US2999801A - Apparatus for supplying current to high amperage electrolytic cells - Google Patents

Description

p 1961 J. WLEUGEL 2,999,801

APPARATUS FOR SUPPLYING 1 CURRENT To HIGH AMPERAGE ELECTROLYTIC CELLS Filed Aug. 2, 1957 3 Sheets-Sheet 1 FIG.I

INVENTOR JOHAN WLEUGEL ATTORNEYS Sept. 12, 1961 .1. WLEUGEL 2,999,801

APPARATUS FOR SUPPLYING CURRENT TO HIGH AMPERAGE ELECTROLYTIC CELLS Filed Aug. 2, 1957 3 Sheets-Sheet 2 PEG. 2

INVENTOR.

JO HAN WLEUGEL.

ATTORNEYS Sept. 12, 1961 J. WLEUGEL 2,999,301

APPARATUS FOR SUPPLYING CURRENT T0 HIGH AMPERAGE ELECTROLYTIC CELLS Flled Aug 2, 1957 a Sheets-Sheet a FIG. 3

0 O O 0 O FIG. 4

INVENTOR. JOHAN WLEUGEL ATTORNEYS United States Patent APPARATUS FOR SUPPLYING CURRENT TO HIGH AMPERAGE ELECTROLYTIC CELLS Johan Wleugel, Oslo, Norway, assignor to Elektrokemisk In electrolysis, especially melt electrolysis such as occurs in aluminum furnaces, where direct current of high amperage is employed, the bus bars lead from one cell to the other. The voltage on each individual cell is so low that the cells must be connected in series to obtain a sufficient voltage for converter or rectifier.

In electrolytic aluminum furnaces, the bus bars are usually led upwards at the end of each furnace and then along the furnace either above or at the side of the anode. The transfer of current from bus bars to anode is effected by means of contact bolts which are inserted vertically or sideways into the anode.

From the anode the current passes through the molten bath, where the electrolysis takes place, and further through the liquid aluminum bath on the bottom, and through the bottom lining and the cathode bars. The current is collected in the cathode bus bars and led over to the next furnace. This system has always been used and is also today a generally used system for bus bars in electrolytic cells connected in series.

The same system has been used for the bigger sizes of furnace units which have now been developed, but on account of the electromagnetic conditions in the melt and the metallic bath difiiculties will arise.

The reason for these difiiculties is that with currents of 80-100,000 amperes or more which are now used in modern plants and which are led through the anode bus bars in one direction, the conductors will be surrounded by magnetic fields which will also cross the molten cryolite bath and the metallic aluminum between anode and cathode.

The direction of these lines of magnetic force is transverse to the length of the furnace. It may be assumed that the electrolysis takes place by the current below the anode being divided into threads through the molten cryolite bath and metal and that these current threads pass vertically from anode to cathode. There will therefore be a power elfect according to Biot-Savarts law between the horizontal transversal lines of force and the vertical current threads. This will result in longitudinally directed forces in the melt.

These forces acting on the individual melt particles will add up under the anode resulting in a force driving the liquid aluminum and the molten electrolyte towards one end of the furnace, opposite to where the current is led to the anode. If, as is done in modern big aluminum furnaces, iron bolts are used for leading the current to.

the anode and these iron bolts are fixed to the anode bus bar, they will lead the magnetic forces down into the bath and the melt and the above mentioned power effect will be multiplied many times.

The above described phenomenon is well known and a difference in level of several inches from one end of the furnace to the other has been measured.

I have found that the best and simplest solution of this problem is to divide the anode bus bars in two parts and feed the current into them so that the current flow through the two parts is in opposite directions.

Ordinarily the anode bus bars in large installations run parallel with the length of the furnace pots above the anode and in accordance with my invention these anode bus bars will be divided near the center, and the current will be supplied to them either from the two outer ends so that the flow of the current will be toward the center of the anode, or it may be supplied from the two inner ends so that the flow of current will be from the outer ends of the anode.

