WO2024100132A2

WO2024100132A2 - Cathode current collector and connector assembly for an aluminum electrolysis cell

Info

Publication number: WO2024100132A2
Application number: PCT/EP2023/081178
Authority: WO
Inventors: Markus Pfeffer; Seweryn MIELNIK; Oscar VERA GARCIA; René VON KAENEL
Original assignee: Novalum Sa; Tokai Cobex Gmbh
Priority date: 2022-11-09
Filing date: 2023-11-08
Publication date: 2024-05-16
Also published as: DE102022129669A1

Abstract

The invention relates to a cathode current collector and connector assembly, a kit-of-parts for manufacturing a cathode current collector and an aluminum electrolysis cell comprising a cathode current collector and connector assembly.

Description

Cathode current collector and connector assembly for an aluminum electrolysis cell

FIELD OF THE INVENTION

The invention relates to a cathode current collector and connector assembly, a kit-of-parts for manufacturing a cathode current collector and an aluminum electrolysis cell comprising a cath- ode current collector and connector assembly.

BACKGROUND OF THE INVENTION

Aluminium is produced by the Hall-Heroult process, by electrolysis of alumina dissolved in cryolite based electrolytes at a temperature up to 1000°C. A typical Hall-Heroult cell is com- posed of a steel shell, an insulating lining of refractory materials and a carbon cathode holding the liquid metal. The cathode is composed of a number of cathode blocks in which collector bars are embedded at their bottom to extract the current flowing through the cell.

A number of patent publications have proposed different approaches for minimizing the voltage drop between the liquid metal to the end of the collector bars. W02008/062318 discloses the use of a high conductive material in complement to the existing steel collector bar and gives reference to WO 02/42525, WO 01/63014, WO 01/27353, WO 2004/031452 and WO 2005/098093 that disclose solutions using copper inserts inside collector steel bars. US patent 4,795,540 splits the cathode in sections as well as the collector bars. WO2001/27353 and W02001/063014 use high conductive materials inside the collector bars. US 2006/0151333 covers the use of different electrical conductivities in the collector bars. WO 2007/118510 proposes to increase the section of the collector bar when moving towards the centre of the cell for changing the current distribution at the surface of the cathode. US 5,976,333 and 6,231 ,745 present the use of a copper insert inside the steel collector bar. EP 2 133446 A1 describes cathode block arrangements to modify the surface geometry of the cathode in order to stabilize the waves at the surface of the metal pad and hence to minimize the ACD (anode to cathode distance). WO 2011/148347 describes a carbon cathode of an aluminium production cell that comprises highly electrically conductive inserts sealed in enclo- sures within the carbon cathode. These inserts alter the conductivity of the cathode body but do not participate in current collection and extraction by the collector bars. The electrical con- ductivity of molten cryolite is very low, and the ACD cannot be decreased much due to the formation of magneto-hydrodynamic instabilities leading to waves at the metal-bath (metal- cryolite electrolyte) interface. The existence of waves leads to a loss of current efficiency of the process and does not allow decreasing the energy consumption under a critical value. On average in the aluminium industry, the current density is such that the voltage drop in the ACD is a minimum at 0.3 V/cm. As the ACD is 3 to 5 cm, the voltage drop in the ACD is typically 1 .0 V to 1 .5 V. The magnetic field inside the liquid metal is the result of the currents flowing in the external busbars and the internal currents. The internal local current density inside the liquid metal is mostly defined by the cathode geometry and its local electrical conductivity. The magnetic field and current density produce the Lorentz force field which itself generates the metal surface contour, the metal velocity field and defines the basic environment for the mag- neto-hydrodynamic cell stability. The cell stability can be expressed as the ability of lowering the ACD without generating unstable waves at the surface of the metal pad. The level of sta- bility depends on the current density and induction magnetic fields but also on the shape of the liquid metal pool. The shape of the pool depends on the surface of the cathode and the ledge shape. The prior art solutions respond to a given level to the needed magneto-hydrodynamic status to satisfy good cell stability (low ACD) but the solutions using copper inserts often need sophisticated machining processes.

