WO2006010818A2 - Scraper for a drilling taper of an electrolytic cell solution crust for use in aluminium production - Google Patents

Abstract

The invention concerns a scraper (40) for a drilling member (33) such as a taper, for forming an opening in a crust of alumina and of a solidified igneous electrolytic solution by a reciprocating movement along an axis of translation T. The inventive scraper (40) is characterized in that it comprises a plurality of fingers (42) arranged about an axis of reference S designed to merge with said axis of translation T in use, so as to clear a space (44) between the fingers and the drilling member, and in that each finger (42) includes at least a scraping member (43) projecting towards the drilling member (33). The inventive scraper eliminates formation of an envelope at the surface of the drilling member which can block the member in the scraper.

Description

 SCRAPER OF AN ORGAN FOR PIERCING A BATH CRUST OF AN ELECTROLYSIS CELL INTENDED FOR PRODUCTION

ALUMINUM

Field of the invention

The invention relates to electrolysis cell equipment for the production of aluminum by igneous electrolysis according to the Hall-Héroult method. It relates in particular to devices for piercing solidified bath crusts of said electrolysis cells.

State of the art

The operation of an aluminum production cell by igneous electrolysis of alumina dissolved in a cryolite bath causes a permanent evolution of the composition of the bath. On the one hand, the alumina is consumed by the electrolysis reactions and, on the other hand, the quantity and the composition of the bath are progressively modified by secondary mechanisms, such as the absorption of constituents of the cryolite by the cell walls or the decomposition of fluorinated constituents by anode effects. It is therefore necessary to regularly add alumina and bath compounds, such as cryolite (Na ₃ AlF ₆ ) or aluminum fluoride (AIF ₃ ), in order to stabilize the operating parameters of the cell.

Alumina and bath compounds are generally introduced into the bath in powder form. In order to be able to introduce the pulverulent material into the electrolyte bath, the electrolysis cells are equipped with one or more distributors of pulverulent materials associated with a device for piercing the crust of alumina and fixed electrolyte which covers the bath surface in normal operation. The piercing device generally comprises a jack and a piercing member (often called "piercer", "plunger" or "chisel") attached to the end of the stem of the cylinder. The breaker, usually placed vertically, is lowered by activation of the cylinder and breaks the crust of alumina and solidified bath. The stitching devices also include, in general, a scraper for removing solidified bath deposits that tend to form on the stingers.

French patent FR 2,455,093, FR 2,487,386 (corresponding to US Pat. No. 4,431,491) and FR 2,527,647 (corresponding to US Pat. No. 4,437,964) in the name of Aluminum Pechiney describe point feed devices made of alumina. an electrolysis cell for the production of aluminum. These devices, known under the name of "lancing-doser" when they are grouped, comprise means for supplying alumina and a device for piercing the crust of alumina and solidified bath. The piercing device is provided with a scraper which closely encloses the piercer.

However, the solidified bath sometimes forms an envelope on the surface of the piercing member which can block the member in the scraper. The applicant has sought ways to avoid this inconvenience.

Description of the invention

The subject of the invention is a scraper of a piercing member (such as a piercer, a plunger or a chisel) that can be used to form an opening in a crust of alumina and solidified bath of an igneous electrolysis cell. by a back and forth movement of the piercing member along a translation axis T.

The scraper according to the invention is characterized in that it comprises at least three fingers arranged around a reference axis S intended to coincide with said translation axis T in use so as to form a space, called "relief", between the fingers and the piercing member, and in that each finger comprises at least one scraper member projecting towards the piercing member. The applicant has had the idea of breaking down the scraper into a set of scraping members, separated from one another, to reduce the contact surface with the scraper and to arrange the scraping members on a plurality of fingers angularly separated from each other. each other. This approach makes it possible to prevent the blocking of the piercing member by limiting the force required to disengage it in the event of accumulation of bath crust between the scraping members and the piercing member. In addition, the applicant has had the idea of substantially move the fingers of the piercing member of the piercing device to promote the accumulation of bath crust debris above the scraping members, rather than their insertion. between the sheath and the piercing member. The accumulated debris can easily be evacuated by the space formed by the gap between the scraper fingers.

