JPS63192904A - Main steam pressure control method for power generating plant - Google Patents

Abstract

PURPOSE:To enable main steam pressure restrained, when a power/load unbalanced relay is operated and a governing valve is suddenly closed during the driving exceeding turbine bypass capacity, by introducing excessive steam to a flash tank and a turbine for driving a feed water pump. CONSTITUTION:In a high speed breeder power generating plant, after steam generated in a steam generator 1 passes a drain separator 2, it is introduced to a turbine 6 through a turbine governing valve 3 from a main steam piping 5 and drives a generator 7. To the main steam piping 5, a turbine bypass system including a turbine bypass valve 15, whose turbine bypass capacity is made less than 100% is divergingly connected. In this case when a power/load unbalanced relay is operated and the governing valve 3 is suddenly closed, opening degree of a drain valve 13 is controlled, and excessive steam is introduced from the drain separator 2 to a flash tank 14. Also, a high pressure side variable valve 19 is made open, and steam from the piping 5 is introduced to a turbine for driving feed water pump 10.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to main steam pressure control of power generation plants such as thermal power plants and nuclear power plants that generate power by rotating power generation turbines using steam. Regarding the method.

(Prior Art) Generally, a turbine bypass system is installed in a power generation plant, such as a thermal power plant or a nuclear power plant, which generates power by rotating a power generation turbine using steam. Such a turbine bypass system has a bypass capacity of 1
Although it is desirable to set it to 00%, it is usually set to about several 10% because it causes an increase in construction cost.

For example, in a nuclear power plant or the like, the valve opening degrees of the turbine bypass valve and the turbine control valve of the turbine bypass system are controlled by EHC (Electtr).

The main steam pressure and the speed of the turbine are controlled as shown below.

This EHC consists of the turbine adjustment valve opening request and its actual opening (
If the hardware is configured so that the required turbine bypass valve opening and its actual opening match, there will be a nearly proportional relationship between the turbine regulator valve opening request, its actual opening, the steam flow rate flowing into the steam bin, and the turbine output. Based on the fact that the following holds true, as shown in FIG. 3, a total flow rate request signal finder 21 calculates a total flow rate request signal from the main steam pressure, and a control valve flow rate detector 21 calculates a control valve flow rate request signal from the turbine speed. It is composed of a request signal calculation unit 22, a low value priority circuit 23, 24, 25, a function generator 26, 27, etc., and outputs an opening request for the turbine control valve and an opening request for the turbine bypass valve as manipulated variables. It is configured.

, when the plant is in normal operation or when there is no frequency disturbance from the power system such as output change by the plant control system, the regulator valve flow rate request signal is larger than the total flow rate request signal, and the turbine regulator valve is opened. The pressure demand is given by the full flow demand signal and pressure priority control is performed.

On the other hand, in control when power system frequency disturbances such as load loss are added, the turbine rotation speed increases, and the regulator valve flow rate request signal becomes smaller than the total flow rate request signal,
The opening degree request of the turbine control valve is given by the control valve flow rate request signal, and turbine speed priority control is performed. ).

This PLU relay is used when a large load loss occurs, for example, 40% or more in terms of rated load, while the plant is operating at a given load, and the difference between the generator load and the turbine output exceeds a predetermined value, e.g. (40%/10 milliseconds) or more, the turbine control valve is fully closed in a few milliseconds, and steam flowing into the turbine is rapidly shut off.

In addition, when the PLU relay is activated, the turbine bypass valve is simultaneously opened rapidly in a few milliseconds, dumping the steam that has nowhere else to go to the condenser, and setting the load to control the turbine output (pressure control is given priority during normal operation). (set to about 110z) to Oz, and P
Hold until the LU relay is reset.

When the steam flowing into the turbine is cut off, the output of the turbine decreases rapidly. At this time, if the EHC detects that the turbine output has decreased until the difference between the generator load and the turbine output is below the predetermined value (40%) mentioned above, it resets the PLU relay and Suddenly change the settings to the old one and restore it. When the load setting is restored, the turbine regulator valve begins to open again due to the regulator flow request signal since the system that lost the load is at a frequency higher than the predetermined value.

