CA2854937A1 - Electrolytic cell, in particular for producing aluminum, having a tub-shaped cathode - Google Patents
Electrolytic cell, in particular for producing aluminum, having a tub-shaped cathode Download PDFInfo
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- 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
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Abstract
The invention relates to an electrolytic cell, which is suitable in particular for producing aluminum, comprises a cathode, a layer of liquid aluminum arranged on the top side of the cathode, a melt layer on top thereof, an anode above the melt layer, at least one and preferably at least two bus bars that contact the cathode from the bottom side of the cathode in a current-supplying manner, and at least one external current supply, wherein each of the at least one external current supply is connected in an electrically conductive manner to at least one respective and preferably at least two respective bus bars at a respective connection point, wherein the top side of the cathode is tub-shaped as viewed in the cross-section of the cathode, wherein the tube has two edge regions and a bottom region, which is arranged between the edge regions and lowered relative to the edge regions as viewed in the width direction of the cathode, wherein a respective side wall region is provided between each edge region and the bottom region, which side wall region connects the respective edge region and the bottom region, wherein i) the width of at least one of the bottom region and the edge regions varies over the length of the cathode, and/or ii) the height of the top side of the cathode determined from the bottom side of the cathode varies over the length of the cathode.
Description
WO 2013/068485 Al ELECTROLYTIC CELL, IN PARTICULAR FOR PRODUCING
ALUMINUM, HAVING A TUB-SHAPED CATHODE
The present invention relates to an electrolytic cell, in particular for producing aluminium, and to a cathode which is suitable for use in such an electrolytic cell.
Electrolytic cells are used for example for the electrolytic production of aluminium, which is usually performed industrially in accordance with the Hall-Heroult process. In the Hall-Heroult process, a melt composed of aluminium oxide and cryolite is electrolysed. Here, the cryolite, Na3[AIF6], is used to lower the melting point from 2,045 C for pure aluminium oxide to approximately 950 C for a mixture containing cryolite, aluminium oxide and additives, such as aluminium fluoride and calcium fluoride.
The electrolytic cell used in this process comprises a cathode base, which may be composed of a plurality of cathode blocks which are adjacent to one another and form the cathode. In order to withstand the thermal and chemical conditions prevailing during operation of the cell, the cathode is usually composed of a carbonaceous material. The undersides of each of the cathode blocks are usually provided with grooves, in each of which at least one busbar is arranged, by means of which the current fed via the anodes is discharged. An anode, in particular formed from individual anode blocks, is arranged approximately 3 to 5 cm above the layer of liquid aluminium, usually 15 to 50 cm high, located on the cathode upper side, the electrolyte, that is to say the melt containing aluminium oxide and cryolite, being located between said anode and the surface of the aluminium. During the electrolysis performed at approximately 1,000 C, the formed aluminium settles beneath the electrolyte layer due to its greater density compared with the electrolyte, that is to say settles as an intermediate layer between the upper side of the cathode and the electrolyte layer. During electrolysis, the aluminium oxide dissolved in the melt is cleaved by electric current flow to form aluminium and oxygen. Considered electrochemically, the layer of liquid aluminium is the actual cathode, since aluminium ions are reduced at the surface thereof to form elemental aluminium. Nevertheless, the term "cathode"
will not be understood hereinafter to mean the cathode from an electrochemical viewpoint, that is to say the layer of liquid aluminium, but the component part forming the electrolytic cell base, for example composed of one or more cathode blocks.
A significant disadvantage of the Hall-Heroult process is that it is very energy intensive. Approximately 12 to 15 kWh of electrical energy are required to generate 1 kg of aluminium, which accounts for up to 40 % of the production costs. In order to reduce the production costs, it is therefore desirable to reduce the specific energy consumption of this method where possible.
Due to the relatively high electrical resistance of the melt in particular compared with the layer of liquid aluminium and the cathode material, relatively high ohmic losses in the form of Joule dissipation occur particularly in the melt. In view of the comparatively high specific losses in the melt, there is a significant effort to reduce the thickness of the melt layer and therefore the distance between the anode and the layer of liquid aluminium as far as possible.
However, due to the electromagnetic interactions present during the electrolysis process and the wave formation thus produced in the layer of liquid aluminium, there is thus the risk with an excessively thin melt layer that the layer of liquid aluminium will come into contact with the anode, which may lead to short circuits of the electrolytic cell and to undesirable re-oxidation of the formed aluminium and to the electrical instability of the electrolysis operation and in particular to a fluctuation of the call voltage. Short circuits that occur may also lead to increased wear and therefore to a reduced service life of the electrolytic cell. For these reasons, the distance between the anode and the layer of liquid aluminium cannot be reduced arbitrarily.
The driving force for the wave formation in the layer of liquid aluminium is the inhomogeneous distribution of the electric current density and the magnetic flux density over the surface of the cathode, which leads to a wave-formation-promoting distribution of the Lorentz force density in the layer of liquid aluminium. Here, the Lorentz force density is defined as the vector product of the electric current density present at a specific point and of the magnetic flux density present at this point. One reason, inter alia, for the inhomogeneous distribution of the electric current density and of the magnetic flux density at the upper side of the cathode is in turn the fact that the current in the cathode and in the aluminium bath preferably takes the path of lowest electrical resistance. For this reason, the electric current flowing through the cathode is concentrated primarily on the lateral edge regions of the cathode, where the cathode is connected to the busbars contacting said cathode, since the resultant electrical resistance with the current flow via the edge regions to the surface of the cathode is lower than with the current flow via the centre of the cathode to the surface of the cathode, in which case a longer route or electrical path has to be covered than with the current flow via the edge regions to the surface of the cathode.
ALUMINUM, HAVING A TUB-SHAPED CATHODE
The present invention relates to an electrolytic cell, in particular for producing aluminium, and to a cathode which is suitable for use in such an electrolytic cell.
Electrolytic cells are used for example for the electrolytic production of aluminium, which is usually performed industrially in accordance with the Hall-Heroult process. In the Hall-Heroult process, a melt composed of aluminium oxide and cryolite is electrolysed. Here, the cryolite, Na3[AIF6], is used to lower the melting point from 2,045 C for pure aluminium oxide to approximately 950 C for a mixture containing cryolite, aluminium oxide and additives, such as aluminium fluoride and calcium fluoride.
The electrolytic cell used in this process comprises a cathode base, which may be composed of a plurality of cathode blocks which are adjacent to one another and form the cathode. In order to withstand the thermal and chemical conditions prevailing during operation of the cell, the cathode is usually composed of a carbonaceous material. The undersides of each of the cathode blocks are usually provided with grooves, in each of which at least one busbar is arranged, by means of which the current fed via the anodes is discharged. An anode, in particular formed from individual anode blocks, is arranged approximately 3 to 5 cm above the layer of liquid aluminium, usually 15 to 50 cm high, located on the cathode upper side, the electrolyte, that is to say the melt containing aluminium oxide and cryolite, being located between said anode and the surface of the aluminium. During the electrolysis performed at approximately 1,000 C, the formed aluminium settles beneath the electrolyte layer due to its greater density compared with the electrolyte, that is to say settles as an intermediate layer between the upper side of the cathode and the electrolyte layer. During electrolysis, the aluminium oxide dissolved in the melt is cleaved by electric current flow to form aluminium and oxygen. Considered electrochemically, the layer of liquid aluminium is the actual cathode, since aluminium ions are reduced at the surface thereof to form elemental aluminium. Nevertheless, the term "cathode"
will not be understood hereinafter to mean the cathode from an electrochemical viewpoint, that is to say the layer of liquid aluminium, but the component part forming the electrolytic cell base, for example composed of one or more cathode blocks.
A significant disadvantage of the Hall-Heroult process is that it is very energy intensive. Approximately 12 to 15 kWh of electrical energy are required to generate 1 kg of aluminium, which accounts for up to 40 % of the production costs. In order to reduce the production costs, it is therefore desirable to reduce the specific energy consumption of this method where possible.
Due to the relatively high electrical resistance of the melt in particular compared with the layer of liquid aluminium and the cathode material, relatively high ohmic losses in the form of Joule dissipation occur particularly in the melt. In view of the comparatively high specific losses in the melt, there is a significant effort to reduce the thickness of the melt layer and therefore the distance between the anode and the layer of liquid aluminium as far as possible.
However, due to the electromagnetic interactions present during the electrolysis process and the wave formation thus produced in the layer of liquid aluminium, there is thus the risk with an excessively thin melt layer that the layer of liquid aluminium will come into contact with the anode, which may lead to short circuits of the electrolytic cell and to undesirable re-oxidation of the formed aluminium and to the electrical instability of the electrolysis operation and in particular to a fluctuation of the call voltage. Short circuits that occur may also lead to increased wear and therefore to a reduced service life of the electrolytic cell. For these reasons, the distance between the anode and the layer of liquid aluminium cannot be reduced arbitrarily.
The driving force for the wave formation in the layer of liquid aluminium is the inhomogeneous distribution of the electric current density and the magnetic flux density over the surface of the cathode, which leads to a wave-formation-promoting distribution of the Lorentz force density in the layer of liquid aluminium. Here, the Lorentz force density is defined as the vector product of the electric current density present at a specific point and of the magnetic flux density present at this point. One reason, inter alia, for the inhomogeneous distribution of the electric current density and of the magnetic flux density at the upper side of the cathode is in turn the fact that the current in the cathode and in the aluminium bath preferably takes the path of lowest electrical resistance. For this reason, the electric current flowing through the cathode is concentrated primarily on the lateral edge regions of the cathode, where the cathode is connected to the busbars contacting said cathode, since the resultant electrical resistance with the current flow via the edge regions to the surface of the cathode is lower than with the current flow via the centre of the cathode to the surface of the cathode, in which case a longer route or electrical path has to be covered than with the current flow via the edge regions to the surface of the cathode.
- 4 '-Besides an intensified wave formation in the layer of liquid aluminium, the inhomogeneous current density distribution and in particular the increased current density at the lateral edge regions of the cathode, as considered in the transverse direction of the cathode, compared with the current density in the centre of the cathode also leads to an intensified wear of the cathode in the lateral edge regions, which typically leads after relatively long operation of the electrolytic cell to a characteristic approximately W-shaped wear profile of the cathode in the cross section of the cathode.
In order to reduce the specific energy consumption of an electrolytic cell, it has been proposed recently to use, in electrolytic cells, cathodes of which the upper side, as considered in the cross section of the cathode, is embodied in the form of a V-shaped tub.
Here, the indentation in the cathode surface configured in the form of a V-shaped tub causes the current density in the lateral edge regions of the cathode to be reduced, whereby the wave formation potential and also the wear are reduced in these regions.
