PREHEATING ARRANGEMENT FOR A COMBINED CYCLE PLANT

Abstract

A power generation station (10), including: a combined cycle plant (12) having a gas turbine engine (20); a HRSG (30) configured to receive engine exhaust from the gas turbine engine and to generate steam, and a steam turbine (38, 40) configured to use the steam to develop mechanical energy; an auxiliary boiler (14) configured to generate heat used to create auxiliary steam for use in the combined cycle plant and to generate auxiliary boiler exhaust (52); and an auxiliary boiler exhaust heat transfer arrangement (16) configured to transfer heat present in the auxiliary boiler exhaust to the combined cycle plant.

Description

FIELD OF THE INVENTION

The invention relates to an arrangement for heating/preheating a component of a combined cycle power plant using heat present in exhaust from an auxiliary steam boiler

BACKGROUND OF THE INVENTION

During operation of a combined cycle plant a gas turbine engine produces all the heat necessary to generate all the steam that is required to run the plant. This includes steam required to operate the steam turbine as well as the steam required to supply the plant's peripheral processes When the gas turbine engine is not operating some of the peripheral plant processes still require steam Conventionally this steam is generated by an auxiliary steam generation system that is a miniature, self-contained boiler system that may include a gas or oil fired burner, a water feed pump, chemical treatment equipment etc. This auxiliary steam may be used for any or all of the steam turbine gland seals, low pressure sparging of condenser hotwell, pegging of the deaerator tank (DA tank), or other purposes. Providing this steam is viewed as essential prior to plant startup and sometimes the auxiliary boiler is sized to accommodate all the essential functions simultaneously. To generate the auxiliary steam a fossil fuel is burned in a combustion chamber and much of the heat from the combustion is transferred to water inside a boiler Byproducts of the combustion, including heated gases, are then discarded by way of an exhaust stack Typically there is no recovery of the energy exhausted into the stack Once the primary source of heat for the steam in the combined cycle plant is operational, such as a gas turbine engine, the auxiliary steam generation plant is shut down until needed again for auxiliary steam

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in the following description in view of the drawings that show:

FIG. 1 is a schematic representation showing an exemplary embodiment of a combined cycle plant incorporating the auxiliary boiler exhaust heat transfer arrangement in a manner that permits a variety of uses

FIG. 2 is a schematic representation showing a prior art cooling arrangement for a turbine of a gas turbine engine.

FIG. 3 is a schematic representation showing an exemplary embodiment of a combined cycle plant incorporating the auxiliary boiler exhaust heat transfer arrangement to provide cooled air to a gas turbine engine and supplement the steam in the cycle.

FIG. 4 is a schematic representation showing an alternate exemplary embodiment of a combined cycle plant incorporating the auxiliary boiler exhaust heat transfer arrangement to provide cooled air to a gas turbine engine.

FIG. 5 is a schematic representation showing an exemplary embodiment of a combined cycle plant incorporating the auxiliary boiler exhaust heat transfer arrangement into a blade tip clearance control arrangement

FIG. 6 is a schematic representation showing an exemplary embodiment of a combined cycle plant incorporating the auxiliary boiler exhaust heat transfer arrangement to preheat HRSG feedwater.

DETAILED DESCRIPTION OF THE INVENTION

The present inventors have devised a way to decrease the startup time and potentially increase the efficiency of a power generation station that includes a combined cycle plant and an auxiliary boiler. Specifically, the inventors propose to utilize heat present in exhaust from the auxiliary boiler to heat/preheat another component in the power generation station In an exemplary embodiment the heat present in the auxiliary boiler exhaust will be transferred to the combined cycle plant to heat a component during a short shutdown or to preheat the component after a long shutdown. Heating/preheating in this manner will shorten startup times and reduce wear and tear on the component(s) due to thermal cycling. In addition, utilizing energy previously lost to the environment from the power generation station will increase the operating efficiency of the power generation station in some of the embodiments. The arrangement proposed herein can be applied to new power generation stations or retrofit into existing power generation arrangements

