GB2250449A

GB2250449A - Filter

Info

Publication number: GB2250449A
Application number: GB9026501A
Authority: GB
Inventors: Richard Hope Knibbs
Original assignee: LSS CONSULTANCY Ltd
Current assignee: LSS CONSULTANCY Ltd
Priority date: 1990-12-05
Filing date: 1990-12-05
Publication date: 1992-06-10
Also published as: GB9026501D0

Abstract

A filter comprises a housing enclosing one or more tubular edge filter elements in the form of stacks of grooved or etched metal or plastics discs, arranged for cross-flow filtration. As shown filtration is outwards through each element, from inlet 16 to filtrate outlets 17, while rejects is discharged at 18, but flow could be inwards. The discs are threaded over fluted rods 21 and compressed together by springs 29, bearing on plate 28 which is axially adjustable by cams 27. The pressure may be released prior to backwashing or forward washing, possibly using acid or alkali. <IMAGE>

Description

FILTER ARRANGEMENTS The present invention relates to filter arrangements and more particularly, but not exclusively, to stacked disc filters which may also be known as etched disc filters or edge filters.

Dead end varieties of these filters are known but have a number of drawbacks, in that they are easily clogged so cannot operate for long periods without careful monitoring, and in that they are difficult to clean.

According to the present invention, there is provided a filter device comprising one or more lengthwise channels, each having a feed inlet and an outlet downstream of said inlet, and a plurality of plate-like elements stacked together, the channel or channels communicating with the joins between adjacent elements so that, in use, a fluid is filtered between adjacent elements. Conveniently, the inlet and outlet are at opposite ends of the or each channel and the stack of elements are located between the inlet and outlet.

Preferably the elements are in the form of annular discs, the stack forming a central hole which at least partly defines said channel or channels. Conveniently, the elements are circular and have a central circular hole, but this is merely an example and any shape hole or outer edge is possible.

In a preferred arrangement, a support is provided within the stack of elements. More preferably, the support comprises a rod having one or more recessed portions which extend along its length, the or each channel being defined by the stack of elements and the or each recessed portion. In one arrangement, three channels of equal angular extent are regularly spaced about the central axis of the filter device.

In a further arrangement, the elements have two generally axially facing surfaces, at least one of which is modified so as to define filtering spacing between adjacent discs. Preferably the modified surface is constituted by raised or depressed areas, or machined areas or chemically etched areas.

In one arrangement, the stack of elements is held against movement at one end, and the other end is acted upon by releasable compression means. Conveniently, said compression means is constituted by cam means acting upon a spring.

In practise, a number of filter devices will be disposed in a housing having a feed inlet communicating with the device inlets, a filtrate outlet and a feed outlet communicating with the device outlets.

Embodiments of the invention will now be described in more detail. The description makes reference to the accompanying drawings in which: Figure 1 is a schematic lengthwise sectional view through a filter system incorporating the present invention, Figure 2 is an enlarged sectional view on line Il-Il of Figure 1, Figure 3 is an enlarged sectional view on line Ill-Ill of Figure 1, Figure 4 is an enlarged sectional view on line IV-rV of Figure 1, Figure 5 is an end view of an end plate of the filter system shown in Figure 1, Figure 6 shows one example of an application of the present invention, and Figure 7 shows another example of an application of the present inventions.

The figures show a filter arrangement 10 comprising a main cylinder 11 having end caps 12, 13 secured to its ends by annular sealing connections 14, 15. The end cap 13 has an inlet 16 for a feed fluid to be filtered, the cylinder is formed with two filtrate outlets 17 and the end cap 13 has an outlet 18 for unfiltered feed. The cylinder is also provided towards its ends with a fixed upstream end plate 19 and a fixed downstream end plate 20, between which a series of elongate fluted rods or spines 21 are disposed. The spines 21 are screw threadedly received in holes 22 in the end plate 20 and the upstream ends are in the form of cylindrical portions 23 which define subinlets 24.

Along the length of each spine 21 are a number of annular discs 25 which form a series of lengthwise extending channels 26 between the recesses in the spine and the discs 25. The stack of discs 25 abut the end plate 20 at the downstream end of the cylinder 11 and extend along the cylindrical portion 23 at the upstream end. There is provided cam means 27 which acts upon a follower 28 which is urged by a series of springs 29 away from the discs 25. The arrangement is such that the discs 25 can be compressed towards the end plate 20 or the compression can be released.

Between the compressed discs 25, which may be made of various metals such as stainless steel, carbon steel, bronze, monel, or plastic, are very small spacings which are governed by formations on the each disc. For example, one side of each disc may be formed with raised or depressed scallops, grooves etc. as are known. These are for coarse filtering. Finer filtering is produced if the surface is :machined in a certain way or even chemically etched.

In this arrangement nine filter elements are shown, but it will be readily appreciated that any number of filter elements are possible, even just one.

The operation of a single filter element will now be described in more detail. The feed enters the filter arrangement through inlet 16 and then passes into the sub-inlet 24 of the filter element so that the feed can then pass along the channels 26.

The filtrate passes between the discs 25 and is able to pass to the outlets 17. Two are shown in this embodiment but any number could be used. Material which cannot pass between the discs is therefore held back by the discs, but a continuously sufficient pressure of feed ensures both a flow of filtrate through the discs as well as a flow of feed across the exposed internal surfaces of the discs. This means that in ideal operation the filter element tends to clean itself with the filtered out material tending to be carried out with the excess feed passing along the filter element for return in time to the inlet.