The invention is particularly suitable for electrolysis cells intended for the production of aluminum.

The invention also relates to a drilling device for an aluminum production cell by igneous electrolysis and comprising a scraper according to the invention.

The invention also relates to a metering pusher for an aluminum production cell by igneous electrolysis and comprising a scraper according to the invention.

The invention further relates to a quilting and measuring device for an aluminum production cell by igneous electrolysis and comprising a scraper according to the invention.

The invention further relates to the use of the scraper according to the invention in an electrolysis cell for the production of aluminum by igneous electrolysis.

The invention is described in detail below with the aid of the appended figures. Figure 1 shows, in a simplified manner, a partial internal view of a typical electrolysis cell for the production of aluminum by igneous electrolysis, seen in vertical section.

Figure 2 gives a perspective view of a preferred embodiment of the pig according to the invention.

Figure 3 gives a side view of the scraper of Figure 2.

Figures 4 and 5 show sectional views of the scraper of Figure 2 according to the sectional planes shown in Figure 3.

Figure 6 is a perspective view of the wiper of Figure 2 attached to the end of a piercing device.

As illustrated in FIG. 1, an electrolysis cell (1) for the production of aluminum by igneous electrolysis, that is to say by molten salt electrolysis, comprises a tank (2), one or several anodes (3) - typically pre-formed anodes made of carbonaceous material - and pulverulent feed means (20, 30), which are generally attached to a superstructure (4) arranged above the vessel.

The electrolytic cell (2) comprises inner lining elements (not shown) and a cathode assembly (5) which form inside the tank (2) a crucible adapted to contain the electrolyte bath (7) and a sheet of liquid aluminum (6) when the cell is in operation. The anodes (3) are normally partially immersed in the liquid electrolyte bath (7) and the cells are conducted to form a crust of alumina and solidified bath (10) above the electrolyte bath.

The pulverulent feed means (20, 30) generally comprise a powder dispenser (20) and a piercing device (30). The pulverulent material dispenser (20) typically comprises a hopper (21) for containing a supply of pulverulent material, and a chute (22) attached to the bottom of the hopper and for conveying the pulverulent material to the vicinity. an opening (11) in the crust (10).

The piercing device (30) includes an actuator (31) and a piercing member (33) (often referred to as a "breaker", "plunger" or "chisel") attached to the end of the actuator stem, which is typically located in a sheath or sheath (32). The piercing member (33) is generally arranged to enter and exit the piercing device (30) through an opening at the free end (34) of the sheath or sheath (32). The piercing member (33) makes it possible to form an opening (11) in a crust (10) of alumina and bath solidified by a back and forth movement of the piercing member (33) along the a translation axis T, which is typically vertical or slightly inclined relative to the vertical. The cross section of the piercing member (33) is typically circular. The actuator (31) is typically a pneumatic actuator, such as a pneumatic cylinder. A scraper (40) ensures the cleaning of the piercing member during its movements back and forth.

A dispenser of powdery materials may be associated with one or more determined stitching devices or, conversely, a stitching device may be associated with one or more dispensers of powdered materials determined. The electrolysis cells are frequently provided with one or more devices comprising a distributor of pulverulent materials and a stitching device. These devices are known as stitching and feeding devices ("Crustbreaking and Feeding Device").

In operation, at least one opening (11) is formed (or possibly kept open) in said crust (10), between the anodes (3), with the aid of the piercing device (s) (30) and the pulverulent material is introduced into the bath electrolyte (7) through the opening (11) (or at least one opening when there are several).

The scraper (40) according to the invention comprises a plurality of fingers (42) arranged around a reference axis S intended to be coincident with said translation axis T in use. The fingers (42) are arranged to release a space (44), called "relief" between the fingers (42) and the piercing member (33). Each finger (42) comprises at least one scraper member (43) projecting towards the piercing member (33).

Figures 2 to 6 illustrate a preferred embodiment of a scraper according to the invention.

