JPH0372886B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a method and apparatus for controlling the water level of a drain tank of a moisture separator or a reheater, and particularly to a method for controlling the water level of a drain tank of a moisture separator or a reheater, and particularly to a method for controlling the water level of a drain tank of a moisture separator or a reheater. The present invention relates to a drain tank water level control method and apparatus suitable for preventing turbine tripping due to an increase in the drain tank level.

[Prior art]

First, problems with the conventional moisture separator drain system will be explained using FIG. 1, taking a general power plant as an example.

Drain dehumidified by steam in the moisture separator 1 is stored in a moisture separator drain tank 2. The water level in the drain tank 2 is detected by a water level transmitter 3,
The regular water level control valve 5 is controlled via the regular water level controller 4, and drain is collected into the feed water heater 7 via the regular drain line 6 and the regulating valve 5 so that the water level in the drain tank 2 is constant. When the water level in the drain tank 2 rises due to insufficient discharge capacity from the regular drain line, the emergency water level control valve 10 is controlled by the water level transmitter 8 and the emergency water level controller 9, and the drain tank 2 is drained from the regular drain line 6. Drain is discharged to the condenser 12 via the branched emergency drain line 11 and the control valve 10.

However, since the drain in the moisture separator drain tank 2 is saturated water, if the pressure of the steam system suddenly decreases when the load of the steam generator and turbine (not shown) drops, the drain in the moisture separator tank 2 will flash (self-recovery). evaporation), leading to a rise in water levels. At this time, when the water level rises to the turbine trip level switch 30, the turbine is tripped to prevent water induction (water intrusion) into the turbine.

Sudden load reduction of steam generators and turbines is carried out for the purpose of plant protection and continuous operation.
The rise in the water level in the drain tank 2 results in the plant being shut down and the power supply being cut off, resulting in a decrease in the operating rate. Furthermore, since an increase in the water level in the drain tank 2 may cause a major accident due to turbine water induction, it is necessary to suppress the increase in the water level as much as possible.

In addition, in plants with moisture separation reheaters,
As shown in FIG. 8, which will be described later, since the drain of the heated steam drain tank 52 is also saturated drain, the water level rises due to a sudden pressure drop. This rise in water level makes it impossible to discharge the drain through the drain pipe 53 and the tube 54 in the reheater, leading to deterioration of performance due to pressure pulsation and equipment damage due to water hammer. In addition, as a conventional countermeasure against drain flush in a drain tank, for example, as in Utility Model Application No. 124704/1983, the water level rise rate caused by flushing of the moisture separator drain tank is detected by a first-order differential detector. The pressure, temperature, and enthalpy at the front of the water level control valve can be used to operate an emergency control valve when the rise rate exceeds a predetermined rate, or to control the water level of a feed water heater as in JP-A No. 56-137004. In addition, a technique has been proposed in which the valve opening degrees of the water level control valves are detected, the insufficient valve opening degrees due to the valve front flush are predicted, and a preceding operation command for the insufficient valve opening degrees is transmitted to the water level control valves. ing.

However, in the former case, there are the following points to be improved.

That is, the rate of rise in the water level of the moisture separator drain tank under such plant conditions is very fast due to saturated drain, reaching a peak in about 10 to 20 seconds.
On the other hand, the time required to fully open the water level control valve is approximately 10 seconds, taking into account the time delay from when the water level begins to rise due to flushing until the rate of water level rise is detected. As a result, the emergency water level control valve will be fully opened after the water level has already begun to rise.
When the valve is fully opened, the entire piping up to the inlet of the water level control valve is already in a two-phase flow due to flashing, so the pressure loss in the pipes and valves increases, and even if the control valve is fully opened, the drain discharge capacity does not increase much. The effect of flashing to suppress water level rise is weakened.

