CA2826328A1 - Cathode arrangement having a surface-profiled cathode block with a groove of variable depth - Google Patents
Cathode arrangement having a surface-profiled cathode block with a groove of variable depth Download PDFInfo
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- CA2826328A1 CA2826328A1 CA2826328A CA2826328A CA2826328A1 CA 2826328 A1 CA2826328 A1 CA 2826328A1 CA 2826328 A CA2826328 A CA 2826328A CA 2826328 A CA2826328 A CA 2826328A CA 2826328 A1 CA2826328 A1 CA 2826328A1
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
- C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
- C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
- C25C3/08—Cell construction, e.g. bottoms, walls, cathodes
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
- C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
- C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
- C25C3/16—Electric current supply devices, e.g. bus bars
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Abstract
The present invention relates to a cathode assembly for an aluminum electrolytic cell, comprising at least one cathode block on the basis of carbon and/or graphite, which has at least in some sections a profiled surface and at least one groove, wherein at least one busbar is provided in the at least one groove, the at least one groove having a varying depth over its length. The invention also relates to a corresponding cathode block.
Description
SGL CARBON SE
18.07.2013 Cathode arrangement having a surface-profiled cathode block with a groove of variable depth The present invention relates to a cathode arrangement for an aluminium elec-trolysis cell.
Such electrolysis cells are used for the electrolytic production of aluminium, which is customarily carried out in industry by the Hall-Heroult process. In the Hall-Heroult process, a melt composed of aluminium oxide and cryolite is electrolysed.
Here, the cryolite, Na3[AlF6], serves to lower the melting point of 2045 C for pure aluminium oxide to about 950 C for a mixture containing cryolite, aluminium oxide and additives, such as aluminium fluoride and calcium fluoride.
The electrolysis cell used in this process has a bottom, which is composed of a multiplicity of adjoining cathode blocks forming the cathode. In order to withstand the thermal and chemical conditions which prevail during operation of the cell, the cathode blocks are customarily composed of a carbon-containing material. The undersides of each of the cathode blocks are provided with grooves, in each of which there is arranged at least one busbar through which the current fed via the anodes is discharged. In this case, the interstices between the individual walls of the cathode blocks, which delimit the grooves, and the busbars are often sealed with cast iron, in order to electrically and mechanically connect the busbars to the cathode blocks by virtue of the resulting encasement of the busbars with cast iron.
An anode formed from individual anode blocks is arranged about 3 to 5 cm above the layer of molten aluminium located on the top side of the cathode, and the elec-trolyte, i.e. the melt containing aluminium oxide and cryolite, is located between said anode and the surface of the aluminium. During the electrolysis carried out at about 1000 C, the aluminium which has formed settles beneath the electrolyte layer, i.e. as an intermediate layer between the top side of the cathode blocks and the electrolyte layer, on account of the fact that its density is relatively large com-pared to that of the electrolyte. During the electrolysis, the aluminium oxide dis-solved in the cryolite melt is cleaved into aluminium and oxygen by a flow of elec-tric current. In terms of electrochemistry, the layer of molten aluminium is the ac-tual cathode, since aluminium ions are reduced to elemental aluminium on the surface thereof. Nevertheless, hereinbelow the term "cathode" will not be under-stood to mean the cathode from an electrochemical point of view, i.e. the layer of molten aluminium, but rather the component which forms the electrolysis cell bot-tom and is composed of one or more cathode blocks.
A significant disadvantage of the Hall-Heroult process is that it requires a large amount of energy. To produce 1 kg of aluminium, about 12 to 15 kWh of electrical energy are required, which amounts to up to 40% of the production costs. To make it possible to lower the production costs, it is therefore desirable to reduce the specific energy consumption of this process as far as possible.
In order to reduce the specific energy consumption, use has recently been made of cathode blocks whose side facing towards the molten aluminium and the elec-trolyte during operation of the electrolysis cell is profiled by one or more recesses and/or elevations. Such cathode blocks, the top sides of which each have between 1 and 8 and preferably 2 elevations with a height of 50 to 200 mm, are disclosed in EP 2 133 446 A1, for example. Here, the cathode blocks are composed of anthra-cite, synthetic graphite, mixtures of anthracite and synthetic graphite or of graph-itized carbon. The surface profiling serves the purpose of reducing the movement of the molten aluminium which is caused by the electromagnetic interaction pre-sent during the electrolysis, and of thereby achieving reduced wave formation and bulging of the aluminium layer. The reduced wave formation is said to avoid short circuits and undesirable reoxidation of the aluminium which has formed; these can otherwise occur if the distance between the layer of molten aluminium and the anode is chosen to be too small. A reduction in wave formation can therefore re-duce the distance between the molten aluminium and the anode, and therefore the ohmic losses which arise in the intermediate layer of cryolite-containing melt and consequently the specific energy consumption can be reduced with this arrange-ment.
However, even the use of a cathode block which is surface-profiled as described above can only reduce the wave formation in the molten aluminium to a certain degree, and therefore the arrangement still has relatively high specific energy consumption during electrolysis operation. This can be attributed, inter alia, to the fact that the electric current flowing through the cathode block is concentrated on the boundary areas of the cathode block, as considered in the longitudinal direc-tion of the cathode block, since this is where the busbars make contact with the current feed elements, and this is why the resulting electrical resistance from the current feed elements up to the surface of the cathode block is lower in the event of flow over the longitudinal-side boundary areas than in the event of flow over the centre of the cathode block. The electric current density is therefore distributed non-uniformly in the cathode block, as a result of which an approximately W-shaped wear profile, as considered in the longitudinal direction of the cathode block, is formed in the cathode block after a certain operating time. On account of the relatively low specific electrical resistivity of graphite, this problem arises to an even greater extent in the case of graphitized cathode blocks than in the case of cathode blocks based on amorphous carbon.
Based on the inhomogeneous current density distribution in the cathode block, the current density distribution is made more uniform in the molten aluminium layer located on the cathode block surface; this means that current vectors arise in the aluminium layer, oriented from the longitudinal-side ends of the cathode block towards the centre of the cathode block and therefore in the horizontal direction.
These horizontally oriented current vectors in the aluminium melt, which are caused by the non-uniform current density distribution in the cathode block, bring about increased electromagnetic interactions on the aluminium material, and these in turn contribute to increased wave formation and therefore counteract the pur-pose of the surface profiling.
The problem of non-uniform current density distribution in the region of the cath-ode block surface arises to an even greater extent in the case of surface-profiled cathode blocks, because the current density is concentrated not only on the longi-tudinal-side boundary areas of the cathode block, but additionally on the recesses or cutouts present in the profiled cathode block surface, on account of the higher electrical conductivity of the molten aluminium compared to the cathode block material. Current densities which are locally increased compared to conventional cathode blocks without surface profiling therefore arise at these points. For these reasons, the current density distribution which arises in a surface-profiled cathode block is inhomogeneous in two respects, as a result of which the service life of the surface-profiled cathode block is limited.
Aside from the fact that the energy efficiency is relatively low on account of the inhomogeneous current density distribution in the surface-profiled cathode block, the inhomogeneous current density distribution in the surface-profiled cathode block also leads to a reduced service life of the cathode block, since the inhomo-geneous current density distribution induces very high current densities in certain regions of the cathode block, and these in turn cause increased wear to the cath-ode block by virtue of electrochemical reactions in these regions.
