JPH1018809A - Starting/stopping method for combined power plant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a starting/stopping method for a combined power plant which can secure reliability of the entire plant without deteriorating total power generation efficiency of the plant. SOLUTION: In this starting/stopping method for a combined power plant, a high temperature part of a gas turbine 14 is cooled by the use of cooling steam generated by cooling air extracted from a compressor 12 and an exhaust heat recovery boiler 31 at the time of starting and stopping the plant. A cooling means 71 is arranged for controlling the temperature of the cooling air. The temperature difference between the cooling air and the cooling steam is eliminated or suppressed within an allowable range at the time of changeover therebetween.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a start / stop method for a combined power plant, and more particularly, to a start / stop method for a combined power plant that switches a cooling medium during a start / stop process to cool a high-temperature portion of gas turbine equipment. About the method.

[0002]

2. Description of the Related Art In recent years, working gas has been increased in temperature and pressure to improve the thermal efficiency of gas turbine equipment. In high-temperature gas turbine equipment, cooling of turbine blades is indispensable to ensure reliability. Conventionally, air extracted from a compressor constituting gas turbine equipment is used for cooling turbine blades. A cooling air path is provided inside the turbine blade, and air extracted from the compressor is guided to the path to cool the turbine blade. After cooling, the air is discharged into the working gas through film cooling holes provided on the outer surface of the blade as air for cooling the film on the outer surface of the blade. However, in a high-temperature gas turbine facility having a working gas temperature exceeding 1400 ° C., the conventional method of cooling turbine blades with air reduces the amount of mainstream gas due to an increase in the amount of air required for cooling, and reduces the amount of cooling air and working gas. The temperature of the working gas decreases, the mixing loss increases, and the like due to the mixing of the working gas, and the merit in the heat cycle due to the high temperature of the working gas tends to be impaired. As a solution to this problem, it has been proposed to use steam having a higher heat transfer coefficient than air as the cooling medium. In order to make effective use of a steam-cooled gas turbine that cools turbine blades with steam, for example, literatures ASM / IEE
E-Power Generation Conference (J
t. ASME / IEEE Power Genera
87-JP
As described in GC-GT-1 (1987),
Without discharging the steam used for cooling into the mainstream gas,
It is necessary to collect it. JP-A-4-124414 is an example of a refrigerant recovery type steam-cooled gas turbine that recovers steam used for cooling. The refrigerant recovery type steam-cooled gas turbine disclosed in this publication is a gas that combines a steam turbine facility and an exhaust heat recovery boiler facility that generates working steam for the steam turbine using exhaust gas exhausted from the gas turbine facility as a heat source. Used in turbine / steam turbine combined cycle power plants. In this case, a part of the working steam of the steam turbine is used as the steam used for cooling the gas turbine blades.

[0003]

SUMMARY OF THE INVENTION In a gas turbine / steam turbine combined power generation plant in which a part of the working steam of a steam turbine is used as cooling steam for a high temperature portion of a gas turbine, an exhaust heat recovery boiler that generates working steam for the steam turbine. Since the exhaust gas of the gas turbine is used as a heat source, it is not possible to generate not only steam for driving the steam turbine but also gas turbine cooling steam during the gas turbine start-up process or the gas turbine stop process. When the cooling steam for the gas turbine cannot be generated as in the start / stop process, it is necessary to separately supply a cooling medium. In order to secure the necessary cooling medium separately during the start / stop process, a compressor for generating cooling air or a boiler for generating cooling steam that is operated only during the start / stop process is added, or the cooling medium is supplied from outside the plant. Means such as adding equipment to be supplied are conceivable, but this is not preferable in view of an increase in overall power generation efficiency and equipment area in consideration of the operation power of these additional equipment. Therefore, gas turbine /
In a start / stop process of a steam turbine combined cycle power plant, a means for using air extracted from a compressor constituting a gas turbine as a cooling medium is generally used. If this means is used, it is necessary to switch between the cooling air system and the cooling steam system. In this switching process, a temperature difference between the cooling air and the cooling steam becomes a problem. In a gas turbine having a cooling medium path through which air flows during a start / stop process and a steam flow during a load operation, such as a cooling medium path provided in a gas turbine blade, if the temperature difference between cooling air and cooling steam is large. When the air / steam switch is performed, the cooling medium path experiences a large temperature change, that is, receives a thermal shock, and the reliability of the cooling medium path or the components including this path, and consequently, This will reduce the reliability of the whole plant.

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to provide a method of starting / stopping a combined power plant that can ensure the reliability of the entire plant without lowering the overall power generation efficiency of the combined power plant. It is in.

