Support assembly for electrolytic cell anodes for producing primary aluminum

Abstract

A support assembly (12) for supporting a prebaked anode (14) of a Hall-Heult cell (10) for producing primary aluminum comprises a plurality of connecting plates (24), where each connecting plate (24) is arranged at the lower end of a respective stub (22) and has a diameter (D4) greater than the diameter (D3) of the stub (22).

Description

Technical Field

[0001] The invention belongs to the field of components for the production of primary aluminium using Hall-Hêroult cells; in particular, the invention relates to an original support assembly for anodes of Hall-Hêroult cells, which allows to extend the service life of the anode operating cycles and reduce the weight of the final anode scrap. Background Art

[0002] Primary aluminum is produced in Hall-Hêroult electrolytic cells. Alumina distributed to the electrolytic cell dissolves in cryolite and aluminum fluoride (AlF 3 ) electrolytic bath and is reduced to aluminum by passing direct current from the anode to the carbon cathode during the electrolysis process.

[0003] The anode support assembly, which is usually a pre-baked type, includes a hook formed from an anode beam, a transition joint, a yoke, and a plurality of stubs.

[0004] To connect to the support assembly, the anode is provided with a number of transverse slotted holes at the top, one for each short post. A predetermined amount of molten cast iron is poured into the remaining space between the short post and the corresponding hole. Once the cast iron solidifies, the short post remains embedded in the hole of the anode, and the solidified cast iron ring becomes the mechanical and electrical connection between the anode beam and the anode.

[0005] The electrolyser is typically mounted with a number of support assemblies, each supporting assembly carrying a respective anode, the current flowing through each anode being substantially equal to the total line current divided by the number of support assemblies in the electrolyser.

[0006] The normal operating cycle of the prebaked anodes according to the prior art is essentially between 25 and 30 days and ends when the anodes have reached a minimum height below which there is a risk of contaminating the molten bath with cast iron rings. In this case, a new support assembly equipped with a new anode is required to replace the support assembly carrying the worn anode.

[0007] The weight of carbon in spent anodes constituting anode butt discard is typically 20-30% of the weight of new anodes and is recovered in lines for recovering anode butt carbon.

[0008] To prevent the cast iron rings from contaminating the molten bath and the aluminium, a layer of carbon is left approximately 50 mm below the rings, which is part of the thickness of the anode scrap. Taking into account the depth of the holes, the total thickness of the anode scrap is between 150 and 200 mm.

[0009] The duration of the anode depends directly on the total thickness of the scrap, which in turn depends directly on the depth of the short post hole in the upper part of the anode. According to the prior art solutions, the average depth H1 of the hole is about 120 mm. Taking into account a safety thickness of about 50 mm, the total thickness of the Hbutt scrap is about 170 mm, which corresponds to about 26% of the height of the new anode, 650 mm.

[0010] Furthermore, in the prior art solutions, the current density distribution is non-uniform, since the current converges towards the stub, but only through limited areas of the cast iron ring (particularly, towards those areas of the ring with higher carbon contact pressure). The contact resistance between the stub and the anode is non-uniform, and the voltage drop between the stub and the anode is typically in the range of about 80 mV to 130 mV. Due to the high density of local current, the Joule effect inside the anode generates heat and causes energy loss in the battery.

[0011] Some patent documents have proposed some methods to improve the energy efficiency of anodes, eliminate the use of cast iron and improve the use of carbon. For example:

[0012] - International application WO-A1-2016 / 130014 by Norsk Hydro proposes to replace cast iron with a mechanical support element that requires anodization and an intermediate layer of metal particles for electrical connection between the carbon and the hook. However, the mechanical particles must be recycled, the support assembly is different from those commonly used in the industry, and makes it impossible to modify existing support assemblies;

[0013] - International application WO-A1-2012 / 100340 of the University of Laval proposes a seamless connection. It provides longitudinal grooves instead of holes for the studs, and the steel part incorporated into the cast iron is a bar with a rectangular cross section;

[0014] - Document US 7,901,560 from Norsk Hydro proposes to create slits at the bottom of the anode to reduce energy consumption;

[0015] - International applications WO-A1-2016 / 108696 by Storvik and WO-A1-2002 / 42525 by Servico propose yokes with copper parts arranged inside steel parts and without stubs welded to the steel arms of the steel yoke.

