FR2946665A1 - SYSTEM AND METHOD FOR TREATING SMOKE AND GAS PRODUCED BY AN ELECTROLYSIS TANK DURING THE MANUFACTURE OF ALUMINUM - Google Patents

Abstract

The invention relates to a system (40) and method for the treatment of fumes and gases (18, 29) produced by at least one igneous electrolysis cell (2) during the production of aluminum, fumes and gases (18). 29) having carbon dioxide; the treatment system (40) comprising a collection device (46) capable of collecting at least a portion of the fumes and gases (18, 29) produced by the electrolytic cell (2); characterized in that the collection device (46) is adapted to collect fumes and gases (18, 29) comprising at least 6% carbon dioxide; and in that the treatment system (40) comprises a capture unit (54) adapted to capture at least a portion of the carbon dioxide contained in the fumes and gases (18, 29).

Description

The present invention relates to a system and a process for the treatment of fumes and gases produced by an electrolytic cell during the manufacture of the fumes and gases produced by an electrolytic cell during the manufacture of aluminum. 'aluminum.

It is known systems and processes for the treatment of fumes and gases comprising devices for recovering fumes and gas under the hood of the electrolysis tanks. However, the fumes and gases recovered by these undercap recovery devices have carbon dioxide concentrations of less than 2%, so that it is difficult to capture this carbon dioxide by the existing techniques.

The object of the present invention is to propose a system for the treatment of fumes and gases produced by an electrolytic cell capable of treating the carbon dioxide of the fumes.

For this purpose, the subject of the invention is a system for treating fumes and gases produced by at least one igneous electrolysis cell during the manufacture of aluminum, the fumes and gases comprising pollutant components; said pollutant components comprising carbon dioxide; the treatment system comprising a primary collection circuit comprising: a collection device adapted to collect at least a portion of the fumes and gases produced by the electrolytic cell; - A capture unit capable of capturing at least a portion of the pollutant components of the fumes and gases collected; characterized in that the collection device is adapted to collect fumes and gases comprising at least 6% carbon dioxide; and in that the capture unit 30 is able to capture at least a portion of the carbon dioxide contained in the fumes and gases collected by the collection device. According to particular embodiments, the treatment system comprises the one or more of the following characteristics: the polluting components comprise sulfur dioxide; and wherein the primary collection circuit comprises a scrubber capable of removing a portion of the sulfur dioxide by absorption and chemical reaction, the fumes and gases being adapted to pass through the scrubber before passing through the capturing unit; the electrolytic cell comprises a molten electrolyte bath covered with a crust, and at least one piercing piercher suitable for piercing the crust; and wherein the collection device is adapted to collect fumes and gases evolved through an opening pierced in the crust by said metering piercer; the polluting components comprise gaseous hydrogen fluoride; and wherein the primary collection circuit comprises a first processing unit adapted to capture a portion of the gaseous hydrogen fluoride by absorption of the fumes and gases collected by the collection device on fresh or partially fluorinated alumina, and by filtering fumes and gases; a first heat exchange loop traversed by a heat transfer fluid; the first heat exchange loop comprising a first heat exchanger traversed by the fumes and gases collected by the collection device, and a recovery unit adapted to recover the heat of the heat transfer fluid; the fumes and gases being adapted to pass through the first heat exchanger before passing through the capture unit; a secondary collection circuit comprising a device for recovering the fumes and gases produced by the electrolytic cell, the fumes and gases collected by the recovery device containing a lower concentration of pollutant components than the fumes and gases collected by the device collection ; - The electrolysis tank is capped with a hood, and wherein the recovery device is a suction system suitable for sucking fumes and gases located under the hood; the secondary collection circuit comprises a second treatment unit able to capture a portion of the gaseous hydrogen fluoride from the fumes and gases collected by the recovery device, by adsorption on fresh alumina to generate partially fluorinated alumina the gaseous hydrogen fluoride gas and gases collected by the collection device being captured by adsorption on the partially fluorinated alumina generated by the second processing unit; the first heat exchange loop comprises a second heat exchanger traversed by the fumes and gases collected by the recovery device, the recovery unit being able to recover the heat of the heat transfer fluid from the heat recovered by the fluid; coolant having passed through the first and second heat exchangers; the first heat exchange loop comprises a third heat exchanger, the treatment system comprising a second heat exchange loop traversed by an intermediate heat transfer fluid, the second heat exchange loop being shaped so that the intermediate heat transfer fluid passes through. the third heat exchanger and the walls of the electrolysis cell, and the recovery unit being adapted to recover the heat of the coolant from the heat recovered by the coolant having passed through at least the second and third heat exchangers .

