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Patent Searching and Data


Title:
POCKET FILTER
Document Type and Number:
WIPO Patent Application WO/2017/125758
Kind Code:
A1
Abstract:
A filter (110), particularly but not exclusively for use with a fluidised bed dryer or granulator, comprises a plurality of elongate pockets or sleeves (120), each having an open end (118) and a closed end, wherein at least a portion of the open end of at least one pocket or sleeve (120) shares a boundary with a portion of the open end of at least one other pocket or sleeve (120).

Inventors:
MCGUINNESS PETER (GB)
MACKECHNIE ROBBIE (GB)
COWBURN HAYLEY (GB)
Application Number:
PCT/GB2017/050150
Publication Date:
July 27, 2017
Filing Date:
January 20, 2017
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
D R M IND FABRICS LTD (GB)
International Classes:
B01D46/02; B01D46/42; B01D46/52; F26B25/00
Foreign References:
US2607436A1952-08-19
US20130199139A12013-08-08
CN203315959U2013-12-04
US5446974A1995-09-05
FR2442653A31980-06-27
Attorney, Agent or Firm:
WP THOMPSON (GB)
Download PDF:
Claims:
CLAIMS

1. A filter comprising a plurality of pockets having an open end and a closed end, wherein at least a portion of the open end of at least one pocket shares a boundary with a portion of the open end of at least one other pocket.

2. A filter as claimed in claim 1 , wherein at least a portion of the open end of each of said pockets shares a boundary with a portion of the open end of at least one other pocket.

3. A filter as claimed in claim 1 or claim 2, comprising at least one pocket whose open end shares a boundary with the open end of a plurality of other pockets.

4. A filter as claimed in claim 3, comprising a plurality of pockets whose open end shares a boundary with the open end of a plurality of other pockets.

5. A filter as claimed in claim 4, wherein the open end of each of said pockets shares a boundary with the open end of the plurality of other pockets.

6. A filter as claimed in any preceding claim, wherein the pockets are extendible.

7. A filter as claimed in any of the preceding claims, wherein the walls of the pockets sharing a common boundary do not touch each other.

8. A filter as claimed in any of the preceding claims, wherein a plurality of said pockets are elongate.

9. A filter as claimed in any preceding claim, comprising a plurality of pockets arranged substantially concentrically.

10. A filter as claimed in any of any preceding claim, wherein a plurality of pockets form a portion which extends continuously over an area of the filter.

11. A filter as claimed in any preceding claim, wherein the pockets comprise a loop for suspending the pockets.

12. A filter as claimed in claim 9, wherein the loop is attached to the closed end of the pockets.

13. A filter as claimed in any preceding claim, comprising one or more pockets whose cross-sectional area decreases from the open end to the closed end.

14. A filter as claimed in claim 11 , comprising one or more pockets which taper from the open end to the closed end.

15. A filter as claimed in claim 12, comprising one or more pockets which are generally conically shaped when in an extended position.

16. A filter as claimed in any preceding claim, wherein the pockets are pleated at the closed end.

17. A filter as claimed in any preceding claim, wherein the pockets are pleated at the open end.

18. A filter as claimed in any preceding claim, wherein the boundaries are connected using seams.

19. A filter as claimed in claim 16, wherein the seams are stitched.

20. A filter as claimed in claim 16 or claim 17, wherein the seams are welded.

21. A filter as claimed in any preceding claim, wherein the open end of at least some of the pockets comprises at least four sides.

22. A filter as claimed in any preceding claim, wherein the open end of at least some of the pockets comprises five sides.

23. A filter as claimed in any preceding claim, wherein the open end of at least one of the pockets comprises six sides.

24. A filter as claimed in any of claims 19 to 21 , wherein at least three of the sides are connected to sides of one or more other pockets.

25. A filter as claimed in claim 22, wherein each of at the least three sides is connected to a side of different other pockets.

26. A filter as claimed in any of claims 16 to 23, wherein the seams of one or more pockets are interconnected.

27. A filter as claimed in any of claims 15 to 24, wherein an innermost side of a sleeve, relative to the centre of the filter, is shorter than an outermost side of the sleeve.

