The present invention relates to filter apparatus, and in particular apparatus for filtering water.

Water filters, or media filters as they are sometimes known, are used in many different applications, but the more common applications are the filtration of drinking water for bottling, or of process water, sea, river, canal or loch water, or swimming pool water. Such media filters are also frequently used for environmental contaminant removal and in cooling tower, chiller or air conditioning applications.

The typical construction of one type of media water filter is a sealed, generally cylindrical pressure vessel with a water inlet at the top and an outlet at the bottom. Contained within the pressure vessel are various layers of filter media grading from a very fine layer at the top to a coarse layer at the bottom. At the top of the vessel, above the media layers, is a receiving area known as the upper plenum into which the inlet conduit feeds; while at the bottom of the vessel (separated from the coarse media by a foraminous plate through which water can pass, but the coarse media cannot) is a water collection area, known as the lower plenum, to which the outlet conduit is connected.

In such media water filters, a process known as reverse flow backwashing is frequently carried out in order to clean the filter on a regular basis. For reverse flow, usually there would be a takeoff or outlet conduit at the top and a feed conduit at the bottom connected either independently or to one of the existing conduits via appropriate valves. Backwashing is generally effected by shutting off valves in the supply inlet or inlets and the outlet to the filter, and then opening valves in the backwash pipes, which therefore effectively reverses the flow of water through the filter, thus driving out contamination through a separate backwash outlet at the top or what is normally the input side of the filter system.

Traditional self-cleaning media filters (where reverse flow backwashing is triggered when a predefined level of contamination is reached) can remove solids down to about 20 micron. At this level efficiencies can be as high as 80% removal, but with undesirably lower efficiency at lower size ranges. Media filters (which employ sand and other minerals as the filter material) are also used but on filtration of solids less than 10 micron, the sand or other minerals soon blinds, and bacteria colonise the sand; when they start to grow this can soon block the filter bed.

Because of this problem of bacterial growth, media based filtration generally only offers reliable filtration down to the 20 micron level. Theoretically, 10 micron filtration is possible but this can only be sustained if the feed water contains only a low level of contamination, thus reducing the amount of work the filter has to perform. The design of such filters relies on a steady "flux rate". The "flux rate" is the rate of unit flow per hour, per unit area of the filter - usually expressed as m ³ /hr/m ² of filter. Traditionally for fine filtration to 10 micron the flux rate is typically 10 to 15 m ³ /hr/m ² . The problem is that by using even when using finer media to give high quality water, the flux rate has to be slow. The finer the media, the finer the filtration, but also there will be a higher pressure drop and a lower flux rate. Biological contamination in this type of filter can cause rapid pressure build up which is the trigger for the system to automatically stop filtration and backwash out the contamination.

Water-borne contaminations can and often do contain biological elements which combine within the bed and start to proliferate; this unwanted proliferation is encouraged by the near ideal conditions within the filter environment. The colonies of bacteria then create high pressure areas within the top bed surface, thereby diverting the water to lower density areas of the filter bed. The result of this diversion is to create high velocity areas, which in turn causes channelling, sometimes known as rat holing, and the result is filter media bypass and a loss of filtration efficiency.

When the filter is backwashed, the higher density bacterial colonies are heavier than normal contamination and are therefore less likely to be removed by the backwashing process; they therefore remain within the bed to act as seed for the next batch of dirty water. This results in ever shortening periods between backwash times, successively using more and more backwash water, which is run out to waste treatment. Filtration efficiency is typically less than 80% at 10 to 20 microns. It is therefore known to generate a vortex above such a filter bed, in order to make the array of filter medium more random, and therefore to reduce the frequency of the need for backwashing. An example of such a media water filter with a vortex generator is disclosed in, for example, GB2461119. The present invention concerns an improved vortex generator for a media water filter.

According to the invention there is provided a water filter comprising a pressure vessel having a main water inlet at the top and a water outlet at the bottom, with a foraminous plate located above the outlet to support a column of filter media within the vessel, wherein the inlet comprises a coaxial downpipe provided with a lower vortex generator at a lowermost end of the downpipe, and an upper vortex generator above the lower vortex generator, each of which vortex generators comprises at least three nozzles equispaced around the downpipe, the nozzles of the upper vortex generator being arranged symmetrically in a first plane around the coaxial downpipe and the nozzles in the lower vortex generator also being arranged symmetrically in a second plane around the coaxial downpipe, the first and second planes being substantially parallel to one another.

The first and second planes are preferably substantially perpendicular to the axis of the downpipe. The downpipe itself should be closed at its lowermost end, such that the only exit for water from the lowermost end is via the lower vortex generator.

The downpipe is typically generally cylindrical, with a smooth surface both internally and externally. It may be of any suitable material of which stainless steel is currently the preferred, but materials such as suitable thermoresistant plastics may alternatively be used. Each of the nozzles of the upper vortex generator is preferably in the form of an elbow-piece having a joint portion with an axis substantially at right angles to the axis of the downpipe, the joint portion being connected to a mouth of the elbow-piece which has an axis substantially at right angles both to the axis of the downpipe and the axis of the joint portion. The mouth of each of the nozzles of the upper vortex generator is preferably circular in section. The internal diameter of the mouth is preferably related to the internal diameter of the downpipe by the following relationship:

diameter of nozzle mouth x number of nozzle mouths— internal diameter of downpipe.

