WO2009129586A1

WO2009129586A1 - Centrifugal separator

Info

Publication number: WO2009129586A1
Application number: PCT/AU2009/000524
Authority: WO
Inventors: Allan Meyer; Stuart Maxwell; Phuong Tan
Original assignee: Filtra Limited
Priority date: 2008-04-24
Filing date: 2009-04-24
Publication date: 2009-10-29

Abstract

The invention provides a centrifugal separator (10) having a disk (12) with a central zone (14) and a perimeter zone (16). The disk (12) is rotatable around a central axis (18). The separator has an inlet (20) for delivering fluid flow including solids or particles to the central zone (14) of the disk (12). An outwardly spiralling conduit (26) receives fluid delivered to the central zone (14) from the inlet (20) and delivers the received fluid flow to the perimeter zone (16). An inwardly spiralling conduit (42) receives flow delivered to the perimeter zone (16) and delivers the received fluid flow to the central zone (14). There a first outlet (24) receives a first portion of the fluid flow delivered to the central zone (14) through the inwardly spiralling conduit (42) and a second outlet (22) receives a second portion of the fluid flow delivered to the central zone (14) through the inwardly spiralling conduit (26). The disks (12) may be stacked within the separator (10, 100). A corresponding method of separating solids or particles in fluids is also provided.

Description

Centrifugal Separator

Technical Field

The present invention concerns a centrifugal separator. In particular the invention is concerned with a centrifugal separator suitable for removing or reducing the quantity of particles or solids contained in a fluid.

Background of the Invention

The separation of particles or solids from fluids is necessary or desirable in many fields and in particular in many chemical or biological processes. While the separator of the present invention can be suitable for a wide range of applications, for the sake of convenience the description below will focus on treatment of sewage. However, it is to be understood that the scope of the invention is not to be limited to this application. For example, the invention may be suitable for treatment of coal, water/oil mixtures and other applications where it is desired to remove or reduce solid/particle content of a fluid.

Sewage treatment processes usually involve separation of entrained particles or biomass from remaining liquid. In the application, entrained particles and biomass are characterised by having a very low density. They are also fragile in terms of physical composition and are difficult to process by general conventional separation methods.

In the case of sewage, it is desirable that the biological materials present are not subject to high shear forces. It is also highly desirable that the addition of chemical agents is avoided, to maximise the opportunity to recycle biomass materials.

Currently, the standard method of physical separation in sewage treatment is sedimentation. However, sedimentation pits can be costly to construct and require large areas of land. In order to cope with any increase in sewage treatment capacity - for example, to take into account a growth in population or increased rainfall - it is necessary to construct further sedimentation pits. Restrictions on land availability or financial considerations can present problems in this regard.

Alternate methods of separation have been attempted to overcome the limitations of sedimentation methods. However, either the addition of chemicals is required or 5 the equipment required involves a high cost and sizeable footprint, or both.

An alternate form of separation is filtration, which involves passing a fluid containing particles or solids to be separated through a porous medium. The filter medium can have surface active properties or may be a type of screen. A primary disadvantage of filtration is that the medium inevitably becomes fouled and needso to be cleaned. Back-flushing, with complex process monitoring and control, is required to ensure that filtration is effective.

It is an object of the present invention, at least in some embodiments, to provide a centrifugal separator which uses centrifugal force to aid in the separation of particles or solids, while being capable of maintaining a high continuous 5 processing rate. It is a further object of the present invention, at least in some embodiments, to provide a centrifugal separator that does not subject the process stream to high shear forces and that does not require the addition of chemical agents.

Disclosure of the Invention o Accordingly, the present invention provides a centrifugal separator including:

a disk having a central zone and a perimeter zone, the disk being rotatable around a central axis;

an inlet for delivering fluid flow including solids or particles to the central zone of the disk; an outwardly spiralling conduit for receiving fluid delivered to the central zone from the inlet and delivering the received fluid flow to the perimeter zone;

an inwardly spiralling conduit for receiving flow delivered to the perimeter zone and delivering the received fluid flow to the central zone;

a first outlet for receiving a first portion of the fluid flow delivered to the central zone through the inwardly spiralling conduit; and

a second outlet for receiving a second portion of the fluid flow delivered to the central zone through the inwardly spiralling conduit.

