EP2440689B1 - System and method for recovering energy - Google Patents

System and method for recovering energy Download PDF

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Publication number
EP2440689B1
EP2440689B1 EP10734229.7A EP10734229A EP2440689B1 EP 2440689 B1 EP2440689 B1 EP 2440689B1 EP 10734229 A EP10734229 A EP 10734229A EP 2440689 B1 EP2440689 B1 EP 2440689B1
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Prior art keywords
fumes
gases
heat
electrolytic cell
collected
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EP10734229.7A
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German (de)
French (fr)
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EP2440689A1 (en
Inventor
El Hani Bouhabila
Thierry Malard
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Fives Solios SA
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Fives Solios SA
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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
    • C25C3/22—Collecting emitted gases

Definitions

  • the present invention relates to a system and a method for recovering energy released by an igneous electrolysis cell during the manufacture of aluminum.
  • an electrolytic cell having a heat exchanger in its walls is difficult to manufacture, and it is very difficult to ensure the maintenance of the exchanger, and its possible replacement.
  • the present invention is intended to provide a simpler energy recovery system and some embodiments allow greater energy recovery.
  • an igneous electrolysis cell 2 comprises a parallelepipedal box 4 open at its upper base and whose bottom carries carbonaceous blocks constituting the cathode 6.
  • This box 4 contains an electrolyte bath 8 constituted by alumina dissolved in the cryolite, brought to a temperature between 950 ° and 1000 ° C.
  • anodes 10 are immersed.
  • the alumina is decomposed into aluminum 12 forming a metal bath which covers the cathode 6, and oxygen which reacts with each anode 10 and causes the progressive combustion.
  • the aluminum 12 is regularly removed from the electrolysis cell 2.
  • the upper part of the electrolyte bath 8 is solidified, thus constituting a crust 14 which covers the bath 8 and thermally insulates it.
  • the reaction at each anode 10 gives rise to an emission of fumes and gases 18, 29 which migrate to the top of the tank comprising pollutants such as carbon dioxide and carbon monoxide, sulfur dioxide, gaseous hydrogen fluoride (HF), carbon and alumina particles, dusts and fluorinated compounds.
  • pollutants such as carbon dioxide and carbon monoxide, sulfur dioxide, gaseous hydrogen fluoride (HF), carbon and alumina particles, dusts and fluorinated compounds.
  • the decomposition of the alumina causes a decrease in its content in the electrolyte bath 8.
  • a movable tubular steel rod installed between two anodes 10, pierces the crust 14 and Alumina is injected into the electrolyte bath 8.
  • This rod hereinafter referred to as a metering injector 16, is operable in a vertical movement by means of a jack, preferably pneumatic, to pierce the crust 14.
  • the energy recovery system 22 comprises a primary circuit 24 for collecting the fumes and gases produced by the electrolytic cell 2, and a heat exchange loop 26, ci after called the first heat exchange loop 26.
  • the primary circuit 24 includes a flue gas recovery device 28 arranged to cause a depression under the hood 20 and to suck fumes and gases 29 situated between the latter and the crust 14, and a unit 30 for treating these gases. smoke and gas 29, hereinafter called the first processing unit 30.
  • the cover 20 is not hermetic and outside air is sucked under the hood 20 by the leaks due to the depression. This air mixes in large quantities with the fumes and gases coming from the tank. In the rest of the text we will no longer distinguish this air smoke and gas and we will call by the generic terms smoke and gas.
  • the fumes and gases 29 are sucked by the recovery device 28 with a specific flow rate of about 75,000 to 100,000 Nm 3 / ton Aluminum (which corresponds to 8400 to 11000 Nm 3 / h for a tank of 350 kA).
  • the fumes and gases 29 collected by the primary circuit 24 have a temperature of about 110 - 160 ° C. They contain 200 - 800 mg / Nm 3 of dust, 150 - 400 mg / Nm 3 of gaseous hydrogen fluoride and 100 - 400 mg / Nm 3 of sulfur dioxide (SO 2 ). These fumes and gases collected by the primary circuit are referenced hereinafter by the reference 29.
  • the first treatment unit 30 is able to filter the dust contained in the fumes and gases 29 collected by the recovery device 28, and to eliminate most of the hydrogen fluoride gas by adsorption of hydrogen fluoride gas from these fumes. and gas on alumina which is then separated from the fumes and gases 29 by filtering.
  • the first processing unit 30 is adapted to treat the fumes and gases 29 according to a dry process known under the name "DRY-SCRUBBER DS". This method allows a dust reduction greater than 98% by filtration and a reduction of hydrogen fluoride gas of about 99.8% by adsorption and filtration.
  • the amount of hydrogen fluoride gas contained in the fumes and gases leaving the first treatment unit 30 is less than 0.5 mg / Nm 3 .
  • the amount of dust contained in the fumes and gases coming out of the first treatment unit 30 is less than 5 mg / Nm 3 .
  • the fluorinated alumina generated by the treatment of fumes and gases 29 by the first treatment unit 30 is introduced into the electrolytic cell 2 by means of the metering piercer 16.
  • the primary circuit 24 further comprises a scrubber 32 with seawater or with a basic solution capable of eliminating, by absorption and chemical reaction, the sulfur dioxide (SO 2 ) contained in the fumes and gases leaving the first treatment unit 30, and a chimney 34 capable of evacuating the remaining fumes and purified gases.
  • a scrubber 32 with seawater or with a basic solution capable of eliminating, by absorption and chemical reaction, the sulfur dioxide (SO 2 ) contained in the fumes and gases leaving the first treatment unit 30, and a chimney 34 capable of evacuating the remaining fumes and purified gases.
  • the flue gases 29 comprise less than 60 mg / Nm 3 of sulfur dioxide.
  • the first heat exchange loop 26 comprises a heat exchanger 36, hereinafter called the first heat exchanger 36, and a heat recovery unit 38 of a heat transfer fluid.
  • the loop 26 is traversed, on the one hand, by the coolant, and on the other hand, at the level of the first heat exchanger 36, by the fumes and gases 29 leaving the recovery device 28 before they pass through the first treatment unit 30.
  • the heat transfer fluid heated by the first heat exchanger 36 is used, for example, to produce electricity by an ORC cycle generator, that is to say a generator.
  • Organic Rankine Cycle is used, for example, to produce electricity by an ORC cycle generator, that is to say a generator.
  • Organic Rankine Cycle is for example constituted by water, oil or an inert gas.
  • the first heat exchanger 36 is disposed outside the electrolysis cell 2. For example, it is disposed at a predefined distance greater than or equal to one meter from the electrolytic cell 2 to avoid any risk of contact between the heat transfer fluid and the electrolysis cell 2.
  • the first heat exchanger 36 is able to cool the fumes and gases 29 of the primary circuit 24 by a temperature of 110-160 ° C. at a temperature of 70-100 ° C.
  • a bypass line 39 is installed on the primary circuit 24 at each end of the first heat exchanger 36 to allow the fumes and gases 29 to bypass the first heat exchanger 36, when it is dirty and must be cleaned or replaced or renovated.
  • the energy recovery method begins with a step 100 of collecting fumes and gases 29 by the recovery device 28.
  • the fumes and gases 29 collected by the primary circuit 24 are transported outside and away from the electrolysis cell 2.
  • the heat transfer fluid of the first heat exchange loop 26 is warmed by passing fumes and gases 29 through the first heat exchanger 36.
  • the recovery unit 38 recovers heat from the heat transfer fluid that has passed through the first heat exchanger 36.
  • the processing unit 30 processes the fumes and gases 29 collected by the primary circuit 24 by filtering the dust and removing most of the hydrogen fluoride gas. Then, the fluorinated alumina generated by the first treatment unit 30 is introduced into the electrolyte bath 8 by the metering injector 16.
  • step 116 part of the sulfur dioxide contained in the fumes and gases 29 collected by the primary circuit 24 is removed by absorption and chemical reaction, by the washer 32.
  • the primary circuit 24 does not include a scrubber 32.
  • the step 116 is not performed.
  • the fumes and gases 29 leaving the first treatment unit 30 are directly discharged through the chimney 34.
  • the recovery unit 38 is a system for using the heat of the coolant to produce cold or heat.
  • the recovery system 40 according to the second embodiment of the invention, illustrated on the figure 3 , comprises a primary circuit 24 similar to the primary circuit 24 of the recovery system 22 according to the first embodiment of the invention, with the exception that this circuit does not include a washer 32.
  • the fumes and gases 29 collected by the recovery device 28 of the primary circuit 24 are sucked at a rate of 70000 to 100000 Nm 3 / ton of aluminum product. They comprise 100-800 mg / Nm 3 of dust, 30-100 mg / Nm 3 of hydrogen fluoride gas, 20-100 mg / Nm 3 of sulfur dioxide, 2-4 g / Nm 3 of carbon dioxide and 0.1 - 0.3 g / Nm 3 of carbon monoxide. These fumes and gases collected by the primary circuit are referenced hereinafter by the reference 29.
  • These fumes and gases 29 collected by the primary circuit have a temperature of about 110-160 ° C. before passing through the first heat exchanger 36, and a temperature of about 70-100 ° C. at the outlet of the first heat exchanger. 36.
  • the fumes and gases 29 comprise less than 5 mg / Nm3 dust and less than 0.5 mg / Nm 3 of gaseous hydrogen fluoride.
  • the recovery system 40 according to the second embodiment comprises a first heat exchange loop 26 similar to the heat exchange loop 26 of the recovery system 22 according to the first embodiment of the invention, with the exception of that this first heat exchange loop 26 further comprises a second heat exchanger 42.
