EP3099841B1 - Hooding system for an electrolytic cell - Google Patents

Description

The present invention relates to an electrolytic cell comprising a cowling system and a method of changing an anode assembly.

Aluminum is conventionally produced in aluminum smelters, by electrolysis, according to the Hall-Héroult process.

An aluminum smelter traditionally comprises several hundred electrolytic cells connected in series and traversed by an electrolysis current whose intensity can reach several hundreds of thousands of amperes. It is known to arrange the electrolytic cells transversely with respect to the flow direction of the electrolysis current at the scale of the series.

Electrolysis tanks conventionally comprise a steel box inside which is arranged a coating of refractory materials, a cathode of carbon material, crossed by cathode conductors for collecting the electrolysis current at the cathode to conduct it up to cathode outlets passing through the bottom or sides of the box, routing conductors extending substantially horizontally to the next tank from the cathode outlets, an electrolytic bath in which the alumina is dissolved, at least one set anode having at least one anode immersed in said electrolytic bath and an anode rod sealed in the anode, an anode frame to which the anode assembly is suspended via the anode rod, and electrolytic current rise conductors, extending from bottom to top, connected to the routing conductors of the preceding electrolytic cell to convey electrolysis current e from the cathode outlets to the anode frame and the anode assembly and the anode of the next vessel. The anodes are more particularly of anode type precooked with precooked carbon blocks, that is to say cooked before introduction into the electrolytic cell.

The anode assemblies are consumed during the electrolysis reaction and must therefore be regularly replaced by new anode assemblies.

The sides of the electrolytic cell define an opening through which the anode assemblies are introduced into the electrolytic cell to be immersed in the electrolytic bath or removed from the electrolytic cell for replacement.

In order to limit the thermal losses and to avoid the diffusion, outside the electrolytic cell, of gases generated during the electrolysis reaction, hereinafter referred to as tank gases, it is intended to close off the opening delimited by the reactor vessel. electrolysis with a rollover system.

Known rollover systems, such as those disclosed in patent documents US4043892 and WO2007067061 , include side caps, removable, inclined compared to the horizontal. These covers rest on the one hand on one side of the electrolytic cell and on the other hand against a part of superstructure, intended to support the anode assemblies, extending in a longitudinal direction of the electrolytic cell, to above the opening defined by the sides of the tank, that is to say, in line with the anode assemblies and the electrolytic bath.

The covers thus form a containment chamber limiting the diffusion of the tank gases when the rollover system is completely closed. This also limits heat losses.

However, in an intervention requiring an opening of the cowling system, as is the case for the replacement of an anode assembly used by a new anode assembly, traditional cowling systems offer a limited response to the problem of diffusion of tank gas out of the electrolysis cell and preservation of the thermal equilibrium of the electrolysis cell.

Indeed, during an intervention as a change of anode assembly, hoods are removed to create an opening through the rollover system. This opening, necessary, allows access to the interior of the tank, in particular to remove a spent anode assembly. However, the opening thus created provides the opportunity for the cell gases to diffuse out of the containment. This opening can also disturb the thermal equilibrium of the tank.

The larger the opening thus created, the greater the amount of leachate gas that can escape, and the greater the heat loss can be. It is the same with the opening time of the cowling during an intervention: the longer the rollover system is open, the greater the amount of flue gas that can escape, and the greater the thermal equilibrium of the tank is disturbed.

Given the presence, above the box, of a superstructure on which the hoods of traditional rollover systems are supported, the hoods having been removed to create the opening required for the intervention are often placed next to the electrolysis cell, in particular in an inter-cell space separating two adjacent tanks. This can pose a congestion problem, and this congestion problem can slow down the intervention, that is to say, increase the duration during which the rollover system is open. This can also pose a safety problem, as an operator may trip over.

In addition, hoods of known rollover systems are designed to have their adjacent edges superimposed on each other. This superposition makes it possible to limit the leakage of vat gas and the energetic losses at the interface between two adjacent covers.

However, the traditional solutions of overlay hoods have a disadvantage: the hoods are nested inside one another, and the removal of one of them requires the movement or removal of one or more adjacent hoods. It is therefore clear that, for a maintenance intervention theoretically requiring the removal of a single cover, several covers must be moved or removed. The open area through the rollover system is then larger than necessary. Patent documents US4043892 and WO2007067061 teach the removal of hoods in groups of three.

Finally, some maintenance interventions may require smaller open areas than for other maintenance operations. For example, in order to break the crusts generated on the electrolytic bath during the electrolysis reaction, all that is required is an opening allowing a suitable tool to be passed in the right place to break these crusts, while for extracting or setting up a anodic assembly, it requires a larger opening adapted to the dimensions of the anode assembly to extract or put in place.

However, the hoods of traditional rollover systems are similar, especially in terms of dimensions, so that the only possibility of selecting an opening surface through the rollover system is the selection of the number of covers to remove. This does not allow a fine adjustment of the opening surface, that is to say the selection of a minimum opening area but sufficient to perform a maintenance intervention to achieve.

Furthermore, the presence of the superstructure and electrolytic current rise conductors above the opening defined by the sides of the tank make it difficult the crust breaking operation being formed between the anode assemblies because the access under the superstructure and climbing conductors is particularly small. It follows that the crust breaking operation, traditionally carried out with a jack hammer mounted on an arm with an angular inclination, requires more time than if there were no such obstacles, which increases the duration opening of the cowling. In addition, because of this problem of accessibility, the crust breaking is sometimes incomplete at the periphery of the anode assembly and the extracted anode assembly comprises solid crust pieces that increase its passage section, its size and can damage adjacent covers still in place.