The scraper (40) according to the invention comprises at least three fingers (42) and preferably at least six fingers. The number of fingers is typically between 6 and 10 inclusive. The exemplary embodiment of the invention illustrated in FIGS. 3 to 6 comprises six fingers.

Offsetting (44) between the fingers (42) and the piercing member (33) - that is, the width E of the space between the inner surface (421) of the fingers (42) and the surface external side (331) of the piercing member (33) - is advantageously greater than 10 mm.

The length L1 of the fingers (42) is preferably greater than 100 mm.

The fingers (42) are arranged to form a gap, called "spacing", (422, 423) between them.

The cross-section of the fingers (42) is preferably substantially uniform over at least 50% of their length L1 in order to maintain, over a significant length, a spacing (422, 423) between the fingers sufficient to allow easy removal of crust debris baths torn off by scraping devices (43). The fingers (42) are preferably straight and parallel to the reference axis S of the scraper.

In order to allow efficient evacuation of bath scrap debris produced by scraping, the distance Cm between the points closest to the surface of the adjacent fingers is preferably greater than 10 mm, and more preferably greater than 20 mm, at least 50% of their length L1. In order to promote the evacuation of bath crust debris towards the outside of the scraper, the gap C between the adjacent fingers preferably increases away from the axis S, that is to say between the inside and outside the scraper, so as to form an opening that flares outward. In the example shown in Figure 5, the gap C increases between the inner end (425) of the fingers and their outer end (426). Preferably, the fingers (42) comprise at least a first (424) and a second (424 ') planar surface element arranged in such a way that the first surface element (424) of each finger and the second surface element ( 424 ') of an adjacent finger are facing each other and are inclined angularly relative to each other so as to form an opening which tapers outwardly of the scraper. With respect to said axis S, said facing surfaces (424, 424 ') are preferably angularly spaced apart by an angle α greater than 10 °, so as to form between the fingers a spacing (422, 423) sufficient to allow the evacuation debris from bath crust produced by scraping.

The center to center angular spacing β between the fingers is typically between 20 ° and 90 °.

Each doctoring member (43) is preferably arranged on the fingers (42) so as to release a space (45), called "scraping space", between the scraper member (43) and the piercing member ( 33). More specifically, each scraper member (43) has an end (431), called "scraping end", located at a determined distance D1 of said axis S so as to release said scraping space. The determined distance D1 is advantageously the same for all the scraping ends (431). The scraping space (45) is typically between 1 and 5 mm inclusive. The scraper distance D1 is smaller than the relief (44) (corresponding to a constant gap E in the embodiment illustrated in FIGS. 3 to 6). The scraper member (43) thus forms a projection turned on the side of the piercing member (33).

Advantageously, each scraper member (43) is located at the free end (420) of each finger (42).

According to an advantageous embodiment of the invention, the scraping end (431) takes the form of a concave surface. The length L2 of this surface, in the direction of the axis S, is typically between 10 mm and 50 mm, and more typically between 10 mm and 30 mm. The area of the concave surface is typically between 10 and 1000 mm ² . Said concave surface is typically parallel to the lateral outer surface (331) of the piercing member (33), i.e. it conforms to the shape of the lateral outer surface (331).

According to another embodiment of the invention, the scraper end (431) takes the form of a tip or an edge.

The fingers (42) are typically attached to a support member (41). The scraping members (43) are preferably arranged at a determined distance D3 of the support member (41) at least equal to 100 mm.

The scraper (40) is advantageously removable in order to be able to change it, in particular in case of damage or wear. In this case, the support element (41) typically comprises fastening means (410, 411), such as a flange or flange (410) provided with through holes (411). The fastening means (410, 411) make it possible, for example, to attach the scraper to a piercing device, typically to the end (34) of a sheath (or sheath) (32) from which the piercing member emerges (33). The support member or body (41) and the fingers (42) are typically in one piece.

The fingers (42) are typically made of steel to provide sufficient rigidity. Figures 4 and 5 illustrate various parameters of a scraper according to a preferred embodiment of the invention, wherein the fingers are straight and have a substantially uniform cross-section over more than 50% of their length L1, and for an organ drilling (33) of circular section. In these figures, R is the radius of the piercing member (33), D1 is said determined distance, D2 is the distance between the axis S and the central axis of the fingers (42) and E is said relief.