However, even with use of such a tub-shaped cathode, an undesirably high wave formation occurs in the layer of liquid aluminium, and, with a low thickness of the cryolite layer between the aluminium and the anode, leads to instabilities and restricts the achievable energy efficiency during electrolysis. In addition, an undesirably high level of non-uniform wear on the upper side of the cathode also occurs during electrolysis with the use of such a cathode. These two factors reduce the service life of the electrolytic cell and therefore the economical viability thereof. This is due to fact that, even with the use of such a cathode, as 5'_ viewed over the surface of the cathode, a relatively inhomogeneous current density distribution and inhomogeneous distribution of the magnetic flux density are still provided, even if these are lower than with a cathode not embodied in a tub-shaped manner. This is because, inter alia, the busbars contacting the cathode are usually connected via collector bars to one or more external current feeds, wherein the distance between the end of the external current feed and the ends, facing this end, of the individual busbars differs, such that the electrical path from the external current feed to the point at which an individual busbar contacts the underside of the cathode is of a different length for different busbars. Longer electrical paths however have a higher electrical resistance for a predefined material compared with shorter electrical paths. The electric current flow through those busbars of which the point contacting the underside of the cathode is closer to the external current feed is thus promoted, as a result of which a greater current flow occurs in the edge regions or longitudinal portions of the cathode arranged over these busbars than in the edge regions or longitudinal portions of the cathode arranged over a busbar of which the point contacting the underside of the cathode is distanced further from the external current feed.
The object of the present invention is therefore to provide an electrolytic cell, which, during operation thereof, has a reduced specific energy consumption and an increased service life. In particular, an electrolytic cell is to be provided in which the thickness of the melt layer is reduced, without the resultant occurrence of instabilities, such as short circuits or re-oxidations of the formed aluminium or fluctuations of the electrolytic cell voltage, caused by increased wave formation tendency in the layer of liquid aluminium.
This object is achieved in accordance with the invention by the provision of an electrolytic cell according to Patent Claim 1 and in particular by the provision of an electrolytic cell for producing aluminium which comprises a cathode, a layer of liquid aluminium arranged on the upper side of the cathode, a melt layer on top thereof, an anode above the melt layer, at least one busbar and preferably at least two busbars contacting the cathode from the underside thereof in a current-feeding manner, and at least one external current feed, wherein the at least one or each external current feed is electrically conductively connected at a respective connection point to at least one busbar and preferably to at least two of the busbars, wherein the upper side of the cathode is tub-shaped as considered in the cross section of the cathode, wherein the tub has two edge regions and a base region, which is arranged between the edge regions and is lowered relative to the edge regions as viewed in the width direction of the cathode, wherein, between each of the two edge regions and the base region, a side wall region connecting the corresponding edge region and the base region is provided, wherein i) the width of at least one of the base region and the edge regions varies over the length of the cathode, and/or ii) the height of the upper side of the cathode determined from the underside of the cathode varies over the length of the cathode.
The width of the base region or of an edge region of the upper side of the cathode is to be understood within the context of the present invention to mean the extension of the base region or of the edge region measured in the width direction of the cathode, that is N
. CA 02854937 2014-05-07 *
.._ 7._ to say the distance from one end of the base region or edge region, as considered in the cross section of the cathode or as considered in the width direction of the cathode, to the other end of the base region or edge region.
Further, the wording "the height of the upper side of the cathode determined from the underside of the cathode" within the context of the present invention refers to the distance of any point on the upper side of the cathode from the point on the underside of the cathode arranged vertically below the first-mentioned point.
Within the context of the present invention an external current feed is understood to mean an arbitrary electrical conductor which is arranged outside the . cathode and which feeds current to the busbar(s) or away therefrom. Here, the external current feed may be connected directly to the busbar(s) via a connection point in each case or may be connected indirectly to the busbar(s) via a collector bar arranged between the external current feed and the busbars. In the latter case, a connection point is understood to mean the point at which the external current feed is connected to the collector bar connected to the busbars. In other words, the wording "connection point between the at least one busbar and preferably at least two busbars and the external current feed" refers to the point at which the electrical paths starting from the busbar(s) electrically conductively connected (directly or indirectly) to the external current feed converge and transition into the external current feed. In this context, the term "electrical path" refers to the current path of lowest electrical resistance between two points.
*
It has been found in accordance with the invention that, by means of a cathode having the cross sectional shape of a tub with a varying width and/or height of the base region and/or of the edge regions of the tub over the length of the cathode, a homogenisation of the electric current density and of the magnetic flux density is achieved at the upper side of the cathode, more specifically not only considered over the cross section of an isolated longitudinal portion of the cathode, but in particular also over the entire surface of the cathode, that is to say both in the longitudinal direction and in the width direction of the cathode.
This is because the cathode material has a low conductivity compared with the layer of liquid aluminium arranged thereabove, as a result of which the current flow in the base region of the tub-shaped cross section is favoured compared with the edge regions of the cathode, which are raised compared with the base region. A widening of the base region or a reduction of the width of an edge region of the cathode in a longitudinal portion of the cathode accordingly leads to a promotion of the current flow in this longitudinal portion on the whole (that is to say compared with another longitudinal portion) and leads to a promotion of the current flow in the base region with respect to the current flow in the edge regions of this longitudinal portion of the cathode, whereas the current flow in a longitudinal portion of the cathode in which the base region is less wide and the edge regions of the cathode are wider is reduced on the whole and the current flow in the base region is reduced with respect to the current flow in the edge regions of this longitudinal portion of the cathode.
Equally, the current flow in this longitudinal portion is promoted on the whole for this reason by a reduction of the height of the cathode upper side in a longitudinal portion of the cathode, whereas the current flow in a longitudinal portion of the cathode in which the upper side of the cathode has a greater height is reduced on the whole. Due to the stepped (with respect to the width and/or height) embodiment of the edge regions and base regions of the cathode, the current flow between the individual longitudinal portions of the cathode and over the width of each longitudinal portion can thus be adjusted such that a more uniform current density is produced, as viewed over the surface of the cathode. In particular, due to the stepped embodiment of the edge regions and base regions of the cathode, the current flow through those longitudinal portions of the cathode which are arranged above busbars of which the point contacting the underside of the cathode is closer to the external current feed can be reduced by widening the edge regions and/or raising the edge regions and/or base regions, and the current flow through those longitudinal portions of the cathode which are arranged above busbars of which the point contacting the underside of the cathode is distanced further from the external current feed can be increased by reducing the width of the edge regions and/or reducing the height of the edge regions and/or base regions, such that the current flow and the magnetic flux through the individual longitudinal portions of the cathode can be homogenised independently of the distance of said longitudinal portions from the external current feed.
Due to the uniform current density and magnetic flux density, as viewed over the surface of the cathode, the wave formation in the layer of liquid aluminium is drastically reduced, and the wear of the cathode as considered over the surface thereof is homogenised. As a result of this, the electrolytic cell according to the invention has a reduced specific energy consumption and an increased service life during operation thereof.
In particular, the thickness of the melt layer can be ' CA 02854937 2014-05-07 =
- lo'--reduced with the electrolytic cell according to the invention without encountering instabilities as a result, such as short circuits or re-oxidations of the formed aluminium or fluctuations of the electrolytic cell voltage, caused by increased wave formation tendency in the layer of liquid aluminium. On the whole, a wave formation in the layer of liquid aluminium is thus effectively avoided during operation of the electrolytic cell according to the invention, and a high energy efficiency with simultaneous high stability and reliability of the electrolysis operation is attained. Here, it is particularly advantageous if the above-described measures used to homogenise the electric current density on the cathode upper side, specifically the adjustment of the width and/or height of individual longitudinal portions of the tub-shaped , cathode, can be easily adjusted to one another, such . that the same bath volume as with the use of a conventional cathode is produced between the cathode and the anode used in the electrolytic cell according to the invention, even with reduced distance between the anode and the layer of liquid aluminium.
In accordance with a particularly advantageous embodiment of the invention, at least one edge region of the cathode comprises at least two longitudinal portions each having a different width, wherein the longitudinal portion of the edge region which is connected via the shortest electrical path to the connection point closest for it has the greatest width of all longitudinal portions of the edge region. In this context, the connection point closest for a longitudinal portion of an edge region is the connection point between at least one busbar, and preferably at least two busbars, and the external current feed, which is connected to the longitudinal portion of the cathode via the shortest electrical = CA 02854937 2014-05-07 - 11.-path. Since, in this embodiment, the edge region is widened in the longitudinal portion which has the shortest electrical path to the closest connection point, the electrical resistance of this longitudinal portion of the cathode is increased compared with the electrical resistances of the other longitudinal portions, and therefore the current flow through this longitudinal portion of the cathode is reduced and that through the other longitudinal portions of the cathode is increased, such that a uniform current density distribution is achieved, as viewed over the individual longitudinal portions of the cathode.
In principle, at least one of a plurality of longitudinal portions of the edge region or of the edge regions having different widths may have a constant width over the respective longitudinal portion, and/or the width of at least one longitudinal portion may decrease gradually from the longitudinal-side end thereof closer to the closest connection point to the longitudinal-side end distanced further. The widths of all longitudinal portions of the edge region or of the edge regions having different widths are preferably constant, such that one of the edge regions or both edge regions of the cathode (based on the width thereof) are step- or stair-shaped, or the widths of all longitudinal portions of the edge region or of the edge regions having different widths decrease gradually from the longitudinal-side end thereof closer to the closest connection point to the longitudinal-side end distanced further.
A particularly uniform distribution of the electric current density is achieved over the surface of the cathode if at least one edge region of the cathode comprises at least three longitudinal portions each having a different width, wherein each of the , = CA 02854937 2014-05-07 .
- 12.-longitudinal portions which is connected to the closest connection point via a longer electrical path than another longitudinal portion has a smaller width than the other longitudinal portion. The influence of the length of the electrical path from the closest connection point to the respective longitudinal portion of the edge region of the cathode on the electric current flow is thus compensated for particularly effectively.
In accordance with a further preferred embodiment of the present invention, the base region of the cathode comprises at least two longitudinal portions each having a different width, wherein the longitudinal portion of the base region which is connected via the shortest electrical path to the connection point closest for it has the smallest width of all longitudinal portions of the base region. Due to the reduction of the width of the base region, the electrical resistance of this longitudinal portion of the cathode is increased, and the current flow is thus diverted partly from this longitudinal portion, in which the highest current flow would otherwise occur, into adjacent longitudinal portions of the cathode, such that a homogenisation of the current density is achieved on the whole over the surface of the cathode.
In principle, one or more longitudinal portions of the base region having different widths may also have a uniform width over the respective longitudinal portion in this embodiment of the present invention, and/or the width of at least one or more longitudinal portions may decrease gradually from its longitudinal-side end arranged closer to the closest connection point to the longitudinal-side end distanced further. Also in this embodiment of the present invention, it is preferable for the widths of all longitudinal portions of the base = CA 02854937 2014-05-07 - 13'-region having different widths to be constant, such that the base region of the cathode (based on the width thereof) is step- or stair-shaped, or for the width of all longitudinal portions of the base region having different widths to decrease gradually from the longitudinal-side end thereof arranged closer to the closest connection point to the longitudinal-side end distanced further.
The base region of the cathode preferably comprises at least three longitudinal portions each having a different width, wherein each of the longitudinal portions which is connected via a longer electrical path to the connection point closest for it than another longitudinal portion has a greater width than the other longitudinal portion. A particularly high uniformity of the electric current density is thus achieved over the surface of the cathode.
