CATHODE ELEMENTS FOR A HALL-HÉROULT CELL FOR ALUMINIUM PRODUCTION AND A CELL OF THIS TYPE HAVING SUCH ELEMENTS INSTALLED

Abstract

A cathode element (1) for an electrolysis cell of Hall-Heroult type for producing aluminium, comprises a body (4) of calcinated carbonaceous material connected with the upper side of a metallic collector plate (2). A space between the said carbonaceous body and the collector plate being filled with an electric conductive material preferably comprising conductive particles. The collector plate (2) further can comprise at least one horizontal outlet (5, 5) on at least one side and/or at least one vertical metallic current outlet (7) connected to the lower side of the collector plate (2). In one embodiment the collector plate is divided in two sections (20; 20). The invention also relates to a cell of Hall-Heroult type utilizing such cathode elements (1).

Claims

1. A cathode element for an electrolysis cell of Hall-Hroult type for producing aluminium, comprising a carbonaceous body (4) of calcinated carbonaceous material connected with the upper side of a metallic collector plate (2), wherein a space between the said carbonaceous body (4) and the collector plate (2) being filled with an electric conductive material, preferably comprising conductive particles, wherein the collector plate (2) further comprises at least one horizontal current outlet (5, 5) on at least one side and/or at least one vertical metallic current outlet (7) connected to the collector plate (2).

2. The cathode element according to claim 1, wherein the carbonaceous body (4) is rodded to the collector plate (2) in a manner where the outer end part of the carbonaceous body (4) is electrically insulated from the collector plate (2), at a distance up to 450 mm from the end thereof and inwards.

3. The cathode element according to claim 1, wherein the carbonaceous body (4) is rodded to the collector plate (2) in a manner where the outer end part of the carbonaceous body (4) is electrically insulated from the collector plate (2) at different lengths on both ends of the plate (asymmetric).

4. The cathode element according to claim 1, wherein at least one thermocouple (TC) is inserted into a metallic component inside of or below the collector plate (2).

5. The cathode element according to claim 1, wherein it comprises at least one horizontal current outlet (5; 50) integrated with the collector plate (2; 20).

6. The cathode element according to claim 5, wherein the at least one horizontal current outlet (5; 50) is integrated in a slot (S) in the collector plate (2; 20).

7. The cathode element according to claim 5, wherein the horizontal current outlet (5; 50) comprises one current conductor part (5; 50) that is integrated to the collector plate (2; 20) by a press-fit (knock) fixation in a recess of the collector plate (2; 20) that is complementary with the corresponding part of the conductor (5, 50).

8. The cathode element according to claim 5, wherein the part of the current conductor (5; 50) integrated to the collector plate (2; 20) has a delta shaped part (51).

9. The cathode element according to claim 5, wherein it comprises at least one horizontal current outlet (5, 5) on each end being integrated with the collector plate (2).

10. The cathode element according to claim 9, wherein the cross section of or the insertion length of the horizontal current outlet at one end is different of that of the other end (asymmetric).

11. The cathode element according to claim 5, wherein the current outlet (5; 50) comprises a copper conductor preferably covered by a protective sheet (6; 60).

12. The cathode element according to claim 1, wherein it comprises at least one vertical current outlet (7) arranged at the opposite side of the collector (2) plate than the said carbonaceous body (4).

13. The cathode element according to claim 12, wherein the vertical outlet (7) comprises of a socket (10) integrated with the collector plate (2) wherein a rod-shaped current conductor (11) is attached to the socket (10).

14. The cathode element according to claim 13, wherein the socket (10) is of a metallic material and further welded to the collector plate (2).

15. The cathode element according to claim 13, wherein the socket (10) has an internal recess (17) where an upper part (17) of the current conductor (11) has a shape complementary with said recess (17) for fixation of said current conductor (11) to the socket (10).

16. The cathode element according to claim 13, wherein the fixation is a press-fit (knock) fixation.

17. The cathode element according to claim 13, wherein the socket (10) has internal threads 13 at its outermost end for receiving a sleeve (12) with complementary external threads (16), wherein the sleeve surrounds the current conductor (11) and where the end of the sleeve abuts an annular flange or ring (14) at the current rod (11) for forcing the rod (11) into the socket (10) when tightened.

18. The cathode element according to claim 13, wherein there is a threaded bolt (17) at the top of the socket communicating with a threaded bore (17).

