GB1604418A

GB1604418A - Separation of particulate materials

Info

Publication number: GB1604418A
Application number: GB46478/77A
Authority: GB
Original assignee: CABLE COMMUNICATION ACCESS
Current assignee: CABLE COMMUNICATION ACCESS
Priority date: 1977-11-08
Filing date: 1977-11-08
Publication date: 1981-12-09
Also published as: ZA786267B; DE2848474A1; JPS54106963A; AU4144078A

Description

(54) IMPROVEMENTS IN OR RELATING TO THE SEPARATION OF PARTICULATE MATERIALS (71) We, CABLE (COMMUNICATION) ACCESSORIES LIMITED, of 15 Clifton Road, St. Peters Road, Huntingdon, Cambridgeshire, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to the separation of particulate materials.

In particular, the invention relates to methods of and apparatus for the separation of three particulate materials of different densities by means of a fluidised bed. A known fluidised bed for separating two particulate materials of different densities comprises an enclosure containing a quantity of particles, typically having a diameter of less than one millimetre. The base, usually, of the enclosure is made porous such that gas, usually air, or liquid can be introduced through the particles into the enclosure under pressure. The particles then become separated from each other by a film of the gas or liquid so that they behave like a liquid.

In this known type of fluidized bed, and also the associated method of separating two particulate materials of different densities, the average fluidised particle density is arranged to be intermediate the densities of the two particulate materials to be separated.

The heavier particulate material sinks to the bottom of the fluidised bed and the lighter material floats on top. The separated materials can then be separately removed from the bed.

Particulate material comprising three (or more) different density materials may be fed to a fluidised bed for separation, and the separation may be carried out in stages by separating the lightest (or heaviest) particulate material at the first stage and supplying the remainder to the next fluidised bed which is chosen to have a higher (or lower) fluidised particle density so that separation of at least one further component of the remainder is effected.In accordance with the method and apparaties of the invention, separation of three particulate materials of different densities is effected in one fluidised bed by providing the bed with two fluidised particle layers of different densities, wherein the lower fluidised particle density is arranged to be between the lowest and intermediate particulate material densities and the higher fluidised particle density is arranged to be between the highest and intermediate particulate material densities, the fluidity of the bed being produced by causing a nonpulsating flow of gas or liquid to be passed therethrough.

It will be appreciated that the separation method of the invention may also be applied to separate more than three particulate materials of different densities by providing more than two different fluidised particle densities, by appropriate choice of the densities, analogously to the method of the invention.

A 'dry' fluidised bed, that is to say one having gas as a fluidising medium, has a lower average fluidised particle density than a 'wet' bed, that is to say one having liquid as a fluidising medium, and so can be used to separate relatively lower density particulate material. Furthermore, contamination of the separated particulate material by fluidised particles is less with a 'dry' bed than with a 'wet' bed so that further processing is minimised.

The apparatus may also comprise means for returning to the fluidised bed any fluidised particles removed by either or both of said removal means.

A method of and apparatus for separating three (or more) particulate materials of different densities, in accordance with the present invention, will now be described, by way of example, with reference to Figure 3 of the accompanying drawings, in which: Figure 1 is a schematic representation of one prior art fluidised bed for the separation of a two-component mixture of particulate materials; Figure 2 is a schematic representation of another prior art fluidised bed for the separation of a three-component mixture of particulate materials; and Figure 3 is a schematic representation of an embodiment of a fluidised bed in accordance with the invention having two layers of fluidised particles.

Referring to the prior art fluidised bed shown in Figure 1, the fluidised bed 2 comprises a layer 4 of fluidised particles disposed within a chamber 6 that has a porous base 8. Air is supplied to the underside of the base 8 via an inlet 10 so as to pass up through the base 8 and maintain the particles of the bed in their fluid state. The particles 4 behave as a fluid having a density that is dependent on the average size of the particles, the material, for example sand, steel or copper shot, of which the particles are made, and the rate of the air flow through the base 8. If the rate of flow of air through the base 8 is increased, the thickness of the air film between the particles is increased so that the density of the fluidised particle layer 4 is decreased. A pressure gradient exists in the fluid, the extent of which is dependent on the depth of the layer 4 in the chamber 6.