In a preferred embodiment, the centrifugal separator of the invention includes a divider in the inwardly spiralling conduit for dividing the first portion of the fluid flow from the second portion of the fluid flow. The first portion of the fluid flow is preferably predominantly solids or collected particles. The second portion of the fluid is preferably filtrate or contains a substantially reduced proportion of solids or particles compared to the fluid flow delivered to the central zone of the disk via the inlet.

The present invention also provides a method for separating solids or particles from a fluid flow including solids or particles, the method including the following steps:

a) delivering fluid flow including solids or particles to a central zone of a disk rotatable around a central axis;

b) causing the fluid flow to travel through an outwardly spiralling conduit from the central zone to a perimeter zone while applying centrifugal force to the disk; c) causing the fluid flow to travel through an inwardly spiralling conduit from the perimeter zone to the central zone while applying centrifugal force to the disk;

d) collecting a first portion of the fluid flow delivered to the central zone through the inwardly spiralling conduit; and

e) collecting a second portion of the fluid flow delivered to the central zone from the inwardly spiralling conduit.

The disk may be constructed of any suitable material, including metal or plastic. In one embodiment, the disk is made of aluminium.

Preferably, the disk is designed to rotate in a substantially horizontal manner around the central axis. However, other orientations are possible. For example, the disk may rotate vertically or at an acute angle to the horizontal.

The inlet and the first and second outlets are preferably provided on a single rotary coupling mounted near the central zone and coupled thereto. However, other forms of the inlet and the first and second outlets are within the scope of this invention.

The outwardly spiralling conduit is preferably located on one surface of the disk (for example, on a lower surface of the disk) while the inwardly spiralling conduit is preferably located on the opposite, upper surface of the disk. In this embodiment, the outwardly spiralling conduit is in communication with the inwardly spiralling conduit at the perimeter zone, so that the fluid flow which travels from the central zone through the outwardly spiralling conduit to the perimeter zone then follows a path through the inwardly spiralling conduit to the central zone.

If desired, the conduits may be coated with a suitable non-stick coating, such as Teflon (trade mark). The centrifugal separator of the invention can be operated continuously, rather than in batches. It will be appreciated by one skilled in the art that this can be advantageous in sewage treatment processes.

5 A suitably-sized single disk used in the centrifugal separator of the invention or the method of the invention may process a significant quantity of fluid, such as 100,000 litres per day. The centrifugal separator and method of the invention can operate extremely efficiently while occupying a relatively small volume in a sewage processing plant. o An added advantage of the centrifugal separator of the invention is that the disks can be stacked - preferably vertically - to greatly increase throughput. For example, if a separator of the invention using a single disk can process 100,000 litres of fluid per day, this may be increased to approximately 1,000,000 litres per day by using a stack of ten disks. In this embodiment, it may only be necessary to5 use a single inlet and one first outlet and one second outlet, the disks being designed to communicate with each other, so that an inwardly spiralling conduit from one disk delivers fluid flow to the central zone of a neighbouring disk, the fluid flow then travelling through the outwardly spiralling conduit of the neighbouring disk, back through the inwardly spiralling conduit of that o neighbouring disk and, optionally, to the first and second outlets or to a central zone of yet a further neighbouring disk.

Accordingly, this invention provides a centrifugal separator including:

a plurality of disks, each having a central zone and a perimeter zone, each disk being rotatable around the same central axis; 5 an inlet for delivering fluid flow including solids or particles to the central zone of the first disk of the plurality of disks; an outwardly spiralling conduit for receiving fluid flow from the central zone of the first disk and delivering it to the perimeter zone of the first disk;

an inwardly spiralling conduit for receiving fluid delivered to the perimeter zone of the first disk and delivering it to the central zone of the first disk;

means for delivering the fluid flow from the central zone of the first disk to the central zone of a further disk in the plurality of disks;

an outwardly spiralling conduit for receiving fluid flow from the central zone of the last disk and delivering it to the perimeter zone of the further disk;

an inwardly spiralling conduit for receiving fluid delivered to the perimeter zone of the further disk and delivering it to the central zone of the further disk;

a first outlet for receiving a first portion of the fluid flow delivered to the central zone through the inwardly spiralling conduit of the further disk; and

a second outlet for receiving a first portion of the fluid flow delivered to the central zone through the inwardly spiralling conduit of the further disk.

