RU2294986C2 - Aluminum cell leakage limiting device - Google Patents

Abstract

FIELD: production of aluminum by electrolysis, namely device for limiting leakage of exhaust gases from aluminum cell.

SUBSTANCE: device for limiting leakage of gases from aluminum cell is provided with members for preventing gas leakage having pass through openings for insertion of anode tie rods. Device includes at least one holder that may embrace anode tie rod wholly or partially, at least one sealing flexible body arranged along the whole perimeter of holder or along part of perimeter. Said sealing flexible body is designed for closing the whole free space between inner edge of said opening and anode tie rod or only part of said space.

EFFECT: improved fluid-tightness of apparatuses for collecting exhaust gases in aluminum cells.

16 cl, 10 dwg

Description

Technical field

The present invention relates to the production of aluminum by melt electrolysis. In particular, it relates to means for retaining waste gaseous products released during electrolysis.

State of the art

Aluminum metal is produced industrially by melt electrolysis, i.e. by electrolysis of alumina dissolved in a bath of molten cryolite, called an electrolyte bath, using a method known as the Hall-Heroux method. The electrolyte bath is contained in tanks called “electrolysis baths” and includes a steel casing lined internally with refractory and / or insulation materials and a cathode device located at the bottom of the electrolysis bath. Anodes of carbon material are partially immersed in an electrolyte bath. The entire installation, consisting of an electrolysis bath, anodes and an electrolyte bath, is called an electrolyzer.

As a result of the electrolysis reaction, secondary reactions and the action of high operating temperatures, off-gases (gaseous wastes) are released, which primarily include carbon dioxide and fluorides. The emission of these exhaust gases into the atmosphere is strictly controlled and regulated, not only with regard to the atmosphere in the electrolysis shop due to the requirements for the working conditions of personnel working near electrolyzers, but also from the point of view of pollution of the external atmosphere. Legislation of many states in the field of environmental protection imposes restrictions on the amount of gaseous waste emitted into the atmosphere.

Currently, there are solutions that allow sufficiently reliable and satisfactory removal, collection and treatment of these exhaust gases. A widespread solution is to equip the electrolysers with devices for trapping exhaust gases. Such a device closes the electrolyzer and contains means of confinement (enclosure in the shell), which include, in particular, a shelter and means for suction and chemical treatment of exhaust gases. Known methods for treating exhaust gases include, in particular, trapping fluoride gases by reaction with alumina. The shelter includes access means, such as covers, usually made removable (movable), and a work hatch that allows you to interfere with the operation of the cell.

The shelter device limits the closed suction zone, limited in size and located under vacuum compared with the surrounding atmosphere, which allows efficient extraction of exhaust gases. Thus, in the most modern industrial installations, a capture coefficient in the continuous mode of more than 97% is achieved, while the level of emissions of fluoride gaseous products into the atmosphere is much lower than the regulated limits.

As a rule, the anodes are connected to the current-carrying bus located outside the capture device through metal rods that pass inside this device through the openings made in it. The free space (or “gap”) left by the rods in these holes is not sealed so as not to interfere with the horizontal and vertical movements of the metal rods. Vertical movements are carried out most often and allow, in particular, to compensate for the consumption of anodes during electrolysis. Horizontal movements are usually associated with operations to replace spent anodes.

US Pat. No. 5,128,012 discloses, for example, a device for closing the anode metal casing of an Soderberg type electrolytic cell (with a self-baking anode), designed to limit the emission of flue gas by-products from the firing into the surrounding atmosphere. The anode device of the electrolyzer described there is equipped with holding means having passage openings for inserting the anode pins. However, this document only provides that the pins are inserted into said holes and moved vertically therein.

In electrolyzers with prebaked anodes, the free spaces between the anode rods and the inner edge of the holes for the passage of these anode rods represent a gap in the bounding shell, which is not very important for each anode rod, but becomes essential for the entire set of anodes in the electrolyzer, and even more so for an electrolysis series of several hundred electrolyzers.

