GB2491417A

GB2491417A - Filter

Info

Publication number: GB2491417A
Application number: GB1109387.9A
Authority: GB
Inventors: Jamie Donaldson; Wim Fekkes
Original assignee: AAF Ltd
Current assignee: AAF Ltd
Priority date: 2011-06-03
Filing date: 2011-06-03
Publication date: 2012-12-05
Also published as: GB201109387D0; WO2012164084A1

Abstract

A filter assembly includes a casing adapted to permit gas to flow therethrough and a filter provided in the casing to filter gas flowing through the casing. A filter medium (24) is bonded to the casing (10) by a bonding agent (29, 31) which itself provides an inclined surface (30,32) so that liquid on the filter medium is able to drain along the incline. Preferably the bonding agent is a solidified fluid material such as a cured resin or potting compound. The bonding agent may be introduced through an inlet aperture of the filter by a dispensing nozzle 28. A method for manufacturing the filter assembly is also provided. Advantageously the filter assembly is particularly suitable for use in filtering intake air for gas turbines.

Description

I :1.

Filter Assembly and Method of Manufacture Thereof

Field of the Invention

The present invention relates to a filter assembly in particular, but not exclusively, for use in filtering intake air for gas turbines.

Background to the Invention

Gas turbines, in particular gas turbines used for power generation, are very sensitive to the quality of inlet air drawn into the combustion chamber of the gas turbIne. Particularly, contaminant particulate matter can dáiie turbine blades and can induce corrosion in the working parts of the turbine. As a consequence, mechanical reliability can decrease, along with operating efficiency.

It is customary in the art of gas turbine manufacture to provide a filter section upstream of the air intake to the combustion chamber of the gas turbine to filter the air drawn in to the required quality. The nature of the filtration will depend on the expected environment in which the turbine is to be operated and particularly on the expected contaminant levels in the air. To cope with a wide variety of contaminant particle sizes while avoiding filters from becoming too-rapidly obstructed, it is known to provide several filtration stages sequentially in the path of the incoming air. Such typically will include coarser pre-filter stages to exclude large-dimension contaminant particles followed by a final filtration stage to exclude the very smallest particles, thereby to achieve the required design

specification for the inlet air to the combustion

chamber.

Figure 1 shows a typical schematic configuration of a conventional gas turbine arrangement, showing major parts only. The gas turbine 1 includes a combustion chamber 3 located between two sets of rotor blades 2.

The two sets of rotor blades are connected by a shaft, which causes the two sets of rotor blades to rotate synchronously. Upstream of the combustion chamber are compressor blades, which compress the air in the combustion chamber, while downstream of the combustion chamber are turbine blades, which extract motive energy from the hot gas leaving the combustion chamber. Into the combustion chamber is injected fuel from a fuel supply 4, the combustion of which fuel elevates the ____ temperature in the combustion chamber to generate th_ --gas flow that drives the turbine blades. Since more power is produced by the combustion of the fuel then is necessary to draw in and to then compress the air in the combustion chamber, useful power may be extracted from the rotation of the shaft while waste heat from the exhaust gases can be further used to produce additional power.

Air is drawn into the combustion chamber by the compressor blades through air transition duct 7, which communicates with the local atmosphere through inlet duct 5, in which is positioned filter assembly 6.

Therefore, the purity of the air entering the combustion chamber is, by means of suitable configuration of filter assembly 6, maintained within the optimal working specification for the working parts of the turbine.

Figures 2 and 3 show examples of configurations of filter assemblies previously known to the Applicant, in diagrammatic longitudinal section.

S

Figure 2 shows a two-stage filter arrangement wherein a final filter 9 is combined with a pre-filter 8 to achieve a two-stage filtration of incoming air, which passes through the filter in the direction shown by the arrow. The final filter 9 includes a casing 10 which houses one or more filter elements 24, which are made of a filter medium having a large number of small pores formed therein to trap particulate matter.

