METHOD

FIELD OF THE INVENTION

This invention relates to a centrifugal separator arrangement and method.

BACKGROUND TO THE INVENTION Centrifugal separators are widely used in the mineral processing industry to separate a feed of materials into at least two fractions according to the size or density of the materials. The feed of materials may include solids, fluids or both. Conventional centrifugal separators are either conically-shaped or cylindrically-shaped. These centrifugal separators include a cylindrical inlet section into which the materials are fed tangentially through an inlet. As a result, a circular motion is imparted to the materials which will cause larger and/or heavier materials to migrate outwardly towards the inner wall of the separator and exit the separator through a first outlet. Smaller and/or lighter materials, on the other hand, will move inwardly and exit the separator through a second outlet. It is known in the art to have a centrifugal separator arrangement consisting of two centrifugal separators connected in series so that a fraction of materials exiting a first or primary centrifugal separator enters a second or secondary centrifugal separator for further separation of the fraction of materials. The first centrifugal separator separates the materials it receives at a first set size and/or density. The second centrifugal separator separates the fraction of materials it receives at a second set size and/or density, which may be similar or different to that of the first centrifugal separator. Such a centrifugal separator arrangement is generally known as a three-product centrifugal separator since three or more products or fraction are obtained from the feed of materials.

A disadvantage associated with the three-product centrifugal separator arrangement described above is that it is difficult to independently control the separation process of the second or secondary centrifugal separator in terms of the density or size of the materials.

OBJECT OF THE INVENTION

It is accordingly an object of the present invention to provide a centrifugal separator arrangement and method that will, at least partially, overcome the above disadvantage, and/or to provide a useful alternative to existing centrifugal separator arrangements and methods. SUMMARY OF THE INVENTION

In accordance with a first aspect of this invention there is provided a centrifugal separator arrangement comprising:

- a first centrifugal separator;

- a second centrifugal separator connected in series to the first centrifugal separator whereby a first fraction of material discharging from an outlet of the first centrifugal separator may enter an inlet of the second centrifugal separator; and

- an auxiliary inlet located between the outlet of the first centrifugal separator and the inlet of the second centrifugal separator through which a control material is added to control one or more characteristics of the first fraction of material selected from pressure, density and volumetric flow rate of the first fraction of material.

A conduit may connect the outlet of the first centrifugal separator to the inlet of the second centrifugal separator and define the auxiliary inlet intermediate the first and second centrifugal separators. The conduit may include a first optional control valve for controlling the rate of discharge of the first fraction of material. The control material may be added through the auxiliary inlet by means of gravity, or through mechanical means, including a pump.

The auxiliary inlet may be defined by at least one of a t-piece, mixing chamber and nozzle. The nozzle may be a fixed nozzle or adjustable.

The control material may be at least one of a fluid and a combination of a fluid and solid material. The fluid may be water and the solid material may be magnetite or ferrosilicon.

The centrifugal separator arrangement may also include a sensing device for sensing at least one or more of the pressure, density and volumetric flow rate of the first fraction of material.

In some embodiments of the invention the auxiliary inlet may be one of a plurality of auxiliary inlets located between the outlet of the first centrifugal separator and the inlet of the second centrifugal separator.

Each of the plurality of auxiliary inlets may be defined by at least one of a t-piece, mixing chamber and nozzle. The nozzle may be a fixed nozzle or adjustable. The first centrifugal separator may be either conically-shaped or cylindrically-shaped.

The second centrifugal separator may be either conically-shaped or cylindrically-shaped.

In accordance with a second aspect of this invention there is provided a method of separating a feed of material into at least two fractions of material, the method including the steps of:

- providing a first centrifugal separator;

- providing a second centrifugal separator connected in series to the first centrifugal separator;

- allowing a first fraction of material discharging from an outlet of the first centrifugal separator to enter an iniet of the second centrifugal separator; and

- controlling one or more characteristics of the first fraction of material selected from pressure, density and volumetric flow rate of the first fraction of material by adding a control material to the first fraction of material.

The control material may be added through an auxiliary inlet defined in a conduit which is used for conveying the first fraction of material from the outlet of the first centrifugal separator to the inlet of the second centrifugal separator.

