US3829365A - Method of operating a cell for the recovery of aluminum by electrolysis of aluminum oxide in a fluoride melt - Google Patents

Method of operating a cell for the recovery of aluminum by electrolysis of aluminum oxide in a fluoride melt Download PDF

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Publication number
US3829365A
US3829365A US00378033A US37803373A US3829365A US 3829365 A US3829365 A US 3829365A US 00378033 A US00378033 A US 00378033A US 37803373 A US37803373 A US 37803373A US 3829365 A US3829365 A US 3829365A
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cell
aluminum
electrolysis
anode
resistance
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Expired - Lifetime
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US00378033A
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English (en)
Inventor
K Chaudhuri
P Bachofner
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Alcan Holdings Switzerland AG
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Alusuisse Holdings AG
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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

Definitions

  • the steel shell 12 which is lined with a thermal insulation 13 of heat-resisting, heat-insulating material and with carbon 11, contains the fluoride melt (the electrolyte).
  • the aluminum 14 separated at the cathode lies on the carbon bottom 15 of the cell.
  • the surface 16 of the liquid aluminum constitutes the cathode.
  • In the carbon lining 11 there are inserted iron cathode bars 17 transverse to the longitudinal direction of the cell, and these conduct the electrical direct current from the carbon lining 11 of the cell laterally outwards.
  • Anodes 18 of amorphous carbon dip from above into the fluoride melt 10, and supply the direct current to the electrolyte. They are firmly connected via conductor rods 19 and clamps 20 with the anode beam 21.
  • the current flows from the cathode bars 17 of one cell to the anode beam 21 of the following cell through conventional current bus bars, not shown. From the anode beam 21 it flows through the conductor rods 19, the anodes 18, the electrolyte 10, the liquid aluminum 14, and the carbon lining 11 to the cathode bars 17.
  • the electrolyte 10 is covered with a crust 22 of solidified melt and there is a layer of aluminum oxide 23 lying .above the crust.
  • cavities 25 occur between the electrolyte 10 and the solidified crust 22.
  • the horizontal extent of the lateral ledge 24 affects the plan area of the bath of liquid aluminum 14 and electrolyte 10.
  • the distance -d from the lower side 26 of the anode to the surface 16 of the liquid aluminum can be adjusted by lifting or lowering of the anode beam 21 with the help of the lifting mechanism 27, which is mounted on pillars 28. This alfects all the anodes.
  • An anode can be adjusted individually by releasing the respective clamp 20, shifting the respective conductor rod 19 upwards or downwards relatively to the anode beam 21, and re-tightening the clamp.
  • the anodes are consumed continuously on their lower side, by about 1.5 to 2 cms. per day according to the type of cell.
  • the height of the liquid aluminum on the bottom of the cell increases continuously by about 1.5 to 2 cms. per day due to the aluminum separated at the cathode.
  • anode When an anode has been consumed, then it is exchanged for a fresh anode.
  • the cell In practice, the cell is operated in such a way that, some days after its start of use, the anodes of the cell no longer have the same degree of consumption, and therefore, they must be exchanged separately over a range of several weeks. For this reason, anodes of different starting dates operate together in the same cell, as appears from the drawing.
  • the interpolar distances d of individual anodes are not exactly equal to each other. It suifices for the purpose of the present invention to consider the average, at any moment in time, of the individual interpolar distances. This average interpolar distance, which itself varies with time, will be termed D.
  • the principle of an aluminum electrolysis cell with one or more self-baking anodes is the same as that of an aluminum electrolysis cell with prebaked anodes. Instead of pre-baked anodes, one or more anodes are used which are continually baked from a green electrode paste in a steel jacket during the electrolytic operation by the heat of the cell.
  • the direct current is supplied by lateral steel rods or from above by vertical steel studs. These anodes are renewed as required by pouring green electrode paste into the steel jacket. Adjustments of interpolar distance are made by vertical adjustments of the steel jacket.
  • the aluminum oxide 23 which is above it is brought into the electrolyte 10. This operation is known as servicing of the cell.
  • the electrolyte becomes depleted in aluminum oxide.
  • the concentration of aluminum oxide in the electrolyte falls to somewhere between 1 and 2%, there arises the anode effect, which results in a sudden increase in cell voltage from the normal 4 to 4.5 volts to 30 volts and above.
  • the crust must be broken in, and the A1 0 concentration be raised by addition of new aluminum oxide.
  • One measurable quantity in the operation of the cell is its base voltage. This depends on the age of the cell, the condition of the carbon lining 1-1, and the composition of the molten electrolyte 10, as well as on the cell current intensity and current density.
  • the base voltage is also affected by the variation of the plan area of the bath in consequence of variation of the horizontal extent of the lateral ledge 24.
  • the base voltage is measured between corresponding points on the anode beams of the cell in question and of the next cell in series.
  • the voltage is the total of the ohmic voltage drops in the parts of the cell through which current flows plus the EMP required for the electrolytic decomposition of the A1 in the electrolyte.