In order to ensure a uniform streamlined profile over the length of a cathode block, WO 2007/118510 A2 has proposed a cathode arrangement having a cathode block, in which the groove provided in the cathode block for receiving a busbar has a depth which varies over its length, wherein the depth of the groove, as consid-ered in the longitudinal direction of the cathode block, increases from the boundary areas to the centre of the cathode block. The busbar here is conventionally en-cased with cast iron, this encasing taking place by pouring liquid cast iron into the interstice between the groove and the busbar. However, the energy efficiency of the cathode blocks described in this document is also relatively low and therefore needs improvement.
It is therefore an object of the present invention to provide a cathode arrangement which, if it is used in an electrolysis cell for fused-salt electrolysis, brings about increased energy efficiency and at the same time, even if it is built up on the basis of graphite, has increased wear resistance to the abrasive, chemical and thermal conditions which prevail during the fused-salt electrolysis.
According to the invention, this object is achieved by a cathode arrangement for an aluminium electrolysis cell having at least one cathode block based on carbon and/or graphite, which has a surface which is profiled at least in certain regions and also at least one groove, wherein at least one busbar is provided in the at least one groove, and wherein the at least one groove has a depth which varies over its length.
According to the invention, it has been realized that the provision of a groove of variable depth in a surface-profiled cathode block reduces wave formation in the molten aluminium to a minimum, and therefore the distance between the layer of molten aluminium and the anode can be further reduced and, as a result, a higher energy efficiency can be achieved for electrolysis operation. This is because the electrical resistance between the busbar received in the groove and the profiled cathode block surface is made more uniform, as seen over the cathode block length, by the variable groove depth, as seen over the cathode block length, and therefore the surface-profiled cathode block has a current density distribution which is uniform as seen over the cathode block length. This largely avoids the horizontal current vectors in the molten aluminium layer which are caused in the case of the cathode blocks known from the prior art on account of the inhomoge-neous current density distribution present therein when they are in operation, and therefore the movements in the aluminium melt which are caused by the interac-tion of electromagnetic fields are reduced considerably or even virtually completely eliminated. As a result, the anode can be arranged at a smaller height above the surface of the layer of molten aluminium. In turn, this reduces the electrical resis-tance of the cryolite-containing layer of melt between the anode and the layer of molten aluminium and increases the energy efficiency of the fused-salt electrolysis carried out.
In addition, the more uniform current density distribution over the longitudinal di-rection of the cathode block according to the invention avoids excessive wear to the surface-profiled cathode block in the region of its longitudinal-side ends com-pared to that in the centre of the cathode block, and thus the formation of a W-shaped wear profile, to be precise even in the case of cathode blocks constructed from graphite. As a result, the present invention provides a cathode arrangement having an improved energy efficiency for electrolysis operation and having an increased wear resistance. It is particularly advantageous here that the advanta-geous effects can be achieved by measures which are technically simple and inexpensive to implement. Since the proportion of busbar steel present in the groove is relatively large on account of the variable groove depth, the overall verti-cal stress measured between the end of the current feed bar and the cathode block surface can be kept approximately constant, which is not the case in other constructions, such as that described in WO 02/068723 A1.
Within the context of the present invention, a "cathode arrangement" is understood to mean a cathode block having at least one groove, wherein at least one busbar, possibly encased by cast iron, is received in each of the at least one groove.
Simi-larly, this term denotes an arrangement of a plurality of cathode blocks each hav-ing at least one groove, wherein at least one busbar, possibly encased by cast iron, is received in each of the at least one groove.
, According to an advantageous embodiment of the present invention, it is provided that the centre of the at least one groove has a greater depth than the two longitu-dinal-side ends thereof, based on the longitudinal direction. This achieves a uni-form distribution of the electric current fed via the cathode arrangement over the entire length of the cathode block, as a result of which an excessive electric cur-rent density at the longitudinal-side ends of the cathode block and thus premature wear at the ends of the cathode block is effectively and reliably avoided.
The cathode arrangement according to the invention can have at least one groove for receiving in each case at least one busbar, it being preferable for each groove to have a depth which varies over its length.
The cathode arrangement according to the invention is suitable in particular for the use of conventional groove and/or busbar cross sections. By way of example, the groove and/or the busbar can conventionally have a substantially rectangular cross section. The busbar, in particular, can also conventionally consist of steel.
According to the invention, the cathode block has a surface which is profiled at least in certain regions. Here, a profiled surface is understood to mean a surface having at least one recess and/or elevation extending in the transverse direction, in the longitudinal direction or in any other desired direction, such as for example in a direction running at an acute or obtuse angle to the longitudinal direction, of the cathode block, the recess or elevation having at least a depth or height of 0.05 mm and preferably of 0.5 mm in demarcation relative to a surface roughness, as seen transversely to the cathode block surface.
In this case, the at least one recess of the cathode block will in practice be delim-ited by two side walls and a bottom wall.
As seen in the height direction of the cathode block, the bottom wall of the at least one recess of the cathode block is advantageously arranged at least substantially exactly above the at least one busbar, wherein the bottom wall of the at least one recess covers the busbar over at least 60%, preferably over at least 80% and particularly preferably 100cY0 of the width of the busbar, as measured in the trans-verse direction of the cathode block. In other words, in this embodiment, as con-sidered in the height direction of the cathode block, the at least one recess and the at least one busbar are arranged so as to lie opposite one another, such that the bottom wall of the recess covers the busbar completely or at least to the greatest possible extent. This increases the energy efficiency for electrolysis operation even further, since a current path is provided between the busbar and the molten aluminium layer along which the electric current must travel only a minimal dis-tance in the relatively poorly electrically conductive cathode block. This further reduces the electrical resistance of the cathode arrangement. If the busbar is en-cased with cast iron, it is preferable for the at least one recess to cover the busbar including the surrounding cast iron encasement, as considered in the width, to an extent of at least 60%, preferably at least 80% and particularly preferably 100%.
In principle, it is possible for the at least one recess to extend only over part of the length of the cathode block. It is possible, however, for the depth and/or width of the at least one recess to vary over the length of the cathode block. It is similarly possible for the geometry of the recess to also vary over the length of the cathode block. In addition, it is preferable for a recess of the cathode block to run over part or substantially the entire length of the cathode block at least approximately paral-lel to the busbar.
In principle, the at least one recess and/or elevation can have any desired geome-try, as seen in the transverse direction of the cathode block. By way of example, the at least one recess or elevation can have a convex, concave or polygonal form, for example a trapezoidal, triangular, rectangular or square form, as seen in the transverse direction of the cathode block.
In order to avoid or at least considerably reduce wave formation during operation of the cathode block according to the invention for the fused-salt electrolysis of aluminium oxide in a cryolite melt, and in order to drastically reduce the height of any waves which do form, it is proposed in a development of the concept of the invention that, if the surface profiling comprises at least one recess, the depth-to-width ratio of the at least one recess is 1:3 to 1:1 and preferably 1:2 to 1:1.
Good results are achieved in particular if the depth of the at least one recess is 10 to 90 mm, preferably 40 to 90 mm and particularly preferably 60 to 80 mm, such as for example about 70 mm.
According to a further preferred embodiment, the width of the at least one recess is 100 to 200 mm, particularly preferably 120 to 180 mm and very particularly pref-erably 140 to 160 mm, such as for example about 150 mm.
If the surface profiling comprises at least one elevation, it is likewise preferable, in order to avoid or at least considerably reduce wave formation during operation of the cathode block according to the invention for the fused-salt electrolysis of alu-minium oxide in a cryolite melt, and in order to drastically reduce the height of any waves which do form, for the height-to-width ratio of the at least one elevation to be 1:2 to 2:1 and preferably about 1:1.