By "equal" we mean subject manufacturing and process tolerances; plus or minus 10% may be tolerated while still producing satisfactory results. Each of the elbow-pieces forming the outlet nozzles of the upper vortex generator is preferably of the same material as the downpipe, such as stainless steel. The elbow-pieces may be secured to the downpipe by drilling through the wall of the downpipe and welding the elbow-pieces to the surround of the borehole. The elbow-pieces preferably have smooth internal faces in order not to disrupt liquid flow to the respective nozzle mouths.

As indicated, there must be at least three equispaced nozzles to form the upper vortex generator; at least three are required to form a vortex. It is particularly preferred that there should be four such equispaced nozzles, at 90 degree intervals around the downpipe.

It is further preferred that the outermost parts of the nozzles forming the upper vortex generator are spaced from the axis of the downpipe by an amount which is from 25 (or 30) to 40% of the diameter of the pressure vessel.

The lower vortex generator generally has an outer diameter that is in the range specified above, and preferably not more than 37% of the internal diameter of the pressure vessel. It is especially preferred that the outer extent of the lower vortex generator is about one-third of the internal diameter of the pressure vessel. Thus, if the pressure vessel has an internal diameter of nominally 600 mm, the outer extent or diameter of the lower vortex generator is typically 200 mm (+ about 15 mm). Similarly, the upper vortex generator generally has an outer diameter that is in the range specified above, and preferably not more than 37% of the internal diameter of the pressure vessel. It is especially preferred that the outer extent of the upper vortex generator is about one-third of the internal diameter of the pressure vessel. Thus, if the pressure vessel has an internal diameter of nominally 600 mm, the outer extent or diameter of the upper vortex generator is typically 200 mm ( ^about 15 mm).

The preferred arrangements of the nozzles forming the upper vortex generator are such as to optimise tangential flow and to permit stable vortex generation.

Each of the nozzles of the lower vortex generator is, like the nozzles of the upper vortex generator preferably in the form of an elbow-piece having a joint portion with an axis substantially at right angles to the axis of the downpipe, the joint portion being connected to a mouth of the elbow-piece which has an axis substantially at right angles both to the axis of the downpipe and the axis of the joint portion. The mouth of each of the nozzles of the lower vortex generator is preferably circular in section. The internal diameter of the mouth is preferably related to the internal diameter of the downpipe by the following relationship:

diameter of nozzle mouth x number of nozzle mouths— internal diameter of downpipe.

By "equal" we again mean subject manufacturing and process tolerances; plus or minus 10% may be tolerated while still producing satisfactory results.

Each of the elbow-pieces forming the nozzles of the lower vortex generator is preferably of the same material as the downpipe, such as stainless steel. The elbow-pieces may be secured to the downpipe by boring through the wall of the downpipe and welding the elbow-pieces to the surround of the borehole. The elbow-pieces preferably have smooth internal faces in order not to disrupt liquid flow to the respective nozzle mouths.

As indicated, there must be at least three equispaced nozzles to form the lower vortex generator; at least three are required to form a vortex. It is particularly preferred that there should be four such equispaced nozzles, at 90 degree intervals around the downpipe. It is further preferred that there should be the same number of nozzles forming the lower vortex generator as there are forming within the upper vortex generator. Each nozzle of the lower vortex generator may be parallel to a corresponding nozzle of the upper vortex generator, or they may be offset, provided of course that both sets are equispaced around the downpipe.

It is further preferred that the outermost parts of the nozzles forming the lower vortex generator are spaced from the axis of the downpipe by an amount which is from 10 to 30% of the diameter of the pressure vessel.

The preferred arrangements of the nozzles forming the lower vortex generator are (like those of the upper vortex generator) such as to optimise tangential flow and to permit stable vortex generation.

The outlet from the vessel according to the invention preferably also functions as an inlet when it is required to backwash; a backwash exit conduit is preferably provided towards the top of the vessel above the media layers, in a zone known as the freeboard; the freeboard includes the upper plenum chamber through which the inlet pipe feeds

As indicated above, in the filter according to the invention, contained within the vessel are various layers of filter media - starting with a very fine layer at the top and finishing with a coarse layer at the bottom. At the top of the vessel above the media layers, is the freeboard which includes the upper plenum chamber through which the inlet pipe feeds. At the bottom of the vessel (separated from the coarse media by a foraminous plate through which water can pass) is a water collection area known as the lower plenum chamber to which the outlet pipe for filtered water is attached. (The outlet pipe alternatively functions as a backwash inlet during a backwash cycle.)

The present invention will now be further described, by way of example with reference to the accompanying drawings, in which: -

Figure 1 is a schematic cross section of an exemplary water filter according to the invention;

Figure 2A is a schematic perspective view of a downpipe conduit and upper and lower vortex generators for use in such a water filter;

Figure 2B is a plan view of the lower vortex generator of the arrangement of Figure 2A; and

Figure 2C is a plan view of the upper vortex generator of the arrangement of Figure 2A.

