GB2107612A - Method of and flotation cell for the flotation of solids - Google Patents

Abstract

A method of floation of solids, e.g. coal or ore, slurry in a flotation cell comprises introducing air into the cell to produce bubbles, the air moving first downwardly in a descent region and then moving upwardly to the surface outside the descent region.

Description

SPECIFICATION Method of and flotation cell for the flotation of coal or ore The invention relates to a method for the flotation of coal or ore slurrys in a flotation cell into which air is introduced for the formation of bubbles as well as to a flotation cell for carrying out the method.

In the flotation of coal or ore, it is known to use flotation cells which comprise an agitator which supplies air to the slurry through its hollow shaft. The agitator ensures a swirling motion of the slurry and a uniform distribution of the air. These known flotations achieve a satisfactory purity of the floated product but it is a disadvantage that during the flotation of coal, for example, the proportion of coal in the ash is not inconsiderable and that very fine coal, for example with grain sizes below 20y, cannot be floated.

The invention seeks to provide a method of flotation and a flotation cell with which it is possible, with substantially the same purity of the floated product, to reduce considerably the proportion of coal in the waste and to extend the range of grain sizes in which a floatation is possible to particles of 3-51l.

According to a first aspect of the invention, there is provided a method of flotation of a coal or ore slurry in a floation cell into which air is introduced to form bubbles, wherein the air, in bubble form in the slurry, first moves from the top downwards in a descent region than reverses its direction of movement and rises to the surface of the flotation cell again, outside the descent region.

As a result of this method, the path of the air bubbles in the slurry becomes longer in an advantageous manner. Furthermore, a slow rise of the bubbles is rendered possible in a calm part of the flotation cell which part, in addition, is considerably larger in size than the entry region. Thus the coal or ore particles can accumulate optimally on the bubbles, which also renders it possible for very small particles of coal or ore, the movements of which in the slurry are very slow, to accumulate on the bubbles. A separation as a result of the different sinking rates of the coal and ash particles in the calm ascent zone also plays a part in this.

The air may be introduced by a free jet of slurry, particularly on extending vertically, into the flotation cell. In this manner, a particularly simple refinement of the flotation method results, with simultaneous satisfactory entry of air in bubble form with the required movement at first leading downwards. Surprisingly, it has been found that a free jet can introduce an amount of air into the slurry which is equivalent to the amount of air which is introduced by a pressure aerated agitator.

The free jet of slurry may comprise a plurality of individual free jets. As a result of the division of the free jet of slurry into a plurality of individual free jets, an effect of air fed into the slurry results which leads to particularly small bubbles with a simultaneous satisfactory distribution in the feed region.

The introduction of the air may be regulated by varying the inlet pressure of the free jet of slurry. As a result of varying the inlet pressure, a particularly simple method of regulating the amount of air which is introduced into the slurry is avialable. Thus a controllability of the amount of flotation air results which corresponds to the controllability of the amount of air with a pressure aerated agitator system.

It may be provided, in this case, for the inlet pressure of the free jet of slurry to amount to 1-5 bar, but particularly 2-3 bar.

The range from 1-5 bar has proved to be the practicable range within which the inlet pressure can be varied. The range of 2-3 bar is particularly favourable for the flotation of coal.

Higher pressure than 5 bar lead to an undesirably severe whirling up of the slurry, at 1-2 bar the outlet velocity of the free jet of slurry is to low for a satisfactory air feed.

According to a second aspect of the invention, there is provided a flotation cell for flotation of a coal or an ore slurry comprising a slurry container and means for introducing air into the slurry container such that it moves initially downwardly and thereafter upwardly outside the region of the downward moving air.

The floatationall may have a slurry container to which the slurry is fed from above. The flotation cell may comprise a free-jet nozzle for the slurry which is disposed above the surface of the slurry container and out of which a free jet of slurry emerges. Thus the carrying out of the method according to the invention is made possible.

The free jet of slurry may comprise a jacket encasing tube which extends below the surface of the slurry.

The feed region and the ascent region inside the floataion cell are separated from one another in an advantageous manner by a sleeve tube. Thus the rise of the air bubbles can be effected in a zone which is calmed with regard to flow. The entry of the free jet with its eddy formation does not influence the ascent region.

