JPH06159608A - Recirculation flow rate control device for water-feeding pump - Google Patents

Abstract

(57) [Summary] [Configuration] The function generator 9 outputs a suction flow rate setting signal in accordance with the rotation speed signal of the water supply pump. The integrator 14 performs a control calculation according to the deviation signal between the suction flow rate setting signal and the suction flow rate detection signal of the water feed pump, and outputs the first recirculation valve opening command signal VA. Further, the signal generating means outputs, as the second recirculation valve opening command, a signal that increases at a predetermined change rate when the water supply pump is stopped or a signal that decreases at a predetermined change rate when the water supply pump is started, and the high value selector. 21 inputs the first recirculation valve opening command signal and the second recirculation valve opening command signal, selects a higher value signal from these signals, and selects the recirculation valve opening command. The signal V'is output to the recirculation valve. [Effect] The recirculation valve prevents the supply water flow rate from suddenly decreasing due to sudden opening.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art A water supply pump in a power plant has a structure in which the number of revolutions of the water supply pump is increased in order to send the amount of water supply required by the boiler to the boiler as the amount of power generation increases. On the other hand, it is necessary for the water supply pump to flow a suction flow rate higher than the minimum suction flow rate in order to prevent heating of the pump. This minimum suction flow rate is a value that changes depending on the rotation speed of the water supply pump. If the suction flow rate falls below the minimum suction flow rate, it is necessary to output an alarm or forcibly stop the water supply pump. Therefore, when the feed water flow rate to the boiler decreases and the suction flow rate decreases, the suction flow rate of the feed water pump can be increased by adjusting the opening of the recirculation valve to increase the recirculation flow rate returned to the deaerator. The minimum suction flow rate is set.

FIG. 3 is a system diagram of this type of water supply pump. In the figure, a water supply pump 1 is arranged in a water supply pipe 2 from a deaerator (not shown) to a boiler, and a recirculation pipe 3 for recirculating to the deaerator branches on the outlet side of the water supply pipe 2. ing. A recirculation valve 4 is arranged in the recirculation pipe 3. Further, a flow rate element 5 is arranged in the water supply pipe 2, a suction flow rate signal Q is output from an oscillator 6 connected to the flow rate element 5, and a rotation speed detector 7 is installed in the water supply pump 1. A rotation speed signal N is output from the rotation speed detector 7.

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

The water supply pump recirculation flow rate control device 8 is shown in FIG.
As shown in FIG. 3, it is composed of a suction flow rate set value function generator 9, a deviation calculator 10, a proportional calculator 11, a deviation calculator 12, a limiter 13, and an integrator 14. The suction flow rate setting value function generator 9 receives the suction flow rate setting signal QT according to the rotation speed signal N.
Is output. The deviation of the suction flow rate setting signal QT and the suction flow rate signal Q is calculated by the deviation calculator 10, and the deviation signal is input to the proportional calculator 11. The proportional calculator 11 performs a proportional calculation according to the deviation signal and outputs a calculation signal.

Now, 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 in accordance with the rotation speed signal N, and the rotation speed signal is set. N increases in accordance with the rotation speed signal N in the range of N1 to N2. Further, it holds a constant value when the rotation speed signal N is N2 or more, and holds a constant value even when the rotation speed signal N is N1 or less. QS (chain line in the figure) in FIG. 5 indicates the suction flow rate signal Q for fully opening the recirculation valve 4, and the minimum suction flow rate of the water supply pump 1 is slightly below QS and is used to control the suction flow rate of the water supply pump 1. The suction flow rate setting signal QT as the target value in is set to the upper side by α from QS. The output of the proportional calculator 11 changes the recirculation valve opening command V from fully closed to fully opened in response to a change α in the suction flow rate signal Q.

That is, when the suction flow rate signal Q matches QS, the output of the proportional calculator 11 is 100% [= K ×
(QT-QS)] to fully open the recirculation valve opening command V.
On the other hand, when the suction flow rate signal Q matches the suction flow rate 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 the 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 it, and has the characteristics shown in FIG. That is, when the polarity of the input signal of the limiter 13 is positive, the 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, and integrates and outputs the input signal.