Therefore, in recent years there has been a trend of substituting steel collector bars equipped with copper inserts, with pure copper collector bars. For example, WO 2016/079605 discloses a highly electrically conductive collector bar that comprises a central part located under a cen- tral part of the carbon cathode, usually directly located into a cathode slot or through-hole or using a U-shaped profile as support, this central part of the highly electrically conductive col- lector bar having at least its upper outer surface in direct electrical contact with the carbon cathode or in contact with the carbon cathode through an electrically conductive interface formed by an electrically conductive glue and/or an electrically conductive flexible foil or sheet applied over the surface of the highly electrically conductive connector bar. The material of the highly electrically conductive collector bar is selected from copper, aluminum, silver and alloys thereof and comprises one or two outer parts located adjacent to and on one side or on both sides of the central part and a terminal end part or parts extending outwardly from said outer part(s). These terminal end part(s) of the highly electrically conductive collector bar is/are elec- trically connected in series each to a steel conductor bar of greater cross-sectional area than the highly electrically conductive collector bar, said steel conductor bar(s) extending outwardly, and the terminal end part(s) of this current collector and connector assembly including the steel conductor bar are serving as a cathode connection point to an external current supply busbar. In an aluminum production plant, a multitude of cells are arranged in line and are connected electrically in series. The busbar system provides the electrical connection from the upstream reduction cell cathodes to the downstream cell anodes, formed by at least one horizontal rigid beam supporting at least one horizontal conducting rod comprising an anode frame on which anode suspension shafts are attached. Regularly, each cell comprises a plurality of parallelly arranged longitudinal cathode current collector and connector assemblies each comprising two connecting points arranged at the terminal ends of the assembly. The connecting points are electrically connected to the supply busbar, to enable the flow of current. In particular due to deviating path lengths of the current from the different cathode connecting points to the down- stream cell anode, an unequal current distribution is observed within the busbar system and consequently in the cathode, with different current pick-ups by the collector bars. Therefore, there have been efforts for improving the current distribution by amending the busbar design, e.g. by adjusting the required path length, grouping cathode bars to common busbar sections or using busbars of differing cross-section.

Still, amending the busbar structure can be laborious and costly and cannot be performed within already existing cells, which is the reason, why there is still a need for improvement as regards a simple and efficient cell design to compensate for unbalanced current flows, which may lead to asymmetric wear behavior, unstable cell performance and the associated delete- rious effects on the cell efficiency.

OBJECT OF THE INVENTION

Consequently, it is an object of the present invention to provide a cathode current collector and connector assembly for an aluminum electrolysis cell, which has a higher and more stable performance, and which enables performing electrolysis with a permanent low contact re- sistance and low voltage drops.

DESCRIPTION OF THE INVENTION

The above problems are solved by cathode current collector and connector assembly for an aluminum electrolysis cell containing ai) a first copper or copper alloy current collector system with an optional protective steel layer cladding, 32) a second copper or copper alloy current collector system with an op- tional protective steel layer cladding, b) at least one longitudinal carbonaceous cathode with at least one groove extending in the longitudinal direction of the carbonaceous cathode for receiving at least a portion of ai) and a2), wherein ai) is at least partially arranged in the at least one groove of b) along the longitudinal direction of the carbonaceous cathode over a length Li with a first portion au), and wherein 82) is at least partially arranged in the at least one groove of b) along the longitudinal direction of the carbonaceous cathode over a length L2 with a first portion 82,1), wherein the portion of b) extending in the longitudinal direction along the length Li is defined as the first portion of b) denoted bi), and wherein the portion of b) extending in the longitudinal direction along the length L2 is defined as the second portion of b) denoted as b2), wherein the cathode current collector and connector assembly com- prises a first connecting point, wherein the cathode current collector and connector assembly com- prises a second connecting point, wherein the first and the second connecting points are electrically con- nectable to an external supply busbar, ci) a first conductor element electrically interconnected between ai) and the first connecting point

C2) a second conductor element electrically interconnected between 82) and the second connecting point, wherein the sum of electrical resistivities of ai), bi) and the optionally contained Ci) is different from the sum of electrical resistivities of a?), ba) and the optionally contained C2).

The cathode current collector and connector assembly comprises a longitudinal carbonaceous cathode with at least one groove recessed in one of the longitudinal surfaces in the longitudinal direction. In the at least one groove at least two current collector systems are at least partially arranged. In case the at least two current collector systems are arranged in a single groove, the current collector systems are electrically separated, e.g. by an insulating material. The electrical contact between carbonaceous cathode and current collectors can be achieved over the whole embedded area. The assembly can further comprise one or more conductor ele- ments, preferably comprising or consisting of steel, to which, preferably, the terminal end part of the current collector(s) (e.g. collector bar) is/are electrically connected. I.e. in the context of the invention the term “cathode current collector and connector assembly” encompasses em- bodiments both without conductor element (regularly denoted as “cathode current collector assembly”) and with conductor element (regularly denoted as “cathode current collector and connector assembly”).

