GB2294648A

GB2294648A - Filter element

Info

Publication number: GB2294648A
Application number: GB9522418A
Authority: GB
Inventors: Christopher John Mould
Original assignee: BTR PLC
Current assignee: BTR PLC
Priority date: 1994-11-02
Filing date: 1995-11-01
Publication date: 1996-05-08
Anticipated expiration: 2015-11-01
Also published as: GB9422107D0; GB2294648B; WO1996014133A1; GB9522418D0; JPH10511597A

Abstract

A filter element (10) comprises two corrugated layers (11, 12) of filter media arranged superimposed to define elongate air flow passages therebetween, and between said corrugated layers an internal support structure (15) which extends across a substantial part of the width of the element and along a substantial part of the length of the element to separate at least a part of one corrugated layer from direct contact with the other layer, the internal support structure facillitating a structural interconnection of the layers of filter media thereby to inhibit separation of the two layers when the pressure within the element exceeds the external pressure, the corrugated layers being structurally interconnected at positions intermediate the edge regions by adhesive. <IMAGE>

Description

FILTER ELEMENT This invention relates to a filter element and an assembly of a plurality of filter elements generally and in particular, though not exclusively, to a filter element and filter element assembly for use in an industrial type filter unit of the kind provided with means for intermittent cleaning or regeneration of a filter element. The invention is particularly applicable to a filter element of a corrugated or so-called pleated type.

A pleated type filter element typically comprises a layer of filter media which has been passed through a pleating machine to produce a pleated web of a predetermined corrugated cross-sectional shape. The filter media may be treated to render it substantially rigid or sufficiently semi-rigid so as to resist deformation and retain the pleated profile despite pressure differential forces which arise when the media is acting as a filter.

Usually two layers of pleated material are arranged in contact with one another and superimposed so that alternate fold regions of one layer lie in contact with respective alternate fold regions of the other layer. In consequence the two layers define a plurality of parallel, internal passages through which filtered fluid, typically air or other gas, can flow to an end region of the filter element.

The ends of two layers may be held in moulded end supports which restrain relative transverse movement of the folds. Thus the folds of the respective layers are maintained aligned and in contact to resist any tendency for nesting together of the layers and effective collapse of the internal passages. Therefore it is not necessary to provide the filter element with an internal support frame of the kind commonly used in a fabric bag filter and comprising a pair of spaced apart layers of support mesh.

Cleaning of the filter elements is achieved in a so-called "regenerative" manner by intermittent internal pressurisation to cause a momentary reversal of flow and consequent dislodgement of an accumulated dust cake. To prevent undue deformation of and damage to the pleated layers during reverse pressurisation use may be made of pleated layers which have a sufficiently great rigidity.

Attainment of that rigidity often necessitates provision of elements made from filter media which is heavier and more expensive than otherwise would be necessary.

Alternatively pleated layers may be bonded together by aligning the folds of confronting layers and using adhesive, pre-applied along the length of each confronting fold, to join the layers.

The need to align and bond every touching pleat can, however, add to assembly costs.

The present invention seeks to provide an improved filter element and an assembly in which the problems of known techniques for withstanding reverse pressurisation are mitigated or overcome.

In one of its aspects the present invention provides a filter element comprising a pair of corrugated layers of filter media arranged superimposed to define at least one internal passage for flow of fluid therethrough, and within said at least one internal passage an internal support structure which extends across a substantial part of the width of the element and along a substantial part of the length of the element and serves to separate at least a part of one corrugated layer from direct contact with the other layer, wherein at positions intermediate edge regions of the layers of filter media said internal support structure facilitates a structural interconnection of said layers so as to inhibit separation of the two layers when the pressure within the element exceeds the external pressure.

The internal support structure may extend across the full width of the filter element or across only part of that width. Preferably it extends across at least 70% of the width of the element. One or both edges defining the width of the internal support structure may be sandwiched between a pair of edge regions of the two layers of filter media.

The internal support structure may, for example, be formed from a metallic material such as aluminium or mild steel or a plastics material such as polyethylene. The material of the support structure may be a perforated, i e apertured type of material.