  • the second heat exchanger 42 is disposed outside and at a distance of at least one meter from the electrolytic cell.
  • the second heat exchanger 42 is disposed downstream of the first heat exchanger 36, that is to say that the coolant passes first through the first heat exchanger 36 and then the second heat exchanger 42 before join the recovery unit 38.
  • the recovery system 40 further includes a secondary circuit 44 for collecting a portion of the fumes and gases 18 produced by the electrolysis cell 2.
  • the fumes and gases collected by the secondary circuit 44 are referenced hereinafter by the reference 18.
  • This secondary circuit 44 comprises a hood, hereinafter called “local hood” 46 directly embedded in the crust 14 which collects the fumes and gases 18, also called anodic gases, escaping through the hole drilled by the metering piercer 16.
  • Local hood 46 houses dosing device 16. Local hood 46 is connected to a flue gas collection tube 48.
  • An opening 50 made in the local hood 46 can suck fumes and gases 29 collected by the primary circuit 24 and located under the hood 20 to lower the temperature of the fumes and gases 18 collected by the secondary circuit 44 and sucked by the hood Local 46.
  • the opening 50 in the local hood can be set to change the ratio of smoke and gas collected by the primary circuit / fumes and gases collected by the secondary circuit to act on the anodic gas capture efficiency and the resulting temperature of the mixture.
  • 4 to 6 local hoods 46 can be installed in an electrolysis cell 2 from 300 to 400 kA to ensure a good distribution of the suction and capture the maximum of fumes and gases 18.
  • the pipes between the second heat exchanger 42 and each local hood 46 may be insulated to avoid energy losses that would be important given the small diameter of the pipes.
  • the fumes and anodic gas 18 collected by the secondary circuit 44 contain 1.2 - 8 g / Nm 3 of gaseous fluorine, 1-8 g / Nm 3 of sulfur dioxide, 110-280 g / Nm 3 of carbon dioxide and 10-26 g / Nm 3 of carbon monoxide.
  • They have a temperature of about 200-350 ° C. before passing through the second heat exchanger 42, and a temperature of about 70-100 ° C. after passing through the second heat exchanger 42.
  • the secondary circuit 44 further comprises a processing unit 52, hereinafter called a second processing unit 52, a washer 53 and a capture unit 54 connected to the chimney 34.
  • the second processing unit 52 is similar to the first processing unit 30 situated in the primary circuit 24. It is capable of removing most of the hydrogen fluoride gas from the fumes and gases 18 collected by the secondary circuit 44 by adsorption and filtering.
  • the second processing unit 52 uses partially fluorinated alumina obtained by the treatment of the fumes and gases 29 collected by the primary circuit 24 by the first treatment unit 30. Then, the fluorinated alumina generated by the second processing unit 52 is introduced into the electrolytic cell 2 by the metering injector 16.
  • the fumes and gases 18 collected by the secondary circuit 44 comprise a value of the order of 1 mg / Nm 3 of gaseous hydrogen fluoride.
  • the scrubber 53 is similar to the scrubber 32 described in the first embodiment of the invention. At the outlet of the scrubber 53, the fumes and gases 18 collected by the secondary circuit 44 have a value of less than 30 mg / Nm 3 of sulfur dioxide. They have a temperature of about 30-40 ° C.
  • the capture unit 54 is intended to capture the carbon dioxide by absorption with a solution of ammonia or with amines or other equivalent techniques.
  • the energy recovery method starts with the same steps 100 and 102 as the recovery method according to the first embodiment of the invention.
  • the fumes and gases 18 located between the crust 14 and the electrolyte bath 8 are collected by the secondary circuit 44, via the local hoods 46.
  • the fumes and gases 18 collected by the secondary circuit 44 pass through the second heat exchanger 42 and heat the preheated heat transfer fluid that has already passed through the first heat exchanger 36.
  • steps 112 and 114 which are identical to steps 112 and 114 of the method illustrated in FIG. figure 2 .
  • the hydrogen fluoride gas of the fumes and gases 18 collected by the secondary circuit 44 is treated by the second processing unit 52.
  • This treatment is similar to the treatment carried out by the first treatment unit 30. the exception that the partially fluorinated alumina generated by the treatment of fumes and gases 29 collected by the primary circuit 24 is used to adsorb the hydrogen fluoride gas from the fumes and gases 18 collected by the secondary circuit 44.
  • the fluorinated alumina is introduced into the electrolyte bath 8 by the metering piercer 16.
  • the fresh alumina is used to adsorb the gaseous hydrogen fluoride of the fumes and gases containing the least pollutants, that is to say the fumes and gases 29 collected by the primary circuit 24, and is then reused to adsorb the gaseous hydrogen fluoride gas and gas 18 containing a higher concentration of pollutants, that is to say the fumes and gases 18 collected by the secondary circuit 44.
  • a mixture, possibly in varying proportions, of fresh alumina and partially fluorinated alumina may be used in second processing unit 52.
  • a step 117 the majority of the sulfur dioxide contained in the fumes and gases 18 collected by the secondary circuit 44 is removed by a washer 53.
  • the capture unit 54 eliminates by absorption or by other techniques (adsorption, membrane filtration, etc.) a portion of the carbon dioxide from the fumes and gases from the scrubber 53.
  • the fumes and gases 29 treated by the treatment unit 30 and the fumes and gases treated by the capture unit 54 are discharged through the stack 34.
  • the secondary circuit 44 does not include a capture unit 54.
  • the fumes and gases leaving the scrubber 53 are directly directed towards the chimney 34.
  • a washer is disposed on the primary circuit 24 between the treatment unit 30 and the chimney 34.
  • bypass line 39 is mounted on either side of one of the first 36 and the second 42 heat exchangers to allow short-circuiting, for example, during the cleaning of these heat exchangers .
  • the recovery system 56 according to a third embodiment of the invention, represented on the figure 5 , comprises a primary circuit 24 and a secondary circuit 44 identical to the primary circuits 24 and secondary 44 of the recovery system 40 according to the second embodiment of the invention.
  • the recovery system 56 further comprises a first 26 and a second 62 heat exchange loops.
  • the first heat exchange loop 26 of the third embodiment is similar to the first heat exchange loop 26 of the recovery system 40 of the second embodiment of the invention with the exception of the existence of a third heat exchanger 60, also outside the tank 2.
  • the third heat exchanger 60 is disposed downstream of the second heat exchanger 42, that is to say that the heat transfer fluid first passes through, the first heat exchanger 36 then, the second heat exchanger 42 and, finally, the third heat exchanger 60 before joining the recovery unit 38.
  • the temperature of the coolant of the first loop 26 is about 80-100 ° C at the inlet of the first heat exchanger 36, about 100 ° -120 ° C at the inlet of the second heat exchanger 42, about 150 ° - 250 ° C at the inlet of the third heat exchanger 60, and finally about 200 ° - 400 ° C at the outlet thereof.
  • the second heat exchange loop 62 comprises a pipe traversed by an intermediate heat transfer fluid.
  • the pipe passes through at least one lateral wall 64 of the electrolytic cell 2 and then the third heat exchanger 60.
  • the intermediate heat transfer fluid comprises, for example, helium, air or other gas inert vis-a-vis the liquid aluminum.
  • the intermediate heat transfer fluid recovers the heat from the walls 64 of the tank, and delivers it to the third exchanger 60. Before entering the third exchanger 60, the temperature of the intermediate heat transfer fluid is between 250-600 ° C.
  • the energy recovery method according to the third embodiment of the invention is identical to the recovery method according to the second embodiment, with the exception that it comprises between steps 106 and 112, a step 108 and a step 110.
  • step 108 the intermediate heat transfer fluid of the second heat exchange loop 62 passes through the wall or walls 64 of the electrolytic cell and is thus heated.
  • step 110 the intermediate heat transfer fluid passes through the third heat exchanger 60 and thus heats the coolant of the first heat exchange loop 26 already preheated in the exchangers 36 and 42.
  • the recovery unit 38 generates electricity from the heat recovered by the coolant having passed through the first 36, the second 42, and the third 60 heat exchangers.
  • branch lines 39 are mounted on either side of the second heat exchanger 42 to allow short-circuiting, for example, during the cleaning of this heat exchanger.
  • a scrubber 32 is further installed between the processing unit 30 and the chimney 34 in the second and third embodiments of the invention.
  • the recovery system 40, 56 of the second and third embodiments of the invention comprises two different smoke and gas treatment circuits having different pollutant percentages and different temperatures.
  • Each circuit 24, 44 for treating fumes and gases is adapted to the pollutant levels therein.
  • the recovery systems 40, 56 of the second and third embodiments make it possible to increase the efficiency of the first heat exchange loop 26 by passing fumes and gases at medium temperature in a first heat exchanger 36, then the passage fumes and gases at a higher temperature in a second heat exchanger 42, and optionally in a third heat exchanger 60 at an even higher temperature.
  • the recovery system 56 comprises two heat exchange loops 26, 62 able to recover the energy, one of the walls 64 of the electrolysis cell, the other, the energy of the two circuits 24, 44 for treating fumes and gases.

Description

La présente invention concerne un système et un procédé de récupération d'énergie dégagée par une cuve d'électrolyse ignée lors de la fabrication d'aluminium.The present invention relates to a system and a method for recovering energy released by an igneous electrolysis cell during the manufacture of aluminum.

