NZ195424A

NZ195424A - Arrangement of linking conductors in a high current intensity transversely disposed electrolytic cell series

Info

Publication number: NZ195424A
Application number: NZ195424A
Authority: NZ
Inventors: P Homsi; M Keinborg; B Langon; P Morel
Original assignee: Pechiney Aluminium
Priority date: 1979-11-07
Filing date: 1980-10-31
Publication date: 1984-12-14
Also published as: DE3070034D1; YU42988B; IN152568B; PL227652A1; WO1981001299A1; BR8008907A; RO82538A; PL132150B1; MX154537A; EP0047246B1; CA1143695A; OA08223A; RO82538B; GR70348B; KR830004457A; EP0047246A1; JPS56501247A; FR2469475A1; FR2469475B1; KR850001537B1

Description

\9b4M Priority Dat^s): 'J.'J I'. 1% ..

'CsmpJeto Cpactfjoaticn Fsiod: 3'./.'.*?/. ^° Cl3sr.: j "• f Publication Bst !?.0. Journal, No: ,..^.D£C.tt4 I Q> bis NEW ZEALAND PATENTS ACT,1453 : 26 AUG 1981 No.: Date: COMPLETE SPECIFICATION a process and device for eliminating magnetic disturbances in transversely positioned, very high intensity, electrolytic cells We, ALUMINIUM PECHINEY, 28, Rue de Bonne1, 69003 Lyon, France, a French Company, hereby declare the invention for whichXK/ we pray that a patent may be granted to jaae/us, and the method by which it is to be performed, to be particularly described in and by the following statement:- (followed bv lal 195 4 — \g. - "A Process and device for eliminating magnetic disturbances in transversely positioned, very high intensity, electrolytic cells" The present invention relates to a new device 5 and a new process for eliminating magnetic disturbances which are detrimental to the perfect operation of transversely positioned, very high intensity electrolytic cells. These cells are intended for the production of aluminium by 10 electrolysis of the alumina dissolved in baths of aluminium and sodium fluorides. The invention relates to the reduction of the magnetic forces applied to the liquid metal contained in these cells. These forces are due to the conjugate action 15 of the horizontal currents appearing in the metal and the magnetic field created by the conductors of one cell and of its neighbours in the same row, as well as by the conductors in the cells in adjacent rows. In fact, the cells are arranged in 20 series with a certain number of adjacent rows so as to permit the current to return to its source.

The invention applies only to the balancing of the magnetic field created by the conductors in the cell and its neighbours in the same row. 25 The influence of one or more adjacent rows, if the rows are positioned relatively close to the row / ! O - n- 195424 under consideration, forms the subject of separate patents: New Zealand Patent No. 182677 and its Patent of Addition No. 183515 and British Patent No. 2,020,700.

Statement of the Problem It is known that, to reduce investment and to lower the running costs, there is a tendency to increase the size of production units, and this 10 leads to an increase in the intensity travei*sing each cell. The intensity range of the new cells, which was recently below 200,00()a, is at present contained in the range of from 200,000 to 300,000a.

At these intensities, the magnetic effects 15 assume such an amplitude that, if special arrangements were not made to weaken the effects, the yield of the electrolytic cells would be greatly reduced and, in the final analysis, normal operation might become quite impossible.

These disturbances are exhibited by several effects: a) Permanent deformation of the sheet of metal with, on the one hand, overall variation in level, the inclination being capable of 25 attaining a value higher than the anode- metal distance in certain cases and, on the other hand, deformation into a symmetrical dome; ^ a < I 195424 b) The existence of permanent movement of the bath and of the metal, the configuration of which can be more or less favourable to the perfect implementation of electrolysis; c) The existence of periodic movements of the bath/metal interface which are detrimental to the electrolysis yield (instability) and can even cause expulsion of the liquid metal outside the cell in certain cases.

In order to eliminate magnetic disturbances, it is possible to act on the horizontal currents, or to act on the magnetic field or on both. The present invention is based on the latter case.

