WO2019193451A1 - Caisson de cuve pour cellule électrolytique destiné à être utilisé avec le procédé hall-héroult - Google Patents

Caisson de cuve pour cellule électrolytique destiné à être utilisé avec le procédé hall-héroult Download PDF

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Publication number
WO2019193451A1
WO2019193451A1 PCT/IB2019/052419 IB2019052419W WO2019193451A1 WO 2019193451 A1 WO2019193451 A1 WO 2019193451A1 IB 2019052419 W IB2019052419 W IB 2019052419W WO 2019193451 A1 WO2019193451 A1 WO 2019193451A1
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WIPO (PCT)
Prior art keywords
potshell
cathode
wall
stiffeners
attachment
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Ceased
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PCT/IB2019/052419
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English (en)
Inventor
Lalit MISHRA
Kasim BASHA
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Dubai Aluminium PJSC
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Dubai Aluminium PJSC
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Publication of WO2019193451A1 publication Critical patent/WO2019193451A1/fr
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
    • C25C3/08—Cell construction, e.g. bottoms, walls, cathodes
    • C25C3/10—External supporting frames or structures
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
    • C25C3/08—Cell construction, e.g. bottoms, walls, cathodes

Definitions

  • the invention relates to the technical field of electrolysis in molten salts for making aluminium using the Hall-Heroult process. More precisely, the invention relates to an improved potshell design that maximizes the usable cathode surface area for a given total outside dimension. This is achieved in particular by redesigning the cradles of the potshell.
  • the Hall-Heroult process is the only continuous industrial process for producing metallic aluminium from aluminium oxide.
  • Aluminium oxide (AI2O3) is dissolved in molten cryolite (Na3AIF 6 ), and the resulting mixture (typically at a temperature comprised between 940 °C and 970 °C) acts as a liquid electrolyte in an electrolytic cell.
  • An electrolytic cell used for the Hall-Heroult process typically comprises a steel shell (so-called “pot shell”), a lining (comprising refractory bricks protecting said steel shell against heat, and cathode blocks usually made from graphite, anthracite or a mixture of both), a superstructure and a plurality of anodes (usually made from carbon) wherein part of anodes is submerged into the liquid electrolyte.
  • Anodes and cathodes are connected to external aluminium busbars.
  • An electrical current is passed through the cell (typically at a voltage between 3.7 V and 5 V) which electrochemically reduces the aluminium oxide, split in the electrolyte into aluminium and oxygen ions, into aluminium at the cathode and oxygen at the anode; said oxygen reacting with the carbon of the anode to form carbon dioxide .
  • the resulting metallic aluminium is not miscible with the liquid electrolyte, has a higher density than the liquid electrolyte and will thus accumulate as a liquid metal pad on the cathode surface from where it needs to be tapped from time to time, usually by suction into a crucible.
  • Industrial electrolytic cells used for the Hall-Heroult process are generally rectangular in shape and connected electrically in series, the ends of the series being connected to the positive and negative poles of an electrical rectification and control substation.
  • the general outline of these cells is known to a person skilled in the art and will not be repeated here in detail. They have a length usually comprised between 8 and 25 meters and a width usually comprised between 3 and 5 meters.
  • the cells also called“pots” are always operated in series of several tens (up to more than four hundred) of pots (such a series being also called a“potline”); within each series DC currents flow from one cell to the neighbouring cell.
  • the cells are arranged in a building, with the cells arranged in rows either side-by-side, that is to say that the long side of each cell is perpendicular to the axis of the series, or end-to-end, that is to say that the long side of each cell is parallel to the axis of the series. It is customary to designate the sides for side- by-side cells (or ends for end-to end cells) of the cells by the terms“upstream” and “downstream” with reference to the current orientation in the series. The current enters the upstream and exits downstream of the cell.
  • the production of aluminium in an electrolytic cell is proportional to the current supplied to the cell.
  • the electrical currents in most modern electrolytic cells using the Hall-Heroult process exceed 200 kA and can reach 400 kA, 450 kA or even more; in these potlines the pots are arranged side by side.
  • Most newly installed pots operate at a current comprised between about 350 kA and 600 kA, and more often in the order of 400 kA to 500 kA.
  • the present invention is more particularly related to the potshell of such electrolysis cells.
  • Potshells are made of low carbon structural steel. Their interior cavity is defined by sheet steel and has a cuboid shape, the potshell bottom being horizontal and the potshell sidewalls being arranged so as to lie approximately vertically.
  • the sheeting is stiffened by means of an external carrying structure.
  • the external carrying structure includes an upper rim (also called“deckplate”) that forms the circumference of the rectangular structures, and lateral structural elements (so-called“cradles”) arranged at a right angle with respect to the direction of the sidewall, at a regular spacing.
