CA2910088C - Cathode block having a slot with a varying depth and a filled intermediate space - Google Patents
Cathode block having a slot with a varying depth and a filled intermediate space Download PDFInfo
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- CA2910088C CA2910088C CA2910088A CA2910088A CA2910088C CA 2910088 C CA2910088 C CA 2910088C CA 2910088 A CA2910088 A CA 2910088A CA 2910088 A CA2910088 A CA 2910088A CA 2910088 C CA2910088 C CA 2910088C
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
- C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
- C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
- C25C3/16—Electric current supply devices, e.g. bus bars
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
- C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
- C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
- C25C3/08—Cell construction, e.g. bottoms, walls, cathodes
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Abstract
A cathode block for an aluminium electrolysis cell based on carbon and/or graphite, wherein the cathode block has at least one slot which extends in the longitudinal direction of the cathode block, wherein at least one of the at least one slots has a depth which varies, as seen over the length of the cathode block, and at least one busbar is provided in the at least one slot, wherein the intermediate space between the at least one busbar and the wall which bounds the at least one slot with a varying depth is at least partially filled with steel.
Description
CATHODE BLOCK HAVING A SLOT WITH A VARYING DEPTH AND A FILLED
INTERMEDIATE SPACE
The present invention relates to a cathode block for an aluminum electrolysis cell, to its utilization and also to a cathode comprising it.
Electrolysis cells are for example used for the electrolytic production of aluminum which, on the industrial scale, is usually carried out according to the Hall-Heroult process. In the Hall-Heroult process, a molten mixture of aluminum oxide and cryolite is electrolyzed. Here, the cryolite, Na3[AlF6], is used to lower the melting point of 2045 C for pure aluminum oxide to approx. 950 C for a mixture containing a cryolite, aluminum oxide and additional substances, such as aluminum fluoride and calcium fluoride.
The electrolysis cell used in this process comprisese a cathode bottom which is composed of a plurality of, for example, up to 28 adjacent cathode blocks forming the cathode. Here, the intermediate spaces between the cathode blocks are usually filled with a carbonaceous ramming paste in order to seal the cathode against molten constituents of the electrolysis cell and in order to compensate for mechanical stresses which arise as the electrolysis cell is put into operation. The cathode blocks are usually made of a carbonaceous material, such as graphite, in order to withstand the thermal and chemical conditions prevailing when the cell is in operation. The undersides of the cathode blocks are usually provided with slots in each of which one or two busbars are arranged through which the current supplied via the anodes is discharged. Here, the intermediate spaces between the busbars and the individual cathode block walls bounding the slots are often filled with cast iron so that the encasement of the busbars with cast iron thus created connects the busbars to the cathode blocks electrically and mechanically. About 3 to 5 cm above the layer of liquid aluminum on the top side of the cathode, which is usually 15 to 50 cm thick, there is an anode, in particular formed of individual anode blocks. The electrolyte, in other words, the molten mass containing aluminum oxide and cryolite, is found between this anode and the surface of the aluminum. During electrolysis, which is carried out at approximately 1000 C, the aluminum thus formed, being denser than the electrolyte, settles below the electrolyte layer - in other words, as an intermediate layer between the top side of the cathode and the electrolyte layer. In electrolysis, the aluminum oxide dissolved in the molten mass is broken down into aluminum and oxygen by the electrical current flow. From the electrochemical point of view, the layer of liquid aluminum is the actual cathode since aluminum ions are reduced to elemental aluminum on its surface.
Nonetheless, in what follows, the term cathode will not refer to the cathode from the electrochemical point of view, in
INTERMEDIATE SPACE
The present invention relates to a cathode block for an aluminum electrolysis cell, to its utilization and also to a cathode comprising it.
Electrolysis cells are for example used for the electrolytic production of aluminum which, on the industrial scale, is usually carried out according to the Hall-Heroult process. In the Hall-Heroult process, a molten mixture of aluminum oxide and cryolite is electrolyzed. Here, the cryolite, Na3[AlF6], is used to lower the melting point of 2045 C for pure aluminum oxide to approx. 950 C for a mixture containing a cryolite, aluminum oxide and additional substances, such as aluminum fluoride and calcium fluoride.
The electrolysis cell used in this process comprisese a cathode bottom which is composed of a plurality of, for example, up to 28 adjacent cathode blocks forming the cathode. Here, the intermediate spaces between the cathode blocks are usually filled with a carbonaceous ramming paste in order to seal the cathode against molten constituents of the electrolysis cell and in order to compensate for mechanical stresses which arise as the electrolysis cell is put into operation. The cathode blocks are usually made of a carbonaceous material, such as graphite, in order to withstand the thermal and chemical conditions prevailing when the cell is in operation. The undersides of the cathode blocks are usually provided with slots in each of which one or two busbars are arranged through which the current supplied via the anodes is discharged. Here, the intermediate spaces between the busbars and the individual cathode block walls bounding the slots are often filled with cast iron so that the encasement of the busbars with cast iron thus created connects the busbars to the cathode blocks electrically and mechanically. About 3 to 5 cm above the layer of liquid aluminum on the top side of the cathode, which is usually 15 to 50 cm thick, there is an anode, in particular formed of individual anode blocks. The electrolyte, in other words, the molten mass containing aluminum oxide and cryolite, is found between this anode and the surface of the aluminum. During electrolysis, which is carried out at approximately 1000 C, the aluminum thus formed, being denser than the electrolyte, settles below the electrolyte layer - in other words, as an intermediate layer between the top side of the cathode and the electrolyte layer. In electrolysis, the aluminum oxide dissolved in the molten mass is broken down into aluminum and oxygen by the electrical current flow. From the electrochemical point of view, the layer of liquid aluminum is the actual cathode since aluminum ions are reduced to elemental aluminum on its surface.