Referring to Figure 1 , the illustrated apparatus comprises a broadly cylindrical upright filter pressure vessel 1 which (in use) contains a bed 2 of filter medium that is supported at the base of the bed by a foraminous plate 3 through which water can penetrate but the filter medium cannot. The foraminous plate 3 sits just above an inwardly curved (concave) bottom portion of the filter vessel 1 to define a lower plenum chamber 4 having a filter outlet conduit 5 (which as shown is mounted to the lowermost central portion of the lower plenum chamber).

The bed 2, supported by plate 3, extends upwardly in the filter vessel 1 to an upper surface 6 of the bed 2 (that is, to the fill level to which filter media forming the bed is allowed to reach). Above the upper surface 6 is the freeboard, the upper part of which constitutes an upper plenum chamber 7 defined by an upper part of the filter vessel 1. The upper plenum chamber 7, like the lower plenum chamber 4, is inwardly curved (concave). The upper plenum chamber 7 extends to an upper cylindrical neck 8 which is coaxial with the body portion 9 of the filter vessel 1 (that is the portion of the filter vessel 1 that extends between, and integrally connects, the lower plenum chamber 4 and the upper plenum chamber 7).

The neck 8 is surmounted by an uppermost access flange 10 and a cylindrical cap 11 having a central coaxial aperture 12. A main inlet downpipe conduit 13 enters the filter vessel 1 via the aperture 12 (there being a tight gasketed seal, not shown, between the aperture 12 and the inlet downpipe conduit 13) and the conduit 13 extends coaxially of the neck 8 and of the upper plenum chamber 7 to terminate above the upper surface 6 of the bed 2.

The downpipe conduit 13 is itself connected to a main cylindrical inlet 14 via a smooth contoured right-angled bend 15 to supply liquid to the upper plenum chamber 7. At the lower end of the downpipe conduit is a closed end 16 and a series of equispaced vortex generating nozzles 17, 18, 19, 20 (see Figures 2A and 2B) encircling the closed end 16 to form a lower vortex generator 21. Intermediate between (but not necessarily equispaced from) the closed end 16 and the bend 15 is a further series of equispaced vortex generating nozzles 22, 23, 24, 25 (see Figures 2A and 2B) encircling the downpipe conduit 13 to form an upper vortex generator 26.

In use, liquid enters the filter vessel 1 below the upper plenum chamber 7 both via upper vortex generator 26 and lower vortex generator 21. Lower vortex generator is located so as to be above the upper surface 6 of the bed 2.

Each of the nozzles 17, 18, 19, 20 (lower vortex generator) and 22, 23, 24, 25 (upper vortex generator) is in the form of an elbow piece having a respective open-ended nozzle outlet 17o, 18o, 19o, 20o (lower vortex generator - see Figure 2B) and 22o, 23o, 24o, 25o (upper vortex generator - see Figure 2C) substantially at right angles to the respective nozzle inlet 17i, 18i, 19i, 20i (lower vortex generator - see Figure 2B) and 22i, 23i, 24i, 25i (upper vortex generator - see Figure 2C) such that liquid flow from each of upper and lower vortex generators 26 and 21 is essentially tangential. The respective nozzle inlets are as shown all substantially at right angles to the axis of downpipe conduit 13.

Extending at right angles to the neck 8, and communicating with the interior of the filter vessel 1 , is a backwash drain conduit 27, and the filter outlet conduit 5 also functions as a backwash inlet.

The filter vessel 1 acts as a filtration module for process water streams;

according to the invention, the vortex generators 26 and 21 constitute effectively a dual vortex generator into the upper plenum chamber 7 of what is otherwise substantially a standard pressure vessel.

In use, water laden with solids enters the vessel 1 via inlet 14 and downpipe 13 and is introduced below the upper plenum chamber 7 of vessel 1 via the upper and lower vortex generators 26 and 21 , whereby a vortex is generated at the upper surface 6 of bed 2 as well as in the upper plenum chamber 7. The upper vortex generator 26 creates a dynamic area in what in a conventional media filter would be a quiet zone that would be susceptible to bio fouling. The lower vortex generator 21 aids in preventing the biofouling forming. The outlets of the lower vortex generator 21 create a second vortex with the effect of scouring the surface of the filtration bed 2, so as to release light organic matter (that would have been deposited by the filtration process) back into the lower vortex. This therefore permits backwashing to be less frequent (that is, the time between backwashing cycles to be increased).

Filtered water leaves the vessel at filter outlet 5 (which as indicated also functions as a backwash inlet).

In the embodiment described and illustrated, the introduction of water via a single entry point permits generation of a dual vortex system that continually levels the filter bed for optimum filtration performance, the system as a whole having minimal separate components.

The filter according to the invention can enable fine filtration to 10 micron to be achieved at a flux rate of from 3 up to 50 m ³ /hr/m ² .