WO2005072848A1

WO2005072848A1 - Filter element arrangement

Info

Publication number: WO2005072848A1
Application number: PCT/GB2005/000278
Authority: WO
Inventors: David Anthony Akerman; Richard Frazer Allen; Joseph Johnson
Original assignee: Madison Filter 981 Limited
Priority date: 2004-01-29
Filing date: 2005-01-26
Publication date: 2005-08-11
Also published as: GB0402063D0

Abstract

A filter element arrangement and a method of manufacture or construction thereof, the arrangement comprising a hollow tube filter element (22, 24) formed from a composite structure of inorganic fibres having a rigid cage reinforcement (30, 32) embedded within the body of the tube (22, 24). In further embodiments the rigid cage reinforcement is alternatively provided about the outer periphery of the tube (22), or extends within the hollow cavity of the tube (22).

Description

Filter Element Arrangement The present invention relates to filter elements, and in particular, elongate hollow tube filters formed from a composite structure of inorganic fibres. A known hollow, elongate (candle-like) filter element 2 is illustrated in Fig. 1 . This known element has an integral outwardly extending, radial flange 4 at one end and its opposite end 6 is closed. In use the filter element is mounted by clamping the flange 4 between a tube plate 8 and a clamping plate 1 0 using a gasket 1 2 of compressed ceramic fibres to effect a seal. Such filter elements have the disadvantage that they are prone to fracture near their flange end 4. This is because large pieces of dust in the fluid to be filtered are often moving at high speed and can impact with significant force the closed end 6 of the element 2. Due to the length of the element, often as much as 3 metres, the force of impact imparts a bending movement to the flange end, which can lead to fracture and thereby failure of the element. In order to enhance the strength of such elements and thereby reduce the incidence of fracture, it is known to dip the filter element in an inorganic binder, for example colloidal silica. However, such dipping reduces element permeability, with the disadvantage that more energy is needed to draw fluid to be filtered through the element. Furthermore, the dip will change the filtration characteristics often inhibiting formation of a conditioned surface layer, which is necessary for effective and efficient particulate removal. To alleviate the above described drawback it is known to dip only a small section of the element at its flanged end, illustrated by the shaded area 1 6 in Fig. 1 . This dip area represents approximately 1 0% of the elements total length. This increases the strength of the aforementioned weak point at the clamped end of the filter, whilst leaving the majority of the element's surface free of binder enabling a more efficient filtration. Whilst this arrangement is acceptable for short and medium length filters, that is elements less than 2 metres in length, it however does not provide sufficient strength to longer elements which remain particularly prone to fracture in the region of the discontinuation of the dip. It is an object of the present invention to provide a reinforced ceramic element which overcomes the above described drawbacks. In accordance with a first aspect of the present invention there is provided a filter element arrangement comprising an elongate, hollow tube semi-permeable main filter body formed from a composite structure of inorganic fibres, the body having a rigid cage reinforcement. This has the advantage that the rigid cage inhibits movement of the filter element in operation thereby enabling the element to withstand much greater bending movements without failure. Furthermore, if a sufficiently large force is applied so as to break the filter element, the reinforcing cage contains the element and thereby changes the mode of failure so that a catastrophic failure, that is the element breaking into two pieces, is eliminated. This has the further advantage of preventing contamination of dust product and facilitates easier recovery. Also, because no treatments have been applied to the body of the element, there is no pressure drop increase or change in filtration characteristics when in use. Also, the costly step of providing treatments, for example dipping the element and then drying, is not required, thereby manufacturing costs are reduced. The filter body may be closed at one end and may carry a radially, outwardly extending flange at its opposite end. The cage reinforcement may be tubular, and concentric to the main filter body and may extend to substantially contain the main body of the filter. The cage reinforcement may be contained substantially within the wall of the filter body and may comprise radially extending locating means. The locating means may extend within the filter's flange. The cage reinforcement may extend substantially internally or externally of the main tubular body. This has the advantage that the cage is reusable. The cage reinforcement may have a radially extending cage flange and extends adjacent to said filter flange. The cage reinforcement may comprise a metallic material. In accordance with a second aspect of the present invention there is provided a method of manufacture of a filter element arrangement comprising the steps of providing a tubular rigid cage, placing said cage in an apparatus for forming a hollow, elongate filter element, providing a slurry of water, inorganic fibres and binder into the forming tool, applying vacuum to draw the water from the tool and deposit the inorganic fibres and binder in the tool completely encapsulating the cage, and drying the filter element thus formed. In accordance with a third aspect of the present invention there is provided a method of assembly of a filter element arrangement comprising the steps of providing a hollow, elongate filter element having an outwardly extending radial flange at one end, providing a tubular reinforcing cage having a radially extending flange, substantially surrounding the element with the cage and fixing the cage to the element by clamping the cage flange to the filter flange. By way of example only specific embodiments of the invention will now be described with reference to the accompanying drawings, in which:- Fig. 1 is a schematic sectional view of a known filter element shown clamped in a filter unit; Fig. 2 is a schematic sectional view of a filter element constructed in accordance with a first embodiment of the present invention; Fig. 3 is a schematic view of the cage reinforcement within the wall of the filter element of Fig. 2; Fig. 4 is a view similar to Fig. 3 of an alternative construction for the cage reinforcement; Fig. 5 is a partial schematic view of a filter element constructed in accordance with a second embodiment of the present invention; Fig. 6 is a longitudinal section view of the cage reinforcement of Fig. 5 with a venturi in place; Fig. 7 is a sectional view along the line A-A of Fig. 6; Fig. 8 is a schematic detail of the top hat collar of Fig. 6; Fig. 9 is a schematic detail of the venturi of Fig. 6; and Fig. 10 is a schematic sectional view of the filter element of Fig. 5 in situ between two clamping plates. In a first embodiment of filter element 20, as illustrated in Fig. 2, the filter element 20 comprises a tube 22 having an integral outwardly extending, radial flange 24 at one end and the tube's opposite end 26 is closed. Embedded within the body of the tube 22 is a cage reinforcement