The final filter 9 is mounted to the inlet duct by means of mounting frame 11, which itself is placed in the inlet duct so as to occlude the entrance thereto. The mounting frame 11 provides an end seat ha against which peripheral flange lOa of the casing 10 of the final filter rests, with a sealing gasket 14 interposed therebetween, so seal the casing to the mounting frame.

Peripheral flange lOa is urged against gasket i4by retaining element 12, to securely hold the casing in position in the frame.

A pre-filter 8 is then positioned upstream of the final filter to occlude the aperture in the mounting frame with at least one further pre-filter element 8a, made of a different filter medium, usually having a pore size suitable for trapping particular matter having a larger diameter than that trapped by filter element 24. Pre-filter 8 is mounted directly to mounting frame 11 by means of retaining springs 13, which engage with fixtures on the pre-filter and urge the pre-filter against the mounting frame. Therefore, gas drawn in through the inlet duct S must pass through both pre-filter 8 and final filter 9 in sequence before reaching the combustion chamber.

Figure 3 shows an alternative configuration to the arrangement of Figure 2 in which like parts are shown with identical reference numbers to those in Figure 2.

The arrangement of Figure 3 differs in that rather than the pre-filter 8 being urged against mounting frame 11 by retaining springs 13, an adaptor plate 15 is provided having a peripheral flange iSa sandwiched between retainer 12 and peripheral flange ba of casing 10, to the principal portion lSb of which one or more filter cartridges are engaged by engaging means not shown in the Figure. This latter arrangement is fully described in detail in co-pending British National patent application number 1016164.4, in the name of the present Applicant.

However, in both these arrangements, a problem exists when the humidity level of the atmosphere is relatively high. Particularly, there is a problem that condensation may form in the filter casing, especially on the filter element 24 with which the inlet air comes into contact -añdS1fiiiraiiy has a high surface area.

Condensation forming on the filter element can block the pores, reducing the intake efficiency of the filter and also, by draining inwardly and accumulating, can cause corrosion to downstream elements of the gas turbine arrangement.

Theref ore, it is desirable to provide a filter assembly which allows condensation to be easily carried away from the filter medium from which the filter element 24 is made.

Summary of the Invention

According to a first aspect of the present invention, there is provided a filter assembly comprising a casing adapted to permit gas to flow therethrough; and a filter provided to the casing to filter gas flowing through the casing, wherein the filter medium is bonded to the casing by a bonding agent, which itself provides an inclined surface so that liquid on the filter medium is

I

able to drain along the incline. The filter assembly provides an easily-manufactured construction in which condensation forming on the filter medium may be effectively removed from the filter assembly, by draining along the inclined surface.

In a particular embodiment of the invention, there is provided a filter assembly wherein the bonding agent is a solidified fluid material that was fluid when applied to the casing to seal the filter medium thereto and which subsequently solidified to form the inclined surface, which embodiment is particularly easy to manufacture, since no separate manufacturing of an inclined component of the filter assembly is required.

In a further particular embodiment of the invention, there is provided a filter assembly wherein the material is a cured resin or potting compound, which can provide an especially reliable seal between the filter medium and the casing, since such materials can effectively bond filter medium to the case while providing an impermeable barrier to gas or liquid.

According to a particular embodiment of the present invention, there is provided a filter assembly wherein the inclined surface is parallel to a plane defined by a surface on which the casing may stably rest, the casing preferably being provided with a projecting portion to permit the casing to rest on a surface at a predetermined angle. Such an embodiment may be easily manufactured without requiring special support arrangements for the casing during manufacture, since the casing can simply be rested on a horizontal work surface prior to bonding agent application.

According to a particular embodiment of the present invention, there is provided a filter assembly wherein a second quantity of bonding agent having a second inclined surface is provided at a location opposite to that of the first inclined surface, the first and second inclined surfaces relatively diverging. Such an embodiment is able to be installed correctly in either of two orientations, thereby guarding against incorrect installation and reducing the time and expertise required to correctly install the filter.

