WO2012020188A1

WO2012020188A1 - Method and device for confining cell gases in an aluminium electrolysis cell

Info

Publication number: WO2012020188A1
Application number: PCT/FR2011/051746
Authority: WO
Inventors: Thierry Malard; Antoine De Gromard
Original assignee: Solios Environnement
Priority date: 2010-08-10
Filing date: 2011-07-20
Publication date: 2012-02-16
Also published as: NO20111050A1; FR2963793B1; FR2963793A1; DE102011052543A1

Abstract

The method of confining the cell gases in a capped cell, at least one cap (18) of which is locally and temporarily removed, consists in blowing at least one jet of air from substantially one edge of the opening bounded by at least one removed cap (18), so as to form an air curtain (21) completely covering the opening and providing a dynamic pneumatic barrier effect between the cell gases (15) inside the cell (1) and the ambient atmosphere outside this cell. The confining device comprises at least one nozzle for blowing at least one air jet, capable of forming the air curtain (21), which is inclined as the caps (18) normally are, the nozzle being supported by at least one part of the cell (1) and/or of at least one cap (18), and at least one air or compressed-air supply source supplies this nozzle, in order to blow the air jet or jets for forming the air curtain (21).

Description

"METHOD AND DEVICE FOR CONTAINING TANK GASES IN AN ALUMINUM ELECTROLYSIS TANK"

The invention relates to a method and a device for confining the tank gases in an aluminum electrolysis cell, and more particularly in a covered tank with at least one cover is locally and temporarily removed, to allow intervention on the tank, including an anode change operation, which requires, generally, to remove the two tank covers adjacent to each other and facing the corresponding anode rod.

For a better understanding of the invention, reference is made to FIG. 1, which is a diagrammatic cross-sectional view of an electrolysis cell of aluminum, that such an igneous electrolytic cell 1 comprises a tubular shell 2 of generally parallelepipedal shape and open at its upper part, and whose bottom carries a refractory insulation 3 itself supporting cathodic carbon blocks constituting a cathode 4, laterally surrounded by a thickness of liquor 5 in pot outward support against a wall 6 of graphite and bricks constituting an inner lining of the ferrule 2. This assembly inside the ferrule 2 contains an electrolysis bath 7 constituted by alumina dissolved in the cryolite, and brought to a temperature between 950 ° and 1000 ° C. In this bath 7 are dipped precut carbon anodes 8, arranged in two parallel rows, and each secured to the lower end of a vertical anode rod 9, serving for the mechanical support of the corresponding anode 8 as well as its power supply, this rod 9 being locked in position of electrically conductive contact against a bar 10 of current supply by a rod locking device 11. In the base of the shell 2, the cathode 4 is traversed horizontally by a bar 12 of current collection, which leaves the shell 2 to be connected to the power supply of other tanks 1 of an aluminum smelter. Thus, when an electric current is applied between the anodes 8 and the cathode 4, the alumina is decomposed into aluminum forming a metal bath 13 which covers the cathode 4, and oxygen which reacts with each anode 8 and causes the combustion thereof progressive.

The liquid metal aluminum of the bath 13 is regularly removed from the electrolytic cell 1. The upper part of the electrolysis bath 7 is solidified, forming a crust 14 which covers the bath 7 and insulates it thermally, upwardly as well as laterally towards the paste 5 and the wall 6.

The electrolysis reaction at each anode 8 causes an emission of fumes and gases that migrate above the vessel 1, around and above the anodes 8 and the crust 14, which is covered with a layer 16 alumina extending from the upper edges of the wall 6 to the side walls of the anodes 8, to provide a certain seal. The alumina of this layer 16 is provided by a hopper 17, supported between the two bars 10 of current supply, and this hopper 17 also feeds the electrolysis bath 7 alumina, through orifices regularly drilled at through the crust 14, using tubular steel rods, not shown to simplify the figure, movable vertically between the anodes 8, to pierce the crust and inject alumina into the electrolysis bath 7. These rods , called dosing-dosers, are operable in a vertical movement using cylinders, preferably pneumatic. Indeed, the decomposition of the alumina by electrolysis causes a decrease in its content in the electrolysis bath 7, and when this content falls below a limit value, it is necessary to refill the bath 7 alumina through to these lancers.

The majority of the fumes and gases concentrated pollutant, some of which are very harmful to the environment and human health, trapped under the crust 14 and the anodes 8 escapes through the holes drilled periodically in the crust 14 by the metering pioneers , and cracks that may exist in the crust 14, to mix, in the upper part of the tank 1, with fumes and less concentrated gases, but also polluted and toxic, from the reactions at the level of the anodes 8. For to prevent the diffusion of all these polluted and toxic fumes and gases to the ambient atmosphere, around the tank 1, where personnel operate, on the one hand rows of removable hoods 18 are arranged on the sides of the tank, for confining these polluted and toxic fumes and gases, hereinafter collectively referred to as tank gas, in a volume delimited by these covers 18 and the equipment in the upper part of the tank 1, above the baths 7 and 13, crust 14 and anodes 8, and, secondly, these tank gases are sucked continuously out of the tank 1 to undergo filtration and depollution treatments, in facilities such as treatment centers gases, in order to capture, recover and optionally recycling pollutants contained in these cell gases, such as carbon dioxide and carbon monoxide, sulfur dioxide, hydrogen fluoride gas (HF), carbon and alumina particles, dusts and fluorinated compounds before the release of gases to the atmosphere.

These tank gases are sucked from the top of the tank by suction passages 19 extending between the central hopper 17 and the two current supply bars 10, then are evacuated through an opening (not shown) to a a collection circuit of the tank gases produced by several tanks 1 of an aluminum smelter, and then to appropriate treatment plants, successively passing gas suction ducts of each tank 1, then collectors collecting the flow rates of 'a group of vats.

