CA2764724A1 - System and method for recovering energy - Google Patents

Abstract

System and method for energy recovery System (22) for recovering energy released by at least one electrolytic cell (2), the recovery system comprising a first heat exchange loop (26) traversed by a heat transfer fluid the first loop (26) comprising: a heat exchanger (36) traversed by the heat transfer fluid; anda recovery unit (38) capable of recovering the heat of the coolant having passed through the heat exchanger (36); a primary collection circuit (24) capable of collecting at least a portion of the fumes and gases generated by the electrolytic cell (2), the heat exchanger (36) being disposed outside and at a distance from the electrolysis tank (2), the heat exchanger (36) being traversed by the fumes and gases collected by the primary circuit (24) for heating the coolant.

Description

System and method for energy recovery The present invention relates to a recovery system and method energy released by an igneous electrolysis cell during the manufacture of aluminum.
Document US Pat. No. 7,465,379 describes a system for recovering energy comprising a heat exchange loop comprising a heat exchanger implanted in the walls of the electrolytic cell, for example by mounting a tube serpentine in the walls of the tank to recover the heat thereof.
However, an electrolytic cell having a heat exchanger in its walls, is difficult to manufacture, and it is very difficult to ensure maintenance of the exchanger, and its possible replacement.

The present invention is intended in particular to propose a system of simpler energy recovery and some embodiments thereof authorize more energy recovery.

For this purpose, the subject of the invention is a system for recovering energy clear by at least one igneous electrolysis cell generating fumes and gases during the aluminum production, the recovery system including a first loop of heat exchange traversed by a coolant, the first loop comprising:
a first heat exchanger traversed by the heat transfer fluid; and a recovery unit able to recover the heat of the coolant having crossed the first heat exchanger;
characterized in that the recovery system further comprises a primary circuit capable of collecting at least a portion of the fumes and gases generated by the electrolysis cell, the first heat exchanger being arranged to outside and away from the electrolysis cell; the first exchanger of heat being crossed by the fumes and gases collected by the primary circuit for heat the coolant.

2 Finally, the subject of the invention is also a method for recovering energy released by an igneous electrolysis cell during the manufacture of aluminum, characterized in that the method comprises the following steps:
- Heating of a coolant by the passage of fumes and gases at through a first heat exchanger forming part of a first loop exchange thermal;
- recovery of the heat of the coolant having passed through the first heat exchanger by a recovery unit, said unit of recovery doing part of the first heat exchange loop;
characterized in that the method further comprises the following steps - collecting at least a portion of the fumes and gases generated by the tank electrolysis, by a primary circuit;
- crossing of the first heat exchanger by the fumes and gases collected and transported outside and away from the electrolysis cell by the primary circuit, for heat the coolant.

The invention will be better understood on reading the description which follows, given only by way of example, and made with reference to the drawings on which :
FIG. 1 is a schematic sectional view of an electrolysis cell and a energy recovery system according to a first embodiment of the invention;
FIG. 2 is a diagram illustrating the steps of the method of recovery of energy according to the first embodiment of the invention;
FIG. 3 is a schematic sectional view of an electrolytic cell and a energy recovery system according to a second embodiment of the invention;
FIG. 4 is a diagram illustrating the steps of the method of recovery of energy according to the second embodiment of the invention;
FIG. 5 is a schematic sectional view of an electrolytic cell and a energy recovery system according to a third embodiment of the invention; and FIG. 6 is a diagram illustrating the steps of the method of recovery of energy according to the third embodiment of the invention.

WO 2010/14289

3 PCT / FR2010 / 051100 Identical or similar elements of the first, second and third modes of the energy recovery system are hereinafter referred to as the same references and are only described once.
With reference to FIG. 1, an igneous electrolysis cell 2 comprises a box

4 parallelepiped open at its upper base and whose bottom bears blocks carbonaceous constituting the cathode 6. This box 4 contains an electrolyte bath 8 consisting of alumina dissolved in cryolite, heated to a temperature of between 950 and 1 In this bath 8, one or more anodes 10 are immersed. when current electrical connection is applied between the anodes 10 and the cathode 6, the alumina is breaks down into aluminum 12 forming a metal bath which covers the cathode 6, and oxygen that reacts with each anode 10 and causes 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 causes an emission of fumes and gases 18, 29 migrating to the top of the tank including pollutants such as dioxide and carbon monoxide, sulfur dioxide, gaseous hydrogen fluoride (HF), carbon and alumina particles, dust and fluorinated compounds.