[0005]

SUMMARY OF THE INVENTION The object of the present invention is to provide a combined power generation system for cooling a high-temperature portion of a gas turbine by using cooling air extracted from a compressor and cooling steam generated by an exhaust heat recovery boiler during a start / stop process. A method for starting / stopping a plant, which is achieved by switching from cooling air to cooling steam or from cooling steam to cooling air by eliminating the temperature difference between the cooling air and the cooling steam or by controlling the temperature to an allowable range. Is done. Here, the control of the temperature difference between the cooling air and the cooling steam is performed by controlling the temperature of the cooling air by cooling means provided in a path for supplying the cooling air extracted from the compressor to the high-temperature portion of the gas turbine, or Control the compressor variable vanes, adjust the compressor suction air flow rate, lower the cooling air temperature, or control the pressure in the steam drum of the steam turbine to raise the temperature of the cooling steam. Performed by

According to the present invention, the temperature difference between the cooling air and the cooling steam can be minimized during the start / stop process of the combined power generation plant, and the thermal stress generated in the cooling medium path when the cooling medium is switched is suppressed. And the reliability of the entire plant can be ensured.
Further, by controlling the compressor suction air flow rate or the steam drum pressure and controlling the temperature of the cooling air or the temperature of the cooling steam, the capacity of the cooling facility can be reduced.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of a gas turbine / steam turbine combined power plant according to the present invention. The gas turbine / steam turbine combined power plant is roughly divided into a gas turbine facility 11, a steam turbine 21, an exhaust heat recovery boiler 31 and a generator 1, and the gas turbine facility 11, the steam turbine facility 21 and the generator 1 have a common shaft. Are linked by The gas turbine facility 11 mainly includes a compressor 12, a combustor 13, and a gas turbine 14. The working steam of the steam turbine facility 21 is supplied to the gas turbine facility 1 at an exhaust heat recovery boiler facility 31 disposed downstream of the gas turbine facility 11.
1 is generated using the exhaust gas discharged from the heat source as a heat source. Also,
A part of the working steam of the steam turbine is supplied to the high temperature part of the gas turbine 14 as cooling steam. However, during the start / stop process of the gas turbine, the temperature or the flow rate of the exhaust gas as a heat source is insufficient, so that not only the working steam necessary for driving the steam turbine but also the gas turbine 14 is cooled. Neither can the required steam be produced.
Therefore, a separate cooling medium for the gas turbine 14 is required during the start / stop process. In the present embodiment, a part of air is extracted from the compressor 12 constituting the gas turbine equipment 11 and supplied as a cooling medium. To do.

Hereinafter, the operation of the power plant according to the present embodiment will be described in the order of the start-up process, the load operation, and the stop process. First, the startup process will be described. The start of the power plant starts with the start of the gas turbine equipment 11.
The gas turbine 14 is started by a motor (not shown) connected to the rotating shaft. At the same time, the compressor 12 which has started to rotate by the prime mover sucks in and compresses the atmosphere 15.
The compressed air is led to the combustor 13. The rotation speed is gradually increased, and when a predetermined rotation speed is reached, the fuel 16
Supply and ignite. The pressure and temperature of the generated combustion gas are considerably lower than those during operation in which the generator 1 is connected to a design rated load (hereinafter, referred to as rated load operation). Are guided to the gas turbine 14, and the stationary blades 41n, 42n, 43n and the moving blades 41b, 4
2b and 43, the cascade of the three-stage structure including the blades 2b and 43 expands and generates axial power. In the startup stroke, no load is connected to the generator 1, and the rotation speed increases due to the generated shaft power. When the gas turbine 14 generates the power required by the compressor 12, the motor is disconnected, and the gas turbine equipment 11 starts an independent operation. Further, as the fuel 16 is added, the shaft power generated in the gas turbine 14 further increases, and eventually reaches the rated speed. In the present embodiment, the variable inlet vanes (not shown) of the compressor 12 are controlled so that the compressor suction air flow rate becomes about 60% of the rated load operation.

