JPS6242123B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a steam temperature control device at the time of startup of a power plant, and in particular, a high pressure (main) turbine bypass valve, a spray valve for regulating the steam temperature at the inlet of a reheater, and a medium/low pressure turbine bypass valve are attached. The present invention relates to a steam temperature control device at the time of startup of a power generation plant that can suitably control steam conditions passing through a turbine at the time of startup. First, with reference to FIG. 1, a schematic configuration of a conventional boiler (once-through boiler) in a thermal power plant will be described. In the figure, 1 is the boiler body, 1A is the furnace water wall, 2 is the burner, 3 is the gas recirculation fan, 4 is the economizer, 5 is the primary reheater, 7 is the secondary reheater, 8 is the 2
A secondary superheater, 9 a main stop valve provided in the main steam pipe 16, 10 an intercept valve provided in the reheat steam pipe 17, 11 a high pressure (main) turbine, and 12 a medium/low pressure turbine. Further, 13 is a condenser, and 14 is the turbine 1.
1, a generator driven by 1 and 12; 15, a high-pressure (main) turbine bypass valve for releasing steam in the main steam pipe 16 to the condenser 13; 18, a desuperheater;
9 is a spray valve, 20 is a main steam temperature detector, 20
A is a desuperheater outlet steam temperature detector, and 21 is a reheat temperature detector. The fuel supplied to the burner 2 is mixed with air and combusted within the boiler main body 1 to become combustion gas.
Combustion gas flows through the furnace water cooling wall 1A, secondary superheater 8, 2
The gas passes through the flue while sequentially exchanging heat in the reheater 7, etc., and is discharged from the chimney. At this time, a part of the combustion gas is returned into the boiler main body 1 by the gas recirculation fan 3 and used to control the reheat steam temperature. On the other hand, the water sent from the water supply pump (not shown) to the energy saver 4 recovers its heat there, then reaches the water cooling wall 1A of the furnace, evaporates on the way up the water cooling wall, and evaporates in the primary superheater 6. enters and becomes overheated. This steam further reaches a superheater spray (not shown). After the temperature of the steam is reduced by the superheater spray so that the main steam temperature reaches a specified value, the steam is further heated for 2 seconds.
Next, it enters the superheater 8, is superheated, and passes through the main steam pipe 16 and main stop valve 9 to the high pressure (main) turbine 1.
1, where it does the job of driving a generator. The steam that has done work in the high pressure (main) turbine 11 is
It enters the primary reheater 5 and is reheated. This steam is 2
It is further reheated in the next reheater 7 and sent to the medium/low pressure turbine 12 via the reheat steam pipe 17 and the intercept valve 10, where it performs further work. However, when the power plant is started up, the main steam temperature has not risen to the specified value, and the turbine and generator 14 are not rotating. On the other hand, at this time, from the secondary superheater 8 to the main steam pipe 1
6 is bypassed to the attemperator 18 via the high-pressure (main) turbine bypass valve 15, where it is cooled to a specified value by the spray valve 19, and then the condenser 13 and feed water pump are The energy is returned to the economizer 4 via the energy saving device 4. FIG. 3 is a block diagram of a conventional main steam temperature control device during startup of the thermal power plant of FIG. 1. Note that such conventional technology includes, for example,
It is disclosed in pages 202-203 of ``Thermal Power Generation Essentials'' published by Thermal Power Generation Technology Association on February 25, 1971. In the figure, 27 is a function generator that determines the relationship between the main steam temperature and the opening degree of the high pressure (main) turbine bypass valve 15, 28 is a high signal selector, 29 is a proportional integrator, 30 is a rate of change limiter, 31 is an adder, 32
33 is a signal generator that determines the main steam temperature target value. Further, 33A is a signal generator that determines the steam temperature target value at the outlet of the desuperheater 18, 34 is a proportional calculator, and 35 is a signal generator that selects a main steam temperature detector signal when the main steam temperature is below a certain predetermined value. , and is a monitor relay that controls the switch 32 so that the signal from the signal generator 33 is selected when the value exceeds the predetermined value. At the beginning of the start-up of the plant, that is, at the ignition time t ₀ shown in FIG. The steam temperature (output of the main steam temperature detector 20) itself is selected and fed to an adder 31 via a rate of change limiter 30. Therefore, adder 31 and proportional integrator 29
