GB2515531A

GB2515531A - A Seal for a Rotary Heat Exchanger

Info

Publication number: GB2515531A
Application number: GB1311397.2A
Authority: GB
Inventors: Paul Benjamin Beauchamp
Original assignee: POWER SYSTEM SERVICES Ltd
Current assignee: POWER SYSTEM SERVICES Ltd
Priority date: 2013-06-26
Filing date: 2013-06-26
Publication date: 2014-12-31
Also published as: GB201311397D0

Abstract

A seal assembly suitable for a rotary heat exchanger comprises a contact member 20 movably mounted on a support 14 and pivotable relative to the support between a first and a second position, and one or more resilient biasing element(s) 24 (spring) arranged to urge the contact member towards the first position. The biasing element(s) may comprise a helical spring(s) coiled around threaded bolt 22 that permits adjustment of the resistive force by tightening or loosening the bolt. When a plurality of bolts and springs are used they may be spaced evenly along a length of the seal assembly. The contact member may be fabricated from an abrasion resistant and or corrosion resistant alloy, may comprise a bent flat plate forming a canopy over the support, and may comprise a plurality of superimposed flexible sheets. The tip of the contact member may be provided with rolling bearings to prevent wear. The heat exchanger may be a regenerative air pre-heater for a furnace or gas turbine, with the support bolted to a radial plate of a thermal wheel, and the contact member in sliding contact with a sector plate 7 during rotation of the wheel.

Description

I

A SEAL FOR A ROTARY HEAT EXCHANGER

Technical Field of the Invention

The present invention relates to a rotary regenerative heat exchanger and, more particularly, to a seal between a rotating radial edge and a stationary sector plate in such a heat exchanger.

Background to the Invention

Rotary regenerative heat exchangers arc widely used in the power industry for pre-heating the air intake and cooling the flue gases of a frirnace or gas turbine. The hot flue gases and cold air are typically ducted in opposite directions through two or more sectors of a cylindrical drum comprising a permeable thermal mass such as a metal honeycomb structure supported between radial vanes. Heat exchange is effected by continually rotating the drum so that the thermal mass is drawn through the hot and cold flows in succession. Leakage of gases between the hot flue and cold air duets can significantly reduce overall power conversion efficiency of the plant, so the duets are separated from one another by sector plates each of which covers at least one pair of vanes at once to reduce leakage.

Since flue gases and cold air pass through the rotating drum in opposite directions, the drum is predominantly heated and cooled at opposite ends. This results in differential thermal expansion during use, so that the vanes droop towards the cold end, which means that clearance gaps between the vanes and the sector plates can vary significantly during use.

It is therefore advantageous to provide a flexible seal between the rotating vanes and static sector plates that can accommodate this variable gap, to reduce leakage across the sector plates between the flue and intake ducts. However, the harsh environment in very high-temperature gases renders many materials unsuitable for forming a flexible seal. Compliant blades formed from multiple layers ofthin, flexible steel sheet have been proposed, but these have been observed to experience significant wear against the sector plates, and must therefore be checked and replaced frequently.

Objects ofembodiments ofthe present invention include the provision ofa radial seal for a rotary heat exchanger that addresses the issues raised above, that accommodates thermal flcxion of the rotor drum relative to the sector plates, that provides improved power conversion efficiency, that may be conveniently and inexpensively retrofitted to an existing rotary heat exchanger, that is durable and requires little maintenance, andior that is convenient and inexpensive to install, inspect, and repair.

Summary of the Invention

According to a first aspect ofthe invention, there is provided a seal assembly for a rotary heat exchanger, the assembly comprising a support, a contact member movably mounted on the support and pivotable relative to the support between a first and a second position, and a resilient biasing element arranged to urge the contact member towards the first position.

