CH623492A5 - Method of removing dust from particles - Google Patents

Description

The present invention relates to a method of dusting particles, aimed at obtaining the separation between particles and much finer dust, attached to the particles.

These can in particular be alumina particles from a circuit capable of bringing them into contact with polluted and dusty gases from electrolytic cells in the aluminum industry, such contacting being carried out in particular for fixing, on the particles, the fluorine contained in said gases, before evacuating them to the atmosphere. Indeed, these alumina particles fix not only fluorine, but also fine dust polluting carbon, iron, phosphorus, nickel ..., which it is advisable to detach and separate larger particles of alumina to be able reuse these and recycle them either in the tanks or in said contacting circuit.

In general, however, the invention relates to all kinds of materials in the form of particles to which adhere finer dust (which may be subcronic), and which should be used, especially when it comes to polluting dust, to rid the larger particles, in case these are to be reused or marketed.

The object of the present invention is to obtain such a separation process, between particles and fine dust, more efficient than the processes known up to now, while being able to be implemented using very simple means.

To this end, a dusting method according to the invention is characterized in that it consists in creating at least one jet of particles charged with fine dust, directing this jet against an obstacle with a sufficient speed so that, under the effect of the impact, the fine dust is released from the particles, and a separation is made between the fine dust and the larger particles thus dedusted.

The aforementioned obstacle may consist of a fixed screen, which the particles to be dusted strike, but it may also be, in a particularly advantageous manner, at least one other jet of particles, in particular of particles also to be dusted.

In other words, the invention then essentially consists in creating, from the particles to be dusted, at least two jets which are directed against each other so that the particles of the jets collide, the impact of the particles and the intense turbulence created causing the detachment of the fine dust which adheres to it, which can then be permanently separated from the particles, for example by suction or blowing, at low speed, or also by means of a centrifugal separator or the like.

We can also provide that the particle jets are created by compressed air streams into which the particles are injected, or that these jets are created by compressed air streams injected into a fluidization bed of the particles to be dusted, this latter arrangement having, compared to the previous one, the advantage of avoiding premature wear of the interior of the blowing nozzles.

According to an equally advantageous embodiment of the invention, the method can also be characterized in that the dedusting of said particles is carried out in several stages in a fluidization bed flowing in a corridor, this corridor being compartmentalized by transverse walls provided particle passage slots.

This is an industrial embodiment more particularly suited to the treatment, on a continuous basis, of relatively large flow rates of particles to be dedusted.

Whatever, moreover, the chosen mode of implementation of a process in accordance with the invention, it may further be characterized in that the separation between the fine dust and the larger dusted particles is carried out by an ascending flow of air at a slow speed, capable of driving the fine dust upwards while letting larger particles fall.

In the case where the jets, directed towards each other, particles to be dusted are created by currents of compressed air injected into a fluidization bed of the particles, this flow of ascending air at slow speed will be automatically created by the air supply of the blowing nozzles which open into the fluidization bed, as well as by the fluidization air.

Different embodiments of the invention will now be described below by way of non-limiting examples, with reference to the schematic figures of the appended drawing, in which:

- fig. 1 shows a first mode of implementation of the method, according to which two blowing nozzles are directed towards each other, and each supplied, on the one hand, with compressed air and, on the other hand, with particles to dust;

- fig. 2 shows a variant in which two nozzles are directed towards one another, each supplied with compressed air, and opening into a fluidization bed of the particles to be dusted;

- fig. 3 shows a variant of the embodiment of FIG. 2, along which the respective axes of the two nozzles form a certain angle, and

- fig. 4 shows, again schematically, another embodiment of a method according to the invention, for the continuous industrial treatment, at high speed, of particles to be dusted.

The installation shown diagrammatically in FIG. 1, for the implementation of a method according to the invention, essentially comprises a chamber 1, which may be called separating chamber, or settling chamber, and whose opposite walls are crossed by two nozzles 2 directed l 'towards each other,

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following the same direction. (There could be more than two converging jets.)

Each nozzle 2 is supplied, on the one hand, with compressed air, for example at 3 bars (at 3), on the other hand, with particles to be dedusted (at 4). Thus, the two jets of particles from the nozzles 2 meet in the middle zone 5, the particles of the two jets collide, and the shocks between particles cause the fine dust which sticks to them to drop out. This fine dust is then entrained towards the top of the chamber 1 by the ascending current, of low speed, created by the air coming from the nozzles, while the larger particles, dedusted, fall to the bottom of the chamber (hopper 6) .

From this hopper, the particles can be removed to be evacuated or reused, or even be recycled to the nozzles 2, to perfect, if necessary, their dusting.

