JPS5845566B2 - combined cycle power plant - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises a gas turbine device, an exhaust gas recovery boiler device that heats a fluid using the exhaust gas of the gas turbine device as a heat source, and a steam turbine device that is operated by the heated fluid. Concerning improvements to combined cycle power plants.

First, a conventional combined cycle power plant of this type will be explained with reference to FIG.

The gas turbine device 2 includes a compressor 4 that pressurizes air, a combustor 6 that combusts the air pressurized by the compressor 4, and a gas turbine 8 that expands high-temperature gas generated by this combustion to do work. and a generator 10 driven by this gas turbine 8.

The combustion gas leaving the gas turbine 8 is then transferred to a conduit 12.
It is guided to the exhaust gas recovery boiler device 14 via the boiler device 14, and is used as a heat source for steam generation within the boiler device 14.

The exhaust gas recovery boiler device 14 is connected with a economizer 16, an evaporator 18, a drum 20, and a superheater 22.
Steam from the steam turbine 26 of the steam turbine device 24 is transferred to the condenser 30 and the feed water heater 3 by the feed water pump 28.
2, the water is sent to the economizer 16 as water.

The water sent to the economizer 16 is heated here, enters the drum 20, is evaporated by the evaporator 18, and the steam is heated in the heater 22 and then led to the steam turbine 26.

The steam then expands within the steam turbine 26 to perform work and drive the generator 34.

Note that the steam in the steam turbine 26 becomes water again in the condenser 30, and the above-described process is repeated.

Figure 2 shows the exhaust gas recovery boiler device 14 in the configuration shown in Figure 1.
This is a graph showing the correlation between the exhaust gas temperature and the water-steam temperature.
is increased to superheated steam (temperature 22b), while the gas temperature decreases from T6 to T7.

This gas is then supplied to the evaporator 18 to turn the saturated water (temperature 18a) into saturated steam at the same temperature (18b), and the gas temperature drops to T8 and enters the economizer 16.

Here, the gas is sent from the water supply pump 28 at a temperature of 1
The water at 6a is heated to 16b and the gas temperature is lowered to T9 before leaving the boiler device 14.

Next, FIG. 3 shows changes in the temperature of each part in the combined cycle power plant as shown in FIG. 1 with respect to the output of the gas turbine 8.

By the way, when the air compressor 4 is directly connected to the gas turbine 8, the rotation speed of the air compressor 4 is constant, and the flow rate of air sent from the compressor 4 to the combustor 6 of the gas turbine 8 is almost constant. be.

Therefore, to reduce the output of the gas turbine 8,
It is necessary to reduce the flow rate of fuel to the gas turbine 8 to lower the temperature of the combustion gas.

Line a in FIG. 3 shows the temperature of the combustion gas of such a gas turbine 8.

Corresponding to this decrease in the temperature of the combustion gas, the exhaust gas temperature of the gas turbine 8 also decreases almost linearly.

Moreover, as shown in FIG. 2, the steam temperature 22b at the outlet of the exhaust gas recovery boiler device 14 depends on the temperature T6 of the exhaust gas of the gas turbine 8, so as the output of the gas turbine 8 is reduced, the line in FIG. As shown in C, boiler device 1
The steam temperature at the outlet of No. 4 will drop.

In addition, in order to match the discharge flow rate of the air compressor with the flow rate required by the gas turbine, conventionally, the drive shaft of the air compressor is separated from the drive shaft of the gas turbine. A technique was used in which a flow rate adjustment means such as a guide vane was provided.

FIG. 4 shows the changes in air amount and gas turbine exhaust temperature under various control methods, and the range of decrease in exhaust gas temperature corresponding to the gas turbine output is:
The case of a single-shaft gas turbine shown by curve A is the worst,
Curve C for a two-shaft gas turbine is the smallest.

Furthermore, in the method using guide vanes, the air volume can be adjusted within a range up to about 80% output, which is in the middle between the two as shown by curve B.

The range of change in steam temperature is 2 between zero output and rated output.
00° C. or higher, and therefore the thermal stress generated in the rotor (not shown) of the steam turbine 26 is sometimes excessive.

Therefore, in order to repeatedly start and stop such a combined cycle power plant every day, the rate of change in steam temperature must be kept gradual so that the generated thermal stress falls within the allowable value of the cyclic fatigue strength of the steam turbine 26. However, this has the disadvantage that it takes a long time to start up and shut down the plant.

