US3756929A - Method of operating an aluminium oxide reduction cell - Google Patents

Method of operating an aluminium oxide reduction cell Download PDF

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Publication number
US3756929A
US3756929A US00203383A US3756929DA US3756929A US 3756929 A US3756929 A US 3756929A US 00203383 A US00203383 A US 00203383A US 3756929D A US3756929D A US 3756929DA US 3756929 A US3756929 A US 3756929A
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United States
Prior art keywords
cell
aluminium oxide
operating
heat
aluminium
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Expired - Lifetime
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US00203383A
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English (en)
Inventor
Hatting W Schmidt
R Pawlek
R Taufenecker
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
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 fluoride melt (the electrolyte) is in a steel shell 12 lined with carbon 11, and provided with a thermal insulation 13 of heat-resistant, heat-insulating lining material.
  • the aluminium 14 separated at the cathode collects on the bottom 15 of the cell.
  • the surface 16 of the fluid aluminium forms the cathode.
  • iron electrode bars 17 which carry the current outwards from the bottom of the cell.
  • Anodes 18 of amorphous carbon dip into the fluoride melt 10 from above, and feed the direct current into the electrolyte. They are fixedly connected via conductor bars 19 and by clamps 20 with the anode beam 21.
  • the electrolyte 10 is covered with a crust 22 of solidified melt, and a layer of aluminium oxide 23 lying above it.
  • the distance d from the anode lower face 24 to the surface of the aluminium 16, also known as interpolar distance, can be varied by raising or lowering the anode beam 21 with the help of jacks 25, which are mounted on pillars 26.
  • these anodes are consumed at their lower face by about 1.5 to 2 cms. daily according to the type of cell.
  • the anodic current density of a cell can not be chosen arbitrarily.
  • the interpolar distance should not go below 4 cms., because otherwise short circuits between metal and anode can occur by reason of electromagnetic forces. Moreover the electrical eificiency (relationship of the amount of aluminium produced to the theoretical amount which could be produced according to Faradays law) is low if the interpolar distance is too small.
  • That density of current must be chosen which produces only so much heat in the electrolyte and in the bottom of the cell, i.e. within the cell bath, as after deduction of the useful energy (that for the decomposition of the aluminium oxide and for heating the raw material to a working temperature of 940 to 975 C. with a suitable covering of aluminium oxide 23 on the solid electrolyte crust) can still be removed.
  • the aluminium oxide covering 23 has several functions. In addition to the function of preparing aluminium oxide for introduction into the molten electrolyte, it must on the one hand protect the anodes from burning away in the air, and on the other hand form a good thermal insulation.
  • the least thickness of aluminium oxide cover 23 on the encrusted surface 22 of the bath can be stated to be about 7 cm. That is the minimum in operational practice.
  • the invention relates to a method of operating a cell of at least 50 ka. for the production of aluminium by electrolysis of aluminium oxide in a molten fluoride bath with pre-baked anodes. With smaller cells there is never developed too much heat.
  • the method comprises operating the cell with that anodic current density with which, with an electrolyte temperature between 940 and 975 C., with an interpolar distance of 5 to 6 cms. and with an aluminium oxide covering of about 14 to 16 cms. thickness on the encrusted surface of the bath, as much heat is produced in the cell as the cell can carry away as losses after deduction of the useful amounts of heat for the decomposition of the aluminium oxide and for heating of the raw materials.
  • FIG. 2 shows the relationship between anodic current density, 1' in a./cm. and the cell current I in ka. for the conditions mentioned. It will be recognised that the anodic current density falls with increasing cell current because the area of the cell in plan must increase more rapidly than the cell current in order to provide sufiicient peripheral wall for the heat dissipation.
  • the specific electrical energy consumption E in kWh/kg. Al is marked, which corresponds to the relevant current density and the associated cell current.
  • anodic current density can be read, which should be provided for according to the invention in relation to the cell current.
  • the current density to be chosen is at 0.67 a./cm.
  • the cell With maintenance of conditions according to the invention, the cell operates in the best range of current density, that is to say with a minimum of production costs.
  • an aluminium oxide layer of about 7 to 8 cms. thickness lies for example on each anode which has passed about half of its insertion time, which protects it from combustion with air.
  • the newer anodes, the upper parts of which extend more out of the aluminium oxide covering are only at a temperature of at the most about 500 C., and are scarcely exposed to burning away in air and require no aluminum oxide covering as protection against the atmospheric oxygen.
  • the interpolar distance is not too small, so that no disturbing magnetic effects can occur; it is also not so high, that unnecessary heat is produced in the electrolyte, that must be carried away out of the cell through artificially increased heat losses.
  • the electrolyte temperature again lies in the optimum range (940 to 975 C.), so that both a good current efiiciency in cells operated according to the invention, and at the same time a low specific consumption of electrical energy can be achieved.
  • a method of operating a cell of at least 50 ka. for the production of aluminium by electrolysis of aluminium oxide in a molten fluoride bath with pre-baked carbon anodes comprising operating the cell with that anodic current density j selected according to FIG. 2 with which, with an electrolyte temperature between 940 and 975 C., with an interpolar distance of to 6 cms., and with an aluminium oxide covering of about 14 to 16 cms. thickness on the encrusted surface of the bath, as much heat is produced in the cell as the cell can carry away as losses after deduction of the useful amounts of heat for the decomposition of the aluminium oxide and for heating of the raw materials.
  • a method of operating a cell of at least ka. for the production of aluminium by electrolysis of aluminium oxide in a 940 to 975 C. hot molten fluoride bath with pre-baked carbon anodes comprising operating the cell simultaneously with an interpolar distance of 5 to 6 cms., with an aluminium oxide covering of about 14 to 16 cms. thickness on the encrusted surface of the bath and with that anodic current density 1' selected according to FIG. 2 with which as much heat is produced in the cell as the cell can carry away as losses after deduction of the useful amounts of heat for the decomposition of the aluminium oxide and for heating of the raw materials.

