SK85397A3 - Powder cleaning process and device - Google Patents

Abstract

In a process for mechanically cleaning a powder (25), the powder is projected at a predetermined speed and at a determined frequency during a defined time against at least one surface in order to separate therefrom particles of impurities (35) that adhere to its surface. The thus obtained powders (30, 31 and 35) are then sorted according to size. A cleaning device (1) for carrying out the process has a separator (2) mounted upstream of a wind sifter (3) or cyclone (4). A simplified embodiment of the cleaning device (1) has only a wind sifter (3).

Description

Technical field

The invention relates to a method of mechanically cleaning a powder, in particular primary alumina, which is cast against a surface for separating impurities in the particles of particles adhering to its surface. The invention further relates to an apparatus for carrying out this method.

BACKGROUND OF THE INVENTION

Method for mechanically removing powder impurities. These methods for purifying the powdered oxide are described. The aluminum powder is initially used as a powder on the surface of the particles, for example, for the production of primary alumina, during cleaning to clean the flue gases produced by the electrolysis of the melt. In this case, the flue gas is passed around the primary alumina, with particles in the dermis of fluoride, iron, phosphorus, carbon, silicon, vanadium and nickel formed during the electrolysis of the melt adhere to the surface of the alumina powder. Before this alumina is fed into the electrolysis, the impurities in the form of iron, phosphorus, carbon, silicon, vanadium and nickel must be removed, otherwise the process would be enriched. However, this would have detrimental effects on the quality of the aluminum and on the efficiency of the whole process. The fluorine required to carry out the electrolysis of the melt must be collected and recycled to the process.

A method for removing impurities from the surface of powder particles is disclosed in FR-A-2 499 057, which is identical to the Norwegian patent 147-91. In this method, the air stream containing the powder to be cleaned is directed against the impact plate. The effect of the impact is that the impurities adhering to the surface of the wrinkle particles are separated. The impurities and the powder are then separated by sieving. This method is very costly to regulate and further has a very low efficiency when the cleaning performance is several tons per hour.

French patent 7 072 072 discloses a method for removing particulate impurities from the surface of powder particles. In this method, the powder to be cleaned is introduced into two intersecting air streams. At the intersection of the two air streams, the powder particles collide with each other. The particles are abraded by one another, thereby separating the impurities adhering to their surface. Since the separated impurities are lighter than the powder particles, they can be removed by a stream of air, with the heavier powder particles falling down. This method is very useful when a large amount of powder is to be cleaned, since it is not intended to clean a large amount of powder.

DE-A-1 607 46ô discloses an impact crusher for crushing hard and medium hard materials. Thus, the impact crusher consists of a housing in which the impact plates are arranged opposite the impact arms of the rotor. The housing is further provided with an inlet line for supplying the material to be processed and an outlet opening. The impact plates are arranged under the supply line and have the shape of a roof. The impact plate has in places a width that is greater than half the diameter of the rotor.

US-A-4 E · ?! 890 discloses a rotary impact mill by which the material particles are reduced to three different sizes and separated from each other. This rotary impact mill is provided with a rotor, the arms of which are provided with plates for reducing the particles of material attached thereto.

EP-A-337 137 discloses a hammer gas for reducing the size of ore and similar materials. The machine is located in a cylindrical housing. Impact plates and a rotor are disposed within the cylindrical housing, hammers are fixed to the rotor at a defined distance from each other, which are used to reduce or throw the ore particles against the impact plates.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for removing impurities adhering to the surface of powder particles, which is inexpensive and has a higher efficiency than the prior art methods, and a device for carrying out the method.

SUMMARY OF THE INVENTION

This object is achieved by a method of mechanically cleaning a powder, in particular of primary alumina, which is thrown against a particle separation surface adhering to its surface, according to the invention, which is based on the fact that the alumina to be cleaned is introduced into the separating device. and by means of the strike mechanism of this separating device, it is thrown at a speed of 30 to 50 m / s more than 10 times per second for 1 to 10 seconds against impact blades rotating in the opposite direction to the strike mechanism, the particles of pure alumina powder having a particle size of 10 μχ, separated from pure alumina particles having a particle size of 10 μη, and from impurities by means of an air screen and / or a cyclone and fed to the electrolysis of the melt, and wherein the alumina powder having a particle size · 10 µm and the impurities are fed to the upper end or further back raced as a raw material.

This task is further accomplished by a cleaning device r and mechanical separation of impurities in the form of timepieces from aluminum, with a separation device in which the powder is directed against the impact surface according to the invention, which is essentially based. that the separating device is realized if: an impact with at least one impact mechanism by which the powder to be cleaned is thrown at a defined speed against the impact vanes rotating in the opposite direction as the impact mechanism, the impact mechanism and the impact mechanism; the vanes are made of a material in the form of a glazed carbide, a ceramic material or a polymeric material, and wherein the air screen and / or the cyclone are / are connected to a separating device.

