JPH1073008A - Combined cycle plant and start-stop method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of drain in a gas turbine during stop by supplying cooling steam from an exhaust heat recovery boiler into the steam cooling part of the gas turbine, leading out gas delivered from the steam cooling part into a steam turbine and a condenser, and leading in air for converting steam into air into a steam cooling part. SOLUTION: Pressurized air from a compressor 2 is led into a combustor 5, operation is carried out by leading in high temperature and high pressure gas which is generated therein into a gas turbine 1, steam is generated by supplying exhaust gas which completes work into an exhaust heat recovery boiler 6, operation is carried out by leading in its steam into a steam turbine 4, and a power generator 3 is driven. When the gas turbine is stopped normally, in the operating condition of non load rated rotational speed, air from the compressor 2 is lead into the steam cooling part 9 of the gas turbine through a first steam air substituting valve 16, remaining steam in the steam cooling part 9 is pushed out through a cooling steam bypass valve 13, and lead out into the condenser 8. After that, a second steam air substituting valve 18 is opened, and steam in a steam cooling system is purged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention combines a gas turbine for cooling a turbine section with steam and a steam turbine operated by steam generated in an exhaust heat recovery boiler for recovering exhaust heat of the gas turbine. The present invention relates to a combined cycle plant and a method for starting and stopping the combined cycle plant.

[0002]

2. Description of the Related Art In recent years, there has been a strong demand for higher efficiency of thermal power plants, and in order to approach this demand, air for boiler combustion is used not only in newly built thermal power plants but also in existing ordinary steam power plants. A combined cycle by repowering, in which a gas turbine used as a source and a gas turbine generates power in addition to an existing steam turbine, is being promoted.

[0003] This combined cycle plant usually introduces fuel into a combustor together with high-pressure air sent from a compressor, burns the fuel, and drives a gas turbine with high-temperature, high-pressure gas obtained by the combustion. The steam turbine system is configured by introducing a flue gas of the gas turbine system into an exhaust heat recovery boiler to generate steam, and driving the steam turbine with the steam. And
In such a combined cycle plant, a method of increasing the gas temperature at the inlet of the gas turbine is employed in order to further improve the thermal efficiency.

[0004] Accordingly, with the rise of the turbine inlet temperature, heat-resistant superalloy materials are used for components exposed to high-temperature gas such as combustors, stationary blades, and moving blades of gas turbines. However, even with these materials, the heat resistance temperature is 800.
On the other hand, the gas turbine inlet temperature has reached about 1300 ° C., which exceeds the material's limit temperature. Therefore, it is essential to use cooling blades in which turbine blades are cooled to the limit temperature of the material.

At present, air obtained from a compressor is used as a cooling medium for this cooling. Therefore, if the gas turbine inlet temperature further rises, it is necessary to increase the cooling air flow rate to cool the material,
This leads to an increase in air extracted from the compressor, which not only causes a decrease in the efficiency of the gas turbine, but also causes a decrease in the efficiency of the combined cycle plant.

Accordingly, a method of cooling a gas turbine using steam as a cooling medium has been proposed. This is because the cooling medium is changed from the conventionally used air to steam that has a specific heat of about 2 times and has excellent cooling characteristics by using a specific heat of about 2 times. Can be reduced, and the efficiency of the gas turbine can be improved,
Alternatively, a higher temperature of 1300 ° C. or higher can be realized, and the thermal efficiency of the combined cycle plant can be improved.

[0007]

However, in order to perform steam cooling of the gas turbine, it is necessary to introduce steam into the gas turbine. When the gas turbine is stopped, residual steam in the gas turbine and in the steam cooling system piping is reduced. It becomes drain and remains. If such a drain remains inside the gas turbine or the like, not only does this drain cause rust inside the gas turbine, but also if the drain in the steam cooling system enters the gas turbine as water droplets, There is a problem that the latent heat generated when the drain evaporates generates thermal stress and causes fatigue of the material.

In view of the foregoing, the present invention has been made in view of the above circumstances, and in a combined cycle plant using a steam-cooled gas turbine, a combined cycle plant capable of preventing generation of drain inside the gas turbine during shutdown and a method for starting and stopping the combined cycle plant The purpose is to obtain.