According to a particular embodiment of the present invention, there is provided a filter assembly wherein the casing comprises top and bottom cell plates for defining a filter cell with the filter medium; first and second side support elements for maintaining the cell plates at a predetermined spacing; and optionally, a plurality of inner support elements for spacing individual elements of the filter medium one from another; wherein the bonding agent is provided to seal the cell plates to the filter medium. Such an embodiment provides a filter assembly which is easily manufactured without recju.iring special tools or techniques, while having good structural rigidity.

According to a particular embodiment of the present invention, there is provided a filter assembly wherein the filter casing defines a plurality of V-shaped filter cells arranged in a row running perpendicular to the direction of gas flow through the casing. Such an embodiment is particularly suitable for the filtration of high-volume gas flows to a high degree of purity, while permitting the filter casing to be compact in size.

According to a particular embodiment of the present invention, there is provided a filter assembly wherein the filter medium is located relative to the top and bottom cell plates by retaining structures formed on the cell plates. Such an arrangement guards against misalignment of the filter medium during manufacture.

According to a particular embodiment of the present invention, there is provided a filter assembly wherein the casing is provided with a rib portion; and the bonding agent is deposited in a trough defined between the rib portion and the filter medium. Such an embodiment is able to guard against overflow of the bonding agent to the front surface of the filter casing during manufacture, According to a particular embodiment of the present invention, there is provided a filter assembly wherein the filter is adapted for use as an air intake filter, preferably an air intake filter for a gas turbine. Such an embodiment is particularly suitable for use in the power generation industry.

According toa second aspect fth ennventig ---there is provided a method of manufacturing an air filter assembly comprising the steps of providing a casing adapted to permit gas to flow therethrough; providing a filter medium to the casing to filter gas flowing through the casing; bonding the filter medium to the casing by means of a bonding agent, in such manner that the bonding agent provides, in the manufactured air intake, an inclined surface so that liquid on the filter medium is able to drain along the incline. Embodiments of this aspect allow easy manufacture of a construction in which condensation toning on the filter medium may be efficiently removed from the filter assembly.

In a particular implementation of the invention, there is provided a method of manufacturing an air filter assembly wherein the step of bonding the filter medium to the casing comprises steps of: orienting the casing such that a horizontal plane defines the intended inclined surface of the seal portion; applying a fluid bonding agent to the casing; allowing the bonding agent to flow to form a horizontal plane surface; and allowing

S

B

or causing the bonding agent to solidify, thereby to form the inclined surface, which is particularly easy to put into practice.

In a further particular implementation of the invention, there is provided a method of manufacturing an air filter assembly wherein the bonding agent is a curable resin, which can provide an especially reliable seal between the filter medium and the casing.

According to a particular implementation of the present invention, there is provided a method of manufacturing an air filter assembly wherein the step of orienting the casing is accomplished by resting the casing on a horizontal surface. Such an embodiment provides a method of manufacturing which does not require special support arrangements for the casing during manufacture.

According to a particular implementation of the present invention, there is provided a method of manufacturing an air filter assembly wherein the method further comprises a step of applying a quantity of bonding agent to form a second inclined surface at a location opposite to that of the first inclined surface, the first and second inclined surfaces being formed so as to relatively diverge. An air filter manufactured according to such a method is able to be installed correctly in either of two orientations, thereby guarding against incorrect installation and reducing the time and expertise required to correctly install the filter.

According to a particula.r implementation of the present invention, there is provided a method of manufacturing an air filter assembly wherein the step of providing the casing comprises the steps of providing top and bottom cell plates for defining a filter cell with the filter medium; providing first and second side support elements for maintaining the cell plates at a predetermined spacing; and optionally, providing a plurality of inner support elements for spacing individual elements of the filter medium one from another; wherein the bonding agent is provided to seal the cell plates to the filter medium. Such an embodiment provides a method of manufacturing an air fiter assembly which does not require special tools or techniques.

According to a particular implementation of the present invention, there is provided a method of manufacturing an air filter assembly wherein the filter casing defines a plurality of V-shaped filter cells arranged in a row running perpendicular to the direction of gas flow through the casing. Such an embodiment is particularly suitable for the manufacture of filters for the filtration of high-volume gas flows to a high degree of purity1 while permitting the filter casing to remain compact in size.