In carrying out the process according to the invention, the powder to be cleaned passes through a mechanically operating cleaning device. According to one embodiment of the invention, a separating device and / or an air screen is formed.

this cleaning device behind

The method and operation of the separation device correspond to the design and operation of the impact crusher.

In this device, the powder is thrown by the rotor or strike mechanism at a predetermined speed against the impact vanes rotating in the opposite direction by the alzc strike meohanlm. By means of the rotational speed of the rotor or the impact mechanism and by a fixed powder delay in the separating device, the impact velocity of the powder particles and the number of impacts of the powder particles into the impact lc-feet can be controlled. Impact velocity It is less than 1 £ / m / s. Preferably, its value is in the range from SO 0 to 4 µm / s. Adjusting the Impact Rate It is particularly important, because only by adjusting the Impact Rate, all impurities will be removed from the surface of the powder and will not melt on the powder particles. After draining the cleaned powder and the separated impurities from the inverting compartment, the 10 μmα particle size clean powder is separated from the 10 μη particle size powder and from impurities that are similarly smaller than 1C gum. This separation is effected, for example, by means of a cyclone and / or an air screen which are connected downstream of the separation device. The production costs of the air screens are very high. Cost It is possible to save money by connecting the air screen downstream of the cyclone. This has the advantage that the powder fractions with a particle size ^of 20 to 30 μιη are already separated in the cyclone. It is therefore possible to use an air screen of smaller size. In certain preferred cases, it is sufficient to connect behind the separating device. 1 is only a cyclone.

In a simplified embodiment of the cleaning device, the impact crusher & cyclone are not used. The cleaning device consists of a ler. from the air screen. In this case, however, the air screen must be designed so that the air passing through its interior causes a disintegration effect. The air screen must be designed so that the powder to be cleaned is thrown at the indicated speed against one or more surfaces so that the impurities adhering to the powder particles are separated. The advantage of using ler. the air screen for cleaning the powder consists in separating the cleaned powder at the same time as cleaning.

All of the above-described cleaning devices are designed so that it is possible to separate the pure powder by size in such a way that a powder with a particle size > 10 μκ is also passed through the electrolysis of the aluminum melt. Particle size powder. 10 με and impurities are stored in the hernen end or further processed as raw material. Using the method of the invention It is possible to remove at least 25% iron, more than 50% phosphorus and 25% carbon adhered as an impurity to the alumina powder particles. Using this method, it is also possible to recycle 60% of fluorine to the melt electrolysis. The amount of separated impurities and the amount of fluorine that can be obtained using the process of the invention represent a significant improvement over the results achieved by the known methods. Since vanadium and nickel adhere to the iron, vanadium and nickel will also separate from the flue gases resulting from the electrolysis of the melt directly in proportion to the amount of iron removed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail below with reference to the accompanying drawings, in which: FIG

Fig. 1 is a cleaning device according to invention, Fig. 3 a variant of the cleaning device according to FIG. 1 Fig. 3 simplified cleaning cleaning • denia a Fig. 4 air it is like separating a • separators device.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows a cleaning device 1 for the chemical separation of impurities 55 adhered to the surface of alumina particles air air equipment implemented

85. This cleaning device 3 and the diagrams are behind the separating device S. It essentially has at least one abrasion or comprises a separating screen 3. As can be seen from slt-o 3 connected directly

S. Separator as well as impact crusher.

and the SE 's striking mechanism by which

The alumina powder 35 is fed to the separating device 2, thrown against the stationary impact plates or even the impact blades 8P. rotating in the opposite direction as the striking mechanism of the SR. The cleaning apparatus 1 shown is intended for cleaning primary alumina powder 25. However, the cleaning apparatus 1 may also be used for cleaning other powder materials.

The impact mechanism 2R and the impact plates or even the impact blades SP are made of materials which are particularly suitable for processing alumina powder. Preferably, the components of the separating device are g. which come into contact with alumina 35 made of bent carbide, ceramic or polymeric material with corresponding properties. By means of the cleaning device 1, impurities 35 adhered to the surface of the alumina powder 85 are separated. These impurities 35 are particles with a size <10 μχ.

The impurities 35 in the primary alumina 85 consist essentially of fluorine, iron, phosphorus, carbon, silicon, nickel, and vanadium.