Rows of removable covers 18 are shown in Figures 2a, 3, 4, 7 and 8 attached to this description, which are described below.

As these rows of covers 18 are not watertight, it is understood that the suction of the tank gases for their treatment generates, in the volume defined in the tank 1 by the covers 18, a slight depression, which causes a suction of air ambient in the tank 1, which is mixed with the tank gases 15 and is evacuated with the latter in the networks of ducts and collectors which connect the electrolysis tanks 1 covered, thus closed, in normal times, filtration facilities and depollution of gas treatment centers.

In operation, interventions on tanks are necessary, if only to cyclically replace the anodes 8 consumed, using a hoisting installation comprising, typically, a crane traveling not only above a group of tanks 1 aligned side by side, but also along each tank, of elongate rectangular shape, this crane allowing, after an opening of the tank by the removal for example of two covers 18 adjacent one to the other and at right or opposite the rod 9 of an anode 8 to be replaced, to lift the anode to be replaced by its rod 9, then to deposit it outside the tank and then replace it by depositing in the tank a new anode 8. After which, the two covers 18 locally and momentarily removed from the tank 1 are again replaced on the latter.

But, to prevent that, during the opening time of the tank 1 by the removal of these two covers 18, tank gases do not come out of the tank and pollute the ambient atmosphere and intoxicating the personnel who get there find, a tank 1 open is subject to over-suction, thanks to an over-suction installation, which aims, on the electrolysis tanks, to reduce gaseous and dust emissions by increasing the suction flow when one or more hoods 18 are open for tank operations.

Several types of over-suction installations are currently used.

According to a first type of installation, in order to carry out the over-aspiration, each gas outlet duct coming from a tank is equipped with a gas deflection flag register, enabling the vessel gases of the normal network to be deflected. suction, with main collector, to a secondary suction network, comprising a secondary collector connected to so-called booster fans, which can suck with the flow required for over-suction, and the over-aspirated tank gases are then reinjected into the main suction network, which leads them to gas treatment facilities. Such an embodiment is disclosed in WO 2008/074386, and may utilize rate deviating flag registers as described in patent application WO 2005/111480 of the applicant of the present application. Such an installation is expensive because it requires a dual network. In addition to at least one main fan, it requires at least one dedicated secondary fan, fixed or mobile. In the case where the secondary fan is fixed, the installation requires flag registers to switch the outlet gases from the tank from one circuit to another, which further increases the costs of installation and maintenance. In the case where the secondary fan is mobile, it requires numerous and important interventions exposing the workforce who works in critical conditions.

In a second type of over-suction installation, as described in patent documents EP 1845775 and US 2009/0159434, the installation comprises a network of compressed air that supplies nozzles or ejectors, each disposed in a sheath. vessel outlet, so that, by ejector effect, the outlet gases of the tank are sucked at a higher speed to create an over-suction flow. But the compressed air network is expensive to install (need to have one or more compressors of large capacity) and to operate (delicate control and positioning of the nozzles to be mounted parallel to the axis of the sheath). In addition, the nozzles are expensive to install and cause abrasion wear problems, resulting in complex maintenance.

A third type of over-suction installation, as described in US Patent 4,668,352 and US 2009/0159434, is such that for each tank, one or several control valves make it possible to regulate the suction flow rate of the tank or of different sections inside a tank, by controlling an actuator by a control valve, in certain cases depending on the difference between a temperature of a tank section in which at least one hood has been opened, and, in other cases or additionally, to limit or eliminate a restriction of flow in normal suction, in order to switch to an over-suction flow, the valves used being for example pivoting diaphragm valves, of the butterfly valve type, or sliding diaphragm valves, of the guillotine type. These single or multiple valve systems applied to each of the tanks of an aluminum smelter result in the installation of a considerable number of control valves, operating actuators and control systems with sensors, for example temperature, possibly associated, resulting in significantly higher installation and maintenance costs. Indeed, such an installation can have a great fragility and be easily disregarded, because the butterfly (s) of the adjustment valve (s) is (are) held by an actuator in a partially closed position, hence a cost very high maintenance and maintenance.

The problem underlying the invention is to provide a method and a device much more economical to implement than the over-suction installations, and to ensure a containment of the tank gases in the covered tank electrolysis in which these tank gases are produced, while at least one hood is locally and temporarily removed from this tank.

The idea underlying the invention is to provide a pneumatic barrier between the inside and the outside of the tank, at the level of the hood or hoods removed, without hindering the execution of interventions on the tank that required the removal of the hood (s), in particular the anode changes of this tank.

US Pat. No. 3,729,399 discloses a method and a device for controlling the gases of an aluminum electrolysis cell without a hood, which allow the recovery, containment and suction of the gaseous emissions of a tank by a suction system without over-suction, but ensuring collection and evacuation above the electrolysis bath of highly concentrated bottom-crust gases which are distinct from the collection and evacuation of the vat gases less concentrated pollutants forming above the crust. This is achieved by means of a blower, through a flow control device, ambient air in a channel peripheral to the upper edge of the vessel shell and opening, over the entire periphery of the tank, by baffles towards the interior of the tank so as to form a curtain of air blown from bottom to top and an edge of the tank inwards, towards the suction lanes, where the air curtain is sucked by a normal suction system for unconcentrated vat gases, around a central chimney, through which the alumina hopper can feed the electrolysis bath, by a hole drilled in the crust, and in which, in the opposite direction, the highly concentrated bottom of the bottom of the crust gases are discharged to a treatment plant for these gases.

This upward air curtain confinement device, for untapped electrolysis tank, has the major disadvantage that the blowing of the air curtain from below upwards, then sucked by the unconcentrated vat gas collection system. , requires a permanent blow, resulting in a large consumption of compressed air, and therefore an installation of an expensive operation. In addition, the permanent absence of rollover of such a tank is a risk factor for personnel working on this tank, due to a lack of physical protection between the inside and the outside of the tank, and, in addition, the peripheral channel and baffles of the device, surrounding the upper edge of the vessel shell, are particularly exposed to damage during anode changing operations, and projections or falls of material that may fall on this channel and these baffles, as well as because of their exposure to intense heat and dust released by the tank.