With this arrangement of the anode bus bars it usually will be advantageous to withdraw the current either from a central point of the cathode bus bars or, if desired, the cathode bus bars may be divided into two lengths longitudinally and the current may be withdrawn from the outer ends of these bus bars. When the electrode bus bars are thus arranged, the equipotential zone of the furnace Wil be moved down from the anode bus bars into the furnace itself and this will result in very important advantages being obtained with regard to the distribution of current in the conductors supplying the current to the two anode halves.

The benefits of this invention can be judged by a more detailed examination of the electrical and magnetic forces.

If, instead of delivering current to the anode bar from one end only, the current is simultaneously fed into opposite ends of an electrically continuous bar, there will result some reduction of the forces tending to displace the bath, because opposing magnetic fields are set up by the oppositely directed currents. However in such an arrangement substantially complete suppression of the transverse component of the magnetic fields could only be obtained if the currents fed into the opposite ends of the anode bar were exactly equal. Expressing it diiferently, if the location of the equipotential point of the circuit were at a location on the anode bar equidistant I from the ends of the furnace, the desired result would be obtained. In practice, because of the differences in length, and therefore of the resistance of the conductors leading from the cathode of one furnace to the opposite ends of the anode bar of the succeeding furnace, the currents so fed to the anode bar are not only unequal but may differ by 300% or more. As a result, there is incomplete magnetic compensation and nonuniform distribution of current flow through the furnace.

In accordance with the invention it has been found that when the anode bar is interrupted electrically at or near the center thereof so that the equipotential point of the circuit is made to occur in or below the furnace (that is in or below the baked and conductive part of the anode), substantial equality of the currents fed to the opposite ends of the bar may be achieved notwithstanding inequality in resistance of the electrical connections to the bar. When the anode bar is so interrupted, the ratio of the anode bar currents does not depend primarily on the ratio of the resistance of the connections to the bar but upon the ratio of the resistances of current paths including these connections and at least part of the furnace. As the resistance of the furnace including the resistance of the electrode is very much higher than that of the anode bar and its connections, these latter will have but small elfect upon the current distribution.

In a typical furnace, the resistance of the anode bar and of 'the connections leading to it is of the order of .029 ohm/mmF/ m. whereas the anode resistance, at the baked or lower zone is of the order of 500 ohms/mm. /m. and of the green paste zone is practically infinite.

It can be shown by calculations based on typical measwhereas with an uninterrupted anode bar and based on the same resistance values of conductors leading the current to both ends of the anode bar their ratio has been found to be as much as 3.00:1. This is enough materially to upset the operation of the furnace.

Even if the lower part of the anode is considered the equipotential point, with an electrically interrupted anode bar and the same resistance values, the current ratio does not exceed about 1.13: 1. The significant improvement effected by interrupting the anode bar to lower the equipotential point into the furnace is thus apparent.

This invention may be readily understood by reference to the accompanying drawings in which- FIG. 1 shows a plan view of a series of pots embodying my invention;

FIG. 2 is a side view of the pots shown in FIG. 1;

FIG. 3 is a diagrammatic showing of a pot with a slightly modified set of connections, and

FIG. 4 is again a diagrammatic arrangement showing yet another set of connections, all of which utilize my invention.

Referring now to FIGS. 1 and 2, in these drawings I show a series of three units, -A, B and C. The unit B is shown complete and enough is shown of units A and C to show the interconnections between adjacent units.

In these figures, represents the pot in which the cryolite is melted and the alumina reduced to aluminum. 12 is the carbon anode of the so-called Soederberg or continuous type which is formed within the permanent casing 14 which in turn is supplied with a gas-collecting channel 16. With electrodes of this type, paste is introduced into the top of the casing and this is carbonized progressively in the furnace. Such an electrode has a relatively high internal resistance. The current to furnaces such as shown Will be 65,000 amperes or more and is supplied to the anode by means of vertically inserted contact rods 18 which on the drawings are shown arranged in four rows running longitudinally along the long axis of the furnace pot. The contact rods are electrically and mechanically connected to the anode bus bars 20 each of which is divided near the central part of the furnace into two separated pieces. The current is fed to the anode bus bars 20 from each end of the furnace pot by the connectors 22.