19. The cathode element according to claim 12, wherein the current conductor (11) is made out of copper or an alloy thereof.

20. The cathode element according to claim 1, wherein at least one metallic collector element (3) is arranged at the upper side of a metallic collector plate (2), where said collector element (3) is embedded in a corresponding recess (9) in the bottom part of said carbonaceous body (4), the recess being wider than the collector element and being filled with an electric conductive material comprising conductive particles.

21. The cathode element according to claim 20, wherein there is one or more collector elements (3), preferably 3 to 7 being separated at a distance of typically 50 mm to 150 mm.

22. The cathode element according to claim 20, wherein the at least one collector element(s) (3) is of same length or shorter length than the carbonaceous body (4).

23. An electrolysis cell of Hall-Hroult type comprising several cathode elements as defined in c1aim 1, wherein a cell is built with several cathode elements and in a configuration of only the same elements.

24. An electrolysis cell of Hall-Hroult type comprising several cathode elements as defined in c1aim 1, wherein a cell is built with several cathode elements and in a configuration of different elements.

Description

[0056] The present invention will in the following be further described by figures and examples where;

[0057] FIG. 1 discloses in a first embodiment a divided cathode element, seen in perspective, where a collector plate is divided in two sections,

[0058] FIG. 2 discloses an embodiment of a non-divided cathode element in a cross-section view, where horizontal conductors extend into a collector plate at different lengths and further seen from one side, the element having a vertical current outlet,

[0059] FIG. 3 discloses a top-side view of the same cathode element as shown in FIG. 2,

[0060] FIG. 4 discloses an alternative embodiment of a cathode element without a vertical current outlet, where horizontal conductors extend into the collector plate at different lengths,

[0061] FIG. 5 discloses in a top-side part view of a collector plate like in FIG. 1, but the horizontal outlet extends to a delta-shaped conductor inside the plate,

[0062] FIG. 6 discloses in an enlarged view a cross-section through the cathode element of FIG. 2, seen from one end and discloses further details of one vertical current outlet,

[0063] FIG. 7 discloses in an enlarged view an alternative embodiment of the outlet as described in FIG. 6,

[0064] FIG. 8 is a principal sketch showing in a cross sectional view the main parts of a Hall-Hroult cell wherein a cathode element corresponding to that shown in FIG. 2 is included.

[0065] From FIG. 8 it can be seen a cross sectional view of the main parts of a Hall-Hroult cell where its superstructure includes alumina/fluoride hoppers, anode stubs, bus bars and feeding devices. Further, a pair of anodes partly covered by a crust is dipped into a liquid bath. Under the liquid bath there is shown a layer of liquid aluminium. The cathode is arranged below the liquid aluminium. The cathode comprises a carbonaceous body 4 arranged onto a collector plate 2. At each end of the collector plate there is arranged horizontal current outlets 5, 5. It is also disclosed a vertical outlet 7. Various embodiments of cathode elements will be disclosed in more detail in the following.

[0066] FIG. 1 discloses a divided cathode element 1 seen in perspective. In this embodiment the collector plate consists of two sections 20, 20. In the disclosed embodiment, collector plate sections 20, 20 can be identical or not and will be described accordingly.

[0067] The collector plate section 20 is provided in this example with six collector elements, 30, 30 30, 30, 30, 30 that are in electrical contact with the collector plate section 20. Preferably, these parts are made out of a steel quality that can easily be welded, and preferably the parts are welded together. A cathode block can be rodded to the collector elements, in a similar manner as disclosed in WO2009/099335A1. The present solution may involve electric conductive particles or a contacting paste. The number of collector elements at the collector plate may differ from six as shown, for instance one to seven or even none.

[0068] At each outer end of the collector plate sections 20; 20, there is arranged two horizontal current outlets 50, 51; 50, 51 respectively. The horizontal current outlets can be made out of conductors of a good conducting material like copper or copper alloy and further being, at least at its outlet ends, covered by a sheet material 60, 61; 60, 61, preferably made out of a metal such as steel. The horizontal current outlets 50, 51; 50, 51 with their corresponding conductors can be integrated in slots S, S; S, S made in the corresponding collector plate sections 20; 20. This integration may be based upon press-fit tolerances or pre-heated plate sections to use thermal expansion for a tight fit. However, any appropriate fixation including welding may be applied. The conducting material in the slots may be covered by a protective steel plate on the upper and lower side.