Finally, the hoods rest in the lower part on the top of the box on which collapses the cover product of the anodes, so that the supports of the hoods are unstable and their positioning is not accurate. They are also exposed at the bottom to flames and hot spots related to discontinuities of the anode cover, resulting in their rapid degradation.

Also, the present invention aims at overcoming all or part of these disadvantages by proposing a rollover system, an electrolysis cell comprising this cowling system and a method of changing an anode assembly, offering the possibility of effectively containing the diffusion tank gas and maintain thermal equilibrium, especially during a maintenance intervention.

• chaque capot comprend deux bords d'appui opposés destinés à reposer sur deux côtés opposés de la cuve d'électrolyse parmi les côtés de la cuve d'électrolyse délimitant l'ouverture, de sorte que chaque capot s'étende d'un côté à l'autre de la cuve d'électrolyse, au-dessus de l'ouverture,
• le système de capotage est conçu pour présenter, de façon sensiblement parallèle aux capots, des fenêtres d'intervention longitudinales, permettant de libérer un passage prédéterminé à travers la pluralité de capots,
• le système de capotage comprend en outre des couvercles d'obturation, chaque couvercle d'obturation étant mobile par rapport aux capots entre une position d'obturation, dans laquelle chaque couvercle d'obturation obture l'une des fenêtres d'intervention, et une position d'intervention, dans laquelle chaque couvercle d'obturation libère un passage à travers le système de capotage via l'une des fenêtres d'intervention, les couvercles d'obturation étant destinés à reposer en position d'obturation au moins en partie sur les capots, et
• les couvercles d'obturation sont conçus pour être déplacés de la position d'obturation à la position d'intervention, indépendamment les uns des autres, sans déplacer les capots sur lesquels les couvercles d'obturation reposent.

For this purpose, the subject of the present invention is an electrolytic cell comprising a plurality of anode assemblies, the sides delimiting an opening through which the anode assemblies are intended to be put in place or removed in a downwardly vertical translation movement respectively or ascending, and a cowling system extending above the anode assemblies to cover said opening, the cowling system comprising a plurality of cowls, characterized in that:

• each cover comprises two opposite support edges intended to rest on two opposite sides of the electrolytic cell among the sides of the electrolytic cell delimiting the opening, so that each cover extends from one side to the other. other of the electrolysis cell, above the opening,
• the rollover system is designed to present, substantially parallel to the hoods, longitudinal intervention windows, to release a predetermined passage through the plurality of covers,
• the rollover system further comprises shutter covers, each shutter cover being movable relative to the covers between a closed position, in which each shutter cover closes one of the intervention windows, and a intervention position, wherein each shutter cover releases a passage through the rollover system via one of the intervention windows, the shutter caps being intended to rest in the closed position at least in part on hoods, and
• the shutter covers are adapted to be moved from the shut-off position to the intervention position, independently of one another, without moving the covers on which the shutter covers rest.

This electrolytic cell has a stable thermal equilibrium and limits the gas discharges from tanks, including during the intervention as an anode assembly replacement.

The rollover system offers the possibility to access the inside of the electrolysis cell by removing only one of the blanking covers, without moving or removing the covers.

This allows to provide a dimensioned opening contained through the rollover system, while leaving in place the covers. In the context of an intervention such as a change of anode assembly, this makes it possible to perform certain preliminary operations, such as sawing crusts formed around the spent anode assembly during the electrolysis reaction, with a surface open minimum through the rollover system.

This limits the off-gas discharge to the outside of the electrolytic cell and prevents disruption of the thermal equilibrium of the electrolytic cell.

By opposite sides of the electrolytic cell is meant sides located on either side of a median plane, in particular a longitudinal median plane, of the electrolytic cell. Thus, each cover is intended to extend on both sides of this median plane to rest simultaneously on these two opposite sides.

The covers and shutter covers have a vertical assembly stroke, which is an important advantage to automate the introduction of the covers, because there is no complex angular movements to achieve unlike the state of the art.

According to a preferred embodiment, the closure covers have longitudinal edges which are intended to rest each on one of the covers. Thus, the seal at the junction between the closure covers and the covers is ensured over the entire length of the covers, respectively the closure covers, by superimposing an edge of the closure cover over a cover. hood edge.

According to a preferred embodiment, the closure covers have a T-shaped cross-section defining two longitudinal returns, the covers have an inverted T-shaped cross-section delimiting two longitudinal returns, each return of one of the closure covers being based on one of the returns of an adjacent cowl, so that the rollover system has an alternation of covers and nested sealing lids.

This configuration offers both a simple solution to allow the shutter covers to be removed without interference with the covers on which they rest and the other shutter covers, and at the same time to improve the tightness of the rollover system. This thus makes it possible to limit tank gas leaks and heat losses.

Advantageously, the returns of the covers and the closure covers have an L-shaped section, so that the engagement of a cover and a closure cover forms a sealing baffle.

This feature also offers the advantage of improved sealing, to contain tank gas leaks and heat losses.

Advantageously, the rollover system comprises sealing means interposed between the returns of each closure cover and the returns of the adjacent covers on which each closure cover rests.

Thus, the seal is improved.

According to an advantageous embodiment, the covers and lids extend horizontally and the longitudinal returns of the hoods comprise chutes containing a powdery material and having an upper opening, the longitudinal returns of the lids having an L-shaped section, so that end portion of the L-section of the lid is pressed into the powder material via the upper opening in the chute when the cover and the cover are nested. The realization of such a seal by means of a powder material is possible because the covers and covers extend horizontally so that the powder material remains distributed with a uniform height over the entire length of the chute. The powder material forms a barrier preventing the vent gases from escaping.