  • the interior cavity contains the lining, i.e., refractory bricks to protect the sheeting, and the cathodes and the side lining intended to be in contact with the liquid electrolyte and liquid metal (in operation, the side lining is protected from the liquid electrolyte by a layer of frozen electrolyte).
  • Potshells represent a significant cost. Their lifetime is limited by deformation: as they support a permanent load at elevated temperature, potshells are subject to creep. Also, transient abnormally high temperatures of the potshell (for example during start-up and during so-called prolonged anode effects or when the pot is“sick”) may lead to transient deformation of the steel potshell due to thermal expansion and softening; overheating can also lead to permanent deformation of the potshell. Over the years of use, the potshell tends to“open”, that is to say permanently deformed; the deformation is quite significant in the longitudinal, in the transverse as well as in the vertical directions.
  • US 2,861 ,036 (Pechiney), US 4 322 282 (Swiss Aluminium Ltd), and US 4,421 ,625 (Swiss Aluminium Ltd) are representative for a potshell design that needs to withstand enormous swelling forces; the first patent uses springs to exert a counterforce against opening forces, in second and third the potshell is stiffened by a set of horizontal expansion rails, with additional springs in the third one.
  • US 3,702,815 uses horizontal rails only for the short sides of the potshell.
  • WO 201 1/028132 discloses a potshell with vertical stiffeners and horizontal webs on its outside, said web having openings for efficient air cooling.
  • WO 2016/077932 presents a potshell design wherein the sidewalls are stiffened using vertical structural elements with free upper ends acting as cantilever springs that can be loaded and adjusted using wedges. These wedges need to be adjusted manually throughout the life of the potshell, using a hammer, a portable hydraulic jack or a wrench. While this design seems indeed to be able to provide a larger cathode surface for a given footprint compared to prior art cells, the perspective of manual fine- tuning of several dozens of wedges per cell during the lifetime of the pot, carried out in the hot working environment of a potroom and at a location of the pot that is particularly hot and not readily accessible is not especially appealing for the workers involved in this operation, and for their supervisors.
  • potshell designs are complex and do not meet all of the multiple goals mentioned above: low capital cost, sufficient strength, long lifetime, small footprint.
  • the present invention aims at providing an improved potshell design that meets at least several of these goals.
  • the problem is solved by a redesign of the potshell that uses modified cradles, thereby increasing their strength and decreasing their dimensions, and more precisely, both their height (i.e. their dimension parallel to the height of the potshell) and their width (i.e. the dimension in the direction protruding out of the sidewall to which they are attached, parallel to the upper rim of the adjacent sidewall).
  • the side stiffeners are not spring-loaded structural elements but rigid profiles. Said profiles can be welded profiles.
  • these stiffeners are fixedly connected to the shoebox along substantially their whole length.
  • fixation means between stiffeners and shoebox are distinct from both said stiffeners and shoebox.
  • said fixation means are external or inserted fixation means.
  • said fixation means are welding means, so that stiffeners are welded against the shoebox; said welding connection can comprise point welding spaced over substantially the whole length of the stiffener, and/or can comprise one or more welding seams, such as one continuous welding seam extending over at least three quarter (and preferably over at least 90%) of the length of the stiffener, or two or more sections of welding seams spaced over substantially the whole length of the stiffener.
  • said fixation means are form-fitting or interlock fixation means.
  • this second variant does not require external fixation means, since the latter are defined by the facing shapes of stiffeners and shoebox themselves.
  • said stiffeners and shoebox are adapted to directly contact one another in view of said form-fitting fixation.
  • stiffeners and shoebox When starting the pot (i.e. starting the electrolysis process), stiffeners and shoebox have been mutually mounted, potentially providing a slight clearance there between; this will help to release stresses.
  • a clearance is inferior to 5 mm, preferably inferior to 3 mm, and still more preferably inferior to 2 mm.
  • said shoebox progressively undergoes a functional deformation, in particular by creep, so that said shoebox and said stiffeners come into close contact and create said form-fitting fixation.
  • the stiffeners are arranged in a way such that between each two neighboring stiffeners there is a cathode collector bar protruding out of the potshell; this is known as such and applies both in the case where each cathode block has one collector bar protruding out of the cathode block on each end, and in the case where each cathode block has two cathode collector bars protruding out of the cathode block on each end.
  • the potshell side stiffener design has been further optimized for the case where each cathode block has two steel collector bars. In this case a T shape stiffener has been introduced in the central part of each cathode block and it does not make a continuous U loop between upstream and downstream of the shell sides.
  • the underneath part of the intermediate cradle has been removed to reduce the overall weight of the potshell. This feature also provides better access to welding of the neighboring continuous cradles.