The decomposition of alumina causes a decrease in its content in the bath 8. When this content falls below a limit value, a rod mobile tubular steel installed between two anodes 10, pierces the crust 14 and injects alumina in the electrolyte bath 8. This rod, hereinafter referred to doser 16, is operable in a vertical motion using a jack, preferably pneumatic, to pierce the crust 14.

The majority of the fumes and gases 18 trapped between the anode 10 and the crust 14 escape through the hole drilled periodically in the crust 14 by the piercer-doser 16 to fit under a hood 20 which covers the open face of the tank electrolysis 2.
Part of the smoke and gas escapes through cracks and openings that exist in the crust 14.

The energy recovery system 22, according to a first embodiment of the invention comprises a primary circuit 24 for collecting fumes and gases produced by the electrolytic cell 2, and a heat exchange loop 26, hereinafter called first heat exchange loop 26.

The primary circuit 24 includes a device 28 for recovering the fumes and gas 29 arranged to cause depression under the hood 20 and suck fumes and gases 29 between it and the crust 14, and a unit 30 for processing these smoke and gas 29, hereinafter referred to as the first processing unit 30. The hood 20 is not hermetic and outside air is sucked under the hood 20 by the leaks because of the depression. This air mixes in large quantities with the fumes and gases coming from the tank.
In the following text we will no longer distinguish this air from fumes and gases and we will call by the generic terms smokes and gases.

The fumes and gases 29 are sucked by the recovery device 28 with a debit specificity of approximately 75 000 to 100 000 Nm3 / tonne Aluminum (which corresponds to 8400 to 11000 Nm3 / h for a tank of 350 kA).

The fumes and gases 29 collected by the primary circuit 24 exhibit a temperature approximately 110 - 160 C. They contain 200 - 800 mg / Nm3 of dust, 150 -mg / Nm3 of gaseous hydrogen fluoride and 100 - 400 mg / Nm3 of sulfur dioxide (S02). These fumes and gases collected by the primary circuit are referenced above.
after by reference 29.

The first processing unit 30 is suitable for filtering the dusts contained in the fumes and gases 29 collected by the recovery device 28, and eliminate the most of gaseous hydrogen fluoride by fluoride adsorption hydrogen gaseous from these fumes and gases on alumina which is then separated from fumes and gases 29 by filtering.

The first processing unit 30 is adapted to treat fumes and gases according to a dry process known as DRY-SCRUBBER DS. This process allows a dust reduction greater than 98% by filtration and a reduction of fluoride

About 99.8% hydrogen gas by adsorption and filtration.

The amount of hydrogen fluoride gas contained in fumes and gases outgoing from the first treatment unit 30 is less than 0.5 mg / Nm3. The number of dust contained in the fumes and gases 29 coming out of the first unit of treatment 30 is less than 5 mg / Nm3.

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 with the aid of piqueur-proportioner 16.
The primary circuit 24 further comprises a scrubber 32 with seawater or solution basic clean to eliminate by absorption and chemical reaction the dioxide of sulfur (S02) contained in the fumes and gases 29 coming out of the first treatment unit 30, and one chimney 34 clean to evacuate the remaining fumes and purified gases.
At the outlet of the scrubber 32, the fumes and gases 29 comprise a quantity lower than 60 mg / Nm3 of sulfur dioxide.

