DK179126B1

DK179126B1 - COVERING SYSTEM FOR AN ELECTROLYTIC CELL

Info

Publication number: DK179126B1
Application number: DKPA201670545A
Authority: DK
Inventors: Steeve Renaudier; Guillaume Girault; Frédéric Brun
Original assignee: Rio Tinto Alcan Int Ltd
Priority date: 2014-01-27
Filing date: 2016-07-19
Publication date: 2017-11-20
Also published as: BR112016015587A2; RU2016134372A3; CA2935478A1; EP3099841A1; FR3016890B1; RU2682498C2; EP3099841A4; DK201670545A1; AU2015208857B2; WO2015110903A1; CA2935478C; AU2015208857A1; FR3016890A1; CN105934537A; CN105934537B; BR112016015587B1; RU2016134372A; EP3099841B1

Abstract

This method (1) comprises hoods (2), each hood (2) comprises two opposite edges designed to rest on two opposite sides of the electrolytic cell so that each hood (2) extends from one side of the electrolytic cell to the other, above the opening (116). In addition, the system (1) is designed to have longitudinal servicing windows (6) parallel to the hoods (2). The system (1) further comprises sealing lids (8), each sealing lid (8) being movable relative to the hoods (2) between a closed posi-tion, wherein each sealing lid (8) closes a window (6), and a servicing position, wherein each sealing lid (8) frees a passage through a window (6). The sealing lids (8) rest at least partly on the hoods (2), and 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.

Description

HOODING SYSTEM FORAN ELECTROLYTIC CELL

The present inventioRT®laies is a covering system for an electrolytic cell an electrolytic ceil comprising the covering system and a method for changing an anode assembly

Aluminum is conventionally produced in aluminum smelters by electrolysis using the Haii-Hérouit process.

An aluminum works traditionally includes hundreds of electrolytic cells connected in series and carrying an electrolysis current which may reach several hundreds of thousands of amperés. It is known that electrolytic ceils can be arranged transversely to the flow direction of the electrolysis current across the series.

Electrolytic cells conventionally comprise a steel pot shell within which there is a lining of refractory materials, a cathode of carbon materia!, through which pass cathode conductors designed to collect the electrolysis current at the cathode to route it to the cathode outputs which pass through the bottom or sides of the pot shelf, linking conductors extending substantially horizontally to the next ceil from the cathode outputs, an electrolyte bath in which the alumina is dissolved, at least one anode assembly comprising at least one anode immersed in this electrolyte bath and an anode rod sealed in the anode, an anode frame on which the anode assembly is suspended via trieanode rod, and risers for the electrolysis current running upwards connected to linking conductors from the preceding electrolytic ceil to route the electrolysis current from the cathode outputs to the anode frame and the anode assembly and anode in the next cell. The anodes are more particularly of the pre-baked anode type with pre-baked carbon blocks, i.e. baked before they are placed in the electrolytic cell.

The anode assemblies are consumed in the course of the electrolysis reaction and have to be periodically replaced with new anode assemblies.

The sides of the electrolytic cel! define an opening through which the anode assemblies are inserted into the electrolytic cell to be immersed in the electrolytic bath or extracted from the electrolytic cell to be replaced.

To limit heat loss and prevent the diffusion out of the electrolytic cell of gases generated during the electrolysis reaction, hereinafter called ceil gases, provision is made to close the opening defined by the electrolytic ceil with a covering system.

Known covering systems, such as those disclosed in patent documents US4043892 and W02007087061, comprise lateral, removable hoods, tilted relative to the horizontal. These hoods rest on one side of the electrolytic cell and also against a portion of superstructure, designed to support the anode assemblies, extending In a longitudinal direction of the electrolytic ceil, above the opening defined by the sides of the cell i.e. directly above the anode assemblies and the electrolytic bath.

Ihe hoods thus form a confinement chamber that limits the diffusion of gases when the covering system is completely closed. This also reduces heat losses.

