WO2013122464A1

WO2013122464A1 - Fibre based filter

Info

Publication number: WO2013122464A1
Application number: PCT/NL2013/050090
Authority: WO
Inventors: Hugo LIEBRAND; Michiel Paul ARNOLDY
Original assignee: Twin Fibra B.V.
Priority date: 2012-02-15
Filing date: 2013-02-15
Publication date: 2013-08-22
Also published as: NL2008295C2

Abstract

A filter comprises a housing defining a flow channel having an inlet end and an outlet with a collar located within the housing such that a flow passage is formed between an outside surface of the collar and an inside surface of the housing. A bundle of fibres have their first ends retained by the collar and their second ends extending freely towards the inlet end of the housing and a pinch member is located within the fibre bundle for constraining the fibres at a position intermediate between their second end and the collar. In use, the fibres clump together upstream of the pinch member and can retain particulates or droplets.

Description

Fibre Based Filter

BACKGROUND OF THE INVENTION

1. Field of the Invention The present invention relates to filters for liquids and in particular to in-line filters capable of removing particulates, droplets and bubbles from a flow of liquid such as water. The invention also contemplates the use of such a filter as a liquid-liquid coalescing filter for separating a dispersed fraction such as oil in water.

2. Description of the Related Art

Various filtration principles are known and employed according to the nature of the substances to be separated. A common form of filter for separating particulates from a liquid is the mesh filter. A liquid to be treated is passed through the filter and particulates greater than the mesh size will be preferentially retained. Smaller particles may pass through the filter. The effectiveness of such a filter is often indicated by a "beta rating" representing the ratio of particles of a given size upstream of the filter compared to those downstream. A significant problem with such filters is their ability to block or clog due as the residue on the filter gradually reduces the flow through area.

Another type of filter that has been suggested uses fibre bundles aligned with the flow. The fibres are held closely together with minute interstices between adjacent fibres. A pinch region may be provided at which the fibres are clamped to a maximum value at which the interstitial passages are at a minimum. Particles may be retained at various positions within the interstices, depending upon their relative size. An advantage of such a construction is that the rating of the filter may effectively be adapted by varying the degree of clamping at the pinch region. The filter may also be conveniently flushed by releasing the clamping force at the pinch region. The filter may be flushed both forwards and backwards as required.

One device of this type has been described in US5690823 in which a displacement member is used to clamp fibres outwardly against a ring shaped ferrule. Another device is described in EP0280052, having a plurality of fibres surrounded by a distendable membrane. The membrane can be inflated by a source of pressure to compress and clamp the fibres. During back flushing, pressure in the membrane may be released.

Although such devices have been shown to operate well, all require some form of activation for the clamping means, which should be releasable for the purpose of flushing.

In order to overcome the need for a separate source of compression for activating a distensible membrane or clamping member, WO2007113512 suggests the use of hollow fibres that can themselves inflate or expand in response to pressure in a first direction and which deflate or contract in response to back-flushing. It is unclear as to whether such an arrangement would, in practice, function as described. Furthermore, the manner in which individual fibres are arranged is complex and manufacture would be costly.

It would thus be desirable to develop a fibre based filter that is simple in use and relatively cost-effective to produce. Preferably, the filter should facilitate flushing.

BRIEF SUMMARY OF THE INVENTION

According to the invention there is provided a filter comprising: a housing defining a flow channel having an inlet end and an outlet end; a collar located within the housing such that one or more flow passages are formed between an outside surface of the collar and an inside surface of the housing; a bundle of fibres having their first ends retained by the collar and their second ends extending freely towards the inlet end of the housing; and a pinch member located within the fibre bundle for constraining the fibres at a position intermediate between their second end and the collar. The pinch member and the housing are rigid and press the fibres firmly against one another leaving only minute interstitial openings between adjacent fibres. They also ensure that the fibres are firmly held and cannot move in the direction of the outlet when a pressure is applied across the filter. The fibres are flexible and on the upstream side of the pinch member are free to move and bend in response to an applied pressure. Without wishing to be bound by theory it is believed that this freedom allows the fibres to clump up or mat together, providing an effective filtration region at and upstream of the pinch member. Downstream of the pinch region, the fibres are less tightly packed and the liquid can flow with relatively less resistance towards the flow passages. This region defines an outflow region as the flow takes place at least partially in a radially outwards direction, out of the fibre bundle. When the flow is reversed, for back-flushing, the liquid can flow more easily through the pinch region as the free second ends of the fibres are carried in the direction of the back-flow while the first ends of the fibres are retained by the collar and cannot clump or mat together. In this manner, an easily flushable filter is produced with no moving parts and which does not require a separate source of pressure. In this context, it may also be noted that although the ends of the housing are described as inlet and outlet, this is in no way limiting on its construction and the filter may be operated in either direction according to the characteristics desired as will be further described below.

