JPH0441903A - Water feed control device - Google Patents

Abstract

PURPOSE:To stably secure the preset water feed flow by providing a signal switch in a water feed system, controlling the water feed pump rotating speed with the output signal of the function generator of the first controller when a plant is activated, and controlling it with that of the second controller during the normal operation. CONSTITUTION:A water feed control valve 22 and a water feed control valve 23 are connected in series to a water feed system including a turbine driving water feed pump 20, a water feed control valve bypass valve 24 and the system of the water feed control valve 22 are arranged in parallel, the opening of a steam governor valve 29 controlling the rotating speed of a pump driving turbine 21 is controlled by the calculated result to a low-value selecting circuit 36, and a switch 2 is provided before an adder 32 in this circuit. A water feed header pressure generator 3 is connected at the downstream of the water feed control valve 23, the signal of the preset function outputted from a function generator 4 is fed to the switch 2 based on the output signal, and the water feed control valve 22 is controlled by a PI controller 1 receiving the differential signal between the water feed flow command 30 and the discharge flow of the turbine driving water feed pump 20 when a plant is activated.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a water supply control device, and particularly to water supply control using a turbine-driven water pump driven by a driving turbine in a thermal power plant. Regarding equipment.

(Conventional technology) In recent years, thermal power plants do not use motor-driven water pumps when starting up the plants as a measure to save energy.
There is a trend towards using turbine-driven water pumps. This allows the abundant steam within the plant to be reused as power.

However, when using the turbine-driven feed water pump in a state where the boiler feed water pressure is close to zero, such as when the plant is started up, the drive turbine has a minimum operating speed set, so the stability of the control is reduced. In order to achieve this, it is controlled in combination with a water supply control valve installed at the water supply pump outlet.

FIG. 6 shows a water supply system diagram of a conventional water supply control device of this type. The reference numeral 20 in the figure is a turbine-driven water pump (T
-BEP), and this turbine-driven water supply pump 20 is driven by a driving turbine 21 to rotate. And this turbine driven water supply pump 2
In the water supply system from 0 to the boiler (not shown), a water supply control valve 22 and a water supply control vent valve 23 are arranged in series, and a water supply control valve bypass valve 24 is arranged in parallel with the system of the water supply control valve 22.

The water supply control valve 22 is operated by a subtractor 2 so that the signals from the discharge pressure transmitter 25 and the pressure set value signal generator 26 provided on the discharge side of the turbine-driven water pump 20 become equal.
7 and is controlled by the PI controller 28.

On the other hand, the steam supply system A upstream of the driving turbine 21
A steam control valve 29 is provided, and the rotation speed of the driving turbine 21 is controlled by this steam control valve 29. The opening degree of this steam control valve 29 is determined by the water supply flow rate command (FWD).
) 30 and the discharge flow rate of the turbine-driven water supply pump, and a PI controller 28 that outputs an opening command signal to the turbine-driven water pump, the minimum rotation speed signal generator 31 and the opening command are input. an adder 32 that inputs a signal, a subtracter 27 that inputs this calculation result and a signal from a pickup 33 that detects the rotation speed of the driving turbine, a P controller 34, and a turbine-driven water pump starting program 3. The command signal from °5 and the above P
The signal from the controller 34 is input to the low value selection circuit 36, and the result of this calculation is input to the steam control valve 29 as an opening command signal.

In the above circuit, the minimum signal rotation speed generator 31 defines the minimum rotation speed of the driving turbine 21. Further, the turbine-driven water pump starting program 35 is a circuit that operates when the pump is started, and does not participate in the control of the turbine-driven water pump 20 during normal operation after completion of startup.

Next, we will briefly explain the details of the control from pump startup to normal operation. When the turbine-driven water supply pump 20 is started by the turbine-driven water supply pump starting program 35, the rotation speed of the pump shows the minimum rotation speed, and the water supply control valve 22 is kept in a fully closed state. Thereafter, as the water supply flow rate command 30 increases, the number of rotations of the pump increases, thereby increasing the pump discharge pressure. This is detected by the pump discharge pressure transmitter 25, the water supply control valve 22 is opened, and water is supplied to the boiler. Furthermore, this value is BF
It is fed back to the subtractor 27 as the P discharge flow rate.

By the way, FIG. 7 is a characteristic curve diagram showing the operation of this type of water supply control device on a water supply pump discharge flow rate-discharge pressure curve (QH curve). In the initial stage, when the rotational speed of the turbine-driven water supply pump is α1 (p■) and the pressure setting value of the water supply control valve is β (kg/cm2g), the operating point of the turbine-driven water supply pump is X, and the flow rate at that time is is γ,
(tlh).

■ If the feed water flow rate command increases and the rotation speed of the turbine-driven water pump increases to α2 (rps), the operating point will be x.
Changes to 2. At this time, the BFP discharge pressure increases slightly, so the feed water control valve opens to maintain it at a constant value β (kg/cs'' g).As a result, the operating point of the turbine-driven water pump becomes X 2- Therefore, the flow rate at that time is γ2 (tlh).