  • the cross sections of the intermediate cradles have been chosen in such a way that the mechanical integrity and strength of the potshell remains intact.
  • a first object of the present invention is a potshell for an electrolytic cell suitable for the Hall-Heroult electrolysis process, said potshell being intended to receive firstly a cathode forming the bottom of said electrolytic cell and comprising a plurality of parallel cathode blocks, each cathode block comprising at least one metallic cathode collector bar protruding out of each of the two ends of the cathode block, and secondly a lateral lining defining together with the cathode a volume containing the liquid electrolyte and the liquid metal resulting from the Hall-Heroult electrolysis process, said potshell comprising a bottom wall and peripheral walls extending upwards from said bottom wall, so as to define an inner reception volume, said peripheral walls comprising side walls and end walls, and said potshell further comprising a plurality of reinforcement members or stiffeners, provided side by side along at least part of said peripheral walls, said potshell being characterized in that at least part of said stiffeners comprise at least one attachment wall, said attachment wall being provided with an
  • fixation means are permanent fixation means such a welding means. In any case they can be distinct from both said attachment region and said facing wall of potshell.
  • fixation means are defined by both said attachment region and said facing wall of potshell, said attachment region and said facing wall being adapted to directly contact one another in view of a form-fitting fixation.
  • said attachment region defines an attachment line, the main dimension of attachment line being superior to 30 millimeters, preferably to 60 millimeters, more preferably to 100 millimeters.
  • Said stiffeners provided with said attachment wall can be located on side walls of said potshell. They can be formed by a hollow body, which is closed by peripheral walls, in cross section, said peripheral walls comprising said attachment wall. Said peripheral walls can for example be polygonal, in particular rectangular. At least the top of said hollow body can be open.
  • the height of the stiffeners is reduced with respect to stiffeners used in prior art pot shells. More precisely, their height does not reach the upper rim of the potshell. Therefore, in another embodiment which can be combined with any other embodiment of the invention, at least part of said stiffeners extend only over a lower region of said side wall of said potshell, so as to define a so- called free upper region of said side wall of said potshell.
  • the ratio between the height of the stiffener and the height of the side wall of the potshell is between 0.4 and 0.7, in particular between 0.45 and 0.55.
  • the height of the stiffeners does not exceed the level of the top of the cathode blocks by more than 15 cm, preferably not by more than 10 cm, still more preferably not by more than 5 cm, and still more preferably not by more than 2 cm. It can be at the same level. There is no advantage not to reach this level, and a loss of mechanical stiffness would result from this option.
  • the design according to the invention has several advantages. First of all, it uses less steel while providing an equivalent stiffness compared to prior art. Secondly, it leaves free a significant portion of the shoebox, that is to say a substantially planar portion of the potshell, for the action of heat exchanger and/or cooling devices. In particular, it leaves free the hottest portion of the potshell, that is to say the zone corresponding to the position and thickness of the liquid metal pad and the molten bath. This zone typically extends until about 30 cm to 50 cm above the bottom of the cathode blocks.
  • said stiffeners extend only over part of said side wall, and in particular only over a lower region of side wall, so as to define a free upper region, as mentioned above.
  • Said free upper region can be equipped with heat exchange means.
  • Said heat exchange means can be fixed against a planar and smooth region of the potshell (shoebox).
  • Said heat exchange means may be of any appropriate type. In particular, they may be similar to those described in patent documents WO 2012/039642, WO 2013/055228, WO 2013/055229 and WO 2014/182176. According to the invention, said heat exchange means extend substantially horizontally, along above cited free upper region of the potshell.
  • Another advantage of the invention is that the total depth of the sidewall stiffeners (measured from the shell outside to the outermost wall of the stiffener) is reduced with respect to prior art; it can be less than 180 mm, preferably less than 165 mm, and still more preferably less than 155 mm, whereas in the design disclosed in WO 2016/077932 this value is given as about 200 mm.
  • Another object of the present invention is an electrolytic cell suitable for the Hall-Heroult electrolysis process, comprising a cathode forming the bottom of said electrolytic cell and comprising a plurality of parallel cathode blocks (each cathode block comprising at least one metallic cathode collector bar protruding out of each of the two ends of the cathode block), a lateral lining defining together with the cathode a volume containing the liquid electrolyte and the liquid metal resulting from the Hall-Heroult electrolysis process, an outer metallic potshell containing said cathode and lateral lining, a plurality of anode assemblies suspended above the cathode (each anode assembly comprising at least one carbon anode and at least one metallic anode rod connected to an anode beam), a cathodic bus bar surrounding said potshell, a plurality of connectors (each connecting one end of a cathode collector bar of a cathode block to said cathodic bus bar
  • Yet another object of the present invention is an aluminium electrolysis plant comprising at least one line of electrolysis cells of substantially rectangular shape, and said plant further comprising means for electrically connecting said cells in series and for connecting the cathodic busbar of a cell to the anode beam of a downstream cell, characterized in that more than 60 % (preferably more than 80%) of the electrolysis cells in at least one of said line, and preferably each electrolysis cell of said line, is an electrolysis cell according to the invention.
