JP2731331B2 - Feedwater pump recirculation flow control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feed water pump recirculation flow control device for a power plant.

[0002]

2. Description of the Related Art A feedwater pump in a power plant is configured to increase the number of revolutions of the feedwater pump in order to supply a feedwater flow rate required by the boiler to the boiler with an increase in power generation. On the other hand, it is necessary for the water supply pump to flow a suction flow rate equal to or more than the minimum suction flow rate in order to prevent the pump from being heated. This minimum suction flow rate is a value that changes according to the feedwater pump rotation speed. If the suction flow rate falls below the minimum suction flow rate, an alarm must be output or the water supply pump must be forcibly stopped. Therefore, when the feedwater flow rate to the boiler decreases and the suction flow rate decreases, the suction flow rate of the feedwater pump is increased by adjusting the opening of the recirculation valve and increasing the recirculation flow rate returned to the deaerator. It is more than the minimum suction flow rate.

FIG. 3 is a system diagram of this type of feed pump. In the figure, a water supply pump 1 is disposed in a water supply pipe 2 from a deaerator (not shown) to a boiler. A recirculation pipe 3 that recirculates to a deaerator is branched from an outlet side of the water supply pipe 2. ing. The recirculation pipe 3 is provided with a recirculation valve 4. Further, a flow element 5 is arranged in the water supply pipe 2, a suction flow signal Q is output from a transmitter 6 coupled to the flow element 5, and a rotation number detector 7 is installed in the water supply pump 1. The rotation speed signal N is output from the rotation speed detector 7.

[0004] The above-mentioned transmitter 6 and rotation speed detector 7 are
The recirculation valve 4 is connected to the input side of the feed water pump recirculation flow control device 8 while being connected to the output side. Thereby, the feed water pump recirculation flow control device 8 opens the recirculation valve based on the suction flow signal Q obtained by the transmitter 6 coupled to the flow element 5 and the rotation speed signal N obtained by the rotation speed detector 7. The degree command V is calculated and output to the recirculation valve 4.

[0005] The feed water pump recirculation flow control device 8 is shown in FIG.
As shown in the figure, the suction flow set value function generator 9, the deviation calculator 10, the proportional calculator 11, the deviation calculator 12, the limiter 13, and the integrator 14 are provided. The suction flow rate setting value function generator 9 generates a suction flow rate setting signal QT according to the rotation speed signal N.
Is output. The deviation calculator 10 calculates a deviation between the suction flow rate setting signal QT and the suction flow rate signal Q, and the deviation signal is input to a proportional calculator 11. The proportional calculator 11 performs a proportional calculation according to the deviation signal and outputs a calculation signal.

Here, the relationship between the suction flow rate setting signal QT and the rotation speed signal N will be described with reference to FIG. 5. The suction flow rate setting signal QT is set in advance according to the rotation speed signal N. N increases according to the rotation speed signal N in the range of N1 to N2. Further, a constant value is held when the rotation speed signal N is equal to or greater than N2, and is held even when the rotation speed signal N is equal to or less than N1. 5 indicates a suction flow signal Q for fully opening the recirculation valve 4. The minimum suction flow of the feed water pump 1 is slightly below QS, and is used to control the suction flow of the feed water pump 1. The suction flow rate setting signal QT as the target value at is set to be α higher than QS. The output of the proportional calculator 11 changes the recirculation valve opening command V from fully closed to fully open in response to a change α in the suction flow rate signal Q.

That is, when the suction flow signal Q coincides with QS, the output of the proportional calculator 11 becomes 100% [= K ×
(QT-QS)], the recirculation valve opening command V is fully opened.
On the other hand, when the suction flow signal Q matches the suction flow setting signal QT, the output of the proportional calculator 11 is 0% [= K × (Q
T-QT)], the recirculation valve opening command V is fully closed.

The deviation calculator 12 calculates a deviation between the output of the proportional calculator 11 and the output of the integrator 14. The limiter 13 limits the input signal and outputs the signal, and has the characteristics shown in FIG. That is, when the polarity of the input signal of the limiter 13 is positive, a predetermined limit signal is output in the positive direction, and when the polarity is negative, the predetermined limit signal is output in the negative direction. The integrator 14 receives the output signal of the limiter 13 as an input signal, performs an integration operation on the input signal, and outputs the result.

The controller composed of the deviation calculator 12, the limiter 13, and the integrator 14 operates so that the output signal of the integrator 14 matches the output signal of the proportional calculator 11.
At this time, with respect to the operation in the opening direction of the recirculation valve 4 (corresponding to the case where the polarity of the input of the restrictor 13 is positive), the recirculation valve 4 is opened at a high speed, and the operation in the closing direction (the operation of the restrictor 13). (Corresponding to the case where the polarity of the input is negative), the recirculation valve 4 is closed at a low speed. Thereby, the high-speed opening operation of the recirculation valve 4 prevents the water supply pump 1 from heating, and the low-speed closing operation of the recirculation valve 4 minimizes disturbance to the feedwater flow rate control of the boiler.