In a preferred form of the invention, the pinch member occupies between 15% and 40%, more preferably around 25% of the cross-sectional area of the flow channel. The difference in area between that occupied by the pinch member and the total area of the flow channel represents approximately the area of the compressed fibre bundle. For a cylindrical channel of constant cross-section the frontal area of the pinch member also defines the free space for liquid flow upstream and downstream of the pinch member.

According to a further aspect of the invention, a distance between the pinch member and the free ends of the fibres defines an inflow region of the fibres having a length at least equal to a diameter of the pinch member. More preferably, the length of the inflow region is at least double the diameter of the pinch member. Without wishing to be bound by theory, it is believed that the length of the inflow region increases the effectiveness of the filter in retaining different sized particulates without clogging. An extended inflow region is particularly desirable for use as coalescent filter for removal of hydrocarbon dispersions. According to another desirable aspect, a distance between the pinch member and the collar defines the outflow region having a length at least equal to a diameter of the pinch member. This region may also have a length that is twice the diameter of the pinch member. Adequate length of this region is believed to facilitate outflow of liquid from the fibre bundle without adverse pressure drop. Most preferably, the inflow region is longer than the outflow region.

The pinch member may have various forms but is preferably a solid of revolution aligned with a centreline or axis of the flow channel. Most preferably it comprises a rigid bulbous member which may be spherical, ovoid, bullet shaped or the like. The widest diameter of the pinch member will generally define the degree to which the fibre bundle is pinched while the longitudinal shape will determine the influence on the flow and may also affect the ease of assembly. Under normal use the pinch member is not intended to move and does not need to move in order to provide back flushing.

Nevertheless, it may be desirable to have an adjustable configuration for set-up purposes. The pinch member may be supported on or form part of an axial rod which is preferably clamped together with the fibre bundle within the collar. The skilled person will understand that the rod may also be held from the inlet end or that the pinch member may be held by a thin wire or the like extending axially from inlet to outlet through the bundle.

Different types of fibres may be used for the filtering device, where the type of fibres may be selected in order to fulfil the requirements of a given filtration process. Thus, the fibres may be porous or non-porous and the fibres may be solid or hollow. In a preferred embodiment the fibres comprise polyester fibres or nylon fibres but materials such as glass, carbon, PTFE and fiuoroelastomers (FKM) may also be employed. It is also preferred that the fibres have a substantially circular cross-section. Here the cross- sectional dimension may vary according to the particles to be filtered from the fluid, but it is preferred that the diameter is of at most 5 mm, such as at most 2 mm, such as in the range of 0.001-1 mm, and preferably in the range of 0.05-0.2 mm. In general, the finer the particulates, the thinner should be the fibres. As an example, fibres of 0.1 mm provide for solid filtration for particles to around 1 micron.

Most preferably, the fibres are hollow. Hollow fibres are more compressible in that they can change shape to close up the interstices. Furthermore, hollow fibres can be more flexible for a given diameter than corresponding solid fibres. Flexible fibres are useful in assisting in the clumping or matting of the fibres upstream of the pinch region. It will be understood that thinner fibres also have increased flexibility but that it may not be desirable to use fibres below a certain fineness. The fibres may be round but may also have a profiled cross-section to enhance characteristics such as stability, bending, particle/droplet entrapment and the like.

According to one embodiment, for use in retaining and removing hydrocarbons from water in a coalescing process, the fibres have a preferential disposition to hydrocarbons. They may thus be formed of a material or provided with a coating that is oleophilic or hydrophobic. Special materials such as PTFE or FKM fibres may hold hydrocarbon droplets allowing them to grow in size: small (~1 micron) droplets may grow to become large (20+ micron) droplets as they migrate along the fibres, allowing better separation downstream. For operation in this manner, the filter may be operated in reverse flow, with the fluid to be filtered leaving from the free ends of the fibres. Such a configuration is believed to enhance the release of oil droplets from the fibre end.