The outputs of both will be 0. As a result, the high signal selector 28 selects the output of the function generator 27, and the opening degree of the high pressure (main) turbine bypass valve 15 is controlled accordingly. That is, as shown by curves D and F in FIG. 2, the main steam temperature and the high pressure turbine bypass flow rate gradually increase over time from the boiler ignition time _t0 . On the other hand, the opening degree of the spray valve 19 is set such that the steam temperature at the outlet of the attemperator 18 (the output value of the attemperator outlet steam temperature detector 20A) is maintained at the target temperature set by the signal generator 33A. This is controlled by a proportional calculator 34. At time t ₁ , when the main steam temperature reaches the predetermined value T ₀ , the monitor relay 35 activates the switch 32 to select the signal from the signal generator 33 . The signal of the signal generator 33 is shown in FIG. 2 by a curve D0. The rate of change of the signal is limited by a rate of change limiter 30, and converted into a main steam temperature target value, for example, as indicated by the straight line D1 in FIG. As a result, the adder 31 and the proportional integrator 29
produces an output, the output is selected by the high signal selector 28, and the opening control of the high pressure (main) turbine bypass valve 15 is executed with the straight line D1 as the target value. When the main steam temperature (curve D) exceeds the specified value,
At time t ₂ , the main stop valve 9 is opened and the flow of steam to the high pressure (main) turbine 11 is started. As a result, the rotation speeds of the turbine and generator 14 begin to increase, as shown by curve A in FIG. The steam that has done work in the high pressure (main) turbine 11 is
As mentioned above, the primary reheater 5 and the secondary reheater 7
The steam is reheated and supplied to the medium/low pressure turbine 12 via the reheat steam pipe 17 and the intercept valve 10. The flow rate of the reheated steam also gradually increases, as shown by curve G in FIG. As is clear from the above explanation, the once-through boiler and drum boiler shown in Fig. 1 do not have a turbine bypass system, so at the time of plant startup - that is,
(Before passing through the turbine), steam does not flow to the primary and secondary reheaters 5 and 7. Therefore, from the viewpoint of protecting the reheater from overheating, the amount of fuel supplied to the boiler is restricted, making it difficult to shorten the unit start-up time. In addition, since the headers of the reheaters 5 and 7 are installed outside the furnace, they are often cooled before steaming through the turbine, and when steaming through the turbine, the reheated steam temperature is As shown by curve E in the figure, the temperature decreases temporarily and becomes much lower than the metal temperature of the medium/low pressure turbine 12. This increases the thermal stress of the turbine, and from this point of view as well, there is a drawback that the unit start-up time cannot be shortened. In addition, in FIG. 2, curve B represents the fuel flow rate supplied to the boiler, and curve C represents the fuel flow rate supplied to the generator 14.
represents the change in load. Further, t ₃ is the timing of load addition. The purpose of the present invention is to improve the conventional drawbacks during power plant start-up, to prevent a temporary drop in reheat steam temperature, thereby minimizing the thermal stress on the turbine and shortening the start-up time. An object of the present invention is to provide a steam temperature control device that can control the temperature of steam at the time of startup of a power generation plant. In order to achieve the above object, in the present invention, a medium/low pressure turbine bypass valve, a medium/low pressure turbine exhaust steam stop valve, a reheat steam warming valve, etc. are additionally equipped to the conventional equipment, and when the plant is started up, Steam is passed not only through the superheater and the main steam pipe, but also through the reheater and the reheat steam pipe, so that the temperatures of the main steam and the reheat steam are maintained at set values, respectively. An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 4 is a schematic diagram of a once-through boiler device for a thermal power plant to which the present invention is applied, FIG. 5 is a diagram similar to FIG. 2 showing the startup characteristics of the plant in FIG. 4, and FIG.
