US2874103A - Method for replacing the pot of an electrolytic cell for the production of aluminum - Google Patents

Description

w. sYz ETAL 2,874,103

ING THE POT OF' AN ELECTROLYTIC RoDUCTIoN oF ALUMI Feb. 17, 1959,

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METHOD FOR REPLAC CELL FOR THE P Filed Feb. 26, 195'7 3 Sheets-Sheet 1 BYPm/L m j MHC .lULr

m mm m Feb. 17, 1959 2,874,103 TROLYTIC 3 Sheets-Sheet 2 W YZ ET METHOD FOR REPLACIN THE PO CELL. FOR THE PRODUCTION Filed Feb. 26, 1957 T OF' AN ELEC OF' ALUMINUM /QAaA BY i L. infr W. SYZ ET Al. 2,874,103

AN ELECTROLYTIC Feb. 17, 1959 METHOD FOR REPLACING THE POT OF' CELL FOR THE PRODUCTION OF ALUMINUM Filed Feb. 26, 1957 5 Sheets-Sheet I5 United AStates Patent METHOD FOR REPLA'CING rTHE POT 0F AN ELECTROLYTIC CELL FOR THE PRODUC- TION OF ALUMINUM Werner Syz, Chippis, and Paul Mller, Kusnacht, Zurich,

Switzerland, assignors to Aluminium-Industrie-Aktien- Gesellschaft, Chippis, Switzerland v Application February 26, 1957, Serial No. 642,434 4 Claims. (Cl. 204-67) In the usual electrolytic cells for the production of aluminum the pot containing the fused salt bath is disposed in the oor. The pot consists chiefly of a metallic casing with a carbon lining, metal bars iitted into the carbon bottom for the current supply (cathode bars) and sometimes a masonry of refractory bricks between the metallic casing and the carbon lining. Such a pot has in normal operation an average duration of life of 3 to 5 years, after which time the carbon lining must be repaired or replaced. Also the cathode bars and other parts of the pot may require repair after this.

The repair of the pot is carried out on the spot. For v this purpose the cell must be electrically shortcircuited and the anode must be lifted out of the melt. Then the fused metal and the electrolyte are pumped out of the pot. After cooling, the remainder of the electrolyte and of the metal as well as the damaged carbon lining are broken up by means of a pneumatic rammer and shoveled out. If necessary also the cathode bars and other parts of the pot Aare removed.

Thereafter the reconstruction of the pot is carried out in the inverse sequence. The new carbon lining is built up from prebaked carbon blocks or by ramming or pouring an unbaked carbon paste, for example according to the method disclosed vin the United States Patent 2,378,142. Then the prebaked ,or self-baking .anodes are put into position and the current is switched on. Normally the current is switched on with its whole intensity at once, that means that thel current is built up to its full intensity within a fewjminutes. But it is also possible and advantageous for the strength of the carbon lining to use a shunt so that the current intensity Ymay be raised from zero to its maximum at will. As

soon as the carbon lining is baked or has attained the desired temperature in the case of prebaked blocks the fused electrolyte can be filled in and the cell put again into operation.

But this mode of working presents some disadvantages: The whole repair of the pot lasts 3 to 4 weeks. During this time the cell isnot in operation. If a series .of cells has to be fully utilized, there must therefore be available a reserve of 5 to 10 percent of the whole number of pots; but thisv is only possible with. a great vcapital investment. The repair is carried outin the pot-room.' that means under complicating circumstances, causing a high expenditure of working hours. As the repair is carried out on the spot, mechanization is hardly Ypossible. These repairs interfere with the normal operation in the pot-room. The baking of the repaired carbon lining is too brusque if theA current is switched on to the full intensity at the very beginning; fissures ariseV and carbon pieces break off or the baking is unequal, thereby decreasing the life of the pot. As a result a carbon lining had to be repaired after a few months, whereas normally it should be working for 3 to 5 years. When using a shunt it is possible t-o control the baking process, but usually one takes no advantage of this possibility because the use of a shunt, for example for 100,000 amfrice peres, is very complicated and wearisome. lMoreover the anodes are worn by scaling off during the baking of the carbon lining, this also causing losses.

To avoid these disadvantages several measures have been proposed,t which arepdescribed for example in the .bookof Fulda and Ginsberg, Tonerde und Aluminium, ll. Teil, Aluminium, Berlin 1953, pages 64 to 66 and 72 to 73. In a pot-house of an aluminum reduction plant the pots were placed on a steel scaffold free over a cellar-room of aY height of over 3 meters and were lowered to one-third into the working iioor. It was then possible to replace the used up pots by sinking them down into the cellar and lifting anew one into its place. In order-to bake the new carbon lining of the repaired pots the latter were put into a baking furnace and heated slowly within 6 to 8 days to a temperature of 900 C., held at this temperature for 2 `days and cooled carefully within 5 to 6 days.` This method has been carried out with cells of a current intensity of V12,500 to 13,000 amperes, butl later on it was abandoned as frequently afterwards in the working cell, pieces of the carbonY bottom as thick asthe bottom were torn off. At1rst the carbon bottom built up on a cathode plate was made in one piece with the carbon side Walls land baked. Later on the carbon bottom was baked separately and the side walls were rammed only afterk baking of the bottom.

