JPS6152361B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas turbine, an exhaust heat recovery boiler that generates steam from its exhaust gas, a steam turbine that is driven by the generated steam, a condenser, and a condenser. a deaerator that deaerates condensate from the water heater using extraction air from the steam turbine and steam from the exhaust heat recovery boiler as a heat source; The present invention relates to a pressure control device for a deaerator in a combined power generation plant equipped with a water supply system that supplies water to the plant.

In this type of combined cycle power plant, water is supplied to the waste heat recovery boiler by installing a deaerator in the middle of the water supply system to prevent corrosion of the waste heat recovery boiler, thereby extracting oxygen from the water supply. Generally, the water is then supplied to an exhaust heat recovery boiler. In order to improve the thermal efficiency of the power generation plant, the deaerator usually uses extracted air extracted from the middle stage of the steam turbine as its heat source.
When the steam turbine is operating at low load or temporarily stopped (combined power generation plants often start early in the morning and shut down at night), the necessary heat source cannot be secured from the steam turbine, so the steam generated by the drum of the heat recovery boiler is used. The reduced pressure is used as a heat source. In addition, the lower the temperature of the water supply at the exhaust heat recovery boiler inlet, the more heat from the exhaust gas can be absorbed.
Improves the thermal efficiency of power plants. For this reason, the operating pressure of the deaerator is generally lower than that of a normal thermal power plant, and low-temperature feed water is sent to the waste heat recovery boiler. In addition, when the steam turbine is stopped, the condenser breaks the vacuum and returns to atmospheric pressure, so if the pressure in the deaerator is below atmospheric pressure, air will leak from the condenser side and remain in the deaerator water storage tank. To prevent this from increasing oxygen concentration in the water, it is necessary to maintain the deaerator pressure slightly above atmospheric pressure.

Figure 1 shows the system of a combined cycle power plant equipped with a conventional deaerator pressure control device, in which 1 is a gas turbine, 2 is an exhaust heat recovery boiler that generates steam from its exhaust gas, a superheater 3, It is equipped with a denitrification device 4 and a carbon saver 5. 6 is a steam turbine driven by the steam generated in the superheater 3 of the exhaust heat recovery boiler 2; 7 is a condenser; 8 is a main steam pipe; 9 is a turbine bypass steam pipe; 10 is a turbine inlet valve; 11
is a bypass stop valve, 12 is a deaerator, 13 is a deaerator water storage tank, and 14 is a condensate pump 1 that transfers the condensate from the condenser 7.
5 is a condensate pipe that increases the pressure and sends it to the deaerator 12; 16 is a turbine bleed pipe that uses steam from the middle stage of the steam turbine 6 as a heat source to send it to the deaerator 12; 17 is a check valve thereof;
18 is a water supply pipe that increases the pressure of water in the deaerator water storage tank 13 by a boiler water supply pump 19 and sends it to the economizer 5 of the exhaust heat recovery boiler 2; 20 is a water supply pipe between the deaerator water storage tank 13 and the boiler water supply pump 19; 21 is a flow meter provided in the water supply pipe 18,
22 is a boiler drum 24 that introduces water superheated by the economizer 5 via piping 23 to generate steam;
25 is a heating steam pipe that sends the generated steam to the superheater 3 as a heat source, and 26 is a deaerator pressure control valve provided in the pipe 25. , 27 is a deaerator pressure regulator that adjusts the opening degree of the pressure regulating valve 26 in accordance with the comparison result between the set pressure of the setting device 28 and the actual pressure of the deaerator 12. Note that 29 is a vent pipe for returning the gas degassed in the deaerator 12 to the condenser 7, and 30 is a chimney for exhaust gas.

As mentioned above, combined cycle power plants with the above configuration are often operated by starting early in the morning and stopping at night.
The steam generated is sent to the deaerator 12 through the deaerator pressure control valve 26 of the heating steam pipe 25,
2 is pressurized above atmospheric pressure. When the gas turbine 1 is started in this state, the exhaust gas is sent to the exhaust heat recovery boiler, passes through the superheater 3, the denitrification device 4, and the economizer 5, and is emitted into the atmosphere from the chimney 30. Steam generated from the boiler drum 22 during operation of the gas turbine 1 is superheated by the superheater 3 and then discharged to the condenser 7 through the main steam pipe 8 and the turbine bypass steam pipe 9, where it is condensed. and becomes water. When ventilation to the steam turbine 6 becomes possible, the turbine bypass stop valve 11 is gradually closed, and steam is sent to the steam turbine 6 through the turbine inlet valve 10.