The control material may be added by means of gravity, or through mechanical means, including a pump.

The auxiliary inlet may be defined by at least one of a t-piece, mixing chamber and nozzle. The nozzle may be a fixed nozzle or adjustable. The control material may be at least one of a fluid and a combination of a fluid and solid material.

The fluid may be water and the solid material may be magnetite or ferrosilicon.

The method may also include the step of providing a first optional control valve intermediate the outlet of the first centrifugal separator and the inlet of the second centrifugal separator for controlling the rate of discharge of the first fraction of material.

The method may include the further step of sensing at least one of the pressure, density and volumetric flow rate of the first fraction of material. The auxiliary inlet may be one of a plurality of auxiliary inlets located between the outlet of the first centrifugal separator and the inlet of the second centrifugal separator. Each of the plurality of auxiliary inlets may be defined by at least one of a t-piece, mixing chamber and nozzle. The nozzle may be a fixed nozzle or adjustable.

The first centrifugal separator may be either conically-shaped or cylindrically-shaped.

The second centrifugal separator may be either conically-shaped or cylindrically-shaped. These and other features of the invention are described in more detail below.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention are described below, by way of non-limiting examples only, and with reference to the accompanying drawings in which: is a schematic side view of a centrifugal separator arrangement according to a first embodiment of the invention wherein first and second centrifugal separators are conically- shaped and wherein a control material is added to a first fraction of material through an auxiliary inlet by means of a pump; is a detail cross-sectional view of the auxiliary inlet of figure 1 , wherein the auxiliary inlet is in the form of a t-piece; is a detail cross-sectional view of the auxiliary inlet of figure 1 , wherein the auxiliary inlet is in the form of a nozzle; is a detail side view of the auxiliary inlet in figure 1 , wherein the auxiliary inlet is in the form of a mixing chamber; is a schematic side view of a centrifugal separator arrangement according to a second embodiment of the invention wherein control material is added through two auxiliary inlets; figure 6 is a schematic side view of a centrifugal separator arrangement according to a third embodiment of the invention wherein first and second centrifugal separators are conically-shaped and wherein a control material is added to a first fraction of material through an auxiliary inlet by means of gravity; figure 7 is a schematic side view of a centrifugal separator arrangement according to a fourth embodiment of the invention wherein a first centrifugal separator is cylindrically- shaped and a second centrifugal separator is conically-shaped and wherein a control material is added to a first fraction of material through an auxiliary inlet by means of a pump; figure 8 is a schematic side view of a centrifugal separator arrangement according to a fifth embodiment of the invention wherein a first centrifugal separator is cylindrically-shaped and a second centrifugal separator is conically-shaped and wherein a control material is added to a first fraction of material through an auxiliary inlet by means of gravity; figure 9 is a schematic side view of a centrifugal separator arrangement according to a sixth embodiment of the invention wherein a first centrifugal separator is conically-shaped and a second centrifugal separator is cylindrically-shaped and wherein a control material is added to a first fraction of material through an auxiliary inlet by means of a pump; figure 10 is a schematic side view of a centrifugal separator arrangement according to a seventh embodiment of the invention wherein a first centrifugal separator is conically- shaped and a second centrifugal separator is cylindrically- shaped and wherein a control material is added to a first fraction of material through an auxiliary inlet by means of gravity; figure 1 1 is a schematic side view of a centrifugal separator arrangement according to a eighth embodiment of the invention wherein first and second centrifugal separators are cylindrically-shaped and wherein a control material is added to a first fraction of material through an auxiliary inlet by means of a pump; figure 12 is a schematic side view of a centrifugal separator arrangement according to a ninth embodiment of the invention wherein first and second centrifugal separators are cylindrically-shaped and wherein a control material is added to a first fraction of material through an auxiliary inlet by means of gravity; figure 13 is a schematic side view of a centrifugal separator arrangement according to a tenth embodiment of the invention wherein a first centrifugal separator is cylindrically-shaped having two inlets and two outlets and a second centrifugal separator is conically-shaped and wherein a control material is added to a first fraction of material through an auxiliary inlet by means of a pump; figure 14 is a schematic side view of a centrifugal separator arrangement according to a eleventh embodiment of the invention wherein a first centrifugal separator is cylindrically- shaped having two inlets and two outlets and a second centrifugal separator is conically-shaped and wherein a control material is added to a first fraction of material through an auxiliary inlet by means of gravity; figure 15 is a schematic side view of a centrifugal separator arrangement according to a twelfth embodiment of the invention wherein first and second centrifugal separators are cylindrically-shaped, the first centrifugal separator including two inlets and two outlets and wherein a control material is added to a first fraction of material through an auxiliary inlet by means of a pump; and figure 16 is a schematic side view of a centrifugal separator arrangement according to a thirteenth embodiment of the invention wherein first and second centrifugal separators are cylindrically-shaped, the first centrifugal separator including two inlets and two outlets and wherein a control material is added to a first fraction of material through an auxiliary inlet by means of gravity.