28. A filter as claimed in any preceding claim, further comprising a rim.

29. A filter as claimed in claim 26, wherein the rim extends around the periphery of the plurality of pockets adjacent the open ends.

30. A filter as claimed in claim 26 or claim 27, wherein the outermost pockets are attached to the rim.

31. A filter as claimed in any of claims 26 to 28, wherein the rim comprises a frame.

32. A filter as claimed in claim 29, further comprising a skirt for attaching to a fluidised bed dryer or granulator.

33. A filter as claimed in any preceding claim, wherein the pockets comprise filter material.

34. A filter as claimed in claim 31 , wherein the filter material is woven.

35. A filter as claimed in claim 32, wherein at least some of the woven filter material has a grams per square metre (gsm) value from 150 to 200.

36. A filter as claimed in claim 32 or claim 33, wherein at least some of the woven filter material has a grams per square metre (gsm) value in excess of 400.

37. A filter as claimed in any of claims 31 to 34, wherein the filter material is electrically conductive.

38. A filter as claimed in any preceding claim, wherein the boundary is defined by a length of material or tape.

39. A filter as claimed in any of claims 1 to 36, wherein the filter comprises a fluid bed dryer bag.

40. A filter as claimed in any of claims 1 to 36, wherein the filter comprises a granulator bag.

41. A filter substantially as herein described with reference to, and as illustrated in, Figures 2 to 5 of the accompanying drawings.

Description:
DESCRIPTION

POCKET FILTER

The present invention relates to a filter, for use with fluidised bed dryers or granulators. Such filters are also known as fluid bed dryer bags or fluid bed dryer filters.

Fluid bed dryer bags are used in the production of a wide range of industrial chemicals, such as pharmaceuticals or dye-stuffs. Typically, a fluidised bed dryer comprises a large, circular pan which is filled with wet particulate matter. Warm air is introduced into the bottom of the pan so that the solid particles become fluidised. The warm air vaporises the liquid present in the wet matter. The vapour and air mixture is then drawn out from above the fluid bed through a fluid bed dryer filter, or bag, which is suspended above the pan. The fluid bed dryer filter retains the fine particles in the vapour and air mixture, which would otherwise be lost during the drying process. Known fluid bed dryer bags generally comprise a disc of sheet filter material extending over the fluidised bed. The sheet of filter material comprises circular apertures, each of which communicates with an individual cylindrically-shaped filter sleeve or bag extending generally perpendicularly from the sheet. The filter sleeves or bags are closed at the top by an end wall and the particulate matter in the water vapour and air mixture is drawn into the sleeves or bags using an extractor. The apertures are generally spaced apart, so that there is a portion of sheet material surrounding each aperture. The fine particles are retained as filter cake on the inside of the filter sleeves and on the sheet material surrounding each aperture. This process is usually run in batches, with the entire filter assembly being removed and replaced, to allow cleaning and recovery of the filter cake, at the end of each batch run. Recovery of the filter cake may be achieved by vibrating the bag to dislodge the filter cake from the surfaces of the bag.

The filter sleeves typically comprise hanging loops at the distal, closed end of the sleeve. Generally, the sleeves are suspended from hooks on a circular frame above the sheet, to maintain them in an upwardly extending configuration, even when air is not being drawn through them. A skirt is also added to the outer edge of the circular sheet material for attaching the fluid bed dryer bag to the dryer, or onto a ring that aids attachment to the dryer. Therefore, the resulting fluid bed dryer bag comprises a skirt that forms a right-angled joint with the sheet of filter material and sleeves that form a right-angled joint with the sheet of filter material.

One particular example of known fluid bed dryer bags is shown in Fig. 1. The fluid bed dryer bag 10 comprises a circular planar disc 12 of woven filter material, folded back on itself at the periphery to form an annular rim 14. The annular rim 14 comprises a frame (not visible) for retaining the circular shape of the disc 12. One edge of a skirt 16 is attached to the periphery of the rim 14 and extends perpendicularly downward from the periphery of the disc 12. The opposing edge of the skirt 16 is, in use, attached to a fluidised bed dryer (not shown).