  • Yet another object of the invention is a method for making aluminium by the Hall-Heroult electrolysis process, characterized in that said method is carried out in an aluminium electrolysis plant according to the invention.
  • Yet another object of the invention is a method for adding heat exchange means to a potshell, wherein said cooling fins are removed from said upper free region, and said heat exchange means are mounted in said upper free region.
  • a last object is a method of operating a potshell according to the invention, characterized in that it comprises mutually mounting said stiffeners and said potshell upon starting the potshell, potentially providing a slight clearance therebetween, and then operating the pot so that said potshell undergoes a functional deformation, in particular by creep, and so that said potshell and said stiffeners come into close contact and create said form-fitting fixation.
  • Figure 1 shows a schematic transverse cross-sectional view of a prior art electrolytic cell for aluminium production according to the HaM-Heroult process.
  • Figure 2 is a schematic cross section along a transversal plane across a Hall-Heroult electrolytic cell. The arrows represent the current flow across the cell.
  • Figure 3 is a schematic perspective view of a prior art potshell.
  • Figure 4 is a schematic perspective view of a potshell according to the invention.
  • Figure 5 is a transverse cross section along line V-V of figure 4, analogous to figure 1 but at a greater scale, showing a stiffener and the end of a cathode bar, provided on the side wall of the potshell illustrated on figure 4.
  • Figure 6 is a front view along arrow VI of figure 4, showing two adjacent stiffeners as well as the end of a cathode bar provided between said stiffeners.
  • Figure 7 is a perspective view, showing at a much greater scale the upper end of a stiffener illustrated on figures 5 and 6.
  • Figure 8 is a perspective view, analogous to figure 4 but at a greater scale, showing some stiffeners provided on potshell of figure 4, the walls of said potshell being not illustrated on said figure 8.
  • Figure 9 is a top view, showing at a much greater scale a stiffener provided on the end wall of the potshell illustrated on figure 4.
  • Figure 10 is a perspective view, showing at a greater scale the end wall of a potshell, which is provided with stiffeners according to a variant of the invention.
  • Figure 1 1 is a perspective view, analogous to figure 10 but along a different angle, showing some stiffeners of figure 10, the walls of the potshell being not illustrated on said figure 1 1.
  • Figure 12 is a perspective view of a potshell according to another variant of the invention.
  • Figure 13 is a perspective view, showing a part of the bottom of potshell illustrated on figure 12.
  • a typical cell 1 includes a potshell comprising a first longitudinal sidewall 2, a second longitudinal sidewall 3, first and second transversal end walls (not visible on figure 1 ) and a bottom 4.
  • the potshell walls define a space lined on its bottom and sides with refractory materials 5 (protecting the potshell against heat) along with the cathode blocks 8, thereby defining a volume containing the molten metal and electrolyte.
  • the side lining 5 comprises a layer of carbonaceous material (not shown on the figures) protected in steady state operation by solid electrolyte in contact with molten liquid material.
  • Said cathode blocks 8 comprise one or more cathode collector bars 9. They protrude out of the potshell. Electrical current enters the cell through anodes 7 (suspended above the cell by anode rods 6 attached to an aluminium frame called anode beam 10), passes through the molten electrolytic bath 11 and the molten aluminium pad 12, and then enters the carbon cathode block 8. The current is carried out of the cell by the cathode collector bar 9 connected to the cathode busbar 20, 21 (shown on figure 2). The cell 1 is closed by a set of hoods 13.
  • FIG 2 explains in more detail the typical current flow in a Hall-Heroult electrolysis cell.
  • the current is fed into the anode frame 10 (called anode beam, shown on figure 1 ), flows from the anode beam 10 to the anode rod 6 and to the anode 7 in contact with the liquid electrolyte 11 where the electrolytic reaction takes place, crosses the liquid metal pad 12 resulting from the process and eventually will be collected at the cathode block 8.
  • Each collector bar end 24, 25 is connected through a flexible connector 22, 23 to the closest cathode busbar 20, 21 extending parallel to each of the longitudinal sidewalls of the potshell.
  • the potshell 30 of an electrolytic cell for the Hall-Heroult process can be represented as a“shoe box” of external length x, width y and depth z, made from steel sheet, comprising two parallel upright sidewalls 31 , 32, two parallel upright endwalls 33, 34, and a bottom 35.
