JPH05223206A - Water level controller for drain tank - Google Patents

Abstract

PURPOSE:To stabilize a level control of a drain tank by differentiating a signal from an emergency water level detector, selecting a calculating mode based on its change rate, and switching an emergency regulating valve. CONSTITUTION:An output of an emergency water level detector 10 is first- differentiated by a change rate calculator, and a change rate of a positive direction, a negative direction of a water level is calculated. Then, this rate is input to a setter, and a trend of the water level is grasped. The setter first- differentiates a water level input signal by differentiating, and outputs the result toward a setter. The setter inputs the output and outputs a condition signal of A or B according to a water level condition. A control calculator selects a calculating mode according to the condition signal. A drain tank water level controller operates an emergency regulating valve 12 by the calculating modes, and controls a water level of the tank. Thus, a stable level control is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drain tank water level control device for a moisture separator or a moisture separation reheater in a nuclear power plant.

[0002]

2. Description of the Related Art Nuclear power plants are
The pressure and temperature of the steam generated in the furnace are considerably lower than those of a thermal power plant (that is, the pressure / temperature is about 24 kg / cm ² g / 538 ° C in a thermal power plant, whereas that in a nuclear power plant is Pressure / temperature is 65kg / cm
² g / 280 ° C.), the steam already contains about 0.2 to 0.4% of water at the turbine inlet. If this steam is expanded to the turbine outlet pressure without being separated into moisture, the wetness of the steam at the final stage outlet of the low-pressure turbine will be about 25
Reaches as high as%. If the turbine is operated in this state, not only the erosion of the mobilization due to the moisture in the steam becomes significant, but also the internal efficiency of the turbine is significantly reduced.

Therefore, in order to effectively remove the water generated during the expansion of steam, a moisture separator is installed. There have been various types of moisture separators since ancient times.For example, by applying a rotary flow to wet steam and separating wet water with a large specific gravity by its centrifugal force, by flowing wet steam between corrugated plates. There is a corrugated plate type in which only water is attached to the wall surface of the corrugated plate.

Further, recently, the amount of reheat of moisture separation, in which the extracted steam from the high-pressure turbine or the main steam is reheated as a heat source to supply the steam to the low-pressure turbine of the next stage, is also frequently used.

The moisture separator and the moisture separator reheater (which are simply referred to as a moisture separator when it is not necessary to distinguish them) are usually installed between the high pressure turbine and the low pressure turbine. The water (drain) separated by the moisture separator is stored in the attached drain tank and discharged to the feed water superheater and the condenser.

FIG. 4 is a schematic system diagram illustrating a conventional drain tank water level control device. A high pressure turbine 2 to which a main steam pipe 1 from a nuclear reactor (not shown) is connected together with a low pressure turbine 3 and a generator 4. To drive. The moisture separator 5 is provided in the middle of the high pressure turbine 2 and the low pressure turbine 3, and a drain tank 6 for storing the generated drain is installed in the moisture separator 5.

In order to control the water level in the drain tank 6, a normal control system consisting of a normal water level detector 7, a normal water level controller 8 and a normal control valve 9 is provided, and also as an emergency control system. An emergency water level detector 10, an emergency water level controller 11 and an emergency control valve 12 are provided. Each of these control systems is controlled by a preset water level.

A drain pipe 13 is connected to the drain tank 6, and one of two pipes branched from the lower end thereof is connected to a feed water heater (not shown) through a regular control valve 9, and The other pipe is connected to a condenser (not shown) via an emergency control valve 12.

Moisture-containing steam sent from the high-pressure turbine 2 is separated in the moisture separator 5 and then sent to the low-pressure turbine 3 to work again, and the water separated from the steam is The water level is controlled by entering the drain tank 6.

The water level control of the drain tank 6 is always carried out by the normal control system, but for some reason, even if the normal control valve 9 of the normal control system is fully closed, the water level rises and exceeds a predetermined level. The emergency control system is activated to open the emergency control valve 12 to allow the drain to flow to a condenser (not shown).