The disc 12 of woven filter material is provided with seven identical spaced apart circular apertures 18, each of which opens into a respective one of seven identical tubular filter bags, in the form of cylindrical sleeves 20, which extend perpendicularly upwardly with respect to the disc 12 and are closed at the upper end by means of a circular planar end wall of filter material (not shown) secured to the upper end of the sleeve 20 via a seam 20a. A loop 22 of flexible material is stitched to the outer face of each end wall, for suspending the upper end of each sleeve 20 from a hanging rack (not shown), so that the sleeves 20 remain in an open configuration even when warm air current is not flowing from the fluidised bed dryer. The sleeves 20 are attached to the disc 12 at the periphery of the open end by means of a stitched seam 20b.

In use, the fluid bed dryer bag 10 is suspended over a fluidised bed dryer (not shown) and secured thereto via the skirt 16. The fluidised bed dryer typically comprises a planar, circular pan over which is spread a layer of damp powdered or granular material to be dried. A warm air supply is fed from below the pan via a plurality of inlet apertures in the bottom of the pan, which dries the material and fluidises it by counteracting agglomerative tendencies such as electrostatic attraction or capillary adhesion due to particle surface water films.

The warm air agitates and dries the particles of powdered or granular material and causes the particles to become entrained by the air current, which moves upwardly and into each of the sleeves. By positioning the fluid bed dryer bag 10 over the dryer, the entrained particles are caught by the fluid bed dryer bag 10 and prevented from escaping from the air stream.

However, it will be appreciated that at least some of the entrained particles will be caught on the disc 12, rather than being directed through the apertures 18 upwardly into the sleeves 20. An accumulation of particles thus gathers on the disc 12, which may increase the frequency of required cleaning intervals and also reduces the efficiency of the filter bag, since not all of the entrained particles are being directed at the larger surface area of the sleeves 20.

Furthermore, it will also be appreciated that, in use, stresses are applied vertically on the bag 10, as indicated by arrow A, by virtue of the air current travelling substantially in direction A and from the hanging loops 22 which suspend the sleeves in a vertical arrangement relative to the disc 12. This tends to urge the sleeves 20 away from the disc 12 during the drying process, which puts significant strain on the curved seams 20a and 20b and causes regions of stress concentration to develop in the seams 20a, 20b. These regions of stress concentration can cause the seams 20a, 20b to rupture, in particular if the seams 20a, 20b are welded.

There are a number of problems arising from the configuration of known fluid bed dryer bags. For example, the spaced apart cylindrical apertures mean that filter cake accumulates on the disc of filter material between the apertures, instead of being drawn up into the sleeves which provide a larger surface area for filtration of the fine particles. This may increase the frequency of required cleaning cycles and/or reduce filter efficiency.

Furthermore, during the drying process, tension is applied vertically to the filter. The joints that link the filter material fabric together are at right angles to this applied tension, which can lead to failure of the joints, either by rupturing, or by causing enlargement of the stitching holes which can result in loss of fine particles through the enlarged holes. Stress concentrations in certain regions of the joints can also occur, leading to damage of the integrity of the fluid bed dryer bag. In particular, the various curved shapes of the seams of known fluid bed dryer bags have regions of high stress concentration. Shock loading from shaking or vibrating the bag during the cleaning process can be particularly detrimental to these areas of high stress concentration, which could cause damage to the bag's integrity. This is particularly apparent if the pieces of filter material are welded together, since, in general, welded seams are not as strong as stitched seams. As a consequence, seams which are welded and subjected to excessive tension can rupture.

The present invention is designed with the foregoing in mind. In accordance with the present invention, a filter comprising a plurality of pockets, the pockets having an open end and a closed end, wherein at least a portion of the open end of at least one pocket shares a boundary with a portion of the open end of at least one other pocket. The invention therefore provides a filter having a plurality of connected or interlinked pockets, or sleeves, rather than the traditional disc/ skirt sleeve arrangement of known fluid bed dryer bags or granulator filters (bags). This increases the surface area for filtration since all particulate matter is directly drawn up into the pockets, as compared to the prior art arrangement in which some particulate matter does not reach the sleeves and instead, accumulates on the disc material in between the sleeves.

