WO2001085302A1

WO2001085302A1 - A filtration device

Info

Publication number: WO2001085302A1
Application number: PCT/AU2001/000524
Authority: WO
Inventors: Clive Allen John Fletcher
Original assignee: Clive Allen John Fletcher
Priority date: 2000-05-09
Filing date: 2001-05-08
Publication date: 2001-11-15
Also published as: AUPQ739100A0

Abstract

A filtration device includes a 200 mm diameter tube which is three metres long. An upstream section which is about one metre long forms a swirl generation chamber. A downstream section which is about two metres long forms a separation chamber. The device is typically used for removing solids from a moving stream of sewage. Swirl is generated in the swirl generation chamber by drawing the fluid carrying the solids almost tangentially into the tube, thus creating a highly swirling flow near the outer wall. The high swirl generates centrifugal forces that progressively move individual flocs to the outer wall of the tube, generating an area of high concentrate slurry. The separator is conical and formed from axial slats which partially overlap in the circumferential direction, with narrow gaps between the slats. An annular passage of gradually deceasing width, is defined between the inlet of the separation chamber and an outlet of that chamber. The high concentrate slurry is continually drawn through grooves in the outer wall of the tube around the seperation chamber. The design of the filtration device allows flow through the device with relatively small pressure drop. This leads to a lower capacity pump being required in the plant. Further, although the device exploits swirl, the motion of the fluid itself, generates a swirl so no moving parts are required.

Description

A FILTRATION DEVICE

FIELD OF THE INVENTION

The present invention relates generally to a filtration device and a tubular separator such as that which is appropriate in the concentration of a sewage stream.

BACKGROUND OF THE INVENTION

A conventional sewage treatment plant typically uses an activated sludge reactor to decompose organic material. The decomposed material flows to the secondary clarification process, which traditionally removes the activated sludge by gravity in large settling tanks (clarifiers). About 30% of the sludge is recycled to the reactor . The size and slowness of the secondary clarifier is a major limiting factor for sewage treatment and the volume flow of sewage that the plant can handle.

A second problem which arises with conventional plants is that the volume flow rate during wet weather usually exceeds the capacity of the plant, and the extra volume has to be allowed to overflow the primary and secondary treatment stages, leading to the discharge of almost raw sewage. Although the present invention is not limited to being used in sewage treatment plant, one aim of the present invention is to provide a separation device which can be used to remove solids from a moving stream of sewage or the like thereby improving the capacity of existing and proposed sewage treatment plants. Any separation device has to deal with floes, which usually result from flocculation of suspended solids and typically have particle diameters from 20 to 300 microns and a relative density in the range 1.00 to 1.05. If the flow stream containing the floes, experiences a high shear, of about 50 to 100 s^"1 , the floes are likely to be reduced in size. Thus, the separation device of the present invention needs to address the problem in a manner in which, ideally, high shear forces are not applied to floes.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed in Australia before the priority date of each claim of this application.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided a filtration device comprising: an elongate housing within which a tubular separator is longitudinally located, a concentrate flow passage being defined between the tubular separator and the housing, the concentrate flow passage including an inlet and an outlet at opposing ends, respectively, of the housing; and swirl inducing means whereby fluid and entrained particles entering the concentrate flow passage at the inlet (the said concentrate flow passage is at the inlet of the overall separation device, of which the tubular separator is a component) include a swirl flow component which both forces the entrained particles outward from the tubular separator towards the elongate housing, inner surface and, in conjunction with a longitudinal flow component, drives the fluid through the tubular separator to provide a flow of a filtrate within the tubular separator. Generally, but not always, the fluid is a liquid such as liquid waste and water, and the particles are in the form of flocculated solids such as that present in a sewage stream.

A filtration device embodying the present invention may be incorporated into a small footprint device that can remove solids continuously from a moving stream, eg in a pipe. Thus by including a filtration device embodying the present invention ahead of a clarifier in an existing sewage facility, more than half of the solids otherwise removed by the clarifier, may be extracted by the filtration device and returned to the reactor. This permits the existing clarifier to handle a higher equivalent population, possibly by more than 50%. If the filtration device also replaces the clarifier in a new sewage plant, the same size facility could handle anywhere between a 100 to 200% increase in the equivalent population that could be serviced. In addition such a plant could also provide a full wet weather service, possibly even with three times the volume flow rate. Further, avoiding the traditional use of settling tanks that are slow and take up a large amount of space. Consequently it is expected that incorporating one or more filtration devices embodying the present invention in a sewage plant will reduce the cost of sewage treatment both by retrofitting and by incorporating into the design of new installations.