[0011]

By the way, the drain tank 6 of the moisture separator 5 is almost equal to the outlet pressure of the high-pressure turbine 2, and the temperature is the saturation temperature of the pressure. When the turbine load decreases, the outlet pressure of the high-pressure turbine 2 decreases almost at the same time, but the drain temperature does not decrease suddenly, and as a result, the drain evaporates by the difference between the pressure drop and the drain temperature saturation pressure. For this reason, the drain becomes a gas-liquid two-phase state, the volume increases, and the drain cannot be discharged only by the regular control valve 9. As a result, the drain 7 water level will rise to the emergency control system water level.

The emergency water level controller 11 has a proportional / integral operation function, and since the actual water level is always lower than the set water level, a fully closed signal is sent to the emergency control valve 12, It is closed. In addition, the emergency water level controller 11
The proportional / integral function of is generally adjusted so that the proportional gain is 1.0 or less and the integration time is long so that stable control can be performed independently when the normal control system is abnormal.

When the actual water level rises above the set water level in this state, it takes a considerable amount of time to move the emergency control valve 12 to an opening degree commensurate with the water level rise, so that the water level further rises during that time.

When this abnormal rise in water level exceeds a predetermined level, the turbine is tripped, the interlock for scramming the reactor is activated, and the plant is stopped.

However, an abnormal situation occurs in a nuclear reactor scrum in a nuclear power plant, and its influence has a wide range, so it must be avoided as much as possible. Therefore, it is necessary to control so that the water level in the drain tank does not become abnormal, but as described above, the conventional control device could not satisfactorily cope with this.

The present invention has been made by subtly modifying the above system. When the water level rises, the emergency control system is promptly activated to drain the drain to the condenser to prevent an abnormal rise in the water level. Moreover, it is an object of the present invention to provide a drain tank water level control device capable of preventing a sharp drop in water level after the emergency control valve is opened suddenly and performing stable level control.

[0017]

SUMMARY OF THE INVENTION A drain tank water level control device according to the present invention is a drain tank for storing water separated by a moisture separator or a moisture separation reheater, and a rate of change of water level in the drain tank. The normal water level detector and the emergency water level detector that detect the, and the normal water level system and the emergency water level system piping that discharges the water in the drain tank are inserted by the signal from the normal water level controller or control calculator. A controlled control valve to be controlled, an emergency control valve, a change rate calculator that differentiates the signal from the emergency water level detector, and a setting device that outputs a switching signal based on the output of this change rate calculator, A control arithmetic unit for selecting an arithmetic mode in accordance with a signal from the setting unit and opening and closing the emergency control valve is provided.

[0018]

In the conventional apparatus of this type, when the actual water level rises above the set water level, the actual water level should converge to the set water level.
Although it takes a relatively long time, the cause of this is that the conventional emergency water level controller has only a proportional / integral function.

The present invention focuses on such a point. While adding the element of the rate of change of the actual water level to the arithmetic unit to the increase in the actual water level, the operating modes are set to the actual water level rising time and the actual water level falling time. A control calculator is provided so that it can be used as desired.

Therefore, according to the present invention, when the actual water level rises or when the actual water level falls, the actual water level can be made to converge to the set water level much faster than before.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, the same parts in FIG. 4 are designated by the same reference numerals, and the description thereof will be omitted to avoid duplication.

As can be seen by comparing FIGS. 1 and 4,
The drain tank water level control device according to the present invention uses the control calculator 16 instead of the emergency water level controller 11, and differentiates the output of the emergency water level detector 10 with the change rate calculator (differentiator) 14. After that, the configuration is such that it is inputted to the control terminal of the control calculator 16 through the setting device 15.

In the above-described drain tank water level control device, the output of the emergency water level detector 10 is first-order differentiated by the change rate calculator 14 to calculate the change rate of the water level in the positive and negative directions.

Next, this rate of change is input to the setter 15,
This operation for grasping the trend of the water level will be described with reference to FIG.

The setter 15 first-order differentiates the water level input signal by a differential operation, and outputs the result to the setter 15. This output is the setting device "HH" 15a in the setting device 15,
The water level can be grasped by "H" 15b, "LL" 15c, and "L" 15d. The set values of the setters 15a to 15d are "HH">"H" in the water level rising direction and "LL" in the water level falling direction.
> L is set, and the condition signal of "A" or "B" is output depending on the water level condition.

