GB2399396A - Bypass valve for a recuperator - Google Patents

Abstract

A bypass valve 100 for a recuperator 50 is situated in a duct 70 that surrounds the recuperator, and may be adapted to open or close an opening of the recuperator to allow a fluid to bypass or enter, respectively. The fluid used may be the exhaust gases from a turbine 20, which may exit via a low angle diffuser 25, and the recuperator, which may be of an annular type, can be mounted around the diffuser. The recuperator comprises a heat exchanger 60, which in turn features cold 62 and hot 64 sides. In use, fluid from the turbine enters the hot side, in order to heat compressor delivery air in the cold side. The valve 100 may be a poppet valve with a conical face 114, and furthermore may features a domed rear surface 58. The valve may move parallel to the plane of the duct, to open or close the recuperator opening.

Description

A BYPASS VALVE

The present invention relates to a bypass valve for a recuperator, and more particularly to a bypass valve for enabling exhaust gas from a turbine to bypass a recuperator.

Bypass valves are generally used in ducting or pipe systems for diverting a fluid flow from a first path to a second path in order to bypass a certain part of the first path. For example, bypass valves are used in gas turbine engines and micro-turbines for diverting turbine exhaust gas flow past a recuperator and directly to a downstream system.

Recuperators are commonly used with gas turbine engines/micro turbines for harnessing the hot exhaust gases from a turbine and passing them through a heat exchanger for heating up cooler compressor delivery air prior to delivery of the air into a combustor.

In a typical prior art gas turbine engine and recuperator arrangement, turbine exhaust gas is ducted to a valve, which typically comprises a casing having one inlet and two outlets, and a valve member for controlling the amount of flow exiting the valve through each outlet. One of the outlets is ducted to the recuperator for feeding of the exhaust gas to the recuperator.

Upon exiting the recuperator, the exhaust gas is usually ducted to a downstream system or to an exhaust stack. However, it is sometimes necessary to bypass the recuperator so that the hot exhaust gas is fed directly to a downstream system. In this case the valve member can be adjusted so that a portion of the exhaust gas exits the valve through the second outlet, which is ducted directly to the downstream system.

The bypass valve of a typical prior art system such as this comprises a rectangular casing having a circular inlet and two circular outlets to the ducting, and a flap member located inside of the casing for controlling the proportions of flow exiting the valve at each outlet. The flap member is adjusted to increase or decrease the amount of the gas that is bypassed past the recuperator. The prior art bypass valves can be inefficient at transporting the gas flow to the outlet ducts, as the gas flow can be disturbed leading to turbulence, pressure loss and acoustic noise with a resultant system energy loss. In addition, the ratio of the valve displacement to flow distribution is non linear and difficult to predict at varying operating conditions.

The turbine/recuperator system of the prior art can also suffer from heat loss from the recuperator unless additional insulation is added around the recuperator to prevent the loss. A cold or cool wall duct is commonly used around engine casings and heat exchangers. Air inside a cool wall duct insulates the engine casing/heat exchanger.

Another known recuperator comprises an annular recuperator having no variable valve.

Thus, it is an object of the present invention to overcome the problems 1 S associated with the prior art in a simple but effective manner.

According to the present invention, there is provided a bypass valve for enabling a fluid to bypass a recuperator, whereby the recuperator is substantially enclosed in a duct and whereby the bypass valve is also situated in the duct. This novel arrangement has several advantages. Firstly, no additional ducting is required to connect the bypass valve to the recuperator. In situating both the recuperator and the valve inside an external duct, the need for external components between the recuperator and engine is reduced. A separate valve casing is not necessary. This minimises efficiency losses due to duct connections or to a bulky valve casing. Furthermore, the external duct provides an escape pathway for the fluid upon flowing through the bypass valve. The external duct may have a lower surface temperature than when the recuperator is operated in a fully recuperated mode without said duct, reducing the requirement for additional thermal insulation.

The fluid to be bypassed is preferably the exhaust gas from a turbine.

Turbine exhaust gas is at a high temperature as it leaves the turbine and is ideal for use in other systems, for example a boiler, once it has been diverted away from the recuperator.