An object of the present invention is to provide a combined cycle plant that suppresses sudden changes in the temperature of steam flowing into a steam turbine and prevents excessive stress from being generated in the steam turbine even when the load of the combined cycle plant suddenly changes. be.

The present invention will be explained below with reference to embodiments shown in FIGS. 4 to 6.

Note that the same components as those of the conventional device described above are denoted by the same reference numerals in the drawings, and the explanation thereof will be omitted.

FIG. 5 shows a first embodiment of the present invention, and the basic configurations of the gas turbine device 2, the exhaust recovery boiler device 14, and the steam turbine device 24 are the same as those of the conventional device explained with reference to FIG. be.

Then, the exhaust gas recovery boiler device 14 and the steam turbine device 2
4 through a water supply pipe 36 and a steam pipe 38.

Further, a pair of control valves 54 and 56 are installed in parallel in a pipe line 52 extending from the drum 20 to the superheater 22.

A bypass line 40 is provided from the drum 20 to the condenser 30, and this line 40 has a control valve 42.
is interposed.

On the other hand, a desuperheater 44 and a control valve 46 are interposed in the conduit 38 that reaches the steam turbine 26 from the superheater 22, and a conduit 48 that communicates the bypass conduit 40 and the desuperheater 44 is provided. A control valve 50 is interposed in this conduit 48 .

Further, a bypass pipe 58 is provided that communicates the pipe 38 with the condenser 30, and this pipe 58 has a control valve 6.
0 is inserted.

In addition, a pressure detector 62 is installed in the pipe line 40, a temperature sensor 64 and a pressure sensor 66 are installed in the @pipe line 38, and the control valves 42, 46, 50, 56, 6 are interposed.
0, the pressure sensors 62, 66 and the temperature sensor 64 are controlled by a main controller 68.

On the other hand, the air compressor 4 of the gas turbine device 2 is for supplying compressed air to the combustor 6, and a part of the air whose temperature has been increased by this compression is returned to the inlet of the compressor 4. A closed conduit TO is provided for this purpose, and a damper 72 is interposed in this conduit 70.

This damper 72 is controlled by a main controller 74 of the gas turbine device 2.

That is, the output request signal from the master controller 74 is input to a controller 76 for producing a temperature set point signal as a function of the output signal.

This set point signal is compared with a signal generated by a detector 78 of the temperature of the air entering the air compressor 4, and the opening of the damper 72 is controlled.

Therefore, the damper 72 functions to circulate the high temperature air at the outlet of the air compressor 4 to the inlet side until the air temperature reaches a set value.

Further, the pipe line 70 branches in the middle to form a pipe line 80 that directly releases a portion of the compressed air into the atmosphere, and this pipe line 80 has a damper 82 controlled by the main controller 74.
is interposed.

Next, the operation of the above-described embodiment will be explained.

In FIG. 5, when the combined cycle power plant is operated at the rated output and the output is reduced, whether the change width of the outlet steam temperature of the exhaust gas recovery boiler device 14 based on the temperature change of the exhaust gas of the gas turbine 8 is equal, Alternatively, in a relatively high load range that does not cause problems for the steam turbine 26, the output of the combined plant can be reduced by reducing the amount of fuel supplied to the gas turbine 8, thereby reducing the output of the generator 10.34. All you have to do is reduce it.

On the other hand, the opening degree of the control valve 46 is controlled so as to keep the steam pressure at the inlet of the turbine 8, which is sensed by the pressure detector 66, substantially constant.

To respond to even larger load drops, the control valve 54, which is normally fully open, is closed, and the main controller 68, which generates a set pressure signal as a function of the steam turbine 26, reduces the opening of the control valve 56. The flow rate of steam flowing into the steam turbine 26 is reduced while keeping the opening degree of the steam turbine 46 substantially constant.

In other words, by narrowing the opening degree of the control valve 56, the drum 20
The steam pipe 38 from the superheater 22 to the steam turbine 26 is reduced by reducing the amount of steam flowing from the superheater 22 to the superheater 22, and reducing the amount of steam that is heat exchanged with the exhaust gas in the exhaust heat recovery boiler in the superheater 22. The temperature of the steam flowing into the steam turbine 26 is maintained at a high temperature within a predetermined value, thereby preventing a sudden change in the temperature of the steam flowing into the steam turbine 26, thereby preventing the generation of excessive stress.

