Cathode assembly for electrolytic cell

Description

Field of invention

[0001] The present invention relates to a cathode assembly for an electrolytic cell. Prior art

[0002] As is known, document US6113756 describes an electrolytic reduction cell for the production of a metal, such as aluminum. Document US6113756 relates in particular to a cathode construction used in such cells.

[0003] Said cathode comprises a carbon block, a plurality of electrical contact pins mounted in electrical contact with a lower portion of the cathode and at least one collector plate in electrical contact with the electrical contact pins.

[0004] The plurality of electrical contact pins are positioned or distributed on the lower surface of the cathode such that an isopotential surface is obtained. In particular, the required number of electrical contact pins can be positioned in space so as to reduce unwanted current flows and produce minimal electric field resistance between the pins. With this approach, the resistance of the assembly can be minimized and the current distribution in the assembly controlled.

[0005] However, these solutions do not give complete satisfaction.

[0006] Indeed, the use of electrical contact pins positioned or distributed on the lower surface of the cathode to obtain an isopotential surface has the effect of stiffening the cathode assembly comprising the cathode and the collector plate.

[0007] Since the collector plate has a coefficient of expansion greater than the coefficient of expansion of the cathode, once the cathode assembly is at operating temperature, the collector plate risks creating cracks in the cathode.

[0008] Document FR 2 251 529 describes a cell for the electrolytic production of aluminium and, more particularly, the cathode lining of such a cell, consisting of pre-baked parallelepiped blocks of carbon or graphite, joined with carbon rammed earth or glued. Most often, the lower face of each block is hollowed out with a groove in which a metal current supply bar, made of mild steel, is sealed, either with cast iron or with carbon paste.

[0009] A cracked cathode has a much shorter lifespan than an uncracked cathode. This lifespan can be reduced to a few days in the case of significant cracks.

[0010] The present invention aims to resolve all or part of the drawbacks mentioned above. Statement of the invention

[0011] To this end, the present invention relates to a cathode assembly for an electrolysis cell comprising: a cathode block having a first surface, at least one sealing groove opening onto the first surface, and a plurality of electrical contact plugs mounted in electrical contact with the first surface of the cathode block; at least one current supply plate in electrical contact with at least one electrical contact plug, the current supply plate being to be connected to at least one unit for connection to an electric current source; and at least one current supply bar sealed in the sealing groove and fixed to the current supply plate, the current supply bar having an expansion coefficient identical to within 10% of the expansion coefficient of the current supply plate.

[0012] For the purposes of the present invention, “a substantially identical coefficient of expansion” means “a coefficient of expansion identical to within 10%”.

[0013] For example, a measurement of an expansion coefficient of a current supply bar is carried out by measuring the change in the size of said current supply bar as a function of temperature.

[0014] According to one advantage, a current supply bar fixed to a current supply plate and sealed to the cathode block makes it possible to reduce the electrical resistance of the cathode assembly and therefore makes it possible to limit the number of electrical contact pins because the mechanical maintenance between the current supply plate and the cathode block is partially ensured by the connection between the current supply bar, the current supply plate and the cathode block.

[0015] Sealing the current feed bar in the sealing groove allows a degree of freedom of the current feed bar relative to the cathode block.

[0016] Furthermore, limiting the number of contact pins also allows for greater mechanical flexibility of the cathode assembly. Thus, the resulting cathode assembly presents limited risks of cracking.

[0017] According to one embodiment, the current supply bar is fixed by welding to the current supply plate.

[0018] According to one advantage, a current feed plate welded to a current feed bar having the same coefficient of expansion allows for extended weld life.

[0019] According to one advantage, a current supply plate welded to a supply bar 30 having the same expansion coefficient makes it possible to limit the risk of cracking of the cathode block.

[0020] According to one embodiment, the electrical contact plugs are mounted in electrical contact with the first surface of the block by inserting said electrical contact plugs into different bores present on the first surface of said cathode block.