Then, based on a request for an output command signal from the plant control system, a set pack operation is performed in which the reactor output is decreased, the feed water flow rate, etc. are decreased, and the steam generator outlet steam flow rate is decreased. Note that the rate of decrease in the steam flow rate at the steam generator outlet due to set pack operation is approximately -5z/min in, for example, a fast breeder reactor plant.

As the set pack operation progresses, the pressure in front of the turbine control valve (main steam pressure) decreases. For this reason, the total flow rate requirement calculated within the EHC decreases, and eventually falls below the regulating valve flow rate requirement. Since the opening degree request of the turbine bypass valve is given by the difference between the full flow rate and the regulating valve flow rate request, at this time, the turbine bypass valve is fully closed and the set pack operation is stopped.

(Problems to be Solved by the Invention) However, the conventional power plant control method described above has the following problems.

That is, as shown in the graph of Figure 4, where the vertical axis is the steam flow rate and the horizontal axis is time, for example, if the turbine bypass capacity is 5.
(In a nuclear power plant that is assumed to be 1%, if a 50% load loss occurs during rated output operation, the PLU
Once the relay is activated, even if the adjustment valve opening request at the moment the PLU relay is reset is, for example, a fully open request,
There is an upper limit to the operating speed of the hydraulic system that drives the valve, and the actual opening degree does not fully open immediately; for example, it starts opening in about 1 second and becomes fully open in about 10-odd seconds. Therefore, the turbine steam flow rate temporarily becomes zero as shown by the solid line a, and PL
50 after a few seconds to 10 seconds after the U relay is reset.
%.

In addition, the turbine bypass steam flow rate becomes 50% immediately after the PLU relay is activated, as shown by the dotted line, and -5
It gradually decreases with setback operation performed at a rate of about %/min.

Therefore, the sum of the turbine steam flow rate and the turbine bypass steam flow rate changes from 100% to 50% once, and then reaches almost 100% after several seconds to ten-odd seconds, as shown by the chain 11c.
However, as shown by the solid line d, the steam flow rate at the steam generator outlet hardly changes because the rate of change in the process amount due to set pack operation is slow, on the order of minutes, and the steam mismatch corresponding to the shaded area occurs.

Therefore, due to the pressure increase due to the excess steam corresponding to the shaded area, the relief valve and the safety valve are opened, and the steam is released into the atmosphere. The release of such vapor into the atmosphere is undesirable as it results in the loss of highly controlled water.

Additionally, as heating steam for the feedwater heater and deaerator is normally extracted from a portion of the steam from the turbine, this heating steam is lost while the turbine steam flow rate is zero. As a result, there is a problem that the temperature of the water supply may drop rapidly and cavitation may occur in the water supply pump.

Furthermore, a turbine for driving a water supply pump also normally extracts a portion of steam from the turbine through a low-pressure side regulating valve. For this reason, as turbine steam is lost, the control system generates a signal to open the high-pressure regulator valve.
Due to the rapid decrease of turbine steam, there is a delay in control,
There is a problem in that it may become difficult to maintain a stable rotational speed.

The present invention has been made in response to such conventional circumstances, and even if the PLU relay is activated and the turbine control valve is quickly fully closed during operation exceeding the turbine bypass capacity, the main steam pressure can be released. It is possible to suppress the main steam to below the operating pressure of valves and safety valves to prevent main steam from being released into the atmosphere, and to secure heating steam for the feed water heater and deaerator to prevent a sudden temperature drop in the feed water and the operation of the feed water pump. The present invention aims to provide a main steam pressure control method for a power generation plant that can prevent the occurrence of cavitation and also maintain stable rotation of a turbine for driving a feedwater pump.

[Structure of the Invention] (Means for Solving the Problems) That is, the present invention provides a main steam pressure control method for a power plant in which the turbine bypass capacity is less than 100%, in which the power / When the load unbalance relay is activated and the turbine regulator valve is quickly fully closed, operate the drain valve opening of the drain separator of the startup bypass system and the high pressure side regulator valve of the water pump driving turbine. It is characterized by introducing excess steam into the flash tank and the turbine for driving the water supply pump, and suppressing the main steam pressure to below the operating pressure of the relief valve and safety valve.

