EA019844B1 - A device for collection of hot gas from an electrolysis process, and a method for gas collection with said device - Google Patents

Abstract

An electrolysis cell producing metals needs to add an accurate amount of feed stock (like alumina) to the cell, and as an effect of the reaction taking place in the cell, one needs to extract the product (like aluminium) and remove any waste product (like HF and CO). In order to cool the cell properly and to ensure collection of all the effluents from the cell, which is not gas tight, a normal suction is about 10-150 times more ambient air than gas volume produced by the cell. The present invention relates to the principles of how one can extract a more CO-concentrated flue gas from the cell than is standard procedure in the aluminium industry today, by means of distributed pot suction (DPS) devices. In one embodiment the DPS can be integrated with a feeder having a breaker bar for feeding raw material to the cell. Heat energy can be extracted from the hot flue gas and be utilized.

Description

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for collecting exhaust gases generated in an electrolyzer, in particular an electrolyzer for aluminum production.

State of the art

In all modern electrolytic cells for the production of aluminum containing a prebaked anode, the upper part of the electrolytic cell structure (the electrolytic cell cover) has several separate point feeders attached to the indicated upper part of the electrolytic cell structure. The gas collection system contains several suction points distributed along the channel for the process gas located on top of the aforementioned upper part of the structure, but as a separate system adjacent to the alumina feed system. Since usually at least one anode should be replaced with a new anode every day, in modern electrolyzers with a prebaked anode, the upper part of the structure contains a large number of covers that cover the area between the cathode and the skirt of the gas collection unit, located just below the crosshead for hauling the anode frames, in order to prevent the escape of exhaust gases from the electrolysis body. To prevent air pollution inside the upper part of the electrolytic cell structure, it is usually necessary to create a negative pressure (below atmospheric), while a large amount of air is sucked in through the existing gaps, which, together with the exhaust gases, enter the exhaust system for subsequent processing, removal of fluoride compounds and, in some cases, desulfurization (desulfurization).

The air entering the upper structure of the electrolyzer also provides air cooling of the upper part of the electrolyzer together with the equipment installed in it (pneumatic, electrical and electronic equipment). When replacing the anode, some covers must be removed. In order to prevent waste gases from escaping from the electrolysis chamber and protect operators from their effects, efficient collection of exhaust gases during this operation can be achieved by significantly increasing the volume by switching on the electrolyzer in the gas suction mode, which is implemented when the electrolyzer is serviced (Ροΐ Tepbshd 8ysyop), for example using a separate gas suction line. By switching the valve, gas suction can vary from normal to suction when servicing the electrolyzer (Ροΐ Teppt 8syop), and the increased suction volume allows manipulation of replacing the anode with several covers removed from the electrolyzer, without any waste gas entering the electrolysis shop, etc. e. by maintaining a vacuum inside the upper structure of the cell.

Alumina was fed into the electrolyzer more than a hundred years ago by manual crushing of the upper alumina crust and feeding aluminum powder into the electrolyzer. Later crust was crushed using a rotor for crust breaking, then using a traverse with a crust breaking machine and, finally, a device for spot crust breaking equipped with electronic control, which is installed in essentially all newly constructed melting furnaces. Therefore, the point feed is considered as corresponding to the prior art.

In the process of aluminum production, waste streams are also generated, mainly СО ₂ with traces of СО, as well as significant quantities of НР and §О ₂ . Such effluent streams are evacuated during the electrolysis process through one layer of the crust hardened above the electrolyte, through loading holes in the crust, and also through the crust itself. Modern melting furnaces remove most of the HP and §O ₂ before the exhaust gases are released into the atmosphere, but do not remove CO ₂ . In order to remove all emitted gases that exit the electrolyzer and to cool the electrolyzer properly, generally accepted typical suction structures have several suction points distributed along the main gas outlet channels located approximately 1 m from the upper crust of the electrolyte. These suction points discharge a large amount of air drawn in from the gaps and junctions in the upper part of the cell, while maintaining a vacuum inside the top covers to ensure that all exhaust flows from the cell are trapped. The collected gas is cold enough for the upper part of the electrolyzer design (100-150 ° C), and the exhaust gases are greatly diluted with air sucked through leaks.