[0010]

However, the above-mentioned conventional feed water pump recirculation flow control device 8 has the following problems.

As an example, a problem in the case where the flow rate of water supplied to the boiler is gradually reduced in the process of stopping the water supply pump with reference to FIG. 7 will be described. In FIG. , QF is the feed water flow signal to the boiler, Q
T is a suction flow rate setting signal, and V in the lower part of the figure indicates a recirculation valve opening command signal.

In the figure, when the rotation speed of the feed water pump 1 is reduced from time t1, the feed water flow signal QF to the boiler gradually decreases. At this time, since the difference between the suction flow rate setting signal QT and the suction flow rate signal Q is equal to or more than α, the feedwater pump recirculation flow rate control device 8 outputs the recirculation valve opening command V to be fully closed. Therefore, water does not flow to the recirculation valve 4, and the suction flow rate Q becomes the same value as the water supply flow rate QF and gradually decreases.

Thereafter, when the suction flow rate signal Q reaches the suction flow rate setting signal QT, the feedwater pump recirculation flow rate control device 8 shifts the recirculation valve opening command signal V from fully closed to open at time t2. Further, when the suction flow signal Q falls below the suction flow setting signal QT, the recirculation valve opening command signal V gradually increases in the opening direction. As a result, the flow rate flowing to the recirculation valve 4 increases, and the suction flow rate signal Q increases, but the water supply flow rate signal QF to the boiler sharply decreases. That is, the recirculation valve opening degree command signal V is increased at a high speed in order to prevent the heating of the water supply pump 1, and the recirculation system has a larger suction force than the boiler system, so that the flow increases to the recirculation system. Correspondingly, the water supply flow rate signal QF to the boiler is at time t2
From time t3.

On the other hand, in water supply flow rate control of the water supply pump 1,
Control is performed such that the required flow rate is secured as the feed water flow rate signal QF of the feed water pump 1 sharply decreases. Thereby, the feedwater flow signal QF increases from time t3 to time t4. afterwards,
The suction flow signal Q drops after increasing greatly from the suction flow setting signal QT, and at time t5, the suction flow signal Q matches the suction flow setting signal QT, and the suction flow signal Q drops below the suction flow setting signal QT. . Therefore, at time t6, the recirculation valve opening command signal V is in the increasing direction. Along with this,
The suction flow signal Q increases again, but from time t3 to time t
As in the case of No. 4, the feedwater flow signal QF decreases sharply. This allows
As described above, the time t
Then, the water supply flow signal QF increases again to 7 and returns. Since such a rapid change and return of the feedwater flow signal QF are repeated, there is a problem that disturbance in boiler feedwater flow control occurs.

Accordingly, an object of the present invention is to provide a feedwater pump recirculation flow control device that minimizes disturbances in boiler feedwater control.

[0016]

According to a first aspect of the present invention, a water supply pump supplies water from a deaerator to a boiler, and a recirculation flow rate for recirculating the supply water to a deaerator through a recirculation valve. In a water supply pump recirculation flow control device controlled by opening and closing a recirculation valve, a function generating means for outputting a suction flow rate setting signal according to a rotation speed signal of the water supply pump, a suction flow rate setting signal and a suction flow rate detection signal of the water supply pump Control means comprising a means for outputting a first recirculation valve opening command signal obtained by performing a control operation in accordance with the deviation signal from the control signal, and a signal increasing at a predetermined rate of change during the stop process of the water supply pump. A signal generating means for outputting as a second recirculation valve opening command a signal that is output and decreases at a predetermined rate during the start-up process of the water supply pump; a first recirculation valve opening command signal and a second recirculation valve opening command signal. Recirculation valve opening command signal Is input, and the second recirculation valve opening command signal, which is a signal that increases at a predetermined change rate in the stop process, is selected as a high value, thereby gradually opening the recirculation valve in the opening direction. High value selecting means is provided for selecting the second recirculation valve opening command signal, which is a signal decreasing at a predetermined rate of change, as a high value to gradually close the recirculation valve.