Finally, the subject of the invention is also a process for the treatment of fumes and gases produced by at least one igneous electrolysis cell during the manufacture of aluminum; the process being carried out by a treatment system, the method comprising the following steps: a) collecting the fumes produced by the electrolytic cell by at least one collection device, the fumes and gases comprising polluting components; said polluting components comprising at least carbon dioxide; b) capturing at least part of the pollutant components by a capture unit, characterized in that the fumes and gases collected during the collection stage comprise at least 6% of carbon dioxide, and in that the capture step b) is a step for capturing the carbon dioxide contained in the fumes and gases, by the capture unit.

According to particular embodiments, the process comprises one or more of the following characteristics: the fumes and gases produced by the electrolytic cell comprise sulfur dioxide; and wherein the process comprises a step of capturing part of the sulfur dioxide by adsorption by a scrubber, and chemical reaction; fumes and gases being able to cross the scrubber before crossing the capture unit; the electrolytic cell comprises a bath of electrolyte covered with a crust, and at least one puncture-maker suitable for piercing the crust; and the collection step is a step of collecting fumes and gases released by an opening pierced in the crust by said picker; the polluting components comprise hydrogen fluoride gas; and the process comprises a step of capturing part of the gaseous hydrogen fluoride by adsorption of fumes and gases on fresh or partially fluorinated alumina, and by filtering fumes and gases; a step of cooling the fumes and gases collected by the collection device by passing them through a first heat exchanger; - The treatment system comprises a first heat exchange loop traversed by a heat transfer fluid, the first heat exchange loop comprising the first heat exchanger and a recovery unit adapted to recover the heat of the heat transfer fluid; and the method comprises a step of recovering the heat of the coolant 20 having passed through the first heat exchanger; a step of collecting fumes and gases carried out by a recovery device, the fumes and gases collected by the recovery device containing a lower concentration of polluting components than the fumes and gases collected by the collection device; The method comprising a step of cooling the fumes and gases collected by the recovery device, through their passage through the second heat exchanger; a step of capturing part of the gaseous hydrogen fluoride from the fumes and gases collected by the adsorption recovery device on fresh alumina to generate partially fluorinated alumina, the gaseous hydrogen fluoride of fumes and gases collected by the collection device being captured by adsorption on the partially fluorinated alumina generated by the capture step; the first heat exchange loop comprises a third heat exchanger, the treatment system comprising a second heat exchange loop traversed by an intermediate heat transfer fluid, the second heat exchange loop being shaped so that the intermediate heat transfer fluid passes through. the third heat exchanger and the walls of the electrolysis cell, and the method comprising a step of recovering the heat of the coolant having passed through the third heat exchanger.

The invention will be better understood on reading the description which follows, given solely by way of example, and with reference to the drawings, in which: FIG. 1 is a diagrammatic sectional view of a tank of electrolysis and a treatment system according to a first embodiment of the invention; FIG. 2 is a diagram illustrating the steps of the processing method according to the first embodiment of the invention; - Figure 3 is a schematic sectional view of an electrolytic cell and a treatment system according to a second embodiment of the invention; and FIG. 4 is a diagram illustrating the steps of the treatment method according to the second embodiment of the invention. Identical or similar elements of the first and second embodiments of the treatment system are hereinafter referred to by the same references and are described only once.

Referring to FIG. 1, an igneous electrolysis cell 2 comprises a parallelepipedic 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 consisting of alumina dissolved in cryolite, heated 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 . 6

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. 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 injects alumina into the electrolyte bath 8. This rod, hereinafter referred to as a metering pusher 16, is operable in vertical movement by means of a jack, preferably pneumatic, to pierce the crust 14.

The majority 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 pusher 16 to fit under a cover 20 which covers the open face of the electrolysis tank 2. Part of the smoke and gas escapes through cracks and openings in the crust 14.