Nonetheless, in what follows, the term cathode will not refer to the cathode from the electrochemical point of view, in
2 , , , other words, the layer of liquid aluminum, but rather to the component composed, for example, of one or more cathode blocks and forming the bottom of the electrolysis cell.
One major disadvantage of the cathode arrangements used in the Hall-Heroult process is their comparatively poor resistance to wear, which manifests itself as a removal of material from cathode block surfaces during electrolysis. Here, due to a heterogeneous distribution of current within the cathode blocks, material is not removed evenly from the cathode block surfaces over the length of the cathode blocks but to a greater extent at the ends of the cathode blocks with the result that after electrolysis has proceeded for a certain amount of time, the surfaces of the cathode blocks assume a W-shaped profile. Due to the uneven removal of material from the cathode block surfaces, the useful life of the cathode blocks is limited by the locations with the greatest removal of material.
In order to combat this problem, a cathode block is proposed in WO 2007/118510 A2 whose slot, intended to accommodate one or more busbars, has with respect to the cathode block length a greater depth in the center than at the cathode block ends. In the operation of the electrolysis cell, this results in an essentially homogeneous vertical current distribution over the cathode block length, whereby the higher wear at the cathode block ends is reduced and the service life of the cathode thus extended. Here, the busbar(s) is or are encased in cast iron in the usual way, whereby this encasement is effected by pouring liquid cast iron into the intermediate space between the slot and the busbar(s). A cathode block of this kind is however encumbered with disadvantages. While the liquid cast iron is being poured into the intermediate space between the slot and the busbar(s) and afterwards, while the electrolysis cell comprising the cathode block is being put into operation and afterwards, while the electrolysis cell is being switched off and subsequently restarted and afterwards, the cathode block is exposed to comparatively large temperature changes which lead to the cast iron and the busbar(s) expanding or contracting relative to the cathode block. This effect of expansion or contraction can be amplified by the temperature gradients which occur. When the phrase 'large temperature change(s)' is used in what follows, it should be understood as indicating that one or both of the effects mentioned - in other words, expansion /
contraction or temperature gradient - is or are present. Since cast iron and the material of the busbar(s) have a higher coefficient of thermal expansion than the cathode block material, when there is a temperature increase, the cast iron and the busbar(s) expand relative to the cathode block while a temperature decrease on the other hand results in them contracting relative to the cathode block. This causes a deterioration in the electrical contact between busbar, cast iron and cathode block, especially in the case of the usual slots with their rectangular cross-section, and this in turn results in a higher electrical resistance of the arrangement and thus a
One major disadvantage of the cathode arrangements used in the Hall-Heroult process is their comparatively poor resistance to wear, which manifests itself as a removal of material from cathode block surfaces during electrolysis. Here, due to a heterogeneous distribution of current within the cathode blocks, material is not removed evenly from the cathode block surfaces over the length of the cathode blocks but to a greater extent at the ends of the cathode blocks with the result that after electrolysis has proceeded for a certain amount of time, the surfaces of the cathode blocks assume a W-shaped profile. Due to the uneven removal of material from the cathode block surfaces, the useful life of the cathode blocks is limited by the locations with the greatest removal of material.
In order to combat this problem, a cathode block is proposed in WO 2007/118510 A2 whose slot, intended to accommodate one or more busbars, has with respect to the cathode block length a greater depth in the center than at the cathode block ends. In the operation of the electrolysis cell, this results in an essentially homogeneous vertical current distribution over the cathode block length, whereby the higher wear at the cathode block ends is reduced and the service life of the cathode thus extended. Here, the busbar(s) is or are encased in cast iron in the usual way, whereby this encasement is effected by pouring liquid cast iron into the intermediate space between the slot and the busbar(s). A cathode block of this kind is however encumbered with disadvantages. While the liquid cast iron is being poured into the intermediate space between the slot and the busbar(s) and afterwards, while the electrolysis cell comprising the cathode block is being put into operation and afterwards, while the electrolysis cell is being switched off and subsequently restarted and afterwards, the cathode block is exposed to comparatively large temperature changes which lead to the cast iron and the busbar(s) expanding or contracting relative to the cathode block. This effect of expansion or contraction can be amplified by the temperature gradients which occur. When the phrase 'large temperature change(s)' is used in what follows, it should be understood as indicating that one or both of the effects mentioned - in other words, expansion /
contraction or temperature gradient - is or are present. Since cast iron and the material of the busbar(s) have a higher coefficient of thermal expansion than the cathode block material, when there is a temperature increase, the cast iron and the busbar(s) expand relative to the cathode block while a temperature decrease on the other hand results in them contracting relative to the cathode block. This causes a deterioration in the electrical contact between busbar, cast iron and cathode block, especially in the case of the usual slots with their rectangular cross-section, and this in turn results in a higher electrical resistance of the arrangement and thus a
3 poor energy efficiency of the electrolytic process. Apart from this, before the liquid cast iron is poured into the intermediate space between the slot and the busbar(s), the busbar(s) are movable not only vertically but also horizontally such that they can move uncontrollably in the slot while the liquid cast iron is being poured in and then while the cast iron is cooling down and solidifying. This can also result in an uneven electrical contact between busbar, cast iron and cathode block. This too results in a higher electrical resistance of the arrangement and thus to poor energy efficiency of the electrolytic process.