The scraper (40) according to the invention may advantageously equip the piercing devices (30) used in the igneous electrolysis aluminum production cells having a piercing member movable in translation along an axis T. In particular, it can advantageously equip the puncture-dosers for aluminum production cells by igneous electrolysis, such as those described above. The scraper (40) according to the invention can also equip the stitching and measuring devices, such as that described in patent EP 0 716 165 (corresponding to US Pat. No. 6,065,867) in the name of Aluminum Pechiney. In these latter devices, the piercing member further comprises measuring means, such as a thermocouple, or serves as a measuring means (it may serve for example as an electrical contact point to detect the contact with the thermocouple). organ and liquid electrolyte bath during its vertical movements).

Claims

1. Scraper (40) of a piercing member (33) of a piercing device (30) operable to form an opening (11) in a crust (10) of alumina and solidified bath of a cell igneous electrolysis (1) by a reciprocating movement of the piercing member (33) along a translation axis T, said scraper being characterized in that it comprises at least three fingers (42); ) arranged around a reference axis S intended to coincide with said translation axis T in use, so as to form a space (44), called "relief", between the fingers (42) and the piercing member ( 33), and in that each finger (42) comprises at least one scraper member (43) projecting towards the piercing member (33). 2. Wiper (40) according to claim 1, characterized in that the number of fingers (42) is between 6 and 10 inclusive. 3. Scraper (40) according to any one of claims 1 or 2, characterized in that the length L1 of the fingers (42) is greater than 100 mm. 4. Wiper (40) according to any one of claims 1 to 3, characterized in that the cross section of the fingers (42) is substantially uniform over at least 50% of their length L1. 5. Scraper (40) according to any one of claims 1 to 4, characterized in that the fingers (42) are straight and parallel to the reference axis S of the scraper. 6. Wiper (40) according to any one of claims 1 to 5, characterized in that the distance Cm between the nearest points of the surface of the adjacent fingers is greater than 10 mm over at least 50% of their length ll. 7. Wiper (40) according to any one of claims 1 to 6, characterized in that the gap C between the adjacent fingers increases away from the axis S, so as to form an opening that flares outwards. 8. Wiper (40) according to claim 7, characterized in that the fingers (42) comprise at least a first (424) and a second (424 ¹ ) planar surface elements arranged in such a way that the first surface element ( 424) of each finger and the second surface element (424 ') of an adjacent finger are facing each other and are inclined angularly with respect to one another so as to form an opening which flares outward from the scraper. 9. Wiper (40) according to claim 8, characterized in that, with respect to said axis S, said facing surfaces (424, 424 ') are spaced angularly from an angle α greater than 10 °. 10. Scraper (40) according to any one of claims 1 to 9, characterized in that the relief between the fingers (42) and the piercing member (33) is greater than 10 mm. 11. Scraper (40) according to any one of claims 1 to 10, characterized in that each scraper member (43) is located at the free end (420) of each finger (42). 12. Scraper (40) according to any one of claims 1 to 11, characterized in that the fingers (42) are fixed to a support member (41). 13. Wiper (40) according to claim 12, characterized in that the scraping members (43) are arranged at a determined distance D3 of the support member (41) at least equal to 100 mm. 14. Wiper (40) according to any one of claims 12 or 13, characterized in that the support member (41) comprises fixing means (410, 411). 15. A piercing device (30) for an igneous electrolysis aluminum production cell and characterized in that it comprises a wiper (40) according to any one of claims 1 to 14. 16. Poineur-doser for an aluminum production cell by igneous electrolysis and characterized in that it comprises a scraper (40) according to any one of claims 1 to 14. 17. Device for stitching and measurement for an aluminum production cell by igneous electrolysis and characterized in that it comprises a scraper (40) according to any one of claims 1 to 14. 18. Use of a wiper (40) according to any one of claims 1 to 14 in an electrolysis cell for the production of aluminum by igneous electrolysis.