According to a particular implementation of the present invention, there is provided a method of manufacturing an air filter assembly wherein the step of providing the filter medium to the casing comprises: locating the filter medium relative to one of the top and bottom cell plates by means of retaining structures formed on the respective cell plate; attaching the side support elements to the respective cell plate; and attaching the other of the top and bottom cell plates to the side support elements to sandwich the filter medium between the cell plates. Such an arrangement guards against misalignment of the filter medium during manufacture.

According to a particular implementation of the present invention, there is provided a method of manufacturing an air filter assembly wherein the casing is provided with a rib portion and the bonding agent is supplied in a trough defined between the rib portion and the filter medium. Such an embodiment is able to guard against overflow of the bonding agent to the front surface of the filter casing during manufacture.

According to a particular implementation of the present invention, there is provided a method of manufacturing an air filter assembly wherein the filter is adapted for use as an air intake filter, preferably an air intake filter for a gas turbine. Such an embodiment is.

particularly suitable for use in the power generation industry.

Brief Description of the Drawinss

To enable a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying Drawings, in which: -Figure 1 is a schematic diagram of a gas turbine arrangement; Figure 2 is a longitudinal section through a filter assembly suitable for use with the arrangement of Figure 1; Figure 3 is an alternative configuration of filter assembly also suitable for use in the arrangement of Figure 1; Figure 4 is an embodiment of the present invention in perspective view; Figure 5 shows a transverse section of an embodiment of the present invention during manufacture; Figure 6 shows a second transverse view of an embodiment of the present invention at a subsequent stage of 1].

manufacture to the stage exemplified in the view of Figure 5; Figure VA to 71( show a manufacturing sequence in accordance with an embodiment of the present invention.

Detailed Description

An exemplary final filter assembly, being an embodiment of the present invention, is shown in Figure 4.

The final filter assembly shown in Figure 4 includes a bottpm cell plate lVb and a top cell plate 17a, between which are positioned, in a vertical orientation, filter elements 24, being portions of a filter medium such as a woven glass fiber mesh. The top cell plate lVa and the bottom cell plate llb together define V-shaped filter --cells, the oppoav:ip;i walls of the filter cells each being formed from filter element 24, mutually inclined to cause the filter cell to taper in a downstream direction. To ensure that the top cell plate 17a and the bottom cell plate 17b are separated by a consistent distance to match the height of the filter elements 24, rod-like side support elements iBa and lBb are provided, which engage with appropriately-formed recesses in the top and bottom cell plates l7a and 17b to fixedly space the cell plates one from the other.

Each of the cell plates 17a and 17b includes a bar portion at an air inlet side thereof, which together with the side support elements l8a and l8b defines a generally rectangular frame surrounding the inlet apertures of the V-shaped filter cells. The top and bottom cell plates, together with the side support elements, and the inner and outer support elements together form the filter casing 10.

In conventional applications, the external dimensions of this rectangular frame is preferably within the range of to 70 cm, but will naturally depend on the dimensions of the inlet duct to which the filter assembly is to be mounted. Specifically, the outer dimensions of this frame should be substantially similar to those of the inlet duct so as to maximise the operating cross-section of the inlet duct, while the inner dimensions will be selected to achieve a suitably large operating cross-section of the inlet apertures without compromising the structural rigidity of the casing. All dimensions are thus suitably variable to suit requirements.

In the embodiments shown in Figure 4, inner support elements 19 and outer support elements 20 are provided respectively to cover the upstream and downstream ends of the filter elements 24, both to add structural rigidity to the filter assembly and to seal any gaps both between the V-shaped filter cells and at the ___ downstream vertices of the filter cells, respectively.

Of course, in one alternative embodiment, a single sheet of filter medium may be repeatedly folded to provide a single filter element to define a plurality of V-shaped cells; in such a case, inner support elements 19 and outer support elements 20 might be omitted. However, they are presently preferred both due to the ease of manufacture of working with individual sheets of filter element and to the improved structural rigidity which the additional support elements confer on the filter assembly as a whole.