Further, in the latter case, the target is a feed water heater, but if this method is applied to a moisture separator drain tank, it cannot be expected to sufficiently suppress the water level rise as described above. In other words, as mentioned above, the water level rises rapidly in the moisture separator drain tank at a rate of approximately 10
It reaches its peak in ~20 seconds. On the other hand, even if the control valve is fully opened after detecting and processing the system state values (pre-valve drain pressure, temperature, enthalpy, valve opening, etc.) in order to predict the insufficient valve opening by flashing, it will take a long time to fully open. It takes at least about 10 seconds. Under these circumstances, in the case of feed water heaters, the drain at the outlet of the feed water heater is generally in a supercooled state, so the flash rate (rate of bubble generation) when pressure drops is small, making it possible to suppress water level rises. However, in a moisture separator drain that processes saturated water, the flashing rate is large, so even if the water level control valve is fully opened after flashing occurs, the effect of increasing the discharge flow rate is small. Therefore, it has been difficult to apply the latter technique to a moisture separator to suppress abnormal water level rise due to flashing.

[Purpose of the invention]

The present invention has been made in view of the above, and its object is to provide a moisture separator or recycler that can prevent a turbine trip due to a rise in the water level of a drain tank when the output of a steam generator or turbine suddenly drops. An object of the present invention is to provide a method and device for controlling the water level of a drain tank of a heating device.

[Summary of the invention]

The present invention provides a drain tank that separates moisture from steam led to a turbine of a power generation plant using a moisture separator or a moisture separation reheater and stores the saturated drain, and a drain tank that controls the water level of the drain tank to a predetermined water level. In a system equipped with a line that collects condensate to the feed water heater via a regular water level control valve, and an emergency line that discharges it to the condenser via an emergency water level control valve, the following problem solving method is used. propose.

The first aspect of the present invention is characterized in that when the internal pressure of the drain tank drops to a sudden load drop operation state such as reactor runback, recirculation pump trip, or turbine load cut-off, a signal is sent to start the operation state. Based on this, the water level in the drain tank is temporarily set to the normal water level by lowering the water level setting value of the drain tank prior to the start of the internal pressure drop in the drain tank, or by suddenly opening the emergency control valve. The water level is controlled to be lower than the above value, and this low water level control suppresses the rise in water level due to flashing of drain in the drain tank when the tank internal pressure suddenly drops.

The second invention is characterized by a low water level setting signal generator that generates a low water level setting signal for lowering the normal water level setting value to a specified value, and a reactor runback and PLR.
A signal to start sudden load drop operation such as pump trick or turbine load cut (hereinafter referred to as
a set value switching device that switches a normal water level setting signal to a low water level setting signal from the low water level setting signal generator according to a signal for starting a sudden load drop operation, and the water level is controlled based on the low water level setting signal. is set to be performed prior to the start of a drop in the internal pressure of the drain tank due to the sudden load drop operation.

The third invention is characterized in that, in addition to the components of the second invention, it further includes a valve opening signal generator that generates a valve opening signal that suddenly opens the emergency water level control valve to a predetermined opening; a valve opening signal switching device that switches a valve opening signal to a quick-open valve opening signal from the valve opening signal generator in response to a load drop operation start signal, and water level control based on the low water level setting signal. In addition to this, the emergency water level control valve is set to be rapidly opened in advance of the start of a drop in the internal pressure of the drain tank due to the sudden load drop operation.

With the above configuration, the following effects are achieved.

During a sudden load drop in a power plant (e.g., reactor runback, PLR pump trip, turbine load shedding, etc.), the plant output generally decreases within 5 to 10 minutes after the sudden load drop operation start signal (output drop request signal) occurs. After a few seconds, it descends rapidly. The internal pressure of a drain tank such as a moisture separator also drops following the sudden load drop.

The present invention focuses on the above phenomenon, and in the first aspect, a signal for starting sudden load drop operation is captured. Based on this start signal, the water level setting value in the drain tank is immediately lowered or the emergency control valve is suddenly opened to temporarily lower the water level in the drain tank before the pressure in the drain tank drops. Therefore, the water level is controlled to be lower than the normal water level setting value.

