DEVICE FOR HOLDING AN ANODE ARRANGEMENT

Description

FIELD OF THE INVENTION

[0001] The present invention belongs to the field of aluminum production by igneous electrolysis, and more particularly relates to a confinement device for an anode assembly. PRIOR STATE OF THE ART

[0002] The production of aluminum by the so-called igneous electrolysis process is now widespread and mastered. The electrolysis of alumina in the presence of molten cryolite produces aluminum. This electrolysis takes place in electrolytic cells containing an electrolyte, the bottom of which constitutes the cathode.

[0003] As a corollary, anodes are immersed in these tanks, traditionally made of carbon material, each of said anodes being equipped with a metal rod, therefore electrically conductive, intended for its electrical and mechanical connection to an anode frame which is mobile relative to a gantry fixed above the electrolysis tanks.

[0004] In the field considered, the assembly consisting of the rod and the anode made of carbon material fixed at its end is called the anode assembly.

[0005] Due to the electrolysis phenomenon, the anodes are consumed as the reaction progresses, requiring periodic replacement. To do this, the anode assembly in question is separated from the anode frame and then removed to a storage location where the anode cools before being either reprocessed to recover the unconsumed carbon material or discarded.

[0006] However, it is known that, at the outlet of the electrolysis tank, a worn or partially worn anode emits fluorinated gases, in particular HF, and dust, the emission of such gases being all the more significant as the anode temperature is high. In fact, and for obvious considerations of operator protection, in addition to the environment, attempts have always been made to reduce these gas and dust emissions as much as possible.

[0007] Thus, in document EP 2 507 413, a technical solution has been proposed consisting of a substantially horizontal plate on which an anode assembly is positioned, associated with a reservoir capable, after receiving the anode assembly, of receiving a smothering powder intended to cover the entire anode, this powder being made up of a fluorinated compound mixed with alumina. While, admittedly, the use of such a smothering powder proves effective in terms, on the one hand, of reducing the temperature of the anode, and on the other hand, of limiting gaseous emissions, in particular HF, its implementation proves relatively complex, since it is necessary to provide hoppers for conveying the smothering powder and then its evacuation.

[0008] Document WO 2012 / 156616 also proposed a device similar to that previously described, comprising a tank containing non-fluidized alumina in sufficient quantity to cover the anode butt, and provided with a device capable of subsequently ensuring the fluidization of the alumina. Here again, this device proves to be complex to implement, due to the presence of alumina, in addition to the device ensuring its fluidization.

[0009] 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, capable of being received at the upper end of the side walls defining said receiving enclosure, and of covering the entire rod of the anode assembly. A closed volume is thus defined, making it possible to overcome sealing problems at the interface with the rod, to avoid the diffusion of gases emitted by the worn anode, in addition to preventing the arrival of ambient air, therefore oxygen, up to the level of the part of the anode still being consumed, and therefore, consequently, to restrict the phenomenon of combustion of the anode, and consequently, the emission of more gas.

[0010] 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 need to cover the anode assembly, i.e. rod and anode, a significant, heavy bulk, the handling of which typically involves the use of MSE (electrolysis service machines), which may consequently, due to their relatively limited number in an aluminium production plant, have their neutralisation affecting other tasks. In addition, the civil engineering capable of allowing the implementation of such a device must be adapted due to the height necessary for its handling, since it is also necessary to take into account the height of the anode assembly as such, added to the height of the rigid cover, in order to allow its positioning above said anode assembly.However, the costs associated with such an adaptation of civil engineering are simply incompatible with the rational management of an aluminum production facility.

[0011] The invention aims to overcome these drawbacks, and in particular to reduce both the size and the weight of such a device for confining an anode assembly, and to facilitate its handling and the associated logistics. STATEMENT OF THE INVENTION

[0012] According to the invention, this device for confining at least one anode assembly, said assembly comprising a used anode fixed to a metal rod, comprises: ▪ a receptacle for receiving the anode assembly, said anode assembly resting within said receptacle by the lower surface of the used anode; ▪ a bell open at its lower end, and capable of forming a closed volume in cooperation with said receptacle, within which said at least one anode assembly is received.