The support and contact member may be clamped together, against the resilient biasing element, by a clamp. The clamp may comprise a threaded bolt, and may comprise a locking nut. The resilient biasing element may comprise a helical spring. The clamp may comprise a threaded bolt about which the helical spring is coiled. The support and contact member may each comprise a hole or slot through which the bolt is secured. The seal assembly may comprise a plurality ofsaid clamps and/or a plurality of said resilient biasing elements distributed along a length of the seal. The clamps and/or resilient biasing elements may be substantially equispaeed along said length, may be spaced ifirther apart towards one end of the seal, and may be spaced apart by a separation distance that increases evenly from one end of the seal to the other.

The contact member may be tiltably secured to the support, and may be pivotable about an edge of the support. The contact member may rest against the edge of the support about which it is pivotable, and may be held firmly against said edge by the resiliently biased element. The contact member may comprise a recess into which said edge ofthe support engages. The recess may comprise a bend in the contact member. The contact member may form a canopy over the support.

The contact member and/or the support may be fabricated from an abrasion-resistant steel, may be fabricated from a weathering steel capable of forming a stable oxide layer, may be fabricated from duplex, super-duplex, austenitic, super-austenitic, martensitic, ferritic, or precipitation-hardened stainless steel, maybe fabricated from 316-grade stainless steel, and may be fabricated from a nickel-based alloy. One or each ofthe contact member and the support may comprise a plate, which may be a substantially rigid plate, may comprise a bend, may comprise a bend in an otherwise substantially flat plate, and may comprise a bend having a bend angle of between 5 and 50 degrees, between 10 and 40 degrees, between 15 and 30 degrees, or substantially 20 degrees. One or each of the contact member and the support may comprise or consist of an elongate strip, which may be a substantially rectangular plate subdivided into two substantially flat regions by a bend in the plate about which the substantially flat regions are angled relative to one another. The bend may define an axis ofcurvature substantially aligned with a lengthwise direction of the strip.

The contact member may be between 1 and 10 mm thick, may be between 1.1 and mm thick, may be between 1.25 and 2mm thick, and may be substantially 1.5 mm thick. The contact mcmbcr may comprisc a plurality of supcrimposcd flcxiblc shccts, which may each be between 0.05 and 0.5 mm thick, may each be between 0.075 and 0.275 mm thick, may each be between 0.10 and 0.25 mm thick, and may each be substantially 0.10 or 0.25 mm thick. Thc number ofsupcrimposed flexible sheets may be greater than two, may be greater than five, may be between ten and 100, may be between 20 and 50, and may be between 30 and 40. The superimposed sheets may be clamped together, such as by threaded bolts. The superimposed sheets may form a compliant lip of the contact member, may be secured to the rigid plate, may be clamped to the rigid plate, such as by threaded bolts, and may be superimposed in progressively increasing sheet sizes to provide a stcppcd or tapered structure.

The resilient biasing element maybe arranged to permit a tilting displacement of a contact edge ofthc contact mcmbcr by pivoting ofthc contact mcmbcr whcn a surfacc is pressed against the contact edge. The resilience of the contact member may permit a flexural displacement of the contact edge by flexion of the contact member when a surface is pressed against the contact edge. The seal assembly and/or the resilient biasing element may be configured to permit said tilting displacement to exceed said flexural displacement when a surface is pressed against the contact edge.

The support may comprise a substantially rigid plate, may comprise a bend, may comprise a bend in an otherwise substantially flat plate, and may comprise a bend having a bend angle of between 5 and 50 degrees, between 10 and 40 degrees, between 15 and degrees, or substantially 20 degrees. The support plate may be between! and 20 mm thick, maybe between 1.5 and 10 mm thick, maybe between 2 and 5 mm thick, and may bc substantially 2.5 mm thick. Thc support plate may comprise elongate slots by which it may be adjustably fastened to a surftce in a rotary heat exchanger.

The seal assembly may comprise an elongate structure along which a plurality of said resilient biasing elements and/or said clamps are spaced, and may coiiq.nise an elongate structure along which is varied at least one physical property of the contact member, the support, the/each clamp, and/or the/each biasing element. The physical property may be varied continuously, may be varied incrementally, and may be varied substantially linearly, along the length of the seal assembly.

