JPH04148101A - Controlling method for steam drum water level at time of switching of feed water control valve - Google Patents

Abstract

PURPOSE:To raise the performance in water level control for a steam drum and reduce the work assigned to the operator by adjusting the value travel of a feed water control valve according to the difference between the feed water volume at the inlet of the feed water control valve and a target feed water flow rate which corresponds to the output of the furnace. CONSTITUTION:A return pipe from a furnace cleaning system merges with he piping from a main feed water control valve 34 and a low flow rate feed water control valve 35 to a steam drum 12 and the temperature and flow rate there are measured. The drum water level signal and set water level are compared by a steam drum water level adjusting device and signal of PI (proportional integration) action is generated from the water level deviation. And, by using the most suitable feed water flow rate curve for the output of the nuclear reactor a target feed water flow rate is calculated and the calculation is added to the output of the steam drum water level adjusting device to seek the final target feed water flow rate. Next, from temperature T1, T2, T3 round the feed water control valve and a flow rate F2 the feed water flow rate F1 is calculated. The final target feed water flow rate the takes the water level deviation in consideration and the feed water flow rate F1 as the result of the calculation are compared by the feed water flow rate control device and final control signal is generated by cascade PI action and the valve travel of the feed water control valve is controlled so as to match the control signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for determining the steam drum water level flI111 during switching of a feedwater control valve in a nuclear power plant or the like.

More specifically, a method for controlling the water level in a steam drum that separates steam-water mixed fluid to a constant level when switching between the main feed water control valve and the low flow rate feed water control valve, which is performed in the low power region of the reactor, for example. It is related to.

[Conventional technology] The following is an explanation using a new converter reactor power plant as an example.

The steam drum in the new converter reactor power plant collects the coolant mixture of steam and water generated from the nuclear reactor, separates the steam and water, and sends only the steam to the turbine system, while the water is mixed with the feed water returned from the turbine system. It has the role of sending it back to the nuclear reactor. At this time, the steam drum water level must be maintained within an appropriate range in order to ensure heat removal from the fuel in the reactor and to prevent water carryover to the turbine. Therefore, the water supply flow rate is controlled to maintain the steam drum water level at the set value. In order to control this water level to a constant level, in principle, the flow rate of the water supply should be controlled by the water supply control valve so that the flow rate of the separated steam matches the flow rate of the water supply.

By the way, in the water supply system from the turbine system to the steam drum,
Normally, two types of water supply control valves with different capacities are installed in parallel and are used depending on the reactor output. Specifically, a low flow water supply water control valve is used in the low power range (low flow range) of about 18% or less of the reactor output, and a main water supply water control valve is used in the higher power range (high flow range). There is. Therefore, the water supply control valve is switched at approximately 18% of the reactor output.

[Problems to be Solved by the Invention] Since the switching of this water supply control valve is performed by manual adjustment by the operator, the water level fluctuation in the steam drum tends to be relatively large. transformation,
Automation was desired.

In order to keep the steam drum water level constant when switching the feedwater control valve, it is necessary to always ensure a feedwater flow rate commensurate with the reactor output, but in the region of about 18% of the reactor output, the feedwater flow rate is small, so the accuracy of the feedwater flow rate is I can't get good measurements. For this reason, operators have to carefully operate the valves little by little and monitor changes in the water level of the steam drum while carefully performing switching operations, which has the disadvantage of lengthening the switching time and placing a heavy burden on the operators.

An object of the present invention is to provide a steam drum water level control method that can shorten the switching time of the water supply control valve, improve the performance of steam drum water level control, reduce the burden on operators, and also enable automation. be.

[Means for Solving the Problems] The present invention provides a steam drum that separates a mixed fluid of steam and water generated from a furnace, a steam system that sends the generated steam to a turbine system, and a steam drum that transports the generated steam from the turbine system to the steam drum. This system is equipped with a water supply system leading to the furnace output, and a furnace purification system that purifies and returns the water in the steam drum. Two types of water supply control valves with different capacities are installed in parallel in the water supply system, and the water supply control valves are used to control the furnace output. This is a method of controlling the water level of the steam drum when switching according to.