The first heat exchange loop 26 comprises a heat exchanger 36, hereinafter called the first heat exchanger 36, and a recovery unit 38 of the heat of a coolant. The loop 26 is covered, on the one hand, by the fluid coolant, and on the other hand, at the level of the first exchanger 36, by the fumes and gases 29 leaving the recovery device 28 before they pass through the first unit treatment 30.
The coolant heated by the first heat exchanger 36, is used by example to produce electricity by an ORC cycle generator, that is, to say a

6 Organic Rankine Cycle. The heat transfer fluid is for example constituted by water, oil or an inert gas.

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

The first heat exchanger 36 is able to cool the fumes and gases 29 of primary circuit 24 with 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 fumes and gases 29 of short circuit the first heat exchanger 36, when it is dirty and that he must be cleaned or replaced or renovated.

With reference to FIG. 2, the energy recovery method, according to FIG.
first embodiment of the invention, starts with a step 100 of collection of smoke and gas 29 by the recovery device 28.
During a step 102, the fumes and gases 29 collected by the circuit primary 24 are transported outside and away from the electrolysis cell 2. The fluid coolant of the first heat exchange loop 26 is warmed by the passage fumes and gases 29 through the first heat exchanger 36.
Then, during a step 112, the recovery unit 38 recovers the heat of heat transfer fluid having passed through the first heat exchanger 36.

During a step 114, the treatment unit 30 processes the fumes and gases 29 collected by the primary circuit 24 by dust filtering and elimination of the major part of gaseous hydrogen fluoride. Then, the fluorinated alumina generated by the first treatment unit 30 is introduced into the electrolyte bath 8 by the picker 16.

7 During a step 116, part of the sulfur dioxide contained in the fumes and gas 29 collected by the primary circuit 24 is removed by absorption and reaction chemical, by the scrubber 32.

Finally, during a step 120, the fumes and gases 29 leaving the scrubber 32 are evacuated by the chimney 34.

In a variant, the primary circuit 24 does not include a scrubber 32. In this case, step 116 is not performed. The fumes and gases 29 coming out of the first unit of treatment 30 are directly discharged through the chimney 34.

In a variant, the recovery unit 38 is a system making it possible to use the heat of the coolant to produce cold or heat.

The recovery system 40 according to the second embodiment of the invention, illustrated in FIG. 3, comprises a primary circuit 24 similar to the circuit primary 24 of the recovery system 22 according to the first embodiment of the invention, except that this circuit does not have a scrubber 32.

According to this embodiment, the fumes and gases 29 collected by the device of recovery 28 of the primary circuit 24 are sucked at a rate of 70000 to Nm3 / ton of Aluminum produced. They contain 100-800 mg / Nm3 of dust, 30-mg / Nm3 of gaseous hydrogen fluoride, 20-100 mg / Nm3 of sulfur dioxide, 2-4 g / Nm3 of carbon dioxide and 0.1 - 0.3 g / Nm3 of carbon monoxide. These smoke and gases collected by the primary circuit are referenced hereafter by the reference 29.

These fumes and gases 29 collected by the primary circuit have a temperature about 110 - 160 C before passing through the first heat exchanger 36, and an temperature of about 70 - 100 C at the outlet of the first heat exchanger 36.
Leaving the first processing unit 30, the fumes and gases 29 include less than 5 mg / Nm3 of dust and less than 0.5 mg / Nm3 of fluoride of gaseous hydrogen.

8 The recovery system 40 according to the second embodiment comprises a first heat exchange loop 26 similar to the exchange loop thermal 26 of recovery system 22 according to the first embodiment of the invention, except that this first heat exchange loop 26 has in addition a second heat exchanger 42.

The second heat exchanger 42 is arranged outside and at a distance at least one meter from the electrolysis cell.
The second heat exchanger 42 is disposed downstream of the first exchanger of heat 36, that is to say that the heat transfer fluid passes first, the first heat exchanger 36 then, the second heat exchanger 42 before rejoin the recovery unit 38.
The recovery system 40 furthermore comprises a secondary circuit 44 of collection of 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 after by reference 18.

This secondary circuit 44 includes a hood, hereinafter called local hood directly embedded in the crust 14 which collects the fumes and gases 18, also called anodic gas, escaping through the hole drilled by the metering piercer 16.
The local hood 46 houses the doser 16. The local hood 46 is connected to a tube smoke and gas collector 48.

