substantially triangular groove. As a result, the above advantages are achieved to an increased extent. According to another preferred embodiment of the present invention, the wall bounding the at least one groove of varying depth comprises a bottom wall and two side walls, each of the two side walls each having at least one recess extending horizontally in the longitudinal direction of the cathode block. In this way, a particularly good vertical fixation of the busbar is achieved in the groove, at the same time sufficiently high mobility of the busbar in the horizontal direction to reliably avoid the occurrence of shearing stresses due to the different thermal expansion coefficients of cast iron, busbar and cathode block, even with large temperature changes.

Preferably, the wall bounding the at least one groove of varying depth comprises a bottom wall and two side walls, each side wall each having exactly one recess extending horizontally in the longitudinal direction of the cathode block. In this way, with comparatively low manufacturing costs, a particularly good vertical fixation of the busbar in the groove is achieved, with sufficiently high mobility in the horizontal direction to reliably detect the occurrence of shear stresses due to the different thermal expansion coefficients of cast iron, busbar and cathode block in the case of large temperature changes to avoid. Likewise, it is preferred that the wall bounding the at least one groove of varying depth comprises a bottom wall and two side walls, each side wall having respective two depressions each extending horizontally in the longitudinal direction of the cathode block. In this way, a particularly good vertical fixation of the busbar in the groove at the same time sufficiently high mobility in the horizontal direction is also achieved when the depth of the individual wells is comparatively low.

In this case, the cathode block may have two grooves arranged on the same side of the cathode block, wherein both grooves have the same dimensions and the limiting walls each comprise a bottom wall and two side walls, each side wall each having a recess which extends horizontally in the longitudinal direction of the cathode block, or wherein each side wall each has two recesses extending horizontally in the longitudinal direction of the cathode block. Thus, for a two-slot cathode block with comparatively low production costs a particularly good vertical fixation of the two busbars in the grooves achieved at the same time sufficiently high mobility in the horizontal direction to large temperature changes, the occurrence of shear stresses due to the different thermal expansion coefficients of cast iron, busbar and To reliably prevent cathode block.

As an alternative to the above embodiment, the cathode block may also comprise only one groove.

In principle, the at least one groove can have all known cross-sectional shapes, but in particular good results are obtained if at least one of the at least one groove and preferably each of the at least one groove has an at least substantially rectangular, preferably rectangular, cross-section. In order to ensure a particularly good fixation of the possibly busbar sheathed busbar in the groove in the vertical direction with sufficient mobility in the horizontal direction, it is proposed in development of the invention that at least one of the at least one recess and more preferably each the at least one recess extends continuously over at least 60%, preferably over at least 80%, more preferably over at least 90%, most preferably over at least 95%, and most preferably at least approximately over the entire length of the at least one groove.

For the same reason, it is preferable that at least one of the at least one recess and more preferably each of the at least one recess has a depth of 0.5 mm to 40 mm, preferably 2 mm to 30 mm, and more preferably 5 mm to 20 mm having.

For the same reason, it is also preferred that at least one of the at least one depression, and more preferably each of the at least one depression, has an opening width of 2 mm to 40 mm, preferably 5 mm to 30 mm and more preferably of the cathode block 10 mm to 20 mm.

In principle, the at least one recess can have any polygonal or curved cross section. Good results with regard to a good engagement of the cast iron casing in the at least one depression and at the same time with regard to a reliable and unproblematic fillability of the recess with cast iron during casting are achieved in particular if at least one of the at least one depression and particularly preferably each of the at least a recess an at least substantially semicircular, triangular, has rectangular or trapezoidal, preferably semi-circular, triangular, rectangular or trapezoidal, cross-section.

According to a further preferred embodiment of the present invention, the at least one recess extends at least substantially perpendicularly, preferably perpendicularly, into the wall of the cathode block bounding the at least one groove.