FIG. 1 is a schematic representation showing an exemplary embodiment of a power generation station 10 including a combined cycle plant 12, an auxiliary boiler 14, and an auxiliary boiler exhaust heat transfer arrangement 16 incorporated in a manner that permits a variety of uses The combined cycle plant 12 includes: a gas turbine engine 20 having a compressor 22, a combustor (not shown), and a turbine 24; a HRSG 30 having a superheater 32, a selective catalytic reduction (SCR) catalyst 34, and a cooler end 36; steam turbines 38, 40; a deaerator tank 42; and a condenser 44 having a condenser hotwell 46. Only a portion of the HRSG 30 is shown Further, a typical HRSG's superheater, evaporator and economizer arrangement may vary from that shown

As shown in this exemplary embodiment the auxiliary boiler exhaust heat transfer arrangement 16 includes an optional auxiliary exhaust heat exchanger 50 configured to receive auxiliary boiler exhaust 52 and transfer heat from the auxiliary boiler exhaust 52 to clean air 54 As used herein the term clean air denotes air that is not exhaust from a combustion process. Instead, clean air 54 may be unfiltered, atmospheric air or the like. The auxiliary exhaust heat exchanger 50 can be installed in a new power generation station 10 or retrofit into an existing power generation station 10. The clean air may be supplied by an air source 56 that may be a low pressure blower or a compressor. Units that would perform satisfactorily in this role are commercially available Heated clean air 58 exits the auxiliary exhaust heat exchanger 50 and can be utilized by any or all of several plant operations. Whether or not the auxiliary exhaust heat exchanger 50 is present, the auxiliary boiler exhaust 52 can be directed into the HRSG 30 which is then heated/preheated by the heat present in the auxiliary boiler exhaust 52 Heating/preheating the HRSG 30 may reduce startup times and may reduce unwanted emissions associated with startup Additionally, there may be a cost savings associated with not needed to purchase, install, and maintain a stack dedicated to the auxiliary boiler 14, because the auxiliary boiler exhaust 52 would exit a stack associated with the HRSG 30.

The heated clean air 58 can be directed toward any component of the power generation system 10 including any component of the combined cycle plant 12. For example, the heated clean air 58 can be directed to the gas turbine engine 20 and may be used to heat/preheat any component therein, such as a rotor (not shown) This could decrease startup time and reduce stress on the metal components within the turbine 24 by moving them from cold to warm before the unit is ever started, or heated during short shutdowns In addition, or alternately, during operation the heated clean air 58 can be used as a mix with clean air 96 to cool components of the gas turbine as required In another exemplary embodiment the heated clean air 58 can be directed into the HRSG 30 in addition to or in place of the auxiliary boiler exhaust 52 Within the HRSG 30, the heated clean air 58 can be used to heat/preheat the superheater 32 and/or the SCR catalyst 34, and/or the cooler end 36 of the HRSG 30. The same advantages experienced by heating/preheating the turbine 24 would apply to heating/preheating the HRSG 30 and/or individual components therein

In another exemplary embodiment the heated clean air 58 can be directed to one or both of the steam turbines 38, 40 to heat/preheat any component, including a steam turbine rotor (not shown). Likewise, heating/preheating may lead to shorter startup times and less stress on the components. In still another exemplary embodiment the heated clean air 58 can be used to heat/preheat plumbing in the power generation station 10, including piping 70 and/or valves 72. This may be done by the heated clean air 58 passing through, or alternately by heating trace lines disposed adjacent to the plumbing

In another exemplary embodiment the heated clean air 58 may be directed to an air/HRSG feedwater heat exchanger 74 configured to receive HRSG feedwater 76 from, for example, the boiler feed pump (not shown) and transfer heat from the heated clean air 58 to the HRSG feedwater 76. In a variation of HRSG feedwater heating, the auxiliary boiler exhaust 52 may be directed into an exhaust/HRSG feedwater heat exchanger 80 that is configured to receive HRSG feedwater 76 and transfer heat directly from the auxiliary boiler exhaust 52 to the HRSG feedwater 76 This would speed up initial steam production and provide some warm up to the HRSG feedwater 76 system piping and valves. Note that the feedwater could be in various pressure levels depending upon the combined cycle plant design.

