Cathode assembly for a hall-heroult cell for aluminium production and method for making same

Abstract

A cathode assembly for an electrolysis cell of Hall-Heroult type for producing aluminium, comprises a cathode block rodded or connected with steel collector bars, Cu rods or a metallic collector plate, the cathode block surface comprises partly of a wear resistant composite material so the cathode block can be designed with a lower height, which may have many advantages. A method for producing the cathode assembly is described.

Description

Further, the size of said solids can be from 0,1 millimetres and close to the minimum opening between the carbonaceous body and conductor plate. Commonly, the size may be 30 up to 2 millimetres. Preferably there can be several thermocouples attached to or inserted into the cathode plate to monitor the temperature in the cathode. For instance, holes up to the centre of the plate can be drilled in the cathode plate at appropriate locations for reception of 35 thermocouples. The steel plate creates a protective housing for the thermocouples to survive the chemical aggressive environment during operation. 2020443557  04 Feb 2025 The insertion length of the horizontal outlets can preferably be limited in that it does not cover the central part of the cathode plate. The length of the insertion can for example be designed to reflect the existence of vertical outlets in that plate, and the path length of the current through the conductors to the next cell. On side-by-side arranged cells the length of 5 the insertion can be made longer on the upstream side to balance the current pick-up in the cathode block to be more balanced. Each cathode element can be fitted with horizontal outlets only for instance for end-to-end arranged cells or when there is no space for busbars under the cell, or with several 10 horizontal outlets and one vertical outlet. To optimize the magnetic field, a configuration with one or two vertical outlets only and no horizontal outlet can be possible for some selected cathode block of the cathode panel as well. A combination of different collector plate configurations can be applied in one cell to create 15 a favourable magnetic field from the electric current distribution or enhance the thermal properties of the cell by reducing the number of outlets where a heat loss is undesired, e.g. on the short ends of the cell which tend to be colder due to the nearby corners. Vertical outlets attached to only some collector plates can be beneficial to optimize the current flow and magnetic field. This may as well reduce the costs of the installation when the current 20 distribution and magnetohydrodynamic stability of the cell is sufficient. The claimed collector plate cathode with the very low height cathode block has multiple advantages compared to a traditional design comprising a carbonaceous body with embedded collector bars: 25 - In the preferred embodiment the block will be significantly lower, due to significantly lower erosion rate of the TiB2-Carbon composite material the lifetime will still be higher. 30       - The cathode voltage drop (CVD) is significantly lower (as low as 150mV) due to the low cathode block height, number of outlets, material electric properties, better electric contact due to initial mobility of particles, total surface of contact resistance and shorter current paths from the existence of vertical outlets 35       - The current distribution into the top cathode block surface is more homogeneous due to the plate geometry, conductance of insertions, and existence of vertical outlets, thus avoiding undesired, instability causing horizontal currents in the liquid 2020443557  04 Feb 2025 aluminium pad above the cathode block surface. The higher stability of the cell can be used to reduce the cell voltage and energy consumption further or increase the amperage and production volume 5       - Due to the above mentioned better current distribution, the erosion of the carbonaceous material is more homogeneous thus increasing the life time of the cell - The vertical space usage of the arrangement is less than with conventional design, thus allowing for a lower cathode shell or - if the shell height is kept, to use the extra 10          space for better bottom insulation, higher and longer-lasting anode blocks, or more height for liquid aluminium or bath - The design has a better ratio of electric to thermal conductivity at the most critical locations of high current density and heat flow, thus improving the energy efficiency 15          of the cell (less heat loss and lower cathode voltage drop CVD) - When retrofitted to an existing cell design, vertical outlets according to the claims may allow to raise the amperage and thus increase production per cell 20       - Better current distribution into the cathode surface giving improved MHD stability and thus options to reduce the ACD or increase the amperage level by up to 15% - Less heat loss because of smaller cross-section and exposed surface of HO and VO avoiding cold cathodes with bottom freeze, specifically if the technology is 25          used to reduce energy consumption - Lower rodding cost in embodiments where there is no cast iron - No risk of cracking of carbon block in embodiments not using cast-in collector bars 30           (cast iron) -   Flexible installation of VOs after placing of the cathode blocks in the lining -   Better balancing of current flow to upstream / downstream / bottom side giving better 35          MHD stability - Considerably lower total height of the assembly giving space for more thermal bottom insulation or larger cavity. The difference could be up to 300 mm 2020443557  04 Feb 2025 - Easier installation of thermocouples inside the plate due to less deep drilling than in collector bars, or direct access from bottom side’ 5       - Reduced amount of conventional cathode material saves costs in general, while the arrangement of the composite material only at selected areas where the wear of the surface of the cathode is expected as being most excessive, reduces the amount of expensive wear resistant material compared to conventional designs.