Ramming paste can also be used instead of cast iron. Ramming pastes based on anthracite, graphite or any mixture thereof can be used as a ramming paste. Preferably a graphite-based ramming paste is used.
When cast iron is mentioned hereinafter, it is to be understood that ramming paste can be substituted for the cast iron without this being stated explicitly each time.
An aspect of the present disclosure is directed to the provision of a cathode block suitable in particular for use in an aluminum electrolysis cell with which an essentially homogeneous vertical current distribution is achieved over the length of the cathode block while the electrolysis cell is in operation, which also has, even with large temperature changes, a low specific electrical resistance and in particular over an extended period of electrolysis a permanently low specific electrical resistance and a low transition resistance between the busbar and the cathode block, and which in the case of large temperature changes is robust with regard to mechanical damage, such as cracking.
According to an aspect of the present invention, there is provided a cathode block for an aluminum electrolysis cell on the basis of carbon or graphite, wherein the cathode block has at least one slot extending in the longitudinal direction of the cathode block, wherein at least one of the at least one slot has a varying depth when viewed over the length of the cathode block and in the at least one slot a busbar is provided, wherein the intermediate space between the at least one busbar and the wall bounding the at least one slot of varying depth is at least partially filled with steel, wherein the steel is selected from the group consisting of steel having a low carbon content of < 0.1 %, a silicon content of < 0.1 % and a phosphorus content of < 0.05 %, metals, alloys, composites of the aforementioned materials, metal-infiltrated graphite or carbon materials or electrically conductive masses.
3a According to another aspect of the present invention, there is provided a cathode arrangement containing at least one cathode block as described above.
According to another aspect of the present invention, there is provided use of a cathode arrangement as described above for carrying out a fused-salt electrolysis to produce metal.
According to an aspect of the invention, there is provided a cathode block for an aluminum electrolysis cell on the basis of carbon and / or graphite, wherein the cathode block has at least one slot extending in the longitudinal direction of the cathode block, wherein at least one of the at least one slot has a varying depth when viewed over the length of the cathode block and in the at least one slot at least one busbar is provided, wherein the intermediate space between the at least one busbar and the wall bounding the at least one slot of varying depth is at least partially filled with steel. Within the intention of the present invention, instead of steel another suitable metal can also be used, such as for example other metals such as copper or silver, alloys, composite materials of the aforementioned materials, such as for example steel bodies with a copper core, composite materials such as for example metal-infiltrated graphite or carbon materials or electrically conductive masses. As metal, any metal can be used in said metal-infiltrated graphite or carbon materials which has a melting point above the operating temperature of the electrolysis cell which is at around 1000 C. Copper with a melting point of 1080 C constitutes a preferred metal. The proportion of metal in the composite material may lie between 40% and 90% by weight. The carbon in the composite material can be anthracite and
Ramming paste can also be used instead of cast iron. Ramming pastes based on anthracite, graphite or any mixture thereof can be used as a ramming paste. Preferably a graphite-based ramming paste is used.
When cast iron is mentioned hereinafter, it is to be understood that ramming paste can be substituted for the cast iron without this being stated explicitly each time.
An aspect of the present disclosure is directed to the provision of a cathode block suitable in particular for use in an aluminum electrolysis cell with which an essentially homogeneous vertical current distribution is achieved over the length of the cathode block while the electrolysis cell is in operation, which also has, even with large temperature changes, a low specific electrical resistance and in particular over an extended period of electrolysis a permanently low specific electrical resistance and a low transition resistance between the busbar and the cathode block, and which in the case of large temperature changes is robust with regard to mechanical damage, such as cracking.
According to an aspect of the present invention, there is provided a cathode block for an aluminum electrolysis cell on the basis of carbon or graphite, wherein the cathode block has at least one slot extending in the longitudinal direction of the cathode block, wherein at least one of the at least one slot has a varying depth when viewed over the length of the cathode block and in the at least one slot a busbar is provided, wherein the intermediate space between the at least one busbar and the wall bounding the at least one slot of varying depth is at least partially filled with steel, wherein the steel is selected from the group consisting of steel having a low carbon content of < 0.1 %, a silicon content of < 0.1 % and a phosphorus content of < 0.05 %, metals, alloys, composites of the aforementioned materials, metal-infiltrated graphite or carbon materials or electrically conductive masses.