Disclosure of invention

The present invention provides a leakage limiter configured to reduce a gap in the bounding shell that occurs in the holes for the passage of the anode rods. More specifically, the leakage limiter according to the invention is intended to limit the passage of air and exhaust gases between the inner and outer spaces of the electrolysis trapping device for producing aluminum by melt electrolysis through the holes for the passage of the anode rods.

The leakage limiter in the electrolyzer according to the invention is characterized in that it comprises at least one holder configured to cover all or part of the anode rod, and at least one flexible sealing body located along the whole or part of the perimeter (circuit ) holder and designed to overlap all or part of the free space between the inner edge of the holes for the passage of the anode rod and the anode rod itself.

A flexible body provides a certain tightness around the anode rod and allows to maintain this tightness due to the flexibility of such a body, despite the inevitable changes in the position of the rod. In particular, the present invention allows to substantially limit gas exchange through said free space.

The holder is preferably made in the form of a socket to simplify the design of the leakage limiter and allows you to insert the anode rod from the side through the hole in this socket.

The present invention also provides an electrolytic cell comprising at least one leakage stopper in accordance with the present invention.

The present invention will be more apparent from the following detailed description of an embodiment with reference to the accompanying drawings.

Figure 1 is a cross-sectional view of a typical electrolytic cell for aluminum production.

Figure 2 is a simplified perspective view of part of a typical electrolytic cell for the production of aluminum, (a) without a leak limiter and (b) with a leak limiter according to the invention.

3-5 illustrate leakage arresters according to the invention.

6 illustrates a view of a U-shaped brush of a leak stop in accordance with one embodiment of the invention.

FIG. 7 illustrates a cross-section along the I axis of the U-shaped brush of the leak stop shown in FIG.

Fig. 8 illustrates a cross-section I'-C 'of the leakage limiter shown in Fig. 5.

Figures 9 and 10 illustrate insertion options of the anode rod into leakage stoppers according to the invention.

As shown in FIG. 1, an electrolytic cell (1) for aluminum production by the Hall-Heroux method typically comprises an electrolysis bath (10), anodes (2) supported by fasteners, typically comprising a rod (3) and anode holder bracket (4) and mechanically and electrically connected to the anode frame (5) by means of a connection (6). The anode rod (3) usually has a substantially rectangular or square section. The electrolysis bath (10) contains a steel casing (7), elements (8) of the inner lining and a cathode device (9). The lining elements (8) and the cathode device (9) form a crucible inside the electrolysis bath (10), which is adapted to contain the electrolyte bath (11) and the liquid metal layer (12).

The electrolyzer (1) also contains a metal supporting structure (13), on which, in particular, the anode frame (5) and an exhaust gas capture device containing means for holding (14, 15) containment and restricting the enclosed inner space (16) are supported, in particular, in a movable manner. The retention means typically comprise removable covers (14) and a fixed cover (15).

As shown in FIG. 2 (a), the capture device comprises openings (17) configured to allow free passage of the anode rod (3). This hole is most often made in the form of a serrated notch to ensure insertion of the anode rod. As a rule, anodes are inserted into or removed from the electrolyzer by insertion from the side after removal of one or more covers (14). As a result, the hole (17) is made in such a way that it enables the insertion of the rod (3) of the anode (2) from the side, with or without its longitudinal movement, that is, with or without its movement along the main axis of the cell.

Figure 2 (b) schematically shows the positioning of the leakage limiter (20) according to the invention in the hole (17) for the passage of the anode rod.

The leakage limiter (20) of the electrolyzer (1) for the production of aluminum, equipped with holding means (14, 15) having passage openings (17) for inserting the anode rods (3), is characterized in that it contains at least one holder ( 21), configured to cover all or part of the anode rod, and at least one flexible sealing body (30, 30a, 30b, 30c) located along the whole or part of the perimeter (23) of the holder (21) and designed to overlapping all or part of the free space between the inner edge (18) of the hole (17) and anode rod (3).

The holder (21) may take various forms, such as substantially straight, curved, or others. In addition, the holder (21) can be formed by several elements.

In a preferred embodiment of the present invention, said holder or holders (21) have an opening or “cutout” (26) that can be inserted laterally into the anode rod (3). The opening (26) is usually U-shaped or made in the form of a three-sided frame. Said sealing body or sealing bodies (30, 30a, 30b, 30c) are located along the inner perimeter (23) of the opening (26).