  • Said sidewalls 31 , 32 and endwalls 33, 34 are connected to a reinforcement structure.
  • Said reinforcement structure comprise stiffeners 36 (so-called “cradles”). They are usually regularly spaced and extend over all the length and width of the potshell. These stiffeners are often T-profiles, as on figure 3, the width of the section parallel to the potshell being larger at the bottom than at the top.
  • a deckplate 37 can be provided over the whole rim of the potshell.
  • Figure 3 does not show the cathode blocks which are positioned on the bottom 35 of the potshell 30, but shows the windows 38 provided in both sidewalls 31 , 32 for allowing the cathode bars to protrude out of the potshell; electrical connectors (usually flexible ones) are used to connect the collector bars to the cathode busbars (not shown on the figure) that extend parallel to both sidewalls 31 , 32.
  • the internal length, width and depth of the potshell are designated by xi, yi and z respectively.
  • FIG 4 shows an embodiment of a potshell 40 according to the invention. It has the same kind of shoebox structure as the prior art potshell 30, with two parallel upright sidewalls 41 , 42, two parallel upright endwalls 43, 44, a bottom 45 and a deckplate 47. Potshell 40 differs from that 30 of prior art, in particular for what concerns the structure of stiffeners. Potshell 40 is equipped with cradles 46, shown on figure 8, which are provided on its side walls 41 , 42, as well as with end wall stiffeners 60, provided on its end walls 43, 44.
  • FIG. 8 shows the structure of some cradles 46, as well as some windows 38 there between, but does not illustrate the walls of potshell for sake of clarity.
  • Each cradle 46 comprises a central part 49, as well as two terminal parts 50 and 50’.
  • Central part 49 extends parallel to the bottom wall of potshell, in particular in a horizontal way, whereas terminal parts extend perpendicular to said bottom wall, in particular in a vertical way.
  • Central part 49 is attached, in particular is welded on the lower face of the bottom wall of potshell. Central part 49 is called bottom beam, whereas terminal parts 50 and 50’ are called side wall stiffeners. Stiffeners 50 are provided on side wall 42, whereas stiffeners 50’ are provided on side wall 41. The structure of stiffeners 50 will now be described, bearing in mind that structure of stiffeners 50’ is analogous.
  • FIGS. 5 to 7 show more in detail some stiffeners 50, provided on side wall 42.
  • Said stiffeners 50 are formed by a hollow body, which is defined and closed by peripheral walls, in cross section.
  • Said walls comprise two so called opposite front walls 51 and 52, as well as two so called opposite lateral walls 53 and 54 (see in particular figure 7).
  • the following typical numeric values are given, with reference to this figure 7:
  • T50 (figure 7) of peripheral walls is between 1 mm and 15 mm, and preferably between 2 mm and 10 mm;
  • distance ( S50 ) between facing faces (53’, 54) of adjacent stiffeners (50, 50’) can be between 250 mm and 300 mm, and preferably between 275 mm and 300 mm.
  • - distance S59 (figure 6) between one cathode bar 9 and facing face of lateral wall 54 of adjacent stiffener 50 is between 30 mm and 70 mm, in particular between 40 mm and 50 mm.
  • This distance S59 substantially corresponds to distance window 38 and facing face of lateral wall 54.
  • Front wall 51 which is adjacent to side wall 42 of the potshell, forms an attachment wall, i.e. it is suitable for a fixation with respect to said potshell.
  • Said attachment wall defines an attachment region, which contacts side wall 42 and is attached thereto by fixation means.
  • Said contact may be a direct contact, or an indirect contact, i.e., said fixation means are interposed between said attachment region and said facing wall.
  • said attachment or contact region extends over a substantial part of the attachment wall, in particular over the entire height of the vertical cradle, preferably tack welded at the edges.
  • the contact between the vertical cradle and the sidewall can be left even free to allow free sliding of the potshell wall against the cradle and would help to release mechanical stresses between the said surfaces.
  • said attachment region defines an attachment line 55, also called a contact line, the length of which is noted L55 (see figure 7).
  • L55 the length of which is noted L55 (see figure 7).
  • the tack weld achieved on the entire length L55 is superior to any weld carried out on part of the cradle height. This allows a reliable fixation of the whole stiffener 50 on the wall 42 of the potshell.
  • L55 is slightly superior to x50, since it takes into account twice the thickness T50 of the walls.
  • attachment wall 51 is welded against the wall 42.
  • Said welding connection can comprise point welding spaced over substantially the whole length of the line 55, and/or can comprise one or more welding seams, such as one continuous welding seam extending over at least three quarter (and preferably over at least 90%) of the length of the line 55, or two or more sections of welding seams spaced over substantially the whole length of the line 55.