Statement of the Invention 15 As a convention, hereinafter, Bx, By and Bz will designate the components of the magnetic field along the axes Ox Oy Oz in a regular trihedron 9 whose origin/is the centre of the cathode plane of the cell, Ox being the transverse axis of the cell 20 pointing in the direction of circulation of the current in the row of cells, Oy the longitudinal axis of the cell and Oz the upward pointing vertical axis.

The sides of the cells are known as "small 25 sides" and "large sides", the latter being perpendicular to the axis of the series in the case of transverse series of cells. The terra "head" is used to designate the ends on the small sides of the cell - k - 195424 as well as of the anode system. As usual, the terms"upstream side" and "downstream side" of each cell will refer to the conventional direction of the current in the series. In the following 5 figures, the direction of the current will run from the bottom to the top of each drawing and will be indicated by an arrow.

Finally, the term "cell under consideration" will designate the cell from which the current is 10 being extracted via a cathode, "preceding cell" the one which supplies the anode system of the cell under consideration from its cathode outlets, and "following cell" the one whose anode cross-piece is supplied with current from the cathode-outlets 15 of the cell under consideration.

All the values of the magnetic fields are given "tesla" (T)( IT = 10-2i gauss).

The invention relates to a series of igneous electrolytic cells intended for the production of aluminium from alumina dissolved in molten cryolite, operating at an intensity capable of attaining 200,000 to 300,000 amperes, each cell in said series comprising a parallelepiped box supporting the cathode blocks in which the cathode current outlets (so-called "cathode outlets") are sealed and an anode system (which can be of the self-baking Soderberg type or 195 of the type having multiple pre-baked anodes) suspended from a bus-bar, the cells being connected electrically in series by conductors joining the cathode outlets of a given cell to the bus-bar of the following cell in the series, the cells also being arranged transversely to the axis of the series, in v/hich series of cells the cathode outlets of each cell are constituted by a plurality of conducting elements which are usually metallic, issuing vertically through the bottom of the box and in which, moreover, a proportion of the linking conductors between cells are arranged, ova- at least a portion of their path, outside the two vertical planes passing through the ends of the anode system.

The invention also relates to a process for eliminating magnetic disturbances in a series of igneous electrolytic cells intended for the production of aluminium from alumina dissolved in molten cryolite, operating at an intensity capable of attaining from 200,000 to 300,000 amperes, the said cells comprising a parallelepiped box supporting carbon cathode blocks in which the cathode current outlets ai~e scaled and an anode system suspended from a bus-bar, the cells being connected electrically in series by conductors joining the cathode outlet of one cell to the bus-bar of the following cell, and being arranged ti-ansvcrsely t AUG 1984 19542 to the axis of the series, a process in which . the cathode^current is extracted by a plurality of conducting elements sealed in the cathode blocks and issuing vertically through the bottom of the box 5 and in which a fraction of the total current circulating in the linking conductors between the cells of between 30 and 5^$ is shunted into conductors arranged, over at least a proportion of their path, outside the two vertical planes passing through the 10 ends of the anode system.

The distribution of this shunted current can by symmetrical about the axis of the series and be distributed evenly over each side of the <pells or can be asymmetrical and be distributed unevenly over 15 each side of the cells.

The bus-bar of a cell under consideration is supplied with current from the cathode outlets of the preceding cell by a plurality of vertical risers which can be connected, either all on the upstream 20 side of the said cross-piece, or on the upstream side as well as the downstream side, a proportion of the current also being capable of being brought to both and/or either of the heads of the said cross-piece.

Figure 1 shows two systems of cathode outlets drawn, for the sake of simplicity, on the same cell: lateral outlets and outlets through the bottom. 195 4 Figure 2 shows schematically the section through a cell, illustrating the three co-ordinate axes used to define the direction of the components of the magnetic field.

Figure 3 shows the distribution of the average of the vertical component Bz of the magnetic field over the four quadrants of the cell.

Figure 4 shows schematically the position of the linking conductors according to the invention relative to the vertical plane zz1 passing through the end of the anode system.