Good results are achieved in particular if the height of the at least one elevation is to 150 mm, preferably 40 to 90 mm and particularly preferably 60 to 80 mm, such as for example about 70 mm.
According to a further preferred embodiment, the width of the at least one eleva-tion is 50 to 150 mm, particularly preferably 55 to 100 mm and very particularly preferably 60 to 90 mm, such as for example about 75 mm.
In principle, it is possible for the at least one elevation to extend only in certain regions, as seen in the longitudinal direction of the cathode block. However, it is preferable for the at least one elevation to extend over the entire length of the cathode block, so as to achieve the effect of reducing or completely reducing wave formation of the molten aluminium. It is possible, however, for the height and/or width of the at least one elevation to vary over the length of the cathode block. It is similarly possible for the geometry of the elevation to also vary over the length of the cathode block.
If the surface profiling comprises both at least one recess and at least one eleva-tion, the ratio of the width of the at least one recess to the width of the at least one elevation is preferably 4:1 to 1:1, such as for example about 2:1.
In order to reliably avoid the deposition of sludge present in the melt, i.e.
of undis-solved aluminium oxide with adherent melt, in the profiled structure of the surface of the cathode block as fused-salt electrolysis is being carried out, it is proposed in a development of the concept of the invention to avoid any angled and in particular right-angled regions in the profiled surface. lf, for example, a substantially rectan-gular cross section is chosen for the at least one recess and/or elevation, it is preferable according to a preferred embodiment of the present invention to round off the right-angled regions. The radius of curvature of these rounded-off sections can be, for example, 5 to 50 mm, preferably 10 to 30 mm and particularly prefera-bly about 20 mm. In order to avoid sharp edges, any desired geometries which all fall under the term "rounded-off' are conceivable, in principle.
The present invention is not restricted in terms of the number of recesses or eleva-tions in the cathode block. Good results are achieved, for example, if the cathode block has 1 to 3 recesses and preferably 2 recesses in the transverse direction thereof.
According to the invention, the composition of the cathode block present in the cathode arrangement is based on carbon and/or graphite, i.e. the cathode block contains amorphous carbon, graphite or a mixture of amorphous carbon, graph-itized carbon and/or graphitic carbon. Aside from the carbon or graphite, the cath-ode block can optionally contain carbonized and/or graphitized binder, such as pitch, in particular coal tar pitch and/or petroleum pitch. If pitch is mentioned here-inbelow, this means all varieties of pitch known to a person skilled in the art.
According to a particularly preferred embodiment of the present invention, the carbon present in the cathode block of the cathode arrangement according to the invention is exclusively graphitic and/or graphitized carbon or a mixture of graphitic or graphitized carbon with amorphous carbon. If a mixture of graphitic or graph-itized carbon and amorphous carbon is used, this mixture preferably contains 10 to 99% by weight, particularly preferably 30 to 95% by weight and very particularly preferably 60 to 90% by weight of graphitic or graphitized carbon. If graphitic car-bon is present in the mixture, this can be both natural graphite and synthetic graphite.
The starting material used for amorphous carbon is preferably anthracite, which is then calcined at a temperature of between 800 and 2200 C and particularly pref-erably between 1200 and 2000 C. By way of example, the production takes place in such a way that a mixture of particulate anthracite and coal tar pitch as binder is brought into a shape which is then compacted to form a green body, before the green body is carbonized by heat treatment at a temperature of, for example, to 1300 C.
, , The present invention also relates to a cathode block for a cathode arrangement of an aluminium electrolysis cell based on carbon and/or graphite, which has a sur-face which is profiled at least in certain regions and also at least one groove for receiving a busbar, wherein the groove has a depth which varies over its length.
Such a cathode block can advantageously be used as a component part of the cathode arrangement described above. Here, the cathode block can be con-structed on the basis of amorphous carbon, graphitic carbon, graphitized carbon or any desired mixture of the above carbons, where graphitic carbon and in particular graphitized carbon are particularly preferred.
Hereinbelow, the present invention is described purely by way of example on the basis of advantageous embodiments and with reference to the attached drawings.
In the drawings:
Figure 1 shows a schematic cross section of a detail of an aluminium electrolysis cell, which comprises a cathode arrangement ac-cording to an exemplary embodiment of the present inven-tion, Figure 2 shows a longitudinal section of the cathode arrangement of the aluminium electrolysis cell shown in Figure 1, and Figures 3A to 3E each shows a schematic cross section of the surface profiling of a cathode block according to other exemplary embodi-ments of the present invention.
Figure 1 shows a cross section of a detail of an aluminium electrolysis cell having a cathode arrangement 12, which at the same time forms the bottom of a tank for aluminium melt 14 produced during operation of the electrolysis cell and for a cryolite-aluminium oxide melt 16 located above the aluminium melt 14.
An anode 18 of the electrolysis cell 10 is in contact with the cryolite-aluminium oxide melt 16. At the side, the tank formed by the lower part of the aluminium electrolysis cell 10 is delimited by a carbon and/or graphite lining (not shown in Figure 1).
The cathode arrangement 12 comprises a plurality of cathode blocks 20, 20', 20", which are each connected to one another via a ramming mass 24, 24' which has been inserted into a ramming mass joint 22, 22' arranged between the cathode blocks 20, 20', 20". Similarly, the anode 18 comprises a plurality of anode blocks 26, 26', the anode blocks 26, 26' each being approximately twice as wide and approximately half as long as the cathode blocks 20, 20', 20". In this case, the anode blocks 26, 26' are arranged above the cathode blocks 20, 20', 20" in such a way that in each case an anode block 26, 26' covers two cathode blocks 20, 20', 20" arranged alongside one another in width and in each case a cathode block 20, 20', 20" covers two anode blocks 26, 26' arranged alongside one another in length.
The cathode blocks 20, 20', 20" each have a graphitized material structure which has been produced, for example, by moulding a mixture of petroleum coke and coal tar pitch with subsequent heat treatment at up to 3000 C.
The distance between the anode blocks 26, 26' and the cathode blocks 20, 20', 20" is approximately 200 to approximately 350 mm, the layer of cryolite-aluminium oxide melt 16 arranged therebetween having a thickness of approximately 50 mm and the layer of aluminium melt 14 arranged thereunder having a thickness of approximately 150 to approximately 300 mm.
Each cathode block 20, 20', 20" has a profiled surface, wherein two recesses 34, 34' of substantially rectangular cross section are provided in each cathode block 20, 20', 20" and are separated from one another by an elevation 36. Each recess 34, 34' is delimited by a bottom wall 33, 33' and two side walls 35, 35'. As shown in the cross-sectional view of Figure 1, the bottom walls 33, 33' here run parallel to the transverse direction of the cathode block 20'. Whereas the width of each of the recesses 34, 34' is 150 mm and the depth of each of the recesses 34, 34' is 70 mm, the elevation 36 has a width of 75 mm and a height of 70 mm. Both the cor-ners in the two recesses 34, 34' and the corners of the elevation 36 are rounded off each with a 20 mm radius.
Finally, each cathode block 20, 20', 20" comprises two grooves 38, 38' on its un-derside each with a rectangular, specifically substantially rectangular cross sec-tion, wherein a steel busbar 40, 40' likewise having a rectangular or substantially rectangular cross section is accommodated in each groove 38, 38'.
Here, the interstice between the busbar 40, 40' and the groove 38, 38' is sealed in each case with cast iron 44, 44'.