The object of the present invention is to provide a room confinement at the level of the tank by a spatially and temporarily limited pneumatic barrier, which does not have the major disadvantages of the device known from US 3,729,399.

For this purpose, the method according to the invention, for the confinement of the tank gases in a covered aluminum electrolytic tank, at least one hood of which is locally and temporarily removed, is characterized in that it comprises least one step of blowing at least one jet of air from substantially an edge of the opening defined by said at least one hood removed, so as to form an air curtain completely covering said opening and providing an effect dynamic pneumatic barrier between the tank gases inside said tank and the ambient atmosphere outside said tank.

Thus, the operator is protected during handling on the tank, without the air curtain is an inconvenience for these handling, and avoiding gas emissions of polluted tank to the outside of the tank. In addition, by limiting the production of an air curtain at the limited surface opening corresponding to one or a few removed hoods, the necessary air flow rate and the power consumed to obtain it are considerably limited. the material means implemented for this purpose are also considerably cheaper, both at installation and in use, than those of an over-suction installation.

Advantageously, the method of the invention consists in blowing said at least one jet of air through at least one nozzle, preferably linear, extending substantially along one of the four sides of the opening defined by the perimeter. a hood or two adjacent hoods removed, and thus inclined from top to bottom and the center of the tank to one side of this tank, and to form an air curtain, inclined preferably substantially plane and s extending substantially into said inclined opening, preferably rectangular.

Indeed, the modern tank covers are inclined, but substantially flat and rectangular, which makes possible the use of linear nozzles to achieve a plane air curtain.

However, the hoods of some tanks may be slightly curved, convexity facing outward. But their curvature is sufficiently moderate so that it is possible to cover the opening defined by the removal of a hood by an air curtain of similar curvature, produced by at least one nozzle also bent. In this case, the curved nozzle (s) producing the curved air curtain is or are disposed substantially on a horizontal or inclined side of the corresponding opening.

Accordingly, in both cases, the method comprises forming said air curtain by blowing at least one air jet, preferably plane, substantially from an inclined side of said inclined opening, at least until opposite inclined side.

But, alternatively, the method of the invention may consist in forming said air curtain by blowing, in the same direction, at least two air jets, planar and substantially coplanar, substantially from a substantially horizontal upper side of said inclined opening, and at least to the substantially horizontal lower side opposite to it.

In the latter case, the method further comprises blowing said at least two jets of air from two nozzles spaced from each other in the direction of said upper side, a distance permitting the passage, between the two nozzles, an anode rod of the tank, and to blow moreover at least one air jet transverse to said minus two air jets to complete the confinement air curtain in the space between said two nozzles.

Therefore, advantageously according to the invention, the air jet or jets forming the air curtain of the invention can or can be blown laterally from one inclined side to the other of the opening released by the removal of at least one hood, or from top to bottom and from the center of the tank to one side of the latter, with an inclination that corresponds substantially to that of the covers.

For the purpose of implementing the method of the invention, the invention also relates to a vessel gas containment device in a covered tank electrolysis of aluminum, at least one hood is locally and temporarily withdrawn, and which is characterized in that it includes:

at least one blowing nozzle of at least one air jet capable of forming an air curtain, preferably substantially plane, extending over a surface sufficient to substantially cover an opening, preferably rectangular, inclined from top to bottom; bottom and from the center to a side of said tank, and delimited by at least one tank cover removed, said at least one nozzle being arranged to be supported by at least a portion of said tank and / or at least one cover of tank, and

at least one supply source of said at least one air or compressed air nozzle, for blowing said at least one air jet for forming said air curtain, providing a dynamic air barrier effect between the vat gases inside said vessel and the ambient atmosphere outside said vessel.

The installation of a local and temporary air curtain, as soon as it is withdrawn, and preferably even slightly before the removal of one or more hoods from the tank, for example during anode change operations, is perfectly compatible with the preservation of the main suction network of the tank gas, the operation of which can proceed absolutely without negative interference with the establishment, the temporary maintenance and then the removal of the air curtain replacing one or a few adjacent covers removed.

Advantageously, the device of the invention is such that said at least one nozzle is a nozzle, preferably linear, blowing at least one air jet, preferably substantially plane, arranged to be supported at least partially on a hood in place on the tank and adjacent to a hood removed, and arranged substantially along an inclined side of said inclined opening defined at least in part by said hood removed, said nozzle being configured to blow said at least one air jet laterally and towards the opposite inclined side of said opening, and preferably substantially in the plane thereof, when said opening is rectangular.

According to a first advantageous arrangement for producing a transverse air curtain, in which the device of the invention is partly integrated with the hoods, at least one nozzle, preferably linear, is integrated into each hood of the vessel, substantially along an inclined side of the perimeter of said hood, and opens towards the outside of said hood being integral with an elongated box-shaped air ejection module fixed to said hood, supplying the nozzle with air , and itself supplied with air, preferably substantially in the middle of its length, by an air or compressed air supply sheath, connected by a tip, possibly flexible, equipped with a connection, preferably self-closing and quick coupling, to a valve, manually or controlled, connected to a source of air or compressed air, consisting of an air distribution network or compressed air extending along the sides tanks of an aluminum smelter.

In another embodiment of the device of the invention, more economical in terms of investments to be made, said at least one nozzle is supported removably on the tank and / or said hood in place which supports it at least partially, and is supplied with air or compressed air by an elongated box-shaped air ejection module, the nozzle of which is integral, and itself supplied with air or compressed air by at least one blower, such as a fan , to which the module is connected.