By the condition signals "A" and "B", the control calculator 16 of FIG. 1 selects a calculation mode according to the combination shown in FIG.

There are three types of calculation modes in this embodiment, and they are selected according to the rate of rise / fall of the water level. That is, during normal operation, the drain is not in a gas-liquid two-phase state and there is no abnormal rise / fall of the water level, so the change rate calculator 14 and the setters 15a to 15d do not operate, and the water level condition "A",
"B" is turned off. In this case, the control signal of (proportion + integration) in the normal calculation mode is output.

In addition, when the water level rises due to drain evaporation that occurs with the pressure change of the load change rate, the change rate calculator
The water level condition is "A" O by 14 and each setter 15a-15d
N and "B" are turned off, and the calculation mode is switched to the calculation mode when the water level rises from the normal calculation mode. Since the main purpose of this water level rising mode is to suppress the water level rising, it is simply calculated as a ratio (K ₁ ).

By this arithmetic operation, the emergency control valve 12 is suddenly opened and the rise in water level is suppressed. At this time, the emergency control valve 12 has reached the fully opened state, the drain tank water level starts to drop, and the speed thereof increases. This is because the drain state has returned from the gas-liquid two-phase state to the liquid phase state, the volume flow rate of the drain has decreased, and the control valve opening has been fully opened.

Further, when the water level is falling, the change rate calculator 14 and the setting devices 15a to 15d are the same as when the water level is rising.
Thus, the water level condition becomes "A" OFF and "B" ON state, and the calculation mode is switched from the water level rising calculation mode to the water level falling calculation mode. Since the calculation mode for lowering the water level is also intended to suppress the lowering of the water level, it is simply calculated as a ratio (K ₂ ). In the drain tank water level control device according to the present invention, the emergency control valve 12 is operated by the above-mentioned calculation modes.
To control the drain tank water level.

As a result, the drain tank water level rises during drain evaporation due to the pressure change in the vessel and the subsequent water level fall,
Alternatively, contradictory control purposes during normal operation can be achieved, and stable level control can be performed.

In the above description, an example in which the water level is raised by detecting the actual water level itself has been described. However, the present invention is not limited to this, and the water level detector can change the pressure inside the vessel. The same effect can be obtained by detecting the rate or turbine load change rate.

[0033]

As described above, according to the present invention, the drain tank water level can be controlled stably and the scram of the reactor due to the abnormal rise of the drain tank water level can be avoided. Therefore, the stability and economic efficiency of the nuclear power plant can be improved. Can be significantly improved.

[Brief description of drawings]

FIG. 1 is a schematic system diagram showing an embodiment of a drain tank water level control device according to the present invention.

FIG. 2 is a schematic diagram illustrating the function of a setting device.

FIG. 3 is an explanatory diagram illustrating the operation of a setting device.

FIG. 4 is a schematic system diagram showing an example of a conventional drain tank water level control device.

[Explanation of symbols]

 1 ... Main steam pipe 2 ... High pressure turbine 3 ... Low pressure turbine 4 ... Generator 5 ... Moisture separator 6 ... Drain tank 7 ... Regular water level detector 8 ... Regular water level controller 9 ... Regular control valve 10 ... Emergency water level detection Device 11 ... Emergency water level controller 12 ... Emergency control valve 13 ... Drain pipe 14 ... Change rate calculator 15 ... Setting device 16 ... Control calculator

Claims (1)

[Claims] 1. In a nuclear power plant, a drain tank for storing water separated by a moisture separator or a moisture separation reheater, a normal water level detector for detecting a water level change rate in the drain tank, and an emergency water. Position detector and a normal control valve and an emergency control valve which are inserted in the normal water level system pipe and the emergency water level system pipe for discharging the water in the drain tank, and which are controlled by signals from the normal water level controller or control calculator. A control valve, a change rate calculator that differentiates the signal from the emergency water level detector, a setter that outputs a switching signal based on the output of this change rate calculator, and a calculation mode based on the signal from this setter. And a control calculator that opens and closes the emergency control valve, and a drain tank water level control device.