EP0834601B1 - Procédé de régulation de la température du bain d'une cuve d'électrolyse pour la production d'aluminium - Google Patents

Procédé de régulation de la température du bain d'une cuve d'électrolyse pour la production d'aluminium Download PDF

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Publication number
EP0834601B1
EP0834601B1 EP97420174A EP97420174A EP0834601B1 EP 0834601 B1 EP0834601 B1 EP 0834601B1 EP 97420174 A EP97420174 A EP 97420174A EP 97420174 A EP97420174 A EP 97420174A EP 0834601 B1 EP0834601 B1 EP 0834601B1
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EP
European Patent Office
Prior art keywords
temperature
bath
rthb
process according
setpoint
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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EP97420174A
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German (de)
English (en)
French (fr)
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EP0834601A1 (fr
Inventor
Olivier Bonnardel
Pierre Homsi
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.)
Rio Tinto France SAS
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Aluminium Pechiney SA
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Application filed by Aluminium Pechiney SA filed Critical Aluminium Pechiney SA
Publication of EP0834601A1 publication Critical patent/EP0834601A1/fr
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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 the temperature of the bath.
  • an aluminum production tank by electrolysis of dissolved alumina in an electrolyte based on molten cryolite, according to the Hall-Héroult process.
  • the conduct of an electrolysis tank for the production of aluminum requires keeping its temperature as close as possible to its optimal operating temperature or equilibrium temperature.
  • the tank temperature is given by the maximum temperature at the heart of the tank, that is to say the temperature of the electrolysis bath.
  • the operating conditions of a tank having been previously fixed and thereby the set temperature of the electrolysis bath is through an adjustment energy supplied to the tank compared to the energy consumed or dissipated by it, that it is possible to maintain the temperature of the bath at its setpoint.
  • the aim is to approach the optimal operating conditions, in particular for the equilibrium temperature. Faraday yields of around 95% can thus be reached, or even 96% in the case of acid baths, therefore containing a large excess of AlF 3 which makes it possible to lower the equilibrium temperature to around 950 °. C or even below.
  • Another advantage of a very efficient thermal regulation is to promote the permanent maintenance of a sufficiently solidified bath slope thick on the sides of the tank and thus protect them against erosion, oxidation, chemical attack by liquids and aluminum.
  • This protection of sides by the solidified bath slope obviously promotes the longevity of the pot lining and insofar as this solidified embankment is sufficiently thick, it causes a decrease in the lateral heat flow, hence a reduction in heat losses resulting in a reduction significant energy consumption.
  • thermowell made of silicon nitride or titanium diboride placed in a side wall of the tank at the level of the bath and in which is housed a temperature probe according to FR 2104781 only makes it possible to measure the temperature of the bath 'in the vicinity of the wall and moreover with significant inertia, therefore without the possibility of rapidly detecting small temperature variations (2 to 3 ° C).
  • the temperature measurements of the electrolysis bath are still very often performed manually and periodically by an operator who open the hood or the tank door and immerse a cane in the bath pyrometric.
  • This procedure clearly presents many disadvantages: releases of fluorinated gases into the surrounding atmosphere, operator exposure to these harmful releases, low frequency of these measurements (typically 1 measurement every one or two days) difficult to perform and therefore not ensuring sufficiently monitored temperature control for perform precise and reliable regulation to meet new requirements of modern electrolytic cells.
  • the thermal of the tank reacts quickly to a thermal stress.
  • the tank reacts very quickly to an increase in power, even if the reaction takes its full extent only after a few hours or ten hours due to the thermal inertia of the tank.
  • the chemistry of the bath in particular the excess of AlF 3 , changes only with a significant delay, the effect of an addition of AlF 3 appearing only several tens of hours at several days after the time of the addition.
