CATHODE DEVICE FOR AN ALUMINIUM ELECTROLYSIS CELL

Abstract

The cathode assembly of a reduction cell for aluminium production contains a metal pot with a bottom, bearing members covering the longitudinal and end walls and the bottom of the pot, with lining enclosed therein and cathode blocks with cathode rods forming the cathode of the reduction cell. On the longitudinal and end walls of the metal pot in the gaps between the bearing members there are fixed plate ribs and/or finger ribs with a developed structure for heat removal, with a belt made of composite material for steady heat removal installed in the upper part of the longitudinal and end walls of the metal pot. The cooling effect is achieved by a convective air flow caused by the lifting force resulting from the air heating in the space between the ribs at the melt level and the resulting temperature difference along the height of the cathode casing walls.

Claims

1. A cathode assembly of a reduction cell for aluminium production, containing a metal pot with a bottom, bearing members covering the longitudinal and end walls and bottom of the pot, with lining enclosed therein and cathode blocks with cathode rods forming the cathode of the reduction cell, characterised in that on the longitudinal and end walls of the metal pot in the gaps between the bearing members there are fixed plate ribs and/or finger ribs with a developed structure for heat removal, with a belt for steady heat removal made of composite material installed in the upper part of the longitudinal and end walls of the metal pot.

2. The cathode assembly of claim 1, wherein the composite material of the belt consists of at least two metal layers.

3. The cathode assembly of claim 2, wherein the top layer of the belt composite material is made of a metal with high thermal conductivity, preferably above 60 W/m.Math.K.

4. The cathode assembly of claim 2 wherein the top layer of the belt composite material is made of aluminium or aluminium alloys.

5. The cathode assembly of claim 2 wherein the top layer of the belt composite material is made of copper or copper alloys.

6. The cathode assembly of claim 2, wherein the belt composite material is made by joining the metal layers by pulse welding.

7. The cathode assembly of claim 2, wherein the belt composite material comprises an intermediate layer made of titanium.

8. The cathode assembly of claim 1, wherein heat removal regulators are installed above the bearing members.

9. The cathode assembly of claim 1, wherein forced cooling devices are placed in the gaps between the bearing members.

10. The cathode assembly of claim 1, wherein the plate fins and/or finger fins are made of a material with a thermal conductivity above 60 W/m.Math.K.

11. The cathode assembly of claim 2, wherein the height of the belt is 0.2-0.5 m.

12. The cathode assembly of claim 3, wherein the high thermal conductivity is above 60 W/m.Math.K.

13. The cathode assembly of claim 3, wherein the top layer of the belt composite material is made of aluminium or aluminium alloys.

14. The cathode assembly of claim 3, wherein the top layer of the belt composite material is made of copper or copper alloys.

15. The cathode assembly of claim 8, wherein the heat removal regulators are designed as pivoting flaps.

16. The cathode assembly of claim 9, wherein the forced cooling devices are fans.

17. The cathode assembly of claim 3, wherein the belt composite material is made by joining the metal layers by pulse welding.

18. The cathode assembly of claim 4, wherein the belt composite material is made by joining the metal layers by pulse welding.

19. The cathode assembly of claim 5, wherein the belt composite material is made by joining the metal layers by pulse welding.

Description

[0048] The essence of the invention is explained by the following drawings.

[0049] FIG. 1 shows a proposed cathode assembly for an aluminium reduction cell.

[0050] FIG. 2 shows a cathode assembly with the upper part of the metal pot wall of a composite material made by a process such as pulse welding. Also, FIG. 2 shows a cathode assembly with the upper part of the metal pot wall of composite material, the outer layer of which is made of metal with high thermal conductivity.

[0051] FIG. 3 shows a cathode assembly having the upper part of the metal pot wall of a composite material, the outer surface of which has a developed surface due to the installation of plate ribs.

[0052] FIG. 4 shows a cathode assembly having the upper part of the metal pot wall of a composite material, the outer surface of which has a developed surface due to the installation of finger ribs.

[0053] FIG. 5 shows a cathode assembly with the upper part of the metal pot wall of composite material, which has regulators designed as pivoting flaps, which control the efficiency of heat removal from the metal pot walls, installed in the upper section of the bearing members.

[0054] FIG. 6 shows a cathode assembly with the upper part of the metal pot wall of composite material, which has a forced cooling device in the gap between the bearing members.

[0055] The cathode assembly of an aluminium reduction cell includes a metal pot 1 having longitudinal and end walls 2, bottom 3 and flange sheet 4; bearing members 5 covering the walls and bottom of the pot; lining 6 enclosed inside the pot 1, cathode blocks 7 with cathode rods 8 forming the cathode of the reduction cell; upper belt 9 made of composite material.

[0056] The air flow 10 passing through the aperture 11 limited by the bearing members 5, longitudinal and end walls 2 flows over (cools) the upper belt 9 made of composite material. The flow 10 is created by the lifting (Archimedes') force due to its heating in the space limited by the bearing members 5, as well as by the flow of air due to the difference in its temperature along the height of the walls of the pot 2.

[0057] As in the prototype, the metal pot 1 with longitudinal and end walls 2, bottom 3 and flange sheet 4 and bearing members 5 comprising the cathode assembly also participate in the heat exchange.

[0058] Composite material is made by pulse welding, that is pressure welding in which workpieces are welded when they collide with each other due to the detonation of a pyrocharge.

[0059] A movable workpiece, which is the upper layer 13 (of a metal different from the base in physical properties, usually softer and less strong) is welded to the base 12 (a fixed steel workpiece). To preserve thermal and mechanical characteristics of the upper belt 9 of composite material in the conditions of operation at elevated temperatures, an intermediate (barrier) layer 14 of Ti (titanium) 0.5-1.5 mm thick is placed at the interface (flat or dovetail type) to prevent the formation of brittle intermetallides. Thus, effective heat removal from the upper belt 9 of the composite material with the upper layer 13 is carried out.

