JPS63192905A - 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 an auxiliary stem header. 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 variable valve 21 is made open, and steam from the piping 5 is introduced to an auxiliary steam header 15 by a piping 22.

Description

[Detailed Description of the Invention] [Purpose of the Invention (Field of Industrial Application) The present invention relates to main steam pressure control of a power generation plant, such as a thermal power plant or a nuclear power generation plant, which rotates a power generation turbine using steam to generate power. 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 0 oz, since it causes an increase in construction cost, it is usually set to about several 10%.

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 turbine speed are controlled by a hydraulic controller (Hydraulic Controller), and the main steam pressure and turbine speed are controlled as shown below.

This EHC consists of the turbine adjustment valve opening request and its actual opening (
The hardware is configured so that the required turbine bypass valve opening and its actual opening) match, and there is a nearly proportional relationship between the turbine regulator valve opening requirement, its actual opening, the turbine inflow steam flow rate, and the turbine output. Based on this fact, as shown in FIG. 3, a full flow rate request signal calculation unit 31 calculates a total flow rate request signal from the main steam pressure, and a control valve flow rate request signal calculates a control valve flow rate request signal from the turbine speed. It consists of a calculating section 32, low value priority circuits 33, 34, 35, function generators 36, 37, etc., and is constituted by an arithmetic circuit that outputs the opening degree request of the turbine control valve and the opening degree request of the turbine bypass valve as manipulated variables. ing.

Then, when the plant is in normal operation or when there is no frequency disturbance from the electric 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 opening is The demand is given by a full flow demand signal and pressure priority control is provided.

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.

The EHC also includes a power/load unbalance relay (PLU relay) to prevent turbine overspeed in an emergency.

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. When a difference of (40χ/10 milliseconds) or more occurs, the turbine control valve is fully closed in several 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 Ox, 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, in the EHC, the difference between the generator load and the turbine output is equal to or less than the above-mentioned predetermined value (40%). When it is detected that the turbine output has decreased to a certain level, the PLU relay is reset, the load setting is suddenly changed to the dark value, and the load is restored. When the load setting is restored,
Since the unloaded system is at a frequency higher than a predetermined value, the turbine regulator valve begins to open again due to the regulator flow request signal.

Then, based on the request of the output command signal of the plant control system, a set pack operation is performed in which the reactor output is reduced, the feed water flow rate, etc. is reduced, and the steam generator outlet steam flow rate is reduced. The rate of decrease in the steam flow rate at the exit of the steam generator due to this is, for example, about -5z1 minute in 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 set to 0%, if a 50% load loss occurs during rated output operation, once the PLU relay is activated, the adjustment valve opening request at the moment the PLU relay is reset is, for example, fully open. Even when requested, 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 the PLU
50% after a few seconds to 10 seconds when the relay is reset
becomes.

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

Therefore, the sum of the turbine steam flow rate and the turbine bypass steam flow rate, as shown by the dashed line C, once becomes 50% from 100x, and becomes almost 100% after several seconds to 10-odd seconds, but the steam generator outlet steam flow rate is the same as the solid line As shown in d, the rate of change in process amount due to set pack operation is
Since it is slow, on the order of minutes, there is almost no change, and a 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.

In addition, since a part of the steam is usually extracted from the turbine and used as heating steam for the feedwater heater and deaerator, while the turbine steam flow rate is zero, these heating steams are There is a problem that this loss may cause a sudden drop in the temperature of the water supply and cavitation of the water supply pump.

The present invention has been made in response to such conventional circumstances, and even when the PLU relay is activated during operation exceeding the turbine bypass capacity and the turbine control valve is quickly fully closed, the main steam pressure is released through the relief valve. It is possible to prevent main steam from being released into the atmosphere by suppressing the pressure to below the operating pressure of the safety valve, and to secure heating steam for the feed water heater and deaerator, thereby preventing a sudden temperature drop in the feed water and cavitation of the feed water pump. The present invention aims to provide a main steam pressure control method for a power plant that can prevent the occurrence of

[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 a regulating valve is inserted between the main steam piping and the main steam pressure. Install piping to connect to the auxiliary steam header, and 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 drain separator of the startup bypass system will be installed. The drain valve opening degree and the adjustment valve opening degree are manipulated to introduce excess steam into the flash tank and the auxiliary steam header, thereby suppressing the main steam pressure to below the operating pressure of the relief valve and the safety valve.

(Function) In the main steam pressure control method for a power generation plant of the present invention, a pipe is inserted with a regulating valve and connects the main steam pipe and the auxiliary steam header, and the power/load is controlled during operation exceeding the turbine bypass capacity. When the unbalance relay is activated and the turbine control valve is quickly fully closed, the drain valve opening of the drain separator in the startup bypass system and the control valve inserted in the pipe connecting the main steam pipe and the auxiliary steam header are By manipulating the valve opening degree, surplus steam is introduced into the flash tank and auxiliary steam header, and the main steam pressure is suppressed below the operating pressure of the relief valve and safety valve.

