EP0062605A2 - Device for the portion-like dosage of fluidisable bulk material - Google Patents

Abstract

A silo for storing alumina having a conical outlet at the bottom thereof is fitted with an exchangeable feeding unit mounted over the conical outlet opening. The feeding unit is adapted to close off the outlet opening when in the non-operative position. The feeding unit can take various forms and includes at least one injection nozzle for fluidizing the particulate material.

Description

The invention relates to a device for portion-wise feeding of a fluidizable bulk material from a silo, which is tapered at the bottom and provided with a closable outlet opening, to a reaction vessel, in particular alumina from a day silo, to a crust breakthrough of a melt flow electrolysis cell for the production of aluminum.

For the production of aluminum by melt flow electrolysis of aluminum oxide, this is dissolved in a fluoride melt, which consists largely of cryolite. The cathodically deposited aluminum collects under the fluoride melt on the carbon bottom of the cell, the surface of the liquid aluminum forming the cathode. Anodes which consist of amorphous carbon in conventional processes are immersed in the melt. At the carbon anodes, the electrolytic decomposition of the aluminum oxide produces oxygen, which combines with the carbon of the anodes to form Co ₂ and CO. The electrolysis takes place in a temperature range of approximately 940-970 ° C.

In the course of electrolysis, the electrolyte becomes poor in aluminum oxide. With a lower concentration of 1-2% by weight aluminum oxide in the electrolyte, there is an anode effect, which results in an increase in the voltage from, for example, 4-5 V to 30 V and above. Then, at the latest, the crust made of solid electrolyte material must be hammered in and the aluminum oxide concentration increased by adding new alumina.

The cell is usually operated periodically in normal operation, even if there is no anode effect. Also For each anode effect, the crust must be hammered in and the alumina concentration increased by adding new aluminum oxide, which corresponds to cell operation.

To operate the cell, the crust between the anodes and the side board of the electrolytic cell has been hammered in for many years and then new aluminum oxide has been added. This practice meets with increasing criticism because of air pollution in the electrolysis hall and the outside atmosphere. In the case of encapsulated electrolysis cells, however, maximum restraint of the process gases can only be guaranteed if the operation takes place automatically. After the crust has been hammered in, the alumina is either supplied locally and continuously according to the "point feeder" principle or not continuously over the entire longitudinal or transverse cell axis.

The known storage bunkers or alumina silos arranged on the electrolysis cells are designed in the form of funnels or containers with a funnel-shaped or conically tapering lower part. The content of the silos arranged on the cell generally covers one to two times a day, so they are also called day silos.

The supply of alumina from the silo to a breakthrough in the crust covering the molten electrolyte takes place in known devices by opening a flap which is pivoted for charging, or according to other systems with metering screws, metering cylinders or the like.

These metering devices have the disadvantage that mechanically movable parts must be installed in the electrolytic cell. As a result, they are subject to the effects of the furnace atmosphere with their heat and dust pollution, which requires more or less extensive maintenance different. In many embodiments, there is also the risk of mechanical damage, in particular when changing the anode.

The inventors have therefore set themselves the task of creating a device for the continuous dosing of a fluidizable bulk material, which has no mechanically movable elements, and which can be installed as a compact, robust unit in a silo, the simple structure of which is inexpensive to manufacture and extensive To ensure freedom from maintenance.

• - einem Siphon, der über einen Chargierschacht zur Austrittsöffnung führt, und
• - einer Blasdüse pro Siphon mit oberhalb des unteren Rands der Siphonscheidewand mündender Düsenaustrittsöffnung.

The object is achieved according to the invention by an interchangeable charging unit which is arranged directly above the outlet opening in the silo and closes it in the resting phase, with at least

• - a siphon which leads to the outlet opening via a charging shaft, and
• - One blowing nozzle per siphon with a nozzle outlet opening opening above the lower edge of the siphon partition.

According to a first, one-stage embodiment, the outer walls of the siphon are formed by a base plate resting on the conical lower part of the silo and the charging shaft. These one-piece or welded outer walls surround the silo outlet opening in the form of a trough.

The bottom plate of the charging unit lies over the entire surface on the conical lower part of the silo and is welded, riveted or preferably screwed to it. A screwed bottom plate has the advantage that the fasteners can be loosened at any time with a few hand movements, and the charging unit can be lifted upwards thanks to the emptied silo can be removed.