However, during an operation requiring the covering system to be opened, as is the case for replacing a spent anode assembly by a new anode assembly, conventional covering systems offer a limited response to the problem of gases diffusing out of the electrolytic cell and the preservation of foe thermal equilibrium of foe electrolytic ceil

During an operation such as changing an anode assembly, the hoods are removed to create an opening through the covering system. This opening - a necessary one - allows access to the inside of the cell, in particular to remove a spent anode assembly. However, the opening thus created allows cell gases to diffuse outside the confinement chamber. This opening may also disturb the thermal equilibrium of the ceil.

The larger the opening thus created, the greater the amount of ceil gases that can escape, and the greater the potential heat losses. The same is true for the time during which the covering system is open during an operation: the longer the covering system remains open, foe greater the amount of ceil gas that can escape, and the greater the disturbance to the thermal equilibrium of the ceil

Given the presence, above the pot shell, of a superstructure on which the hoods of conventional covering systems are supported, the hoods that have been removed to create the opening required for the operation are often placed next to the electrolytic cell, especially in a space between celis separating two adjacent ceils. This can cause a problem of congestion, and this congestion probiem can slow down the operation, i.e, increase the length of time the covering system remains open, it can also cause a safety problem:, in that an operator may stumble.

In addition, the hoods of known covering systems are designed to have their adjacent edges overlapping each other. This overlap limits cel! gas ieaks and energy losses at the interface between two adjacent hoods.

However, conventional solutions with overlapping hoods have a disadvantage: the hoods are interlocked with each other, and the removal of one of them requires one or more adjacent hoods to be moved or removed, it is therefore clear that, for maintenance work theoretically requiring a single hood to be removed, several hoods must be moved or removed. The open area through the covering system is then larger than necessary. From patent documents US4043892 and W02007067061 we ieam of the removal of hoods in groups of three.

Finally, some maintenance operations may require smaller open areas than for other maintenance operations. For example, to break the crusts generated in the electrolytic bath during the electrolysis reaction, it is sufficient to have an opening large enough to insert a suitable tool to break these crusts at the right place while to extract or set up an anode assembly requires a larger opening suited to ihe size of the anode assembly to be extracted or set up.

However, the hoods of conventional covering systems are similar, especially in terms of dimensions, so that the only way of selecting an opening area through the covering system is to select the number of hoods to be removed. This does not allow for fine adjustment of the opening area, i.e. the selection of a minimum but sufficient opening area for performing a given maintenance operation.

Furthermore, the presence of the superstructure and risers for the electrolysis current above the opening defined by the sides of the cel! makes it difficult to break the crusts formed between the anode assemblies because access under the superstructure and the current risers is particularly cramped. It follows that crust breaking operation, conventionally performed with a chipping hammer mounted on an arm with angular inclination requires more time than if there were no such obstacles, which increases the time during which the covering system is open. In addition, because of this accessibility problem, breaking the crust is sometimes incompiete around the edges of the anode assembly and the anode assembly extracted has solid crust pieces that increase its section and its dimensions, and may damage the adjacent hoods still in place.

Finally, the lower parts of the hoods rest on on top of the pot shell on which the anode covering material collapses, so that the supports of the hoods are unstable and their positioning inaccurate. They are also exposed at the bottom part to the flames and hot spots associated with discontinuities in ihe anode covering, causing them to deteriorate rapidly.

The present invention therefore aims to overcome some or all of these drawbacks by proposing a covering system, an electrolytic cell comprising this covering system and a method for changing an anode assembly, making it possible to effectively contain the diffusion of cell gas and to maintain thermal equilibrium, in particular during a maintenance operation.