The primary alumina powder 35 is first used to purify the flue gases produced by melt electrolysis. Then, it is itself cleaned and supplied to the melt electrolysis for aluminum production. Flue gas cleaning involves collecting the impurities described above. Flue gas cleaning involves collecting impurities. Alumina 35 must be electrolysis of the melt not described above to be purified, which is enriched:

dirt. If the purification is not done, phosphorus and vanadium will reduce the efficiency of the electrolysis means that the overall efficiency of the process will be reduced, the aluminum rivalry being impaired by the presence of iron and silicon. The primary alumina powder (85) is fed to the separator (3) through a metering device (40). The output of the separator (3) shown must be high enough to allow about 30 tons of alumina 85 to be cleaned per hour. Aluminum oxi powder 35 is supplied automatically. The frequency of rotation of the impact mechanism 8R in this case is set so that the alumina particles 85 impinge dc impact pads or even impact paddles SE at a speed SO up to 30 m / s. The impurities 35 adhered to the surface of the alumina powder 35 are separated in this process. Approximately 50% of the aluminum cleaning composition 85 has a particle size of 5%. μη. The remaining alumina 85 has a larger particle size. The speed at which alumina is thrown against the impact plates or even the impact blades SP. Is it sufficient for segregation of impurities 35. and does not occur?

breakage of the alumina powder particles 35. After the alumina 86 has been thrown at least more than ten times per second at a rate of 33 to 30 m / s onto the impact pads or even the impact paddles £. it is discharged together with the separated contaminants 35 from the separating device 3 and is led into the air screen automatically. Particle impurities Is 10 μχ, e alumina cell. particle size.

t: the pure powder μη shown, the process size being the same as the sides, have a size out of with the aid of FIG. 1, -’.- ΙΆ r. '' R LTY

£. Ter.t ·: 1 :: the current air flow, • c J ** Λ. * i ^J * «L *« Μ * Vb w · a W no. The particle is removed under the effect of the earth's gravity of the air screen and further d (not shown).

In the cleaning apparatus 1 shown r.a c: r. S. having substantially the same construction as the cleaning apparatus of FIG. The pure alumina particles having a size greater than 80 μη to 30 μη are separated and fed to the melt electrolysis in the cyclone 4. The remaining powder particles having a size of <80 to 30 μη are passed to the air screen for further separation. This cleaning device 1 is advantageous over the cleaning device L of FIG. 1 in that a substantially smaller air screen 3 can be used since the fraction of pure alumina 32 whose particles are greater than 80 to 50 gm is already taken out directly back to the melt electrolysis. Since 50% of pure alumina 50 has a particle size greater than 50 μη, the amount of powder to be further processed in the air sieve 3 by the inclusion of cyclone 4 is greatly reduced.

In FIG. 5 A cleaning device 1 of substantially the same construction as the cleaning device 4 of FIG. 1. The embodiment of FIG. 5 Behind the separator g. Only the cyclone 4 is connected. This cleaning device 1 can be used if particle separation of smaller actions of 16 gm is sufficient.

In another embodiment of FIG. 4 Only an air screen 6 is provided for separating the impurities 35 from the alumina powder 85 and for separating the powder according to the particle size. The alumina powder 85 to be cleaned is supplied to the air screen 3 from the dosing device 40. In this case, an air screen použité having a disintegration zone (not shown) is used. This disintegration zone allows the alumina powder 35 to be cleaned to be guided at a desired speed of 80 to 30 m / s against at least one surface (not shown here), thereby separating impurities 35. After this air screen, it is subsequently possible to separate the powder particles according to their size. This allows separation up to a particle size tS gm.

By means of the abovementioned separating devices 1, it is possible to remove at least 25% of iron, more than 50% of phosphorus and 25% of carbon, which are adhering to impurity 5. on alumina powder particles 25. Using the method of the invention, it is also possible to recycle 60% of fluorine into the melt electrolysis. The amount of separated impurities 55 and the amount of fluorine that can be obtained using the process of the invention represent a significant improvement over the results obtained by known methods.

Claims (1)

PATENT CLAIMS First A method of mechanically cleaning a powder, in particular of primary alumina, which is thrown against a surface (2P) for separating impurities (35) in the form of particles adhering to its surface, characterized in that the alumina (85) to be cleaned is introduced. into the separating device (8) and by means of an impact mechanism (2R) this is thrown at a speed of 80 to 30 seconds for 1 to blades (8P) rotating the mechanism (SR), wherein the separating device (8) is m / s more than ten times in 10 Seconds against impact in the opposite direction to the impact particles of pure alumina powder (30) having a size> 10 µm are separated from the particles of pure alumina powder (31) having a size of · 10 µm and from impurities (35) by means of an air screen (3) and / or a cyclone (4) and are fed into the electrolysis of the melt, and wherein the alumina powder (31) with a particle size <10 µm and the impurities (35) are fed to the upper co or further processed as raw material. A cleaning device for mechanically separating impurities (35) in the form of particles from the surface of particles of powder (25), in particular primary alumina, with a separating device (8) in which the powder (85) is directed against the impact surface (SP). characterized in that the separating device (8) is implemented as an impact mill with at least one impact mechanism (8R) by means of which the cleaning powder (85) is thrown at a defined speed against the impact blades (SP) rotating in the opposite direction as the impact mechanism (8R), wherein the impact mechanism (8R) and impact blades (SP) are made of a material in the form of cemented carbide, ceramic material or polymer material, and wherein the air screen (5 'and / or cyclone (4) are / It is connected to the separation device (8).