Le document US 7,465,379 décrit un système de récupération d'énergie comprenant une boucle d'échange thermique comportant un échangeur de chaleur implanté dans les parois de la cuve d'électrolyse, par exemple par le montage d'un tube en serpentin dans les parois de la cuve pour récupérer la chaleur de celle-ci.The document US 7,465,379 discloses an energy recovery system comprising a heat exchange loop having a heat exchanger implanted in the walls of the electrolysis cell, for example by mounting a serpentine tube in the walls of the tank to recover the heat of it.

Le document US 4,222,841 décrit une cuve d'électrolyse comportant un système de récupération d'énergie incluant trois échangeurs de chaleurs disposés en différentes parties de la cellule et distribuant leur fluide caloporteur à une canalisation commune.The document US 4,222,841 discloses an electrolysis cell comprising an energy recovery system including three heat exchangers arranged in different parts of the cell and distributing their heat transfer fluid to a common pipe.

Toutefois, une cuve d'électrolyse comportant un échangeur de chaleur dans ses parois, est difficile à fabriquer, et il est très difficile d'assurer la maintenance de l'échangeur, et son remplacement éventuel.However, an electrolytic cell having a heat exchanger in its walls, is difficult to manufacture, and it is very difficult to ensure the maintenance of the exchanger, and its possible replacement.

La présente invention a notamment pour but de proposer un système de récupération d'énergie plus simple et dont certains modes de réalisation autorisent une récupération d'énergie plus importante.The present invention is intended to provide a simpler energy recovery system and some embodiments allow greater energy recovery.

A cet effet, l'invention a pour objet une cuve d'électrolyse ignée et un système de récupération d'énergie dégagée par la cuve d'électrolyse ignée selon la revendication 1. L'invention a également pour objet un procédé de récupération d'énergie dégagée par une cuve d'électrolyse ignée lors de la fabrication d'aluminium selon la revendication 8. L'invention sera mieux comprise à la lecture de la description qui va suivre, donnée uniquement à titre d'exemple, et faite en se référant aux dessins sur lesquels :

  • la figure 1 est une vue schématique en coupe d'une cuve d'électrolyse et d'un système de récupération d'énergie selon un premier mode de réalisation de l'invention ;
  • la figure 2 est un diagramme illustrant les étapes du procédé de récupération d'énergie selon le premier mode de réalisation de l'invention ;
  • la figure 3 est une vue schématique en coupe d'une cuve d'électrolyse et d'un système de récupération d'énergie selon un second mode de réalisation de l'invention ;
  • la figure 4 est un diagramme illustrant les étapes du procédé de récupération d'énergie selon le second mode de réalisation de l'invention ;
  • la figure 5 est une vue schématique en coupe d'une cuve d'électrolyse et d'un système de récupération d'énergie selon un troisième mode de réalisation de l'invention ; et
  • la figure 6 est un diagramme illustrant les étapes du procédé de récupération d'énergie selon le troisième mode de réalisation de l'invention.
For this purpose, the subject of the invention is an igneous electrolysis cell and a system for recovering energy released by the igneous electrolysis cell according to claim 1. The subject of the invention is also a method of recovering energy released by an igneous electrolysis cell during the manufacture of aluminum according to claim 8. The invention will be better understood on reading the following description, given only by way of example, and made with reference to the drawings in which:
  • the figure 1 is a schematic sectional view of an electrolysis cell and a system for energy recovery according to a first embodiment of the invention;
  • the figure 2 is a diagram illustrating the steps of the energy recovery method according to the first embodiment of the invention;
  • the figure 3 is a schematic sectional view of an electrolysis cell and a system for energy recovery according to a second embodiment of the invention;
  • the figure 4 is a diagram illustrating the steps of the energy recovery method according to the second embodiment of the invention;
  • the figure 5 is a schematic sectional view of an electrolysis cell and a system for energy recovery according to a third embodiment of the invention; and
  • the figure 6 is a diagram illustrating the steps of the energy recovery method according to the third embodiment of the invention.

Les éléments identiques ou analogues des premier, deuxième et du troisième modes de réalisation du système de récupération d'énergie sont désignés ci-après par les mêmes références et ne sont décrits qu'une seule fois.The same or similar elements of the first, second and third embodiments of the energy recovery system are hereinafter referred to by the same references and are described only once.

En référence à la figure 1, une cuve d'électrolyse ignée 2 comprend un caisson 4 parallépipédique ouvert à sa base supérieure et dont le fond porte des blocs carbonés constituant la cathode 6. Ce caisson 4 contient un bain d'électrolyte 8 constitué par de l'alumine dissoute dans de la cryolithe, porté à une température comprise entre 950° et 1 000° C. Dans ce bain 8, une ou plusieurs anodes 10 sont plongées. Lorsqu'un courant électrique est appliqué entre les anodes 10 et la cathode 6, l'alumine se décompose en aluminium 12 formant un bain métallique qui recouvre la cathode 6, et en oxygène qui réagit avec chaque anode 10 et en provoque la combustion progressive.With reference to the figure 1 an igneous electrolysis cell 2 comprises a parallelepipedal box 4 open at its upper base and whose bottom carries carbonaceous blocks constituting the cathode 6. This box 4 contains an electrolyte bath 8 constituted by alumina dissolved in the cryolite, brought to a temperature between 950 ° and 1000 ° C. In this bath 8, one or more anodes 10 are immersed. When an electric current is applied between the anodes 10 and the cathode 6, the alumina is decomposed into aluminum 12 forming a metal bath which covers the cathode 6, and oxygen which reacts with each anode 10 and causes the progressive combustion.

L'aluminium 12 est régulièrement retiré de la cuve d'électrolyse 2.The aluminum 12 is regularly removed from the electrolysis cell 2.

La partie supérieure du bain d'électrolyte 8 est solidifiée, constituant ainsi une croûte 14 qui recouvre le bain 8 et l'isole thermiquement.The upper part of the electrolyte bath 8 is solidified, thus constituting a crust 14 which covers the bath 8 and thermally insulates it.

La réaction à chaque anode 10 provoque une émission de fumées et de gaz 18, 29 qui migrent sur le dessus de la cuve comprenant des polluants tels que du dioxyde et du monoxyde de carbone, du dioxyde de soufre, du fluorure d'hydrogène gazeux (HF), des particules de carbone et d'alumine, des poussières et des composés fluorés.The reaction at each anode 10 gives rise to an emission of fumes and gases 18, 29 which migrate to the top of the tank comprising pollutants such as carbon dioxide and carbon monoxide, sulfur dioxide, gaseous hydrogen fluoride ( HF), carbon and alumina particles, dusts and fluorinated compounds.

La décomposition de l'alumine entraîne une diminution de sa teneur dans le bain d'électrolyte 8. Lorsque cette teneur tombe au dessous d'une valeur limite, une tige tubulaire mobile d'acier installée entre deux anodes 10, perce la croûte 14 et injecte de l'alumine dans le bain d'électrolyte 8. Cette tige, ci-après appelée piqueur-doseur 16, est manoeuvrable selon un mouvement vertical à l'aide d'un vérin, de préférence pneumatique, pour percer la croûte 14.The decomposition of the alumina causes a decrease in its content in the electrolyte bath 8. When this content falls below a limit value, a movable tubular steel rod installed between two anodes 10, pierces the crust 14 and Alumina is injected into the electrolyte bath 8. This rod, hereinafter referred to as a metering injector 16, is operable in a vertical movement by means of a jack, preferably pneumatic, to pierce the crust 14.

La majorité des fumées et gaz 18 emprisonnés entre l'anode 10 et la croûte 14 s'échappent par le trou percé périodiquement dans la croûte 14 par le piqueur-doseur 16 pour se loger sous un capot 20 qui recouvre la face ouverte de la cuve d'électrolyse 2. Une partie des fumées et du gaz s'échappe par les fissures et ouvertures qui existent dans la croûte 14.Most of the fumes and gases trapped between the anode 10 and the crust 14 escape through the hole drilled periodically in the crust 14 by the metering piercer 16. to be housed under a cover 20 which covers the open face of the electrolytic cell 2. Part of the fumes and gas escapes through the cracks and openings that exist in the crust 14.

Le système de récupération d'énergie 22, selon un premier mode de réalisation de l'invention, comporte un circuit primaire 24 de collecte des fumées et gaz produits par la cuve d'électrolyse 2, et une boucle d'échange thermique 26, ci-après appelée première boucle d'échange thermique 26.The energy recovery system 22, according to a first embodiment of the invention, comprises a primary circuit 24 for collecting the fumes and gases produced by the electrolytic cell 2, and a heat exchange loop 26, ci after called the first heat exchange loop 26.

Le circuit primaire 24 comporte un dispositif de récupération 28 des fumées et gaz 29 agencé pour provoquer une dépression sous le capot 20 et aspirer les fumées et les gaz 29 situés entre celui-ci et la croûte 14, et une unité 30 de traitement de ces fumées et gaz 29, ci-après appelée première unité de traitement 30. Le capot 20 n'est pas hermétique et de l'air extérieur est aspiré sous le capot 20 par les fuites du fait de la dépression. Cet air se mélange en quantité importante avec les fumées et gaz venant de la cuve. Dans la suite du texte nous ne distinguerons plus cet air des fumées et gaz et nous appellerons par les termes génériques fumées et gaz.The primary circuit 24 includes a flue gas recovery device 28 arranged to cause a depression under the hood 20 and to suck fumes and gases 29 situated between the latter and the crust 14, and a unit 30 for treating these gases. smoke and gas 29, hereinafter called the first processing unit 30. The cover 20 is not hermetic and outside air is sucked under the hood 20 by the leaks due to the depression. This air mixes in large quantities with the fumes and gases coming from the tank. In the rest of the text we will no longer distinguish this air smoke and gas and we will call by the generic terms smoke and gas.