The charging shaft and thus the outlet opening of the silo is closed with a cover plate. Its side walls protrude into the trough formed by the base plate and charging shaft and form the siphon partition. The fluidizable bulk material solidifies in the lower area of the siphon due to the silo pressure. In order to get into the charging shaft, the bulk material would have to flow upwards around the siphon partition. The height of the charging shaft is selected so that the bulk material cannot flow to the upper edge of the shaft due to the static pressure when the silo level is sufficient.

The geometric shape of the outlet opening and the charging shaft is adapted to the impact device used. When adding punctiform alumina, the opening is expediently round, square or rectangular. The inner wall of the charging shaft preferably corresponds exactly to the outlet opening.

The part of the cover plate which covers the inlet opening of the charging shaft is preferably flat or slightly concave for production-related and economic reasons, although it has any practical geometric shape, such as e.g. a cone, pyramid or saddle roof.

The inner diameter of the blow nozzles can be, for example, 4-10 mm, with an outlet opening that has the same diameter or is narrowed down to 1 mm. In the case of round or square silo outlet openings, which are preferably used in particular for the punctiform alumina addition, the number of blowing nozzles is expediently 3 to 6. In the case of elongated outlet openings for central or transverse operation, there are, for example, 3 nozzles on the long sides arranged, while the end faces are without nozzles.

In the resting phase, i.e. if there is no charging, but there is sufficient aluminum oxide in the silo, this increases by an amount determined by the flow properties of the filling material and the geometry of the charging unit in the space between the cover plate and the shaft. The flow properties can be described, for example, by the angle of repose. However, the charging system is not sensitive when bulk goods with different flow properties are used. The distance between the upper edge of the charging shaft and the lower edge of the cover plate is selected so that the variation in the height of the rise as a function of the bulk material properties is smaller than this distance.

In the working phase, compressed air is introduced into the solidified bulk material through the blowing nozzles arranged in the siphon. The applied pressing pressure is - also in the following design variants with the same blowing nozzles - preferably 1-10, in particular 3-6 bar. The bulk material fluidized by the compressed air can now flow under the action of the silo pressure over the upper edge of the charging shaft and fall into it. In a melt flow electrolysis cell for the production of aluminum, the alumina falls into the area of the crust.

If the compressed air supply is interrupted, the fluidized bulk solidifies immediately, the material flow cannot be maintained by the silo pressure.

When using a single-stage charging unit with a siphon, the discharge quantities of the bulk material fluctuate by a maximum of 5%.

The batch quantity can be kept constant much better when two single-stage charging devices are connected in series. In the working phase, with the upper blowing nozzles switched on, the bulk material initially flows from the silo into a charging chamber located directly below the upper siphon. In relation to the lower, second charging unit, this charging room is the silo for the bulk material. If the upper blowing nozzles are switched off and the lower blowing nozzles are switched on, the bulk material located in the charging chamber can flow out through the outlet opening.

The ventilation when filling or the ventilation when emptying the charging space can be of essential importance.

With two charging units connected in series, the fluctuations in the quantity of bulk material charged can be reduced to around 1%, assuming a homogeneous quality of the bulk material.

A further improvement of the device according to the invention, in particular with regard to the structural simplification, results in the formation of a charging space which is constantly open at the top and which merges into a siphon at the bottom. A little below the inlet opening preferably at least one blowing nozzle opens into the charging space.

In the resting phase, the charging room is completely filled with bulk goods. In the working phase, air is blown through the blower nozzle α for a certain time and with a certain pressure. The bulk material flows through the siphon into the charging shaft. Although bulk material flows from the silo into the charging room during the entire work phase, the charging accuracy is surprisingly below 1%. For this reason, it is normally not necessary in practice to provide the inflow opening to the charging space with a closure system that can be activated during the working phase.

In all embodiments of the exchangeable charging unit, care must be taken to ensure that the angle of repose of the material which is most difficult to fluidize is smaller than the slope of the walls of the charging space or of the conical lower part of the silo. Otherwise the requirements regarding charging accuracy cannot be met. Therefore, the slope of the corresponding walls is at least 45 °.

The alumina flowing into the charging shaft is fed to the crust breakthrough in free fall. This inflow can be made more precise if an outflow pipe is arranged below the charging shaft. However, this is an increased susceptibility to mechanical damage.

