WO2000018987A1

WO2000018987A1 - A method and a device for feeding an electrolysis cell

Info

Publication number: WO2000018987A1
Application number: PCT/NO1999/000279
Authority: WO
Inventors: Leif Meisingseth
Original assignee: Norsk Hydro Asa
Priority date: 1998-09-14
Filing date: 1999-09-10
Publication date: 2000-04-06
Also published as: NO984224D0; NO984224L; AU5885399A; NO310731B1

Abstract

The present invention relates to a method and a device for point-feeding of an electrolysis cell, in particular an electrolysis cell for the production of aluminium according to the Hall-Héroult process. According to the invention, materials are feeded from a reservoir such as a silo (20) via a distribution pipe (23) to at least two outlets (26, 27). In use the invention can provide more even distribution of the mateirals that are feeded to the cell, which will render a more stable operation of the cell.

Description

A method and a device for feeding an electrolysis cell

The present invention relates to a method and a device for point-feeding of an electrolysis cell, preferably an electrolysis cell for the production of aluminium according to the Hall- Heroult process.

Point-feeders for dosing aluminium oxide or alumina, fluoride and other materials to an electrolysis cell for production of aluminium, represent today well-established technology. In combination with a crust-breaker or a bar, a point-feeder can dose the prescribed amount of feeding-material to a defined point in the cell with good precision. One cell may have plural point-feeders, for instance 2 - 6 feeders. With respect to investment- and maintenance costs, the feeding will normally be performed in a few limited points. In course of time, the feeding of materials to the cell in just some few single points may cause building up of sludge (excess material) below and in the vicinity of the feeding points. In electrolysis cells with prebaked anodes arranged in two rows, it is common to provide the feeding along a centre line between the two rows of anodes. In course of time a ridge of sludge may build up on the cell floor, having an orientation corresponding to the length direction of the cell. Such a more or less continuous built-up of relatively great amounts of sludge may influence the operating conditions of the cell and cause unstable operation.

DE 3047533 relates to a beam to be arranged above the electrolysis cell, where the beam supports a mobile point-feeding unit. A disadvantage relating to this solution is that it comprises a plurality of movable parts in addition to the point-feeding unit itself, which may involve intensive maintenance and operating disturbances caused by the high temperatures and a dusty and corrosive environment.

With the present invention the above mentioned disadvantages can be reduced, together with that the investment- and maintenance costs will not be prohibitively high. In accordance with the present invention it is possible to feed smaller doses at more points. In this manner the oxide will mainly be dissolved directly in the cryolite melt without building up of sludge on the cathode. The operation of the cell will become more stable, resulting in lesser work for the cell-workers and the workers tapping metal. Another advantage is that the dosing holes can be held open without operating the crust-breaker each time feeding of oxide is performed because the dosing in each hole is smaller. This implies cost savings related to wear and reduced energy need (pressurised air) to operate the crust breakers. Further, it may be possible to obtain improvements related to the current efficiency of the cell, caused by more stable and optimal operation. In the following, the invention shall be further described by example and figures where:

Fig. 1 shows, seen from one side, a point-feeder according to the present invention,

Fig. 2 shows, seen from in front, a point -feeder according to the present invention,

Fig. 3 shows, seen from in front, a crust-breaker for use in connection with a point- feeder according to the present invention, Fig. 4 shows, seen from above, a first schematic distribution of feeding points in an electrolysis cell, Fig. 5 shows, seen from above, a second schematic distribution of feeding points in an electrolysis cell.

Figure 1 shows a point-feeder 1 in accordance with the present invention, seen from one side. The feeder comprises an oxide silo 2 and a fluoride silo 3 arranged in the upper superstructure 4,5 of the cell. The shown silos are funnel-shaped and converge downwards to an outlet 6, 7. In this embodiment there are arranged dosing-devices such as scoop-feeders 8, 9, at the outlets, but other types of feeders such as fluidised feeders or screw-feeders may be applied as well. The oxide feeder in this embodiment is provided with two outlets 10, 11 , that feeds oxide directly into the bath between anodes 12, 13. The anodes are positioned partly submerged into the bath-crust (not shown) and a double-bar 14 arranged for vertical movement can be pushed through the crust for keeping the feeding holes in the crust open.

The fluoride silo 3 as shown in the Figure is provided with one outlet 18, where fluoride can be feeded through one of the mentioned feeding holes.