As shown in Figure 1, as seen in the height direction of the cathode block 20', the recesses 34, 34' are arranged exactly above the respectively associated busbar 40, 40', such that the bottom walls 33, 33' cover the respective busbars 40, 40' including the surrounding cast iron encasement 44, 44' over the complete width thereof. This increases the energy efficiency for electrolysis operation even further, since a path having good electrical conductivity is provided between the busbar and the molten aluminium layer along which the electric current must travel only a minimal distance in the relatively poorly electrically conductive cathode block. The current yield of the cathode arrangement is thereby increased further.
Figure 1 specifically shows the cross section of the cathode arrangement 10 at a longitudinal-side end of the cathode block 20, 20', 20". The depth of the grooves 38, 38' of the cathode block 20, 20', 20" varies over the length of the grooves 38, 38'. The groove cross section in the region of the centre of the groove 38, 38' is indicated by a dashed line 46, 46' in Figure 1. In the present exemplary embodi-ment, the difference between the groove depth at the longitudinal-side ends of the groove 38, 38' and in the centre of the groove 38, 38' is approximately 10 cm.
The width 48 of each groove 38, 38' is substantially constant over the entire groove length and is approximately 15 cm, whereas the width 50 of each of the cathode blocks 20, 20', 20" is approximately 65 cm.
Figure 2 is a longitudinal section showing the cathode block 20, 20', 20"
shown in Figure 1. As can be seen from Figure 2, the groove 38, 38', considered in its longi-tudinal section, tapers towards the centre of the cathode block 20, 20', 20"
in the form of a triangle, as a result of which a substantially uniform vertical electric cur-rent density is ensured over the entire cathode length. This prevents horizontal vectors of the current flowing in the aluminium melt 14 and resulting wave forma-tion of the aluminium melt 14 to the greatest possible extent.
In the present exemplary embodiment, the busbar 40, 40', which is not shown in Figure 2 for the sake of greater clarity, has a bar-like form and has a rectangular longitudinal section, such as to form an interstice between the busbar and the groove bottom, which interstice increases in size towards the centre of the groove 38, 38' and can be filled either by cast iron 44, 44' or by additional metal plates connected to the busbar 40, 40'. Similarly, it would also be possible to use a bus-bar 40, 40' which is at a substantially constant distance from the groove bottom and is matched, in particular in its longitudinal section, to the triangular profile of the groove 38, 38'.
It is preferable for both the grooves 38, 38' and the recesses 34, 34' to be put in the top side of the cathode blocks 20, 20', 20" during the shaping process, to be precise for example by vibrating moulds and/or punches.
Figures 3A to 3E show examples of different configurations of the recesses 34, 34' and of the elevations 36 of the surface profiling of the cathode blocks 20, 20', 20", specifically, in each case in cross section, a rectangular configuration with rounded-off corners (not shown) (Figure 3A), a substantially undulatory configura-tion (Figure 3B), a triangular configuration (Figure 3C), a convex configuration (Figure 3D) and a sinusoidal configuration (Figure 3E), the rectangular and undu-latory surface profilings of Figure 3A and Figure 3B having recesses 34, 34' which are each delimited by a bottom wall 33, 33' and two side walls 35, 35'.
List of reference symbols Aluminium electrolysis cell 12 Cathode arrangement 14 Aluminium melt 16 Cryolite-aluminium oxide melt 18 Anode 20, 20', 20" Cathode block 22, 22' Ramming mass joint 24, 24' Ramming mass 26, 26' Anode block 33, 33' Bottom wall 34, 34' Recess 35, 35' Side wall 36 Elevation 38, 38' Groove 40, 40' Busbar 44, 44' Cast iron 46, 46' Groove cross section in the region of the centre of the groove 48 Width of the groove 50 Width of the cathode block
18.07.2013 Cathode arrangement having a surface-profiled cathode block with a groove of variable depth The present invention relates to a cathode arrangement for an aluminium elec-trolysis cell.
Such electrolysis cells are used for the electrolytic production of aluminium, which is customarily carried out in industry by the Hall-Heroult process. In the Hall-Heroult process, a melt composed of aluminium oxide and cryolite is electrolysed.
Here, the cryolite, Na3[AlF6], serves to lower the melting point of 2045 C for pure aluminium oxide to about 950 C for a mixture containing cryolite, aluminium oxide and additives, such as aluminium fluoride and calcium fluoride.
The electrolysis cell used in this process has a bottom, which is composed of a multiplicity of adjoining cathode blocks forming the cathode. In order to withstand the thermal and chemical conditions which prevail during operation of the cell, the cathode blocks are customarily composed of a carbon-containing material. The undersides of each of the cathode blocks are provided with grooves, in each of which there is arranged at least one busbar through which the current fed via the anodes is discharged. In this case, the interstices between the individual walls of the cathode blocks, which delimit the grooves, and the busbars are often sealed with cast iron, in order to electrically and mechanically connect the busbars to the cathode blocks by virtue of the resulting encasement of the busbars with cast iron.
An anode formed from individual anode blocks is arranged about 3 to 5 cm above the layer of molten aluminium located on the top side of the cathode, and the elec-trolyte, i.e. the melt containing aluminium oxide and cryolite, is located between said anode and the surface of the aluminium. During the electrolysis carried out at about 1000 C, the aluminium which has formed settles beneath the electrolyte layer, i.e. as an intermediate layer between the top side of the cathode blocks and the electrolyte layer, on account of the fact that its density is relatively large com-pared to that of the electrolyte. During the electrolysis, the aluminium oxide dis-solved in the cryolite melt is cleaved into aluminium and oxygen by a flow of elec-tric current. In terms of electrochemistry, the layer of molten aluminium is the ac-tual cathode, since aluminium ions are reduced to elemental aluminium on the surface thereof. Nevertheless, hereinbelow the term "cathode" will not be under-stood to mean the cathode from an electrochemical point of view, i.e. the layer of molten aluminium, but rather the component which forms the electrolysis cell bot-tom and is composed of one or more cathode blocks.
A significant disadvantage of the Hall-Heroult process is that it requires a large amount of energy. To produce 1 kg of aluminium, about 12 to 15 kWh of electrical energy are required, which amounts to up to 40% of the production costs. To make it possible to lower the production costs, it is therefore desirable to reduce the specific energy consumption of this process as far as possible.
In order to reduce the specific energy consumption, use has recently been made of cathode blocks whose side facing towards the molten aluminium and the elec-trolyte during operation of the electrolysis cell is profiled by one or more recesses and/or elevations. Such cathode blocks, the top sides of which each have between 1 and 8 and preferably 2 elevations with a height of 50 to 200 mm, are disclosed in EP 2 133 446 A1, for example. Here, the cathode blocks are composed of anthra-cite, synthetic graphite, mixtures of anthracite and synthetic graphite or of graph-itized carbon. The surface profiling serves the purpose of reducing the movement of the molten aluminium which is caused by the electromagnetic interaction pre-sent during the electrolysis, and of thereby achieving reduced wave formation and bulging of the aluminium layer. The reduced wave formation is said to avoid short circuits and undesirable reoxidation of the aluminium which has formed; these can otherwise occur if the distance between the layer of molten aluminium and the anode is chosen to be too small. A reduction in wave formation can therefore re-duce the distance between the molten aluminium and the anode, and therefore the ohmic losses which arise in the intermediate layer of cryolite-containing melt and consequently the specific energy consumption can be reduced with this arrange-ment.