Les fumées et gaz 29 sont aspirés par le dispositif de récupération 28 avec un débit spécifique d'environ 75 000 à 100 000 Nm3/tonne Aluminium (qui correspond à 8400 à 11000 Nm3/h pour une cuve de 350 kA).The fumes and gases 29 are sucked by the recovery device 28 with a specific flow rate of about 75,000 to 100,000 Nm 3 / ton Aluminum (which corresponds to 8400 to 11000 Nm 3 / h for a tank of 350 kA).

Les fumées et gaz 29 collectés par le circuit primaire 24 présentent une température d'environ 110 - 160° C. Ils contiennent 200 - 800 mg/Nm3 de poussière, 150 - 400 mg/Nm3 de fluorure d'hydrogène gazeux et 100 - 400 mg/Nm3 de dioxyde de soufre (SO2). Ces fumées et gaz collectés par le circuit primaire sont référencés ci-après par la référence 29.The fumes and gases 29 collected by the primary circuit 24 have a temperature of about 110 - 160 ° C. They contain 200 - 800 mg / Nm 3 of dust, 150 - 400 mg / Nm 3 of gaseous hydrogen fluoride and 100 - 400 mg / Nm 3 of sulfur dioxide (SO 2 ). These fumes and gases collected by the primary circuit are referenced hereinafter by the reference 29.

La première unité de traitement 30 est propre à filtrer les poussières contenues dans les fumées et gaz 29 collectés par le dispositif de récupération 28, et à éliminer la majeure partie de fluorure d'hydrogène gazeux par adsorption du fluorure d'hydrogène gazeux de ces fumées et gaz sur de l'alumine qui est ensuite séparée des fumées et gaz 29 par filtrage.The first treatment unit 30 is able to filter the dust contained in the fumes and gases 29 collected by the recovery device 28, and to eliminate most of the hydrogen fluoride gas by adsorption of hydrogen fluoride gas from these fumes. and gas on alumina which is then separated from the fumes and gases 29 by filtering.

La première unité de traitement 30 est adaptée pour traiter les fumées et gaz 29 selon un procédé sec connu sous le nom « DRY-SCRUBBER DS». Ce procédé permet une réduction de poussière supérieure à 98% par filtration et une réduction du fluorure d'hydrogène gazeux d'environ 99,8% par adsorption et filtration.The first processing unit 30 is adapted to treat the fumes and gases 29 according to a dry process known under the name "DRY-SCRUBBER DS". This method allows a dust reduction greater than 98% by filtration and a reduction of hydrogen fluoride gas of about 99.8% by adsorption and filtration.

La quantité de fluorure d'hydrogène gazeux contenue dans les fumées et gaz 29 sortant de la première unité de traitement 30 est inférieure à 0,5 mg/Nm3. La quantité de poussière contenue dans les fumées et gaz 29 sortant de la première unité de traitement 30 est inférieure à 5 mg/Nm3.The amount of hydrogen fluoride gas contained in the fumes and gases leaving the first treatment unit 30 is less than 0.5 mg / Nm 3 . The amount of dust contained in the fumes and gases coming out of the first treatment unit 30 is less than 5 mg / Nm 3 .

L'alumine fluorée générée par le traitement des fumées et gaz 29 par la première unité de traitement 30 est introduite dans la cuve d'électrolyse 2 à l'aide du piqueur-doseur 16.The fluorinated alumina generated by the treatment of fumes and gases 29 by the first treatment unit 30 is introduced into the electrolytic cell 2 by means of the metering piercer 16.

Le circuit primaire 24 comporte en outre un laveur 32 à eau de mer ou à solution basique propre à éliminer par absorption et réaction chimique le dioxyde de soufre (SO2) contenu dans les fumées et gaz 29 sortant de la première unité de traitement 30, et une cheminée 34 propre à évacuer les fumées et gaz épurés restants.The primary circuit 24 further comprises a scrubber 32 with seawater or with a basic solution capable of eliminating, by absorption and chemical reaction, the sulfur dioxide (SO 2 ) contained in the fumes and gases leaving the first treatment unit 30, and a chimney 34 capable of evacuating the remaining fumes and purified gases.

A la sortie du laveur 32, les fumées et gaz 29 comportent une quantité inférieure à 60 mg/Nm3 de dioxyde de soufre.At the outlet of the scrubber 32, the flue gases 29 comprise less than 60 mg / Nm 3 of sulfur dioxide.

La première boucle d'échange thermique 26 comporte un échangeur de chaleur 36, ci-après appelé premier échangeur de chaleur 36, et une unité de récupération 38 de la chaleur d'un fluide caloporteur. La boucle 26 est parcourue, d'une part, par le fluide caloporteur, et d'autre part, au niveau du premier échangeur 36, par les fumées et gaz 29 sortant du dispositif de récupération 28 avant que ceux-ci ne traversent la première unité de traitement 30.The first heat exchange loop 26 comprises a heat exchanger 36, hereinafter called the first heat exchanger 36, and a heat recovery unit 38 of a heat transfer fluid. The loop 26 is traversed, on the one hand, by the coolant, and on the other hand, at the level of the first heat exchanger 36, by the fumes and gases 29 leaving the recovery device 28 before they pass through the first treatment unit 30.

Le fluide caloporteur chauffé par le premier échangeur de chaleur 36, est utilisé par exemple pour produire de l'électricité par un générateur à cycle ORC, c'est-à-dire un Cycle de Rankine Organique. Le fluide caloporteur est par exemple constitué par de l'eau, de l'huile ou d'un gaz inerte.The heat transfer fluid heated by the first heat exchanger 36 is used, for example, to produce electricity by an ORC cycle generator, that is to say a generator. Organic Rankine Cycle. The coolant is for example constituted by water, oil or an inert gas.

Le premier échangeur de chaleur 36 est disposé à l'extérieur de la cuve d'électrolyse 2. Par exemple, il est disposé à une distance prédéfinie supérieure ou égale à un mètre de la cuve d'électrolyse 2 pour éviter tout risque de contact entre le fluide caloporteur et la cuve d'électrolyse 2.The first heat exchanger 36 is disposed outside the electrolysis cell 2. For example, it is disposed at a predefined distance greater than or equal to one meter from the electrolytic cell 2 to avoid any risk of contact between the heat transfer fluid and the electrolysis cell 2.

Le premier échangeur de chaleur 36 est propre à refroidir les fumées et gaz 29 du circuit primaire 24 d'une température de 110 - 160° C à une température de 70 - 100° C.The first heat exchanger 36 is able to cool the fumes and gases 29 of the primary circuit 24 by a temperature of 110-160 ° C. at a temperature of 70-100 ° C.

Une conduite de dérivation 39 est installée sur le circuit primaire 24 à chaque extrémité du premier échangeur de chaleur 36 pour permettre aux fumées et gaz 29 de court-circuiter le premier échangeur de chaleur 36, lorsque celui-ci est encrassé et qu'il doit être nettoyé ou remplacé ou rénové.A bypass line 39 is installed on the primary circuit 24 at each end of the first heat exchanger 36 to allow the fumes and gases 29 to bypass the first heat exchanger 36, when it is dirty and must be cleaned or replaced or renovated.

En référence à la figure 2, le procédé de récupération d'énergie, selon le premier mode de réalisation de l'invention, débute par une étape 100 de collecte des fumées et gaz 29 par le dispositif de récupération 28.With reference to the figure 2 , the energy recovery method, according to the first embodiment of the invention, begins with a step 100 of collecting fumes and gases 29 by the recovery device 28.

Au cours d'une étape 102, les fumées et gaz 29 collectés par le circuit primaire 24 sont transportés à l'extérieur et à distance de la cuve d'électrolyse 2. Le fluide caloporteur de la première boucle d'échange thermique 26 est réchauffé par le passage des fumées et gaz 29 au travers du premier échangeur de chaleur 36.During a step 102, the fumes and gases 29 collected by the primary circuit 24 are transported outside and away from the electrolysis cell 2. The heat transfer fluid of the first heat exchange loop 26 is warmed by passing fumes and gases 29 through the first heat exchanger 36.

Puis, au cours d'une étape 112, l'unité de récupération 38 récupère la chaleur du fluide caloporteur ayant traversé le premier échangeur de chaleur 36.Then, during a step 112, the recovery unit 38 recovers heat from the heat transfer fluid that has passed through the first heat exchanger 36.

Au cours d'une étape 114, l'unité de traitement 30 traite les fumées et gaz 29 collectés par le circuit primaire 24 par filtrage des poussières et élimination de la majeure partie du fluorure d'hydrogène gazeux. Puis, l'alumine fluorée générée par la première unité de traitement 30 est introduite dans le bain d'électrolyte 8 par le piqueur-doseur 16.During a step 114, the processing unit 30 processes the fumes and gases 29 collected by the primary circuit 24 by filtering the dust and removing most of the hydrogen fluoride gas. Then, the fluorinated alumina generated by the first treatment unit 30 is introduced into the electrolyte bath 8 by the metering injector 16.