On the other hand, the condensate stored in the condenser 7 is pressurized by the condensate pump 15 and passes through the condensate pipe 14 to the deaerator 12.
sent to. The condensate sent to the deaerator 12 is superheated and deaerated by the steam generated in the boiler drum 22, and then stored in the deaerator water storage tank 13. The stored water passes through the downcomer pipe 20, is pressurized by the boiler water supply pump 19, and is sent to the energy saver 5 of the waste heat recovery boiler 2 via the water supply pipe 18, where it is heated by exhaust gas and then pumped to the boiler. It is sent to the drum 22.
Then, when the extraction pressure of the steam turbine 6 rises and exceeds the set pressure of the deaerator pressure regulator 27, the deaerator pressure control valve 26 closes and the heat source of the deaerator 12 is extracted from the steam in the boiler drum 22. Switch to steam.

FIG. 4 is a graph showing an example of the pressure characteristics of a conventional deaerator in the combined power generation plant, in which the vertical axis shows pressure and the horizontal axis shows steam turbine output. When starting the steam turbine, the deaerator pressure controller is set to a pressure slightly higher than atmospheric pressure (1.3Kg/cm ² A) as shown in a, and the steam generated in the boiler drum is transferred to the deaerator. The pressure in the deaerator is controlled to be constant by adjusting the pressure with a pressure regulating valve 26. It is at the point when the steam turbine reaches high output (77% output) that the extraction pressure of the steam turbine exceeds the set pressure of the deaerator pressure regulator 27 and switches to the steam generated in the boiler drum. .
Therefore, when the output of the steam turbine is 77% or less, the deaerator is heated by the steam generated in the boiler drum, which has a higher pressure than the steam turbine bleed air. That is, the temperature of the water supplied to the waste heat recovery boiler increases, which reduces the thermal efficiency of the power generation plant.

In the conventional pressure control device, even at low output, the setting value of the deaerator pressure regulator is set as shown by b.
It is set at 0.45Kg/cm ² A. That is, when the steam turbine reaches its minimum stable output (25% output), the heat source of the deaerator is switched to the extraction pressure.

However, in the above-mentioned pressure control device, once the set value is set, it is held in a fixed state, so when the steam turbine reaches the minimum stable output operation after starting, the deaerator The setting value of the pressure regulator is 1.3Kg/cm ² as shown by the chain arrow c.
If the drop is from A to 0.45Kg/ ^cm2A , if the drop is rapid, there will be a large amount of water in the deaerator water storage tank (generally, at 25% output of the steam turbine, the capacity will be about 20 to 40 minutes of water supply). ), there is a risk that flash will occur in the deaerator water storage tank or downcomer pipe, causing cavitation of the boiler feed pump. Therefore, it is necessary to perform the setting value switching operation very slowly, but since this operation is generally performed manually, it requires considerable skill.

Also, set the deaerator pressure controller to 0.45Kg/cm ² A.
If the steam turbine were to trip when the deaerator was operated with the deaerator pressure increasing as shown by d due to the extraction pressure,
Air bleed to the deaerator stops, and the pressure in the deaerator drops rapidly from the pressure inside the chamber during turbine bleed to the set pressure of the deaerator pressure controller, causing a flash in the deaerator water storage tank and downcomer pipe. occurs, causing cavitation of the boiler feed pump.

Furthermore, in conventional pressure control devices, when shutting down the power plant, in order to maintain the deaerator above atmospheric pressure as described above, the setting value of the deaerator pressure regulator is raised to 1.3 Kg/cm ² A again. I had to.

In view of the above points, the present invention has been developed to control the operating pressure of the deaerator every day, including when the steam turbine is tripped.
It is an object of the present invention to provide a pressure control device for a deaerator that can automatically control the power plant to be in an optimal state even when the power plant is shut down, and that can facilitate the operation of a power plant.

In order to achieve the above object, the pressure control device of the present invention includes a deaerator pressure control valve provided in a pipe that sends steam from an exhaust heat recovery boiler to a deaerator, and an opening degree of the deaerator pressure control valve. A deaerator pressure regulator that adjusts the deaerator pressure according to the comparison result between the actual deaerator pressure and the set pressure, and a deaerator pressure regulator that adjusts the set pressure given to the deaerator pressure control valve so that the exhaust heat recovery boiler feed water flow rate is below a predetermined amount. In the range above, the pressure is gradually decreased as the flow rate increases, and in the range above a predetermined amount, the pressure is gradually increased at a point that is always lower than the extraction pressure from the steam turbine. However, the above-mentioned predetermined amount of water supply flow rate is a water supply flow rate corresponding to the minimum stable output of the steam turbine.

