US2739113A - Electrolytic cell with self-baking anode - Google Patents

Description

March 20, 1956 B. T. HoRsFlELD ETAL 2,739,113

ELECTROLYTIC CELL WITH SELF-BAKING ANODE Filed April l2. 1952 4 Sheets-Sheet l ML T5 INVENTORS BASIL 7.77096 F/Ez. 0

March 20, 1956 B. T. HoRsFlELD ET A1. 2,739,113

ELECTROLYTIC CELL WITH SELF-BAKING ANODE Filed April 12, 1952 4 Sheets-Sheet 2 March 20, 1956 B. T. HoRsFlELD ET AL 2,739,113

ELECTROLYTIC CELL WITH SELF-BAKING ANODE Filed April l2, 1952 4 Sheets-Sheet 5 March 20, 1956 B. T. HoRsFlELD ETAL 2,739,113

Y ELECTROLYTIC CELL WITH SELF-BAKING ANODE Filed April 12, 1952 4 Sheets-Sheet 4 INVENTORS BASI b 7.' HaHa/w51. o

United States Patent O ELECTRQLYTIC CELL 1ITH SELF-BAKING ANODE Basil T. Horsfeld and Dwight l. Keller, Florence, Ala.,

assiguors to Reynolds Metals Company, Richmond,

This invention relates to an improved apparatus which is adapted particularly Afor use in the production of metallic aluminum.

In commercial practice, aluminum is manufactured by the electrolysis of a bath which comprises a solution of alumina in fused cryolite, ,the anode and the cathode both being composed of carbon. Since cryolite is a salt which has a very high melting point, the molten bath is necessarily maintained at a very high temperature, usually of the order of 1000f C. Because of lthe very high temperature at which the bath 4is maintained, the loss in sensible heat from the bath is necessarily -very large.

This heat is supplied to the cell in the form of electrical energy, and this means that the ,electrical energy efficiency of the cell is low, the amount of electrical energy consumed per amount of aluminum produced being high. The cost of the electrical energy used in producing metallic aluminum is a very important item, and the art has therefore strivcd continuously to improve the energy efficiency of the cell. Thus, the art has turned to the expedient of increasing the size of the cell, the reason being that cells of larger size have a proportionately smaller surface area from which heat can be dissipated.

Increasing the size of the `cell has meant that the size of the anode must also be increased, since the anode current density must be held within permissible limits. In cells in which larger anodcs are used, the anode is frequently of the Sderberg or self-baking type. This particular anode is formed by feeding a plastic, carbonaceous mixture to a bottomless mold which is positioned at some distance vertically above the bath, the mixture being gradually fed downwardly as the lower part of the anode is consumed and the mixture in its downward passage gradually becoming baked into a hard condition as it approaches the high temperature bath. As is apparent, the use of self-baking electrodes is advantageous in that they are continuous and also in that at the same time they eliminate the necessity for handling pre-baked electrodes of large size, which are cumbersome.

The art has also paid particular attention to the horizontal, cross-sectional configuration of self-baking anodes, and as a result has found that such anodes, at least in the larger sizes, should have a cross-section which is substantially rectangular, rather than a round or square one, for example. That is, the anode should be greater in length along its side than along its end.

There are several sound technical reasons for this. In the rst place, oxygen is formed at the interface between the anode and the bath. This oxygen, as well as the gases which are produced by its reaction with the carbon anode at the high temperature existing in the bath, has the elect of blanketing the anode, thereby reducing the area of contact between the anode and the bath and increasing the voltage drop across the cell. Therefore, it is advisable to provide the oxygen and the gases produced therefrom with the shortest possible route for escaping from the underside of the anode. In the second place, the oxygen formed at the anode reacts with the anode,

2,739,113 Patented Mar. 20, 1956 as has been just mentioned, resulting in consumption of the anode. The cost of anodes is also an important item in laluminum production, the ratio of the weight of anode carbon consumed to the weight of aluminum produced generally being about 0.6, so that here again it is advisable to provide the shortest possible path for the oxygen to escape from the underside of the anode, thereby reducing the amount of time during which the oxygen and the anode can react and hence reducing the anode consumption.