[0017]

According to the above construction, the function generating means outputs a suction flow rate setting signal in response to the rotation speed signal of the feed water pump, and controls in accordance with a deviation signal between the suction flow rate setting signal and the suction flow rate detection signal of the feed water pump. Calculation is performed, and this control calculation signal is output as a first recirculation valve opening degree command signal. on the other hand,
The signal generating means outputs, as a second recirculation valve opening degree command, a signal that increases at a predetermined rate when the water supply pump is stopped or a signal that decreases at a predetermined rate when the water supply pump is started. The first recirculation valve opening command signal and the second recirculation valve opening command signal are input to the high value selection means, and a signal having a higher value is selected from these signals and the recirculation valve opening command is selected. A signal is output to the recirculation valve. Thus, in the stop process of the water supply pump, a signal that increases at a predetermined rate of change is selected as the second recirculation valve opening command, and the recirculation valve is gradually opened, so that the suction flow rate becomes equal to the suction flow rate. Even if the value is lower than the set value, the recirculation valve is prevented from being repeatedly opened and closed repeatedly to secure a required suction flow rate of the water supply pump. At this time, if the suction flow rate of the water supply pump suddenly decreases, the first recirculation valve opening degree command signal becomes high and is selected according to the deviation signal between the suction flow rate setting signal and the suction flow rate detection signal, and the recirculation valve is selected. Open quickly to prevent water pump heating. In the process of starting the water supply pump, a signal that decreases at a predetermined rate of change is selected as the second recirculation valve opening command, and the recirculation valve is gradually closed. Therefore, it is necessary to suppress the fluctuation of the recirculation valve from being repeatedly opened and closed repeatedly when the suction flow rate falls below the suction flow rate set value in the process of stopping or starting the water supply pump, thereby reducing disturbance to the boiler water supply control side. Can be.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a control block diagram of a feed water pump recirculation flow control device showing one embodiment of the present invention. In the figure,
4 denote the same parts, and the differences from FIG.
The difference is that a portion surrounded by a dashed line in the figure, which includes a setting device 15, a setting device 16, a signal switching device 17, a deviation calculator 18, a limiter 19, an integrator 20, and a high value selector 21, is additionally provided.

Here, a value for fully opening the recirculation valve 4 is set in the setting device 15, and a value for fully closing the recirculation valve 4 is set in the setting device 16 in advance. The signal switch 17 is provided for the water supply pump 1.
Is in the stop process, the signal from the setter 15 is selected and output, and the feeder pump 1 selects and outputs the signal from the setter 16 during the startup process other than the stop process and during normal operation.

The deviation calculator 18 calculates the deviation between the output signal of the signal switch 17 and the output signal of the integrator 20. The limiter 19 limits the input signal and outputs the signal.
When the polarity of the input signal to the limiter 19 is positive, a signal in the positive direction is output, and when the polarity is negative, a signal in the negative direction is output. The integrator 20 integrates and outputs the output signal of the limiter 19 as an input signal.

The controller composed of the deviation calculator 18, the limiter 19, and the integrator 20 operates so that the output signal of the integrator 20 matches the output signal of the signal switch 17, so that recirculation is performed. The operating speed of the valve 4 in the opening direction and the closing direction is set to a value that opens and closes in the time required for stopping and starting the water supply pump 1. The high value selector 21 receives the output signal of the integrator 14 and the output signal of the integrator 20, and selects and outputs the high value input among these.

Next, the operation of this embodiment will be described with reference to FIG.

As an example, a description will be given of an operation in the case where the flow rate of water supplied to the boiler is gradually reduced in the process of stopping the water supply pump 1. In FIG. 2, the lower-stage recirculation valve opening command VA is calculated by integrating The recirculation valve opening command VB is an output signal of the integrator 20.

Here, the signal switch 17 selects and outputs the fully closed setting signal from the setting unit 16 until time t1 when the feed water pump 1 is operating normally, and the output signal V of the integrator 20 is output.
B is a fully closed signal, and the output signal of the integrator 14 is also outputting a fully closed signal. Now, when the stop of the feedwater pump 1 is started at the time t1, the suction flow rate signal Q gradually decreases due to the decrease in the rotation speed, and the feedwater flow rate signal QF also gradually lowers accordingly. At this time, the output signal of the signal switch 17 switches from the setting device 16 to the fully open setting signal of the setting device 15, and the output signal VB of the integrator 20 gradually increases. In the high value selector 21, the output signal VB is selected, and the recirculation valve opening command V 'gradually increases. Correspondingly, the recirculation valve 4
Also gradually increases without a sudden decrease in the suction flow signal Q. Therefore, if the increase of the recirculation valve opening command signal V is appropriately determined with respect to the drop of the suction flow signal Q, the suction flow signal Q does not become lower than the suction flow setting signal QT, and the recirculation valve 4 is rapidly opened. There is no rapid decrease of the feedwater flow signal QF associated with.