The above split-cell design with two halves (in longitudinal direction) of a current collector and connector assembly comprises (at least) two connecting points, which are located at the cur- rent collector system or the conductor element of each respective half. Each connecting point is electrically connectable to an external supply busbar. The electrical current flows from the carbon cathode into the copper current collector system of each half and then through the optional conductor elements to the busbar via the connecting point. Preferably, the connecting points are located at the current collectors (or the conductor elements, in case the assembly comprises one or more), in particular at the respective terminal end parts.

The groove as well as the corresponding (“negative”) current collector system can have differ- ent shapes. Regularly, the current collector system is bar shaped, in particular rectangular bar shaped, however, also elliptical or rounded forms are possible.

The current collector systems can consist of one or more elements, in particular bar shaped elements. Preferably, the current collector systems comprise at least two longitudinal, rectan- gular bar elements, which are spaced apart by a thermal expansion gap or insulating material. The “sum of electrical resistivities” also includes contact resistivities occurring at the interface between the elements ai), bi) and the optionally containecd1) , respectively aa), ba) and the optionally contained ca).

According to the invention, the term ''carbonaceous" means all types of materials based on anthracite and/or graphite and/or coke, regardless whether these cathodes are baked or graphitized.

In a preferred embodiment of the invention, the cathode current collector assembly is config- ured in such a way that the groove is arranged at the bottom side of the cathode current col- lector assembly in the operating position of the cathode current collector assembly in the elec- trolysis cell.

In a preferred embodiment of the invention, the cathode is a rectangular cathode block.

Preferably, the current collector systems exhibit a bar shape, most preferably a rectangular- bar shape.

Preferably, the difference between the sum of electrical resistivities of ai), bi) and the optionally containecd1) and the sum of electrical resistivities of as), b2) and the optionally contained C2). is £ 1 %, more preferred £ 2%, even more preferred 3%, and most preferred s 4%, but pref- erably also less than 30%. The foregoing values are in reference to the higher electrical resis- tivity value.

In clear contrast to the established teaching of the prior art proposing a symmetric cell design, the inventors have found out that by using an asymmetric design of the current collector and connector assembly, the current pick up at both connecting points of the current collector and connector assembly can be equalized. Thereby, an aluminum electrolysis cell with an en- hanced current efficiency is obtained, which in turn decreases the overall specific energy con- sumption. Further, the erosion of the cathode block is more homogeneous, reducing the asym- metry of the typical so-called W-shape erosion. Consequently, the inventive cathode current collector and connector assembly enables obtaining an aluminum electrolysis cell, which has a higher and more stable performance, and which enables performing electrolysis with a per- manent low contact resistance and low cathode voltage drops. With aid of the inventive asym- metric cell design it is possible to compensate for unbalanced current flows without the neces- sity of implementing a complex busbar design. A first option found by the inventors to influence the sum of electrical resistivities is amending the amount of copper or copper alloy and/or the geometric shape of the current collector sys- tems ai) and as).

Hence, in a preferred embodiment deviating amounts of copper or copper alloy are used in the current collector systems ai) and a2). A significantly reduced amount of copper or copper alloy on one side of the cathode current collector and connector assembly will result in a higher resistivity, which means this side will have a resistance, which in turn decreases the current pick up at the respective connecting point.

In a preferred embodiment of the invention, the amount of copper or copper alloy of ai) is < 0.9 times the mass of copper or copper alloy of a2), more preferred < 0.8 times the mass of copper or copper alloy of az), even more preferred s 0.7 times the mass of copper or copper alloy of 32) and most preferred £ 0.6 times the mass of copper or copper alloy of a2), but preferably also s 0.3 times the mass of copper or copper alloy of a2).

The same effect can be achieved with a deviating geometric shape of ai) and az). E.g. in case the current collector systems are bar shaped, the cross-sectional area of the ai) bar may be smaller than the one of a2), or vice versa, thereby increasing the resistivity on one side of the current collector and connector assembly. In this case, preferably, the cross-sectional area of the ai) bar is £ 0.9 times the cross-sectional area of the az) bar, more preferred s 0.8 times the cross-sectional area of the a2) bar, even more preferred < 0.7 times the cross-sectional area of the a2) bar and most preferred < 0.6 times the cross-sectional area of the az) bar, but pref- erably also > 0.3 times the cross-sectional area of the a2) bar.

Another option for increasing or decreasing the resistivity of one side of the current collector and connector assembly is adjusting the contact surface between cathode and current collec- tor systems. This can be accomplished by varying the length the collector system is extending in the longitudinal direction of the groove of the cathode. With an increasing length Li and L₂ a higher contact surface is obtained, thereby decreasing the contact resistance. In a preferred embodiment of the invention, Li is < 0.9*l_2, more preferred < 0.8*l_2, even more preferred < 0.7*L₂ and most preferred < 0.6*L₂, but preferably also > 0.3 L₂.