[0009]

According to a first aspect of the present invention, there is provided a gas turbine in which a turbine section is cooled by steam.
In a combined cycle plant consisting of a steam turbine operated by steam generated by recovering the exhaust heat of the gas turbine, cooling is performed from a waste heat recovery boiler for recovering the exhaust heat of the gas turbine to a steam cooling section of the gas turbine. A cooling steam supply pipe for supplying steam, an exhaust pipe for selectively leading gas discharged from the steam cooling section to a steam turbine and a condenser, and a first steam-air replacement valve for the steam cooling section. And a replacement air supply pipe for introducing air for replacing steam air.

According to a second aspect of the present invention, in the first aspect, an exhaust pipe for leading exhaust discharged from a steam cooling section of the gas turbine is connected to a gas turbine exhaust duct via a second steam-air displacement valve. It is characterized by being.

A third aspect of the present invention is characterized in that an exhaust pipe from which the exhaust gas discharged from the steam cooling unit of the gas turbine is led is opened to the atmosphere through a second steam-air displacement valve.

According to a fourth aspect of the present invention, an exhaust pipe for discharging exhaust gas discharged from a steam cooling section of a gas turbine is connected to a blowdown tank connected to an exhaust heat recovery boiler via a second steam-air replacement valve. And are connected.

According to a fifth aspect, in the first aspect, the air for replacing steam air is supplied by a compressor of a gas turbine.

A sixth invention is characterized in that the air for replacing steam air is supplied by a separate blower.

A seventh aspect of the present invention comprises a gas turbine having a turbine section cooled by steam, and a steam turbine operated by steam generated in an exhaust heat recovery boiler for recovering exhaust heat of the gas turbine. In the startup method of the combined cycle plant, the air for replacing the steam air is supplied to the steam cooling section of the gas turbine, and the gas discharged from the steam cooling section is led out to the condenser, and the steam cooling is performed while the plant is stopped. The method includes a step of purging steam or drain remaining in the system, and a step of cooling the cooling section of the gas turbine by steam after the purging step and introducing the cooled steam to the steam turbine.

Further, an eighth invention comprises a gas turbine in which a turbine section is cooled by steam, and a steam turbine operated by steam generated in an exhaust heat recovery boiler for recovering exhaust heat of the gas turbine. In the method of stopping the combined cycle plant, the process of changing the recovery destination of the steam after passing through the steam cooling section of the gas turbine from the steam turbine to the condenser, and the introduction destination of the cooling steam before cooling from the steam cooling section to the condensing section A step of gradually changing the steam turbine to a steam cooler, introducing steam-air replacement air into the steam cooling unit, replacing the gas turbine steam cooling unit with the air, and exhausting the replacement air to an exhaust system. Features.

[0017]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a schematic system diagram of a first embodiment of the present invention, in which a gas turbine 1, a compressor 2, a generator 3 and a steam turbine 4 are connected on the same shaft. Then, the air pressurized by the compressor 2 is introduced into the combustor 5,
The fuel is burned together with the fuel supplied to the combustor 5 to form a high-temperature and high-pressure gas, which is introduced into the gas turbine 1, and performs work there.

The exhaust gas thus worked by the gas turbine 1 is sent to the exhaust heat recovery boiler 6, where steam is generated by the exhaust heat in the exhaust gas. This generated steam is introduced into the steam turbine 4 through the main steam stop valve 7,
The steam turbine 4 is driven, and the generator 3 is driven together with the gas turbine 1 to generate power. The steam that has performed the work in the steam turbine 4 is condensed in the condenser 8 and is returned to the exhaust heat recovery boiler 6 as feed water.

The gas turbine 1 is provided with a steam cooling section 9 for cooling the turbine blades and the like. A cooling steam connected to the exhaust heat recovery boiler 6 is provided at a steam inlet of the steam cooling section 9. The supply pipe 10 is connected. An exhaust pipe 11 is connected to a steam outlet of the steam cooling unit 9, and a distal end of the exhaust pipe 11 is connected to a downstream side of the main steam stop valve 7 via a cooling steam stop valve 12. .