Furthermore, a secondary advantage is that the interconnected arrangement of seams in the present invention eliminates areas of high stress concentration in the seams, since stresses can be distributed along a number of seams, rather than being confined to individual seams. This enables all seams in the bag to be welded, which assists in greater retention of solid matter. In contrast, with the prior art fluid dryer bags, only some seams, i.e. those which are not subjected to excessive tension, can be welded, meaning that it is necessary to use at least some stitched seams to form the bag. In one embodiment, at least a portion of the open end of each of said pockets shares a boundary with a portion of the open end of at least one other pocket.

The filter may comprise at least one pocket whose open end shares a boundary with the open end of a plurality of other pockets.

The filter may comprise a plurality of pockets whose open end shares a boundary with the open end of a plurality of other. In one embodiment, the open end of each of said pockets shares a boundary with the open end of a plurality of other pockets.

Optionally, the boundary may be defined by a length of material or tape, for example textile tape. In such an embodiment, the pockets are interconnected via the boundary material or tape, rather than being directly connected via a boundary line, for example, a stitch or weld line. In other words, a narrow piece of material defines the shared boundary between the pockets.

The plurality of pockets may be arranged substantially concentrically.

The pockets may be extendible and/or flexible. Preferably, the walls of the pockets sharing a common boundary do not touch each other.

Preferably, a plurality of said pockets are elongate.

A plurality of pockets may form a portion which extends continuously over an area of the fluid bed dryer bag. The pockets may comprise a loop or other means for suspending the pockets above the fluidised bed dryer, for example, by connecting the loops to a hanging rack positioned above the fluidised bed dryer or granulator. The loop may be attached to the closed end of the pockets, to allow the open ends of the pockets to be positioned directly above the fluidised bed dryer or granulator. Preferably, one or more pockets have a cross-sectional area which decreases from the open end to the closed end, such that the open end of each pocket is wider than the closed end of the pocket. This allows the pockets to be connected to one another, as will be described, instead of being separated by the sheet filter material as per known fluid bed dryer bags. Preferably, one or more pockets taper from the open end to the closed end.

One or more pockets are preferably generally conically shaped, when in an extended configuration.

The pockets are preferably pleated at the closed end. This enables the loop to be secured to the closed end, whilst the pleating allows the distal end (i.e. the closed end) of the pocket to expand, or extend outwardly during the drying process, to increase the available surface area of the pocket for filtration.

The pockets may also be pleated, for example, box-pleated, at the open end, which also allows the pockets to expand or be extendible during the drying process, thus increasing the filtration surface area.

The filter may comprise an electrically conductive (anti-static) material, such as a polyester or other synthetic material, comprising stainless steel wire or carbonised filament woven through the material to dissipate static electricity. In some embodiments, the filter may comprise a non-conductive material, which may be any suitable material, such as polyester or any other suitable synthetic fabric, which does not comprise conductive wires or filaments.

To form the filter, the open ends of the pockets are preferably manipulated into shapes that enable the pockets to be abutted against one another, for example in a concentric pattern. For example, in a three layer concentric arrangement, the open end of the outer pockets may be manipulated into a substantially rectangular or slightly tapered rectangular arrangement; the open end of the intermediate pockets may take a form resembling a generally pentagonal shape; and the open end of the inner pocket(s) may take the form of a generally hexagonal shape. A possible configuration of pockets is a three layer concentric arrangement comprising twelve outermost pockets, six intermediate pockets, and one central pocket. However, it will be appreciated that other configurations, including non- concentric, such as rectangular or square configurations, are also possible, which may or may not have different numbers or arrangements of pockets, without departing from the scope of the invention.

The boundaries (of the open ends) of the pockets are preferably connected to one another using seams, which may be, for example, stitched, or welded seams. At least some of the seams may be formed using a three needle chain stich feed, or a more simplified seam. Optionally, the seams may be bound with tape to hide the cut edges. At least some of the seams may comprise "seam and fell" seams, with two rows of locking stitch sewing. By "seam and fell" it is meant a seam made by placing one edge inside a folded edge of fabric, then stitching the fold down and including a topstitched finish. The open end of each pocket preferably comprises at least four sides, and may comprise five or more sides. In any fluid bed dryer bag according to the present invention, there may be different configurations of pockets, for example, some of the pockets may comprise four sides and some of the pockets may comprise five or more sides at the open end. At least one of the pockets may comprise six sides.