[0016] Finally, further exemplary embodiments are shown in CA2838113A1 and GB2569382A, however, these embodiments only show a cast iron ring around the stub. Summary of the invention

[0017] The object of the present invention is to meet the industrial needs while overcoming the disadvantages mentioned in the prior art, mainly in order to increase the service life of the anode and reduce the weight of the anode butt end discard.

[0018] This object is achieved by a support assembly according to claim 1. The claims dependent thereon define further advantageous embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The characteristics and advantages of the support assembly of the invention will become apparent from the following description given by way of non-limiting example with reference to the figures of the accompanying drawings, in which:

[0020] - Figure 1 A schematic depiction of a Hall-Hêroult cell for producing primary aluminum and a pair of support assemblies for corresponding anodes;

[0021] - Figures 2 to 6 relate to the prior art, in particular:

[0022] a) Figure 2 shows the support assembly assembled and connected to the anode;

[0023] b) FIG. 3 shows the support assembly of FIG. 2 in separate parts;

[0024] c) Figures 4a and 4b show examples of cast iron rings of the support assembly after solidification;

[0025] d) FIG5 shows a support assembly for anode wear;

[0026] e) Figure 6 shows the slots and associated studs.

[0027] - Figures 7 to 17 The invention relates to a support assembly according to the invention, in particular:

[0028] a) Figure 7 A support assembly assembled and connected to the anode is shown;

[0029] b) Figure 8 Depicted Figure 7 an arm of a support assembly in which is assembled and connected to an associated anode;

[0030] c) Fig. 9 depicts the assembled arm of the support assembly with corresponding slots;

[0031] d) Fig.10a and Fig.10b shows the ring of the support assembly after curing;

[0032] e) Fig.11a , Fig.11b and Fig.11cA further embodiment of an arm of a support assembly is shown;

[0033] f) Figures 12 to 17 Other shapes of arms of the support assembly are shown. DETAILED DESCRIPTION

[0034] Figure 1 A Hall-Hêroult cell 10 for producing primary aluminium is schematically depicted with a pair of support assemblies 12 in an operating position, immersed in the cell. Each support assembly 12 comprises an anode beam 16, typically made of aluminium, connected to an anode 14, typically of the prebaked type, made of carbon.

[0035] In particular, for the connection between the anode beam 16 and the anode 14, the support assembly 12 includes a transition joint 18 welded to the lower end of the anode beam 16 and a yoke 20 welded at the transition joint 18, the yoke 20 is usually made of steel, usually bimetal (steel-aluminum). In addition, the yoke 20 includes a plurality of independent arms 20a, and the support assembly includes a plurality of short posts 22, which are usually made of steel, and each short post 22 is welded to the corresponding arm 20a of the yoke 20.

[0036] The generally cylindrical stud 22 has a characteristic width, ie, a dimension that characterizes the stud's largest overall dimension, such as a maximum outer diameter D3.

[0037] according to Figure 7 , Figure 8 and Fig. 9 The support assembly 12 further comprises a plurality of connecting plates 24, each of which is generally cylindrical and preferably made of steel, connected to the lower end of the corresponding short column 22. According to the present invention, the connecting plate 24 is defined by an upper surface 24a at the top and a lower surface 24b at the bottom, and has a maximum outer diameter D4, wherein the diameter D4 of the connecting plate 24 is greater than the diameter D3 of the short column (D4>D3).

[0038] For example, the connecting plate 24 is welded to the short column 22; in a variant embodiment, the short column and the connecting plate constitute a single body.

[0039] Finally, the support assembly 12 comprises a plurality of rings 26, usually made of cast iron and solidified iron, for connecting the support assembly 12 to the anode; according to a further embodiment, the rings are made of carbon paste or consist of a carbon-based glue. Each cast iron ring 26 connects the connection plate 24 of the corresponding short column 22 and the anode 14 by engaging with the corresponding transverse slot 14a of the anode 14.

[0040] In order to achieve the connection between the connecting plate 24 and the anode 14, a plurality of slots 14a are implemented on the upper part of the anode 14; each slot 14a is provided with a plurality of grooves 14b on its side surface, wherein each groove 14b generally extends axially and is inclined.

