WO2022234215A1

WO2022234215A1 - Device for the containment of an anode assembly

Info

Publication number: WO2022234215A1
Application number: PCT/FR2022/050796
Authority: WO
Inventors: Guillaume Girault
Original assignee: Reel Alesa
Priority date: 2021-05-06
Filing date: 2022-04-27
Publication date: 2022-11-10
Also published as: CA3209815A1; FR3122777B1; EP4334510A1; FR3122777A1

Abstract

The invention relates to a device for the containment of at least one anode assembly, said assembly comprising a spent anode (12') attached to a metal rod (13), comprising:  a receptacle (20) for receiving the anode assembly, the anode assembly resting inside the receptacle via the lower surface of the spent anode (12');  a bell housing (21) open at its bottom end and able to form a closed volume (27) in collaboration with the receptacle (20), inside which volume the at least one anode assembly is housed. The bell housing (21) is able to adopt two shapes:  a shape for storing the device, in a non-operational position, in which it is folded onto itself;  a deployed operational shape in which, with the receptacle (20), said closed volume (27) is defined.

Description

CONTAINMENT DEVICE FOR AN ANODIC ASSEMBLY

FIELD OF THE INVENTION

The present invention belongs to the field of the production of aluminum by igneous electrolysis, and relates more particularly to a confinement device for an anode assembly.

PRIOR STATE OF THE TECHNIQUE

The production of aluminum by the so-called igneous electrolysis process is currently widespread and mastered. The electrolysis of alumina in the presence of molten cryolite leads to the production of aluminium. This electrolysis takes place at the level of electrolysis tanks comprising an electrolyte, and the bottom of which constitutes the cathode.

As a corollary, anodes, traditionally made of carbonaceous material, are immersed in these tanks, each of the said anodes being provided with a metal rod which is therefore electrically conductive, intended for its electrical and mechanical connection to an anode frame which is mobile with respect to a fixed gantry. above the electrolytic cells.

In the field considered, the assembly consisting of the rod and the anode made of carbonaceous material attached to its end, is referred to as the anode assembly.

Due to the phenomenon of electrolysis, the anodes are consumed as the reaction progresses, therefore requiring a periodic change. To do this, the anode assembly considered is detached from the anode frame, then evacuated to a storage location at which the anode cools before being either reprocessed, in order to recover the carbonaceous material not consumed, or pier.

However, it is known that, at the outlet of the electrolytic cell, a worn or partially worn anode emits fluorinated gases, in particular HF, and dust, the emission of such gases being all the greater as the temperature of the anode is high. In fact and for obvious operator protection considerations, in addition to the environment, we have I have always tried to reduce these gas and dust emissions as much as possible.

A technical solution has thus been proposed in document EP 2 507 413 consisting of a substantially horizontal plate on which an anode assembly is positioned, associated with a reservoir capable, after reception of the anode assembly, of receiving a powder of choking intended to cover the entire anode, this powder consisting of a fluorinated compound mixed with alumina. If, of course, the implementation of such a choking powder proves effective in terms, on the one hand, of reducing the temperature of the anode, and on the other hand, of limiting gaseous emanations in particular HF, its implementation is relatively complex, since it is necessary to provide hoppers for conveying the choking powder and then its evacuation.

Also proposed in document WO 2012/156616 is a device similar to that previously described, comprising a container containing non-fluidized alumina in sufficient quantity to cover the anode butt, and provided with a device capable of ensuring then the fluidization of the alumina. Again, this device is complex to implement, due to the presence of alumina, in addition to the device ensuring its fluidization.

Finally, document WO 2016/103020 has proposed a containment system for at least one anode assembly, comprising a support capable of receiving said anode assembly, said support defining with side walls a receiving enclosure, and a rigid cap , adapted to be received at the upper end of the side walls defining said receiving enclosure, and to cover the entire stem of the anode assembly. It is thus defined a closed volume, making it possible to overcome the problems of tightness at the interface with the rod, to avoid the diffusion of the gases emitted by the spent anode, in addition to preventing the arrival of air ambient, therefore oxygen, up to the level of the part of the anode still consuming, and therefore consequently, to restrict the phenomenon of combustion of the anode, and as a corollary, the emission of more gas .