Claims

5   1. A cathode assembly for an electrolysis cell of Hall-Heroult type for producing aluminium,comprising a graphitized cathode block of an electronic conductive material rodded to steel collector bars, Cu rods or a metallic collector plate, wherein, selected areas or parts of the surface of the cathode block are made of a wear resistant 10      composite material comprising 5 - 80 wt% of a refractory metal boride powder such asTiB2, HfB2, ZrB2, CrB2, WB2, or refractory metal carbide powder such as SiC, Cr3C2, B4C, TiC, or Al2O3, together with a carbonaceous material, the rest of the cathode block comprises conventional graphitized cathode material, wherein the wear resistant composite material is placed in the areas towards the ends 15       of the cathode block, i.e. the areas 0-80 cm from the end of the cathode block,wherein the selected areas or parts of the surface of the cathode block made of a wear resistant composite material correspond to less than 100% of the total surface of the cathode block, wherein the cathode assembly is obtained by a method, wherein either:(i) a green cathode block is prepared by adding a conventional cathode paste in the 20          bottom of a conventional vibromold for cathode block production which is evenedout with a rake or a similar tool before preparing pits in selected areas of the surface, wherein wear resistant composite material is filled in these pits and vibromolding is performed, followed by heat treatment such as baking or graphitization of the green cathode block in a similar manner as for conventional cathode blocks; or25          (ii) a green cathode block is prepared by adding a wear resistant composite materialin selected areas in the bottom of a conventional vibromold for cathode block production, before adding the conventional cathode paste on top, which is then evened out by a rake or a similar tool and then vibromolded followed by heat treatment such as baking or graphitization of the green cathode block in a similar30          manner as for conventional cathode blocks.

2. A cathode assembly according to claim 1, wherein,the wear resistant composite material has a thickness between 3 and 10 cm.

353. A cathode assembly according to claim 1, wherein,2020443557   10 Jul 2026the selected areas or parts of the surface of the cathode block made of a wear resistant composite material corresponds to less than 50% of the total surface of the cathode block.5   4. A cathode assembly according to claim 1,wherein,the selected areas or parts of the surface of the cathode block made of a wear resistant composite material corresponds to less than 30% of the total surface of the cathode block.

105. A cathode assembly according to claim 1,wherein,the selected areas or parts of the surface of the cathode block made of a wear resistant composite material corresponds to less than 10% of the total surface of the cathode 15        block.

6. A cathode assembly according to any one of claims 1 to 5, wherein,the cathode block after graphitization, is rodded to steel collector bars where the total 20      height of the cathode block is between 25 and 35 cm.

7. A cathode assembly according to any one of claims 1 to 5,wherein,the cathode block after graphitization, is rodded to Cu rods where the total height of the 25      cathode block is between 13 and 28 cm.

8. A cathode assembly according to any one of claims 1 to 5,wherein,the cathode block after graphitization, is rodded to a metallic collector plate where the 30       total height of the cathode block is between 8 and 28 cm.

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