Preferred features of the present invention which may contribute to the efficiency and usefulness of the device are set out below.

Typically the swirl inducing means includes an inlet duct, containing the entering fluid and entrained particles, at an angle of between zero and ninety degrees to a longitudinal axis of the elongate housing and the flow passage. Preferably the elongate housing is a tubular housing in which the tubular separator is coaxially located wherein the concentrate flow passage is an annular flow passage. More preferably the tubular housing is of a generally consistent internal diameter whereas an external diameter of the tubular separator increases in a longitudinal direction wherein the annular flow passage is tapered.

Generally the inlet and the outlet of the concentrate flow passage are defined by the relatively large and small annular openings at opposing ends, respectively, of the tubular housing whilst an opening within the tubular separator adjacent to the outlet defines a filtrate outlet. Typically the tubular separator includes a plurality of longitudinally extending and circumferentially spaced vanes which longitudinally diverge relative to one another. More typically the plurality of vanes are arranged so that a filtrate flow passage is provided between adjacent of said vanes whereby fluid flowing along the flow passage following a helical path flows through one or more of the filtrate flow passages. Generally adjacent of said vanes circumferentially overlap one another.

Preferably the plurality of vanes are located within the elongate housing by means of a support structure to which one or more of the vanes is connected. The walls of the elongate housing may define a series of apertures following a generally helical path around the housing and protrusions extending into the device separate the apertures from one another. The housing may be enclosed by an external casing into which matter passing through the apertures from the housing, passes. The helical profusions create parallel ridges and grooves with a slot in the base of each groove. A slot and two adjacent ridges form an aperture. The ridges and grooves are preferably shaped and oriented to create swirling flow, suppress turbulence and trap floes.

According to another aspect of the present invention there is provided a tubular separator comprising a plurality of longitudinally extending and circumferentially spaced vanes connected to a support structure wherein the vanes longitudinally diverge relative to one another and wherein a filtrate flow passage is provided between adjacent of said vanes whereby fluid flowing along a periphery of the tubular separator flows through said filtrate flow passages to within the tubular separator. Preferably each of the plurality of vanes is in the form of an elongate fin which in transverse cross-section includes opposing concave and convex foiled surfaces, the vanes each being oriented wherein the concave and convex surfaces face generally inward and outward, respectively. More preferably each of the vanes is of an aerodynamic form including a leading edge of an enlarged profile whilst being tapered toward its trailing edge, the leading edge facing the flow passage. In one embodiment each of the vanes is oriented about the tubular separator wherein an imaginary chord extending between its leading and trailing edges is at an angle of between about 5° to 15° relative to a tangent taken at the leading edge of a curve which intersects or adjoins the leading edges of the vanes.

Typically the tubular separator also comprises a filtration membrane located about the plurality of vanes. More typically the filtration membrane is in the form of a filtration "sock" which envelopes said vanes.

Preferably the support structure includes an axially oriented support rod located within the tubular separator, and a plurality of radially extending mounting elements each being coupled to the support rod and arranged to fix to and thus support at least one and constrain all of the plurality of vanes. More preferably the plurality of radial mounting elements are connected to a hub which is slid over the support rod.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to achieve a better understanding of the nature of the present invention a preferred embodiment of a filtration device incorporating a tubular separator will now be described in some detail, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a general arrangement shown in elevation of a solids separation and clarification device including a swirl generation chamber and a separation chamber;

Figure 2 is a section through the swirl generation chamber of Figure 1;

Figure 3 is a side view of the separation chamber of Figure 1 showing a tubular separator in more detail;

Figure 4 is a perspective view of the tubular separator shown in Figure 3 part of which is shown, for the purposes of clarity, with some vanes of a separator of the device removed;

Figure 5 is a perspective view of a "spider" of the support structure of the filtration device of Figure 1;