EMBODIMENT OF THE INVENTION Hereinafter, one embodiment of the pressure control device for a deaerator of the present invention will be described based on FIGS. 2 and 3. Second
The figure shows a system of a combined power generation plant equipped with the pressure control device of the present invention, and the same reference numerals as in FIG. 1 indicate the same ones. The heating steam pipe 25 is equipped with a deaerator pressure regulating valve 260, and the opening degree of the deaerator pressure regulating valve 260 is adjusted by a deaerator pressure regulator 270. That is, it is adjusted according to the comparison result between the actual pressure of the deaerator 12 and the set pressure. The pressure setting device 31 that provides a set pressure to the deaerator pressure regulator 270 is a flow meter 2 provided in the water supply pipe 18.
A first computing unit 32 and a second computing unit 33 to which the water supply flow rate signal S of 1 is input;
The signal selector 34 selects the larger output signal from among the output signals of the arithmetic unit 33. The first arithmetic unit 32 is configured to decrease its output reliability as the input signal increases, and the second arithmetic unit 33 is configured to increase the output signal as the input signal increases. The pressure setting device 31 configured as described above changes the set pressure given to the deaerator pressure regulator 270 to increase the exhaust heat recovery boiler feed water flow rate, that is, the feed water flow rate flowing through the water supply pipe 18 in a range below a predetermined amount. In addition, in a range exceeding a predetermined amount, the pressure is always gradually reduced compared to the extraction pressure from the steam turbine. The point at which the output signal of the pressure setting device 31 changes from "decrease" to "increase" is the flow point at which the feed water flow rate corresponds to the lowest stable output of the steam turbine.

The above-mentioned pressure setting will be specifically explained with reference to FIG. FIG. 3 is a graph showing an example of the pressure characteristics of the deaerator in the present invention, in which the vertical axis shows the pressure and the horizontal axis shows the exhaust heat recovery boiler feed water flow rate. e indicates the set pressure characteristic of the first computing unit 32, f indicates the set pressure characteristic of the second computing unit 33, and d indicates the pressure characteristic in the deaerator during turbine extraction. That is, the first computing unit 32 outputs a setting signal of a pressure slightly higher than atmospheric pressure (1.3 Kg/cm ² A) when the feed water flow rate signal S is 0%, and when the feed water flow rate signal S is When the flow rate corresponds to the lowest stable output, a setting signal of a pressure (0.35 Kg/cm ² A) slightly lower than the extraction pressure is output. In addition, the second computing unit 33 calculates a pressure ⁽ 1.6 Kg/cm ² A) setting signal is output. Also, when the water supply flow rate signal is 25%, a setting signal of a pressure (0.35 Kg/cm ² A) slightly lower than the extraction pressure is output.

Next, the function of pressure control of the deaerator of the present invention will be explained. As mentioned above, combined cycle power plants are often operated in such a way that they start up early in the morning and shut down at night, so we will explain starting up after shutting down at night as an example. Steam generated in the boiler drum 22 by the heat retained in the exhaust heat recovery boiler 2 is sent to the deaerator 12 through the deaerator pressure control valve 260 provided in the heating steam pipe 25, and the deaerator 12 is brought to atmospheric pressure. Pressurize above (1.3Kg/cm ² A).
When the gas turbine 1 is started in this state,
The exhaust gas is sent to the exhaust heat recovery boiler 2, passes through the superheater 3, the denitrification device 4, and the economizer 5, and is released into the atmosphere from the chimney 30. Steam generated in the boiler drum 22 by the operation of the gas turbine 1 is superheated by the superheater 3 and then discharged to the condenser 7 through the main steam pipe 8 and the turbine bypass steam pipe 9, where it is It condenses and becomes condensate. steam turbine 6
Turbine bypass stop valve 1
1 is gradually closed, and steam is sent to the steam turbine 6 through the turbine inlet valve 10. On the other hand, the condensate stored in the condenser 7 is pressurized by the condensate pump 15 and sent to the deaerator 12 through the condensate pipe 14. The condensate sent to the deaerator 12 is heated and deaerated by the steam generated in the boiler drum 22, and then stored in the deaerator water storage tank 13. The stored water passes through the downpipe 20, is pressurized by the boiler feed pump 19, passes through the flow meter 21 of the water supply pipe 18, and is sent to the energy saver 5 of the waste heat recovery boiler 2, where it is heated by exhaust gas. After that, it is sent to the boiler drum 22. The above is exactly the same as described in the prior art. However, in the present invention, when the output of the gas turbine 1 increases, the amount of steam generated by the boiler also increases (the amount of water supply also increases), and when the water supply flow rate signal S reaches 25%, the set pressure of the deaerator pressure controller 270 changes. It becomes 0.35Kg/cm ² A. When increasing the output of the steam turbine 6 in accordance with the output of the gas turbine 1, the point in time when the steam turbine extraction pressure becomes higher than the set pressure of the deaerator pressure controller 270 (in the example of FIG. 3, the feed water flow rate signal After that (when S is 23%), the heating steam source for the deaerator 12 is switched from the steam generated by the boiler drum 22 to the extracted steam from the steam turbine 6. The bleed air is sent to the deaerator 12 through the bleed pipe 16. By the way, when starting up an actual combined cycle power plant, due to its startup characteristics, the rise in the output of the steam turbine 6 is often delayed by about 10 to 20 minutes with respect to the rise in the output of the gas turbine 1. In this case, the steam generated by the boiler is It is discharged through a bypass steam pipe 9 to a condenser. Furthermore, when reducing the output of the steam turbine 6 while the gas turbine 1 and the steam turbine 6 are operating at high output, or when continuing to operate the gas turbine 1 even when the steam turbine 6 trips, exhaust heat recovery is required. The operation of the boiler 2 continues, and the steam generated from the boiler 2 is discharged to the condenser 7 through the turbine bypass steam pipe 9. When the output of the steam turbine 6 is reduced or the steam turbine 6 trips, the extraction pressure decreases. In this case, the set pressure of the deaerator pressure regulator 270 is always slightly lower than the deaerator operating pressure during normal operation (0.1 Kg/cm ² in the example shown in FIG. 3). Immediately after the pressure drops to the set pressure, the deaerator pressure control valve 260 opens in response to an output signal from the deaerator pressure regulator 270, and the steam generated in the boiler drum 22 is sent to the deaerator 12. That is, the extraction pressure is backed up and the deaerator 1
2, the occurrence of flash in the deaerator water storage tank 13 and the downcomer pipe 20 is eliminated. Therefore, the boiler feed pump 19 can continue to operate safely.