[0021] According to one embodiment, the cooperation space between the at least one current supply bar and the cathode block defines a first zone. The cooperation space between the electrical contact plugs and the cathode block defines a second zone excluded from the first zone.

[0022] According to one advantage, a plurality of electrical contact pins mounted in electrical contact with the first surface of the cathode block makes it possible to improve the distribution of the current lines in said cathode block.

[0023] According to one advantage, improving the distribution of the current lines in said cathode block makes it possible to improve the performance of the cathode assembly for an electrolytic cell.

[0024] According to one advantage, improving the distribution of the current lines in said cathode block makes it possible to limit the wear of the cathode block and thus makes it possible to extend the service life of the cathode assembly for the electrolysis tank.

[0025] According to one advantage, the use of several current feeder plates reduces the differential expansion between each current feeder plate and the cathode block. The reduction of the differential expansion between each current feeder plate and the cathode block makes it possible to limit the risks of cracking of said cathode block.

[0026] According to one advantage, limiting the risks of cracking of the cathode block makes it possible to extend the life of the cathode assembly for the electrolysis tank.

[0027] According to one advantage, the use of several current supply bars makes it easier to handle the cathode assembly.

[0028] According to one advantage, the use of several current supply bars makes it possible to limit the risk of cracking of the cathode block.

[0029] According to one embodiment, the sealing of the current supply bar in the sealing groove of the cathode block is a cast iron sealing.

[0030] According to one embodiment, the cast iron sealing is carried out with a white phosphorus cast iron.

[0031] According to one embodiment, the cast iron sealing is carried out with phosphorus gray cast iron.

[0032] According to one advantage, a cast iron seal allows a degree of freedom of the current supply bar relative to the cathode block sufficient to limit the risks of cracking of said cathode block.

[0033] According to one embodiment, the sealing of the current supply bar in the sealing groove of the cathode block is a sealing with sealing paste.

[0034] According to one embodiment, the sealing with the sealing paste is carried out with a paste comprising a carbon powder and a binder.

[0035] According to one advantage, the sealing paste 40 shrinks when the temperature of the electrolytic cell rises. A sealing paste shrinking when the temperature of the electrolytic cell rises makes it possible to limit the risks of cracking of the cathode block 10 induced by the expansion of the current supply bar 30.

[0036] According to one advantage, the sealing paste 40 is a paste free of tar and pitch as well as polycyclic aromatic hydrocarbons.

[0037] According to one advantage, the sealing paste 40 is a paste free of phenolic resin.

[0038] According to one embodiment, the paste sealing is carried out cold. According to one advantage, cold paste sealing is economical.

[0039] According to one embodiment, each electrical contact plug has a cylinder shape comprising a deformation groove, allowing local deformation of the electrical contact plug.

[0040] According to one advantage, a deformation groove allows local deformation of an electrical contact plug and allows said electrical contact plug to have a low elastic resistance. An electrical contact plug with a low elastic resistance makes it possible to limit the risks of cracking of the cathode block.

[0041] According to one embodiment, the deformation groove extends over 5% to 50% of the length of an electrical contact plug.

[0042] According to one embodiment, the deformation groove preferably extends over 15% to 35% of the length of the electrical contact plug.

[0043] For the purposes of the present invention, length is a dimension that is substantially longer than other dimensions.

[0044] According to one advantage, a deformation groove 51 allows local deformation of an electrical contact plug 50 and allows said electrical contact plug 50 elastic and plastic deformation of said electrical contact plug 50. An electrical contact plug 50 capable of undergoing elastic and plastic deformation makes it possible to limit the risks of cracking of the cathode block 10.

[0045] According to one embodiment, the deformation groove has a circular section.

[0046] According to one embodiment, the deformation groove has a rectangular section. A rectangular section allows guided deformation of the deformation groove.

[0047] According to one embodiment, the deformation groove is adapted to at least partially delimit a connecting head and a connecting member on either side of an electrical contact plug.

[0048] According to one advantage, the connecting member of an electrical contact plug is adapted to be connected to the cathode block while the connecting head of an electrical contact plug is adapted to be connected to a current supply plate.