[0069] Further, close to the edge of the short and long sides of the collector plate sections, there can be arranged a flexible sealing rope or stopper plates (not shown) intended to facilitate the rodding of the plate to a carbonaceous body by means of electrically conductive metal particles. When rodding the cathode block to the cathode plate, the outer part of the carbonaceous material closer to the horizontal outlets can preferably be electrically insulated from the cathode plate, for instance 100 mm and up to 450 mm from the end of the cathode block and inwards to avoid high current densities at the upper surface of the cathode block close to the ends. The electric insulation can be asymmetric on each of the ends and also differ between the cathode elements in the cell.

[0070] In FIG. 2 it can be seen a second embodiment of a cathode element 1 in a cross-section view seen from one side, where a carbonaceous body 4 is arranged onto a collector plate 2 which is not divided. In this embodiment the collector plate 2 has collector elements, where only one 3 is seen from the side. At each end of the collector plate 2 there is arranged horizontal current outlets 5, 5. The horizontal current outlets can be made out of a copper material and being covered by a sheet material 6, 6, preferably made out of a metal such as steel. It is also briefly disclosed a vertical outlet 7, that will be further described with reference to FIGS. 6 and 7.

[0071] The cross section of the horizontal outlets may be different at one end of the plate versus the other to compensate for different electric current path lengths of the conducting busbars to the next cell, e.g. for side-by-side arranged cells in a row of plural cells. The outlets on the upstream side could have a larger cross-sectioneither by a greater width or height or bothto reduce the electric resistance on that side of the cell and thus equalize the current distribution into the top of the cathode block surface. If the conductors of the horizontal outlets are of a better conducting material than the plate, they can be applied with different insertion length on each side of the plate when appropriate.

[0072] FIG. 3 discloses a top-side view of the same cathode as shown in FIG. 2, with the carbonaceous body 4 laying onto a collector plate 2 with one outlet on each side 5, 5 covered by sheet material 6, 6. Further, it is indicated a bore B in the collector plate for insertion of a thermocouple TC.

[0073] The embodiment shown in FIG. 4 relates to the same embodiment as shown in FIG. 2, however without a vertical outlet. It discloses a cathode element 1 in a cross-section view seen from one side, where a carbonaceous body 4 is arranged onto a collector plate 2 which is not divided, see below. In this embodiment the plate 2 has collector elements, where only one 3 is seen from the side. At each end of the collector plate 2 there is arranged horizontal current outlets 5, 5. The conductors of the horizontal current outlets can be made out of a copper material and being covered by a sheet material 6, 6, preferably made out of a metal such as steel. The dividing line D in the drawing indicates that the extension of the cathode element can be varied, i.e. also the intrusion length of the current conductors 5, 5 in the plate 2 may vary depending upon the actual design.

[0074] The current conductors may in principle have a rectangular or round cross-section and as an alternative be out of any suitable electrical current conducting material.

[0075] FIG. 5 discloses partly one end of a collector plate 2 or similarly a collector plate section that may have one single horizontal current outlet 5 at its end which comprises a triangle or delta shaped electric conductor 51 made of copper or similar good conducting material to ensure a better distribution of the currents leaving the plate 2 and entering into the conductor 51 and further to its outlet 5, and by that reducing the electric resistance. The conductor 51 can be press-fit inserted into a recess of the plate 2, or attached to it by any appropriate means. In one alternative, the conductor could be cast into the recess, by for instance of melt copper. In case there is cast an extension beyond the recess outside the plate, it could be done by applying an appropriate mould or the similar.

[0076] FIG. 6 discloses further details of the vertical current outlet 7 as shown in FIG. 2 and represents an enlarged end-view of a cross-section through one end of the cathode of FIG. 2. A carbonaceous body 4 is resting onto a collector plate 2 having collector elements 3, 3, 3, 3, 3. The carbonaceous body has recesses or slots 9, 9, 9, 9, 9 complementary with said collector elements. The remaining space between the collector elements and the slots is filled with electric conductive material or particles. The collector elements are in this embodiment fixed to a metallic collector plate 2 that collects the current and secures stability.

[0077] The vertical outlet 7 comprises a socket 10 integrated with the collector plate 2 where a rod-shaped current conductor 11 can be attached to the socket 10. The conductor 11 can be made of a material with good electric conductivity like copper. The socket 10 can be made of a metallic material like steel and welded or press-fit to the collector plate 2. The vertical outlet can be placed in the centre of the plate or asymmetric towards one of the horizontal outlets to improve the magnetic field situation or to change the current distribution between horizontal and vertical outlets in a desired way.