Moreover, in operating a cell, the bottom of the anode should be in close proximity to the layer of molten aluminum lying on the bottom of the cell, in order to provide a low voltage drop across the cell. However, the molten aluminum is only slightly more dense than is the cryolite bath, and excessive agitation in the bath can cause globules of molten aluminum to rise and contact the anode. This agitation can be caused by the oxygen formed at the anode and also by the gases formed by the reaction of the oxygen with the anode, so that for this reason also it is advisable to provide the shortest possible path for gases to escape from beneath the anode, and thereby avoid short eircuiting of the cell caused by globules of molten aluminum separated from the molten aluminum layer by excessive agitation, and also avoid oxidation of molten aluminum metal. In addition, the electric current is usually passed into the anode through steel pins inserted in the anode and out of the cathode supporting the bath and molten aluminum through Steel bars. These pins and bars should be as short as possible, in order to minimize the voltage drop across them.

Having concluded that the use of self-baking anodes of substantially rectangular cross-section is advantageous, the art has found it necessary to provide means for supporting the anode, which weighs many tons when the anode is large, and also for lowering the anode gradually into the bath as the anode is consumed. This has been done by encasing the anode on its four vertical sides with several courses of steel channels, each course being removed when it approaches sufficiently close to the hot bath and additional channels being used to form a new top course as required.

The webs of the side channels on the long sides of the anode are provided with a series of holes, through which are inserted steel anode pins which are driven into the anode while it is still in the plastic or unbalted condition. These pins, when a given course of channels around 'the periphery of the anode is bottommost, serve to support the anode and at the same time also serve as conductors for the electric current passing to the anode, such pins being attached to the anode bus bars by suitable iiexible connections. In turn, the lowermost course of channels is supported at its corners by suitable hooks which are connected to a steel framework forming a part ot the superstructure which is positioned at some distance above the bath. Suitable means, generally screw jacks, form a part of this framework and enable the framework to be raised and lowered, thereby also permitting raising and lowering of the lowermost course of channels.

For an illustration of a cell in which channels and anode pins are used in connection with a self-baking electrode, reference is made to the drawings which con stitute a part of the disclosure of United States Patent No. 2,169,563 to Legeron. In the specific apparatus there illustrated, the means for supplying current to the anode pins also serve to support the pins, which in turn support both the anode and the channels. It is apparent, however, that this specific apparatus could easily be modiiied in such manner that the lowermost course of channels is supported at its four corners by the superstructure, the channels serving to support the pins and the pins serving to support the anode. In such a moditication, the electric current can be supplied to the lowervide the greaterstructural strength lneeded to support the increased weightof the anode. Thus, the plastic car'- bonaceous mixture, before it is baked, must be supported laterally. At the same time, when the suspending means which depend from the-superstructure of -the cell are connected with the channels, rather than with the anodepins, the bottom course of channels must support the weightof the anode as well as the weight of the upper courses of channels.

ln building cells of larger and larger dimensions,l there is, however, a practical Vlimit tothe depth, and hence strength, of the channels which can be used. Thus, the greater the depth of the channels, the greater is the average distance between the anode pins, which are inserted through the holes in the bottom course of side channels and through which the electric current is passing to the anode, and the interface between the anode and the bath, thus increasing the average voltage drop across the cell as the cell is operated over a period of time. Also, as the channels become longer and of greater depth, their weight becomes correspondingly greater, and hence they become more and-more difhcult to handle when being removed from the lowest course and placed as an uppermost course.

