WO2011092316A2

WO2011092316A2 - A heat exchange unit

Info

Publication number: WO2011092316A2
Application number: PCT/EP2011/051270
Authority: WO
Inventors: Mark Platts; John Stephen Williams
Original assignee: Tanjung Citech Uk Limited
Priority date: 2010-01-29
Filing date: 2011-01-28
Publication date: 2011-08-04
Also published as: GB201001475D0; WO2011092316A3; GB2477316A

Abstract

A heat exchange unit for hot gas heat recovery comprising: a heat exchange duct housing a heat exchange array; a bypass duct; an arrangement configured to cause variable amounts of hot gas to flow through the bypass duct and the heat exchange duct; and a barrier intermediate the heat exchange duct and bypass duct and including a cavity through which a fluid may be introduced so as to extract heat that would otherwise transfer from the bypass duct to the heat exchange duct and/or vice versa.

Description

A Heat Exchange Unit

The present application relates to a heat exchange unit. More particularly, the present application relates to a heat exchange unit incorporating a seal on a bypass valve thereof. The present application further relates to a heat exchange unit incorporating a cavity into which fluid may be introduced.

It is known from EP1088194 granted to a predecessor company of the present applicant for the general layout of a heat exchange unit to comprise an annular heat exchange duct with an array of heat exchange pipes located therein and a bypass duct located concentrically within the heat exchange duct. A cylindrical sleeve valve is located between the two ducts and is moveable along its axis to switch the flow of exhaust gas between a duty mode, in which the gas flows through the heat exchange duct and a bypass mode which, as the name suggests, causes the gas to flow through the bypass duct and therefore not to transfer heat to the array of heat exchange pipes. When in the bypass mode, the lower edge of the sleeve contacts a flat metal surface to form a "knife edge" seal.

Such an arrangement prevents around 99% of the exhaust gas from flowing through the heat exchange duct when not in duty mode. The remaining approximately 1% of the exhaust gas flows through the heat exchange duct and transfers some unwanted heat to the array of heat exchange pipes. If fluid is not be circulated within the pipes when the heat exchange unit is not in duty mode (e.g. during maintenance), this heat is not dissipated and can lead to overheating or boiling absent other measures. The current solution to this problem is to provide a "dump cooler" through which the otherwise stationary water, water glycol or oil is circulated to keep it cool. This requires additional plant, and therefore increases cost.

The arrangement of EP1088194 additionally permits a degree of unwanted heat transfer between the heat exchange duct and the bypass duct via the wall of the sleeve. Unwanted heat may therefore be transferred to the array of heat exchange pipes when exhaust gas is flowing through the bypass duct. Again, this can lead to overheating or boiling as described above, and contributes to the requirement for a dump cooler.

The present invention seeks to overcome, or at least mitigate, the problems of the prior art. According to the present invention there is provided a heat exchange unit for hot gas heat recovery comprising:

a heat exchange duct housing a heat exchange array;

a bypass duct;

an arrangement configured to cause variable amounts of hot gas to flow through the bypass duct and the heat exchange duct; and

a barrier intermediate the heat exchange duct and bypass duct and including a cavity through which a fluid may be introduced so as to extract heat that would otherwise transfer from the bypass duct to the heat exchange duct and/or vice versa.

The cavity, and the fluid within the cavity, provide a layer of insulation between the heat exchange duct and the bypass duct. When the heat exchange unit is in bypass mode the cavity and the fluid within the cavity prevent unwanted heat transfer from hot gas passing through the bypass duct to the heat exchange array within the heat exchange duct.

The arrangement may advantageously comprise a valve. The valve provides a simple means of switching between bypass and heat exchange ducts.

The barrier may be integral to the arrangement, and may further include a layer of insulating material. The insulating material provides further insulation against heat transfer and attenuates noise caused by operation of the heat exchange unit.

The cavity may have a fluid inlet and a fluid outlet. The fluid outlet may be brought into fluid flow communication with the hot gas flow, at least when a proportion of the hot gas is caused to flow through the heat exchange duct, and may advantageously be configured to provide a curtain of fluid to inhibit a backwash of hot gas into the heat exchange duct.