In this embodiment, the leakage limiter (20) covers at least three sides of the anode rod (3). The sealing body (30) may be shaped to also overlap the fourth side of the rod. If necessary, the leakage limiter (20) may include an additional blocking element (20 ') made movable or removable with the possibility of limiting leaks through the fourth side after the insertion of the rod. This additional overlapping element (20 ') may comprise a holder (21') equipped with a flexible sealing body (30 '). This additional element can be mounted, if necessary, on a fixed cover (15) or on a movable cover (14) located next to the anode rod.

Figure 3 shows the case when the sealing body is formed by one element (30). Figure 4 shows the case when the sealing body is formed by three separate elements located next to each other (30a, 30b, 30c).

As shown in FIG. 5, the sealing body is adjacent to the anode rod, but is not necessarily in contact with it. It can be separated from the rod by a distance of several millimeters, usually 2 or 3 mm, without substantially breaking the tightness achieved by the device according to the invention.

A flexible sealing body may be formed by any flexible element configured to effectively overlap all or part of said free space. It can be made, for example, of threads, strips (petals), spongy bodies or flexible (soft) tubes, or any combination thereof. It may be metallic or non-metallic.

The flexible sealing body (30) is preferably adapted to resist the atmosphere of the interior space (16) of the electrolyzer and to maintain its mechanical properties when exposed to temperatures reached in this medium.

The flexible sealing body (30) is preferably formed by a bundle of metallic and / or non-metallic threads. The Applicant has determined that the bundle of filaments maintains a certain tightness around the anode rod due to the density of the filaments, and that this tightness is maintained due to the flexibility of the filaments, despite the inevitable changes in the position of the rod. The threads also ensure good tightness, regardless of surface defects of the anode rod.

As noted, a satisfactory result is achieved using stainless steel threads. Sealing bodies made of such threads are well resistant to mechanical stresses under the action of the anode rod during its movements and have good flexibility.

The strands of the bundle (30) are located close enough to each other in order to ensure the loss of pressure between the outer space and the inner space of the capture device. As it was found, it is enough to provide a linear density of 100-1000 threads per centimeter along the perimeter. Typically, the thickness of the beam exceeds 0.5 cm. The diameter of the threads is usually in the range from 0.1 to 1 mm. The angle α of the opening of the bundle of metal filaments is usually from 0 to 45 °, and preferably from 0 to 30 °. The length L of the metal threads protruding from the holder is usually 1 to 10 cm.

According to a preferred embodiment of the present invention, at least one flexible sealing body (30, 30a, 30b, 30c) is secured to a second holder or “frame” (32) movable with respect to the holder (21), i.e. made (s) with the possibility of movement relative to the holder (21).

In this embodiment, the holder (21) usually contains an elongated slot (22) along its inner perimeter (23), and a frame (32) is movably mounted in this slot. In this case, the frame (32) and the flexible sealing body (30, 30a, 30b, 30c) form a movable unit or “pull-out unit” (31), which improves the self-positioning of the sealing means when moving the anode rod. The movement of the assembly (31) of the frame / sealing body is essentially perpendicular to the anode rod (3).

In this embodiment of the present invention, the flexible sealing body (30, 30a, 30b, 30c) and the frame (32) are preferably made of non-magnetic materials in order to avoid creating a magnetic force in the presence of the intense magnetic field that is present around the cell, which avoids blocking the aforementioned movement of this magnetic field. For example, the frame (32) is preferably made of aluminum or an aluminum alloy, and the threads are made of non-magnetic stainless steel.

The mobility of the elements (31) in the holder (21) can facilitate their maintenance or replacement in case of wear or damage.

Preferably, the leak limiter (20) further comprises at least one connecting element (25) between the holder (21) and one or each frame (32) for controlling the movement of said or said sealing bodies (30, 30a, 30b, 30c ) relative to the holder (21). Typically, the connecting element is fixed to the frame (32). At least one connecting element is, preferably, an elastic element, such as a spring or elastic plate, to ensure self-positioning of the brush or brushes relative to the anode rod (3). If necessary, you can use earrings and / or guiding means, if necessary, in combination with the mentioned or mentioned elastic elements.