If the device thus described makes it possible to achieve satisfactory confinement of the anode assembly, on the other hand, it generates, due to the very reason of the need to cover the anode assembly, that is to say rod and anode, a bulk important, heavy, and whose handling typically involves the implementation of MSE (service machines electrolysis), susceptible as a result, due to their relatively limited number in an aluminum production plant, their neutralization affecting other tasks. In addition, the civil engineering likely to allow the implementation of such a device must be adapted because of the height necessary for its manipulation, since as well, it is necessary to take into account the height of the anode assembly in as such, plus the height of the rigid cap, in order to allow its positioning above said anode assembly. However, the costs associated with such an adaptation of civil engineering are quite simply incompatible with the rational management of an aluminum production facility.

The invention aims to overcome these drawbacks, and in particular to reduce both the size and the weight of such a device for containing an anode assembly, and to facilitate its handling and the associated logistics.

DISCLOSURE OF THE INVENTION

According to the invention, this confinement device for at least one anode assembly, said assembly comprising a spent anode fixed to a metal rod, comprises:

^■ a receptacle for receiving the anode assembly, said anode assembly resting within said receptacle via the lower surface of the spent anode;

^■ a bell open at its lower end, and adapted to form a closed volume in cooperation with said receptacle, within which is received said at least one anode assembly.

According to the invention, the bell is likely to take two forms:

^■ a shape for storing said device, in the non-operational position, in which it is folded back on itself;

^■ an operational form, deployed, according to which is defined, with the receptacle, said closed volume.

In other words, the invention consists in implementing a bell, for example flexible or flexible, capable of being deployed between a non-operational storage position and a deployed operational position. In doing so, the device of the invention is easier to handle and to store, consequently making it possible to avoid necessarily having recourse to electrolysis bridges or MSEs, and in addition, to be able to be implemented within existing installations, without causing any modification of the civil engineering.

The implementation of such a bell also makes it possible to overcome the difficulties of sealing around the rod, and consequently optimizes the effectiveness of the containment device of the invention.

According to the invention, the bell has a symmetry of rotation, even of revolution, which appears in particular when said bell is in the operational position, that is to say deployed.

According to a first embodiment, the bell is made of flexible material, provided at its periphery with rigid arches oriented along planes substantially parallel to each other, and perpendicular to the axis of revolution of the bell, distributed more or less regular according to all or part of the height of said bell.

Typically, the flexible material is advantageously a refractory material, due to the high temperature of the anode at the vessel outlet. It is indeed recalled that the typical temperature of the anode at the outlet of the tank is close to 1000°C. This material can, for example, be chosen from the group comprising ceramic fabrics and/or fabrics based on basalt and/or glass fibers. This fabric, regardless of the material that composes it, can also be coated or coated with one or more layers of a protective material, such as silicone or PTFE (polytetrafluoroethylene), providing the functions of sealing and protection against attacks inherent to HF.

According to another embodiment of the invention, the bell comprises, in its lower part, a rigid cover or base, capable of being fitted onto the receiving receptacle of the anode assembly, and a rigid plate, in particular metallic , connected by means of a flexible zone or skirt to the upper peripheral edge of said cover, said rigid plate being pierced with through holes communicating with the flexible or flexible part of the bell. According to this embodiment, the upper part of the flexible zone of the bell is also provided with a rigid plate, in particular metallic, called the upper rigid plate, capable of resting at the level of the upper end of the anode rod.

According to yet another embodiment of the invention, the upper bell comprises at its base a rigid plate, in particular metallic, the dimensions of which correspond to the upper surface of the receptacle for receiving the anode assembly, so as to come to rest on the upper end of said receptacle, said rigid plate being pierced with through holes able to communicate with the flexible part of the bell.

According to these two embodiments, said rigid plate is provided with means for storing the flexible zone of the bell in the non-operational position. Typically, these storage means consist of walls, in particular metal, emanating from the upper face of said rigid plate essentially perpendicular thereto, capable of favoring the storage of the flexible zone of the bell in non-operational mode. Their respective spacing is chosen so as to facilitate said storage without altering the deployment of said flexible zone of the bell.

Advantageously, said rigid plate, and generally the bell itself, is provided with means for receiving or cooperating with members for gripping and manipulating said bell. Typically, these reception or cooperation means may consist of zones for receiving the forks of a forklift, or even lifting rings capable of cooperating with lifting means mounted on a self-propelled crane, or even on the MSE , or even on a portal dedicated to this purpose. The objective is to facilitate handling of the entire device, in particular when the latter receives one or more anode assemblies.

BRIEF DESCRIPTION OF FIGURES

The way in which the invention can be implemented and the resulting advantages will emerge better from the examples of embodiment which follow, given by way of indication and not limitation, in support of the appended figures. FIG. 1 is a schematic cross-sectional representation of a conventional electrolysis cell.