According to one embodiment, the collar comprises external projections which engage the inside surface to define an annular space between the collar and the housing. The collar may also be provided with openings allowing it to be more easily crimped onto the fibre bundle. In an alternative construction, the rod may pass through the collar and be attached at the outlet end of the housing. The collar may be manufactured of metal, in particular, stainless steel and may also be manufactured from plastic materials or composites. In one alternative the fibres may be clamped by binding with a cord, made of e.g. carbon or aramid fibres.

According to a further aspect of the preferred embodiment, the housing is of a constant cross-section, preferably cylindrical and a cross-sectional area of the flow passages corresponds at least to a frontal area of the pinch member. In other words, the fibres may be as tightly packed at the pinch region as in the clamping region. In general, the fibres in the clamping region of the collar will be packed to a maximum in order to maintain them in position. It will be understood that this may cause the fibres to be crushed, especially in the case of hollow fibres.

In general, the invention covers a filter comprising a bundle of fibres suspended in a flow channel such that the fibres are aligned with and substantially fill the channel such that a flow through the channel must pass along and between the fibres, the bundle having a first clamped end or region adjacent an outlet of the flow channel and a second loose end or region adjacent an inlet of the flow channel, the first end being provided with outlet passages allowing a flow to exit the fibre bundle at an intermediate outflow location and the filter further comprising a pinch member located between the intermediate location and the second end. The invention may also be defined by a housing defining a flow channel and a bundle of fibres located within the flow channel, the bundle having in series and in the direction of forward flow through the flow channel: an inflow region in which the fibres are relatively loosely packed; a pinch region in which the fibres are tightly packed leaving minute interstices between adjacent fibres; an outflow region in which the fibres are relatively loosely packed and flow can exit the bundle at least partially radially; and a clamped region in which flow through the bundle along the fibres is prevented. In the clamped region, the flow bypasses the bundle and passes through one or more flow passages surrounding the bundle or formed through the bundle. In one configuration, two pinch regions may be provided with an outflow region located in between. Such a back-to-back configuration allows increased filtration capacity from a single fibre bundle.

Furthermore, the invention also relates to a method of filtering a liquid using a fibre bundle filter, the method comprising: retaining the bundle within a flow channel whereby at a first end the fibres are tightly packed together and at a second end the fibres are relatively loosely spaced; pinching the bundle at an intermediate position between the first and second ends to cause the fibres to be tightly packed in a pinch region to define interstitial gaps between the fibres; flowing the liquid through the flow channel into the second end of the bundle and towards a first end of the bundle;

allowing the fibres upstream of the pinch region to clump or mat together to filter relatively large particulates or droplets from the liquid; filtering relatively small particulates or droplets from the liquid at the pinch region; and allowing the liquid to exit the fibre bundle at a radial outflow region downstream of the pinch region and upstream of the first end, whereby the fibres in the radial flow region are loosely packed relative to the pinch region.

In one embodiment of the method, filter aid may be added to the filter during or prior to use. Such filter aid is generally known in the art and may comprise fine particulates such as diatomaceous earth. These particulates assist in the filtering function and can help achieve a fine filtration even when using relatively coarse fibres. The method may further comprise back-flushing the filter by reversing the flow from the first end towards the second end, whereby during back-flushing, the fibres between the second end and the pinch region can straighten and release entrapped particulates or droplets. Back-flushing may take place without relative movement of the pinch member or otherwise release of the clamping or pinching action. This may also include the use of a gas such as air and/or nitrogen to boost the cleaning process. A container vessel with nitrogen can be provided and purged into the backflush water to create extra pressure drop and velocity.