(Function) In the main steam pressure control method for a power plant of the present invention, if the power/load imbalance relay is activated during operation exceeding the turbine bypass capacity and the turbine control valve is quickly fully closed, the startup bypass By manipulating the opening of the drain valve of the drain separator of the system and the opening of the high-pressure side regulating valve of the turbine for driving the feedwater pump, excess steam is introduced into the flash tank and the turbine for driving the feedwater pump, and the main steam pressure is
Suppress pressure below the operating pressure of relief valves and safety valves.

Therefore, it is possible to prevent surplus steam from being released into the atmosphere from the relief valve and the safety valve by using existing equipment without adding new equipment. In addition, in normal power plants, piping is installed to supply heated steam from the flash tank to the feed water heater and deaerator.
Heating steam for the feed water heater and deaerator can also be ensured.

Furthermore, by forcibly opening the high-pressure side control valve of the feedwater pump driving turbine, it is possible to prevent a sudden decrease in the driving steam and maintain stable rotation of the driving turbine.

(Embodiment) Hereinafter, an embodiment of the main steam pressure control method for a power plant according to the present invention will be described with reference to the drawings.

Figure 1 shows a fast breeder reactor power plant. Steam generated by heat exchange with the secondary sodium system in the steam generator 1 passes through the drain separator 2 of the start-up bypass system, and then flows into the turbine. A regulator valve 3 etc. is inserted, and a safety valve 4a
, a turbine 6 through a main steam pipe 5 equipped with a relief valve 4b.
The generator 7 is introduced to rotate the generator 7 and generate electricity.

The steam after rotating the turbine 6 is returned to water in the condenser 8, and the steam is removed in the deaerator 9, and then the water supply pump 11 is driven by the water supply pump driving turbine 10.
The water is sent to the feed water heater 12 by the motor-driven feed water pump 11a (at startup, etc.), heated there, and then sent to the steam generator 1.

The drain separator 2 is connected to a flash tank 14 via a drain valve 13, and the steam introduced into the flash tank 14 is sent to a condenser 8, a deaerator 9, a feed water heater 12, Water is sent to condenser 8.

In addition, a turbine bypass system is formed in the main steam pipe by branching from the upstream side of the turbine control valve 3, connected to the condenser 8, and having a turbine bypass valve 15 inserted therein. is, for example, 50X. Then, a deaerator 9, a turbine 1 for driving the water supply pump
0, the feedwater heater 12 is connected to a system g16, 17, 18 for extracting and supplying a part of the main steam from the turbine 6, and the drive turbine 10 is connected to the main steam in addition to the piping 17. A pipe 17a that introduces a portion of steam from the pipe is connected, and a low pressure side control valve 19 and a high pressure side control valve 19a are inserted into these pipes 17, 17a4, respectively.

During normal operation in the power plant with the above configuration, the pressure target value of the drain separator pressure control system is set to a sufficiently high value, and the drain valve 13 of the drain separator 2 is
It is said to be completely closed. The low pressure side regulating valve 1 is inserted into the pipe 17.17a that introduces steam into the driving turbine 10.
9. Of the high-pressure side control valves 19a, the high-pressure side control valve 19a is fully closed, and the turbine 6 is connected to the water supply pump driving turbine 10 by manipulating the opening degree of the low-pressure side control valve 19.
Steam extracted from the pipe is introduced.

“In this embodiment method, for example, during rated output operation, 50
If a % load loss occurs and the PLU relay does not operate, the operating signal changes the pressure target value of the drain separator pressure control system, opens and closes the drain valve 13, and drains the drain separator 2 from the flash tank 14. excess steam is introduced into the At the same time, the high pressure side control valve 19a is forcibly opened to introduce steam from the main steam pipe 5 to the feedwater pump driving turbine 10.