Figure 6 is a transverse sectional view taken through an inlet of the separation chamber of Figure 1;

Figure 7 is a transverse sectional view taken through an outlet of the separation chamber of Figure 1; Figure 8 is an enlarged transverse sectional view of several of the adjacent vanes; and

Figure 9 is a detailed view of area IX of Figure 1 being a transverse view through the tubular housing illustrating the groove and ridge arrangement in the wall of that tubular housing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, Figure 1 shows a filtration device shown generally as 10 including an elongate housing 12 which is typically about 3m long defining a longitudinal central axis A within which housing a tubular separator 14 which is about 2m long, is longitudinally located. The filtration device 10 further comprises swirl inducing means shown generally as 16 which includes an inlet duct 18 oriented at an acute angle relative to the central axis A of the elongate housing 12. The front end or first part of the device functions as a swirl generation chamber 10a and the second part as a separation chamber 10b.

The swirl inducing means are best shown in Figure 2. The duct 18 is oriented such that it is oriented almost tangentially to the circumference of the elongate housing, as in a hydrocyclone. The entry area is about 12.5% of the cross-sectional area of the housing (which is 31400 mm²] . As is best seen in Figure 2 the inlet duct defines a central axis which is oriented at 7 degrees to a transverse cross-section through the housing. In this particular embodiment of the invention, as is best seen in Figures 1 and 3, the elongate housing 12 is a tubular housing in part of which the tubular separator 14 is coaxially positioned so as to define an annular concentrate flow passage 20. The tubular housing 12b is of a generally consistent internal diameter whereas an external diameter of the tubular separator 14 increases in a longitudinal direction such that the annular flow passage 20 is tapered. A relatively large annular opening at one end of the housing 12b forms a concentrate inlet 22 whereas a relatively small annular opening at an opposite end of the housing 12b defines a concentrate outlet 24. Otherwise, an internal bore of the tubular separator 14 defines an intermediate filtrate plenum chamber and/or passageway 26 (Figure 4) having a filtrate outlet 28 (Figure 3) adjacent and concentric with the concentrate outlet 24.

The tubular separator 14 of this preferred embodiment comprises a plurality of longitudinally extending and circumferentially spaced vanes such as 30 and 32 (Figure 4). The vanes such as 32 slightly overlap one another circumferentially and are longitudinally divergent relative to one another. The vanes such as 30 and 32 of this particular construction of the filtration device 10 are arranged in -two (2) banks of adjacent and coaxial forms. The hydrodynamic shape and orientation of the separator vanes 30 and 32 further promotes the flow of filtrate through the vane passageways and into the filtrate plenum chamber or passageway 26. It is preferable that a filtration membrane (not illustrated) in the form of a filter "sock" is formed as an envelope about the separator vanes such as 32 for improved filtration of the sewage. The surface of the filtration membrane forms a cone increasing from a diameter of 100mm at the inlet 22 to a diameter of 180mm at the outlet 24.

The vanes such as 30 and 32 are mounted within the housing 12b via a support and constraining structure. Opposing ends of each of the vanes such as 30 and 32 are fixed to a mounting plate such as 34. The mounting plate 34 is ring-shaped and includes a plurality of recesses (not designated) shaped complementary to and in which opposing ends of the vanes such as 30 are seated.

In this embodiment the support structure includes a coaxial support rod 70 to which "spiders" 40 such as that shown in Figure 5 is slidably mounted. The "spider" 40 includes a hub 42 to which a series of radial locating elements such as 44 are connected. The locating elements 44 are each in the form of blades having a free end to which one of the vanes such as 30 is fixed. The mounting plates 34 support the vanes 30 whereas the "spiders" 40 constrain the vanes 30 from "flapping".