It is also possible to run the filter in reverse so that feed under pressure passes between the discs from outside to inside so that the filtrate is removed from the inside of the filter element. Such a method of operation is particularly suitable in filtering feeds which may contain relatively large particles, say 2 to 5 nrn, which could cause one or more of the channels 26 to become blocked. Clearly such blockages are to be avoided if at all possible.

The cross or through flow of feed is, as stated, self cleaning to some extent, and thus enables the filter element to be operated continuously o-;er long periods whilst retaining a good rate of filtration. However, periodic cleaning is necessary.

To clean the filter elements of the present arrangements, firstly the feed is drained and then the cam means 27 is operated so as to release the springs 29 holding the discs under compression. The discs are thus able to separate to some extent. A washing fluid, which may be acidic, alkaline or even neutral depending on the type of fouling, is then introduced either through filtrate outlets 17 or inlet 16 or even outlet 18 and, depending Dn the circumstances, is allowed to flow over the freed discs or to soak them. The wash fluid is then drained, the filter arrangement rinsed as necessary, and the stacks of discs recompressed ready for the standard filter operation to begin again.

The cam operated spring means clearly provides easy access to the entire filter surface so that not only is the filter arrangement more efficient and robust during operation, b-t is also able to be cleaned m#e effectively and more quickly.

It will be appreciated that any suitable means could be employed to compress and release the discs. For example, reliance could be placed on the cam means only without using the springs and/or compression could take place at the upstream and downstream ends, provided of course the discs cover all recessed areas of the spine. Also the spine or central support may be of any suitable shape and could for example, have helical channels or even be omitted if the stack of discs is solid enough. The releasable compression means could also be applied to known dead-end stacked disc filters to improve the cleaning of such filters.

The two simple examples of filtering application shown in figures 6 and 7 require little explanation. The feed is held in a reservoir 50 and is kept moving by means of an agitator 51.

A pump 52 in figure 6 moves the feed through filters 53 and 55 and is returned to the reservoir 50 via a valve or restrictor 54 The valve or restrictor 54 provides sufficient pressure in the circuit to force filtrate through the stacked discs. Since the filtrate is continuously removed the concentration of solids in the reservoir increases. The process is continued, with fresh feed being fed to the reservoir until the desired concentration of solids in the reservoir 50 is achieved. In figure 7, there is a pressurising pump 52 and a circulating pump 56. The pressurising pump fills the circuit containing the filters 53 and 55 and raises it to the operating pressure whilst the circulating pump 56 moves the feed through the circuit. As filtrate is removed from the circuit, the pressure is maintained by pump 52. At regular intervals of time, some of the concentrated slurry in the circuit is discharged via 57 and the circuit pressure is raised after each discharge, by pump 52 introducing further dilute feed fran the reservoir 50. Cther arrangements are of course possible, and these examples are by no means limiting.

Claims

1) A filter device comprising one or more lengthwise channels, each having a feed inlet and an outlet downstream of said inlet, and a plurality of plate-like elements stacked together, the channel or channels communicating with the joins between adjacent elements so that, in use, a fluid is filtered between adjacent elements.

2) A filter device as claimed in claim 1 wherein the inlet and outlet are at opposite ends of the or each channel and the stack of elements are located between the inlet and outlet.

3) A filter device as claimed in claim 1 or claim 2 wherein the elements are in the form of annular discs, the stack forming a central hole which at least partly defines said channel or channels.

4) A filter device as claimed in any one of claims 1 to 3 wherein the elements are circular and have a central circular hole.

5) A filter device as claimed in any one of claims 1 to 4 wherein a support is provided within the stack of elements.

6) A filter device as claimed in claim 5 wherein the support comprises a rod having one or more recessed portions which extend along its length, the or each channel being defined by the stack of elements and the or each recessed portion.

7) A filter device as claimed in claim 6 wherein three channels of equal angular extent are regularly spaced about the central axis of the filter device.

8) A filter device as claimed in any one of claims 1 to 7 wherein the elements have two generally axially facing surfaces, at least one of which is modified so as to define filtering spacing between adjacent discs.

9) A filter device as claimed in claim 8 wherein the modified surface is constituted by raised or depressed areas, or machined areas or chemically etched areas.

10) A filter device as claimed in any one of claims 1 to 9 wherein the stack of elements is held against movement at one end and the other end is acted upon by releasable compression means.

11) A filter device as claimed in claim 10 wherein said compression means is constituted by cam means acting upon a spring.

12) A filter arrangement comprising a plurality of the filter devices claimed in claims 1 to 11 disposed in a housing having a feed inlet communicating with the device inlets, a filtrate outlet and a feed outlet communicating with the device outlets.

13) A method of operating the filter device as claimed in any one of claims 1 to 11 comprising the steps of introducing a feed fluid to the or each channel inlet, collecting filtrate passing between the elements and removing unfiltered feed from the or each channel outlet.

14) A method as claimed in claim 13 wherein the unfiltered feed is returned to the inlet or inlets.

15) A method of operating the filter device as claimed in any one of claims 1 to 11 comprising the steps of filtering a feed fluid from the outside of the device, between adjacent elements and removing the filtrate from either or both ends of the or each channel.

16) A filter device substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

17) A filter arrangement substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.