The at least one physical property may coi"p' ise a stilThess an&oradimensionof or a constraint applied to, the/each resilient biasing element; may comprise a stiffliess and/or natural length of; or a compression applied to, each spring; may comprise a dimension or position of the/each clamp, may comprise the tightness and/or length of each bolt, and may comprise the separation between consecutively spaced clamps/bolts and/or biasing elements/springs.

The at least one physical property may comprise a height at which a contact member is mounted, may comprise the separation of the contact edge from an axis of rotation about which the contact member is tiltable against the resilient biasing element(s), may comprise the separation between a said clamp/bolt and/or a said resilient biasing element/spring from an axis of rotation about which the contact member is tiltable against the resilient biasing elements, and may comprise the angle of a bend or curve in the contact member.

The at least one physical property may comprise a height at which the support is mounted relative to a radial plate ofa rotary heat exchanger; may comprise the separation of an edge ofthc radial platc from an axis ofrotation about which thc contact member is tihable, and may comprise the angle of a bend or curve in the support.

Thc at least onc physical property may comprise the number and/or thickness of said superimposed sheets.

According to a second aspect of the invention, there is provided a rotary heat exchanger comprising a seal assembly as described above.

The heat exchanger may be a regenerative air pre-heater tbr a furnace or a gas turbine. The seal assembly may be mounted on a radial plate ofa thermal wheel, andmay be arranged to engage in sliding contact with a sectorplate during rotation ofthe thermal wheel.

According to a third aspect of the invention, there is provided a method of flibricating a seal assembly fbr a rotary heat exchanger, the method including the steps of providing a contact member lbr lbrming a seal, a support lbr supporting the contact member, and a resilient biasing means; and clamping the contact member and support together against the resilient biasing means, to permit the contact member to pivot relative to the support between a first and a second position, and to bias the contact member towards the first position.

The resilient biasing means may comprise one or more resilient biasing elements, which may be helical springs. Clamping the contact member and support together may include the step ofpassing a threaded bolt through a respective opening in the contact member and support, may comprise the step ofpassing a threaded bolt along thc ccntrc of a helical spring, may comprise tightening the threaded bolt to compress the spring, and may comprisc tightening the threaded bolt to achieve a desired rotational stiffness opposing pivoting of the contact member relative to the support.

Thc third aspect ofthc invention may incorporatc any combination ofthe fcatures of the first and second aspects of the invention.

Dctailcd Dcscription of thc Invcntion In order that the invention may be more clearly understood, embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a plan view of part of a typical rotary heat exchanger; Figure 2 is a cross-section of a radial seal for use with such a heat exchanger; Figure 3 is a cross-section ofa radial seal according to the present invention; and Figure 4 is a cross-section ofthe seal of Figure 3 in contact with a sector plate.

A rotary regenerative heat exchanger as discussed above is s1owi iii Figure 1, in which a rotating thermal mass 1 comprises a set of baskets' 2 formed as substantially wedge-shaped blocks of a highly permeable metal honeycomb construction. The baskets 2 arc supported between vanes 3 in the form of platcs securcd to and radiating from the hub 4 ofthe rotating drum 1. A hot flue gas duct 5 and a cold air intake duct 6 are separated by a pair of sector plates 7 at one end of the drum 1 and a corresponding pair ofsector plates (not shown) at the other end ofthe drum. To ensure maximumpower conversion efficiency, the radial plates 3 should come into close proximity with the sector plates 7 to minimise air leakage from one duct to the other. However, due to non-uniform heating of the drum by hot flue gases from above and cold air from below, the radial plates 3 tend to sag downwards during extended operation of the heat exchanger, so that space is required to accommodate the distortion and so that the depth of air gaps formed between the radial plates 3 and sector plates 7 will vary considerably over time and with radial position from the hub 4.