• - Keine mechanisch oder sonstwie bewegten Elemente, daher verschleissunempfindlich in staubbelasteter Umgebung.
• - Vor Hitze und mechanischer Beschädigung weitgehend geschützt, weil im Silo eingebaut.
• - Kompakte, robuste und wartungsfreie Einheit, im Reparaturfall durch den entleerten Silo nach oben leicht ausbaubar.
• - Einfacher, kostengünstig herzustellender Aufbau.
• - Automatisierungsfreundlich.
• - Unabhängig von den Fliesseigenschaften des eingesetzten Schüttgutes.
• - Keine Undichtigkeitsprobleme in Ruhestellung.

All of the devices according to the invention are distinguished by the following advantages:

• - No mechanically or otherwise moving elements, therefore insensitive to wear in dusty environments.
• - Largely protected against heat and mechanical damage because it is installed in the silo.
• - Compact, robust and maintenance-free unit, easily removable upwards in the event of a repair due to the emptied silo.
• - Simple, inexpensive to manufacture.
• - Automation friendly.
• - Regardless of the flow properties of the bulk material used.
• - No leakage problems at rest.

• - Entfernung der Tonerdedosierklappen,
• - Verschliessen der Siloöffnungen bis auf die Austrittsöffnungen,
• - Einbau der Chargiereinheiten und Verlegen der Druckluftleitungen,
• - Umbau der Brechbalken zu punktförmig arbeitenden Meisselbrechern,
• - Anpassung der Pneumatiksteuerung,
• - Anschluss an Prozessrechner.

Another advantage of using a charging unit for supplying alumina to aluminum melt flow electrolysis cells is that existing means of operation cells can be converted to point operation, preferably with two units, without high costs. It is not necessary to replace the entire anodic part of the cell with considerable investment. Rather, only the following measures need to be taken:

• - removal of the alumina dosing flaps,
• - closing the silo openings except for the outlet openings,
• - Installation of the charging units and laying of the compressed air lines,
• - Conversion of the crushing beams to point-operated chisel breakers,
• - adjustment of the pneumatic control,
• - Connection to process computer.

• - Fig. l und 2 aufgeschnittene Ansichten von einstufigen Chargiereinheiten;
• - Fig. 3 . einen Vertikalschnitt durch zwei übereinander in Reihe geschaltete Chargiereinheiten;
• - Fig. 4 eine aufgeschnittene Ansicht einer zweistufigen Chargiereinheit, oben offen, unten mit einem Siphon;
• - Fig. 5 eine Draufsicht der Chargiereinheit von Fig. 4.

The invention is explained in more detail with reference to the drawing. They show schematically:

• - Figures 1 and 2 cut views of single-stage charging units.
• - Fig. 3. a vertical section through two batching units connected in series;
• 4 shows a cut-away view of a two-stage charging unit, open at the top, with a siphon at the bottom;
• 5 is a top view of the charging unit of FIG. 4.

1 shows an interchangeable, prefabricated charging unit 10, which essentially consists of a siphon 12, a cover plate 14 and blowing nozzles 16, that is to say in one stage is formed. The part 18 of a silo, which tapers down conically at the bottom, ends in a circular or rectangular outlet opening 20. In the present case, the bottom part of the silo merges into a drain pipe 22.

The bottom plate 24 of the charging unit 10 lies over the entire area on the conical part 18 of the silo. Together with the charging shaft 26, the base plate 24 forms a trough surrounding the outlet opening. The base plate and charging shaft can be made in one piece or welded.

A support device 28, designed as a closed or open profile, for cover plate 14 and blow nozzles 16 is supported on base plate 24.

The vertical part of the cover plate 14, the siphon partition 30, has the distance a from the charging shaft; the distance between the lower edge of the cover plate 32 and the base plate 24 is of the same order of magnitude. The charging shaft 26 has the height h, the upper edge 34 of the lower edge 32 of the cover plate has a vertical distance of b. Normally, a and b are approximately the same size or b is slightly larger than a.

The part of the cover plate 14 arranged above the opening of the charging shaft 26 is designed as a cone, pyramid or gable roof 36, this part is briefly referred to as the roof.