This low water level control reduces the drain capacity in the drain tank before the pressure inside the drain tank drops (flash occurs), and quickly responds to the subsequent rise in water level due to drain flash.
Abnormal rise in water level in the drain tank when the tank internal pressure suddenly drops can be sufficiently suppressed.

The second and third inventions relate to a device used in the first water level control method.

Among these, the second invention is a low water level setting signal that, when a sudden load drop operation start signal is generated, a low water level setting signal that is outputted from a low water level setting signal generator by a setting value switching device that changes the conventional normal water level setting signal based on this signal. Switch to Then, the water level control valve performs water level control based on this low water level setting signal, so that the water level in the drain tank can be lowered below the normal water level prior to the start of a drop in the internal pressure of the drain tank due to a sudden load drop. can.

Further, in the third invention, in addition to the water level control based on the low water level setting signal executed in the second invention by the sudden load operation start signal, the sudden opening valve opening selected by the valve opening signal switching device is also provided. Since the emergency water level control valve is controlled to open quickly by the temperature signal, proactive low water level control can be performed more effectively.

[Embodiments of the invention]

The present invention will be described in detail below with reference to the embodiments shown in FIGS. 5 to 8 and FIGS. 2 to 4.

First, the state change inside the drain tank according to the present invention will be explained using FIGS. 2 to 4. Generally, when the load suddenly drops from the rated or partial load operation of the power plant, that is, when there is a reactor runback by controlling the PLR pump rotation speed, a PLR pump trip, or a turbine load drop,
As shown in FIG. 2, the output of the nuclear reactor drops rapidly with a delay of 5 to 10 seconds after the output drop request signal 61 is generated. Under these conditions, in the conventional case, the state change inside the moisture separator drain tank 2 is as shown in Fig. 3a.
As shown in the curve 62, the pressure inside the drain tank 2 is
5 after the output drop request signal 61 is generated as shown in
After a delay of ~10 seconds, the pressure suddenly decreases, and with this sudden pressure decrease, the water level in tank 2 suddenly rises as shown by curve 63 due to the flash of saturated drain in drain tank 2 and drain lines 6 and 11, and the normal water level (NWL) 64
When the dump water level (DWL) 70 above is reached, the emergency water level control valve 10 begins to open as shown by a curve 67 in FIG. However, since the opening operation of the control valve 10 is gradual as the water level rises,
The turbine trip water level reached 65,
The plant will be shut down. Note that the curve 66 in FIG. 3b
indicates the opening degree of the regular water level control valve 5, and when the water level in the tank 2 rises above the normal water level 64, the opening degree is set to 100%.

Therefore, in the present invention, the control water level setting value of the drain tank 2 is lowered in advance under operating conditions where the pressure inside the drain tank 2 suddenly decreases. A diagram corresponding to FIG. 3 in that case is shown in FIG. A curve 62 in FIG. 4a shows the pressure change inside the tank 2, which is similar to the case in FIG. 3a, but as shown in FIG. Since the emergency water level control valve 10 is fully opened and the water level set value is lowered to the low water level 71 to make the amount of drain held in the tank 2 smaller than usual, the water level rise when the pressure suddenly decreases is The curve 63' shown in FIG. 4a is obtained, so that the water level does not rise above the normal water level 64, and can be prevented from reaching the turbine trip water level 65. In this case, it goes without saying that simply lowering the water level setting in advance is effective. Fourth
The curve 66' in Figure b is the normal water level control valve 5 in this case.
is the valve opening degree.

FIG. 5 is a system diagram showing an embodiment of the moisture separator drain tank water level control device of the present invention. The same parts as in FIG. In FIG. 5, in addition to the normal water level setting signal generator 21, the emergency water level controller 9 includes an emergency water level setting signal generator 22 at the time of a sudden load drop of the steam generator and turbine; , the water level setting value is switched from the normal water level setting value by the signal generator 21 to the low water level setting value (water level value sufficiently lower than the normal water level setting value) by the signal generator 22 by the plant output drop signal when the plant output drops. A set value switching device 23 is provided. In addition, a valve opening signal generator 24 is used to instantly fully open the emergency water level control valve 10, and a valve opening signal is generated from the emergency valve opening signal generator 24 according to the output drop signal. A valve opening signal switching device 25 for switching to a fully open valve signal is provided, and serves as an emergency switching controller 29. Furthermore, a switching device interlock function as shown below has been added.