Advantageously, the powdery material contains alumina. More particularly, the pulverulent material may be formed of alumina or crushed electrolysis bath which comprises alumina. These materials have the advantage of being available in an aluminum smelter and are further introduced into the electrolysis tanks so that they do not risk polluting the electrolytic cell in case of accidental spillage into the tank. In addition, alumina is a very good adsorbent for the HF and SO2 released by the electrolytic cell so that any infiltration of vat gas through the powder material will have a lower environmental impact.

Advantageously, the covers and / or the covers comprise a shutter arranged to close the opening of the chute when the cover and the cover are nested. This flap that can be fixed or mobile, including pivoting is intended to retain the powder material in the chute.

According to an advantageous embodiment, the sealing means comprise elastic seals intended to compensate for a difference in relative deformation between two consecutive covers of the cowling system between which is intended to extend a closure cover in position. shutter.

In other words, the space or clearance between covers and closure covers is side so that the crushing of the seals separating them, taking into account the deflection of the covers and the closure covers, is in the range elastic crushing seals. Thus, the seal is improved.

According to an advantageous embodiment, the covers comprise a face provided with at least one reinforcing rib intended to limit the bending of the covers.

This makes it possible to stiffen the covers. Thus, the crushing of the seals is relatively uniform. The seal is thus improved.

According to a preferred embodiment, the covers comprise a face provided with thermal insulation means.

This limits thermal losses through the rollover system.

Preferably, the isolation means are arranged on the underside of the covers so as to limit the warpage and therefore the degradation of the covers.

Advantageously, the covers comprise a substantially longitudinal tubular body, the tubular body defining a cavity inside which is arranged a thermally insulating material.

These characteristics make it possible to protect the thermally insulating material and to limit thermal losses, by synergistic effect between the thermally insulating material, which slows down the propagation of heat through the rollover system, and the improved rigidity of the covers due to the tubular nature. of the body, this rigidity allowing a uniform support of the cover against the surface on which it rests and a uniform support of the closure covers which rest on this cover.

According to a preferred embodiment, the covers comprise a bottom face provided with deflection means for deflecting a flow of vat gas.

Thus, the tank gases can be diverted towards a capture system that can equip the electrolysis tank, so that the tank gas leaks are limited.

According to a preferred embodiment, the closure covers comprise gripping means designed to allow a substantially vertical lifting of each shutter cover without moving the covers and independently of the other sealing covers.

A substantially vertical withdrawal of the closure covers limits the risk of moving the adjacent covers during removal and is the simplest solution to implement a sealing system between the closure covers and covers that they are adjacent.

According to an advantageous embodiment, the closure covers comprise a lower bearing surface designed to allow the closure covers to rest stably on one of the covers or on another closure cover.

Thus, the closure covers, when removed, can be stacked on an adjacent hood or other close shutter cover. Consequently, the trajectories described by the electrolysis service machine during an intervention are minimal, so that the duration of opening of the intervention window is also minimal. This results in a decrease in the leakage of the tank gas and thermal losses that may occur during an intervention.

According to a preferred embodiment, the covers comprise a bottom support face designed to allow the covers to rest stably on one of the closure covers.

Thus, the hoods, when removed, can be stacked on an adjacent hood or a close shutter cover. This reduces the trajectories of the electrolysis service machine, thus the opening time of the intervention window. Tank gas leaks and heat losses during the intervention, in particular an anode assembly change, are less.

According to a preferred embodiment, the covers and the closure covers extend in a substantially horizontal plane.

Thus, it is easier to stack them quickly during an intervention, which reduces the duration of this intervention, thus the opening time of the rollover system.

Advantageously, the intervention window has a width less than that of the covers that the intervention window separates.

This small opening area of the cowling allows to create in combination with the traditional suction of the tank gases a suction effect of the outside air to the inside of the tank, against the movement of the tank gases. Tank gas leaks are thus limited.

Also, each shutter cover has a width less than the width of the covers.

Preferably, the hoods have a bending stiffness greater than that of the closure covers.

In other words, the hoods deform more difficultly than the shutter covers, and the shutter caps deform more easily than the hoods under the effect of their weight, so that the shutter covers can deform to compensate the deformations, the least, of the hoods on which they rest. This improves the seal.

According to a preferred embodiment, the electrolytic cell comprises sealing means interposed between the support edges of the covers and the sides of the electrolytic cell on which the support edges rest.

Thus, the seal is improved. Tank gas leaks are prevented and heat losses are limited.

Advantageously, the sealing means, interposed between the support edges of the covers and the sides of the tank on which the support edges rest, comprise a seal, and the electrolysis cell comprises means pinching the seal.

This makes it possible to correct any lack of flatness of the covers and, where appropriate, of the closure covers, with a view to limiting the leakage of the tank gas and the heat losses.

According to a preferred embodiment, each shutter cover extends above and all along a subjacent interanode space separating two adjacent anode assemblies from the electrolytic cell.

Thus, it is possible to provide access to the plumb with the inter-anode spaces, so that a crust sawing type of operation can be performed with a minimum open area. This intervention, prior to a change of anode assembly, is therefore performed with a minimum of tank gas leaks and heat losses.

By inter-anode space is meant space separating anodes from two adjacent anode sets.

According to a preferred embodiment, each cap extends above and along an anode assembly subjacent to the electrolytic cell.

Thus, it is necessary to remove covers when the removal of an anode assembly must be achieved. The rest of the time, the covers can remain in place, to prevent leakage of the tank gas and to limit heat losses. This configuration also minimizes the risk of falling into the tank for the operating personnel.

According to a preferred embodiment, the electrolysis cell comprises indexing means adapted to indicate a predetermined position of the covers such that the covers extend to the right of the anode assemblies.

This feature allows fast, repeatable and accurate placement of covers, to quickly close the opening and prevent them from moving.

By covers extending to the right of the anode assemblies is meant that under each cover extends a single anode assembly.