In a development of the inventive concept, it is proposed for at least one edge region of the cathode to comprise at least two longitudinal portions each having a different height, wherein the longitudinal portion of the edge region of the cathode which is connected via the shortest electrical path to the closest connection point has the greatest height of all longitudinal portions of the edge region, as determined from the underside of the cathode. The electrical resistance of the longitudinal portion of the edge region of the cathode which is connected via the shortest electrical path to the closest connection point is thus increased compared with the electrical resistances of the other longitudinal portions, such that the current flow through this longitudinal portion of the cathode is reduced and that through the other longitudinal portions of the cathode is increased, such that a uniform current density distribution is achieved, as = CA 02854937 2014-05-07 - 14.-viewed over the individual longitudinal portions of the cathode.
Here, the aforementioned embodiments can also be combined with one another, for example more specifically such that the edge region of the cathode in the longitudinal portion which is connected via the shortest electrical path to the closest connection point has a greater width and a greater height than the longitudinal portions which are connected via a longer electrical path to the closest connection point.
In a further development of the inventive concept, the base region of the cathode may comprise at least two longitudinal portions each having a different height, wherein the longitudinal portion of the base region of the cathode which is connected via the shortest electrical path to the closest connection point has the greatest height of all longitudinal portions of the base region, as determined from the underside of the cathode. Also in this embodiment of the present invention, a particularly good homogenisation of the distribution of the electric current density over the cathode surface is achieved.
In principle, at least one of a plurality of longitudinal portions of one of the edge regions, the two edge regions and/or the base region having different heights may have a uniform height over the respective longitudinal portion, and/or the height of at least one longitudinal portion may gradually decrease from the longitudinal-side end thereof closer to the closest connection point to the longitudinal-side end distanced further. The heights of all longitudinal portions of one of the edge regions, the two edge regions or the base region having different heights are preferably constant, and therefore one of , = CA 02854937 2014-05-07 ' the edge regions, both edge regions or the base region of the cathode (based on the height thereof) is/are step- or stair-shaped, or the heights of all longitudinal portions of one of the edge regions, the edge regions or the base region having different heights decrease gradually from the longitudinal-side end thereof closer to the closest connection point to the longitudinal-side end distanced further.
Within the scope of the invention it is also possible for the height of the cathode upper side, as viewed in the longitudinal direction of the cathode, to vary for the edge region and the base region of one or more longitudinal portions in opposite direction, that is to say for example the height of both edge regions of a longitudinal portion is greater than that of the edge regions of the adjacent longitudinal portions, wherein . however the height of the base region of this longitudinal portion is smaller than that of the base regions of the adjacent longitudinal portions. It is preferable however for the height of the edge regions and the height of the base region of each longitudinal portion of the cathode to vary in parallel, that is to say the heights both of the edge regions and of the base region of each longitudinal portion of the cathode are greater or smaller than those of the edge regions and of the base region of the adjacent longitudinal portions.
A particularly high uniformity of the distribution of the electric current density at the cathode upper side is achieved if the edge region of the cathode comprises at least three longitudinal portions each having a different height, wherein each of the longitudinal portions which is connected to the connection point closest for it via a longer electrical path than , ' CA 02854937 2014-05-07 - 16.- -another longitudinal portion has a lower height than the other longitudinal portion.
Alternatively to the above-mentioned embodiment or preferably additionally to the above-mentioned embodiment, the base region of the cathode may comprise at least three longitudinal portions each having a different height, wherein each of the longitudinal portions which is connected to the closest connection point via a longer electrical path than another longitudinal portion has a lower height than the other longitudinal portion. A particularly uniform distribution of the current density in the base region of the tub formed by the cathode upper side is thus achieved.
A particularly favourable distribution of the electric current density can be achieved if the ratio of the maximum to minimum width of at least one of the edge regions of the cathode is between 2:1 and 1.05:1, preferably 1.5:1 and 1.05:1 and more preferably between 1.3:1 and 1.05:1 and/or the ratio of the maximum to minimum height of at least one of the edge regions of the cathode is between 2:1 and 1.05:1, preferably between 1.5:1 and 1.05:1 and more preferably between 1.3:1 and 1.05:1 and/or the ratio of the maximum to minimum width of the base region of the cathode is between 2:1 and 1.05:1, preferably between 1.5:1 and 1.05:1 and more preferably between 1.3:1 and 1.05:1 and/or the ratio of the maximum to minimum height of the base region of the cathode is between 2:1 and 1.05:1, preferably between 1:5 and 1.05:1 and more preferably between 1.3:1 and 1.05:1.
In the embodiments of the present invention in which the height of the cathode upper side varies over the length of the cathode, the difference between the = CA 02854937 2014-05-07 -maximum height in the edge regions of the cathode and the minimum height in the edge regions of the cathode and/or the difference between the maximum height in the base region of the cathode and the minimum height in the base region of the cathode is preferably less than 30 cm, more preferably less than 20 cm and even more preferably 10 cm at most. Equally, it is preferable if the difference between the maximum height in the edge regions of the cathode and the minimum height in the base region of the cathode is at most 50 % of the distance between the highest point on the cathode upper side and the cathode underside.
In the embodiments of the present invention in which the width of one of the edge regions, of both edge regions or of the base region varies over the length of the cathode, the difference between the maximum width of the base region and the minimum width of the base region, as considered over the entire longitudinal extension of the cathode, is preferably less than 30 cm, more preferably less than 20 cm, and even more preferably less than 10 cm. Equally, it is preferable for the difference between the maximum width of the base region and the minimum width of the base region, as considered over the entire longitudinal extension of the cathode, to be at most 20 % and more preferably at most 10 % of the cathode length.
In accordance with a development of the inventive concept, the electrolytic cell comprises at least two busbars contacting the cathode from the underside thereof in a current-feeding manner, wherein the, or each, external current feed is electrically conductively connected at a respective connection point to at least two of the busbars, and the at least two busbars contacting the cathode from the underside thereof in a current-feeding manner are arranged = CA 02854937 2014-05-07 =
- 18"-parallel to one another and at a fixed distance from one another, extend over the entire width of the cathode, and contact the cathode from the underside thereof in a current-feeding manner, wherein the individual busbars are electrically conductively connected via one of their ends to a collector bar or via each of their ends to separate collector bars, and the collector bar(s) is/are electrically conductively connected to one or more external current feeds.
Alternatively, the individual busbars may be arranged parallel to one another and at a fixed distance from one another, but may not extend over the entire width of the cathode. For example, the individual busbars may only extend over approximately half of the width of the cathode. In this embodiment, 2 busbars for example are arranged in succession, as viewed in the width direction of the cathode, that is to say the busbars are almost formed in a number of pieces, wherein each of these two busbars arranged in succession is connected via its end facing the cathode to an external current feed, possibly via a collector bar. In this embodiment, only the adjacent busbars, as viewed in the longitudinal direction of the cathode, are naturally each connected at a respective connection point to an external current feed.
In accordance with a further preferred embodiment of the present invention the electrolytic cell comprises 2 to 60, preferably 10 to 48, more preferably 16 to 40, even more preferably 20 to 40, and most preferably 36 busbars arranged parallel to one another and at a fixed distance from one another, extending over the entire width of the cathode and contacting the cathode from the underside thereof in a current-feeding manner, and 2 to 6 external current feeds.
* CA 02854937 2014-05-07 Here, the cathode of the electrolytic cell may be composed for example of 2 to 60, preferably 10 to 48, more preferably 16 to 40, even more preferably 20 to 40, and most preferably 36 cathode blocks arranged side by side, wherein each of the cathode blocks on the underside thereof has at least one groove extending in the longitudinal direction of the cathode block or in the width direction of the cathode, at least one busbar being arranged in said groove.
In order to increase yet further the uniformity of the distribution of the electric current density over the cathode surface and in particular to prevent a superelevation of the electric current density in the edge regions of the cathode upper side, it is proposed in a further development of the inventive concept for each of the grooves to have a rectangular cross section and a depth varying over their length, wherein each of the grooves at the longitudinal-side end thereof has a shallower depth than in the centre thereof. Here, a groove, as considered in the cross section of the cathode, may have a substantially triangular form, for example.
In order to achieve in particular a uniform distribution of the electric current density even within the edge regions of the cathode, it is proposed in a development of the inventive concept for at least one of the two edge regions and preferably both edge regions of the cathode to run in a downwardly sloping manner towards the centre of the cathode, as considered in the cross section of the cathode and in the width direction of the cathode, wherein the angle of inclination of the edge region or of the edge regions with respect to the horizontal plane is preferably between 20 and 45 , more preferably between 3 and 20 , and even more preferably between 10 and 15 .
=
Here, it is preferable if at least one of the two edge regions and preferably both of the edge regions extends/extend over at least 30 %, preferably over at least 50 %, more preferably over at least 75%, and even more preferably over 100 % of the width thereof, as considered in the cross section of the cathode and in the width direction of the cathode, in a manner sloping downwardly towards the centre of the cathode. However, at least one of the edge regions may also run substantially horizontally.
In accordance with a further preferred embodiment of the present invention, the base region of the cathode runs in a planar manner, at least in regions, wherein the surface of the base region with respect to the plane running in the vertical direction has an angle between -20 and 20 , preferably between -10 and 10 and more preferably of 0 .
The upper side of the cathode is preferably formed in a tub-shaped manner over at least 25 %, preferably at least 50 %, in particular preferably at least 75 %, more preferably at least 90 %, and most preferably approximately 100 % of the length of the cathode, as considered in the cross section of the cathode, wherein the tub has two edge regions and a base region, which is arranged between the edge regions and is lowered relative to the edge regions, as viewed in the width direction of the cathode, wherein, between each of the two edge regions and the base region, a side wall region connecting the corresponding edge region and the base region is provided.
Here, it is preferable if i) the width of at least one of the base region and the edge regions varies over at least 25 %, preferably at least 50 %, in particular = CA 02854937 2014-05-07 - 21.-preferably at least 75 %, more preferably at least 90 %
and most preferably approximately 100 % of the length of the cathode, and/or ii) the height of the upper side of the cathode, determined from the underside of the cathode, varies over at least 25 %, preferably at least 50 %, in particular preferably at least 75 %, more preferably at least 90 %, and most preferably approximately 100 % of the length of the cathode.
The present invention also relates to a cathode for an electrolytic cell, in particular for an electrolytic cell for producing aluminium, wherein the upper side of the cathode is tub-shaped as considered in the cross section of the cathode, wherein the tub comprises two edge regions and a base region, which is arranged between the edge regions and is lowered relative to the edge regions, as viewed in the width direction of the = cathode, wherein, between each of the two edge regions and the base region, a side wall region connecting the corresponding edge region and the base region is provided, wherein i) the width of at least one of the base region and the edge regions varies over the length of the cathode, and/or ii) the height of the upper side of the cathode, as determined from the underside of the cathode, varies aver the length of the cathode. The preferred embodiments described above in respect of the cathode contained in the electrolytic cell according to the invention also apply to the cathode according to the invention.
The invention will be described hereinafter purely by way of example on the basis of advantageous embodiments with reference to the accompanying drawings, in which:
Fig. 1 shows a perspective view of a portion of a cathode of an electrolytic cell in accordance with an embodiment of the present invention, = CA 02854937 2014-05-07 =
Fig. 2 shows a partially cut-away perspective view of a cathode of an electrolytic cell in accordance with a further embodiment of the present invention, Fig. 3a shows a partially cut-away perspective view of a cathode of an electrolytic cell in accordance with a further embodiment of the present invention, Fig. 3b shows a front view of the cathode of Fig. 3a, and Fig. 4 shows a plan view of an electrolytic cell in accordance with an embodiment of the present invention.