As an alternative to a transverse air curtain, the device of the invention also makes it possible to produce a curtain of air blown up and down and inclined from the center of the tank towards one side thereof, and in this case the device comprises at least two linear nozzles each blowing at least one substantially plane air jet, removably supported by said tank, on which said nozzles are disposed substantially along the upper side of said inclined opening and spaced from each other in the direction of said upper side, so as to allow the passage between them of an anode rod of the tank, said air curtain being formed by said air jets substantially planar directed in the same direction and substantially coplanar with the inclined plane passing through the substantially horizontal upper and lower sides of said inclined opening, each of said at least two linear nozzles being integral with one respectively of two air ejection modules, each shaped elongated box, each of which supplies the nozzle or nozzles integral with it in air or compressed air, the two air ejection modules being themselves supplied with air or compressed air by at least one blower, such as a fan, to which the modules are connected.

In the latter case, the device advantageously furthermore comprises at least one lateral nozzle, preferably linear, extending transversely with respect to said two linear nozzles, on one side of at least one of said two air ejection modules. which is directed towards the other module, so as to blow at least one secondary air jet, preferably substantially plane, which completes the air curtain in the gap between said two modules, said lateral nozzle being supplied with air or compressed air by said at least one blower which feeds the air ejection module whose side nozzle is secured.

In embodiments of the device in which the nozzles are not integrated in the covers, the device is advantageously such that said at least one nozzle is secured to a removable assembly, provided with attachment means to lifting means that can be used for the changes of anodes of the tank, and / or means of displacement along the tank, such as roller and / or slide feet, and for moving said removable assembly respectively from one tank to another, and a hood or set of two hoods adjacent to another hood or other set of two adjacent hoods on the same side of a tank.

In this case, it is always the same removable set or some, in limited number compared to the number of tanks of an aluminum smelter that can be moved, as needed, on the rows of hoods of one or more tanks of an aluminum smelter, to bring a removable assembly where at least one hood must be removed, and the tank thus opened locally and temporarily.

In this case, it is advantageous that said removable assembly comprises a rigid frame, supporting said at least one nozzle and at least partially flanking said inclined opening, said frame being mounted movably on the tank along one of its normally closed sides by covers, said frame preferably also supporting at least one blower supplying air or compressed air to said at least one nozzle.

In addition, in a simple and economical embodiment of the device, at the level of at least one air ejection module of the latter, said ejection module advantageously comprises an elongate rectangular parallelepiped box of cross section square or rectangular, a lower face of which constitutes the support surface of the module on the vessel and / or a vessel hood, and whose front face, perpendicular to the lower face, forms, between its lower edge and said lower face, a linear longitudinal nozzle extending preferably over substantially the entire length of said box, and delimited between at least two longitudinal fins parallel to each other, guiding the air jet substantially blown plane, and whose orientation relative to the faces front and bottom determines the direction of the air curtain substantially blown plane.

When this module is one of two modules spaced from each other for the passage of an anode rod between them, it is further advantageous that said module further comprises a lateral nozzle, delimited between at least two lateral fins on the base of a small end side of said box, and supplied with air or compressed air by the same fan feeding the longitudinal linear nozzle of the same box.

In the last embodiments presented above, the air supply of a module can be advantageously provided by at least one fan connected by a sheath to a nozzle opening substantially in the box, facing a planar baffle, inclined obliquely against the front face and against the underside, to deflect the incoming air flow to the sides of the baffle and distribute it over the entire length of said corresponding longitudinal nozzle.

Alternatively, at least one blower supplying air or compressed air at least one air ejection module is at least one tangential fan, integrated in the corresponding box.

Other advantages and characteristics of the invention will become apparent on reading the description given below, in a nonlimiting manner, of exemplary embodiments described with reference to the appended drawings in which:

- Figure 1 is a schematic cross-sectional view of an aluminum electrolysis cell, shown flipped on the right half-section, and with an air curtain in place of at least one cover, on the left half-section of this figure, already described above, except for the air curtain of the left half-cut;

FIG. 2a is a side perspective view of a vessel, two adjacent removable hoods 18 have been removed from the row of hoods inclined along the large visible side of the tank, to allow the exit of an anode 8 and the corresponding rod 9; Figure 2b is an enlarged detail view of the open area of the tank of Figure 2a with a containment device providing a transverse air curtain;

FIG. 3 is a partial schematic representation in perspective of a device similar to that of FIGS. 2a and 2b for producing a transverse air curtain, which is traversed by an anode rod 9 during an anode change. ;

Figure 4 is a view similar to Figure 3 for a device in which a blowing nozzle of a transverse curtain is integrated in each cover;

Figure 5 is a side elevational view of two adjacent covers of a device according to Figure 4, and showing the connection of the nozzles to a compressed air network;

Figure 6 is a schematic end view of inclined hoods and equipped with Figure 5 connected to the supply compressed air network;

Figure 7 is a view similar to Figure 2a for a two-nozzle containment device mounted on the upper edge of the opening to achieve a ri air blown from top to bottom and inclined substantially like the hoods;

Figures 9a, 9b and 9d, for an air ejection module with a side nozzle, for the equipment of the device shown in Figures 7 and 8;

FIG. 13 diagrammatically represents the two air ejection modules of such a device according to FIGS. 7 and 8, the two spaced modules of which to allow the passage of an anode rod are fed by the same and only centrifugal fan connected to the modules by sheaths, and

Figure 14 is a view similar to Figure 13, the two spaced modules are each supplied with air by one respectively two centrifugal fans connected to the modules by ducts.

In the various figures, the identical or similar components of the various embodiments described are identified by the same numerical or alphanumeric references.

The tank 1, shown in cross section in FIG. 1, is covered by planar covers 18 inclined, in this example at an angle of about 45 ° to the horizontal, and rectangular, the two opposite large sides of which are slanted and the two short sides, upper and lower, are substantially horizontal and respectively rest against a horizontal spar 20 of the structure of the tank, having rectangular slots housing the rods 9 of anodes 8, and against the upper edge of the ferrule 2 and the wall 6 of the tank.