Figures 5, 6 and 7 indicate schematically the different variations in paths which the linking conductors can follow within the scope of the 15 invention.

Figure 8 shows how the links between cells would be constituted by utilising the prior art.

Figures 9 to 13 show the implementation of the invention in five different variations which 20 each form the subject of an embodiment.

Figure 14 is the layout of a practical embodiment and Figure 15 a section in the axial direction of the series of this same embodiment, indicating the actual position of the conductors. 25 In these various figures, the same elements are designated by the same reference numerals. 1 designates the lateral cathode outlets 1 O: K A according to the invention, 2 the cathode outlets through the "bottom of the box, 3 the box, k the contour of the anode blocks, 5 the anode system, 6 the electrolysis bath, 7 the sheet of liquid 5 aluminium formed on the cathode, 8 the shunt conductor (or group of conductors), 9 bus-bar.

In the conventional cells, the horizontal currents.are generated mainly by the method of 10 collecting the cathode current. The current is extracted by lateral cathode rods 1 which have the disadvantage of concentrating the current on the two large sides of the cathode. If the size of the cell is increased, it is necessary to widen the 15 cathode, and this increases the horizontal currents in the liquid metal.

In the present invention, the current is extracted from the carbon cathode through vertical outlets 2 which will be designated hereinafter by 20 the term "outlets through the bottom1'. This process permits a considerable reduction of the horizontal currents in the metal while producing a gain of the order of 0.1 V on the cathode drop. This improvement in the cathode drop is translated by a reduction of 25 300 kWh/t in the specific energy consumed by the cell Owing to the outlets through the bottom, we will no longer make a distinction between the cathode current extracted upstream from that extracted down 195424 stream, as was the custom in the case of cells having lateral cathode outlets, since all the cnrrent leaves through the bottom of the cell.

The definition of the number, position and arrange-5 ment for fixture in the carbon cathode of the vertical outlets in the bottom will be considered as known to the skilled man.

The idea of the outlets through the bottom has been described in several earlier patents.

Three of them only make use of outlets through the bottom, to the exclusion of a description of the linking conductors: United States Patent No. 2,528,905, Italian Patent No. 451,183 and United States Patent No. 2,846,388. The first of these patents relates only 15 to cells having a relatively low intensity of approximately 100,000.4. Two other patents, also only applying to cells having an intensity of approximately 100,000A, describe expensive arrangements of conductors leading to scanty balancing with 20 respect to the magnetic field: Norwegian Patent No. 838S3 and United States Patent No. 3,063,919.

The paths of the linking conductors are long, necessitating high investment in conductors and high drops of line voltage. The 25 invention permits elimination of magnetic disturbances in these cells by eliminating horizontal currents and by balancingUja magnetic field. ,■■■- X, 195424 With regard to the magnetic field, a component will be described as being "anti-symmetrical" to a given plane if two opposite values of the component correspond to each couple 5 of points symmetrical to this plane.

In transverse cells, in the absence of the effect of adjacent rows, the components Bx and Bz are, by design, anti-symmetrical to the plane x o z.

With regard to the balancing of the magnetic field which directs the choice of the arrangement of the linking conductors, we have adopted the following two criteria: i) A principal criterion applied to the vertical 15 component consisting in the equality of the averages of Bz per quarter cell. The numbering of the quadrants of the cell is defined in Figure 3. The equality of the averages is written: Bz^ = - Bz0 In view of the anti-symmetr3r, this equality will lead to the following, in the absence of adjaccnt rows: Bzn =-Bz, = Bz„ = - Bz„ 1 .4 _ 2 Moreover, the value of Bz at any given point should be low. The field will be calculated by talcing into consideration the effect of the ferroma.gnetic parts of the cell and its environment. //4/ 'Otjyi X - ^ 1 954 A secondary criterion involving the reduction in the maximum value of the horizontal component Bx. The maximum value will generally be situated at the end of the anode plane on the small sides of the cell.