The figure is a control block diagram of one embodiment of the present invention. In FIG. 4, the same reference numerals as in FIG. 1 represent the same or equivalent parts. Further, in the same figure, 22 is a medium/low pressure turbine bypass valve, 18A is a desuperheater for lowering the temperature of the medium/low pressure turbine bypass steam that has passed through the bypass valve 22, and 21A is the outlet steam temperature of the desuperheater 18A. Detector 23 is a medium/low pressure turbine bypass steam spray valve, 24A is a high pressure turbine exhaust steam stop valve, 25 is a reheater forming valve, and 26 is a high pressure turbine bypass condenser steam valve. At the time of plant startup - before the start of steam flow to the turbine, the main stop valve 9, intercept valve 10, high pressure turbine exhaust steam stop valve 24A, and high pressure turbine bypass condenser steam flow valve 26 are fully closed. On the other hand, the reheater warming valve 25 and the medium/low pressure turbine bypass valve 22 are fully opened. Further, the opening degrees of the high pressure (main) turbine bypass valve 15 spray valve 19 and the medium/low pressure turbine bypass steam spray valve 23 are controlled as described later. At time t ₀ , when fuel supply is started and burner 2 is ignited as shown by curve B in FIG. The main steam pipe and reheat steam pipe will be reinstated. Secondary superheater 8 → main steam pipe 16 → high pressure (main) turbine bypass valve 15 → desuperheater 18 → reheater warming valve 25 → primary reheater 5 → secondary reheater 7 → reheat steam pipe 17 → Medium/low pressure turbine bypass valve 22
→ Desuperheater 18A → Condenser 13 → Economizer → Furnace water wall 1A → Primary superheater 6 → Secondary superheater 8 At that time, as will be described later with reference to FIG. The main steam temperature is adjusted by the opening degree of the main turbine bypass valve 15, and the more this valve 15 is opened, the lower the main steam temperature is. In addition, the reheat steam temperature is
It is controlled by adjusting the opening degree of the spray valve 19, and the more the spray valve 19 is opened, the lower the reheat steam temperature becomes. Furthermore, the temperature of the steam entering the condenser 13 is
Controlled by adjusting the opening degree of the low pressure turbine bypass steam spray valve 23, the spray valve 2
3 is larger, the temperature of the steam returned to the condenser 13 decreases. Next, control of the main steam temperature and reheat steam temperature at the time of startup will be explained with reference to FIG. 6. In this figure, the same reference numerals as in FIG. 3 and the reference numerals with the suffix B added represent the same or equivalent parts, respectively. Control of the main steam temperature by adjusting the opening degree of the high pressure (main) turbine bypass valve 15 is almost the same as in the case of FIG. 3. The difference from the case in FIG. 3 is that the target temperature is set not by the signal generator 33 but by a control computer (not shown) based on the allowable value of the temperature difference between the inner and outer walls of the turbine. The only point is provided by an analog memory 36A that stores the settings determined to optimize the turbine thermal stress. Note that a control computer (not shown) calculates set values for the main steam temperature and reheat steam temperature based on the temperature difference between the inner and outer walls of the turbine, and stores the values in the analog memory 3.
It functions to set 6A and 36B. As a result, as in the conventional example, the opening degree of the high-pressure (main) turbine bypass valve 15 is controlled so that the detected output of the main steam temperature detector 20 - that is, the main steam temperature - matches the set value. Then, the main steam temperature gradually increases as shown by curve D in FIG. On the other hand, the reheated steam temperature is controlled by adjusting the opening degree of the spray valve 19 as follows. At the beginning of the plant startup, the reheat steam temperature is below the scheduled value, so the switch 32B switches the reheat steam temperature (output of the reheat steam temperature detector 21) itself under the control of the monitor relay 35B. is selected and supplied to the adder 31B via the rate of change limiter 30B. Therefore, adder 31B and proportional integrator 29
Both outputs of B become 0. Furthermore, at this time,
The switch 37B is switched to the ground side. Therefore, the opening degree of the spray valve 19 is controlled only by the advance control signal of the function generator 27B which receives the output of the main steam temperature detector 20 as input. In this way, the reheat steam temperature gradually increases over time, as shown by curve E in FIG. Eventually, when the reheat steam temperature reaches a predetermined value, monitor relay 35B operates switchers 32B and 37B to select the signal in analog memory 36B. 36B is the setting value from the control computer (fifth
The set value is converted into a reheat steam temperature target value as shown by the curve E1 in FIG. be done. As described above, when the reheat steam temperature reaches the predetermined value, the switch 37B is also switched to the proportional integrator 29B side. Therefore, the spray valve 19 performs advance control based on a signal obtained by proportional integration of the deviation between the output of the reheat steam temperature detector 21 and the reheat steam temperature set value, and the output of the main steam temperature detector 20. Becomes controlled by a signal. At this time, the high pressure turbine bypass flow rate, the high pressure turbine bypass spray flow rate, and the intermediate and low pressure turbine bypass flow rates increase as shown by curves F, I, and H, respectively, in FIG. 5. Further, an example of the state in which the temperature of reheated steam increases when such control is performed is shown by curve E in FIG. 5. On the other hand, the opening degree of the medium/low pressure turbine bypass steam spray valve 23 is determined so that the steam temperature at the outlet of the attemperator 18A (the output value of the attemperator outlet steam temperature detector 21A) is the target set by the signal generator 33A. It is controlled by a proportional calculator 34 so that the temperature is maintained. When the main steam temperature rises to the specified value at time _t2 , the main stop valve 9 and the intercept valve 1 are activated.