  • R is the ohmic base resistance in ohms
  • U the base voltage in volts
  • 1.65 the electromotive force in volts
  • I the cell current intensity in amps.
  • the correct value of the base voltage corresponds to an optimum average interpolar distance D.
  • the actual interpolar distance is sometimes larger or smaller than it corresponds to the optimum interpolar distance.
  • the departures are substantially produced by increase of the height of the liquid aluminum 14 above the carbon bottom 15, by burning away of the anodes 18 at their lower side 26 and by variation of the dimension of the bath in consequence of variation of the thickness of the lateral ledge 24.
  • every anode lower side 26 has the same spacing d from the surface 16 of the liquid aluminum 14.
  • significant differences in the interpolar distance can appear from anode to anode, which can lead to the fact that individual anodes even touch the liquid metal 14 -(local short circuit of the cell).
  • These differences of the interpolar distance of individual anodes of the same cell are caused by defective insertion of new anodes during anode exchange, slipping of the conductor rods 19 as a result of insufficient tightening of the clamps 20, unequal anode quality, bulging of the surface 16 of the liquid aluminum 14 as a consequence of magnetic effects.
  • Large differences of the interpolar distance from anode to anode, especially when it attains local short circuit lead to heavy disturbances of the cell.
  • the problem which has led to the present invention was the recognition in gOOd time of a disturbance of the cell by analysis of the course in time of its base resistance.
  • a cell for the recovery of aluminum by electrolysis of aluminum oxide in a fluoride melt is operated by a method in which values of instantaneous resistance of the cell are calculated from instantaneous values of cell current intensity and cell voltage which are sampled by a computer at regular intervals of time during electrolysis, except during periods associated with anode effects and with manipulations on the cell, the absolute difference between each value of instantaneous resistance and the base resistance of the cell is added to a cumulative total, and a disturbance indication results from the computer when the cumulative total exceeds a predetermined value which is dependent on the number of intervals per period for a given cell, whereupon the resistance of the cell is raised, by increase of the interpolar distances of the anodes of the cell by a fixed amount, until the cause of the disturbance is eliminated, and finally the original interpolar distances are restored: or if no disturbance indication results within a predetermined period of sampling, then the cumulative total is returned to zero.
  • the predetermined value is expressed in ohms and is in effect the limit of permissible departure from the base resistance of the sum of differences of resistances over each predetermined period.
  • time intervals for the sampling of instantaneous values by the computer are chosen at will. Small time intervals of for example 15 to 60 seconds, give statistically more reliable data than large time intervals, of for example 30 minutes and above, for within large time intervals significant alterations in the electrolytic process can usually occur.
  • the intended alteration of the interpolar distance may be efiectuated either automatically :at the command of the computer, or by hand.
  • the computer stores the quantities R and R R
  • the special brackets indicate the absolute value of R R independently of the sign of the difference.
  • the predetermined value of the sum of the absolute differences R- R is an empirical value. With a kA cell, it lies between about 1.5 and 3 microhms for values which are summed up in a period of four hours. It is proportional to the said predetermined period.
  • the period for summing up the instantaneous values amounts to at least 1 hour and does not exceed 8 hours.
  • the base resistance of a 100 kA cell in undisturbed conditions amounts to 20 to 30 microhms. If the sum of the absolute differences of resistances following one another in time exceeds a limiting value of 2 microhms in a period of four hours, the cell is indicated by the computer as disturbed.
  • the interpolar distance is increased by an amount which in this case produces an increase of the cell voltage of about 0.2 volts.
  • the cell voltage and likewise the interpolar distance are reduced to the original value (before increase of the interpolar distance), when the cause of the disturbance has been eliminated.
  • the continuous monitoring of the cell leads to a steady operation, from which results an increase of the current efficiency and a reduction of the specific consumption of energy and anodes.
  • a method of operating a cell for the recovery of aluminum by electrolysis of aluminum oxide in a fluoride melt in which values of instantaneous resistance of the cell are calculated from instantaneous values of cell current intensity and cell voltage which are sampled by a computer at regular intervals of time during electrolysis,
  • the absolute difference between each value of instantaneous resistance and the base resistance of the cell is added to a cumulative total, and a disturbance indication results from the computer when the cumulative total exceeds a predetermined value which is dependent on the number of intervals per period for -a given cell, whereupon the resistance of the cell is raised, by increase of the interpolar distances of the anodes of the cell by a fixed amount, until the cause of 1 the disturbance is eliminated, and finally the original interpolar distances are restored; or if no disturbance indication results within a predetermined period of sampling, then the cumulative total is returned to zero.