Au cours d'une étape 116, une partie du dioxyde de soufre contenu dans les fumées et gaz 29 collectés par le circuit primaire 24 est éliminée par absorption et réaction chimique, par le laveur 32.During a step 116, part of the sulfur dioxide contained in the fumes and gases 29 collected by the primary circuit 24 is removed by absorption and chemical reaction, by the washer 32.

Enfin, au cours d'une étape 120, les fumées et gaz 29 sortants du laveur 32 sont évacués par la cheminée 34.Finally, during a step 120, the fumes and gases leaving the scrubber 32 are discharged through the chimney 34.

En variante, le circuit primaire 24 ne comporte pas de laveur 32. Dans ce cas, l'étape 116 n'est pas réalisée. Les fumées et gaz 29 sortant de la première unité de traitement 30 sont directement évacués par la cheminée 34.In a variant, the primary circuit 24 does not include a scrubber 32. In this case, the step 116 is not performed. The fumes and gases 29 leaving the first treatment unit 30 are directly discharged through the chimney 34.

En variante, l'unité de récupération 38 est un système permettant d'utiliser la chaleur du fluide caloporteur pour produire du froid ou de la chaleur.Alternatively, the recovery unit 38 is a system for using the heat of the coolant to produce cold or heat.

Le système de récupération 40 selon le deuxième mode de réalisation de l'invention, illustré sur la figure 3, comporte un circuit primaire 24 similaire au circuit primaire 24 du système de récupération 22 selon le premier mode de réalisation de l'invention, à l'exception du fait que ce circuit ne comporte pas de laveur 32.The recovery system 40 according to the second embodiment of the invention, illustrated on the figure 3 , comprises a primary circuit 24 similar to the primary circuit 24 of the recovery system 22 according to the first embodiment of the invention, with the exception that this circuit does not include a washer 32.

Selon ce mode de réalisation, les fumées et gaz 29 collectés par le dispositif de récupération 28 du circuit primaire 24 sont aspirés à un débit de 70000 à 100000 Nm3/tonne d'Aluminium produit. Ils comportent 100-800 mg/Nm3 de poussière, 30-100 mg/Nm3 de fluorure d'hydrogène gazeux, 20-100 mg/Nm3 de dioxyde de soufre, 2-4 g/Nm3 de dioxyde de carbone et 0,1 - 0,3 g/Nm3 de monoxyde de carbone. Ces fumées et gaz collectés par le circuit primaire sont référencés ci-après par la référence 29.According to this embodiment, the fumes and gases 29 collected by the recovery device 28 of the primary circuit 24 are sucked at a rate of 70000 to 100000 Nm 3 / ton of aluminum product. They comprise 100-800 mg / Nm 3 of dust, 30-100 mg / Nm 3 of hydrogen fluoride gas, 20-100 mg / Nm 3 of sulfur dioxide, 2-4 g / Nm 3 of carbon dioxide and 0.1 - 0.3 g / Nm 3 of carbon monoxide. These fumes and gases collected by the primary circuit are referenced hereinafter by the reference 29.

Ces fumées et gaz 29 collectés par le circuit primaire présentent une température d'environ 110 - 160° C avant de traverser le premier échangeur de chaleur 36, et une température d'environ 70 - 100° C à la sortie du premier échangeur de chaleur 36.These fumes and gases 29 collected by the primary circuit have a temperature of about 110-160 ° C. before passing through the first heat exchanger 36, and a temperature of about 70-100 ° C. at the outlet of the first heat exchanger. 36.

En sortant de la première unité de traitement 30, les fumées et gaz 29 comprennent moins de 5 mg/Nm3 de poussière et une quantité inférieure à 0,5mg/Nm3 de fluorure d'hydrogène gazeux.Out of the first processing unit 30, the fumes and gases 29 comprise less than 5 mg / Nm3 dust and less than 0.5 mg / Nm 3 of gaseous hydrogen fluoride.

Le système de récupération 40 selon le second mode réalisation comporte une première boucle 26 d'échange thermique similaire à la boucle d'échange thermique 26 du système de récupération 22 selon le premier mode de réalisation de l'invention, à l'exception du fait que cette première boucle d'échange thermique 26 comporte en outre un deuxième échangeur de chaleur 42.The recovery system 40 according to the second embodiment comprises a first heat exchange loop 26 similar to the heat exchange loop 26 of the recovery system 22 according to the first embodiment of the invention, with the exception of that this first heat exchange loop 26 further comprises a second heat exchanger 42.

Le deuxième échangeur de chaleur 42 est disposé à l'extérieur et à une distance d'au moins un mètre de la cuve d'électrolyse.The second heat exchanger 42 is disposed outside and at a distance of at least one meter from the electrolytic cell.

Le deuxième échangeur de chaleur 42 est disposé en aval du premier échangeur de chaleur 36, c'est-à-dire que le fluide caloporteur traverse tout d'abord, le premier échangeur de chaleur 36 puis, le deuxième échangeur de chaleur 42 avant de rejoindre l'unité de récupération 38.The second heat exchanger 42 is disposed downstream of the first heat exchanger 36, that is to say that the coolant passes first through the first heat exchanger 36 and then the second heat exchanger 42 before join the recovery unit 38.

Le système de récupération 40 comporte, de plus, un circuit secondaire 44 de collecte d'une partie des fumées et gaz 18 produits par la cuve d'électrolyse 2.The recovery system 40 further includes a secondary circuit 44 for collecting a portion of the fumes and gases 18 produced by the electrolysis cell 2.

Les fumées et gaz collectés par le circuit secondaire 44 sont référencés ci-après par la référence 18.The fumes and gases collected by the secondary circuit 44 are referenced hereinafter by the reference 18.

Ce circuit secondaire 44 comporte une hotte, ci-après appelée « hotte locale » 46 directement enchâssée dans la croûte 14 qui recueille les fumées et gaz 18, aussi appelés gaz anodique, s'échappant par le trou percé par le piqueur-doseur 16.This secondary circuit 44 comprises a hood, hereinafter called "local hood" 46 directly embedded in the crust 14 which collects the fumes and gases 18, also called anodic gases, escaping through the hole drilled by the metering piercer 16.

La hotte locale 46 loge le piqueur-doseur 16. La hotte locale 46 est reliée à un tube collecteur de fumées et gaz 48.Local hood 46 houses dosing device 16. Local hood 46 is connected to a flue gas collection tube 48.

Une ouverture 50 pratiquée dans la hotte locale 46 permet d'aspirer des fumées et gaz 29 collectés par le circuit primaire 24 et situés sous le capot 20 pour abaisser la température des fumées et gaz 18 collectés par le circuit secondaire 44 et aspirés par la hotte locale 46. L'ouverture 50 dans la hotte locale peut être réglée de façon à changer le rapport fumées et gaz collectés par le circuit primaire / fumées et gaz collectés par le circuit secondaire pour agir sur le rendement de captation de gaz anodique et la température résultante du mélange.An opening 50 made in the local hood 46 can suck fumes and gases 29 collected by the primary circuit 24 and located under the hood 20 to lower the temperature of the fumes and gases 18 collected by the secondary circuit 44 and sucked by the hood Local 46. The opening 50 in the local hood can be set to change the ratio of smoke and gas collected by the primary circuit / fumes and gases collected by the secondary circuit to act on the anodic gas capture efficiency and the resulting temperature of the mixture.

En pratique, 4 à 6 hottes locales 46 peuvent être installées dans une cuve d'électrolyse 2 de 300 à 400 kA pour assurer une bonne répartition de l'aspiration et capter le maximum de fumées et gaz 18.In practice, 4 to 6 local hoods 46 can be installed in an electrolysis cell 2 from 300 to 400 kA to ensure a good distribution of the suction and capture the maximum of fumes and gases 18.

75 à 85% environ des fumées et gaz produits sous la croûte 14 dans la cuve d'électrolyse 2 sont aspirés par la hotte locale 46 et collectés par le circuit secondaire 44. Le reste des fumées et gaz s'échappe par les fissures et les ouvertures existantes dans la croûte 14 et il est aspiré par le dispositif de récupération 28 et collecté par le circuit primaire 24.About 75 to 85% of the fumes and gases produced under the crust 14 in the electrolytic cell 2 are sucked by the local hood 46 and collected by the secondary circuit 44. The remainder of the fumes and gases escape through the cracks and existing openings in the crust 14 and is sucked by the recovery device 28 and collected by the primary circuit 24.

Les conduites entre le deuxième échangeur de chaleur 42 et chaque hotte locale 46 peuvent être calorifugées pour éviter les pertes énergétiques qui seraient importantes compte tenu du faible diamètre des tuyauteries.The pipes between the second heat exchanger 42 and each local hood 46 may be insulated to avoid energy losses that would be important given the small diameter of the pipes.

Les fumées et gaz anodique 18 collectés par le circuit secondaire 44 contiennent 1,2 - 8 g/Nm3 de fluor gazeux, 1-8 g/Nm3 de dioxyde de soufre, 110-280 g/Nm3 de dioxyde de carbone et 10-26 g/Nm3 de monoxyde de carbone.The fumes and anodic gas 18 collected by the secondary circuit 44 contain 1.2 - 8 g / Nm 3 of gaseous fluorine, 1-8 g / Nm 3 of sulfur dioxide, 110-280 g / Nm 3 of carbon dioxide and 10-26 g / Nm 3 of carbon monoxide.

Ils présentent une température de l'ordre de 200-350° C avant leur passage dans le deuxième échangeur de chaleur 42, et une température d'environ 70-100° C après leur passage dans le deuxième échangeur de chaleur 42.They have a temperature of about 200-350 ° C. before passing through the second heat exchanger 42, and a temperature of about 70-100 ° C. after passing through the second heat exchanger 42.