  • EP 0671488A describes a thermal regulation process according to which a theoretical calculation of the energy dissipated in and by the electrolysis cell in its various forms is periodically carried out: energy necessary for the reduction of alumina but also energy absorbed by the various additives, such as alumina and AIF 3 , as well as by operating operations (changes of anode for example).
  • This dissipated energy is compared to the energy supplied to the tank for a predefined operating speed.
  • the deviations are then corrected by acting on the set resistance, which is increased by increasing the anode-metal distance (DAM), if there is a deficit in the energy supplied, or which is reduced by decreasing the anode-metal distance if there is an excess of energy.
  • DAM anode-metal distance
  • the author's certificate SU 1 183 565 describes a method of regulation temperature according to which the temperature of the bath of the tank and the anode-metal distance is directly and only modified proportionally, on the one hand, to the difference between the last temperature measured and the set temperature, and on the other hand, the difference between the last measured temperature and the previous one.
  • This approach does not hold account of the various disturbances that are part of industrial operations normal electrolytic cells, such as anode changes and solid bath additions, which disturbances cause variations in temperature up to several tens of degrees. For example, after the installation of a new anode, the temperature of the bath drops very quickly and very strongly, especially in the vicinity of this anode.
  • the method according to the invention provides a solution to the problem of individual thermal regulation of electrolytic cells. It consists of acting on the temperature of the tank via the setpoint resistance Ro, which is modulated so as to correct the temperature both in advance and by feedback.
  • the correction in advance known as “a priori”
  • the correction by feedback known as "a posteriori”
  • a posteriori consists, starting from the direct measurement of the bath temperature at regular time intervals electrolysis, to determine an average temperature corrected according periodic operations and to compensate for variations and deviations of this temperature from a set temperature.
  • the corrections are made by regularly adjusting a so-called value of additional resistance, positive or negative, added to the resistance of tank setpoint, so that it warms the tank temperature towards the setpoint and limits variations over time.
  • RTHb is advantageously calculated using a regulator, preferably according to an algorithm comprising a proportional action, integral and derivative.
  • the calculation of RTHb is performed such that, if the corrected average temperature of the bath is lower than the temperature of setpoint, i.e. if ⁇ mc ⁇ o, this additional resistance is increased consequently, if the corrected average temperature ⁇ mc is on the way to decrease we also increase this additional resistance in consequence, if the corrected average temperature is higher than the set temperature, i.e. if ⁇ mc> ⁇ o, this resistance is reduced accordingly and if the corrected average temperature ⁇ mc is in the process of increasing, this additional resistance is also reduced Consequently.
  • the values of RTHb are limited so as to keep them at within an allowable range, including a lower safety threshold (RTHb min) and an upper safety threshold (RTHb max).
  • RTHb min lower safety threshold
  • RTHb max upper safety threshold
  • the values calculated from RTHb which go outside the admissible range are brought back to the closest threshold value.
  • Such a limitation of the values allowed for RTHb make it possible in particular to avoid over-corrections that could cause abnormal temperature values.
  • the bath temperature measurement is a point measurement in space (at a given point in the tank) and over time (at a given point in time a periodic measurement cycle).
  • the temperature of the bath varies at the same time according to the place of the tank where we are placed (at a given time) and according to the time of the measurement (at a given location). If we consider the effect of change of an anode for example, at a given time, the temperature the lower the measured anode is, the closer it is to the point of measure, and over time, the measured temperature is lower as the change of anode is recent.
  • the temperature measurement is therefore not directly usable, even when the tank is in normal and fixed operating conditions, i.e. correctly regulated, stable and avoiding, by appropriate waiting, the direct impact of disturbing operations of operation or adjustment such as change anode, metal casting or specific regulation procedure.
  • the bath temperature must be measured at least once per cycle of thermal regulation Tr corresponding to a work sequence. This measurement can be done manually discontinuously but much more efficiently using a special semi-continuously submerged sensor in the bath and allowing for much greater temperature measurements frequency for example every hour.