3a According to another aspect of the present invention, there is provided a cathode arrangement containing at least one cathode block as described above.
According to another aspect of the present invention, there is provided use of a cathode arrangement as described above for carrying out a fused-salt electrolysis to produce metal.
According to an aspect of the invention, there is provided a cathode block for an aluminum electrolysis cell on the basis of carbon and / or graphite, wherein the cathode block has at least one slot extending in the longitudinal direction of the cathode block, wherein at least one of the at least one slot has a varying depth when viewed over the length of the cathode block and in the at least one slot at least one busbar is provided, wherein the intermediate space between the at least one busbar and the wall bounding the at least one slot of varying depth is at least partially filled with steel. Within the intention of the present invention, instead of steel another suitable metal can also be used, such as for example other metals such as copper or silver, alloys, composite materials of the aforementioned materials, such as for example steel bodies with a copper core, composite materials such as for example metal-infiltrated graphite or carbon materials or electrically conductive masses. As metal, any metal can be used in said metal-infiltrated graphite or carbon materials which has a melting point above the operating temperature of the electrolysis cell which is at around 1000 C. Copper with a melting point of 1080 C constitutes a preferred metal. The proportion of metal in the composite material may lie between 40% and 90% by weight. The carbon in the composite material can be anthracite and
4 the graphite composite material can contain graphitized or graphitic carbon as graphite. The term steel will hereinafter be used in this regard for all of these materials.
According to the invention, it was recognized that due to the at least partial filling of the intermediate space which, due to the installation of a bar-shaped busbar in the slot of a cathode block, said slot having a varying depth when viewed along the length of the cathode block, is formed between the busbar and the wall bounding the at least one slot of varying depth, a cathode arrangement is created simply and cheaply with steel, which due to the slot of varying depth over the length of the cathode arrangement is characterized by an essentially homogeneous vertical current distribution and has at the same time, despite the slot of varying depth, a permanently low electrical resistance and low transition resistance between the busbar and the cathode block, and which in the case of large temperature changes is robust as regards mechanical damage, such as cracking. In the cathode arrangements known from the prior art, the additional volume of the intermediate space, which arises with use of a conventional bar-shaped busbar due to the depth of the slot varying over the length of the cathode block, is filled entirely or partially with cast iron. A greater quantity of cast iron does however mean a higher heat input when the cast iron is poured in and this results in increased thermal stresses, due to which cracks can form in the cathode block, namely in some circumstances not forming until electrolysis is in progress, which can result in poor operational behavior or even in premature failure of the entire electrolysis cell.
Furthermore, such a voluminous layer of cast iron results in a poor electrical contact between the busbar and the cathode block via the interjacent cast iron since the cast-iron layer between the time of its solidification until the operation of the electrolysis cell undergoes a net shrinkage since the operating temperature of the electrolysis cell at 850 to 950 C is considerably below the solidification temperature of cast iron of about 1150 C. It has admittedly already been proposed in WO 2007/118510 A2 to overcome these disadvantages by at least partially filling the intermediate space with steel plates or even by using a busbar with a geometry matched to the shape of the slot. However, these solutions involve a greater outlay as regards the process technology. In particular, furthermore, manufacturing a busbar with a geometry matched to the shape of the slot is expensive. By the intermediate space being filled according to the invention with steel, in other words with the material of which conventional busbars are made, this material behaves like the busbar in the case of temperature changes and in particular with abrupt temperature changes so that a net shrinkage is reliably prevented and a poor electrical contact in the intermediate space is thereby reliably prevented.
The intermediate space can be filled by one or more filling materials made of steel, which can be made separately by casting, rolling, milling or other suitable shaping methods. This means that the solution according to the invention can be realized particularly simply, rapidly and inexpensively.
According to some embodiments of the present invention, at least 50% of the intermediate space is filled with steel, preferably at least 75%, especially preferably at least 90%, more especially preferably at least 95%, extremely preferably at least 98% and maximally preferably 100%.
In some embodiments, in a development of the inventive concept, it is proposed that the steel with which the intermediate space is at least partially filled is preferably the same as that of which the at least one busbar is composed. In this case, the coefficients of thermal expansion of the two materials are the same so that mechanical stresses between the busbar and the steel with which the intermediate space is at least partially filled are reliably minimized during the heating up to set the operating temperature of the electrolysis cell.
Preferably steel with a very high electrical conductivity is used here as material for the busbars and the shaped bodies filling the intermediate space. This steel is characterized for example by a low carbon content of <0.1%, a silicon content of <0.1% and a phosphorus content of <0.05%.