According to a preferred embodiment, the electrolytic cell comprises means for capturing the bottom gases, designed to capture and collect the cell gases emitted during the electrolysis reaction.

Thus, this limits the amount of leachate gas flowing through an opening in the rollover system.

Advantageously, the capturing means comprise suction holes arranged under the hoods and the closure covers.

This limits the air temperature near the hoods and closure covers, so as not to degrade the mechanical strength of the materials in which the covers and the closure covers are made. This limits the deformations of the covers and closure covers, these deformations may cause leakage of the tank gas and heat losses.

Also, in cooperation with deflection means arranged on the underside of the covers for deflecting a flow of gas, it improves the capture efficiency of the tank.

Advantageously, the capturing means comprise a diaphragm for modifying an air passage section in order to modify a capture rate of the tank gases.

This characteristic offers the possibility of increasing the capture rate when a cover and / or a shutter cover are removed, for example during an anode assembly change. Thus, the diffusion of vat gas during an intervention is substantially limited.

According to a preferred embodiment, the width of each cap is less than the width of an anode assembly of the electrolytic cell.

• une étape de déplacement d'un premier couvercle d'obturation parmi les couvercles d'obturation du système de capotage, de la position d'obturation à la position d'intervention, sans déplacer les capots du système de capotage et les autres couvercles d'obturation, en vue de libérer un passage à travers le système de capotage via l'une des fenêtres d'intervention, et
• une étape de cassage ou de sciage d'une croûte formée en surface d'un bain électrolytique, par insertion d'un outil adapté pour casser ou scier la croûte à travers le passage libéré à l'étape précédente.

According to another aspect, the invention also relates to a method of changing a spent anode assembly of the electrolytic cell having the aforementioned characteristics by a new anode assembly, the method comprising:

• a step of moving a first shutter cover among the shutter covers of the rollover system, from the shut-off position to the intervention position, without moving the covers of the rollover system and the other covers; shutter, to release a passage through the rollover system via one of the intervention windows, and
• a step of breaking or sawing a crust formed on the surface of an electrolytic bath, by inserting a tool adapted to break or saw the crust through the passage released in the previous step.

This method provides the possibility of providing access to the interior of the electrolytic cell with a minimum opening area, and thus breaking or sawing the crust formed during the electrolysis reaction with a minimum of gas leaks and thermal losses. During the change of anode assembly, the diffusion of vat gas and heat losses are therefore substantially limited.

According to a preferred embodiment, the method comprises a step of placing the first closure cover on one of the covers adjacent to the first closure cover.

This minimizes the paths of the electrolysis service machine as it handles the first blanking cover. The duration of the intervention is therefore limited, so that the duration during which the intervention window is open is also limited.

According to a preferred embodiment, the method comprises a step of moving a second shutter cover, from the shut-off position to the intervention position, without moving the covers of the rollover system and the other covers. shutter, the second shutter cover being arranged on the other side of one of the covers beside which was arranged the first shutter cover, so as to release a second passage on the other side of this cover, and a step of breaking or sawing a crust formed on the surface of an electrolytic bath, by inserting a tool adapted to break or saw the crust through this second passage.

This allows, in anticipation of an overall change of anode, to saw, break or prick crust on both sides of the spent anode assembly to be replaced, that is to say on both sides. other hood initially arranged between the first and second shutter covers, but without opening all the space above this set anodic worn. As a result, gas leaks and heat losses during an anode assembly change are limited.

According to a preferred embodiment, the method comprises a step of placing the second closure cover on the first closure cover.

The stacking of the closure covers limits the paths of the electrolysis service machine, thus the duration during which the corresponding intervention windows are open.

According to a preferred embodiment, the method comprises a step of removing a cover initially adjacent to the first closure cover.

Thus, it is only at the last moment, that is to say when grasping and lifting the used anode assembly to replace it, that one of the covers is removed. During all the previous steps necessary for the change of anode assembly, this cover was in place. Thus, the method according to the invention limits the leakage of vat gas and preserves the thermal equilibrium of an electrolytic cell during an anode assembly change.

Advantageously, the method comprises a step of stacking said cover on the first shutter cover or, if appropriate, on the second shutter cover.

This reduces the path of the electrolysis service machine having removed the hood, so that the opening resulting from the removal of the hood, and the first and second shutter covers for the anode assembly change, is performed during a period of time. limited time.

The method may then comprise a step of extracting the spent anode assembly, underlying the cap previously removed, and then a step of inserting the new anode assembly inside the electrolytic cell.

These steps can be performed by substantially vertical upward or downward translation, respectively of the used anode assembly and the new anode assembly.

Finally, the method may comprise a step of repositioning the cover previously removed, then the first and second closure cover.

The fact of starting with the introduction of the cover makes it possible to close a larger part of the open surface than that which would be closed with a closure cover.

• la figure 1 est une vue schématique et en coupe d'une cuve d'électrolyse et d'un système de capotage selon un mode de réalisation de l'invention, dans un plan sensiblement longitudinal de la cuve d'électrolyse,
• la figure 2 est une vue schématique et de dessus de l'intérieur de la cuve d'électrolyse de la figure 1,
• les figures 3 et 4 sont des vues schématiques et en coupe de la cuve d'électrolyse et du système de capotage de la figure 1, dans un plan sensiblement longitudinal de la cuve d'électrolyse, et à travers lequel une fenêtre d'accès est ménagée,
• les figures 5 à 7 sont des vues schématiques et de côté d'une partie d'un système de capotage selon un mode de réalisation de l'invention,
• la figure 7bis est une vue schématique et de côté d'une partie d'un système de capotage selon un mode de réalisation de l'invention.
• la figure 8 est une vue schématique et de dessous d'un capot d'un système de capotage selon un mode de réalisation de l'invention,
• la figure 9 est une vue schématique et en coupe d'une cuve d'électrolyse et d'un système de capotage selon un mode de réalisation de l'invention, dans un plan sensiblement longitudinal de la cuve d'électrolyse,
• la figure 10 est une vue schématique et de dessus de la cuve d'électrolyse de la figure 9,
• la figure 11 est une vue schématique et en coupe d'une cuve d'électrolyse et d'un système de capotage selon un mode de réalisation de l'invention, dans un plan sensiblement transversal de la cuve d'électrolyse,
• les figures 12 à 14 sont des vues schématiques et en coupe d'une partie d'une cuve d'électrolyse et d'un système de capotage selon un mode de réalisation de l'invention, illustrant différentes étapes d'un procédé de changement d'ensemble anodique selon un mode de réalisation de l'invention.

