Combined cycle electric power generation plant and heat exchanger

A loss of heat that can be recovered in a heat recovery steam generator is eliminated, whereby a combined cycle electric power generation plant with high heat recovery efficiency is provided. A combined cycle electric power generation plant is adopted that includes a heat recovery steam generator 30 that generates steam for driving a steam turbine 20 using heat of exhaust gas of a gas turbine 10, a cooling air cooler 71 that causes high-pressure feed water supplied from a low-pressure economizer 37 of the heat recovery steam generator 30 and compressed air for turbine cooling extracted from a compressor 11 of the gas turbine 10 to perform heat exchange to heat the high-pressure feed water to thereby cool the compressed air, and a fuel gas heater 72 that causes the compressed air cooled in the cooling air cooler 71 and a fuel gas of the gas turbine 10 to perform heat exchange to further cool the compressed air to thereby heat the fuel gas.

RELATED APPLICATIONS

The present application is National Phase of International Application No. PCT/JP2008/067817 filed Oct. 1, 2008, the disclosure of which is hereby incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention relates to a combined cycle electric power generation plant employing an exhaust heat recovery system and a heat exchanger included in the plant.

BACKGROUND ART

As a power generation system for a combined cycle electric power generation plant, a so-called exhaust heat recovery system for leading exhaust gas after work in a gas turbine to a heat recovery steam generator (H.R.S.G.), generating steam using the exhaust heat, and driving a steam turbine using the steam is generally used.

In a combined cycle electric power generation plant of such an exhaust heat recovery system, efforts for refinement and improvement are always performed for improvement of efficiency and stability of operation.

For example, in a gas turbine, in order to realize improvement of efficiency by raising of combustion temperature, the temperature of a fuel gas is raised. Specifically, a fuel gas heater for heating the fuel gas of the gas turbine is provided. The fuel gas heater heats the fuel gas with intermediate-pressure feed water supplied to the heat recovery steam generator. The heated fuel gas is supplied to a combustor of the gas turbine and consumed (see Patent Document 1 described below).

As an example of heat balance in the fuel gas heater, as shown inFIG. 7, the temperature of a fuel gas supplied to a fuel gas heater172is 6.8° C. and the temperature of intermediate-pressure feed water supplied from an intermediate-pressure economizer139to the fuel gas heater172is 255° C. The temperature of a fuel gas discharged from the fuel gas heater172after heat exchange and supplied to a combustor112of a gas turbine100is 210° C. and the temperature of intermediate-pressure feed water also discharged from the fuel gas heater172after heat exchange and supplied to a pre-heater137is 65° C.

In order to prevent overheating of the turbine and realize stable operation of the gas turbine, moving blades and stationary blades of the turbine are cooled. For this cooling, compressed air extracted from a compressor of the gas turbine is used. Since the compressed air is heated by compression, a cooling air cooler for cooling this compressed air is provided. The cooling air cooler cools, with high-pressure feed water supplied to the heat recovery steam generator, the compressed air extracted from the compressor of the gas turbine. The cooled air is supplied to the moving blades and the stationary blades of the turbine and cools the moving blades and the stationary blades (see, for example, Patent Document 2 described below).

As an example of heat balance in the cooling air cooler, as shown inFIG. 7, the temperature of high-pressure feed water supplied from the pre-heater137to the conventional cooling air cooler171is 172° C. and the temperature of compressed air supplied from a compressor111of the gas turbine100to the cooling air cooler171is 456° C. The temperature of high-pressure feed water discharged from the cooling air cooler171after heat exchange and supplied to a high-pressure drum134is 326° C. and the temperature of compressed air also discharged from the cooling air cooler171after heat exchange and supplied for cooling of the turbine113is 200° C.Patent Document 1: Japanese Patent Laid-Open No. 2003-343283Patent Document 2: Japanese Patent Laid-Open No. H10-169414

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

Further improvement of efficiency is always requested for the conventional technique explained above. From such a viewpoint, there is still room for improvement in the conventional technique.