[0041] The connecting plate 24 is positioned in the corresponding slot 14a, and a predetermined amount of cast iron is poured into the slot. The solidified cast iron forms a ring 26. The ring 26 is firmly connected to the plate 24 by virtue of the thermal contraction experienced by the cast iron after solidification, and is firmly connected to the anode 14 by virtue of the groove 14b; in particular, the cast iron that has solidified in the groove 14b constitutes a plurality of fins 26b of the ring 26.

[0042] exist Figure 8 In the embodiment, the slot 14a has a diameter D2 (excluding the groove), a characteristic depth H2 and a side surface extension S2. Hsafety is the safety thickness of the consumed anode, Hbutt is the thickness of the anode scrap, and H3 is the protrusion height of the connecting plate 24 from the upper surface of the anode 14.

[0043] Compared to the prior art, for example, as shown in FIG6 , it is obvious that the diameter D2 of the slot 14a is greater than the diameter D1 of the slot of the prior art solution due to the use of the connecting plate 24; the depth H2 of the slot 14a is less than the depth H1 of the slot of the prior art solution. In particular, H4=H1-H2 is the height reduction between the solution of the present invention and the solution of the prior art, and corresponds to the height reduction of the anode butt scrap.

[0044] Fig.10a and Fig.10b An embodiment of a ring 26 is shown, comprising a tubular body 26a of thickness "t" and a plurality of fins 26b projecting radially outwards from the body 26a, the fins 26b having a significant axial and oblique extension relative to the central axis of the body.

[0045] Fig.11a An embodiment of the invention is depicted in which the connecting plate 24 is a steel disc welded to the lower end of the short column 22, the height of the connecting plate partially overlapping with respect to the height of the short column.

[0046] Fig.11b Another embodiment of the invention is depicted, in which the connecting plate 24 is a steel disc welded to the lower end of the short column 22, the height of the connecting plate completely overlapping with respect to the height of the short column.

[0047] Fig.11c Another embodiment of the invention is depicted in which the connecting plate 24 is a steel disc welded to the lower end of the stub 22, completely underneath the stub.

[0048] Furthermore, according to one embodiment of the invention, the number of grooves 14b of the slot 14a is between 11 and 30, ie more than provided in prior art solutions.

[0049] exist Fig.11a , Fig.11b and Fig.11c In the embodiment shown, the position of the ring relative to the stub can be varied, thereby varying the contact area accordingly. Thus, the heat flow from the anode to the arm of the corresponding stub can be controlled.

[0050] In the solution according to the invention, the heat generated by the current inside the anode through the Joule effect is less than in the known solutions, because the larger surface area of ​​the slots S2 reduces the current density and the contact resistance in the interface area between the connecting plate (steel), the ring (cast iron) and the anode (carbon).

[0051] The contact resistance also depends on the pressure between the side surface 14a of the slot 14 and the carbon anode, and on the profile of the side surface 14a, which may be flat or knurled, for example.

[0052] Fig.12 Another embodiment of the invention is depicted, wherein the slot 14a has a tapered side surface with an extension S2, preferably obtained by tool machining, and the connecting plate 24 has a tapered side surface with an extension S2.

[0053] Fig.13 Another embodiment of the present invention is shown, in which the side surface of the connecting plate 24 is knurled to increase the electrical contact area and mechanical support of the anode. In addition, preferably, the slot 14a has a tapered side surface, and the connecting plate 24 has a tapered side surface.

[0054] Fig.14 It is another embodiment of the present invention, in which the support assembly 12 is matched with a cover 28, which is arranged to cover the transition area between the short column 22 and the connecting plate 24 and is suitable for covering the end of the short column 22 and the upper part of the connecting plate 24. Preferably, the cover 28 rests on the upper surface 14c of the anode 14 and, depending on the internal shape, rests on the connecting plate 24.

[0055] Preferably, the cover 28 has an overall height H5 such that when the anode 14 is fully immersed in the electrolytic bath, the stubs are protected and do not be lapped by the liquid electrolytic bath.

[0056] For example, the cover 28 has an overall flanged annular shape and comprises two coupleable half-shells 28a, 28b held together, for example, by carbon glue or metal wires or carbon fibers.

[0057] Fig.15 Another embodiment of the invention is shown in which the cover 28 consists of a tube section partially resting on the upper surface 14c of the anode 14, which is open at the top and has a height H5.

[0058] The tube thus defines an internal space 30 which is preferably filled with a plurality of protective chips 32 , for example consisting of unbaked carbon paste, in order to prevent the ingress of the liquid bath and to better thermally isolate the upper part of the anode.