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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)
US00203383A 1970-12-01 1971-11-30 Method of operating an aluminium oxide reduction cell Expired - Lifetime US3756929A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CH1776370A CH536360A (de) 1970-12-01 1970-12-01 Verfahren für die Gewinnung von Aluminium durch Elektrolyse von Aluminiumoxid im Fluoridschmelzfluss

Publications (1)

Publication Number Publication Date
US3756929A true US3756929A (en) 1973-09-04

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US00203383A Expired - Lifetime US3756929A (en) 1970-12-01 1971-11-30 Method of operating an aluminium oxide reduction cell

Country Status (12)

Country Link
US (1) US3756929A (enrdf_load_stackoverflow)
AR (1) AR192900A1 (enrdf_load_stackoverflow)
AU (1) AU3631871A (enrdf_load_stackoverflow)
BE (1) BE776031A (enrdf_load_stackoverflow)
BR (1) BR7107974D0 (enrdf_load_stackoverflow)
CH (1) CH536360A (enrdf_load_stackoverflow)
DE (1) DE2153293A1 (enrdf_load_stackoverflow)
FR (1) FR2116478A1 (enrdf_load_stackoverflow)
GB (1) GB1328310A (enrdf_load_stackoverflow)
IT (1) IT941804B (enrdf_load_stackoverflow)
NL (1) NL7115830A (enrdf_load_stackoverflow)
NO (1) NO129154B (enrdf_load_stackoverflow)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4045309A (en) * 1975-04-10 1977-08-30 Norsk Hydro A.S Method for measuring and control of the energy in aluminum reduction cells
US6551489B2 (en) 2000-01-13 2003-04-22 Alcoa Inc. Retrofit aluminum smelting cells using inert anodes and method
US6558526B2 (en) 2000-02-24 2003-05-06 Alcoa Inc. Method of converting Hall-Heroult cells to inert anode cells for aluminum production
US20070045104A1 (en) * 2005-08-30 2007-03-01 Alcoa Inc. And Elkem As Method for reducing cell voltage and increasing cell stability by in-situ formation of slots in a soderberg anode
CN102808198A (zh) * 2012-07-27 2012-12-05 中国铝业股份有限公司 一种实现铝电解槽氧化铝浓度稳定控制的方法
RU2586184C1 (ru) * 2015-02-03 2016-06-10 Федеральное государственное автономное образовательное учреждение высшего образования "Сибирский федеральный университет" Способ укрытия анодного массива

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4045309A (en) * 1975-04-10 1977-08-30 Norsk Hydro A.S Method for measuring and control of the energy in aluminum reduction cells
US6551489B2 (en) 2000-01-13 2003-04-22 Alcoa Inc. Retrofit aluminum smelting cells using inert anodes and method
US6558526B2 (en) 2000-02-24 2003-05-06 Alcoa Inc. Method of converting Hall-Heroult cells to inert anode cells for aluminum production
US20070045104A1 (en) * 2005-08-30 2007-03-01 Alcoa Inc. And Elkem As Method for reducing cell voltage and increasing cell stability by in-situ formation of slots in a soderberg anode
US7384521B2 (en) 2005-08-30 2008-06-10 Alcoa Inc. Method for reducing cell voltage and increasing cell stability by in-situ formation of slots in a Soderberg anode
CN102808198A (zh) * 2012-07-27 2012-12-05 中国铝业股份有限公司 一种实现铝电解槽氧化铝浓度稳定控制的方法
RU2586184C1 (ru) * 2015-02-03 2016-06-10 Федеральное государственное автономное образовательное учреждение высшего образования "Сибирский федеральный университет" Способ укрытия анодного массива

Also Published As

Publication number Publication date
BE776031A (fr) 1972-03-16
AR192900A1 (es) 1973-03-21
NO129154B (enrdf_load_stackoverflow) 1974-03-04
FR2116478A1 (enrdf_load_stackoverflow) 1972-07-13
AU3631871A (en) 1973-06-07
IT941804B (it) 1973-03-10
BR7107974D0 (pt) 1973-04-05
CH536360A (de) 1973-04-30
NL7115830A (enrdf_load_stackoverflow) 1972-06-05
DE2153293A1 (de) 1972-06-15
GB1328310A (en) 1973-08-30

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