Specifically, in the conventional combined cycle electric power generation plant, the fuel gas heater uses the intermediate-pressure feed water for a heat source for heating the fuel gas and causes the fuel gas and the intermediate-pressure feed water to perform heat exchange to deprive heat from the intermediate-pressure feed water. Thereafter, the intermediate-pressure feed water is supplied to the high-pressure drum and vaporized by heat of exhaust gas. However, since the intermediate-pressure feed water is cooled in the fuel gas heater, a heat quantity of the intermediate-pressure feed water decreases. Therefore, in the heat recovery steam generator, since the intermediate-pressure feed water is vaporized after the exhaust gas supplements the intermediate-pressure feed water with the decreased heat quantity, the exhaust gas has to apply excess work to the intermediate-pressure feed water. In other words, in the conventional combined cycle electric power generation plant, a large heat quantity is necessary for evaporating the intermediate-pressure feed water in the high-pressure drum. Therefore, it can be said that there is room for improvement of heat energy that can be recovered in the heat recovery steam generator.

In the conventional combined cycle electric power generation plant, the cooling air cooler needs to deprive an extremely large heat quantity from high-temperature compressed air and perform cooling. Therefore, there is room in terms of effective use of heat energy. A heat transfer area of the cooling air cooler has to be increased in order to deprive a large heat quantity from the compressed air. As a result, there is also a problem in that the cooling air cooler is increased in size.

The present invention has been devised in view of the circumstances and it is an object of the present invention to provide a combined cycle electric power generation plant with high heat recovery efficiency and provide a heat exchanger included in the plant, small in size, and having high thermal efficiency.

Means for Solving the Problems

In order to solve the problems, a combined cycle electric power generation plant having a configuration explained below is adopted.

A combined cycle electric power generation plant according to the present invention is a combined cycle electric power generation plant including a heat recovery steam generator that generates steam for steam turbine driving using heat of exhaust gas of a gas turbine, the combined cycle electric power generation plant including: a first heat exchanger that causes high-pressure feed water supplied from an economizer of the heat recovery steam generator and compressed air for turbine cooling extracted from a compressor of the gas turbine to perform heat exchange to heat the high-pressure feed water to thereby cool the compressed air; and a second heat exchanger that causes the compressed air cooled in the first heat exchanger and a fuel gas of the gas turbine to perform heat exchange to further cool the compressed air to thereby heat the fuel gas.

In the combined cycle electric power generation plant, it is also possible to arrange a shroud in a casing that forms an outer shell, form an inner channel on the inner side of the shroud, form, between the casing and the shroud, an outer channel that communicates with the inner channel on one end side of the shroud, arrange the first heat exchanger on the inner channel, and arrange the second heat exchanger on the inner channel further on a downstream side than the first heat exchanger. In this case, the compressed air for turbine cooling flows into the inner channel from the other end side of the shroud and, after sequentially passing through the first heat exchanger and the second heat exchanger, reverses the direction of the flow on one end side of the shroud and flows into the outer channel, and is discharged to the outside of the casing from the outer channel.

The present invention can be a heat exchanger included in a heat recovery steam generator that generates steam for steam turbine driving using heat of exhaust gas of a gas turbine. This heat exchanger includes: a first heat transfer unit that causes high-pressure feed water supplied from an economizer of the heat recovery steam generator and compressed air for turbine cooling of the gas turbine to perform heat exchange to heat the high-pressure feed water to thereby cool the compressed air; and a second heat transfer unit that causes the compressed air cooled in the first heat transfer unit and a fuel gas of the gas turbine to perform heat exchange to further cool the compressed air to thereby heat the fuel gas.

In such a heat exchanger, it is also possible to include a casing that forms an outer shell of the heat exchanger and a shroud arranged in the casing, form an inner channel on the inner side of the shroud, and form, between the casing and the shroud, an outer channel that communicates with the inner channel on one end side of the shroud. The first heat transfer unit is arranged on the inner channel and the second heat transfer unit is arranged on the inner channel further on a downstream side than the first heat transfer unit. In the heat exchanger having such a configuration, the compressed air for turbine cooling flows into the inner channel from the other end side of the shroud and, after sequentially passing through the first heat exchanger and the second heat exchanger, reverses the direction of the flow on one end side of the shroud and flows into the outer channel, and is discharged to the outside of the casing from the outer channel.