In FIG. 1, the left half-section on the left is schematically represented at the level of a cover 18 removed, and replaced, according to the invention, by an air curtain 21, schematically represented by dotted lines, which is inclined substantially as the cover 18 that this air curtain replaces, that is to say from top to bottom and from the inside to the side of the tank 1, and this air curtain 21 is obtained by an air jet plane oriented from top to bottom, as indicated by the arrow at the end of the dashes, and issuing from a linear nozzle, defined in this example by a longitudinal slot formed in the side wall of an air ejection module 22 shaped elongated cylindrical box, supplied with air by a blower (not shown) connected to the box 22 by a sheath, the box 22 being disposed and removably attached to the structure of the tank 1 along and above the substantially horizontal upper edge of a hood 18 removed, so that the e air curtain 21 extends over the entire opening defined by the removal of the hood 18, and completely covers this opening, sufficient for some interventions on the tank.

Thus, the tank gases remain confined inside the tank, even at the level of the opening released by the removal of a cover 18, thanks to the air curtain 21 which constitutes a dynamic pneumatic barrier separating the polluted volume internal to the chamber of the ambient atmosphere outside the tank. In FIG. 2a, the tank 1 of FIG. 1 is shown open on one side by the removal of two adjacent hoods 18, after the arrangement and the removable attachment of an air ejection module 23 on and the along the long inclined side of a cover 18 bordering the opening, and the side of this opening, so that this module 23 can produce a transverse air curtain, plane and inclined substantially as are the covers 18, and will extend from the module 23 to the large inclined side of the other cover 18 still in place which delimits the opposite inclined side of the opening defined by the two removed covers, and visible on a larger scale in Figure 2b, on which we distinguish the anode well 24 which has been removed the corresponding anode 8 and the rod 9 which supports it, and which was housed, when in position, in the notch 20a rectangular formed in the spar 20 horizontal structure of the tank 1, while the anodes 8 fixed so the two rods 9 still in place and adjacent to the rod removed from the notch 20a are partially visible by the opening released by the two adjacent covers removed. The transverse air curtain 21 which can thus be obtained is schematically represented in FIG. 3 by transverse arrows corresponding to the plane and inclined air jet delivered by the linear nozzle extending over substantially the entire length of the ejection module. 23, in this elongated box-shaped rectangular parallelepipedal shape of quadrangular cross section, which extends and is removably attached to the edge adjacent to the opening of the cover 18 bordering on the left this opening, completely covered by the air curtain 21, which extends to the hood 18 in place defining the opening to the right.

In FIG. 3, the rod 9 of the anode housed in the well 24 of FIGS. 2a and 2b is in position in the notch 20a in the structural spar 20 of the vessel 1, as is the case before removal and after the repositioning of the two covers 18 replaced in some way by the air curtain 21 for the change operation of the corresponding anode 8.

The air ejection module 23 is arranged and fixed in place on the cover 18 which supports it before the removal of the two covers defining the opening through which the corresponding anode 8 will be changed, and the air curtain 21 can be formed either immediately after removal of the two covers 18 or, preferably, immediately before, and, similarly, the air curtain 21 can be removed by stopping the air supply of the module 23 and its linear or ejection nozzles (s) air immediately before replacing the two covers 18 previously removed, or preferably shortly after this surrender in place, and then only the air ejection module 23 can be removed to be moved, by operators or with the help of the traveling crane which allowed the change of anode, to be arranged on another hood, for another tank operation.

FIG. 4 schematically represents the formation of another transverse air curtain 21 by an installation comprising air ejection modules 25, arranged as the module 23 of FIGS. 2a, 2b and 3, but each integrated with the one of the hoods 18, along one of its two long inclined sides, always on the same side from one hood to the other, and all connected to the same network 26 of compressed air distribution, extending the along the sides of the tanks such as 1, and as shown in Figures 5 and 6.

In this embodiment, a module 25 of an air ejection device, is integrated on a large side of each cover 18 and has a linear nozzle 27 delimited by a slot which opens laterally towards the outside of the cover 18 over substantially the entire length of its long inclined side, the compressed air supply of the module 25 being effected by a sheath 28 extending over the lower half of the module 25, along its side turned towards the inside of the hood 18 which supports it, and the lower end of this sheath 28 is connected by a tip 29 which can be flexible, and equipped with a coupling 30 of the self-closing type and fast coupling, to a valve 31 manually controlled connection the network 26 of compressed air distribution.

FIGS. 7 and 8 show a vessel gas confinement device which, like the left half-section of FIG. 1, provides the formation from the top of a plane and inclined air curtain 21 as the two adjacent covers 18 removed from a row of covers 18, and to which the air curtain is substituted to confine the tank gases in the tank 1 without hindering the operation of changing an anode and the corresponding rod 9 under the same conditions as in FIGS. 2a and 2b, but with an air expulsion device with two modules 32, each in the form of an elongate well and having a longitudinal nozzle, along and at the base of the one the large sides of the corresponding module 32, the two modules 32 being supported and removably attached to the horizontal spar 20 of the vessel structure, on which the two modules 32 are arranged so that the nozzles extend substantially along the side upper sloped opening imitated by the two hoods 18 removed, and the two modules 32, and therefore the two corresponding longitudinal nozzles, are spaced apart from one another, in the direction of the upper side of this inclined opening, so as to allow the passage between them (they) of the rod 9, the anode 8 is changed. Thus, the air curtain is formed by the two jets of substantially plane air, directed in the same direction and substantially coplanar with the inclined plane passing through the substantially horizontal upper and lower sides of the inclined opening, the two jets d air shots delivered by the two nozzles being oriented up and down and laterally joining to ensure good continuity of the air curtain on virtually the entire opening.

