CA2811361A1 - Cathode for electrolytic cells - Google Patents
Cathode for electrolytic cells Download PDFInfo
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- CA2811361A1 CA2811361A1 CA2811361A CA2811361A CA2811361A1 CA 2811361 A1 CA2811361 A1 CA 2811361A1 CA 2811361 A CA2811361 A CA 2811361A CA 2811361 A CA2811361 A CA 2811361A CA 2811361 A1 CA2811361 A1 CA 2811361A1
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- cathode
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- intermediate layer
- current supply
- aluminium
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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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- Chemical Kinetics & Catalysis (AREA)
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- Electrolytic Production Of Metals (AREA)
- Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
Abstract
The invention relates to a cathode (1) for an electrolysis cell for extracting aluminium from its oxide in an electrolysis bath, said cathode comprising an upper part (1a) facing the electrolysis bath, and a lower part (1b) provided with connections (1b1) for the supply line. According to the invention, the upper part (1a) and the lower part (1b) can be detachably connected, at least in sections, by means of an intermediate layer.
Description
1 06.03.2013 Cathode for electrolytic cells The invention relates to a cathode for an electrolytic cell for extracting aluminium by fused-salt electrolysis.
The Hall-Heroult process is currently used for the industrial extraction of aluminium from its oxide. This is an electrolytic process in which aluminium oxide (A1203) is dissolved in molten cryolite (Na3 [AlF6]) and the resulting mixture acts as a liquid electrolyte in an electrolytic cell. In principal, the design of this sort of electrolytic cell used to carry out the Hall-Heroult process is depicted schematically in Figures 1a to 1c, wherein Figure 1a shows a cross-section through a traditional cell, while Figure lb shows an external side is view of the cell. Fig. lc shows a perspective view of an electrolytic cell.
Reference symbol 1 denotes a cathode, which may, for example, be made from graphite, anthracite or a mixture of these. Alternatively, coke-based graphitised cathodes may also be used. The cathode 1 is generally enclosed in a mounting 2 made from steel and/or a fire-resistant material or similar.
The cathode 1 may be made in one-piece or also from individual cathode blocks.
Over the entire length of the cell, a number of current supply bars 3 are introduced into the cathode 1, although only a single current supply bar 3 can be seen in the cross-sectional view in Figure la. It can be seen in Fig. 1c that two current supply bars, for example, may be provided for each cathode block. The current supply bars are used to supply the cell with the current required for the electrolytic process. There is a plurality of typically prismatic anodes 4 opposite the cathode 1, wherein two anodes 4 are schematically depicted in Figure 1a. Fig. 1c shows a detailed configuration of anodes in an electrolytic cell. During the performance of the process, the aluminium oxide dissolved in cryolite is split into aluminium and oxygen ions by applying a voltage between the cathode 1 and the anodes 4, in which case the WO
The Hall-Heroult process is currently used for the industrial extraction of aluminium from its oxide. This is an electrolytic process in which aluminium oxide (A1203) is dissolved in molten cryolite (Na3 [AlF6]) and the resulting mixture acts as a liquid electrolyte in an electrolytic cell. In principal, the design of this sort of electrolytic cell used to carry out the Hall-Heroult process is depicted schematically in Figures 1a to 1c, wherein Figure 1a shows a cross-section through a traditional cell, while Figure lb shows an external side is view of the cell. Fig. lc shows a perspective view of an electrolytic cell.
Reference symbol 1 denotes a cathode, which may, for example, be made from graphite, anthracite or a mixture of these. Alternatively, coke-based graphitised cathodes may also be used. The cathode 1 is generally enclosed in a mounting 2 made from steel and/or a fire-resistant material or similar.
The cathode 1 may be made in one-piece or also from individual cathode blocks.
Over the entire length of the cell, a number of current supply bars 3 are introduced into the cathode 1, although only a single current supply bar 3 can be seen in the cross-sectional view in Figure la. It can be seen in Fig. 1c that two current supply bars, for example, may be provided for each cathode block. The current supply bars are used to supply the cell with the current required for the electrolytic process. There is a plurality of typically prismatic anodes 4 opposite the cathode 1, wherein two anodes 4 are schematically depicted in Figure 1a. Fig. 1c shows a detailed configuration of anodes in an electrolytic cell. During the performance of the process, the aluminium oxide dissolved in cryolite is split into aluminium and oxygen ions by applying a voltage between the cathode 1 and the anodes 4, in which case the WO
06.03.2013 aluminium ions move to the molten aluminium ¨ actually the cathode from an electrochemical point of view ¨ where they accept electrons. Due to the greater density, aluminium 5 gathers in the liquid phase beneath the molten mixture 6 of aluminium oxide and cryolite. The oxygen ions are reduced to oxygen at the anode, said oxygen reacting with the carbon of the anodes.
Reference symbols 7 and 8 are the schematic representations of the negative and positive poles, respectively, of a voltage source for supplying the voltage required for the electrolytic process, the value of which lies between around 3.5 and 5 V, for example.
As can be seen in the side view in Figure lb, the mounting 2 and therefore the entire electrolytic cell has an elongated form, in which a plurality of current-carrying bars 3 are conducted vertically through the side walls of the mounting 2. The longitudinal expansion of cells currently in use is typically between around 8 and 15 m, while the width expansion is about 3 to 4 m. A cathode, as is shown here in Figure 1a, is disclosed in EP 1845174, for example.