The embodiment shown in Figure 4 exhibits four inlet apertures defined between the side support elements and the inner support elements, each associated with a single V-shaped cell. Depending on the quantity of air to be filtered and the flow velocity, fewer or more such cells may be provided, without limitation.

The depth of the V-shaped cells in the air flow direction will depend on the volume of air to be filtered, but is presently preferred to be around four times the width of the inlet apertures transverse to the air flow direction.

Present, but not explicitly labelled in Figure 4, is a quantity of bonding agent applied to the inner surfaces of the top and bottom cell plates l7a, ivb which enclose the v-shaped filter cells. This bonding agent is provided to attach the top cell plates to the filter elements, and also to seal any gaps which might exist between the cells plates and the filter medium.

Particularly, if gaps exist around the filter medium through which particulate matter might pass, the effectiveness of the filter will be compromised, However, in embodiments of the present invention, the bonding agent also itself provides an inclined surface, running away from the surface of the filter element and toward the inlet aperture of the filter cell such that water which condenses on the filter elements during operation does not accumulate on the top and bottom cell plates but rather drains downwardly along the incline towards the inlet apertures, thereby to exit the filter assembly.

All component parts of the filter assembly are preferably moulded from acrylonitrile butadiene stearate (ASS), except the filter medium, which is preferably a glass fiber mat. However, other material and fabrication techniques are possible, as will occur to the skilled reader.

The process of manufacturing the filter assembly of Figure 4 will now be described.

Firstly, the bottom cell plate iTh is supported, and the side support elements iSa and 18b are introduced to the respective recesses provided in the bottom cell plate, so as to extend vertically from the cell plate. Next, the outer support elements 20 and inner support elements 19 are positioned as required in respective recesses, to arrive at the configuration shown in Figure 5.

Also visible in Figure 5 are tapered dowels 22b and locating stud 2lb which project upwardly from the surface of bottom cell plate 17b. Equivalent tapered dowels 22a and locating stud 2la are provided on top cell plate l7a, not yet attached, to project downwardly in a corresponding manner. These elements are spaced on the inner surfaces of the cell plates such that, when the cell plates are mounted to the side support elements ISa, 18b to define the filter cells, h PQr!t2YJ!lffi 22a arid 22b and locating studs 21a and 2lb project inwardly to the cell to position the filter medium close against inwardly-projecting walls 23a, 23b which define the edge of the cell on the top and bottom cell plates respectively. This wall is shown as element 23b on Figure 5; a corresponding wall 23a is similarly provided on top cell plate 70a. Each wall 23a, 23b projects upwardly a short distance to surround at least the entire downstream side of each filter cell sufficient to define the exterior downstream contours of the filter cell.

The dowels 22b are placed in a V configuration parallel to the wall 23b running from the inlet aperture at its widest point to the vertex of the V1 at which point the wider-diameter locating stud 21b, corresponding to an equivalent stud 21a on the top cell plate, is located.

The dowels and the locating studs thus define barriers running parallel to the walls 23a, 23b of the cell plate to enable the filter medium to be securely inserted therebetween, such that the top and bottom of the filter

I

element contact the cell walls 23a and 23b respectively when abutting the inner surfaces of the cell plates 17a, 17b. Naturally, therefore, the spacing of the dowels from the cell walls will be selected to match the thickness of the intended filter medium.

Since the dowels taper, they progressively apply. greater positioning force to the filter medium, the deeper the filter element is inserted between the dowels and the cell wall, thereby to progressively restrict the position of the filter element until it. is securely held when fully inserted and in contact with the inner surface of the cell plate.

It is worth noting that the tapered dowels 22a and 22b and locating studs 2la and 2lb can be integrally formed with the cell plates 17a arid l7bor can be separate] manufactured and provided thereto by any conventional method, without limitation.