According to the present invention, the at least one depression, viewed in the depth direction of the groove, is delimited at each of its ends by a transitional area between the depression and an adjoining portion of the groove wall. When this transition region is angled, the angle between the adjacent portion of the groove wall and the wall of the depression, viewed from the cathode block inner side, is preferably 90 degrees to 160 degrees, more preferably 90 degrees to 135 degrees, and most preferably 100 degrees up to 120 degrees.

In the event that this transition region is curved, possibly but not necessarily ideally circularly curved, the radius of curvature of the transition region is preferably not more than 50 mm, more preferably not more than 20 mm and most preferably not more than 5 mm.

In addition, the present invention relates to a cathode assembly, which contains at least one cathode block described above, wherein at least one of the at least one groove with varying depth of the at least one cathode block at least one bus bar is provided which at least partially has a cladding made of cast iron, which at least partially in which engages at least one depression. According to a preferred embodiment of the present invention, the portion of the cast-iron casing engaging in the at least one recess is designed to be complementary to the recess. In this way, a particularly good positive engagement of the casing of cast iron in the recess and thus a particularly effective mechanical attachment of the cast iron casing and the associated bus bar to the cathode block can be achieved, which nevertheless due to avoid shear stress between cast iron, busbar and cathode block of large temperature changes sufficient mobility of the busbar in the horizontal direction allows.

Preferably, the cast iron shell engages over at least 50%, more preferably at least 80%, more preferably at least 90%, most preferably at least 95%, and most preferably at least substantially all of its length into the at least one recess. As a result, the advantages described above are achieved to a particularly high degree.

For the same reason, according to a further preferred embodiment of the present invention, it is provided that the section of the enclosure engaging in the at least one recess and, if appropriate, the busbar covered thereby, at least 70%, preferably at least 80%, particularly preferably at least 90%. , most preferably at least 95% and most preferably 100% of the well fills. As a result, an undesired displacement of the busbar in the vertical direction of the cathode block and in particular falling out of the busbar from the groove can be avoided particularly reliably.

In a further development of the inventive idea, it is proposed that the cathode block of the cathode arrangement has a groove with an at least substantially rectangular, preferably a rectangular, cross-section and in the groove one or two adjacent busbar (s) are used, wherein the gap between the groove and the busbar (s) is filled with cast iron so that the cast iron on at least substantially the same entire length engages the at least one depression.

A further subject of the present invention is a cathode, which comprises at least one previously described cathode block or at least one previously described cathode arrangement.

Furthermore, the present invention relates to the use of a previously described cathode block, a previously described cathode assembly or a previously described cathode for performing a fused-salt electrolysis to produce metal, preferably for the production of aluminum.