Alternatively the fluid outlet may be external to the heat exchange duct and the bypass duct. The heat exchanger may further comprise a pump to pump fluid into the fluid flow path via the fluid inlet, which may be closeable, thus advantageously preventing fluid entering the cavity when the heat exchanger is not in bypass mode. The inlet may include a seal configured to inhibit hot gas to flow from the bypass duct to the heat exchange duct when the hot gas is configured to flow through the bypass duct fluid flow, thus minimising unwanted heat transfer to the heat exchange array. The seal may be a labyrinth seal, which further improves sealing between the bypass duct and heat exchange duct.

The fluid may be a gas, preferably air. Alternatively, the fluid may be a liquid, preferably water. Both air and water are effective coolants that are easily obtained and easily re-used or disposed of.

The heat exchange duct and the bypass duct may be concentrically and compactly arranged, and the arrangement may be a sleeve valve, in which case the cavity may be in the form of an annulus within the sleeve valve. The sleeve valve is a simple and effective means of switching flow between the bypass and heat exchange ducts. An annular cavity works well in a sleeve valve, providing efficient and effective insulation between ducts. The fluid inlet may comprise a series of apertures in the barrier. Alternatively, the fluid inlet may comprise at least one slot in the barrier. An inlet in the form of a series of apertures limits the flow of unwanted fluid into the cavity when the unit is not in bypass mode.

The arrangement may be a damper arrangement, or may be a rotating damper valve.

According to a second aspect of the present invention there is provided a heat exchange unit for hot gas heat recovery comprising a heat exchange duct concentrically arranged with a bypass duct, and a bypass valve configured to cause variable amounts of hot gas to flow through the bypass duct instead of the heat exchange duct dependent upon the position thereof, the heat exchange unit comprising a seal arrangement to inhibit the passage of gas through the heat exchange duct when the valve is in a bypass position; the seal arrangement comprising at least one of a brush seal, a compression seal and a labyrinth seal. The bypass valve is preferably a concentric sleeve valve and the brush seal is preferably annular. The seal arrangement may comprise a brush seal mounted on a valve seat at the base of the sleeve valve. The brush seal may comprise high-temperature ceramic fibres and/or a U-shaped fibre mount. The brush seal may further comprise cooling fins, a cooling fan and/or liquid cooling. The brush seal fibres may be substantially horizontal, or may be inclined at an angle of up to 45° to the horizontal. The sleeve valve may be vertical and use a labyrinth seal. The bypass valve may be a rotary valve with a brush seal arrangement rather than a concentric sleeve valve.

Embodiments of the present invention will now be described with reference to the accompanying drawings in which:

FIGURE 1 is a vertical cross-sectional view through a known heat exchange unit in a duty condition; FIGURE 2 is a similar vertical cross-sectional view of the heat exchange unit of figure 1 in a bypass condition;

FIGURE 3 is a detail view of the circled portion of the vertical cross section of figure 2 incorporating an embodiment of the present invention;

FIGURE 4 is a section of a brush seal according to the embodiment of figure 3;

FIGURE 5 is a detail view of a vertical cross section showing the compression seal of the embodiment of figure 3;

FIGURE 6 is a detail view of a vertical cross section showing a labyrinth seal according to a further embodiment of the present invention;

FIGURE 7 is a vertical cross-sectional view through a heat exchange unit according to a third embodiment of the present invention;

FIGURE 8 is a plan view of the underside of a sleeve valve according to the embodiment of figure 7; and FIGURES 9 and 10 are a detail cross-sectional views of a fourth and fifth embodiment of the present invention.