In the case of transverse cells having an intensity of between 200,000a and 300,000a, the invention involves a combination of the outlets through the bottom and shunting of a proportion of the current in conductors arranged outside the two vertical planes passing through the ends of the anode system. In reality, this definition of the positioning of the shunt conductors should be restricted as 15 it covers a portion of the box, and it is obvious that the linking conductors cannot pass inside the box.

In practice, the shunt conductors are therefore placed in the hatched zone A,B,C,D,E,F 20 in Figure k. This zone is defined on the box side by the vertical wall A,B of the small side of the box and, below the box, by the bottom to "the perpendicularity of the end of the anode system (BC). However, the conductor will be offset slightly from 25 the wall of the box at a distance compatible with the regulations governing electrical safety. On the side opposite the box wall, there is no theoretical limit to the zone. However, to avoid lengthening the path ii) 1 954 of the conductors needlessly, the conductor will not be offset beyond a plane EP situated at about 1 metre from the box wall. The height of the zone is theoretically unlimited but, to economise in the path 5 and to prevent the shunt. conductor from obstructing operations on the cell, the height of the zone will be defined in its upper portion by the top of the box (FA) and, at its lower portion, by a boundary ED situated about 1 metre below the bottom of the box. 10 Figures 5, 6 and 7 permit clarification of the term V shunt conductor".

In Figure 5, the cathode current collected beneath the cell under consideration circulates in the conductor 10 and is shunted through the heads 15 of the cell under consideration (outside the vertical plane passing through the end of the anode system 4) by the shunt conductor 11 which turns about the two angles upstream and downstream of the end 12 of the anode plane. The shunt conductor 11 passes beneath 20 the box 3 of the cell under consideration and is connected to the bus-bar of the following cell by the ascent 13.

In Figure 6, ~the cathode current collected beneath the cell under consideration circulates in the conductor 14 and is shunted via the heads of the following cell by the shunt conductor 15 which turns \ about the two angles upstream and downstream of the end 12 of the anode plane of the following cell (outside the vertical plane passing through the end of the said anode system). The shunt conductor 15 runs along the box 3 of the following cell over its small side.

In Figure 7, a proportion of the cathode current collected beneath the cell under consideration circulates in the conductor 16 and is shunted through the heads of the cell under consideration by the shunt conductor 17 which turns about the two angles 10 upstream and downstream of the end 12 of the anode plane of the cell under consideration. The shunt conductor 17 runs along the box 3 of the cell under consideration on its small side. Another proportion of the cathode current collected beneath the cell 15 under consideration circulates in the conductor 18 and is shunted through the heads of the following cell by the same shunt conductor 19 which turns about the two angles upstream and downstream of the end 12 of the anode plane of the following cell. The 20 shunt conductor 19 runs along the box 3 of the following cell on its small side.

The proportion of the current which is shunted through each of the heads of the cell is between 15$ and 27$ of the sum total of the current of the cell. 25 More specifically: - if the shunt conductor supplies the cross- piece of the following cell through a positive ascent situated on the large upstream side of the following cell, the fraction of the current shunted through each of the heads of the cell under consideration will be between 15$ and 27$ of the total intensity; - If the shunt conductor supplies the cross- piece of the following cell through a positive ascent situated on the large downstream side of the following cell, the fraction of current - shunted through each of the heads of the following cell will be between 15$ and 27$ of the total intensity.

Within these ranges, the compensation for the effect of one or more rows adjacent to the row under consideration is not taken into consideration.

In the case of high intensity cells, the number of positive ascents will generally be greater than or equal to four. However, if the invention is applied to cells having an intensity lower than 200,000A, less than four positive ascents may be sufficient.

We will illustrate,in an Example, the importanc of a suitable choice of the linking conductors for a cell having outlets through the bottom.