In traditional cathode blocks, all component parts are essentially made from only one material. However, this does not allow for the fact that different requirements are made of different parts of a cathode in a fused-salt electrolytic process. Hence, there is a material loss due to cathode material wear within the range of the electrolytic bath or in that part of the cathode that comes into contact with the molten aluminium in the process described, particularly due to chemical and mechanical processes involved in the electrolytic process like for example flow movements. For this reason, the cathode has to be renewed from time to time, i.e. in this case the entire lining of the electrolytic cell has to be replaced. In general, this sort of change will take place every 1500 to 3000 days. In addition, compromises must be made in relation to optimum design when it comes to individual components, since the requirements made of individual components are irreconcilable in some cases. Moreover, because of the frequent replacement of all materials, such as cathode blocks, ramming mass, side mounting and insulating material top-' WO
3 06.03.2013 quality materials have to be dispensed with, 'so that aluminium production costs do not become excessively high.
One problem addressed by the invention is therefore to specify a cathode for an electrolytic cell used to extract aluminium, which allows the aforementioned disadvantages of the state of the art to be overcome, a material cost saving to be made in particular and, at the same time, the cathode to be optimised in terms of its functionality.
to This problem is solved according to the invention by a cathode with the features contained in claim 1. Preferred embodiments are specified in the dependent claims.
A cathode for an electrolytic cell used to extract aluminium from its oxide in an is electrolytic bath in accordance with the embodiments of the invention exhibits the following: a) an upper part facing the electrolytic bath and b) a lower part provided with current supply connections. According to the invention, the upper part and the lower part are detachably connected to one another at least in sections by an intermediate layer. The upper part in this case is a 20 base tray, which is in direct contact with the electrolytic bath during use.
The term "cathode" denotes the upper part connected to the lower part in the context of the present invention. Within the meaning of the invention, the term cathode is interpreted quite generally. It may be, for example (although not 25 exclusively), a so-called cathode bottom, which is made from a plurality of cathode blocks, so that the core aspects according to the invention ¨ namely, the structure described above comprising an upper part connected to a lower part ¨ are realised as a whole by this cathode bottom. However, the term cathode is also intended to refer to the partial structures forming such a 30 cathode bottom, as in cathode blocks. All features that may contribute to the invention in relation to a "cathode" do so in the same way in relation to a "cathode block", without this having to be expressly explained below.
Reference symbols 7 and 8 are the schematic representations of the negative and positive poles, respectively, of a voltage source for supplying the voltage required for the electrolytic process, the value of which lies between around 3.5 and 5 V, for example.
As can be seen in the side view in Figure lb, the mounting 2 and therefore the entire electrolytic cell has an elongated form, in which a plurality of current-carrying bars 3 are conducted vertically through the side walls of the mounting 2. The longitudinal expansion of cells currently in use is typically between around 8 and 15 m, while the width expansion is about 3 to 4 m. A cathode, as is shown here in Figure 1a, is disclosed in EP 1845174, for example.
In traditional cathode blocks, all component parts are essentially made from only one material. However, this does not allow for the fact that different requirements are made of different parts of a cathode in a fused-salt electrolytic process. Hence, there is a material loss due to cathode material wear within the range of the electrolytic bath or in that part of the cathode that comes into contact with the molten aluminium in the process described, particularly due to chemical and mechanical processes involved in the electrolytic process like for example flow movements. For this reason, the cathode has to be renewed from time to time, i.e. in this case the entire lining of the electrolytic cell has to be replaced. In general, this sort of change will take place every 1500 to 3000 days. In addition, compromises must be made in relation to optimum design when it comes to individual components, since the requirements made of individual components are irreconcilable in some cases. Moreover, because of the frequent replacement of all materials, such as cathode blocks, ramming mass, side mounting and insulating material top-' WO
3 06.03.2013 quality materials have to be dispensed with, 'so that aluminium production costs do not become excessively high.
One problem addressed by the invention is therefore to specify a cathode for an electrolytic cell used to extract aluminium, which allows the aforementioned disadvantages of the state of the art to be overcome, a material cost saving to be made in particular and, at the same time, the cathode to be optimised in terms of its functionality.
to This problem is solved according to the invention by a cathode with the features contained in claim 1. Preferred embodiments are specified in the dependent claims.
A cathode for an electrolytic cell used to extract aluminium from its oxide in an is electrolytic bath in accordance with the embodiments of the invention exhibits the following: a) an upper part facing the electrolytic bath and b) a lower part provided with current supply connections. According to the invention, the upper part and the lower part are detachably connected to one another at least in sections by an intermediate layer. The upper part in this case is a 20 base tray, which is in direct contact with the electrolytic bath during use.
The term "cathode" denotes the upper part connected to the lower part in the context of the present invention. Within the meaning of the invention, the term cathode is interpreted quite generally. It may be, for example (although not 25 exclusively), a so-called cathode bottom, which is made from a plurality of cathode blocks, so that the core aspects according to the invention ¨ namely, the structure described above comprising an upper part connected to a lower part ¨ are realised as a whole by this cathode bottom. However, the term cathode is also intended to refer to the partial structures forming such a 30 cathode bottom, as in cathode blocks. All features that may contribute to the invention in relation to a "cathode" do so in the same way in relation to a "cathode block", without this having to be expressly explained below.
4 06.03.2013 Due to the cathode's two-part design,. it is possible to optimise the different functional areas during manufacture. Hence, the upper part is used to hold the liquid electrolyte and the end product, namely the molten aluminium, during the process.
