US2959527A

US2959527A - Self-restoring anode in multi-cell furnaces particularly for the electrolytic production of aluminum

Info

Publication number: US2959527A
Application number: US706077A
Authority: US
Inventors: Giuseppe De Varda
Original assignee: Montedison SpA
Current assignee: Montedison SpA
Priority date: 1957-01-05
Filing date: 1957-12-30
Publication date: 1960-11-08
Anticipated expiration: 1977-11-08
Also published as: BE563730A; CH378543A; FR1195391A; NL223669A; DE1148755B; NL109837C; ES239416A1; IS1014A7; AT208090B; GB852899A

Description

Nov. 8, 1960 G. DE VARDA 2,959,527 SELF-RESTORING ANODE IN MULTI-CELL. FURNACES PARTICULARLY FOR THE ELECTROLYTIC PRODUCTION OF ALUMINUM Filed Dec. 50, 1957 3 Sheets-Sheet 1 1 I i v if? 22 27 I 2/ f A 1;: M :11 20 a E- ii :5: 2.5: "21-512? 6 a ,7 n "J 2' 1 I I B 5 r l 15 6 14 G. DE VARDA Nov. 8, 1960 2,959,527 MULTI-CELL. FURNACES PARTICULARLY YTIC PRODUCTION OF ALUMINUM SELF-RESTORING ANODE IN FOR THE ELECTROL Filed D80. 30, 1957 s Sheets-Sheet 2 Filed Dec. 30, 1957 Nov. 8, 1960 G. DE VARDA SELF-RESTORING ANODE IN MULTI-CELL FURNACES PARTICULARLY FOR THE ELECTROLYTIC PRODUCTION OF ALUMINUM 5 Sheets-Sheet 3 SELF-RESTORING ANODE IN MULTI-CELL FUR- NACES PARTICULARLY FOR THE ELECTRO- LYTIC PRODUCTION OF ALUMINUM Giuseppe de Varda, Milan, Italy, assignor to Montecatini Societa Generale per lindustria Mlnerana e Chimica, a corporation of Italy Filed Dec. 30, 1957, Ser. No. 706,077

Claims priority, application Italy Jan. 5, 1957 24 Claims. (Cl. 204-67) This invention relates to an electrolytic apparatus and a method of operation thereof. It particularly relates to the continuous restoration of the electrolytically consumed surface of an electrode thereof, particularly the consumable carbonaceous anode face of an electrolytic furnace employed to produce aluminum from alumina, in a fused salt bath.

This application presents an improvement over the processes and apparatus described in the copending applications of G. de Varda, Serial No. 551,679, filed December 7, 1955; Serial No. 587,985, filed May 29, 1956; Serial No. 480,509, filed January 7, 1955, and Serial No. 600,055, filed July 25, 1956. Consistent details of these applications are incorporated herein by reference.

An object of the present invention is to automatically maintain constant the distance between opposed anode and cathode surfaces, one of which is being electrochemically consumed in the electrolysis.

Another object of the invention is to continuously feed restoring electrode material to a face of an electrode as it is being consumed.

A still further object is to operate electrolytic furnaces, having inclined or vertical electrode bath-facing surfaces, at least one of which is consumed in the process, in such manner that the distance between the surfaces is kept constant, by automatically and continuously feeding or replenishing the restoring electrode material, the latter being guided and being under an applied force, or under gravity, so that the restoring electrode material continuously re-occupies, or enters, the space which ordinarily would be left free by the consumption of the electrode.

Copending G. de Varda US. application Serial No. 551,679 describes a special type of three-layer anode in multi-cell furnaces with anodically consumable but stationary bipolar electrodes, as well as a method of restoring said anode periodically. This type of three-layer anode, having two solid layers and an intermediate liquid layer, finds special employment in the electrolysis of aluminum oxide dissolved in fused salts. The anode is preferably composed of a permanent and fixed layer of carbon, preferably graphite, which in the bipolar electrodes, or intermediate electrodes, forms one body with the cathodic carbon." The terms carbon or electrodic carbon or anodic carbon are intended to designate herein any substance based on or comprising amorphous carbon; as well as graphite and carbonaceous masses or agglomerates that are capable of acting as an anodic electrode, or as a cathodic electrode, or as a bipolar electrode. Leaning against said permanent and fixed anodic layer there is provided from the bath side a second solid layer, which is consumable, and restorable, and is constituted by pre-baked anodic carbon held in situ by the hydrostatic upwardly directed buoyancy exerted thereon by the fused bath. Hereinafter the term ice active anodic layer will be used to designate that portion of said second layer, which being in contact with the electrolysis bath, is subjected to consumption by electrolysis. The term anodic restoring assembly will be used to designate said second layer, or restoring carbon, when referring not only to the active anodic layer as defined herein, but also to a portion emerging from the bath, or protected from contact therewith, as will appear hereinafter.