A further subject of the present invention is a cathode block for an aluminum electrolytic cell based on carbon and / or graphite, in particular a previously described cathode block which has at least one groove extending in the longitudinal direction of the cathode block for accommodating at least one bus bar, wherein at least one of the at least one groove has a varying depth across the length of the cathode block, said groove being bounded by a wall, at least one projection extending into the groove being provided on the wall. According to the invention, it has been recognized that by providing at least one protrusion extending into the groove, which serves as a bearing surface for busbar ends or their cast iron cladding, a cathode block is also provided in the cathode block in particular when the groove of varying depth is formed in which the busbar inserted in the groove and, in particular also in the case of two mutually adjoining into the groove. brachter busbars, each with respect to the length of the cathode block half length - the busbar (s) - depending on the configuration of the projection - are fixed in the vertical and / or horizontal direction, so that an uncontrolled movement or displacement of the busbars in the at Producing a cathode assembly with a cathode block and inserted in the groove cast iron busbar (s) carried out pouring of liquid cast iron in the space between the groove and the busbar (s) and in particular during the subsequent cooling and solidification of the cast iron despite the usually higher Thermal expansion of cast iron and the material of the bus bar (s) compared to the thermal expansion of the cathode block material, which movement or displacement can lead to a bad or uneven electrical contact between busbar, cast iron and cathode block reliably avoided that will. The at least one projection extending into the groove is therefore a support nose or a support journal on which an end piece of a busbar or two end pieces of two busbars rest. Because of this, the produced cathode assembly of cathode block with inserted and cast iron busbar (s) has a low electrical resistivity and low contact resistance between the cast iron sheathed busbar (s) and the cathode block, and in particular also a permanently low electrical resistivity and low contact resistance between the cast iron sheathed busbar (s) and the cathode block, even at high temperature changes. Consequently, the cathode block according to the invention is particularly suitable for receiving two busbars inserted adjacent to one another into the groove, each having a half length relative to the length of the cathode block, in which 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 support surface formed by the projection. Furthermore, the cathode block according to the invention is suitable in particular also for cross-sectionally rectangular busbars. In particular, in the case that in the groove wall of the cathode block is additionally provided in the longitudinal direction of the cathode block horizontally extending recess is in the groove bounding the cathode block wall, even with large changes in temperature mechanical damage to the cathode block with inserted into the groove and with Cast iron sheathed busbar, such as cracking of the cathode block, reliably avoided. In this case, the use of a groove with variable depth in the longitudinal direction of the cathode block achieves such a uniform current density distribution on the cathode block surface that the operation of the electrolytic cell comprising the cathode block effectively avoids excessive removal of cathode block material in those regions where when using a cathode block with in the longitudinal direction of the cathode block the same groove depth a high local current density would be present. By correspondingly adjusting the groove depth, the current density distribution can be modified and evened out within wide limits. Overall, a control of - due to the different thermal expansion coefficients of cast iron, busbar and cathode block occurring - tensile stresses, shear stresses and compressive stresses is thus achieved even at large or high temperature changes, which excellent electrical conductivity and excellent mechanical stability of the cathode block with in the groove inserted and cast iron sheathed busbar guaranteed.

In order to achieve a particularly uniform vertical flow density distribution at the cathode block surface in the electrolysis operation, it is proposed in the development of the invention that at least one of the at least one groove and preferably all of the grooves of varying depth have or have a smaller depth at their longitudinal ends than in their middle (s). In this way, a uniform distribution of the supplied during the electrolysis operation electric current over the entire length of Cathode blocks reached, whereby an excessive electric current density at the longitudinal ends of the cathode block and thus premature wear at the ends of the cathode block is avoided. As a result of such a uniform current density distribution over the length of the cathode block, movements in the aluminum melt caused by the interaction of electromagnetic fields during electrolysis are also avoided, making it possible to arrange the anode at a lesser height above the surface of the aluminum melt. This reduces the electrical resistance between the anode and the aluminum melt and increases the energy efficiency of the fused-salt electrolysis carried out. A further particular advantage of this embodiment is that, in this embodiment, the bus bar (s), which is fixed by the at least one projection and may be covered with cast iron, during and after the increase in temperature in the horizontal direction occurring during the startup of the electrolysis cell As a result, the bus bar (s) are respectively pressed against the bottom wall of the cathode block groove (s) delimiting the groove at that point, thereby reducing the contact resistance between the cast iron covered bus bar (s) and the cathode block , In the above embodiment, the depth of at least one of the at least one groove of varying depth, seen in the longitudinal direction of the cathode block, preferably at least substantially monotonically increases from one longitudinal end to the center of the cathode block and takes it from the center to the other longitudinal side End of the cathode block at least substantially monotonically, so that, as seen in the longitudinal section of the cathode block, results in an at least substantially triangular groove. As a result, the above advantages are achieved to an increased extent. According to a further preferred embodiment of the present invention, the wall delimiting the at least one groove of varying depth comprises a bottom wall and two side walls, wherein at least one projection extending into the groove is provided on the bottom wall, which preferably extends vertically into the at least a groove extends into it. 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 occur even with large temperature changes, the occurrence of shear stresses due to the different thermal expansion coefficients of cast iron, busbar and cathode block avoid.