The exhaust pipe 11 is provided with the cooling steam stop valve 1.
A cooling steam bypass pipe 14 having a cooling steam bypass valve 13 is branched out from the upstream side of the pipe 2 and connected to the condenser 8.

The cooling steam supply pipe 10 is provided with a cooling steam inlet valve 15, and a first portion for supplying a part of the air discharged from the compressor 2 to the downstream side of the cooling steam inlet valve 15. Replacement air supply pipe 17 having steam-air replacement valve 16
Is connected. The cooling steam bypass pipe 14
A replacement air discharge pipe 19 having a second steam-air replacement valve 18 branches out from the upstream side of the cooling steam bypass valve 13, and the replacement air discharge pipe 19 is connected to a gas turbine exhaust duct 20.

The cooling steam supply pipe 10 is connected to the condenser 8 via a cooling steam stop valve 21 on the upstream side of the cooling steam inlet valve 15. Reference numeral 22 in the figure denotes a main steam bypass pipe connecting the upstream side of the main steam stop valve 7 and the condenser 8, and reference numeral 23 denotes a main steam bypass valve provided in the main steam bypass pipe 22. .

However, during operation of the plant,
A part of the steam generated in the exhaust heat recovery boiler 6 is sent to the steam cooling unit 9 of the gas turbine 1 via the cooling steam supply pipe 10 to cool the steam cooling unit of the gas turbine. Then, the high-temperature steam that has cooled the steam cooling unit is supplied to the steam turbine 4.
To be used for power generation.

In a normal starting method of a gas turbine, turning is performed by a starting motor, ignition is performed after purging residual unburned components in an exhaust system, and thereafter, the gas turbine is rotated by itself. And after the rotation speed reaches the rated rotation, it is incorporated into the power generation system,
After that, it shifts from load increase to rated load operation.

When the gas turbine is cooled by the steam, the first steam-air replacement valve 16 and the second steam-air replacement valve 18 are opened during the purge operation, and the cooling steam stop valve 12 and the cooling steam are stopped. The inlet valve 15 is closed, and the discharge air of the compressor 2 is guided to the steam cooling section 9 of the gas turbine 1 via the first steam-air replacement valve 16, and the remaining steam and the drain in the steam cooling system are converted to the second steam. Purge into the gas turbine exhaust duct 20 via the air displacement valve 18.

After purging, the first and second steam-air replacement valves 16 and 18 are closed to replace the steam-replaced air in the steam cooling system. Then, when the combustor is ignited and steam starts to be generated in the waste heat recovery boiler 6, the cooling steam stop valve 21 is opened, and the steam generated in the waste heat recovery boiler 6 is dropped into the condenser 8, and during that time, Steam cooling valve 15 by steam
Until the cooling steam supply pipe 10 is warmed up. The initial steam of the steam turbine main steam system is dropped to the condenser 8 by opening the main steam bypass valve 23.

Therefore, when this plant is incorporated into the power generation system, the main steam bypass valve 23 is closed and the main steam stop valve 7 is opened, so that the main steam is supplied to the steam turbine 4, 4 is activated.

When the combustion gas temperature of the gas turbine approaches the critical metal temperature of the blades during the load increase process, the cooling steam stop valve 2
1 is closed, and the cooling steam inlet valve 15 and the second steam-air displacement valve 18 are opened. Therefore, part of the steam generated in the exhaust heat recovery boiler 6 is introduced into the steam cooling unit 9 of the gas turbine via the cooling steam supply pipe 10, and the air trapped in the steam cooling unit 9 is replaced with the replacement air discharge pipe. The gas is discharged to the gas turbine exhaust duct 20 through 19 and steam cooling of the gas turbine is started.

Thereafter, the second steam-air displacement valve 18 is closed,
The cooling steam bypass valve 13 is opened, and steam which may be mixed with air discharged from the steam cooling unit 9 of the gas turbine is introduced into the condenser 8 and degassed there. Then, when the inside of the steam cooling system including the steam cooling unit is completely replaced with steam, the cooling steam bypass valve 13 is closed, the cooling steam stop valve 12 is opened, and the high-temperature steam after cooling the steam cooling unit 9 is steam. After being introduced into the turbine 4, the load is increased and the operation is shifted to the rated load operation.