The valve may be adapted to open or close an opening in a wall of the recuperator. The opening is preferably directly downstream of the turbine exhaust. This configuration helps to minimise losses. The valve may have at least an open configuration in which gas flows through the valve and away from the recuperator, and a closed configuration in which all of the gas exiting the turbine flows toward the recuperator. Here, the 'open' configuration may be 90% and above open, whilst the 'closed' configuration may be 90% and above closed. Thus, with the valve in the open configuration, a substantial portion of the exhaust air is diverted away from the recuperator, allowing the recuperator to cool down if necessary. However, if substantially all of the gas is required to heat up the compressor delivery air, the valve can remain closed.

The valve may be variably openable in proportion to an external demand signal between the open and closed configuration so as to control the amount of exhaust gas flowing through the valve and thus bypassing the recuperator.

Thus at any one time, a pre-determined portion of the exhaust gas can exit the recuperator through the valve whilst the remainder can flow to the recuperator heat exchanger.

The bypass valve is preferably adapted to open up or close over an opening in the recuperator wall by engagement with a periphery of the opening itself. This not only helps to reduce flow transportation losses when the valve is open but also allows the valve to be configured to produce a smooth and aerodynamic flow through the recuperator when the valve is closed.

The bypass valve may enable exhaust gas to be diverted to a downstream system. Thus the gas may be utilised in a separate apparatus or component such as to heat water in a boiler.

The recuperator is preferably an annular recuperator, allowing a compact arrangement of the turbine exhaust, recuperator, external duct and bypass valve. However, the recuperator could also be a box recuperator. The valve is preferably a poppet valve. A poppet valve is easily installed in the duct S so that its valve member is oriented in a plane substantially parallel to the plane of the duct.

According to another aspect of the invention, the gas to be bypassed may be compressor delivery air. The air may bypass the recuperator through the bypass valve and directly into the combustor. Used in this mode, the recuperator core can be more rapidly cooled during an engine rundown and post-operation air purging process.

According to a further aspect of the invention, a gas turbine engine comprising a turbine, compressor and combustor also includes a bypass valve according to the first aspect of the invention.

Another aspect of the invention comprises a recuperator system having a recuperator, a duct substantially enclosing the recuperator and a bypass valve located in the duct.

The present invention will now be explained in more detail in the following non-limiting description of a preferred embodiment and with reference to the accompanying drawings, in which: Fig. 1 is a schematic of a gas turbine engine and recuperator arrangement according to a preferred embodiment of the invention; Fig.2 is a schematic of a section of an embodiment of a bypass valve for a recuperator according to the invention; and Fig.3 is a schematic of a gas turbine engine and a recuperator arrangement according to a second embodiment of the invention.

Fig.1 shows a gas turbine engine 1 and recuperator system 5 with recuperator 50, duct 70 and bypass valve 100. The gas turbine engine comprises a compressor 10, turbine 20 and combustor 30. During normal operation of the gas turbine engine, compressed air exits compressor 10 through duct 40 and into recuperator 50. The recuperator 50 includes a heat exchanger 60. Compressor delivery air is fed to the "cold" side of the heat exchanger 60 where it is heated. Upon exiting the recuperator 50, the compressor delivery air is fed into combustor 30.

Turbine 20 is mounted on the same shaft as compressor 10, for driving thereof. Fig.2 shows a part of turbine 20. The exhaust 25 of turbine 20 comprises a long, low angle diffuser having a bell-mouth exit 27. Surrounding the exhaust diffuser 25 is the recuperator 50. Recuperator 50 is an annular recuperator having an annular cross-section and an axial centreline, shown in Fig. 2 as line C-C. The recuperator 50 has an outer wall 52, inner wall 54, front face 56 and rear face 58. Between the inner wall 54 and outer wall 52 lies heat exchanger 60, extending substantially the length of the outer wall 52 and the inner wall 54. Front face 56 is generally flat, and is joined to outer wall 52.

Rear face 58 is rounded, creating a low dome shape extending outwards of the recuperator 50.

The exhaust diffuser 25 of turbine 20 extends through the centre of the annular recuperator 50 such that its bell-mouth exit 27 lies proximate to the domed rear face 58 of the recuperator 50. The bell-mouth exit 27 blends with a U-turn radius into inner wall 54 of recuperator 50.