Other features and advantages of the present invention will emerge clearly from the following description of a particular embodiment, given by way of non-limiting example, with reference to the appended drawings in which:

• the figure 1 is a schematic sectional view of an electrolytic cell and a cowling system according to one embodiment of the invention, in a substantially longitudinal plane of the electrolytic cell,
• the figure 2 is a schematic and top view of the inside of the electrolysis cell of the figure 1 ,
• the figures 3 and 4 are schematic and sectional views of the electrolysis cell and the rollover system of the figure 1 in a substantially longitudinal plane of the electrolytic cell, and through which an access window is provided,
• the Figures 5 to 7 are diagrammatic and side views of a part of a rollover system according to one embodiment of the invention,
• the figure 7bis is a schematic and side view of a portion of a cowling system according to one embodiment of the invention.
• the figure 8 is a schematic view from below of a hood of a cowling system according to one embodiment of the invention,
• the figure 9 is a schematic sectional view of an electrolytic cell and a cowling system according to one embodiment of the invention, in a substantially longitudinal plane of the electrolytic cell,
• the figure 10 is a schematic view from above of the electrolysis cell of the figure 9 ,
• the figure 11 is a schematic sectional view of an electrolytic cell and a cowling system according to one embodiment of the invention, in a substantially transverse plane of the electrolytic cell,
• the Figures 12 to 14 are schematic sectional views of a portion of an electrolysis cell and a cowling system according to one embodiment of the invention, illustrating various steps of a method of changing the anode assembly according to a embodiment of the invention.

The figure 1 shows, according to one embodiment of the invention, an electrolysis tank 100, intended to produce aluminum by electrolysis, and a rollover system 1 for closing an opening of the electrolytic cell.

The electrolysis tank 100 can equip an electrolysis plant, such as an aluminum smelter. The electrolysis plant may comprise a plurality of electrolytic cells 100 aligned and electrically connected to each other to form a line or series of electrolysis cells. The electrolytic tanks 100 are intended to be traversed by an electrolysis current of up to several hundreds of thousands of amperes. The electrolysis tanks 100 may be arranged transversely with respect to the direction of the line or series, that is to say substantially perpendicularly to the overall direction of flow of electrolysis current at the scale of the line or from the Serie.

As can be seen in the figures, the electrolysis tank 100 may comprise two opposite longitudinal sides 101 which may be substantially parallel to each other and two opposite transverse sides 103 which may be substantially parallel to each other and perpendicular to the longitudinal sides 101, so that the electrolysis tank 100 may have a substantially rectangular shape.

The electrolysis tank 100 comprises a fixed structure. The fixed structure comprises a box 102 and / or a side wall 105 of a gas containment enclosure.

The box 102 may contain a bottom 104 of refractory materials, a plurality of cathode blocks 106 and conductors 108 for collecting an electrolysis current passing through the cathode blocks 106.

The electrolytic cell 100 also comprises a plurality of anode assemblies 109 that are movable in a substantially vertical translation relative to the fixed structure of the electrolytic cell so that they can be immersed in an electrolytic bath 110 as they progress. consumption.

The anode assemblies 109 herein comprise a plurality of carbonaceous blocks 112, supported by an electrically conductive anode crosshead 114. The anode cross-member 114 advantageously extends in a substantially transverse direction Y of the electrolytic cell, in a substantially horizontal plane. The ends of this crosspiece 114 are electrically connected to routing conductors (not shown) for routing the electrolysis current from a previous electrolysis tank.

The sides of the electrolysis tank 100 define an opening 116 which is intended for insertion or extraction of the anode assemblies 109 respectively inside or outside the electrolysis tank 100.

It will be noted that this opening 116 is adapted to allow this insertion or extraction by substantially vertical displacement, respectively descending or ascending, of the assembly 109 anodic.

The electrolysis tank 100 further comprises the cowling system 1. The rollover system 1 is intended to seal the opening 116, to prevent the diffusion of tank gases generated during the electrolysis reaction, out of the electrolysis tank 100. The rollover system 1 also makes it possible to limit heat losses.

As can be seen on the Figures 1, 3 at 5 , 9 and 11 to 14 , the rollover system 1 extends above the anode assemblies 109 in order to completely cover the opening 116.

The rollover system 1 comprises a plurality of covers 2.

The covers 2 are self-supporting. Each cover 2 comprises two opposite support edges 4, visible in particular on the figure 11 , intended to rest on two opposite sides of the electrolysis tank 100, in particular on an upper edge of the two longitudinal sides 101 of the electrolysis tank 100.

Each cover 2 thus rests integrally on the electrolytic cell 100, extending between the two longitudinal sides 101, above the opening 116.

The cowling system 1 is also designed to present, substantially parallel to the cowls 2, longitudinal intervention windows 6, as is visible for example on the figure 4 . Each intervention window 6 makes it possible to release a predetermined passage through the plurality of covers 2.

According to the embodiment of the figure 4 the intervention windows 6 extend longitudinally between two adjacent covers 2.