On the other hand, when performing normal shutdown of the gas turbine, load reduction is started by reducing the fuel from the rated load operation, and the gas turbine is disconnected from the power generation system when the load becomes zero, and the no-load rated speed is reduced. In the operating state, the fuel is further throttled, the number of revolutions is reduced, and then the fuel is stopped to extinguish the fire and stop.

By the way, when the steam cooling of the gas turbine is performed as described above, at the time of stoppage, the cooling steam is purged from the steam cooling system to replace the steam in the steam cooling system with air.

That is, the cooling steam inlet valve 15 and the cooling steam stop valve 12
Is closed, and the first steam-air replacement valve 16, the cooling steam bypass valve 13, and the cooling steam stop valve 21 are opened. Therefore, the air discharged from the compressor 2 is introduced into the steam cooling section 9 of the gas turbine via the first steam-air replacement valve 16, and the steam accumulated in the steam cooling section 9 is cooled by the cooling steam bypass valve 13. Through the condenser 8. After that, the cooling steam bypass valve 13 is closed, the second steam-air replacement valve 18 is opened, and the replacement air possibly containing the cooling steam is purged to the gas turbine exhaust duct 20.

As described above, according to the present invention, when the gas turbine is started and stopped, the air discharged from the compressor is introduced into the steam cooling section of the gas turbine and is replaced with steam. It is possible to purge the drain in the system, prevent the entry of steam that may be drained during the warm-up, and prevent the steam from remaining in the steam cooling system during shutdown. Therefore, during start-up, no unnecessary thermal stress is generated due to the latent heat of drain evaporation which causes fatigue, and during stoppage, drain which causes rust in the steam cooling system is not generated. Is prevented, and the reliability of the plant is improved.

FIG. 2 is a view showing another embodiment of the present invention. A replacement air discharge pipe 19 is connected to a blowdown tank 24 provided in the exhaust heat recovery boiler 6, and the replacement air discharge pipe is provided. 19 is provided with a check valve 25 downstream of the second steam-air displacement valve 18.

Thus, the air discharged from the steam cooling section 9 at the time of startup or the replacement air possibly containing cooling steam at the time of stoppage is discharged to the blowdown tank 24. Therefore, if the blowdown tank 24 is continuously purged until the air in the steam cooling system is replaced with steam by selecting the opening / closing timing of the valve, the condenser 8
, The amount of air mixed in the air can be reduced, and the load can be increased quickly. Further, in the plant shown in FIG. 1, the replacement air containing the steam is purged into the gas turbine exhaust duct, so it is necessary to consider the effect of the steam on the gas turbine exhaust duct.
As described above, since the replacement air and the like are discharged to the blowdown tank 24 in the plant described above, it is not necessary to consider the effect of steam on the gas turbine exhaust duct.

FIG. 3 is a view showing still another embodiment, in which a replacement air discharge pipe 19 is opened to the atmosphere. Thus, in this case, the replacement steam or the replacement air that has been purged to the gas turbine exhaust duct in the plant of FIG. 1 is purged into the atmosphere.

In this plant, since the steam in the system is released to the atmosphere, there is a disadvantage that water must be supplied during the start and stop operations. However, by selecting the valve opening / closing timing, the steam is selected. If the air in the cooling system is continuously purged into the atmosphere until the air is replaced with steam, the amount of air mixed into the condenser can be reduced.

FIG. 4 is a view showing another embodiment of the present invention. A separate blower 26 is connected to the cooling steam supply pipe 10 via a first steam-air replacement valve 16. is there. Therefore, in this case, when replacing the steam in the steam cooling system with air, it is not necessary to perform control for obtaining an appropriate replacement air amount from the compressor during a change in the load of the gas turbine. Control becomes easy.