Advantages of the Invention

With the combined cycle electric power generation plant according to the present invention, since the cooling of the compressed air for turbine cooling is performed by a feed water heater (the first heat exchanger of the present invention) and a fuel gas heater (the second heat exchanger of the present invention) of the heat recovery steam generator, a heat loss is small. Therefore, thermal efficiency of the plant is improved.

With the heat exchanger according to the present invention, since an average temperature difference between the heat exchangers can be set larger, heat transfer areas of the heat exchangers are reduced. The heat exchanger can be reduced in size.

DESCRIPTION OF SYMBOLS

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of a combined cycle electric power generation plant according to the present invention is explained with reference toFIG. 1.

InFIG. 1, a combined cycle electric power generation plant of a single shaft type employing an exhaust heat recovery system is shown. As shown in the figure, this combined cycle electric power generation plant includes, as main components, a generator1, a gas turbine10, a steam turbine20, a heat recovery steam generator30, a condenser60, and a condensing pump62.

The gas turbine10includes a compressor11, a combustor12, and a turbine13. The steam turbine20includes low-pressure, intermediate-pressure, and high-pressure three turbines21,22, and23. The gas turbine10shares, with the steam turbine20, a main shaft2connected to the generator1. The gas turbine10extracts, as a rotating force of the main shaft2, work applied to the turbine13by a combustion gas. The steam turbine20extracts, as rotating force of the main shaft2, work applied to the turbines21,22, and23by steam to thereby drive the compressor11and the generator1.

In the heat recovery steam generator30, in the inside of a housing30athat forms a channel of exhaust gas generated in the gas turbine10, high-pressure, intermediate-pressure, and low-pressure three evaporators31,32, and33are arranged in order along a direction in which the exhaust gas flows. In the evaporators31,32, and33, high-pressure, intermediate-pressure, and low-pressure three drums34,35, and36are respectively annexed.

A low-pressure economizer37that heats, with heat of the exhaust gas, water supplied from the condenser60via a water supply channel45is provided on an exhaust gas channel further on a downstream side than the low-pressure evaporator33. The low-pressure feed water heated by the low-pressure economizer37is supplied to the low-pressure drum36via a water supply channel46. In an exhaust gas channel between the low-pressure evaporator33and the intermediate-pressure evaporator32, a primary high-pressure economizer38that heats, with the heat of the exhaust gas, the high-pressure feed water supplied from the low-pressure economizer37via a water supply channel47and an intermediate-pressure economizer39that heats, with the heat of the exhaust gas, the intermediate-pressure feed water supplied from the low-pressure economizer37via a water supply channel48are provided. The intermediate-pressure feed water heated in the intermediate-pressure economizer39is supplied to the intermediate-pressure drum35via the water supply channel48.

On an exhaust gas channel between the high-pressure evaporator31and the intermediate-pressure evaporator32, a low-pressure superheater40that overheats, with the heat of the exhaust gas, low-pressure steam supplied from the low-pressure drum36via a steam channel49, an intermediate-pressure superheater41that overheats, with the heat of the exhaust gas, intermediate-pressure steam supplied from the intermediate-pressure drum35via a steam channel50, and a secondary high-pressure economizer42that heats, with the heat of the exhaust gas, high-pressure feed water supplied from the primary high-pressure economizer38via a water supply channel51are provided. The high-pressure feed water heated in the secondary high-pressure economizer42is supplied to the high-pressure drum34via the water supply channel51.

On an exhaust gas channel further on an upstream side than the high-pressure evaporator31, primary and secondary two high-pressure superheaters43aand43bthat overheat, with the heat of the exhaust gas, high-pressure steam supplied from the high-pressure drum34via a steam channel52and primary and secondary two reheaters44aand44bthat reheat, with the heat of the exhaust gas, steam that has applied work to the high-pressure turbine23are set.

The secondary high-pressure superheater43bis connected to the high-pressure turbine23via a steam channel53. The secondary reheater44bis connected to the intermediate-pressure turbine22via a steam channel54. The intermediate-pressure turbine22is connected to the low-pressure turbine21via a steam channel55. The low-pressure superheater40is connected to the low-pressure turbine21via steam channels56and55.

The high-pressure turbine23is connected to the primary reheater44avia a steam channel57and the intermediate-pressure superheater41is connected to the primary reheater44avia steam channels58and57.