  • the hollow stiffeners 50 have a rectangular shape, in cross section. As an alternative, this shape may be different. However, providing a polygonal shape is advantageous: a side of this polygon is adapted to be in contact with the side wall of the potshell and, therefore, to create a reliable attachment wall. As shown in particular on figure 7, the top of said hollow body preferably is closed to avoid accumulation of loose alumina and other foreign material.
  • stiffeners 50 extend advantageously over only part of the height of side wall 42 of potshell.
  • z50 and z42 the respective heights of said stiffener 50 and said side wall 42 (see figure 6).
  • Height z42 is considered from the bottom of deckplate 47.
  • the ratio ( z50/z42 ) is between 0.4 and 0.7, in particular between 0.45 and 0.55.
  • Z58 the distance, along vertical axis, between top of stiffener 50 and top of cathode blocks 8.
  • Z58 is inferior to 100 millimeters, preferably inferior to 50 millimeters, and still more preferably inferior to 20 millimeters.
  • FIGS 4 and 9 show more particularly the structure of a first embodiment of stiffeners 60, provided on both end walls 43 and 44.
  • Stiffeners 60 differ from those 50, such as described above, essentially in that they are not hollow. On the other hand, they are substantially H or l-shaped.
  • Each stiffener is formed by three walls, i.e. two parallel opposite walls 61 and 62, and a medium wall 63 which links said walls 61 and 62.
  • Wall 61 adjacent potshell end wall 43, is called front wall, whereas wall 62, opposite potshell end wall 43, is called rear wall. Both walls 61 and 62 extend parallel to potshell end wall 43, whereas medium wall 63 extends perpendicular to said potshell end wall. Stiffeners 60 rest each on a base beam 68, said beams being attached to a base plate 69 which extends also under the central parts 49a and 49b of last and last but one cradles 46a and 46b (see also figures 10 and 1 1 for details).
  • thickness T61 of wall 61 and thickness T62 of wall 62 are between 8 mm and 12 mm;
  • T63 of wall 63 is between 5 mm and 7 mm;
  • width W61 of wall 61 and width l/l/62 of wall 62 are between 120 mm and 140 mm;
  • - length L63 of wall 63 is between 160 mm and 185 mm;
  • front wall 61 forms an attachment wall.
  • the contacting face thereof defines an attachment line 65 (figure 9), the length of which is noted L65, which is equal to W61.
  • L65 the length of which is noted L65, which is equal to W61.
  • line 55 the entire length L65 is to be welded on its edges.
  • attachment wall 61 is advantageously welded against the wall 43.
  • the stiffeners extend only over the lower part of potshell end wall 43.
  • this makes it possible to define a so called free, or smooth, upper region 43’ of said end wall 43 of potshell.
  • said free upper region is equipped with heat exchange means (not shown on the figures), typically similar to those described here above.
  • height z43’ ⁇ see figure 4) of upper region 43’ is between 450 mm to 600 mm, in particular between 470 mm to 520 mm. This allows an easy positioning and a reliable fixation of above mentioned heat exchange means.
  • FIGS 10 and 1 1 show another embodiment of end wall stiffeners of potshell end walls 43, which are referenced as 70.
  • said stiffeners 70 extend over the whole height of end wall 43.
  • each stiffener 70 rests on a base beam 78, said beams being attached to a base plate 79 which extends also under the central parts 49a and 49b of last and last but one cradles 46a and 46b.
  • the so called intermediate panels between two adjacent stiffeners.
  • Said intermediate panels 76 are part of the potshell end wall 43.
  • the upper region of panels 76 is equipped with cooling fins 77. These fins are vertical plate-like elements. In a typical way, between 3 and 8 fins are provided on each panel 76.
  • the height H77 of each fin is between 40 to 60 % of the whole height of said end wall 43.
  • cooling fins 77 in the upper free region (42’) are to provide sufficient cooling of the potshell when there are no heat exchangers. That is to say that the potshell according to the invention, equipped with said cooling fins 77 if required in order to ensure a convenient thermal equilibrium, can be mounted in an electrolysis cell and operated without heat exchangers; if the potshell is to undergo a retrofit with heat exchangers, said cooling fins 77 can be removed, totally or in part, in order to ensure thermal equilibrium. If required, heat exchangers can be put in place at the section of the end walls 43 that were previously covered by said cooling fins 77.