The treatment system 40, according to a first embodiment of the invention, comprises a circuit 24 for collecting the fumes and gases produced by the electrolytic cell 2, and a first heat exchange loop 26. The collection 24 is hereinafter called the secondary collection circuit for reasons which will appear later.

The secondary circuit 24 includes a flue gas recovery device 28 arranged to cause a depression under the hood 20 and suck up the fumes and gases 29 located between the latter and the crust 14, and the treatment unit 30. of these fumes and gases 29, hereinafter called the second processing unit for reasons which will appear later. 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 second processing unit 30 is suitable for filtering the dust contained in the fumes and gases collected by the recovery device 28, and for removing most of the gaseous hydrogen fluoride by adsorption of the gaseous hydrogen fluoride of these fumes. and gas on alumina which is then separated from the fumes and gases by filtering.

The second processing unit 30 is adapted to treat the fumes and gases 29 according to a dry process known as 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 exiting the second treatment unit 30 is less than 0.5 mg / Nm3. The amount of dust contained in the fumes and gases leaving the second processing unit 30 is less than 5 mg / Nm3.

The fluorinated alumina generated by the treatment of the fumes and gases 29 by the second treatment unit 30 is introduced into the electrolytic cell 2 by means of the metering injector 16. The secondary circuit 24 further comprises a washer 32 to sea water or basic solution clean to remove by absorption and chemical reaction the sulfur dioxide (SO2) contained in the fumes and gases 29 leaving the second treatment unit 30, and a chimney 34 able to evacuate fumes and purified gases remaining. At the outlet of the scrubber 32, the fumes and gases 29 comprise an amount of less than 60 mg / Nm.sup.3 of sulfur dioxide.25 The heat exchange loop 26, hereinafter referred to as the first thermal loop, comprises a heat exchanger 36 , hereinafter referred to as second heat exchanger 36 for reasons which will become apparent later, and a unit 38 for recovering the heat of a coolant. The first thermal loop 26 is traversed, on the one hand, by the coolant, and on the other hand, at the level of the second heat exchanger 36, by the fumes and gases 29 leaving the recovery device 28 before they pass through. the second processing unit 30.

The heat transfer fluid heated by the second heat exchanger 36 is used for example to produce electricity by an ORC cycle generator, that is to say an Organic Rankine Cycle. The coolant is for example constituted by water, oil or an inert gas.

The second heat exchanger 36 is disposed outside the electrolytic cell 2. For example, it is disposed at a predefined distance greater than or equal to one meter from the electrolytic cell to avoid any risk of contact between the electrolytic cell. heat transfer fluid and the electrolysis cell.

The second heat exchanger 36 is adapted to cool the fumes and gases 29 of the secondary circuit 24 by a temperature of 110-160 ° C at a temperature of 70-100 ° C.

A bypass line 39 is installed on the first heat exchange loop 26 at each end of the second heat exchanger 36 to allow fumes and gases 29 to bypass the second heat exchanger 36, when the latter is fouled. and that it must be cleaned or replaced or renovated.

The fumes and gases 29 collected by the recovery device 28 of the secondary circuit 24 are sucked at a rate of 70000 to 100000 Nm3 / ton of aluminum produced. They contain 100-800 mg / Nm3 of dust, 30-100 mg / Nm3 of hydrogen fluoride gas, 20-100 mg / Nm3 of sulfur dioxide, 2-4 g / Nm3 of carbon dioxide and 0.1 - 0.3 g / Nm3 of carbon monoxide. The fumes and gases collected by the secondary circuit 24 are referenced hereinafter by the reference 29.

These fumes and gases 29 collected by the secondary circuit have a temperature of about 110-160 ° C. before passing through the second heat exchanger 36, and a temperature of about 70-100 ° C. at the outlet of the second heat exchanger. 36. The first heat exchange loop 26 further comprises a first heat exchanger 42 disposed outside and at a distance of at least one meter from the electrolysis cell.

The first heat exchanger 42 is disposed downstream of the second heat exchanger 36, that is to say that the heat transfer fluid first passes through, the second heat exchanger 36 and then the first heat exchanger 42 before to join the recovery unit 38.

The treatment system 40 further includes a primary circuit 44 for collecting a portion of the fumes and gases 18 produced by the electrolytic cell 2.