However, to complete the air curtain at the space defined between the two modules 32, and which is traversed by the rod 9 of the replaced anode, one of the two modules 32 has, in addition to its nozzle linear longitudinal, aligned substantially along the upper edge of the opening, a second nozzle or lateral nozzle, which is also linear and capable of delivering a planar and substantially horizontal air jet, between the two modules 32, two examples of which embodiment are described hereinafter with reference to FIGS. 9a to 14, respectively without and with lateral nozzle and also with supply by a single fan for the two modules 32 or by a fan per module 32.

As shown in FIG. 8, the two modules 32 can be secured to one another by a common frame 33, which is rigid, of a rectangular shape corresponding to that of the opening defined by the hood (s). removed, and not closed in the middle of its small horizontal and upper side, between the two modules 32 supported respectively on each of the two parts of this small open side, to release the passage for anode rod 9 8.

Thus, this frame 33 partially frames the inclined opening and constitutes with the modules 32 a removable assembly, which is moved in one piece, by operators or by lifting means, to be positioned on the perimeter of two other covers 18 to be removed at another location, for a new anode change operation.

For this purpose, the frame 33 of this removable assembly is advantageously provided with hooking means (not shown) such as eyelets or suction cup devices, allowing it to be attached to lifting means used for the anode changes, in particular In particular, the above-mentioned traveling crane, and this removable assembly also comprises displacement means along one side of the vessel 1, in order to allow the operators to easily move the removable assembly without having to use the traveling crane. These moving means may comprise feet equipped with rollers and mounted under the lower and upper horizontal sides of the frame 33, for example or slides, so that the frame 33, the two air ejection modules 32, and preferably also at least one fan (not shown ) which supplies them with air or compressed air for the formation of the air jets, can be moved along the same side of a tank, from a set of two covers adjacent to another set of two adjacent covers 18 on this same side of tank. It is understood that the removable assembly, equipped with these lateral displacement means along a tank, can be moved from one tank to another, and from one longitudinal side to the other longitudinal side of the same. tank, by the lifting means such as the traveling crane.

Optionally, rails can be installed at the feet of the long sides of a tank, to guide rollers feet secured, possibly removably, to the frame 33, to allow this frame 33 to be mounted movably on the vessel 1 along its sides normally closed by hoods 18.

Another advantage of the rectangular and rigid frame 33 of the removable assembly supporting the two air ejection modules 32 of FIG. 8, or an air ejection module 23 of FIGS. 2a to 3, is that the frame 33 may comprise a side opposite to that on which is or are worn (s) or the air ejection modules, and that this opposite side may, if necessary, receive a suction recovery grid or the jets d air forming the air curtain, as known from the state of the art, for example in the patent document EP 0 944 802, which mentions the recovery of air jets participating in the constitution of a curtain air through a return grid installed in front of the air jet injection nozzles and located in a plane substantially perpendicular to the direction of the latter.

In this case, the suction at the grid can advantageously be provided, at least partially, by the fan or at least one of the fans used as a supply blower of the blowing nozzles or air jets forming the air curtain.

Figures 9a and 9b show in perspective, respectively from the front and from the rear, an air ejection module comprising an elongate rectangle rectangular box, of square or rectangular cross section, which may be the module 23 of the figures 2a, 2b and 3, with a certain orientation, specified below, of its single longitudinal linear nozzle, where one of the two modules 32 which is devoid of nozzle (s) lateral (s), a device according to the Figures 7 and 8, Figure 9c showing a section cross section of the box of the module 23 or 32 by half of its length, while Figure 9d shows a horizontal longitudinal section at half height. The corresponding casing has an elongated lower face 34, which constitutes the bearing surface of a module such as 23 on the edge of an inclined side of an adjacent cap 18, in the example of FIGS. 2a to 3, and a module 32 on a portion of the structural spar 20 of the tank 1, along the upper edge of an opening released by the removal of two covers 18, in the embodiment of Figures 7 and 8. The box parallelepiped also comprises a front face 35, perpendicular to the lower face 34, and which forms, between its lower edge and the lower face 34, a longitudinal linear nozzle 36, extending over substantially the entire length of the box. In order to guide the jet of substantially plane air blown by the nozzle 36, the latter is delimited between two external longitudinal fins 37, parallel to each other, and also by two internal longitudinal fins 38, parallel to the outer fins 37, in order to guide the plane air jet blown and oriented by the orientation given by the fins parallel to each other 37 and 38 relative to the front 35 and lower 34, to obtain that the air curtain 21 is well inclined in the plane of the inclined opening delimited by the removal of two covers 18.

Thus, if the box of FIGS. 9a to 9d is used to produce the module 23 producing a transverse or lateral air curtain of FIGS. 2a to 3, the fins 37 and 38 are oriented all parallel to the bottom bearing face 34, while if this box is used to make at least one of the two modules 32 of the devices according to Figures 7 and 8, the fins 37 and 38 are oriented at 45 ° with respect to the lower face 34 or the front face 35 , to provide the desired inclination to the air curtain, given the flat layout of the module 32 on the upper edge of the opening.

The air supply of the box is provided by at least one fan connected by a sheath to a cylindrical nozzle 40 opening substantially in the middle of the rear face 39 of the box, opposite and parallel to its front face 35. This tip 40 opens into the box facing a plane deflector 41, of rectangular shape, inclined at an angle and supported along a long side against the front face 35 and along the other long side against the lower face 34, as shown in FIG. section of Figure 9c. This deflector 41 thus deflects the flow of air entering the box towards the sides of the deflector 41 to distribute the incoming air over the entire length of the longitudinal nozzle 36, the central portion is supplied with air passing on either side of the short sides of the deflector 41 to return below the latter, towards the central zone of the nozzle 36. As an example of embodiment only, the width L of the lower face 34 as the upper face 42, and the width L of the front 35 and rear faces 39 may be 200mm, for a box length of 670mm for example for a module 32. The diameter D of the cylindrical feed nozzle can be 100mm and its length 1 of 50mm. The deflector 41 may have a length of 110 mm, and a width of 100 mm, and be centered relative to the axis of the tubular nozzle 40, and the width of the two outer longitudinal fins 37 may be 20 mm, and their spacing which corresponds to the thickness substantially of the substantially plane air jet blown by the module 23 or 32.