[0013] According to the invention, the bell can take two forms: ▪ a form for storing said device, in a non-operational position, in which it is folded back on itself; ▪ an operational, deployed form, according to which said closed volume is defined, with the receptacle.

[0014] In other words, the invention consists of implementing a bell, for example flexible or supple, 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 store, consequently making it possible to avoid necessarily having to resort to electrolysis bridges or MSEs, and furthermore, to be able to be implemented within existing installations, without causing any modification to the civil engineering.

[0015] 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.

[0016] According to the invention, the bell has a rotational, or even revolutionary, symmetry, which appears in particular when said bell is in the operational position, i.e. deployed.

[0017] According to a first embodiment, the bell is made of flexible material, provided at its periphery with rigid hoops oriented along planes substantially parallel to each other, and perpendicular to the axis of revolution of the bell, distributed more or less regularly along all or part of the height of said bell.

[0018] Typically, the flexible material is advantageously a refractory material, due to the high temperature of the anode at the tank outlet. It is indeed recalled that the typical temperature of the anode at the tank outlet is close to 1000°C. This material can, for example, be chosen from the group comprising ceramic and / or basalt-based and / or glass fiber fabrics. This fabric, whatever the material it is made of, can also be coated or coated with one or more layers of a protective material, such as silicone or PTFE (polytetrafluoroethylene), ensuring the sealing and protection functions against attacks inherent to HF.

[0019] According to another embodiment of the invention, the bell comprises, in its lower part, a rigid cover or base, capable of fitting 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-orifices communicating with the flexible or supple part of the bell.

[0020] 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.

[0021] 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-orifices capable of communicating with the flexible part of the bell.

[0022] 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 metallic walls, emanating from the upper face of said rigid plate essentially perpendicular to it, capable of facilitating 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.

[0023] Advantageously, said rigid plate, and generally the bell itself, is provided with means for receiving or cooperating with members for gripping and handling said bell. Typically, these means for receiving or cooperating may consist of areas for receiving the forks of a forklift, or even lifting rings capable of cooperating with lifting means mounted on a self-propelled crane, or on the MSE, or even on a gantry dedicated to this purpose. The objective is to facilitate the handling of the entire device, in particular when the latter receives one or more anode assemblies. BRIEF DESCRIPTION OF THE FIGURES

[0024] The manner in which the invention can be implemented and the advantages which result therefrom will become more apparent from the following examples of implementation, given for informational and non-limiting purposes, in support of the appended figures. There figure 1is a schematic cross-sectional representation of a conventional electrolysis cell. The figure 2 is a schematic sectional representation of the principle of the anode assembly confinement device according to the invention. The figure 3 is a schematic perspective representation illustrating a first embodiment of the invention, with the containment device in operational mode. The figure 4 is a view analogous to the figure 3 top view. The Figure 5 is a view analogous to the figure 3 in side view. The figure 6 is a schematic sectional view along line VI-VI of the Figure 5 . There figure 7 is a schematic perspective view of the containment device of the figure 3 in non-operational mode. The figure 8 is a schematic perspective view of a second embodiment of the containment device of the invention. The figure 9is a more detailed schematic view of the device of the figure 8 . There figure 10 is a schematic perspective view of the device of the figures 8 And 9 in non-operational mode. The figure 11 is a schematic perspective view of a third embodiment of the containment device of the invention. The figure 12 is a more detailed schematic view of the device of the figure 11 . There figure 13 is a schematic perspective view of the device of the figures 11 And 12 in non-operational mode. DETAILED DESCRIPTION OF THE INVENTION

[0025] We have schematically represented on the figure 1 a sectional view of a conventional electrolysis tank (1).

[0026] This figure shows the essential elements used for the 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 are fixed 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, topped with a liquid bath (10) of alumina and molten cryolite, itself covered with a cover (11) based on solid bath and alumina.

[0027] Correspondingly, anodes (12, 12') associated with a metal rod (13) are immersed in the bath of molten alumina and cryolite (10), 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).

[0028] The reference (16) represents the device for supplying the tank in question with alumina and / or AIF3.

[0029] Finally, the reference (17) represents the removable hood(s), typically metallic, intended to confine the effluents resulting from the electrolysis reaction, then direct them to an effluent treatment center.