The depth of immersion of the jacket encasing tube may amount to 0.25 to 0.65 times the depth of the cell, 0.3 to 0.4 times the depth of the cell being particularly suitable. It has been found that 0.25 times the depth of the cell is the minimum in order to obtain a satisfactory separation of the feed region from the ascent region. An extension below 0.65 times the depth of the cell has proved unfavourable. About 0.3 to 0.4 times the depth of the cell is the most favourable and leads to a satisfactory separation of the feed region from the ascent region as well as a favourable development of flow in the lower portion of the flotation cell.

The flotation cell may comprise a free-jet nozzle for the slurry, which nozzle is constructed in the form of a nozzle head with a plurality of outlets. Thus the feed of the slurry into the flotation cell can be equalized and an advantageous prior mixing of the slurry with the air before entry into the flotation cell is rendered possible.

The flotation cell may comprise a plurality of free-jet nozzles for the slurry. As a result, it is possible, in an advantageous manner, to work with large amounts of slurry with small nozzle heads which ensure a satisfactory mixing of slurry and air.

The outlets of the nozzle head may have a diameter of 1-5mm but particularly of 2-3mm. It has been found that outlets of less than 1 mm wear greatly and produce jets which are too fine. Above 5mm, the jets are too thick so that the mixing of the slurry with the air may be disturbed. The range from 2-3 mm has proved particularly favourable.

The flotation cell may be cylindrical in construction with a central slurry feed and a rotating foam stripping device may be disposed round the free-jet sleeve tube. In a cylindrical construction, a flotation cell may result having a particularly favourable ratio of the feed area to the ascent area with simultaneous favourable stripping off of foam in a rotating foam collecting chamber for example.

The flotation cell may be rectangular in construction with a pluarlity of free jets of slurry disposed in the longitudinal direction.

This embodiment is favourable to manufacture and can be installed in a particularly spacesaving manner. The slurry feed may be effected in a feed trough either at one side or centrally along the centre axis of the cell. The ratio of the width of the feed trough to the width of the ascent zone may be selected so that the width of the ascent zone amounts to a multiple of the width of the feed trough.

The flotation method according to the invention may work particularly favourably, in the case of very fine coal slurrys, if the slurry travels in succession through a plurality of flotation cells, particularly three, and if a conditioner device, in which the flotation adjuvant is distributed, is disposed before the first flotation cell. It can also be operated, howev er,--depending on the nature of the substance to be floated and/or its grain size- with a larger or smaller number of cells and without preconditioning.

The invention will now be described in greater detail, by way of example, with reference to drawings in which: Figure 1 shows an individual cell of cylindrical construction and; Figure 2 shows a nozzle head in section.

In Fig. 1, 1 designates the flotation cell with the slurry 2 present therein. Projecting into the slurry 2 is the jacket encasing tube 3 which surrounds the free jet of slurry 5 emerging from the nozzle head 4. Disposed at the top on the jacket encasing tube 3 is the drive 6 for the foam stripper 8. The drive 6 rotates the jacket encasing tube 3 and so moves the foam stripper 8 at the same time.

The bridge element 7 is mounted fixed in a manner not shown. Between the carrier 9 for the nozzle head 4 and the jacket encasing tube 3 there is a ball bearing so that the jacket encasing tube 3 can rotate freely round the nozzle-head holder 9.

The lower portion of the flotation cell 1 is conical in construction. Thus the waste sinking down reaches the outlet 10 and from here passes into the equalising tank 11 which serves at the same time as a storage container for the pump which causes the feed to the next cell. Also mounted on the outlet 10, at the bottom, is a valve 1 2 so that a complete emptying of the floatation cell is possible.

With a rectangular construction, the equalizing and storage container should form part of the floatation cell, for example at one longitudinal wall, and is only separated from the ascent area by a partition which is extended down to just above the bottom of the flotation cell. Thus a particularly economical and compact form of construction results with which it is a particular advantage if the centrifugal pump for conveying the slurry into the next cell is disposed directly below the flotation cell.