The upper section, which can also be referred to as the "consumption part" of the cathode, should be designed to be as resistant as possible to wear, such as that resulting from mechanical, thermal and/or chemical loads. Due to the fact that the upper section has to be occasionally replaced in any event, due io to the consumption of cathode material during the electrolytic reaction, the cost of the material used in the upper section should be kept low. The lower part of the cathode, on the other hand, must be designed for optimum current supply and distribution. Due to this two-part construction, which is a feature of the present invention, both parts (upper part and lower part) can now be is produced separately from one another and then combined by means of the intermediate layer. In this way, each part can be optimised in terms of its function, without this having a detrimental effect on the function of the other part in each case. So, for example, the lower part may be made from higher-grade, expensive, yet at the same time barely wear-resistant material, 20 because it is unaffected by wear or replacement of the upper part due to wear.
A substantial material cost saving is made as a result of this, because an entire cathode is not affected by the replacement in each case or all cathode blocks do not have to be replaced.
25 A further advantage of the invention is that the lower part can be protected from the chemical effects of the electrolytic bath by the intermediate layer.
The intermediate layer therefore not only makes a design possible with a separate upper and lower part, but it also helps that the advantage that the lower part can be made from high-grade material, is not destroyed again by corrosive 30 liquids or gases penetrating as far as to the lower part, such as liquid aluminium or electrolyte components.
The intermediate layer, which connects the upper part to the lower part, may 06.03.2013 be produced from graphite foil, for example, Particularly being a graphite foil.
A graphite foil is particularly well-suited to avoiding or at least largely preventing the penetration of the lower part by liquid and/or gaseous bath components, like for example liquid aluminium or electrolyte components, 5 while leaving the actual function of the cathode as a whole largely unchanged.
As an intermediate layer, graphite foil has similar electrical properties as the cathode components, particularly as the lower part. Graphite foil, which is produced by the at least partial compression of expanded graphite, is particularly well-suited as a barrier layer acting against chemical influences from the electrolytic bath, due to its anisotropy in the foil surface and therefore low permeability perpendicular to the foil. Graphite foil furthermore has the effect of balancing differences in surface structure between the upper part and the lower part, as well as thermal expansion and contraction movements, particularly in the upper part. Graphite foil has a low electrical contact resistance to other carbon materials and a very good electrical conductivity.
Although the specific electrical resistance perpendicular to the graphite foil is higher than in the foil surface, very low absolute electrical resistance can be achieved due to the very low thickness of graphite foil.
In the event of that the cathode is produced from individual cathode blocks, the intermediate layer is preferably not provided to fit the size of the cathode blocks, but advantageously covers a larger area than the lower part of the cathode blocks in each case. The intermediate layer may advantageously display an area that corresponds to the size of the cathode as a whole.
The intermediate layer may be designed with a very low thickness. For example, the layer may simply be a single sheet of graphite foil. A range of 1 mm to 5 mm range, for example, has proved to be a suitable foil thickness.
This thickness is sufficient to fulfil the functions described, yet it is thin enough for the foil properties not to adversely affect the functionality of the cathode as a whole to any significant extent.
It may also be advantageous to use a plurality of graphite foils layered on top 6 06.03.2013 of one another or graphite foils with greater thicknesses. The intermediate layer may be adjusted as desired or as necessary in relation to its specific electrical conductivity and/or its electrical contact resistance. A coating of the intermediate layer may also be provided in this respect, which reduces contact resistance. The specific electrical conductivity of the graphite foil in direction of the thickness may also be selectively increased by known measures.
According to the state of the art a suitable current supply within the cathode is used to keep the material loss at the cathode surface inside the cathode tank Jo as uniform as possible. Since optimisation of the current supply in embodiments of the invention can be selectively undertaken in the lower part, it is possible for the upper part to be correspondingly simple in terms of its design and therefore its manufacture.
In a cathode according to the invention, the upper part may be formed in one piece together with a side wall of the electrolytic cell. This means that the base wall and the side walls are formed from a single piece. Problems associated with sealing and jointing between the base wall and side walls are thereby avoided.
Since the lower part of the cathode does not come into contact with the liquid electrolyte or the aluminium melt during use in a fused-salt electrolytic process, resistance to mechanical or chemical wear is not a criterion in this part. Consequently, this part only has low maintenance requirements, if any at all, and does not have to be replaced at regular intervals, as is the case with the upper part. For this reason, higher-grade materials can be used for the lower part. An example of such a material is highly-conductive graphite, as a crucial disadvantage of graphite, namely its low mechanical wear resistance, does not apply to this application.
According to a preferred embodiment, the lower part may be produced using, for example, needle coke as the raw material. As is generally known, needle coke is the highest-grade petroleum or pitch coke, its name being derived WO
The upper section, which can also be referred to as the "consumption part" of the cathode, should be designed to be as resistant as possible to wear, such as that resulting from mechanical, thermal and/or chemical loads. Due to the fact that the upper section has to be occasionally replaced in any event, due io to the consumption of cathode material during the electrolytic reaction, the cost of the material used in the upper section should be kept low. The lower part of the cathode, on the other hand, must be designed for optimum current supply and distribution. Due to this two-part construction, which is a feature of the present invention, both parts (upper part and lower part) can now be is produced separately from one another and then combined by means of the intermediate layer. In this way, each part can be optimised in terms of its function, without this having a detrimental effect on the function of the other part in each case. So, for example, the lower part may be made from higher-grade, expensive, yet at the same time barely wear-resistant material, 20 because it is unaffected by wear or replacement of the upper part due to wear.