According to some embodiments of the present invention, at least 50% of the intermediate space is filled with steel, preferably at least 75%, especially preferably at least 90%, more especially preferably at least 95% and extremely preferably at least 98%, and cast iron is provided between the steel and the wall bounding the at least one slot of varying depth. The cast iron creates a good mechanical connection between on the one hand the steel with which the intermediate space is at least partially filled and the at least one busbar and on the other hand the cathode block of the cathode arrangement, wherein due to the steel with which the intermediate space is at least 50% filled and preferably at least 90% filled, comparatively small quantities of cast iron are required so that the disadvantages previously described with regard to filling the intermediate space entirely with cast iron are at least to the greatest possible extent overcome.
According to a further embodiment of the present invention, at least 50% of the intermediate space is filled with steel, preferably at least 75%, and especially preferably at least 90%, wherein one or more steel plates or balls are provided between the busbar and the wall bounding the at least one slot of varying depth.
In some embodiments, in order to achieve an especially even vertical current density distribution at the cathode block surface during the electrolytic process, it is proposed in a development of the inventive concept that at least one of the at least one slot or preferably all of the slots of varying depth has or have at its or their longitudinal ends less depth than at its or their center(s).
In this way, an even distribution of the electrical current supplied during electrolysis operation is achieved over the entire length of the cathode block, whereby an excessively high electrical current density is avoided at the longitudinal ends of the cathode block and thus premature wear at the ends of the cathode block is prevented. Due to such an even current density distribution over the length of the cathode block, movements in the aluminum melt caused by the interaction of electromagnetic fields during electrolysis are avoided, whereby is becomes possible to arrange the anode at a lower height above the surface of the aluminum melt. This reduces the electrical resistance between the anode and the aluminum melt and boosts the energy efficiency of the fused-salt electrolysis being carried out.
In some embodiments, preferably each of the at least one slot has a cross-section which is at least essentially rectangular, preferably rectangular.
In some embodiments, it is equally preferred that the at least one busbar is at least essentially cuboid or bar-shaped, preferably cuboid or bar-shaped.
According to some embodiments of the present invention, the cathode block according to the invention is thereby obtainable and is especially preferably obtained in that a cathode block with at least one slot of varying depth when viewed over the length of the cathode block is provided, that at least one preferably bar-shaped busbar is inserted into the at least one slot, that the intermediate space between the at least one busbar and the wall bounding the at least one slot of varying depth is at least partially filled with one or more shaped bodies made of steel.
With this embodiment, it is especially preferable for the reasons given above for only a part of the intermediate space to be filled with one or more shaped bodies made of steel, such as for example at least 50%, preferably at least 75%, and especially preferably at least 90%, and between them and the cathode block wall bounding the at least one slot of varying depth for molten cast iron to be placed and the molten cast iron allowed to solidify.
A further subject matter of the present invention is a cathode arrangement which comprises at least one previously described cathode block.
Finally, the present invention relates to the use of a previously described cathode arrangement for carrying out a fused-salt electrolysis to produce metal, preferably to produce aluminum.
In what follows, the present invention is described purely by way of example by means of an advantageous embodiment and with reference to the accompanying drawing.
Here Fig. 1 shows a longitudinal section of a cathode arrangement in accordance with an embodiment of the present invention.
Fig. 1 shows a longitudinal section of a cathode arrangement 12' in accordance with an embodiment of the present invention, namely inverted. The cathode arrangement 12' comprises a cathode block 20 in whose bottom a slot 26 is provided whose depth varies over the length of the slot 26, namely in such a way that the slot 26 has a shallower depth at its longitudinal end than at its center. The difference between the slot depth at the longitudinal ends of the slot 26 and at the center - with respect to the longitudinal direction of the cathode block - of the slot 26 amounts in the present exemplary embodiment to about 5 cm. Here, the depth of the slot 26 at the two longitudinal ends of the slot 26 is about 16 cm while on the other hand the depth of the slot 26 at the center - with respect to the longitudinal direction of the cathode block -of the slot 26 is about 21 cm. The width 44 of each slot 26 is essentially constant over the entire slot length and measures approximately 15 cm while on the other hand the width 46 of the cathode blocks 20 in each case measures about 42 cm. A bar-shaped busbar 28 with a rectangular longitudinal section is arranged in the slot 26 wherein between the busbar 28 and the slot bottom 34, there is an intermediate space 56 which becomes larger towards the center of the slot 26.
According to the invention, this intermediate space 56 is at least partially and in the case shown in Fig. 1 is entirely filled with steel, namely with the same steel as that of which the busbar 28 is made.
' List of reference numbers 12, 12 cathode arrangement 20 cathode block 26 slot 28 busbar 34 bottom wall 56 intermediate space
According to the invention, it was recognized that due to the at least partial filling of the intermediate space which, due to the installation of a bar-shaped busbar in the slot of a cathode block, said slot having a varying depth when viewed along the length of the cathode block, is formed between the busbar and the wall bounding the at least one slot of varying depth, a cathode arrangement is created simply and cheaply with steel, which due to the slot of varying depth over the length of the cathode arrangement is characterized by an essentially homogeneous vertical current distribution and has at the same time, despite the slot of varying depth, a permanently low electrical resistance and low transition resistance between the busbar and the cathode block, and which in the case of large temperature changes is robust as regards mechanical damage, such as cracking. In the cathode arrangements known from the prior art, the additional volume of the intermediate space, which arises with use of a conventional bar-shaped busbar due to the depth of the slot varying over the length of the cathode block, is filled entirely or partially with cast iron. A greater quantity of cast iron does however mean a higher heat input when the cast iron is poured in and this results in increased thermal stresses, due to which cracks can form in the cathode block, namely in some circumstances not forming until electrolysis is in progress, which can result in poor operational behavior or even in premature failure of the entire electrolysis cell.