The mixture of particulate materials to be separated is introduced to the bed 2 at the top of the chamber 6. In Figure 1, the mixture contains components having only two different (known) densities. The density of the fluidised particle layer 4 is arranged to be intermediate these two densities. The particulate materials separate under the action of gravity such that the component particles 12 that are of lower density than the fluidised particles 4 float on top of the fluidised particle layer 4, and the higher density component particles 14 sink through the layer 4 to the base 8.

In the second prior art fluidised bed shown in Figure 2, the mixture of particulate materials comprises components having three different densities. In this case, intermediate density component particles 16, having a density comparable to that of the fluidised particle layer 4, take up a location part way down the depth of the fluidised particle layer 4. Care has to be taken in the choice of the density of the fluidised particle layer 4 so as to ensure separation of the component particles 16 from the lighter and heavier particles 12 and 14 respectively.

It will be appreciated that if the particulate mixture introduced to the fluidised bed 2 for separation comprises three or more different density components, then the components will float on or sink through the layer 4 depending on whether the individual compo- nent density is less than or greater respectively than the density of the layer 4. Thus, sequential separation can be employed, by arranging in stages a plurality of fluidised beds having different (either step-wise increasing or decreasing) fluidised particle densities, each chosen to separate specific particulate components.

The separation method and apparatus of the present invention may be used with a fluidised bed modified from the prior art bed 2 of Figures 1 and 2, so as to provide two layers of fluidised particles.

Referring to Figure 3, a fluidised bed 18 in accordance with the invention comprises two layers 20, 22 of fluidised particles of different densities, one, the lower density layer 20, floating on top of the other. The particulate mixture to be separated comprises three different (known) density components. The density of the fluidised particle layer 20 is arranged to be between that of the lowest density components 24, which, therefore, floats on top of the layer 20, and that of the intermediate density component 26, which, therefore, sinks together with the highest density component 28 through the fluidised particle layer 20.The density of the fluidised particle layer 22 is arranged to be between that of the components 26 and 28, so that the intermediate density component 26 becomes suspended at the top of the layer 22 below the layer 20, and the highest density component 28 sinks through the layer 28 to the porous base 30 of the bed 18.

It will be appreciated that the means for removing separated particulate materials from a fluidised bed will be spaced from a material inlet a distance sufficient to allow the required degree of separation to occur.

furthermore, it may be desirable to dispose means for removing the lighter and heavier materials at different distances from the material inlet.

The total depth of a plurality of fluidised particulate layers should not be too large with respect to the surface dimension of the bed, since otherwise "slugging" may occur.

"Slugging" is the disturbance of a fluidised bed in which the fluidising medium forms a large bubble in the bed which rises and breaks through to the surface, thereby producing turbulence in the bed which hinders the required separation process.

It will also be appreciated that the invention can be used for the separation of three or more components of a mixture for which respective intermediate density fluidised layers can be provided. An example of such use is the separation of different metals in scrap metal to provide batches each containing only one metal. This use is particularly relevant in separating the various metal components in swarf resulting from met alworking by hand or by machine. It may be desirable to remove contamination from the particular material, and in some cases this can be carried out at the same time as the separation. In metal separation, for example, the particulate material may be degreased by heating the fluidised bed to evaporate or burn off the grease or oil.

It will be appreciated that it is necessary to be able to separate the three or more separated components of the mixture from the particles of the fluidised bed, and this may be carried out by griddling or by similar means. Accordingly, it is necessary that the particulate material to be separated by the fluidised bed be of sufficiently different particle size from the fluidised particles.

It will also be appreciated that in general the fluidised bed has a substantially rectangular shape in plan, the longer dimension extending away from the inlet of the bed.

This is particularly advantageous when a flow of the fluidised particles along the bed is arranged to assist in separation of the particulate material.

The separated particulate material may be removed from the or each fluidised bed by being scooped therefrom, the scooping can be effected by a movable conveyor which enters the fluidised particles and which has projections thereon for entraining the lightest particulate material at the upper part of the bed.

Apart from moving the fluidised particles longitudinally of the or each bed, they may also be arranged to move transversely of the or each bed.