As mentioned above, one method ofimproving efficiency ofthe heat exchanger is to provide a respective flexible seal at each of the top and bottom edges of each radial plate 3, such as the flexible seal shown in cross-section in Figure 2. The seal comprises a flexible blade 10 formed by many superposed layers 12 of thin steel sheet. The flexible blade 10 is mounted on a fixing plate 14 that is secured along an edge of the radial plate 3. The flexible blade 10 presses against the sector plate 7 in sliding contact, helping to reduce leakage between the flue duct and air intake duct. However, such a seal has been observed to wear out relatively quickly.

Furthermore, a build-up of ash from the flue gases may accumulate along the top surfaces ofthe seal, and particularly within the gap 16 that opens up between the flexible blade 10 and the fixing plate 14 when the blade is in contact with a sector plate 7. This particulate ingress impairs the flexibility of the blade and can therefore reduce its effectiveness in sealing the gap between the radial plate and sector plate, as well as potentially interfering with wear mechanisms and generally obscuring and hampering inspection and repair of the blade.

An arrangement is shown in cross-section in Figures 3 and 4 which may overcome these problems. A respective angled fixing plate 14 is secured to each of the top and bottom edges of each radial plate 3 that forms a vane of the rotating drum. A wear plate 20 is then attached to the fixing plate 14 by means of fasteners, such as threaded bolts 22, spaced along the length of the wear plate 20. A coil spring 24 is fastened against the fixing plate 14 and/or the wear plate 20 by means of the bolt 22, and a locking nut 26 is tightened on the boh to a specified level to compress the spring and control its stiffliess and/or the range ofrotational movement allowed of the wear plate.

The wear plate 20 and fixing plate 14 are each formed as an elongate strip divided into two substantially planar, rectangular regions 28, 28a, 28b by a bend 30a, 30b that runs along the length of the strip to define an axis of curvature aligned with the lengthwise direction of the strip (i.e. normal to the plane of the image as shown in Figures 3 and 4) and about which the planar regions 28, 28a, 28b are inclined relative to one another at an angle 32 of approximately 20 degrees. One ofthe flat regions 28a ofthe wear plate 20 overlaps one of the flat regions 28b of the fixing plate 14, the overlapping regions being pressed tightly together by the spring 24 to support the wear plate in a stable return position when not in contact with a sector plate (as illustrated in Figure 3) and being forced apart from one another against the resilient bias ofthe spring when the wear plate engages in sliding contact with a sector plate 7 (as illustrated in Figure 4).

The wear plate 20 canrotate about an edge 36 ofthe fixing plate 14 against which it rests, and against which it is urged by the spring 24, and can thereby tilt against the resilient bias provided bythe spring, between the first stable returnposition and a second tihed position, about a fulcrum defined by the edge 36 of the fixing plate 14 and preferably engaged with the bend 30 in the wear plate 20. Thus, the wear plate can accommodate significant variation in the depth of gaps in a similar manner to the flexible layered blade of Figure 2.

However, since the flexion is provided by the springs 24 rather thanthe flexibility of the wear plate itself, the wear plate 20 may be made of a much more hardwearing matcrial sciected to withstand cxtensive frictional contact without wearing away and/or to provide corrosion resistance to withstand the high-temperature chemical environment.

For example, the wear plate maybe fabricated from an abrasion-resistant steel such as of the type provided under the HARDOX trade mark by SSAB (Oxelosund, Sweden), or may be fabricated from a weathering steel capable of forming a stable oxide layer, such as of the type provided under the COR-TEN trade mark by United States Steel Corporation (Pittsburgh, Philadelphia, USA). Other corrosion-resistant alloys may also be appropriate, such as stainless steels (for example, duplex'super-duplex, martensitic, ferritic, or precipitation-hardened stainless steels, or austenitic/super-austenitic stainless steels such as 316-grade stainlcss steels) or nickel-based alloys such as thosc provided under the HASTELLOY trade mark by Haynes International, Inc. (Kokomo, Indiana, USA) or under the INCONELtrade mark by Special Metals Corporation (New Hartford, New York, USA). Similar alloys may be used to form the fixing plate 14.