Preferably, at least three of the sides are connected to sides of other pockets. This eliminates the requirement for the sheet material (disc or similar arrangement) having apertures as per known arrangements, and instead, allows the plurality of pockets to be interlinked. Each of the at least three sides is preferably connected to a side of a different other pocket. This arrangement ensures that the open ends of each pocket are retained in a substantially open configuration, which also eliminates the need for an expansion ring or other such device that may be positioned around the open end of the apertures of known fluid bed dryer bags to maintain the pocket in an open configuration.

It will be appreciated that, due to the deformable nature of the material comprising the filter, the degree to which the pockets are open when the bag is not in use may vary, and the pockets may partially collapse when the bag is not in use, although the individual pockets and open ends will still be apparent. However, it will be clear that the open ends of the pockets will expand fully during the drying process when exposed to the air current.

The filter may further comprise a rim. The rim preferably extends around the periphery of the plurality of outermost pockets at the open ends and optimally, is complementarily shaped with respect to the shape of the fluidised bed dryer. For example, the rim may be circular, rectangular, square, or any other suitable shape to enable the fluid bed dryer bag of the invention to be used in conjunction with and connected to different shapes of fluidised bed dryer.

Preferably, the outermost pockets are attached to the rim. This provides an anchor point for the outer pockets, from which the inner pockets ultimately depend, by virtue of their connections to adjacent pockets. This arrangement also ensures that the outer pockets in particular, are held in an open configuration.

The rim may comprise a frame, which is preferably complementarily shaped with respect to the shape of the fluidised bed dryer with which the filter is to be used. The frame is preferably attachable to the fluidised bed dryer, optionally, via a skirt, attached to and depending from the rim.

The filter, in particular, the pockets, preferably comprise filter material, which may be woven. At least some of the woven material may have a grams per square metre (gsm) value from 150 to 200, and/or at least some of the woven material may have a grams per square metre (gsm) value in excess of 400. The filter material is preferably electrically conductive and will not lose fibres and will have a smooth surface for ease of releasing filtered particles. The heavier, coarser fabrics of over 400 gsm that will only pass minimal amounts of air, may preferably be used for parts of the bag that are prone to physical damage, such as around the rim area.

The filter may comprise a fluid bed dryer bag, or a granulator bag.

Specific embodiments of the present invention will now be described, by way of example only and with reference to the accompanying Figures, in which: Figure 1 is a perspective view from the side and underneath of a typical prior art fluid bed dryer bag;

Figure 2 is a perspective view from the side and underneath of one embodiment of filter according to the present invention, in the form of a fluid bed dryer bag;

Figure 3 is a side view of the fluid bed dryer bag of Figure 2; Figure 4 is an underneath view of the fluid bed dryer bag of Figure 2; and

Figure 5 is an exploded view of Figure 4.

An embodiment of filter 110 in accordance with the invention is shown in Figures 2 to 5. in the present embodiment, the filter comprises a fluid bed dryer bag 110. Features of the bag of the embodiment of Figures 2 to 5 which correspond with features of the prior art fluid bed dryer bag, are identified using the same reference numerals as used in Figure 1 , increased by 100.

The fluid bed dryer bag 110 comprises nineteen substantially concentrically arranged filter bags, in the form of generally conical shaped sleeves or pockets 120, having an open end at the base of the sleeve 120 and a closed end at the top of the sleeve 120. As best seen in Figures 2 and 4, the substantially concentric arrangement of sleeves 120 comprises a ring of twelve identical outermost sleeves 120i, a ring of six identical intermediate sleeves 120ii and one central sleeve. The sleeves 120 comprise electrically conductive woven filter material of 150 to 200 gsm of polyester fabric.