The method is particularly advantageous for use in the coalescence of dispersed hydrocarbons, whereby the flow takes place at a relatively low flow rate and negligible pressure drop. In this process, the low flow rate may not lead to clumping of the fibres and the hydrocarbon droplets may be retained at least partially by other mechanisms. In particular, the fibres may be chosen for their surface tension or attractive effects with respect to the droplets. Small droplets may be entrapped and may grow by coalescing together until they reach a specific volume. At that point, the buoyant effect due to the specific gravity of the hydrocarbon may overcome the retaining force and the droplet may float up to the surface of the container which is being separated. In one embodiment of such a coalescer, flow takes place downwards into the inflow region against gravity. It is also considered that flow may take place in the opposite direction i.e. from the outflow region towards the free ends of the fibre. For low flow rates, the forward and reverse flow pressure characteristics are similar but release of oil droplets from the free ends of the fibres may be easier than from the outflow region. According to a yet further aspect of the invention, the method may also comprise electrical oxidation of the liquid, prior to flowing the liquid through the flow channel. This may be carried out in an electrical oxidation cell comprising one or more pairs of spaced conductive electrodes separated, arranged so that the water to be treated flows between the plates at a low flow rate. A direct current voltage is applied across the plates. This may provide: electronic charge destabilisation of suspended colloids and emulsions; release of reactive oxygen, hydroxyl and other radicals which react with dissolved organic and ammonia compounds, oxidising them and causing heavy metals to separate from solution as oxides/ hydroxides; large amounts of fine gas bubbles promoting the flotation of coagulated solids and coalesced hydrocarbons; and production of smaller amounts of denser, less hydrated flocculants than conventional chemical flocculation. BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the invention will be appreciated upon reference to the following drawings of a number of exemplary embodiments, in which:

Figure 1 shows a perspective cut-away view of a filter according to a first embodiment of the present invention;

Figure 2 shows a longitudinal section of the filter of Fig. 1;

Figure 3 shows an end view of the filter of Fig. 1;

Figure 4 A to 4C show detail views of part of the filter of Fig. 3 in forward and back- flow operation; Figures 5 A to 5C show three alternative embodiments of the filter according to the present invention;

Figure 6 shows in cut-away perspective view a water treatment system according to the present invention;

Figure 7 shows a similar device to Figure 6 being used as a coalescing filter; and Figure 8 shows an alternative embodiment of the filter of the invention in longitudinal section.

DESCRIPTION OF ILLUSTRATIVE EMBODFMENTS

Figure 1 shows a perspective view of a filter 1 according to the present invention having a cylindrical housing 2 which has been opened over half of its circumference to reveal the interior of the filter. The housing 2 forms a flow channel 4 in which is located a fibre bundle 6. The fibre bundle 6 is retained by a collar 8 and is provided at its core with a pinch member 10 supported on a rod 12.

Figure 2 shows an elongate cross-sectional view of the filter of Fig. 1. According to this view, there is shown that the housing has an inlet end 20 and an outlet end 22 and the collar 8 is located adjacent to the outlet end 22. The collar 8 may be supported from the housing by appropriate supporting elements (not shown) extending radially outwardly to support against an inside surface 26 of the housing 2. Flow passage 28 is formed between the inside surface 26 of the housing and an outside surface 30 of the collar.

The fibre bundle 6 is composed of a multitude of fine fibres 32. The bundle has a first end 34 which is retained within the collar 8. A second end 36 of the fibre bundle 6 extends beyond the pinch member 10 towards the inlet end 20. The fibres 32 at the second end 36 are free i.e. they are not constrained apart from by the housing 2. Four regions are defined along the fibre bundle 6, namely: an inflow region 40 between the second end 36 and the pinch member; a pinch region 42 at the position of the pinch member 10; an outflow region 44 between the pinch member 10 and the collar 8; and a clamped region 46 within the collar 8.

Figure 3 shows the filter 1 viewed from the outlet end 22, showing the collar 8 and flow passage 28. The axial location of the rod 12 and pinch member 10 can also be seen. In the illustrated embodiment, the housing 2 is made of polypropylene (PP) and has an internal diameter of 60 mm; the fibre bundle 6 has a compressed diameter within the collar 8 of 50 mm and has an overall length of 250 mm; the pinch member 10 has a diameter of 32 mm and has its midpoint spaced 60 mm from the collar 8 and 80 mm from the free end 36 of the fibres 32; the fibres comprise hollow fibres of nylon having a nominal outer diameter of 0.1 mm. The skilled person will understand that these values are exemplary and that other dimensions, relative sizes and materials may be employed as required.