Figures 6 to 8 depict in cross-section the particular angular orientation of the vanes such as 30 or 32 of the tubular separator 14 and their relative dispositions. The cross-sectional view of Figure 6 is taken at the inlet 22 of the filtration device 12, just downstream of the front swirl inducing device, whereas the sectional view of Figure 7 is taken at its outlet 24. In this example the dimensions of the filtration device 10 at its inlet 22 and outlet 24 are as follows:

Figure 8 illustrates in enlarged detail several of the vanes such as 32 of the separator 14. This sectional view is taken approximately midway between the inlet and outlet 22 and 24 of the filtration device 10. Each of the vanes such as 32 is in the form of an elongate fin which in cross-section includes opposing concave and convex foiled surfaces. The concave surface faces radially inward whereas the convex surface faces outwards. A rounded leading edge of each of the fins such as 32 forms part of the inner boundary of the concentrate flow passage 20 whereas its tapered trailing edge is directed inwardly from the concentrate flow passage 20. The relative proximity and overlap of the fin trailing edges create the filtrate flow passage to the intermediate filtrate plenum chamber 26. The following dimensional data applies to the dimensions and relative positions of the fins such as 30 and 32 of the separator 14.

In this example the fins such as 30 or 32 are each of a thickness of about 15% of the chord length (C) at a point 25% rearward of the leading edge. Otherwise, the fins are orientated at an angle of about 5 to 10° although an adjustable angle of rotation of between 0 to 15° is preferable. This angular "rotation" is measured via an imaginary chord extending between the leading and trailing edges of each of the fins and projecting this imaginary chord to intersect with a tangent of a circle which intersects with the leading edges of adjacent of the vanes such as 32.

As is best seen in Figure 9, the outer wall of the part of the elongate housing in which the tubular separator is located defines a series of grooves with slots 60 having widths " W" of 2mm which are cut into the outer wall following the local flow angle, in a tight helical path which is typically about 7 deg to the plane of a transverse cross-section through the housing. Tapered ridges 62 which project a distance "D" (about 5 mm) in the radial direction and have rounded edges "t" approximately 1mm wide are defined between adjacent grooves. The grooves are a distance "d" (4mm) apart. Although only three ridges are illustrated, there are ninety six equally-spaced ridges and grooves extending around the circumference. The ridges and grooves extend the full length of the part of the housing which encloses the tubular separator. The grooves are in fluid communication with an outer annular plenum or casing 64 (refer to Figure 3) which is external to the housing 12b.

At the inlet 22 to the separation chamber 10b a streamlined boss 66 is defined which faces the swirl generation chamber 10a. The boss defines a through aperture 68 which is in fluid communication with the filtrate passageway 26 via the forward end of tube 70 which is locally hollow and has holes cut in the surface.

Although the filtration device 10 of this example includes a tangential inflow any one or more devices or swirl inducing means may be used to effect swirling of fluid through the tapered concentrate annulus 20. The ridges 62 and grooves 60 in the outer wall of the tubular housing also induce swirl.

In another embodiment the overlapping slat assembly may be replaced with a cone surface including a ridge and groove assembly following the local flow angle to enhance swirl and with a slot at the base of each groove to transfer fluid into the passageway 26.

Operation of the device 10 will now be described in some detail focusing in particular on its flow characteristics. To avoid excessively large equipment there is a need to design for relatively high through-flow velocities (U = 1.5 m/s). In turn this can generate locally high levels of turbulence. Because of the low relative density, there is a risk that the turbulence levels associated with the fluid motion may cause the individual floes to diffuse radially inwards while travelling through the device 10. If this happens it becomes more difficult to prevent small floes from getting into the filtrate in the passageway 26. In the present design the entry to the swirl generation chamber ( refer to Figure 4) is carefully shaped to minimise the generation of turbulence.

The inflow 16 is arranged to generate an approximately linear variation of circumferential velocity with radius, which is important to avoid turbulence generation associated with high velocity gradients. The entry duct is shaped so that the inner boundary creates a flow direction parallel to the swirling flow at the outer tube inner surface. This minimises turbulence generation. The outer inflow duct contour is shaped to blend into the circular tube profile after turning through 180 degrees as shown in Figure 2. In addition the inflow duct is angled to match the flow angle, 7 deg, in the swirl generation chamber 10a. These various features minimise turbulence creation and migration of the flow to the housing central axis A along the back-wall, due to the swirl-induced radial pressure gradient

Fluid and entrained particles typically liquid waste and water and solids including floes such as are present in a sewage system are fed into the device via the inlet duct 16. Swirl is generated in the device since the carrier fluid carrying the solids enters via the inlet duct almost tangentially into the small diameter (200mm) housing 12 creating highly swirling flow (W = 10 m/s) near the outer wall. This combination creates a minimum flow angle of about 7 deg near the outer wall of the housing 12. This means a floe located near the outer wall travels 8 m in making 13 turns of the part 12a of the housing 12 before it reaches the beginning of the concentrate flow passage. Thus a 120 micron floe initially located at 50mm from the central axis A of the housing will experience a centrifugal force of about 100 g. If the floe has a relative density of 1.02 it will have moved out to 76mm from the central axis A by the end of the part 12a of the housing.