However, even the use of a cathode block which is surface-profiled as described above can only reduce the wave formation in the molten aluminium to a certain degree, and therefore the arrangement still has relatively high specific energy consumption during electrolysis operation. This can be attributed, inter alia, to the fact that the electric current flowing through the cathode block is concentrated on the boundary areas of the cathode block, as considered in the longitudinal direc-tion of the cathode block, since this is where the busbars make contact with the current feed elements, and this is why the resulting electrical resistance from the current feed elements up to the surface of the cathode block is lower in the event of flow over the longitudinal-side boundary areas than in the event of flow over the centre of the cathode block. The electric current density is therefore distributed non-uniformly in the cathode block, as a result of which an approximately W-shaped wear profile, as considered in the longitudinal direction of the cathode block, is formed in the cathode block after a certain operating time. On account of the relatively low specific electrical resistivity of graphite, this problem arises to an even greater extent in the case of graphitized cathode blocks than in the case of cathode blocks based on amorphous carbon.
Based on the inhomogeneous current density distribution in the cathode block, the current density distribution is made more uniform in the molten aluminium layer located on the cathode block surface; this means that current vectors arise in the aluminium layer, oriented from the longitudinal-side ends of the cathode block towards the centre of the cathode block and therefore in the horizontal direction.
These horizontally oriented current vectors in the aluminium melt, which are caused by the non-uniform current density distribution in the cathode block, bring about increased electromagnetic interactions on the aluminium material, and these in turn contribute to increased wave formation and therefore counteract the pur-pose of the surface profiling.
The problem of non-uniform current density distribution in the region of the cath-ode block surface arises to an even greater extent in the case of surface-profiled cathode blocks, because the current density is concentrated not only on the longi-tudinal-side boundary areas of the cathode block, but additionally on the recesses or cutouts present in the profiled cathode block surface, on account of the higher electrical conductivity of the molten aluminium compared to the cathode block material. Current densities which are locally increased compared to conventional cathode blocks without surface profiling therefore arise at these points. For these reasons, the current density distribution which arises in a surface-profiled cathode block is inhomogeneous in two respects, as a result of which the service life of the surface-profiled cathode block is limited.
Aside from the fact that the energy efficiency is relatively low on account of the inhomogeneous current density distribution in the surface-profiled cathode block, the inhomogeneous current density distribution in the surface-profiled cathode block also leads to a reduced service life of the cathode block, since the inhomo-geneous current density distribution induces very high current densities in certain regions of the cathode block, and these in turn cause increased wear to the cath-ode block by virtue of electrochemical reactions in these regions.
In order to ensure a uniform streamlined profile over the length of a cathode block, WO 2007/118510 A2 has proposed a cathode arrangement having a cathode block, in which the groove provided in the cathode block for receiving a busbar has a depth which varies over its length, wherein the depth of the groove, as consid-ered in the longitudinal direction of the cathode block, increases from the boundary areas to the centre of the cathode block. The busbar here is conventionally en-cased with cast iron, this encasing taking place by pouring liquid cast iron into the interstice between the groove and the busbar. However, the energy efficiency of the cathode blocks described in this document is also relatively low and therefore needs improvement.
It is therefore an object of the present invention to provide a cathode arrangement which, if it is used in an electrolysis cell for fused-salt electrolysis, brings about increased energy efficiency and at the same time, even if it is built up on the basis of graphite, has increased wear resistance to the abrasive, chemical and thermal conditions which prevail during the fused-salt electrolysis.
According to the invention, this object is achieved by a cathode arrangement for an aluminium electrolysis cell having at least one cathode block based on carbon and/or graphite, which has a surface which is profiled at least in certain regions and also at least one groove, wherein at least one busbar is provided in the at least one groove, and wherein the at least one groove has a depth which varies over its length.
According to the invention, it has been realized that the provision of a groove of variable depth in a surface-profiled cathode block reduces wave formation in the molten aluminium to a minimum, and therefore the distance between the layer of molten aluminium and the anode can be further reduced and, as a result, a higher energy efficiency can be achieved for electrolysis operation. This is because the electrical resistance between the busbar received in the groove and the profiled cathode block surface is made more uniform, as seen over the cathode block length, by the variable groove depth, as seen over the cathode block length, and therefore the surface-profiled cathode block has a current density distribution which is uniform as seen over the cathode block length. This largely avoids the horizontal current vectors in the molten aluminium layer which are caused in the case of the cathode blocks known from the prior art on account of the inhomoge-neous current density distribution present therein when they are in operation, and therefore the movements in the aluminium melt which are caused by the interac-tion of electromagnetic fields are reduced considerably or even virtually completely eliminated. As a result, the anode can be arranged at a smaller height above the surface of the layer of molten aluminium. In turn, this reduces the electrical resis-tance of the cryolite-containing layer of melt between the anode and the layer of molten aluminium and increases the energy efficiency of the fused-salt electrolysis carried out.
In addition, the more uniform current density distribution over the longitudinal di-rection of the cathode block according to the invention avoids excessive wear to the surface-profiled cathode block in the region of its longitudinal-side ends com-pared to that in the centre of the cathode block, and thus the formation of a W-shaped wear profile, to be precise even in the case of cathode blocks constructed from graphite. As a result, the present invention provides a cathode arrangement having an improved energy efficiency for electrolysis operation and having an increased wear resistance. It is particularly advantageous here that the advanta-geous effects can be achieved by measures which are technically simple and inexpensive to implement. Since the proportion of busbar steel present in the groove is relatively large on account of the variable groove depth, the overall verti-cal stress measured between the end of the current feed bar and the cathode block surface can be kept approximately constant, which is not the case in other constructions, such as that described in WO 02/068723 A1.
Within the context of the present invention, a "cathode arrangement" is understood to mean a cathode block having at least one groove, wherein at least one busbar, possibly encased by cast iron, is received in each of the at least one groove.
Simi-larly, this term denotes an arrangement of a plurality of cathode blocks each hav-ing at least one groove, wherein at least one busbar, possibly encased by cast iron, is received in each of the at least one groove.
, According to an advantageous embodiment of the present invention, it is provided that the centre of the at least one groove has a greater depth than the two longitu-dinal-side ends thereof, based on the longitudinal direction. This achieves a uni-form distribution of the electric current fed via the cathode arrangement over the entire length of the cathode block, as a result of which an excessive electric cur-rent density at the longitudinal-side ends of the cathode block and thus premature wear at the ends of the cathode block is effectively and reliably avoided.
The cathode arrangement according to the invention can have at least one groove for receiving in each case at least one busbar, it being preferable for each groove to have a depth which varies over its length.
The cathode arrangement according to the invention is suitable in particular for the use of conventional groove and/or busbar cross sections. By way of example, the groove and/or the busbar can conventionally have a substantially rectangular cross section. The busbar, in particular, can also conventionally consist of steel.
According to the invention, the cathode block has a surface which is profiled at least in certain regions. Here, a profiled surface is understood to mean a surface having at least one recess and/or elevation extending in the transverse direction, in the longitudinal direction or in any other desired direction, such as for example in a direction running at an acute or obtuse angle to the longitudinal direction, of the cathode block, the recess or elevation having at least a depth or height of 0.05 mm and preferably of 0.5 mm in demarcation relative to a surface roughness, as seen transversely to the cathode block surface.
In this case, the at least one recess of the cathode block will in practice be delim-ited by two side walls and a bottom wall.