The first method is the feed water temperature monitoring method, in which the feed water temperature at the inlet of the feed water control valve is T1, the temperature of the reactor purification system return water is T1, the feed water temperature at the steam drum inlet is T, and the flow rate of the reactor purification system return water is When is F2, the water supply flow rate F1 at the inlet of the water supply control valve is,
It is calculated using the following formula, and the opening degree of the water supply control valve is controlled to be adjusted based on the deviation between the value and the target water supply flow rate according to the furnace output at the time of switching.

The second method is the water supply flow rate maintenance method, in which the differential pressure before and after the water supply control valve is determined, and the water supply flow rate is determined from the CV value for the opening degree of the multiple valve and the differential pressure before and after the valve. The valve opening degree is automatically controlled so that the sum of the water supply flow rates of the control valves is constant.

Furthermore, there is also a combined control method that combines the above two methods, automatically switching using the second method (water supply flow rate maintenance method), and then correcting water level fluctuations based on the flow rate evaluation error using the first method (water supply temperature monitoring method). Yes, it is also included in the present invention.

In the present invention, the term "steam drum" refers to a device that separates steam and water from a mixed fluid of steam and water, and includes steam drums in nuclear reactors as well as steam and water separators and steam separators in various similar cooling systems. Also included is a generator.

[Operation] Depending on the reactor output, a low flow rate water control valve is used in a low flow rate region, and a main feed water control valve is used in a high flow rate region. Switching of these water supply control valves is carried out, for example, at a reactor output of 18
It is done at %. At this time, in order to keep the steam drum water level constant, it is sufficient to always ensure a feed water flow rate commensurate with the furnace output, but the feed water flow rate and steam flow rate cannot be accurately measured in the low flow rate region.

In the control method of the present invention, the water level in the steam drum is maintained constant by indirectly determining the feed water flow rate without using the measured values of the feed water flow rate or the steam flow rate.

In the first method, the water supply flow rate is determined from measured values such as the temperature of the piping system around the water supply control valve. In the second method, the water supply flow rate is determined from the CV value for the opening degree of the valve and the differential pressure before and after the valve.

By adjusting the opening degrees of both feedwater control valves based on these values, the water level in the steam drum is controlled when the feedwater control valves are switched.

[Example] Fig. 4 is a schematic diagram showing an example of a water supply/steam system in a new type converter plant. First, the overall configuration of the plant will be briefly explained.

A mixed coolant of steam and water generated in the nuclear reactor IO enters the steam drum 12 and is separated from air and water. The separated steam passes through a steam isolation valve 14, a steam stop valve 16 and a steam control valve 18.
It passes through the turbine 20, drives the generator 22, and reaches the condenser 24. A portion of the steam from the steam isolation valve 14 is...
It passes through the turbine bypass valve 26 and reaches the condenser 24 . Water in the condenser 24 returns to the steam drum 12 through the condensate pump 28 , desalter 29 , feedwater heater 30 , feedwater pump 32 , main feedwater control valve 34 or low flow feedwater control valve 35 . This is the water supply system. This feed water is mixed with the separated water in the steam drum 12 and returned to the reactor IO by a recirculation pump 36. A portion of the water in the steam drum 12 is also returned to the steam drum 12 through a demineralizer 38 .

This is the furnace purification system.

Under normal conditions, each signal from the drum water level detector 42 that measures the water level of the steam drum 12, the steam flow meter 44 that measures the steam flow rate of the steam system, and the feed water flow meter 46 that measures the water flow rate of the water supply system is sent to the water supply control device. 48, and the opening degrees of the main water supply control valve 34 and the low flow water supply control valve 35 are controlled by the output thereof.

A schematic diagram of the piping system around the water supply control valve is shown in Figure 3. A return pipe from the furnace purification system joins between the main water supply control valve 34 and the low flow rate water supply control valve 35 to the steam drum 12, and its temperature and flow rate are measured. The energy balance regarding these process values is described by the following equation.

h(T1.PI)XFI+h(T2.Pt)XF! =h
(Ts, Ps) x (F+ +Fri...(1)
h(T, P) A function that gives the specific enthalpy (kcal/kg) of water at two temperatures T and pressure P, T, , P, , F, : Feed water temperature at the inlet of the water supply control valve C)
.