This primary circuit 44 comprises a collection device 46, hereinafter called local hood 46 directly embedded in the crust 14 which collects the fumes and gases 18, 20 also called anodic gas, escaping through the hole drilled by the pesteur-doseur 16. Local hood 46 is suitable for collecting fumes and gases with at least 6% carbon dioxide. The fumes and gases collected by the collection device 46 are referenced hereinafter by the reference 18.

Local hood 46 houses dosing device 16. Local hood 46 is connected to a gas collection tube 48.

An opening 50 made in the local hood 46 makes it possible to suck fumes and gases 29 collected by the secondary circuit located under the hood 20 to lower the temperature of the fumes and gases 18 sucked by the local hood 46. The opening 50 in FIG. the local hood can be set to change the ratio of fumes and gases 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.

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.

About 75 to 85% of the fumes and gases 18 produced under the crust 14 in the electrolytic cell 2 are sucked by the local hood 46. The remainder of the fumes and gases 29 escape through cracks and existing openings in the crust and is sucked by the recovery device 28.

The pipes between the first 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 sucked by each local hood 46 contain 1.2 to 8 g / Nm3 of gaseous hydrogen fluoride, 1-8 g / Nm3 of sulfur dioxide, 110-280 g / Nm3 of carbon dioxide. and 10-26 g / Nm3 of carbon monoxide.

They have a temperature of about 200-350 ° C. before passing through the first heat exchanger 42, and a temperature of about 70-100 ° C. after passing through the first heat exchanger 42.

The primary circuit 44 further comprises a treatment unit 52, said first processing unit 52, a washer 53 and a capture unit 54 connected to the stack 34.

The first processing unit 52 is similar to the second processing unit 30 located in the secondary circuit 24. It is capable of removing most of the hydrogen fluoride gas from the fumes and gases 18 collected by the local hood 46 by adsorption and filtering.

According to this embodiment, the first processing unit 52 uses partially fluorinated alumina obtained by the treatment of the fumes and gases 29 collected by the secondary circuit 24 by the second treatment unit 30. Then, the fluorinated alumina 25 Generated by the first processing unit 52 is introduced into the electrolytic cell 2 by the metering piercer 16.

Leaving the first processing unit 52, the fumes and gases 18 collected by the local hoods 46 have a value of the order of 1 mg / Nm3 of gaseous hydrogen fluoride.

The scrubber 53 is similar to the scrubber 32. At the exit of the scrubber 53, the fumes and gases 18 collected by the local hoods 46 have a value of less than 30 mg / Nm3 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. Since the carbon dioxide concentration of the fumes and gases taken by the local hoods 46 is greater than the carbon dioxide concentration of the fumes and gases taken by other known recovery devices, and in particular with respect to a recovery device 28 fumes and gas under hood, the capture of carbon dioxide is facilitated.

Finally, the fumes and gases treated by the capture unit 54 are discharged through the chimney 34.

With reference to FIG. 2, the treatment method, according to the first embodiment of the invention, begins with a step 100 for collecting the fumes and gases 29 by the recovery device 28.

During a step 102, the fumes and gases 29 collected by the secondary circuit 24 are transported outside and away from the electrolytic cell 2. The heat transfer fluid of the first heat exchange loop 26 is warmed by passage of the fumes and gases 29 through the second heat exchanger 36. Simultaneously, the fumes and gases 29 are cooled.

Then, during a step 104, the fumes and gases 18 located between the crust 14 and the electrolyte bath 8 are collected by the primary circuit 24, via the local hoods 46.

During a step 106, the fumes and gases 18 collected by the local hoods 46 pass through the first heat exchanger 42 and heat the preheated heat transfer fluid that has already passed through the second heat exchanger 36. Simultaneously, the fumes and gases 18 are cooled.

Then, during a step 112, the recovery unit 38 recovers the heat of the coolant having passed through the first 42 and the second 36 heat exchangers.

During a step 114, the second processing unit 30 processes the fumes and gases 29 collected by the recovery device 28 by filtering the dust and removing most of the hydrogen fluoride gas. Then, the fluorinated alumina generated by the second treatment unit 30 is fed to the first treatment unit 52.