28 comprising a main tubular body section 30 and two sets of guides 32, 34. As best illustrated in Fig. 3 the tubular body section 30 is of welded mesh having substantially square openings and is formed from stainless steel wire. Each guide 32, 34 us in the form of L-shaped locator tag with one side of its L-shape welded to the tube 30 and its other side extending radially outwardly of the tube 30. In the illustrated example there are four such guides 32 and 34 located at equidistant intervals at each end of the tube 30. The guides 32, 34 act to position the cage 28 concentrically in the mould used to manufacture the filter element. For example to produce a filter element of overall length of 3 metres and having an outer diameter to its main body 22 of 1 50mm and an inner diameter of 1 10mm, giving a wall thickness of 20mm, a cage 28 of length 2500mm, diameter 1 30mm with 25mm width square mesh formed from 1 .6mm stainless steel wire is placed in the mould (not illustrated) . The guides 32 at one end of the tube 30 extend outwards in a radial direction to provide an effective overall diameter of 1 95mm to that portion of the tube 30. This diameter corresponds to the outer diameter of the elements flange 24 and these guides extend within the flange forming portion of the mould. The guides 34 present an overall diameter of 1 50mm which corresponds to the outer diameter of the main body 22 of the filter element 20 and extend within the main body 22 forming portion of the mould, remote from the flange portion. To form the filter element a slurry of water, ceramic fibre and binder is then introduced into the mould and a vacuum applied so that the ceramic fibres and binder are deposited in the mould, completely encapsulating the reinforcing cage, while water is drawn through the mould and away from the forming tool. When the mould is full, the damp element is removed from the mould and dried in an oven for 8 hours at 1 20°C. The element is then ready for installation between, for example a tube sheet and a clamping plate in the same manner as standard non- reinforced elements. In an alternative design of cage 28, as illustrated in Fig. 4 and which is suitable for encapsulation within the filter elements body as described above, the tube 30 is formed by a plurality of spaced steel wire stringers 36 which are adapted to run along the length of the main body 22 of the filter element 20. The stringers 36 are held in a rigid tube shape by a plurality of evenly spaced steel hoops 38 welded thereto. The terminal guides 32, 34 can be provided by providing a hoop larger diameter 32 which is welded to the stringers 36, or by bending the ends of the stringers radially outwards by a predetermined distance 34. In a second embodiment of filter element, as illustrated in Fig. 5, the cage reinforcement is not provided within the filter elements wall, but is provided instead inside its central cavity. Like the cage illustrated in Fig. 4 the cage 28 comprises a plurality of stringers 36 connected by a plurality of hoop reinforcements 38, but of a diameter just smaller than that of the central cavity of the filter element. The stringers 36 are additionally welded to a top hat collar 42 which presents an outwardly extending annular flange 44. In use the cage 28 is inserted into the cavity of a formed filter element such that the annular flange 44 of the collar sits flush with the top surface 46 of the filter elements flange 24. The tight-fit of the cage 28 within the filter element 20 enables the filter element 20 to withstand in use, large bending movements caused by