Figure 4A is a schematic detail of part of the filter 1 of Fig 1 in close up during forward filtering. Flow F enters the inflow region 40 and flows towards the outlet end 22.

Because the fibres 32 at their second ends 36 are free, they are partially entrained by the flow F which causes them to bend. At the pinch region 42, the pinch member 10 holds the fibres 32 tightly, preventing them from moving past the pinch region 42. This causes the fibres 32 to become bunched or clumped together in the inflow region 40. Large particles LP entrained by the flow F are retained by the fibres 32 in the inflow region. Small particles SP are captured in interstices 48 formed between the fibres 32 in the pinch regions 42. Figure 4B is a cross-section taken in the direction IVB showing the interstices 48 between fibres 32 in the pinch region 42. The hollow interiors 33 of the fibres 32 can also be seen.

Once the flow F has passed the pinch region 42, the fibres 32 become less tightly packed together and the flow F can pass out from between the fibres 32 in the outflow region 44. In this region, the flow F has a component directed radially outwardly, in addition to a component in the direction of the outlet end 22. The flow F exits the fibre bundle 6 and passes through flow passages 28 along the outside surface 30 of the collar 8. The fibres 32 insert into the collar 8 and are retained thereby within the clamping region 46.

Figure 4C shows the same schematic detail of the filter 1 as Fig 4A during back- flushing of the filter. In this case, the flow F takes place in a direction from the outlet end 22 in the direction of the second ends 36. The free second ends 36 of the fibres 32 are entrained by the flow F and the bunching of the fibres 32 in the inflow region 40 is reduced. Particulates P are flushed out of the fibre bundle 6. Although the flow restriction at the pinch region 42 remains the same as in forward flow, the pressure drop across the filter during back flushing has been found to be significantly lower. In tests, four times the flow has been achieved during back- flushing, with less than half the pressure drop across the filter. Alternatively, for the same pressure drop, a flow increase during back-flushing of more than 20x forward flow has been achieved.

Figures 5A to 5C illustrate cross-sectional views of three filters with three alternative forms of pinch member 1 OA- IOC, embodied as filter cartridges 50. Each cartridge 50 is provided with an inlet stub 52 connected to the inlet end 20 of the housing 2. The inlet stub 52 includes O-rings 54 for sealing as will be described below. Although not shown, they may also be provided with connecting elements in the form of screw or bayonet mounts. The stub 52 is also made of plastics material and is glued or welded to the housing 2. It will be understood that mechanical connection may also be provided. In Fig 5 A, pinch member 10A has a lenticular longitudinal cross-section allowing the fibres 32 to closely follow its surface contour. Such a shape may be advantageous in allowing the fibres to collapse in a controlled manner onto the pinch member and may lead to relatively less clumping of the fibres in forwards flow.

In Fig. 5B, pinch member 10B has a pear-shaped longitudinal cross-section with the blunt end facing in the direction of the inlet end 20. Such a shape increases the space immediately upstream of the pinch member 10B and is believed to encourage clumping of the fibres in forward flow, leading to improved filter action.

In Fig. 5C, the pinch member IOC is elongate and of substantially constant cross- section into the outflow region 40. In the pinch region 42, the fibres are not completely packed but become steadily more tightly compressed in the outflow region 44 as they approach the collar 8. Such an arrangement provides a greater filter length which may be advantageous under certain conditions. In Figure 6, a number of filter cartridges 50 are shown according to the present invention installed in a water treatment system 70. Water treatment system 70 comprises a vat 80 having a connection bulkhead 82 provided with a plurality of apertures 84. The bulkhead 82 separates the vat into a lower plenum 86 and an upper plenum 88. A plurality of filter cartridges 50 is located in the upper plenum 88, with their inlet stubs 52 inserted into a respective aperture 84. O-rings 54 provide for the necessary sealing. Each cartridge 50 has a cap 56 which supports the rod 12. In the disclosed embodiment, seven cartridges are shown although in reality a single vat may hold up to fifty cartridges or more, providing an overall flow rate of up to 5 cubic meters/hour. A cage structure 94 in the upper plenum 88 is held in place by cover 96 and prevents the cartridges 50 from lifting from the bulkhead 82. In use, water W is supplied to the lower plenum 86 through a first port 90. The water flows upwards through the filter cartridges 50 in parallel and exits via the upper plenum 88 through a second port 92. An appropriate controller 100 may be provided to control pumps 102, sensors 104 and valves 106 to ensure forward and reverse flow according to a predefined program or in response to predefined process parameters. This may include the use of air and/or nitrogen gas to boost the cleaning process. A container vessel with nitrogen can be provided and purged into the backflush water to create extra pressure drop and velocity. Periodically or as monitored by the controller 100, the pump 102 may be stopped and the vat 80 opened to allow removal and exchange of one or more cartridges 50. These may be disposed of or recycled.