An opening 50 made in the local hood 46 makes it possible to suck fumes and gases 29 collected by the primary circuit 24 and located under the hood 20 for lower the temperature of the fumes and gases 18 collected by the secondary circuit 44 and sucked by the local hood 46. The opening 50 in the local hood can be adjusted so to change the ratio of fumes and gases collected by the primary circuit / fumes and gases collected by the

9 secondary circuit to act on the efficiency of anodic gas capture and the resulting temperature of the mixture.

In practice, 4 to 6 local hoods 46 can be installed in a tank electrolysis 2 from 300 to 400 kA to ensure a good distribution of aspiration and capture the maximum amount of smoke and gas 18.

75 to 85% of the fumes and gases produced under crust 14 in the tank electrolysis 2 are sucked by the local hood 46 and collected by the secondary circuit 44.
The rest of the smoke and gas escapes through cracks and openings existing in the crust 14 and it is sucked by the recovery device 28 and collected by the circuit primary 24.

The pipes between the second heat exchanger 42 and each local hood can be insulated to avoid the energy losses that would be important given the small diameter of the pipes.

Fumes and anodic gas 18 collected by the secondary circuit 44 contain 1,2 8 g / Nm3 of gaseous fluorine, 1-8 g / Nm3 of sulfur dioxide, 110-280 g / Nm3 of dioxide of carbon and 10-26 g / Nm3 of carbon monoxide.

They have a temperature of the order of 200-350 C before their passage in the second heat exchanger 42, and a temperature of about 70-100 C after their passage in the second heat exchanger 42.
The secondary circuit 44 further comprises a processing unit 52, hereinafter after called second processing unit 52, a scrubber 53 and a capture unit 54 connected to the chimney 34.

The second processing unit 52 is similar to the first unit of treatment 30 located in the primary circuit 24. It is able to eliminate most of fluoride of gaseous hydrogen from the fumes and gases 18 collected by the secondary circuit 44 by adsorption and filtering.

According to this second embodiment, the second processing unit 52 uses of the partially fluorinated alumina obtained by the treatment of fumes and gases 29 collected by the primary circuit 24 by the first processing unit 30. Then, fluorinated alumina 5 generated by the second processing unit 52 is introduced into the tank Electrolysis 2 by the feeder 16.

Leaving the second processing unit 52, the fumes and gases 18 collected by the secondary circuit 44 have a value of the order of 1 mg / Nm3 of fluoride

10 g of hydrogen gas.

The scrubber 53 is similar to the scrubber 32 described in the first mode of realisation of the invention. At the exit of the scrubber 53, the fumes and gases 18 collected by the circuit 44 have a value of less than 30 mg / Nm3 of sulfur. They have a temperature of about 30-40 C.

The capture unit 54 is intended to capture the carbon dioxide by absorption by an ammonia solution or by amines or other techniques equivalent.

Finally, the fumes and gases treated by the capture unit 54 are evacuated.
over there fireplace 34.

With reference to FIG. 4, the energy recovery method, according to FIG.
second embodiment of the invention, begins with the same steps 100 and 102 as the recovery method according to the first embodiment of the invention.

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.
During a step 106, the fumes and gases 18 collected by the circuit secondary 44 pass through the second heat exchanger 42 and heat the fluid heat preheated having already passed through the first heat exchanger 36.

11 The method continues with the implementation of steps 112 and 114, these being identical to steps 112 and 114 of the method illustrated in FIG.

In a step 115, the gaseous hydrogen fluoride gas and gas 18 collected by the secondary circuit 44 is processed by the second unit of 52. This treatment is similar to the treatment performed by the first unit of treatment 30 to except that the partially fluorinated alumina generated by the treatment of fumes and gases 29 collected by the primary circuit 24, is used to adsorb fluoride of gaseous hydrogen from the fumes and gases 18 collected by the secondary circuit 44.
Then, the fluorinated alumina is introduced into the electrolyte bath 8 by the piqueur-proportioner 16.