0, and the high pressure turbine exhaust steam stop valve 24A are opened, while the medium/low pressure turbine bypass valve 2
2. Medium/low pressure turbine bypass steam spray valve 2
3. The high pressure (main) turbine bypass valve 15, the spray valve 19 and the high pressure (main) turbine bypass condenser flow valve 26 are closed. As a result, the main steam is transferred to the high pressure (main) turbine 11
The steam is then driven to rotate the generator 14. Steam exiting the high-pressure (main) turbine 11 passes through the high-pressure turbine exhaust steam stop valve 24A and the reheater warming valve 25, and then passes through the primary reheater 5 and the secondary reheater 7.
and reheated. The reheated steam leaving the secondary reheater 7 is supplied to the medium/low pressure turbine 12 via the reheat steam pipe 17 and the intercept valve 10 . An example of an increasing state of the reheat steam flow rate is shown by curve G in FIG. After that, the turbines 11, 12 and the generator 14
The rotational speed increases as shown by curve A in FIG.
When the rotational speed reaches the specified value, load addition is performed at time _t3 . As a result, the generator 14
The load increases as shown by curve C, and the amount of fuel supplied also increases as shown by curve B. In addition, in the reheat steam control system shown in FIG. 6, the function generator 27B may be omitted and no advance control may be performed. Furthermore, as is clear from the above description, the high pressure (main) turbine bypass valve 15, spray valve (for controlling the steam temperature at the reheater inlet) 19, and medium/low pressure turbine bypass valve 22 in FIG. The purpose is to warm the steam of time. Therefore, these capacities can be set to a short-term model of about 1/10 of the rated output of the plant. In addition, medium/low pressure turbine exhaust steam stop valve 2
4. The reheater warming valve 25 and the high pressure turbine bypass condenser steam valve 26 are provided to ensure the safety of the plant. As can be seen from the above description, according to the present invention,
Since the steam is passed through the reheater and the reheat steam pipe before passing through the turbine, there is no problem that the temperature of the reheated steam decreases when the steam passes through the turbine, unlike the conventional method. Moreover, the set (target) values for the main steam temperature and reheat steam temperature at startup are determined as a function based on the allowable value of the temperature difference between the inner and outer walls of the turbine, and the main steam temperature is maintained at the specified value. At the same time as the temperature rises, the reheat steam temperature can also be raised to a predetermined value, making it possible to reduce the startup time to the shortest possible time while keeping the thermal stress in the turbine within tolerance. Furthermore, since the control device of the present invention is a system suitable for unit startup, the scale of the plant system can be minimized, and not only controllability is maintained, but construction costs can also be significantly reduced.

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram of a boiler in a conventional thermal power plant, Figure 2 is a time chart showing various characteristics at startup of the plant in Figure 1, and Figure 3 is a time chart showing various characteristics at startup of the plant in Figure 1.
Figure 1 is a main steam temperature control block diagram in the plant shown in Figure 1, Figure 4 is a schematic configuration diagram of a boiler in a thermal power plant showing an embodiment of the present invention, and Figure 5 is a diagram of a thermal power plant implementing the present invention. FIG. 6 is a time chart showing various characteristics at startup, and is a block diagram of a main steam temperature and reheat steam temperature control device according to an embodiment of the present invention. 1...boiler body, 1A...furnace water cooling wall, 3...