Figure 2 shows, seen from in front, a point-feeder according to the present invention, where an oxide silo 20 having a funnel-shaped lower part 21 is provided with an outlet stub 22. The outlet stub 22 is connected with a horizontal distribution pipe 23 provided with outlet pipes 24, 25 having outlets 26, 27. It shall be understood that the distribution pipe 23 may be provided with more than two outlet pipes (not shown) for distribution of material to plural points. In the embodiment shown in Figure 2, there is shown a motor driven screw-feeder with a motor 28 driving one end (30) of the feeding screw through a transmission element 29. Screw-feeders are well-known for those skilled in the art, and therefore screw-feeders will not be further described here.

Figure 3 shows a bar-device 40 (crust-breaker) constituted by multiple bars which in this embodiment comprises two bars 41 , 42 (double-bar) connected with a yoke 43 attached to an actuator 44 or cylinder via a rod 45. It should be understood that further bars can be arranged in connection with the yoke for the maintenance of even more feeding holes in the bath crust. The rod 45 may be shielded by a housing 46 for the protection against corrosion and dust, together with up-take of transversal forces acting on the piston rod 45. The actuator may be driven by pressurised air, but other types of actuators may also be applied, for instance of hydraulic-, mechanical- or electrical types. The upper end of the actuator may be attached to a silo 47. In Figure 1 a similar crust-breaker is shown from one side, with actuator 15, rod 16 and house 17.

In Figure 4 there is shown a schematic distribution (location) of feeding-points in an electroly- sis cell 60, seen from above. In this embodiment, twenty anodes 63 are arranged in two rows 61 , 62. Further, the anodes in each row are arranged in three groups with one slit between each group, that will say two slits. In the slits, there is in accordance with the present inven- tion, located feeding-holes 64, 65, 66, 67. The feeding through the holes is performed in pair by two centrally placed feeders or groups of feeders 68, 69 for instance for oxide, fluoride or soda, and material is distributed to the holes 64, 65 and 66, 67 respectively.

Figure 5 shows schematically a distribution of feeding-points in an electrolysis cell 80, seen from above. In this embodiment the cell is provided with thirty-two anodes 83 distributed in two rows 81 , 82. In each row the anodes are arranged in four groups in such a manner that there is provided a slit between each group, that will say three slits here. In these slits there are arranged feeding-holes 84, 85, 86, 87, 88, 89, for feeding material such as oxide, fluoride, soda etc., to the cell for the operation thereof. In the same manner as described above, the feeding-holes (84, 85), (86, 87), together with (88, 89) may be feeded by three feeders or groups of feeders (not shown).

It should be understood that the technology described here may be applied in other fields where it is important to obtain that the dosed material is spreaded in a proper manner. Thus the invention can be applied in other electrolysis processes, such as for instance production of aluminium by the Søderberg-process.

Claims

1. Method for point-feeding materials such as oxide, fluoride, etc., to an electrolysis ceil (60), preferably an electrolysis cell for production of aluminium according to the Hall-Heroult process, characterised in that material arranged in a reservoir, for instance a silo (2), is distributed to two or more points (64, 65) in the bath crust of the cell.

2. Method in accordance with claim 1 , characterised in that the points where material is feeded is arranged in slits located between groups of anodes.

3. Device for point-feeding of materials, such as oxide, fluoride, etc., to an electrolysis cell

(60), preferably an electrolysis cell for the production of aluminium according to the Hall- Heroult process, comprising a reservoir (2) for material, a dosing device 8 with an outlet, together with a bar (14) or crust breaker for keeping open feeding holes in the bath crust of the cell, characterised in that the dosing device is provided with a distribution pipe (23) having at least two outlets (10,

11) for the distribution of material to two or more points (64, 65) in the cell (60).

4. Device in accordance with claim 3, characterised in that the dosing device is a scoop-feeder.

5. Device in accordance with claim 3, characterised in that the dosing device is a fluidised feeder.

6. Device in accordance with claim 3, characterised in that the dosing device is a screw-feeder.

7. Device in accordance with claim 3, characterised in that the bar is a multiple bar (40) with two or more bars (41 , 42) connected with a yoke (43) moved by an actuator (44).

8. Device in accordance with claim 3, where the electrolysis cell (60) is rectangular, seen from above and where the anodes (63) are arranged in two rows and distributed in groups within each row, characterised in that the distribution pipe (23) is arranged in a transversal direction with respect to the lenghtwise direction of the cell, where the outlets (10, 11) protrudes into each row and are further located in slits arranged between the groups of anodes (63).