[0030] Conventionally, the anodes (12) are made of pre-baked carbon 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).

[0031] When the anode (12) is consumed (anode (12') on the right on the 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 used anode (12'). Fluorinated gases are emitted by the anode thus extracted, in quantities that increase as the temperature of the anode is high, typically around 1000°C.

[0032] It is therefore appropriate, as mentioned in the preamble, to limit this emission of fluorinated gases.

[0033] For this purpose, the invention, the principle of which is illustrated in figure 2 , aims to enable this limitation, then this extinction of fluorinated gas emissions. Within figure 2has been illustrated a receptacle (20), typically metallic, capable of receiving the anode assembly (12', 13) and more particularly the anode itself (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 said receptacle (20), and the upper end of which comes to bear on the upper end (18) of the rod (13). In doing so, an internal volume (27) is defined consisting of the receptacle (20) and the bell (21), capable of confining said gaseous effluents emanating from the anode (12') outside the covering crust (11), and of prohibiting or drastically reducing the introduction of ambient air and therefore of oxygen likely to promote the continuation of the combustion of the anode (12').

[0034] According to a first embodiment illustrated in relation to the figures 3 has 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 the figures 3 to 7 , said receptacle (20) is capable of receiving six anode assemblies positioned two by two, as can be clearly observed in the Figures 3 and 4 In this example, the bell (21) is configured to simultaneously cover two anode assemblies received within said receptacle (20).

[0035] According to a characteristic of the invention, this bell (21) is capable of being presented in two forms, respectively a deployed form ( figures 3, 4 , 5 and 6 ), and a folded shape ( figure 7 ).

[0036] Said bell (21) comprises a flexible peripheral envelope (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 presented 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 the figure 7 , to fold on top of each other, 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 secured, for example by bolting, at the level of the corresponding folds.

[0037] 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 therein 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 the figure 7 , in the vicinity of the upper end of the rods (13), so as to rest a cover (26) integral with the last folds constituting the bell (21) and typically made of metal, said cover (26) in this case of parallelepiped 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) deploys until it reaches its operational position illustrated for example on the Figures 5 and 6In doing so, we define the internal volume (27) of confinement sought.

[0038] We have represented, in relation to the 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 edge 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 smaller 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 on the figure 8. In fact, a flexible zone (33) is capable of deploying into operational position from these through holes, as can be observed in the figures 8 And 9 The upper end of said flexible zone (33) receives a rigid upper closure plate (34), for example metallic, intended to come to bear on the upper end (18) of the anode rods (13).

[0039] Thus and similarly to what has been described in relation to the method of carrying out the figures 3 to 7, the deployment of the bell (21) thus constituted in operational mode involves the support of the upper plates (34) on the upper end (18) of the metal rods (13), the progressive lowering of said bell thus constituted until the metal plate (32) comes to bear on the upper surface of the tripods (14) of the corresponding anode assemblies. The continuation of the lowering causes the deployment of the skirt (31), until the base (30) comes to bear on the upper edge of the receptacle (20). Although not shown on the figures 8 to 10 , the device is also provided with gripping and handling means similar to those shown in the figures 3 to 7 .

[0040] In non-operational mode ( figure 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 it, dimensioned in such a way as to receive without friction said upper flexible zone (33) in the folded position.

[0041] THE figures 11 , 12 and 13illustrate 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 situated 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 is constituted, for its part, by a rigid metal plate (41), similar to the metal plate (32) of the previous embodiment, dimensioned so as to be received in a sealed or substantially sealed manner on the upper edge (42) of the riser (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 to have a square, and not a circular, cross-section, but the principle nevertheless remains identical.Likewise, the deployment of the bell thus constituted in operational mode involves the support of rigid upper closure plates (44), again for example metallic, 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 edge (42) of the extension (40).

[0042] Corollarily and like the embodiment described in relation to the figures 8 to 10 , in folded mode, i.e. non-operational ( figure 13 ), said flexible zone (43) is received within means (45) capable of storing it, the means consisting of metal plates erected perpendicularly from the upper surface of the rigid metal plate (41).

[0043] Likewise, 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 anode rods until the desired confinement volume (27) is defined.