[0060] When the upper layer 13 of the belt 9 is made of a metal having high thermal conductivity, aluminium, copper, bronze or special steel may be used as such metals.

[0061] To improve efficiency, the surface of the upper layer 13 may be developed by installing plate ribs 15 made of a metal with high thermal conductivity, which are fixed by welding, brazing or other mechanical means (bolted and/or riveted) and by having previously made a flat surface 13 by milling or installing a spacer, for example made of a fusible heat conducting material, graphite- or silver-based thermal paste, aluminium foil, refractory cement, etc., which will level the uneven surface of the wall.

[0062] Further increase of efficiency is possible due to even greater development of the surface 13 by installing finger ribs 16 made of a metal with high thermal conductivity making it possible to increase the heat-removing surface by 20-30% and ensure heat energy dissipation.

[0063] To regulate heat removal from the upper part of the walls of the pot (belt) 9 of composite material, heat removal regulators 17 designed as pivoting flaps 18, can be installed in the aperture 11 above the bearing members 5 to change the open area in the aperture 11. This makes it possible to adjust the scale thickness depending on seasonal changes in the ambient temperature and changes in the reduction cell current.

[0064] To increase the intensity of heat removal from the cathode assembly, and in particular by reducing the surface temperatures of the upper belt 9 of the metal pot 1, a forced cooling device 19 may be installed in the gap between the bearing members 5. The device is, for example, a centrifugal fan with a capacity of 1000-2000 m.sup.3/h. The heat dissipation can thus be increased by a further 30-50%.

EMBODIMENT OF INVENTION

[0065] Mounting and dismounting of the cathode assembly of the aluminium reduction cell is carried out as follows.

[0066] When manufacturing the cathode assembly of the proposed design, in which intensive heat removal from the pot and its dissipation by the upper belt 9 of a composite material guarantees the formation of a stable layer of solidified bath (scale) on the inner surface of the side lining of the cathode assembly at overheating above 25 C. and, accordingly, ensures stable and steady operation of the aluminium reduction cell.

[0067] The bottom 3, flange sheet 4 and longitudinal and end walls 2 of the metal pot 1 are made of 12-20 mm thick sheet steel of sufficient ductility and quality. Inside the metal pot 1, lining 6 is placed consisting of refractory and heat-insulating materials, and cathode blocks 7 with cathode rods 8 installed in them.

[0068] Bearing members 5 covering the walls and bottom of the pot 1 are made in the form of either shell stiffening rods (T- or I-beams) or hinged counterforce cradles (a structure with a box cross-section or two I-beams welded together). In the upper part of the longitudinal and end walls a belt 9 made of composite material consisting of 2 or more layers of different metals with a height of 0.2-0.5 m is installed. The lower part of the belt is welded to the walls 2, the upper part of the belt is welded to the flange sheet 4, and the upper layer 13 surface is either welded to the bearing members 5 or rests in them, ensuring free contact.

[0069] The belt 9 is manufactured of composite material separately. Pulse welding is a mechanical type of pressure welding in which the joint is made by the explosion-induced collision of the parts to be welded. The composite belt material comprises typically a steel base 12, an upper layer 13 of high thermal conductivity material and an intermediate layer 14 of titanium. The intermediate layer 14 is required to be installed when the belt is operated in the device at temperatures greater than 300 C.

[0070] The greatest efficiency is achieved when the upper layer 13 of the belt 9 of composite material has a developed surface, which is achieved by inserting plate ribs 15 and/or finger ribs 16 made of a highly thermally conductive material such as special steel, aluminium or aluminium alloy, copper or copper alloy. The plate rib 15 is made in the form of a rectangle or trapezoid with a height of 300-600 mm, a width of 100-500 mm and a thickness of 6-10 mm. The number of ribs is selected based on the required heat transfer coefficient. For example, the installation of 7 ribs from St3 steel 6 mm thick with an area of 0.3 m.sup.2 with a distance of 50 mm between the ribs resulted in a heat transfer coefficient n=75 W/m.sup.2.Math.K in the free convection mode. For comparison, without plate ribs, the maximum possible heat transfer coefficient is n=30 W/m.sup.2.Math.K. Installing 7 plate ribs made of aluminium grade A5 with a thickness of 10 mm and area of 0.3 m.sup.2 with a distance of 50 mm between the fins resulted in a heat transfer coefficient of approx. n=150 W/m.sup.2.Math.K.

[0071] These values of heat transfer coefficients were obtained on a heat bench simulating the wall of the metal pot of the reduction cell cathode assembly in experimental studies of different variations of plate ribs.

[0072] Replacing the plate ribs 15 with finger ribs 16 increases the heat transfer surface by 20-30% and makes it possible to increase the heat transfer coefficient by 15-20%.

[0073] If it is not necessary to dissipate such amount of heat, the heat dissipation coefficient can be reduced by closing the pivoting flaps 18 of the heat removal regulators 17.

[0074] When it is necessary to increase the amount of heat dissipated from the cathode assembly, forced cooling devices 19 in the form of a fan and blower may be used, as well as other suitable cooling devices.

[0075] Thus, the proposed cathode assembly can provide a stable layer of solidified bath (scale) on the inner surface of the side lining of the cathode assembly at overheating above 25 C. and guarantee stable and steady operation of the aluminium reduction cell. For example, the test sample was operated at overheating of 40 C., in summer (the worst conditions) and there was a minimum layer of protective scale on the walls.