The rollover system 1 further comprises closure caps 8, each intended to close a window 6 intervention.

Each shutter cover 8 is movable relative to the covers 2 between a closed position, in which each shutter cover 8 closes one of the intervention windows 6, and an intervention position, in which each cover Shutter 8 releases a passage through the rollover system 1 via one of the intervention windows 6.

The closure caps 8 are intended to rest at least partly on the covers 2, as can be seen for example on the figure 5 .

The closure caps 8 have longitudinal edges which are intended to rest each on one of the covers 2 and have side edges which can rest on an upper edge of the longitudinal sides 101 of the electrolysis tank 100, and.

Thus, the closure lids 8 can rest straddling two adjacent covers 2 and extend between these two adjacent covers 2.

It is important to note that the shutter covers 8 are designed to be moved from the shutter position to the intervention position without moving the covers 2 on which the shutter covers 8 rest.

The shutter covers 8 can also be moved from the shutter position to the intervention position independently of each other, that is to say without the movement of one of the closure lids 8 involves that of another cover 8 shutter.

As can be seen in the figures, the covers 2 and, if appropriate, the closure covers 8 advantageously extend in one piece from one longitudinal side to the other of the electrolysis tank 100.

The covers 2 and, if applicable, the closure covers 8 extend substantially parallel to a transverse direction Y of the electrolytic cell 100.

It will also be noted that the covers 2 and the closure lids 8 extend in a substantially horizontal plane. The covers 2 and the closure covers 8 preferably extend above the working floor, which limits the risk of falling in the tank of the operating personnel.

It should be noted that the covers 2 and the closing lids 8 are intended to extend above the electrolytic bath, the temperature of which can reach about 1000 ° C. The covers 2 and the closure lids 8 must therefore be adapted to withstand a temperature of the order of several hundred degrees Celsius, without prejudice to their mechanical properties and, where appropriate, thermal insulation.

As can be seen on the Figures 6 and 7 , the closing lids 8 have a T-shaped cross section defining two longitudinal returns 10. The covers 2 have in turn an inverted T cross section delimiting two longitudinal returns 12.

Each return 10 of one of the closure lids 8 rests on one of the returns 12 of an adjacent cover 2.

Thus, the rollover system 1 has an alternation of T right and inverted T formed by an alternation of covers 2 and nested closure caps 8.

Moreover, as shown on the figure 7 the returns 10, 12 of the covers 2 and the closure lids 8 have an L-shaped section.

Thus, the engagement of a cover 2 and a closure cover 8 forms a sealing baffle.

The cowling system 1 advantageously also comprises sealing means interposed between the returns 10 of each closure cover 8 and the returns 12 adjacent covers 2.

The sealing means comprise, for example, elastic seals 14. The elastic sealing seals 14 are intended to compensate for a difference in relative deformation between two consecutive covers 2 between which a closure cover 8 extends.

Also, as visible on the figure 7bis , the returns 12 of the covers have chutes having an upper opening and containing a powder material 31. The returns 10 of the lids have an L-shaped section and an end portion of the L-shaped section of the lid is pressed into the powder material 31 via the upper opening in the chute when the cover and the cover are nested. The realization of such a seal by means of a powder material is possible because the covers and covers extend horizontally so that the powder material remains distributed with a uniform height over the entire length of the chute. The powder material serves as a sealing means to form a barrier which prevents the vent gases from escaping.

The pulverulent material may in particular comprise alumina or crushed electrolysis bath which comprises alumina. These materials have the advantage of being available in an aluminum smelter and are also introduced into the electrolytic cells so that they do not risk polluting the electrolysis cell in the event of an accidental spill in the electrolysis cell. . In addition, alumina is a very good adsorbent for the HF and SO2 released by the electrolytic cell so that any infiltration of vat gas through the powder material will have a lower environmental impact.

On the figure 7bis , the cover further comprises on its upper face pivoting flaps 32 arranged to close the opening of the chute when the cover and the cover are nested. These flaps are intended to retain the powder material in the chute. Flaps may alternatively be arranged on the lid and be fixed.

The covers 2 have a lower face 16, visible in particular on the figure 8 .

The lower face 16 may be provided with at least one reinforcing rib 18 intended to limit the bending of the hoods 2. According to the example of the figure 8 , the covers 2 may comprise two crossed ribs 18.

Furthermore, the lower face 16 may be provided with thermal insulation means. The thermal insulation means comprise for example rock wool, advantageously maintained and protected by a steel plate.

According to the embodiment illustrated on the Figures 6 to 8 the covers 2 and the closure covers 8 comprise a substantially flat plate-like main body. This body 20 is intended to extend longitudinally along a transverse direction Y of the electrolysis tank 100.

The body 20 may be tubular. Thus, the body 20 advantageously delimits a cavity inside which can be arranged a thermally insulating material, such as rock wool.

The body 20 may be alternately full, so that the mass of the covers 2 is larger. This allows compression or pinching of a seal 22, visible on the figure 5 and on the figure 11 extending between the support edges 4 of the covers 2 and the part of the electrolysis tank 100 on which these support edges 4 rest, in order to improve the sealing.

Although this is not shown, the lower face 16 of the hoods 2 may be provided with deflection means for diverting a flow of tank gas to holes 120 of a tank gas collection system that can equip the tank 100 electrolysis, as will be described in more detail below.

The closure lids 8 advantageously comprise gripping means, such as a handle 24. The gripping means are designed to allow a substantially vertical lift of each closure cover 8 by an electrolysis service machine, such as a bridge. handling, without having to move caps 2 or other caps 8 shutter.

The lower face 16 may also be designed to allow the covers 2 to rest stably on one of the closure lids 8, to allow the stacking of covers 2 on closure lids 8.

For example, the lower surface 16 may have a housing (not shown) adapted to receive the gripping means 8 shutter covers.