DETAILED DESCRIPTION OF THE INVENTION With reference to the drawings, in which like numerals refer to like features, a centrifugal separator arrangement, for use in a centrifugal separation process including, but not limited to dense medium separation, classification and liquid-liquid separation, is generally indicated by reference numeral 10.

Referring to figures 1 to 4, which show a first embodiment of the invention, the separator arrangement 10 comprises a first centrifugal separator, in the form of a conical separator 12, and a second centrifugal separator, also in the form of a conical separator 14. The centrifugal separators 12 and 14 are connected in series by means of a conduit 16 so that, in use, a first fraction of material (flow indicated by arrow A) that discharges from an outlet 18 of the first conical separator 12 enters an inlet 20 of the second conical separator 14. A first optional control valve 22 is provided on the conduit 16 for controlling the rate of discharge of the first fraction of material A from the first centrifugal separator 12. It is envisaged that the first optional control valve 22 does not have to be included in all the embodiments of the invention.

The conduit 16 defines an auxiliary inlet 24 intermediate the first and second centrifugal separators 12 and 14 through which, in use, a control material (flow indicated by arrow B) is added to control one or more characteristics of the first fraction of material A selected from pressure, density and volumetric flow rate of the first fraction of material A. According to the embodiment shown, the control material B is added through mechanical means, by using a pump 26. A second optional control valve 28 is provided adjacent the auxiliary inlet 24 for controlling the rate of addition of the control material B.

The rate of addition of the control material B by the pump 26 is dependent on any one of the pressure, density and volumetric flow rate of the first fraction of material A. The pressure, density and volumetric flow rate of the first fraction of material A could thus be manipulated through the addition of the control material B to it. The control material B could be either a fluid, such as water, or it could be a combination of a fluid, such as water and a solid material, such as magnetite or ferrosilicon.

As illustrated in figures 2 to 4, the auxiliary inlet 24 could be defined by a t- piece (figure 2), nozzle (figure 3) and mixing chamber (figure 4). The nozzle shown in figure 3 is a fixed nozzle, although it is foreseen that the nozzle could also be adjustable.

The separator arrangement 10 further includes a sensing device 30 connected to the conduit 16 for sensing at least one or more of the pressure, density or volumetric flow rate of the first fraction of material A in the conduit 16. Any deviation in the sensed pressure, density or volumetric flow rate from the required will be communicated to the pump 26 or second optional control valve 28, or both, which will perform accordingly to counteract such deviation . It should be noted that the sensing device 30 could be placed at any location along the length of the conduit 16. In this instance the sensing device 30 is located between the auxiliary inlet 24 and the inlet 18, but it could be located before the auxiliary inlet 24 on the conduit 16. As discussed further below, it is also envisaged that more than one sensing device 30 could also be used. In use, the first conical separator 12 receives through an inlet 32 a feed of raw material (flow indicated by the arrow C), such as coal, for example, which is to be separated centrifugally according to size and/or density. It should be noted that the feed material may be a fluid, or a combination of a fluid and solid material. A circular motion is imparted to the feed material C as a result of the position and orientation of the inlet 32 on the first centrifugal separator 12. Generally, the first fraction of material A which comprises larger and/or heavier materials will migrate outwardly and exit the conical separator 12 through outlet 18, which outlet 18 is at a general tangential angle relative to the separator 12. Also, a second fraction of materials which comprises generally smaller and/or lighter materials will move inwardly and exit the separator 12 through a second outlet 34, as indicated by the arrow D. The separator 12 is designed and controlled so that materials of a pre-determined size and/or density will exit through the outlet 18, and materials of a different pre-determined size and/or density will exit through the second outlet 34.