In a preferred embodiment of the invention, the contact surface between ai) and bi) is < 0.9 times the contact surface between a2) and b2), more preferred < 0.8 times the contact surface between a2) and b2), even more preferred < 0.7 times the contact surface between a2) and b2) and most preferred 0.6 times the contact surface between a,₂) and b2), but preferably also £ 0.3 times the contact surface between aa) and bg).

Another option for increasing or decreasing the resistivity of one side of the current collector and connector assembly is using an at least partial isolation of ai) and/or 82).

In a preferred embodiment of the invention, ai) and/or 82) are at least partially electrically iso- lated, preferably with a refractory material such as alumina, silica, silicon carbide or boron nitride, preferably in form of a sheet.

In a preferred embodiment of the invention, the surface of ai) being electrically isolated is < 0.9 times the electrically isolated surface of 82), more preferred < 0.8 times the electrically isolated surface of 82), even more preferred s 0.7 times the electrically isolated surface of a.2) and most preferred £ 0.6 times the electrically isolated surface of 82), but preferably also £ 0.3 times the electrically isolated surface of 82).

In another preferred embodiment, the current collector system is bar shaped and ai) and 82) are surrounded by an electrically isolating layer over a length Lj_S0-i (ai)) and Lj_S0-2 (a2)), where L iso-1 is S 0.9* Liso-2, more preferred 0.8* Lj_S0-2, even more preferred S 0.7* Lj_S0-2 and most preferred S 0.6* Lj_S0-2, but preferably also 0.3* Lj_S0-2.

Another option for increasing or decreasing the resistivity of one side of the current collector and connector system is using different copper alloys.

Hence, in a preferred embodiment of the invention, the specific electrical conductivity of the copper or copper alloy of ai) and 82) is different.

In a preferred embodiment of the invention, the cathode current collector and connector as- sembly comprises one or more conductor elements, being preferably arranged at the terminal end parts of the current collector systems. The optional conductor elements Ci) and C2) both preferably comprise at least one recess each, whereas a1) is at least partially arranged in a recess ofc1) with a second portion 81.2), and/or C2) is at least partially arranged in a recess of C2) with a second portion 82,2). The type of conductor element, i.e. its composition, as well as its size and geometry also impact the resistivities of the sides of the current collector and con- nector assembly. A simple and efficient way to adjust the resistivities of the sides of the current collector and connector assembly is changing the contact surface between such an optional conductor ele- ment and the current collector system. This turned out to be particularly preferred as the design restrictions are comparably low at this position.

In a preferred embodiment of the invention, the contact surface between ai) andc1) is < 0.9 times the contact surface between 82) and C2), more preferred < 0.7 times the contact surface between 82) and C2), even more preferred < 0.4 times the contact surface between 82) and C2) and most preferred < 0.2 times the contact surface between a.2) and C2), but preferably also > 0.1 times the contact surface between 82) and C2).

Preferably, the recess of the steel bar is formed to block the movement of the second portion of the copper current collector system in two or more, more preferably three or more, even more preferably four or more or even five of the six spatial directions normal conditions ac- cording to DIN 1341 , when the second portion 81,2) respectively 82,2) of the copper current collector system is arranged in the recess of the steel conductor element.

Preferably, the recess of the steel bar is formed to block the movement of the second portion of the current collector system in one or more additional spatial directions under operating conditions of a Hall-Heroult process in comparison to normal conditions.

Preferably, the recess of the steel bar is formed to block the movement of the second portion of the current collector system by friction and/or material fit.

In a particularly preferred embodiment, the recess has the form of a pocket, which blocks the movement in four (one side open pocket) or five (fully surrounding pocket) of the six spatial directions. As with increasing movement constraints the pressure increases, the above effects are enhanced in such embodiments and a tight friction and material fit can be obtained. In case the recess is a pocket, which fully surrounds the steel bar, the beneficial effects are maximized.

For the purposes of fixing the copper current collector system in its position, the steel conductor element may comprise several elements, e.g. the pocket can be formed by two half sections, which can be assembled to surround the second portion of the current collector system. An- other option is to create a pocket, which solely blocks the movement in four spatial directions, place the second portion of the current collector system and close, i.e. cover, the pocket with a steel plate, which may be welded or otherwise connected to the rest of the steel conductor element. After arranging the second portion of the copper current collector system in the recess (e.g. in form of a pocket), a cover element can be used to completely “close” the recess, i.e. cover the accessible interspace between copper current collector system and steel conductor element inside the recess.