According to a further preferred embodiment of the present invention, the at least one projection in the embodiment described above on its side opposite the bottom wall at least one support surface for at least one bus bar, which at least partially 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 of the groove bounding the cathode block. Such a bearing surface is particularly well suited to rest a busbar or to support two busbars.

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

In order to achieve a sufficiently large support surface, in particular for two adjoining end pieces of two busbars, it is proposed in further development of the idea of the invention that the bottom wall opposite Overlying side of the at least one projection is bounded by a support surface which is completely planar, preferably at least substantially rectangular and parallel, particularly preferably rectangular and parallel, designed to extend to the surface of the opposite side of the groove of the cathode block. In this embodiment, therefore, all of the bottom wall of the cathode block opposite surface of the projection is formed as a support surface for one or two end pieces of one or two busbar (s). The above embodiment can be realized, for example, by the at least one projection, seen in the longitudinal extent of the cathode block cut over its entire height at least substantially rectangular or trapezoidal, preferably rectangular or trapezoidal configured, wherein the bottom wall opposite side of the at least one Projection is limited by a support surface, which is planar, at least substantially rectangular and parallel, preferably rectangular and parallel, designed to extend to the surface of the opposite side of the groove of the cathode block. Preferably, the extension of the rectangular support surface extending in the longitudinal extent of the cathode block is 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 200 mm, whereas the in the widthwise extension of the cathode block, the expansion of the rectangular support surface is preferably at least 50%, more preferably at least 80%, particularly preferably at least 90% and most 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, which is alternative to the above embodiment, the wall opposite side of the at least one projection is bounded by a surface which comprises two, as seen in the longitudinal direction of the cathode block, outer portions and a central portion arranged therebetween, wherein the two outer portions each form a support surface for a busbar and each planar, preferably at least substantially rectangular and parallel, particularly preferably rectangular and parallel, are designed to extend to the surface of the opposite side of the groove of the cathode block and, based on the depth of the groove, are at the same height, whereas the middle section opposite to the two outer sections , Seen from the bottom wall, is formed raised in the groove. This embodiment is particularly preferred for cathode blocks, which are designed to receive two each, based on the length of the cathode block, busbars, approximately half the length. This is because by the elevation provided in the middle portion of the protrusion, the two adjacent outer portions of the protrusion forming the abutment surface for each one end of a bus bar are separated from each other by a partition wall extending in the depth direction of the groove, so that the End pieces of the two busbars rest on opposite sides of the partition, whereby the two bus bars are fixed not only in the vertical direction, but also at these two end pieces in the horizontal direction. This ensures that the two busbars in the case of an expansion due to a temperature increase in a defined direction, namely in the direction of the cathode end block, expand. As a result, the two power rails, which may have been encased with cast iron, are pressed against the bottom wall of the cathode block delimiting the groove at this point during and after the increase in temperature in the horizontal direction occurring during the startup of the electrolysis cell due to the expansion in the direction of the cathode block end. whereby the contact resistance between the cast iron sheathed busbar and the cathode block is reduced. In order to achieve the above-described advantages to a particularly great extent, it is preferred that the central portion of the projection, as seen in the longitudinal direction of the cathode block cut, rectangular - ie in the form of a rectangular nose - is designed so that between the two outer Sections and the middle section in each case a step is formed. This step may be at right angles or rounded at the transition region 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 extent of the steps extending in the widthwise extension of the cathode block is preferably at least 50% preferably at least 80%, particularly preferably at least 90% and very particularly preferably 100% of the width of the groove.