During normal operation of the separator 12, the volumetric flow rate, pressure and/or density of the materials exiting through outlets 1 8 and 34 could differ. To compensate for these variations in respect of the first fraction of material A exiting through outlet 18, the control material B is added to the first fraction of material A so to control the volumetric flow rate, pressure and/or density thereof in the conduit 16. The addition of the control material B is advantageous in that it allows for the control of the second separator 14 without affecting the first separator 12 within certain limits. This also improves the efficiency of the second separator 14. The material received by the second centrifugal separator 14 are further separated and discharged in two fractions through outlets 36 and 38 respectively, indicated by arrows E and F in figure 1.

Referring now to figure 5, which illustrates a second embodiment of the invention which is constructed the same and functions the same as the first embodiment shown in figures 1 to 4, except for a few differences mentioned below. The auxiliary inlet 24 is one of two or a plurality of auxiliary inlets 24 which are spaced along the length of the conduit 16. Each of the plurality of auxiliary inlets 24 could be defined by at least one of the t-piece, nozzle and mixing chamber, shown in figures 2 to 4 and discussed above. A further first optional control valve 22 sensing device 30 are provided in the conduit 16. It should be appreciated that amount and positions of the control valves 22 and sensing devices 30 are merely provided as an example, and should not be construed to limit the scope of the invention. Any number of control valves 22 and sensing devices 30 could be used, and if used, could be positioned at any location along the conduit 16. By having more than one auxiliary inlet 24 is especially useful for regulating the pressure in the conduit 16, and in particular at the outlet 18 of the first separator 12 and inlet 20 of the second separator 14. For example, by adding the control material B by means of a t-piece only could result in a back pressure being created at the outlet 18 of the first separator 12. Similarly, by adding the control material B by means of a nozzle only could create a suction at the outlet 18 of the first separator 12. Therefore, by utilizing two or more auxiliary inlets 24 in series, for example one being a t-piece and the other a nozzle, and by selectively discharging the control material B through the respective inlets 24, the pressure inside the conduit 16 could relatively easily and effectively be manipulated. It should be noted that the t-piece shown in figure 2 is not limited to the configuration shown and could, for example, also extend to a t-piece having an angled side arm. This form of a t-piece would reduce the amount of back pressure being created.

Turning now to figure 6, it illustrates a third embodiment of the centrifugal separator arrangement 10. This third embodiment of the invention is constructed the same and functions the same as the first embodiment shown in figures 1 to 4 and described above, save for the omission of the pump 26 and the location of the measuring device 30 on the conduit 16. According to the third embodiment, the control material B is stored in a vessel, container or receptacle 40 located at a position which is higher than inlet 24, The control material B is fed by means of gravity through the auxiliary inlet 24. By having the sensing device 30 located, for example, between the outlet 18 and the auxiliary inlet 24, the pressure, density or volumetric flow rate of the first fraction of material A could be sensed before it passes the auxiliary inlet 24. The measurement is then used, similarly as explained above, to determine the rate of addition of control material, if any needs to be added. It is also envisaged that more than one sensing devices can be used to independently control the two separators 12 and 14.

A fourth embodiment of the centrifugal separator arrangement 10 is shown in figure 7, wherein the conically-shaped first centrifugal separator 12 of the first embodiment of the invention, shown in figure 1 , is merely substituted with a cylindrically-shaped separator 42.

Referring to figure 8, it shows a fifth embodiment of the centrifugal separator arrangement 10 which is same as the third embodiment of the invention, shown in figure 6, save for the substitution of the conically- shaped first centrifugal separator 12 with a cylindrically-shaped separator 42 and the position of the sensing device 30 on the conduit 16. It is envisaged that more than one sensing device 30 could also be used. With reference to figure 9, a sixth embodiment of the centrifugal separator arrangement 10 is similar to the first embodiment of the invention, shown in figure 1 , save for the substitution of the conically-shaped second centrifugal separator 14 with a cylindrically-shaped separator 44.