Le circuit secondaire 44 comporte en outre une unité de traitement 52, ci-après appelée seconde unité de traitement 52, un laveur 53 et une unité de captation 54 reliée à la cheminée 34.The secondary circuit 44 further comprises a processing unit 52, hereinafter called a second processing unit 52, a washer 53 and a capture unit 54 connected to the chimney 34.

La seconde unité de traitement 52 est similaire à la première unité de traitement 30 située dans le circuit primaire 24. Elle est apte à éliminer la majeure partie du fluorure d'hydrogène gazeux des fumées et gaz 18 collectés par le circuit secondaire 44 par adsorption et filtrage.The second processing unit 52 is similar to the first processing unit 30 situated in the primary circuit 24. It is capable of removing most of the hydrogen fluoride gas from the fumes and gases 18 collected by the secondary circuit 44 by adsorption and filtering.

Selon ce second mode de réalisation, la seconde unité de traitement 52 utilise de l'alumine partiellement fluorée obtenue par le traitement des fumées et gaz 29 collectés par le circuit primaire 24 par la première unité de traitement 30. Puis, l'alumine fluorée générée par la seconde unité de traitement 52 est introduite dans la cuve d'électrolyse 2 par le piqueur-doseur 16.According to this second embodiment, the second processing unit 52 uses partially fluorinated alumina obtained by the treatment of the fumes and gases 29 collected by the primary circuit 24 by the first treatment unit 30. Then, the fluorinated alumina generated by the second processing unit 52 is introduced into the electrolytic cell 2 by the metering injector 16.

En sortant de la seconde unité de traitement 52, les fumées et gaz 18 collectés par le circuit secondaire 44 comportent une valeur de l'ordre de 1mg/Nm3 de fluorure d'hydrogène gazeux.Leaving the second processing unit 52, the fumes and gases 18 collected by the secondary circuit 44 comprise a value of the order of 1 mg / Nm 3 of gaseous hydrogen fluoride.

Le laveur 53 est similaire au laveur 32 décrit dans le premier mode de réalisation de l'invention. A la sortie du laveur 53, les fumées et gaz 18 collectés par le circuit secondaire 44 comportent une valeur inférieure à 30 mg/Nm3 de dioxyde de soufre. Ils présentent une température d'environ 30-40°C.The scrubber 53 is similar to the scrubber 32 described in the first embodiment of the invention. At the outlet of the scrubber 53, the fumes and gases 18 collected by the secondary circuit 44 have a value of less than 30 mg / Nm 3 of sulfur dioxide. They have a temperature of about 30-40 ° C.

L'unité de captation 54 est destinée à capter le dioxyde de carbone par absorption par une solution d'ammoniaque ou par des amines ou autres techniques équivalentes.The capture unit 54 is intended to capture the carbon dioxide by absorption with a solution of ammonia or with amines or other equivalent techniques.

Enfin, les fumées et gaz 18 traités par l'unité de captation 54 sont évacués par la cheminée 34.Finally, the fumes and gases treated by the capture unit 54 are discharged through the stack 34.

En référence à la figure 4, le procédé de récupération d'énergie, selon le second mode de réalisation de l'invention, débute par les mêmes étapes 100 et 102 que le procédé de récupération selon le premier mode de réalisation de l'invention.With reference to the figure 4 , the energy recovery method, according to the second embodiment of the invention, starts with the same steps 100 and 102 as the recovery method according to the first embodiment of the invention.

Ensuite, au cours d'une étape 104, les fumées et gaz 18 situés entre la croûte 14 et le bain d'électrolyte 8 sont collectés par le circuit secondaire 44, via les hottes locales 46.Then, during a step 104, the fumes and gases 18 located between the crust 14 and the electrolyte bath 8 are collected by the secondary circuit 44, via the local hoods 46.

Au cours d'une étape 106, les fumées et gaz 18 collectés par le circuit secondaire 44 traversent le deuxième échangeur de chaleur 42 et réchauffent le fluide caloporteur préchauffé ayant déjà traversé le premier échangeur de chaleur 36.During a step 106, the fumes and gases 18 collected by the secondary circuit 44 pass through the second heat exchanger 42 and heat the preheated heat transfer fluid that has already passed through the first heat exchanger 36.

Le procédé se poursuit par la mise en oeuvre des étapes 112 et 114, celles-ci étant identiques aux étapes 112 et 114 du procédé illustré sur la figure 2.The method continues with the implementation of steps 112 and 114, which are identical to steps 112 and 114 of the method illustrated in FIG. figure 2 .

Au cours d'une étape 115, le fluorure d'hydrogène gazeux des fumées et gaz 18 collectés par le circuit secondaire 44 est traitée par la seconde unité de traitement 52. Ce traitement est similaire au traitement réalisé par la première unité de traitement 30 à l'exception du fait que l'alumine partiellement fluorée générée par le traitement des fumées et gaz 29 collectés par le circuit primaire 24, est utilisée pour adsorber le fluorure d'hydrogène gazeux des fumées et gaz 18 collectés par le circuit secondaire 44.During a step 115, the hydrogen fluoride gas of the fumes and gases 18 collected by the secondary circuit 44 is treated by the second processing unit 52. This treatment is similar to the treatment carried out by the first treatment unit 30. the exception that the partially fluorinated alumina generated by the treatment of fumes and gases 29 collected by the primary circuit 24 is used to adsorb the hydrogen fluoride gas from the fumes and gases 18 collected by the secondary circuit 44.

Puis, l'alumine fluorée est introduite dans le bain d'électrolyte 8 par le piqueur-doseur 16.Then, the fluorinated alumina is introduced into the electrolyte bath 8 by the metering piercer 16.

Avantageusement, l'alumine fraîche est utilisée pour adsorber le fluorure d'hydrogène gazeux des fumées et gaz contenant le moins de polluants, c'est-à-dire les fumées et gaz 29 collectés par le circuit primaire 24, puis est réutilisée pour adsorber le fluorure d'hydrogène gazeux des fumées et gaz 18 contenant une concentration plus élevée de polluants, c'est-à-dire les fumées et gaz 18 collectés par le circuit secondaire 44.Advantageously, the fresh alumina is used to adsorb the gaseous hydrogen fluoride of the fumes and gases containing the least pollutants, that is to say the fumes and gases 29 collected by the primary circuit 24, and is then reused to adsorb the gaseous hydrogen fluoride gas and gas 18 containing a higher concentration of pollutants, that is to say the fumes and gases 18 collected by the secondary circuit 44.

En variante, un mélange, éventuellement en proportions variables, d'alumine fraîche et d'alumine partiellement fluorée peut être utilisé dans seconde unité de traitement 52.Alternatively, a mixture, possibly in varying proportions, of fresh alumina and partially fluorinated alumina may be used in second processing unit 52.

Au cours d'une étape 117, la majeure partie du dioxyde de soufre contenu dans les fumées et gaz 18 collectés par le circuit secondaire 44 est éliminée par un laveur 53.During a step 117, the majority of the sulfur dioxide contained in the fumes and gases 18 collected by the secondary circuit 44 is removed by a washer 53.

Au cours d'une étape 118, l'unité de captation 54 élimine par absorption ou par d'autres techniques (adsorption, filtration membranaire,..) une partie du dioxyde de carbone des fumées et gaz 18 provenant du laveur 53.During a step 118, the capture unit 54 eliminates by absorption or by other techniques (adsorption, membrane filtration, etc.) a portion of the carbon dioxide from the fumes and gases from the scrubber 53.

Au cours d'une étape 120, les fumées et gaz 29 traités par l'unité de traitement 30 et les fumées et gaz 18 traités par l'unité de captation 54 sont évacués par la cheminée 34.During a step 120, the fumes and gases 29 treated by the treatment unit 30 and the fumes and gases treated by the capture unit 54 are discharged through the stack 34.

En variante, le circuit secondaire 44 ne comporte pas d'unité de captation 54. Dans ce cas, les fumées et gaz 18 sortant du laveur 53 sont directement dirigés vers la cheminée 34.In a variant, the secondary circuit 44 does not include a capture unit 54. In this case, the fumes and gases leaving the scrubber 53 are directly directed towards the chimney 34.

En variante, un laveur est disposé sur le circuit primaire 24 entre l'unité de traitement 30 et la cheminée 34.Alternatively, a washer is disposed on the primary circuit 24 between the treatment unit 30 and the chimney 34.

En variante, une conduite de dérivation 39 est montée de part et d'autre de l'un parmi le premier 36 et le deuxième 42 échangeurs de chaleur pour permettre de les court-circuiter, par exemple, lors du nettoyage de ces échangeurs de chaleur.Alternatively, a bypass line 39 is mounted on either side of one of the first 36 and the second 42 heat exchangers to allow short-circuiting, for example, during the cleaning of these heat exchangers .

Le système de récupération 56 selon un troisième mode de réalisation de l'invention, représenté sur la figure 5, comporte un circuit primaire 24 et un circuit secondaire 44 identiques aux circuits primaire 24 et secondaire 44 du système de récupération 40 selon le second mode de réalisation de l'invention.The recovery system 56 according to a third embodiment of the invention, represented on the figure 5 , comprises a primary circuit 24 and a secondary circuit 44 identical to the primary circuits 24 and secondary 44 of the recovery system 40 according to the second embodiment of the invention.

