This invention relates generally to apparatus for separating or classifying materials and more particularly, to hydrocyclones.

Hydrocyclones have been used in the past as liquid-liquid separators, solid-solid separators and thickeners. They have been used in many industries including the paper industry, chemical industry and minerals industry. In the mining industry they have often been used as classifiers in applications such as mine fill preparation and coal preparation.

A conventional hydrocyclone generally comprises a main body which is conical in shape, which is connected at the bottom to an open apex piece, and at the top to a cylindrical inlet section. Feed material is injected tangentialiy into the cylindrical inlet section. The top of the cylindrical section has an outlet in the form of an overflow pipe passing through it. The overflow pipe is axially mounted and extends into the body of the hydrocyclone. The extension of the pipe into the hydrocyclone is known as the vortex finder. An underflow outlet is provided at the apex piece.

The design variables of a hydrocyclone are shown in Figure 1 and consist of the following :

1. hydrocyclone diameter, D _c ; 2. vortex finder length, L _v ;

3. vortex finder diameter, D ₀ ;

4. vortex finder outer diameter, D ₀ ';

5. cone angle, θ;

6. cyclone length, L; 7. apex diameter, D _u and

8. feed inlet diameter, D,.

In operation fluid containing the material to be separated is led tangentialiy into

the cyclone near the vortex finder and moves down adjacent to the walls of the cyclone body and creates the outer downward spiral.

The rotational flow component results in particles experiencing an outwards centrifugal force tending to move them towards the wall and to discharge with the underflow, but this force is opposed by the fluid drag which tends to make particles flow with the bulk of the fluid and exit with the overflow. Depending on the balance of these forces, the underflow is chiefly composed of coarser particles while fines report to the overflow, but the classification process is not perfect and misplacement of both coarse and fine particles occurs to the overflow and underflow streams respectively. In particular, fine particles tend to become entrained in the flow of material down the walls of the cyclone and pass out in the under flow. Il is desirable to try and reduce this misplaced material.

It is object of the present invention to provide an improved hydrocyclone which improves the separation of finer and coarse materials.

According to one aspect of the present invention there is provided a hydrocyclone including means to inject fluid into the hydrocyclone having a sidewall whereby the fluid forms a boundary layer between an interior surface of the hydrocyclone and the slurry for separation by the cyclone whereby friction between the slurry and said side wall is minimised.

According to another aspect of the present invention there is provided a hydrocyclone which includes a main body having a wall having a generally conically shaped inner surface forming a separating chamber therein with a base end and an apex end. A feed inlet is provided for delivering material to be separated into the separating chamber at the base end thereof. An overflow outlet and underflow outlet are provided for the discharge of the separated portions of the feed material. At least a section of the conically shaped wall of the separating chamber is comprised of a fluid permeable material and the hydrocyclone further includes means for causing the passage of fluid through the permeable wall section from externally thereof into the separating chamber when in operation.

In one preferred form substantially the entire wall of the main body forming separating chamber is comprised of fluid permeable material.

The fluid permeable wall may be formed from any suitable material such as. for example, a fluid permeable plastics material. One example material for the wall is high density permeable polyethylene. The wall may, for example, be formed of high density polyethylene of 40 micro metres pore size. The thickness of the wall may be about 12mm, although it will be appreciated that other thicknesses could equally be used. An example of a suitable material is POREX "Porto-aire". The wall may be strengthened by the use of a series of reinforcing ribs which permit it to operate under higher pressures.

Preferably, the fluid permeable portion of the wall is disposed within a jacket or sleeve which forms a reservoir of fluid externally of the wall. In operation, the fluid in the reservoir may be maintained at a pressure greater than the operating pressure of the hydrocyclone when in use, so that fluid from the reservoir will tend to pass through the porous wall into the separating chamber. Fluid may be delivered to the reservoir continually so that the pressure within the reservoir is maintained at the selected pressure. Any suitable fluid may be used and preferably, the fluid is a liquid. One example of a suitable fluid is water.

Locating ribs may be provided on the outer surface of the wall so that the separating section can be correctly located within the jacket or sleeve. The locating flanges or ribs may have holes therein so that the fluid can pass through the flange.

In order to enable a clearer understanding of the invention, drawings illustrating an example embodiment are attached and in those drawings :

Figure 1 is a diagrammatic view of a hydrocyclone showing the various design variables;

Figure 2 is a schematic side elevation of a hydrocyclone according to (he present

invention;

Figure 3 is a detail of the separation section of the hydrocyclone shown in Figure 1 ; and

Figure 4 is a diagrammatic view of the test rig used for comparative testing

Referring to Figures 1 and 2 of the drawings, the hydrocyclone generally indicated at 1 comprises a inlet section 2, a separating section 3 and an apex 4. The separating section 3 comprises a main body having conically shaped inner wall with a base end 6 and an apex end 7. The main body is formed of a fluid permeable material which can be of the type described earlier.