FIG. 2 is a schematic sectional representation of the principle of the anode assembly confinement device according to the invention.

Figure 3 is a schematic representation in perspective illustrating a first embodiment of the invention, with the containment device in operational mode.

Figure 4 is a view similar to Figure 3 seen from above.

Figure 5 is a view similar to Figure 3 in side view.

Figure 6 is a schematic sectional view along line VI -VI of Figure 5.

Figure 7 is a schematic perspective view of the containment device of Figure 3 in non-operational mode.

Figure 8 is a schematic perspective view of a second embodiment of the containment device of the invention.

Figure 9 is a more detailed schematic view of the device of Figure 8.

Figure 10 is a schematic perspective view of the device of Figures 8 and 9 in non-operational mode.

Figure 11 is a schematic perspective view of a third embodiment of the containment device of the invention.

Figure 12 is a more detailed schematic view of the device of Figure 11.

Figure 13 is a schematic perspective view of the device of Figures 11 and 12 in non-operational mode.

ATTT.EE DF.T DESCRIPTION OF THE INVENTION

Schematically shown in Figure 1 is a sectional view of an electrolytic cell (1) of conventional construction.

This figure shows the essential elements implemented for the purposes of operation of such a tank. Typically, this tank (1) comprises a metal box (2), receiving refractory materials (3) and (4), a cathode assembly (5) secured to a metal bar (6) to which the electrical conductors (7 , 8) intended to carry the electrolysis electric current. The cathode assembly (5) is covered with a bath of liquid aluminum (9) resulting from the electrolysis reaction, surmounted a liquid bath (10) of alumina and molten cryolite, itself covered with a cover (11) based on solid bath and alumina.

As a corollary, immerse in the bath of alumina and molten cryolite (10) anodes (12, 12') associated with a metal rod (13), in particular fixed to the anode (12, 12') by means of a base (14) or tripod. The rods (13) are mechanically fixed and electrically connected to a supporting structure (15).

Reference (16) represents the device for supplying the tank in question with alumina and/or A1F3.

Finally, the reference (17) represents the removable cover(s), typically metallic, intended to confine the effluents resulting from the electrolysis reaction, then direct them to an effluent treatment center.

Conventionally, the anodes (12) are made of prebaked carbonaceous material. They are gradually consumed during the electrolytic reduction reaction of the aluminum and the worn anodes (12') must therefore be replaced by new anodes (12).

When the anode (12) is consumed (anode (12') on the right in figure 1), it should be replaced with a new anode. The anode assembly (12', 13, 14) is therefore extracted from the tank with, in addition, pieces of bath cover (11) forming a crust remaining attached to said spent anode (12'). Fluorinated gases are emitted by the anode thus extracted, in quantity all the more important as the temperature of the anode is high, typically close to 1000°C.

It is therefore appropriate, as mentioned in the preamble, to limit this emission of fluorinated gases.

To this end, the invention, the principle of which is illustrated in FIG. 2, is intended to allow this limitation, then this extinction of the emission of fluorinated gases. In Figure 2 has been illustrated a receptacle (20), typically metallic, capable of receiving the anode assembly (12', 13) and more particularly the anode proper (12'). This receptacle is then closed by means of a bell (21), the base (22) of which is received at the level of the upper edge (23) of the said receptacle (20), and the upper end of which bears on the end superior (18) of the rod (13). In doing so, an internal volume (27) formed by the receptacle is defined

(20) and the bell (21), able to confine the said gaseous effluents emanating from the anode (12') beyond the covering crust (11), and to prohibit or drastically reduce the introduction of ambient air and therefore of oxygen likely to favor the continuation of the combustion of the anode (12').

According to a first embodiment illustrated in relation to FIGS. 3 to 7, the bell

(21) has in the deployed position, that is to say in operational mode, a shape in this case pyramidal, or even conical, the base of said bell (21) being adapted by simple deposit on the upper edge of a receptacle (20). In the example described in relation to Figures 3 to 7, said receptacle (20) is capable of receiving six anode assemblies positioned two by two, as can clearly be seen in Figures 3 and 4. In this example, the bell (21) is configured to simultaneously cover two anode assemblies received within said receptacle (20).

According to a characteristic of the invention, this bell (21) is likely to be in two forms, respectively an extended form (figures 3, 4, 5 and 6), and a folded form (figure 7).