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

According to a further preferred embodiment of the present invention, it is provided that the at least one projection, with respect to the longitudinal extension of the cathode block, is arranged at the point at which the groove has the highest depth, wherein the projection itself is disregarded here. If, which is particularly preferred as set out above, the groove with varying depth at its longitudinal ends has a smaller depth than in its center and in particular the depth of the groove seen in the longitudinal direction of the cathode block, at least substantially continuously increases from a longitudinal end to the center of the cathode block and this from the center to the other longitudinal end of the cathode block decreases at least substantially monotonically, the at least one projection is therefore preferably, based on the longitudinal extent of the cathode block, arranged centrally. Furthermore, it has proved to be advantageous for the at least one projection to extend 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 on the one hand achieves sufficient mechanical stability of the projection and, on the other hand, ensures that the busbar (s) with its end piece (s) over at least a large part or the entire width thereof are supported on the support surface formed by the projection (n) rest.

In principle, the at least one projection may 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 remaining cathode block. Particularly preferably, the at least one projection consists 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 in terms of a sufficiently high electrical conductivity and a sufficiently high wear resistance are obtained in particular when 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 remainder of the cathode block are monolithic, i. in one piece, are. As a result, a particularly high mechanical stability of the connection of the projection to the remaining part of the cathode block is achieved.

Alternatively, the at least one projection on the bottom wall of the cathode block may also be connected to a connection means. This can be achieved, for example, by adhering the at least one protrusion to the remainder of the cathode block via an adhesive such as synthetic resin, putty, tar, or the like, or any mixture of the foregoing, or with a mechanical fastener to the remainder of the cathode block Cathode blocks is connected.

In addition, the present invention relates to a cathode assembly, which contains at least one cathode block described above, wherein at least one of the at least one groove with varying depth of the at least one cathode block at least one bus bar is provided which preferably at least partially has a cladding of cast iron, wherein possibly covered with cast iron busbar rests at least on a portion of the at least one projection. Preferably, the cathode assembly comprises at least one cathode block, wherein in at least one of the at least one groove of varying depth of the at least one cathode block two preferably at least partially a sheath of cast iron having busbars are provided, each with one of its end pieces at least on a portion of the at least one projection rest. According to a further preferred embodiment of the present invention, the at least one busbar is at least partially and particularly preferably completely encased in cast iron.

Another object of the present invention is a cathode assembly comprising at least one previously described cathode block or at least one previously described cathode assembly. Furthermore, the present invention relates to the use of a previously described cathode block, a previously described cathode arrangement or a previously described cathode arrangement for carrying out a fused-salt electrolysis for the production of metal, preferably for the production of aluminum.

Hereinafter, the present invention will be described purely by way of example with reference to advantageous embodiments and with reference to the accompanying drawings. Showing:

1 is a cross-sectional view of a portion of an aluminum electrolytic cell having a cathode assembly according to a first embodiment of the present invention;

FIG. 2 shows a longitudinal section of the cathode arrangement of the aluminum electrolytic cell shown in FIG. 1, FIG. 3 shows a longitudinal section of a detail of an aluminum electrolysis cell with a cathode arrangement according to a second exemplary embodiment of the present invention; FIG. 4 shows a cross section of the cathode arrangement of the aluminum electrolysis cell shown in FIG.

5a-d are exemplary cross-sections of recesses provided in a groove of a cathode block according to the invention,

6 is a longitudinal section of a cathode block according to a third embodiment of the present invention,

7 is a longitudinal sectional view of a cathode block according to a fourth embodiment of the present invention and FIG

FIG. 1 shows in cross-section a section of an aluminum electrolysis cell 10 with a cathode arrangement 12 which at the same time forms the bottom of a trough for an aluminum melt 14 produced during operation of the electrolytic cell 10 and for a cryogen above the aluminum melt 14. lith-alumina melt 16 forms. With the cryolite-alumina melt 16 is an anode 18 in contact. Laterally, the trough formed by the lower part of the aluminum electrolytic cell 10 is limited by a lining of carbon and / or graphite, not shown in FIG. 1.

The cathode arrangement 12 comprises a plurality of cathode blocks 20, which are each connected to one another via a ramming mass 24 inserted into a ramming mass gap 22 arranged between the cathode blocks 20. A cathode block 20 in this case comprises two grooves 26 arranged on its underside and having a rectangular, namely substantially rectangular cross section, wherein in each case Groove 26 each a bus bar 28 made of steel is also included with rectangular cross-section.