The internal support structure may comprise substantially only a single sheet of material or may comprise a plurality of strips of material arranged spaced apart. In the latter case the strips preferably extend transversely or obliquely relative to the direction of the length of the internal passage(s) of the filter element. Spaced apart strips may be located in a preferred relative orientation prior to assembly with the layers of filter media, for example, by means of one or more edge members. The edge members may provide in part a frame within which the strips are secured.

The strips of material may extend fully across the width of the element and be secured to respective opposite regions of a frame.

If the internal support structure comprises a plurality of strips, preferably those strips have a total width, measured along the length of the element, which is less than 60%, preferably less than 40%, of the length of the element. The strips may total less than 20% of the length of the element, and may comprise in the order of 10% of said length.

The structural connection of the corrugated layers of filter media may be achieved by the use of an adhesive. The layers of filter media may each be secured to the support structure by an adhesive such that the support structure serves to interconnect the two layers. Preferably the support structure facilitates interconnection of the layers of filter media by being of a perforated type. This allows adhesive additionally or alternatively to form a direct connection between the corrugated layers when folds of the two layers are aligned. Particularly, but not necessarily only, if the support structure and layers of filter media are of the same or similar materials they may be welded, e g heat fused, together.

The corrugated layers of filter media may be shaped to define therebetween a plurality of elongate passages for flow of air or other fluid.

The layers may be corrugated to have a pleated zig-zag type shape in transverse cross-section or, for example, a corrugated curved, e g sinusoidal shape.

The filter element preferably is of a type having an aspect ratio greater than 1.0, more preferably greater than 1.5 wherein said aspect ratio is the ratio of the length of the element in the direction of the length of said internal passage(s) to the width in a relative transverse direction.

Alternate folds of one layer, i e those nearest the other layer, may be aligned with respective alternate folds of that other layer so as to define a plurality of discrete, i e separate, elongate fluid flow passages.

Alternatively, the alternate folds of one layer which are nearest the other layer may lie off-set relative to folds of that other layer. In that case the internal support structure will serve to prevent the two corrugated layers nesting one within the other as well as inhibiting their separation.

Suitable materials for the corrugated layers include flexible airpermeable fibre fabrics. Such fabrics may be or be rendered substantially rigid or semi-rigid to resist undue deformation when subject in use to a pressure differential as air flows through the corrugated layers to within the element. Other suitable materials include rigidised paper, e g resin impregnated paper, and polyester. The corrugated layers may comprise randomly arranged fibres or filaments. The invention may be applied also to filter elements constructed from a relatively rigid filter media such as point bonded polyester and a brittle type material such as resin impregnated paper. The structural interconnection facilitated by the internal support structure may serve to reinforce the filter element whereby it is better able to resist damage. It will also allow thinner, lighter and cheaper materials to be used.

The filter media may be of a kind having a capacity to collect at least 2.0 and preferably at least 3.5 mg/m3 but may be a significantly higher collection of particulate matter from an air flow, e g at least 10.0 mg/m3.

Preferably it allows an air flow rate, during normal usage, of at least 0.1 m3/min/m2, more preferably at least 0.5 m3/min/m2.

A filter element of the invention may be generally planar, or of e g a circular or spiral form as shown in United Kingdom Patent Publication GB-A2220588.

The invention contemplates that the filter element may be selfsupporting against expansion in a transverse, width direction perpendicular to an internal passage. It does not need to rely on external structure to restrain any such tendency for expansion e g under reverse pressurisation.

The corrugated layers may be electrically conductive. This may be achieved by using a material which is inherently conductive due to the manner in which it is manufactured or by applying a surface coatinglimpregnation of carbon or similar material. A longitudinal edge or other region of a conductive filter element may be provided with a strip of conductive material, e g a metal strip, for electrical contact with a part of the filter housing thereby to allow, e g static charge to be conducted from the filter element to the housing and its earth connection.

The invention provides also a filter element assembly comprising at least one filter element of the invention mounted in a housing and arranged for dust laden air to impinge on external surfaces of the element. The assembly may comprise air supply means for intermittent internal pressurisation of an element for the purpose of regenerative cleaning.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a filter element of the invention; Figure 2 is a section on line 2-2 of Figure 1; Figure 3 is a plan view of an internal part of the element of Figures 1 and 2; Figure 4 is a detail of part of Figure 2, and Figure 5 is a section corresponding to that of Figure 2 but for another filter element of the invention.