A seventh embodiment of the centrifugal separator arrangement 10, shown in figure 10 which, is similar to the third embodiment of the invention, shown in figure 6, save for the substitution of the conically- shaped second centrifugal separator 14 with a cylindrically-shaped separator 44 and the position of the sensing device 30 on the conduit 16. It is envisaged that more than one sensing device 30 could also be used.

Referring to figure 1 1 , it shows an eighth embodiment of the centrifugal separator arrangement 10. The eighth embodiment of the invention is the same as the first embodiment of the invention, shown in figure 1 , save for the substitution of both conically-shaped first and second centrifugal separators 12 and 14 with cylindrically-shaped separators 42 and 44.

With reference to figure 12, a ninth embodiment of the centrifugal separator arrangement 10 is similar to the third embodiment of the invention, shown in figure 6, save for the substitution of both conically- shaped first and second centrifugal separators 12 and 14 with cylindrically- shaped separators 42 and 44 and the position of the sensing device 30 on the conduit 16.

Figure 13 shows a tenth embodiment of the centrifugal separator arrangement 10. The tenth embodiment of the invention is the same as the fourth embodiment of the invention, shown in figure 7, except for the substitution of the cylindrically-shaped first centrifugal separator 42 with a different cylindrically-shaped separator 46 having two inlets 32 and 33 and two outlets 18 and 34.

Referring to figure 14, it shows an eleventh embodiment of the centrifugal separator arrangement 10. The eleventh embodiment of the invention is the same as the fifth embodiment of the invention, shown in figure 8, save for the substitution of the cylindrically-shaped first centrifugal separator 42 with a different cylindrically-shaped separator 46 having two inlets 32 and 33 and two outlets 18 and 34.

A twelfth embodiment of the centrifugal separator arrangement 10, shown in figure 15, is similar to the sixth embodiment of the invention, shown in figure 9, save for the substitution of the conically-shaped first centrifugal separator 12 with a cylindrically-shaped separator 46 having two inlets 32 and 33 and two outlets 18 and 34. Referring to figure 16, it shows a thirteenth embodiment of the centrifugal separator arrangement 10. The thirteenth embodiment of the invention is the same as the seventh embodiment of the invention, shown in figure 10, save for the substitution of the conicaliy-shaped first centrifugal separator 12 with a cylindrically-shaped separator 46 having two inlets 32 and 33 and two outlets 18 and 34.

It is envisaged that the centrifugal separator arrangement 10 described herein will improve the efficiency of the second centrifugal separator 14 and 44. Also, with the centrifugal separator arrangement 10 described herein, it will be easier to independently control the second centrifugal separator 14 and 44 in terms of the material's density and/or size without affecting the first separator 12, 42 and 46 within certain limits. It will be appreciated by those skilled in the art that the invention is not limited to the precise details as described herein and that many variations are possible without departing from the scope of the invention. For example, and referring to figures 1 , 5 - 8, 13 and 14, the outlet 36 of the second centrifugal separator 14 does not necessarily have to be in an axial direction relative to the separator 14, but could also be angled tangentially. Also, the separator arrangement 10 may also include more than two centrifugal separators arranged in series. Further, the separator arrangement 10 may also be configured so that the second centrifugal separator 14 and 38 is connectable to the outlet 34 of the first centrifugal separator 12, 42 and 46 so that material exiting through the outlet 34 enters the inlet 20. The separator arrangement 10 may also, for instance, include two second centrifugal separators 14 and 44 connectable to the first centrifugal separator 12, 42 and 46 and configured so that material exiting outlets 18 and 34 enters the inlet 20 of the second centrifugal separators 14 and 44. Yet further, the location and quantity of the sensing device 30 as depicted in figures 1 and 5 to 16 are not limited to those specific locations shown and may be located anywhere along the length of the conduit 16.

It will further be appreciated that the foregoing examples have been provided merely for the purposes of explanation and is in no way to be construed as limiting of the present invention. While the present invention has been described with reference to exemplary embodiments only, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. The present invention is also not intended to be limited to the particulars disclosed herein. Rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.