As described above, during the start-up stroke, air extracted from the compressor 12 is used for cooling the gas turbine 14. In this case, the open / close valve 5 provided in the cooling medium path
1, 52, 53 and 54 are closed, and open / close valves 61, 62, 63 and 64 provided in the cooling medium path are opened,
The air extracted from the compressor 12 is supplied to the gas turbine 14 as a cooling medium. A part of the air extracted from the compressor 12 passes through a cooler 71 and is supplied as a cooling medium to a high-temperature portion of the gas turbine 14, for example, a turbine blade. In the present embodiment, as described later, control is performed so that the temperature of the cooling air becomes the same as the temperature difference of the cooling steam (or falls within the allowable temperature difference). A cooling medium path is formed inside each turbine blade, and when the cooling medium passes through this path, it absorbs heat from the blade body and cools the blade body. Unlike the conventional air-cooled turbine blades, this cooling medium path has no film cooling air holes on the blade surface, and all the supplied cooling medium is collected without being released into the mainstream gas. Is done. The collected cooling air is supplied to the open / close valve 6
It is opened to the atmosphere via 2, 63 and 64. In the present embodiment, at this stage, the gas turbine
Exhaust gas 17 at 20 ° C. is exhausted. The exhaust heat recovery boiler facility 31 generates steam using the thermal energy of the exhaust gas 17. Here, the exhaust heat recovery boiler facility 31
Is a double-pressure boiler facility, which has a first steam drum 32a, a second steam drum 32b, and a third steam drum 32c from upstream along the flow of the exhaust gas 17, and 112at, 36ata and 10
It produces steam at a pressure of about ata. Here, pressure 1
High pressure steam is used for steam of 00 to less than 150 ata, medium pressure steam is used for steam of 20 to less than 40 ata and 5 to 15 at
a is defined as low-pressure steam, and the first steam drum 32
a, the second steam drum 32b and the third steam drum 32c
To the high-pressure steam drum 32a and the medium-pressure steam drum 32, respectively.
b and the low-pressure steam drum 32c. During the start-up stroke, the temperature of the exhaust gas 17 is about 180 ° C. lower than at the time of rated load operation, and the flow rate is about 40% less, but sufficient for generating turbine blade cooling steam in the medium-pressure steam drum 32b. It is a heat source. When the cooling steam is generated in the intermediate-pressure steam drum 32b with the passage of time, the on-off valve 51 is opened, the first-stage stationary blade 41n of the gas turbine 14 passes through the intermediate-pressure superheater of the exhaust heat recovery boiler facility 31, and the The cooling steam is supplied to the second-stage stationary blades 42n and the third-stage stationary blades 43n, the first-stage moving blades 41b, the second-stage moving blades 42b, and the third-stage moving blades 43b. The temperature of the cooling steam at this time is about 280 ° C.
Which is the same as the temperature during rated load operation. Normally, the exhaust heat recovery boiler equipment 31 is controlled such that the temperature of steam generated in each steam drum is constant even if the temperature or flow rate of exhaust gas of the gas turbine equipment 11 as a heat source changes. At this stage, the cooling air and the cooling steam are mixed and flow in the cooling medium path provided in the gas turbine 14. In the next stage, the on-off valve 61 is closed and the compressor 12
Supply of cooling air from is stopped. After confirming that the cooling medium is completely steam only, the opening and closing valves 52, 53 and 54 are opened, the opening and closing valves 62, 63 and 64 are closed, and this cooling steam is collected in the steam turbine equipment 21.
As described above, the switching of the cooling medium from the air to the steam in the startup process is completed, and the load is gradually connected to the generator 1 to perform the load operation. The suction air flow rate and the fuel flow rate of the compressor 12 are controlled according to the load amount, and at the same time, the temperature of the exhaust gas rises and the flow rate increases, and the exhaust heat recovery boiler equipment 3
One heat source also increases. Thereby, the amount of generated steam also increases, and load operation of the steam turbines 22a, 22b, and 22c becomes possible.

A method for controlling the temperature difference between the cooling air and the cooling steam to be the same (or the temperature difference between the cooling air and the cooling steam within an allowable range) will be described with reference to FIGS. The first method is control for lowering the temperature of the cooling air by the cooler 71. In FIG. 2, the cooler 71
A temperature sensor 71T for detecting a cooling temperature is provided at an outlet of the valve, and a temperature sensor 51T for detecting a cooling temperature is provided at an inlet of the on-off valve 51. When switching from the cooling air to the cooling steam during the start-up process, the temperature of a part of the air extracted from the compressor 12 is compared with the temperature of the cooling steam extracted from the exhaust heat recovery boiler facility 31, and the temperature measured by the temperature sensor 71T. Is controlled so as to become equal to the temperature measured by the temperature sensor 51T (or within the allowable temperature difference), and the temperature of the cooling air is reduced. The second method is to adjust the suction air flow rate of the compressor 12 (I
This is a control for lowering the temperature of the cooling air by performing GV modulation. In FIG. 2, a temperature sensor 12T for detecting a discharge air temperature of the compressor 12 is provided. The suction air flow rate of the compressor 12 is controlled by the compressor variable stationary blade 12IG.
It can be adjusted by controlling V. Here, when switching from the cooling air to the cooling steam during the startup process, if the compressor variable vane 12IGV is controlled so that the air flow rate becomes smaller than that during the rated load operation, the discharge air temperature of the compressor 12 decreases. Therefore, the compressor variable vane 12IGV is controlled so that the temperature of the cooling air is reduced so that the temperature measured by the temperature sensor 12T becomes the same as the temperature measured by the temperature sensor 51T (or falls within the allowable temperature difference). The third method is control for increasing the temperature of the cooling steam by the pressure of the steam drum. In FIG. 3, a pressure sensor 32bP for detecting a pressure in the medium-pressure steam drum 32b is provided. The temperature of the generated cooling steam can be adjusted by controlling the pressure in the drum. Here, when switching from the cooling air to the cooling steam during the startup process, the pressure in the medium-pressure steam drum 32b is increased, the temperature of the cooling steam is increased, and the temperature of the cooling steam is measured by the temperature sensor 51T. Therefore, the pressure in the medium-pressure steam drum 32b is controlled so that the temperature of the cooling steam is increased so that the temperature of the temperature sensor 51T becomes the same as the temperature of the temperature sensor 71T (or falls within the allowable temperature difference).