A flat type filter element 10 for filtration of dust laden air comprises two superimposed corrugated layers 11,12 of pleated filter media. The ends of the corrugations are embedded in moulded plastics open header and closed tail end sections 13,14.

The corrugated layers are formed by passing spun bonded polyester through a pleating machine to produce a pleated structure of zig-zag shape in cross-section (Figure 2). A chosen length of pleated material is then folded so as to form the two superimposed layers 11,12 with edges of the material being overlapped in the form of a half pleat overlap 19 (Figure 4) at which the edges are sealed together.

The two corrugated layers 11,12 are spaced by an interposed insert 15 which facilitates a structural interconnection between the layers 11,12.

The insert 15 comprises a series of strips 16 (see Figure 3) of perforated (i e apertured) steel which are held spaced apart by two U-section edge channels 17,18 held crimped to the ends of the perforated strips. The width and spacing of the strips 16 is selected such that the total width of the strips is less than 121/2% of the length of the insert, which in this embodiment is the length of the U-section channels 17,18.

The width of the insert 15 (i e length of the strips 16) is slightly less than the width of the filter element so that the insert can fit within the internal width of the element (see Figure 2).

In manufacture of the element the pair of corrugated layers are formed with an overlap joint as aforedescribed and the insert 15 is then inserted between the corrugated layers prior to moulding of the header and tail sections 13,14.

Before insertion the strips 16 are coated with an adhesive which, subsequent to insertion, provides a structural interconnection that resists any tendency for the confronting aligned folds 21,22 of the two corrugated layers to separate under reverse jet pressurisation. The adhesive forms a bond between each corrugated layers 11,12 and the insert 15 so that the insert forms a direct connection between the corrugated layers. The adhesive also forms a direct link between the two corrugated layers by extending through the perforations of the insert, the insert thus additionally serving to facilitate a direct interconnection of the two corrugated layers.

In the resulting construction of the filter element 10 the insert 15 acts in combination with the end sections 13,14 to resist relative transverse movement of the two corrugated layers as well as separation of those layers as described above. It also resists any tendency for the layers to nest one in the other during normal use in which contaminated air flows through and is filtered by the layers due to a pressure differential in which the space within the element is less than that external thereof.

In this embodiment the insert 15 holds alternate folds 21 of one layer aligned with alternate folds 22 of the other layer. This results in a plurality of parallel and substantially discrete air flow passages 23 which extend to the header section 13. The insert achieves this without creating any significant impediment to flow of filtered air.

During reverse air jet cleaning the insert 15 assists in helping to achieve a substantially uniform dispersion of air and thus promotes a substantially uniform cleaning action.

The invention will now be described as applied to another pleated filter 30 (see Figure 5). This is formed from two separate layers 31,32 of pleated filter media which are laid one on top of the other in a sandwich arrangement in which an adhesive coated insert 33 (optionally perforated) is positioned between the layers. The insert extends the full width of the corrugated layers and at each edge of the part-formed element the edges of the two layers and the insert are gripped together by an external metal channel 34 of U-shape in section. That part-assembly is then provided with moulded head and tail sections as aforedescribed.

The pleated layers may each have a surface coatinglimpregnation of carbon laden material which is in electrical contact with the metal edge strips. In use the filter element is fitted in a housing having spring loaded metal contacts which bear firmly against the metal edge strips. By connecting the filter housing to earth any static electricity is safely discharged from the element via its coating and the metal edge strips.

Claims

CLAIMS:

1. A filter element comprising a pair of corrugated layers of filter media arranged superimposed with alternate folds of one layer aligned with respective alternate folds of the other layer thereby to define a plurality of separate elongate fluid flow passages, and within said filter element an internal support structure which separates a part of one corrugated layer from direct contact with the other layer, said internal support structure comprising a plurality of strips of perforate material which extend transversely or obliquely relative to the direction of the fluid flow passages, and a frame structure having edge members to which the perforate strips are secured and maintained spaced apart, said corrugated layers being structurally interconnected at positions intermediate edge regions of the corrugated layers of filter media by adhesive which acts at least through the perforations to form a direct interconnection between aligned folds of said layers.