The blowing nozzles 16 arranged directly outside the siphon partition 30 of the cover plate have their own compressed air connection 38 for each nozzle or a communicating connection for several or all nozzles. The valves for controlling the compressed air supply are preferably operated electromagnetically and triggered by an EDP program. In melt flow electrolysis for production The aluminum valves are arranged as far as possible in the edge area of the cell. The nozzle outlet openings 40 are located just above the edge 32 of the siphon partition 30.

• - Das Dach 42 des Deckblechs 14 ist flach.
• - Die Austrittsöffnungen 40 der kommunizierend angeschlossenen Blasdüsen 16 sind deutlich weiter oberhalb des Randes 32 der Siphonscheidewand 30 angeordnet.

The likewise single-stage charging unit shown in FIG. 2 is in principle designed like that in FIG. 1 and has only two essential differences (the lower part of the silo is not shown):

• - The roof 42 of the cover plate 14 is flat.
• - The outlet openings 40 of the communicating blow nozzles 16 are arranged significantly further above the edge 32 of the siphon partition 30.

3 shows a two-stage interchangeable charging unit which is “plugged” onto the charging shaft 26. This shaft 26 is therefore not part of the charging unit, but is welded along the outlet opening 20 to the lowermost part 18 of the silo or is formed integrally therewith.

• - Ein horizontales, auf der linken Seite zur oberen Siphonwand 30' abgewinkeltes Deckblech 14',
• - eine im Abstand a' von der Siphonscheidewand 30' vertikal angeordnete Seitenwand 46, welche im unteren Teil in die U-förmige Aussenwand 48 des unteren Siphons 12" übergeht, und
• - eine steiler als der grösste Schüttwinkel der dosierten Materialien angeordnete Seitenwand 52.

The metering chamber 44, which is essentially prismatic and has a rectangular cross section, has the following side surfaces:

• - A horizontal cover plate 14 ', angled on the left side to the upper siphon wall 30',
• a vertically arranged side wall 46 at a distance a 'from the siphon partition 30', which merges in the lower part into the U-shaped outer wall 48 of the lower siphon 12 ", and
• a side wall 52 arranged steeper than the largest angle of repose of the metered materials.

Immediately outside the upper siphon partition 30 ' three upper blowing nozzles 16 'arranged, which are fed by a common gas pipe 54. The blowing nozzle openings 40 'are in the region of the edge 32' of the siphon partition 30 '.

The lowermost horizontal region of the prism-shaped metering space 44 merges into a part of the lower siphon 12 "with a U-shaped outer wall 48. The siphon 12" is delimited on the inside by the lower siphon partition 30 ", formed by the vertical lower extension of the oblique side wall 52. The lower three blowing nozzles 16 ″, fed by a common gas dividing tube 56 still arranged in the metering space 44, protrude into the lower siphon 12 ″. Depending on the flow properties of the metered material, the lower nozzle outlet openings 40 ″ may be higher than lower.

When the dosing chamber 44 is filled, the exhaust air escapes through an opening 58 into a dust separator 60 and from there via a gas channel 62 into the space under the cell encapsulation. From there, the exhaust air, together with the furnace gases, is extracted and cleaned. On the other hand, when the dosing chamber 44 is emptied, ventilation takes place in the opposite direction.

In the resting phase, the dosing room is completely filled with bulk goods. Compared to the dust separator 60, the opening 58 is the pouring limit, in the lower siphon 12 "the pouring cone 64.

In the working phase, the lower blowing nozzles 16 "are initially switched on until the metering chamber 44 and the lower siphon 12" are completely emptied. A pouring cone 66 is formed in the upper siphon 12 '.

Immediately after. switching off the lower blow nozzles 16 ", the upper blow nozzles 16 'are switched on until the Dosing chamber 44 is completely filled again.

In the embodiment according to FIGS. 4 and 5, a structurally significantly simplified embodiment of a charging unit is shown.

The charging space 44 has the shape of a raised prism with a rhombus-shaped cross section with short, horizontally arranged side edges. Of course, as variants of this embodiment, charging rooms can have a shape of vertically arranged double pyramids or double cones, as well as cuboids or cylinders with pyramid or conical ends on both sides, etc. As an essential requirement, however, the above explanations regarding the angle of repose must be observed. For this reason, e.g. spherical charging rooms out of consideration.

The charging space 44 is fed via a pipe socket 68 projecting vertically into the silo filled with the bulk material. This is welded to the charging space by means of a sleeve 70. The inlet opening 72 is dimensioned such that the charging space 44 is filled in approximately 30-90 seconds. The inlet opening can be provided with a closure system known per se.