A substantial material cost saving is made as a result of this, because an entire cathode is not affected by the replacement in each case or all cathode blocks do not have to be replaced.
25 A further advantage of the invention is that the lower part can be protected from the chemical effects of the electrolytic bath by the intermediate layer.
The intermediate layer therefore not only makes a design possible with a separate upper and lower part, but it also helps that the advantage that the lower part can be made from high-grade material, is not destroyed again by corrosive 30 liquids or gases penetrating as far as to the lower part, such as liquid aluminium or electrolyte components.
The intermediate layer, which connects the upper part to the lower part, may 06.03.2013 be produced from graphite foil, for example, Particularly being a graphite foil.
A graphite foil is particularly well-suited to avoiding or at least largely preventing the penetration of the lower part by liquid and/or gaseous bath components, like for example liquid aluminium or electrolyte components, 5 while leaving the actual function of the cathode as a whole largely unchanged.
As an intermediate layer, graphite foil has similar electrical properties as the cathode components, particularly as the lower part. Graphite foil, which is produced by the at least partial compression of expanded graphite, is particularly well-suited as a barrier layer acting against chemical influences from the electrolytic bath, due to its anisotropy in the foil surface and therefore low permeability perpendicular to the foil. Graphite foil furthermore has the effect of balancing differences in surface structure between the upper part and the lower part, as well as thermal expansion and contraction movements, particularly in the upper part. Graphite foil has a low electrical contact resistance to other carbon materials and a very good electrical conductivity.
Although the specific electrical resistance perpendicular to the graphite foil is higher than in the foil surface, very low absolute electrical resistance can be achieved due to the very low thickness of graphite foil.
In the event of that the cathode is produced from individual cathode blocks, the intermediate layer is preferably not provided to fit the size of the cathode blocks, but advantageously covers a larger area than the lower part of the cathode blocks in each case. The intermediate layer may advantageously display an area that corresponds to the size of the cathode as a whole.
The intermediate layer may be designed with a very low thickness. For example, the layer may simply be a single sheet of graphite foil. A range of 1 mm to 5 mm range, for example, has proved to be a suitable foil thickness.
This thickness is sufficient to fulfil the functions described, yet it is thin enough for the foil properties not to adversely affect the functionality of the cathode as a whole to any significant extent.
It may also be advantageous to use a plurality of graphite foils layered on top 6 06.03.2013 of one another or graphite foils with greater thicknesses. The intermediate layer may be adjusted as desired or as necessary in relation to its specific electrical conductivity and/or its electrical contact resistance. A coating of the intermediate layer may also be provided in this respect, which reduces contact resistance. The specific electrical conductivity of the graphite foil in direction of the thickness may also be selectively increased by known measures.
According to the state of the art a suitable current supply within the cathode is used to keep the material loss at the cathode surface inside the cathode tank Jo as uniform as possible. Since optimisation of the current supply in embodiments of the invention can be selectively undertaken in the lower part, it is possible for the upper part to be correspondingly simple in terms of its design and therefore its manufacture.
In a cathode according to the invention, the upper part may be formed in one piece together with a side wall of the electrolytic cell. This means that the base wall and the side walls are formed from a single piece. Problems associated with sealing and jointing between the base wall and side walls are thereby avoided.
Since the lower part of the cathode does not come into contact with the liquid electrolyte or the aluminium melt during use in a fused-salt electrolytic process, resistance to mechanical or chemical wear is not a criterion in this part. Consequently, this part only has low maintenance requirements, if any at all, and does not have to be replaced at regular intervals, as is the case with the upper part. For this reason, higher-grade materials can be used for the lower part. An example of such a material is highly-conductive graphite, as a crucial disadvantage of graphite, namely its low mechanical wear resistance, does not apply to this application.
According to a preferred embodiment, the lower part may be produced using, for example, needle coke as the raw material. As is generally known, needle coke is the highest-grade petroleum or pitch coke, its name being derived WO
7 06.03.2013 from its needle-like structure. Needle coke is characterised by, among other things, its lower thermal coefficient of expansion and its low specific electrical resistance after graphitisation, in longitudinal direction of the needle-like structure. This is advantageous particularly in the lower part of the cathode, where high-density currents flow. By means of a suitable design, alignment of the needle-shaped coke particles can be achieved in a perpendicular position.
The reduction in specific electrical resistance causes a smaller voltage drop at the cathode and thereby helps greater energy efficiency to be achieved during fused-salt electrolysis. Because energy costs constitute a major part of the total process costs, significant savings can be made in this way.
The upper part of the cathode may be made from any known materials suitable for use as a cathode. Raw materials particularly worth mentioning in this context are calcined anthracite, coke or graphite. The raw material is is ground and sorted according to particle size. A defined mixture of fractions in the grain size is combined with pitch and then used to form the upper part.
Subsequent to this, one or more production steps are carried out at an increased temperature, a distinction being made between a graphitised, a graphitic and an amorphous cathode material based on the heat treatment temperature and raw materials.
The cathode may advantageously have a vertical current supply. This means that current is introduced into the lower part of the cathode vertically from below. This means that an uneven current distribution in the cathode, as is the case with a traditional horizontal current supply, can be advantageously avoided.