A heat exchange unit shown in Figure 1 is an exhaust gas heat recovery unit 10 suitable for use in, for example, the offshore oil and gas industries. The circuit may also be used, with suitable adaptations, as a once-through steam generator (OTSG). Heat exchange units used in the offshore oil and gas industries are generally cylindrical in shape and are typically used with their major axis orientated vertically. As indicated in Figure 1, such a unit is intended to receive hot gas 11 through gas inlet duct 12 from a gas turbine engine or other type of engine (not shown), cool the gas by heat exchange with a fluid circulating in a heat exchange array 13, and pass the cooled gas 15 onwards for venting from a gas exit duct 18. Heat exchange fluid is passed in and out of the heat exchange array 13 through inlet and outlet manifolds (not shown) and can be used as a process fluid or for generating steam or the like. The heat exchange unit 10 comprises a generally cylindrical outer casing or shell 14, containing an annular heat exchange array 13, an internal bypass valve in the form of a sleeve valve 16 and a valve plug 27. The shell 14 and sleeve valve 16 define a duty passage 23 in which the heat exchange array 13 is located. The interior of the sleeve valve 16 defines a bypass passage 17. The sleeve valve 16 is slidable axially within the heat exchange array between two extreme positions.

With reference to figures 3 and 4, an annular brush seal 19 comprising a U-shaped mount 20 is mounted on a valve seat 22 on the inner surface of the shell 14. The fibres 28 of the brush seal 18 are aligned substantially horizontally, the ends of the fibres being substantially vertically aligned.

In Figures 2 and 3, the sleeve valve 16 is shown at its lower extreme position, so that the valve sleeve duty passage 23 is effectively closed. The brush seal 19 inhibits flow of the exhaust gas through the duty passage 23 by forming a seal with the radially external surface of the sleeve valve 16. Figure 4 shows the brush seal in more detail. The brush seal 18 is formed in this embodiment from multiple high temperature ceramic fibres e.g. aluminoborosilicate fibres such as Nextel fibres produced by DuPont. Advantageously, by using a brush seal a degree of tolerance in the position of the sleeve can be accommodated whilst seal integrity is maintained.

In order to ensure substantially complete sealing of the duty passage, there is in this embodiment, provided a compression seal 24 in a groove 26 of the valve seat 22, as shown in figure 5. The compression seal is formed in this embodiment from a high temperature resistant material, in the form of a multi-layer compressive gasket or similar. When in the lower extreme position, the sleeve valve 16 compresses the seal 24 so that it conforms around the lower tip of the sleeve and enhances the sealing.

Figure 6 shows an alternative embodiment of the present invention where a labyrinth seal 29 is used to inhibit flow of the exhaust gas through the duty passage. In this case, the sleeve valve 16 is inserted into a groove 30 in the valve seat 22, thus obstructing the flow path of the exhaust gas.

A brush seal, compression seal or labyrinth seal could also be used as an alternative seal for a heat exchange unit such as that of figure 4 of WO2007/0804011 (Kanfa-Tec AS), or that of figures 1 or 6 of WO2010/013053 (Heat Recovery Solutions Limited) where instead of a sleeve valve a rotating damper valve is used to regulate a bypass, or other valve arrangements. The seals shown in figure 4 of that application could, for example, be replaced with substantially vertical brush seals.

In alternative embodiments (not shown) one or more of the brush 18, compression 24 and labyrinth seals may be used alone or in combination. The angle of the brush seal fibres may be altered to be closer or further from that of the valve sleeve up to approximately 45° from the horizontal. The cross-section of the fibres may be circular, square, hexagonal or some other shape. The brush seal fibres may be formed from other high temperature material, such as cobalt or nickel alloy, or a polymeric material e.g. synthetic aromatic polyamide polymer such as Nomex produced by DuPont. The angle created by the ends of the brush seal fibres may be other than vertical. The lower end of the sleeve valve 16 may be flared outwards rather than inwards, or may be vertical as in figure 6. Alternative higher temperature resistant compression seals may be used, such as ceramic fibre mats, or knitted wire mesh pads. To provide a good mating surface, the tip of the sleeve 16 may be stainless steel. In other embodiments, an annular flexible stainless steel facing may be provided on the valve seat 22, configured so that the descending valve sleeve deflects the facing before coming into contact with the compression seal, or so that the facing is sandwiched between the tip and the compression seal, but nevertheless can flex or give to achieve a good seal.

In certain embodiments a suitable method of passive or active cooling may be used in order to keep the brush seal within working temperatures. For example, cooling fins may be incorporated into the seal mount 20. A fan may be used to air-cool the seal, and/or liquid cooling by means of a pump may be used.