Le système de récupération 56 comprend en outre une première 26 et une seconde 62 boucles d'échange thermique.The recovery system 56 further comprises a first 26 and a second 62 heat exchange loops.

La première boucle d'échange thermique 26 du troisième mode de réalisation est similaire à la première boucle d'échange thermique 26 du système de récupération 40 du second mode de réalisation de l'invention à l'exception de l'existence d'un troisième échangeur de chaleur 60, également à l'extérieur de la cuve 2.The first heat exchange loop 26 of the third embodiment is similar to the first heat exchange loop 26 of the recovery system 40 of the second embodiment of the invention with the exception of the existence of a third heat exchanger 60, also outside the tank 2.

Dans la première boucle d'échange thermique 26, le troisième échangeur de chaleur 60 est disposé en aval du deuxième échangeur de chaleur 42, c'est-à-dire que le fluide caloporteur traverse tout d'abord, le premier échangeur de chaleur 36 puis, le deuxième échangeur de chaleur 42 et, enfin, le troisième échangeur de chaleur 60 avant de rejoindre l'unité de récupération 38.In the first heat exchange loop 26, the third heat exchanger 60 is disposed downstream of the second heat exchanger 42, that is to say that the heat transfer fluid first passes through, the first heat exchanger 36 then, the second heat exchanger 42 and, finally, the third heat exchanger 60 before joining the recovery unit 38.

La température du fluide caloporteur de la première boucle 26 est d'environ 80-100°C à l'entrée du premier échangeur de chaleur 36, d'environ 100°- 120°C à l'entrée du deuxième échangeur de chaleur 42, d'environ 150°- 250°C à l'entrée du troisième échangeur de chaleur 60, et enfin d'environ 200°- 400°C à la sortie de celui-ci.The temperature of the coolant of the first loop 26 is about 80-100 ° C at the inlet of the first heat exchanger 36, about 100 ° -120 ° C at the inlet of the second heat exchanger 42, about 150 ° - 250 ° C at the inlet of the third heat exchanger 60, and finally about 200 ° - 400 ° C at the outlet thereof.

La seconde boucle d'échange thermique 62 comporte une conduite parcourue par un fluide caloporteur intermédiaire. La conduite traverse au moins une paroi 64 latérale de la cuve d'électrolyse 2, puis le troisième échangeur de chaleur 60.The second heat exchange loop 62 comprises a pipe traversed by an intermediate heat transfer fluid. The pipe passes through at least one lateral wall 64 of the electrolytic cell 2 and then the third heat exchanger 60.

Le fluide caloporteur intermédiaire comprend, par exemple, de l'hélium, de l'air ou un autre gaz inerte vis-à-vis de l'aluminium liquide.The intermediate heat transfer fluid comprises, for example, helium, air or other gas inert vis-a-vis the liquid aluminum.

Le fluide caloporteur intermédiaire récupère la chaleur des parois 64 de la cuve, et la délivre au troisième échangeur 60. Avant d'entrer dans le troisième échangeur 60, la température du fluide caloporteur intermédiaire est comprise entre 250-600°C.The intermediate heat transfer fluid recovers the heat from the walls 64 of the tank, and delivers it to the third exchanger 60. Before entering the third exchanger 60, the temperature of the intermediate heat transfer fluid is between 250-600 ° C.

En référence à la figure 6, le procédé de récupération d'énergie selon le troisième mode de réalisation de l'invention est identique au procédé de récupération selon le second mode de réalisation, à l'exception du fait qu'il comporte entre les étapes 106 et 112, une étape 108 et une étape 110.With reference to the figure 6 , the energy recovery method according to the third embodiment of the invention is identical to the recovery method according to the second embodiment, with the exception that it comprises between steps 106 and 112, a step 108 and a step 110.

Au cours de l'étape 108, le fluide caloporteur intermédiaire de la seconde boucle d'échange thermique 62, traverse la ou les parois 64 de la cuve d'électrolyse et est ainsi réchauffé.During step 108, the intermediate heat transfer fluid of the second heat exchange loop 62 passes through the wall or walls 64 of the electrolytic cell and is thus heated.

Au cours de l'étape 110, le fluide caloporteur intermédiaire traverse le troisième échangeur de chaleur 60 et réchauffe ainsi le fluide caloporteur de la première boucle d'échange thermique 26 déjà préchauffé dans les échangeurs 36 et 42.During step 110, the intermediate heat transfer fluid passes through the third heat exchanger 60 and thus heats the coolant of the first heat exchange loop 26 already preheated in the exchangers 36 and 42.

Au cours de l'étape 112, l'unité de récupération 38 génère de l'électricité à partir de la chaleur récupérée par le fluide caloporteur ayant traversé le premier 36, le deuxième 42, et le troisième 60 échangeurs de chaleur.During step 112, the recovery unit 38 generates electricity from the heat recovered by the coolant having passed through the first 36, the second 42, and the third 60 heat exchangers.

En variante, des conduites de dérivation 39 sont montées de part et d'autre du deuxième échangeur de chaleur 42 pour permettre de le court-circuiter, par exemple, lors du nettoyage de cet échangeur de chaleur. Ainsi, avantageusement, les systèmes de récupération d'énergie peuvent continuer à récupérer de l'énergie à plus faible rendement, lors du nettoyage d'un échangeur de chaleur.Alternatively, branch lines 39 are mounted on either side of the second heat exchanger 42 to allow short-circuiting, for example, during the cleaning of this heat exchanger. Thus, advantageously, energy recovery systems can continue to recover energy at lower efficiency, when cleaning a heat exchanger.

En variante, un laveur 32 est en outre installé entre l'unité de traitement 30 et la cheminée 34 dans les deuxième et troisième modes de réalisation de l'invention.Alternatively, a scrubber 32 is further installed between the processing unit 30 and the chimney 34 in the second and third embodiments of the invention.

Comme les échangeurs de chaleur 36, 42 et 60 sont à l'extérieur de la cuve, ils sont facilement nettoyables et leur remplacement est facilité.As the heat exchangers 36, 42 and 60 are outside the tank, they are easily cleaned and their replacement is facilitated.

Comme les échangeurs 36 et 42 sont traversés par des fumées, ils peuvent s'encrasser et doivent pouvoir être nettoyés facilement.As the exchangers 36 and 42 are traversed by fumes, they can become dirty and must be easily cleaned.

Comme les échangeurs de chaleur 36, 42 et 60 sont à l'extérieur de la cuve, le risque d'attaque par l'aluminium est évité et les changements d'anode 10 ne sont pas gênés.Since the heat exchangers 36, 42 and 60 are outside the tank, the risk of attack by aluminum is avoided and the anode changes are not hindered.

Avantageusement, le système de récupération 40, 56 des deuxième et troisième modes de réalisation de l'invention comprend deux circuits de traitement des fumées et gaz différents présentant des pourcentages de polluants différents et des températures différentes. Chaque circuit 24, 44 de traitement des fumées et gaz est adapté aux taux de polluants dans ceux-ci.Advantageously, the recovery system 40, 56 of the second and third embodiments of the invention comprises two different smoke and gas treatment circuits having different pollutant percentages and different temperatures. Each circuit 24, 44 for treating fumes and gases is adapted to the pollutant levels therein.

Avantageusement, les systèmes de récupération 40, 56 des deuxième et troisième modes de réalisation permettent d'augmenter le rendement de la première boucle d'échange thermique 26 par le passage des fumées et gaz à température moyenne dans un premier échangeur 36, puis le passage des fumées et gaz à plus haute température dans un deuxième échangeur de chaleur 42, et éventuellement dans un troisième échangeur de chaleur 60 à température encore plus élevé.Advantageously, the recovery systems 40, 56 of the second and third embodiments make it possible to increase the efficiency of the first heat exchange loop 26 by passing fumes and gases at medium temperature in a first heat exchanger 36, then the passage fumes and gases at a higher temperature in a second heat exchanger 42, and optionally in a third heat exchanger 60 at an even higher temperature.

Avantageusement, le système de récupération 56 selon le troisième mode de réalisation de l'invention comporte deux boucles d'échange thermiques 26, 62 aptes à récupérer l'énergie, l'une, des parois 64 de la cuve d'électrolyse, l'autre, l'énergie des deux circuits 24, 44 de traitement des fumées et gaz.Advantageously, the recovery system 56 according to the third embodiment of the invention comprises two heat exchange loops 26, 62 able to recover the energy, one of the walls 64 of the electrolysis cell, the other, the energy of the two circuits 24, 44 for treating fumes and gases.