Fig.1 shows a perspective view of a cathode 10 of an electrolytic cell in accordance with an embodiment of the invention.
The cathode 10 composed of a carbonaceous material has an upper side 12, on which the layer of liquid aluminium of the electrolytic cell is arranged during operation of the electrolytic cell, for example in accordance with the Hall-Heroult process. In practice, the cathode 10 is composed of a plurality of cathode blocks arranged side by side as viewed in the longitudinal direction y of the cathode, wherein the longitudinal directions of the individual cathode blocks each run in the width direction x of the cathode 10. The busbars which contact the cathode 10 from the underside 14 thereof in a current-feeding manner and are electrically conductively connected to at least one external current feed are not shown in Fig. 1. Here, each busbar is preferably inserted in a groove which is provided in each cathode block and runs in the width direction x of the cathode 10, that is to say in the longitudinal direction of the respective cathode block.
As illustrated in Fig. 1, the upper side 12 of the cathode 10, as considered in the cross section of the cathode 10, is tub-shaped, wherein the tub has two edge regions 16, 16' and a base region 18, which is arranged between the edge regions 16, 16' and is lowered relative to the edge regions 16, 16', as viewed in the width direction x of the cathode 10, wherein, between each of the edge regions, 16, 16' and the base region 18, a side wall region 20, 20' connecting the corresponding edge region 16, 16' and the base region 18 is provided. During operation of the electrolytic cell, for example in accordance with the Hall-Heroult process, the edge regions 16, 16', the base region 18 and the side wall regions 20, 20' of the upper side 12 are covered by the layer of liquid aluminium. Here, the edge regions 16, 16', the base region 18 and the side wall regions 20, 20' of the cathode 10 are preferably dimensioned such that the bath volume, that is to say the volume between the upper side of the cathode 10 and the underside of the anode, corresponds at least approximately to the bath volume of an electrolytic cell having a conventional cathode.
The edge regions 16, 16' of the cathode 10 shown in Fig. 1 have a width b, measured in the width direction x of the cathode 10, which varies over the length measured in the longitudinal direction y of the cathode 10, as can be seen from Fig. 1. More specifically, the details of the edge regions 16, 16' shown in Fig. 1 have five longitudinal portions L1-L5, wherein the width b of each of the edge regions 16, 16' is constant within each longitudinal portion 1,1-L5 and varies from longitudinal portion 1,1-L5 to longitudinal portion Ll-, r =
- 24 "-L5, more specifically such that a step-shaped variation of the widths b of the edge regions 16, 16' is produced here, as considered in the longitudinal direction y of the cathode 10.
Here, the cathode 10 shown in Fig. 1 is symmetrical with respect to its median longitudinal plane running parallel to the longitudinal direction y, and the width b of the base region 18 thus also varies in the longitudinal direction y of the cathode 10, as does the width of the edge regions 16, 16'.
A further embodiment of a cathode 10 for an electrolytic cell is illustrated in a partially cut-away perspective view in Fig. 2.
This embodiment is similar to the embodiment shown in Fig. 1 in that the cathode 10, as considered in the cross section of the cathode 10, is tub-shaped, wherein the tub has two edge regions 16, of which only the left edge region is shown in the cut-away illustration of Fig. 2, and has a base region 18, which is arranged between the edge regions 16 and is lowered relative to the edge regions 16, as viewed in the width direction x of the cathode 10, wherein, between each of the edge regions and the base region 18, a side wall region 20 connecting the corresponding edge region 16 and the base region 18 is provided. In contrast to the embodiment illustrated in Fig. 1, the width of the edge and base regions 16, 18 does not vary in the longitudinal direction y of the cathode 10 in the embodiment shown in Fig. 2, but instead the height h of the upper side 12 of the cathode 10 varies in the longitudinal direction y of the cathode 10, as measured from the underside 14 of the cathode 10 in the vertical direction z. More specifically, the detail of the upper side 12 of the cathode 10 shown in Fig. 2 has three =
longitudinal portions 1,1-L3, wherein the height h of the upper side 12 of the cathode 10 is constant within each of the longitudinal portions 1,1-L3 (in the longitudinal direction y of the cathode 10), but varies from longitudinal portion 1,1-L3 to longitudinal portion 1,1-L3, more specifically such that a step-shaped variation of the height h of the upper side 12 of the cathode 10, as considered in the longitudinal direction y of the cathode 10, is produced here both in the edge regions 16 and in the base region 18 and in the side wall regions 20.
As can be seen from Fig. 2, the edge region 16, as considered in the width direction x of the cathode 10, is inclined with respect to the horizontal by an angle 0, which in the present case is slightly less than 10 .
= Fig. 3a shows a perspective, partially cut-away illustration of a portion of a cathode 10 in accordance with a further embodiment of the present invention which corresponds largely to the embodiment shown in Fig. 2, specifically in that the height h of the upper side 12 of the cathode 10 varies as viewed in the longitudinal direction y of the cathode 10; however, the cathode shown in Fig. 3 differs from that illustrated in Fig. 2 in that the height h of the edge region 16 on the one hand and the height h of the base region 18 on the other hand vary in the opposite direction, specifically the height h of the edge region 16 increases in the longitudinal direction y running from the longitudinal portion L1 to the longitudinal portion L2f whereas the height h of the base region 18 decreases in this direction.
Fig. 3b shows the cathode detail of Fig. 3a in the longitudinal direction y as considered from the front side of the cathode 10 and illustrates the oppositely directed change in the height h of the edge region 16 and of the base region 18. Here, the dashed line shows the course of the longitudinal portion L2 hidden by the longitudinal portion L1 of the cathode 10.
Fig. 4 shows a plan view of an electrolytic cell in accordance with an embodiment of the present invention.
Here, the anode structure and the part of the current supply connected to the anode structure are not shown in order to uncover the view of the cathode 10 and the components arranged beneath and beside said cathode.
In cross section, the cathode 10 has the shape of a tub comprising two edge regions 16, 16', comprising a base region 18 and comprising side wall regions 20, 20' = arranged between the base region 18 and the edge regions 16, 16'. Here, the cathode 10 per se = corresponds to the embodiment shown in Fig. 1, more specifically in particular in that the cathode 10 shown in Fig. 4 has a plurality of longitudinal portions L1 to L9, wherein the widths b of the individual edge regions 16, 16' and of the base region 18 vary in the longitudinal direction y of the cathode 10.
The electrolytic cell comprises nine bar-shaped busbars 22, 22', which each contact the cathode 10 from the underside thereof in a current-feeding manner and each extend via their longitudinal direction in the width direction x of the electrolytic cell. The electrolytic cell additionally comprises two collector bars 24, 24', which are arranged such that each of these collector bars 24, 24' is connected to a respective end of all busbars 22, 22'. The collector bars 24, 24' accordingly run the longitudinal direction y in a manner laterally offset in relation to the cathode 10.
, , ' Each collector bar 24, 24' is associated with two external current feeds 26, 26' and 26", 26"' respectively, by means of which current is fed externally to the busbars 22, 22' arranged on the underside 14 of the cathode 10. Here, the external current feeds 26, 26', 26", 26"' are connected at respective connection points 28, 28', 28", 28"' to one of the collector bars 24, 24' and therefore at this point also indirectly to the busbars 22, 22' connected to said collector bar 24, 24'.
As can be seen from Fig. 4, the distances between the individual connection points 28, 28', 28", 28"' and the entry points of the individual busbars 22, 22' in the cathode 10, that is to say the electrical paths P1-P3, via which the electric current must flow from the individual connection points 28, 28' 28", 28"' to the entry points of the individual busbars 22, 22' into the edge regions 16, 16' of the cathode 10, are of different length. Here, a longitudinal portion 1,1-L9, of the cathode 10 which has a shorter electrical path P1-P3 to the connection point 28, 28', 28", 28"' closest to this longitudinal portion 1,1-L9 has a greater width b in its edge regions 16, 16' than a longitudinal portion 1,1-L9 of the cathode 10 having a longer electrical path to the connection point 28, 28', 28", 28"' closest to this longitudinal portion.
Equally, a longitudinal portion 1,1-L9 of the cathode 10 which has a shorter electrical path P1-P3 to the connection point 28, 28', 28", 28"' closest to this longitudinal portion 1,1-L9 has a smaller width b in its base region 18 than a longitudinal portion 1,1-L9 of the cathode 10 having a longer electrical path to the connection point 28, 28', 28", 28"' closest to this longitudinal portion.
, - 28 ' LIST OF REFERNCE SIGNS
cathode 12 upper side 14 underside 16, 16' edge regions 18 base region 20, 20' side wall region 22, 22' busbar 24, 24' collector bar 26, 26', 26", 26"' external current feed 28, 28', 28", 28"' connection point x, y, z width, longitudinal and vertical direction width 1 length height L1-L9 longitudinal portion Pi-P3 electrical path angle of inclination
In order to reduce the specific energy consumption of an electrolytic cell, it has been proposed recently to use, in electrolytic cells, cathodes of which the upper side, as considered in the cross section of the cathode, is embodied in the form of a V-shaped tub.
Here, the indentation in the cathode surface configured in the form of a V-shaped tub causes the current density in the lateral edge regions of the cathode to be reduced, whereby the wave formation potential and also the wear are reduced in these regions.
However, even with use of such a tub-shaped cathode, an undesirably high wave formation occurs in the layer of liquid aluminium, and, with a low thickness of the cryolite layer between the aluminium and the anode, leads to instabilities and restricts the achievable energy efficiency during electrolysis. In addition, an undesirably high level of non-uniform wear on the upper side of the cathode also occurs during electrolysis with the use of such a cathode. These two factors reduce the service life of the electrolytic cell and therefore the economical viability thereof. This is due to fact that, even with the use of such a cathode, as 5'_ viewed over the surface of the cathode, a relatively inhomogeneous current density distribution and inhomogeneous distribution of the magnetic flux density are still provided, even if these are lower than with a cathode not embodied in a tub-shaped manner. This is because, inter alia, the busbars contacting the cathode are usually connected via collector bars to one or more external current feeds, wherein the distance between the end of the external current feed and the ends, facing this end, of the individual busbars differs, such that the electrical path from the external current feed to the point at which an individual busbar contacts the underside of the cathode is of a different length for different busbars. Longer electrical paths however have a higher electrical resistance for a predefined material compared with shorter electrical paths. The electric current flow through those busbars of which the point contacting the underside of the cathode is closer to the external current feed is thus promoted, as a result of which a greater current flow occurs in the edge regions or longitudinal portions of the cathode arranged over these busbars than in the edge regions or longitudinal portions of the cathode arranged over a busbar of which the point contacting the underside of the cathode is distanced further from the external current feed.
The object of the present invention is therefore to provide an electrolytic cell, which, during operation thereof, has a reduced specific energy consumption and an increased service life. In particular, an electrolytic cell is to be provided in which the thickness of the melt layer is reduced, without the resultant occurrence of instabilities, such as short circuits or re-oxidations of the formed aluminium or fluctuations of the electrolytic cell voltage, caused by increased wave formation tendency in the layer of liquid aluminium.