[0059] Fig.16 Another embodiment of the present invention is depicted, in which the cover 28 has an overall flanged annular shape and consists of a lower portion 28a and an upper portion 28b, wherein the lower portion 28a consists of two half shells 281, which are connected and rest on the upper surface 14c of the anode 14 and the connecting plate 24; the upper portion 28b consists of two half shells 283, 284, which are connected and rest on the upper portion 28a.

[0060] Preferably, the half shells 281 , 282 , 283 , 284 are connected together using carbon glue or steel tips or pins protruding from the connecting plate 24 .

[0061] In the last 3 or 4 days of the anode life cycle, in order to maintain the same distance between anode and cathode, the anode must be moved deeper into the liquid bath, which may flood the upper part of the stub by an additional segment H4 = H1-H2. The liquid bath will attack and dissolve the steel unless a cover 28 made of, for example, carbon paste is used to protect the vertical part of the stub and the upper part of the plate.

[0062] The cap can be made in one piece, in two halves or in four or more parts and made of non-prebaked carbon paste, or rammed paste, or carbon glue mixed with a binder. For example, using agglomerates of calcined coke particles mixed with pitch particles, joined together using inorganic polymer binders from processing plant products such as lignite or molasses or other organic derivatives, or using phenolic resins or epoxy resins. Such binders are intended to function at temperatures from room temperature to about 450°C, from which the pitch begins to carbonize, and to function as a binder at temperatures of about 1000°C and above.

[0063] Preferably, a non-prebaked carbon paste is used, the same paste used to produce the anode. In this case, the cover is realized by arranging a preformed casing around the stud and over the plate, the casing being made in one piece or in several parts.

[0064] Fig.17Another embodiment of the present invention is shown, in which the connecting plate 24 is partially hollow or empty; for example, the connecting plate has a cavity 34 that opens towards the lower surface 24b facing the electrolytic bath. Advantageously, this feature makes it possible to reduce the weight of the connecting plate and control the heat flow.

[0065] According to this embodiment, preferably, the support assembly 12 cooperates with a cover composed of pipe segments 36, and the pipe segments 36 are partially resting on the upper surface 14c of the anodes 14 with open tops. The pipe 36 defines an internal space 30, and the internal space 30 is preferably filled with debris 32.

[0066] Furthermore, preferably, the connecting plate 24 has one or more channels 38 connecting the upper surface 24a and the cavity 34, which are adapted to allow a part of the debris 32 to enter the cavity 34 from the internal space 30. Advantageously, this allows the cavity 34 to be filled with debris 32 and restricts the molten bath from entering the cavity 34.

[0067] According to the present invention, the ratio between the diameter D4 of the connecting plate and the diameter D3 of the short post is between 1 and 3.5 (1 < D4 / D3 ≤ 3.5), preferably between 1.5 and 3 (1.5 ≤ D4 / D3 ≤ 3).

[0068] According to one aspect of the present invention, the ratio D4 / H2 between the diameter D4 of the connecting plate and the depth H2 of the connecting plate is between 1.92 and 10 (1.92 ≤ D4 / H2 ≤ 10). For example, the ratio D4 / H2 = 220 mm / 115 mm = 1.92 or D4 / H2 = 400 mm / 40 mm = 10.

[0069] However, according to the prior art solution, the ratio D3 / H1 between the diameter D3 of the short post and the depth H1 of the short post is between 1.12 (180 mm / 160 mm) and 1.83 (220 mm / 120 mm).

[0070] Advantageously, in order to ensure the same or better mechanical holding force between the support assembly and the anode, according to the prior art, the lateral contact area π * D4 * H2 of the plate is equal to or greater than the lateral area π * D3 * H1 of the short post.

[0071] According to another aspect of the present invention, the ratio D2 / H2 between the slot hole diameter D2 and the slot hole depth H2 is between 2.2 and 11. For example, the ratio D2 / H2 = 390 mm / 80 mm = 4.875.

[0072] According to another variant embodiment of the present invention, the slot hole has a square or rectangular cross-section or any other polygon. However, such a cross-sectional shape can only be obtained by machining the pre-baked anode. Therefore, from the perspective of production economy, the circular cross-section is the preferred embodiment.