  • Said cooling fins 77 can be removed for instance by simple cutting operations. This can be useful because the installation of heat exchangers in a potline will require various installations for the circulation of heat transfer fluids that will transport the heat from the heat exchanger to the point where said heat is needed; these installation may not be ready when a potshell according to the invention is mounted and the pot is put into operation. As a consequence, the pot will have to operate without heat exchangers for a certain period of time, and the potshell should therefore be designed such as to reach a convenient thermal equilibrium with natural cooling only. The use of removable cooling fins 77 meets this target.
  • a method for adding heat exchange means to a potshell according to the invention equipped with cooling fins 77 in the upper free region 42’ comprises therefore the steps of removing said cooling fins 77 from said upper free region 42’, and mounting said heat exchange means in said upper free region 42’.
  • cooling fins 77 can be provided at the side walls of the potshell, and during a retrofit operation they can be replaced, totally or in part, by heat exchangers; this variant is not shown on the figures.
  • FIGS 12 and 13 illustrate a further embodiment of a potshell according to the invention.
  • the mechanical elements analogous to those of figures 4 to 1 1 are given the same references added by the number 100.
  • Potshell 140 of figures 12 and 13 differs from that with reference number 40, essentially by the shape and dimensions of its cradles. Indeed some first cradles 146 are identical to those 46 of first embodiment: they comprise two sidewalls stiffeners 150 and 150’ as well as a continuous beam 149 extending under the bottom wall of potshell. On the other hand, bottom part of said potshell is also provided with further cradles 166, which are different from those 46 and 146. In a typical way, as illustrated on figures 12 and 13, these two different types of cradles 146 and 166 are arranged in an alternate manner, along main dimension of potshell.
  • Cradles 166 are so called partial, in that they do not extend over the whole width of the bottom part of the potshell.
  • a first so-called half cradle 167 comprises a sidewall stiffener 170, which is T shaped in a similar way as end wall stiffener 70, as well as a cutout beam 171 extending from said stiffener 170, under only part of bottom wall of potshell.
  • a second half cradle 167’ comprises a sidewall stiffener 170’ as well as a cutout beam 171’.
  • Cooling fins 177 are provided above top end of at least some stiffeners 170 and/or 170’.
  • Facing ends of said beams 171 and 171’ define an intercalary space or gap 190.
  • the latter provides a satisfactory access to the neighboring continuous beams 149, in particular in view of their welding.
  • This embodiment of figures 12 and 13 is especially adapted and advantageous, in case each cathode block has two collector bars.
  • the invention has many advantages.
  • the side wall and end wall stiffeners 50, 60 are wider (i.e. their main dimension Z.55 is greater) than the cradles used in prior art potshells, but their height z50 is less than that of the cradles used in prior art potshells. It both increases the available surface of the cavity (i.e. the surface that is available for the cathodes forming the bottom of the electrolytic cell) of the potshell (at a given“footprint” (i.e. at a given total outside dimension) and decreases the height of the cradles (fins) below the deckplate.
  • potshell according to the invention allows to increase the cathode surface area by about 10 % to about 21% depending on the cell technology. It should be noted that potshells according to the invention can be used for virtually any cell technology using the Hall-Heroult process. The increase in cathode surface area allows using longer anodes, thereby reducing the voltage drop in the electrolyte region and reducing the anodic current density at any given amperage. As a consequence, end-of-life electrolytic cells can be replaced by new electrolytic cells, using pothshells according to the invention, that fit into the footprint of the old ones but having a higher production capacity.
  • the new design leads to decreased heat loss because of the smaller surface area of the cradles that unavoidably act not only as stiffeners but also as cooling fins. This is due to their smaller height and (optionally) smaller width.
  • Another advantage of the potshell according to the invention is that the upper part of the sidewalls and/or endwalls is fully accessible over a height designated as z42 This allows providing the potshell with heat exchangers in contact with the upper part of the sidewalls and/or endwalls of the potshell.
  • a test cell was based on so-called DX+ technology that is used and offered for sale by Emirates Global Aluminium for many years.
  • Concerning the potshell two major changes were made in side and end wall cradle design in accordance to the present invention: narrowing down the portion of the cradle width to bare minimum, and reducing the cradle height below the deckplate up to the top of the cathode blocks. Additionally the potshell height was reduced by about 150 mm from the top of the deckplate to the bottom of the side cradles at the location of concrete support where potshell rests.
  • the structural features of the new potshell design are the following: narrower side cradles, shorter side cradles, side cradles at every cathode block, increased inner cavity width, increased inner cavity length, maintaining similar mass of the potshell, reduced shell height by 165 mm.
  • This innovative potshell design also enables to install heat recovery system in the upper portion of the potshell facing the meal and bath, utilizing the full perimeter on the potshell. This thermal energy can be utilized further for other purposes and potentially can be helpful to reduce energy consumption of the cell.