By connecting the outlets through the bottom directly to the anode plane of the following cell by means of five positive ascents of equal intensity / distributed over the large side of a 250,000 ampere cell (Figure 8), as would be the case according to $ the prior art, a vertical magnetic field crossing from the centre of the cell towards the heads is obtained, with average values per quadrant, after deducting the effect of the ferromagnetic parts: 5 x .10 h T Bz average: - 30.10 h T Bz average: 0 .10"4 T - 30.10_it T The condition: Bz^ = - BZg is not verified absolutely since the opposite is true: Bz^ = Bz2 Although this circuit has the advantage of the shortest electric path, it does not permit the balancing of the magnetic field of a cell having outlets through the bottom.

Some embodiments of the invention, showing the improvement obtained in the balancing of the magnetic field, are provided below. For the sake of clarity, Figures 9 and 13 only show very 25 schematically the conductors connecting the cathode outlets 2 of the cell under consideration to the bus- bar 9 supplying the anodes of the following <4 gets ^ i V J ^ —IS £*-Cr-^+ cell. In practice, the linking conductors pass "beneath the level of the plane of operation and then rejoin the bus-bars through vertical or slightly oblique risers. .

In all the Examples given, each cathode block arranged parallel to the axis Ox has 3 vertical outlets. However, the actual number of outlets can naturally be different without departing from the scope of the invention.

EXAMPLE 1 - Cells with outlets through the bottom, having five positive risers, whose current shunted through the heads of the following cell supplies the latter through the large downstream side.(Figure 9) The current received at the two ends of the cathode is shunted through the heads of the following cell and then supplies its bus-bar downstream by two positive ascents situated _ at l/k and 3/4.

The fraction of current travelling through each of the two shunt conductors is equal to 3/l6, that is to say 18.75$, of the total intensity. The remainder of the current supplies the bus-bar of the following cell upstream, along three positive ascents, one situated along the Ox axis of the cell and the two others at the heads of the bus-bars. , It is immaterial whether these last two ascents are placed on the large side or the small side of the cell. per quadrant The average vertical fielc}/of this cell at *8 /'X f\ W 250,OOOA, and taking into consideration the effect of the ferromagnetic parts, is: x s. + 3.10 k T - 3.10-il T Bz average: Bz average: / 0 \ - 3.10"4 T + 3.10"4 T The horizontal field Bx maximum is 60.10 EXAMPLE 2: - Cells with outlets through the "bottom, having six positive risers, whose current shunted through the heads of the following cell is collected in the inter-cell space and is transmitted downstream of the 0-f ^he following cell (Figure 10) The current received at the two ends of the cathode is collected on each side of the cell under consideration in the inter-cell space. A proportion of this current is shunted over the heads of the cell under consideration. The shunt conductor then runs along the heads of the following cell and supplies its cross-piece,'downstream at l/4'and 3/4 of the large side. Each of the conductors for shunting through the heads of the following cell is traversed by l/5 of the total current. The remainder of the cathode current supplies via the 1 95A-? 4 upstream side the cross-piece of the following cell through four positive ascents situated at 1/8, 3/8, 5/8, and 7/«.

The average vertical field per quadrant of this cell at 250,OOOA, and taking into consideration the effect of the ferromagnetic parts, is: x /N f- -4 + 10 T Bz average: -4 - 10 T Bz average: 0 -4 - 10 T + i—1 o i £- i-3 -4 The horizontal field Bx maximum is 25.10 T.

EXAMPLE 3 - Cell with outlets through the bottom, having five positive risers, whose current shunted through the heads of the cell under consideration is received at lA and lA of the cathode (Figure ll) The current received at l/4 and 3/4 of the cathode joins, along the large upstream side of the cell under consideration, the shunt conductor circulating over the heads of the cell under consideration before supplying via the upstream side the heads of the bus-bar of the following cell through a positive riser on each side of the cell. It is immaterial whether the Tisers are placed on *1 0/ ^ A & J * * the large side or the small side of the cell.

Each of the conductors for shunting through the heads of the cell under consideration is traversed by 3/l6, that is 18.75$ of the total intensity. The remainder of the cathode current directly supplies, via the upstream side as indicated in Figure 11, the cross-piece of the following cell through three positive ascents situated at l/4, l/2 and 3/4 of Uelarge side.

