EP0455590B1 - Régulation et stabilisation de la teneur en A1F3 d'une cave d'électrolyse de l'aluminium - Google Patents

Régulation et stabilisation de la teneur en A1F3 d'une cave d'électrolyse de l'aluminium Download PDF

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EP0455590B1
EP0455590B1 EP91810305A EP91810305A EP0455590B1 EP 0455590 B1 EP0455590 B1 EP 0455590B1 EP 91810305 A EP91810305 A EP 91810305A EP 91810305 A EP91810305 A EP 91810305A EP 0455590 B1 EP0455590 B1 EP 0455590B1
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Prior art keywords
alf3
days
content
addition
time delay
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German (de)
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EP0455590A1 (fr
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Peter Entner
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3A Composites International AG
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Alusuisse Lonza Services Ltd
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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 invention relates to a method for regulating and stabilizing an AlF3 content of at least 10% by weight in the bath of an electrolysis cell for the production of aluminum from aluminum oxide dissolved in a cryolite melt.
  • a bath or an electrolyte which essentially consists of cryolite, a sodium aluminum fluorine compound (3NaF.AlF3).
  • This cryolite in addition to the aluminum oxide to be dissolved, in particular also has substances which lower the melting point, for example aluminum trifluoride AlF3, lithium fluoride LiF, calcium difluoride CaF2 and / or magnesium difluoride MgF2.
  • a bath in an electrolysis cell for the production of aluminum contains 6 to 8% by weight of AlF3, 4 to 6% by weight of CaF2, 1 to 2% by weight of LiF, the rest being cryolite.
  • the melting point of the bath is lowered in the range of 940 to 970 ° C, the industrial temperature range.
  • bath additives do not only have positive effects, e.g. a lowering of the melting point, but often also have a negative effect.
  • the addition of lithium fluoride, for example, does not allow film qualities for capacitors without special metal treatment.
  • the inventor has set itself the task of creating a method of the type mentioned, with which the fluctuations in the AlF3 content and thus the bath temperature can be brought to a small standard deviation even without lithium fluoride additives, for the AlF3 content to about 1 up to 2%.
  • Counteractive additives with neutralizing Effects, such as soda or sodium fluoride, should not be used or should only be used in exceptional cases.
  • AlF3 During aluminum electrolysis there is always a loss of AlF3, on the one hand by evaporation, which does not affect the environment or only to a very small extent in encapsulated aluminum electrolysis cells, and on the other hand by reaction with Na2O contained in the added alumina.
  • AlF3 there are tables listing the units to be added depending on the bath temperature and the AlF3 content to be set. These tables can be refined by using general correction factors such as Cell age, number of anode effects, trend of concentration are taken into account.
  • the measurement and analysis of the individual state of aluminum electrolysis and the determination of the optimal time shift are not only carried out separately for each cell, but also at different intervals, if need be. In the case of healthy, normally working cells, this is preferably done every 1 to 2 months, in the case of poor oven operation, repeated 1 to 5 days apart from the program until the oven operation improves and the intervals can be extended again. Thanks to the individual, up-to-date recording of the cell status, general Tables that do not take into account either the cell type or its condition are omitted.
  • the measurement of the AlF3 content can be replaced by a temperature measurement. This is not only easier, but inevitably records a temperature dependency of the AlF3 content and can be used directly.
  • the most important parameters for the model calculation used according to the invention are the flux mass M and the daily AlF3 losses v. These parameters are calculated from measurements of the concentration c and the additions z of AlF3 in the electrolyte over a period t1 of preferably 10 to 60 days, in particular 20 to 30 days.
  • the period t 1 is so short on the one hand that the individual condition of a cell can currently be recorded, but on the other hand so long that random, short-term changes without a trend are not taken into account.
  • the calculated flux mass M and daily AlF3 losses v are included in the model calculation and calculated with time shifts ZV of preferably 1 to 10 whole days.
  • the best parameter set is selected in accordance with known statistical criteria and the addition z of AlF3 is calculated by specifying an AlF3 content c of between 10 and 15% by weight.
  • the specification for the AlF3 content c depends on the electrolysis temperature which is considered optimal. This can be obtained, for example, with about 12% by weight aluminum fluoride.
  • the best parameter set containing the time shift ZV is used for the addition of z of aluminum fluoride for the next n days.
  • M the flux mass
  • c s the target value for the AlF3 content
  • c m the instantaneous value for the AlF3 content
  • v the daily AlF3 loss.
  • the period of n days should generally not be greater than the period t 1 during which the basics for determining the parameters were measured.
  • the time period is corrected by the time difference ZV.
  • a modified formula can be used to predict how high the aluminum fluoride content c x should be on the day t x according to the model calculation.
  • the model can be checked for suitability by a measurement on the relevant day t x and adjusted if necessary.
  • intraday values can also be used to determine the optimal time shift ZV for the AlF3 addition z can be entered. Since the optimal time shift ZV determined for the addition of aluminum fluoride for electrolysis cells used in the aluminum industry is generally in the range from 2 to 5 days, in particular 3 days, according to a further developed embodiment of the invention, intraday time shifts ZV are calculated in this period and listed to determine the best parameter set. The rough grid for the time shift ZV can be brought down to the fineness required in practice by the introduction of a decimal place.
  • the aluminum fluoride is conventionally introduced in bags, more modern cells work with dosing devices, and increasingly the dense phase conveyance is used.
  • the metering devices or devices are preferably controlled by a process computer and release the aluminum fluoride in portions or continuously.
  • the fluctuations in the AlF3 concentration in the electrolyte can be reduced to a standard deviation of 1 to 2%, which in a concentration range of 10 to 15% by weight of aluminum fluoride leads to simplified process control and a well-known increase in the production of aluminum. Excessive target values can be prevented, as can the addition of an antidote such as soda or sodium fluoride. Electrolyte additives, such as lithium fluoride, which have a detrimental effect in certain uses, are not necessary.
  • Fig. 1 the typical time course of the AlF3 concentration (wt .-%) with the corresponding AlF3 additions in kg / day is given. You can see the strong fluctuations between 5 and 15% of the AlF3 excess, caused by the delayed reaction of the electrolytic cell to the AlF3 addition.
  • Table II shows the calculation of the optimal addition for stabilizing the AlF3 concentration.