  • Another aspect of the wider cavity and narrower cradle potshell design is to increase cell productivity by increasing cell current or reducing the specific energy consumption.
  • This increase in cell current can be easily calculated by the % gain in anode panel surface area due to longer anodes.
  • reduction in specific energy consumption can be estimated by taking into the account of reduction in bath voltage for a given anode to cathode distance and anode size.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electrolytic Production Of Metals (AREA)

Abstract

L'invention concerne un caisson de cuve (40) pour une cellule électrolytique (1) convenant pour le procédé d'électrolyse Hall-Heroult, ledit caisson de cuve étant destiné à recevoir une pluralité de blocs cathodiques parallèles (8), chaque bloc cathodique comprenant une barre de collecteur cathodique métallique (9) sortant de chacune des deux extrémités du bloc cathodique (8), et un chemisage latéral (5) délimitant, conjointement avec la cathode, un volume contenant l'électrolyte liquide (11) et le métal liquide (12) résultant du procédé d'électrolyse Hall-Heroult, ledit caisson de cuve (40) comprenant : une paroi de fond (45) et des parois périphériques (41-44) s'étendant vers le haut à partir de ladite paroi de fond (45), lesdites parois périphériques comprenant des parois latérales (41, 42) et des parois d'extrémité (43, 44) et une pluralité d'éléments de renfort ou de raidisseurs (50, 60), ledit caisson de cuve étant caractérisé en ce qu'au moins une partie desdits raidisseurs comprennent une paroi de fixation (51), pour la fixation à la paroi en regard (42) du caisson de cuve, ladite paroi de fixation comprenant une zone de fixation (51), ladite zone de fixation et ladite paroi en regard (42) dudit caisson de cuve étant fixées par des moyens de fixation.
PCT/IB2019/052419 2018-04-03 2019-03-26 Caisson de cuve pour cellule électrolytique destiné à être utilisé avec le procédé hall-héroult Ceased WO2019193451A1 (fr)

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GB1805436.1A GB2572564A (en) 2018-04-03 2018-04-03 Potshell for electrolytic cell to be used with the Hall-Heroult process

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP4403673A4 (fr) * 2021-09-16 2026-01-14 Obshchestvo S Ogranichennoy Otvetstvennostyu Obedinennaya Kompaniya Rusal Inzhenerno Tekh Tsentr Dispositif cathodique pour électrolyseur d'aluminium

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US4087345A (en) * 1977-07-19 1978-05-02 Ardal Og Sunndal Verk A.S. Potshell for electrolytic aluminum reduction cell
US4322282A (en) * 1979-10-17 1982-03-30 Swiss Aluminium Ltd. Tank for an electrolytic cell
US4421625A (en) * 1981-05-20 1983-12-20 Swiss Aluminum Ltd. Lower part of a fused salt electrolytic cell
WO2006053372A1 (fr) * 2004-10-21 2006-05-26 Bhp Billiton Innovation Pty Ltd Refroidissement interne d’une cellule de fusion électrolytique
WO2016077932A1 (fr) * 2014-11-21 2016-05-26 Hatch Ltd. Caisson de cellule de réduction d'aluminium à profil bas et procédé d'augmentation de la capacité de production d'une ligne de cuves de cellule de réduction d'aluminium

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CN201183834Y (zh) * 2007-12-17 2009-01-21 贵阳铝镁设计研究院 铝电解槽用的加强型摇篮架
CN201553785U (zh) * 2009-12-04 2010-08-18 贵阳铝镁设计研究院 一种铝电解槽侧部保温结构

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4087345A (en) * 1977-07-19 1978-05-02 Ardal Og Sunndal Verk A.S. Potshell for electrolytic aluminum reduction cell
US4322282A (en) * 1979-10-17 1982-03-30 Swiss Aluminium Ltd. Tank for an electrolytic cell
US4421625A (en) * 1981-05-20 1983-12-20 Swiss Aluminum Ltd. Lower part of a fused salt electrolytic cell
WO2006053372A1 (fr) * 2004-10-21 2006-05-26 Bhp Billiton Innovation Pty Ltd Refroidissement interne d’une cellule de fusion électrolytique
WO2016077932A1 (fr) * 2014-11-21 2016-05-26 Hatch Ltd. Caisson de cellule de réduction d'aluminium à profil bas et procédé d'augmentation de la capacité de production d'une ligne de cuves de cellule de réduction d'aluminium

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP4403673A4 (fr) * 2021-09-16 2026-01-14 Obshchestvo S Ogranichennoy Otvetstvennostyu Obedinennaya Kompaniya Rusal Inzhenerno Tekh Tsentr Dispositif cathodique pour électrolyseur d'aluminium

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GB201805436D0 (en) 2018-05-16

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