Advantageously, fresh alumina is used to adsorb fluoride of gaseous hydrogen fumes and gases containing the least pollutants, that is to say say the fumes and gases 29 collected by the primary circuit 24, then is reused to adsorb the hydrogen fluoride gas fumes and gases 18 containing a concentration more pollutants, that is to say the fumes and gases 18 collected by the secondary circuit 44.
Alternatively, a mixture, possibly in variable proportions, of alumina fresh and partially fluorinated alumina can be used in second unit of treatment 52.

During a step 117, most of the sulfur dioxide contained in the fumes and gases 18 collected by the secondary circuit 44 is eliminated by a washer 53.

During a step 118, the capture unit 54 eliminates by absorption or by other techniques (adsorption, membrane filtration, ..) part of the dioxide of carbon fumes and gases 18 from the scrubber 53.

12 During a step 120, the fumes and gases treated by the unit of treatment 30 and the fumes and gases treated by the capture unit 54 are evacuated by the fireplace 34.

In a variant, the secondary circuit 44 has no pick-up unit 54.
In In this case, the fumes and gases leaving the scrubber 53 are directly directed around the fireplace 34.

Alternatively, a scrubber is disposed on the primary circuit 24 between the scrubber unit treatment 30 and the chimney 34.

In a variant, a bypass line 39 is mounted on either side of Mon among the first 36 and the second 42 heat exchangers to allow for the short circuit, for example, when cleaning these heat exchangers.
The recovery system 56 according to a third embodiment of the invention, shown in FIG. 5, comprises a primary circuit 24 and a circuit secondary 44 identical to the primary circuits 24 and secondary 44 of the system of recovery 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 system of recovery 40 from second embodiment of the invention with the exception of the existence of a third heat exchanger 60, also outside the tank 2.

In the first heat exchange loop 26, the third heat exchanger heat 60 is disposed downstream of the second heat exchanger 42, i.e.
the fluid coolant passes first, the first heat exchanger 36 and then the second heat exchanger 42 and finally the third heat exchanger 60 before of join the recovery unit 38.

13 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 to entry of the second heat exchanger 42, about 150 - 250 C at the entrance of the third heat exchanger 60, and finally about 200 - 400 C at the exit of this-this.

The second heat exchange loop 62 comprises a pipe traveled by an intermediate heat transfer fluid. The pipe passes through at least one wall 64 lateral of the electrolytic cell 2, then the third heat exchanger 60.
The intermediate heat transfer fluid comprises, for example, helium, the air or another gas inert vis-à-vis the liquid aluminum.

The intermediate heat transfer fluid recovers heat from the walls 64 of the tank, and delivers it to the third exchanger 60. Before entering the third exchanger 60, the intermediate heat transfer fluid temperature is between 250-600 C.

With reference to FIG. 6, the energy recovery method according to FIG.
third embodiment of the invention is identical to the recovery method according to second 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 loop heat exchange 62, passes through the wall or walls 64 of the electrolytic cell and is so warmed.

In step 110, the intermediate heat transfer fluid passes through the third heat exchanger 60 and thus heats the heat transfer fluid of the first loop heat exchange 26 already preheated in the exchangers 36 and 42.
In step 112, the recovery unit 38 generates electricity at from the heat recovered by the coolant having passed through the first 36, the second 42, and the third 60 heat exchangers.

14 Alternatively, branch lines 39 are mounted on either side of the second heat exchanger 42 to allow it to be short-circuited by example, when cleaning this heat exchanger. Thus, advantageously, the systems of energy recovery can continue to recover energy to more low efficiency, when cleaning a heat exchanger.

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.
Since the heat exchangers 36, 42 and 60 are outside the tank, they are easy to clean and easy to replace.

As the exchangers 36 and 42 are traversed by fumes, they can dirty and must be easily cleaned.