The seal arrangement of the present invention provides a number of advantages. Reduction of unwanted gas exhaust escaping to the duty passage leads to a reduced likelihood of local boiling of fluid in the array during part plant shut down. The brush and compression seals are of a simple circular design making installation straightforward. The positioning of the brush seal at the base of the shell means that it is away from direct hot gas flow, and allows it to be cooled by heat transfer to the shell. Similarly, the positioning of the compression seal in a groove removes it from direct hot gas flow. The seals may have sacrificial wear characteristics and yet maintain an effective seal over their working lives.

Figures 7 and 8 show a third embodiment of the present invention wherein features which are substantially the same as those of the previous embodiments are given corresponding reference numbers with the additional prefix "1".

Figure 7 shows an exhaust gas heat recovery unit similar to that of figures 1 and 2. As in the previous embodiment, the unit 110 comprises a shell 114 containing an annular heat exchange array 113, an internal bypass valve in the form of a sleeve valve 116 and a valve plug 127. Hot gas 111 enters the unit 110 via a gas inlet duct 112. The gas 111 passes through the unit 110 via either a duty passage 123 (so passing through the heat exchange array 113) or a bypass passage 117, or a combination of the two dependent upon the position of the sleeve valve. The sleeve valve 116 is slidable axially between two extreme positions, thus controlling gas flow through the duty passage 123 and bypass passage 117. Figure 7 shows the sleeve valve 116 at its lower extreme position, closing off the upstream end of the duty passage 123 and allowing hot gas 111 to flow through the bypass passage 117. When in its lower extreme position, the sleeve valve 116 contacts a valve seat 122 on the shell 114, forming a knife-edge seal 146 that inhibits the flow of hot gas 111 into the duty passage 123.

In this embodiment, the sleeve valve 116 includes a barrier 132 comprising an inner wall 133 and an outer wall 135 which are spaced apart to define an internal annular cavity 134. The cavity 134 has an inlet 136 at the lower end of the sleeve valve 116 and an outlet 138 at the upper end of the sleeve valve 116. In this embodiment the inlet 136 takes the form of a series of apertures 140 (shown in figure 8) equidistantly spaced around the sleeve valve 116. In alternative embodiments the inlet 136 may be in the form of a series of elongate curved slots around the lower end of the sleeve valve 116, or a single annular aperture. The cavity 134 is configured to allow ambient air to be pumped into the inlet 136 (or drawn through as a result of the motion of the hot gas 111).

The air passes through the cavity 134 and leaves the cavity 134 via the outlet 138. In this embodiment, the outlet 138 is positioned in the outer wall 135 at the upper end of the sleeve valve 116, facing radially outward. In this embodiment, the outlet is a single annular aperture.

The cavity 134 is preferably provided with baffles (not shown) that act to evenly distribute the airflow throughout the cavity and also connect the inner 133 and outer 135 walls of the sleeve 116 and enhance its structural stability. In embodiments where a single continuous aperture, or a series of curved slots with minimal spacing therebetween are provided, the baffles may not be needed.

The valve seat 122 defines a series of apertures 142 aligned with each of the inlets 136. The apertures 142 provide access to the inlet 136, allowing air to be pumped into the cavity 134 when the sleeve valve 116 is in its lower extreme position. A pump (not shown) pumps the air to the apertures via a manifold (not shown) and pipes 137.

In use, when hot gas 111 is flowing through the bypass passage 117 it is desirable that heat transfer between the bypass passage 117 and the duty passage 123 is limited so that temperature increase of the liquid heat exchange array 113 is prevented or minimised. Ambient air 144 is pumped into the cavity 134 at the inlets 136. The air 144 provides insulation between the bypass and the duty passage and so minimises the transfer of heat by radiation or conduction from the hot gas 111 to the heat exchange array 113. "Dump cooler" requirements and the associated costs are thus limited.