The invention also provides a method for separating solids or particles from a fluid flow including solids or particles, the method including the following steps:

a) delivering fluid flow including solids or particles to a central zone of a first disk rotatable around a central axis;

b) causing the fluid flow to travel through an outwardly spiralling conduit from the central zone of the first disk to the perimeter zone of the first disk while applying centrifugal force to the first disk; c) causing the fluid flow to travel through an inwardly spiralling conduit from the perimeter zone of the first disk to the central zone of the first disk while applying centrifugal force to the first disk;

d) delivering fluid flow from the central zone of the first disk by delivery means to a central zone in a further disk;

e) causing the fluid flow to travel through an outwardly spiralling conduit of the further disk from a central zone of the further disk to a perimeter zone of the further disk while applying centrifugal force to the further disk;

f) causing the fluid flow to travel through an inwardly spiralling conduit of the further disk from the perimeter zone of the further disk to the central zone of the further disk while applying centrifugal force to the further disk;

g) collecting a first portion of the fluid flow delivered to the central zone of the further disk through the inwardly spiralling conduit of the further disk; and

h) collecting a second portion of the fluid flow delivered to the central zone of the further disk from the inwardly spiralling conduit of the further disk.

Where the centrifugal separator of the invention includes a plurality of disks, there may be only two disks, in which case the further disk referred to above is the last disk. Where there are more than two disks, there may be one or more disks interposed between the first and further disk.

The means for delivering the fluid flow from the central zone of the first disk to the central zone of the further disk may include additional disks or may simply be a coupling between the first disk and the further disk. Other delivery means are also possible.

In an especially preferred embodiment, the shape of the outwardly spiralling conduit changes shape between the central zone and the perimeter zone. In one embodiment, the conduit is circular in cross section at the central zone, gradually changing to a square cross sectional shape, then to a rectangular cross sectional shape, with the rectangle becoming progressively wider but decreasing in height until the conduit reaches the perimeter zone, where the conduit reduces in width and increases in depth.

Preferably, at the perimeter zone, the inwardly spiralling conduit or the outwardly spiralling conduit, or both, changes to a trapezoidal cross sectional shape, an example of which is given in connection with the description relating to the drawings, below. Where the cross sectional shapes of the inwardly spiralling conduit and outwardly spiralling conduits are different, it is preferred that the trapezoidal shape is incorporated at or near the perimeter zone for the inwardly spiralling conduit.

The cross sectional shape of the outwardly spiralling conduit may be different, in its various changes, compared to the cross sectional shape for the inwardly spiralling conduit. In another embodiment, the cross sectional shapes may be the same or more similar.

It has been found that fluid flow travelling through the outwardly spiralling conduit through changing internal shape can enjoy laminar flow, with no detectable vortices. Vortices normally form when a fluid flows down a channel of constant cross section. In the embodiment where the conduit changes shape as described, this can prevent vortices from forming, resulting in delivery of fluids and particles/solids to the inwardly spiralling conduit in laminar flow without eddies or vortices. The inwardly spiralling conduit preferably has its cross sectional shape in the special trapezoidal form referred to above at the perimeter zone, and this continues towards the central zone, where it is preferred that the conduit changes cross sectional shape to a rectangle, being wide and shallow in depth.

5 If a divider is included, this is preferably situated in the inwardly spiralling conduit where it has formed the rectangular shaped cross section, to facilitate separation of the solids from the filtrate.

The disk or disks may be rotated by any suitable means, such as a motor. As the disk or disks rotate, the fluid flow passes from the outwardly spiralling conduit,o preferably located on the lower surface of each disk, to the inwardly spiralling conduit, preferably located on the top surface of each disk. As the fluid flows, centrifugal force provided by rotation of the disk or disks acts on the particles travelling through the spiral to move the particles to the outer surface of the trapezoidal channel. As the trapezoidal conduit of the inwardly spiralling conduit5 changes to a wide, shallow rectangle near the central zone, the solids will be collected through centrifugal force on the outside area of the fluid stream, having been separated from the remainder of the fluid. The solids so collected can then be delivered through the appropriate first or second outlet.

The optional divider, especially where it is located in the rectangular crosso sectional shape of the inwardly spiralling conduit, can be designed so that it separates the fluid flow into, say, a one-fifth width and a four-fifths width. The solids are directed through the one-fifth wide part of the conduit. However, because at this point in this preferred embodiment the conduit is wide, the fluid carrying the solids still has a relatively wide distance between the outer wall of the5 conduit and the divider. This width can help to prevent a build up of particles/ solids/fibre which may be carried in the fluid and which, in smaller widths, may tend to clog up the separator. The optional divider operates to split the fluid flow into one carrying the separated particles or solids in, say, 20% of the fluid and the other 80% carrying less than 20% of the solids in the filtrate stream. The divided streams can continue to spiral to the central zone to the first and second outlets. The solids stream preferably discharges through the optional rotary coupling through the first outlet, while the second stream preferably discharges through the rotary coupling via the second outlet.