[0044] In order to facilitate the operations of placing the bell above the anode assemblies concerned, the upper plate (41) is also provided with means defining sleeves (46), allowing the insertion therein of the forks of a forklift, and de facto facilitating the handling of said bell.

[0045] Whatever the embodiment of the invention, a certain sealing of the confinement volume is achieved, 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 the rigid plate (41) with the upper edge of the receptacle (20) or the upper edge of the riser (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 receiving groove for said base in the vicinity of the peripheral edge of the receptacle or the riser. Optionally, it may also be envisaged to provide this cooperation zone with a seal, for example made of silicone.

[0046] In doing so, we have optimal sealing, sufficient in any case to reduce if not eliminate any leakage of fluorinated gases and other dust accompanying the change of anodes.

[0047] The whole point of the present invention is easy to understand, as it allows, in a simple manner, the handling of a device for confining anode assemblies, and in particular to define a confinement volume making it possible to drastically limit the emission of fluorinated gases, to virtually prohibit the introduction into said volume of oxygen likely to promote the combustion of the anode, and therefore, as a corollary, to reduce more quickly the duration of temporary storage of said anode assemblies when the anode is consumed.

Claims

1. 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, said anode assembly resting inside said receptacle via the lower surface of the spent anode (12'); ▪ a bell housing (21) open at its lower end, and able to form a closed volume (27) in collaboration with said receptacle (20), inside which said at least one anode assembly is housed; characterised in that the bell housing (21) is able to adopt two shapes: ▪ a shape for storing said device, in the non-operational position, in which it is folded back on itself; ▪ a deployed, operational shape, according to which said closed volume (27) is defined, with the receptacle (20).

2. The device for the containment of at least one anode assembly according to claim 1, characterised in that at least part of the bell (21) is made of a flexible or soft material.

3. The device for the containment of at least one anode assembly according to claim 2, characterised in that the flexible or soft material constituting at least part of the bell housing (21) is selected from the group comprising ceramic and / or basalt-based and / or glass fibre fabrics.

4. The device for the containment of at least one anode assembly according to any one of claims 1 to 3, characterised in that the bell housing (21) has rotational symmetry or even symmetry of revolution.

5. The device for the containment of at least one anode assembly according to claim 4, characterised in that the bell (21) is provided at its periphery with rigid hoops (25) oriented along planes substantially parallel to one another, and perpendicular to the axis of rotation or revolution of the bell housing, distributed more or less uniformly along all or part of the height of said bell housing when the latter is in the operational position.

6. The device for the containment of at least one anode assembly according to one of Claims 2 to 4, characterised in that the bell (21) comprises, in its lower part, a rigid lid or base (30), capable of fitting on the receptacle (20) for receiving 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 lid, said rigid plate (32) being pierced with through-holes communicating with the flexible or soft zone (33) of the bell housing.

7. The device for the containment of at least one anode assembly according to any one of claims 2 to 4, characterised in that the bell housing (21) comprises at its base a rigid plate (41), the dimensions of which correspond to those of the upper surface of the receptacle (20) for receiving the anode assembly, so as to rest on the upper end of said receptacle, said rigid plate (41) being pierced with through-holes capable of communicating with the flexible zone (43) of the bell housing.

8. The device for the containment of at least one anode assembly according to claim 7, characterised in that the receptacle (20) for receiving the anode assembly is surmounted by a raised portion (40) on which the rigid plate (41) of the bell housing (21) rests.

9. The device for the containment of at least one anode assembly according to any one of claims 6 to 8, characterised in that the upper part of the flexible or soft zone (24, 33, 43) of the bell housing is also provided with a lid (26) or a rigid sealing plate (34, 44), capable of resting at the upper end (18) of the anode rod (13).

10. The device for the containment of at least one anode assembly according to any one of claims 6 to 9, characterised in that the rigid plate (32, 41) with which the bell (21) is provided is provided with means (35, 45) for storing the flexible or soft zone (33, 43) of the bell housing in the non-operational position.

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

12. The device for the containment of at least one anode assembly according to one of claims 5 to 11, characterised in that the bell (21) is provided with handling means (28, 46) capable of cooperating with gripping, handling and / or lifting members.