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 input polarity of the limiter 13 is positive), the recirculation valve 4 is opened at high speed and the operation in the closing direction (the limiter 13 (For the case where the input polarity is negative), the recirculation valve 4 is closed at a low speed. As a result, the high-speed opening operation of the recirculation valve 4 serves to prevent heating of the water feed pump 1, and the low speed closing operation of the recirculation valve 4 minimizes disturbance to the feed water flow rate control of the boiler.

[0010]

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

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

In the figure, when the rotation speed of the water supply pump 1 is decreased from time t1, the water supply flow rate signal QF to the boiler gradually decreases. At this time, since the deviation between the suction flow rate setting signal QT and the suction flow rate signal Q is α or more, the feed water pump recirculation flow rate control device 8 outputs the recirculation valve opening degree command V to be fully closed. Therefore, the water supply 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.

After that, when the suction flow rate signal Q reaches the suction flow rate setting signal QT, the feed water pump recirculation flow rate control device 8 shifts the recirculation valve opening command signal V from the fully closed state to the open direction at time t2. Further, when the suction flow rate signal Q falls below the suction flow rate setting signal QT, the recirculation valve opening command signal V gradually increases in the opening direction. As a result, the flow rate flowing through the recirculation valve 4 increases and the suction flow rate signal Q increases, but the feed water flow rate signal QF to the boiler sharply decreases. That is, the recirculation valve opening command signal V is increased at a high speed to prevent the heating of the feed water pump 1, and since the recirculation system has a larger suction force of the flow rate than the boiler system, the flow rate increases to the recirculation system. In response to this, the feed water flow rate signal QF to the boiler is at time t2.
Rapidly decreases from time t3.

On the other hand, in the water supply flow rate control of the water supply pump 1,
Control is performed so as to ensure the required flow rate with a sharp decrease in the feed water flow rate signal QF of the water feed pump 1. As a result, the water supply flow rate signal QF increases from time t3 to time t4. afterwards,
The suction flow rate signal Q drops after greatly increasing from the suction flow rate setting signal QT, and at time t5, the suction flow rate signal Q matches the suction flow rate setting signal QT, and the suction flow rate signal Q drops from the suction flow rate setting signal QT. . Therefore, at time t6, the recirculation valve opening command signal V is in the increasing direction. With this,
The suction flow rate signal Q increases again, but from time t3 to time t
As in the case of 4, the feed water flow rate signal QF sharply decreases. This allows
As described above, the time t is controlled by controlling the feed water flow rate of the boiler 1.
7, the feed water flow rate signal QF increases again and returns. Since such a rapid fluctuation of the feed water flow rate signal QF and a fluctuation thereof are repeated, there is a problem that disturbance occurs in the boiler feed water flow rate control.

Therefore, it is an object of the present invention to provide a feed water pump recirculation flow rate control device which minimizes disturbances in boiler feed water control.

[0016]

SUMMARY OF THE INVENTION The present invention relates to a water supply pump for supplying water from a deaerator to a boiler, and a recirculation flow rate for recirculating the water supply to the deaerator through a recirculation valve. In a water supply pump recirculation flow rate control device that is controlled by opening and closing, a function generating means that outputs a suction flow rate setting signal according to the rotation speed signal of the water supply pump, and a deviation signal between the suction flow rate setting signal and the suction flow rate detection signal of the water supply pump And a signal that increases at a predetermined rate of change when the water supply pump is stopped, and a second control circuit that outputs a first recirculation valve opening command signal. A signal generating means for outputting, as the second recirculation valve opening command, a signal that decreases as the recirculation valve opening command signal at a predetermined change rate when the water supply pump is started; and a first recirculation valve opening command signal. Second recirculation valve opening command signal Enter the door, it is obtained as provided with the high value selector means for outputting a recirculation valve opening instruction signal to select a signal of either high among these signals to the recirculation valve.