[0049] According to one embodiment, the electrical contact plugs are twisted wire bundle electrical contact plugs.

[0050] According to one advantage, electrical contact plugs with twisted wire bundles allow low elastic resistance and thus limit the risks of cracking of the cathode block.

[0051] Cathode assembly for an electrolytic cell according to any one of claims 1 to 4 in which the electrical contact pins are anisotropic electrical contact pins.

[0052] According to one advantage, an anisotropic electrical contact plug allows a lower elastic resistance of said electrical contact plug and thus limits the risks of cracking of the cathode block.

[0053] According to one embodiment, the electrical contact plugs have elastic resistances that differ from one another.

[0054] According to one advantage, electrical contact plugs having elastic resistances that differ from one another make it possible to combine good fixing of the at least one current supply plate to the cathode block while limiting the risks of cracking of said cathode block.

[0055] According to one embodiment, the cathode block is made of a mixture of anthracite and graphite.

[0056] According to one advantage, a cathode block consisting of a mixture of anthracite and graphite improves the distribution of the current lines in said cathode block.

[0057] According to one advantage, a cathode block made from a mixture of anthracite and graphite improves current distribution and makes it possible to limit wear of said cathode block and thus prolong the life of the cathode assembly for an electrolysis tank.

[0058] According to one embodiment, the cathode block 10 is made of graphite.

[0059] According to one advantage, a cathode block 10 made of graphite makes it possible to limit energy consumption during operation of the electrolysis tank.

[0060] According to one embodiment, the number of electrical contact pins per square meter is between 10 and 80.

[0061] According to one embodiment, the number of electrical contact pins per square meter is preferably between 20 and 65.

[0062] According to one embodiment, the number of electrical contact pins per square meter is ideally between 30 and 50.

[0063] According to an advantage, a number of electrical contact pins per square meter between 10 and 80 allows a good connection between the at least one current supply plate and the cathode block.

[0064] Another advantage is that a number of electrical contact pins per square meter between 10 and 80 helps to limit the risk of cracking of the cathode block.

[0065] According to one advantage, a number of electrical contact pins per square meter between 10 and 80 improves the distribution of current lines in said cathode block.

[0066] The invention also relates to an electrolysis cell for the production of a metal, comprising: an outer steel shell; a layer of insulating material adjacent to the outer steel shell; a carbonaceous layer covering the insulating material and protecting the insulating material from an electrolytic bath intended to be contained in the cell; and a cathode assembly for an electrolytic cell according to any one of claims 1 to 9. Brief description of the figures

[0067] The invention will be further understood with the aid of the detailed description set out below with reference to the appended drawings in which: there figure 1 represents a sectional view of a cathode assembly in accordance with the present invention; the figure 2 represents a sectional view of a cathode assembly in accordance with the present invention; the figure 3 represents a sectional view of a cathode assembly in accordance with the present invention; the figure 4 represents a current supply plate in accordance with the present invention; the Figure 5 represents a current supply bar in accordance with the present invention; the figure 6 represents an electrical contact plug in accordance with the present invention; and the figure 7 represents a cathode block in accordance with the present invention. Description with reference to figures

[0068] THE figures 1 to 3represent a cathode assembly for an electrolytic cell comprising a cathode block 10, a current supply plate 20 and two current supply bars 30.

[0069] There figure 4 illustrates a current supply plate 20 comprising several insertion holes 21.

[0070] There Figure 5 illustrates a current supply bar 30.

[0071] There figure 7 represents a cathode block 10 having a second surface 11 and a first surface 12, two sealing grooves 13 opening onto the first surface 12 and a plurality of electrical contact pins 50.

[0072] According to one embodiment, the cathode block 10 is made of graphite.

[0073] According to one advantage, a cathode block 10 made of graphite makes it possible to limit energy consumption during operation of the electrolysis tank.

[0074] According to one embodiment, the cathode block 10 is made of a mixture of anthracite and graphite.