Further, this combined cycle electric power generation plant includes a cooling air cooler (a first heat exchanger)71that cools compressed air for turbine cooling and a fuel gas heater (a second heat exchanger)72that heats a fuel gas of the gas turbine10. The cooling air cooler71and the fuel gas heater72are connected in series along a supply path for the compressed air. The cooling air cooler71and the fuel gas heater72are integrated.

The cooling air cooler71causes high-pressure feed water supplied from the low-pressure economizer37to the high-pressure drum34via a water supply channel59and compressed air extracted from the compressor11of the gas turbine10via an air channel61to perform heat exchange to heat the high-pressure feed water and cool the compressed air. For the cooling air cooler71, for example, a heat exchanger of a shell and tube type is adopted.

The fuel gas heater72causes the compressed air cooled by the cooling air cooler71and the fuel gas to perform heat exchange to further cool the compressed air and heat the fuel gas. The compressed air further cooled in the fuel gas heater72is supplied to moving blades and stationary blades of the turbine13. The heated fuel gas is supplied to the combustor12.

InFIG. 2toFIG. 5, the structure of an integral heat exchanger80having a configuration in which the cooling air cooler71and the fuel gas heater72are integrated is shown. As shown in the figures, this integral heat exchanger80includes a casing81that forms an outer shell of the heat exchanger, a shroud82arranged in the inside of the casing81, a heat transfer pipe bundle83arranged in the inside of the shroud82, and plural plate fins84arranged in the inside of the shroud82and below the heat transfer pipe bundle83. An inner channel88is formed in the inside of the shroud82. An outer channel89that communicates with the inner channel88on a lower end side of the shroud82is formed between the casing81and the shroud82. The heat transfer pipe bundle83is an element included in the cooling air cooler71(i.e., the first heat transfer unit) and is arranged on the inner channel88of the shroud82. The plate fins84are elements included in the fuel gas heater72(i.e., the second heat transfer unit) and are arranged on the inner channel88on the downstream side of the heat transfer pipe bundle83to not prevent a flow of the compressed air.

One end of an air supply duct82afor leading the compressed air extracted from the compressor11of the gas turbine10via the air channel61into the inside of the shroud82is connected to the shroud82. The other end of the air supply duct82aprojects to the outside of the casing81and is connected to the air channel61on the upstream side. One end of an exhaust duct82bfor discharging the compressed air flowing out from the lower end of the shroud82to the outside is connected to the casing81. The exhaust duct82bis located above the lower end of the shroud82. The other end of this exhaust duct82bis connected to the air channel61on the downstream side.

A water supply header83aand a drain header83bare respectively provided above and below the heat transfer pipe bundle83.

Upper ends of the plural heat transfer pipes85, to which the high-pressure feed water supplied from the low-pressure economizer37via the water supply channel59is supplied, are connected to the water supply header83a. The water supply header83aprojects to the outside of the casing81piercing through the shroud82and is connected to the water supply channel59on the upstream side.

Lower ends of the plural heat transfer pipes85are connected to the drain header83b. The high-pressure feed water served for heat exchange is collected. The drain header83bprojects to the outside of the casing81piercing through the shroud82and is connected to the water supply channel59on the downstream side.

The heat transfer pipes85connected to the water supply header83aand the drain header83bare provided to be bent in, for example, a zigzag shape between the water supply header83aand the drain header83band sends the high-pressure feed water from the water supply header83ato the drain header83b.

In such a heat transfer pipe bundle83, the high-pressure feed water supplied from the low-pressure economizer37via the water supply channel59flows from the water supply header83ato the drain header83bthrough the heat transfer pipes85. The compressed air sent into the inner channel88from the upper end side of the shroud82through the air supply duct82apasses through gaps among the heat transfer pipes85included in the heat transfer pipe bundle83and, at this point, performs heat exchange with the surfaces of the heat transfer pipes85. Consequently, the high-pressure feed water is heated and the compressed air is cooled. For the heat transfer pipe bundle83, a pipe with fins, a pipe with studs, or the like may be adopted.

The plate fins84are provided to project to a space around a fuel gas pipe87through which the fuel gas is caused to pass. One end of the fuel gas pipe87projects to the outside of the casing81and is connected to a not-shown fuel supply path. The other end of the fuel gas pipe87also projects to the outside of the casing81and is connected to the combustor12of the gas turbine10.