[0078] Further, the socket 10 has an internal recess 17 where an upper part 17 of the current conductor 11 has a shape complementary with said recess 17 for fixation of said current conductor 11 to the socket 10. The upper part 17 of the current conductor 11 can be provided with threads mating corresponding threads in the upper part of the socket 10. The fixation can be optionally a press-fit (knock) fixation.

[0079] Further, in an embodiment or in addition, see FIG. 7, the socket 10 may have internal threads 13 at its outermost end for receiving a sleeve 12 with complementary external threads 16, wherein the sleeve surrounds the current conductor 11 and where the end of the sleeve abuts an annular flange or ring 14 at the current rod 11 for forcing the rod 11 into the socket 10 when tightened. The current conductor 11 is preferably made out of copper or an alloy thereof. The sleeve 12 both serves for fixation and protection against reactions of conductor 11 with liquids or volatiles from the process. Further, it is disclosed a bore B for insertion of a thermocouple TC.

[0080] As an alternative to the internal thread 13 a threaded bolt can be attached inside the top of the socket (not shown) and the conductor 11 is fitted with a corresponding threaded bore to fix the conductor to the socket (similar to that shown in FIG. 6). A removable connection of the outlet might be needed to allow for a vertical outlet conductor to be attached after the cathode is placed with a swing-in movement on top of the bottom lining in the cell during installation.

[0081] Advantageously, the whole assembly with the carbonaceous body 4 and the collector plate 2 are tilted somewhat during the filling procedure of the particles, to allow the particles to fill the recess in a smooth and complete manner. Additionally some vibration might be applied to the plate or plate sections for homogeneous filling with the particles.

[0082] The recesses or slots 9 can be made in a green condition of the carbonaceous body by commonly used techniques or in a calcinated condition by commonly available process equipment. The geometry of the slots has to fit the plates.

[0083] It should be understood that the electrical conducting solids or particles can be of any appropriate metal such as steel, iron, copper, aluminium etc., or alloys of same. Further, the shape of the solids can be spherical, oval or elliptic, flaked, or have any appropriate shape. The size and particle distribution may vary. The maximum size will in general be restricted by the width of the space to be filled. A non-homogenous distribution of particle sizes may be convenient to obtain a compact filling as possible, with little space between the particles.

[0084] Apart from having good electrical conducting properties, the applied material should have good mechanical properties (crushing properties) and be able to sustain high temperatures. As mentioned later, magnetic properties may be advantageous.

[0085] 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 up to 2 millimetres.

[0086] 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 center of the plate can be drilled in the cathode plate at appropriate locations for reception of thermocouples. The steel plate creates a protective housing for the thermocouples to survive the chemical aggressive environment during operation.

[0087] 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 the insertion can be made longer on the upstream side to balance the current pick-up in the cathode block to be more balanced.

[0088] 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 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 as well.

[0089] A combination of different plate configurations can be applied in one cell to create 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 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 distribution and magnetohydrodynamic stability of the cell is sufficient.

[0090] The claimed plate cathode has multiple advantages compared to a traditional design comprising a carbonaceous body with embedded collector bars: [0091] The cathode voltage drop (CVD) is significantly lower due to the 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 [0092] 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 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 [0093] 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 [0094] The vertical space usage of the arrangement is less than with conventional design, thus allowing for a lower cathode shell orif the shell height is kept, to use the extra space for better bottom insulation, higher and longer-lasting cathode blocks, or more height for liquid aluminium or bath [0095] 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 of the cell (less heat loss and lower cathode voltage drop CVD) [0096] 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 [0097] Lower voltage drop (CVD), as less as 150 mV [0098] 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% [0099] 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 used to reduce energy consumption [0100] Lower rodding cost as there is no cast iron [0101] No risk of cracking of carbon block compared to cast-in collector bars (cast iron) [0102] Flexible installation of VOs after placing of the cathode blocks in the lining [0103] Better balancing of current flow to upstream/downstream/bottom side giving better MHD stability [0104] Less total height of the assembly giving space for more thermal bottom insulation or larger cavity. This could be up to 150 mm [0105] Longer life time of carbon cathode block at same assembly height like traditional design with collector bars, as the height of the usable carbon block can be up to 150 mm higher [0106] Easier installation of thermocouples inside the plate due to less deep drilling than in collector bars, or direct access from bottom side