The grooves 26 are each bounded by two side walls 32 and a bottom wall 34 of the cathode block 20, wherein in each of the side walls 32 is provided a substantially perpendicular in the side wall 32 extending recess 36 having an approximately semicircular cross-section. Each recess 36 is bounded by an upper and a lower transition region 37 of the cathode block 20, respectively. The transition areas 37 are in the present embodiment at an angle with an angle α between the adjacent

Section of the groove wall and the wall of the recess formed by 90 degrees. The space between the busbar 28 and the groove 26 is in each case cast with cast iron 38. In this case, the cast iron 38 forms an envelope 39 for the busbar 28 and is connected to the busbar 28 in a materially bonded connection.

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

In FIG. 1, the cross section of the cathode assembly 12 is shown concretely at a longitudinal end of the cathode block 20. 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 - in relation to the longitudinal direction of the cathode block - the middle of the groove 26 is indicated in Fig. 1 by a dashed line 42. The difference between the groove depth at the longitudinal ends of the groove 26 and in the - with respect to the longitudinal direction of the cathode block - the middle of the groove 26 in the present embodiment is about 5 cm. The depth of the groove 26 at the two longitudinal ends of the groove 26 is about 16 cm, whereas the depth the groove 26 in the - relative to the longitudinal direction of the cathode block - center of the groove 26 is about 21 cm. The width 44 of each groove 26 is substantially constant over the entire groove length and is about 15 cm, whereas the width 46 of the cathode blocks 20 is about 42 cm each.

In the present embodiment, a plurality of anodes 18 and a plurality of cathode blocks 20 are arranged one above the other in such a way that each anode 18 covers two juxtaposed cathode blocks 20 and covers in length half of a cathode block 20, wherein each two adjacent anodes 18, the Cover length of a cathode block 20.

FIG. 2 shows the cathode block 20 shown in FIG. 1 in longitudinal section. As can be seen in FIG. 2, the groove 26 viewed in its longitudinal section extends towards the center of the cathode block 20 in the shape of a triangle, thereby ensuring a substantially uniform electrical vertical current density over the entire cathode length. The recess 36 extends as indicated in Fig. 2 by the correspondingly indicated line parallel to the horizontal direction, i. parallel to the surface of the groove 26 opposite side of the cathode block 20. The in Fig. 2 sake of clarity not shown busbar 28 is formed barren in the present embodiment and has a rectangular longitudinal section, so that between the busbar and the groove bottom 34 is a to the center of the groove 26 towards increasing space, which may be filled either by cast iron 38 or by additional connected to the busbar 28 metal plates.

The cathode arrangement and cathode block shown in longitudinal section and cross section in FIGS. 3 and 4 according to a second exemplary embodiment of the present invention differs from the cathode arrangement and cathode block shown in FIGS. 1 and 2. in that in the cathode block 20 only one groove 26 is provided which has two depressions 36, 36 '.

Furthermore, FIGS. 5a to d show exemplary depressions 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 a substantially semicircular cross-section (FIG. 5a), a substantially trapezoidal cross-section (FIG. 5b) or a substantially triangular cross-section (FIG. 5c). The angle α of the transition regions 37 between the wall of the recess 36 and the adjoining portion of the groove wall 32, viewed from the inside of the cathode block 20, is approximately 90 degrees in FIG. 5a, approximately 120 degrees in FIG in Fig. 5c about 125 degrees. FIG. 5 d shows an embodiment in which a plurality of depressions 36 with a triangular cross-section, as shown in FIG. 5 c, are arranged consecutively in the depth direction of the groove 26 in order to effect a particularly reliable support of an inserted bus bar 28. The transition regions 48 between two adjoining recesses 36 have between the walls of two adjacent recesses 36, seen from the inside of the cathode block 20, an angle ß of about 70 degrees. The depressions 36 shown in FIGS. 5 a to d each extend perpendicularly into the side wall 32 of the cathode block 20 delimiting the groove 26, so that they form a fixation with cast iron received in the depressions 36 which acts in the depth direction of the groove 26 and prevents unwanted movement of the bus bar 28 parallel to the depth direction of the groove 26 after the bus bar 28 is cast iron 38, but a horizontal movement of the cast iron sheathed busbar, for example due to expansion of the busbar sheathed by a large temperature change, allows.