To this end, the present invention relates to a covering system for sealing an opening defined by the sides of an electrolytic cell, the covering system comprising a plurality of hoods, characterized in that: each hood comprises two opposite heating edges designed to rest on two opposite sides of the electrolytic cell from the sides of the electrolytic cel! defining the opening, so that each hood extends from one side of the electrolytic cell to the other, above the opening, the covering system is designed to have, substantially parallel to the hoods, longitudinal servicing windows to free a predetermined path through the plurality of hoods the covering system further comprises sealing lids, each sealing lid being movable relative to the hoods between a closed position, wherein each sealing lid closes one of the servicing windows, and a servicing position, wherein each closing cover frees a passage through the covering system via one of the servicing windows, the sealing lids being designed to rest at least partly on the hoods, and the sealing lids are designed to be moved from the closed position to the servicing position, independently of each other, without moving the hoods on which the sealing lids rest.

The covering system according to the Invention therefore offers the possibility of accessing the inside of the electrolytic cell by removing only one of the sealing lids, without movi ng or removing the hoods.

This makes it possible to form an opening of contained dimension through the covering system while leaving the hoods in place. For an operation such as an anode assembly change, this allows for certain preliminary operations, such as sawing through crusts formed around the anode assembly consumed during the electrolysis reaction, with a minimum open surface area through the covering system.

This limits the discharge of cell gas outside the electrolytic ceil and prevents disturbance to the thermal equilibrium of the electrolytic cell.

Opposite sides of the electrolytic ceil means the sides located on either side of a median plane especially a longitudinal median plane of the electrolytic ceil, in this way. each hood is designed to extend on either side of this median plane to rest simultaneously on these two opposite sides.

The hoods and sealing lids have a vertical assembly travel, which has a significant advantage with a view to automating the installation of the hoods, because there are no complex angular movements to be made, in contrast to the state of the art.

According to a preferred embodiment, the sealing lids have longitudinal edges which are designed to rest on each one of the hoods. Sealing at the junction between the sealing lids and the hoods is provided over the entire length of the hoods, and tie sealing isds respectively, by overlapping one edge of the sealing || over oho edge of the hood.

According toa preferred ^ have a T-shaped cross-section defining two longitudinal flanges, tie hoods have a cross-section in the shape of an inverted T delimiting two longitudinal flanges, each flange of one of the sealing lids resting on one of the flanges of an adjacent hood, so that the covering system has an alternation of interlocking hoods and sealing lids.

This configuration provides a simple solution to enable removal of the sealing lids without interfering with the hoods on which they rest and the other sealing lids, and at the same time to improve the sealing of the covering system. This makes it possible to limit the leakage of cell gas and heat losses.

Advantageously, the flanges of the hoods and sealing lids have an L-shaped section, so that the interlocking of a hood and a sealing lid forms a sealing baffle.

This feature also provides the advantage of an improved seal, containing ceil gas leakage and heat loss.

Advantageously, the covering system comprises sealing means interposed between the flanges of each sealing lid and the flanges of the adjacent hoods on which each sealing Sid rests.

Sealing is thereby improved.

According to an advantageous embodiment, the hoods and lids extend horizontally and the longitudinal flanges of the hoods comprise channels containing a powder material and having a top opening, the longitudinal flanges of the lids having an L-shaped section, so that an end portion of the L-shaped section of the lid is pressed into the powder material through the top opening in the channel when the hood and the lid are interlocked. Making such a seal by means of a powder materia! is possible because the hoods and lids extend horizontally so that the powder material remains distributed with a uniform height throughout the length of the channel . The powder materia! forms a barrier preventing cell gas from escaping.

Advantageously, the powder material contains alumina. More particularly, the powder material may be formed of alumina or crushed electrolytic bath comprising alumina. These materials have the advantage of being available in an aluminum works and are additionally introduced into the electrolytic cells so they are not likely to pollute the electrolytic ceil in the event of accidental spillage in the celt. In addition, alumina is a very good adsorbent for the HF and S02 generated by the electrolytic cell so that any infiltration of ceil gas through the powder mate rial wiii havea Sesser environmental impact.

Advantageously, the hoods and / or iids comprise a shutter arranged to close the opening of the channel when the hood and the lid are interlocked, lie purpose of this shutter, which can be fixed or mobile, especially swiveling, is to retain the powder material in the channel.