Pressure (at) and flow rate (kg/h) T, , P, ,
F2: Temperature (℃), pressure (at) of the return water of the furnace purification system,
and flow rate (kg/h) Ts, Ps: Water supply temperature at steam drum inlet ("C)
.

and pressure (at) From the +11 formula, the water supply flow rate F1 can be determined by the following formula.

Since all process values used in equation (2) can be measured, the water supply flow rate can be calculated using these values, but in an environment below the saturation temperature in the pressure cuff range of 0 to 120 at, Since enthalpy is approximately the same value as temperature, equation (2) can be simplified as shown below.

Therefore, based on the above equation (3), the switching operation of the water supply control valve is performed according to the block diagram of the l control system shown in FIG. This is the feed water temperature monitoring method. In this example, the steam drum water level! The drum water level signal is compared with the set water level using the II moderator, and a PI (proportional integral) operation signal is generated from the water level deviation. Further, the target feed water flow rate is calculated using the optimum feed water flow rate curve for the reactor output, and is added to the output of the steam drum water level controller to obtain the final target feed water flow rate.

Next, using equation (3) above, the temperature around the water supply control valve Tl
! T1. The water supply flow rate F+ is calculated from Tl and the flow rate F.

The water supply flow rate controller compares the final target water supply flow rate considering the water level deviation with the calculated water supply flow rate F1, generates the final # control signal by cascade PI operation, and adjusts the water supply l1 node valve opening to match it. Control. As a result, even if the reactor output changes during the feed water control valve switching period, it can be followed.

Next, when switching the feed water control valve in a state where the steam drum water level is stable, it is sufficient to always keep the total flow rate of the main feed water control valve and the low flow rate feed water control valve constant. Therefore, when switching from the main water supply control valve to the low-flow water supply control valve, calculate the flow rate of the main water supply control valve from the 07 curve and the differential pressure before and after the valve, and reduce the flow rate that decreases by closing the main water supply control valve. The control system is configured to set the target value of the water supply flow rate controller of the flow rate water supply control valve. Also, when switching from a low-flow water supply control valve to a main water supply control valve, this can be achieved by the reverse method.

With this switching method, by operating the changeover switch by the operator, one valve can be automatically closed at a set speed, and the other valve can be automatically opened to compensate. It is.

FIG. 2 shows a block diagram of the control system when switching the water supply regulating valve using this method of maintaining the water supply flow rate. Before switching, both switches A and A are connected to the controller 50.52 in the normal state, and are controlled by the signal from the controller 50.52 in the normal state.

Here, we will take the case of switching from the main water supply control valve to the low flow water supply control valve as an example. Due to the switch operation of the switching command, switches A + and A t perform cascade PI operation54.5
6 side, the main water supply control valve and the low flow water supply control valve are placed under the control of the controller at the time of switching. At the same time, switch C enters the self-holding side, and the water supply flow rate at that time is input as a target value to the cascade PI operation, and is self-held until the switching is completed. Next, switch B enters the main water supply control valve automatic opening/closing speed setting device 58 side, and switch B enters the cascade PI operation 56 side. In this state, the water supply flow rate holding circuit is established, and from then on, the main water supply control valve automatic opening/closing speed setting device 5
The main water supply control valve is automatically closed at the speed set in step 8. When the main water supply control valve closes, the flow rate of the main water supply control valve flow rate calculation 60 becomes small, so the output of the adder 62 becomes small, and the cascade Pl operation 56 works to compensate for this, and the low flow rate control valve open. This is continued until the main water supply control valve is fully closed, and when the switching is completed, both switches At and At enter the normal state of the controller 50°52, and thereafter the control shifts to the normal state of the controller.

Switching from the low flow rate water supply control valve to the main water supply control valve is also basically performed in the same procedure as described above, so a description thereof will be omitted.

Here, the differential pressure ΔP across the valve is determined by the following equation.

ΔP=P, -Pl-PI-P.

Pl: Water supply pump outlet pressure P,: Steam drum pressure P,: Hydrostatic head from the center of the steam drum to the water supply control valve P4: Fluid friction loss from the water supply control valve to the steam drum Also, the formula for calculating the flow rate from the CV value of the valve is as follows.