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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)
  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)

Claims (10)

  1. Procédé pour la régulation et la stabilisation d'une teneur en AlF₃ (c) étant au moins égale à 10 % en poids dans un bain d'une cellule d'électrolyse destinée à la préparation d'aluminium à partir d'oxyde d'aluminium dissous dans une masse fondue de cryolithe, caractérisé en ce qu'on analyse l'état individuel d'une cellule d'électrolyse d'aluminium, en particulier de sa cuve cathodique en carbone pendant une période (t₁) au moins à partir de mesures de la concentration (c) et des additions (z) d'AlF₃ dans l'électrolyte, on calcule la masse en fusion (M) et les pertes journalières en AlF₃ (v), on choisit avec un calcul de modèle le délai optimal (ZV) entre l'addition d'AlF₃ et son effet dans l'électrolyte selon des critères statistiques, on calcule les additions (z) d'AlF₃ en se donnant auparavant une valeur de consigne de la teneur en AlF₃ (c) dans un certain domaine en considérant le délai (ZV) et on ajoute AlF₃ par portions ou en continu.
  2. Procédé selon la revendication 1, caractérisé en ce qu'on répète l'analyse de l'état individuel d'une cellule d'électrolyse d'aluminium et la recherche du délai optimal (ZV) tous les 1 à 2 mois pour une cellule travaillant normalement, selon un écart de 1 à 5 jours en dehors du programme pour une mauvaise descente de la charge.
  3. Procédé selon la revendication 1 ou 2, caractérisé en ce qu'on effectue la mesure de la teneur en AlF₃ par une mesure de température.
  4. Procédé selon l'une quelconque des revendications 1 à 3, caractérisé en ce qu'on calcule la masse en fusion (M) et les pertes journalières en AlF₃ (v) à partir de mesures de la concentration (c) et des additions (z) d'AlF₃ dans l'électrolyte pendant une période (t₁) de 10 à 60 jours, de préférence de 20 à 30 jours, et on utilise dans le calcul de modèle des délais (ZV), de préférence de 1 à 10 jours entiers, on choisit le meilleur jeu de paramètres selon des critères statitiques et on calcule l'addition (z) d'AlF₃ en se donnant préalablement une teneur en AlF₃ comprise entre 10 et 15 % en poids.
  5. Procédé selon l'une quelconque des revendications 1 à 4, caractérisé en ce qu'on calcule l'addition (z) d'AlF₃ pour les n prochains jours en appliquant le meilleur jeu de paramètres contenant le délai (ZV) selon la formule