Figure 7 shows an alternative arrangement of a water treatment system 70

corresponding to Figure 6 in use as a coalescing filter. In this case, the filter cartridges 50 are mounted upside-down, with the free ends 36 of the fibre bundles uppermost. The remaining elements of the system 70 are substantially identical to that described in Figure 6. Unlike the arrangement of Figure 6, the system is operated with flow F entering through second port 92 and flowing downwards at a low flow rate through the upper plenum 88 and cartridges 50 to the first port 90. The flow F comprises a mixture of water contaminated with oil which is to be cleansed. As the water passes into the inflow region 40, minute oil droplets entrained by the water are trapped by the fibres 32 at positions corresponding to the sizes of the droplets. Subsequent droplets arriving within the filter coalesce with the entrapped oil droplets to form globules G which are sufficiently buoyant to rise to the surface where they form a layer of oil. The relatively low flow rate through the inflow region 40 and the gradual reduction in the interstitial spacing make it easier for the globules to escape against the flow F. Back- flushing may take place periodically as the flow through the filter falls below a given value due to clogging at the pinch region 42. Also shown in Figure 7 is an electrical oxidation (elox) cell 108 placed upstream of the second port 92. Elox cell 108 is generally conventional and comprises multiple pairs of conductive electrodes separated by a few millimetres and arranged so that the water to be treated flows between the plates at a low flow rate. A direct current voltage is applied across the plates. A number of processes take place simultaneously and may be summarised as:

• Electronic charge destabilisation of suspended colloids and emulsions;

• Release of reactive oxygen, hydroxyl and other radicals which react with

dissolved organic and ammonia compounds, oxidising them and causing heavy metals to separate from solution as oxides/ hydroxides; · Large amounts of fine gas bubbles promote the flotation of coagulated solids and coalesced hydrocarbons;

• Production of smaller amounts of denser, less hydrated flocculants than

conventional chemical flocculation.

Although the embodiment of Figure 7 is shown operating in downwards flow mode, it is recognized that this may operate with upwards flow, whereby the oil/water mixture enters the filter from the outflow region and exits at the free ends 36 of the fibres 32. Such an arrangement is believed to be advantageous in encouraging release of globules of oil from the free ends 36.

Figure 8 shows a further embodiment of a cartridge 250 according to an alternative aspect of the invention, allowing double the filter capacity from a single fibre bundle. Cartridge 250 comprises a housing 202 having inlet stubs 252A and 252B at upper and lower ends respectively. A bundle 206 of fibres 232 similar to that of Figure 1 is supported within the housing 202 by a collar 208 which in this case is clamped at a clamping region 246 at a mid-point of the housing 202. The fibres 232 in the fibre bundle 206 extend to first free ends 234 and second free end 236. The collar 208 is held within the housing 202 by appropriate fixation means. Around the collar 208 is formed a flow passage 228 which communicates with radial ports 258 through the housing 202. Clamped within the collar 208 at the centre of the fibre bundle 206 is a rod 212 carrying two pinch members 21 OA, 21 OB at its ends. The pinch members 210 A,B form pinch regions 242 A, 242B. Between the pinch regions 242 A,B and the first and second free ends 234, 236 are formed inflow regions 240A, 240B respectively.

In use, flow F through the inlet stubs 252A, 252B flows into the respective inflow regions 240A, 240B, through pinch regions 242A, B and out through outflow regions 244A, B to radial ports 258. The cartridge 250 may be used in a treatment system as described in Figure 6, by incorporating an additional bulkhead to connect onto the upper end of the flow cartridge 250 and an additional port in the cover.