FIG. 6 is an explanatory diagram of the switching device interlock. As shown in FIG. 6, a plant output drop signal 28, such as a PLR pump runback signal 48,
The set value switching device 23 and valve opening signal switching device 25 shown in FIG. 5 are activated by the PLR pump trip signal 49 or the power load unbalance relay 50 for shifting to in-house single load operation in the event of trouble in the plant power transmission system. In this case, timers 32 and 33 are provided as a means for restoring the water level to the normal operating water level after a specified time, and the timer 32 is set to have a time limit of, for example, 60 seconds, and when the timer 32 is turned on after 60 seconds, the set value is The switching device 23 is returned to its original state so as to output the normal water level setting value from the normal water level setting signal generator 21, and the timer 33 is set to a time limit of 10 seconds, for example, and when 10 seconds have elapsed. When the timer 33 is turned on, the valve opening signal switching device 25 is returned to its original state so as not to output the valve full open signal from the valve opening signal generator 24.

Although FIG. 5 shows the water level control device for the moisture separator drain tank 2 of the moisture separator 1, the present invention is also applicable to the case of the moisture separator drain tank 2, and the same effective. Fig. 7 is a system diagram showing an embodiment in which the drain tank water level control device according to the present invention is applied to a nuclear power plant having a moisture separation reheater, and the same parts as Figs. 1 and 5 are the same. It is indicated by a symbol. In FIG. 7, 1a is a moisture separation reheater, 2a is a drain tank, 40 is a reactor pressure vessel, 41 is a high pressure turbine, 42 is a low pressure turbine, 43 is a generator, 44 is a condenser, (5th 45 is a pump, 46 is a feed water heater (corresponds to the feed water heater 7 in FIG. 5), 47 is a recirculation pump, 48 is a pump control device, 49 is an output detector, 50 is a trip detector, and the drain tank 2a includes water level transmitters 3, 8, a regular water level controller 4, an emergency switching controller 29, a regular water level control valve 5,
A water level control device according to the present invention consisting of an emergency water level control valve 10 is installed and is exactly the same as that shown in FIG. The operation will be explained below.

The output control of the reactor pressure vessel 40 is performed in Fig. 7.
A sudden decrease signal from the control device 48 of the PLR pump 47, a PLR that monitors the malfunction of the PLR pump 47
Output detector 4 that monitors the output sudden decrease signal from the pump trip detection device 50 or a malfunction in the power transmission system
The switching devices 23 and 25 are actuated by the output sudden decrease signal from the power load unbalance relay 9 through the interlock path shown in FIG. The pressure in the drain tank 2a drops 5 to 10 seconds after this output sudden decrease signal occurs, but when the output sudden decrease signal occurs, the water level setting value of the drain tank 2a is lowered to the low water level setting value by the emergency water level setting signal generator 22. . Simultaneously with the above operation, the output of the emergency switching controller 29 is
The valve fully open signal is given by the valve opening signal generator 24, and the emergency water level control valve 10 is fully opened. . After that, in order to prevent the water level of the drain tank 2a from dropping below the minimum water level, after about 10 seconds, the valve opening signal generator 2
The valve full open signal from 4 is released, and after 60 seconds, the water level setting value is changed to the emergency water level setting signal generator 2.
Normal water level setting signal generator 21 from the set value from 2
The setting value from
operation).