The means for removing the separated particles from the bed may, alternatively, comprise one or more perforated plates so as to allow fluidised particles, but not particulate material, to pass therethrough. A further alternative for removing the separated particles from the bed comprise vane means at least partially immersed in the fluidised bed and inclined to the particles flow, so as to direct the particulate material to outlet means at a wall of the bed. In this case, said vane means can comprise a first vane disposed at the upper part of the bed to direct lighter particulate material to a first wall opening and a second vane disposed at a lower part of the bed to direct heavier particulate material to a second wall opening.

The fluidised bed, in accordance with the invention, may also have a base arranged to induce a flow of the fluidised particles, such flow preferably being induced by inclining the bed base to the horizontal. This base may be pervious to the fluidising medium so as to induce the flow longitudinally of a particle inlet of the bed. Optionally, this previous bed base may induce such flow transversely of the particle inlet.

In a preferred further form of the apparatus in accordance with the invention, the bed comprises a substantially cylindrical wall containing the particles to be fluidised and arranged to transmit the fluidising medium.

This wall is also disposed substantially horizontally and is rotatably mounted about its axis. At least one member projects generally radially inwardly from the wall, whereby, on rotation of the wall, the or each member entrains heavier separated particulate material, carries it out of the fluidised particles and deposits it on collector means mounted within the cylindrical wall.

The apparatus may also comprise means for returning to the bed any fluidised particles removed therefrom by the said particulate material removal means.

WHAT WE CLAIM IS: 1. A method of separating three particulate materials of different densities, wherein the mixed materials are fed to a fluidised bed having two fluidised particle layers of different densities, wherein the lower fluidised particle density is arranged to be between the lowest and intermediate particulate material densities and the higher fluidised particle density is arranged to be between the highest and intermediate particulate material densities, and wherein the fluidity of the bed is produced by causing a non-pulsating flow of a fluid to be passed therethrough.

2. A method according to claim 1, wherein one of the separated particulate materials is removed from the said fluidised bed and fed to at least one further fluidised bed to enhance the separation.

3. A method according to claim 2, wherein the or each further fluidised bed has a different average fluidised particle density from that of the preceding bed.

4. A method according to any preceding claim, wherein the fluidity of the or each bed is produced by passing gas there-through.

5. A method according to claim 4, wherein the gas is air.

6. A method accoring to any of claims 1 to 3 wherein the fluidity of the or each bed is produced by passing liquid there-through.

7. A method according to any preceding claim, wherein separated particulate material is removed from the or each fluidised bed by being scooped therefrom.

8. A method according to claim 7, wherein the scopping is effected by a movable conveyor which enters the fluidised particles and which has projections thereon for entraining the lightest particulate material at the upper part of the fluidised bed.

9. A method according to any preceding claim, wherein the particles of the or each fluidised bed are arranged to move longitudinally of the bed, thereby to carry the particulate material along the bed.

10. A method according to claim 10,

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. desirable to remove contamination from the particular material, and in some cases this can be carried out at the same time as the separation. In metal separation, for example, the particulate material may be degreased by heating the fluidised bed to evaporate or burn off the grease or oil. It will be appreciated that it is necessary to be able to separate the three or more separated components of the mixture from the particles of the fluidised bed, and this may be carried out by griddling or by similar means. Accordingly, it is necessary that the particulate material to be separated by the fluidised bed be of sufficiently different particle size from the fluidised particles. It will also be appreciated that in general the fluidised bed has a substantially rectangular shape in plan, the longer dimension extending away from the inlet of the bed. This is particularly advantageous when a flow of the fluidised particles along the bed is arranged to assist in separation of the particulate material. The separated particulate material may be removed from the or each fluidised bed by being scooped therefrom, the scooping can be effected by a movable conveyor which enters the fluidised particles and which has projections thereon for entraining the lightest particulate material at the upper part of the bed. Apart from moving the fluidised particles longitudinally of the or each bed, they may also be arranged to move transversely of the or each bed. The means for removing the separated particles from the bed may, alternatively, comprise one or more perforated plates so as to allow fluidised particles, but not particulate material, to pass therethrough. A further alternative for removing the separated particles from the bed comprise vane means at least partially immersed in the fluidised bed and inclined to the particles flow, so as to direct the particulate material to outlet means at a wall of the bed. In this case, said vane means can comprise a first vane disposed at the upper part of the bed to direct lighter particulate material to a first wall opening and a second vane disposed at a lower part of the bed to direct heavier particulate material to a second wall opening. The fluidised bed, in accordance with the invention, may also have a base arranged to induce a flow of the fluidised particles, such flow preferably being induced by inclining the bed base to the horizontal. This base may be pervious to the fluidising medium so as to induce the flow longitudinally of a particle inlet of the bed. Optionally, this previous bed base may induce such flow transversely of the particle inlet. In a preferred further form of the apparatus in accordance with the invention, the bed comprises a substantially cylindrical wall containing the particles to be fluidised and arranged to transmit the fluidising medium. This wall is also disposed substantially horizontally and is rotatably mounted about its axis. At least one member projects generally radially inwardly from the wall, whereby, on rotation of the wall, the or each member entrains heavier separated particulate material, carries it out of the fluidised particles and deposits it on collector means mounted within the cylindrical wall. The apparatus may also comprise means for returning to the bed any fluidised particles removed therefrom by the said particulate material removal means. WHAT WE CLAIM IS:

1. A method of separating three particulate materials of different densities, wherein the mixed materials are fed to a fluidised bed having two fluidised particle layers of different densities, wherein the lower fluidised particle density is arranged to be between the lowest and intermediate particulate material densities and the higher fluidised particle density is arranged to be between the highest and intermediate particulate material densities, and wherein the fluidity of the bed is produced by causing a non-pulsating flow of a fluid to be passed therethrough.

5. A method according to claim 4, wherein the gas is air.

10. A method according to claim 10,

wherein the particles of the or each fluidised bed are arranged to move transversely of the bed.

II. A method of separating particulate materials, substantialy as hereinbefore described with reference to Figure 3 of the accompanying drawings.

12. Apparatus when for separating three particulate materials of different densitites in accordance with the method of claim 1, comprising a fluidised bed having two fluidised particle layers of different densities, the density of the lower fluidised particle layer being arranged to be between the density of the lowest and intermediate particulate materials to be separated and the density of the higher fluidised particle layer being arranged to be between the densities of the highest and intermediate particulate materials to be separated, means for causing a non-pulsating flow of fluid to be passed through the bed, and means for removing the separated particulate materials from the bed.

13. Apparatus according to claim 12, wherein said removal means comprises a conveyor having projections thereon, the conveyor being arranged to enter the fluidised bed and entrain the separated particles by means of the projections.

14. Apparatus according to claim 13, wherein the removal means comprises one or more perforated plates so as to allow fluidised particles but not particulate material to pass therethrough.

15. Apparatus according to any of claims 12 to 14, wherein the removal means comprises vane means at least partially immersed in the fluidised bed and inclined to the particle flow so as to direct the particulate material to outlet means at a wall of the bed.

16. Apparatus according to claim 15, wherein said vane means comprises a first vane disposed at the upper part of the bed to direct lighter particulate material to a first wall opening and a second vane disposed at a lower part of the bed to direct heavier particulate material to a second wall opening.

17. Apparatus according to any of claims 12 to 16, wherein the fluidised bed has a base arranged to induce a flow of the fluidised particles.

18. Apparatus according to claim 17, wherein the base of the bed is inclined to the horizontal to induce said flow.

19. Apparatus according to claim 17 or 18, wherein the base is pervious to a fluidising medium of the bed so as to induce a flow of fluidised particles longitudinally of a particle inlet of the bed.

20. Apparatus according to any of claims 17 to 19, wherein the base is pervious to a fluidising medium of the bed so as to induce a flow of fluidised particles transversely of a particle inlet of the bed.

21. Apparatus according to any of claims 17 to 20, wherein the base has apertures therein directed so as to induce said flow.

22. Apparatus according to claim 13, the fluidised bed comprising a substantially cylindrical wall containing the particles to be fluidised, the wall being arranged to transmit a medium for fluidising the particles, wherein the wall is disposed substantially horizontally and is rotatably mounted about its axis, the wall having at least one member projecting generally radially inwardly, whereby on rotation of the wall the or each projecting member entrains heavier separated particulate material, carries it out of the fluidised particles and deposits it on collector means mounted within the cylindrical wall.

23. Apparatus according to any of claims 12 to 22, comprising means for returning to the fluidised bed any fluidised particles removed therefrom by said particulate material removal means.

24. Apparatus when used for separating three particulate materials of different densities in accordance with the method of any one of claims I to 11, substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.