Here, normally, the compressor discharge air temperature, ie, the cooling air temperature at the time of switching the cooling medium, is about 380 ° C. when the compressor suction air flow rate is reduced to 60% of the rated time, and is equal to that during the rated load operation. It is about 420 ° C. for the same suction air flow rate. In FIG. 1, since the cooling steam temperature is about 280 ° C., the cooling air is not temperature-controlled as in the prior art. A temperature difference of about 100 ° C. and about 140 ° C. if not throttled will cause a thermal stress corresponding to this temperature difference in the cooling medium path when the cooling medium is switched. The thermal stress impairs the strength and life of the material, and lowers the reliability of the gas turbine equipment 11 as a whole. On the other hand, in the present embodiment, since the temperature of the cooling air is controlled by the cooler 71 to be the same as the cooling steam temperature (or within the allowable temperature difference), the cooling medium path is changed even if the cooling medium is switched. There is no temperature change, and as a result, there is no thermal shock such as generation of thermal stress. This leads to ensuring the reliability of the cooling medium path, and hence the gas turbine equipment 11 as a whole. Further, in the present embodiment, when the compressor suction air flow rate is reduced to reduce the compressor discharge air temperature, that is, the cooling air temperature, or when the temperature of the cooling steam is increased by the pressure of the steam drum, And the temperature difference between the cooling device 71 and the cooling device 71 can be reduced.

Next, load operation will be described. In the power plant according to the present embodiment, during load operation, high-pressure steam, medium-pressure steam, and low-pressure steam generated by the exhaust heat recovery boiler 31 correspond to the first steam turbine 22a and the second steam The turbine 22b and the third steam turbine 22c are guided, drive each steam turbine, and generate shaft power. The generated shaft power is generated by the generator 1
Is converted to electric power. The high-pressure steam guided to the high-pressure steam turbine 22a performs expansion work in the steam turbine 22a, and its pressure is reduced. However, since this pressure is sufficient to drive the medium-pressure steam turbine 22b,
It is led to the medium-pressure steam turbine 22b. The medium-pressure steam guided to the medium-pressure steam turbine 22b is
In this case, the pressure decreases due to the expansion work, but the pressure is sufficient to drive the low-pressure steam turbine 22c, and is guided to the low-pressure steam turbine 22c. The low-pressure steam guided to the low-pressure steam turbine 22c performs expansion work in the steam turbine 22c, is then guided to a condenser 33, is converted into water, and is then converted into water by a water pump 34.
Returned to 1. The working steam of the high-pressure steam turbine 22a is:
It also works in the medium-pressure steam turbine 22b and the low-pressure turbine 22c.

Here, the path of steam used to cool the turbine blades of the gas turbine facility 11 will be described. As described above, the steam generated by the exhaust heat recovery boiler 31 is used for cooling the gas turbine blades. The intermediate-pressure steam generated in the intermediate-pressure steam drum 32b passes through the intermediate-pressure superheater, and the first-stage stationary blades 41n, the second-stage stationary blades 42n, the third-stage stationary blades 43n, and the first-stage moving blades 41n of the gas turbine 14 are provided.
b, supplied as cooling steam to the second stage rotor blades 42b and the third stage rotor blades 43b to cool the turbine blades. First stage stationary blade 4
The steam that has cooled 1n is collected by the low-pressure steam turbine 22c. The steam that has cooled the second-stage stationary blades 42n is guided to the third-stage stationary blades 43n, and cools the stationary blades. Third stage stationary blade 4
The steam having cooled 3n is recovered by the medium-pressure steam turbine 22b. The steam that has cooled the first-stage moving blade 41b, the second-stage moving blade 42b, and the third-stage moving blade 43b is supplied to the intermediate-pressure steam turbine 2
2b.