This object is achieved in accordance with the invention by the provision of an electrolytic cell according to Patent Claim 1 and in particular by the provision of an electrolytic cell for producing aluminium which comprises a cathode, a layer of liquid aluminium arranged on the upper side of the cathode, a melt layer on top thereof, an anode above the melt layer, at least one busbar and preferably at least two busbars contacting the cathode from the underside thereof in a current-feeding manner, and at least one external current feed, wherein the at least one or each external current feed is electrically conductively connected at a respective connection point to at least one busbar and preferably to at least two of the busbars, wherein the upper side of the cathode is tub-shaped as considered in the cross section of the cathode, wherein the tub has two edge regions and a base region, which is arranged between the edge regions and is lowered relative to the edge regions as viewed in the width direction of the cathode, wherein, between each of the two edge regions and the base region, a side wall region connecting the corresponding edge region and the base region is provided, wherein i) the width of at least one of the base region and the edge regions varies over the length of the cathode, and/or ii) the height of the upper side of the cathode determined from the underside of the cathode varies over the length of the cathode.
The width of the base region or of an edge region of the upper side of the cathode is to be understood within the context of the present invention to mean the extension of the base region or of the edge region measured in the width direction of the cathode, that is N
. CA 02854937 2014-05-07 *
.._ 7._ to say the distance from one end of the base region or edge region, as considered in the cross section of the cathode or as considered in the width direction of the cathode, to the other end of the base region or edge region.
Further, the wording "the height of the upper side of the cathode determined from the underside of the cathode" within the context of the present invention refers to the distance of any point on the upper side of the cathode from the point on the underside of the cathode arranged vertically below the first-mentioned point.
Within the context of the present invention an external current feed is understood to mean an arbitrary electrical conductor which is arranged outside the . cathode and which feeds current to the busbar(s) or away therefrom. Here, the external current feed may be connected directly to the busbar(s) via a connection point in each case or may be connected indirectly to the busbar(s) via a collector bar arranged between the external current feed and the busbars. In the latter case, a connection point is understood to mean the point at which the external current feed is connected to the collector bar connected to the busbars. In other words, the wording "connection point between the at least one busbar and preferably at least two busbars and the external current feed" refers to the point at which the electrical paths starting from the busbar(s) electrically conductively connected (directly or indirectly) to the external current feed converge and transition into the external current feed. In this context, the term "electrical path" refers to the current path of lowest electrical resistance between two points.
*
It has been found in accordance with the invention that, by means of a cathode having the cross sectional shape of a tub with a varying width and/or height of the base region and/or of the edge regions of the tub over the length of the cathode, a homogenisation of the electric current density and of the magnetic flux density is achieved at the upper side of the cathode, more specifically not only considered over the cross section of an isolated longitudinal portion of the cathode, but in particular also over the entire surface of the cathode, that is to say both in the longitudinal direction and in the width direction of the cathode.
This is because the cathode material has a low conductivity compared with the layer of liquid aluminium arranged thereabove, as a result of which the current flow in the base region of the tub-shaped cross section is favoured compared with the edge regions of the cathode, which are raised compared with the base region. A widening of the base region or a reduction of the width of an edge region of the cathode in a longitudinal portion of the cathode accordingly leads to a promotion of the current flow in this longitudinal portion on the whole (that is to say compared with another longitudinal portion) and leads to a promotion of the current flow in the base region with respect to the current flow in the edge regions of this longitudinal portion of the cathode, whereas the current flow in a longitudinal portion of the cathode in which the base region is less wide and the edge regions of the cathode are wider is reduced on the whole and the current flow in the base region is reduced with respect to the current flow in the edge regions of this longitudinal portion of the cathode.
Equally, the current flow in this longitudinal portion is promoted on the whole for this reason by a reduction of the height of the cathode upper side in a longitudinal portion of the cathode, whereas the current flow in a longitudinal portion of the cathode in which the upper side of the cathode has a greater height is reduced on the whole. Due to the stepped (with respect to the width and/or height) embodiment of the edge regions and base regions of the cathode, the current flow between the individual longitudinal portions of the cathode and over the width of each longitudinal portion can thus be adjusted such that a more uniform current density is produced, as viewed over the surface of the cathode. In particular, due to the stepped embodiment of the edge regions and base regions of the cathode, the current flow through those longitudinal portions of the cathode which are arranged above busbars of which the point contacting the underside of the cathode is closer to the external current feed can be reduced by widening the edge regions and/or raising the edge regions and/or base regions, and the current flow through those longitudinal portions of the cathode which are arranged above busbars of which the point contacting the underside of the cathode is distanced further from the external current feed can be increased by reducing the width of the edge regions and/or reducing the height of the edge regions and/or base regions, such that the current flow and the magnetic flux through the individual longitudinal portions of the cathode can be homogenised independently of the distance of said longitudinal portions from the external current feed.
Due to the uniform current density and magnetic flux density, as viewed over the surface of the cathode, the wave formation in the layer of liquid aluminium is drastically reduced, and the wear of the cathode as considered over the surface thereof is homogenised. As a result of this, the electrolytic cell according to the invention has a reduced specific energy consumption and an increased service life during operation thereof.
In particular, the thickness of the melt layer can be ' CA 02854937 2014-05-07 =
- lo'--reduced with the electrolytic cell according to the invention without encountering instabilities as a result, such as short circuits or re-oxidations of the formed aluminium or fluctuations of the electrolytic cell voltage, caused by increased wave formation tendency in the layer of liquid aluminium. On the whole, a wave formation in the layer of liquid aluminium is thus effectively avoided during operation of the electrolytic cell according to the invention, and a high energy efficiency with simultaneous high stability and reliability of the electrolysis operation is attained. Here, it is particularly advantageous if the above-described measures used to homogenise the electric current density on the cathode upper side, specifically the adjustment of the width and/or height of individual longitudinal portions of the tub-shaped , cathode, can be easily adjusted to one another, such . that the same bath volume as with the use of a conventional cathode is produced between the cathode and the anode used in the electrolytic cell according to the invention, even with reduced distance between the anode and the layer of liquid aluminium.
In accordance with a particularly advantageous embodiment of the invention, at least one edge region of the cathode comprises at least two longitudinal portions each having a different width, wherein the longitudinal portion of the edge region which is connected via the shortest electrical path to the connection point closest for it has the greatest width of all longitudinal portions of the edge region. In this context, the connection point closest for a longitudinal portion of an edge region is the connection point between at least one busbar, and preferably at least two busbars, and the external current feed, which is connected to the longitudinal portion of the cathode via the shortest electrical = CA 02854937 2014-05-07 - 11.-path. Since, in this embodiment, the edge region is widened in the longitudinal portion which has the shortest electrical path to the closest connection point, the electrical resistance of this longitudinal portion of the cathode is increased compared with the electrical resistances of the other longitudinal portions, and therefore the current flow through this longitudinal portion of the cathode is reduced and that through the other longitudinal portions of the cathode is increased, such that a uniform current density distribution is achieved, as viewed over the individual longitudinal portions of the cathode.
In principle, at least one of a plurality of longitudinal portions of the edge region or of the edge regions having different widths may have a constant width over the respective longitudinal portion, and/or the width of at least one longitudinal portion may decrease gradually from the longitudinal-side end thereof closer to the closest connection point to the longitudinal-side end distanced further. The widths of all longitudinal portions of the edge region or of the edge regions having different widths are preferably constant, such that one of the edge regions or both edge regions of the cathode (based on the width thereof) are step- or stair-shaped, or the widths of all longitudinal portions of the edge region or of the edge regions having different widths decrease gradually from the longitudinal-side end thereof closer to the closest connection point to the longitudinal-side end distanced further.
A particularly uniform distribution of the electric current density is achieved over the surface of the cathode if at least one edge region of the cathode comprises at least three longitudinal portions each having a different width, wherein each of the , = CA 02854937 2014-05-07 .
- 12.-longitudinal portions which is connected to the closest connection point via a longer electrical path than another longitudinal portion has a smaller width than the other longitudinal portion. The influence of the length of the electrical path from the closest connection point to the respective longitudinal portion of the edge region of the cathode on the electric current flow is thus compensated for particularly effectively.
In accordance with a further preferred embodiment of the present invention, the base region of the cathode comprises at least two longitudinal portions each having a different width, wherein the longitudinal portion of the base region which is connected via the shortest electrical path to the connection point closest for it has the smallest width of all longitudinal portions of the base region. Due to the reduction of the width of the base region, the electrical resistance of this longitudinal portion of the cathode is increased, and the current flow is thus diverted partly from this longitudinal portion, in which the highest current flow would otherwise occur, into adjacent longitudinal portions of the cathode, such that a homogenisation of the current density is achieved on the whole over the surface of the cathode.
In principle, one or more longitudinal portions of the base region having different widths may also have a uniform width over the respective longitudinal portion in this embodiment of the present invention, and/or the width of at least one or more longitudinal portions may decrease gradually from its longitudinal-side end arranged closer to the closest connection point to the longitudinal-side end distanced further. Also in this embodiment of the present invention, it is preferable for the widths of all longitudinal portions of the base = CA 02854937 2014-05-07 - 13'-region having different widths to be constant, such that the base region of the cathode (based on the width thereof) is step- or stair-shaped, or for the width of all longitudinal portions of the base region having different widths to decrease gradually from the longitudinal-side end thereof arranged closer to the closest connection point to the longitudinal-side end distanced further.
The base region of the cathode preferably comprises at least three longitudinal portions each having a different width, wherein each of the longitudinal portions which is connected via a longer electrical path to the connection point closest for it than another longitudinal portion has a greater width than the other longitudinal portion. A particularly high uniformity of the electric current density is thus achieved over the surface of the cathode.
In a development of the inventive concept, it is proposed for at least one edge region of the cathode to comprise at least two longitudinal portions each having a different height, wherein the longitudinal portion of the edge region of the cathode which is connected via the shortest electrical path to the closest connection point has the greatest height of all longitudinal portions of the edge region, as determined from the underside of the cathode. The electrical resistance of the longitudinal portion of the edge region of the cathode which is connected via the shortest electrical path to the closest connection point is thus increased compared with the electrical resistances of the other longitudinal portions, such that the current flow through this longitudinal portion of the cathode is reduced and that through the other longitudinal portions of the cathode is increased, such that a uniform current density distribution is achieved, as = CA 02854937 2014-05-07 - 14.-viewed over the individual longitudinal portions of the cathode.
Here, the aforementioned embodiments can also be combined with one another, for example more specifically such that the edge region of the cathode in the longitudinal portion which is connected via the shortest electrical path to the closest connection point has a greater width and a greater height than the longitudinal portions which are connected via a longer electrical path to the closest connection point.
In a further development of the inventive concept, the base region of the cathode may comprise at least two longitudinal portions each having a different height, wherein the longitudinal portion of the base region of the cathode which is connected via the shortest electrical path to the closest connection point has the greatest height of all longitudinal portions of the base region, as determined from the underside of the cathode. Also in this embodiment of the present invention, a particularly good homogenisation of the distribution of the electric current density over the cathode surface is achieved.