The average vertical field per quadrant of this 250,OOOA cell, and taking into consideration the effect of the ferromagnetic parts, is: x A -4 -4 + 2.10 T - 2.10 T Bz average: Bz average: 0 y f V -4 - 10 T + 10"^ T -4 The horizontal field Bx maximum is 40.10 T.

EXAMPLE 4 - Cell with outlets through the bottom. having five positive risers, whose current shunted by the heads of the cell under consideration is received at the two ends of the cathode (Figure 12) 25 The current received at the two ends of the cathode joins, along the large upstream side of the cell under consideration, the shunt conductor 1954 2 circulating over the heads of the cell under consideration before supplying the upstream end of the bus-bar of the following cell through a positive ascent on each side of the cell. It is immaterial whether the ascents are placed on the large side or the small side. Each of the conductors for shunting through the heads of the cell under consideration is traversed by l/4 of the total intensity. The remainder of the cathode current directly supplies, through the upstream side, the cross-piece of the following cell through three positive ascents situated at 1/4, l/2 and 3/4 of the large side.

The average vertical field per quadrant of this cell at 250,OOOA, and taking into consideration the effect of the ferromagnetic parts, is: x /N + 5.10 4 T - 5.10 h T Bz average: Bz average: o • y - 4.10"4 T + 4.10—^ T The horizontal field Bx maximum is 48.10"^ T.

EXAMPLE 5 — A cell with outlets through the bottom. having four positive risers, whose current shunted through the heads of the cell under consideration is collected in the upstream inter-cell space of the cell under consideration (Figure 13) This collector supplies the conductor for shunting through the heads of the cell under consideration. The shunted current then supplies the upstream bus-bar of the following cell 5 through two positive ascents situated at l/8 and 7/8 of the large side. Each of the conductors for shunting through the heads of the cell under consideration is traversed by l/4 of the total intensity. The remainder of the cathode current 10 supplies, through the upstream side, the cross-piece of the following cell through two positive risers situated at 3/8 and 5/8 of the large side.

The average vertical field per quadrant of this 250,OOOA cell, and "taking into consideration 15 the effect of the ferromagnetic parts, is: x A + to • O 1 i-3 - 2.10 k T Bz average: Bz average: y / 0 \ - 3. lO-2* T + 3.10"^ T -4 The horizontal field Bx maximum is 22.10 T. IMPLEMENTATION OF THE INVENTION 25 We have built a series of cells according to the invention whose operating intensity has been fixed at 250,OOOA.

Figure 14 shows schematically the arrangement 1 O. C a i *■ *j> - of all the linking conductors between the cell under consideration and the following cell.

Figure 15 is a transverse section along an axis parallel to Ox of the cell under consideration 5 and the following cell. The numbering of the elements is common to the two figures. In Figure 15, the alumina supply device, the super-structure, the anodes and the suspension system thereof have been omitted or shown very schematically for the sake of 10 clarity. In reality, they comply with the prior art.

The cathode outlets through the bottoms 20 are connected to several negative collectors 21. The current collected at the two ends of the cathode is connected by the conductors 22 to the conductors 8 15 for shunting through the heads of the following cell and then supplies the bus-bar 9 of this cell through the risers 23 situated on the downstream side at l/4 and 3/4.

Each of the conductors for shunting through 20 the heads is traversed by 3/l6, that is 18.75$ of the total intensity. The side along Oz of these «r> conductors is determined so as to permit the balancing of the magnetic field. The location of these conductors has been defined above (Figure 4). 25 The current collected at the centre of the cathode is connected by the conductors 24 to three vertical risers connected to the heads and to the centre of the - bus-bar, on the upstream side". Each 195424 of the conductors supplying the heads of the cross-piece is traversed by l/4 of the total intensity and the conductor supplying the centre of the cross-piece is traversed by l/8 of the 5 total intensity.

The cells in the series constructed according to the invention have the following characteristics: Anode surface area: 348,000 cm2 Internal Dimensions of the box:13.68 x 4.15 (in metres) 10 During operation thereof, the following results have been obtained: Average intensity: 252,OOOA Faraday yield: 92.5$ Voltage: 3.94 V The corresponding specific energy consumption is 12,690 kWh/tonne Al, constituting a value associated with cells operating at such a high intensity.