In accordance with an embodiment of the cathode in the invention, the lower part may be provided with vertical pins as current supplies. These pins may be in the form of grub screws, with the lower part exhibiting threaded holes as connections to hold the grub screws. Pins with an external thread may be screwed into the threaded holes in the lower part of the cathode vertically or approximately vertically. In this way, the current can be introduced into the 8 06.03.2013 cathode roughly vertically during fused-salt electrolysis. The current supply can be kept very uniform during this by adapting the number and diameter of the pins to the cathode geometry.
The geometry of the pins may advantageously match the geometry of threaded nipples for graphite electrodes used in electric steel production.
This geometry has proved to be particularly good in relation to the current distribution, mechanical strength and screwability. The relatively large pin cross-section effects a high electrical current flow, the length effects a sufficiently large interval between the cathode and therefore the electrolytic cell and the current supply bars, so that a high level of cooling is possible.
In accordance with a preferred embodiment, the pins are made from graphite.
This enables a high thermal stability of the pins and low electrical resistance is to be achieved, which leads to a reduction in specific energy costs associated with the performance of the fused-salt electrolysis.
In terms of a uniform current supply, it has also proved to be beneficial if the lower part of the cathode is designed in the form of a trapezoidal body tapering downwards. In this way, the current introduced vertically or approximately vertically is distributed uniformly and evenly in the upper part of the cathode. In the case that the cathode is made from individual cathode blocks, at least some of the cathode blocks of the cathode preferably have this sort of trapezoidal, downward-tapering body, in which case these advantageously extend parallel to one another. The trapezoidal bodies may, for example, run longitudinally to the cathode or perpendicular to it.
It should be noted that in the context of the invention the expression "approximately vertical" is used to cover all directions that include an angle of less than roughly 20 to the perpendicular. However, "vertical" in the broadest sense should include all vertical supplies that are not horizontally in the traditional manner.
The reduction in specific electrical resistance causes a smaller voltage drop at the cathode and thereby helps greater energy efficiency to be achieved during fused-salt electrolysis. Because energy costs constitute a major part of the total process costs, significant savings can be made in this way.
The upper part of the cathode may be made from any known materials suitable for use as a cathode. Raw materials particularly worth mentioning in this context are calcined anthracite, coke or graphite. The raw material is is ground and sorted according to particle size. A defined mixture of fractions in the grain size is combined with pitch and then used to form the upper part.
Subsequent to this, one or more production steps are carried out at an increased temperature, a distinction being made between a graphitised, a graphitic and an amorphous cathode material based on the heat treatment temperature and raw materials.
The cathode may advantageously have a vertical current supply. This means that current is introduced into the lower part of the cathode vertically from below. This means that an uneven current distribution in the cathode, as is the case with a traditional horizontal current supply, can be advantageously avoided.
In accordance with an embodiment of the cathode in the invention, the lower part may be provided with vertical pins as current supplies. These pins may be in the form of grub screws, with the lower part exhibiting threaded holes as connections to hold the grub screws. Pins with an external thread may be screwed into the threaded holes in the lower part of the cathode vertically or approximately vertically. In this way, the current can be introduced into the 8 06.03.2013 cathode roughly vertically during fused-salt electrolysis. The current supply can be kept very uniform during this by adapting the number and diameter of the pins to the cathode geometry.
The geometry of the pins may advantageously match the geometry of threaded nipples for graphite electrodes used in electric steel production.
This geometry has proved to be particularly good in relation to the current distribution, mechanical strength and screwability. The relatively large pin cross-section effects a high electrical current flow, the length effects a sufficiently large interval between the cathode and therefore the electrolytic cell and the current supply bars, so that a high level of cooling is possible.
In accordance with a preferred embodiment, the pins are made from graphite.
This enables a high thermal stability of the pins and low electrical resistance is to be achieved, which leads to a reduction in specific energy costs associated with the performance of the fused-salt electrolysis.
In terms of a uniform current supply, it has also proved to be beneficial if the lower part of the cathode is designed in the form of a trapezoidal body tapering downwards. In this way, the current introduced vertically or approximately vertically is distributed uniformly and evenly in the upper part of the cathode. In the case that the cathode is made from individual cathode blocks, at least some of the cathode blocks of the cathode preferably have this sort of trapezoidal, downward-tapering body, in which case these advantageously extend parallel to one another. The trapezoidal bodies may, for example, run longitudinally to the cathode or perpendicular to it.
It should be noted that in the context of the invention the expression "approximately vertical" is used to cover all directions that include an angle of less than roughly 20 to the perpendicular. However, "vertical" in the broadest sense should include all vertical supplies that are not horizontally in the traditional manner.
9 06.03.2013 The invention will now be described in greater detail with reference to the attached drawing using a non-restrictive exemplary embodiment. In the drawing:
Fig. la shows a schematic cross section of an electrolytic cell for the extraction of aluminium oxide according to the state of the art;
Fig. lb shows the electrolytic cell from Fig. lain an external longitudinal view;
Fig. lc shows a perspective view partially in section of an electrolytic cell for the extraction of aluminium from aluminium oxide according to the state of the art;
Fig. 2a shows a perspective view of a cathode unit according to an embodiment of the invention; and Fig. 2b shows a representation of the cathode unit in Fig. 2a from a rotated perspective.
The same reference symbols are used in the figures to refer to the same or corresponding elements in the different representations.