The liquid waste and solids pass through the swirl generation chamber 10a towards the filtration device 10b. The boss 66 defined at the start of the filtration device 10b forces the axial flow into the outer annulus 20.

Importantly the swirl flow component imparted to the concentrate assists in concentration of the concentrate in the tapered concentrate annulus 20. That is, the centrifugal force exerted on the concentrate due to the swirl flow component drives the entrained solids outwardly from the separator 14 toward an inner wall of the tubular housing 12b. Thus, the swirl flow component assists in separation of the entrained solids from the liquid or water of the concentrate sewage stream. The liquid or water relatively free of entrained solids flows tangentially and axially through the passageways defined between adjacent vanes such as 32.

The overlapping slats create 12 narrow longitudinal gaps of thickness, typically t = 4 mm, and length of 2.0 m. These gaps point towards the swirling flow so allow clean fluid to escape into the filtrate stream. The aerodynamic shape of the slats means that relatively little pressure drop occurs through the slots, providing an aerodynamically enhanced separation process. Because of the taper in the axial direction (Fig 3), part of the axial flow also occurs through the gaps. The overall effect is to allow 90% of the inflow to the device 10 to leave via the filtrate stream parallel to the axis of the housing 28. The clean carrier fluid passes into the passageway 26 through the slats and out of the outlet 28 and typically will contain less than lOmg of solids per litre.

The annular region between the slats and the outer tube narrows in moving downstream. As more fluid is drawn into the filtrate stream, the solids concentration of the annular stream increases. The concentrate is drawn from the downstream boundary of the annular chamber (Fig 3). The swirl in the outer annular chamber will assist floes to migrate away from the slats towards the outer wall in travelling downstream. For a floe of 120 micron diameter and RD = 1.02 located at r = 70mm at the upstream end of the separation chamber 10b, the floe will be at r = 94 mm at the exit. At the concentrate exit of the separation chamber 24 the average axial velocity is about 1.8 m/s, and the average swirl velocity is about 4 m/s.

As discussed above, the effect of the swirl is to move the solids such as the floes progressively closer to the wall of the housing 12 as the fluid moves downstream. However close to the inner surface of the housing 12b, a boundary layer of reduced axial and swirl velocity will form. The locally high radial velocity gradients generate turbulence. The turbulence can cause some of the floes close to the wall to be dispersed away from the wall. This process is reduced in the described preferred embodiment of the separation device by drawing some fluid and associated solids through the outer tube into the external annulus 64 through the slots at the base of the grooves 60. The grooves, which are cut into the outer wall (Fig 9), following the local flow angle, which is typically about 7 deg to the cross-section. This suppresses turbulent fluctuations. Because the ridges and grooves are parallel to the local flow direction, floes become trapped between adjacent ridges and are drawn out through the grooves, by centrifugal forces and pressure differential. The fluid in the external plenum 64 has a high concentration of solids and is eventually fed via a pipe 71 into a concentrate stream 72 containing the fluid and solid exiting outlet 24 and sent back to the reactor (not shown). As the flow moves downstream the continuous concentrate capture provided by the slots and grooves significantly reduces the migration of the floes towards the filter mesh. The swirl flow is also assisted by the ridges 62 which reinforce the swirl.