The heat exchanger 60 of recuperator 50 comprises a "cold" side 62 and a "hot" side 64 (schematically shown in Fig.2). Compressor delivery air can enter the cold side 62 of heat exchanger 60 according to the flow path as shown in Fig.2 in dotted lines. The exit of the cold side of the heat exchanger 60 is via an opening in inner wall 54, which exits into the internal space between inner wall 54 and turbine exhaust diffuser 25 for delivery to the combustor 30.

External duct 70 surrounds the recuperator 50. The external duct 70 is essentially a casing having a substantially rounded cross-section. It is preferably a 'cool wall' duct of a type suitable for providing insulation of the recuperator. The duct 70 extends from upstream of the recuperator 50, front face 56 to beyond its rear face 58. The duct 70 has a front face 72, sidewall 74, rear face 76 and a neck portion 78. The neck portion 78 is substantially narrower than the main body of the duct 70 and affixes to a casing that surrounds the components of gas turbine engine 1. Front face 76 of external duct 70 is domed, following the curvature of rear face 58 of recuperator 50.

Attached to a portion of sidewall 74 of external duct 70 is an exit 90 to either an exhaust stack or to another system or systems 80 (shown schematically only).

The bypass valve 100 is a poppet valve. The valve 100 is situated in the space between rear face 58 of recuperator 50 and rear face 76 of external duct 70. The valve 100 comprises a valve member 110 mounted on a retractable stem 120. The valve member 110 has a rounded plan and a generally triangular cross-section, producing a generally conical shape. Its upper surface 112 is domed as the curvature of the rear face 76 of external duct 70, such that when the bypass valve is in its fully open configuration, the valve member 110 upper surface 112 fits closely adjacent the inner side of rear face 76.

The conical lower surface 114 of the valve member 110 narrows from a base to an apex 116 and is slightly concaved from the base toward the apex 116. The valve member 110 includes a narrow central bore from its upper surface 112 through to the apex 116, through which is fixedly attached stem 120. Stem 120 is an elongate cylindrical member for retraction and extension of valve member 110 away from or towards the recuperator 50. Stem 120 is positively located along the axial centre line C-C of the recuperator by a housing 130 such that it can be moved either toward or away from the recuperator in a straight line, housing 130 sealing with rear face 76.

The domed rear face 58 of recuperator 50 includes a circular cut-out portion 59 at its centre, that is designed to receive valve member 110 in a close fitting manner when it is desired to close the bypass valve 100. The valve 100 must fit the cutout 59 such that exhaust gas will not seep through the join between them when the valve 100 is fully closed.

Operation of the valve 100 is performed by moving stem 120 toward the recuperator 50 in order to move the valve member toward the cut-out 59, to close the valve 100 either fully or partially. Retracting the stem 120 away from the recuperator moves valve member ll0 away from cutout 59 to open the valve either fully or partially. Movement of the valve may be controlled by a control system. Valve member 110 is shown twice in Fig.2 it is fully shown in the fully open position thereof but only partially shown in the fully closed l 0 position for reasons of clarity.

During operation of the gas turbine engine 1, turbine exhaust gas exits the turbine 20 exhaust diffuser 25. The flow path of the exhaust gas is shown in dashed lines in Fig.2. If all or substantially all of the exhaust gas is required for use in the recuperator in order to heat up compressor delivery air, then bypass valve 100 remains closed, as in position 'B' of Fig. 2, with valve member 110 fitting closely over cut- out 59 of recuperator rear face 58. The exhaust gas therefore flows around the bell-mouth exit 27 of exhaust diffuser and is directed into the space between inner wall 54 and outer wall 52 of the recuperator. From here the gas flows into the "hot" side 64 of heat exchanger 60 for heating of the compressor delivery air. As the exhaust gas flows through the heat exchanger 60 it cools before exiting recuperator 50 into the external duct 70. The gas then flows into exit 90 for use with another system 80 or to an exhaust stack.

However, if a substantial portion of the exhaust gas is required for direct application to another system then bypass valve 100 is opened fully to position A' as shown in Fig.2. In this configuration, the exhaust gas exiting exhaust diffuser 25 escapes the recuperator 50 to cutout 59 and flows into external duct and through exit 90 to another system as before. The gas remains at a high temperature although it will cool somewhat upon entering duct 70.