The inventors observed that combination of the above measures is beneficial for obtaining an equalized current distribution. Particularly preferred for altering the resistivities is using a con- tact of collector system and conductor system in form of a pocket (conductor element) and respective negative form (collector system). By using differently sized pockets or inserting the collector system asymmetrically on both sides, deviating resistivities can be obtained in a sim- ple and efficient way, which even enables a simple modification of existing current collector and connector assemblies.

In a preferred embodiment of the invention, the cathode current collector and connector as- sembly is at least partially cladded with the optional protective steel layer cladding, wherein ai,2) and/or 32,2) are at least partially, preferably completely free, of the optional protective steel layer cladding.

Preferably, at least 50 % of the surface of the current collector systems 81,2) and/or 32,2) are cladded with a protective steel layer cladding, more preferably at least 60 %, even more pref- erably at least 70 % and most preferably at least 80 %. In a particularly preferred embodiment, the surface of the current collector system with exception of the second portion is completely cladded with a protective steel cladding.

Preferably, at least 50 % of the surface of the first portion of the current collector system is cladded with a protective steel layer cladding, more preferably at least 60 %, even more pref- erably at least 70 % and most preferably at least 80 %. In a particularly preferred embodiment, the surface of the first portion of the current collector system is completely cladded. Thereby, deleterious effects of the diffusion of aluminum or other products produced in operation of the electrolysis cell can be reduced.

Preferably, the volume ratio of the copper or copper alloy of the current collector system to the thin steel protective layer is at least 200 % and preferably at least 300 % or more preferably at least 400 %. Preferably, the thin protective steel layer has a thickness from 0.05 mm up to 6 mm, more preferred from 0.15 mm up to 4 mm, even more preferred from 1 .5 mm to 3 mm.

The thin protective steel layer preferably comprises or consists of a steel selected from carbon steel, low-carbon steel, chromium-based steel, nickel-based steel or chromium nickel-based steel or alloy steel.

In a preferred embodiment of the invention, the copper or copper alloy is in the form of a bar of rectangular cross-section that is protected at least on one side facing the cathode with the protective thin steel layer, preferably on all sides facing the cathode.

In case the current collector system comprises a steel protective layer, i.e. is at least partially cladded with a steel protective layer, the protective steel layer is in direct contact with the walls of a groove of the carbonaceous cathode.

Preferably, the protective thin steel layer is coated with an additional top layer and/or under layer of copper, nickel and/or chromium and/or a graphite paint or foil layer, wherein more preferably the additional top layer and/or underlayer has a thickness of from 1 pm to 1 mm.

The surface of the current collector system can be roughened or provided with recesses such as grooves or projections such as fins or ribs to increase surface area between the cathode and the current collector system thereby enhancing contact between the elements.

In a preferred embodiment of the invention, the current collector system is at least partially cladded with an insulator in particular with sheets of insulating material such as alumina, insu- lating glue or cement or any insulating material capable to withstand up to 1200 °C.

In a preferred embodiment of the invention, ai) comprises a third portion a-i ,3) different from the first and the second portion, which is arranged outside the groove of the carbonaceous cathode and the recess of the optional steel conductor element and wherein this third portion is sur- rounded by a protective shell. Further, 82) preferably comprises a third portion a2,3> different from the first and the second, which is arranged outside the groove of the carbonaceous cath- ode and the recess of the optional steel conductor element and wherein this third portion is surrounded by a protective shell, preferably, the protective shell comprises a material selected from SiC, ramming paste, steel cover plate, refractory material or a mixture of the foregoing. Most preferred is a shell with an inner layer of SiC, ramming paste, refractory material or mixtures of the foregoing and an outer steel cover layer, whereby the inner layer is arranged in between current collector system and outer steel cover layer.

The invention also relates to a kit-of-parts, i.e. a system of separate elements, comprising ai) a first copper or copper alloy current collector system with an optional protective steel layer cladding, a2) a second copper or copper alloy current collector system with an op- tional protective steel layer cladding, b) at least one longitudinal carbonaceous cathode with at least one groove extending in the longitudinal direction of the carbonaceous cathode for receiving at least a portion of ai) and a?), optionally: c1) a first conductor element

C2) a second conductor element, wherein the sum of electrical resistivities of ai), bi) and the optionally containecd1) is different from the sum of electrical resistivities of 82), b2) and the optionally contained C2).

The invention also relates to an aluminium electrolysis cell comprising the inventive cathode current collector and connector assembly and at least one supply busbar, wherein the cathode current collector and connector assembly is electrically connected to the at least one supply busbar via the first and the second connecting points.