[0075] According to one advantage, a cathode block 10 made of a mixture of anthracite and graphite improves the distribution of the current and makes it possible to limit the wear of said cathode block 10 and thus makes it possible to extend the life of the cathode assembly for the electrolysis tank.

[0076] There figure 6 illustrates an electrical contact plug 50 in the shape of a cylinder comprising a deformation groove 51.

[0077] According to one advantage, a deformation groove 51 allows local deformation of an electrical contact plug 50 and allows said electrical contact plug 50 to have low elastic resistance.

[0078] According to one embodiment, the deformation groove 51 extends over 5% to 50% of the length of the electrical contact plug 50.

[0079] According to one embodiment, the deformation groove 51 preferably extends over 15% to 35% of the length of the electrical contact plug 50.

[0080] For the purposes of the present invention, length is a dimension that is substantially longer than other dimensions.

[0081] According to one advantage, a deformation groove 51 extending over 5% to 50% of the length of an electrical contact plug 50 allows elastic and plastic deformation of said electrical contact plug 50.

[0082] According to one embodiment, the deformation groove 51 has a circular section.

[0083] According to one embodiment, the deformation groove 51 has a rectangular section. A rectangular section allows guided deformation of the deformation groove 51.

[0084] According to one embodiment, the deformation groove 51 is adapted to at least partially delimit a connecting head 52 and a connecting member 53 on either side of the electrical contact plug 50.

[0085] As illustrated in the figure 1 , the electrical contact pins 50 are mounted in electrical contact with the first surface 12 of the cathode block 10.

[0086] According to one embodiment, the electrical contact plugs 50 are mounted in electrical contact with the first surface of the block by inserting said electrical contact plugs 50 into different bores present on the first surface of said cathode block 50.

[0087] According to one embodiment, the current supply bar 30 is sealed in the at least one sealing groove 13.

[0088] The sealing of the current supply bar 30 in the sealing groove 13 allows a degree of freedom of the current supply bar 30 relative to the cathode block 10.

[0089] According to one embodiment, the sealing of the current supply bar 30 in the sealing groove 13 of the cathode block 10 is a cast iron sealing.

[0090] According to one embodiment, the cast iron sealing is carried out with a white phosphorus cast iron.

[0091] According to one embodiment, the cast iron sealing is carried out with phosphorus gray cast iron.

[0092] According to one advantage, a cast iron seal allows a degree of freedom of the current supply bar 30 relative to the cathode block 10 sufficient to limit the risks of cracking of said cathode block 10.

[0093] According to one advantage, limiting the risks of cracking of the cathode block 10 makes it possible to extend the service life of the cathode assembly for the electrolysis tank.

[0094] According to one embodiment, the sealing of the current supply bar 30 in the sealing groove 13 of the cathode block 10 is a sealing with the sealing paste 40.

[0095] According to one embodiment, the sealing with the sealing paste 40 is carried out with a paste comprising a carbon powder as well as a binder.

[0096] According to one advantage, the sealing paste 40 shrinks when the temperature of the electrolytic cell rises. A sealing paste shrinking when the temperature of the electrolytic cell rises makes it possible to limit the risks of cracking of the cathode block 10 induced by the expansion of the current supply bar 30.

[0097] By way of example, a measurement of an expansion coefficient of a current supply bar 30 is carried out by measuring the change in the size of said current supply bar 30 as a function of the temperature.

[0098] According to one advantage, the sealing paste 40 is a paste free of tar and pitch as well as polycyclic aromatic hydrocarbons.

[0099] According to one advantage, the sealing paste 40 is a paste free of phenolic resin.

[0100] According to one embodiment, the paste sealing is carried out cold. According to one advantage, cold paste sealing is economical.

[0101] According to one embodiment, the cooperation space between the at least one current supply bar 30 and the cathode block 10 defines a first zone. The cooperation space between the electrical contact pins 50 and the cathode block 10 defines a second zone excluded from the first zone.

[0102] According to one embodiment, the current supply bar 30 is fixed to at least one current supply plate 20.