The fuel gas flows through the fuel gas pipe87. Heat of the fuel gas is transmitted to the plate fins84via the fuel gas pipe87. On the other hand, the compressed air cooled by the heat transfer pipe bundle83comes into contact with the plate fins84in the shroud82. At this point, heat exchange is performed. Consequently, the fuel gas is heated and the compressed air is cooled.

Such plate fins84are located on the downstream side in the flowing direction of the compressed air with respect to the heat transfer pipe bundle83. Therefore, the compressed air cooled by the heat exchange with the high-pressure feed water in the heat transfer pipe bundle83is further cooled by heat exchange with the fuel gas in the plate fins84.

The compressed air sequentially passed through the heat transfer pipe bundle83and the plate fins84reverses the direction of the flow on the lower end side of the shroud82and flows into the outer channel89. The compressed air flown into the outer channel89is supplied to the turbine13through the exhaust duct82band the air channel61.

A current plate90for straightening the compressed air blowing out from the lower end of the shroud82is provided on the inner side of the casing81. A drain pipe92for discharging condensate generated in the inside of the casing81is provided in the bottom section of the casing81. A gas leak detector94is provided in the casing81. The gas leak detector94is provided in an upper part or a lower part according to the specific gravity of the fuel gas.

Subsequently, a method of actuating the combined cycle electric power generation plant configured as explained above is explained.

First, the main shaft2is rotated to drive the gas turbine10and the condensing pump62is driven to start water supply from the condenser60to the high-pressure, intermediate-pressure, and low-pressure drums34,35, and36of the heat recovery steam generator30.

The gas turbine10is driven and the temperature of the air (exhaust gas) flowing in the inside of the heat recovery steam generator30rises, whereby steam is generated in the high-pressure, intermediate-pressure, and low-pressure evaporators31,32, and33respectively annexed to the high-pressure, intermediate-pressure, and low-pressure drums34,35, and36.

The high-pressure steam generated in the high-pressure evaporator31is pushed out from the high-pressure drum34and, after being overheated in the primary and secondary high-pressure superheaters43aand43b, supplied to the high-pressure turbine23.

The intermediate-pressure steam generated in the intermediate-pressure evaporator32is pushed out from the intermediate-pressure drum35and, after being overheated in the intermediate-pressure superheater41, reheated in the primary and secondary reheaters44aand44btogether with the steam returned to the heat recovery steam generator30through the high-pressure turbine23. The intermediate-pressure steam reheated in the primary and secondary reheaters44aand44bis supplied to the intermediate-pressure turbine22.

The low-pressure steam generated in the low-pressure evaporator33is pushed out from the low-pressure drum36, overheated in the low-pressure superheater40, and supplied to the low-pressure turbine21.

When the gas turbine10is driven, work applied to the turbine13by the combustion gas is extracted as rotating force of the main shaft2. When the high-pressure steam is supplied to the high-pressure turbine23, work applied to the high-pressure turbine23by the high-pressure steam is extracted as rotating force of the main shaft2. When the intermediate-pressure steam is supplied to the intermediate-pressure turbine22, work applied to the intermediate-pressure turbine22by the intermediate-pressure steam is extracted as rotating force of the main shaft2. When the low-pressure steam is supplied to the low-pressure turbine21, work applied to the low-pressure turbine21by the low-pressure steam is extracted as rotating force of the main shaft2. Consequently, the generator1connected to the main shaft2is driven and electric power generation is started.

During steady operation of the combined cycle electric power generation plant, the cooling air cooler71causes the high-pressure feed water supplied to the high-pressure drum34and the compressed air extracted from the compressor11to perform heat exchange to heat the high-pressure feed water to thereby cool the compressed air. The fuel gas heater72causes the compressed air cooled by the cooling air cooler71and the fuel gas to perform heat exchange to further cool the compressed air to thereby heat the fuel gas.

The integral heat exchanger80causes the high-pressure feed water circulating in the inside of the heat transfer pipes and the compressed air circulating in the inside of the shroud82to perform heat exchange to heat the high-pressure feed water to thereby cool the compressed air. The integral heat exchanger80causes the compressed air passed through the heat transfer pipe bundle83and the fuel gas circulating in the inside of the fuel gas pipe87to perform heat exchange to further cool the compressed air.