Preferably, the difference of the current pick-up at the two connecting points is < 4%, more preferred < 3%, even more preferred < 2%, and most preferred less < 1 %. The foregoing values are in reference to the higher current value.

The invention also relates to an aluminium electrolysis cell comprising a cathode current col- lector and connector assembly with two connecting points and at least one supply busbar, wherein the cathode current collector and connector assembly is electrically connected to the at least one supply busbar via the first and the second connecting points, preferably by means of a copper or aluminium flexible, wherein the difference of the current pick-up at the two connecting points is 5%, more preferred 3%, even more preferred s 2%, and most preferred less s 1%. The foregoing values are in reference to the higher current value.

The invention also relates to an aluminium electrolysis plant comprising the above-mentioned inventive cell.

The invention also relates to the use of an asymmetric resistivity distribution in a cathode cur- rent collector and connector assembly to compensate non-balanced upstream and down- stream current flow in an aluminum electrolysis cell.

EXAMPLES

The invention will now be explained in more detail with the aid of specific embodiments and with the aid of the accompanying figures.

Inventive example

A cathode block with dimensions 550 x 450 x 3200 mm (width x height x length) is equipped with two central rectangular grooves of dimensions 40 x 135 mm (width x depth), the first groove having a length of 1200 mm from the first end and the second groove1400 mm from the second end of the cathode block. The two rectangular collector bars consist of a copper core with a 2.0 mm thick steel cladding around it, while the steel cladding is excluding the bar portion housed in the steel conductor bars. Length of first and second collector bar is 1480 and 1720 mm, with applied dimensions inside cathode block Li 1180 mm, L2 1380 mm and received depths in the steel conductor bars of ai,2 200 mm and 82,2 240 mm. The outer dimensions of ci) and C2) were the same, and distances of cathode block to steel conductor bar ai,3 and 82,3 are both 100 mm.

With this design, the observed difference in current pick-up of the two collector bars in that block is less than 2 %.

Comparative example

A cathode block with dimensions 550 x 450 x 3200 mm (width x height x length) is equipped with two central rectangular grooves of dimensions 40 x 135 mm (width x depth), both having a length of 1300 mm from the first end and the second end of the cathode block. The two rectangular collector bars consist of a copper core with a 2.0 mm thick steel cladding around it, while the steel cladding is excluding the bar portion housed in the steel conductor bars. Length of first and second collector bar is 1620 mm, with applied dimensions inside cathode block Li and L₂ of 1280 mm and received depths in the steel conductor bars of ai,2 and 82,2 of 240 mm. The outer dimensions of Ci) and C2) were the same, and distances of cathode block to steel conductor bar ai,3 and 82,3 are both 100 mm.

With this design, the observed difference in current pick-up of the two collector bars in that block is more than 5 %.

Figures

Further advantages, features and possible applications will become apparent from the follow- ing description of preferred embodiments and the associated figures. The figures show: Fig. 1 shows a longitudinal section of an aluminum electrolysis plant.

Fig. 2 shows a longitudinal section of an aluminum electrolysis cell with two anodes and a cathode current collector and connector assembly with anodes arranged.

Fig. 3 shows a longitudinal section of a current collector assembly according to the state of the art.

Fig. 4 shows a longitudinal section of a current collector and connector assembly according to the state of the art.

Fig. 5 shows a longitudinal section of an inventive current collector and connector assembly.

Detailed description

Fig. 1 depicts a longitudinal section of an aluminum electrolysis plant. In the electrolysis plant, a rectangular cathode block 1 comprises a groove recessed in a horizontal surface, in which two current collector bars 2a and 2b are arranged along the longitudinal direction. In general, the current collector bars can be in direct contact with the cathode block or a conductive car- bonaceous layer, e.g. of ramming paste, can be arranged between the surfaces. Each current collector bar is connected to the supply busbar (4 & 5) via a connecting point 6a and 6b located at the respective collector bar.

Fig. 2 depicts a longitudinal section of an aluminum electrolysis cell with two anodes 3 and a cathode current collector and connector assembly. In the electrolysis cell, a rectangular cath- ode block 1 comprises a groove recessed in a horizontal surface, in which two current collector bars 2a and 2b are arranged along the longitudinal direction. In general, the current collector bar can be in direct contact with the cathode block or a conductive carbonaceous layer, e.g. of ramming paste, can be arranged between the surfaces. Each current collector bar is connected at its terminal end part to a conductor element 7a/7b, preferably made of steel. The connection is achieved by arranging the terminal end part of the current collector bar within a recess of the conductor element. Each conductor element provides a connecting point 6a respectively 6b to be connected to the external supply busbar.