Furthermore, such a voluminous layer of cast iron results in a poor electrical contact between the busbar and the cathode block via the interjacent cast iron since the cast-iron layer between the time of its solidification until the operation of the electrolysis cell undergoes a net shrinkage since the operating temperature of the electrolysis cell at 850 to 950 C is considerably below the solidification temperature of cast iron of about 1150 C. It has admittedly already been proposed in WO 2007/118510 A2 to overcome these disadvantages by at least partially filling the intermediate space with steel plates or even by using a busbar with a geometry matched to the shape of the slot. However, these solutions involve a greater outlay as regards the process technology. In particular, furthermore, manufacturing a busbar with a geometry matched to the shape of the slot is expensive. By the intermediate space being filled according to the invention with steel, in other words with the material of which conventional busbars are made, this material behaves like the busbar in the case of temperature changes and in particular with abrupt temperature changes so that a net shrinkage is reliably prevented and a poor electrical contact in the intermediate space is thereby reliably prevented.
The intermediate space can be filled by one or more filling materials made of steel, which can be made separately by casting, rolling, milling or other suitable shaping methods. This means that the solution according to the invention can be realized particularly simply, rapidly and inexpensively.
According to some embodiments of the present invention, at least 50% of the intermediate space is filled with steel, preferably at least 75%, especially preferably at least 90%, more especially preferably at least 95%, extremely preferably at least 98% and maximally preferably 100%.
In some embodiments, in a development of the inventive concept, it is proposed that the steel with which the intermediate space is at least partially filled is preferably the same as that of which the at least one busbar is composed. In this case, the coefficients of thermal expansion of the two materials are the same so that mechanical stresses between the busbar and the steel with which the intermediate space is at least partially filled are reliably minimized during the heating up to set the operating temperature of the electrolysis cell.
Preferably steel with a very high electrical conductivity is used here as material for the busbars and the shaped bodies filling the intermediate space. This steel is characterized for example by a low carbon content of <0.1%, a silicon content of <0.1% and a phosphorus content of <0.05%.
According to some embodiments of the present invention, at least 50% of the intermediate space is filled with steel, preferably at least 75%, especially preferably at least 90%, more especially preferably at least 95% and extremely preferably at least 98%, and cast iron is provided between the steel and the wall bounding the at least one slot of varying depth. The cast iron creates a good mechanical connection between on the one hand the steel with which the intermediate space is at least partially filled and the at least one busbar and on the other hand the cathode block of the cathode arrangement, wherein due to the steel with which the intermediate space is at least 50% filled and preferably at least 90% filled, comparatively small quantities of cast iron are required so that the disadvantages previously described with regard to filling the intermediate space entirely with cast iron are at least to the greatest possible extent overcome.
According to a further embodiment of the present invention, at least 50% of the intermediate space is filled with steel, preferably at least 75%, and especially preferably at least 90%, wherein one or more steel plates or balls are provided between the busbar and the wall bounding the at least one slot of varying depth.
In some embodiments, in order to achieve an especially even vertical current density distribution at the cathode block surface during the electrolytic process, it is proposed in a development of the inventive concept that at least one of the at least one slot or preferably all of the slots of varying depth has or have at its or their longitudinal ends less depth than at its or their center(s).
In this way, an even distribution of the electrical current supplied during electrolysis operation is achieved over the entire length of the cathode block, whereby an excessively high electrical current density is avoided at the longitudinal ends of the cathode block and thus premature wear at the ends of the cathode block is prevented. Due to such an even current density distribution over the length of the cathode block, movements in the aluminum melt caused by the interaction of electromagnetic fields during electrolysis are avoided, whereby is becomes possible to arrange the anode at a lower height above the surface of the aluminum melt. This reduces the electrical resistance between the anode and the aluminum melt and boosts the energy efficiency of the fused-salt electrolysis being carried out.
In some embodiments, preferably each of the at least one slot has a cross-section which is at least essentially rectangular, preferably rectangular.
In some embodiments, it is equally preferred that the at least one busbar is at least essentially cuboid or bar-shaped, preferably cuboid or bar-shaped.
According to some embodiments of the present invention, the cathode block according to the invention is thereby obtainable and is especially preferably obtained in that a cathode block with at least one slot of varying depth when viewed over the length of the cathode block is provided, that at least one preferably bar-shaped busbar is inserted into the at least one slot, that the intermediate space between the at least one busbar and the wall bounding the at least one slot of varying depth is at least partially filled with one or more shaped bodies made of steel.