Each sleeve 120 is formed by folding a length of sheet filter material in half down its longitudinal axis to form an elongate double layered length of material. The two layers are secured along their longitudinal edges using a three needle chain stitch, to form a hollow, generally conically-shaped sleeve 120. One end of the sleeve 120 is gathered and pleated as shown at 121 to form a substantially pointed end, which is subsequently welded at the end edge to form a seam 120a to close the pointed end. The pleated arrangement results in the cross-sectional area of each sleeve gradually decreasing from the open end to the closed end. The sleeves 120 thereby taper from the open end towards the pointed end, to form a generally conical shape.

A fabric loop 122 is stitched to the closed, substantially pointed end of each sleeve 120, to enable the sleeve 120 to be suspended from a hanging rack 124 located above a fluidised bed dryer. This ensures that the sleeves 120 remain in an open configuration even when the warm air current is not flowing. The open ends 11 Si of the outermost sleeves 120Ί provide a larger opening as compared to the open ends 118ii, 18iii of the intermediate and central sleeves, which increases the surface area of the outermost sleeves 120i, as compared to the remaining sleeves. Similarly, the open ends 118ii of the intermediate sleeves 120Π each have a greater cross-sectional area than the open end 1 18iii of the central sleeve.

In isolation, i.e. before being formed into part of the fluid bed dryer bag, the opening 118 of each sleeve 120 is substantially circular in shape.

However, because of the flexible nature of the filter material, the substantially circular configuration of the open ends 118 of the sleeves 120 can be manipulated to enable the sleeves 120 to be abutted in a concentric arrangement, as shown in the Figures.

As best shown in Figures 4 and 5, this is achieved by manipulating each of the circular open ends 118i of the outermost sleeves 120i into a four-sided, generally trapezoidal arrangement, having two lateral sides 126a, 126b, an inner side 128 and an outer side 130. The length of the outer side 130 is slightly longer than the length of the inner side 128, meaning that the open end 118i has a slightly tapered, generally trapezoidal configuration.

The open ends 118Π of the intermediate sleeves 120Π are arranged into a five- sided configuration, which resembles a generally pentagonal shape, having an inner peripheral side 132, two lateral sides 134a, 134b outwardly inclined from the inner side 132 and two outer sides 136a, 136b converging from the top or outermost point of the lateral sides 134a, 134b to form an apex 138 substantially in line with the mid-point of the inner side 132. The open end 118iii of the central sleeve is manipulated into a generally hexagonal arrangement, as its border comprises the inner side 132 of each of the open ends 118ii of the intermediate sleeves 120N.

To form the substantially concentric arrangement, the twelve outermost sleeves 1201 are arranged in a circular pattern, with the outer sides 130 outermost and the narrower inner sides 128 innermost and the lateral sides 126a, 126b of each sleeve 120i abutting the lateral sides 126a, 126b of an adjacent outermost sleeve 120L The lateral sides 126a, 126b of adjacent sleeves 120i are welded together to form a connecting seam 140 between each of the outermost sleeves 120L The six intermediate sleeves 120i are also arranged in a circular pattern, with the narrow inner side 132 innermost and the outer sides 136a, 136b outermost and each abutting the inner side 128 of the adjacent outermost sleeve 120i of the layer of outermost sleeves 120L The inclined lateral sides 134a, 134b of each intermediate sleeve 120ii abut the inclined lateral sides 134b, 134a, respectively, of each of the two sleeves 120N located either side of the sleeve 120N. The lateral sides 134a, 134b are welded together to form a connecting seam 142 between adjacent sleeves 120ii located either side of each of the intermediate connecting seam 142. Connecting each adjacent lateral side 134a, 134b of the intermediate sleeves 120ii as described secures the intermediate sleeves 120N together in a circular pattern, which fits concentrically inside the circular arrangement formed by the outermost sleeves 120L

The intermediate sleeves 120ii are positioned inwardly of the outermost sleeves 120i as follows. The apex 138 of each of the intermediate sleeves 120Π is positioned at the inner end of a respective connecting seam 140 of two adjacent outer sleeves 120i, i.e. the seam 140 formed by joining the right lateral side 126b of a first outer sleeve 120i with the left lateral side 126a of a second, adjacent sleeve 120L