Said bell (21) comprises a flexible peripheral casing (24), typically made of a fabric based on ceramics, basalt or even glass fibers, advantageously coated with silicone or PTFE. In this case, this flexible envelope (24) is in deployed mode in the form of alternating folds. Due to the pyramidal or conical shape of the bell, these folds have larger dimensions at the base than at its upper end, said folds being capable, as illustrated in FIG. 7, of folding over one another. others, and thus considerably reduce the size of the bell (21) when it is not in the operational position. In order to give a certain hold to the bell (21) when it is deployed, rigid hoops (25), more or less periodically distributed, are joined together, for example by bolting, at the level of the corresponding folds.

In order to position said bell (21) on the anode assemblies, the base of the bell is provided with means, in this case consisting of sheaths (28), capable of allowing the insertion within them of the forks of a forklift . Thus, when at least two anode assemblies have been positioned in the receptacle (20), the forklift positions the bell in the folded position, and as illustrated in FIG. 7, near the upper end of the rods (13), so as to resting a lid (26) integral with the last folds constituting the bell (21) and typically made of metal, said lid (26) in this case of parallelepipedic shape, being able to simply come to bear simultaneously on the end ( 18) of the two rods (13), so that, by simply lowering the forklift, the bell (21) unfolds until it reaches its operational position illustrated for example in FIGS. 5 and 6. In doing so, we define the internal volume (27) of desired confinement.

There is shown, in relation to Figures 8 to 10, a second embodiment of the invention. According to this embodiment, the bell (21) comprises a base (30) intended to be received on the upper rim of the receptacle (20). This base (30), in this case made of metal, has a generally parallelepiped shape, and is associated by means of a flexible skirt (31) with a rigid metal plate (32), the surface of which is of dimension less than that of the surface defined by a cross section of the base (30). This metal plate (32) is pierced, in the example described, with two through holes, intended to allow the passage at this level of the anode rods (13), as can be seen for example in Figure 8. In fact, a flexible zone (33) is capable of being deployed in the operational position from these through-holes, as can be seen in FIGS. 8 and 9. The upper end of said flexible zone (33) receives a rigid upper closing plate (34), for example metallic, intended to bear on the upper end (18) of the anode rods (13).

Thus and following the example of what has been described in relation to the embodiment of FIGS. 3 to 7, the deployment of the bell (21) thus constituted in operational mode passes through the support of the upper plates (34) on the upper end (18) of the metal rods (13), the progressive lowering of the said bell thus formed until the metal plate (32) comes to rest on the upper surface of the tripods (14) of the corresponding anode assemblies . Continued lowering causes the skirt (31) to deploy until the base (30) comes to rest on the upper edge of the receptacle (20). Although not shown in Figures 8 to 10, the device is also provided with gripping and manipulation means similar to those shown in Figures 3 to 7. In non-operational mode (FIG. 10), it can be observed that the upper flexible zone (33) is received in folded mode in means (35) erected from the metal plate (32) and secured to the latter, dimensioned so as to receive without friction said upper flexible zone (33) in the folded position.

Figures 11, 12 and 13 illustrate a third embodiment of the invention. According to this embodiment, the receptacle (20) is surmounted by a riser (40) whose upper edge is inscribed in a plane located above the upper surface of the tripods (14). This riser (40) is secured, for example following a welding operation, to said receptacle (20). The flexible bell as such consists, for its part, of a rigid metal plate (41), similar to the metal plate (32) of the previous embodiment, dimensioned in such a way as to be received in a sealed or substantially sealed manner. on the upper edge (42) of the socket (40). The flexible zone (43) of said bell is substantially similar to that described in relation to the second embodiment. In the example described, it has been shown with a square cross-section, and not circular, but the principle remains the same. Similarly, the deployment of the bell thus constituted in operational mode requires the support of upper rigid closing plates (44), again for example metal, on the upper end (18) of the metal rods (13), the progressive lowering of said bell thus constituted until the metal plate (41) comes to bear on the peripheral rim (42) of the socket (40).

As a corollary and like the embodiment described in relation to FIGS. 8 to 10, in folded mode, that is to say non-operational (FIG. 13), said flexible zone (43) is received within means (45) suitable for storing it, the means being constituted by metal plates erected perpendicularly from the upper surface of the rigid metal plate (41).

Similarly, said metal plate (41) is pierced with through holes, in order to allow the passage of the anode rods (13) through said plate, and thus allow the positioning of the bell above and around said rods anode until defining the desired confinement volume (27). In order to facilitate the operations for positioning the bell above the anode assemblies concerned, the upper plate (41) is also provided with means defining sleeves (46), allowing the insertion within them of the forks of a forklift, and de facto facilitating the handling of said bell.