impacts of particulate material at the opposite closed end 26 of the filter element 20. For example to reinforce a 3 metre filter element of outer diameter 1 25mm and inner diameter 95mm, a cage 28 length of 2700mm and outer diameter 85mm is used. The stringers 36 and hoops 38 are each of 4mm diameter stainless steel wires. Referring of Fig. 6 and 7, there are eight stringers 36 of length 2700mm, with twenty-five hoops 38 welded onto their inner faces, such that the stringers 36 form the outside of the main cage body 30. Working along the stringers 36 from the top hat collar 42, the hoops 38 are spaced 75mm apart for the first 900mm and then 1 50mm apart for the next 1 800mm. This provides a greater concentration of hoops in the region of the cage body nearest to the flange end 24 of the filter element. This provides an increase in the reinforcement at said flange end 24, which region of the filter element 20 is subject to the greatest bending moments in use, thereby providing efficient use of the hoops 38 while not over-complicating the design. As best illustrated in Fig. 8 the top hat collar 42 is made from 3mm thick stainless steel and comprises a tubular section 48 having an outer diameter of 85mm and the annular flange 44 extending radially outward therefrom at an angle A of 90° to the tubular section. The stringers 36 are welded to the inside of the tubular section 48 and slightly inwardly bent to fit inside the tubular section 48, thereby maintaining the overall outer diameter of the cage 28 at 85mm. A venturi 50, as best illustrated in Figs. 6 and 9, has an outwardly extending annular flange 52 which provides a flush fit to the outer surface of the top hat collar flange 44 and is welded thereto. The main body of the venturi 50 extends in use within the main body of the cage 28 and within the filter elements 20 cavity. The venturi has a tapered body and an outwardly extending flared end 51 , this improves the efficiency of the reverse pulse cleaning in long filter elements. Providing a cage 28 with a diameter of 85mm, whilst the internal diameter of the filter elements cavity is 95mm, enables the cage to fit easily inside the element 20 whilst providing a close enough fit to the wall of the cavity to press against it should there be any sideways displacement of the element in use. In use, as best illustrated in Fig. 10 the flange 24 of the filter element 20 is clamped between a tube plate 8 and clamping plate 1 0 using a gasket 1 2 of compressed ceramic fibres to effect a seal. This additionally clamps the flange 44 of the top hat collar 42 and venturi 50 (not illustrated) between the clamping plate 1 0 and flange 24 of the filter element 20. The right-angle A between the flange 44 and its main body 48 ensures that the cage 28 hangs vertically within the filter element. As the top hat collar is of 3mm thick stainless steel this is strong enough to withstand large bending moments. Therefore, if an impact occurs at the far end of the filter element then the inner cavity wall presses against the cage 28, which stays rigid and vertical due to the 90° angle on the top hat collar 42. The top-hat collar 42 absorbs the bending moment thus generated so that the element does not fracture; sideways displacement of the bottom of the element is also reduced. Tests were conducted on a 3 metre reinforced filter element and on a standard 3 metre non-reinforced filter element, each clamped in situ as shown in Fig. 1 0 and subjected to the same conditions, the results are as follows:- Failure Load The standard element, i.e. with no reinforcement, snapped with