This is useful when one of the hoods 2 is removed from its location, since it is possible to place the cover 2 on one of the adjacent closure lids 8.

The closure caps 8 may also have a bottom face 26 designed to allow the closure caps 8 to rest stably on one of the covers 2, or on another cover 8 shutter.

Similarly, the lower surface 26 may have a housing (not shown) adapted to receive gripping means of the hoods 2, these gripping means being intended to allow lifting of the hoods 2 by an electrolysis service machine.

Thus, when one of the shutter covers 8 is removed from its location, this cover 8 shutter can be placed on one of the adjacent covers 2.

The lower face 26 of the closure lids 8 may also be provided with thermal insulation means and / or means for deflecting the vat gases.

It will be noted that the hoods 2 advantageously have a greater bending stiffness than that of the closing lids 8. In other words, the hoods 2 are more rigid than the closure lids 8.

As can be seen on the figure 4 , the intervention window 6 has a width less than that of the covers 2 that it separates.

The closure caps 8 may also have a width less than the width of the covers 2.

Thus, the opening formed by the withdrawal of a closure cover 8 is small, the function of the closure lids 8 being able to provide access to the interior of the electrolysis tank 100 with a surface open minimum.

The invention also relates to the electrolysis tank 100 comprising the cowling system 1.

This electrolysis tank 100 advantageously comprises sealing means interposed between the support edges 4 of the covers 2 and the sides of the electrolysis tank 101 on which the support edges 4 rest.

These sealing means comprise for example the seal 22, which extends along the longitudinal sides 101, that is to say in a longitudinal direction X of the electrolytic cell.

In addition, the electrolysis tank 100 advantageously comprises means for clamping this seal 22. The clamping means may comprise a screw pressing the support edges 4 of the covers 2 against the upper edge of the longitudinal sides 101, where the seal 22 is located. The clamping means may comprise a ballast equipping the covers 2 and / or the closure caps 8, the weight of the covers 2 and / or the closure covers 8 compressing the seal 22.

As can be seen for example on the figure 5 each closure cover 8 advantageously extends above and all along a space 111 inter-anodes subjacent. This inter-anode gap separates two adjacent anode assemblies 109 from the electrolytic cell 100.

Each cover 2 extends above and all along an assembly 109 anode subjacent electrolytic tank 100.

The electrolysis tank 100 may comprise indexing means adapted to indicate a predetermined position of the hoods 2, this predetermined position being such that the hoods 2 extend to the right of the anode assemblies 109, that is to say to the above sets 109 and parallel to these sets 109 anode. The indexing means comprise, for example, lugs, pions or crenellations.

According to the embodiment of Figures 1 to 4 and 9 to 11 the electrolysis tank 100 comprises means for capturing the tank gases. These tank gas collection means are designed to capture and collect the tank gases emitted during the electrolysis reaction.

The capturing means here comprise suction holes 120, represented on the Figures 10 and 11 , arranged under the hoods 2 and the closure lids 8.

The suction holes 120 allow an air communication between the inside of the electrolysis tank 100 and a collection duct 122 which is intended to conduct the sucked tank gases to a collector where these tank gases will be treated. As can be seen on the figures 2 and 10 , the sheath 122 extends along the longitudinal sides 101 of the electrolytic tank 100. The sheath 122 may also be along the transverse sides 103.

The capturing means may also comprise a diaphragm (not shown), arranged for example at the connection between the capture sheath and the collector. The diaphragm is intended to modify an air passage section in order to modify a capture rate of the tank gases.

As can be seen in particular on the figure 5 the width I of each cap 2 is smaller than the width 1 'of the underlying anode assembly 109.

By way of example, the intervention window 6 may have a width l "of the order of 350-480 mm, in particular 360 mm, and each bonnet has a width I less than a width of 700 mm. 2000mm.

The invention also relates to a method of changing a used anode assembly 130 of an electrolytic cell, in particular of the electrolytic cell 100 described above, with a new anode assembly.

The method comprises a step of moving a first closure cover 8a among the closure caps 8 of a rollover system 1 as described above, from the shut-off position to the intervention position, as shown in FIG. is represented on the figure 12 .

This step is performed without moving the covers 2 and the other covers 8 shutter. Thus, a passage is released through the rollover system 1 via one of the intervention windows 6.

The method advantageously comprises a step of placing the first closure cover 8a on one of the covers 2 adjacent to this first closure cover 8a, as shown in FIG. figure 13 .

The method also comprises a step of breaking or sawing a crust formed on the surface of the electrolytic bath, by inserting a tool adapted to break or saw the crust through the passage previously released.

According to the embodiment of Figures 12 to 14 the method comprises a step of moving a second closure cover 8b shutter, the shutter position to the intervention position, without moving the covers 2 and the other covers 8 shutter.

Still according to the example of realization of Figures 12 to 14 , the second closure cover 8b is initially arranged on the other side of one of the covers 2, in particular the cover 2, where the first shutter cover 8a is not placed, next to which was arranged the first cover 8a shutter, so that a second passage is released on the other side of the cover 2.

In addition, the method comprises a step of breaking or sawing the crust formed on the surface of the electrolytic bath, by inserting a tool adapted to break or saw the crust through this second passage.

Still according to the example of realization of Figures 12 to 14 , the method may comprise a step of placing the second closure cover 8b on the first closure cover 8a, as is more particularly visible on the figure 13 .

As is visible on the figure 14 , the method further comprises a step of removing one of the covers 2 initially arranged next to the first 8a shutter cover, in particular the cover 2 which is not posed if necessary the first cover 8a shutter.

The method may comprise an additional step of stacking this cover on the second closure cover 8b.