Thus, the invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art. In particular, the connections to and from the housing may be distinct from the

schematically illustrated design.

Many modifications in addition to those described above may be made to the structures and techniques described herein without departing from the spirit and scope of the invention. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention.

Claims

1. A filter comprising: a housing defining a flow channel having an inlet end and an outlet; a collar located within the housing such that a flow passage is formed between an outside surface of the collar and an inside surface of the housing; a bundle of fibres having their first ends retained by the collar and their second ends extending freely towards the inlet end of the housing; a pinch member located within the fibre bundle for constraining the fibres at a position intermediate between their second end and the collar.

2. The filter according to claim 1, wherein the pinch member occupies between 15% and 40%, preferably around 25% of the cross-sectional area of the flow channel.

3. The filter according to claim 1 or claim 2, wherein a distance between the pinch member and the second ends defines an inflow region of the fibres having a length at least equal to a diameter of the pinch member

4. The filter according to any preceding claim, wherein a distance between the pinch member and the collar defines an outflow region having a length at least equal to a diameter of the pinch member.

5. The filter according to claim 3 and claim 4, wherein the inflow region is longer than the outflow region.

6. The filter according to any preceding claim, wherein the pinch member

comprises a rigid bulbous member located on a centreline of the flow channel.

7. The filter according to any preceding claim, wherein the fibres have diameters of between 0.05 mm and 0.5 mm, preferably between 0.1 and 0.2 mm.

8. The filter according to any preceding claim, wherein the fibres are hollow.

9. The filter according to any preceding claim, wherein the fibres are oleophilic or hydrophobic.

10. The filter according to any preceding claim, wherein the housing is cylindrical and a cross-sectional area of the flow passage corresponds to at least a frontal area of the pinch member.

11. A filter comprising a bundle of fibres suspended in a flow channel such that the fibres are aligned with and substantially fill the channel such that a flow through the channel must pass along and between the fibres, the bundle having a first clamped end adjacent an outlet of the flow channel and a second loose end adjacent an inlet of the flow channel, the first end being provided with outlet passages allowing a flow to exit the fibre bundle at an intermediate outflow location and the filter further comprising a pinch member located between the intermediate location and the second end.

12. A method of filtering a liquid using a fibre bundle filter, the method

comprising: retaining the bundle within a flow channel whereby at a first region the fibres are tightly packed together and at a second region the fibres are relatively loosely spaced; pinching the bundle at an intermediate region between the first and second regions to cause the fibres to be tightly packed in a pinch region to define interstitial gaps between the fibres; flowing the liquid through the flow channel into the second region of the bundle and towards the first region of the bundle; allowing the fibres upstream of the pinch region to clump together to filter relatively large particulates or droplets from the liquid; filtering relatively small particulates or droplets from the liquid at the pinch region; and allowing the liquid to exit the fibre bundle at a radial flow region downstream of the pinch region and upstream of the first region, whereby the fibres in the radial flow region are loosely packed relative to the pinch region.

13. The method of claim 12, further comprising back-flushing the filter by reversing the flow from the first region towards the second region, whereby during back-flushing, the fibres between the second region and the pinch region unclump.

14. The method according to claim 12 or 13, further comprising the addition of filter aid to the filter in the form of fine particulates such as diatomaceous earth.

15. The method according to claim 12 for use in the coalescence of dispersed

hydrocarbons, whereby the flow takes place downwards at a relatively low flow rate and pressure drop such that clumping is minimised and whereby

hydrocarbon droplets are retained by the fibres by surface tension effects.

16. The method of any of claim 12 to 15, further comprising electrical oxidation of the liquid, prior to flowing the liquid through the flow channel.

17. A fibre filter comprising a housing defining a flow channel and a bundle of fibres located within the flow channel, the bundle having in series and in the direction of forward flow through the flow channel: an inflow region in which the fibres are relatively loosely packed; a pinch region in which the fibres are tightly packed leaving minute interstices between adjacent fibres; an outflow region in which the fibres are relatively loosely packed and flow can exit the bundle at least partially radially; and a clamped region in which flow through the bundle along the fibres is prevented.

18. A water treatment system comprising a vat having a connection bulkhead

provided with a plurality of apertures and a plurality of filters according to any of claims 1 to 11 or 17, removably engaged with the apertures.