Until now, much attention has not been paid to scrubbing CO ₂ , since it is part of the generally accepted purification cycle, however, the increased attention that has recently been paid to the problem of the effect of CO ₂ on the climate has changed the existing priorities. A structural limitation of modern electrolyzers for the capture and removal of CO ₂ is the low concentration of CO ₂ in the process gas, which is usually less than 1%. The removal of CO ₂ with a low concentration is a complex and expensive process, and therefore no information on such a process has been found in any published literature. CO2 removal costs generally generally decrease with increasing CO2 concentration in the exhaust gases.

The present invention relates generally to a gas collection device, preferably combined with an alumina feed feeder. The invention relates to a method for collecting concentrated process gas with a view to its further processing. In addition, the proposed device provides the collection of process gas at sufficiently high temperatures suitable for utilization

- 1 019844 heat, for example waste gases, the temperature of which is more than 100 ° C, preferably more than 150 ° C.

Patent Document \ ¥ O 2006/009459 describes a method and equipment for recovering the heat of exhaust gases leaving a process plant, for example a process gas from an electrolysis plant for aluminum production. Such a technical solution can be advantageously combined with the present invention.

Various manufacturing processes generate process gases, which can be contaminated with particulate matter, dust and other particles, which can cause the formation of deposits in equipment for utilization (recovery) of thermal energy. Such deposits will reduce disposal efficiency and may require extensive maintenance, such as cleaning surfaces exposed to gas flow. The process gas, before it can be cleaned, can contain dust and / or solid particles that will form deposits on the heat recovery equipment and, thus, reduce the efficiency of utilization to an undesirably low level. Therefore, usually downstream from the gas treatment plant, units are placed to recover the heat produced after gas treatment.

From the point of view of optimizing energy utilization, it is of interest to place utilization units as close as possible to the production process, which is characterized by the maximum content of thermal energy in the process gas. This suggests that heat recovery units should be located upstream of the gas treatment plant, since such plants are concentrated at a relative distance from the production process. For example, process gas from electrolysis cells for aluminum production contains a large amount of thermal energy at a relatively low temperature level. This energy is currently used only to a small extent, but it can be used for heating, for technological needs and energy production, if technically and economically acceptable solutions for heat recovery are identified. The temperature level reached in a heated fluid is critical to the magnitude and usefulness of the recovered thermal energy. Therefore, heat must be extracted from the process gas at the highest possible temperature of the process gas.

Cooling the process gas will contribute to reduced gas flow and pressure drop with a corresponding reduction in fan power. The greatest reduction in pressure drop is achieved by cooling the process gas as close as possible to aluminum electrolysis cells.

The heat energy contained in the process gas can be removed in a heat exchanger (heat recovery system), in which the process gas, when cooled, transfers the waste heat to another fluid suitable for the selected application. In principle, a waste heat recovery system can be located:

a) upstream from the place of cleaning, where the specified heat recovery system must operate with a process gas containing solid particles;

b) downstream of the purification site, where contaminated components and particles contained in the gas have already been removed;

c) in the cell itself.

Since the cleaning processes that can be used at present are most optimally carried out at a low temperature level, thermal energy recovery in practice meets the requirements of only such an alternative in which the heat recovery system is located upstream from the place of the cleaning process. This in practice means that this heat recovery system must be able to work with hot gas containing solid particles.

The cooling of the raw gas upstream of the fan in combination with heat recovery is a technical solution that can reduce both the volumetric flow of the process gas and the pressure drop in the duct system and in the gas treatment plant. As a result, the amount of intake gas can be increased if there is no need to change the size of the channels and the gas treatment plant.