Accordingly, once the side support elements ISa and l8b are provided to the bottom cell plate, the filter elements 24 can be inserted in to the spaces between the tapered dowels and the walls of the cell plate to arrive at the configuration shown in Figure 6. Here, each filter element is shown sandwiched between the tapered dowels 22b and the cell wall 23b, abutting the outer support 20 at one end and the inner support elements 19 at the other end. At this stage in the manufacture, the top cell plate l7a may then be placed in an inverted and opposed configuration to the bottom cell plate and lowered onto the assembly so that the side support elements 18a and lSb, the inner supports 19, and the outer supports 20 engage with the top cell plate 17a to form an assembled filter unit. Of course, other permutations of these operations will suffice to arrive at the assembled filter unit, as will occur to the reader.

S

However, at this point, while the filter elements are reasonably securely held in the filter casing 10 defined by support elements iSa, l8b, 19, 20 and top and bottom cell plates 17a and l7b, small non-uniformities in the inner surfaces of the cell plates, the inner surfaces of the supports, or the edges of the filter elements may result in gaps which permit the passage of particles under, above or around the filter elements during operation. To guard against such possibilities1 a bonding agent is applied to secure the filter elements to the respective upper and lower cell plates, and the supports iSa, l8b, 19, 20 as appropriate, and to provide a seal between the edges of the filter elements and the abutting surfaces.

This process is shown in Figures VA to 7H, as will be described below. ---First the assembled casing is stably placed on a surface 27 such that a horizontal plane defines a desired inclined plane running from the tip of the v-shaped cell outwardly toward the inlet aperture of the cell. In the embodiment shown in Figures 7A to 71'!, this is achieved by providing a projection 25b to bottom cell plate 17b such that when the bottom cell plate l7b is placed on horizontal surface 27 with the projection 25 being down most, the cell plates 17a and 17b are tilted by some small angle to the horizontal, preferably around 5 degrees. Alternatively, if no projection were present on the lower surface of bottom cell plate l7b, cell plate could be positioned on a surface having a suitable angle to the horizontal to achieve the equivalent degree of tilt.

When the filter has been placed in the inclined position shown in Figure 7A, a dispensing nozzle 28 shown in Figure 73 is introduced through the inlet aperture of the filter and a bonding agent 29 in fluid form is dispensed onto the upper surface of bottom cell plate 17b lying within the filter cell so as to cover that surface and particularly to contact both the surface and the inner surface of the filter elements 24 associated with the cell in question. This is then repeated in each of the cells in turn to arrive at the configuration shown in Figure 7C. It should be noted that rib 2Gb is provided to the bottom cell plate to provide a barrier to excess bonding agent overflowing the border of the cell plate in the upstream direction and contaminating the inlet surface of the filter.

The bonding agent 29, which is therefore located in a trough running between rib 26 arid respective outer support 20b, forms a surface which is horizontal relative to the vertically downward direction of gravity. --The bonding agent is then subsequently allowed or caused to solidify, to achieve the configuration shown in Figure 7D, at which stage reorientation of the filter will not cause the shape or dimensions of bonding agent 29 to vary. Thereby, bonding agent 29 provides on its top surface a first inclined surface 30 which will enable any liquid that accumulates on the filter medium to drain along the incline and exit the filter, when the filter is positioned normally, i.e. with side support elements 18a and lab oriented vertically.

In the present embodiment, the bonding agent is a resin such as polyurethane adhesive; however, any suitable material which is initially liquid and can be caused to become solid while holding and sealing the filter elements to the top and bottom cell plates is conceivably used. For example, a thermoplastic resin could be used, having a melting temperature less than the material from which the remaining, components of the filter are manufactured, which could be heated to a melt and then poured in to the filter cell as described above. Alternatively, an epoxy resin could be used which is applied in liquid form and which subsequently cures to form a solid. Other materials which could be of use include potting compounds, light-curable resins, UV-curable resins, and resins which can be baked to transition from solid to liquid by the action of e.g. microwave heating.

Since the resin 29 is geometrically and dimensionally stable once solidified, the filter cell as a whole can be inverted and rested in an inverted configuration on a corresponding projection 25a extending from the top plate l7a which is now positioned lower than bottom cell plate 17b, This configuration is shown in Figure 7E.