[0103] According to one embodiment, the current supply bar 30 is fixed by welding to the current supply plate 20.

[0104] According to one embodiment, the current supply bar 30 has an expansion coefficient substantially identical to the expansion coefficient of the current supply plate 20.

[0105] For the purposes of the present invention, “a substantially identical coefficient of expansion” means “a coefficient of expansion identical to within 10%”.

[0106] According to one advantage, a current supply plate 20 welded to a supply bar 30 having the same coefficient of expansion allows for an extended service life of the weld.

[0107] According to one advantage, a current supply plate 20 welded to a supply bar 30 having the same expansion coefficient makes it possible to limit the risk of cracking of the cathode block 10. According to one embodiment, the current supply plate 20 is in electrical contact with at least one electrical contact plug 50, and comprises at least one unit for connection to an electrical current source.

[0108] According to one embodiment, the electrical contact plugs 50 are inserted into insertion holes 21 of the current supply plate 20.

[0109] According to one advantage, a current supply bar 30 fixed to a current supply plate 20 and sealed to the cathode block 10 makes it possible to reduce the electrical resistance of the cathode assembly and therefore makes it possible to limit the number of electrical contact pins 50 because the mechanical support between the current supply plate 30 and the cathode block 20 is partially ensured by the connection between the current supply bar 30, the current supply plate 20 and the cathode block 10.

[0110] Furthermore, limiting the number of contact pins 50 also allows greater mechanical flexibility of the cathode assembly. Thus, the resulting cathode assembly presents limited risks of cracking of the cathode block.

[0111] According to one advantage, a plurality of electrical contact pins 50 mounted in electrical contact with the first surface 12 of the cathode block 10 makes it possible to obtain a better distribution of the current lines in the cathode block 10.

[0112] According to one advantage, a cathode block 10 made of a mixture of anthracite and graphite improves the distribution of the current lines in said cathode block 10.

[0113] According to one advantage, a better distribution of the current lines in the cathode block 10 makes it possible to improve the performance of the cathode assembly for an electrolytic cell.

[0114] According to one advantage, a better distribution of the current lines in the cathode block 10 makes it possible to limit the wear of the cathode block 10 and thus makes it possible to extend the service life of the cathode assembly for the electrolysis tank.

[0115] According to one embodiment, the electrical contact plugs 50 are in the shape of a cylinder comprising a deformation groove 51.

[0116] According to one advantage, a deformation groove 51 allows local deformation of an electrical contact plug 50 and allows said electrical contact plug 50 elastic and plastic deformation of said electrical contact plug 50. An electrical contact plug 50 capable of undergoing elastic and plastic deformation makes it possible to limit the risks of cracking of the cathode block 10.

[0117] According to one advantage, the connecting member 53 of an electrical contact plug 50 is adapted to be connected to the cathode block 10 while the connecting head 52 of an electrical contact plug 50 is itself adapted to be connected to a current supply plate 20.

[0118] According to one embodiment, the electrical contact plugs 50 are electrical contact plugs 50 with twisted wire bundles.

[0119] According to one advantage, electrical contact plugs 50 with twisted wire bundles allow low elastic resistance and thus limit the risks of cracking of the cathode block 10.

[0120] According to one embodiment, the electrical contact plugs 50 are anisotropic electrical contact plugs 50.

[0121] According to one advantage, an anisotropic electrical contact plug 50 allows a lower elastic resistance of said electrical contact plug 50 and thus limits the risks of cracking of the cathode block 10.

[0122] According to one embodiment, the electrical contact plugs 50 have elastic resistances that differ from one another.

[0123] According to one advantage, electrical contact pins 50 having elastic resistances that differ from one another make it possible to combine good fixing of the at least one current supply plate 20 to the cathode block 10 while limiting the risks of cracking of said cathode block 10.

[0124] According to one embodiment, the number of electrical contact pins 50 per square meter is between 10 and 80.

[0125] According to one embodiment, the number of electrical contact pins 50 per square meter is preferably between 20 and 65.