In one embodiment, the fixing plate 14 is formed of a 2.5 mm-thick COR-TEN steel or 316-grade stainless steel, the wear plate 20 is formed of 1.5 mm-thick 316-grade stainless steel, and the springs 24 are made of a high-temperature INCONEL alloy.

Since the wear plate 20 contacts a sector plate 7 along a single contact edge 38, the wear plate as a whole may be fabricated from an alloy primarily selected for its corrosion resistance while the edge where sliding contact occurs may be speciallytreated to resist wear. For example, the tip 38 of the wear plate may be provided with a tempering, work-hardening, or solid-solution hardening treatment, coated with a film or reinforcing strip of a more wear-resistant alloy, and/or provided with a wear-resistant ceramic coating or oxidised layer.

However, to preserve the scctor plate 7 from cxccssivc wear, it may bc preferred that the wear plate tip 38 is not abrasive. Alternative wear-reducing strategies could include providing rolling bearings such as small rollers mounted to the tip of the wear plate.

As further alternatives, a flexible blade 10, such as seen in the multi-layered arrangement of Figure 2, may be secured to the end ofthc spring-biased wear plate 20 of Figures 3 and 4 to provide a compliant lip, or may replace the rigid wear plate 20 of Figures 3 and 4 altogether. In either case, the flexibility of the blade 10 provides a compliant contact surface to minimise wear of the sector plates 7 but, in contrast to the arrangement ofFigure 2, it is primarily the coil springs 24 that are responsible fbr biasing the blade against the sector plate, rather than the stiffness of the blade itself This provides an advantage over thc arrangement of Figure 2, sincc thc stiffness of the tracking coil springs may be selected to support the flexible blade against the sector plate with a relatively low contact reaction force to minimise wear to the blade tip. For a given flexible blade construction, the addition and suitable adjustment of the tracking springs can therefore improve the longevity of the blade. Conversely, even where a similar contact reaction force against the sector plate is maintained, a lesser degree of blade flexibility is required than in the arrangement of Figure 2, since the tracking movement necessary to accommodate a variable gap height is provided primarily by rotation ofthe blade under the bias of the coil springs. Thus, in comparison to the arrangement of Figure 2, a significantly more sturdy, durable, and wear-resistant flexible blade design may be used without compromising its range of movement for sealing a gap of variable height.

The flexible blade may be formed of a multiple layers of suitable corrosion-resistant and preferably wear-resistant alloy, as discussed above for the wear plate 20, such as 31 6-grade stainless steel. Layers need not necessarily be formed of the same alloy-the outermost layer or a few of the outermost layers may be formed of an alloy selected primarily for wear resistance, while ffirther layers are formed ofan alloy selected primarily for its elastic resilience and/or corrosion resistance.

In one embodiment, the blade is formed of 30-40 leaves of 0.1-0.25 mm-thick 316-grade stainless steel sheet, clamped between 1.5 mm-thick 316-grade stainless steel plates. The successive layers of steel sheet are provided in progressively increasing widths to provide a tiered or tapered blade structure similar to that illustrated in Figure 2.

The wear plate 20 of Figures 3 and 4-or the spring-biased flexible blade 10, if used instead of the rigid wear plate, as discussed above-is preferably mounted outwardly ofthe fixing plate 14 as shown, i.e. above the fixing plate in the orientation of Figures 3 and 4 (for seals mounted on top edges of the rotating radial plates), to form a canopy over the fixing plate. This provides a further advantage over the arrangement of Figure 2 in that no upward-facing ridge is provided in which ash or other debris may settle between the plates during operation of the heat exchanger. This ensures that any debris that accumulates in the system during use does not clog up moving parts of the seal or otherwise impede the movement of the spring-biased and/or flexible parts. In contrast, the arrangement of Figure 2 may become clogged with a build-up of ash over time, reducing the blade's flexural range of movement and increasing the risk of gas leakage between the ducts and consequent reduction in power plant efficiency.