In an exemplary embodiment where the air source 56 is a compressor, compressed air 90 may be directed to a blade clearance control arrangement 92 to thermally regulate blade clearance in the turbine 24 of the gas turbine engine 20. Alternately, the compressed air 90 may be directed to plant instrumentation that requires compressed air 90 to operate After the heated clean air 58 has performed its intended function, the spent heated clean air 94 can be returned as inlet air 96 for the air source 56 and/or inlet air 98 for the auxiliary boiler 14 where it can be used for combustion, which may boost operating efficiency In an exemplary embodiment where the compressor is an interstage cooled compressor, boiler feedwater 100 can be used to cool the interstage cooled compressor, and the preheated boiler feedwater 102 can be used to supply the auxiliary boiler 14.

FIG. 2 is a schematic representation showing a prior art cooling arrangement 104 for the turbine 24 of the gas turbine engine 20 Compressed heated air 106 is drawn from the compressor 22 at a high temperature and pressure and passed through two water-to-air kettle boilers 108, 110. Inside the kettle boilers 108, 110 heat is transferred from the compressed heated air 106 to kettle boiler feedwater 112 to produce steam 114 which is used to augment or boost the main system steam production. During this process the compressed heated air 106 is cooled by the kettle boilers 108, 110. The kettle boiler cooled air 116 is directed into the turbine 24 which it cools While the steam provides a boost to the process and therefore to the overall efficiency there is a significant cost associated with bleeding the compressed heated air 106 from the compressor 22. In this exemplary embodiment the auxiliary boiler (not shown) is used only to provide the plant with steam as required prior to startup.

FIG. 3 is a schematic representation showing an exemplary embodiment of the combined cycle plant 12 incorporating the auxiliary boiler exhaust heat transfer arrangement 16 to provide cooled air to the gas turbine engine 20 and supplement the steam in the cycle. This exemplary embodiment eliminates the prior art bleeding of compressed heated air 106 from the compressor 22 In this exemplary embodiment the heated clean air 58 is directed into the kettle boilers 108, 110 where it would contribute heat to the kettle boiler feedwater 112 to produce steam 114. This would cool the heated clean air 58 which would then become the kettle boiler cooled air 116 used to cool the turbine 24 This would require the auxiliary burner to operate while the gas turbine engine 20 is operating, and this would represent a fundamental change because typically both are not run simultaneously.

FIG. 4 is a schematic representation showing an alternate exemplary embodiment of the combined cycle plant 12 incorporating the auxiliary boiler exhaust heat transfer arrangement 16 to provide cooled air to the gas turbine engine 20 This exemplary embodiment also eliminates the prior art bleeding of compressed heated air 106 from the compressor 22. However, in this exemplary embodiment no heat is transferred to the kettle boiler feedwater 112 to produce steam 114. This exemplary embodiment may be used when, for example, there is not enough heat present in the auxiliary boiler exhaust 52 to heat the kettle boiler feedwater 112 In this exemplary embodiment the heated clean air 58 exits the auxiliary exhaust heat exchanger 50 and flows directly to the turbine 24. In a variation of this exemplary embodiment, when a compressor is used as the air source 56, relatively cooler compressed air 90 may be mixed with the heated clean air 58 to produce a mixed heated clean air 120 of a lower temperature than the heated clean air 58. The mixed heated clean air 120 may then be used to cool the turbine 24. Alternately, or in addition, inlet air 96, which is clean and cool, may be mixed with the heated clean air 58 to produce the heated clean air 120 of a lower temperature than the heated clean air 58. A temperature of the mixed heated clean air 120 may be controlled by, for example, controlling an amount of mixing of the heated clean air 58 and the mixed heated clean air 120 Further, in the scenarios of FIGS. 3 and 4 heat is still being transferred to the combined cycle plant 12 from the auxiliary boiler exhaust 52. The heated clean air 58 may ultimately have a cooling effect on the turbine 24, but nonetheless the heat is still transferred and thus permits control over the amount of cooling provided.