Between said two carbon layers, which may even touch each other at some points, there is interposed a liquid layer in such a way as to fill completely the inter stice formed between said two layers of solid carbon.

The intermediate thin liquid layer is formed by one :or more of the fused'substances already contained in the electrolysis cell, that is, the fused bath, fused aluminum, etc. The resistance opposed by said layer to the passage of DC). electric current is low; that of the two solid layers, carbons, is quite negligible. The consumable and restorable carbon layer described in said application is constituted by one single plate of uniform thickness or by a plurality of individual pieces forming said plate or layer and which too have uniform and equal thickness. This restoring layer is periodically introduced and accommodated in the cell. The periodical restoration is car'- ried out preferably when the consumable solid layer has been nearly completely burnt by effect of the electrolysis. Alumina decomposed electrolytically produces metal and burns the anodic carbon:

The aluminum produced is discharged on the cathode, and fiows downwards. The oxygen burns the anodic carbon and the gas CO thus formed tends to rise in the heat balance of the bath. Operation at a constant inter- V electrodic distance is obtained in practice, although the electrodes require no mechanical device for adjusting said distance. There is thus an appreciable saving inunit consumption of carbon, bath liquor, and in the labor required.

In a preferred form, the invention comprises the form ing of a layer of consumable, restoring anodic carbon having a thickness decreasing downwardly, and feeding said layer downwardly. This has a special advantage over a vertical section having the shape of a rectangle or parallelogram. The preferred form has a triangular sec tion, with the apex extending downwardly.

Preferred embodiments of the invention are illustrated in the drawing, in which:

Fig. 1 represents a vertical section taken along the line CC of Figs. 2 and 3, of contiguous cells of a multicell furnace having stationary bipolar electrodes of the type described in my copending applications, but modified according to the present invention; V a

Fig. 2 presents a top view, and an upper horizontal section of two cells taken along the line AA of Fig. 1;

Fig. 3 presents two further horizontal sections, one at' a medium level and the other at a lower level, of two cells of Fig. 1, taken along the line BB of the latter;

Fig. 4 presents a vertical section, analogous to that of Fig. 1, of contiguous cells of a multi-cell furnace with bipolar electrodes. Fig. 4 illustrates a modified form of the invention.

Referring to Fig. 1, the individual elemental cells of a multi-cell furnace for the electrolysis of aluminum oxide dissolved in fused fluorinated salts, comprise two inclined bipolar electrodes 9 positioned close to each other, and provided with self-restoring external

anodic layers

1, 2, 3, 4, 5, 6 or 27. These electrodes, with bipolar function, comprise graphite for their permanent portions and pieces of pre-baked electrodic carbon for their restorable portions 1, 2, 3, 4, 5 and 6 or, as to the latter, by cokified Soderberg paste for layer 27. The current conductors are not shown. They are to be connected to terminal monopolar electrodes, not shown.

The bipolar electrodes have no metallic conductors, and no mechanical device outside the furnace is needed for varying the interelectrodic distance. The restoring anodic assembly, namely the

body

1, 2, 3, 4, 5, 6 or 27, having a density less than 1.6, is thrust by the bath (which has a density higher than 2) against the permanent portion of the electrode 9.

The interstice between said anodic assembly and the corresponding permanent electrode becomes filled with one or more of the liquids present in the cell (fused bath, fused metal, etc.) and thus forms the. thin intermediate layer 29 between the anode. layer of restoring carbon and,

the anode layer of permanent carbon. Between each pair of adjacent electrodes 9 there is the electrolysis gap 14 for the fused bath, which gap is in communication at the bottom with the lower chamber 12 for the collecting of the fused aluminum 11. Tap holes are provided for the chambers 12.

The lower chamber, and the inter-electrodic gap are coated, except for the electrodically active walls formed by the bipolar carbons, with

inert material

13 and 15 resistant to the. hot bath and metal and impermeable, as well as electrically insulating, for instance with dense electrofused magnesite, sintered at very high temperature and treated by the process according to applicants Italian patent application No. 41,944 (19,153), filed Dec. 29, 1956; or with any other suitable, commercially avail able material (such as silicon nitride bonded silicon carbide refractories).

Theelectrodic carbons are surmounted over their whole width by massive strips or blocks 19 of such inert, nonattackable, and impermeable material. Thev blocks are provided, with communication channels 17 between one cell and another, through which the bath can be circulated as indicated by arrows 18. Said massive blocks are surmounted in turn by a heat-insulating layer 24 coated superficially at the points accessible for the bath, by inert material 28, which material may comprise electrofused magnesite, densified and sintered at a very high temperature.

The electrodic gap is in communication, at the top, with a gas collecting chamber fiared upwardly, and which too is filled with bath, in its lower portion. The walls of this chamber are formed, as already stated, by

inert material

19 and 28. Said chamber is in turn in communication at the top with an upper chamber which serves to discharge the gases through outlet 21.

The flared chamber 20 is conveniently separated from the upper chamber by removable slabs (not shown in the drawings) of a porous material which allows for discharge of the electrolysis gases, for which however there may be provided also passageways proper in said slabs. Similar slabs are shown in my copending application Serial No. 480,509..

The slabs forming the ceiling of the cells may be of magnesia and/or asbestos material, that is, of very good heat-insulating material resisting 1000" C., possibly or preferably porous, fibrous, and light. They should be constituted, and proportioned, in such way as to keep 4 the gas cushion above the bath at a temperature which will not permit surface freezing of the bath.

The anodic restoration assembly comprises carbonaceous material attackable electrolytically, and known per so, such as pre-baked anodic carbon, cokified Soderberg paste, etc.

The upper chamber is covered by a heat-insulating layer 22 in which there are provided for and in correspondence with each elemental cell, three apertures, each closed by an easily removable cover 23, of very good heatinsulating material, such as porosite, alumina, etc. On opening said covers a conduit passage 26 is uncovered. The passage is in a refractory, inclined chimney 25 formed of inert material, at least in its lower portion contacting with the bath.

As indicated above, Fig. 2 presents the cells of Fig. l as seen from the top respectively, and in a section taken horizontally at level of the upper chamber.

Fig. 3 presents two horizontal sections of two contiguous cells of Fig. 1, in a section taken at the level of the communicating channel for bath circulation 17 and a section at the level of member 4 of the anodic restoring assembly.

The single-lined arrows 16 indicate the path of the electric current which passes from the bipolar electrode through the thin liquid contact layer 29 into the assembly of anodic restoration. It then leaves the consumable anodic face thereof to enter the corresponding interelectrode interspace or gap 14 filled with fluorinated fused bath, to enter the adjacent permanent graphite bipolar electrode through the cathodic face thereof facing upwards and so on.

The double-lined arrows indicate diagrammatically the main circulation flow direction of the electrolysis bath, which here is in a sense contrary to that of the electric current.

In the embodiment of Fig. 4, the numerals employed in Fig. 1 have been used to designate corresponding parts of the two furnaces. Here the anodic restoration assemblies (always with a vertical triangular section having its apex directed downwards) attain initial thicknesses which are larger because the inclination of the liquid contact layer between the permanent anode and the restoration assembly is reverse. The small channels 30 shown in the permanent bipolar electrode deviate or direct a small percentage of the aluminum produced on the cathode, towards the intermediate liquid layer. This is useful if one wants to further facilitate the regular descent of the anodic restoring assembly, and to reduce the ohmic drops, due to the passage of electric current through the intermediate anodic liquid layer, to negligible values. This variation is suitable for feeding, from the top, crude, fused or solid Soderberg paste. The invention is carried out in the cells shown in Figs. 1, 2, 3 and 4 by operating in the following manner, by way of example:

The furnace, containing metal and fused bath, is brought to operating temperature, between 900 and 1000 C., and is kept at that temperature, for instance by means of alternate current. Then the anodic restoration assembly for each cell is placed in position by introducing the anodic assemblies 1+2+3+4+5+6, in one single piece or individual pieces, into the cells successively, from the top, through the respective chimneys. Since the anodic carbon has a density of about 1.5 and the bath has a density of about 2, the hydrostatic buoyancy of the bath will cause the submerged individual pieces, or the whole assembly, to be thrust upwards, so that the Whole assembly will bear against the face of the permannet, or stationary, downwardly facing bipolar electrode face (Fig. 1). By pressing downwardly from the top it is easy to push said assembly downwardly until the tip 7 touches the threshold formed or provided. by the inert layer which serves as a base for the bipolar electrode. After repeating said operation for all the individual cells and respective chimneys of the multi-cell furnace, thefurnace is ready for the starting of the electrolysis.

Direct current is substituted for alternate current so that the active surfaces of the bipolar electrodes facing upwards may act as a cathode and those facing downwards may act as an anode, and the bath circulating device is set in operation, and so are the continuous alumina feeders (neither of which is shown in the drawings).

As the electrolysis proceeds, the aluminum produced at the cathode flows down and is collected in the lower chamber, from which it may be discharged through the individual channels 10.

The distribution of current in the electrodes, as well as the electrolytic attack on the active anodic surface, take place, if the operations are well-conducted, with the same intensity at all points of the active anodic surface of the restoring assembly. Consequently the restoring assembly present initially, comprising triangular section or assembly 3+4+5+6, is consumed with regularity at its superficial layer, from the bath side. The consumed tip 7 thus would be above position 7'. However, the thrust exerted from top makes the whole assembly glide down slowly in such a way that the tip 7 continues to occupy the position 7 consttiuted by the stop provided by the threshold of inert material 8. Since the pressure exerted from top downwards, constituted by the active component, parallel to the chimney walls, of the weight of the portion of the anodic assembly that is outside the bath, is sufficient to overcome the ascending thrust, due to buoyancy, of the anodic assembly portion submerged in the bath, a self-adjusting anodic restoring assembly is obtained which automatically maintains constant the interelectrodic distance between the anodic active surfaces and the cathodic surfaces of any interelectrocle gap.

If the anodic restoring assembly is formed of small carbon blocks of prebaked anodic carbon, as represented in the first elementary cell at the left in Fig. 1, it will suffice to replace the consumed anodic carbon by periodically opening the cover and introducing into the aperture 26 a new small block 1 when the small block that previously occupied the position 1 has descended to position 2 by effect of electrode consumption. All this can take place with a minimum use of labor, without disturbing by any means the heat balance of the furnace and cell and the regularity of the electrolysis. Obviously, the magazine constituted by chimney 5 can be extended upwardly to hold more blocks 1.

The small block 1 may be simply superimposed on block 2, or a little binder may be applied between one block and the other, for example Stiderberg paste, pitch, or tar may be used to make the anodic restoring assembly of Fig. 1 more rigid.

If, on the contrary, the self-restoring anodic assembly formed of Stiderberg paste is adopted, as shown in the second cell from the left in Fig. 1 or in Fig. 4, the anodic consumption is made up for by proceeding in a way analogous to that already described, but with small blocks of Stiderberg paste in lieu of the procedure employing prebaked anodes. green fused Stiderberg paste. In those cases it is advantageous to line the inner walls of the chimney in the upper portion, and down to a level a little higher than that of the bath, with sheet metal (not shown). Here too it is necessary to contrive to have the downward thrust, exerted for example by the weight of the non-submerged assembly, overcome the ascending thrust exerted by the bath on the submerged assembly.

The invention is utilizable with all of the types of cathodic surfaces described in the copending applications listed above. Preferably, a free graphite active cathode face substantially plane and parallel to and of same size as the opposite active anode face is used.

As will be seen, in contrast to the solution as supplied in this field at present, namely mechanically adjustingthe interelectrode spacing, and with respect to the solution However it is also possible to supply proposed recently by the same inventor, of periodic vari a tion of the interelectrocle spacing, the present innovation radically solves, for the first time, the problem of continuous self-adjusting interelectrocle spacing and of continuous self-adjusting anodic restoration in electrolysis with consumable anodes, by providing perfect constancy of said spacing, which is not disturbed either by the progressive anodic consumption or by the successive anodic restorations. It should be understood that the embodiments described and illustrated are only by way of example and without intended limitation. The scope of the invention, as defined in the claims appended, comprises all variations which embody the principle of automatically keeping constant the distance between the electrodes (in cells and furnaces for electrolysis preferably with inclined or vertical consumable electrode layers), by feeding the restoring electrode material, while guided,

with such a thrust as to re-occupy continuously the space which electrochemical consumption would ordinarily leave free.

These surprising results are obtained without needing any expensive regulating devices whatsoever external to the furnace as must be provided with conventional commercial furnaces.

Furthermore, said results are obtained by keeping eachv permanent part (which in every intermediate electrode forms one body with the cathode) of the anodic structures, fixed and stationary.

I claim:

1. In a process of producing a metal by electrolysis of a fused salt bath in which an electric current is passed.

sumable in the electrolysis from above downwardly along-- side the bath-facing surface of the anode, to continuously enter the space made available by the consumption of the anodic surface, the anode otherwise remaining fixed in permanent and stationary position during the renewal and during the electrolysis, the electrolysis continuing during the said restoring.

2. In a process of producing aluminum by electrolysis of alumina in a fused bath in which an electric current is passed through a cell comprising an anode, an intervening upwardly-downwardly extending electrolysis gap, and a cathode, the major component of direction of which is vertical, the anode having an upwardly-downwardly extending bath-facing anodic surface, the improvement comprising continuously and automatically restoring the said bath-facing anodic surface of the anode in situ by continuously directing renewing carbonaceous material consumable in the electrolysis from above downwardly alongside the bath-facing surface of the anode, to continuously enter the space made available by the consumption of the anodic surface, the anode otherwise remaining fixed in permanent and stationary position during the renewal and during the electrolysis, the cell remaining closed and the electrolysis continuing during the said ponent of direction of which is vertical, the improvement. comprising continuously and automatically restoring the said anodic surface of the anode in situ with self-regulation of the electrode spacing by continuously guiding renewing carbonaceous material consumable in the electrolysis downwardly to submerge in the bath alongside the surface of the anode, to continuously enter the space made available by the consumption of the anodic surface, the anode otherwise remaining fixed in position during the renewal and during the electrolysis, the renewing carbonaceous material being moved downwardly under gravity, the weight of the renewing carbonaceous material above the bath level being sutficient to overcome the buoyant upward thrust of the bath liquid upon the submerged renewing material, the electrolysis continuing during the said restoring, and the distribution of current in the electrodes being made with the same intensity at all points of the active anodic surface of the restoring assembly.

4. In a cell for electrolytic production of metals from fused compounds, comprising an anode electrode structure and a cathode electrode structure with opposed, substantially plane and parallel, upward-downwardly extending bath-facing walls having between them an upwardlydownwardly extending electrolysis gap containing the fused compound, the major component of direction of the walls being vertical, the improvement in the anode structure and in the automatic renewal of the consumable face thereof, the anode structure comprising a permanent element which is stationed during the electrolysis and a separate pro-shaped layer disposed alongside an upwardly-downwardly extending anode face of the element, said layer forming an electrochemically consumable face for the anode, said face of the stationed element forming an upwardly opening acute dihedral angle with the plane of the opposite cathode face across the electrolysis gap, said layer being under a downwardly thrusting force sufiicient to cause it to continuously enter space freed by electrochemical consumption of the material, thereby continuously and automatically restoring the layer from the top, the layer moving downwardly generally parallel to said face of the element as said layer is being consumed electrolytically, means for limiting the descent of said layer, the proceeding consumption of the layer being thus of longer duration at the bottom than the top, whereby the descending layer assumes a shape substantially triangular in cross-section, narrowing downwardly, the anodically active face of the layer remaining at a substantially uniform and constant distance from the opposite cathode face across the electrolysis gap.

5. The apparatus defined in claim 4, the said anode face of the stationed element being inclined to the vertical, the cathode having a cathodically active surface facing upwardly.

6. In a cell for electrolytic production of aluminum from aluminum oxide dissolved in a fused fluorine salt bath, comprising an anode electrode structure and a cathode electrode structure with opposed, substantially plane and parallel, upward-downwardly extending active anode and cathode faces having between them an upwardlydownwardly extending electrolysis gap containing the fused compound, the major component of direction of the faces being vertical, the improvement in the anode structure and in the renewal of the consumable anode face thereof, the anode structure comprising an element which is permanent and stationary during the electrolysis and a separate pre-shaped carbonaceous layer disposed alongside an upwardly-downwardly extending face of the element, said layer forming an electrochemically consumable face for the anode, said face of the element forming an upwardly opening acute dihedral angle with the plane of the opposite cathode face situated across the electrolysis gap, said layer being under a downwardly thrusting force sufficient to cause it to continuously enter space freed by electrochemical consumption of the carbonaceous material thereby continuously and automatically restoring the layer from the top, the layer moving downwardly along said face of the element as said layer is being consumed electrolytically, means for limiting the descent of said layer, the proceeding consumption of the layer being thus of longer duration at the bottom than the top, whereby the descending layer assumes a shape substantially triangular in cross-section, with the apex directed downwardly, the anodically active face of the layer remaining at a substantially uniform and constant distance from the opposite, cathode face across the electrolysis gap.

7. In a cell for electrolytic production of aluminum from aluminum oxide dissolved in a fused salt bath, comprising an anode electrode structure and a graphite cathode electrode structure with opposed, inclined, substantially plane and parallel, upward-downwardly extending active anode and cathode faces having between them an upwardly-downwardly extending electrolysis gap containing the fused compound, the major component of direction of the faces being vertical, the improvement in the anode structure and in the renewal of the consumable anode face thereof, the anode structure comprising a permanent graphite element which is stationary during the electrolysis and a pre-shaped carbonaceous layer which is separate from said element and is disposed alongside an upwardly downwardly extending face of the element, said layer forming an electrochemically consumable face of the anode, said face of the element forming an upwardly opening acute dihedral angle with the plane of the opposite cathode face situated across the electrolysis gap, carbonaceous replenishing means for the layer, the replenishing means and said layer being under a downwardly thrusting force sufficient to cause the layer to continuously enter space freed by electrochemical consump' tion of the carbonaceous material, thereby continuously and automatically restoring the layer from the top, the layer moving downwardly generally parallel to said face of the element as said layer is being consumed electrolytically, guide means for the carbonaceous replenishing means comprising refractory conduit means whose axes are respectively substantially parallel to the plane of contact between the layer and the stationary anode element, and individual heat-insulating covers for said conduit means, means for limiting the descent of said layer comprising a lower fixed stop of material inert to the fused bath, the proceeding consumption of the layer being thus of longer duration at the bottom than the top, whereby the descending layer assumes a shape substantially triangular in cross-section, narrowing downwardly, the anodically active face of the layer remaining at a substantially uniform and constant distance 'from the opposite cathode face across the electrolysis gap.

8. The apparatus defined in claim 6, said layer comgrising superimposed blocks of pro-baked electrodic car- 9. The apparatus defined in claim 6, said layer comprising baked Siiderberg paste.

10. The apparatus defined in claim 7, the said conduit elements being lined internally with sheet metal, the carbonaceous replenishing material being formed of S6derberg paste.

11. In a cell for electrolytic production of aluminum from aluminum oxide dissolved in a fused fluorine salt bath, the cell comprising an anode electrode structure and a cathode electrode structure with opposed, substantially plane and parallel, upward-downwardly extending active anode and cathode faces having between them an upwardly-downwardly extending electrolysis gap containing the fused compound, the major component of direction of which faces is vertical, the improvement comprising an anode structure comprised of a permanent element which is stationary during the electrolysis and a separate carbonaceous layer disposed alongside an upwardly-downwardly extending face of the element, said layer forming an electrochemically consumable face for the anode, said face of the element forming an upwardly opening acute dihedral angle with the, plane of the opposite cathode face,

assess? situated across the electrolysis gap, said layer being under a downwardly thrusting force sufficient to cause it to continuously enter space freed by electrochemical consumption of the carbonaceous material, thereby continuously and automatically restoring the layer from the top, the layer moving downwardly generally parallel to said face of the element as said layer is being consumed electrolytically, means for limiting the descent of said layer, the proceeding consumption of the layer being thus of longer duration at the bottom than the top, whereby the descending layer assumes a shape substantially triangular in cross-section, with the apex directed downwardly, the anodically active face of the layer remaining at a substantially uniform and constant distance from the opposite cathode face across the electrolysis gap, an insulated containing structure for the cell, the heat insulation means being suificient to maintain the upper free surface of the bath at a tempearture higher than the freezing temperature thereof.

12. In a multi-cell furnace for production of aluminum by fused salt bath electrolysis of alumina, comprising a housing structure, electrode structure in fixed spaced relationship therein, said electrode structures comprising at least one bipolar electrode structure located in said furnace and having opposite upwardly-downwardly extending bath-facing walls, said bipolar electrode structure providing thereon opposite bath-facing cathodic and anodic surfaces, said electrode structures further comprising an anode electrode element and a cathode electrode element each having upwardly-downwardly extending bath-facing Walls, the bipolar electrode structure being positioned between said anode and cathode electrode elements, to provide a number of intervening electrolysis gaps each extending upwardly-downwardly, the major component of direction of the gaps being vertical, the electric current passing serially through the electrode structures and intervening electrolysis gaps, cover means heat insulating the top of the furnace, the improvement comprising means operative with the cover in place to continuously and automatically renew the anode surfaces of the electrode structures from the bathside during the electrolysis, said means forming columns comprised of pre-shaped solidified carbonaceous material consumable in the electrolysis and means for guiding the respective column downwardly adjacent the respective anode surface, each columnbeing subject to downwardly thrusting force sufiicient to cause it to continuously enter space freed by electrochemical consumption of the carbonaceous material.

13. In a multi-cell furnace for production of aluminum by fused salt bath electrolysis of alumina, comprising a housing structure, electrode structures in fixed spaced relationship therein, said electrode structures comprising at least one bipolar electrode structure located in said furnace and having opposite upwardly-downwardly extending bath-facing walls, said bipolar electrode structure providing thereon opposite bath-facing cathodic and anodic surfaces, said electrode structures further comprising an anode electrode element and a cathode electrode element each having upwardly-downwardly extending bath-facing walls, the bipolar electrode structure being positioned between said anode and cathode electrode elements, to provide a number of intervening electrolysis gaps each extending upwardly-downwardly, the major component of direction of the gaps being vertical, the electric current passing serially through the electrode structures and intervening electrolysis gaps, cover means heat insulating the top of the furnace, the improvement comprising means operative with the cover in place to continuously renew the anode surface of the bipolar electrode structure during the electrolysis, said means comprising a layer comprised of solidified carbonaceous material consumable in the electrolysis, said layer being subject to a downwardly thrusting force suflicient to cause it to continuously enter space freed by electrochemical consumption of the carbonaceous material, said bipolar elec- 10 trode structure comprising a permanent graphite block that remains stationed in the furnace during the electrolysis and the said renewal, means for guiding the carbonaceous layer downwardly adjacent a bath-facing surface of the block, there being an interstice between said surface and the layer.