... Gas recirculation fan, 4 ... Energy saver, 5 ... Primary reheater, 6 ... Primary superheater, 7 ... Secondary reheater,
8... Secondary superheater, 9... Main stop valve, 10...
Intercept valve, 11... High pressure (main) turbine, 12... Medium/low pressure turbine, 13... Condenser, 14... Generator, 15... High pressure (main) turbine bypass valve, 16... Main steam pipe , 17... Reheat steam pipe, 18A... Attemperator, 19... Spray valve, 22... Medium/low pressure turbine bypass valve, 23
...Medium/low pressure turbine bypass steam spray valve.

Claims (1)

[Claims] 1. A main steam pipe that guides main steam generated in a superheater to a high-pressure (main) turbine, a main stop valve provided in front of the high-pressure (main) turbine, and a main steam pipe that leads main steam generated in a superheater to a high-pressure (main) turbine. Piping that returns exhaust steam to the reheat pipe, reheat steam pipe that guides the reheat steam generated in the reheater to the medium and low pressure turbine, an intercept valve installed in front of the medium and low pressure turbine, and the medium and low pressure turbine. means for directing the exhaust steam of the steam to the condenser, and means for bypassing the main steam to the reheater from before the main stop valve through the high pressure (main) turbine bypass valve; and means for bypassing the main steam to the reheater from before the main stop valve. an attemperator and spray valve means for controlling the temperature of the steam;
A steam temperature control device at the time of startup of a power plant, which is equipped with a means for bypassing reheated steam to a condenser via a low-pressure turbine bypass valve, and is equipped with a means for bypassing reheated steam to a condenser through a low-pressure turbine bypass valve. A main steam temperature detector that detects the main steam temperature, a reheat steam temperature detector that detects the reheat steam temperature in the reheat steam pipe from the reheater outlet to the intercept valve, and the main steam temperature and reheat steam temperature. The system is equipped with means for determining the set value of・Maintain the main steam temperature at the set value by opening the low pressure turbine bypass valve and controlling the opening degree of the high pressure turbine bypass valve based on the main steam temperature and the deviation of the set value, and Steam at startup of a power generation plant, characterized in that the reheat steam temperature is maintained at the set value by controlling the opening degree of the spray valve based on the reheat steam temperature and the deviation of the set value. Temperature control device. 2. A main steam pipe that guides the main steam generated in the superheater to the high-pressure (main) turbine, a main stop valve installed in front of the high-pressure (main) turbine, and a main steam pipe that directs the exhaust steam from the high-pressure (main) turbine to the reheat pipe. A return piping, a reheat steam pipe that guides the reheat steam generated in the reheat pipe to the medium/low pressure turbine, an intercept valve installed in front of the medium/low pressure turbine, and a condenser for the exhaust steam of the medium/low pressure turbine. high pressure (main) from before the main stop valve.
means for bypassing main steam to a reheater via a turbine bypass valve; attemperator and spray valve means for controlling the temperature of said steam bypassed to the reheater; and a medium/low pressure turbine from before the intercept valve. A steam temperature control device at startup of a power generation plant, which is equipped with a means for bypassing reheated steam to a condenser via a bypass valve, and is equipped with a means for bypassing reheated steam to a condenser. A main steam temperature detector that detects the temperature, a reheat steam temperature detector that detects the reheat steam temperature in the reheat steam pipe from the reheater outlet to the intercept valve, and settings for the main steam temperature and reheat steam temperature. When starting up the power plant, the main stop valve and the intercept valve are fully closed, while the high pressure turbine bypass valve and the medium and low pressure turbine bypass valves are opened, and the opening degree of the high pressure turbine bypass valve is is controlled based on the main steam temperature and its set value to maintain the main steam temperature at the set value, and the opening degree of the spray valve is controlled based on the reheat steam temperature and its set value. A steam temperature control device at the time of startup of a power generation plant, characterized in that the reheat steam temperature is maintained at the set value by controlling based on the deviation and performing advance control based on the main steam temperature.