With reference to Figures 2a and 2b, an electrolytic cell with an embodiment of a cathode 1 according to the invention is shown from different perspectives in each case. The cathode 1 shown is suitable for use in the extraction of aluminium from aluminium oxide using the Hall-Heroult process. In this case the electrolytic cell is provided with two side walls lal, which, along with a base wall 1a2, hold the electrolyte bath. In the case shown, the side walls lal extend along the longitudinal side of the cathode I. The side wall lal is made from individual side wall blocks 1a3. The base wall 1a2 represents an upper or first part 1 a of the cathode 1. The cathode 1 is made from individual cathode blocks 11 in this embodiment.
06.03.2013 In the exemplary embodiment shown a lower part lb of the cathode 1 comprises a number of connections lbl, which are formed from trapezoidal bodies 1b2 in a lower section, which taper downwards in a V-shape. The 5 connections lbl may be in the form of internal threads, for example, (not shown in the figures), so that they can each hold a pin 9 with a corresponding external thread for the current supply to the cathode 1. Several of the pins 9 are connected at their sides lying opposite the connections lbl to current supply bars 3, which lead to busbars 10, in order to connect cathode 1 to the 10 corresponding pole of a voltage source.
The upper part la and the lower part lb are connected to one another by an intermediate layer lc, which may be a graphite foil, for example. This foil enables the upper part of the cathode to be removed without damaging the lower part. At the same time, the graphite foil guarantees that no liquid aluminium or electrolyte penetrates as far as the lower part and, to this extent, acts as a barrier layer. Despite having poorer specific electrical conductivity perpendicular to the foil plane compared with the conductivity within the foil plane, on account of its very low thickness of a few millimetres, for example, the graphite foil has a very low absolute electrical resistance and effects a very good electrical contact between the upper part and the lower part, so that the cathode's functionality is not affected. Moreover, the intermediate layer balances an expansion of the two parts la, lb, on account of thermal fluctuations, for example.
Since the upper part la and the lower part lb are formed separately from one another, the two parts may be made from different materials and exhibit different properties in relation to thermal expansion and electrical resistance.
This means that each part can be specially optimised in functional terms. In particular, the upper part la must be designed such that it is able to withstand wear, due for example to mechanical abrasion and also uneven electrochemical decomposition, as effectively as possible.
Fig. la shows a schematic cross section of an electrolytic cell for the extraction of aluminium oxide according to the state of the art;
Fig. lb shows the electrolytic cell from Fig. lain an external longitudinal view;
Fig. lc shows a perspective view partially in section of an electrolytic cell for the extraction of aluminium from aluminium oxide according to the state of the art;
Fig. 2a shows a perspective view of a cathode unit according to an embodiment of the invention; and Fig. 2b shows a representation of the cathode unit in Fig. 2a from a rotated perspective.
The same reference symbols are used in the figures to refer to the same or corresponding elements in the different representations.
With reference to Figures 2a and 2b, an electrolytic cell with an embodiment of a cathode 1 according to the invention is shown from different perspectives in each case. The cathode 1 shown is suitable for use in the extraction of aluminium from aluminium oxide using the Hall-Heroult process. In this case the electrolytic cell is provided with two side walls lal, which, along with a base wall 1a2, hold the electrolyte bath. In the case shown, the side walls lal extend along the longitudinal side of the cathode I. The side wall lal is made from individual side wall blocks 1a3. The base wall 1a2 represents an upper or first part 1 a of the cathode 1. The cathode 1 is made from individual cathode blocks 11 in this embodiment.
06.03.2013 In the exemplary embodiment shown a lower part lb of the cathode 1 comprises a number of connections lbl, which are formed from trapezoidal bodies 1b2 in a lower section, which taper downwards in a V-shape. The 5 connections lbl may be in the form of internal threads, for example, (not shown in the figures), so that they can each hold a pin 9 with a corresponding external thread for the current supply to the cathode 1. Several of the pins 9 are connected at their sides lying opposite the connections lbl to current supply bars 3, which lead to busbars 10, in order to connect cathode 1 to the 10 corresponding pole of a voltage source.
The upper part la and the lower part lb are connected to one another by an intermediate layer lc, which may be a graphite foil, for example. This foil enables the upper part of the cathode to be removed without damaging the lower part. At the same time, the graphite foil guarantees that no liquid aluminium or electrolyte penetrates as far as the lower part and, to this extent, acts as a barrier layer. Despite having poorer specific electrical conductivity perpendicular to the foil plane compared with the conductivity within the foil plane, on account of its very low thickness of a few millimetres, for example, the graphite foil has a very low absolute electrical resistance and effects a very good electrical contact between the upper part and the lower part, so that the cathode's functionality is not affected. Moreover, the intermediate layer balances an expansion of the two parts la, lb, on account of thermal fluctuations, for example.
Since the upper part la and the lower part lb are formed separately from one another, the two parts may be made from different materials and exhibit different properties in relation to thermal expansion and electrical resistance.
This means that each part can be specially optimised in functional terms. In particular, the upper part la must be designed such that it is able to withstand wear, due for example to mechanical abrasion and also uneven electrochemical decomposition, as effectively as possible.
11 06.03.2013 By contrast, the lower part lb should be designed for the most uniform current supply possible and the highest possible energy efficiency. To achieve this, it can be optimised in terms of the materials used, since the relatively fast-wearing upper part 1 a, which must be replaced more frequently, is produced separately from the lower part lb. This means that expensive materials, such as needle coke, for example, can also be chosen, in order to optimise the long-lasting lower part lb in relation to the desired uniform current distribution.
Copper and aluminium have proved to be particularly suitable as materials for the current supply bars 3, due to their low specific electrical resistances.