With this embodiment, it is especially preferable for the reasons given above for only a part of the intermediate space to be filled with one or more shaped bodies made of steel, such as for example at least 50%, preferably at least 75%, and especially preferably at least 90%, and between them and the cathode block wall bounding the at least one slot of varying depth for molten cast iron to be placed and the molten cast iron allowed to solidify.
A further subject matter of the present invention is a cathode arrangement which comprises at least one previously described cathode block.
Finally, the present invention relates to the use of a previously described cathode arrangement for carrying out a fused-salt electrolysis to produce metal, preferably to produce aluminum.
In what follows, the present invention is described purely by way of example by means of an advantageous embodiment and with reference to the accompanying drawing.
Here Fig. 1 shows a longitudinal section of a cathode arrangement in accordance with an embodiment of the present invention.
Fig. 1 shows a longitudinal section of a cathode arrangement 12' in accordance with an embodiment of the present invention, namely inverted. The cathode arrangement 12' comprises a cathode block 20 in whose bottom a slot 26 is provided whose depth varies over the length of the slot 26, namely in such a way that the slot 26 has a shallower depth at its longitudinal end than at its center. The difference between the slot depth at the longitudinal ends of the slot 26 and at the center - with respect to the longitudinal direction of the cathode block - of the slot 26 amounts in the present exemplary embodiment to about 5 cm. Here, the depth of the slot 26 at the two longitudinal ends of the slot 26 is about 16 cm while on the other hand the depth of the slot 26 at the center - with respect to the longitudinal direction of the cathode block -of the slot 26 is about 21 cm. The width 44 of each slot 26 is essentially constant over the entire slot length and measures approximately 15 cm while on the other hand the width 46 of the cathode blocks 20 in each case measures about 42 cm. A bar-shaped busbar 28 with a rectangular longitudinal section is arranged in the slot 26 wherein between the busbar 28 and the slot bottom 34, there is an intermediate space 56 which becomes larger towards the center of the slot 26.
According to the invention, this intermediate space 56 is at least partially and in the case shown in Fig. 1 is entirely filled with steel, namely with the same steel as that of which the busbar 28 is made.
' List of reference numbers 12, 12 cathode arrangement 20 cathode block 26 slot 28 busbar 34 bottom wall 56 intermediate space
Claims (16)
1. A cathode block for an aluminum electrolysis cell on the basis of carbon or graphite, wherein the cathode block has at least one slot extending in the longitudinal direction of the cathode block, wherein at least one of the at least one slot has a varying depth when viewed over the length of the cathode block and in the at least one slot a busbar is provided, wherein the intermediate space between the at least one busbar and the wall bounding the at least one slot of varying depth is at least partially filled with steel, wherein the steel is selected from the group consisting of steel having a low carbon content of < 0.1 %, a silicon content of < 0.1 % and a phosphorus content of < 0.05 %, metals, alloys, composites of the aforementioned materials, metal-infiltrated graphite or carbon materials or electrically conductive masses.
2. A cathode block according to claim 1, wherein at least 50% of the intermediate space is filled with steel.
3. A cathode block according to claim 1, wherein at least 75% of the intermediate space is filled with steel.
4. A cathode block according to claim 1, wherein at least 90% of the intermediate space is filled with steel.
5. A cathode block according to claim 1, wherein at least 95% of the intermediate space is filled with steel.
6. A cathode block according to claim 1, wherein at least 98% of the intermediate space is filled with steel.
7. A cathode block according to claim 1, wherein 100% of the intermediate space is filled with steel.
8. A cathode block according to any one of claims 1 to 7, wherein the steel with which the intermediate space is at least partially filled is the same as that of which the at least one busbar is composed.
9. A cathode block according to any one of claims 2 to 6, wherein cast iron is provided between the steel and the wall bounding the at least one slot of varying depth.
10. A cathode block according to any one of claims 2 to 4, or 9 wherein one of (1) at least 50% of the intermediate space is filled with steel, (2) at least 75% of the intermediate space is filled with steel and (3) at least 90% of the intermediate space is filled with steel, and, in addition to any one of (1), (2) and (3), one or more steel plates or balls are provided between the steel and the wall bounding the at least one slot of varying depth.
11. A cathode block according to any one of claims 1 to 10, wherein at least one of the at least one slot of varying depth has a greater depth at its longitudinal ends than at its center.
12. A cathode block according to any one of claims 1 to 11, wherein each of the at least one slot has an at least essentially rectangular cross-section.
13. A cathode block according to any one of claims 1 to 12, wherein the at least one busbar has an at least essentially cuboid shape.
14. A cathode arrangement containing at least one cathode block according to any one of claims 1 to 13.
15. Use of a cathode arrangement in accordance with claim 14 for carrying out a fused-salt electrolysis to produce metal.