The heat removed from the process gas is useful for use as process heat for various heating and processing purposes, similar to the removal of carbon dioxide.

The proposed suction device for collecting gas is capable of efficiently collecting exhaust gases obtained in the electrolyzer, in the absence of alumina or anode coating material (MPA) entering the suction device. The combination of this device with a point feeder allows you to create a compact design.

In patent document I8 4770752, 1988, a system is described in which a gas collection hood is installed in contact with a crust at a location of an opening formed in this crust. The objective of this invention is to ensure the collection of exhaust gases from the electrolyzer for its purification from fluorine-containing components using alumina, after which the alumina and fluorides are returned again

- 2 019844 was introduced into the electrolyzer using a separate alumina feeder. The CO ₂ flushing and heat recovery are not mentioned in this document, with the exception of preheating alumina. The known invention has a limitation with respect to maintenance and possible damage during the replacement of the anodes, since said cap is placed too close to the anodes and the crust. For any installation using this invention, there is no reason to save these disadvantages.

Patent Document 1 57174483, 1981, describes a method and apparatus for continuously measuring current efficiency in an electrolytic cell for aluminum production. The task is to quickly and continuously measure the current efficiency and control the feed of raw materials by collecting gases continuously produced by the electrolyzer, sequentially measuring the concentrations of CO ₂ and CO, converting them into electrical signals and sending these signals to the controller. The device for collecting gases is not fully disclosed, but it seems to be in contact with the crust with the disadvantages inherent in such an arrangement.

In patent document I8 4770752, 1988, a system is described in which a gas collection hood is installed at the location of the hole formed in the crust and in contact with the crust. The objective of the known invention is to provide for the collection of exhaust gases generated in the electrolysis cell for purification from components containing fluorine, using alumina located near the electrolyzer, after which the alumina and these components are fed directly back to the same electrolyzer from which the exhaust gases.

Document I8 5968334 describes a process for removing from the exhaust gases leaving the electrolyzer at least one of the gases including CP ₄ and C ₂ P ₆ using a membrane.

SUMMARY OF THE INVENTION

The present invention also relates to principles of distributed suction for an electrolytic bath in the case where it is possible to combine the supply of crude material containing alumina to the electrolyzer and at the same time to extract exhaust gases with a higher concentration of CO2 from the hole in the upper crust of the electrolyte compared to a procedure currently accepted in the aluminum industry. However, if necessary, suction can also be arranged in other places above the crust in the cell.

With respect to exhaust gases, four resulting effects are obtained, namely:

1) a smaller total volume of gas discharged from the electrolyzer, which makes it possible to reduce the overall size of the plants / unit for the purification of exhaust gases or gas purification unit;

2) as a consequence of the above effect, the temperature of the collected process gas will increase to a greater extent than before, and therefore, such a gas is more suitable for heat recovery;

3) the absorption of a smaller amount of air sucked in through the leaks into the gas collection chambers significantly increases the concentration of CO2 in the exhaust gases, which allows the capture and removal of CO2 using conventional technologies used to capture CO2 emitted from power plants;

4) improving the nature of the flow of gas flow inside the upper part of the design of the cell.

These and other advantages can be achieved using the invention, the scope of which is set forth in the attached claims.

List of drawings

Below the invention will be further explained using examples and drawings.

FIG. 1 is one embodiment of a device for distributed suction from an electrolyzer (RWE) in accordance with the invention.

FIG. 2 illustrates the gas-dynamic picture of the collection of exhaust gases using a suction device containing a cap made with a single wall.

FIG. 3 illustrates the gas-dynamic picture of the collection of exhaust gases using a suction device comprising a double-walled hood.

FIG. 4 is a view of a part of a double-walled gas cap, bottom view.

FIG. 5a is a second embodiment of a device for distributed suction from an electrolytic cell, a cross-sectional view.