With the sleeve valve 116 in its lower extreme position the, outlet 138 leads to the air 144 being directed radially outwardly towards the shell 114 at the downstream end of the duty passage. At this location the duty passage 123 and the bypass passage 117 merge back together, allowing air 144 passing through the cavity 134 to rejoin the gas 111 flowing out of the downstream end of the bypass passage 117. This advantageously creates an air curtain directed across the downstream end of the duty passage 123 which limits backwash of the gas 111 into duty passage 123 and therefore the heat exchanger array 113, further limiting unwanted heating of the heat exchange fluid therein..

A further advantage is provided by pumping ambient air 144 into the inlet 136. As described above, it is desirable to achieve substantially complete sealing of the duty passage from the bypass passage 117 at the valve seat 122 when in bypass mode. Pumping air 144 into the inlet 136 creates positive pressure at the seal 146, thereby inhibiting the flow of hot gas 111 from the bypass passage 117 into the duty passage 123.

In a further embodiment, shown in figure 9, a double labyrinth seal 149 is provided at the valve seat 122 by virtue of the interface of the inner and outer walls 133 and 135 and corresponding recesses in the valve seat, in order to further improve sealing between the bypass passage 117 and the duty passage 123.

Figure 10 shows a further embodiment having an alternative seal 150 where the lower end of the sleeve valve is V-shaped and fits into a corresponding V-shaped recess in the valve seat 122. The inlet is provided as a slot along the apex of the V in this embodiment. In other embodiments, the inlet may be provided on the outer face of the V. One advantage of the V- shape may be to minimise the hot gas passing through the cavity when the sleeve is in the duty (upper) position. In alternative embodiments, compression seals or brush seals of the type shown in Figures 4 and 5 could be used.

Other knock-on benefits of these aspects of the present invention include the possibility of allowing a reduced minimum flow of fluid through the coils of the heat exchange array to be specified to avoid overheating during bypass. A reduced minimum flow through the heat exchange array, and corresponding increased ratio between minimum and maximum flow through the array is beneficial for application with respect to pumping requirements. The bulk of the air 144 pumped into the cavity 134 exits the unit 110 through the gas exit duct (not shown) so does not come into contact with the heat exchange array. Contamination issues are thus minimised.

In further embodiments, the barrier 132 may include a layer of insulating material/fibre (not shown) for noise attenuation. In this embodiment, a third wall, and suitable spacers may separate the insulation from the cavity for the air. The air may be cooled below ambient temperature before entering the cavity. Alternative gas or liquid coolants may be used in the cavity in place of air, such as water. In embodiments where a liquid coolant is used, this would be collected at the outlet externally of the ducts rather than entering the hot gas stream. The inlet 136 and/or outlet 138 may be closeable in duty mode to prevent unwanted fluid entering or passing through the cavity 134. In a further variant, the pipes 137 may also act as supports to raise and lower the sleeve to move between bypass and duty positions. In this embodiment a suitable lift mechanism (not shown - e.g. hydraulic rams) may be provided. Although described in relation to a sleeve valve used with concentric bypass and duty passages, the barrier and cavity may be adapted for use with alternative heat exchange units, such as those disclosed in WO2007/0804011 (Kanfa-Tec AS) or WO2010/013053 (Heat Recovery Solutions Limited) and some, if not all, benefits described above may be achieved.. For example, a cavity through which air can be pumped could be integrated within a rotary damper valve, or could be provided between two side -by- side (rather than concentrically arranged) bypass and duty passages, or provided between a concentric arrangement where the bypass passage is radially outside the duty passage.

Claims

1. A heat exchange unit for hot gas heat recovery comprising:

a heat exchange duct housing a heat exchange array;

a bypass duct;

2. A heat exchange unit according to claim 1 wherein the arrangement comprises a valve.

3. A heat exchange unit according to claim 1 or claim 2 wherein the barrier is integral to the arrangement.

4. A heat exchange unit according to any preceding claim wherein the barrier further includes an layer of insulating material.

5. A heat exchange unit according to any preceding claim wherein the cavity has a fluid inlet and a fluid outlet.

6. A heat exchange unit according to claim 5 wherein the fluid outlet may be brought into fluid flow communication with the hot gas flow, at least when a proportion of the hot gas is caused to flow through the heat exchange duct.