FELow (t): Low flow water supply control valve flow rate FEP
III (t)・Main water supply control valve flow rate ρ Fluid density CVLov (FV LQ-(t)): Function that gives the CV value for low flow rate water control valve opening FVLo* (t) CVp** (FV pal (t) ): Function that gives the CV value for the main water supply control valve opening degree FVp-(1) After automatic switching is performed using the water supply flow rate maintenance method, the water supply temperature is controlled to be constant using the water supply temperature monitoring method for a while, and then normal control is performed. Combined methods of switching are also possible. This makes it possible to correct water level fluctuations due to flow rate evaluation errors in the water supply flow rate maintenance method using the water supply temperature in the water supply temperature monitoring method, thereby making it possible to suppress fluctuations to a smaller level.

It goes without saying that these control systems can be realized by analog circuits or easily configured by a digital controller for control. In addition, here we have shown an example in which a cascade PI controller is used as a controller to obtain control signals, but other types of controllers may be used as long as they are equipped with a means to obtain control signals that match input signals to target values. There may be.

[Effects of the Invention] According to the present invention, in the switching operation of the water supply control valve of the furnace,
Even if the measured values of steam flow rate or feed water flow rate cannot be obtained, it is possible to indirectly determine the feed water flow rate and control the value to be maintained, and the feed water control valve switching operation can suppress fluctuations in the steam drum water level to a minimum. It becomes possible. At the same time, it is possible to shorten the switching time and reduce the burden on the operator.

Furthermore, the water supply flow rate maintenance method enables automatic switching of the water supply control valve, which can greatly contribute to improving plant operation control performance and reducing the burden on operators.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the control system when switching the water supply regulating valve to which the feed water temperature monitoring method of the present invention is applied, and Fig. 2 is a block diagram of the control system when switching the water supply regulating valve to which the method of maintaining the water supply flow rate of the present invention is applied. Figure 3 is a schematic diagram of the piping system around the water supply control valve, and Figure 4 is a schematic diagram of the water supply and steam system of the new converter plant. lO...Nuclear reactor, 12...Steam drum, 20...
Turbine, 34... Main water supply control valve, 35... Low flow water supply control valve. Patent applicant Shigeru Hitoshi, representative of Power Reactor and Nuclear Fuel Development Corporation Estimate diagram

Claims (1)

[Claims] 1. A steam drum that separates a mixed fluid of steam and water generated from a furnace, a steam system that sends the generated steam to a turbine system, and a water supply system that extends from the turbine system to the steam drum. , a system equipped with a furnace purification system that purifies and returns water in the steam drum, in which two types of water supply control valves with different capacities are installed in parallel in the water supply system, and the water supply control valves are switched according to the furnace output. In the method for controlling the water level of the steam drum, the temperature of the feed water at the inlet of the feed water control valve is T_1, the temperature of the return water of the reactor purification system is T_2, the temperature of the feed water at the inlet of the steam drum is T_3, and the flow rate of the return water of the reactor purification system is F_2. Then, the water supply flow rate F_1 at the inlet of the water supply control valve is calculated using the following formula F_1={(T_3-T_2)/(T_1-T_3)}
×F_2, and the opening degree of the feed water control valve is adjusted based on the deviation between the value and a target feed water flow rate according to the furnace output. 2. A system comprising a steam drum that separates a mixed fluid of steam and water generated from a furnace, a steam system that sends the generated steam to a turbine system, and a water supply system that extends from the turbine system to the steam drum. In a method for controlling the water level of the steam drum when two types of feed water control valves with different capacities are arranged in parallel in a water supply system and the feed water control valves are switched according to the furnace output, the differential pressure before and after the feed water control valve is The water supply flow rate is determined from the CV value for the opening degree of each water supply control valve and the differential pressure before and after the valve, and the valve opening degree is automatically controlled so that the sum of the water supply flow rates of both water supply control valves is constant. Features: Steam drum water level control method when switching the water supply control valve. 3. A method for controlling the water level of a steam drum when switching a water supply control valve, in which after automatically controlling the water level by the method of claim 2, the water level fluctuation based on the flow rate evaluation error is corrected by the method of claim 1.