This gain has been obtained, among other factors, by a reduction in the cathode drop of 0.25V on 20 average.

Although the invention applies more particularly to series of electrolytic cells operating at intensities of between 200,000 and 300,000 amperes, it can also apply to series of cells operating at lower intensities of 25 between 100,000 and 200,000 amperes, for example.

Q •iIAUG|?84 - 2k - 195424

Claims

WHAT WE CLAIM IS:

1. A series of igneous electrolytic cells intended for the production of aluminium from alumina dissolved in molten cryolite, operating at a very-high intensity capable of attaining from 200,000 to 300,000 amperes, each cell in said series comprising a parallelepiped box supporting cathode blocks in which there are sealed the cathode current outlets and an anode system suspended from a bus-bar the cells being connected electrically in series by linking conductors and arranged transversely to the axis of the series, characterised in that the cathode outlets of each cell are constituted by a plurality of conducting elements sealed in cathode blocks and issuing vertically through the bottom of the box, and in that a proportion of the linking conductors connecting the cathode outlets of one cell to the bus-bar.; of the following cell are arranged, over at least a proportion of their path, outside the two vertical planes passing through the ends of the anode system.

2. A process for eliminating magnetic disturbances in a series of igneous electrolytic cells intended for the production of aluminium from alumina dissolved in molten cryolite, operating at an intensity capable of attaining 200,000 to 500-000 ^e,'/ - - > r - 25 - 195424 amperes, said cells comprising a parallelepiped box supporting carbon cathode blocks in which there are sealed the outlets of the cathode current, and an anode system suspended from a bus-bar, the cells being connected electrically in series by conductors connecting the cathode outlets of one cell to the bus-bar of the following cell, and being arranged transversely to the axis of the series, characterised in that the cathode current is extracted by a plurality of conducting elements sealed in cathode blocks and issuing vertically through the bottom of the box, and in that a fraction of the total current, of between 30 and 54$ , circulating in the linking conductors between the cells, is shunted in conductors arranged, over at least a proportion of their path, outside the two vertical planes passing through the ends of the anode system.

3. A process for eliminating magnetic disturbances in a series of igneous electrolytic cells according to Claim 2, characterised in that the shunted current is distributed in the shunt conductors symmetrically to the ax-is of the series.

4. A process for eliminating magnetic disturbances in a series of igneous electrolytic cells according to Claim 2, characterised in that the shunted current is distributed in the shunt conductors asymmetrically - j 195424 - 26 - to the axis of the series.

5. A process for eliminating magnetic disturbances in a series of igneous electrolytic cells according to any one of Claims 2 to 4, characterised in that the bus-bar 0£ each cell is supplied with current from the cathode outlets of the preceding cell by a plurality of vertical risers connected to its -upstream side.

6. A process for eliminating magnetic disturbances in a series of igneous electrolytic cells according to any one of Claims 2 to 5, characterised in that the bus-bar Df each cell is supplied with current from the cathode outlets of the preceding cell, partially through a plurality of vertical risers connected to its upstream side, and partially through a plurality of vertical risers - connected to its downstream side.

7. A process for eliminating magnetic disturbances in a series of igneous electrolytic cells according to any one of Claims 2 to 6, characterised in that the bus-bar °f each cell is partially supplied with current from the cathode outlets of the preceding cell through vertical risers ,connected to either or to both of its ends. 195424 27

8. A process for eliminating magnetic disturbances in a series of igneous electrolytic cells according to Claim 2, substantially as hereinbefore described with particular reference to any one of the foregoing Examples.

9. A series of igneous electrolytic cells according to Claim 1, substantially as hereinbefore described with particular reference to the accompanying drawings. DATlLw THIS ?>Otk QAY OF 19 A. j. PARK & SON PER S. AGENTS FOR THE APPLICANTS J AUGf984r