[0073] Inventively, according to the present invention, the carbon utilization efficiency of the anode and the duration of the anode are increased.

[0074] In particular, the depth H2 of the slotted hole according to the invention is less than the depth H1 of the hole according to the prior art, and the diameter D2 of the slotted hole according to the invention is greater than the diameter D1 of the hole according to the prior art, resulting in a lower thickness of the anode butt scrap. This corresponds to a greater useful height of the anode, i.e., "anode height gain" H4 = H1-H2, and thus an increase in the operating cycle time of the anode.

[0075] Furthermore, the contact area A2+S2 of the slots according to the invention with the carbon is greater than the contact area A1+S1 of the holes according to the prior art. Thus, the volume V2 of the slots according to the invention is equal to A2*H2 and is greater than the volume V1=A1*H1 of the holes of the prior art. Advantageously, the carbon cost of the anode of the invention is lower than that of the prior art because the weight is reduced by a factor (V2-V1)*1.6 (where 1.6 is the apparent density of the carbon).

[0076] Furthermore, the slotted holes according to the invention are obtained by the same process as in the prior art, namely by vibratory pressing of carbon paste. Advantageously, therefore, the same production line as in the prior art solutions can be used, after modifying the cover of the vibratory pressing station to adapt it to the larger diameter and smaller depth of the mandrel for making the holes.

[0077] Advantageously, according to the invention, the mechanical support of the anode is improved or remains unchanged relative to the solutions of the prior art. In particular, this advantage is achieved by the connection plate and the associated slots having a lateral surface area S2 greater than or at least equal to the area of ​​the average lateral surface S1 of the prior art.

[0078] Furthermore, according to the invention, in order to compensate for the decrease in hole depth from H1 to H2, the number of grooves of the slotted hole is greater than the number of grooves of the slotted hole in the prior art solutions. In fact, the total length of the grooves according to the invention is greater than or equal to the total length of the grooves relative to the prior art. In particular, 6 to 10 grooves, preferably 8, are provided in the prior art solutions; according to the invention, 11 to 30 grooves are conceivable.

[0079] Furthermore, advantageously, prior art anodes and anode assemblies can be retrofitted and improved according to the invention. It is sufficient to weld the connection plates at the locations of the stubs and to modify the corresponding slots.

[0080] In addition, another vibratory press forming unit produces the caps within the green anode production line or within the anode assembly line, depending on logistical and economic aspects. For example, a preheated mixture of carbon paste or granules fills the mold and the press serves to form and compact the caps so that they can also be processed without baking.

[0081] Example of embodiment

[0082] Exemplary embodiments of a support assembly according to the present invention are defined in Table 1.

[0083]

[0084] In Table 1, the dimensions are defined as follows:

[0085] - Anode dimensions according to prior art:

[0086] a) Anode size: W 655mm×H 650mm×W 1,605mm;

[0087] b) Hole diameter: D1 = 15 + 220 + 15 = 250 mm;

[0088] c) Hole depth: H1 = 120 mm;

[0089] d) Hole base area: A1 = 49,087 mm 2 ;

[0090] e) Pore volume: V1 = 5.890 dm 3 .

[0091] - Dimensions of the anode according to the invention:

[0092] a) Anode size: W 655mm×H 650mm×W 1,605mm;

[0093] b) Hole diameter: D2 = 15 + 360 + 15 = 390 mm;

[0094] c) Hole depth: H2 = 80 mm;

[0095] d) Base area of ​​the hole: A2 = 119,459 mm 2 ;

[0096] e) Pore volume: V2 = 9.557 dm 3 .

[0097] In this example, the thickness of the anode scrap is reduced by 40 mm relative to prior art solutions; this increases the operating cycle duration of the anode from two days to four days, corresponding to an increase in the operating cycle time from 6% to 15%. The carbon weight utilization of the anode is improved by about 10%.

[0098] The initial weight of the anode according to the invention is about 3% lower than the prior art solution, due to the lower weight given by the difference between the volume of the slots according to the invention and the volume of the prior art slots (V2-V1).

[0099] According to the invention, due to the combination of reduced anode scrap thickness and reduced anode weight, the costs of scrap recycling are reduced by about 35% compared to prior art solutions.

[0100] The volume V2 of the connecting plate reduces the anode weight of each hole by: (9.557-5.890) dm 3 *1.6kg / dm 3 = 5.867 kg. 5.867 kg*4 (4 holes) = 23.46 kg, or about 3% less anode weight than prior art anodes.