Again, nozzle 28 is inserted and a second quantity 31, preferably equal in quantity to the firgtq914y,_9f bonding agent is introduced to the trough 4 between rib 26a extending inwardly from top cell plate 17a and the filter elements 24 and outer support 20 of the cell into which nozzle 28 has been introduced. This process has been repeated for the various cells to arrive at the configuration shown in Figure 7G. The quantity 31 of bonding agent is caused again to solidify to provide seccSnd inclined surface 32. Finally, the configuration is shown in Figure 7H is achieved.

At this point, further sealant may be applied to the remaining contact points between casing and filter elements, as appropriate to seal the filter cell.

When this filter is installed in the inlet duct S of a gas turbine with the side support element oriented vertically, the top and bottom cell plates 17a and l7b will be oriented horizontally, but inclined surfaces formed from the quantities of bonding agent 29 and 3].

will nri outwardly from the filter media forming the filter elements 24 to the inlet apertures of the filter.

Therefore, any liquid which accumulates on the filter, for example, dense atmospheric water vapour, can flow down the surface of the filter medium and further flow down the inclined surface to drain along the incline, out of the inlet aperture, and thus out of the filter assembly. This can prevent accumulation of liquid condensate that would otherwise accumulate and either block the filter or corrode downstream parts.

Of course, a variety of alternative embodiments of the invention can be devised by those skilled in the art on the basis of the foregoing examples in the light of their own technically requirements, general knowledge and custom and practice in their respective situations.

For example, the present invention can be applied equally to filter media such as pleated paper, planar porous material, or woven mats, depending on th_ ---contalliaTnC(tbThe removed. ---Also, the invention can be put into effect, according to preferred practical implementations, in situations where there are a greater or lesser number of apertures, or wherein the filter elements form a completely or partially continuous folded path across one or more filter cells; that is to say, the inner and outer ends of filter elements 24 shown in Figure 6 may be variously joined together, rendering either or both or inner support elements 29 and outer support elements 20 redundant.

The inclined surface 30, and optionally the second inclined surface 32, can be formed by the action of gravity in the manner described, or can be formed by, e.g. applying an inflexible sheet of planar material, having interior dimensions to match those of one of the cells, to the liquid or semi-solid bonding agent prior to or during the solidification process in order to form the inclined surface thereon. The material may then be removed to leave the surface of the bonding agent having the incline thereon. Additional layers of material may be deposited on the inclined surface, for example to provide for a particularly hydrophobic surface to enable water to easily run off. Such considerations may also influence the selection of the bonding agent to be used.

Indeed, in some embodiments the cells need not be V-shaped, but could also be rectangular, or curved in form. Such constructions would equivalently realise the advantageous benefits of the claimed invention. Other locating means to the tapered dowels and/or locating studs are also to be used in embodiments of the invention; such alternatives may include grooves provided to the inner surfaces of the top and bottom cell plates ha and 17b to locate the filter elements, projecting walls between which the filter elernes2 are to be sandwiched, or similar configurations. The casing could be formed as a one-piece or two-piece clamshell structure.

Generally, once the advantage of providing such an inclined surface to a layer of bonding agent which bonds the casing to the filter medium is taught, those skilled in the art will be able to realise other configurations which achieve the advantageous effect. All such variations and configurations are considered to be within the scope of the claimed invention.