35N lateral force (bending moment of 105Nm) applied at the closed end of the element. Whereas the reinforced element was judged to have failed at 1 00N (moment of 300Nm) applied at the closed end of the element.

Displacement Load Despite the significantly higher failure load, the base of the reinforced element had not displaced as far as the standard element when failure occurred. Mode of Failure The standard element suffered a "classic" failure at 35N i.e. a complete fracture into two pieces at a point on the element - 30cm from the flange. This position corresponded to the boundary between dipped and undipped material. However, with the cage in place the point of failure moved to the area where the element wall meets the flange. The loading did not cause catastrophic failure, but only a 10cm circumferential crack where the outside wall meets the flange. There was a similar crack on top of the flange near the inside wall. Each marked as 60 on Fig. 1 0. Neither of these cracks penetrated through the entire flange or element wall and the element was able to withstand a further 40N (to a total of 140N), still without a catastrophic failure or a crack completely breaching the wall. Clamping The top-hat flange 44 fits on top of the element with only a 1 -2mm gap between top-hat and element flange 24 before clamping. The 3mm thick steel is strong enough so that when clamped into the test rig without an element it was very rigid and resisted sideways displacement. Conclusions • The failure mode of the reinforced element was different to that of the standard element. • The failure load of the reinforced element was 3-4 times that of the standard element. • The failure of the standard element was catastrophic however the wall of the reinforced element was not breached within the scope of the test. Tests further indicate that there is no significant air-flow interference from the cage and the presence of the cage creates no reduction in the cleaning capacity of the reverse-pulse system used to clean the filter elements. Although the cage of Figs. 5 to 1 0 has been illustrated as providing reinforcement to a filter element from the interior of the element, it is to be understood that this cage could be modified such that it has a diameter larger than the outer diameter of the element and thereby can provide reinforcement by surrounding the outer surface of the filter element. The mesh style cage, or indeed an alternative construction to the cage could alternatively be used to provide exterior reinforcement to the element. Although specific mesh sizes, and shapes and wire diameters have been described it is to be understood that such could be varied, likewise the spacing, size and number of the stringers and hoops of the various cage designs could also be varied. Although stainless steel has been described, other materials could be used to construct the cage, for example corrosion resistant metals such as Hastelloy ™ or Inconel ™ . An external cage may also extend to enclose the closed end of the filter element, to this end the cage may carry an end cap 62 at one end. Although a slurry comprising ceramic fibres and binders has been described to form the filter element, other materials could be used for example an aqueous slurry of refractory fibres or any slurry of solids in a liquid carrier. Although the filter element has been described as a flanged tubular element, closed at one end, it is to be understood that the cage reinforcement could also be used with a filter which is open at both ends such that in use it can open into a tube sheet at each end. Also the flange could be omitted. Also although a venturi 50 has been described, this too could be omitted.

Claims

Claims: 1 . A filter element arrangement comprising an elongate, hollow tube semi-permeable main filter body formed from a composite structure of inorganic fibres, the body having a rigid cage reinforcement.

2. A filter element arrangement according to claim 1 , in which the filter body is closed at one end.

3. A filter element arrangement according to claim 2, wherein the filter body carries a radially, outwardly extending flange at its opposite end.

4. A filter element arrangement according to claim 1 , 2 or 3, wherein the cage reinforcement is tubular, and concentric to the main filter body.

5. A filter element arrangement according to any one of the preceding claims, wherein the cage reinforcement extends to substantially contain the main body of the filter.

6. A filter element arrangement according to any one of the preceding claims, wherein the cage reinforcement is contained substantially within the wall of the filter body.

7. A filter element arrangement according to any one of the preceding claims, wherein the cage reinforcement comprises radially extending locating means.

8. A filter element arrangement according to claim 7, wherein the filter body carries a radially, outwardly extending flange and the locating means extends within said flange.

9. A filter element arrangement according to any one of claims 1 to 5, wherein the cage reinforcement extends substantially internally or externally of the main tubular body.

1 0. A filter element arrangement according to claim 9, wherein the cage reinforcement has a radially extending flange adapted to extend adjacent to a or the radially, outwardly extending flange to the filter body.

1 1 . A filter element arrangement according to any one of the preceding claims, wherein the cage reinforcement comprises a metallic material.

1 2. A filter element arrangement according to any one of the preceding claims, comprising a venturi.

1 3. A filter element arrangement according to claim 1 2, wherein the venture extends within the filter body cavity, has a tapered body and an outwardly extending flared end.

14. A method of manufacture of a filter element arrangement comprising the steps of providing a tubular rigid cage, placing said cage in an apparatus for forming a hollow, elongate filter element, providing a slurry of water, inorganic fibres and binder into the forming tool, applying vaccum to draw the water from the tool and deposit the inorganic fibres and binder in the tool completely encapsulating the cage, and drying the filter element thus formed.

1 5. A method of assembly of a filter element arrangement comprising the steps of providing a hollow, elongate filter element having an outwardly extending radial flange at one end, providing a tubular reinforcing cage having a radially extending flange, substantially surrounding the element with the cage and fixing the cage to the element by clamping the cage flange to the filter flange.6. A filter element arrangement constructed, arranged and adapted to operate substantially as described herein with reference to the accompanying drawings.7. A method of manufacture of a filter element arrangement substantially as herein described.8. A method of assembly of a filter element arrangement substantially as herein described.