In principle, at least one of a plurality of longitudinal portions of one of the edge regions, the two edge regions and/or the base region having different heights may have a uniform height over the respective longitudinal portion, and/or the height of at least one longitudinal portion may gradually decrease from the longitudinal-side end thereof closer to the closest connection point to the longitudinal-side end distanced further. The heights of all longitudinal portions of one of the edge regions, the two edge regions or the base region having different heights are preferably constant, and therefore one of , = CA 02854937 2014-05-07 ' the edge regions, both edge regions or the base region of the cathode (based on the height thereof) is/are step- or stair-shaped, or the heights of all longitudinal portions of one of the edge regions, the edge regions or the base region having different heights decrease gradually from the longitudinal-side end thereof closer to the closest connection point to the longitudinal-side end distanced further.
Within the scope of the invention it is also possible for the height of the cathode upper side, as viewed in the longitudinal direction of the cathode, to vary for the edge region and the base region of one or more longitudinal portions in opposite direction, that is to say for example the height of both edge regions of a longitudinal portion is greater than that of the edge regions of the adjacent longitudinal portions, wherein . however the height of the base region of this longitudinal portion is smaller than that of the base regions of the adjacent longitudinal portions. It is preferable however for the height of the edge regions and the height of the base region of each longitudinal portion of the cathode to vary in parallel, that is to say the heights both of the edge regions and of the base region of each longitudinal portion of the cathode are greater or smaller than those of the edge regions and of the base region of the adjacent longitudinal portions.
A particularly high uniformity of the distribution of the electric current density at the cathode upper side is achieved if the edge region of the cathode comprises at least three longitudinal portions each having a different height, wherein each of the longitudinal portions which is connected to the connection point closest for it via a longer electrical path than , ' CA 02854937 2014-05-07 - 16.- -another longitudinal portion has a lower height than the other longitudinal portion.
Alternatively to the above-mentioned embodiment or preferably additionally to the above-mentioned embodiment, the base region of the cathode may comprise at least three longitudinal portions each having a different height, wherein each of the longitudinal portions which is connected to the closest connection point via a longer electrical path than another longitudinal portion has a lower height than the other longitudinal portion. A particularly uniform distribution of the current density in the base region of the tub formed by the cathode upper side is thus achieved.
A particularly favourable distribution of the electric current density can be achieved if the ratio of the maximum to minimum width of at least one of the edge regions of the cathode is between 2:1 and 1.05:1, preferably 1.5:1 and 1.05:1 and more preferably between 1.3:1 and 1.05:1 and/or the ratio of the maximum to minimum height of at least one of the edge regions of the cathode is between 2:1 and 1.05:1, preferably between 1.5:1 and 1.05:1 and more preferably between 1.3:1 and 1.05:1 and/or the ratio of the maximum to minimum width of the base region of the cathode is between 2:1 and 1.05:1, preferably between 1.5:1 and 1.05:1 and more preferably between 1.3:1 and 1.05:1 and/or the ratio of the maximum to minimum height of the base region of the cathode is between 2:1 and 1.05:1, preferably between 1:5 and 1.05:1 and more preferably between 1.3:1 and 1.05:1.
In the embodiments of the present invention in which the height of the cathode upper side varies over the length of the cathode, the difference between the = CA 02854937 2014-05-07 -maximum height in the edge regions of the cathode and the minimum height in the edge regions of the cathode and/or the difference between the maximum height in the base region of the cathode and the minimum height in the base region of the cathode is preferably less than 30 cm, more preferably less than 20 cm and even more preferably 10 cm at most. Equally, it is preferable if the difference between the maximum height in the edge regions of the cathode and the minimum height in the base region of the cathode is at most 50 % of the distance between the highest point on the cathode upper side and the cathode underside.
In the embodiments of the present invention in which the width of one of the edge regions, of both edge regions or of the base region varies over the length of the cathode, the difference between the maximum width of the base region and the minimum width of the base region, as considered over the entire longitudinal extension of the cathode, is preferably less than 30 cm, more preferably less than 20 cm, and even more preferably less than 10 cm. Equally, it is preferable for the difference between the maximum width of the base region and the minimum width of the base region, as considered over the entire longitudinal extension of the cathode, to be at most 20 % and more preferably at most 10 % of the cathode length.
In accordance with a development of the inventive concept, the electrolytic cell comprises at least two busbars contacting the cathode from the underside thereof in a current-feeding manner, wherein the, or each, external current feed is electrically conductively connected at a respective connection point to at least two of the busbars, and the at least two busbars contacting the cathode from the underside thereof in a current-feeding manner are arranged = CA 02854937 2014-05-07 =
- 18"-parallel to one another and at a fixed distance from one another, extend over the entire width of the cathode, and contact the cathode from the underside thereof in a current-feeding manner, wherein the individual busbars are electrically conductively connected via one of their ends to a collector bar or via each of their ends to separate collector bars, and the collector bar(s) is/are electrically conductively connected to one or more external current feeds.
Alternatively, the individual busbars may be arranged parallel to one another and at a fixed distance from one another, but may not extend over the entire width of the cathode. For example, the individual busbars may only extend over approximately half of the width of the cathode. In this embodiment, 2 busbars for example are arranged in succession, as viewed in the width direction of the cathode, that is to say the busbars are almost formed in a number of pieces, wherein each of these two busbars arranged in succession is connected via its end facing the cathode to an external current feed, possibly via a collector bar. In this embodiment, only the adjacent busbars, as viewed in the longitudinal direction of the cathode, are naturally each connected at a respective connection point to an external current feed.
In accordance with a further preferred embodiment of the present invention the electrolytic cell comprises 2 to 60, preferably 10 to 48, more preferably 16 to 40, even more preferably 20 to 40, and most preferably 36 busbars arranged parallel to one another and at a fixed distance from one another, extending over the entire width of the cathode and contacting the cathode from the underside thereof in a current-feeding manner, and 2 to 6 external current feeds.
* CA 02854937 2014-05-07 Here, the cathode of the electrolytic cell may be composed for example of 2 to 60, preferably 10 to 48, more preferably 16 to 40, even more preferably 20 to 40, and most preferably 36 cathode blocks arranged side by side, wherein each of the cathode blocks on the underside thereof has at least one groove extending in the longitudinal direction of the cathode block or in the width direction of the cathode, at least one busbar being arranged in said groove.
In order to increase yet further the uniformity of the distribution of the electric current density over the cathode surface and in particular to prevent a superelevation of the electric current density in the edge regions of the cathode upper side, it is proposed in a further development of the inventive concept for each of the grooves to have a rectangular cross section and a depth varying over their length, wherein each of the grooves at the longitudinal-side end thereof has a shallower depth than in the centre thereof. Here, a groove, as considered in the cross section of the cathode, may have a substantially triangular form, for example.
In order to achieve in particular a uniform distribution of the electric current density even within the edge regions of the cathode, it is proposed in a development of the inventive concept for at least one of the two edge regions and preferably both edge regions of the cathode to run in a downwardly sloping manner towards the centre of the cathode, as considered in the cross section of the cathode and in the width direction of the cathode, wherein the angle of inclination of the edge region or of the edge regions with respect to the horizontal plane is preferably between 20 and 45 , more preferably between 3 and 20 , and even more preferably between 10 and 15 .
=
Here, it is preferable if at least one of the two edge regions and preferably both of the edge regions extends/extend over at least 30 %, preferably over at least 50 %, more preferably over at least 75%, and even more preferably over 100 % of the width thereof, as considered in the cross section of the cathode and in the width direction of the cathode, in a manner sloping downwardly towards the centre of the cathode. However, at least one of the edge regions may also run substantially horizontally.
In accordance with a further preferred embodiment of the present invention, the base region of the cathode runs in a planar manner, at least in regions, wherein the surface of the base region with respect to the plane running in the vertical direction has an angle between -20 and 20 , preferably between -10 and 10 and more preferably of 0 .
The upper side of the cathode is preferably formed in a tub-shaped manner over at least 25 %, preferably at least 50 %, in particular preferably at least 75 %, more preferably at least 90 %, and most preferably approximately 100 % of the length of the cathode, as considered in the cross section of the cathode, wherein the tub has two edge regions and a base region, which is arranged between the edge regions and is lowered relative to the edge regions, as viewed in the width direction of the cathode, wherein, between each of the two edge regions and the base region, a side wall region connecting the corresponding edge region and the base region is provided.
Here, it is preferable if i) the width of at least one of the base region and the edge regions varies over at least 25 %, preferably at least 50 %, in particular = CA 02854937 2014-05-07 - 21.-preferably at least 75 %, more preferably at least 90 %
and most preferably approximately 100 % of the length of the cathode, and/or ii) the height of the upper side of the cathode, determined from the underside of the cathode, varies over at least 25 %, preferably at least 50 %, in particular preferably at least 75 %, more preferably at least 90 %, and most preferably approximately 100 % of the length of the cathode.
The present invention also relates to a cathode for an electrolytic cell, in particular for an electrolytic cell for producing aluminium, wherein the upper side of the cathode is tub-shaped as considered in the cross section of the cathode, wherein the tub comprises two edge regions and a base region, which is arranged between the edge regions and is lowered relative to the edge regions, as viewed in the width direction of the = cathode, wherein, between each of the two edge regions and the base region, a side wall region connecting the corresponding edge region and the base region is provided, wherein i) the width of at least one of the base region and the edge regions varies over the length of the cathode, and/or ii) the height of the upper side of the cathode, as determined from the underside of the cathode, varies aver the length of the cathode. The preferred embodiments described above in respect of the cathode contained in the electrolytic cell according to the invention also apply to the cathode according to the invention.
The invention will be described hereinafter purely by way of example on the basis of advantageous embodiments with reference to the accompanying drawings, in which:
Fig. 1 shows a perspective view of a portion of a cathode of an electrolytic cell in accordance with an embodiment of the present invention, = CA 02854937 2014-05-07 =
Fig. 2 shows a partially cut-away perspective view of a cathode of an electrolytic cell in accordance with a further embodiment of the present invention, Fig. 3a shows a partially cut-away perspective view of a cathode of an electrolytic cell in accordance with a further embodiment of the present invention, Fig. 3b shows a front view of the cathode of Fig. 3a, and Fig. 4 shows a plan view of an electrolytic cell in accordance with an embodiment of the present invention.
Fig.1 shows a perspective view of a cathode 10 of an electrolytic cell in accordance with an embodiment of the invention.
The cathode 10 composed of a carbonaceous material has an upper side 12, on which the layer of liquid aluminium of the electrolytic cell is arranged during operation of the electrolytic cell, for example in accordance with the Hall-Heroult process. In practice, the cathode 10 is composed of a plurality of cathode blocks arranged side by side as viewed in the longitudinal direction y of the cathode, wherein the longitudinal directions of the individual cathode blocks each run in the width direction x of the cathode 10. The busbars which contact the cathode 10 from the underside 14 thereof in a current-feeding manner and are electrically conductively connected to at least one external current feed are not shown in Fig. 1. Here, each busbar is preferably inserted in a groove which is provided in each cathode block and runs in the width direction x of the cathode 10, that is to say in the longitudinal direction of the respective cathode block.