The anode bus bars 20 are mechanically supported from the beam 24 but are insulated from this beam electrically. The beam 24 carries the weight of the anode, the bus bars and the anode casing. The vertical position of the anode is controlled by the jacks 26 which rest on the supporting columns 28. The connections 22 which supply the current to the anode bus bars 20 from the cathode connections of the preceding furnace are somewhat flexible so that they can bend to permit vertical movement of the anode.

As is well known in this art, the bottom of the pot 10 forms the cathode of the furnace and cathode rods 29 run through the bottom of the pot. The position of these rods is clearly illustrated, for example, in Sejersted Patent No. 2,526,876 where the rod is indicated as passing through the bottom portion of the pot. As shown in these figures, a cathode bus bar 30 is connected with the cathode collecting rods 29 toward the left-hand end of the furnace shown at B, and the cathode bus bar 32 is connected with the cathode-collecting rods 29 toward the right-hand end of that furnace. The cathode bus bar 30 runs under the pot and is connected to the connector 22 at the far end of the next adjacent unit. The cathode bus bar 32, on the other hand, is connected to the nearest connector 22 of the next adjacent unit.

From this description it will be seen that as to each unit the current is fed into the anode bus bars from opposite ends and the flow is toward the center. The

current then passes down through the anode and the bath and flows out through the cathode bus bars which are here shown as connected adjacent a central point of the furnace pot and from them thecurrent is taken on to the next adjacentset ofanodebus bars,

In FIG. 3 I show diagrammatically an arrangement quite similar to that shown in FIGS. 1 and 2. Here the anode bus bars 34 are shown separated in the middle, as before, and are connected externally of the pot by the connections 36. Cathode bus bars are shown at 38 and the current from these is taken oit' by connections 40 which conduct the current to the connections 36 of the next adjacent unit.

It will be noted that in this case the two sets of connections. 36 for each unit are interconnected as shown at 42. This tends to keep the pots in equilibrium and prevents any inequality from one pot being carried forward into the next pot.

In FIG. 4 an arrangement is shown in which the pots are arranged side-by-side instead of end-to-end. In this case the anode bus bars 44 are supplied with current at a central pointof the furnace by connections 46. The cathode bus bars 48 are split in the middle as in FIGS. 1 and 2 butare interconnected at the ends by connections 50. Current is taken oil? from central points of the connections 50 by connectors 52 which in turn carry the current to the connectors 46 which conduct the current to the anode bus bars of the next adjacent furnace.

In designing the connections of the furnace of my invention it is advisable that the cross-section of the cathode bus bars should be such as to have a conductivity equal to that of the anode bus bars. In this way each individual current thread from the anode bar through electrode, bath, metal and cathode will get the same ohmic resistance throughout the whole length of the furnace.

By the arrangement shown the flow of current and, the magnetic force affecting the furnace are equalized so that the upsetting efiect is reduced to a minimum.

This application is a continuation-in-part of my earlier applications, Serial No. 384,555, filed October 7, 1953,

7 nowabandoned and Serial No. 407,421, filed February 1, 1954, now Patent No. 2,804,429, issued August 27, 1957.

What I claim is:

1. In an electrolytic cell of the type comprising a pot serving as a cathode, a carbon anode of rectangular crosssection with one axis longer than the other of the type which is carbonized in the furnace suspended abovethe pot and adapted to extend down into a bath within the pot, andconta-ct'bolts entering the anode by means of which current may be transmitted to the anode, two sets of anode bus bars adjacent the upper part of the anode running. parallel with a major horizontal axis of the anode but. electrically separated from each other near thecenter of their combined length, and means for transmitting current to such-bus bars at corresponding ends of the bus bars relative tothe outside faces of the anode, so that the flow of 'currentin the respective members of the sets will be in opposite directions.