7. A heat exchange unit according to claim 6 wherein the fluid outlet is configured to provide a curtain of fluid to inhibit a backwash of hot gas into the heat exchange duct.

8. A heat exchange unit according to claim 5 wherein the outlet is external to the heat exchange duct and the bypass duct.

9. A heat exchange unit according to any one of claims 5 to 8 further comprising a pump to pump fluid into the fluid flow path via the fluid inlet.

10. A heat exchange unit according to any one of claims 5 to 9 wherein the inlet is arranged to be closeable.

11. A heat exchange unit according to any one of claims 5 to 9 wherein the flow path inlet includes a seal configured to inhibit hot gas to flow from the bypass duct to the heat exchange duct when the hot gas is configured to flow through the bypass duct .

12. A heat exchange unit according to claim 11 wherein the seal is a labyrinth seal.

13. A heat exchange unit according to any preceding claim wherein the fluid is a gas, preferably air.

14. A heat exchange unit according to any one of claims 1 to 12 wherein the fluid is a liquid, preferably water.

15. A heat exchange unit according to any preceding claim wherein the heat exchange duct and the bypass duct are concentrically arranged.

16. A heat exchange unit according to claim 15 wherein the arrangement is a sleeve valve.

17. A heat exchange unit according to claim 16 wherein the cavity is in the form of an annulus within the sleeve valve.

18. A heat exchange unit according to any one of claims 5 to 17 wherein the fluid inlet comprises a series of apertures in the barrier.

19. A heat exchange unit according to any one of claims 5 to 18 wherein the fluid inlet comprises at least one slot in the barrier.

20. A heat exchange unit according to claim 15 wherein the arrangement is a damper arrangement.

21. A heat exchange unit according to claim 15 wherein the arrangement is a rotating damper valve.

22. A heat exchange unit for hot gas heat recovery comprising a heat exchange duct concentrically arranged with a bypass duct, and a bypass valve configured to cause variable amounts of hot gas to flow through the bypass duct instead of the heat exchange duct dependent upon the position thereof, the heat exchange unit comprising a seal arrangement to inhibit the passage of gas through the heat exchange duct when the valve is in a bypass position; the seal arrangement comprising at least one of a brush seal, a compression seal and a labyrinth seal.

23. A heat exchange unit according to claim 22 wherein said bypass valve is a concentric sleeve valve.

24. A heat exchange unit according to claim 23 wherein said brush seal is annular.

25. A heat exchange unit according to claim 23 or claim 24 wherein the seal arrangement comprises a brush seal mounted on a valve seat at the base of the sleeve valve.

26. A heat exchange unit according to claim 25 wherein the brush seal is located radially outboard of the sleeve valve.

27. A heat exchange unit according to any one of claims 22 to 26 wherein the brush seal comprises high-temperature resistant ceramic fibres or metallic fibres.

28. A heat exchange unit according to any one of claims 22 to 27 wherein the brush seal comprises a U-shaped fibre mount.

29. A heat exchange unit according to any one of claims 22 to 28 wherein the brush seal further comprises cooling fins.

30. A heat exchange unit according to any one of claims 22 to 29 further comprising a fan configured to cool the brush seal.

31. A heat exchange unit according to any one of claims 22 to 30 further comprising a liquid cooling system configured to cool the brush seal.

32. A heat exchange unit according to any one of claims 22 to 31 wherein the brush seal fibres are substantially horizontal.

33. A heat exchange unit according to any one of claims 22 to 32 wherein the brush seal fibres are inclined at an angle of up to approximately 45° to the horizontal.

34. A heat exchange unit according to any one of claims 22 to 33 wherein the sleeve valve is substantially vertical and the seal arrangement comprises a labyrinth seal.

35. A heat exchange unit according to any one of claims 22 to 34 wherein the seal arrangement comprises a compression seal.

36. A heat exchange unit according to claim 35 further comprising an annular stainless steel facing mounted intermediate the compression seal and sleeve.

37. A heat exchange unit according to claim 22 wherein said bypass valve is a rotary valve.