  • Figures 1a to 1c illustrate the calculation of the corrected average temperature, which is used to determine the correction term RTHb at item j, in the case where an anode change was made after measuring the temperature at station d - 4 and where the calculation of the average temperature is performed using the temperature values measured at stations j - 3 to j.
  • the figure la corresponds to the case where the changed anode is at a so-called position intermediate with respect to the measurement point, hence the fact that ⁇ is zero.
  • the Figure 1b corresponds to the case where the changed anode is relatively close to the measuring point, hence a positive ⁇ .
  • Figure 1c corresponds to the case where the anode changed is relatively far from the measurement point, resulting in a negative ⁇ .
  • RTHb either the corrected average temperature ⁇ mb, or the temperature corrected mean differential ⁇ md usually called overheating corrected mean, that is to say the 2 parameters at the same time, for example as it is described in the implementation of the invention (example e), where the temperature corrected mean ⁇ mb is chosen as the basic setting parameter for the additional resistance and where the corrected average superheat ⁇ md is taken into account if it exceeds a fixed threshold.
  • the corrected average superheat ⁇ md is used as the setting, the corresponding temperature ⁇ l of the liquidus, traditionally calculated from the chemical composition of bath which should therefore be determined simultaneously during the work sequence considered. Liquidus temperature and overheating can also be obtained by direct measurement on the tank electrolysis using an appropriate device.
  • the additional resistance includes a term RTHa, for which it is required account at certain items, intended to compensate in advance for irregular disturbances but known and quantified as the additions of solid bath, and an RTHb term calculated according to the values of ⁇ mb and ⁇ md compared to the set values, as well as their evolution.
  • DAM anode-metal distance
  • the term RTHb was calculated by a regulator including an action proportional, integral and derived, and in some cases including a term of correction of overheating.
  • the correction coefficient of overheating s was - 0.0150 ⁇ / ° C in the cases described, this coefficient corrector s preferably being in the range - 0.5000 ⁇ / ° C ⁇ s ⁇ 0.0000 ⁇ / ° C.
  • RTHa correction which term was equal to + 0.058 ⁇ in the cases presented (in proportion of the bath addition flow crushed by the automatic device power supply).
  • Cases a) to e) presented below correspond to different situations observed during the months of implementation of the method according to the invention. These cases correspond respectively to Figures 2 to 5, in which the evolution of the values between two successive values is shown in line thin for ⁇ m and thick line for ⁇ mc.
  • An anode change was made during station j - 4, before the temperature measurement, and during station j, also before the temperature measurement.
  • the temperature correction ⁇ determined by the regulator according to the correction tables stored and applied to the average temperature was + 4.2 ° C for station j, which corresponds to the fact that the anode changed at station j was very close to the temperature measurement point, and - 0.9 ° C for station j - 1, which corresponds to the fact that the anode changed at station j - 4 was relatively far from the point of temperature measurement.
  • RTH correction is actually slightly positive because the a priori correction term RTHa, which counterbalances the term of RTHb a posteriori regulation, anticipates cooling.
  • the combined effect of the a posteriori correction term and the a priori correction can largely compensate for a negative deviation, and significant, compared to the set point combined with a tendency to predictable cooling.
  • RTHb value greater than zero and superheat value greater than the set superheat may be subject to certain conditions, namely in this case: RTHb value greater than zero and superheat value greater than the set superheat.
  • the overheating correction can be applied to RTHb in example d).
  • correction coefficients p, i, d and s as well as their ranges of variation were first determined by theoretical calculations using the formulas and calculation tools of the Research Laboratory of Aluminum Fabrications Pechiney. They were then refined experimentally on the basis of the results obtained during the implementation of temperature regulation on test vessels, knowing that the configuration is all the more suitable as it allows bath temperatures to be obtained. more stable and tighter around the target temperature.