FIG. 5 is a schematic representation showing an exemplary embodiment of the combined cycle plant 12 incorporating the auxiliary boiler exhaust heat transfer arrangement 16 into a blade tip clearance control arrangement 130, which is used to reduce thermal transients on the tips of blades in the turbine 24 of the gas turbine engine 20 This allows for faster startup from the warm condition by ensuring the blade tips have the proper clearance, thereby eliminating contact between the blade tips and adjacent abradable ring segments This, in turn, reduces wear and tear on the blade tips which typically causes a loss in efficiency and increased downtime for blade maintenance. Optionally, in this exemplary embodiment, compressed air could also be taken to supply plant instrumentation Prior art power generation stations might use several compressors to supply the blade tip clearance control arrangement 130 and the plant instrumentation air. In the proposed arrangement all of the compressed air could be supplied by the compressor of the air source 56. If the compressor is an interstage cooled compressor, the boiler feedwater 100 can be used to cool the interstage cooled compressor, and the preheated boiler feedwater 102 can be used to supply the auxiliary boiler 14. As in the previous exemplary embodiments the heated clean air 58 can be used to heat plant components

FIG. 6 is a schematic representation showing exemplary embodiments of the combined cycle plant 12, incorporating the auxiliary boiler exhaust heat transfer arrangement 16 to preheat HRSG feedwater 76. In a first exemplary embodiment the auxiliary boiler exhaust 52 can be directed into an exhaust/HRSG feedwater heat exchanger 80 configured to receive the HRSG feedwater 76 and transfer heat from the auxiliary boiler exhaust 52 to the HRSG feedwater 76. The preheated HRSG feedwater 76 is then directed to the HRSG 30. In a second exemplary embodiment the heated clean air 58 can be directed into air/HRSG feedwater heat exchanger 74 configured to receive HRSG feedwater 76 and transfer heat from the heated clean air 58 to the HRSG feedwater 76, which then enters the HRSG 30 Alternately the preheated HRSG feedwater 76 and/or the heated clean air 58 could be provided to a condensate preheater region 82 in the cooler end 36 of the HRSG 30. The HRSG 30 can be heated/preheated in this manner and this can help speed up steam production/startup as well as reduce stress associated with cold start up.

From the foregoing it can be seen that the inventors have devised a new arrangement that takes advantage of heat previously wasted. The new arrangement will increase operating efficiency and can further be incorporated into many of the plant's other systems, allowing for a more consolidated power generation station. Consequently, the proposed arrangement represents an improvement in the art

While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.

Claims

1. A power generation station, comprising:

a combined cycle plant comprising a gas turbine engine; a heat recovery steam generator (HRSG) configured to receive engine exhaust from the gas turbine engine and to generate steam, and a steam turbine configured to receive the steam to operate;

an auxiliary boiler configured to generate heat used to create auxiliary steam for use in the combined cycle plant and to generate auxiliary boiler exhaust; and

an auxiliary boiler exhaust heat transfer arrangement configured to transfer heat present in the auxiliary boiler exhaust to the combined cycle plant

2. The power generation station of claim 1, wherein the HRSG is configured to receive the auxiliary boiler exhaust and the heat present therein

3. The power generation station of claim 1, wherein the auxiliary boiler exhaust heat transfer arrangement comprises an auxiliary exhaust heat exchanger configured to receive clean air and to transfer heat from the auxiliary boiler exhaust to the clean air, and wherein the power generation station is configured to deliver clean air heated by the auxiliary exhaust heat exchanger to a component of the combined cycle plant.

4. The power generation station of claim 3, wherein the component comprises at least one of a rotor of the gas turbine engine, a turbine of the gas turbine engine, the HRSG, a catalyst of the HRSG, a superheater of the HRSG, a rotor of the steam turbine, plumbing of the power generation station, a clearance control arrangement for a blade of the gas turbine engine, and a HRSG feedwater heat exchanger configured to receive and heat HRSG feedwater.

5. The power generation station of claim 3, wherein the component comprises the rotor of the gas turbine engine, wherein the auxiliary boiler exhaust heat transfer arrangement further comprises an air source configured to generate the clean air, and wherein the auxiliary boiler exhaust heat transfer arrangement is configured to mix the clean air heated by the auxiliary exhaust heat exchanger with relatively cooler air supplied by the air source.