By the way, as shown in FIG. 2, when the suction flow signal Q falls below the suction flow setting signal QT at time t2,
It does the following: The output signal VA of the integrator 14 increases rapidly. For this reason, at time t3, the output signal VA of the integrator 14 becomes larger than the output signal VB of the integrator 20, and the high value selector 21 selects the output signal VA of the integrator 14 to generate the recirculation valve opening command V '. Output. As a result, the suction flow signal Q
Gradually increases and then gradually decreases after reaching a peak.
When the suction flow signal Q drops, the output signal V of the integrator 14
A also drops and at time t4, the output signal VB of the integrator 20 becomes higher. Therefore, in the high value selector 21, the output signal VB of the integrator 20 is selected, and the recirculation valve opening degree command V 'is selected.
Is output to the recirculation valve 4.

Therefore, generally, the suction flow signal Q does not interrupt the suction flow setting signal QT or less, and the recirculation valve opening command VA does not increase.
As a result, the feedwater flow rate does not suddenly decrease due to rapid opening, and disturbance to the boiler feedwater control is eliminated.

In this case, during the stoppage of the feedwater pump 1, the feedwater flow signal QF to be fed to the poiler suddenly decreases, and FIG.
When the suction flow rate signal Q interrupts the suction flow rate setting signal QT as after time t2, the recirculation valve opening command VA corresponding to the decrease in the suction flow rate signal Q sharply increases. The recirculation valve opening command VA is selected to prevent the recirculation valve opening command V from suddenly opening, thereby preventing the suction flow signal Q from becoming less than or equal to QS.

Conversely, in the process of starting the water supply pump 1, the recirculation valve opening command VB is gradually reduced so that the suction flow rate signal Q does not interrupt the suction flow rate setting signal QT or less. The circulation valve 4 does not suddenly open.

As described above, it is possible to prevent heating due to a decrease in the suction flow rate of the water supply pump, and to prevent a sudden decrease in the flow rate of the water supply to the poirer due to the rapid opening of the recirculation valve in the process of starting and stopping the water supply pump. It is possible to reduce disturbance to the boiler water supply control.

[0031]

As described above, according to the present invention, in the process of stopping the feedwater pump, the flow rate of the feedwater to be fed to the boiler is set such that the recirculation valve gradually opens in the direction of the opening operation by a signal increasing at a predetermined rate of change. The suction flow required by the water supply pump can be secured without abrupt reduction of the water supply. Further, in the process of starting the water supply pump, the recirculation valve is gradually closed by a signal that decreases at a predetermined rate. Therefore, the fluctuation of the recirculation valve at the time when the suction flow rate falls below the suction flow rate set value is suppressed, so that the water supply flow rate does not suddenly decrease and disturbance to the boiler water supply control can be reduced.

[Brief description of the drawings]

FIG. 1 is a control block diagram of a feedwater pump recirculation flow control device showing one embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the operation of FIG.

FIG. 3 is a system diagram of a water supply pump.

FIG. 4 is a control block diagram corresponding to FIG. 1 of the conventional feedwater pump recirculation flow control device.

FIG. 5 is a characteristic diagram of a suction flow rate set value function generator.

FIG. 6 is a characteristic diagram of a limiter.

FIG. 7 is an explanatory view corresponding to FIG. 2 and showing the operation of the feedwater pump recirculation flow control device of FIG. 4;

[Explanation of symbols]

 Reference Signs List 4 recirculation valve 5 flow element 6 transmitter 7 speed detector 8 feed water pump recirculation flow control device 9 suction flow set value function generator 10 deviation calculator 11 proportional calculator 12 deviation calculator 13 limiter 14 integrator 15 Setter 16 Setter 17 Signal switch 18 Deviation calculator 19 Limiter 20 Integrator 21 High value selector

Claims (1)

(57) [Claims] 1. A water supply, wherein water is supplied from a deaerator to a boiler by a water supply pump, and a recirculation flow rate for recirculating the water to the deaerator via a recirculation valve is controlled by opening and closing the recirculation valve. In the pump recirculation flow control device, a function generating unit that outputs a suction flow rate setting signal in accordance with a rotation speed signal of the feed water pump, and a function of a deviation signal between the suction flow rate setting signal and the suction flow rate detection signal of the feed water pump. And a means for outputting a first recirculation valve opening command signal obtained by performing a control operation, and outputting a signal that increases at a predetermined rate of change during a stop process of the water supply pump, Signal generating means for outputting, as a second recirculation valve opening command, a signal that decreases at a predetermined rate of change during the start-up process of the water supply pump; the first recirculation valve opening command signal and the second recirculation Valve opening command And the second recirculation valve opening command signal, which is a signal that increases at a predetermined rate of change during the stop process, is selected as a high value to gradually open the recirculation valve. On the other hand, high value selecting means for gradually closing the recirculation valve by causing the second recirculation valve opening degree command signal, which is a signal decreasing at a predetermined rate of change in the starting process, to be selected as a high value. A water supply pump recirculation flow control device, comprising: