US3090744A - Electrolytic furnace for producing aluminum having a crust breaking apparatus - Google Patents

Electrolytic furnace for producing aluminum having a crust breaking apparatus Download PDF

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US3090744A
US3090744A US78346A US7834660A US3090744A US 3090744 A US3090744 A US 3090744A US 78346 A US78346 A US 78346A US 7834660 A US7834660 A US 7834660A US 3090744 A US3090744 A US 3090744A
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Prior art keywords
crust
furnace
anodes
gap
alumina
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US78346A
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English (en)
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Muller Paul
Schmitt Johannes
Wittner Hubert
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Aluminium Industrie AG
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Aluminium Industrie AG
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Priority claimed from CH8238659A external-priority patent/CH379775A/de
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
    • C25C3/20—Automatic control or regulation of cells
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
    • C25C3/08—Cell construction, e.g. bottoms, walls, cathodes

Definitions

  • the crust upon which the alumina is charged from time to time, is broken when anode polarization, the socalled anode effect, occurs. This effect is made apparent by the considerable increase in voltage necessary to maintain the operating current.
  • the anode effect occurs the crust, on which further alumina has been placed, is broken and the fresh alumina is stirred into the melt.
  • the crust may also be broken one or more times for the addition of more alumina when no anode effect is observed, so as to increase the time interval between successive anode effects.
  • crust-breakers operated by compressed air have generally been used. These are movable, involve the use of manpower and serve to break the crusts of furnaces in succession.
  • alumina After the breaking of the crust and as soon as the surface of the melt has solidified once more, alumina is applied. Today the alumina is mostly mechanically conveyed to hoppers over the furnace, from which it passes onto the crust.
  • Furnaces are also known in which two rows each composed of pre-baked anode blocks pushed closely together are so arranged that a longitudinal gap remains between the rows in the longitudinal axis of the furnace, and above this gap there are alumina containers from which batches of alumina can be released onto the crust by manual operation of a handle. At each end there are rollers from which long rods with bent ends extend through the gap as far as the middle of the furnace, these rods being moved manually to break the crust. Thus the crustbreaking and the supply of alumina are manually controlled.
  • the furnace begins to go hollow, i.e. the electrolyte coating that has solidified on the pot walls and finally also the carbon lining are hollowed out in their lower part, and the current efficiency usually falls considerably in time; the highest current efiiciency obtainable may be no more than 87%.
  • these furnaces are often provided with particularly thin carbon linings and the distance between each anode and carbon lining is kept as small as possible.
  • the carbon linings become coated with a thin solidified crust of melt, which is a good electrical insulator and which causes the current to flow from the anodes at first predominantly vertically.
  • the lateral deviation of the current at the outer anode corners increases with the time, so that the carbon linings are nevertheless comparatively quickly hollowed out.
  • the cathode pots of these furnaces must be exchanged'or renewed frequently, that is to say at least every 1 /2 years, if the furnace is to work satisfactorily.
  • the life of the cathode pots of furnaces the outer sides of which are normally lined is from three to four years.
  • German patent specification No. 895,379 discloses a rotary roller with working teeth of heat, resistant material such as quartz, special ceramic compositions or the like, in the middle of the furnace. At each anode effect the increase in voltage causes a driving motor to set the roller in motion.
  • This apparatus occupies a very large space in the middle of the furnace.
  • at least one tooth always remains immersed in the melt when the apparatus is not working, so that the roller must consist of a material that resists very strongly corrosive fluoride elec trolytes at the working temperature of about 990 C. Such materials are not only very expensive, but also brittle.
  • the anode area of the furnace is divided into two parts with a gap between them and a mechanically operated crust-breaker works substantially vertically in and extends over the whole length of the gap.
  • the anodes may be of the usual Stiderberg type or self-baking Soderberg anodes or may be prebaked and by the anode area we mean the horiiontal surface covered by the anodes together with any spaces between them.
  • the invention is particularly applicable to furnaces of elongated rectangular or elliptical shape, and preferably the gap extends along the longitudinal centre line.
  • the crust breaker preferably comprises one or' more beams extending throughout the gap and having downwardly directed teeth.
  • the supports and operating mechanism or mechanisms for the crust-breaker are situated on the sides of the furnace outside the anode area. This not only protects them from the furnace Waste gases and the heat but also leaves the gap over the crust-breaker free for the installation of exhaust gas collecting devices and advantageously also one or more supply hoppers for alumina.
  • the crust breaker should be so constructed and mounted that not only is the crust surface broken, but also the resulting crust fragments are thrust into the liquid bath.
  • the alumina lying on the crust falls into the melt so that the concentration of alumina in the melt is increased.
  • an exactly measured amount of alumina may be discharged from the hopper or hoppers preferably under automatic control, onto the reformed crust.
  • FIGURE 1 is a side view, partly in section, of a furnace with pre-baked carbon anodes
  • FIGURE 2 is a similar view of a furnace with Stiderberg anodes and lateral current-supply bolts;
  • FIGURE 3 is a similar view of a furnace with Sederberg anodes and vertical current-supply bolts;
  • FIGURE 4 is a central longitudinal section through a furnace, showing one form of crust-breaking device.
  • FIGURE 5 is a section similar to FIGURE 4, showing an alternative form of crust-breaker, but not showing the anode in detail.
  • the electrolytic furnaces shown in the drawings each comprises a pot 1, which is lined with refractory bricks 2 and 3. Cathodic current-supply bars 4 are embedded in the carbon lining 3.
  • the pot contains a layer 5 of separated molten aluminum and a bath 6 of molten fluoride, the surface of which solidifies to a crust 7.
  • the anode part of the furnace is supported on a framework 8 which includes upper cross-beams carrying lifting mechanism 9, operated by a motor 14) through gearing 11, cross-shafts 12 and longitudinal shafts 13.
  • This lifting mechanism 9 actuates lifting and lowering shafts 14-, which carry an anode carrier 15 and anodic conductors 16.
  • Anode rods 17 fixed to the anode carrier 15 are connected to the conductors 16, and to current-supply bolts or studs 20 (FIGURE 1), 21 (FIGURE 2) or 22 (FIGURE 3) embedded in anodes 13 (FIGURE 1) or 19 (FIGURES 2 and 3), and thus both support the anode or anodes and supply electric current.
  • the anodes 18 are prebaked blocks arranged in two rows running in the longitudinal direction of the furnace to leave a gap 23 between them.
  • the width of this gap is preferably from 8 to 28 inches.
  • the anode area is therefore divided in two halves and a crust-breaker is mounted to work in the gap 23 between them.
  • This crust-breaker consists of two beams 24 and 25 which carry crushing teeth 26.
  • the beams of the crust-breaker are movable vertically and in the drawings they are shown in the working position. When the crust breaker is working one beam lies in its highest position while the other is in its lowest position; the position is subsequently reversed, as is shown in broken lines. When the crust is not being broken both beams are held in the raised position, so that the tips of the teeth do not lie permanently in the strongly corrosive electrolyte melt. Alternatively both the beams 2 and 25 may be simultaneously raised and lowered in operation.
  • An alumina hopper 27 lies above the central gap 23 and has bottom outlets 28 which can be opened or shut as desired.
  • the furnaces shown in FIGURES 2 and 3 each have two self-baking anodes 18 separated from one another longitudinally to leave a gap 23.
  • the anodes are surrounded by a casing 29, partly double-walled, which is suspended from the frame-work 8 by rod 39 and forms a gas-collecting hood 31 around the anode area.
  • the current-supply studs 21 enter the anodes laterally, and to allow them to move downwards with the anode vertical slits are provided in the casing 29.
  • the anode casing is therefore not continuous, but consists of individual box-like vertical chambers in which the exhaust gases flow upwards into the upper channel and between which the studs 21 are arranged.
  • FIGURE 2 one side wall of such a vertical chamber is shown behind the studs 21.
  • the current-supply bolts 22 are arranged vertically.
  • the alumina hopper 27 (shown in FIGURES 2 and 3) discharges into two passages 36 at the sides of the gap 23.
  • This hopper has a double bottom for the admission of compressed air to fiuidise the alumina, the upper bottom consisting of porous'plates 32.
  • compressed air is admitted into the space between the Ibottom through pipes 33 and jets 34, it passes through the porous plates 32 and loosens the alumina in the hopper, so that the alumina flows freely through perforated walls 35 and out through the passages 36.
  • the crust-breakers used in the invention can take various forms, two of which .are shown in FIGURES 4 and 5.
  • the crust-breaker shown in FIGURE 4 consists of two lever-like beams extending over and beyond both ends of the anode area, but only the beam 25 is shown,
  • This beam 25 is carried at one end of the furnace by a pivot shaft 37 mounted in the furnace frame and connected at its other end to a ram 38 which can be hydraulically or pneumatically operated and which is carried by a flange 39 on the furnace frame.
  • the beam 25 carries teeth 26 only on that half of the beam remote from the shaft 37, since the other half, near the shaft 37, has only a relatively small stroke.
  • the beam is slightly bent at its centre so that the teeth may lie in a substantially horizontal plane when the beam is lowered and hence can thrust the crust into the molten electrolyte to an even depth.
  • a stop 49 prevents the teeth from dipping too far into the bath.
  • the beam 25 is shown in dotted lines in its raised or rest position.
  • a catch 41 is provided to latch the beam in this position.
  • the second beam 24 is identical to the beam 25, but is pivoted at the opposite end of the furnace so that its teeth break the crust below that part of the beam 25 which does not carry teeth.
  • the gap between the anode is closed at its ends by a metal hood 42 to collect the exhaust gases escaping between the two anodes.
  • the exhaust gases are burnt in the chimney 43 to which air is supplied and are led to a purification plant.
  • the discharge outlets of the gascollecting hoods 31 also discharge into this chimney 43. It is however also possible to install a collecting channel corresponding to the collecting channel 31 and thus leave the gap 23 open at both ends so that, if necessary, the inner walls of the anode can be kept cooler.
  • the crustbrea'ker shown in FIGURE 5 has a straight beam 25 extending over and projecting beyond both ends of the whole anode area, and this is connected at each end to a ram 38.
  • This beam 25 can thus be moved vertically over its whole length through the same distance and is therefore provided with teeth 26 over its whole useful length.
  • the anode part of the furnace is merely outlined in FIGURE 5.
  • the crust-breakers shown in FIGURES 4 and 5 can be used in any of the furnaces shown in FIGURES 1, 2 and 3.
  • the crushing teeth can be moved practically purely vertically.
  • the beam may also be mounted for movement across or along the gap between the anodes in order better to agitate the bath in addition to breaking the crust.
  • an eccentric drive may for example be used in combination with the ram or each ram to produce three-dimensional movement of the teeth.
  • the voltage in the furnace can be controlled by known methods, for example by regulating the eifective voltage to the estimated voltage.
  • the voltage is regulated by adjusting the distance between the anodes and the bottom of the cathode pot.
  • the furnaces according to our invention are particularly suitable for automatic control by a programme controller.
  • This controller may control the movements of the crustbreakers, the addition of the alumina and the regulation of the furnace potential, in particular re-adjustment of the estimated potential after the breaking of the crust.
  • the sequence of events is as follows: When an anode effect occurs, the crust-breaker is set in motion and the crust is broken into pieces by the crushing teeth. There should be enough teeth on the crustbreaker to ensure that the crust is broken into small fragments.
  • the voltage across the electrodes is adjusted once more to the desired value.
  • the amount of alumina discharged is controlled as accurately as possible to ensure the desired concentration in the electrolyte.
  • the alumina should be separated evenly over the crust to facilitate an even distribution of it in the electrolyte, and to avoid local high concentrations in the electrolyte.
  • Early application of the layer of alumina to the crust helps to prevent the crust from cooling, thus keeping it relatively soft, and preheats the alumina before it enters the molten electrolyte.
  • the driving mechanism of the crust-breaking device may be set in motion and stopped under manual control by a push-button system, but we prefer to control the operation automatically by means of a programme controller.
  • the programme controller advantageously controls the time intervals between individual breaking operations, the duration of each breaking operation, (cg. /23 min), the time interval between the end of the breaking operation and the beginning of the alumina addition (e.g. /2 to 5 min), the duration of the flow of alumina from the hoppers, and also the furnace voltage.
  • This cycle of operations may conveniently be set in motion as a result of the increase in voltage through the furnace voltage controller when an anode efiect occurs.
  • the cycle is conveniently repeated at intervals of e.g.
  • the alumina concentration in the electrolyte should be at least 3% by weight, and preferably at least 3.5%. Although it is possible to increase the concentration of alumina to 8 to 10%, we obtain the best results at concentration of 3.5 to 5%, at which concentration we have obtained current yield values of 90 to 96%.
  • the side lining of the pot is not made by damming the usual carbonaceous mass, but by damming a mixture of 40 to 85 percent (of weight) powdered silicon carbide, 45 to 7 percent coke powder and 15 to 8 percent pitch, which mixture has a very low conductivity for heat and for electric current.
  • a mixture of the following composition Preferably we use a mixture of the following composition:
  • Medium-hard pitch 1510 Very suitable is a mixture of percent silicon carbide, 14 percent coke and 11 percent medium-hard pitch. Of course, the mixture may contain supplemental substances, if the same do not impair the results.
  • the particle size of the silicon carbide should be between 0 and about 6 mm., the particle size of the coke between 0 and about 22 mm.
  • the components are mixed suitably at a temperature between 50 and 250 C.
  • an electrolytic furnace for the production of aluminum with the use of a molten salt bath
  • the combination comprising a frame, anodes for said furnace, means supporting said anodes from said frame in two rows separated by a gap therebetween extending along the full length of the region occupied by said anodes and directly above the area where a crust is formed on the electrolyte, and, a crust breaker comprising one or more substantially hori zontal beams extending in and along substantially the full length of said gap and provided with substantially vertically downwardly directed teeth distributed substantially along the full length of said gap, and means supported from said frame for operating each beam substantially vertically at least at one end through successive strokes, comprising means for moving said beam during each stroke of a cycle from a position in which the teeth on the beam are located above the crust downwardly to a position in which the teeth perforate and break the crust and for moving the beam during the next stroke of the cycle upwardly to the first-mentioned position, and means for bringing the beam to rest in said first-mentioned
  • a crust breaker comprising two horizontal beams inthe form of levers extending side by side in and along substantially the full length of said gap and provided with substantially vertically downwardly directed teeth distributed substantially along the full length of said gap, each of said beams being pivoted at one end, and means supported on said frame and connected to the other end of the beam for operating each beam substantially vertically at said other end through successive strokes from a position in which the teeth on the beam are located above the crust to a position in which the teeth perforate and break the crust and then back upwardly to said first-mentioned position, in which latter position the beam may be brought to rest.
  • an electrolytic furnace for the production of aluminum from alumina with the use of a molten salt bath
  • the combination comprising a frame, anodes for said furnace, means supporting said anode in two rows separated by a gap therebetween extending along the full length of the region occupied by said anodes, and a crust breaker comprising two horizontal beams in the form of levers extending side by side in and along substantially the full length of said gap and provided with substantially vertically downwardly directed teeth distributed substantially along the.
  • each of said beams being pivoted at one end, and means supported on said frame and connected to the other end of the beam for operating each beam substantially vertically at said other end through successive strokes from a position in which the teeth on the beam are located above the crust to a position in "which the teeth perforate and break the crust and then back upwardly to said first-mentioned position,-
  • the combination comprising a frame, anodes for said furnace, means supporting said anodes from said frame in two rows separated by a gap therebetween extending along the full length of the region occupied by said anodes, and a crust breaker comprising one or more substantially horizontal beams extending in and along substantially the full length of said gap and provided with substantially vertically downwardly directed teeth distributed substantially along the [full length of said gap, and means supported on said frame and connected to both ends of each beam for operating each beam substantially vertically through successive strokes from a position in which the teeth on the beam are located above the crust to a' position in which the teeth perforate and break the crust and then back upwardly to said first-mentioned position, in which latter position the beam may be brought to rest.
  • an electrolytic furnace for the production of aluminum with the use of a molten salt bath
  • the combination comprising a frame, anodes for said furnace, means supporting said anodes from said frame in two rows separated by a gap therebetween extending along the full length of the region occupied by said anodes from one end of said region to the other, and a crust breaker comprising one or more substantially horizontal beams extending in and along substantially the full length of said gap and provided with substantially vertically downwardly directed teeth distributed substantially along the full length of said gap, means located beyond said anode region and beyond said gap for operating each beam substantially vertically at least at one end through successive strokes from a position in which the teeth on the beam are located above the crust to a position in which the teeth perforate and break the crust and then backwardly to said first-mentioned position, andim'eans for bringing the beam to rest in said first-mentioned position.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electrolytic Production Of Metals (AREA)
  • Carbon And Carbon Compounds (AREA)
US78346A 1959-12-29 1960-12-27 Electrolytic furnace for producing aluminum having a crust breaking apparatus Expired - Lifetime US3090744A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CH8238659A CH379775A (de) 1959-12-29 1959-12-29 Aluminiumelektrolyseofen und Verfahren zu dessen Betrieb
CH1209260A CH388633A (de) 1959-12-29 1960-10-28 Aluminiumelektrolyseofen