As seen in the height direction of the cathode block, the bottom wall of the at least one recess of the cathode block is advantageously arranged at least substantially exactly above the at least one busbar, wherein the bottom wall of the at least one recess covers the busbar over at least 60%, preferably over at least 80% and particularly preferably 100cY0 of the width of the busbar, as measured in the trans-verse direction of the cathode block. In other words, in this embodiment, as con-sidered in the height direction of the cathode block, the at least one recess and the at least one busbar are arranged so as to lie opposite one another, such that the bottom wall of the recess covers the busbar completely or at least to the greatest possible extent. This increases the energy efficiency for electrolysis operation even further, since a current path is provided between the busbar and the molten aluminium layer along which the electric current must travel only a minimal dis-tance in the relatively poorly electrically conductive cathode block. This further reduces the electrical resistance of the cathode arrangement. If the busbar is en-cased with cast iron, it is preferable for the at least one recess to cover the busbar including the surrounding cast iron encasement, as considered in the width, to an extent of at least 60%, preferably at least 80% and particularly preferably 100%.
In principle, it is possible for the at least one recess to extend only over part of the length of the cathode block. It is possible, however, for the depth and/or width of the at least one recess to vary over the length of the cathode block. It is similarly possible for the geometry of the recess to also vary over the length of the cathode block. In addition, it is preferable for a recess of the cathode block to run over part or substantially the entire length of the cathode block at least approximately paral-lel to the busbar.
In principle, the at least one recess and/or elevation can have any desired geome-try, as seen in the transverse direction of the cathode block. By way of example, the at least one recess or elevation can have a convex, concave or polygonal form, for example a trapezoidal, triangular, rectangular or square form, as seen in the transverse direction of the cathode block.
In order to avoid or at least considerably reduce wave formation during operation of the cathode block according to the invention for the fused-salt electrolysis of aluminium oxide in a cryolite melt, and in order to drastically reduce the height of any waves which do form, it is proposed in a development of the concept of the invention that, if the surface profiling comprises at least one recess, the depth-to-width ratio of the at least one recess is 1:3 to 1:1 and preferably 1:2 to 1:1.
Good results are achieved in particular if the depth of the at least one recess is 10 to 90 mm, preferably 40 to 90 mm and particularly preferably 60 to 80 mm, such as for example about 70 mm.
According to a further preferred embodiment, the width of the at least one recess is 100 to 200 mm, particularly preferably 120 to 180 mm and very particularly pref-erably 140 to 160 mm, such as for example about 150 mm.
If the surface profiling comprises at least one elevation, it is likewise preferable, in order to avoid or at least considerably reduce wave formation during operation of the cathode block according to the invention for the fused-salt electrolysis of alu-minium oxide in a cryolite melt, and in order to drastically reduce the height of any waves which do form, for the height-to-width ratio of the at least one elevation to be 1:2 to 2:1 and preferably about 1:1.
Good results are achieved in particular if the height of the at least one elevation is to 150 mm, preferably 40 to 90 mm and particularly preferably 60 to 80 mm, such as for example about 70 mm.
According to a further preferred embodiment, the width of the at least one eleva-tion is 50 to 150 mm, particularly preferably 55 to 100 mm and very particularly preferably 60 to 90 mm, such as for example about 75 mm.
In principle, it is possible for the at least one elevation to extend only in certain regions, as seen in the longitudinal direction of the cathode block. However, it is preferable for the at least one elevation to extend over the entire length of the cathode block, so as to achieve the effect of reducing or completely reducing wave formation of the molten aluminium. It is possible, however, for the height and/or width of the at least one elevation to vary over the length of the cathode block. It is similarly possible for the geometry of the elevation to also vary over the length of the cathode block.
If the surface profiling comprises both at least one recess and at least one eleva-tion, the ratio of the width of the at least one recess to the width of the at least one elevation is preferably 4:1 to 1:1, such as for example about 2:1.
In order to reliably avoid the deposition of sludge present in the melt, i.e.
of undis-solved aluminium oxide with adherent melt, in the profiled structure of the surface of the cathode block as fused-salt electrolysis is being carried out, it is proposed in a development of the concept of the invention to avoid any angled and in particular right-angled regions in the profiled surface. lf, for example, a substantially rectan-gular cross section is chosen for the at least one recess and/or elevation, it is preferable according to a preferred embodiment of the present invention to round off the right-angled regions. The radius of curvature of these rounded-off sections can be, for example, 5 to 50 mm, preferably 10 to 30 mm and particularly prefera-bly about 20 mm. In order to avoid sharp edges, any desired geometries which all fall under the term "rounded-off' are conceivable, in principle.
The present invention is not restricted in terms of the number of recesses or eleva-tions in the cathode block. Good results are achieved, for example, if the cathode block has 1 to 3 recesses and preferably 2 recesses in the transverse direction thereof.
According to the invention, the composition of the cathode block present in the cathode arrangement is based on carbon and/or graphite, i.e. the cathode block contains amorphous carbon, graphite or a mixture of amorphous carbon, graph-itized carbon and/or graphitic carbon. Aside from the carbon or graphite, the cath-ode block can optionally contain carbonized and/or graphitized binder, such as pitch, in particular coal tar pitch and/or petroleum pitch. If pitch is mentioned here-inbelow, this means all varieties of pitch known to a person skilled in the art.
According to a particularly preferred embodiment of the present invention, the carbon present in the cathode block of the cathode arrangement according to the invention is exclusively graphitic and/or graphitized carbon or a mixture of graphitic or graphitized carbon with amorphous carbon. If a mixture of graphitic or graph-itized carbon and amorphous carbon is used, this mixture preferably contains 10 to 99% by weight, particularly preferably 30 to 95% by weight and very particularly preferably 60 to 90% by weight of graphitic or graphitized carbon. If graphitic car-bon is present in the mixture, this can be both natural graphite and synthetic graphite.
The starting material used for amorphous carbon is preferably anthracite, which is then calcined at a temperature of between 800 and 2200 C and particularly pref-erably between 1200 and 2000 C. By way of example, the production takes place in such a way that a mixture of particulate anthracite and coal tar pitch as binder is brought into a shape which is then compacted to form a green body, before the green body is carbonized by heat treatment at a temperature of, for example, to 1300 C.
, , The present invention also relates to a cathode block for a cathode arrangement of an aluminium electrolysis cell based on carbon and/or graphite, which has a sur-face which is profiled at least in certain regions and also at least one groove for receiving a busbar, wherein the groove has a depth which varies over its length.
Such a cathode block can advantageously be used as a component part of the cathode arrangement described above. Here, the cathode block can be con-structed on the basis of amorphous carbon, graphitic carbon, graphitized carbon or any desired mixture of the above carbons, where graphitic carbon and in particular graphitized carbon are particularly preferred.
Hereinbelow, the present invention is described purely by way of example on the basis of advantageous embodiments and with reference to the attached drawings.
In the drawings:
Figure 1 shows a schematic cross section of a detail of an aluminium electrolysis cell, which comprises a cathode arrangement ac-cording to an exemplary embodiment of the present inven-tion, Figure 2 shows a longitudinal section of the cathode arrangement of the aluminium electrolysis cell shown in Figure 1, and Figures 3A to 3E each shows a schematic cross section of the surface profiling of a cathode block according to other exemplary embodi-ments of the present invention.
Figure 1 shows a cross section of a detail of an aluminium electrolysis cell having a cathode arrangement 12, which at the same time forms the bottom of a tank for aluminium melt 14 produced during operation of the electrolysis cell and for a cryolite-aluminium oxide melt 16 located above the aluminium melt 14.
An anode 18 of the electrolysis cell 10 is in contact with the cryolite-aluminium oxide melt 16. At the side, the tank formed by the lower part of the aluminium electrolysis cell 10 is delimited by a carbon and/or graphite lining (not shown in Figure 1).