5-8 show a preferred embodiment of the present invention, in which the sealing body (30, 30a, 30b, 30c) is made of threads fixed in one movable frame (32), made with the possibility of movement relative to the frame (21).

FIG. 5 (b) shows a longitudinal sectional view of the stopper shown in FIG. 5 (a), with the frame / thread assembly (31) called a “brush” and partially located inside the holder (21). The profile of the anode rod (3) is shown by a dashed line. Figure 6 separately shows the brush (31) in its main plane (a) and side (b).

The insertion of the anode rod (3) at the side is usually carried out along the axis I-I 'shown in Figures 5 and 6. Figures 9 and 10 show two options for inserting the anode rod. Fig.9 corresponds to the case of insertion in one direction. Figure 10 corresponds to the case of insertion in two directions with the movement of the leakage limiter relative to the cell.

The holder (21) and the frame (32) are preferably made of metal to provide sufficient mechanical strength. Preferably, aluminum and aluminum alloys that are non-magnetic can be used.

The rigidity of the holder (21) allows, in addition, the operator, if necessary, to lean his foot on the leak limiter without the risk of damage.

The leak limiter (20) can be fixed rigidly or movably in the electrolyzer and, in particular, on any element of its structure or on the capture device. For this, the holder (21) preferably comprises means (24) for attaching it, preferably detachable, to the electrolyzer. A detachable fastening, for example, performed using bolts and nuts (29), makes it easy to remove the leak stop without touching the anode.

Although in many cases a rigid mount is sufficient, the movable mount provides an additional degree of freedom to the leak limiter and makes it easier to take the appropriate position relative to the anode rod. This additional degree of freedom is especially important when the hole (17) for the passage of the anode rod is large compared to the cross section of the rod, and provides the latter with a large backlash during installation and / or use.

This degree of freedom also matters when the hole (17) has a more complex shape than a simple serrated notch, and when the anode rod (3) is inserted into the hole (17) in two directions, that is, when the rod is installed, it is moved in the longitudinal and transverse directions relative to the main axis of the cell, as shown in Fig.10. In this case, the leakage limiter typically has an open position (FIG. 10 (a)) and a closed position (FIG. 10 (b)). In this case, the leak limiter (20) preferably contains one or more additional overlapping elements (33, 34), such as a plate, designed to maintain the tightness of the limiter during its movements. These additional elements can be made stationary or movable. If necessary, the movable leakage limiter (20) can interact with one or more fixed overlapping elements (20 ') to maintain the tightness of the device during its movements. The movements of the leakage limiter can be guided by a guide member (35), such as a rail.

When the leakage limiter (20) contains metal elements, in particular near the anode rod, such as a metal holder or metal threads, it is preferable to electrically isolate the leakage limiter from the electrolyzer in order to avoid short circuit during manipulation (control) of the anode. Such insulation can be achieved by placing an electrical insulator (27, 28, 28 ') between the leakage limiter and the electrolyzer. For example, as shown in Fig. 8, the leakage limiter (20) is isolated from the electrolyzer (1) by means of an insulating plate (27) installed between the holder (21) and the holding means (15), and by means of the tube (28) and the washer (28 ') mounted between the fastening means (29) and the holding means (15).

The simplicity of the sealing mechanism of the leakage limiter according to the invention provides it with sufficient resistance to environmental conditions and, in particular, to the presence of alumina dust or a crushed electrolyte bath, which can block or interfere with the operation of mechanisms containing rotary or rotary axes.

The advantage of the leakage limiter according to the invention is also that it occupies a small volume. The total thickness of the limiter according to the invention is usually only 3 to 4 cm, which makes it easy to position it between the anode frame (5) and the cover (15).

An advantage of the present invention is also that it does not require either manual operations or a special drive device, which makes its use simpler and increases its reliability.