6, a cathode block 20 according to a third embodiment of the present invention is shown in longitudinal section, in difference 1 to 4 upside down, based on the later installation in the electrolysis cell to illustrate the arrangement during pouring with liquid cast iron. This cathode block 20 differs from that shown in FIGS. 1 to 4 in that it has no recess in the groove 26 delimiting wall. Instead, this cathode block 20 has in its groove 26 a projection 50, which is arranged centrally with respect to the longitudinal direction of the cathode block 20 and, seen in the longitudinal direction of the cathode block cut, is designed trapezoidal. In this case, the surface of the projection 50 delimiting the bottom wall 34 of the cathode block 20 is designed to be planar, rectangular and parallel to the surface of the side of the cathode block opposite to the groove, thereby forming a contact surface for the end pieces of two busbars 28. Of course or can be provided on at least one or both of the groove 26 delimiting side walls of the cathode block 20 and a recess, as shown in FIGS. 1 and 2, or two recesses, as shown in FIGS. 3 and 4, respectively.

In addition, in FIG. 7, a cathode block 20 according to a fourth embodiment of the present invention is shown in longitudinal section, in turn, in contrast to that shown in FIGS. 1 to 4 standing upside down. This cathode block 20 differs from that shown in FIG. 6 in that the projection 50 shown hatched here, not cut in the longitudinal direction of the cathode block, is designed trapezoidal, but is designed rectangular in its lower part, wherein on the bottom wall 34 of the cathode block 20 opposite side of this portion of the projection 50 is a seen in the longitudinal extent of the cathode block 20 centrally disposed nose 54 is provided, which extends over the remaining height of the projection 50. In other words, the side of the at least one protrusion 50 opposite the bottom wall 34 is bounded by a surface which is two outer, viewed in the longitudinal direction of the cathode block Sections 52, 52 'and a central portion 54 disposed therebetween, wherein the two outer portions 52, 52' each form a support surface for a bus bar 28 and each planar, rectangular and parallel to the surface of the groove 26 opposite side of the cathode block 20th are designed to extend and, based on the depth of the groove 26, are at the same height, whereas the central portion 54 with respect to the two outer portions 52, 52 ', seen from the bottom wall 34, formed in the groove 26 is raised. In this case, the central portion 54, as seen in the longitudinal direction of the cathode block 20 cut, is designed rectangular, so that between the two outer portions 52,52 'and the central portion 54 each have a step is formed. Of course, at least one or both of the groove 26 delimiting side walls of the cathode block 20 and one recess, as shown in FIGS. 1 and 2, or two recesses, as shown in Figs. 3 and 4, respectively provided be.

LIST OF REFERENCE NUMBERS

10 aluminum electrolysis cell

12, 12 'cathode arrangement

14 aluminum melt

16 cryolite-alumina melt

18 anodes

20 cathode block

22 ramming joint

24 ramming mass

26 groove

28 busbar

32 side wall

34 bottom wall

36, 36 'recess

37 transition region between the wall of the recess and the adjacent portion of the groove wall

38 cast iron

39 serving

40 arrow

42 dashed line

44 width of the groove 26

46 width of the cathode block 20

48 transition area between two adjoining depressions

50 advantage

52, 52 'outer portion of the projection

54 middle section of the projection / nose Angle between the wall of the recess and the adjacent portion of the groove wall

Angle between the walls of two adjoining depressions

Claims

Patent claims

Cathode block (20) for an aluminum electrolytic cell based on carbon and/or graphite, the cathode block (20) having at least one groove (26) extending in the longitudinal direction of the cathode block (20) for receiving at least one busbar (28), wherein at least one of the at least one groove (26) has a varying depth, viewed over the length of the cathode block (20), in which the wall (32, 34) of the cathode block (20) delimiting the at least one groove (26) with varying depth ) at least one recess (36, 36 ') is provided, which extends horizontally in the longitudinal direction of the cathode block (20).