The apex 138 therefore meets the lower right corner, i.e. intersection 144 of the inner side 128 and right lateral side 126b, of the first outer sleeve 1201 and the lower left corner, i.e. intersection 144 of the inner side 128 and left lateral side 126a, of the second outermost sleeve 120i, such that the two outer sides 136a, 136b of the intermediate sleeve 120ii abut the two inner sides 128 of the two outermost sleeves 120i located above. The outer sides 136a, 136b and inner sides 128 are welded together to form a flattened V-shaped connecting seam 146. This seaming process is completed for each of the intermediate sleeves 120ii, so as to connect the circular arrangement of intermediate sleeves 120Π to the circular arrangement of outermost sleeves 120L

As will be apparent, at least a portion of the lower, open end of each sleeve shows a boundary with a portion of the lower, open end of at least one other sleeve. The lower end 118i of each of the outer sleeves 120i shares a boundary with the lower end 1 1 Si of two other outer sleeves and the lower end 118ii of an intermediate sleeve 120N; the lower end 118ii of each of the intermediate sleeves 120Π shares a boundary with the lower end 118i of the outer sleeves 120i, the lower end 118ii of the intermediate sleeves 120Π and the lower end 118iii of the inner sleeve 120iii; and the lower end 1 18iii of the inner sleeve 120iii shares a boundary with the lower end 118ii of each of the intermediate sleeves 120ii.

The generally hexagonal central sleeve 118iii fits in the generally hexagonally- shaped gap formed in the middle of the circular arrangement of intermediate sleeves 120Π. Each of the six sides 148 of the central sleeve 118iii is arranged to abut the inner side 132 of each of the intermediate sleeves 120Π. Each side 148 is welded to the abutted inner side 132 to form a connecting seam 150 between the central sleeve 118iii and the intermediate sleeves 120ii.

As mentioned above, the sleeves 120 of both the outermost layer 120i and intermediate layer 120ii are arranged such that the narrower inner sides 128, 132 of each sleeve 120i, 120ii are innermost and the wider outer sides(s) 130, 136a, 136b are outermost, with respect to the concentric arrangement. This creates a tapered configuration which causes the open ends 11 Si, 118ii of the sleeves 120i, 120Π to collectively form a concave arrangement, as best illustrated in Figure 2. In other words, the open ends 11 Si, 118ii, 118iii of the sleeves 120i, 120N form a portion which extends continuously over substantially the whole area of the underside of the fluid bed dryer bag 1 10.

The peripheral edges of the open ends 118i of the outermost sleeves 120i are box-pleated 123 and stitched to an annular piece of filter material 152 located outwardly of the outermost sleeves 120i and forming the periphery of the fluid bed dryer bag 110. An annular frame 154 of an approximate width and height of 1 inch (25.4mm) and 3 inches (76.2mm), respectively, is placed over the annular piece of material 152, which extends outwardly beyond the width of the frame 154. The periphery of the annular piece of material 152 comprises a seam 156, having a drawstring (not shown) threaded therein. The excess annular material 152 extending beyond the frame 154 is folded back on itself, up the height of the frame 154 and back over the top or uppermost surface of the frame 154 to form a skirt 114, which surrounds the periphery of the open ends 1 Si of the outermost sleeves 120i. The drawstring is adjusted to tighten the skirt 114 around the frame 154. The fluid bed dryer bag 110 is positioned and secured above a fluidised bed dryer (not shown), via the skirt 114, in accordance with known arrangements. The fluidised bed dryer is operated in the conventional manner to fluidise and dry particles. However, with the present invention, the available surface area for filtration is significantly improved as compared to the prior art arrangements, since at least one of the sleeves 120 shares a boundary with a portion of the open end of at least one other sleeve 120, rather than being attached independently to a disc 12, as per the prior art arrangements. Therefore, filter cake build up on the disc 12 is eliminated and air flow and filtration occurs directly within the sleeves 120.

Furthermore, the pleated nature of the sleeves 120 allows each sleeve 120 to expand in the air current, further increasing the available surface area for filtration, as compared to the fixed arrangements of the prior art, such as that shown in Figure 1.