FIG. 5b is a side view of the device for the EWF shown in FIG. 5a rotated 90 ° about a longitudinal axis.

FIG. 5c is an enlarged view of the mounting plate of the RWE device shown in FIG. 5a and 5b.

FIG. 6 is a graph showing the concentration of CO2 in an electrolytic cell with conventional collection of exhaust gases from the internal volume of the upper structure of the electrolytic cell.

FIG. 7 is a graph showing the concentration of CO ₂ when conditions change from normal (on the left) to the collection only with the help of the EW (on the right).

FIG. 8 is a plan view of the gas flow pattern in the upper part of the design of an electrolytic cell operating with five devices for electronic equipment;

- 3 019844

FIG. 9 is a diagram showing the distribution of pressure / gas flow in the electrolytic cell with suction from the top of the upper part of the electrolytic cell structure.

FIG. 10 is a diagram that shows the pressure / gas flow distribution in the suction cell corresponding to the use of the EW apparatus according to the present invention, carried out without suction from the top of the upper part of the cell structure.

To ensure maximum gas collection by the device for distributed suction from the electrolyzer (RWE), the gas collection hood may have a different design. In one of the prototypes created during the development of the invention, the gas collection cap 4 'was made with a single wall (see in Fig. 2 an illustration of gasdynamics of gas collection, showing the efficiency of collection). Another embodiment of the suction cap 4 was made with double walls (see Fig. 3), and in this embodiment, the flow rate in the suction channel formed between the double walls is much higher than in the center. The thicker lines in the figure show higher absorption intensities.

Such additional suction creates an artificial air wall, which provides a more efficient collection of exhaust gases leaving the hole (s) N, punched in the crust C of the electrolyte, and reduces disturbances from transverse flows. It is also possible to supply the RWE device with compressed air and blow air through this opening, with the manifestation of the negative side of using more compressed air in the electrolysis case. In the figures, reference numeral 7 shows a metal pin for punching an electrolyte crust.

Information confirming the possibility of carrying out the invention

The following is a description of the operation of the device for the electronic equipment, combined with a point feeder.

In FIG. 1, position 1 shows the pneumatic cylinder of the device (mechanism) for punching the crust, attached to the supporting elements of the device RVE. This figure shows a gas collection cap 4, a pipe 3 for loading alumina, a pipe 5 for suctioning gas, equipped with a valve 6. On the other side of the valve, a pipe 2 is shown.

During the operation of the device, a normal gas stream flowing to the upper part of the electrolytic cell structure passes through the device for the electrical equipment, while the location of the device for the electronic equipment is in each of the supply points of the electrolyzer. The suction pipe for the RVE, which is introduced through the pipe 2 intended for it, can preferably be connected to the existing feeder with its modification, or alternatively, the feeder can be part of a new design, replacing the existing feeder. Alumina can be fed using a fluidized bed feeder, but mechanically driven feeders can also be used.

When gases are aspirated through pipeline 2, they will be collected in the main pipeline / collector installed on the upper part of the electrolyzer transporting gases coming from all feeding points of alumina (not shown). From these transition gases are transported to a gas cleaning system (i.e., the extraction and removal of fluoride 8o _2), and of these systems are introduced into any industrial _CO2 washing system able to carry out washing with currently existing concentrations of CO _2, or the gases are sent as an input stream to systems operating with fuel combustion, such as gas turbine plants, coal-fired power plants, or biomass combustion plants.

If it is necessary to carry out maintenance of the electrolyzer, the main channel for collecting gas from the locations of the devices for the electronic equipment located on the upper part of the structure can be closed, and the main channels located in the upper part of the cell are activated in order to maintain absorption from the cell during its maintenance (i.e., the suction volume from the cell increases 2-4 times compared with conventional suction).