2. A filter element comprising a pair of corrugated layers of filter media arranged superimposed to define at least one internal passage for flow of fluid therethrough, and within said at least one internal passage an internal support structure which extends across a substantial part of the width of the element and along a substantial part of the length of the element and serves to separate at least a part of one corrugated layer from direct contact with the other layer, wherein at positions intermediate edge regions of the layers of filter media said internal support structure facilitates a structural interconnection of said layers so as to inhibit separation of the two layers when the pressure within the element exceeds the external pressure.

3. A filter element in accordance with claim 2 wherein the internal support structure comprises a plurality of strips of material arranged spaced apart and each extending transversely or obliquely relative to the direction of the length of the internal passage(s) of the filter element.

4. A filter element in accordance with claim 3 wherein the strips are secured to at least one edge member which, at least prior to assembly of the strips with the layers of filter media, serves to locate said strips in a preferred relative orientation.

5. A filter element in accordance with claim 4 wherein the internal support structure comprises a frame having edge members to which the spaced apart strips are secured.

6. A filter element according to claim 1 or any one of claims 3 to 5 wherein said strips have a total width, measured along the length of the element, which is less than 60% of the length of the element.

7. A filter element according to claim 6 wherein the strips total less than 40% of said length.

8. A filter element according to claim 6 wherein the strips total less than 20% of said length.

9. A filter element in accordance with claim 2 wherein the internal support structure comprises substantially only a single sheet of material.

10. A filter element in accordance with any one of claims 2 to 9 wherein the material of the internal support structure is of an apertured type.

11. A filter element in accordance with any one of claims 2 to 10 wherein the structural interconnection of the corrugated layers of filter media is achieved by the use of an adhesive.

12. A filter element in accordance with claim 11 wherein the corrugated layers of filter media are each secured to the support structure by an adhesive whereby the support structure interconnects the two layers.

13. A filter element in accordance with claim 11 or claim 12 wherein the internal support structure comprises material of a perforated type and adhesive acts through said perforations to form a direct interconnection between aligned folds of the corrugated layers.

14. A filter element in accordance with any one of claims 2 to 10 wherein the support structure is welded e g heat fused, to each of the layers of filter media.

15. A filter element in accordance with any one of claims 2 to 14 wherein alternate folds of one layer of filter media are aligned with respective alternate folds of the other layer of filter media to provide a plurality of discrete elongate fluid flow passages.

16. A filter element in accordance with any one of the preceding claims wherein the internal support structure extends across at leat 70% of the width of the element.

17. A filter element according to claim 16 wherein the internal support structure comprises strips which extend fully across the width of the element and are secured to respective opposite regions of a frame.

18. A filter element in accordance with claim 16 or claim 17 wherein at least one edge defining a width dimension of the internal support structure is sandwiched between a pair of the edge regions of the two layers of filter media.

19. A filter element in accordance with any one of the preceding claims wherein the corrugated layers of filter media comprise flexible air permeable fabric rendered substantially rigid or semi rigid.

20. A filter element according to any one of the preceding claims wherein the ratio of the length of the element in a direction of the length of an internal passage to the width in a relative transverse direction is at least 1.0.

21. A filter element according to claim 20 wherein said ratio is at least 1.5.

22. A filter element according to any one of the preceding claims wherein the corrugated layers comprise randomly arranged fibres or filaments.

23. A filter element according to any one of the preceding claims wherein the filter media has a capacity to collect at least 2 mg/m3 of particulate matter from the air flow.

24. A filter element in accordance with claim 2 and substantially as described with reference to and as shown in the drawings.

25. A filter assembly comprising a housing and a filter element according to any one of the preceding claims mounted in said housing and arranged for dust laden air to impinge on external surfaces of the element.

26. A filter assembly according to claim 25 and comprising air supply means for intermittent internal pressurisation of the filter element for regenerative cleaning of said element.

27. A filter assembly according to claim 25 and substantially as described with reference to and as shown in the drawings.