Claims (14)

  1. Fused bath electrolytic cell (2) and system (22; 40; 56) for recovering energy released by said fused bath electrolytic cell (2), said fused bath electrolytic cell (2) being suitable for generating fumes and gases (18; 29) during the manufacture of aluminum (12), the recovery system (22; 40; 56) comprising :
    • a first heat exchange loop (26) traveled by a heat transfer fluid, said first loop (26) comprising:
    - a first heat exchanger (36) and a second heat exchanger (42) traveled by the heat transfer fluid; and
    - a recovery unit (38) suitable for recovering the heat from the heat transfer fluid that has passed through the first (36) and the second (42) heat exchangers;
    the recovery system (22; 40; 56) additionally comprising:
    • a primary circuit (24) suitable for collecting a first portion of the fumes and gases (29) generated by the electrolytic cell (2),
    characterized in that the first and the second heat exchangers are arranged externally to and at a distance from the electrolytic cell (2); the fumes and gases collected by the primary circuit (24) passing through first heat exchanger (36) in order to heat the heat transfer fluid,
    and in that system (22; 40; 56) for recovering energy additionally comprises :
    • a secondary circuit (44) suitable for collecting a second portion of the fumes and gases (18) generated by the electrolytic cell (2), the fumes and gases collected by the secondary circuit (44) passing through second heat exchanger (42) in order to heat the heat transfer fluid,
    the fumes and gases (18) collected by the secondary circuit (44) being hotter and containing a higher concentration of pollutants than the fumes and gases (29) collected by the primary circuit (24).
  2. Fused bath electrolytic cell (2) and system (22; 40; 56) for recovering energy according to claim 1, wherein the first heat exchange loop (26) comprises a third heat exchanger (60),
    and wherein the energy recovery system (22; 40; 56) comprises a second heat exchange loop (62) traveled by an intermediate heat transfer fluid, the second heat exchange loop (62) being formed such that the intermediate heat transfer fluid passes through the third heat exchanger (60) and at least one wall (64) of the electrolytic cell (2),
    the recovery unit (38) being suitable for recovering the heat from the heat transfer fluid that has passed through at least the first (36) and the third (60) heat exchangers.
  3. Fused bath electrolytic cell (2) and system (22; 40; 56) for recovering energy according to claim 2, which comprises at least one bypass line (39) suitable for bypassing at least one of the first (36), second (42), and third (60) heat exchangers.
  4. Fused bath electrolytic cell (2) and system (22; 40; 56) for recovering energy according to any one of claims 1 to 3, wherein the electrolytic cell (2) comprises:
    - a molten electrolyte bath (8) covered with a solidified crust (14);
    - at least one cover (20) covering the solidified crust (14);
    - at least one piercing-dosing device (16) suitable for piercing the solidified crust (14) and injecting alumina into the electrolyte bath (8);
    and wherein the primary circuit (24) and/or the secondary circuit (44) each comprise a means (28; 46) for recovering fumes and gases that is either a means (28) for recovering fumes and gases (29) situated under the cover (20) or a means (46) for recovering fumes and gases (18) released through a hole periodically pierced in the solidified crust (14) by the piercing-dosing device (16).
  5. Fused bath electrolytic cell (2) and system (22; 40; 56) for recovering energy according to any one of claims 1 to 4, wherein the fumes and gases (18; 29) generated by the electrolytic cell (2) comprise dust, gaseous hydrogen fluoride, and sulfur dioxide; the primary circuit (24) and/or the secondary circuit (44) comprising:
    - a treatment unit (30; 52) for treating fumes and gases (18; 29), suitable for filtering out the dust contained in the fumes and gases (18; 29) collected by the primary circuit (24) and/or the secondary circuit (44), and for eliminating a portion of the gaseous hydrogen fluoride of the fumes and gases (18; 29) by adsorption on fresh or partially fluorinated alumina; and
    - a scrubber (32; 53) suitable for eliminating a portion of the sulfur dioxide by absorption and chemical reaction.
  6. Fused bath electrolytic cell (2) and system (22; 40; 56) for recovering energy according to claim 5, wherein the treatment unit (30; 52) is suitable for eliminating a portion of the gaseous hydrogen fluoride from the fumes and gases collected by the secondary circuit (44), by adsorption on partially fluorinated alumina, said partially fluorinated alumina being obtained by processing the fumes and gases (29) collected by the primary circuit (24).
  7. Fused bath electrolytic cell (2) and system (22; 40; 56) for recovering energy according to any one of claims 1 to 6, wherein the fumes and gases (18; 29) generated by the electrolytic cell (2) comprise carbon dioxide; the secondary circuit (44) comprising a capture system (54) suitable for eliminating a large portion of the carbon dioxide contained in the fumes and gases (18; 29), for example by absorption.
  8. A process for recovering energy released by a fused bath electrolytic cell (2) during the manufacture of aluminum (12), said process comprising the following steps:
    - the heating (102) of a heat transfer fluid by the passage of fumes and gases (18; 29) through a first heat exchanger (36) which is part of a first heat exchange loop (26);
    - the recovery (112) by a recovery unit (38) of heat from the heat transfer fluid that has passed through the first heat exchanger (36), said recovery unit (38) being part of the first heat exchange loop (26);
    - the collection (200) by a primary circuit (24) of a first portion of the fumes and gases (29) generated by the electrolytic cell (2);
    characterized in that the process additionally comprises the following steps :
    - the passage (102) through the first heat exchanger (36) of the fumes and gases (29) collected and transported externally to and at a distance from the electrolytic cell (2) by the primary circuit (24), in order to heat the heat transfer fluid,
    - the collection (104) of a second portion of the fumes and gases (18) generated by the electrolytic cell (2) by a secondary circuit (44), the fumes and gases (18) collected by the secondary circuit (44) being hotter and containing a higher concentration of pollutants than the fumes and gases (29) collected by the primary circuit (24); and
    - the heating (106) of the heat transfer fluid by the passage of fumes and gases (29) collected by the secondary circuit (44) through a second heat exchanger (42) that is part of the first heat exchange loop (26).
  9. A process according to claim 8, wherein the recovery unit (38) generates electricity and/or cold and/or heat from the heat of the heat transfer fluid.
  10. A recovery process according to either of claims 8 or 9, which additionally comprises the following steps:
    - the heating (108) of an intermediate heat transfer fluid by its passage through at least one wall (64) of the electrolytic cell (2), said intermediate heat transfer fluid traveling a second heat exchange loop (62);
    - the heating (110) of the heat transfer fluid by the passage of the intermediate heat transfer fluid through a third heat exchanger (60) which is part of the second heat exchange loop (26); and
    - the recovery (112) by the recovery unit (38) of heat from the heat transfer fluid that has passed through at least the first (36), second (42) and third (60) heat exchangers.
  11. A recovery process according to any one of claims 8 to 10, wherein the fumes and gases (18; 29) produced by the electrolytic cell (2) comprise dust and gaseous hydrogen fluoride, said process comprising a step (114, 115) of processing the fumes and gases (18; 29) collected by the primary circuit (24) and/or the secondary circuit (44) by filtering out dust and eliminating the major portion of the gaseous hydrogen fluoride by adsorption on fresh or partially fluorinated alumina and by filtering.
  12. A recovery process according to claim 11, which comprises a step (115) for processing a portion of the gaseous hydrogen fluoride of the fumes and gases (29) collected by the secondary circuit (44), by adsorption on partially fluorinated alumina, said partially fluorinated alumina being obtained by processing the fumes and gases (29) collected by the primary circuit (24).
  13. A recovery process according to any one of claims 8 to 12, wherein the fumes and gases (18; 29) generated by the electrolytic cell (2) comprise dust and sulfur dioxide, said process comprising a step (116, 117) that eliminates a portion of the sulfur dioxide contained in the fumes and gases (18; 29) collected by the primary circuit (24) and/or in the fumes and gases (18) collected by the secondary circuit (44) by absorption and chemical reaction, in a scrubber (32; 53).
  14. A recovery process according to any one of claims 8 to 13, which comprises a step (118) that eliminates by means of a capture unit (54), for example by absorption, a portion of the carbon dioxide contained in the fumes and gases (18) collected by the secondary circuit (44).
EP10734229.7A 2009-06-10 2010-06-04 System and method for recovering energy Active EP2440689B1 (en)

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FR0953834A FR2946666B1 (en) 2009-06-10 2009-06-10 SYSTEM AND METHOD FOR ENERGY RECOVERY
PCT/FR2010/051100 WO2010142893A1 (en) 2009-06-10 2010-06-04 System and method for recovering energy

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US9234286B2 (en) * 2012-05-04 2016-01-12 Alstom Technology Ltd Recycled pot gas pot distribution
CN106567105B (en) * 2016-11-07 2018-09-25 中国铝业股份有限公司 A kind of method of river diversion of aluminium cell flue gas
NO20190343A1 (en) * 2019-03-14 2020-09-15 Norsk Hydro As Arrangement for collection of hot gas from an electrolysis process, and a method for such gas collection

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FR2455093A1 (en) * 1979-04-24 1980-11-21 Pechiney Aluminium Removing gases from molten aluminium - during prodn. by adding alumina to melt and aspirating off gases as they leave surface

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FR2262700B1 (en) 1974-02-28 1978-12-29 Pechiney Aluminium
BR8208071A (en) * 1981-11-04 1984-03-07 Hb Consult Raodgivande Ing Ab PROCESS FOR HEAT RECOVERY IN OVEN FOR MANUFACTURING ALUMINUM FOR ALUMINUM FUSION BY ELECTROLYSIS
DE19845258C1 (en) * 1998-10-01 2000-03-16 Hamburger Aluminium Werk Gmbh Installation for sucking away waste gases and using their heat for aluminum multi cell electrolysis plant comprises waste gas collector hoods and suction ducts for each electrolysis cell of the plant
NO318012B1 (en) 2003-03-17 2005-01-17 Norsk Hydro As Structural elements for use in an electrolytic cell
GB0705439D0 (en) * 2007-03-22 2007-05-02 Alstom Intellectual Property Improved flue gas cooling and cleaning arrangment

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US4222841A (en) * 1979-04-23 1980-09-16 Alumax Inc. Hall cell
FR2455093A1 (en) * 1979-04-24 1980-11-21 Pechiney Aluminium Removing gases from molten aluminium - during prodn. by adding alumina to melt and aspirating off gases as they leave surface

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CA2764724C (en) 2018-03-27
EP2440689A1 (en) 2012-04-18
FR2946666B1 (en) 2015-08-07

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