Brief Description of the Drawings

The invention may be better understood from the following non-limiting description of one or more preferred embodiments, in which:

Figure 1 is a front elevation of an embodiment of centrifugal separator of the invention set in a frame with electric motor;

Figure 2 is a plan view from below of the disk in Figure I, showing a first embodiment of outwardly spiralling conduit;

Figure 3 is a sectional view taken along the line A-A of Figure 2;

Figure 4 is a plan view of a second embodiment of outwardly spiralling conduit;

Figure 5 is a sectional view taken along the line A-A of Figure 4;

Figure 6 is a perspective view of an embodiment of inwardly spiralling conduit;

Figure 7 shows a detail of the circled area marked A in Figure 6;

Figure 8 is a plan view of the inwardly spiralling conduit of Figure 6;

Figure 9 is a plan view of the circled area marked B in Figure 8, showing detail A in Figure 7 in plan view; Figure 10 is a perspective view of the outwardly spiralling conduit of Figure 2, showing direction of fluid flow;

Figure 11 is a side view of the disk having the inwardly spiralling conduit shown in Figure 10, indicating direction of fluid flow;

Figure 12 shows the conduit of Figure 6, indicating direction of fluid flow;

Figure 13 is an embodiment of a trapezoidal shape of the inwardly spiralling conduit;

Figure 14 is a perspective view of an embodiment of a rotary coupling including an inlet and first and second outlets;

Figure 15 is a side elevation of the coupling of Figure 14;

Figure 16 is a sectional view of the coupling of Figure 15, taken along the line A-A of Figure 15;

Figure 17 is a result of computational fluid dynamic analysis to illustrate laminar flow, after dividing of the streamlines by use of a divider;

Figure 18 is a front elevation of a second embodiment of the invention showing use of a plurality of disks in a centrifugal separator;

Figure 19 is a plan view of a third embodiment of outwardly spiralling conduit, being a mirror reverse of the inwardly spiralling conduit in Figure 8; and

Figure 20 is a sectional view taken along the line A-A of Figure 19. Detailed Description of the Drawings

Possible and preferred features of the invention will now be described with particular reference to the accompanying drawings. However, it is to be understood that the features illustrated in and described with reference to the drawings are not to be construed as limiting on the scope of the invention.

It will also be appreciated that the drawings are not all drawn to the same scale.

Referring first to Figure 1, the embodiment of centrifugal separator 10 shown has disk 12 mounted for horizontal rotation about central axis 18. Disk 12 has central zone 14 and perimeter zone 16. Disk 12 includes upper and lower covers 32.

Rotary coupling 34 couples fluid flow inlet 20, first fluid flow outlet 22 and second fluid flow outlet 24 to disk 12. Motor 36 causes rotation of disk 12 about central axis 18. Frame 38 provides support for disk 12 and motor 36.

With reference to Figure 2, this shows a first embodiment of outwardly spiralling conduit 26. This represents essentially a bottom plan view of disk 12 from Figure 1 with lower cover 32 removed.

Central zone 14 and perimeter zone 16 are indicated on Figure 2. Fluid flow enters outwardly spiralling conduit 26 at 28 and exits at 30. Also visible in Figure 2 is first outlet 22 and second outlet 24 which continue through rotary coupling 34 of Figure 1 as shown in that Figure.

The cross-sectional view of disk 12 in Figure 3 illustrates how outwardly spiralling conduit 26 changes shape from central zone 14 to perimeter zone 16. The conduit is relatively narrow at 26A and becomes progressively wider through 26B, 26C and 26D.

The embodiment of outwardly spiralling conduit 26 shown in Figures 2 and 3 can be contrasted with the second embodiment of outwardly spiralling conduit 40 shown in Figures 4 and 5. (The same labels are used for the same or similar parts as in Figures 2 and 3). In the second embodiment, there is far less variation in the cross-sectional shape of the conduit between central zone 14 and perimeter zone 16.

The sectional view in Figure 5 shows how outwardly spiralling conduit 40 is rectangular at 40a and varies only to a small extent at 40b, 40c and 4Od being essentially of the same dimensions as the conduit at 40b.