It is also feasible to mount the blade 10 or wear plate 20 inwardly of the fixing plate (i.e. beneath it, for the seal mounted on a top edge of a radial plate), or to mount the blade or wear plate directly on the radial plate 3 (i.e. without the usc of a fixing plate) if space is limited, for example. Whether or not a fixing plate is provided, the seal assembly is provided with elongate slots 40 and flat washers 42 through which it is bolted to the radial plate 3 to permit convenient manual height adjustment of the seal assembly relative to the radial plate.

The simple bolted-together assembly enables the seal to be easily fitted to and removed from a rotary heat exchanger without special tools. The use of simple parts-a rigid wear plate that may be relatively simple to fabricate, and standard parts such as nuts, bolts, washers, and springs-further ensures that the seal may be quickly and conveniently fabricated and repaired. Where the wear plate is outwardly mounted onthe fixing plate or radial plate, the avoidance ofaccumulated ash/debris on the top-mounted seals helps to keep their moving parts free, reduces particulate ingress that may affect wear behaviour, and reduces the need for layers of debris to be cleaned away before the seal can be inspected or repaired. Therefore, in addition to maintaining and/or improving plant efficiency and providing a long-lasting wear-resistant seal assembly, embodiments ofthe present invention also provide many further advantages in terms of simplicity and convenience of fabrication, installation, inspection, and repair.

Due to the differential thermal expansion of the cylinder, the gaps between the radial plates and sector plates would in use be expected widen on the hot end of the cylinder and to narrow on the cold end and, on both the hot and cold ends, for this change in gap thickness to become more pronounced with radial distance from the hub. Itmay be preferable for the range of movement of the seal to progressively increase with radial distance from the hub, in order to accommodate the changes in gap size without any reduction in the efficacy of the seal. Therefore, it is envisaged that various properties of the radial seal may be varied along its length. This may be achieved by providing a number of short seals mounted in a row along an edge of a radial plate, with physical parameters of the seals being sequentially varied from one to the next along the radius.

Alternatively, a single seal or a number of shorter seals may be mounted along an edge of a radial plate with physical parameters in the/each seal being varied continuously (e.g. linearly) along its length. These parameters could include, but are not limited to: (a) the stifihess of each spring 24, the natural length of each spring, the compression ofeaeh spring as determined by the tightness ofthe respective bolt 22, the length ofeach bolt, and/or the radial separation between adjacent springs; (b) the axial height at which a wear plate 20 and/or flexible blade is mounted relative to the radial plate 3, the separation between the sliding contact edge 38 of a wear plate and/or flexible blade and the substantially radial axis of rotation about which it tilts against the spring bias, the separation between the axis of rotation 36 about which the wear plate and/or flexible blade tilts and the centre of a bolt 22 and/or coil spring 24 at which it is biased, and/or the angle of a bend or curve 30a in the wear plate; e) the axial height at which a fixing plate 14 is mounted relative to the radial plate 3, the separation between the axis ofrotation 36 about which the wear plate tilts and the top or bottom edge ofthe radial plate 3, and/or the angle of a bend or curve 30b in the fixing plate; and/or (d) the stiffness of a flexible blade, including the number and/orthicknessof layers of sheet metal from which it is formed.

In the above description, it is assumed that the axial direction of a rotary heat exchanger is aligned with a vertical axis. Where this is not the case, directions and locations described above as up', down', top', etc., may be relative totheorientationof the heat exchanger, rather than absolute, as will be apparent to the skilled reader.

The above embodiments are described byway ofexample only. Many variations are possible without departing from the scope ofthe invention as defined in the appended claims.