The swirl inducing means may include flow jets or the like which direct the concentrate so that it swirls through the concentrate flow passage. The relative flow into the filtrate stream, compared with the flow in the concentrate stream, is controlled by the differential pressure of the filtrate outlet compared with that of the concentrate outlet. The relatively large filter area, allows 90% of the flow to pass through the filter mesh with a relatively low normal velocity, and hence a small pressure drop. This velocity is less than 1% of the swirl flow. So the flow is almost parallel to the physical filter mesh due to the swirl, this creates a local shear force at the mesh providing an important cleaning mechanism, as any floes carried by the flow will tend to bounce off the physical filter mesh, unless individual floes are very much smaller than the mesh openings, about 20 microns. Because of the high swirl rates, there is a significant radial pressure gradient in both the swirl generation chamber 10a and the separation chamber 10b. However there is relatively little swirl inside the filtrate passage way 26 inside the physical mesh. As a result the pressure at the back of the boss in the filtrate region is higher than the pressure on the central axis of the swirl generation chamber. A controlled (throttled) flow of filtrate is permitted upstream through the connecting duct 68 into the swirl generation chamber 10b which forms a layer over the boss 66. This clean flow opposes the "dirty" inlet flow. As a result the inlet flow into the swirl generation chamber (Figure 2) is pushed towards the outer tube wall, and the recycled filtrate flow is turned and travels along the boss surface creating a clean film on the outside of the physical mesh, at least at the beginning of the separation chamber. For a recycled filtrate flow equal to 10% of the inlet flow, a clean flow film of thickness 14mm is created at the entrance to the separation chamber. Depending on how quickly this film is drawn through the filter mesh, a barrier to floe migration towards the filter mesh is created, which acts to dilute the concentration of solids that may have diffused towards the filter mesh due to turbulence

In another embodiment, a cylindrical section (replacing the boss 66 ) extends parallel to the central axis up to the most forward wall of the swirl generation chamber 10a. A chamber, approximately 300mm long, is formed inside the cylindrical section which is fed with clean filtrate along the central axis through a throttled orifice. The surface of the cylindrical section has slots allowing flow of clean filtrate fluid into the annular region adjacent to the entry of the swirl generation chamber, In this embodiment, the overall length of the swirl generation chamber is 300mm.

A bank of ten devices 10 as described above would require a footprint of 3m by 0.30m and a height of 3m. Such a bank may be fed from a single inflow manifold. Also filtrate and concentrate from each individual device 10 would preferably be collected into one filtrate and one concentrate outflow manifolds. Such a bank would handle a local flow of about 24 m³ per minute. This would correspond to a sewage plant handling about 20 ML per day, for an equivalent population of about 85,000, if the secondary clarifier is retained. If this is eliminated as well, the bank could service an equivalent population of about 120,000 The present invention provides primary solids separation with secondary clarification in an in-line through flow device which may achieve a filtrate stream solids concentration of not more than lOmg/L.

It is to be noted that the filtration device allows operation with a relatively low pressure drop. Also that although the device utilises swirl, the motion of the fluid itself generates the swirl so that no moving parts are required.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. For example, according to an alternative aspect of the invention the filtration device may include the radially divergent separator without relying on swirl inducement means. Furthermore, the separator may vary from that described provided it defines an effective "wall" between the concentrate flow passage or annulus and the inner filtrate plenum chamber or passage, the "wall" including passageways or opening for the passage of filtrate. For example the overlapping slats may be dispensed with but the physical filter mesh retained . In this case the flow through the mesh into the filtrate stream is radial and axial, rather than tangential and axial. This is likely to produce a larger pressure drop across the filter mesh which must be provided by an external pump. This alternative design permits the capital cost to be reduced, but with higher running costs.

Further, whilst the specific embodiment is described as an element of a sewage treatment plant it will be appreciated that the separation apparatus described above would also clearly be effective for many de-watering processes such as are used in the downstream mineral processing industry. The invention would also be applicable for many industrial gas cleaning processes, particularly where high concentration of small diameter particles is a major issue.

All such variations and modifications are to be considered within the scope of the present invention the nature of which is to be determined from the foregoing description.

Claims

1. A filtration device comprising: an elongate housing within which a tubular separator is longitudinally located, a concentrate flow passage being defined between the tubular separator and the housing, the concentrate flow passage including an inlet and an outlet at opposing ends, respectively, of the housing; and swirl inducing means whereby fluid and entrained particles entering the concentrate flow passage at the inlet of the said concentrate flow passage include a swirl flow component which both forces the entrained particles outward from the tubular separator towards the elongate housing inner surface and, in conjunction with a longitudinal flow component, drives the fluid through the tubular separator to provide a flow of a filtrate within the tubular separator.