As illustrated in Fig. 1, the upper side 12 of the cathode 10, as considered in the cross section of the cathode 10, is tub-shaped, wherein the tub has two edge regions 16, 16' and a base region 18, which is arranged between the edge regions 16, 16' and is lowered relative to the edge regions 16, 16', as viewed in the width direction x of the cathode 10, wherein, between each of the edge regions, 16, 16' and the base region 18, a side wall region 20, 20' connecting the corresponding edge region 16, 16' and the base region 18 is provided. During operation of the electrolytic cell, for example in accordance with the Hall-Heroult process, the edge regions 16, 16', the base region 18 and the side wall regions 20, 20' of the upper side 12 are covered by the layer of liquid aluminium. Here, the edge regions 16, 16', the base region 18 and the side wall regions 20, 20' of the cathode 10 are preferably dimensioned such that the bath volume, that is to say the volume between the upper side of the cathode 10 and the underside of the anode, corresponds at least approximately to the bath volume of an electrolytic cell having a conventional cathode.
The edge regions 16, 16' of the cathode 10 shown in Fig. 1 have a width b, measured in the width direction x of the cathode 10, which varies over the length measured in the longitudinal direction y of the cathode 10, as can be seen from Fig. 1. More specifically, the details of the edge regions 16, 16' shown in Fig. 1 have five longitudinal portions L1-L5, wherein the width b of each of the edge regions 16, 16' is constant within each longitudinal portion 1,1-L5 and varies from longitudinal portion 1,1-L5 to longitudinal portion Ll-, r =
- 24 "-L5, more specifically such that a step-shaped variation of the widths b of the edge regions 16, 16' is produced here, as considered in the longitudinal direction y of the cathode 10.
Here, the cathode 10 shown in Fig. 1 is symmetrical with respect to its median longitudinal plane running parallel to the longitudinal direction y, and the width b of the base region 18 thus also varies in the longitudinal direction y of the cathode 10, as does the width of the edge regions 16, 16'.
A further embodiment of a cathode 10 for an electrolytic cell is illustrated in a partially cut-away perspective view in Fig. 2.
This embodiment is similar to the embodiment shown in Fig. 1 in that the cathode 10, as considered in the cross section of the cathode 10, is tub-shaped, wherein the tub has two edge regions 16, of which only the left edge region is shown in the cut-away illustration of Fig. 2, and has a base region 18, which is arranged between the edge regions 16 and is lowered relative to the edge regions 16, as viewed in the width direction x of the cathode 10, wherein, between each of the edge regions and the base region 18, a side wall region 20 connecting the corresponding edge region 16 and the base region 18 is provided. In contrast to the embodiment illustrated in Fig. 1, the width of the edge and base regions 16, 18 does not vary in the longitudinal direction y of the cathode 10 in the embodiment shown in Fig. 2, but instead the height h of the upper side 12 of the cathode 10 varies in the longitudinal direction y of the cathode 10, as measured from the underside 14 of the cathode 10 in the vertical direction z. More specifically, the detail of the upper side 12 of the cathode 10 shown in Fig. 2 has three =
longitudinal portions 1,1-L3, wherein the height h of the upper side 12 of the cathode 10 is constant within each of the longitudinal portions 1,1-L3 (in the longitudinal direction y of the cathode 10), but varies from longitudinal portion 1,1-L3 to longitudinal portion 1,1-L3, more specifically such that a step-shaped variation of the height h of the upper side 12 of the cathode 10, as considered in the longitudinal direction y of the cathode 10, is produced here both in the edge regions 16 and in the base region 18 and in the side wall regions 20.
As can be seen from Fig. 2, the edge region 16, as considered in the width direction x of the cathode 10, is inclined with respect to the horizontal by an angle 0, which in the present case is slightly less than 10 .
= Fig. 3a shows a perspective, partially cut-away illustration of a portion of a cathode 10 in accordance with a further embodiment of the present invention which corresponds largely to the embodiment shown in Fig. 2, specifically in that the height h of the upper side 12 of the cathode 10 varies as viewed in the longitudinal direction y of the cathode 10; however, the cathode shown in Fig. 3 differs from that illustrated in Fig. 2 in that the height h of the edge region 16 on the one hand and the height h of the base region 18 on the other hand vary in the opposite direction, specifically the height h of the edge region 16 increases in the longitudinal direction y running from the longitudinal portion L1 to the longitudinal portion L2f whereas the height h of the base region 18 decreases in this direction.
Fig. 3b shows the cathode detail of Fig. 3a in the longitudinal direction y as considered from the front side of the cathode 10 and illustrates the oppositely directed change in the height h of the edge region 16 and of the base region 18. Here, the dashed line shows the course of the longitudinal portion L2 hidden by the longitudinal portion L1 of the cathode 10.
Fig. 4 shows a plan view of an electrolytic cell in accordance with an embodiment of the present invention.
Here, the anode structure and the part of the current supply connected to the anode structure are not shown in order to uncover the view of the cathode 10 and the components arranged beneath and beside said cathode.
In cross section, the cathode 10 has the shape of a tub comprising two edge regions 16, 16', comprising a base region 18 and comprising side wall regions 20, 20' = arranged between the base region 18 and the edge regions 16, 16'. Here, the cathode 10 per se = corresponds to the embodiment shown in Fig. 1, more specifically in particular in that the cathode 10 shown in Fig. 4 has a plurality of longitudinal portions L1 to L9, wherein the widths b of the individual edge regions 16, 16' and of the base region 18 vary in the longitudinal direction y of the cathode 10.
The electrolytic cell comprises nine bar-shaped busbars 22, 22', which each contact the cathode 10 from the underside thereof in a current-feeding manner and each extend via their longitudinal direction in the width direction x of the electrolytic cell. The electrolytic cell additionally comprises two collector bars 24, 24', which are arranged such that each of these collector bars 24, 24' is connected to a respective end of all busbars 22, 22'. The collector bars 24, 24' accordingly run the longitudinal direction y in a manner laterally offset in relation to the cathode 10.
, , ' Each collector bar 24, 24' is associated with two external current feeds 26, 26' and 26", 26"' respectively, by means of which current is fed externally to the busbars 22, 22' arranged on the underside 14 of the cathode 10. Here, the external current feeds 26, 26', 26", 26"' are connected at respective connection points 28, 28', 28", 28"' to one of the collector bars 24, 24' and therefore at this point also indirectly to the busbars 22, 22' connected to said collector bar 24, 24'.
As can be seen from Fig. 4, the distances between the individual connection points 28, 28', 28", 28"' and the entry points of the individual busbars 22, 22' in the cathode 10, that is to say the electrical paths P1-P3, via which the electric current must flow from the individual connection points 28, 28' 28", 28"' to the entry points of the individual busbars 22, 22' into the edge regions 16, 16' of the cathode 10, are of different length. Here, a longitudinal portion 1,1-L9, of the cathode 10 which has a shorter electrical path P1-P3 to the connection point 28, 28', 28", 28"' closest to this longitudinal portion 1,1-L9 has a greater width b in its edge regions 16, 16' than a longitudinal portion 1,1-L9 of the cathode 10 having a longer electrical path to the connection point 28, 28', 28", 28"' closest to this longitudinal portion.
Equally, a longitudinal portion 1,1-L9 of the cathode 10 which has a shorter electrical path P1-P3 to the connection point 28, 28', 28", 28"' closest to this longitudinal portion 1,1-L9 has a smaller width b in its base region 18 than a longitudinal portion 1,1-L9 of the cathode 10 having a longer electrical path to the connection point 28, 28', 28", 28"' closest to this longitudinal portion.
, - 28 ' LIST OF REFERNCE SIGNS
cathode 12 upper side 14 underside 16, 16' edge regions 18 base region 20, 20' side wall region 22, 22' busbar 24, 24' collector bar 26, 26', 26", 26"' external current feed 28, 28', 28", 28"' connection point x, y, z width, longitudinal and vertical direction width 1 length height L1-L9 longitudinal portion Pi-P3 electrical path angle of inclination
Claims (18)
1. An electrolytic cell, in particular for producing aluminium, comprising a cathode (10), a layer of liquid aluminium arranged on the upper side (12) of the cathode (10), a melt layer on top thereof, an anode above the melt layer, at least one busbar and preferably at least two busbars (22, 22') contacting the cathode (10) from the underside (14) thereof in a current-feeding manner, and at least one external current feed (26, 26', 26", 26"'), wherein the at least one or each external current feed (26, 26', 26", 26'") is electrically conductively connected at a respective connection point (28, 28', 28", 28"') to at least one busbar and preferably at least two busbars (22, 22'), wherein the upper side (12) of the cathode (10), as considered in the cross section of the cathode (10), is tub-shaped, wherein the tub has two edge regions (16, 16') and a base region (18), which is arranged between the edge regions (16, 16') and is lowered relative to the edge regions (16, 16'), as viewed in the width direction (x) of the cathode (10), wherein, between each of the two edge regions (16, 16') and the base region (18), a side wall region (20, 20') connecting the corresponding edge region (16, 16') and the base region (18) is provided, wherein i) the width (b) of at least one of the base region (18) and the edge regions (16, 16') varies over the length of the cathode (10), and/or ii) the height (h) of the upper side (12) of the cathode (10) varies over the length of the cathode (10), as determined from the underside (14) of the cathode (10).
2. The electrolytic cell according to Claim 1, characterised in that at least one edge region (16, 16') of the cathode (10) comprises at least two longitudinal portions (L1-L9) each having a different width (b), wherein the longitudinal portion (L1-L9) of the edge region (16, 16') which is connected via the shortest electrical path (P1-P3) to the connection point (28, 28', 28", 28"') closest for it has the greatest width (b) of all longitudinal portions (L1-L9) of the edge region (16, 16').
3. The electrolytic cell according to at least one of the preceding claims, characterised in that at least one edge region (16, 16') of the cathode (10) comprises at least three longitudinal portions (L1-L9) each having a different width (b), wherein each of the longitudinal portions (L1-L9) which is connected to the closest connection point (28, 28', 28", 28"') via a longer electrical path (P1-P3) than another longitudinal portion (L1-L9) has a smaller width (b) than the other longitudinal portion (L1-1,9).
4. The electrolytic cell according to at least one of the preceding claims, characterised in that the base region (18) of the cathode (10) comprises at least two longitudinal portions (L1-L9) each having a different width (b), wherein the longitudinal portion (L1-1,9) of the base region (18) which is connected via the shortest electrical path (P1-P3) to the connection point (28, 28', 28", 28"') closest for it has the smallest width (b) of all longitudinal portions (L1-L9) of the base region (18).
- 3µ
- 3µ
5. The electrolytic cell according to at least one of the preceding claims, characterised in that the base region (18) of the cathode (10) comprises at least three longitudinal portions (L1-L9) each having a different width (b), wherein each of the longitudinal portions (L1-L9) which is connected to the connection point (28, 28', 28", 28"') closest for it via a longer electrical path (P1-P3) than another longitudinal portion (L1-L9) has a greater width (b) than the other longitudinal portion (L1-L9).
6. The electrolytic cell according to at least one of the preceding claims, characterised in that at least one edge region (16, 16') of the cathode (10) comprises at least two longitudinal portions (L1-L9) each having a different height (h), wherein the longitudinal portion (L1-L9) of the edge region (16, 16') of the cathode (10) which is connected via the shortest electrical path (P1-P3) to the closest connection point (28, 28', 28", 28"') has the greatest height (h) of all longitudinal portions (L1-L9) of the edge region (16, 16'), as determined from the underside (14) of the cathode (10), and/or the base region (18) of the cathode (10) comprises at least two longitudinal portions (L1-L9) each having a different height (h), wherein the longitudinal portion (L1-L9) of the base region (18) of the cathode (10) which is connected via the shortest electrical path (P1-P3) to the closest connection point (28, 28', 28", 28"') has the greatest height (h) of all longitudinal portions (L1-L9) of the base region (18), as determined from the underside (14) of the cathode (10).