In accordance with the present invention, an apparatus has been provided which permits the use of selfbaking anodes having a length greater than has been heretofore used, thus making possible the construction of a cell of lJreater size, with accompanying increased energy eiciency. At the same time, although the channels support the anode adequately and properly, they are neither of excessive length nor of excessive depth, so that they are conveniently handled and at the same time do not cause excessive voltage drop between the operatively connected anode pins and the interface between the anode andthe bath.

These advantages are obtained by providing two or more individual pieces of channel on each long side of the anode for each channel course and at the same time providing suitable means for supporting the channels on the long sides of the anode both vertically and laterally.

For a more complete understanding of the apparatus of the present invention, reference is made to the accompanying drawings which illustrate one speciiic embodiment of this invention and in which:

Fig. l is a general diagrammatic view of one of the long sides of the apparatus, showing the anode, courses of side channels, means for supporting the side channels vertically at the corners of the anode, means for supporting the side channels vertically at the middle ot a long side of the anode, means for supporting the side channels laterally at the middle of the long sides of the anode, anode pins, channel clips, the bath, and so forth;

Fig. 2 is a section taken along line 2 2 of Fig. 1;

Fig. 3 is a diagrammatic view showing in further detail the construction at the middle of the long sides of the anode and showing specifically the side channels, the means whereby the side channels are connected at the middle of the long side of the anode, the means whereby the connecting means are supported vertically, and the means whereby the channels are temporarily supported vertically while the channels are being changed;

Fig. 4 is a section taken along line 4-4 of Fig. 3;

Fig. 5 is a view of the construction of the ends of a pair of horizontally adjacent side channels at the middle of the side of the anode;

Fig. 6 shows in detail the means for supporting vertically a horizontal pair of side channels at the middlevof the anode; n n

Fig. 7 shows the relationship between a side channel and an` end channel at a corner of the anode Yand also shows the means for supporting vertically the end of a -lowermost side channel;

Fig. 8 shows in detail the-end of a side channel and the end of an end channel;

Fig. 9 gives a View of the locking pin used to connect one side channel and one end channel at a corner of ythe anode;

Fig. 10 shows a view of the means used for supporting the side channels at the corners of the anode;

Figs. 11 and l2 are views of a channel clip in position on a pair of vertically positioned side channels;

Fig. 13 is a section taken along line 13-13 of Fig. l; and

Fig. 14 shows an auxiliary hook in position at a corner of an anode.

Referring now to the drawings, particularly Fig. 1 and Fig. 2, the numeral 1 represents the self-baking anode which is formed by periodically placing a quantity of plastic, carbonaceous mixture in the bottomless mold Z supported on the superstructure (not shown) of the cell in the conventional manner. This anode is gradually baked into a hard condition as it passes downwardly towards the hot bath 3 composed of alumina dissolved in cryolite. The numeral 4 represents the layer of molten aluminum which lies on top of the carbon cathode 5. Also, the ynumerals 6 represent the side channels, which are prevented from moving laterally by the bent angle irons 7. These angle irons are held in rigid position by supporting framework (not shown) and a clearance of about 1z-inch is provided in order that the channels may slip past the angles freely as the channels are lowered with the consumption of the anode.

Still referring particularly to Fig. 1 and Fig. 2, the numerals S represent holes through which conventional anode pins 9 are driven while the anode is still in the plastic or green state, the pins serving to support the anode when the channel through which they are inserted is on the bottom course. Serving to connect the adjacent ends of the side channels at the middle of the anode there is provided a channel bar 1t), shaped as shown in Fig. 6.

The center jack hanger strap 11, shaped as shown in Fig. 3 and Fig. 4, is provided to support the channel bar 10, which in turn supports the side channels at the middle of the anode when those channels are a part of the bottom course. This strap 11 is supported by suitable means (not shown) attached to the superstructure of the cell. This superstructure can be conventional in design and usually has jack screws which serve to raise and lower the center jack hanger strap as desired during the operation of the cell.