Cathode block (20) according to claim 1,

thereby marked that

at least one of the at least one groove (26) with varying depth has a smaller depth at its longitudinal ends than in its middle.

Cathode block (20) according to claim 1 or 2,

thereby marked that

the wall (32, 34) delimiting the at least one groove (26) with varying depth comprises a bottom wall (34) and two side walls (32), each side wall (32) having at least one recess (36, 36 '), which extends horizontally in the longitudinal direction of the cathode block (20).

4. cathode block (20) according to claim 3,

characterized in that at least one of the least one depressions (36, 36') extends continuously over at least 60% of the entire length of the at least one groove (26).

Cathode block (20) according to claim 4,

thereby marked that

at least one of the at least one recess (36, 36') has a depth of 0.5 mm to 40 mm.

Cathode block (20) according to claim 5,

thereby marked that

at least one of the at least one recess (36, 36') has an opening width of 2 mm to 40 mm based on the height of the cathode block (20).

Cathode arrangement, which contains at least one cathode block (20) according to at least one of claims 1 to 6, wherein at least one busbar (28) is provided in at least one of the at least one groove (26) with varying depth of the at least one cathode block (20), which at least partially has a casing (39) made of cast iron (38) or ramming mass, which engages at least in sections in the at least one recess (36, 36 ').

Cathode block (20) for an aluminum electrolytic cell based on carbon and / or graphite, which has at least one groove (26) extending in the longitudinal direction of the cathode block (20) for receiving at least one busbar (28), at least one of the at least a groove (26) has a depth that varies over the length of the cathode block (20), this groove (26) being surrounded by a wall (32, 34). is bordered, with at least one projection (50) extending into the groove (26) being provided on the wall (32, 34).

Cathode block (20) according to claim 8,

thereby marked that

the wall (32, 34) comprises a bottom wall (34) and two side walls (32), with at least one projection (50) extending into the groove (26) being provided on the bottom wall (34), which is preferably extends vertically into the at least one groove (26).

Cathode block (20) according to claim 8 or 9,

thereby marked that

the at least one projection (50) on its side opposite the bottom wall (34) has at least one support surface for at least one busbar (28), which at least in sections is essentially parallel to the surface of the side of the cathode block (20) opposite the groove (26). runs.

Cathode block (20) according to claim 10,

thereby marked that

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, wherein the two outer sections (52, 52') each form a support surface for a busbar (28) and are each designed to be planar, at least substantially rectangular and running parallel to the surface of the side of the cathode block (20) opposite the groove (26). and are at the same height in relation to the depth of the groove (26), whereas the middle section (54) is opposite the two outer ones ren sections (52, 52 '), seen from the bottom wall (34), is designed to be raised into the groove (26).

12. Cathode block (20) according to claim 11,

thereby marked that

the middle section (54), seen in the longitudinal direction of the cathode block (20), is rectangular, so that a step is formed between the two outer sections (52, 52 ') and the middle section (54).

13. Cathode block (20) according to claim 11,

characterized in that

the at least one projection (50), based on the longitudinal extent of the cathode block (20), is arranged at the point at which the groove (26) has the greatest depth.

14. Cathode block (20) according to claim 13,

characterized in that

the at least one projection (50) is composed of the same material as the remaining part of the cathode block (20).

15. Use of a cathode block (20) according to at least one of claims 1 to 6 or 8 to 14 or a cathode arrangement (12) according to claim 7 for carrying out fusion electrolysis for the production of metal, preferably for the production of aluminum.