6. The power generation station of claim 5, wherein the component comprises the turbine of the gas turbine engine, wherein the combined cycle plant further comprises a kettle boiler configured to transfer heat to water used to operate the steam turbine, and wherein the auxiliary boiler exhaust heat transfer arrangement is configured to deliver the heated clean air to the kettle boiler before the clean heated air reaches the turbine of the gas turbine engine

7. The power generation station of claim 3, wherein the auxiliary boiler is configured to receive the heated clean air after the heated clean air is delivered to the component.

8. The power generation station of claim 3, wherein the auxiliary boiler exhaust heat transfer arrangement further comprises an air source configured to generate the clean air, and wherein the air source is configured to receive the heated clean air after the heated clean air is delivered to the component.

9. The power generation station of claim 1, wherein the auxiliary boiler exhaust heat transfer arrangement comprises a HRSG feedwater heat exchanger configured to receive the auxiliary boiler exhaust and to transfer heat from the auxiliary boiler exhaust to HRSG feedwater.

10. The power generation station of claim 3, wherein the auxiliary boiler exhaust heat transfer arrangement further comprises an air source configured to generate the clean air, and wherein the gas turbine engine further comprises a blade clearance control arrangement configured to receive the clean air.

11. The power generation station of claim 3, wherein the auxiliary boiler exhaust heat transfer arrangement further comprises a compressor configured to generate the clean air, wherein the auxiliary boiler is configured to heat feedwater that is preheated by cooling the compressor.

12. The power generation station of claim 3, wherein the auxiliary boiler exhaust heat transfer arrangement further comprises a compressor configured to generate the clean air, wherein the power generation station comprises instrumentation configured to receive the clean air.

13. In a power generation station comprising a combined cycle plant and an auxiliary boiler configured to generate auxiliary steam used in the combined cycle plant, an improvement comprising:

an auxiliary boiler exhaust heat transfer arrangement configured to transfer heat present in exhaust from the auxiliary boiler to a component of the combined cycle plant

14. The power generation station of claim 13, wherein the combined cycle plant comprises a heat recovery steam generator (HRSG) configured to receive exhaust from a gas turbine engine,

wherein the auxiliary boiler exhaust heat transfer arrangement is configured to direct the auxiliary boiler exhaust into the HRSG.

15. The power generation station of claim 13, wherein the auxiliary boiler exhaust heat transfer arrangement comprises an auxiliary exhaust heat exchanger configured to receive clean air and to transfer heat from the auxiliary boiler exhaust to the clean air, and wherein the component of the combined cycle plant is configured to receive the heated clean air.

16. The power generation station of claim 15, wherein the component comprises at least one of a gas turbine engine of the combined cycle plant, a heat recovery steam generator (HRSG) of the combined cycle plant, a steam turbine of the combined cycle plant, plumbing of the power generation station, and a HRSG feedwater heat exchanger configured to receive and heat HRSG feedwater.

17. The power generation station of claim 15, wherein the combined cycle plant further comprises a steam turbine and a kettle boiler configured to transfer heat to water used to operate the steam turbine, and wherein the auxiliary boiler exhaust heat transfer arrangement is configured to deliver the heated clean air to the kettle boiler before the clean heated air reaches the component

18. The power generation station of claim 15, wherein the auxiliary boiler exhaust heat transfer arrangement further comprises an air source configured to generate the clean air, and wherein a gas turbine engine of the combined cycle plant further comprises a blade clearance control arrangement configured to receive the clean air.

19. The power generation station of claim 15, wherein the auxiliary boiler exhaust heat transfer arrangement further comprises an air source configured to generate the clean air, and wherein at least one of the air source and the auxiliary boiler is configured to receive the heated clean air after the heated clean air is delivered to the component.

20. The power generation station of claim 15, wherein the auxiliary boiler exhaust heat transfer arrangement further comprises a compressor configured to generate the clean air, wherein the auxiliary boiler is configured to heat feedwater that is preheated by cooling the compressor.