In the above embodiment, the deaerator pressure regulator 27
The feed water flow rate signal of the waste heat recovery boiler 2 was given as a signal to change the set value of 0, but signals equivalent to this feed water flow rate signal, that is, the amount of steam generated by the waste heat recovery boiler, the amount of water fed to the deaerator, and the gas turbine output The signal may have a state value that is proportional or approximately proportional to the water supply flow rate.

As described above, according to the present invention, the operating pressure of the deaerator can be maintained at the optimum state at all times, not only during daily startup and shutdown, but also during steam turbine trips, without increasing the heat loss of the combined cycle power plant. Since automatic control is possible, plant operation becomes easier.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a combined cycle power plant equipped with a conventional deaerator pressure control device, and FIG. 2 is a system diagram of a combined cycle power plant equipped with an embodiment of the deaerator pressure control device of the present invention. FIG. 3 is a graph showing the operating characteristics of the deaerator according to the present invention, and FIG. 4 is a graph showing the operating characteristics of the conventional deaerator. 1...Gas turbine, 2...Exhaust heat recovery boiler,
6... Steam turbine, 7... Condenser, 12... Deaerator, 18... Water supply pipe, 21... Flow meter, 22...
... Boiler drum, 25 ... Heating steam pipe, 260 ...
... Deaerator pressure control valve, 270 ... Deaerator pressure regulator, 31 ... Pressure setting device, 32 ... First calculation unit, 33 ... Second calculation unit, 34 ... Signal selector,
S...Water supply flow rate signal.

Claims (1)

[Scope of Claims] 1. A gas turbine, an exhaust heat recovery boiler that generates steam using its exhaust gas, a steam turbine that is driven by the generated steam, a condenser, and a steam turbine that generates steam from the condenser. a deaerator that deaerates condensate using extraction air from the steam turbine and steam from the exhaust heat recovery boiler as a heat source; and a water supply system that sends water deaerated by the deaerator to the exhaust heat recovery boiler. A combined power generation plant comprising: a) a deaerator pressure control valve provided in a pipe that sends steam from the waste heat recovery boiler to the deaerator; b; c) a deaerator pressure regulator that adjusts the actual pressure according to a comparison result with a set pressure, and c a pressure setting device that provides a set pressure to the deaerator pressure regulator; 1st and 2nd for inputting the feed water flow rate signal of the heat recovery boiler or its equivalent signal;
and a signal selector that selects the larger output signal of the output signals of the first and second arithmetic units, and the first arithmetic unit increases the output as its input signal increases. The second computing unit is configured such that the output signal increases as the input signal increases, and the pressure setting device is configured such that: Under conditions where the flow rate is less than the minimum stable output of
The set pressure is gradually decreased as the feed water flow rate increases, and (b) when the feed water flow rate of the exhaust heat recovery boiler exceeds the flow rate corresponding to the minimum stable output of the steam turbine, the set pressure is reduced to a range below the steam turbine extraction pressure. 1. A pressure control device for a deaerator in a combined power generation plant, characterized in that it is configured to gradually increase the pressure within the deaerator.