According to an advantageous embodiment, the sealing means comprise elastic seals designed to compensate for a difference in relative deformation between two consecutive hoods of the covering system between which a sealing lid in closed position is designed to extend. in other words, the space or clearance between hoods arid sealing lids Is sized so that flattening of the seals separating them, taking into account the bending of the hoods and sealing lids, fails within the elastic range of flattening of the seals. Sealing is thereby improved.

According to an advantageous embodiment, the hoods inciude a surface provided with at least one reinforcing rib designed to limit bending of the hoods.

This stiffens the hoods. In this way, flattening of seals is relatively uniform. Sealing is thereby improved.

According to a preferred embodiment, the hoods include a surface provided with thermal insulation means.

This helps reduce heat loss through the hood system.

Preferably, the insulating means are arranged on the underside of the hoods in order to limit distortion and thereby degradation of the hoods.

Advantageously, the hoods include a substantially longitudinal tubular body, the tubular body defining a cavity within which is arranged a thermally insulating material.

These features help protect the thermally insulating material and limit heat losses, by synergistic effect between the thermally insulating material, which slows the spreading of heat through the covering system and the improved rigidity of the hoods due to the tubular nature of the body, this rigidity aliowing the hood to bear uniformiy against the surface on which it rests and the sealing lids to bear uniformly on this hood.

According to a preferred embodiment, the hoods comprise a lower surface provided with deflection means for deflecting a flow of ceil gas.

Ceil gases can be diverted toward a capture system that the electrolytic cell can be equipped with, so that cell gas leaks are limited.

According to a preferred embodiment, the sealing lids comprise gripping means designed to allow substantially vertical lifting of each sealing lid without moving the hoods and independently of the other sealing lids.

Substantially vertical removal of the sealing lids limits the risk of moving adjacent hoods during withdrawal and is the easiest solution to implement a sealing system between the sealing lids and the hoods adjacent to them.

According to an advantageous embodiment, the sealing lids comprise a lower bearing surface designed to allow the sealing lids to rest stably on one of the hoods or on another sealing lid.

The sealing lids, when removed, may therefore be stacked on an adjacent hdbd Of on another nearby sealing Sid. Consequently, the trajectories described by the pot tending machine during an operation are minimal, so that the opening time of the servicing window is also minimal. This results in a reduction in cell gas leaks and heat losses that are likely to occur during an operation.

According to a preferred embodiment, the hoods comprise a bottom bearing surface designed to allow the hoods to rest stably on one of the sealing lids.

The hoods, when removed, may therefore be stacked on an adjacent hood or on another nearby sealing lid. This reduces the trajectories described by the pot tending machine, and therefore the opening time of the servicing window. Cell gas leakage and heat losses during the operation, in particular when changing an anode assembly, are lower.

According to a preferred embodiment, the hoods and the sealing lids extend in a substantially horizontal plane.

It is therefore easier to stack them quickly during an operation, which reduces the duration of the operation, and thereby the opening time of the covering system.

Advantageously, the servicing window has a width less than that of the hoods that the servicing window separates.

This small opening surface area of the cover means makes it possible to create, in combination with the conventional suction of cell gases, a suction effect of external air towards the inside of frii cell, against the movement of the cell gases. Cell gas leaks are thereby limited .

Aiso, each sealing lid has a width less than the width of the hoods.

Preferably, the hoods have a bending stiffness greater than that of the sealing lids, in other words, the hoods are more difficult to bend than the sealing lids, and the sealing lids are easier ίο bead than the hoods due to their weight, so that the sealing lids can bend to compensate for the lesser bending of the hoods on which they rest. This improves sealing

The present invention also relates to an electrolytic cell comprising a plurality of anode assemblies, sides defining an opening through which anode assemblies are designed to be set up or withdrawn with a respectively ascending or descending vertical translational movement, and a covering system having the above characteristics, the covering system extending above the anode assemblies in order to cover said opening.