Therefore, excess steam can be prevented from being released into the atmosphere from the relief valve and the safety valve. Further, heated steam can be supplied from the auxiliary steam header to the feedwater heater and the deaerator, and heated steam for the feedwater heater and the deaerator can also be secured.

(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 is transferred to the drain separator 2 of the startup bypass system.
After passing through the turbine, a turbine control valve 3 etc. is inserted, and a safety valve 4 is inserted.
a, the steam is introduced into a turbine 6 through a main steam pipe 5 equipped with a relief valve 4b, and a generator 7 is rotated to 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 the condenser 8 or sent to auxiliary steam via a ladder 15. Deaerator 9, feed water heater 1
2 and the water is sent to condenser 8.

In addition, the main steam pipe 5 is branched from the upstream side of the turbine control valve 3 and connected to the condenser 8, and is connected to the turbine bypass valve 1.
6 is inserted, a turbine bypass system is formed,
The turbine bypass capacity is, for example, 50%. A deaerator 9 and a turbine 10 for driving the water supply pump
, and the feedwater heater 12 are connected to piping 17, 18, and 19 for extracting and supplying a portion of main steam from the turbine 6, respectively, and the driving turbine 10 is connected to main steam piping in addition to the piping 18. A pipe 18a is connected to introduce a portion of steam from the pipe 18.18a, and a low-pressure side control valve 20 and a high-pressure side control valve 20 hole are inserted into each of these pipes 18.18a.

In this embodiment method, the main steam pipe 5 and the ladder 15 are connected to the auxiliary steam, and the pipe 2 into which the control valve 21 is inserted
2 will be placed.

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.

In this embodiment method, for example, during rated output operation, 50%
If a load loss occurs and the PLU relay is activated, the pressure target value of the drain separator pressure control system is changed according to the activation signal, and the drain valve 13 is opened and closed.
Excess steam is introduced from the drain separator 2 to the flash tank 14. At the same time, the control valve 21 is suddenly opened,
Main steam piping 5 to ladder 15 to auxiliary steam by distribution percentage F 22
Steam is introduced from

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, 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 piping 5 to the auxiliary steam to the ladder 15 is determined according to the mismatch flow rate corresponding to the shaded area. , the steam flow rate as shown by the solid line e is calculated in advance, 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 mass in the main steam pipe 5 is disrupted and steam is accumulated. Inside the main steam pipe 5, the following mass balance equation and pressure calculation equation hold true.

1;1 =dM/dt...(1) clP/dt= (KP/M)dM/dt...
(2) However, W: Total main steam flow rate of n steam generators SG+ W: Turbine steam flow rate B W: Turbine bypass steam flow rate YP WR: Relief valve steam flow house WS: Safety valve steam flow rate W, □: Water supply pump Drive turbine high pressure side steam flow rate M: Steam mass P: Steam pressure: Adiabatic index (constant) By integrating equation (1) over time, the instantaneous value of the amount of accumulated steam can be obtained, and equation (2) can be The instantaneous value of steam pressure can be determined by integrating over time.

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, the safety valve 4a
Also, excess steam can be prevented from being released into the atmosphere from the relief valve 4b. Moreover, by supplying heated steam to the feed water heater 12 and the deaerator 9 from the ladder 15 to the auxiliary steam, the heated steam for the feed water heater 12 and the deaerator 9 can also be secured.

In addition, in power generation plants etc. where a drain separator is placed between the evaporator and the superheater, the amount of steam introduced into the superheater can be reduced by a smaller amount than when steam is introduced only from the drain separator to the flash tank. It is possible to suppress the change in the superheater outlet steam temperature to a small extent.

[Effects of the Invention] As described above, the main steam pressure #I of the power plant of the present invention
In a power generation plant with a turbine bypass capacity of less than 100X, this method allows the main steam pressure to be released even if the PLU relay is activated and the turbine control valve is quickly fully closed during operation exceeding the turbine bypass capacity. The operating pressure of the valve and safety valve can be suppressed to below the operating pressure, preventing main steam from being released into the atmosphere, and ensuring heating steam for the feedwater heater and deaerator, preventing sudden temperature drops in the feedwater and preventing the main steam from being released into the atmosphere. Pump cavitation can be prevented.

[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 13 ... Drain valve 14 ... Flash tank 15 ... Auxiliary steam Header 16...Turbine bypass valve 21...Adjustment valve 22...Piping

Claims (1)

[Claims] (1) In a main steam pressure control method for a power plant where the turbine bypass capacity is less than 100%, a pipe is installed that connects the main steam pipe and the auxiliary steam header with a regulating valve inserted, and the turbine bypass capacity is increased. If the power/load unbalance relay is activated and the turbine regulator valve is quickly fully closed during operation in excess of A method for controlling main steam pressure in a power generation plant, comprising introducing steam into a flash tank and an auxiliary steam header to suppress the main steam pressure to below the operating pressure of a relief valve and a safety valve.