Figs. 7 to 10, inclusive, set forth details of the construction of the cell at a corner of the anode. Thus, in Fig. 8 there is shown a view of the end of a side channel 6 located at a corner of the anode. The end of the channel is formed as shown, and to the end of the channel are welded plates 12 and 13, the channel and the plate 12 being provided with keyhole slots 14.

The end channel 15 (Fig. 8) is placed against the vertical end of the anode in order to support the anode laterally when still in the plastic state. The channel 15 does not support the anode vertically, however, and hence does not have any holes therein corresponding to the holes S of the side channels 6. End channel 1S has, however, a plate 16 welded thereon, that plate also having keyhole slots 1.4. Channels 6 and 15 are connected by means of the locking pins 1'7 (Fig. 9), each pin being simply inserted through corresponding keyholes and given a half-turn.

Fig. l0 sets forth details of the end hook 1S which is used to support the ends of the channels 6 located at the corner of the anode. This hook comprises a hooked portion which is hooked under the projection 19 of the side channel 6 as shown in Figs. 1, 7 and 14, and also comprises parts Zlland 21 which are supported by the cell superstructure in a manner similar to that in which the center jack hanger strap ,11 is supported. Each pair of end hooks is connected by a spacer channel 22 (Fig. of suitable length welded to the hooks, the purpose of the spacer channel being to give the structure greater strength.

For the same reason, channel clips 23 (Figs. l, 1l and 12) are provided in the half points of the side channels, that is, the one-quarter and three-quarter points along the length of the anode. These clips are shaped as shown and have holes through which a pin 24 can be inserted, the pin also passing through corresponding holes in the flanges of the side channels.

As those skilled in this art will understand, the present invention is an improvement in that type of cell in which a substantially rectangular, self-baking anode is used, in which the anode in passing downwardly towards the bath is surrounded on its four vertical sides by several courses of channels, in which the channels adjacent the long vertical faces of the anodes support the anode by means of pins passing through holes in the webs or those channels and driven into the anode, and in which the channels are supported vertically by suitable attachments to a conventional cell superstructure which is adapted to raise and lower the channels as desired. Hence, in the present cell, the channels of a given course are similarly connected at the corners of the anode and also are similarly connected at the middles of the long vertical sides of the anode.

The particular novelty of the present cell resides in the construction at the middles of the long vertical sides of the anode, where suitable means are provided for supporting the channels laterally and also for supporting the lowest course of channels vertically. As is apparent, this construction is also adapted for use in a cell wherein more than two pieces of side channel are used in a given course on a given side of the anode. For example, where three pieces of side channel are so used, in a given course on a given side of the anode, the side channels specifically illustrated can be used. However, instead of being connected to each other, they will be connected to third or center channels having at each end the construction shown in Fig. 5. In such case, two angle irons 7 will be provided on each side of the anode.

Although no dimensions have been given in the preceding description, such description is based upon a cell which has been successfully operated, the cell having an anode which has a horizontal cross-section 35 feet long and 5 feet wide, the channels surrounding the anode being 10 inches in depth. The current passing through this cell is about 125,000 amperes.

The operation of this cell has presented no unusual ditiiculties and will be apparent to those skilled in this particular iield of art. As the anode is consumed and the lowest course of channels approaches as close to the bath as is reasonable, auxiliary hooks (the use of which is conventional in operating cells with removable channels) supported by the superstructure are put in place on the next to the lowest course of channels to support the channels. Thus, as is shown in Fig. 3 and Fig. 4, auxiliary hooks 25 are used to provide support for the channels at the middles of the long sides of the anode and, as is shown in Fig. 14, auxiliary hooks 26 are used to support the channels at the corners of the anode. After the auxiliary hooks have been adjusted upwardly by means of auxiliary jack screws so that they support the anode, thus relieving the strain on the channel bars 10 on the lowest course and on the end hooks 18, the jack assembly which normally supports the anode load is lowered slightly and the lowest course of channels and its pins are removed. The jack assembly which normally supports the load is then raised until it supports the lowest course of channels, following which the temporary suspension means are removed. In the meantime, the flexible electrical connections from the anode bus bars to the anode pins have been removed from the lowest to the next to the lowest course of anode pins. This cycle is continuous as the anode is consumed, additional courses of channels being put into place as uppermost courses as needed.