Claims

CLAIMS1. A seal assembly fbr a rotary heat exchanger, the assembly comprising a support, a contact member movably mounted on the support and pivotable relative to the support between a first and a second position, and one or more resilient biasing elements arranged to urge the contact member towards the first position.
2. A seal assembly according to claim I wherein the support and contact member are clamped together, against the one or more resilient biasing elements, by a clamp.
3. A seal assembly according to claim 2 wherein the clamp comprises a threaded bolt.
4. A seal assembly according to claim 2 or 3 comprising a plurality of said clamps spaced along a length of the seat assembly.
5. A seal assembly according to any one of claims2to 4 whereinthe one ormore resilient biasing elements comprise one or more helical springs and wherein the or cach clamp comprises a thrcaded bolt about which a respective helical spring is coiled.
6. A seal assembly according to any one of claims I to 4 wherein the one or more resilient biasing elements comprise one or morc helical springs spaced along a length of the seal assembly.
7. A seal assembly according to claimS or 6 wherein the spacing between adjacent springs increases evenly along a length of the seal assembly.
8. A seal assembly according to any preceding claim wherein the contact member is tiltably secured to the support.
9. A seal assembly according to any preceding claim wherein the contact member is pivotable about an edge of the support.
10. A seal assembly according to claim 9 wherein the contact member rests against the edge of the support about which it is pivotable.
11. A seal assembly according to claim 9 or 10 wherein the contact member is urged against said edge of the support by the resiliently biased element.
12. A seal assembly according to any preceding claim wherein the contact member comprises a recess into which said edge of the support is engageable.
13. A seal assembly according to any preceding claim wherein the contact member forms a canopy over the support.
14. A seal assembly according to any preceding claim wherein the contact member and the support are each fabricated from an abrasion-resistant andior conosion-resistant alloy.
15. A seal assembly according to any preceding claim wherein the contact member is between 1 and 10 mm thick.
16. A seal assembly according to any preceding claim wherein the contact member comprises a bend in an otherwise substantially flat plate.
17. A seal assembly according to any preceding claim wherein the contact member comprises a bend having a bend angle of between 5 and 50 degrees.
18. A seal assembly according to any preceding claim wherein the contact member comprises a plurality of superimposed flexible sheets.
19. A seal assembly according to any preceding claim arranged to permit displacement of a contact edge of the contact member through tilting of the contact member when a surface is pressed against the contact edge, wherein said displacement through tilting exceeds any flexural displaccmcnt of the contact edge arising from flexion of the contact member under said pressure of the surface against the contact edge.
20. A seal assembly according to any preceding claim wherein at least one mechanical or geometric parameter of a part of the assembly is varied evenly along a length of the seal assembly.
21. A seal assembly substantially as herein described with reference to the appended figures.
22. A rotary heat exchanger comprising a seal assembly according to any preceding claim.
23. A rotary heat exchanger according to claim 22 wherein the seal assembly is mounted on a radial plate of a thermal wheel and arranged to engage the contact member in sliding contact with a sector plate of the heat exchanger during rotation of the thermal wheel.
24. A rotary heat exchanger substantially as herein described with reference to the appended figures.
25. A method of fabricating a seal assembly for a rotary heat exchanger, the method including the steps of: providing a contact member for forming a seal, a support for supporting the contact member, and a resilient biasing means; and clamping the contact member and support together agaiiist the resilient biasing means, to permit the contact member to pivot relative to the support between a fir st and a second position, and to bias the contact member towards the first position.
26. A fabrication method according to claim 25 wherein clamping the contact member and support together includes providing a threaded bolt and a helical spring and at least one of the steps of: passing the bolt through a respective opening in each of the contact member and the support; passing the bolt through the centre of the spring; and tightening the bolt to compress the spring.
27. A fabrication method according to claim 25 or 26 comprising the step of adjusting a clamping means to control a resistive force with which pivoting ofthe contact member is opposed by the resilient biasing means.
28. A fabrication method according to claim 27 wherein the adjustment comprises tightening a threaded boh to compress a spring.
29. A method of fabricating a seal assembly for a rotary heat exchanger substantially as herein described with reference to the appended figures.