As for the fine dust entrained upwards, they can be separated from the carrier air by means of electrostatic precipitators or the like, after which the purified air can be evacuated to the atmosphere.

To avoid excessive wear of the interior of the nozzles, especially in the frequent case where the particles to be dusted are very abrasive, it is possible, in accordance with the variant of implementation shown in FIG. 2, create the two convergent jets of particles by injecting only compressed air, into a fluidization bed 7 of the particles to be dedusted. The air coming from the two nozzles 8 supplied with compressed air and also directed towards each other in the same direction sucks in and in fact drives, towards a central impact area 9, the particles to be dusted from the bed 7. The fine dust thus detached from the particles are again entrained towards the top of the chamber, then towards a filter, by the ascending current at low speed created, on the one hand, by the air coming from the nozzles 8, on the other hand, by the fluidizing air supplied at 10 under the porous separating wall 11. Again, the larger particles, most of which are dusted, fall to the bottom of the chamber 1, in the fluidized bed 7, where they can still be subjected to a dusting effect by impacts, or from where they can be evacuated gradually.

Fig. 3 shows a variant of the embodiment of FIG. 2, according to which the nozzles supplied with compressed air 8 ′, opening into the fluidization bed 7 of the chamber 1, are further arranged to create jets of particles to be dusted directed against each other, the axes of these nozzles making however a certain angle, so that the zone of impacts 9 'can be located

623,492

in the upper region, and even slightly above, of the fluidization bed 7. This embodiment can promote separation between the particles and the dust.

It should be noted that, here too, more than two jets could converge towards the impact zone 9 '. In this example, the nozzles 8 'would then be arranged in a cone.

Finally, fig. 4 shows yet another embodiment of the invention, for the continuous treatment, at an industrial rate, of particles to be dusted, for example particles of alumina having fixed fine impurities.

A slightly inclined fluidization corridor 12 is then used, the particles to be dusted flowing by gravity, from the entrance of the corridor 12 to its exit, on a porous separating wall 13 (the air supply pipe under the wall 13 has not been shown).

The upper part of this corridor 12 (above the wall 13) is equipped with transverse partitions 14, for example three in number, each of which is provided with a horizontal slot 15, for the passage of particles from one of the compartments thus formed to the next. In addition, for the implementation of the general principle of the invention, the two opposite side walls of each compartment are traversed by compressed air blowing nozzles 16 directed in pairs towards each other and connected to distribution ramps such as 17. Finally, above the compartmented area extends a separating or settling chamber 18 similar to the chambers 1 of the preceding figures.

The operating mode of the installation is essentially the same here as that of the installations previously described: the fine dust detached from larger particles in each compartment, under the effect of the collision of the jets two by two, are evacuated towards the part upper part of the chamber 18 by the ascending air flow which arises therein, while the dusted alumina particles continue their path on the porous partition 13.

It has been found that a process in accordance with the invention makes it possible to obtain an excellent dust removal yield of at least 50%, and that it also makes it possible to obtain separation between particles, in particular particles of alumina, and submicron dust which adheres very strongly to it, as is the case with phosphorus.

As is obvious, and as it follows from the above, the invention is in no way limited to those of its modes of application and embodiments which have been more particularly envisaged; on the contrary, it embraces all its variants.

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1 sheet of drawings

Claims (7)

623,492 1. A method of dusting particles, aimed at obtaining the separation between particles and much finer dust, attached to the particles, characterized in that it consists in creating at least one jet of particles charged with fine dust, to be directed this jet against an obstacle with sufficient speed so that, under the effect of the impact, the fine dust is released from the particles, and to effect a separation between the fine dust and the larger particles thus dusted. 2. Method according to claim 1, characterized in that said obstacle consists of at least one other jet of particles. 2 3. Method according to claim 2, characterized in that the particles of the or other jets are also particles to be dusted. 4. Method according to any one of the preceding claims, characterized in that the or the particle jets are created by compressed air currents in which the particles are injected. 5. Method according to any one of claims 1 to 3, characterized in that the or the particle jets are created by currents of compressed air injected into a fluidization bed of the particles to be dusted. 6. Method according to claim 5, characterized in that the dedusting of said particles is carried out in several stages in a fluidization bed flowing in a corridor, this corridor being compartmentalized by transverse walls provided with slots for passage of the particles. 7. Method according to any one of the preceding claims, characterized in that the separation between the fine dust and the larger dusted particles is carried out by an ascending air flow at slow speed, capable of driving the fine dust upwards. letting larger particles fall.