When the box of FIGS. 9a to 9d is used as an inclined mounted module 23 for producing an inclined lateral or transverse air curtain, its air supply can be as shown diagrammatically in FIG. 10. In this case, the module 23 is powered. by a single centrifugal fan 42 connected to the air inlet nozzle 40 of the module 23 by a sheath 48.

FIGS. 11a and 11b are similar to FIGS. 9a and 9b for a module 32 having the same structure as previously described with reference to FIGS. 9a to 9d, but having in addition a lateral nozzle 43, delimited at the base of a short side end 45 of the parallelepipedal box by two small transverse and horizontal rectangular fins 44, parallel to each other and to the underside 34 of the box, as shown in FIGS. 11b and 12, to produce a small plane horizontal air curtain, for a plane jet of the same orientation directed from this box 32 to the other, to complete the air curtain at the spacing between the two modules 32 which is traversed by the anode rod 8 during the operations of anode changes. As an exemplary embodiment, the length of this side nozzle may be 160mm and its thickness of 20mm.

For the air supply of the two modules 32, one of which is made as shown in Figures 9a to 9d, and the other as in Figures 9a to 12, and as shown in Figures 13 and 14, both modules 32 may be powered by the same centrifugal fan 42 via ducts 46 and 47 in parallel on the outlet duct 48 of the fan 42 and each connected to the nozzle 40 of the corresponding module 32, as shown in FIG. 13 , or each of the two modules 32 can be powered by one respectively two centrifugal fans 42, by via one respectively of two sheaths 48 each connected to the tip 40 of the corresponding module 32.

Alternatively, the centrifugal fan (s) 42 may or may be replaced by one or more tangential fans which are directly integrated into the parallelepiped box (s) of the modules 23 or 32.

In addition, the blowing rate of the fan or fans can be adjusted by controlling the fan or fans, whose speed or frequency of rotation is variable depending for example on a measurement of the blowing flow rate in the duct downstream of the fan, to be aligned with a setpoint. Simultaneously, it ensures a precise adjustment of the normal suction flow in the tank, which can be modulated by a butterfly for example. In addition, a valve downstream of the fan or fans may be provided to derive a variable portion of the supply air flow.

In these various examples, the centrifugal fan (s) 42 and / or the tangential fan (s) constitute one or more blowers supplying air or compressed air to the corresponding air jet blower (s).

Alternatively also, and as known from the state of the art, including EP 0 944 802 already mentioned, the air curtain 21 may consist of several parallel air blades resulting from several air jets blown by different nozzles arranged in one or more boxes of an air ejection device, in which case it is possible that each of the nozzles is fed from an internal chamber specific to the corresponding box, with a feed rate adjusted by a adjustable air inlet valve in this chamber, so that the different substantially planar air jets can be blown with different flow rates and speeds, so as to produce different air knives of which at least one, blown at a speed greater than that of the other (s) allows it to be stabilized so that the air curtain as a whole is stabilized and provides an effective dynamic air barrier between the polluted interior of the tank and the ambient atmosphere external to the tank.

It will be understood that a device according to the invention makes it possible to economize on an over-suction installation, and that a flow rate of 1500 m / hour per tank may suffice to achieve a confinement of ambience, while conventional over-suction requires of the order of 10000m / hour of gas flow per tank and high pressure, which represents a considerable gain of energy in favor of the device of the invention.

Claims

1. A method for confining the tank gases (15) in a tank (1) covered with electrolysis of aluminum, at least one hood (18) is locally and temporarily removed, characterized in that it comprises at least a step of blowing at least one jet of air from substantially an edge of the opening defined by said at least one hood (18) removed, so as to form an air curtain (21) completely covering said opening and providing a dynamic pneumatic barrier effect between the tank gases (15) inside said tank (1) and the ambient atmosphere outside said tank (1).

2. Method according to claim 1, characterized in that it consists in blowing said at least one jet of air by at least one nozzle (27, 36), preferably linear, extending substantially along one side. on all four sides of the opening defined by the perimeter of a hood (18) or two adjacent hoods (18) removed, and thus inclined from top to bottom and from the center of the tank (1) to a side of this vessel, and to form an air curtain (21) inclined preferably substantially plane and extending substantially in said inclined opening, preferably rectangular.

3. Method according to claim 2, characterized in that it consists in forming said air curtain (21) by blowing at least one air jet, preferably plane, substantially from an inclined side of said opening inclined, at least to the opposite inclined side.

4. Method according to claim 2, characterized in that it consists in forming said air curtain (21) by blowing, in the same direction, at least two air jets, planar and substantially coplanar, substantially from a substantially horizontal upper side of said inclined opening, and at least to the substantially horizontal lower side opposite thereto.

5. Method according to claim 4, characterized in that it further comprises blowing said at least two jets of air from two nozzles (36) apart one of the other in the direction of said upper side, a distance allowing the passage, between the two nozzles (36), of an anode rod (9) (8) of the tank (1), and to blow from at least one air jet transverse to said at least two air jets to complete the air curtain (21) for confinement in the space between said two nozzles (36).