The version shown in Figures 2 and 3 will result in slower flow than the second embodiment shown in Figures 4 and 5.

Figure 6 represents a perspective view of an embodiment of inwardly spiralling conduit 42, being a view of the upper surface of disk 12 with upper cover 32 removed.

After outwardly spiralling conduit 26 or 40 delivers fluid to perimeter zone 16, fluid flows inwardly towards central zone 14 of inwardly spiralling conduit 42.

This embodiment includes divider 46, shown in magnified detail in Figure 7.

It will be seen from Figure 3 that inwardly spiralling conduit 42 has relatively narrow, trapezoidal shaped cross section at the perimeter zone 16, between 42a and 42i. Thereafter, conduit 42 changes shape as shown at 42j, 42k and 421.

Conduit 42 becomes relatively wide in the region indicated as detail A in Figures 6 and 7. Conduit 42m is split by divider 46 into a relatively wide path 48 and a relatively narrow path 50. It will be noted from Figure 9 that path 48 is approximately four times wider than path 50.

Figures 10 to 12 show direction of fluid flow and assist to illustrate the method of the invention. Fluid, such as sewerage, is delivered to central zone 14 of disk 12, which is rotatable around central axis 18. The fluid enters outwardly spiralling conduit 26 at 28 and flows from there through the conduit to the perimeter zone 16, in the direction indicated by arrows 52.

The fluid flow transitions from outwardly spiralling conduit 26 to inwardly spiralling conduit 42 at point 30, where the fluid flow travels from perimeter zone 16 towards central zone 14. Secondary cover 44 is shown in this illustration.

The fluid flow, having been delivered from inlet 20 (refer Figure 1) is subject to centrifugal force by reason of rotation of disk 12 during the separation procedure. It will be recalled that disk 12 is caused to rotate within frame 38 by motor 36. By combined effect of the paths followed by the fluid flow through outwardly spiralling conduit 26 and inwardly spiralling conduit 42, and the centrifugal force caused by rotation of disk 12, particles or solids within the fluid are moved to the outer surface of the channels of the conduit. Consequently, by the time the fluid flow reaches the wide, shallow rectangular shaped channel at 42m (refer Figure 7) the particles are also concentrated in narrow path 50, assisted by divider 46, while the remainder of the fluid travels through wider path 48.

Solids or particles travelling down narrow path 50 proceed through outlet 22 (under secondary cover 44 in Figure 12 but visible in Figures 8 and 10). Fluid travelling down path 48 is collected through second outlet 24.

Figure 13 is a diagrammatic version of the cross-sectional shape of one of the trapezoidal channels 42a to 42i.

Rotary coupling 34 in this embodiment is shown in Figures 14 to 16. Rotary coupling 34 has a central shaft 54 which in this embodiment is rotated with disk 12. Outer sleeve 56 remains stationary. Figure 16 shows bearings 58 at top and bottom of sleeve 56, to assist in rotation of central shaft 54. Fluid flow enters inlet 20a through sleeve 56 and travels through channel 60 to communicate with passageway 20b in central shaft 54 and exits at 20c where it is coupled directly or indirectly to commencement 28 of outwardly spiralling conduit 26 (refer Figure 2).

5 Fluid exiting disk 12 at outlet 22 or 24 (refer Figure 2) enters rotary coupling 34 directly or indirectly through outlet 22c or 24c, respectively.

Fluid entering outlet 24c travels through central shaft 54 through a passageway (not shown but similar to passageway 20b), to communicate via channel 62 with outlet 24c.

io In a similar manner, although this cannot be seen in Figures 14 to 16, solids fluid entering outlet 22c travels through central shaft 54to exit via channel 64 at an outlet similar to that shown at 24c and located in sleeve 56 radially above outlet 24c but below inlet 20a.

Referring now to Figure 17, divider 46 is located as shown. Laminar flow within 15 channel 42m is shown dividing at divider 46 into wide path 48 (not labelled in this Figure) and narrow path 50.

Figure 18 shows centrifugal separator 100 having a stack of ten disks 12, each having upper and lower cover plates 32.

Motor 36 causes the whole stack of disks 12 to rotate simultaneously within frame 20 38.