During a step 115, the gaseous hydrogen fluoride gas and gases collected by the local hoods 46 is treated by the first processing unit 52. This treatment is similar to the treatment performed by the second processing unit 30 to 20. the exception that the partially fluorinated alumina generated by the treatment of flue gases and gases of the secondary circuit 24 is used to adsorb the hydrogen fluoride gas from the fumes and gases of the primary circuit 44.

Then, the fluorinated alumina is introduced into the electrolyte bath by the stirrup-doser.

Advantageously, the fresh alumina is used to adsorb the hydrogen fluoride gas fumes and gases containing the least pollutants, that is to say the fumes and gases collected by the secondary circuit 24, then is reused to adsorb the Hydrogen fluoride gas fumes and gases containing a higher concentration of pollutants, that is to say the fumes and gases collected by the primary circuit 44.

Alternatively, a mixture, optionally in variable proportions, of fresh alumina and partially fluorinated alumina may be used in the primary circuit.

During a step 116, part of the sulfur dioxide contained in the fumes 5 and gas 29 collected by the recovery device 28 is removed by absorption and chemical reaction, by the washer 32.

During a step 117, most of the sulfur dioxide contained in the fumes and gases 18 collected by the local hoods 46 is removed by a scrubber 53. During a step 118, the capture unit 54 eliminates by absorption or by other techniques (adsorption, membrane filtration, ..) part of the carbon dioxide of the fumes and gases 18 from the scrubber 53.

Finally, during a step 120, the fumes and gases 29 leaving the washer 32 and the fumes and gases 18 leaving the capture unit 54 are discharged through the chimney 34.

In a variant, the secondary circuit 24 does not include a scrubber 32. In this case, the step 116 is not performed. The fumes and gases leaving the treatment unit 30 are directly discharged through the chimney 34.

A bypass line 39 is mounted on either side of the first heat exchanger 42 to allow short-circuiting, for example, during the cleaning of this heat exchanger. Alternatively, a bypass line 39 is also mounted on either side of the second heat exchanger 36. Thus, advantageously, the treatment systems can continue to recover energy at lower efficiency, when cleaning the dies. a heat exchanger.

Alternatively, the recovery unit 38 is a system for utilizing the heat of the coolant to produce cold or heat.

The processing system 56 according to a second embodiment of the invention, shown in FIG. 3, comprises a primary circuit 44 and a secondary circuit 24 10 identical to the primary 44 and secondary 24 circuits of the treatment system 40 according to the first embodiment. embodiment of the invention.

The treatment system 56 further comprises a first 26 and a second 62 5 heat exchange loops.

The first heat exchange loop 26 is similar to the first heat exchange loop 26 of the treatment system 40 of the first embodiment of the invention with the exception of the existence of a third heat exchanger 60, 10 also outside the tank 2.

In the first heat exchange loop 26, the third heat exchanger 60 is disposed downstream of the first heat exchanger 42, that is to say that the coolant passes first through the second heat exchanger 36 then the first 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 second heat exchanger 36, about 100 ° -120 ° C at the inlet 20 of the first heat exchanger 42 from about 150 ° - 250 ° C at the inlet of the third heat exchanger 60, and finally from 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 of the electrolysis tank 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.

With reference to FIG. 4, the treatment method according to the second embodiment of the invention is identical to the treatment method according to the first embodiment, except that it comprises between steps 106 and 112 , a step 108 and a step 110. 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.

During step 110, the intermediate heat transfer fluid passes through the third heat exchanger 60 and thus heats the heat transfer fluid of the first heat exchange loop 26 already preheated in the first exchanger 42 and the second exchanger 36.

In step 112, the recovery unit 38 generates electricity from the heat recovered by the coolant having passed through the first 42, the second 36, and the third 60 heat exchangers.

Alternatively, the washer 32 is removed. As the heat exchangers 36, 42 and 60 are outside the tank, they are easily cleaned and their replacement is facilitated.

Since the heat exchangers 36 and 42 are flue-passed, they can become dirty and must be easily cleaned.

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. Advantageously, the treatment systems 40, 56 of the first and second embodiments of the invention comprise two circuits 24, 44 for collecting different fumes and gases with different pollutant percentages and different temperatures. Each circuit 24, 44 for collecting fumes and gases is adapted to the pollutant levels therein.

Advantageously, the treatment system 40, 56 of the first and second 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 second heat exchanger 36, then the passage fumes and gases at a higher temperature in a first heat exchanger 42, and optionally in a third heat exchanger 60 at an even higher temperature.