14. A furnace according to claim 13, in which said block is provided with narrow channels in said block downwardly inclined toward the said face to permit a limited flow thereto of fused aluminum formed on the cathode face of the bipolar electrode, to enter said interstice, to facilitate passage of electric current across the interstice.

15. In an electrolytic furnace a cell for electrolysis of a molten material in which carbonaceous material is anodically consumed, said cell comprising an anode structure and a cathode structure, the anode structure comprising a permanent graphite layer which remains stationed in the furnace during the electrolysis, the anode structure having a continuously restoring anodic face comprising a moving layer of electrochemically consumable carbonaceous material having a substantially triangular cross-section narrowing downwardly, there being a narrow interstice between the graphite layer and the moving layer, said interstice containing a molten substance, and guide means in the upper part of the furnace permitting introduction of said layer of consumable carbonaceous material and guiding the latter downwardly.

16. An electrolytic furnace for production of aluminum by electrolysis of a fused salt bath, in which carbonaceous material is anodically consumed, said cell comprising an anode structure and a cathode structure providing.upwardly-downwardly extending bath-facing anodic and cathodic faces the major component of direction of which is vertical, the anode structure comprising a permanent graphite layer which remains stationed in the furnace during the electrolysis, the anode structure having an automatically continuously restoring anodic face comprising a moving layer of electrochemically consumable solid carbonaceous material having a substantially triangular cross-section narrowing downwardly, there being a narrow interstice between the graphite layer and the moving layer, said interstice containing molten aluminous material, and guide means in the upper part of the furnace providing an upwardly-downwardly directed passage adapted for reception of the said layer of consumable carbonaceous material and for feeding the latter downwardly therein.

17. The apparatus defined in claim 6, said face of the element and the anodically active face of the layer being. inclined and facing downwardly.

V 18. The apparatus defined in claim 6, said face of the element being inclined and facing upwardly, the anodically active face of the layer being inclined and facing downwardly.v

19. A multi-cell furnace for production of aluminum by.fused salt bath electrolysis of alumina, comprising a housing structure, electrode structures in fixed spaced relationship therein, said electrode structures comprising at least one bipolar electrode structure located in said furnace and having opposite upwardly-downwardly extending bath-facing walls, said bipolar electrode structure providing thereon opposite bath-facing cathodic and anodic surfaces, the anodic surface being inclined and facing. downwardly, the cathodic surface facing upwardly, said electrode structures further comprising an anode electrode and a cathode electrode each having upwardlydownwardly extending bath-facing walls, the bipolar electrode being positioned between said anode and cathode electrodes, to provide a number of intervening electrolysis gaps each extending upwardly-downwardly, the electric current passing serially through the electrode structures and intervening electrolysis gaps, means to continuously and automatically renew the anode surface of the bipolar electrode structure during the electrolysis, said means comprising a column of carbonaceous material consumable in the electrolysis, the column being fed downwardly into the fused bath adjacent to and coextensive with at least the major part of the anode surface, said column being subject to a gravity force sufficient to overcome the buoyancy of the submerged part thereof, to cause the column to continuously enter space freed by electrochemical consumption of the. carbonaceous material.

20. In a process of producing a metal by electrolysis of a fused salt bath in which an electric current is passed through an anode, through an intervening electrolysis fused-salt-bath-containing gap, and through a cathode, the anode having an upwardly downwardly extending bathfacing anodic surface, the major component of direction of which is vertical, the improvement comprising con tinuously and automatically restoring the said bath-facing anodic surface of the anode in situ by continuously directing renewing solidified carbonaceous material consumable in the electrolysis from above downwardly alongside at least the major part of the bath-facing surface of the anode, to continuously enter the space made available by the consumption of the anodic surface, the anode otherwise remaining fixed in permanent and stationary position during the renewal and during the electrolysis, the electrolysis continuing during the said restoring.

21. In a process of producing aluminum by electrolysis of alumina in a fused bath in which an electric currentv is passed through a cell comprising an anode, an intervening upwardly-downwardly extending electrolysis gap, and a cathode, the major component of direction of which is vertical, the anode having an upwardly-downwardly extending bath-facing anodic surface, the improvement comprising continuously and automatically restoring the said bath-facing anodic surface of the anode in situ by continuously directing renewing solidified, pre-baked carbonaceous material consumable in the electrolysis from above downwardly alongside at least the major part of the bath-facing surface of the anode, to continuously enter the space made available by the consumption of the anodic surface, the anode otherwise remaining fixed in permanent and stationary position during the renewal and during the electrolysis, the cell remaining closed and the electrolysis continuing during the said restoring, the aluminum produced being removable during said restoration, the bath being circulated and the alumina being feedable during said restoration.