The inlet section 2 is generally cylindrical in shape and has a feed inlet 15 for delivering material to be separated into that section. The feed inlet 15 is generally tangential with respect to the inlet section 2. The hydrocyclone further includes an underflow outlet 8 at the apex end and an overflow outlet 10 at the inlet section end.

There is further provided a vortex finder 16 at the overflow outlet.

The conical inner wall of the separating section defines a separating chamber 3.

The conically walled separating section is disposed within a jacket or sleeve 12 forming a fluid reservoir externally of the fluid permeable wall. An inlet 14 enables water to be delivered to the reservoir within the jacket 12. Locating ribs 18 are disposed on the inner wall of the jacket or sleeve 12, the ribs having holes therein to permit the passage of fluid to all areas of the reservoir.

EXAMPLE

A comparative test between a conventional hydrocyclone and one according to the invention was conducted. A hydrocyclone having a porous conical wall with the water jacket constructed in such a way as to be easily attached to existing cylindrical and apex sections of a 90mm Warman (Trade Mark) cyclone. A conventional cyclone with the same dimensions as the porous cyclone was also used. The relevant dimensions of the

fluid permeable and conventional cyclone are set out below.

Cyclone cone length, L 370mm

Inlet diameter, D; 38mm

Apex diameter, D _u 20mm

Vortex finder internal diameter, D ₀ 40mm

Cone Angle, θ 10°

The hydrocyclone test rig used for the Warman cyclones of the present invention is illustrated in Figure 4. The cyclone was arranged in closed circuit with a slurry pump and sump. The pump was driven by a 7.5 kW motor. An impeller, mounted vertically in the sump, ensured adequate mixing of the solid suspension. The impeller was driven by a 1.5 kW motor. The feed rate to the cyclone was controlled by valves on a by-pass line and regulated using a pressure gauge fitted to the by-pass line.

Mounted on the top of the sump was a sampling device for collecting the overflow and underflow streams.

The water jacket for the cyclone of the present invention was connected by a hose to mains pressure. The flow rate was adjusted by tap control and measured by an in-linc flow meter. A single flow meter was used having a capacity of 0 - 3000 cc/min.

The tests conducted on the fluid permeable cyclone and the Warman cyclone used 60G silica. The technical information provides a typical analysis, physical characteristics and sizing of the material.

Typical Analysis: Silica (SiO ₂ ) 99.0%

Iron Oxide (Fe ₂ O ₃ ) 0.03%

Physical Characteristics: pH 6.9

Specific Gravity 2.65

Hardness (Mohs) 7

Sizing:

Size (μm) % below (60G)

250 95

150 92

75 78

53 65

45 50

30 40

20 30

10 12

5 8

3 4

The following procedure was adopted for all of the tests.

1. The water jacket was connected to mains pressure and the tap turned on to give a much larger llow rate than actually required.

2. The sump was filled to capacity with water and the pump started. The feed pulp density was adjusted by adding solids as required. The pulp density was measured using a Marcy gauge.

3. The feed pressure and water injection rate were adjusted and the system allowed to run for sufficient time to achieve stable conditions of solids dispersion, feed pressure and water injection.

4. Underflow and overflow samples were collected simultaneously for a recorded period of time using the sampling device described earlier.

5. The samples were sized using a Master Sizer E series size analyser.

6. The pulp densities of the underflow and overflow were obtained by weighing the samples wet and oven dried at 105°C for 48 hours.

Four tests were carried out with the porous hydrocyclone, namely:

1. no injection (using conventional cyclone of the same dimensions); 2. 600 cc/min injection;

3. 800 cc/min injection and

4. 1000 cc/min injection.

The feed pressure of all of the tests was 20 kPa. The feed pressure was kept to a minimum because of the fragile nature of the porous polyethylene making up the conical section of the cyclone. To prevent any flow of pulp out of the cyclone through the porous walls, the injection water was turned on before the pump was started.

The results of the tests revealed that the amount of fines escaping through the underflow outlet were reduced when compared with the conventional Warman hydrocyclone.

Finally, it is to be understood that the inventive concept in any of its aspects can

be incorporated in many different constructions so that the generality of the preceding description is not to be superceded by the particularity of the attached drawings. Various alterations, modifications and/or additions may be incorporated into the various constructions and arrangements of parts without departing from the spirit or ambit of the invention.