This electrolytic cell has a stable thermal equilibrium and limits cell gas emissions, including during servicing work such as anode assembly replacements.

According to a preferred embodiment, the electrolytic cell comprises sealing means interposed between the bearing edges of the hoods and the sides of tie electrolytic ceil on which the bearing edges rest.

Sealing is thereby improved. Cell gas leaks are prevented and heat loss limited.

Advantageously, the sealing means, interposed between the bearing edges of ihe hoods and the sides of the cell upon which the bearing edges rest, comprise a seal, and the electrolytic cel! comprises means for pinching the seal.

This makes it possible to correct possible defects in flatness of the hoods and optionally the sealing lids, in order to limit celt gas leakage and heat loss.

According to a preferred; embodiment, each sealing lid extends above and along a subjacent space between anodes separating two adjacent anode assemblies of the electrolytic cell.

It is therefore possible to provide access in line with the space between anodes, so that an operation such as crust sawing can be achieved with a minimum open area. This operation, prior to changing an anode assembly is therefore performed with a minimum of ceil gas leakage and heat loss.

Space between anodes means space between two adjacent anode assemblies.

According to a preferred embodiment, each hood extends above arid along a subjacent anode assembly of the electrolytic cell.

It is therefore necessary to remove the covers only when an anode assembly has to be removed. The rest of the time, the hoods can remain in place to prevent cel! gas leaks and to limit heat loss. This configuration also greatly minimizes the risk of operating personnel falling into the cell.

Still according to the embodiment of figures 12 to 14, the second sealing lid 8b is initially arranged on the other side of one of the hoods 2, particularly the hood 2 where the first sealing lid 8a, if appropriate, is not placed, next to which hoods the first sealing lid 8a was arranged so that a second passage is freed on the other side of this hood 2. in addition, the method indudes a step involving breaking or sawing a crust formed on the surface of the electrolytic bath 110, by inserting a suitable too! for breaking or sawing the crust around this second passage,

Stiil according to the embodiment of figures 12 to 14, the method may include a step involving placing the second sealing lid 8b on the first sealing lid 8a, as is particularly visible in figure 13,

As can be seen in figure 14 the method further comprises a step involving withdrawal of one of the hoods 2 initially arranged beside the first sealing lid 8a, particularly hood 2 where the first sealing iid 8a, if appropriate, is not placed.

The method may comprise an additional step involving stacking this hood on the second sealing iid 8b.

Note that the first and if appropriate the second sealing iid 8a, 8b and the hood 2 are stacked above an unchanged anode assembly 109.

The method may then inciude a step involving extraction of the spent anode assembly 130, below the previously removed hood 2, and a step involving inserting the new anode assembly inside the electrolytic ceil.

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

Finally, the method may comprise a step involving repositioning the previously removed hood 2, and then the first and second sealing lid 8a, 8b.

It will be noted that movement of the first sealing ltd 8a and of the second sealing iid 8b and of the hood 2, is achieved by means of a pot tending machine, such as a handling crane, suitable for approaching these shutter covers 8 and the hood with their gripping means.

Claims

P81603398DK00 COVER SYSTEM FOR AN ELECTROLYTIC CELL Patent Claims

A cover system (1) for sealing an opening (116) defined by the sides of an electrolytic cell, said cover system (1) comprising a plurality of caps (2), characterized in that: each cap (2) comprises two opposing bearing edges (4), formed such that they rest on two opposite sides of the electrolytic cell from the sides of the electrolytic cell defining the opening (116) such that each cap (2) extends from one side of the electrolytic cell to the other over the opening (116), in that the cover system (1) is configured to have longitudinal service windows (6) extending parallel to the caps (2) to release a predetermined passage through the plurality of caps (2), the covering system (1) further comprising sealing flaps (8), each sealing flap (8) being movable relative to the caps (2) between a closed position, each sealing flap (8) closing one of the service windows (6) , and a service position, wherein each sealing flap (8) releases a passage through the cover system (1) via one of the service windows (6), which sealing flaps (8) are designed to rest at least partially on the caps (2) by sealing flaps. (8) are configured to move from the closed position to the service position independently of one another without moving the caps (2) on which the sealing flaps (8) rest.