Sometimes' the 'side walls were also made from prebaked carbon blocks. outsidethe pot-line it was possible to reduce considerably the time in which the cellwas not working. But therewere other disadvantages: The 'cooling of the `carbon lining after prebaki'ng made itnecessary. to heat Ait again after reinstalling ythe pot. This heating took much time and the temperatureY change was the cause `of the above menf tio'ned breaking ofi of 'carbon pieces from 'the pot lining.

The heating of the whole pot in a coke-fired furnace had the further disadvantage that the pot casing subjected -to heavyk scaling and warping; moreoverv with increasingfsize of' the pots the construction and operaL 'tion' o'f'lthe furnace encountered considerabletechnical difficulties and 'neededhigh' investment costs.r For all these reasons theimeth'od of prebaking-'the pots in cokeiired furnaces, which method had been 'carried out on anv experimental -scaleZO-'yearsago, has 'been abandoned. VSince -then the size lof the :electrolytic cells forV the production ofaluminu'mhas been'increased many times. Today 'the 'carbon bottoms are no longer built upon a vcathode plat'ejf thecurrent is fed to the carbon bottoni by means of cathode bars embedded in it. "'One bakes always the green rammed carbon bottoms on kthe spot by thedisadva'ntag'esof the-known lrhodes of operation and toprovide a 'method 'for replacing: the'used up pots with.

embedded cathode bars with a minimal break-down also with electrolytic 'cells ofr a current intensity of 60,000 amper/es andmore. f 1 i E Accordingjto ourlnvention the whole carbon lining of the new potiis baked outside the cell series," preferably by passage offelect'ric current andA thepot is placed yat a temperatureA of 500 C. or more, preferably yat red heat, in the series. p e i The carbon lining of the pot may be made either 'from a conventional green carbon paste poured or rammed into the casing, or from prebaked carbon blocks stuck together by means of unbaked carbon paste or from unbaked, pressed carbon blocks. In each case it is necessary Ytoheat the pot in order to bake either the Whole carbon lining or at least the joints between the carbon blocks; in the latter case also the temperature ofthe whole lining is raised to the baking temperature.

The baking of the carbon lining is carried out preferably according to the method described in the United States Patent 2,378,142. The lining is heated slowly up to 700-800 C. Preferably one holds it at this temperature till the pot is needed for replacing a damaged pot. That is to say that the heating of the pot is discontinued only just before bringing the pot to the desired place. As a result, the pot cools only during the steps of transporting, installing and filling with the electrolyte. These operations can be carried out within 1 to 2 hours. Because of its heat capacity the pot cools during this time only by 50 to 100 C. Y

The method according to our invention has several advantages. The new pot is already almost at the operating temperature. After installation it must be heated only from about 500 to 700 C. up to 950 C. This can be done rather quickly and makes it possible to apply at once the full current intensity without a shunt.

As the pot does not cool down to room temperature after the baking of the carbon lining and as it is therefore not necessary to heat it to working temperature after installing, it is not subjected to strong temperature changes, so that the main cause of fissures is eliminated. The whole time required for replacing a used pot from the moment of switching oi the current of the cell till the moment of starting the electrolysis in the new pot is cut down to a minimum.

The replacement of the pot may be done by sinking the used up one down into a cellar-room and conveying it. away, for instance on a lorry, or by lifting the pot and removingit above-ground. In the latter case it is however necessary to first remove the anode.

- It is a further object of our invention to provide a pot which may be advantageously used for carrying out the method according to our invention. A preferable embodiment of this pot is shown in the accompanying drawing in which Fig. l is a longitudinal section through the pot along the line 1 1 of Figs. 2 and 3, Fig. 2 is a cross-section through the pot along the line 2-2 of Fig. 3 and Fig. 3 is a plan view of the supporting frame for the pot.

The pot 1 consists of a metal casing 2 and a carbon lining 3 in which the cathode bars 4 are embedded. The pot 1 is placed over the passable cellar-room 10.

' -The casing 2 is welded on a supporting frame 5 of strong I-beams. On both longitudinal sides the supporting frame is provided with two projecting parts 6, each resting on a supporting beam 7, placed on the projectionsY 8 of two consoles 9, the supporting beams 7 being arranged removable on the projections 8. The whole width of the supporting frame must be smaller than the distance between the opposite consoles beneath their projections 8, so that the pot after sinking down can be conveyed away horizontally together with the supporting frame.

