GB2059810A - Process and installation for removing dust from particles - Google Patents

Abstract

In a process and installation for obtaining selective separation between particles and much finer dust clinging thereto, at least one jet of particles is created in a fluidized bed, e.g. by means of a compressed- air blowing nozzle (21) and this jet is directed against an obstacle, possibly formed by another jet of particles as shown. The particles of the fluidized bed are subjected to sustained vibrations and the rising stream of fluidizing air carries upwards only the fine dust (22) of a grain size less than a given threshold. <IMAGE>

Description

SPECIFICATION Process and installation for removing dust from particles The present invention relates to a process for removing dust from particles, with a view to obtaining selective separation between particles and much finer dust clinging to these particles, consisting in creating at least one jet of particles charged with fine dust in a fluidized bed of these particles, formed in a fluidization chamber, and in directing this jet against an obstacle at a sufficient speed to cause the fine dust, under the effect of the impact, to be loosened from the particles, the fluidizing of the particles being achieved by a rising stream of fluidization and separation gas.

The aim of the present invention is principally to increase the efficiency of the separation obtained with known arrangements, and particularly to obtain the completest possible separation and with good selectivity in difficult cases of application, i.e. when the very fine particles adhere firmly to the largest particles.

For this, a process in accordance with the present invention of the general type defined at the beginning, is characterized in that, by causing said chamber to vibrate, the particles of the fluidized bed are subjected to sustained vibrations, said rising stream carrying upwards only the fine dust having a granulometry less than a given threshold, thus effecting said selective separation between the fine dust and the largest particle from which the dust has thus been removed.

The above-mentioned vibrations contribute, concurrently with the impact of the jet(s) of particles on a fixed obstacle or on other jets, in causing repeated impacts of the particles against one another and against the dividing walls of the enclosure or of the passage which they occupy (fluidization chamber), and it has been discovered that that contributed greatly to overcoming the clinging forces between the very fine particles and the largest particles to which they adhere.

Furthermore there is obtained through these vibrations a more rapid renewing effect of the particles of the fluidized bed in the jet(s) of particles which are created therein, which increases the efficiency of these jets and also makes the removal of dust more rapid. Because the particles are subjected to much more complex movements than those to which the single rising current of fluidization gas would subject them, they are projected also more rapidly into the jets. In other words, the induction created by the jets of particles is much better used when the particles are subjected to vibrations.

The invention allows then exceilent cooperation to be obtained between, on the one hand, the effects proper to the impacts resulting from the creation of the jets in the fluidized bed and to their impact on an obstacle and, on the other hand, the effects proper to the vibrating of the particles.

The result is a great effeciency of the separation in the fluidized bed and the possibility of increasing the flow rates of treated material.

Of course, the fine particles carried upwards will be able to be separated from the fluidization gas, before this latter is discharged to the outside, by any known means, for example by means of a filter with filtering pockets. As for the largest particles they will be able to be removed from the fluidized bed by overflow and by simple gravity, also in a known way.

It may be advisable to create the jets of particles in the fluidized bed by simply injecting therein jets of compressed air (or any other gas), directed towards each other.

The present application also relates to the means for implementing the above-described process, i.e. to an installation for removing the dust from particles, formed essentially by a fluidization chamber comprising a duct for introducing particles from which the dust is to be removed, a duct for removing the particles from which the dust has been removed, connected on the side opposite the preceding one, and a permeable dividing wall forming a bottom, separating an upper part of the chamber, forming a fluidization space defined moreover by lateral walls, from a lower part forming blowing box and able to be placed in communication with a duct for compressed fluidization and separation gas, the input of a pipe being furthermore in communication with the upper part of said space for discharging upwards the fine particles separated from the largest ones in the bed and carried along by the rising current of fluidization gas, the outlet of this pipe being possibly connected to a separator of the filter kind or similar, means being furthermore provided on the lateral walls of the fluidization space for generating jets of particles directed against each other.

In accordance with the invention, such an installation is characterized in that it comprises means for vibrating the particles in said fluidization space, adapted to subject to sustained vibrations said permeable dividing wall and possibly said lateral walls of the fluidization space, means being furthermore provided for adjusting the speed of the rising stream of fluidizing gas.

Advantageously, said vibrating means comprise a resilient suspension of the fluidization chamber and, connected thereto, at least one shaft pivoting at an adjustable speed, carrying at least one eccentric mass, also with adjustable eccentricity.

Thus the frequency and the amplitude of the vibrations may be conveniently adjusted.

The stiffness of the suspension and this frequency are as a rule chosen so as to obtain the maximum amplitude.

Even with a resilient suspension supporting the chamber and acting therefore vertically, there is obtained, with this vibratory system, horizontal vibrations, although of a smaller amplitude than the vertical vibrations, which contributes to increasing the number of impacts between particles.

It may further be provided that said means comprise at least two parallel pivotable shafts each carrying at least one eccentric mass, and means for adjusting the angular offset of the masses, which provides an additional adjusting facility.

One embodiment of the invention will now be described by way of non-limiting example with reference to the figures of the accompanying drawings in which: Figure 1 is a schematical and partial representation in axial section of an installation in accordance with the invention, for implement- ing the process; and Figure 2 is a cross-sectional view along line Il-Il of Fig. 1.

The installation shown in the figures is for example intended for removing the dust from particles of alumina whose grain size (particles and fine dust) varies from 1 to 100 ,u, and this so as to obtain removal of all the particles less than 30 iu.