Fig. 3 depicts a longitudinal section of a current collector assembly according to the state of the art. In this assembly, a cathode block 1 comprises a groove recessed in a horizontal surface, in which two current collector bars 2a and 2b are arranged along the longitudinal direction. In general, the current collector bar can be in direct contact with the cathode block or a conductive carbonaceous layer, e.g. of ramming paste, can be arranged between the surfaces. Each current collector bar can be connected to an external supply busbar via a re- spective connecting point 6a/6b. The figure also shows the first portion of the first current col- lector ai,i being arranged in the groove, the third portion ai,3 being arranged outside the groove. The figure further shows the first portion of the second current collector a2,i being arranged in the groove and the third portion a2,3 being arranged outside the groove. The figure also depicts the length of the first collector bar being arranged in the cathode block Li. The figure also depicts the length of the second collector bar being arranged in the cathode block l_2. The first portion of b) extending in the longitudinal direction along the length Li is defined as bi), and the second portion of b) extending in the longitudinal direction along the length L₂ is defined as b2). As can be seen, the cathode current and collector assembly is symmetrically constructed in the longitudinal direction, i.e. ai,i = a2,i, ai,2 = a2,2and l_i=l_2.

Fig. 4 depicts a longitudinal section of a current collector and connector assembly according to the state of the art. In this assembly, a cathode block 1 comprises a groove recessed in a horizontal surface, in which two current collector bars 2a and 2b are arranged along the longi- tudinal direction. In general, the current collector bar can be in direct contact with the cathode block or a conductive carbonaceous layer, e.g. of ramming paste, can be arranged between the surfaces. Each current collector bar is connected at its terminal end part to a conductor element 7a/7b, preferably made of steel. The connection is achieved by arranging the terminal end part of the current collector bar within a recess of the conductor element. The conductor element further provides a connecting point 6a/6b to be connected to the external supply bus- bar. The figure also shows the first portion of the first current collector ai,i being arranged in the groove, the second portion ai,2 being arranged in the recess of the conductor element and the third portion ai,3 being arranged outside the groove. The figure further shows the first por- tion of the second current collector a2,i being arranged in the groove, the second portion ai,2 being arranged in the recess of the conductor element and the third portion a2,3 being arranged outside the groove. The figure also depicts the length of the first collector bar being arranged in the cathode block Li. The figure also depicts the length of the second collector bar being arranged in the cathode block l_₂. The first portion of b) extending in the longitudinal direction along the length Li is defined as bi), and the second portion of b) extending in the longitudinal direction along the length L₂ is defined as b2). As can be seen, the cathode current and collector assembly is symmetrically constructed in longitudinal direction, i.e. ai,i = a2,i, ai,2 = a2,2. ai,3 = a2,3and LI=L₂. Fig. 5 depicts a longitudinal section of a current collector and connector assembly according to the state of the art. In this assembly, a cathode block 1 comprises a groove recessed in a horizontal surface, in which two current collector bars 2a and 2b are arranged along the longi- tudinal direction. In general, the current collector bar can be in direct contact with the cathode block or a conductive carbonaceous layer, e.g. of ramming paste, can be arranged between the surfaces. Each current collector bar is connected at its terminal end part to a conductor element, preferably made of steel. The connection is achieved by arranging the terminal end part of the current collector bar within a recess of the conductor element. Each conductor ele- ment further provides a connecting point 6a/6b to be connected to the external supply busbar. The figure also shows the first portion of the first current collector ai,i being arranged in the groove, the second portion ai,2 being arranged in the recess of the conductor element and the third portion ai,3 being arranged outside the groove. The figure further shows the first portion of the second current collector a2,i being arranged in the groove, the second portion ai,2 being arranged in the recess of the conductor element and the third portion a2,3 being arranged out- side the groove. The figure also depicts the length of the first collector bar being arranged in the cathode block Li. The figure also depicts the length of the second collector bar being ar- ranged in the cathode block l_2. The first portion of b) extending in the longitudinal direction along the length Li is defined as bi), and the second portion of b) extending in the longitudinal direction along the length l_2 is defined as b2). As can be seen, the cathode current and collector assembly is unsymmetrically constructed in longitudinal direction, as the second portion a2,2) of the second current collector 2b (denoted a2)) being arranged in the recess of the second conductor element 7b (denoted C2j) is smaller than the second portion ai,2) of the first current collector 2a (denoted ai>) being arranged in the recess of the first conductor element 7a (de- noted Ci)) .