The cathode arrangement 12 comprises a plurality of cathode blocks 20, 20', 20", which are each connected to one another via a ramming mass 24, 24' which has been inserted into a ramming mass joint 22, 22' arranged between the cathode blocks 20, 20', 20". Similarly, the anode 18 comprises a plurality of anode blocks 26, 26', the anode blocks 26, 26' each being approximately twice as wide and approximately half as long as the cathode blocks 20, 20', 20". In this case, the anode blocks 26, 26' are arranged above the cathode blocks 20, 20', 20" in such a way that in each case an anode block 26, 26' covers two cathode blocks 20, 20', 20" arranged alongside one another in width and in each case a cathode block 20, 20', 20" covers two anode blocks 26, 26' arranged alongside one another in length.
The cathode blocks 20, 20', 20" each have a graphitized material structure which has been produced, for example, by moulding a mixture of petroleum coke and coal tar pitch with subsequent heat treatment at up to 3000 C.
The distance between the anode blocks 26, 26' and the cathode blocks 20, 20', 20" is approximately 200 to approximately 350 mm, the layer of cryolite-aluminium oxide melt 16 arranged therebetween having a thickness of approximately 50 mm and the layer of aluminium melt 14 arranged thereunder having a thickness of approximately 150 to approximately 300 mm.
Each cathode block 20, 20', 20" has a profiled surface, wherein two recesses 34, 34' of substantially rectangular cross section are provided in each cathode block 20, 20', 20" and are separated from one another by an elevation 36. Each recess 34, 34' is delimited by a bottom wall 33, 33' and two side walls 35, 35'. As shown in the cross-sectional view of Figure 1, the bottom walls 33, 33' here run parallel to the transverse direction of the cathode block 20'. Whereas the width of each of the recesses 34, 34' is 150 mm and the depth of each of the recesses 34, 34' is 70 mm, the elevation 36 has a width of 75 mm and a height of 70 mm. Both the cor-ners in the two recesses 34, 34' and the corners of the elevation 36 are rounded off each with a 20 mm radius.
Finally, each cathode block 20, 20', 20" comprises two grooves 38, 38' on its un-derside each with a rectangular, specifically substantially rectangular cross sec-tion, wherein a steel busbar 40, 40' likewise having a rectangular or substantially rectangular cross section is accommodated in each groove 38, 38'.
Here, the interstice between the busbar 40, 40' and the groove 38, 38' is sealed in each case with cast iron 44, 44'.
As shown in Figure 1, as seen in the height direction of the cathode block 20', the recesses 34, 34' are arranged exactly above the respectively associated busbar 40, 40', such that the bottom walls 33, 33' cover the respective busbars 40, 40' including the surrounding cast iron encasement 44, 44' over the complete width thereof. This increases the energy efficiency for electrolysis operation even further, since a path having good electrical conductivity is provided between the busbar and the molten aluminium layer along which the electric current must travel only a minimal distance in the relatively poorly electrically conductive cathode block. The current yield of the cathode arrangement is thereby increased further.
Figure 1 specifically shows the cross section of the cathode arrangement 10 at a longitudinal-side end of the cathode block 20, 20', 20". The depth of the grooves 38, 38' of the cathode block 20, 20', 20" varies over the length of the grooves 38, 38'. The groove cross section in the region of the centre of the groove 38, 38' is indicated by a dashed line 46, 46' in Figure 1. In the present exemplary embodi-ment, the difference between the groove depth at the longitudinal-side ends of the groove 38, 38' and in the centre of the groove 38, 38' is approximately 10 cm.
The width 48 of each groove 38, 38' is substantially constant over the entire groove length and is approximately 15 cm, whereas the width 50 of each of the cathode blocks 20, 20', 20" is approximately 65 cm.
Figure 2 is a longitudinal section showing the cathode block 20, 20', 20"
shown in Figure 1. As can be seen from Figure 2, the groove 38, 38', considered in its longi-tudinal section, tapers towards the centre of the cathode block 20, 20', 20"
in the form of a triangle, as a result of which a substantially uniform vertical electric cur-rent density is ensured over the entire cathode length. This prevents horizontal vectors of the current flowing in the aluminium melt 14 and resulting wave forma-tion of the aluminium melt 14 to the greatest possible extent.
In the present exemplary embodiment, the busbar 40, 40', which is not shown in Figure 2 for the sake of greater clarity, has a bar-like form and has a rectangular longitudinal section, such as to form an interstice between the busbar and the groove bottom, which interstice increases in size towards the centre of the groove 38, 38' and can be filled either by cast iron 44, 44' or by additional metal plates connected to the busbar 40, 40'. Similarly, it would also be possible to use a bus-bar 40, 40' which is at a substantially constant distance from the groove bottom and is matched, in particular in its longitudinal section, to the triangular profile of the groove 38, 38'.
It is preferable for both the grooves 38, 38' and the recesses 34, 34' to be put in the top side of the cathode blocks 20, 20', 20" during the shaping process, to be precise for example by vibrating moulds and/or punches.
Figures 3A to 3E show examples of different configurations of the recesses 34, 34' and of the elevations 36 of the surface profiling of the cathode blocks 20, 20', 20", specifically, in each case in cross section, a rectangular configuration with rounded-off corners (not shown) (Figure 3A), a substantially undulatory configura-tion (Figure 3B), a triangular configuration (Figure 3C), a convex configuration (Figure 3D) and a sinusoidal configuration (Figure 3E), the rectangular and undu-latory surface profilings of Figure 3A and Figure 3B having recesses 34, 34' which are each delimited by a bottom wall 33, 33' and two side walls 35, 35'.
List of reference symbols Aluminium electrolysis cell 12 Cathode arrangement 14 Aluminium melt 16 Cryolite-aluminium oxide melt 18 Anode 20, 20', 20" Cathode block 22, 22' Ramming mass joint 24, 24' Ramming mass 26, 26' Anode block 33, 33' Bottom wall 34, 34' Recess 35, 35' Side wall 36 Elevation 38, 38' Groove 40, 40' Busbar 44, 44' Cast iron 46, 46' Groove cross section in the region of the centre of the groove 48 Width of the groove 50 Width of the cathode block
Claims (19)
1. Cathode arrangement (12) for an aluminium electrolysis cell (10) having at least one cathode block (20, 20', 20") based on carbon and/or graphite, which has a surface which is profiled at least in certain regions and also at least one groove (38, 38'), wherein at least one busbar (40, 40') is provided in the at least one groove (38, 38'), wherein the at least one groove (38, 38') has a depth which varies over its length.
2. Cathode arrangement according to Claim 1, characterized in that the longitudinal-side ends of the at least one groove (38, 38') have a smaller depth than the centre thereof.
3. Cathode arrangement according to Claim 1 or 2, characterized in that the cathode block (20, 20', 20") has one or two grooves (38, 38') for receiv-ing in each case at least one busbar (40, 40').
4. Cathode arrangement according to at least one of the preceding claims, characterized in that each of the at least one groove (38, 38') and/or each of the at least one busbar (40, 40') has an at least substantially rectangular cross section.
5. Cathode arrangement according to at least one of the preceding claims, characterized in that the surface of the cathode block (20, 20', 20") is profiled by at least one recess (34, 34') and/or at least one elevation (36).
6. Cathode arrangement according to Claim 5, characterized in that at least one recess (34, 34') of the cathode block (20, 20', 20") is delimited by two side walls (35, 35') and a bottom wall (33, 33').