The process gas concentrated at the top is hotter than usual, making it suitable for heat recovery. On the other hand, warmer gas can damage the top of the structure and the electronic equipment housed here. One of the solutions to this new problem is the thermal insulation of the elements of the gas collection systems located inside the upper part of the electrolyzer structure and outside the electrolyzer, to the place where heat recovery can be carried out.

Another alternative may be the arrangement of gas collection caps and their corresponding piping systems with a certain gap relative to other equipment located inside the upper part of the cell.

Process gases from several electrolyzers can be connected to one common heat recovery unit. The process gas is then sent to conventional gas cleaning, dust removal, HP and 8O ₂ . Depending on whether the flue gas will be directed to another process as combustion air or directly to the CO2 flushing apparatus, the flue gases should probably be substantially purified to avoid disruption of these process steps.

- 4 019844

The main features of one embodiment of the present invention are to combine a point suction system with a point alumina feeder equipped with a mechanism for punching an electrolyte crust. A step forward made by using the device for the EWF is the changed composition and increased temperature of the collected process gas. The gas collected through the EWF will contain much less sucked-in air and, accordingly, will have a higher concentration of explosive gas (fluoride compounds, 8О _X and СО ₂ ). This will facilitate the capture of fluoride compounds and the removal of 8O _X. The problem is to increase the concentration of CO ₂ to a level at which to remove CO ₂ can be used at the disposal of industrial washing technology CO _2. In addition, due to the smaller amount of air and the placement of devices directly above the supply points, the collected exhaust gases have a higher temperature compared to conventional process gas, which improves the heat transfer efficiency.

Any specialist in the art should understand that the cap for collecting process gas can be adapted to any type of point feeder and can also be placed in the immediate vicinity of such a feeder, not being an integral part thereof.

Suction in the pipe 2 in FIG. 1 can also be divided into two independent suction flows, which can be controlled, in the case when they can be independently controlled: suction from the annular gap 11 between the inner and outer walls 14, 13 and suction into the inner cavity 12 of the hood 4; see also FIG. 4.

The inner wall 14 of the suction cap 4 can be either continuous or perforated, i.e. made with holes or without holes (not shown). In addition, the walls of the suction cap 4 can be made diverging at an angle outward so that the gas suction velocity vector can be directed at any angle in the range from 0 to 180 ° below in the direction of the crust.

In FIG. 5a is a cross-sectional view of a second embodiment of a device for electronic equipment connected with a point feeder (TP).

In this embodiment, the inner wall 28 is shown having a rectangular sleeve shape, and the outer wall 26 also has a rectangular sleeve shape. The gap between the inner and outer walls forms a suction gap between the two walls with the suction hole 15. The inner wall extends closer to the crust direction than the outer wall and has a suction hole 16. In addition, an alumina feed pipe 23, 23 'is shown, a suction pipe 22, a pneumatic cylinder 21, and a punch (metal pin) 27 for piercing the crust.

In FIG. 5b is a side view of the EWF device shown in FIG. 5a rotated 90 ° about the longitudinal axis. This figure shows the outer wall 26, the outlet pipes 22 and 22 'and the mounting plate 30. The specified mounting plate is shown in more detail in an enlarged view in FIG. 5s The task of the mounting plate is to evenly distribute the suction gases exiting through the exhaust pipes 22 and 22 ', in the gap between the outer and inner walls. This is achieved due to the location in the specified plate of the corresponding through holes O, O ', O, O' or slots. The plate, in addition, has additional holes for the feed pipe 23 ', which serves to supply alumina, and one barrel point feeder.

In addition, the lower part of the outer wall 26 can be made with an expanding deflector (not shown). This deflector may be a part of all sides of the wall, having the shape of a plate and preferably the angle of inclination β relative to the horizontal plane. The deflector's task is to direct the flow of gases that are sucked into the gas hood. The angle β may preferably be in the range from 30 to 60 °.