    z = M . (c s - c m ) + n . v
    Figure imgb0009

    M indiquant la masse en fusion, cs la valeur de consigne pour la teneur en AlF₃, cm la valeur instantanée pour la teneur en AlF₃ et v la perte journalière en AlF₃.
  6. Procédé selon la revendication 5, caractérisé en ce que, pour une valeur d'addition négative (z) pour AlF₃, on neutralise avec du carbonate de sodium ou du fluorure de sodium ou en adaptant la tension.
  7. Procédé selon la revendication 6, caractérisé en ce qu'on ajoute le carbonate de sodium selon la formule
    Figure imgb0010
  8. Procédé selon l'une quelconque des revendications 1 à 7, caractérisé en ce qu'on introduit pour le calcul de modèle pour la recherche du délai optimal (ZV) pour l'addition d'AlF₃ (z) des valeurs de la journée affinée, de préférence dans un domaine de 2 à 5 jours.
  9. Procédé selon l'une quelconque des revendications 4 à 8, caractérisé en ce que la position de la matière en fusion dans la cellule d'électrolyse d'aluminium, son bilan thermique et/ou la chute de tension sont intégrés comme affinement dans le calcul du modèle pour la recheche du délai (ZV) et de l'addition (z) d'AlF₃.
  10. Procédé selon l'une quelconque des revendications 1 à 9, caractérisé en ce qu'on ajoute AlF₃ par sacs ou avec un dispositif de dosage commandé par un ordinateur.
EP91810305A 1990-05-04 1991-04-24 Régulation et stabilisation de la teneur en A1F3 d'une cave d'électrolyse de l'aluminium Expired - Lifetime EP0455590B1 (fr)

Applications Claiming Priority (2)

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CH152790 1990-05-04
CH1527/90 1990-05-04

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EP0455590B1 true EP0455590B1 (fr) 1995-06-28

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Country Status (9)

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US (1) US5094728A (fr)
EP (1) EP0455590B1 (fr)
AU (1) AU643006B2 (fr)
CA (1) CA2041440A1 (fr)
DE (1) DE59105830D1 (fr)
ES (1) ES2075401T3 (fr)
IS (1) IS1632B (fr)
NO (1) NO304748B1 (fr)
ZA (1) ZA913260B (fr)

Families Citing this family (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19805619C2 (de) 1998-02-12 2002-08-01 Heraeus Electro Nite Int Verfahren zur Regelung des AlF¶3¶-Gehaltes in Kryolithschmelzen
FR2821364B1 (fr) * 2001-02-28 2004-04-09 Pechiney Aluminium Procede de regulation d'une cellule d'electrolyse
FR2821363B1 (fr) * 2001-02-28 2003-04-25 Pechiney Aluminium Procede de regulation d'une cellule d'electrolyse
EP1344847A1 (fr) * 2001-12-03 2003-09-17 Alcan Technology & Management AG Régulation d'une cave d'électrolyse de l'aluminium
CA2901615C (fr) * 2013-03-13 2018-01-02 Alcoa Inc. Systemes et procedes permettant de proteger les parois laterales de cellule d'electrolyse
CN104451779B (zh) * 2014-12-17 2017-01-18 湖南创元铝业有限公司 铝电解槽氟化铝控制方法
WO2020190271A1 (fr) * 2019-03-16 2020-09-24 General Electric Company Système et procédé de commande de conduite de creuset de fusion

Family Cites Families (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3380897A (en) * 1964-11-16 1968-04-30 Reynolds Metals Co Method of determining ore concentration
US3471390A (en) * 1965-03-24 1969-10-07 Reynolds Metals Co Alumina concentration meter
NO166821C (no) * 1985-02-21 1991-09-04 Aardal & Sunndal Verk As Fremgangsmaate for styring av aluminiumoksyd-tilfoerselen til elektrolyseovner for fremstilling av aluminium.
EP0195142B1 (fr) * 1985-03-18 1988-09-07 Alcan International Limited Procédé pour réguler l'addition de AlF3 à l'électrolyte d'une cuve d'électrolyse pour la production d'aluminium
FR2581660B1 (fr) * 1985-05-07 1987-06-05 Pechiney Aluminium Procede de regulation precise d'une faible teneur en alumine dans une cuve d'electrolyse ignee pour la production d'aluminium
US4654130A (en) * 1986-05-15 1987-03-31 Reynolds Metals Company Method for improved alumina control in aluminum electrolytic cells employing point feeders
US4814050A (en) * 1986-10-06 1989-03-21 Aluminum Company Of America Estimation and control of alumina concentration in hall cells
FR2620738B1 (fr) * 1987-09-18 1989-11-24 Pechiney Aluminium Procede de regulation de l'acidite du bain d'electrolyse par recyclage des produits fluores emis par les cuves d'electrolyse hall-heroult

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CA2041440A1 (fr) 1991-11-05
DE59105830D1 (de) 1995-08-03
AU643006B2 (en) 1993-11-04
US5094728A (en) 1992-03-10
AU7601591A (en) 1991-11-07
NO911708D0 (no) 1991-04-30
ES2075401T3 (es) 1995-10-01
IS1632B (is) 1996-07-19
EP0455590A1 (fr) 1991-11-06
NO304748B1 (no) 1999-02-08
NO911708L (no) 1991-11-05
ZA913260B (en) 1992-01-29
IS3698A7 (is) 1991-11-05

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