Note that the first and optionally the second cover 8a, 8b shutter and the cover 2 are stacked above an anodic assembly 109 unchanged.

The method may then comprise a step of extracting the spent anode assembly 130, underlying the cap 2 previously removed, and then inserting the new anode assembly inside the electrolysis cell.

These steps can be performed by substantially vertical upward or downward translation, respectively of the used anode assembly 130 and the new anode assembly.

Finally, the method may comprise a step of repositioning the cover 2 previously removed, then the first and second closure cover 8a, 8b.

It will be noted that the displacement of the first shutter cover 8a and the second shutter cover 8b, as well as of the cover 2, is achieved by means of an electrolysis service machine, such as a handling bridge, suitable for docking these caps 8 shutter and the cover by their gripping means.

Of course, the invention is not limited to the embodiment described above, this embodiment having been given as an example. Modifications are possible, in particular from the point of view of the constitution of the various elements or by the substitution of technical equivalents, without departing from the scope of the invention limited by the subject of the claims.

Claims (15)

1. Electrolytic cell (100) comprising a plurality of anode assemblies (109), sides (101, 103) defining an opening (116) through which anode assemblies (109) are designed to be set up or withdrawn with a respectively ascending or descending vertical translational movement, and a covering system (1) extending above the anode assemblies (109) in order to cover said opening (116), the covering system (1) comprising a plurality of hoods (2), characterized in that:

   each hood (2) comprises two opposite bearing edges (4) designed to rest on two opposite sides of the electrolytic cell from the sides of the electrolytic cell defining the opening (116), so that each hood (2) extends from one side of the electrolytic cell to the other, above the opening (116), in that

   the covering system (1) is designed to have, substantially parallel to the hoods (2), longitudinal servicing windows (6) to free a predetermined path through the plurality of hoods (2),

   the covering system (1) further comprises sealing lids (8), each sealing lid (8) being movable relative to the hoods (2) between a closed position, wherein each sealing lid (8) closes one of the servicing windows (6), and a servicing position, wherein each sealing lid (8) frees a passage through the covering system (1) via one of the servicing windows (6), the sealing lids (8) being designed to rest at least partly on the hoods (2), and in that

   the sealing lids (8) are designed to be moved from the closed position to the servicing position, independently of each other, without moving the hoods (2) on which the sealing lids (8) rest.
2. Electrolytic cell (100) according to claim 1, in which the sealing lids (8) have longitudinal edges which are designed to rest on each one of the hoods (2), in closed position.
3. Electrolytic cell (100) according to any one of claims 1 and 2, in which the sealing lids (8) have a T-shaped cross-section defining two longitudinal flanges (10), the hoods (2) have a cross-section in the shape of an inverted T delimiting two longitudinal flanges (12), each flange (10) of one of the sealing lids (8) resting on one of the flanges (12) of an adjacent hood (2), so that the covering system (1) has an alternation of interlocking hoods (2) and sealing lids (8).
4. Electrolytic cell (100) according to claim 3, in which the flanges (10, 12) of the hoods (2) and sealing lids (8) have an L-shaped section, so that the interlocking of a hood (2) and a sealing lid (8) forms a sealing baffle.
5. Electrolytic cell (100) according to claim 3 or 4, in which the covering system (1) comprises sealing means interposed between the flanges (10) of each sealing lid (8) and the flanges (12) of the adjacent hoods (2) on which each sealing lid (8) rests.
6. Electrolytic cell (100) according to any of claims 3 to 5, in which, the hoods (2) and lids (8) extend horizontally and the longitudinal flanges (12) of the hoods (2) comprise channels containing a powder material (31) and having a top opening, the longitudinal flanges (10) of the lids (8) having an L-shaped section, so that an end portion of the L-shaped section of the lid (8) is pressed into the powder material through the top opening in the channel when the hood (2) and the lid (8) are interlocked.
7. Electrolytic cell (100) according to any of claims 1 to 6, in which the hoods (2) include a surface (16) provided with thermal insulation means.
8. Electrolytic cell (100) according to any of claims 1 to 7, in which the sealing lids (8) comprise gripping means designed to allow substantially vertical lifting of each sealing lid (8) without moving the hoods and independently of the other sealing lids.
9. Electrolytic cell (100) according to any of claims 1 to 8, in which the hoods (2) and the sealing lids (8) extend in a substantially horizontal plane.
10. Electrolytic cell (100) according to one of claims 1 to 9, in which the servicing window (6) has a smaller width than that of the hoods (2) that the servicing window (6) separates.
11. Electrolytic cell (100) according to one of claims 1 to 10, in which each sealing lid (8) has a smaller width than the width of the hoods (2).
12. Electrolytic cell (100) according to one of claims 1 to 11, in which the hoods (2) have a bending stiffness greater than that of the sealing lids (8).
13. Electrolytic cell (100) according to one of the preceding claims in which the electrolytic cell (100) advantageously includes sealing means (22) interposed between the bearing edges (4) of the hoods (2) and the sides of the electrolytic cell (100) on which the bearing edges (4) rest.
14. Electrolytic cell (100) according to one of the preceding claims, in which each sealing lid (8) extends above and along a subjacent space (111) between anodes separating two adjacent anode assemblies (109) of the electrolytic cell (100).
15. Method for changing a spent anode assembly (130) of an electrolytic cell according to one of the preceding claims for a new anode assembly, the method comprising:

    - a step involving moving a first sealing lid (8a) from among the sealing lids (8) of the covering system (1), from the closed position to the servicing position, without moving the hoods (2) of the covering system (1) and the other sealing lids (8), in order to free a passage through the covering system (1) via one of the servicing windows (6), and

    - a step involving breaking or sawing a crust formed on the surface of an electrolytic bath (110), by inserting a suitable tool for breaking or sawing the crust around the path freed in the previous step.

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