In addition, a dust collector 29 can be placed inside the hood (see FIG. 5a) so that alumina and other particulate components are not carried away by the suction exhaust gases further into the gas evacuation system. The dust collector in such an embodiment may be formed by one or more slot holes 29 formed in the inner wall, i.e. in the wall separating the volume formed between the double walls from the volume inside the suction cap. Preferably, the slot opening is located near the upper wall defining the internal volume in the cap, such that, when gases are sucked into the annular gap, gas will also be sucked through the specified slot hole. With this tool, a gas containing particulate materials that enters the inner volume of the hood will accelerate, hit the roof of the hood and sink down to the crust or hole of the feeder below the hood.

In addition, the equivalent diameter of the slit openings for the gas flow can be designed in such a way that suction into the volume formed between the outer and inner walls will also result in corresponding suction into the volume bounded by the inner wall of the hood, thus establishing a relationship between the number suction gas into the inlet 15 depending on the suction in the inlet 16.

- 5 019844

Preferably, the cross-sectional area between the inner wall and the outer wall increases downstream from the second inlet 15, whereby the gas velocity decreases.

The gas collection cap is preferably placed at a distance from the crust of the electrolyte, which allows them to be passed below the cap during the replacement of the anodes. Mostly the cap is placed at a minimum distance from the crust, depending on the intensity of absorption. Preferably, this distance is from 10 to 1000 mm.

The specified distance must be selected taking into account the speed at which the alumina / anode coating material (MPA) is captured and which is of the order of 7 m / s. Therefore, the distance between the cap and the top of the crust should be such that the indicated level of speeds at the surface of the crust is not reached.

Such an embodiment of the EWD device is designed in such a way that, by means of physical action, the hot gas to be sucked off is separated from the technical elements of the electrolyte crust piercing device as much as possible so that as small thermal stresses as possible of the critical elements of the crust piercing device are created.

In FIG. Figure 6 shows a graphical dependence of the concentration of CO ₂ in the electrolyzer with the traditional collection of exhaust gases evacuated from the internal volume of the upper part of the electrolyzer design.

In FIG. Figure 7 presents a graphical dependence showing the concentration of CO2 under changing conditions from ordinary (on the left) to gas collection only with the help of the WEC (on the right).

FIG. 8 is a schematic view of the gas flow pattern in the electrolyzer for the case of using five RWE devices in the electrolyzer, top view. The arrows show the pattern of gas flow above the crust, which, as can be clearly seen, is directed to individual suction points.

In this way, you can divert most of the process gases that are released in the electrolyzer. In addition, the extraction of a very large volume of gases directly above the crust in the place where the caps are placed will positively affect the overall picture of the gas flow inside the upper part of the cell. This will be explained below with reference to FIG. 9 and 10.

In FIG. 9 shows the distribution of pressure / gas flow in a well-known type electrolyzer with evacuation of process gas E from the top of the upper part of the electrolyzer. In this design, the effect of natural traction will be manifested, which, together with the gas suction going up the electrolyzer, determines the picture of the gas flow inside the electrolyzer. In this figure, the electrolyzer operates in the usual way with the top closed, with all the covers closed. In FIG. 10 shows the pressure distribution in the electrolytic cell with evacuation of the process gas E in accordance with the present invention with the help of five units of electronic equipment without suctioning from the top of the upper part of the cell. As in FIG. 9, the electrolyzer operates in the usual manner with the closed top of the structure.

In accordance with the present invention, the capture and accumulation of CO2 in one embodiment can be carried out through the following steps:

1) generation of CO _{2 by an} electrolyzer;

2) the collection of exhaust gases having a high content of CO ₂ ;

3) utilization of the heat of said gas;

4) pre-flushing;

5) the direction of the gases to other processes and / or the gas supply to the CO2 scrubber;

6) the removal of purified gas from the scrubber, the direction of CO2 in the node increase pressure;

7) transportation of liquefied CO2 for storage.