2. A structure as specified in claim 1 in which the current is. transmitted to the outer ends of the bus bars.

3. A structure-as specified in claim 1 in which each set of bus barsconsists of a pair of elements each of which comprises a plurality of bus bar members within which the current flows in substantially parallel lines and in substantially the same direction.

4. A structure as specified in claim 2 which includes a set of such pots arranged iuseries and which further includes cathode collecting bars running transversely through each pot and cathode bus bars on the sides of each pot connected to such collecting bars, and connections from pointsnear the center of the length of such cathode bars adapted to conduct current through the aforesaid transmitting means to the anode bus bars of the next adjacent pot.

5. A series of electrolytic cells for the production of aluminum of the type comprisinga pot serving as a cathode, .a carbon anode of rectangular cross-section with one 5 ,7 axis longer than the other, such anode being of the continuous type in which the material of the anode has an upper unbaked part and a lower baked and conductive part and in which the carbonized portion of the anode is adapted to extend down into a bath within the pot, vertical contact bolts extending down into the anode by means of which the anode is suspended and current is transmitted to the anode, two sets of anode bus bars run ning parallel to the major horizontal axis of the anode, connections between said contact bolts and said bus bar sets, one such bus bar set being connected to the contact bolts at one end half of the anode and the other bus bar set being connected to the contact bolts at the other end half of the anode but without direct electrical connection between said bus bar sets above the center of the anode, cathode collecting bars running transversely through each pot and cathode bus bars on the sides of each pot connected to such collecting bars, means for transmitting a current of at least 65,000 amperes to the anode bus bars of one pot at corresponding ends of the bus bar sets relative to the end faces of the anode so that the flow of current in such respective bus bar sets will be 6 in opposite directions and connections from points near the center of the length of the said cathode bars adapted to conduct current to the anode bus bar sets of an adjacent pot.

6. A structure as specified in claim 5 in which the cathode bus bars are subdivided adjacent the longitudinal center of each pot and the bus bars from one end of one pot are connected to the anode bus bars at one end of an adjacent pot and the cathode bus bars at the other end of the first pot are connected to the anode bus bars at the other end of the second pot.

References Cited in the file of this patent UNITED STATES PATENTS 2,761,830 Kibby Sept. 4, 1956 2,804,429 1 Wleugel Aug. 27, 1957 FOREIGN PATENTS 740,025 Great Britain Nov. 9, 1955 616,450 Great Britain Jan. 21, 1949 88,098 Norway Oct. 1, 1956 1,010,744 Germany June 19, 1957

Claims (1)

1. IN AN ELECTROLYTIC CELL OF THE TYPE COMPRISING A POT SERVING AS A CATHODE, A CARBON ANODE OF RECTANGULAR CROSSSECTION WITH ONE AXIS LONGER THAN THE OUTER OF THE TYPE WHICH IS CARBONIZED IN THE FURNACE SUSPENED ABOVE THE POT AND ADAPTED TO EXTEND DOWN INTO A BATH WITHIN THE POT, AND CONTACT BOLTS ENTERING THE ANODE BY MEANS OF WHICH CURRENT MAY BE TRANSMITTED TO THE ANODE, TWO SETS OF ANODE BUS BARS ADJACENT THE UPPER PART OF THE ANODE RUNNING PARALLEL WITH A MAJOR HORIZONTAL AXIS OF THE ANODE BUT ELECTRICALLY SEPARATED FROM EACH OTHER NEAR THE CENTER OF THEIR COMBINED LENGTH, AND MEANS FOR TRANSMITTING CURRENT TO SUCH BUS BARS AT CORRESPONDING ENDS OF THE BUS BARS RELATIVE TO THE OUTSIDE FACES OF THE ANODE, SO THAT THE FLOW OF CURRENT IN THE RESPECTIVE MEMBERS OF THE SETS WILL BE IN OPPOSITE DIRECTIONS.

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