List of Symbols

1 Electrolyzer

2 Anodes

3 Means of fastening and supply of current (rod)

4 Means of fastening and current supply (bracket)

5 anode frame

6 Rod connection with anode frame

7 Casing

8 Inner lining

9 Cathode device

10 Electrolysis bath

11 Electrolyte bath

12 Liquid aluminum

13 Metal supporting structure

14 Retention tool (removable cover)

15 Retention aid (fixed cover)

16 Closed interior

17 hole for the passage of the anode rod

18 The inner edge of the hole for the passage of the anode rod

20 Leakage limiter

20 'Optional overlapping element

21, 21 'Leak limiter holder

22 Extra Long Slit

23 Internal perimeter of the holder

24 Mounting Tool

25 Connecting element

26 Aperture limiter

27 Electrical insulator (plate)

28 Electrical insulator (tube)

28 'Electrical insulator (washer)

29 Bolt and nut

30, 30a, 30b, 30 s, 30 'Flexible sealing body

31 Socket / movable sealing body

32 Rim

33, 34 Additional overlapping element

35 Guide means

Claims (16)

1. The leakage limiter (20) of the electrolyzer (1) for the production of aluminum, equipped with holding means (14, 15) having passage openings (17) for inserting the anode rods (3), characterized in that it contains at least one holder ( 21), configured to cover all or part of the anode rod, and at least one flexible sealing body (30, 30a, 30b, 30c) located along the whole or part of the perimeter (23) of the holder (21) and designed to cover the whole or part of the free space between the inner edge (18) of the hole (17 ) and the anode rod (3), and the fact that the holder or holders (21) have an aperture or cutout (26), configured to insert the anode rod (3) on the side. 2. Leakage limiter (20) of claim 1, characterized in that said or each of said flexible sealing bodies (30, 30a, 30b, 30c) is formed by at least one element selected from threads, strips, spongy bodies, flexible tubes or combinations thereof. 3. Leakage limiter (20) according to claim 1, characterized in that said or each of said flexible sealing bodies (30, 30a, 30b, 30c) is formed by a bundle of metallic and / or non-metallic threads. 4. Leakage limiter (20) according to claim 3, characterized in that the said bundle of threads is made of stainless steel. 5. Leakage limiter (20) according to any one of claims 1 to 4, characterized in that at least one flexible sealing body (30, 30a, 30b, 30c) is mounted on a second holder or “frame” (32), movable ( th) in relation to the holder (21). 6. Leakage limiter (20) according to claim 5, characterized in that said flexible sealing body (30, 30a, 30b, 30c) and the frame (32) are made of non-magnetic materials. 7. Leakage limiter (20) according to claim 5, characterized in that it further comprises at least one connecting element (25) between the holder (21) and said or each of said frames (32) for controlling the movement of said or mentioned sealing bodies (30, 30a, 30b, 30c) relative to the holder (21). 8. Leakage limiter (20) according to claim 6, characterized in that it further comprises at least one connecting element (25) between the holder (21) and said or each of said frames (32) for controlling the movement of said or mentioned sealing bodies (30, 30a, 30b, 30c) relative to the holder (21). 9. Leakage limiter (20) according to claim 7 or 8, characterized in that at least one connecting element (25) is elastic. 10. The electrolyzer (1) for the production of aluminum, characterized in that it contains at least one leakage limiter (20) according to any one of claims 1 to 9. 11. The electrolyzer (1) according to claim 10, characterized in that said or each of said leakage limiters (20) is rigidly fixed in the electrolyzer. 12. The cell (1) according to claim 10, characterized in that said or each of said leakage limiters (20) is movably fixed in the cell. 13. The electrolyzer (1) according to claim 12, characterized in that said or each of said leakage arresters (20) contains at least one additional overlapping element (33, 34) designed to maintain the tightness of each restrictor (20) when it movements. 14. The electrolyzer (1) according to any one of claims 10 to 13, characterized in that said or each of said leakage limiters (20) is fixed in the electrolyzer in a removable manner. 15. The electrolyzer (1) according to any one of claims 10 to 13, characterized in that at least one electrical insulator (27, 28, 28 ′) is installed between the electrolyzer and at least one leak limiter (20). 16. The electrolyzer (1) according to 14, characterized in that between the electrolyzer and at least one leakage limiter (20), at least one electrical insulator (27, 28, 28 ′) is installed.

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