Also, by this operation, the control valve 42 is operated so that the pressure of the drum 20 of the exhaust gas recovery boiler device 14 detected by the pressure detector 62 does not exceed a certain value, and excess generated steam is routed through the pipe 40. It is discharged to the condenser 30 through the condenser 30.

During this operation, since the same amount of fuel is supplied to the gas turbine 8, the gas temperature at the inlet of the exhaust recovery boiler device 14 remains constant, which is effective in producing a high steam temperature.

Furthermore, the steam pressure flowing through the superheater 22 is lowered by the throttle operation of the control valve 56, and the heat absorption efficiency is improved, thereby further increasing the outlet steam temperature.

Next, another embodiment of the present invention will be described.

In other words, in FIG.
is provided, and a portion of the air that has been compressed to a high temperature by the air compressor 4 is supplied to the compressor 4 again to increase the temperature of the intake air of the compressor 4.

As a result, the discharge air flow rate can be reduced, and as a result, the temperature of the gas exiting the combustor 6 can be brought closer to the rated value, and therefore the temperature of the exhaust gas exiting the gas turbine 8 can be kept high.

Furthermore, the air compressor 4 is provided with a pipe line 80 that can directly discharge a portion of the compressed air into the atmosphere.

Therefore, in partial load operation of the gas turbine 8,
It is possible to prevent the flow rate of air from being sent to the combustor 6 in excess of that required, thereby keeping the temperature of the gas supplied from the combustor 6 to the gas turbine 8 high, and reducing the exhaust gas supplied to the exhaust gas recovery boiler device 14. temperature can be kept high.

FIG. 6 shows still another embodiment of the present invention,
Illustration of the steam turbine device is omitted.

In FIG. 6, in order to increase the inlet air temperature of the air compressor 4, a gas cooler 84 is provided on the exhaust gas outlet side of the exhaust gas recovery boiler device 14, and an air preheater 86 is provided on the inlet side of the air compressor 4. , these coolers 84 and preheaters 86
A closed pipe line 88 is communicated between the two, and hot water is recirculated by a recirculation pump 90.

Therefore, the air supplied to the air compressor 4 is preheated.

According to the present invention, even if the load of the combined cycle plant suddenly changes, the amount of steam flowing through the exhaust heat recovery boiler is adjusted so that the temperature of the steam flowing into the steam turbine does not change significantly. This has the effect of preventing excessive stress from being generated in the steam turbine.

[Brief explanation of drawings]

Fig. 1 is a system diagram showing a conventional combined cycle power plant, Fig. 2 is a graph showing temperature changes of the gas and steam in Fig. 1, and Fig. 3 is a graph showing temperature states according to the output of the gas turbine. FIG. 4 is a graph showing the relationship between output and temperature depending on the type of gas turbine, and FIGS. 5 and 6 are system diagrams showing embodiments of the combined cycle power plant according to the present invention. 2...Gas turbine device, 14...Exhaust recovery boiler device, 24...Steam turbine device, 40...Pipe line, 42...・Control valve.

Claims (1)

[Claims] 1. A gas turbine device, an exhaust heat recovery boiler device that generates steam using the exhaust gas of the gas turbine device as a heat source,
In a combined cycle power plant equipped with a steam turbine device driven by steam generated by this boiler device, a steam flow path is installed in the middle of the steam flow path in the exhaust heat recovery boiler device according to load changes of the plant. A combined cycle power generation plant characterized by installing a steam flow rate control device for regulation. 2. The steam flow rate control device described in @ is a steam flow rate control valve installed in a steam pipe that communicates between a drum that generates saturated steam that is included in the exhaust heat recovery boiler device and a heater that heats the saturated steam. The combined cycle power plant according to claim 1, further comprising: a control device that controls the opening degree of the steam flow rate control valve in accordance with changes in plant load. 3. The combined cycle according to claim 1 or 2, characterized in that the steam flow path of the exhaust heat recovery boiler device is provided with a derivation pipe for deriving surplus steam to a condenser. power plant. 4 In the steam flow path of the waste heat recovery boiler device mentioned in @, a branch pipe is installed to guide excess steam to the main steam pipe leading from the heater to the steam turbine, and a junction between this branch pipe and the main steam pipe is installed. The combined cycle power plant according to claim 1, 2 or 3, characterized in that a temperature reduction device is installed at each location.