Claims

Claims: 1. A filter assembly comprising: a casing adapted to permit gas to flow therethrough; and a filter provided to the casing to filter gas flowing through the casing, wherein the filter medium is bonded to the casing by a bonding agent, which itself provides an inclined surface so that liquid on the filter medium is able to drain along the incline.
2. The filter assembly according to Claim 1, wherein the bonding agent is a solidified fluid material that ---was fluid when applied to the casing to sea]. the filter --.medium thereto and which subsequently solidif led to form the inclined surface.
3. The filter assembly according to Claim 2, wherein the material is a cured resin or potting compound.
4. The filter assembly according to Claim 2 or 3 wherein the inclined surface is parallel to a plane defined by a surface on which the casing may stably rest, the casing preferably being provided with a projecting portion to permit the casing to rest on a surface at a predetermined angle.
S. A filter assembly according to any preceding claim, wherein a second quantity of bonding agent having a second inclined surface is provided at a location opposite to that of the first inclined surface, the first and second inclined surfaces relatively diverging.
6. The filter assembly according to any preceding claim, wherein the casing comprises: top and bottom cell plates for defining a filter cell with the filter medium; first and second side support elements for maintaining the cell plates at a predetermined spacing; and optionally, a plurality of inner support elements for spacing individual elements of the filter medium one from another; wherein the bonding agent is provided to seal the cell plates to the filter medium.
7. The filter assembly according to Claim 6, wherein the filter casing defines a plurality of V-shaped filSr cells arranged in a row running perpendicular to the direction of gas flow through the casing.
8. A filter aSsembly according to Claim 7, wherein the -filter medium is located relative to the top and bottom cell plates by retaining structures formed on the cell plates.
9. A filter assembly according to any preceding claim, wherein: the casing is provided with a rib portion; and the bonding agent is deposited in a trough defined between the rib portion and the filter medium.
10. A filter assembly according to any preceding claim, wherein the inclined surface is a planar surface.
11. A filter assembly according to any preceding claim, wherein the filter is adapted for use as an air intake filter, preferably an air intake filter for a gas turbine.
12. A method of manufacturing an air filter assembly, comprising the steps of: providing a casing adapted to permit gas to flow therethrough; providing a filter medium to the casing to filter gas flowing through the casing; bonding the filter medium to the casing by means of a bonding agent, in such manner that the bonding agent provides, in the manufactured filter assembly, an inclined surface so that liquid on the filter medium is able to drain along the incline.
13. The method of Claim 12, wherein the step of bonding the filter medium to the casing comprises steps of: orienting the casing such that a horizontal plane defines the intended inclined surface of the seal portion; applying a fluid bonding agent to the casing; allowing the bonding agent to flow to fra__ -. -horizontal plane surface; and allowing or causing the bonding agent to solidify, thereby to form the inclined surface.
14. The method of Claim 13, wherein the bonding agent is a curable resin.
15. The method according to Claims 13 or 14, wherein the step of orienting the casing is accomplished by resting the casing on a horizontal surface.
16. The method according to any one of Claims 12 to 15, wherein the method further comprises a step of applying a quantity of bonding agent to form a second inclined surface at a location opposite to that of the first inclined surface, the first and second inclined surfaces being formed so as to relatively diverge.
17. The method according to any one of Claims 12 to 16, wherein the step of providing the casing comprises the steps of: providing top and bottom cell plates for defining a filter cell with the filter medium; providing first and second side support elements for maintaining the cell plates at a predetermined spacing; and optionally, providing a plurality of inner support elements for spacing indiv±dual elements of the filter medium one from another; wherein the bonding agent is provided to seal the cell plates to the filter medium.
18. The method according to Claim 17, wherein the filter casing defines a plurality of V-shaped filter cells arranged in a row running perpendicular to the direction of gas flow through the casing.
19. A Method according to Claim 18, wherein the stepsf_ -providing the filter medium to the casing comprises: locating the filter medium relative to one of the top and bottom cell plates by means of retaining structures formed on the respective cell plate; attaching the side support elements to the respective cell plate; and attaching the other of the top and bottom cell plates to the side support elements to sandwich the filter medium between the cell plates.
20. A method according to any one of claims 12 to 20, wherein the casing is provided with a rib portion and the bonding agent is supplied in a trough defined between the rib portion and the filter medium.
21. A method according to any one of claims 12 to 20, wherein the inclined surface is a planar surface.
22. A method according to any one of claims 12 to 21, wherein the filter is adapted for use as an air intake filter, preferably an air intake filter for a gas turbine.
23. A filter assembly as herein.before described, with reference to Figures 4 to 711 of the accompanying Drawings.
24. A method of manufacturing a filter assembly as hereinbefore described, with ref ererice to Figures 4 to 711 of the accompanying Drawings.
25. A filter assembly as hereinbefore described, with reference to the disclosed embodiments.
26. A method of manufacturing a filter assembly as hereinbefore described, with reference to the disclosed embodiments. ----