With the combined cycle electric power generation plant, the cooling air is cooled stepwise by the cooling air cooler71and the fuel gas heater72. Therefore, work applied to the cooling air by the high-pressure feed water in the cooling air cooler71is smaller than that in the past. Moreover, since an average temperature difference between the cooling air cooler71and the fuel gas heater72can be set large, a heat transfer area in the heat exchanges may be small. As a result, it is possible to reduce the cooling air cooler71in size.

For comparison with the conventional combined cycle electric power generation plant, an example of heat balance in the cooling air cooler71and the fuel gas heater72is explained. As shown inFIG. 6, the temperature of the high-pressure feed water supplied from the low-pressure economizer37to the cooling air cooler71is 172° C. and the temperature of the compressed air supplied from the compressor11of the gas turbine10to the cooling air cooler71is 465° C. The temperature of the high-pressure feed water discharged from the cooling air cooler71after heat exchange and supplied to the high-pressure drum34is 326° C. and the temperature of the compressed air also discharged from the cooling air cooler71after heat exchange is 357° C.

The temperature of the fuel gas supplied to the fuel gas heater72is 6.8° C. and the temperature of the compressed air discharged from the cooling air cooler71and supplied to the fuel gas heater72is 357° C. The temperature of the fuel gas discharged from the fuel gas heater72after heat exchange and supplied to the combustor12of the gas turbine10is 210° C. and the temperature of the compressed air also discharged from the fuel gas heater72after heat exchange and served for cooling of the turbine13is 200° C.

In the conventional combined cycle electric power generation plant shown inFIG. 7, the fuel gas heater172uses the intermediate-pressure feed water for a heat source for heating the fuel gas (6.8° C. to 210° C.) and causes the fuel gas and the intermediate-pressure feed water to perform heat exchange to deprive heat from the intermediate-pressure feed water (255° C. to 65° C.). Thereafter, the intermediate-pressure feed water is supplied to the high-pressure drum134at 65° C. and vaporized by heat of exhaust gas. However, since the intermediate-pressure feed water is cooled in the fuel gas heater172, a heat quantity of the intermediate-pressure feed water decreases. Therefore, in the heat recovery steam generator, the exhaust gas has to apply excess work to the intermediate-pressure feed water. In other words, in the conventional combined cycle electric power generation plant, an excess heat quantity is necessary for evaporating the intermediate-pressure feed water in the high-pressure drum134. Therefore, heat that can be recovered in the heat recovery steam generator is wastefully consumed.

On the other hand, in the combined cycle electric power generation plant according to this embodiment, the fuel gas heater72uses the compressed air for a heat source for heating the fuel gas (6.8° C. to 210° C.) and causes the fuel gas and the compressed air to perform heat exchange to deprive heat from the compressed air (357° C. to 200° C.). Thereafter, the compressed air is supplied to the turbine13at 200° C. and used as a cooling medium for the stationary blade and the moving blades. Heat that can be recovered in the heat recovery steam generator30is not consumed. Moreover, since the intermediate-pressure feed water is not used for the heat source of the fuel gas, the intermediate-pressure feed water is supplied to the high-pressure drum34while keeping 255° C. Therefore, since a wasteful heat loss in the heat recovery steam generator30does not occur, it is possible to improve thermal efficiency of the plant.

In the conventional combined cycle electric power generation plant, the cooling air cooler171needs to deprive an extremely large heat quantity from the compressed air (400° C. to 200° C.). Therefore, a heat transfer area of the cooling air cooler171has to be increased. As a result, the cooling air cooler171is increased in size.

On the other hand, in the combined cycle electric power generation plant according to this embodiment, the cooling air cooler71does not need to deprive a heat quantity as large as that in the past from the compressed air (465° C. to 357° C.). Therefore, a heat transfer area of the cooling air cooler71may be small. Therefore, it is possible to reduce the cooling air cooler71in size.

In this embodiment, the combined cycle electric power generation plant of the single shaft type is explained. However, it goes without saying that the present invention can also be applied not only to the combined cycle electric power generation plant of the single shaft type but also to a combined cycle electric power generation plant of a multi-shaft type.