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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)
US00378033A 1972-07-18 1973-07-10 Method of operating a cell for the recovery of aluminum by electrolysis of aluminum oxide in a fluoride melt Expired - Lifetime US3829365A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CH1075172A CH576530A5 (enrdf_load_stackoverflow) 1972-07-18 1972-07-18

Publications (1)

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US3829365A true US3829365A (en) 1974-08-13

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ID=4366446

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US00378033A Expired - Lifetime US3829365A (en) 1972-07-18 1973-07-10 Method of operating a cell for the recovery of aluminum by electrolysis of aluminum oxide in a fluoride melt

Country Status (16)

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US (1) US3829365A (enrdf_load_stackoverflow)
JP (1) JPS5244286B2 (enrdf_load_stackoverflow)
AT (1) AT327579B (enrdf_load_stackoverflow)
BE (1) BE802249A (enrdf_load_stackoverflow)
BR (1) BR7305359D0 (enrdf_load_stackoverflow)
CH (1) CH576530A5 (enrdf_load_stackoverflow)
EG (1) EG11360A (enrdf_load_stackoverflow)
GB (1) GB1413727A (enrdf_load_stackoverflow)
IE (1) IE38062B1 (enrdf_load_stackoverflow)
IS (1) IS1026B6 (enrdf_load_stackoverflow)
IT (1) IT992636B (enrdf_load_stackoverflow)
NL (1) NL168013C (enrdf_load_stackoverflow)
NO (1) NO133940C (enrdf_load_stackoverflow)
PH (1) PH9453A (enrdf_load_stackoverflow)
TR (1) TR17293A (enrdf_load_stackoverflow)
ZA (1) ZA734765B (enrdf_load_stackoverflow)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4008142A (en) * 1973-07-25 1977-02-15 Siemens Aktiengesellschaft Apparatus for operating the furnaces of an electrolysis plant
US4024034A (en) * 1973-07-25 1977-05-17 Siemens Aktiengesellschaft Method for operating the furnaces of an electrolysis plant
EP0671488A2 (en) 1989-02-24 1995-09-13 Comalco Aluminium, Ltd. Process for controlling aluminium smelting cells
WO2010065989A1 (en) * 2008-12-08 2010-06-17 University Of South Australia Formation of nanoporous materials

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103088369B (zh) * 2013-02-27 2015-06-10 云南铝业股份有限公司 一种铝电解槽母线电流在线测量方法

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4008142A (en) * 1973-07-25 1977-02-15 Siemens Aktiengesellschaft Apparatus for operating the furnaces of an electrolysis plant
US4024034A (en) * 1973-07-25 1977-05-17 Siemens Aktiengesellschaft Method for operating the furnaces of an electrolysis plant
EP0671488A2 (en) 1989-02-24 1995-09-13 Comalco Aluminium, Ltd. Process for controlling aluminium smelting cells
WO2010065989A1 (en) * 2008-12-08 2010-06-17 University Of South Australia Formation of nanoporous materials

Also Published As

Publication number Publication date
CH576530A5 (enrdf_load_stackoverflow) 1976-06-15
NO133940C (enrdf_load_stackoverflow) 1976-07-21
BE802249A (fr) 1973-11-05
IE38062L (en) 1974-01-18
PH9453A (en) 1975-12-04
GB1413727A (en) 1975-11-12
JPS5244286B2 (enrdf_load_stackoverflow) 1977-11-07
IE38062B1 (en) 1977-12-21
JPS4944922A (enrdf_load_stackoverflow) 1974-04-27
ATA631373A (de) 1975-04-15
NO133940B (enrdf_load_stackoverflow) 1976-04-12
NL168013C (nl) 1982-02-16
NL168013B (nl) 1981-09-16
BR7305359D0 (pt) 1974-08-22
AT327579B (de) 1976-02-10
IS1026B6 (is) 1980-04-14
ZA734765B (en) 1974-06-26
AU5805973A (en) 1975-01-16
DE2335029A1 (de) 1974-01-31
IT992636B (it) 1975-09-30
NL7309861A (enrdf_load_stackoverflow) 1974-01-22
EG11360A (en) 1977-08-15
IS2164A7 (is) 1974-01-19
TR17293A (tr) 1975-03-24
DE2335029B2 (de) 1976-08-05

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