In Fig. 2, 1 2 designates the supply pipe for the slurry-as in Fig. 1. Inserted in the supply pipe 1 2 for the slurry is a sleeve 1 3 which carries, at its outlet end, a retaining nut 1 5 which holds a nozzle plate 1 4. Disposed between the nozzle plate 14 with the outlets 1 6 for the slurry and the inserted sleeve 1 3 is an annular seal 1 5 so that the nozzle plate 14 is sealed off from the retaining nut 1 5. The number of outlets 1 6 in the nozzle plate is optional and, like the diameter of the aperture 16, is selected according to the nature of the slurry and the amount of slurry. For a round individual cell, it has proved satisfactory to provide four slurry outlets 1 6. The four represents the minimum number of outlets, with large amounts of slurry, in particular, a multiple of this number of outlets is used.

The flotation method according to the invention has been developed in particular for the flotation of coal. Without departing from the scope of the invention, however, it can also be used for the flotation of ore, communal sewage, slurrys containing fibres etc. The advantageous effect, according to the invention, of the long path of the air bubbles through the slurry is always obtained, with the possibility of accumulation of even the finest particles and the rise of the air bubbles in a calm zone not influenced by the eddy field of an agitator.

Claims (21)

1. A method of flotation of a coal or ore slurry in a flotation cell into which air is introduced to form bubbles, wherein the air, in bubble form in the slurry, first moves from the top downwards in a descent region then reverses its direction of movement and rises to the surface of the flotation cell again, outside the descent region.

2. A method as claimed in claim 1, wherein the air is introduced into the floation cell through a free jet of slurry particularly one extending vertically.

3. A method as claimed in claim 2, wherein the jet extends vertically.

4. A method as claimed in claim 1 or 2, wherein the free jet of slurry consists of a plurality of individual free jets.

5. A method as claimed in any of claims 1 to 4, wherein the introduction of the air is regulated by varying the inlet pressure of the free jet of slurry.

6. A method as claimed in any one of claims 1 ot 5, wheren the inlet pressure of the free jet of slurry amounts to 1-5 bar.

7. A method as claimed in claim 6, wherein pressure is 2-3 bar.

8. A flotation cell for flotation of a coal or an ore slurry comprising slurry container and means for introducting air into the slurry container such that it moves initially downwardly and thereafter upwardly outside the region of the downward moving air.

9. A flotation cell as claimded in claim 8, with a slurry container to which the slurry is fed from above, wherein a free-jet nozzle is provided for the slurry, which nozzle is disposed above the surface of the slurry container and out of which a free jet of slurry emerges.

10. A flotation cell as claimed in claim 9, wherein the free jet comprises a sleeve tube surrounding the nozzle and extending below the surface of the slurry.

11. A floation cell as claimed in claim 10, wherein the depth of immersion of the sleeve tube amounts to 0.25 to 0.65 times the depth of the cell.

1 2. A flotation cell as claimed in claim 10 or 11, wheren the depth of immersion of the sleeve tube amounts to 0.3 to 0.4 times the depth of the cell.

1 3. A flotation cell as claimed in any one of claims 9 to 11, wherein the free jet nozzle is constructed in the form of nozzle head with a plurality of outlets.

1 4. A flotation cell as claimed in any one of claims 9 to 13, wherein a plurality of freejet nozzles are provided for the slurry.

1 5. A flotation cell as claimed in claim 13, wherein the outlets of the nozzle heads have a diameter of 1-5 mm.

1 6. A flotation cell as claimed in claim 1 3 or 15, wherein the outlet of the nozzle head have a diameter of 2-3mm.

1 7. A flotation cell as claimed in any one of claims 8 to 16, wherein the slurry container is cylindrical in construction with a central slurry feed.

18. A flotation cell as claimed in claim 1 7 when appendent directly or indirectly to claim 10, wheren a rotating foam stripping device is disposed round the free-jet sleeve tube.

19. A flotation cell as claimed in any one of the claims 9 to 16, wherein the slurry container is rectangular in construction with a plurality of free jets of slurry disposed in the longitudinal direction.

20. A method of flotation of coal or ore slurry in a flotation cell substantially as described herein with reference to the drawings.

21. A flotation cell for coal or ore slurry substantially as described herein with reference to the drawings.