7. The electrolytic cell according to Claim 6, characterised in that the edge region (16, 16') of the cathode (10) comprises at least three longitudinal portions (L1-L9) each having a different height (h), wherein each of the longitudinal portions (L1-L9) which is connected to the connection point (28, 28', 28", 28"') closest for it via a longer electrical path (P1-P3) than another longitudinal portion (L1-L9) has a smaller height (h) than the other longitudinal portion (L1-L9) and/or the base region (18) of the cathode (10) comprises at least three longitudinal portions (L1-L9) each having a different height (h), wherein each of the longitudinal portions (L1-L9) which is connected to the closest connection point (28, 28', 28", 28"') via a longer electrical path (P1-P3) than another longitudinal portion (L1-L9) has a smaller height (h) than the other longitudinal portion (L1-L9) .
8. The electrolytic cell according to at least one of the preceding claims, characterised in that the ratio of the maximum to minimum width (b) of at least one of the edge regions (16, 16') of the cathode (10) is between 2:1 and 1.05:1, preferably between 1.5:1 and 1.05:1 and more preferably between 1.3:1 and 1.05:1, and/or the ratio of the maximum to minimum height (h) of at least one of the edge regions (16, 16') of the cathode (10) is between 2:1 and 1.05:1, preferably between 1.5:1 and 1.05:1 and more preferably between 1.3:1 and 1.05:1, and/or the ratio of the maximum to minimum width (b) of the base region (18) of the cathode (10) is between 2:1 and 1.05:1, preferably between 1.5:1 and 1.05:1 and more preferably between 1.3:1 and 1.05:1, and/or the ratio of the maximum to minimum height (h) of the base region (18) of the cathode (10) is between 2:1 and 1.05:1, preferably between 1.5:1 and 1.05:1 and more preferably between 1.3:1 and 1.05:1.
9. The electrolytic cell according to at least one of the preceding claims, characterised in that the at least one busbar and preferably at least two busbars (22, 22') contacting the cathode (10) from the underside (14) thereof in a current-feeding manner are arranged parallel to one another and at a fixed distance from one another, extend over the entire width (b) of the cathode (10) and contact the cathode (10) from the underside (14) thereof in a current-feeding manner, wherein the individual busbars are each electrically conductively connected via one of their ends to a collector bar or via each of their ends to separate collector bars (24, 24'), and the collector bar(s) (24, 24') is/are electrically conductively connected to one or more external current feeds (26, 26', 26", 26"').
10. The electrolytic cell according to at least one of the preceding claims, characterised in that this comprises 2 to 60, preferably 10 to 48, more preferably 16 to 40, even more preferably 20 to 40 and most preferably 36 busbars (22, 22') arranged parallel to one another and at a fixed distance from one another, extending over the entire width (b) of the cathode (10) and contacting the cathode (10) from the underside (14) thereof in a current-feeding manner, and 2 to 6 external current feeds (26, 26', 26", 26"').
11. The electrolytic cell according to at least one of the preceding claims, characterised in that the cathode (10) is comprised of 2 to 60, preferably 10 to 48, more preferably 16 to 40, even more preferably 20 to 40, and most preferably 36 cathode blocks arranged side by side, wherein each of the cathode blocks on its underside has at least one groove which extends in the longitudinal direction of the cathode block or in the width direction (x) of the cathode (10) and in which at least one busbar (22, 22') is arranged.
12. The electrolytic cell according to Claim 11, characterised in that each of the grooves has a rectangular cross section and a depth varying over its length, wherein each of the grooves at the longitudinal-side end thereof has a shallower depth than in the centre thereof.
13. The electrolytic cell according to at least one of the preceding claims, characterised in that at least one of the two edge regions (16, 16') and preferably both edge regions (16, 16') runs/run in a manner sloping downwardly towards the centre of the cathode (10), as considered in the width direction (x) of the cathode (10), wherein the angle of inclination (0) of the edge region (16, 16') or the edge regions (16, 16') is preferably between 2° and 45°, more preferably between 3° and 20° and even more preferably between 10° and 15°
with respect to the horizontal plane.
with respect to the horizontal plane.
14. The electrolytic cell according to at least one of the preceding claims, characterised in that at least one of the two edge regions (16, 16') and preferably both of the edge regions (16, 16') runs/run in a manner sloping downwardly towards the centre of the cathode (10) over at least 30 %, preferably over at least 50 %, more preferably over at least 75 % and even more preferably over 100 % of the width (b) thereof, as considered in the cross section of the cathode (10) and in the width direction (x) of the cathode (10).
15. The electrolytic cell according to at least one of the preceding claims, characterised in that the base region (18) runs in a planar manner at least in regions, wherein the surface of the base region (18) has an angle between -20° and 20°, preferably between -10° and 10° and more preferably of 0° with respect to the plane running in the vertical direction (z).
16. The electrolytic cell according to at least one of the preceding claims, characterised in that the upper side (12) of the cathode (10) is tub-shaped, as considered in the cross section of the cathode (10), over at least 25 %, preferably at least 50 %, in particular preferably at least 75 %, more preferably at least 90 % and most preferably approximately 100 % of the length of the cathode (10), wherein the tub has two edge regions (16, 16') and a base region (18), which is arranged between the edge regions (16, 16') and which is lowered relative to the edge regions (16, 16'), as viewed in the width direction (x) of the cathode (10), wherein, between each of the two edge regions (16, 16') and the base region (18), a side wall region (20, 20') connecting the corresponding edge region (16, 16') and the base region (18) is provided.
17. The electrolytic cell according to Claim 16, characterised in that i) the width (b) of at least one of the base region (18) and the edge regions (16, 16') varies over at least 25 %, preferably at least 50 %, in particular preferably at least 75 %, more preferably at least 90 % and most preferably approximately 100 % of the length of the cathode (10), and/or ii) the height (h) of the upper side (12) of the cathode (10), as determined from the underside (14) of the cathode (10), varies over at least 25 %, preferably at least 50 %, in particular preferably at least 75 %, more preferably at least 90 % and most preferably approximately 100 % of the length of the cathode (10).
18. A cathode for an electrolytic cell, in particular for an electrolytic cell for producing aluminium, wherein the upper side (12) of the cathode (10) is tub-shaped, as considered in the cross section of the cathode (10), wherein the tub has two edge regions (16, 16') and a base region (18), which is arranged between the edge regions (16, 16') and is lowered relative to the edge regions (16, 16'), as viewed in the width direction (x) of the cathode (10), wherein, between each of the two edge regions (16, 16') and the base region (18), a side wall region (20, 20') connecting the corresponding edge region (16, 16') and the base region (18) is provided, wherein i) the width (b) of at least one of the base region (18) and the edge regions (16, 16') varies over the length of the cathode (10), and/or ii) the height (h) of the upper side (12) of the cathode (10), as determined from the underside (14) of the cathode (10), varies over the length of the cathode (10).
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE201110086040 DE102011086040A1 (en) | 2011-11-09 | 2011-11-09 | Electrolysis cell, in particular for the production of aluminum, with a trough-shaped cathode |
| DE102011086040.1 | 2011-11-09 | ||
| PCT/EP2012/072170 WO2013068485A1 (en) | 2011-11-09 | 2012-11-08 | Electrolytic cell, in particular for producing aluminum, having a tub-shaped cathode |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2854937A1 true CA2854937A1 (en) | 2013-05-16 |
Family
ID=47221338
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2854937A Abandoned CA2854937A1 (en) | 2011-11-09 | 2012-11-08 | Electrolytic cell, in particular for producing aluminum, having a tub-shaped cathode |
Country Status (8)
| Country | Link |
|---|---|
| EP (1) | EP2776609A1 (en) |
| JP (1) | JP2014532817A (en) |
| CN (1) | CN103958739A (en) |
| CA (1) | CA2854937A1 (en) |
| DE (1) | DE102011086040A1 (en) |
| IN (1) | IN2014CN03393A (en) |
| RU (1) | RU2014123000A (en) |
| WO (1) | WO2013068485A1 (en) |
Family Cites Families (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NO122558B (en) * | 1968-03-26 | 1971-07-12 | Montedison Spa | |
| CA2287362A1 (en) * | 1997-05-23 | 1998-11-26 | Moltech Invent S.A. | Aluminium production cell and cathode |
| DE69837966T2 (en) * | 1997-07-08 | 2008-02-28 | Moltech Invent S.A. | CELL FOR ALUMINUM MANUFACTURE WITH DRAINABLE CATHODE |
| EP1233083A1 (en) * | 2001-02-14 | 2002-08-21 | Alcan Technology & Management AG | Carbon bottom of electrolysis cell used in the production of aluminum |
| 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 |
| CN201049966Y (en) * | 2007-05-23 | 2008-04-23 | 冯乃祥 | Abnormal structure cathode carbon block of aluminum electrolysis bath |
| CN101413136B (en) * | 2008-10-10 | 2010-09-29 | 沈阳北冶冶金科技有限公司 | Novel cathode structured aluminum cell with longitudinal and transversal wave damping functions |
| CN201411494Y (en) * | 2009-03-10 | 2010-02-24 | 彭稳乐 | Chinese-character-feng-shaped stepped cathodic carbon block of aluminum reduction cell |
| DE102010039638B4 (en) * | 2010-08-23 | 2015-11-19 | Sgl Carbon Se | Cathode, apparatus for aluminum extraction and use of the cathode in aluminum production |
| CN201873762U (en) * | 2010-11-26 | 2011-06-22 | 贵阳铝镁设计研究院 | Cathode block with protective cover |
| DE102011004010A1 (en) * | 2011-02-11 | 2012-08-16 | Sgl Carbon Se | Cathode arrangement with a surface profiled cathode block with a groove of variable depth |
-
2011
- 2011-11-09 DE DE201110086040 patent/DE102011086040A1/en not_active Withdrawn
-
2012
- 2012-11-08 JP JP2014540469A patent/JP2014532817A/en not_active Withdrawn
- 2012-11-08 CN CN201280055258.0A patent/CN103958739A/en active Pending
- 2012-11-08 CA CA2854937A patent/CA2854937A1/en not_active Abandoned
- 2012-11-08 IN IN3393CHN2014 patent/IN2014CN03393A/en unknown
- 2012-11-08 WO PCT/EP2012/072170 patent/WO2013068485A1/en active Application Filing
- 2012-11-08 RU RU2014123000/02A patent/RU2014123000A/en not_active Application Discontinuation
- 2012-11-08 EP EP12790471.2A patent/EP2776609A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| CN103958739A (en) | 2014-07-30 |
| IN2014CN03393A (en) | 2015-07-03 |
| JP2014532817A (en) | 2014-12-08 |
| EP2776609A1 (en) | 2014-09-17 |
| DE102011086040A1 (en) | 2013-05-16 |
| RU2014123000A (en) | 2015-12-20 |
| WO2013068485A1 (en) | 2013-05-16 |
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| EEER | Examination request |
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| FZDE | Discontinued |
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