Fluid entering inlet 20 through rotary coupling 34 communicates with lowermost disk 12a and travels through an outwardly spiralling conduit on disk 12a and an inwardly spiralling conduit on disk 12a. Then the fluid flow communicates with disk 12b and the fluid flow path is repeated. The first and second portions of the fluid flow may be collected from each disk separately or may be collected only from top disk 12j, the intermediate disks communicating with one another with regard to fluid flow.

With reference to Figure 19, this shows a third embodiment of outwardly spiralling conduit 70. This is different from the first and second embodiments 26 and 40 respectively, in that conduit 100 is essentially a mirror reverse of inwardly spiralling conduit 42.

As can be seen from Figure 20, the channels of conduit 70 echo those of conduit

42.

The outwardly spiralling conduit may be chosen depending on the nature of the fluid to be separated.

Especially where disks 12 are disposed horizontally as shown in the drawings, fluid is preferably pumped through the separator, although no pump is shown in the Figures.

Industrial Applicability

The centrifugal separator and method of the invention represents a significant improvement over previously known separation techniques for a wide range of applications. The separator and method enable continuous separation of particles or solids from fluids and enhance the ability to recycle or reuse separated components.

In selected embodiments, the separator can have the spiralling conduits in one plane. The inlet and outlets can be located at the centre of the disk in the separator.

Claims

The Claims

1. A centrifugal separator including:

an inlet for delivering fluid flow including solids or particles to the central zone of the disk;

an outwardly spiralling conduit for receiving fluid delivered to the central zone from the inlet and delivering the received fluid flow to the perimeter zone;

2. The centrifugal separator of claim 1 which includes a divider in the inwardly spiralling conduit for dividing the first portion of the fluid flow from the second portion of the fluid flow.

3. The centrifugal separator of claim 1 or 2 wherein the first portion of the fluid flow is predominantly solids or collected particles and the second portion of the fluid contains a substantially reduced proportion of solids or particles compared to the fluid flow delivered to the central zone of the disk via the inlet.

4. The centrifugal separator of any one of claims 1 to 3, wherein the disk is designed to rotate in a substantially horizontal manner around the central axis.

5. The centrifugal separator of any one of claims 1 to 4, wherein the inlet and the first and second outlets are provided on a single rotary coupling mounted near the central zone and coupled thereto.

6. The centrifugal separator of any one of claims 1 to 5, wherein the outwardly spiralling conduit is located on one surface of the disk while the inwardly spiralling conduit is located on an opposite of the disk.

7. The centrifugal separator of claim 6, wherein the outwardly spiralling conduit is in communication with the inwardly spiralling conduit at the perimeter zone, so that the fluid flow which travels from the central zone through the outwardly spiralling conduit to the perimeter zone then follows a path through the inwardly spiralling conduit to the central zone.

8. A centrifugal separator including:

a plurality of disks, each having a central zone and a perimeter zone, each disk being rotatable around the same central axis;

an inlet for delivering fluid flow including solids or particles to the central zone of the first disk of the plurality of disks;

an outwardly spiralling conduit for receiving fluid flow from the central zone of the first disk and delivering it to the perimeter zone of the first disk;

an outwardly spiralling conduit for receiving fluid flow from the central zone of the last disk and delivering it to the perimeter zone of the further disk; an inwardly spiralling conduit for receiving fluid delivered to the perimeter zone of the further disk and delivering it to the central zone of the further disk;

9. A method for separating solids or particles from a fluid flow including solids or particles, the method including the following steps:

b) causing the fluid flow to travel through an outwardly spiralling conduit from the central zone to a perimeter zone while applying centrifugal force to the disk;

c) causing the fluid flow to travel through an inwardly spiralling conduit from the perimeter zone to the central zone while applying centrifugal force to the disk;

e) collecting a second portion of the fluid flow delivered to the central zone from the inwardly spiralling conduit

10. A method for separating solids or particles from a fluid flow including solids or particles, the method including the following steps: a) delivering fluid flow including solids or particles to a central zone of a first disk rotatable around a central axis;

b) causing the fluid flow to travel through an outwardly spiralling conduit from the central zone of the first disk to the perimeter zone of the first disk while applying centrifugal force to the first disk;

c) causing the fluid flow to travel through an inwardly spiralling conduit from the perimeter zone of the first disk to the central zone of the first disk while applying centrifugal force to the first disk;

11. A centrifugal separator substantially as herein described with reference to any one of Figures 1 to 20.

12. A method for separating solids or particles from a fluid flow including solids or particles, substantially as herein described with reference to any one of Figures 1 to

5 20.

0 S