Advantageously, the treatment system 56 according to the second embodiment of the invention comprises two heat exchange loops 26, 62 able to recover the energy, one of the walls 64 of the electrolytic cell, the other, the energy of the two circuits 24, 44 for collecting fumes and gases.

Claims (1)

CLAIMS.- System (40; 56) for the treatment of fumes and gases (18, 29) produced by at least one igneous electrolysis cell (2) during the manufacture of aluminum, fumes and gases (18, 29) having polluting components; said pollutant components comprising carbon dioxide; the treatment system (40; 56) having a primary collection circuit (44) comprising: - a collection device (46) capable of collecting at least a portion of the fumes and gases (18, 29) produced by the reaction vessel; electrolysis (2); - a capture unit (54) capable of capturing at least a portion of the pollutant components of the collected fumes and gases (18, 29); characterized in that the collection device (46) is adapted to collect fumes and gases (18, 29) comprising at least 6% carbon dioxide; and in that the capture unit (54) is adapted to capture at least a portion of the carbon dioxide contained in the fumes and gases (18, 29) collected by the collection device (46). The treatment system (40; 56) according to claim 1, wherein the polluting components comprise sulfur dioxide; and wherein the primary collection circuit (44) comprises a scrubber (53) adapted to remove a portion of the sulfur dioxide by absorption and chemical reaction, the fumes and gases (18, 29) being adapted to pass through the scrubber (53). ) before crossing the capture unit (54). 3. Treatment system (40; 56) according to any one of claims 1 and 2, wherein the electrolytic cell (2) comprises a molten electrolyte bath (8) covered with a crust (14). ), and at least one lancing device (16) suitable for piercing the crust (14); and wherein the collection device (46) is adapted to collect the fumes and gases (18, 29) released by an opening pierced in the crust (14) by said metering piercer (16). 30 4. Treatment system (40; 56) according to any one of claims 1 to 3, wherein the polluting components comprise hydrogen fluoride gas; and wherein the primary collection circuit (44) comprises a first treatment unit (52) adapted to capture a portion of the gaseous hydrogen fluoride by absorption of the fumes and gases (18, 29) collected by the collection device (46). ) on fresh or partially fluorinated alumina, and by filtering fumes and gases. 5. Treatment system (40, 56) according to any one of claims 1 to 4, which comprises a first heat exchange loop (26) traversed by a heat transfer fluid; the first heat exchange loop (26) comprising a first heat exchanger (42) traversed by the fumes and gases (18, 29) collected by the collection device (46), and a recovery unit (38) suitable for recover heat from the heat transfer fluid; the fumes and gases (18, 29) being adapted to pass through the first heat exchanger (42) before passing through the capture unit (54). 6. Treatment system (40; 56) according to any one of claims 1 to 5, which comprises a secondary collection circuit (24) comprising a recovery device (28) fumes and gases (18, 29) produced by the electrolytic cell (2), the fumes and gases (18, 29) collected by the recovery device (28) containing a lower concentration of pollutant components than the fumes and gases (18, 29) collected by the device collection (46). 7. Treatment system (40; 56) according to claim 6, wherein the electrolytic cell (2) is capped with a hood (20), and wherein the recovery device (28) is a system of suction adapted to suck fumes and gases (18, 29) located under the hood (20). 8. Treatment system (40; 56) according to any one of claims 6 and 7, wherein the secondary collection circuit (24) comprises a second processing unit (30) adapted to capture a portion of the fluoride d ' hydrogen gas from fumes and gases (18, 29) collected by the recovery device (28), by adsorption on fresh alumina to generate partially fluorinated alumina, gaseous hydrogen fluoride gas and gas (18 , 29) collected by the collection device (46) being adsorbed on the partially fluorinated alumina generated by the second treatment unit (30). 9. Treatment system (40; 56) according to any one of claims 6 to 8, wherein the first heat exchange loop (26) comprises a second heat exchanger (36) traversed by the fumes and gases ( 18, 29) collected by the recovery device (28), the recovery unit (38) being adapted to recover the heat of the coolant from the heat recovered by the heat transfer fluid having passed through the first (42) and the second (36) heat exchangers. The treatment system (40; 56) according to any one of claims 5 to 9, wherein the first heat exchange loop (26) comprises a third heat exchanger (60), and wherein the system treatment unit (40; 56) comprises a second heat exchange loop (62) traversed by an intermediate heat transfer fluid, the second heat exchange loop (62) being shaped so that the intermediate heat transfer fluid passes through the third heat exchanger (60) and the walls (64) of the electrolysis tank (2), the recovery unit (38) being adapted to recover the heat of the heat transfer fluid from the heat recovered by the heat transfer fluid having passed through at least the second (36) and the third (60) heat exchangers. 