[0017]

With the above structure, the function generating means outputs the suction flow rate setting signal according to the rotation speed signal of the water supply pump, and controls according to the deviation signal between the suction flow rate setting signal and the suction flow rate detection signal of the water supply pump. Calculation is performed, and this control calculation signal is output as the first recirculation valve opening command signal. on the other hand,
The signal generating means outputs, as the second recirculation valve opening command, a signal that increases at a predetermined change rate when the water supply pump is stopped or a signal that decreases at a predetermined change 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 selecting means, and one of these signals having a higher value is selected to recirculate the valve opening command. A signal is output to the recirculation valve. As a result, in the process of stopping 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 it is fed to the boiler. The suction flow rate required by the water supply pump will be secured without the supply water flow rate suddenly decreasing. At this time, when the suction flow rate of the water supply pump sharply decreases, the first recirculation valve opening command signal is selected as a high value 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. Quickly open to prevent heating of the water supply pump. In the starting process of the water supply pump, a signal that decreases at a predetermined rate of change is selected as the second recirculation valve opening command,
The recirculation valve is gradually closed. Therefore, it is possible to prevent the recirculation valve from being suddenly opened more than necessary in the process of stopping or starting the water supply pump, and to minimize the decrease in the flow rate of water supply to the boiler.

[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 rate control apparatus showing an embodiment of the present invention. In the figure,
4 that are the same as those in FIG. 4 are the same as those in FIG.
A point surrounded by a broken line in the drawing, which includes the setter 15, the setter 16, the signal switcher 17, the deviation calculator 18, the limiter 19, the integrator 20, and the high value selector 21, is additionally provided.

Here, the setting device 15 is preset with a value for fully opening the recirculation valve 4, and the setting device 16 is preset with a value for completely closing the recirculation valve 4. The signal switch 17 is the water supply pump 1
Is in the stopping process, the signal of the setting device 15 is selected and output, and the water feed pump 1 selects and outputs the signal of the setting device 16 during the starting process other than the stopping process and the 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 it.
This is similar to the characteristic shown in (1), and when the polarity of the input signal of the limiter 19 is positive, the signal in the positive direction is output, and when the polarity is negative, the signal in the negative direction is output. The integrator 20 receives the output signal of the limiter 19 as an input signal, performs integration calculation, and outputs the result.

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 coincides with the output signal of the signal switching unit 17, and is recirculated. The operating speeds of the valve 4 in the opening direction and the closing direction are set to values that open and close in the time required to stop and start the water supply pump 1. The high value selector 21 inputs the output signal of the integrator 14 and the output signal of the integrator 20, and selects and outputs the high value input among them.

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

As an example, the operation of gradually decreasing the flow rate of the feed water to be fed to the boiler in the process of stopping the feed water pump 1 will be described. In FIG. 2, the lower recirculation valve opening command VA is the integral value. The recirculation valve opening command VB is an output signal of the integrator 14 and is an output signal of the integrator 20.

Here, the signal switching device 17 selects and outputs the fully closed setting signal from the setting device 16 until time t1 when the water supply pump 1 is normally operated, and the output signal V of the integrator 20 is output.
B becomes a fully closed signal, and the output signal of the integrator 14 also outputs a fully closed signal. Now, at time t1, when the stop of the water supply pump 1 is started, the suction flow rate signal Q gradually decreases due to the decrease in the rotation speed, and accordingly, the water supply flow rate signal QF also gradually decreases. At this time, the output signal of the signal switching unit 17 is switched from the setting unit 16 to the fully open setting signal of the setting unit 15, and the output signal VB of the integrator 20 gradually increases. The high value selector 21 selects the output signal VB, and the recirculation valve opening command V ′ gradually increases. Corresponding to this, the recirculation valve 4
Since the flow rate of the suction flow rate also gradually increases, the suction flow rate signal Q does not decrease sharply but gradually decreases. Therefore, if the increase of the recirculation valve opening command signal V is appropriately determined with respect to the decrease of the suction flow rate signal Q, the suction flow rate signal Q will not become the suction flow rate setting signal QT or less, and the recirculation valve 4 will be rapidly opened. There is no sudden decrease in the feed water flow rate signal QF.