Finally, the stop process will be described. In stopping the power plant, first, the load on the steam turbine facility 21 is gradually reduced to bring the steam turbine facility 21 into a no-load operation state.
Next, the load on the gas turbine equipment 11 is gradually reduced to bring the apparatus into a no-load operation state. At this stage, the cooling medium of the gas turbine equipment 11 is steam. Here, the open / close valve 6
2, 63 and 64 are opened, and the on-off valves 52, 53 and 54 are closed. In this state, the collected cooling steam is released to the atmosphere. Further, the opening / closing valve 61 is opened, and the cooling air is controlled so that the temperature of the cooling air becomes the same as the temperature difference of the cooling steam (or falls within the allowable temperature difference) as in the start-up process. Thereafter, when the on-off valve 51 is closed, the cooling steam is not supplied to the gas turbine equipment 11, and the gas turbine equipment 11 is stopped by reducing the fuel 16. In this embodiment,
In the stop stroke, similarly to the start stroke, when the cooling steam and the cooling air are switched, the cooling medium path does not receive a temperature change, that is, no thermal stress is generated. 11 can be ensured.

[0014]

As described above, according to the present invention,
Controlling the temperature of the cooling air or the temperature of the cooling steam during the switching of the cooling medium in the high-temperature portion of the gas turbine during the start / stop process of the combined power plant minimizes the temperature difference between the cooling air and the cooling steam. Therefore, it is possible to suppress the thermal stress generated in the cooling medium path when the cooling medium is switched, and it is possible to secure the reliability of the entire plant. Further, by controlling the compressor suction air flow rate or the steam drum pressure and controlling the temperature of the cooling air or the temperature of the cooling steam, the capacity of the cooling facility can be reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a gas turbine / steam turbine combined power generation plant showing an embodiment of the present invention.

FIG. 2 is a diagram illustrating a method for controlling a temperature difference between cooling air and cooling steam according to the present invention.

FIG. 3 is a diagram illustrating a method for controlling a temperature difference between cooling air and cooling steam according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Generator 11 Gas turbine equipment 12 Compressor 12T Temperature sensor 12IGV Compressor variable stationary vane 14 Gas turbine 21 Steam turbine equipment 22a, 22b, 22c Steam turbine 31 Exhaust heat recovery boiler equipment 32a, 32b, 32c Steam drum 32bP Pressure sensor 51T Temperature sensor 71 Cooler 71T Temperature sensor

Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display F22B 1/18 F22B 1/18 D (72) Inventor Shinya Enjima 7-2-1, Omika-cho, Hitachi City, Ibaraki Prefecture No.Hitachi, Ltd.

Claims (5)

[Claims] 1. A method for starting / stopping a combined power plant that cools a high-temperature portion of a gas turbine by using cooling air extracted from a compressor and cooling steam generated by an exhaust heat recovery boiler during a start / stop process. In switching the cooling air from the cooling air to the cooling steam or from the cooling steam to the cooling air, control is performed so as to eliminate a temperature difference between the cooling air and the cooling steam or within an allowable range. How to start / stop the power plant. 2. A gas turbine for cooling a high-temperature portion using cooling air extracted from a compressor during a start / stop stroke and cooling steam generated by a waste heat recovery boiler during a load operation. In a method for starting / stopping a combined power generation plant including a waste heat recovery boiler that generates steam by using a combustion gas exhausted from the gas turbine and a steam turbine driven by the steam, the method includes the steps of: A combined power generation plant that switches from the cooling air to the cooling steam or from the cooling steam to the cooling air, and at this time, eliminates the temperature difference between the cooling air and the cooling steam, or controls the temperature to an allowable range. Start / stop method. 3. The cooling device according to claim 1, wherein cooling means is provided in a path for supplying cooling air extracted from the compressor to a high-temperature portion of the gas turbine, and controls a temperature of the cooling air. Start / stop method of the combined power plant. 4. The control of a temperature difference between the cooling air and the cooling steam according to claim 1, 2 or 3,
A method for starting / stopping a combined power generation plant, comprising controlling a variable stator vane of the compressor to adjust a compressor suction air flow rate to lower a temperature of the cooling air. 5. The control of the temperature difference between the cooling air and the cooling steam according to claim 1, 2 or 3,
A method for starting / stopping a combined power generation plant, wherein a pressure in a steam drum of the steam turbine is controlled to increase a temperature of the cooling steam.