22. In a process of producing aluminum by electrolysis of alumina in a fused bath in which an electric current is passed through an anode, through an intervening upwardly-downwardly extending electrolysis gap containing fused bath, and through a cathode, the anode having an upwardly-downwardly extending, inclined, downwardly facing bath-contacting anodic surface, the major component of direction of which is vertical, the improvement comprising continuously and automatically restoring the said anodic surface of the anode in situ with selfregulation of the electrode spacing by continuously guiding renewing solid, pre-baked carbonaceous material consumable in the electrolysis downwardly to submerge in the bath alongside at least the major part of the surface of the anode, to continuously enter the space made available by the consumption of the anodic surface, the anode otherwise remaining fixed in position during the renewal and during the electrolysis, the renewing carbonaceous material being moved downwardly under gravity, the

Weight of the renewing carbonaceous material above the bath level being sufficient to overcome the buoyant upward thrust of the bath liquid upon the submerged renewing material, the electrolysis continuing during the said restoring, and the distribution of current in the electrodes being made with the same intensity at all points of the active anodic surface of the restoring assembly.

23. In a process of producing a metal by electrolysis of a fused salt bath in which an electric current is passed through an anode, through an intervening electrolysis fused-salt-bath-co-ntaining gap, and through a cathode, the anode having an upwardly-downwardly extending bath-facing anodic surface, the major component of direction of which is vertical, the improvement comprising continuously and automatically restoring the said bathfacing anodic surface of the anode in situ by continuously directing pre-shaped renewing carbonaceous material consumable in the electrolysis from above downwardly alongside the bath-facing surface of the anode, to continuously enter the space made available by the consumption of the anodic surface, the anode otherwise remaining fixed in permanent and stationary position during the renewal and during the electrolysis, the electrolysis continuing during the said restoring, there being left an interstice, narrower than the mean thickness of the renewing carbonaceous material, between the latter material and the anode surface being restored, which interstice contains conductive molten substance during the process.

24. In a process of producing aluminum by electrolysis of alumina in a fused bath in which an electric current is passed through a cell comprising an anode, an intervening upwardly-downwardly extending electrolysis gap, and a cathode, the major component of direction of which is vertical, the anode having an upwardly-downwardly extending bath-facing anodic surface, the improvement comprising continuously and automatically restoring the said bath-facing anodic surface of the anode in situ by continuously directing renewing carbonaceous material consumable in the electrolysis from above downwardly alongside the bath-facing surface of the anode, to continuously enter the space made available by the consumption of the anodic surface, the anode otherwise remaining fixed in permanent and stationary position during the renewal and during the electrolysis, the cell remaining closed and the electrolysis continuing during the said restoring, the aluminum produced being removable during said restoration, the bath being circulated and the alumina being feedable during said restoration, there being left an interstice, narrower than the mean thickness of the renewing carbonaceous material, between the latter material and the anode surface being restored, which interstice contains conductive molten substance during the process.

References Cited in the file of this patent UNITED STATES PATENTS 1,921,377 Ward Aug. 8, 1933 2,480,474 Johnson Aug. 30, 1949 2,545,566 Booe Mar. 20, 1951 2,569,578 Rieger Oct. 2, 1951 2,680,142 Graybeal June 1, 1954 FOREIGN PATENTS 784,695 Great Britain Oct. 16, 1957 1,119,832 France June 26, 1956

Claims

1. IN A PROCESS OF PRODUCING A METAL BY ELECTROLYSIS OF A FUSED SALT BATH IN WHICH AN ELECTRIC CURRENT IS PASSED THROUGH AN ANODE, THROUGH AN INTERVENING ELECTROLYSIS FUSED-SALT-BATH-CONTAINING GAP, AND THROUGH A CATHODE, THE ANODE HAVING AN UPWARDLY-DOWNWARDLY EXTENDING BATHFACEING ANODIC SURFACE THE MAJOR COMPONENT OF DIRECTION OF WHICH IS VERTICAL, THE IMPROVEMENT COMPRISING CONTINUOUSLY AND AUTOMATICALLY RESTORING THE SAID BATH-FACING ANODIC SURFACE OF THE ANODE IN SITU BY CONTINUOUSLY DIRECTING PRE-SHAPED RENEWING CARBONACEOUS MATERIAL CONSUMABLE IN THE ELECTROLYSIS FROM ABOVE DOWNWARDLY ALONGSIDE THE BATH-FACING SURFACE ON THE ANODE, TO CONTINUOUSLY ENTER THE SPACE MADE AVAILABLE BY THE CONSUMPTION OF