REFERENCE SIGNS

1 Cathode block

2a Current collector bar ai)

2b Current collector bar a2)

3 Anode

4 Anode busbar part

5 Cathode busbar part

6a First connecting point

6b Second connecting point

7a First conductor element Ci>

7b Second conductor element C2>

Claims

CLAIMS Cathode current collector and connector assembly for an aluminum electrolysis cell containing ai) a first copper or copper alloy current collector system with an optional protective steel layer cladding, a2) a second copper or copper alloy current collector system with an op- tional protective steel layer cladding, b) at least one longitudinal carbonaceous cathode with at least one groove extending in the longitudinal direction of the carbonaceous cathode for receiving at least a portion of ai) and a2), wherein ai) is at least partially arranged in the at least one groove of b) along the longitudinal direction of the carbonaceous cathode over a length Li with a first portion au), and wherein a2) is at least partially arranged in the at least one groove of b) along the longitudinal direction of the carbonaceous cathode over a length L2 with a first portion 32,1), wherein the first portion of b) extending in the longitudinal direction along the length Li is defined as bi), and wherein the second portion of b) extending in the longitudinal direction along the length L₂ is defined as b2), wherein the cathode current collector and connector assembly com- prises a first connecting point, which is electrically connectable to an ex- ternal supply busbar and wherein the cathode current collector and connector assembly com- prises a second connecting point, which is electrically connectable to the supply busbar, optionally: c1) a first conductor element electrically interconnected between ai) and the first connecting point,

C2) a second conductor element electrically interconnected between 82) and the second connecting point, characterized in that the sum of electrical resistivities of ai), bi) and the optionally containecd1) is different from the sum of electrical resistivities of 82), b2) and the optionally contained C2). Cathode current collector and connector assembly according to claim 1 , wherein the mass of copper or copper alloy of ai) and 82) is different. Cathode current collector and connector assembly according to any of the pre- ceding claims, wherein Li and L2 are different. Cathode current collector and connector assembly according to any of the pre- ceding claims, wherein ai) and/or az) are at least partially electrically isolated, pref- erably with boron nitride. Cathode current collector and connector assembly according to any of the pre- ceding claims, wherein the geometric shape of ai) and az) is different. Cathode current collector and connector assembly according to any of the pre- ceding claims, wherein the specific electrical conductivity of the copper or copper alloy of ai) and az) is different. Cathode current collector and connector assembly according to any of the pre- ceding claims, wherein

■ the cathode current collector and connector assembly comprises c1) and C2),

■ c1) and C2) both comprise at least one recess each, ai) is at least partially arranged in a recess of Ci) with a second portion ai,2), and aa) is at least partially arranged in a recess of C2) with a section portion 32,2).

8. Cathode current collector and connector assembly according to claim 7, wherein the cathode current collector and connector assembly is at least partially cladded with the optional protective steel layer cladding, wherein 81,2) and/or az, 2) are at least partially, preferably completely free, of the optional protective steel layer cladding.

9. Cathode current collector and connector assembly according to any of the pre- ceding claims, wherein

■ ai) comprises a third portion 81,3) different from the first and the second por- tion, which is arranged outside the groove of the carbonaceous cathode and the recess of the optional steel conductor element and wherein this third portion is surrounded by a protective shell,

■ 82) comprises a third portion 82,3) different from the first and the second, which is arranged outside the groove of the carbonaceous cathode and the recess of the optional steel conductor element and wherein this third portion is surrounded by a protective shell,

■ preferably, the protective shell comprises a material selected from SiC, ram- ming paste or refractory materials.

10. Kit-of-parts for manufacturing a cathode current collector and connector assembly according to any of the preceding claims comprising ai) a first copper or copper alloy current collector system with an optional protective steel layer cladding,

82) a second copper or copper alloy current collector system with an op- tional protective steel layer cladding, b) at least one longitudinal carbonaceous cathode with at least one groove extending in the longitudinal direction of the carbonaceous cathode for receiving at least a portion of ai) and 82), optionally: c1) a first conductor element

C2) a second conductor element characterized in that the sum of electrical resistivities of ai), bi) and the optionally contained c1) is different from the sum of electrical resistivities of 82), b2) and the optionally contained C2). 11. Aluminum electrolysis cell comprising a cathode current collector and connector assembly, preferably according to any of the claims 1-9, and at least one supply busbar, wherein the cathode current collector and connector assembly is electri- cally connected to the at least one supply busbar. 12. Use of an asymmetric resistivity distribution in a cathode current collector and con- nector assembly to compensate non-balanced upstream and downstream current flow in an aluminum electrolysis cell.