As mentioned above, the pressure suddenly decreases at a low water level, so in this case, the water level in the drain tank 2a changes as shown by the curve 63' in Figure 4a,
The water level rise due to drain flushing will no longer reach the turbine trip water level 65. The plant output stabilizes approximately 60 seconds after the output sudden decrease signal is issued, but at this point the water level setting value is set to the normal water level of 64.
Therefore, the actual water level gradually rises from the low water level state toward the dump water water level 70 (see FIG. 3). Note that when the actual water level reaches the normal water level 64, the regular water level controller 4 enters normal control, and the water heater 4 is turned on via the regular water level control valve 5.
6, the drain is discharged. The same applies to the case of FIG.

As described above, according to the embodiment of the present invention, the water level of the moisture separation drain tank 2 or the moisture separation reheater 1a drain tank 2a when the steam generator (reactor pressure vessel 40) and turbine output suddenly decreases. Turbine trips due to rising can be prevented. In addition, when controlling the water level, not only the water level set value is changed, but also the output of the emergency controller 9 is changed, so the response is excellent and the normal P. After entering I operation and stabilizing the plant load, it is possible to gradually shift to normal drain discharge. Therefore, control stability can be improved. Furthermore, it is also possible to reduce the size of the drain tank.

Note that the valve opening signal generator 24 and valve opening signal switching device 25 of the emergency switching controller 29 may be deleted and the water level set value may be simply switched to a low water level, and substantially the same effect can be obtained. This is very effective in plants where the rate of output decline is gradual, and has the new effect of simplifying control.

FIG. 8 is a system diagram corresponding to FIG. 7 showing another embodiment of the present invention, and the same parts as in FIG. 8 are indicated by the same symbols. In FIG. 8, the same emergency switching controller 29a as described above is used as an emergency water level controller for the emergency water level regulating valve 10a of the reheater heated steam drain tank 52. The operating principle of the emergency switching controller 29a is basically the same as that described in FIG. 5, and the output sudden decrease signal as the switching signal is also the same as in FIGS. 6 and 7.

The function of the water level control system of the heated steam drain tank 52 is to discharge stable drain, but when the output suddenly decreases, the pressure inside the heated steam line 51, tube 54, and drain tank 52 decreases, causing the pressure inside the drain tank 52 to drop. The flashing of condensate causes a rise in water level and backflow of condensate into tube 54, causing flow pulsation and water hammer. Therefore, by discharging the drain in the drain tank 52 in advance, the occurrence of these problems can be avoided, and stable control and reliability can be improved. Further, there is no need to design the drain tank 52 with excessive dimensions. In addition, in FIG. 8, 3a and 8a are water level transmitters,
4a is a regular water level controller, 5a is a regular water level control valve,
53 is a drain pipe.

〔Effect of the invention〕

As described above, according to the present invention, the tank water level is controlled to a low level prior to the start of a drop in the internal pressure of the drain tank that occurs during a sudden load drop in a power plant, so that an abnormal water level increase in saturated drain due to flashing occurs. can be effectively suppressed, and turbine tripping can be reliably prevented. Further, it has the effect of improving control stability.

[Brief explanation of drawings]

Figure 1 is a system diagram of a conventional water level control device for a moisture separator drain tank, Figure 2 is a line diagram showing the state of decrease in reactor output when the load suddenly drops, and Figures 3 and 4 are each a diagram of a conventional water level control system for a moisture separator drain tank. A line diagram showing changes in the water level and pressure in the moisture separator drain tank according to the present invention and the opening degree of the water level control valve at that time, FIG. 5 is a diagram showing the moisture separator drain tank water level control according to the present invention. A system diagram showing one embodiment of the device, FIG. 6 is an explanatory diagram of a switching device interlock, and FIG. 7 shows an embodiment of a nuclear power plant equipped with the moisture separator reheater drain tank water level control device of the present invention. The system diagram shown in FIG. 8 is a system diagram corresponding to FIG. 7 showing another embodiment of the present invention. 1...Moisture separator, 1a...Moisture separation reheater,
2... Moisture separator drain tank, 2a... Moisture separator reheater drain tank, 3, 3a, 8, 8a...
Water level transmitter, 4, 4a... Regular water level controller, 5,
5a... Regular water level control valve, 6... Regular drain line, 7, 46... Feed water heater, 9... Emergency water level controller, 10, 10a... Emergency water level regulating valve, 1
1... Emergency drain line, 12, 44... Condenser, 21... Normal water level setting signal generator, 22...
Emergency water level setting signal generator (low water level setting signal generator), 23... Setting value switching device, 24... Emergency valve opening signal generator (sudden opening valve opening signal generator), 2
5... Valve opening signal switching device, 28... Plant output drop signal, 29, 29a... Emergency switching controller, 32, 33... Timer, 40... Reactor pressure vessel, 41... High pressure turbine, 42...Low pressure turbine.