Since the current supply bars are spaced away from the cathode 1 by pins 9, they are substantially cooled and it is therefore not necessary for them to be made from high-temperature-resistant steel. Due to the lower specific electrical resistance of the aforementioned metals for the current supply bars 3, less energy is converted into waste heat and the energy efficiency during fused salt electrolysis can be markedly improved. The tapering ld of the trapezoidal bodies shown serves to increase the distance between the upper part 1 a of the cathode 1 and the current-carrying current supply bars 3 and therefore supports the cooling of the current supply bars 3.
In relation to cathode materials, any materials known to the person skilled in the art and suitable for the electrolysis of aluminium from its oxide may be used. Suitable materials are specified in DE 10261745, for example, the content of which, in this respect, is to be incorporated herein by reference.
The pins 9, in particular, may be made from the same materials as the cathode 1. Graphite has proved to be particularly favourable in this respect, due to its temperature resistance and due to its low specific electrical resistance.
Copper and aluminium have proved to be particularly suitable as materials for the current supply bars 3, due to their low specific electrical resistances.
Since the current supply bars are spaced away from the cathode 1 by pins 9, they are substantially cooled and it is therefore not necessary for them to be made from high-temperature-resistant steel. Due to the lower specific electrical resistance of the aforementioned metals for the current supply bars 3, less energy is converted into waste heat and the energy efficiency during fused salt electrolysis can be markedly improved. The tapering ld of the trapezoidal bodies shown serves to increase the distance between the upper part 1 a of the cathode 1 and the current-carrying current supply bars 3 and therefore supports the cooling of the current supply bars 3.
In relation to cathode materials, any materials known to the person skilled in the art and suitable for the electrolysis of aluminium from its oxide may be used. Suitable materials are specified in DE 10261745, for example, the content of which, in this respect, is to be incorporated herein by reference.
The pins 9, in particular, may be made from the same materials as the cathode 1. Graphite has proved to be particularly favourable in this respect, due to its temperature resistance and due to its low specific electrical resistance.
12 06.03.2013 Reference list 1 Cathode 1 a Upper part la 1 Side wall la2 Base wall 1a3 Side wall block lb Lower part 1 bl Connection 1b2 Trapezoidal body 1 c Intermediate layer 2 Mounting 3 Current supply bars, current bar 4 Anode 5 Aluminium 6 Electrolytic bath mixture (aluminium oxide, cryolite) 7 Negative pole, voltage source 8 Positive pole, voltage source 9 Pin 10 Busbar 11 Cathode block
Claims (10)
1. A cathode (1) for an electrolytic cell used to extract aluminium from its oxide in an electrolytic bath, exhibiting an upper part (1a) facing the electrolytic bath and a lower part (1b), which is provided with current supply connections (1b1), characterised in that the upper part (1a) and the lower part (1b) are detachably connected to one another at least in sections by an intermediate layer (1c).
2. The cathode (1) according to claim 1, characterised in that the intermediate layer (1c) is produced from graphite.
3. The cathode (1) according to claim 1 or 2, characterised in that the intermediate layer (1c) is a graphite foil.
4. The cathode (1) according to one or more of the preceding claims, characterised in that the lower part (1b) is produced using needle coke as the raw material.
5. The cathode (1) according to one or more of the preceding claims, characterised in that the lower part (1b) exhibits a vertical current supply.
6. The cathode (1) according to one or more of the preceding claims, characterised in that the lower part (1b) is provided with threaded holes as connections (1b1) to hold grub screws.
7. The cathode (1) according to one or more of the preceding claims, characterised in that the upper part (1a) is produced from anthracite, coke or graphite.
8. The cathode (1) according to one or more of the preceding claims, characterised in that the lower part (1b) is designed in the form of a trapezoidal body (1b2) tapering downwards.
9. The cathode (1) according to one of the preceding claims, characterised in that the cathode (1) comprises a multiplicity of cathode blocks (11), is particularly made from a multiplicity of cathode blocks (11), wherein the cathode blocks (11) are particularly geometrically and/or structurally identical or have an identical effect and/or are disposed adjacent to one another particularly laterally.