We claim:

1. In an electrolytic cell suitable for use in the production of aluminum by the electrolysis of a bath of molten cryolite having alumina dissolved therein, which cel is provided with a downwardly feeding, self-baking anode which in horizontal cross-section is substantially rectangular and of substantially greater length than breadth and which during its downward passage is encased on its vertical faces by several courses of channels which are supported vertically from above at the four corners of the anode and which in turn support the anode by means of pins inserted into the anode through holes in the webs of the channels, such pins also serving as means whereby electrical current is supplied to the anode, the improvement which comprises the combination of at least two individual sections of channel in each course adjacent each of the long vertical faces of the anode, first means slidably received horizontally at its opposite ends by the adjacent ends of each adjacent pair of individual sections of channel in the lowest course in the long vertical faces of the anode whereby said sections are maintained in horizontal alignment, second means suspended from above said cell connected to said lirst means providing vertical support therefor, and an elongated member rigidly supported in vertical position along each line of adjacent ends of said adjacent individual sections of channel, said elongated member being closely spaced to said channels to permit vertical sliding Contact therewith and to prevent lateral movement of said adjacent ends in a direction away from said anode and perpendicular to the adjacent long vertical face thereof.

2. A cell as in claim 1, in which said first means is a bar and in which each of said sections of channel comprises at its end which is adjacent a like section in a given course a framework forming a hole having its axis parallel to the length of the section, one of said bars being inserted through each horizontally adjacent pair of holes.

3. A cell as in claim 1, in which each course adjacent a given long vertical face of the anode comprises only two of said sections.

References Cited in the tile of this patent UNITED STATES PATENTS 1,253,387 Kane Jan. 15, 1918 2,134,008 Sharp Oct. 25, 1938 2,169,563 Legeron Aug. 15, 1939 FOREIGN PATENTS 387,585 Great Britain Feb. 9, 1933

Claims (1)

1. IN AN ELECTROLYTIC CELL SUITABLE FOR USE IN THE PRODUCTION OF ALUMINUM BY THE ELECTROLYSIS OF A BATH OF MOLTEN CRYOLITE HAVING ALUMINA DISSOLVED THEREIN, WHICH CELL IS PROVIDED WITH A DOWNWARDLY FEEDING, SELF-BAKING ANODE WHICH IN HORIZONTAL CROSS-SECTION IS SUBSTANTIALLY RECTANGULAR AND OF SUBSTANTIALLY GREATER LENGTH THAN BREADTH AND WHICH DURING ITS DOWNWARD PASSAGE IS ENCASED ON ITS VERTICAL FACES BY SEVERAL COURSES OF CHANNELS WHICH ARE SUPPORTED VERTICALLY FROM ABOVE AT THE FOUR CORNERS OF THE ANODE AND WHICH IN TURN SUPPORT THE ANODE BY MEANS OF PINS INSERTED INTO THE ANODE THROUGH HOLES IN THE WEBS OF THE CHANNELS, SUCH PINS ALSO SERVING AS MEANS WHEREBY ELECTRICAL CURRENT IS SUPPLIED TO THE ANODE, THE IMPROVEMENT WHICH COMPRISES THE COMBINATION OF AT LEAST TWO INDIVIDUAL SECTIONS OF CHANNEL IN EACH COURSE ADJACENT EACH OF THE LONG VERTICAL FACES OF THE ANODE, FIRST MEANS SLIDABLY RECEIVED HORIZONTALLY AT ITS OPPOSITE ENDS BY THE ADJACENT ENDS OF EACH ADJACENT PAIR OF INDIVIDUAL

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