The entire lowest area of the charging space 44 is designed as a siphon 12. The lower edge 32 of the siphon partition 30 is so deep that the cone 64 does not reach the upper edge 34 of the U-shaped siphon outer wall 48. The charging shaft is indicated by the baffle 74. The conical lowermost part of the silo with the outlet opening is omitted for the sake of simplicity. They are designed as in the previous exemplary embodiments.

A blowing nozzle 16 with a horizontal action is arranged on an end face of the charging space 44, just below the inlet opening 72.

In the resting phase, the charging space 44 is completely filled with bulk material, the lower limit is the cone 64.

In the working phase, air is blown through the nozzle 16. The fluidized bulk material flows through the siphon 12 within a few seconds. Bulk material continues to flow during the entire emptying time. After the blowing nozzle 16 has been switched off, the charging space is completely filled again.

The charging unit shown in FIGS. 4 and 5 is not only characterized by simple construction, which results in robustness and economy, but also by surprising metering accuracy. Various series of measurements have shown deviations of less than 10 grams with a dosage of 2500 grams of aluminum oxide. The accuracy of the charging unit is well below 1% when dosing aluminum oxide.

The present invention has been illustrated primarily by the supply of alumina to a melt flow electrolysis cell for the manufacture of aluminum. However, it is not limited to these special embodiments, but can generally be used for metering fluidizable bulk goods with homogeneous quality, such as Cryolite and cement, but also rice, grain and sugar.

Claims (10)

l. Device for the batchwise supply of a fluidizable bulk material from a silo, which tapers out at the bottom and has a closable outlet opening, to a reaction vessel, in particular alumina from a day silo, to a crust breakthrough in a melt flow electrolysis cell for the production of aluminum,
marked by
an interchangeable charging unit (10) arranged directly above the outlet opening (20) in the silo and closing it in the resting phase, with at least - A siphon (12), which leads via a charging shaft (26) to the outlet opening (20), and - A blow nozzle (16) per siphon (12) with above the lower edge (32) of the siphon partition (30) opening nozzle outlet opening (40). 2. Device according to claim ^- 1, characterized in that the outer walls of the siphon (12) of a single-stage charging unit (10) are formed by a bottom plate (24) lying on the conical lower part (18) of the silo and the charging shaft (26) that a cover plate (14) roofs over the charging shaft (26), the vertical part of which, arranged at a distance a, forms the siphon partition (30), and that the blowing nozzles (16) are arranged between this partition and the base plate (24). 3. Device according to claim 2, characterized in that the bottom plate (24) of the charging unit (10) is screwed to the conical part (18) of the silo. 4. The device according to claim 2 or 3, characterized in that the roof area (36) of the cover plate (14) over the charging shaft (26) is flat, slightly concave, conical, pyramidal or gable roof-shaped. 5. The device according to at least one of claims 2 to 4; characterized in that 3 to 6 blowing nozzles (16) are provided per charging unit (10). 6. The device according to claim 1, characterized in that a two-stage charging unit (10) from an upper siphon (12 ') with upper blowing nozzles (16'), a ventilated metering chamber (44) and a lower siphon (12 ") with lower Blowing nozzles (16 "), upper and lower blowing nozzles being operable in succession. 7. The device according to claim 6, characterized in that the ventilation of the dosing chamber (44) via an outlet opening (58), a dust separator (60) and a gas channel (62) leads to the reaction vessel. 8. The device according to claim 1, characterized in that a two-stage charging unit (10) from a metering chamber (44) with an open, vertically projecting into the bulk material in the silo pipe socket (68) in the uppermost region, one over the entire horizontal length extending siphon (12) in the lowest region and at least one blow nozzle (16) arranged a little below the inlet opening (72) of the pipe socket (68). 9. The device according to claim 8, characterized in that the dosing chamber (44) in the form of a raised prism, rhombus-shaped in cross section with short horizontally arranged side edges, a double pyramid or a double cone and a cuboid or cylin which is formed with a pyramid or conical end on both sides. 10. The device according to at least one of claims 1 to 9, characterized in that the slope of all the walls of the conical lower part (18) of the silo and / or the metering space (44) is above the largest angle of repose of the charged materials and is at least 45 ⁰ .

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