This pressure target value is based on the second equation, where the vertical axis is the flow rate and the horizontal axis is the time.
As shown in the graph of the figure, the sum of the steam flow rate from the drain separator 2 to the flash tank 14 and the steam flow rate from the main steam pipe 5 to the feed water pump driving turbine 10 is calculated according to the mismatch flow rate corresponding to the shaded area. is calculated in advance so that the steam flow rate is as shown by the solid line e, and is given to the drain separator pressure control system as a function of time.

Note that the main steam pressure increases because the balance of steam quality and weight within the main steam pipe 5 is disrupted and steam is accumulated. In the main steam pipe 5, the following mass balance equation and pressure calculation equation hold true.

ΣwSGi ”TB+wBYP +wR+WS +
WPT) i = 1 = dM/dt (1) dP/dt = (KP/M) dM/dt (
2) However, W: Total sum of main steam meteors of n steam generators SG+ W: Turbine steam flow rate B WBYP 'Turbine bypass steam meteor WR: Relief valve steam flow rate WS: Safety valve steam meteor W, 1: Water supply pump drive turbine high pressure Side steam flow rate M: Steam mass P: Steam pressure: Adiabatic index (constant) Therefore, by integrating equation (1) over time, the instantaneous value of the amount of accumulated steam can be obtained, and by integrating equation (2) over time. The instantaneous value of steam pressure can be found by integrating with . Therefore, the pressure target value given to the drain separator pressure control system described above can be calculated from these equations.

That is, in this embodiment method having the above configuration, it is possible to prevent excess steam from being released into the atmosphere from the safety valve 4a and the relief valve 4b by using the existing startup bypass system without adding new equipment. . In addition, by supplying heated steam from the flash tank 14 to the feedwater heater 12 and the deaerator 9, the feedwater heater 12 and the deaerator 9
heating steam can also be secured. Furthermore, by forcibly opening the high-pressure side control valve 19a, a sudden decrease in drive steam is prevented, and the feed water pump drive turbine 1
0 rotation can be maintained stably.

Also, a drain separator was placed between the evaporator and superheater:! In P, electric plants, etc., compared to, for example, introducing steam only from a drain separator to a flash tank, the decrease in steam introduced to the superheater can be suppressed to a small extent, and changes in the steam temperature at the exit of the superheater can be suppressed. It can be suppressed to a small extent.

[Effects of the Invention] As described above, in the main steam pressure control method for a power generation plant of the present invention, in a power generation plant in which the turbine bypass capacity is set to 100X, the PLO relay is activated during operation exceeding the turbine bypass capacity. Even if the turbine control valve is quickly fully closed, the main steam pressure can be suppressed to below the operating pressure of the relief valve and safety valve without adding new equipment, preventing main steam from being released into the atmosphere. In addition, heating steam for the feed water heater and deaerator can be secured, and rapid temperature drops in the feed water and cavitation of the feed water pump can be prevented. The rotation of the turbine can be maintained stably.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a fast breeder reactor power plant for explaining an embodiment method of the present invention, Fig. 2 is a graph showing temporal changes in steam flow rate in the embodiment method, and Fig. 3 is a diagram showing the configuration of an EHC. The configuration diagram shown in FIG. 4 is a graph showing the change in steam flow rate over time in the conventional method. 1...Steam generator 2...Drain separator 3...
... Turbine control valve 4a ... Safety valve 4b ... Relief valve 10 ... Water pump drive turbine 13 ...
... Drain valve 14 ... Flash tank 15 ... Turbine bypass valve 19a ... High pressure side adjustment valve

Claims (1)

[Claims] (1) In the main steam pressure control method of a power plant where the turbine bypass capacity is less than 100%, the power/load imbalance relay is activated during operation exceeding the turbine bypass capacity, and the turbine control valve is quickly fully closed. If this occurs, operate the drain valve opening of the drain separator in the start-up bypass system and the high-pressure side regulating valve opening of the feed water pump driving turbine to introduce excess steam into the flash tank and the feed water pump driving turbine, and then release the main steam. A method for controlling main steam pressure in a power generation plant, characterized by suppressing pressure below the operating pressure of a relief valve and a safety valve.