Since the heat exchangers 36, 42 and 60 are outside the vessel, the risk of attack by aluminum is avoided and the anode changes 10 do not are not Genoa.
Advantageously, the recovery system 40, 56 of the second and third embodiments of the invention comprises two circuits for processing the smoke and different gases with different percentages of pollutants and temperatures different. Each circuit 24, 44 of fumes and gas treatment is adapted at the rates of pollutants in these.

Advantageously, the recovery systems 40, 56 of the second and third Embodiments make it possible to increase the efficiency of the first loop heat exchange 26 by passing fumes and gases at medium temperature in one first heat exchanger 36, then the passage of fumes and gases to higher temperature in a second heat exchanger 42, and possibly in a third exchanger heat 60 at even higher temperature.

Advantageously, the recovery system 56 according to the third mode of embodiment of the invention comprises two heat exchange loops 26, 62 able to recover energy, one of the walls 64 of the electrolysis cell, the other, the energy of two circuits 24, 44 for treating fumes and gases.

Claims (14)

1.- System (22; 40; 56) for recovering energy released by at least one tank igneous electrolysis system (2) generating fumes and gases (18; 29) during the manufacturing aluminum (12), the recovery system (22; 40; 56) having a first heat exchange loop (26) traversed by a coolant, the first loop (26) comprising:
- a first heat exchanger (36) traversed by the heat transfer fluid; and a recovery unit (38) able to recover the heat of the fluid heat having passed through the first heat exchanger (36);
the recovery system (22; 40; 56) further comprising a primary circuit (24) capable of collecting at least a portion of the fumes and gas (29) generated by the electrolytic cell (2), the first heat exchanger (36) being disposed outside and away from the electrolytic cell (2); the first interchange of heat (36) being traversed by the fumes and gases (29) collected by the circuit primary (24) for heating the coolant, characterized in that it further comprises a secondary circuit (44) adapted to collect at least a portion of the fumes and gases (18) generated by the electrolytic cell (2) and wherein the first heat exchange loop (26) has a second heat exchanger (42) traversed by the fumes and gases (18) collected by the circuit secondary (44) for heating the coolant; fumes and gases (18) collected by the secondary circuit (44) being hotter and containing a concentration higher of pollutants as fumes and gases (29) collected by the primary circuit (24);
the recovery unit (38) being adapted to recover the heat of the fluid heat having passed through the first (36) and second (42) heat exchangers. 2. Energy recovery system (22; 40; 56) according to claim 1, in which the first heat exchange loop (26) comprises a third exchanger heat (60), and wherein the energy recovery system (22; 40; 56) comprises a second heat exchange loop (62) traversed by a coolant intermediate, the second heat exchange loop (62) being shaped to that the intermediate heat transfer fluid passes through the third heat exchanger (60) and least one wall (64) of the electrolytic cell (2), the recovery unit (38) being adapted to recover the heat of the fluid heat having passed through at least the first (36) and third (60) heat exchangers heat. 3. Energy recovery system (22; 40; 56) according to claim 2, who has at least one bypass line (39) capable of bypassing a least one among the first (36), second (42) and third (60) heat exchangers heat. 4.- Energy recovery system (22; 40,56) 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 metering pusher (16) suitable for piercing the solidified crust (14) and at injecting alumina into the electrolyte bath (8), and wherein the primary circuit (24) and / or the secondary circuit (44) behave each a device (28; 46) for recovering fumes and gases from a device (28) for recovering fumes and gases (29) located under the hood (20) and a device (46) of recovery of fumes and gases (18) released through a drilled hole periodically in the solidified crust (14) by the picker (16). 5.- energy recovery system (22; 40, 56) according to any one of Claims 1 to 4, wherein the fumes and gases (18; 29) generated by the tank electrolysis units (2) comprise dusts, gaseous hydrogen fluoride and of sulphur dioxide ; the primary circuit (24) and / or the secondary circuit (44) comprising:
a treatment unit (30; 52) for fumes and gases (18; 29) suitable for filter dust contained in the fumes and gases (18; 29) collected by the circuit primary (24) and / or the secondary circuit (44), and to remove some of the fluoride of gaseous hydrogen fumes and gases (18; 29) by adsorption on fresh alumina or partially fluoro; and a scrubber (32; 53) capable of removing part of the sulfur dioxide by absorption and chemical reaction. 6. Energy recovery system (22; 40; 56) according to claim 5, in which the processing unit (30; 52) is adapted to eliminate a part of the fluoride of gaseous hydrogen from fumes and gases collected by the secondary circuit (44) by adsorption on partially fluorinated alumina, said alumina partially fluorinated being obtained by the treatment of fumes and gases (29) collected by the primary circuit (24). 7.- Energy recovery system (22; 40,56) according to any one of Claims 1 to 6, wherein the fumes and gases (18; 29) generated by the tank electrolysis (2) comprise carbon dioxide; the secondary circuit (44) having a capture system (54) capable of eliminating a large part of the dioxide of carbon contained in fumes and gases (18; 29), for example by absorption. 8.- Method for recovering energy released by an electrolytic cell (2) igneous during the manufacture of aluminum (12), the method comprising the steps following:
- Warming (102) of a coolant by the passage of fumes and gases (18;
29) through a first heat exchanger (36) forming part of a first heat exchange loop (26);
recovery (112) of the heat of the coolant having passed through the first heat exchanger (36) by a recovery unit (38), said recovery (38) forming part of the first heat exchange loop (26);
- collection (200) of at least a portion of the fumes and gases (29) generated by the tank electrolysis (2), by a primary circuit (24);
- Crossing (102) of the first heat exchanger (36) by the fumes and gases (29) collected and transported outside and away from the electrolysis cell (2) by the circuit primary (24), for heating the coolant, characterized in that the method further comprises the following steps:
- collection (104) of at least a portion of the fumes and gases (18) generated by the tank electrolysis (2) by secondary circuit (44), fumes and gases (18) collected by the secondary circuit (44) being hotter and containing a higher concentration high of pollutants as fumes and gases (29) collected by the primary circuit (24);
and - Warming (106) of the coolant by the passage of fumes and gases (29) collected by the secondary circuit (44) through a second heat exchanger heat (42) forming part of the first heat exchange loop (26). The method of claim 8, wherein the recovery unit (38) generates electricity and / or cold and / or heat from the heat of the fluid coolant. 10.- recovery process according to any one of claims 8 and 9, who further comprises the following steps:
- Warming (108) of an intermediate heat transfer fluid through the crossing at least one wall (64) of the electrolytic cell (2), the coolant intermediate traversing a second heat exchange loop (62);
- Heating (110) of the heat transfer fluid through the fluid passage heat intermediate of a third heat exchanger (60) forming part of the first heat exchange loop (26); and recovery (112) by the recovery unit (38) of the heat of the fluid coolant having passed through at least the first (36), the second (42) and the third (60) heat exchangers. 11.- recovery process according to any one of claims 8 to 10, in which fumes and gases (18; 29) produced by the electrolysis cell (2) behave dust and gaseous hydrogen fluoride, the process comprising a step of treatment (114, 115) of fumes and gases (18; 29) collected by the circuit primary (24) and / or the secondary circuit (44) by dust filtering and elimination of the major part of gaseous hydrogen fluoride, on the one hand, by adsorption on alumina fresh or partially fluorinated, on the other hand by filtering. 12. A recovery method according to claim 11, which comprises a step of treatment (115) of a part of the gaseous hydrogen fluoride gas and gas (29) collected by the secondary circuit (44) by adsorption on alumina partially fluorinated, said partially fluorinated alumina being obtained by the treatment fumes and gas (29) collected by the primary circuit (24). 13.- recovery process according to any one of claims 8 to 12, in which the fumes and gases (18; 29) generated by the electrolysis cell (2) behave dust and sulfur dioxide, the method comprising a step elimination (116, 117) of 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.- recovery process according to any one of claims 8 to 13, who comprises a step of elimination (118), for example by absorption, of a part of carbon dioxide contained in the fumes and gases (18) collected by the circuit secondary (44) by a pickup unit (54).