Whatever the embodiment of the invention, a certain tightness of the containment volume inherent on the one hand, to the flexible zone (24, 33, 43), and on the other hand, by the cooperation of the base of the bell, and for example of the base (30) or of the rigid plate (41) with the upper edge of the receptacle (20) or the upper edge of the socket (40). More specifically, the metal/metal contact at the base of the bell can be optimized by increasing the covering surface of the base of the bell on the receptacle or on the riser, or even by providing a groove for receiving said base at the vicinity of the peripheral edge of the receptacle or the riser. Optionally, it can also be envisaged to provide this cooperation zone with a seal, for example made of silicone.

In doing so, there is optimal sealing, sufficient in any case to reduce if not eliminate any leakage of fluorinated gases and other dust accompanying the change of the anodes. One can see the whole point of the present invention which allows, in a simple manner, the manipulation of a confinement device for anode assemblies, and in particular to define a confinement volume making it possible to drastically limit the emission of fluorinated gases, virtually prohibit the introduction within said volume of oxygen likely to promote the combustion of the anode, and therefore as a corollary to reduce more quickly the temporary storage time of said anode assemblies when the anode is consumed.

Claims

1. Device for containing at least one anode assembly, said assembly comprising a spent anode (12') fixed to a metal rod (13), comprising:

^■ a receptacle (20) for receiving the anode assembly, said anode assembly resting within said receptacle via the lower surface of the spent anode (12');

^■ a bell (21) open at its lower end, and capable of forming a closed volume (27) in cooperation with said receptacle (20), within which said at least one anode assembly is received; characterized in that the bell (21) is capable of taking two forms:

^■ an operational form, deployed, according to which is defined, with the receptacle (20), said closed volume (27).

2. Device for containing at least one anode assembly according to claim

1, characterized in that at least part of the bell (21) is made of flexible or flexible material.

3. Device for containing at least one anode assembly according to claim

2, characterized in that the flexible or flexible material constituting at least part of the bell (21) is chosen from the group comprising ceramic and/or basalt-based and/or fiberglass fabrics.

4. Containment device for at least one anode assembly according to one of claims 1 to 3, characterized in that the bell (21) has rotational or even rotational symmetry.

5. Device for containing at least one anode assembly according to claim 4, characterized in that the bell (21) is provided at its periphery with rigid hoops (25) oriented along planes substantially parallel to each other, and perpendicular to the axis of rotation or revolution of the bell, distributed more or less regularly along all or part of the height of said bell when the latter is in the operational position.

6. Containment device for at least one anode assembly according to one of claims 2 to 4, characterized in that the bell (21) comprises, in its lower part, a rigid cover or base (30), capable of coming to fit on the receiving receptacle (20) of the anode assembly, and a rigid plate (32) connected by means of a flexible zone or skirt (31) to the upper peripheral edge of said cover, said rigid plate (32) being pierced with through holes communicating with the flexible or flexible zone (33) of the bell.

7. Device for containing at least one anode assembly according to one of claims 2 to 4, characterized in that the bell (21) has at its base a rigid plate (41), the dimensions of which correspond to those of the upper surface of the reception receptacle (20) of the anode assembly, so as to come to rest on the upper end of the said receptacle, the said rigid plate (41) being pierced with through orifices able to communicate with the flexible zone (43 ) of the bell.

8. Device for containing at least one anode assembly according to claim 7, characterized in that the receptacle (20) for receiving the anode assembly is surmounted by a socket (40), on which the rigid plate rests. (41) of the bell (21).

9. Device for containing at least one anode assembly according to one of claims 6 to 8, characterized in that the upper part of the flexible or flexible zone (24, 33, 43) of the bell is also provided with a cover (26) or a rigid closing plate (34, 44), capable of resting at the level of the upper end (18) of the anode rod (13).

10. Device for containing at least one anode assembly according to one of claims 6 to 9, characterized in that the rigid plate (32, 41) with which the bell (21) is provided is provided with storage means (35 , 45) of the flexible or flexible zone (33, 43) of the bell in the non-operational position.

11. Device for containing at least one anode assembly according to claim 10, characterized in that the storage means (35, 45) consist of walls, in particular metal, emanating from the upper face of said rigid plate (32, 41) essentially perpendicular to it.

12. Device for containing at least one anode assembly according to one of claims 5 to 11, characterized in that the bell (21) is provided with handling means (28, 46) able to cooperate with gripping members , handling and/or lifting.