Claims (1)

[Scope of Claims] 1. A drain tank that separates moisture from steam led to a turbine of a power generation plant by a moisture separator or a moisture separator reheater and stores the saturated drain, and a water level of the drain tank that is set to a predetermined level. In a system equipped with a line that collects condensate to the feed water heater via a regular water level control valve to control the water level, and an emergency line that discharges condensate to the condenser via an emergency water level control valve,
When the internal pressure of the drain tank is in a sudden load drop operation state such as reactor runback, recirculation pump trip, or turbine load shear, the internal pressure of the drain tank starts to drop based on a signal to start the operation state. The water level in the drain tank is temporarily lowered to a level lower than the normal water level setting value by lowering the water level setting value of the drain tank in advance of this, or by suddenly opening the emergency control valve. A method for controlling water level in a drain tank of a moisture separator or reheater, characterized in that the low water level control suppresses a water level rise due to flashing of drain in the drain tank when the internal pressure of the tank suddenly drops. 2. The dampening system according to claim 1, wherein the water level in the drain tank is suppressed from rising when the internal pressure of the tank suddenly drops by suddenly opening the emergency water level control valve at the same time as lowering the water level set value in the drain tank. A method for controlling the water level in the drain tank of a separator or reheater. 3. A drain tank that separates the moisture from the steam introduced to the turbine of the power generation plant using a moisture separator or a moisture separator and reheater and stores the saturated drain, and the water level of the drain tank is set to a predetermined water level based on a water level setting signal. In a system equipped with a line that collects condensate to the feed water heater via a normal water level control valve and an emergency line that discharges drain to the condenser via an emergency water level control valve, the normal water level setting value a low water level setting signal generator that generates a low water level setting signal to reduce the and a setting value switching device for switching a normal water level setting signal to a low water level setting signal from the low water level setting signal generator, the water level control based on the low water level setting signal is controlled by the drain due to the sudden load drop operation. A water level control device for a drain tank of a moisture separator or reheater, characterized in that the device is configured to control the water level of a moisture separator or reheater prior to the start of a drop in internal pressure of the tank. 4. A drain tank that separates the moisture from the steam introduced to the turbine of the power generation plant using a moisture separator or a moisture separator and reheater and stores the saturated drain, and the water level of the drain tank is set to a predetermined water level based on a water level setting signal. In a system equipped with a line that collects condensate to the feed water heater via a normal water level control valve and an emergency line that discharges drain to the condenser via an emergency water level control valve, the normal water level setting value a low water level setting signal generator that generates a low water level setting signal to lower the water level to a specified value; and a valve opening signal generator that generates a valve opening signal that quickly opens the emergency water level control valve to a predetermined opening. , a setting for switching the normal water level setting signal to the low water level setting signal from the low water level setting signal generator by a signal for starting sudden load drop operation such as reactor runback, recirculation pump trip or turbine load shear. a value switching device; and a valve opening signal switching device that switches a valve opening signal to a quick-open valve opening signal from the valve opening signal generator in response to the start signal of the sudden load drop operation; The water level control based on the setting signal and the quick opening control of the emergency water level control valve are set to be performed prior to the start of a drop in the internal pressure of the drain tank due to the sudden load drop operation. Separator or reheater drain tank water level control device. 5. The drain tank of a moisture separator or reheater according to claim 4, wherein the set value switching device and the valve opening signal switching device are provided with means for self-resetting after a plant load change becomes stable. Water level control device.