This installation comprises a fluidization chamber 1 provided with a duct 2 for introducing particles from which the dust is to be removed, fed by a hopper 3, and a duct for discharging the particles from which the dust has been removed, so the largest particles, 4, which discharge duct is connected on the side opposite the inlet duct 2. Chamber 1 is limited by a permeable dividing wall forming a bottom 6, which bottom forms the lower wall of what was called above an upper part of the chamber, forming a fluidization space 7 defined furthermore by lateral walls 8a and 8b. Below this permeable dividing wall 6 is located what was called above a lower part forming blowing box, shown at 9 and being able to be placed in communication with a fluidizing and separating compressed air duct 10, itself able to be fed by an adjustable output fan.

At the upper part of the installation there is provided a pipe 11 in communication with the top of the fluidization space 7. The other end of this pipe 11 is connected to a dust separator 12, for example with filtering pockets, the filtered air leaving at 13, and the separated particles falling into a hopper 14 provided with a drain valve 15.

In accordance with the invention there are further provided means for vibrating the particles in the fluidization space 7. These means have been shown very schematically in the form of vibrators 16. These may advantageously be shafts rotatably mounted on bearings of the frame 1 7 of the installation, these shafts being driven by electric motors and carrying one or more eccentric masses.

As mentioned above, an adjustment may be provided for the angular offset of the masses carried by different shafts for creating vibrations having several components.

In any case, the vibrating means used are adapted to subject the chassis 17, the fiuidization space 7, the permeable dividing wall 6, the side walls 8a and 8b and the blowing box 9 to vibrations whose principal component is directed vertically. To this end, a resilient system, formed for example by helical springs 18, is placed between supports 1 9 of the frame and bearing pieces 20 placed on the ground. Such a system allows not only vertical vibration but also the appearance of horizontal vibratory components.

Finally, there is shown at 21 (Fig. 2) two compressed-air blowing nozzles disposed opposite one another and in the same direction, on the two opposite lateral walls 8a and 8b of the fluidization space 7.

The role of these nozzles is to induce in the fluidization bed of particles from which the dust has to be removed jets of particles directed against each other so as to subject the particles to impacts adapted to dislodge therefrom the finest dust which adheres thereto.

For example four pairs of opposite nozzles 21 may be provided, as is shown in Fig. 1.

These impacts to which the particles from which the dust has to be removed are subjected combine very efficiently with the vibratory movements to which they are also subjected because of the vibrating of space 7, and thus an excellent efficiency in the removal of dust may be obtained. By way of example, with particles of alumina having the grain size indicated above, all the dust of dimensions less than 30 iu may be conveniently eliminated. It should be noted that it is impossible to reach this result with conventional installations of the industrial vibrating screen type, in which a very rapid clogging up of the screen may furthermore be noted.

Then, the fine dust 22 loosened from the largest particles is carried along in the upper pipe 11 by the stream of fluidizing air, and it is separated from this air in the dust separator 1 2. As for the largest particles, they remain or fall back into the fluidized bed, and by natural flow pass through the fluidization space 7 from the inlet duct 2 to the outlet duct 4 which thus supplies large particles 23 from which the dust has been removed.

Claims (7)

1. A process for removing the dust from particles, with a view to obtaining selective separation between particles and much finer dust clinging to these particles, consisting in creating at least one jet of particles charged with fine dust in a fluidized bed of these particles, formed in a fluidization chamber, and in directing this jet against an obstacle at a speed sufficient for the fine dust, under the effect of the impact, to be loosened from the particles, the fluidization of the particles being achieved by means of a rising current of fluidizing and separating gas, characterized in that, by causing said chamber to vibrate, the particles of the fluidized bed are further subjected to sustained vibrations, said rising stream carrying upwards only the fine dust of a grain size less than a given threshold, thus effecting said selective separation between the fine dust and the largest particles from which the dust has thus been removed.

2. An installation for implementing the process of claim 1, formed essentially by a fluidization chamber comprising an inlet duct for particles from which the dust has to be removed, an outlet duct for the particles from which the dust has been removed, connected on the side opposite the preceding one, and a permeable dividing wall forming a bottom, separating an upper part of the chamber, forming a fluidization space defined moreover by lateral walls, from a lower part forming a blowing box and able to be placed in communication with a duct for compressed fluidizing and separating gas, the inlet of a pipe being furthermore in communication with the upper part of said space, for removing upwards the fine particles separated from the largest particles in the bed and carried along by the rising stream of fluidizing gas, the output of this pipe being possibly connected to a separator of the filter kind or similar, means being further provided on the lateral walls of the fluidization space for generating jets of particles directed against each other, characterized in that it comprises means for vibrating the particles in said fluidization space, adapted to subject to sustained vibrations said permeable dividing wall and possibly said lateral walls of the fluidization space.

3. The installation according to claim 2, characterized in that said vibrating means comprise a resilient suspension of the fluidization chamber and, connected thereto, at least one shaft pivoting at an adjustable speed, carrying at least one eccentric mass, also with adjustable eccentricity.

4. The installation according to claim 3, characterized in that said means comprise at least two parallel pivoting shafts each carrying at least one eccentric mass, and means for adjusting the angular offset of the masses.

5. A process for removing dust from particles, substantially as hereinbefore described with reference to the accompanying drawings.

6. An installation for removing dust from particles, substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

7. Any novel feature or combination of features described herein.