By the way, as shown in FIG. 2, when the suction flow rate signal Q becomes less than or equal to the suction flow rate setting signal QT at time t2,
It has the following effects. The output signal VA of the integrator 14 suddenly increases. Therefore, 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 give the recirculation valve opening command V '. Output. As a result, the suction flow rate signal Q
Gradually increases, reaches a peak, and then gradually decreases.
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 has a higher value. Therefore, in the high value selector 21, the output signal VB of the integrator 20 is selected and the recirculation valve opening command V '.
Is output to the recirculation valve 4.

Therefore, in general, the suction flow rate signal Q does not fall below the suction flow rate setting signal QT, and the recirculation valve opening command VA does not increase.
The sudden decrease in the water supply flow rate due to the sudden opening of the water tank will eliminate the disturbance to the boiler water supply control.

In this case, in the process of stopping the water supply pump 1, the water supply flow rate signal QF to be sent to the boiler is sharply reduced, and FIG.
When the suction flow rate signal Q interrupts the suction flow rate setting signal QT after the time t2, the recirculation valve opening command VA corresponding to the decrease of the suction flow rate signal Q sharply increases and the high value selector 21 restarts. It is prevented that the circulation valve opening command VA is selected and the recirculation valve opening command V is suddenly opened, and the suction flow rate signal Q becomes QS or less.

On the contrary, in the starting process of the water feed pump 1, the recirculation valve opening command VB is gradually decreased so that the suction flow rate signal Q does not fall below the suction flow rate setting signal QT. The circulation valve 4 will not open suddenly.

In this way, heating is prevented by reducing the suction flow rate of the water supply pump, and a rapid decrease in the flow rate of water supply to the boiler caused by the rapid opening of the recirculation valve during the process of starting and stopping the water supply pump is prevented. 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 water supply pump, the recirculation valve is gradually opened in the opening direction by the signal increasing at the predetermined change rate, and the flow rate of water supplied to the boiler is increased. It is possible to secure the suction flow rate required by the water supply pump without sharply reducing the flow rate. Further, in the starting process of the water supply pump, the recirculation valve is gradually closed by the signal that decreases at a predetermined change rate. Therefore, there is no sudden decrease in the feedwater flow rate due to the rapid opening of the recirculation valve, and disturbance to the boiler feedwater control is reduced.

[Brief description of drawings]

FIG. 1 is a control block diagram of a feed water pump recirculation flow rate control device showing an embodiment of the present invention.

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

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

FIG. 4 is a control block diagram of a conventional water supply pump recirculation flow rate control device corresponding to FIG. 1.

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 diagram corresponding to FIG. 2, showing an operation of the water supply pump recirculation flow rate control device of FIG. 4.

[Explanation of symbols]

 4 Recirculation valve 5 Flow element 6 Transmitter 7 Rotation speed detector 8 Water supply pump Recirculation flow controller 9 Suction flow set value function generator 10 Deviation calculator 11 Proportional calculator 12 Deviation calculator 13 Limiter 14 Integrator 15 Setting device 16 Setting device 17 Signal switching device 18 Deviation calculator 19 Limiter 20 Integrator 21 High value selector

Claims (1)

[Claims] 1. A water supply system for supplying water from a deaerator to a boiler by a water supply pump and controlling a recirculation flow rate for recirculating the water supply to the deaerator through a recirculation valve by opening and closing the recirculation valve. In the pump recirculation flow rate control device, a function generating means for outputting a suction flow rate setting signal according to a rotation speed signal of the water supply pump, and a deviation signal between the suction flow rate setting signal and a suction flow rate detection signal of the water supply pump And a control means comprising means for performing a control calculation to output a first recirculation valve opening command signal, and a signal increasing at a predetermined rate of change during the stoppage process of the water supply pump, and the water supply pump. Signal generating means for outputting a signal that decreases at a predetermined rate of change as a second recirculation valve opening command during the starting process of the first recirculation valve opening command signal, and the second recirculation valve opening command signal. Degree command signal And a high value selecting means for inputting and selecting one of these signals having a higher value and outputting a recirculation valve opening command signal to the recirculation valve. Flow control device.