- 6 019844

Claims (24)

CLAIM 1. A device for collecting hot gas released during the electrolytic process for the production of metals, containing a gas collection cap (4) located above the gas evolution zone, characterized in that the gas collection cap (4) contains at least two inlets (11, 12; 15, 16) for the gas to be collected, while one first internal inlet (12; 16) is surrounded on the outside by a second inlet (11; 15), and the gas collection cap (4) is made in the form of a double-wall structure containing one internal wall ( 14; 28) and one external wall (13; 26), with the specified second inlet (11; 15) formed by the gap between these two walls. 2. The device according to claim 1, characterized in that the cross-sectional area between the inner wall (14; 28) and the outer wall (13; 26) increases in the downstream direction from the second inlet (11; 15) and, thus , the gas velocity increases. 3. The device according to claim 1, characterized in that the inner wall (28) extends closer to the gas evolution zone than the outer wall (26). 4. The device according to claim 1, characterized in that the inner wall (28) has at least one slotted opening (29) in its upper part, which allows gas to pass from the first inlet opening (16) into the gap between the two walls. 5. The device according to claim 2, characterized in that the lower part of the outer wall (26) deviates outward relative to the inner wall. 6. The device according to claim 1, characterized in that it is made integral with a point feeder equipped with a mechanism (27) for penetration of the crust. 7. The device according to p. 6, characterized in that the loading of raw materials carried out inside and / or near the gas collection cap (4). 8. The device according to claim 1, characterized in that the gas collection cap (4) has the shape of a circle, ellipse, square or rectangle in cross section. 9. The device according to claim 1, characterized in that the shape of the gas collection cap (4) is optimized for the required intake volume, for example, it is made conical. 10. The device according to claim 1, characterized in that in the electrolysis process produce aluminum or other metals. 11. The device according to claim 1, characterized in that the specified device within the upper part of the design of the electrolyzer is connected to a thermally insulated system / pipes for collecting exhaust gases. 12. The method of collecting hot gas released in the electrolysis process, using the device according to one or more of paragraphs.1-11, characterized in that the gas is collected in the immediate vicinity of the peel (C), as well as the composition of the process gas includes CO ₂ with a content of at least in the range from 0.5 to 10%. 13. The method according to p. 12, characterized in that the gas is collected in the immediate vicinity of the peel (C) of the loading opening (H), punched in the specified peel (C). 14. The method according to p. 12, characterized in that the exhaust gases have a temperature of more than 100 ° C, preferably more than 150 ° C. 15. The method according to p. 12, characterized in that heat is extracted from the flue gases by means of suitable heat exchange means, for example, by means of the flue gas heat exchanger. 16. The method according to p. 12, characterized in that the exhaust gases downstream share with the separation of components rich in CO2. 17. The method according to p. 12, characterized in that in the device for collecting hot gas the flow rate of gas passing through the first inlet is different from the speed of gas passing through the second inlet, and preferably less than the speed of gas passing through the second inlet . 18. The method according to p. 12, characterized in that the device for collecting hot gas is placed over a single inlet (H), pierced in the crust using a mechanism for crushing the crust, combined with a point feeder, preferably at a distance from 10 to 1000 mm above peel (C). 19. The method according to p. 12, characterized in that all process gases are collected with proper suction efficiency without trapping any other gases in the upper part of the design of the electrolyzer during its normal operation. 20. The method according to p. 12, characterized in that the absorption of gas in the cap is produced like a normal absorption during the loading of alumina. 21. The method according to p. 12, characterized in that during the loading of alumina gas absorption is blocked. 22. The method according to p. 12, characterized in that the collected exhaust gases are used for the purpose of heat recovery. - 7 019844 23. The method according to p. 12, characterized in that the collected exhaust gases are cleaned to separate gases like HP pairs, 8O ₂ CO ₂ and dust. 24. The method according to p. 12, characterized in that the device for collecting hot gas is combined with a separate gas collection system used during normal operations, such as replacing anodes and pouring metal from the electrolyzer.