The tapered, concave arrangement of the sleeves 120 is also important because it more evenly distributes the stress concentrations on the seams which occur during the drying and cleaning processes, as will be explained. During use of a fluid bed dryer bag, vertical stresses are applied to the bag, as a result of upwardly directed air flow, extraction and by virtue of suspending the bag over the fluidised bed dryer. The majority of these stresses are borne by the seams which secure the individual sleeves together. In prior art arrangements, such as illustrated in figure 1 , the seams 20b connecting the sleeves 20 to the disc 12 and the seams 20a connecting the planar end wall with the upper end of the sleeves 20 bear these stresses. Since the sleeves 20 are connected to the disc 12 and end wall at substantially 90 degrees, significant stress concentrations form in regions of the seams 20b, 20a. In contrast, the seams of the present invention interconnect in an inwardly tapering manner, due to the particular shapes and arrangement of the concentric layers, as best illustrated in Figure 4. More specifically, the lateral connecting seams 140 of the outermost layer 120i are connected, alternately, to the apex 138, and intersection 144 of the outer side 146 and lateral connecting seam 142, respectively, of the adjacent intermediate sleeve 120ii. Each lateral connecting seam 142 of the intermediate layer 120N is connected to an intersection 158 of two adjacent lateral sides 148 of the generally hexagonal centre sleeve.

This arrangement means that vertical stresses applied to the bag are distributed, via the connecting seams 140, 146 and centre sleeve intersections 158, through each layer, rather than being concentrated on one individual seam, as in the prior art arrangement. Since the centre sleeve intersections are joined by the connecting seam 150 between the intermediate sleeves and centre sleeve, stress can be distributed from the centre sleeve intersections around the connecting seam 150.

For example, stress can be transferred or distributed from the outermost lateral connecting seams 140 towards the intermediate sleeves 120ii, by travelling along the lateral connecting seams 140 of the outermost layer 120i and along the connecting lateral seams 142 and outer side seam 146 of adjacent sleeves 120ii in the intermediate layer.

Stress can also be distributed from the lateral connecting seams 140 of the outermost layer 120ii which meet the apex 138 of the adjacent intermediate sleeve 120ii, since on reaching the apex 138, the stresses will be distributed either side of the apex 138 and along the outer side seam 146, until they reach the intersection 144 with the corresponding lateral side. Stress is transferred from the lateral connecting seams 142 of the intermediate layer 120ii via the intersection 158 between the base of the lateral connecting seam 142 and the two adjacent sides 148 of the generally hexagonal centre sleeve. It will of course be appreciated that stresses can be distributed in the reverse manner, i.e. outwards from the centre sleeve 118iii via the interconnecting seams.

Such stress distribution significantly reduces the risk of the seams rupturing, as compared with prior art arrangements, in which stresses cannot be distributed between seams. This enables all seams within the fluid bed dryer bag to be welded, if desired. This is not feasible with prior art arrangements, since welded seams are typically weaker than stitched seams and so cannot be used to secure seams subjected to significant stress.

It will also be observed that when the fluid bed dryer is in use, such that the sleeves/pockets are extended as shown in the drawings, the walls of the sleeves/pockets do not touch each other.

The embodiment of fluid bed dryer bag described above is described by way of example only and the invention is not intended to be restricted to this embodiment alone, as it will be apparent that other arrangements and embodiments of fluid bed dryer bag will be possible within the scope of the present invention as described herein.

For example, although a circular-shaped fluid bed dryer bag is described, other shapes and configurations of bag and sleeves may be possible, such as rectangular, or square. These other shapes and configurations may comprise a different interconnected pattern of sleeves than that described above, but which nevertheless achieve the same effect in distributing stress concentrations between multiple, interconnected seams in the fluid bed dryer bag. Alternative materials might be used to form the fluid bed dryer bag, again, without departing from the scope of the invention. In addition, although the specific embodiment describes an arrangement in which the shared boundary between the open end of two or more pockets is essentially along a line, in practice the shared boundary will have a finite width. Indeed, it may be appropriate to form a shared boundary between the open ends of two or more pockets from a length of material having a defined width, e.g. a length of tape, to which the open ends of the pockets are secured.

By way of further example, although the description relates primarily to use of the filter as a fluid bed dryer bag, it will be appreciated that the filter can also be used with a granulator machine, since the machine and filter is essentially the same as that of a fluid bed dryer bag.