6. Apparatus for confining the tank gases (15) in a tank (1) covered with electrolysis of aluminum, at least one hood (18) is locally and temporarily removed, characterized in that it comprises:

at least one nozzle (27, 36) for blowing at least one air jet capable of forming an air curtain (21), preferably substantially plane, extending over a surface sufficient to substantially cover an opening, preferably rectangular, inclined from top to bottom and from the center to a side of said tank (1), and delimited by at least one hood (18) removed tank, said at least one nozzle (27, 36) being arranged so to be supported by at least a portion of said vessel (1) and / or at least one vessel hood (18), and

at least one source (26, 42) supplying said at least one nozzle (27, 36) with air or compressed air, for blowing said at least one air jet for forming said air curtain (21) , providing a dynamic pneumatic barrier effect between the tank gases (15) inside said tank (1) and the ambient atmosphere outside said tank (1).

7. Device according to claim 6, characterized in that said at least one nozzle is a nozzle (27, 36), preferably linear, blowing at least one air jet, preferably substantially plane, arranged to be supported at least partially on a hood (18) in place on the tank (1) and adjacent to a hood (18) removed, and disposed substantially along an inclined side of said inclined opening defined at least in part by said hood (18) removed, said nozzle (27, 36) being configured to blow said at least one air jet laterally and towards the opposite inclined side of said opening, and preferably substantially in the plane thereof, when said opening is rectangular.

8. Device according to claim 7, characterized in that at least one nozzle (27), preferably linear, is integrated with each cover (18) of the tank (1), substantially along an inclined side of the perimeter of said cover, and opens towards the outside of said cover (18) being integral with an elongated box-shaped elongated module (25) attached to said cover (18), supplying the nozzle (27) with air, and itself supplied with air, substantially in the middle of its length, by a sheath (28) supplying air or compressed air, connected by a nozzle (29) , optionally flexible, equipped with a coupling (30), preferably self-sealing and quick-coupling, with a valve (31), with manual or controlled actuation, for connection to a source of air or compressed air, consisting of a network (26) for distribution of air or compressed air extending along the sides of tanks (1) of an aluminum smelter.

9. Device according to claim 7, characterized in that said at least one nozzle (36) is removably supported on the vessel (1) and / or said cover (18) in place which supports at least partially, and is fed with air or compressed air by an elongate box-shaped air ejection module (32), the nozzle (36) of which is secured to itself, and itself supplied with air or compressed air by at least one blower, such as a fan (42) to which the module (32) is connected.

10. Device according to claim 6, characterized in that it comprises at least two linear nozzles (36) each blowing at least one substantially plane air jet, and removably supported by said vessel (1), on which said nozzles ( 36) are disposed substantially along the upper side of said inclined opening and spaced from each other in the direction of said upper side, so as to allow the passage between them of anode rod (9) (8). ) of the tank (1), said air curtain (21) being formed by said substantially plane air jets directed in the same direction and substantially coplanar with the inclined plane passing through the substantially horizontal upper and lower sides of said opening inclined, each of said at least two linear nozzles (36) being integral with one respectively of two air ejection modules (32), each in the form of an elongate box, and each of which supplies the nozzle or nozzles (36) who are solidly air or compressed air, the two air ejection modules (32) being themselves supplied with air or compressed air by at least one blower, such as a fan (42), to which the modules (32) ) are related.

11. Device according to claim 10, characterized in that it further comprises at least one lateral nozzle (43), preferably linear, extending transversely with respect to said two linear nozzles (36), on one side (45). at least one of said two air ejection modules (32) which is directed towards the other module (32), so as to blow at least one secondary air jet, preferably substantially plane, which completes the air curtain (21) in the gap between said two modules (32), said lateral nozzle (43) being supplied with air or compressed air by said at least one blower (42) which supplies the module (32) with ejection of air whose side nozzle (43) is integral.

12. Device according to any one of claims 7 and 9 to 11, characterized in that said at least one nozzle (36) is integral with a removable assembly (32, 33) provided with fastening means to means lifting devices that can be used for the anode changes (8) of the tank (1), and / or means of movement along the tank (1), such as roller and / or slide feet, and allowing moving said removable assembly (32, 33) respectively from one tank (1) to another, and a hood (18) or set of two hoods (18) adjacent to another hood (18) or other set of two covers (18) adjacent on the same side of a tank (1).

13. Device according to claim 12, characterized in that said assembly (32, 33) removable comprises a rigid frame (33) supporting said at least one nozzle

(36) and at least partially flanking said inclined opening, said frame (33) being mounted movably on the tank (1) along one of its sides normally closed by covers (18), said frame (33) supporting preferably also at least one blower (42) supplying air or compressed air to said at least one nozzle (36).

14. Device according to any one of claims 8 to 11, characterized in that at least one module (23, 32) of air ejection comprises an elongate rectangular parallelepiped box, of square or rectangular cross section, one of which lower face (34) constitutes the bearing face of the module (23, 32) on the tank (1) and / or a tank cover (18), and of which a front face (35), perpendicular to the lower face ( 34), forms, between its lower edge and said lower face (34), a longitudinal linear nozzle (36) extending, preferably, over substantially the entire length of said box, and delimited between at least two longitudinal fins (37, 38) parallel to each other, guiding the air jet substantially blown plane, and whose orientation relative to the front faces (35) and lower (34) determines the direction of the air curtain (21) substantially blown plane.

15. Device according to claim 14, characterized in that said module

(32) further comprises a lateral nozzle (43) delimited between at least two lateral fins (44) on the base of a small end side (45) of said box, and supplied with air or compressed air by the same blower (42) supplying the longitudinal linear nozzle (36) of the same box.

16. Device according to any one of claims 14 and 15, characterized in that the air supply of at least one module (23, 32) is provided by at least one fan (42) connected by a sheath (46). , 47, 48) to a tip (40) opening substantially in the box, opposite a deflector (41) plane inclined at an angle against the front face (35) and against the underside (34), to deflect the air flow entering the sides of the deflector (41) and distribute it over the entire length of said corresponding longitudinal nozzle (36).

17. Device according to any one of claims 8 to 11, 14 and 15, characterized in that at least one blower supplying air or compressed air at least one module (23, 32) of air ejection is at least less a tangential fan, integrated in the corresponding box.