In a preferable embodiment the supporting frame consists of two cross-beams 12 with projecting ends 6, connected by two longitudinal beams 11, and other crossbeams13 supporting the pot 1 between the two longitudinal beams 11.

The projections 8 of the console are provided with a metal slip plane 14. On each supporting beam 7 is mounted anfisolating plate 15, isolating the supporting frame electrically against the earth. V16 designates the working floor 'of the pot-room. Over the pot 1 is suspended the anode 17.

For replacing a pot, a lorry is placed beneath this pot, this lorry consisting chiey and preferably of a frame mounted on mobile axles and provided in its four corners with spindles. These spindles are motor driven and every two on one side carry a girder beam. The distance between both girder beams corresponds preferably to the,

distance between both longitudinal beams 11 of the supporting frame.

The lorry is placed beneath the pot with the girder beams just below the longitudinal beams 11. By operating the spindles the pot is lifted, so that the supporting beams 7 are released. The supporting beams 7 are removed and the pot can be sunk down, the projecting parts 6 of the frame moving down between the two consoles 9.

It is also possible that each projecting part 6 of the frame is supported only by one console 9. In this case the pot is lifted slightly laterally displaced and sunk down, the projecting parts 6 moving beside the consoles.

The new pot having a temperature of red heat, is brought on a second similar lorry, lifted and after placing again the supporting beams 7l on the projection 8 of the consoles 9 set down on these supporting beams. Thereafter the bus bars for the electrolysis current are switched in again.

By the possibility of a quick replacement of a used pot also the anodes are preserved from great burning losses and from too great cooling, the formation of fissures being therefore avoided.

What we claim is:

1. The method of replacing the worn pot of an electrolytic cell in a cell line in the production of aluminum from a bath of molten fluorides, which method comprises baking outside the cell line a fresh carbon lining on a replacing pot while the latter pot is outside the cell line, maintaining the temperature of the fresh baked carbon lining in the replacing pot at a temperature of at least 500 C. until said replacing pot is installed in the cell line, replacing the worn pot in the cell line by the replacing pot while the baked carbon lining in the latter pot is at said temperature, and placing the latter pot in operation in said cell line while its baked lining is at said temperature, the fresh carbon lining in said replacing pot being maintained at said temperature continuously throughout the operations from the time said fresh carbon lining is baked in said replacing pot to the time said replacing pot is placed into operation in said cell line.

2. The method according to claim l, in which the carbon lining is at red heat when the replacing pot is installed in the place of the used up one.

3. The method according to claim 1, comprising replacing the used up pot by lowering it down into a cellarroom and using pots mounted each on a metallic frame provided on both longitudinal sides with two projectingparts resting on horizontal projections of consoles when the pot is in the cell series, the width of the supporting frame being smaller than the distance between two opposite consoles beneath their projections, so that the pot after lowering together with the Vsupporting frame can be conveyed away horizontally. l

4. The method according to claim 1, comprising replacing the used up pot .by lowering it into a cellarroom and using pots mounted each on a metallic supporting frame provided on both longitudinalsides with two projecting parts resting on supporting beams placed on horizontal projections of two consoles when the pot is in the cell series, so that the pot may be lowered between the consoles when the supporting beams have been removed. v

No references cited.

Claims (1)

1. THE METHOD OF REPLACING THE WORN POT OF AN ELECTROLYTIC CELL IN A CELL LINE IN THE PRODUCTION OF ALUMINUM FROM A BATH OF MOLTEN FLUORIDES, WHICH METHOD COMPRISES BAKING OUTSIDE THE CELL LINE FRESH CARBON LINING ON A REPLACING POT WHILE THE LATTER POT IS OUTSIDE THE CELL LINE, MAINTAINING THE TEMPERATURE OF THE FRESH BAKED CARBON LINING IN THE REPLACING POT AT A TEMPERATURE OF AT LEAST 500*C. UNTIL SAID REPLACING POT IS INSTALLED IN THE CELL LINE, REPLACING THE WORN POT IN THE CELL LINE BY THE REPLACING POT WHILE THE BAKED CARBON LINING IN THE LATTER POT IS AT SAID TEMPERATURE, AND PLACING THE LATTER POT IN OPERATION IN SAID CELL LINE WHILE ITS BAKED LINING IS AT SAID TEMPERATURE, THE FRESH CARBON LINING IN SAID REPLACING POT BEING MAINTAINED AT SAID TEMPERATURE CONTINUOUSLY THROUGHOUT THE OPERATION FROM THE TIME SAID FRESH CARBON LINING IS BAKED IN SAID REPLACING POT TO THE TIME SAID RELPACING POT IS PLACED INTO OPERATION IN SAID CELL LINE.

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