[0101] The yield based on the weight of the anodes according to the invention is 6% to 15% higher than that of anodes of the same size according to the prior art. This corresponds to an average increase in the life cycle of the anodes from two days to three days, which is equivalent to an increase in the cycle time from 6% to 10% compared to the cycle time of the anodes according to the prior art. This corresponds to an average reduction in the scrap recycling costs of 35%.

[0102] Additional positive effects of the anode according to the invention resulting from the size of the holes and stubs are a larger contact area, better current distribution and a reduction in the voltage drop across the anode by about 50 to 80 mV.

Claims

1. A support assembly (12) for supporting a pre-baked anode (14) of a Hall-Héroult cell (10) for the production of primary aluminium, comprising an anode beam (16), a yoke (20) made of steel supported by the anode beam (16), and a plurality of short columns (22), the yoke (20) having a plurality of individual arms (20a), wherein each short column (22) welded to the lower end of a corresponding arm (20a) of the yoke (20) has a characteristic diameter (D3), the support assembly being characterized in that it further comprises a plurality of connection plates (24) made of steel, wherein each connection plate (24) is arranged at the lower end of a corresponding short column (22) and has a diameter (D4), and wherein the ratio between the diameter (D4) of the connection plate and the diameter (D3) of the short column is between 1 and 3.5 (1 < D4 / D3 ≤ 3.5), preferably between 1.5 and 3 (1.5 ≤ D4 / D3 ≤ 3).

2. The support assembly according to claim 1, wherein: The connection plate (24) is welded to the short column (22).

3. The support assembly according to claim 1, wherein: The connection plate (24) and the corresponding short column (22) form a single body.

4. A support assembly according to any one of the preceding claims, wherein: The connection plate (24) has a cylindrical outer surface.

5. A support assembly according to any one of claims 1 to 3, wherein: The connection plate (24) has a frustoconical outer surface.

6. A support assembly according to any one of the preceding claims, wherein: The connection plate (24) has a knurled outer surface.

7. The support assembly according to any one of the preceding claims, comprising a plurality of cast iron rings (26), wherein each ring (26) comprises a tubular body (26a) internally fastened to the connection plate (24) and a plurality of fins (26b) radially protruding outwardly from the body (26a), the plurality of fins (26b) having axial and inclined extensions for connection to the anode (14).

8. The support assembly according to claim 7, wherein: The number of the fins (26b) is from 11 to 30.

9. A support assembly according to any one of the preceding claims, wherein: The connection plate (24) is a disc welded to the lower end of the short column (22), and the height of the connection plate partially overlaps the height of the short column.

10. A support assembly according to any one of claims 1 to 8, wherein: The connection plate (24) is a disc welded to the lower end of the short column (22), and the height of the connection plate completely overlaps the height of the short column.

11. A support assembly according to any one of claims 1 to 8, wherein: The connection plate (24) is a disc welded to the lower end of the short column (22) and is completely located below the short column.

12. The support assembly according to any one of the preceding claims, comprising a transition joint (18), one side of the transition joint (18) being welded to the lower end of the anode beam (16) and the other side being welded to the yoke (20).

13. An anode assembly, comprising: - the support assembly (12) according to any one of claims 1 to 12; and - an anode (14) fastened to the support assembly (12).

14. The anode assembly according to claim 13, wherein: The ratio (D4 / H2) between the diameter (D4) of the connection plate (24) and the characteristic depth (H2) of the corresponding slot (14a) is between 1.92 and 10 (1.92 ≤ D4 / H2 ≤ 10).

15. A cover assembly, comprising: - the support assembly (12) according to any one of claims 1 to 12; and - A cover (28) applied to the support assembly to cover the transition area between the studs (22) and the connecting plates (24).

16. An anode and cap assembly comprising: - A support assembly (12) according to any one of claims 1 to 12; - an anode (14) fastened to said support assembly (12); as well as - A cover (28) applied to the support assembly to cover the transition area between the studs (22) and the connecting plates (24).

17. An electrolytic cell (10) for producing primary aluminium, comprising an anode assembly according to claim 13 or 14.

18. An electrolytic cell (10) for producing primary aluminium comprising an anode and cover assembly according to claim 16.

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