20 11.- Process for treating fumes and gases (18, 29) produced by at least one electrolysis cell (2) igneous during the manufacture of aluminum; the process being carried out by a treatment system (40; 56), the process comprising the following steps: a) collecting (104) fumes (18, 29) produced by the electrolytic cell (2) by at least one device collecting (46), fumes and gases (18, 29) comprising polluting components; said polluting components comprising at least carbon dioxide; b) capturing (118) at least a portion of the pollutant components by a capture unit (54); characterized in that the fumes and gases (18, 29) collected during the collection step (104) comprise at least 6% carbon dioxide, and that the capture step b) (118) is a step of capturing the carbon dioxide contained in the fumes and gases (18, 29) by the capture unit (54). 12. A treatment method according to claim 11, wherein the fumes and gases (18, 29) produced by the electrolytic cell (2) comprise sulfur dioxide; and wherein the process comprises a step of capturing (117) part of the sulfur dioxide by adsorption by a scrubber (53), and chemical reaction; the fumes and gases (18, 29) being adapted to pass through the scrubber (53) before passing through the capture unit (54). 13. A treatment method according to claim 12, wherein the electrolytic cell (2) comprises a bath of electrolyte (8) covered with a crust (14), and at least one metering pinteur (16) clean piercing the crust (14); and wherein the collecting step (104) is a step of collecting fumes and gases (18, 29) released by an opening pierced in the crust (14) by said metering piercer (16). 14. A treatment method according to any one of claims 11 to 13, wherein the polluting components comprise hydrogen fluoride gas; and wherein the process comprises a step of capturing (115) a part of the gaseous hydrogen fluoride by adsorption of the fumes and gases (18, 29) on fresh or partially fluorinated alumina, and by filtering the fumes and gas (18, 29). 15. A method of treatment according to any one of claims 11 to 14, which comprises a step of cooling (106) fumes and gases (18, 29) collected by the collection device (46) through their passage through a first heat exchanger (42). 16. A treatment method according to claim 15, wherein the treatment system (40; 56) comprises a first heat exchange loop (26) traversed by a heat transfer fluid, the first heat exchange loop (26) comprising the first heat exchanger (42) and a recovery unit (38) adapted to recover the heat of the coolant; and wherein the method comprises a heat recovery step (112) of the heat transfer fluid having passed through the first heat exchanger (42). 17. A treatment method according to any one of claims 14 to 16, which comprises a step (100) for collecting fumes and gases (18, 29) carried out by a recovery device (28), fumes and gases ( 18, 29) collected by the recovery device (28) containing a lower concentration of polluting components than the fumes and gases (18, 29) collected by the collection device (46); the method comprising a step of cooling (102) fumes and gases (18, 29) collected by the recovery device (28), through their passage through the second heat exchanger (36). 18. A method of treatment according to claim 17, which comprises a step of capturing (115) a portion of the hydrogen fluoride gas fumes and gases (18, 29) collected by the recovery device (28) by adsorption on fresh alumina to generate partially fluorinated alumina, the hydrogen fluoride gas of the fumes and gases (18, 29) collected by the collection device (46) being adsorbed on the partially fluorinated alumina generated by the capturing step (117). 19. A treatment method according to any one of claims 16 to 18, wherein the first heat exchange loop (26) comprises a third heat exchanger (60), and wherein the treatment system (56) comprises a second heat exchange loop (62) traversed by an intermediate heat transfer fluid, the second heat exchange loop (62) being shaped so that the intermediate heat transfer fluid passes through the third heat exchanger (60) and the walls (64) of the electrolytic cell (2), and wherein the method comprises a step (112) for recovering the heat of the coolant having passed through the third heat exchanger (60). 30