10. An electrolytic cell used to extract aluminium from its oxide, characterised in that it contains a cathode (1) according to one or more of the claims 1 to 9.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE102010041081.0A DE102010041081B4 (en) | 2010-09-20 | 2010-09-20 | Cathode for electrolysis cells |
| DE102010041081.0 | 2010-09-20 | ||
| PCT/EP2011/066322 WO2012038427A1 (en) | 2010-09-20 | 2011-09-20 | Cathode for electrolysis cells |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2811361A1 true CA2811361A1 (en) | 2012-03-29 |
Family
ID=44675581
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2811361A Abandoned CA2811361A1 (en) | 2010-09-20 | 2011-09-20 | Cathode for electrolytic cells |
Country Status (8)
| Country | Link |
|---|---|
| EP (1) | EP2619352A1 (en) |
| JP (1) | JP2013537940A (en) |
| CN (1) | CN103140610A (en) |
| CA (1) | CA2811361A1 (en) |
| DE (1) | DE102010041081B4 (en) |
| RU (1) | RU2529432C1 (en) |
| UA (1) | UA104827C2 (en) |
| WO (1) | WO2012038427A1 (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102012218958A1 (en) * | 2012-10-17 | 2014-04-30 | Sgl Carbon Se | Block, useful in cathode of electrolysis cell, which is useful for producing aluminum, where block has cross section perpendicular to a longitudinal axis of the cathode block and shape of trapezium |
| DE102012218959A1 (en) * | 2012-10-17 | 2014-04-30 | Sgl Carbon Se | Block, useful in cathode of electrolysis cell, which is useful for producing aluminum, where block has cross section perpendicular to a longitudinal axis of the cathode block and shape of trapezium |
| DE102012218960B4 (en) * | 2012-10-17 | 2014-11-27 | Sgl Carbon Se | Cathode comprising cathode blocks with a partially trapezoidal cross-section |
| CN104141154A (en) * | 2013-07-18 | 2014-11-12 | 成都精容电子有限公司 | Device for aluminum electrolysis |
| DE102015011952A1 (en) * | 2015-09-18 | 2017-03-23 | Sgl Carbon Se | Cathode bottom, method for producing a cathode bottom and use thereof in an electrolytic cell for the production of aluminum |
| RU169863U1 (en) * | 2016-04-12 | 2017-04-04 | Открытое акционерное общество "Тамбовское опытно-конструкторское технологическое бюро" (ОАО "Тамбовское ОКТБ") | ELECTROLYZER FOR PRODUCING SODIUM HYPOCHLORITE SOLUTION |
| JP6089137B1 (en) * | 2016-06-16 | 2017-03-01 | Ｓｅｃカーボン株式会社 | Cathode |
Family Cites Families (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1187809B (en) * | 1963-11-22 | 1965-02-25 | Vaw Ver Aluminium Werke Ag | Electrolysis cell for the production of aluminum by melt flow electrolysis |
| DE2008215A1 (en) * | 1970-02-21 | 1971-09-02 | Sigri Elektrographit Gmbh | Graphite sheathing for aluminium electrolysi |
| DE2833381A1 (en) * | 1978-07-29 | 1980-02-14 | Sigri Elektrographit Gmbh | Electrolysis cell for winning aluminium - where carbon cathode hearth is connected to bus=bars via spaced graphite pegs increasing the efficiency of aluminium prodn. |
| CH660030A5 (en) * | 1982-07-12 | 1987-03-13 | Alusuisse | CATHODE PAN OF AN ALUMINUM ELECTROLYSIS CELL. |
| FR2566002B1 (en) * | 1984-06-13 | 1986-11-21 | Pechiney Aluminium | MODULAR CATHODE BLOCK AND LOW VOLTAGE DROP CATHODE FOR HALL-HEROULT ELECTROLYSIS TANKS |
| AUPO053496A0 (en) * | 1996-06-18 | 1996-07-11 | Comalco Aluminium Limited | Cathode construction |
| US6258224B1 (en) * | 1998-12-16 | 2001-07-10 | Alcan International Limited | Multi-layer cathode structures |
| DE10261745B3 (en) | 2002-12-30 | 2004-07-22 | Sgl Carbon Ag | Cathode system for electrolytic aluminum extraction |
| RU2245397C1 (en) * | 2003-07-08 | 2005-01-27 | Открытое акционерное общество "ВСЕРОССИЙСКИЙ АЛЮМИНИЕВО-МАГНИЕВЫЙ ИНСТИТУТ" ОАО "ВАМИ" | Cathodic device of aluminum electrolyzer |
| RU2281986C1 (en) * | 2005-02-22 | 2006-08-20 | Общество с ограниченной ответственностью "Инженерно-технологический центр" | Electrolyzer for production of aluminum from mixture of molten salts and alumina |
| PL1845174T3 (en) | 2006-04-13 | 2011-10-31 | Sgl Carbon Se | Cathodes for aluminium electrolysis cell with non-planar slot design |
| US8404090B2 (en) * | 2008-04-30 | 2013-03-26 | Rio Tinto Alcan International Limited | Multi-layer cathode block |
| CN201416035Y (en) * | 2009-03-03 | 2010-03-03 | 沈阳铝镁设计研究院 | Cathode structure of energy-saving aluminum electrolyzer |
| CN201420096Y (en) * | 2009-06-25 | 2010-03-10 | 贵阳铝镁设计研究院 | Cathode steel bar assembling structure capable of vertical electric conduction |
-
2010
- 2010-09-20 DE DE102010041081.0A patent/DE102010041081B4/en not_active Expired - Fee Related
-
2011
- 2011-09-20 RU RU2013118311/02A patent/RU2529432C1/en not_active IP Right Cessation
- 2011-09-20 EP EP11760760.6A patent/EP2619352A1/en not_active Withdrawn
- 2011-09-20 JP JP2013529634A patent/JP2013537940A/en not_active Ceased
- 2011-09-20 CN CN2011800452821A patent/CN103140610A/en active Pending
- 2011-09-20 CA CA2811361A patent/CA2811361A1/en not_active Abandoned
- 2011-09-20 UA UAA201305117A patent/UA104827C2/en unknown
- 2011-09-20 WO PCT/EP2011/066322 patent/WO2012038427A1/en active Application Filing
Also Published As
| Publication number | Publication date |
|---|---|
| WO2012038427A1 (en) | 2012-03-29 |
| RU2529432C1 (en) | 2014-09-27 |
| DE102010041081B4 (en) | 2015-10-29 |
| JP2013537940A (en) | 2013-10-07 |
| UA104827C2 (en) | 2014-03-11 |
| EP2619352A1 (en) | 2013-07-31 |
| CN103140610A (en) | 2013-06-05 |
| DE102010041081A1 (en) | 2012-03-22 |
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| EEER | Examination request |
Effective date: 20130314 |
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| FZDE | Discontinued |
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