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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)
EP97420174A 1996-09-25 1997-09-24 Procédé de régulation de la température du bain d'une cuve d'électrolyse pour la production d'aluminium Expired - Lifetime EP0834601B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR9611962A FR2753727B1 (fr) 1996-09-25 1996-09-25 Procede de regulation de la temperature du bain d'une cuve d'electrolyse pour la production d'aluminium
FR9611962 1996-09-25

Publications (2)

Publication Number Publication Date
EP0834601A1 EP0834601A1 (fr) 1998-04-08
EP0834601B1 true EP0834601B1 (fr) 2000-04-26

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EP97420174A Expired - Lifetime EP0834601B1 (fr) 1996-09-25 1997-09-24 Procédé de régulation de la température du bain d'une cuve d'électrolyse pour la production d'aluminium

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US (1) US5882499A (enrdf_load_stackoverflow)
EP (1) EP0834601B1 (enrdf_load_stackoverflow)
AU (1) AU717983B2 (enrdf_load_stackoverflow)
BR (1) BR9704860B1 (enrdf_load_stackoverflow)
CA (1) CA2215186C (enrdf_load_stackoverflow)
EG (1) EG20880A (enrdf_load_stackoverflow)
ES (1) ES2146967T3 (enrdf_load_stackoverflow)
FR (1) FR2753727B1 (enrdf_load_stackoverflow)
IN (1) IN192036B (enrdf_load_stackoverflow)
NO (1) NO317403B1 (enrdf_load_stackoverflow)
NZ (1) NZ328743A (enrdf_load_stackoverflow)
ZA (1) ZA978544B (enrdf_load_stackoverflow)

Families Citing this family (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2789407B1 (fr) 1999-02-05 2001-03-23 Pechiney Aluminium Arrangement de cuves d'electrolyse pour la production d'aluminium
FR2806742B1 (fr) 2000-03-24 2002-05-03 Pechiney Aluminium Implantation d'installations d'une usine d'electrolyse pour la production d'aluminium
FR2821363B1 (fr) * 2001-02-28 2003-04-25 Pechiney Aluminium Procede de regulation d'une cellule d'electrolyse
US20030057102A1 (en) * 2001-09-24 2003-03-27 Beck Theodore R. Temperature control for low temperature reduction cell
CN101410555A (zh) * 2006-03-24 2009-04-15 通用汽车环球科技运作公司 合成铝烷的装置和方法
US9285280B2 (en) 2013-03-07 2016-03-15 Joel S. Faden Systems and methods of determining load temperatures
RU2730828C1 (ru) * 2020-02-04 2020-08-26 Общество с ограниченной ответственностью "Объединенная Компания РУСАЛ Инженерно-технологический центр" Способ управления технологическим процессом в алюминиевом электролизере
CN120010595B (zh) * 2025-04-22 2025-06-10 鄂尔多斯市蒙泰铝业有限责任公司 一种电解铝硅合金过程的智能温控方法及系统

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3632488A (en) * 1969-01-23 1972-01-04 Reynolds Metals Co Reduction cell control system
NO135034B (enrdf_load_stackoverflow) * 1975-04-10 1976-10-18 Norsk Hydro As
US4333803A (en) * 1980-10-03 1982-06-08 Aluminum Company Of America Method and apparatus for controlling the heat balance in aluminum reduction cells
SU1183565A1 (ru) * 1983-05-30 1985-10-07 Boris D Ovsyannikov Способ регулирования режима работы алюминиевого электролизера
DE3564825D1 (en) * 1985-03-18 1988-10-13 Alcan Int Ltd Controlling alf 3 addition to al reduction cell electrolyte

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ES2146967T3 (es) 2000-08-16
NZ328743A (en) 1999-01-28
CA2215186C (fr) 2003-01-28
BR9704860A (pt) 1998-12-29
FR2753727B1 (fr) 1998-10-23
CA2215186A1 (fr) 1998-03-25
US5882499A (en) 1999-03-16
BR9704860B1 (pt) 2009-01-13
NO974304L (no) 1998-03-26
FR2753727A1 (fr) 1998-03-27
EG20880A (en) 2000-05-31
NO974304D0 (no) 1997-09-18
NO317403B1 (no) 2004-10-25
EP0834601A1 (fr) 1998-04-08
ZA978544B (en) 1998-05-11
IN192036B (enrdf_load_stackoverflow) 2004-02-14
AU717983B2 (en) 2000-04-06
AU3920097A (en) 1998-04-02

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