2. A filtration device as claimed in claim 1 wherein the swirl inducing means includes an inlet duct oriented at an angle of between zero and ninety degrees to a longitudinal axis of the elongate housing and the flow passage.

3. A filtration device as claimed in any preceding claim wherein the elongate housing is a tubular housing in which the tubular separator is coaxially located and wherein the concentrate flow passage is an annular flow passage.

4. A filtration device as claimed in claim 3 wherein the tubular housing is of a generally consistent internal diameter whereas an external diameter of the tubular separator increases in a longitudinal direction wherein the annular flow passage is tapered.

5. A filtration device as claimed in any preceding claim wherein the inlet and the outlet of the concentrate flow passage are defined by relatively larger and smaller annulus openings at opposing ends, respectively, of the tubular housing and wherein an opening within the tubular separator adjacent the outlet defines a filtrate outlet.

6. A filtration device as claimed in any preceding claim wherein the tubular separator includes a plurality of longitudinally extending and circumferentially spaced vanes which longitudinally diverge relative to one another.

7. A filtration device as claimed in claim 6 wherein the plurality of vanes are arranged, so that a filtrate flow passage is provided between adjacent of said vanes whereby fluid flowing along the flow passage following a helical path flows through one or more of the filtrate flow passages.

8. A filtration device as claimed in claim 6 wherein adjacent vanes circumferentially overlap one another.

9. A filtration device as claimed in any one of claims 6 to 8 wherein the plurality of vanes are located within the elongate housing by means of a support structure to which one or more of the vanes is connected.

10. A filtration device as claimed in any preceding claim wherein the walls of the elongate housing define a series of apertures (grooves and slots) following a generally helical path around the housing and protrusions extending into the device separate the apertures from one another and wherein the housing is enclosed by a casing into which matter passing through the apertures passes.

11. A filtration device as claimed in claim 10 wherein ridges and grooves are shaped and orientated to create swirling flow in the device, suppress turbulence and trap floes

12. A tubular separator comprising a plurality of longitudinally extending and circumferentially spaced vanes connected to a support structure wherein the vanes longitudinally diverge relative to one another and wherein a filtrate flow passage is provided between adjacent of said vanes whereby fluid flowing along a periphery of the tubular separator flows through said filtrate flow passages to within the tubular separator.

13. A tubular separator as claimed in claim 12 wherein each of the plurality of vanes is in the form of an elongate fin which in transverse cross- section includes opposing concave and convex foiled surfaces, the vanes each being oriented wherein the concave and convex surfaces face generally inward and outward, respectively.

14. A tubular separator as claimed in claim 13 wherein each of the vanes is of an aerodynamic form including a leading edge of an enlarged profile whilst being tapered toward its trailing edge, the leading edge facing the flow passage.

15. A tubular separator as claimed in any one of claims 10 to 14 wherein each of the vanes is oriented about the tubular separator wherein an imaginary chord extending between its leading and trailing edges is at an angle of between about 5° to 15° relative to a tangent taken at the leading edge of a curve which intersects or adjoins the leading edges of the vanes.

16. A tubular separator as claimed in any one of claims 12 to 15 wherein the tubular separator also comprises a filtration membrane located about the plurality of vanes.

17. A tubular separator as claimed in claim 16 wherein the filtration membrane is in the form of a filtration "sock" which envelopes said vanes.

18. A tubular separator as claimed in any one of claims 12 to 17 wherein the support structure includes an axially oriented support rod located within the tubular separator, and a plurality of radially extending mounting elements each being coupled to the support rod and arranged to fix to and thus support at least one and constrain all of the plurality of vanes.

19. A sewage treatment plant incorporating one or more tubular separators as claimed in any one of claims 12 to 18 wherein the fluid is liquid waste and water, and the particles are in the form of solids such as that present in a sewage stream.

20. A sewage treatment plant incorporating one or more filtration devices as claimed in any one of claims 1 to 9 wherein the fluid is liquid waste and water, and the particles are in the form of solids such as that present in a sewage stream.