16. Use of a cathode arrangement in accordance with claim 14 for carrying out a fused-salt electrolysis to produce aluminum.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE102013207738.6A DE102013207738A1 (en) | 2013-04-26 | 2013-04-26 | Cathode block with a groove of varying depth and filled gap |
| DE102013207738.6 | 2013-04-26 | ||
| PCT/EP2014/058554 WO2014174108A1 (en) | 2013-04-26 | 2014-04-28 | Cathode block having a slot with a varying depth and a filled intermediate space |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2910088A1 CA2910088A1 (en) | 2014-10-30 |
| CA2910088C true CA2910088C (en) | 2018-01-23 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2910088A Active CA2910088C (en) | 2013-04-26 | 2014-04-28 | Cathode block having a slot with a varying depth and a filled intermediate space |
Country Status (8)
| Country | Link |
|---|---|
| EP (1) | EP2989234A1 (en) |
| JP (1) | JP6612737B2 (en) |
| CN (1) | CN105247110A (en) |
| CA (1) | CA2910088C (en) |
| DE (1) | DE102013207738A1 (en) |
| RU (1) | RU2642815C2 (en) |
| UA (1) | UA118349C2 (en) |
| WO (1) | WO2014174108A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US11242604B2 (en) | 2016-07-26 | 2022-02-08 | Cobex Gmbh | Cathode assembly for the production of aluminum |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2595460A (en) * | 2020-05-26 | 2021-12-01 | Dubai Aluminium Pjsc | Cathode assembly with metallic collector bar systems for electrolytic cell suitable for the Hall-Héroult process |
Family Cites Families (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2318244A1 (en) * | 1975-07-17 | 1977-02-11 | Savoie Electrodes Refactaires | PROCESS FOR JOINING METAL BARS WITH CARBON BLOCKS |
| JPS55141587A (en) * | 1979-04-24 | 1980-11-05 | Nikkei Giken:Kk | Jointing method of current-collecting bar to cathode carbon block of aluminum electrolysis furnace |
| GB8331769D0 (en) * | 1983-11-29 | 1984-01-04 | Alcan Int Ltd | Aluminium reduction cells |
| RU2060303C1 (en) * | 1994-02-05 | 1996-05-20 | Акционерное общество открытого типа "Братский алюминиевый завод" | Hearth section of aluminum electrolyzer |
| EP0905284B1 (en) * | 1994-09-08 | 2002-04-03 | MOLTECH Invent S.A. | Aluminium electrowinning cell with drained cathode |
| JP3806653B2 (en) * | 2002-02-06 | 2006-08-09 | 株式会社神戸製鋼所 | Steel for electrical parts excellent in cold forgeability and electrical conductivity, electrical parts excellent in electrical conductivity, and manufacturing method thereof |
| RU2303654C2 (en) * | 2005-10-07 | 2007-07-27 | Общество с ограниченной ответственностью "Русская инжиниринговая компания" | Mounting method for cathode section |
| PL1845174T3 (en) * | 2006-04-13 | 2011-10-31 | Sgl Carbon Se | Cathodes for aluminium electrolysis cell with non-planar slot design |
| DE102010039638B4 (en) * | 2010-08-23 | 2015-11-19 | Sgl Carbon Se | Cathode, apparatus for aluminum extraction and use of the cathode in aluminum production |
| BRPI1004950A2 (en) * | 2010-09-03 | 2012-07-03 | Incotep Ind E Com De Tubos Especiais De Precisao Ltda | low carbon steel composition for electric conduction purposes in electrolytically reduced reduction tanks |
| DE102010041082A1 (en) * | 2010-09-20 | 2012-03-22 | Sgl Carbon Se | Cathode for electrolysis cells |
| DE102011004011A1 (en) * | 2011-02-11 | 2012-08-16 | Sgl Carbon Se | Cathode assembly having a surface profiled cathode block with a graphite foil-lined groove of variable depth |
-
2013
- 2013-04-26 DE DE102013207738.6A patent/DE102013207738A1/en not_active Withdrawn
-
2014
- 2014-04-28 JP JP2016509497A patent/JP6612737B2/en active Active
- 2014-04-28 UA UAA201511662A patent/UA118349C2/en unknown
- 2014-04-28 CA CA2910088A patent/CA2910088C/en active Active
- 2014-04-28 RU RU2015150377A patent/RU2642815C2/en active
- 2014-04-28 EP EP14720118.0A patent/EP2989234A1/en not_active Withdrawn
- 2014-04-28 CN CN201480023606.5A patent/CN105247110A/en active Pending
- 2014-04-28 WO PCT/EP2014/058554 patent/WO2014174108A1/en active Application Filing
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US11242604B2 (en) | 2016-07-26 | 2022-02-08 | Cobex Gmbh | Cathode assembly for the production of aluminum |
Also Published As
| Publication number | Publication date |
|---|---|
| CN105247110A (en) | 2016-01-13 |
| DE102013207738A1 (en) | 2014-10-30 |
| JP6612737B2 (en) | 2019-11-27 |
| RU2015150377A (en) | 2017-06-02 |
| WO2014174108A1 (en) | 2014-10-30 |
| UA118349C2 (en) | 2019-01-10 |
| RU2642815C2 (en) | 2018-01-26 |
| EP2989234A1 (en) | 2016-03-02 |
| JP2016520720A (en) | 2016-07-14 |
| CA2910088A1 (en) | 2014-10-30 |
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