[0040]

Since the present invention is constructed as described above, it is possible not only to perform steam cooling having a higher cooling efficiency than air cooling, but also to reduce rust in the steam cooling system accompanying the steam cooling. In addition, it is possible to reliably prevent the occurrence of drain that causes thermal stress at the time of starting, and to prevent deterioration of the steam cooling system.

[Brief description of the drawings]

FIG. 1 is a schematic system diagram of a combined cycle plant of the present invention.

FIG. 2 is a schematic system diagram of another embodiment of the present invention.

FIG. 3 is a schematic system diagram of still another embodiment of the present invention.

FIG. 4 is a schematic system diagram of another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gas turbine 2 Compressor 3 Generator 4 Steam turbine 6 Exhaust heat recovery boiler 7 Main steam stop valve 8 Condenser 9 Steam cooling unit 10 Cooling steam supply pipe 12, 21 Cooling steam stop valve 13 Cooling steam bypass valve 15 Cooling steam Inlet valve 16 First steam-air replacement valve 17 Replacement air supply pipe 18 Second steam-air replacement valve 20 Gas turbine exhaust duct 23 Main steam bypass valve 24 Blow-down tank 26 Separate blower

Claims (9)

[Claims] 1. A combined cycle plant comprising a gas turbine having a turbine section cooled by steam and a steam turbine operated by steam generated by recovering exhaust heat of the gas turbine.
A cooling steam supply pipe for supplying cooling steam from a waste heat recovery boiler for recovering waste heat of the gas turbine to a steam cooling part of the gas turbine, and a gas discharged from the steam cooling part to a steam turbine and a condenser. A combined cycle plant comprising: an exhaust pipe that is selectively led out; and a replacement air supply pipe that introduces steam-air replacement air into the steam cooling unit via a first steam-air replacement valve. 2. An exhaust pipe for guiding exhaust gas discharged from a steam cooling section of a gas turbine is connected to a gas turbine exhaust duct via a second steam-air displacement valve. The combined cycle plant as described. 3. The gas turbine according to claim 1, wherein an exhaust pipe for guiding exhaust gas discharged from the steam cooling section of the gas turbine is opened to the atmosphere via a second steam-air displacement valve. Combined cycle plant. 4. An exhaust pipe for discharging exhaust gas discharged from a steam cooling section of a gas turbine is connected to a blowdown tank connected to an exhaust heat recovery boiler via a second steam-air replacement valve. The combined cycle plant according to claim 1, wherein: 5. The combined cycle plant according to claim 1, wherein the air for steam-air replacement is supplied by a compressor of a gas turbine. 6. The combined cycle plant according to claim 1, wherein the air for replacing steam air is supplied by a separate blower. 7. A method of starting a combined cycle plant comprising a gas turbine having a turbine section cooled by steam and a steam turbine operated by steam generated by an exhaust heat recovery boiler for recovering exhaust heat of the gas turbine. At the same time, the air for replacing steam air is supplied to the steam cooling section of the gas turbine, and the gas discharged from the steam cooling section is led out to the condenser, and the steam remaining in the steam cooling system while the plant is stopped A combined cycle plant comprising: a step of purging a drain; and, after the purging step, a step of steam-cooling a cooling section of the gas turbine and introducing the cooled steam to the steam turbine. 8. A process for purging steam or drain remaining in a steam cooling system during a plant stoppage and then trapping purge air in a steam cooling section of the gas turbine, and thereafter trapping purge air in a steam cooling section of the gas turbine. Discharging the discharged air to a condenser by cooling steam. The combined cycle plant according to claim 7, wherein 9. A method for stopping a combined cycle plant comprising a gas turbine in which a turbine section is cooled by steam and a steam turbine operated by steam generated in an exhaust heat recovery boiler for recovering exhaust heat of the gas turbine. In the process of changing the recovery destination of the steam after passing through the steam cooling section of the gas turbine from the steam turbine to the condenser, and gradually changing the introduction destination of the cooling steam before cooling from the steam cooling section to the condenser And a process of introducing steam-air replacement air into the steam cooling unit, replacing the gas turbine steam cooling unit with the air, and exhausting the replacement air to an exhaust system. How to stop the plant.