The system (1) of claim 1, wherein the sealing flaps (8) have longitudinal edges which are formed such that they rest on each of the caps (2).

System (1) according to any one of claims 1 and 2, wherein the sealing flaps (8) have a T-shaped cross-section defining two longitudinal flanges (10), the caps (2) having a cross-section in the form of a inverted T, which limits two longitudinal flanges (12), each flange (10) of one of the sealing flaps (8) resting on one of the flanges (12) of an adjacent cap (2) such that the cover system (1) has a the interchange of interlocking caps (2) and sealing flaps (8).

System (1) according to claim 3, wherein the flanges (10, 12) of the caps (2) and the sealing flaps (8) have an L-shaped section so that the interlocking of a cap (2) and a sealing flap (8) forms a sealing plate.

The system (1) of claim 3 or 4, wherein the cover system (1) comprises sealing means disposed between the flanges (10) of each sealing flap (8) and the flanges (12) of the adjacent caps (2), as each sealing flap. (8) rests on.

The system (1) of any of claims 3 to 5, wherein the caps (2) and flaps (8) extend horizontally and the longitudinal flanges (12) of the caps (2) comprise channels containing a powder material. (31) and one having a top opening which has longitudinal flanges (10) of the flaps (8) having an L-shaped section such that an end portion of the L-shaped section of the flap (8) is pressed into the powder material through the top opening of the channel when the cap (2) and the flap (8) are locked together.

The system (1) of any one of claims 1 to 6, wherein the caps (2) include a surface (16) provided with thermal insulating means.

The system (1) of any one of claims 1 to 7, wherein the sealing flaps (8) comprise gripping means designed to permit substantially vertical lifting of each sealing flap (8) without moving the caps and independently of the caps. the other sealing flaps.

System (1) according to any one of claims 1 to 8, wherein the caps (2) and the sealing flaps (8) extend in a substantially horizontal plane.

System (1) according to any one of claims 1 to 9, wherein the service window (6) has a smaller width than that of the caps (2) which the service window (6) separates.

System (1) according to any one of claims 1 to 10, wherein each sealing flap (8) has a smaller width than the width of the caps (2).

The system (1) of any one of claims 1 to 11, wherein the caps (2) have a bending stiffness greater than that of the sealing flaps (8).

An electrolytic cell (100) comprising a plurality of anode assemblies (109), sides (101, 103) defining an aperture (116) through which anode assemblies (109) are configured to be erected or removed with a respective rising or decreasing vertical translational movement, and a cover system (1) according to any one of claims 1 to 12, said cover system (1) extending over the anode joints (109) to cover the opening (116).

The electrolytic cell (100) of claim 13, wherein the electrolytic cell (100) conveniently includes sealing means (22) disposed between the bearing edges (4) of the caps (2) and the sides of the electrolytic cell (100) as the bearing edges. (4) rests on.

An electrolytic cell (100) according to any one of claims 13 and 14, wherein each sealing flap (8) extends across and along an underlying region (111) between anodes separating two adjacent anode assemblies (109) of the electrolytic cell. (100).

A method of replacing an spent anode assembly (130) of an electrolytic cell with a new anode assembly, comprising: - a step including moving a first sealing flap (8a) among the sealing flaps (8) of a cover system (1) according to any one of claims 1 to 12, from the closed position to the service position, without moving the caps (2) of the cover system (1) and the other sealing flaps (8) to release a passage through the cover system (1) via one of the service windows ( 6), and - a step including crushing or sawing a crust formed on the surface of an electrolytic bath (110) by inserting a suitable crushing or sawing tool around the passage released in the previous step. 5