Alternatively, if it is required that a portion of the exhaust is to be directed to the recuperator heat exchanger 60, and the remaining gas is to bypass the recuperator and be used for other systems, then the bypass valve 100 can be opened to an appropriate level to provide the right proportions of gas for each flow path. It will be evident that as valve 100 is opened further, a larger amount of gas flow will be bypassed through the valve 100 and into duct 70 for use with other systems.

Gas duct 70 assists to provide insulation for the recuperator against heat loss.

It will be apparent that the poppet valve 100 could be replaced by a butterfly valve, rotary valve, flap valve or any other suitable valve means. The valve may be circular or rectangular, hinged, e.g. on a centreline thereof or about one edge.

According to a second embodiment of the invention, the bypass valve 100 is used for bypassing compressor delivery air past the recuperator 150 directly to combustor 140 as shown schematically in Fig.3. In normal use of the gas turbine engine according to this embodiment, the bypass valve 100 would remain closed. However, if it was desired to cool the combustor for any reason then the valve 100 could be opened to allow cool compressor delivery air to be fed directly to the combustor. It will be apparent that more than one bypass valve could be used in a single embodiment of the invention such that both compressor delivery air and turbine exhaust air could bypass the recuperator if necessary.

Various modifications may be made to the embodiment described without departing from the scope of the invention as defined by the following claims, as interpreted under patent law.

Claims (20)

1. A bypass valve for enabling a fluid to bypass a recuperator, whereby the recuperator is substantially enclosed in a duct and whereby the bypass valve is also situated in the duct.

2. A bypass valve as claimed in claim 1 whereby the fluid is exhaust gas from a turbine.

3. A bypass valve as claimed in claim 1 or claim 2 in which the valve has at least an open configuration and a closed configuration, whereby in its open configuration it allows the fluid to bypass the recuperator and in its closed configuration allows the fluid to enter the recuperator.

4. A bypass valve as claimed in claim 3 wherein the valve is adapted to be variably openable between the open configuration and the closed configuration for varying the amount of fluid that is to bypass the recuperator.

5. A bypass valve as claimed in any preceding claim in which the valve is adapted to open up or close over an opening in a wall of the recuperator.

6. A bypass valve as claimed in claim 5 when dependent upon claim 2 in which the opening in the recuperator wall is directly downstream of the turbine exhaust.

7. A bypass valve as claimed in any preceding claim in which the fluid is bypassed to a downstream system.

8. A bypass valve as claimed in any preceding claim wherein the valve comprises a valve member that is adapted to be oriented in a plane substantially parallel to the plane of the duct.

9. A bypass valve as claimed in any preceding claim in which the valve is a poppet valve.

10. A bypass valve as claimed in claim 9 in which the valve has a conical surface on one side thereof.

11. A bypass valve as claimed in claim 9 or claim 10 in which the conical surface is concave towards cooperating fluid.

12. A bypass valve as claimed in claim 9 or claim 10 in which the poppet valve has a domed surface on one side thereof.

13. A bypass valve as claimed in claim 1 in which the fluid to be bypassed is compressor delivery air.

14. A bypass valve as claimed in claim 13 wherein the bypass valve bypasses the compressor delivery air past the recuperator and to a combustor.

15. A recuperator system comprising a recuperator surrounded by a duct and a recuperator bypass valve located in the duct, the bypass valve being as claimed in any preceding claim.

16. A system as claimed in claim 15 in which the recuperator is an annular recuperator.

17. A gas turbine engine comprising at least a turbine, a compressor and a combustor, and a bypass valve as claimed in any of claims 1 to 16.

18. A micro-turbine comprising at least a turbine, a compressor and a combustor, and a bypass valve as claimed in any of claims 1 to 16.

19. A recuperator system, gas turbine engine or micro-turbine substantially as described herein with reference to Figs.1 and 2, or Figs. 2 and 3, of the accompanying drawings.

20. A bypass valve for a recuperator for a gas turbine, the valve being substantially as described herein with reference to Fig.2 of the accompanying drawings.