[0126] According to one embodiment, the number of electrical contact pins 50 per square meter is ideally between 30 and 50.

[0127] According to one advantage, a number of electrical contact pins 50 per square meter of between 10 and 80 allows a good connection between the at least one current supply plate 20 and the cathode block 10.

[0128] According to another advantage, a number of electrical contact pins 50 per square meter between 10 and 80 makes it possible to limit the risks of cracking of the cathode block 10.

[0129] According to one advantage, a number of electrical contact pins 50 per square meter of between 10 and 80 improves the distribution of the current lines in said cathode block 10.

[0130] According to one embodiment, the cathode assembly comprises two current supply bars 30 per sealing groove 13.

[0131] According to one advantage, the use of two current supply bars 30 makes it easier to handle the cathode assembly.

[0132] According to one advantage, the use of two current supply bars 30 makes it possible to limit the risk of cracking of the cathode block 10.

[0133] According to an embodiment not shown, several current supply plates 20 are fixed to the current supply bar 30.

[0134] According to one advantage, the use of several current supply plates 20 reduces the differential expansion between each current supply plate 20 and the cathode block 10. The reduction of the differential expansion between each current supply plate 20 and the cathode block 10 makes it possible to limit the risks of cracking of said cathode block 10.

[0135] The invention also relates to an electrolysis cell for the production of a metal, comprising: an outer steel shell; a layer of insulating material adjacent to the outer steel shell; a carbonaceous layer covering the insulating material and protecting the insulating material from an electrolytic bath intended to be contained in the cell; and a cathode assembly for an electrolytic cell according to any one of claims 1 to 9.

Claims

1. A cathode assembly for an electrolytic cell comprising: a cathode block (10) having a first surface (12), at least one sealing groove (13) opening onto the first surface (12), and a plurality of electrical contact plugs (50) mounted in electrical contact with the first surface (12) of the cathode block (10); at least one current supply plate (20) in electrical contact with at least one of the electrical contact plugs (50), the current supply plate (20) being to be connected to at least one unit for connection to an electric current source; at least one current supply bar (30) sealed within the at least one sealing groove (13) and fastened to at least one current supply plate (20), the current supply bar (30) having a thermal expansion coefficient identical within a 10% margin to the thermal expansion coefficient of the current supply plate (20).

2. The cathode assembly for an electrolytic cell according to claim 1, wherein sealing of the current supply bar (30) within the sealing groove (13) of the cathode block (10) is a sealing with cast iron.

3. The cathode assembly for an electrolytic cell according to claim 1, wherein sealing of the current supply bar (30) within the sealing groove (13) of the cathode block (10) is a sealing with a sealing paste (40).

4. The cathode assembly for an electrolytic cell according to any one of claims 1 to 3, wherein each of the electrical contact plugs (50) has a cylinder shape comprising a deformation groove (51) enabling a local deformation of the electrical contact plug.

5. The cathode assembly for an electrolytic cell according to any one of claims 1 to 4, wherein the electrical contact plugs (50) are electrical contact plugs (50) with twisted wires bundles.

6. The cathode assembly for an electrolytic cell according to any one of claims 1 to 4, wherein the electrical contact plugs (50) are anisotropic electrical contact plugs (50).

7. The cathode assembly for an electrolytic cell according to any one of claims 1 to 6, wherein the electrical contact plugs (50) have elastic strengths that are different from each other.

8. The cathode assembly for an electrolytic cell according to any one of claims 1 to 7, wherein the cathode block (10) is constituted by a mixture of anthracite and graphite.

9. The cathode assembly for an electrolytic cell according to any one of claims 1 to 8, wherein the number of electrical contact plugs (50) per square meter is comprised between 10 and 80.

10. An electrolytic cell for the production of a metal, comprising: a. an external envelope made of steel; b. a layer of an insulating material adjacent to the steel-made external shell; c. a carbonaceous layer covering the insulating material and protecting the insulating material of an electrolytic bath intended to be contained in the cell; and d. a cathode assembly for an electrolytic cell according to any one of claims 1 to 9.