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US (1) US3090744A (en:Method)
CH (1) CH388633A (en:Method)
DE (2) DE1136121B (en:Method)
GB (1) GB899509A (en:Method)
SE (1) SE304612B (en:Method)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1210994B (de) * 1963-07-08 1966-02-17 Adolf Nann Einschlagvorrichtung eines Krustenbrechers fuer Aluminium-Schmelzflusselektrolyseoefen
US3371026A (en) * 1964-02-04 1968-02-27 Reynolds Metals Co Electrolytic reduction cell with crustbreaking and ore feeding means
US3372105A (en) * 1962-10-22 1968-03-05 Arthur F. Johnson Aluminum reduction cell and insulation material therefor
US3410786A (en) * 1965-04-09 1968-11-12 Pechiney Prod Chimiques Sa Superstructure for electrolytic cells
US3470075A (en) * 1967-02-06 1969-09-30 Arthur F Johnson Process and apparatus for filtering effluent produced from aluminum reduction cells
US3931130A (en) * 1973-01-19 1976-01-06 Du Pont Of Canada, Ltd. Process for removing residual volatile solvent impurities from polymer molding pellets

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3960696A (en) * 1974-06-18 1976-06-01 Gebr. Giulini Gmbh Aluminum electrolysis furnace
CN103510110A (zh) * 2013-09-10 2014-01-15 河南中孚实业股份有限公司 一种铝电解槽全空腔装炉方法

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR631358A (fr) * 1927-03-24 1927-12-19 Agitateur pour fours de fusion électriques
DE895379C (de) * 1942-11-13 1953-11-02 Aeg Elektrolyseofen fuer Schmelzflusselektrolyse zur Gewinnung des Aluminiums
US2713024A (en) * 1959-04-24 1955-07-12 Montedison Spa Process for the continuous feeding of electrolytic aluminum cells
AT193619B (de) * 1954-09-03 1957-11-25 Ver Aluminium Werke Ag Oeffent Fahrbarer Krustenbrecher für Schmelzflußelektrolyseöfen

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR631358A (fr) * 1927-03-24 1927-12-19 Agitateur pour fours de fusion électriques
DE895379C (de) * 1942-11-13 1953-11-02 Aeg Elektrolyseofen fuer Schmelzflusselektrolyse zur Gewinnung des Aluminiums
AT193619B (de) * 1954-09-03 1957-11-25 Ver Aluminium Werke Ag Oeffent Fahrbarer Krustenbrecher für Schmelzflußelektrolyseöfen
US2713024A (en) * 1959-04-24 1955-07-12 Montedison Spa Process for the continuous feeding of electrolytic aluminum cells

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3372105A (en) * 1962-10-22 1968-03-05 Arthur F. Johnson Aluminum reduction cell and insulation material therefor
DE1210994B (de) * 1963-07-08 1966-02-17 Adolf Nann Einschlagvorrichtung eines Krustenbrechers fuer Aluminium-Schmelzflusselektrolyseoefen
US3371026A (en) * 1964-02-04 1968-02-27 Reynolds Metals Co Electrolytic reduction cell with crustbreaking and ore feeding means
US3410786A (en) * 1965-04-09 1968-11-12 Pechiney Prod Chimiques Sa Superstructure for electrolytic cells
US3470075A (en) * 1967-02-06 1969-09-30 Arthur F Johnson Process and apparatus for filtering effluent produced from aluminum reduction cells
US3931130A (en) * 1973-01-19 1976-01-06 Du Pont Of Canada, Ltd. Process for removing residual volatile solvent impurities from polymer molding pellets

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GB899509A (en) 1962-06-27
SE304612B (en:Method) 1968-09-30
CH388633A (de) 1965-02-28
DE1136121B (de) 1962-09-06
DE1153538B (de) 1963-08-29

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