7. Cathode arrangement according to Claim 6, characterized in that, as seen in the height direction of the cathode block (20, 20', 20"), the bot-tom wall (33, 33') of the at least one recess (34, 34') of the cathode block (20, 20', 20") is arranged above the at least one busbar (40, 40'), wherein the bottom wall (33, 33') of the at least one recess (34, 34') covers the bus-bar (40, 40') over at least 60%, preferably at least 80% and particularly preferably 100% of the width of the busbar (40, 40'), as measured in the transverse direction of the cathode block (20, 20', 20").
8. Cathode arrangement according to at least one of Claims 5 to 7, characterized in that the at least one recess (34, 34') runs substantially parallel to the busbar (40, 40').
9. Cathode arrangement according to at least one of Claims 5 to 8, characterized in that the at least one recess (34, 34') and/or the at least one elevation (36) has a convex, concave or polygonal form, for example a trapezoidal, triangular, rectangular or square form, as seen in the transverse direction of the cath-ode block (20, 20', 20").
10. Cathode arrangement according to at least one of Claims 5 to 9, characterized in that the surface of the cathode block (20, 20', 20") has at least one recess (34, 34'), the depth-to-width ratio of the at least one recess (34, 34') being 1:3 to 1:1 and preferably 1:2 to 1:1.
11. Cathode arrangement according to at least one of Claims 5 to 10, characterized in that the surface of the cathode block (20, 20', 20") has at least one recess (34, 34'), the depth of the at least one recess (34, 34') being 10 to 90 mm, pref-erably 40 to 90 mm and particularly preferably 60 to 80 mm.
12. Cathode arrangement according to at least one of Claims 5 to 11, characterized in that the surface of the cathode block (20, 20', 20") has at least one recess (34, 34'), the width of the at least one recess (34, 34') being 100 to 200 mm, par-ticularly preferably 120 to 180 mm and very particularly preferably 140 to 160 mm.
13. Cathode arrangement according to at least one of Claims 5 to 12, characterized in that the surface of the cathode block (20, 20', 20") has at least one elevation (36), the height-to-width ratio of the at least one elevation (36) being 1:2 to 2:1 and preferably 1:1.
14. Cathode arrangement according to at least one of Claims 5 to 13, characterized in that the surface of the cathode block (20, 20', 20") has at least one elevation (36), the height of the at least one elevation (36) being 10 to 150 mm, pref-erably 40 to 90 mm and particularly preferably 60 to 80 mm.
15. Cathode arrangement according to at least one of Claims 5 to 14, characterized in that the surface of the cathode block (20, 20', 20") has at least one elevation (36), the width of the at least one elevation (36) being 50 to 150 mm, par-ticularly preferably 55 to 100 mm and very particularly preferably 60 to 90 mm.
16. Cathode arrangement according to at least one of Claims 5 to 15, characterized in that the surface of the cathode block (20, 20', 20") comprises at least one recess (34, 34') and at least one elevation (36), the ratio of the width of the at least one recess (34, 34') to the width of the at least one elevation (36) being 4:1 to 1:1 and particularly preferably 2:1.
17. Cathode arrangement according to at least one of Claims 5 to 16, characterized in that the surface of the cathode block (20, 20', 20") has 1 to 3 and particularly preferably 2 recesses (34, 34').
18. Cathode arrangement according to at least one of the preceding claims, characterized in that the cathode block is composed of graphitic and/or graphitized carbon and optionally carbonized and/or graphitized binder, or preferably consists thereof.
19. Cathode block for a cathode arrangement (12) of an aluminium electrolysis cell (10) based on carbon and/or graphite, which has a surface which is pro-filed at least in certain regions and also at least one groove (38, 38') for re-ceiving a busbar (40, 40'), wherein the at least one groove (38, 38') has a depth which varies over its length.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE102011004010A DE102011004010A1 (en) | 2011-02-11 | 2011-02-11 | Cathode arrangement with a surface profiled cathode block with a groove of variable depth |
| DE102011004010.2 | 2011-02-11 | ||
| PCT/EP2012/051965 WO2012107403A1 (en) | 2011-02-11 | 2012-02-06 | Cathode assembly comprising a surface-profiled cathode block having variable groove depth |
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| Publication Number | Publication Date |
|---|---|
| CA2826328A1 true CA2826328A1 (en) | 2012-08-16 |
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| CA2826328A Abandoned CA2826328A1 (en) | 2011-02-11 | 2012-02-06 | Cathode arrangement having a surface-profiled cathode block with a groove of variable depth |
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| Country | Link |
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| EP (1) | EP2673397A1 (en) |
| CN (1) | CN103403227A (en) |
| CA (1) | CA2826328A1 (en) |
| DE (1) | DE102011004010A1 (en) |
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| WO (1) | WO2012107403A1 (en) |
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| DE102011086040A1 (en) * | 2011-11-09 | 2013-05-16 | Sgl Carbon Se | Electrolysis cell, in particular for the production of aluminum, with a trough-shaped cathode |
| CN113445079B (en) * | 2021-06-17 | 2023-09-22 | 合肥工业大学 | Cathode steel bar structure capable of reducing horizontal current of aluminum liquid for aluminum electrolysis cell |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2786024A (en) * | 1953-04-16 | 1957-03-19 | Elektrokemisk As | Arrangement of cathode bars in electrolytic pots |
| DE3538016A1 (en) * | 1985-10-25 | 1987-05-07 | Vaw Ver Aluminium Werke Ag | Cathode bottom for aluminium electrolytic cells |
| WO1992003597A1 (en) * | 1990-08-20 | 1992-03-05 | Comalco Aluminium Limited | Improved aluminium smelting cell |
| AU688098B2 (en) * | 1994-09-08 | 1998-03-05 | Moltech Invent S.A. | Aluminium electrowinning cell with improved carbon cathode blocks |
| FR2821365A1 (en) | 2001-02-28 | 2002-08-30 | Carbone Savoie | GRAPHITE CATHODE FOR ALUMINUM ELECTROLYSIS |
| EP1801264A1 (en) * | 2005-12-22 | 2007-06-27 | Sgl Carbon Ag | Cathodes for aluminium electrolysis cell with expanded graphite lining |
| PL1845174T3 (en) | 2006-04-13 | 2011-10-31 | Sgl Carbon Se | Cathodes for aluminium electrolysis cell with non-planar slot design |
| CN100478500C (en) * | 2007-03-02 | 2009-04-15 | 冯乃祥 | Abnormal cathode carbon block structure aluminum electrolysis bath |
| CN201261809Y (en) * | 2008-08-12 | 2009-06-24 | 高德金 | Cathode inner lining with molten aluminum magnetic vortex stream adjustment device |
-
2011
- 2011-02-11 DE DE102011004010A patent/DE102011004010A1/en not_active Withdrawn
-
2012
- 2012-02-06 CN CN2012800086355A patent/CN103403227A/en active Pending
- 2012-02-06 RU RU2013141552/02A patent/RU2013141552A/en not_active Application Discontinuation
- 2012-02-06 WO PCT/EP2012/051965 patent/WO2012107403A1/en active Application Filing
- 2012-02-06 EP EP12702044.4A patent/EP2673397A1/en not_active Withdrawn
- 2012-02-06 CA CA2826328A patent/CA2826328A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| EP2673397A1 (en) | 2013-12-18 |
| CN103403227A (en) | 2013-11-20 |
| DE102011004010A1 (en) | 2012-08-16 |
| RU2013141552A (en) | 2015-03-20 |
| WO2012107403A1 (en) | 2012-08-16 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request |
Effective date: 20130801 |
|
| FZDE | Discontinued |
Effective date: 20150206 |