(Problem to be solved by the invention) However, since the above-mentioned water supply control device uses a region close to the left end of the water pump discharge flow rate-discharge pressure curve (Q-H curve), the rotation speed of the turbine-driven water pump is Even a slight change in flow rate will result in a large change in flow rate, and the gain of the control system will become extremely high. In addition, there is a problem in that the delay time of the control system becomes long because a large number of devices in addition to the two-stage PI controller are involved in the circuit until the actual flow rate is obtained in the water supply system. For this reason, it is difficult to obtain stable control, and there is a risk of blunt tripping or damage to the boiler tube due to a decrease in the water supply flow rate.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the problems of the above-mentioned conventional technology, to make the gain and control delay time of the control system appropriate, and to provide a turbine-driven water pump that can be operated from a low flow rate at startup to a normal operation. It is an object of the present invention to provide a water supply control device that can stably secure a predetermined water supply flow rate throughout the period.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention includes a water supply control valve, a water supply control post-control valve, and a water supply control valve bypass valve on the discharge side of a turbine-driven water supply pump driven by a driving turbine. 2, comprising a first control section that controls the feed water flow rate by adjusting the opening and closing of the feed water control valve; A water supply control device comprising a second control unit that adjusts the opening degree and controls the rotation speed of the water supply pump,
Sends an opening command to the first control section to the water supply control valve P
It is composed of an I controller, a water supply header pressure transmitter provided downstream of the water supply control post-valve, and a function generator that receives a signal from the water supply header pressure transmitter and generates a predetermined output signal, Furthermore, a signal switch is provided in the water supply system, and by switching this signal switch, the rotation speed of the water pump is controlled by the output signal of the function generator of the first control section when the plant is started, and during normal operation, The water supply pump rotation speed is controlled by the second control section, and the first control section is configured to include a PI controller that sends an opening command to the water supply control valve, and a PI controller that sends an opening command to the water supply control valve. It consists of a valve opening detector and a function generator that inputs the signal from this opening detector and generates a predetermined output signal, and furthermore, a signal switch is installed in the water supply system, and this signal switch When the plant is started up, the rotation speed of the water supply pump is controlled by the output signal of the function generator of the first control section, and during normal operation, the rotation speed of the water supply pump is controlled by the second control section. It is characterized by this.

(Function) According to the present invention, a water supply control valve, a post-water supply control valve, and a water supply control valve bypass valve are arranged on the discharge side of a turbine-driven water supply pump driven by a driving turbine, and the opening and closing of the water supply control valve is adjusted. a first control unit that controls the feed water flow rate according to the method, and further detects a deviation between the feed water flow rate command and the feed water pump discharge flow rate, adjusts the opening degree of the steam control valve of the drive turbine, and adjusts the rotation speed of the feed water pump. a PI controller that sends an opening command to the water supply control valve; and a water supply control device provided downstream of the water supply control valve. Input the header pressure transmitter and the signal from this water supply header pressure transmitter,
A function generator that generates a predetermined output signal is further provided in the water supply system, and by switching this signal switch, the output signal of the function generator of the first control section is changed at the time of plant startup. The rotation speed of the feed water pump is controlled by the second control section during normal operation, so that the rotation speed of the water bottle drive water pump increases as the water supply header pressure increases. Therefore, if it exceeds the control range of the feedwater control valve alone, the feedwater control valve bypass valve is fully opened, the opening of the steam control valve is adjusted, and the rotation speed of the turbine-driven feedwater pump is controlled solely. You can smoothly transition to

Further, the first control section is connected to a PI controller that sends an opening command to the water supply control valve, an opening detector of the water supply control valve, and a signal from this opening detector, and a predetermined output signal. Furthermore, a signal switch is provided in the water supply system, and when the signal switch is switched, the output signal of the function generator of the first control section is used to switch the water supply pump to the water supply pump. During normal operation, the second control section controls the rotation speed of the water supply pump, so that the rotation speed of the turbine-driven water supply pump reaches a predetermined level as the opening degree of the water supply control valve increases. It rises according to the function, so if it exceeds the control area of only the water supply control valve,
By fully opening the feedwater control valve bypass valve and adjusting the opening degree of the steam control valve, it is possible to smoothly shift to control based only on the rotation speed of the turbine-driven feedwater pump.

(Embodiment) An embodiment of the water supply control device according to the present invention will be described below with reference to FIGS. 1 to 5.

In FIG. 1, the same components as in the conventional example are given the same reference numerals as in FIG. 6 and will be described below.

Reference numeral 20 in the figure is a turbine-driven water pump (T-BEP)
This turbine-driven water supply pump 20 is driven by a driving turbine 21 and rotates. In the water supply system from the turbine-driven water pump 20 to the boiler, a water supply control valve 22 and a water supply control vent valve 23 are arranged in series, and a water supply control valve bypass valve 24 is arranged in parallel with the water supply control valve system.

A Pl controller 1 is connected to the water supply control valve 22, which receives a deviation signal between the water supply flow rate command and the discharge flow rate of the turbine-driven water pump.

On the other hand, the rotation speed of the driving turbine 21 is determined by the steam control valve 2.
9, and the opening degree of this steam control valve 29 is determined by using the feed water flow rate command (FWD) 30 and the turbine-driven water pump discharge flow rate as input values, as in the conventional example, and the calculation result up to the low value selection circuit 36. is input to the steam control valve 29 as an opening command signal. A switch 2 is provided in front of the adder 32 in this circuit.

Further, a water supply header pressure transmitter 3 is connected downstream of the water supply control vent valve 23. This water supply header pressure transmitter 3 outputs the water supply head pressure from the water supply system as a signal. Furthermore, this water supply header pressure transmitter 3
A function generator 4 is connected to the switch 2, and can output a signal of a predetermined function to the switch 2 according to the input signal.

Since the switching device 2 is connected to the b-c side when the plant is started, the water supply control valve 22 is connected to the PI controller that receives the deviation signal between the water supply flow rate command and the discharge flow rate of the turbine-driven water supply pump. 1.

That is, a program command value generated by a function generator 4 from a signal from the water supply header pressure transmitter 3 is given as a rotation speed command for the turbine-driven water supply pump 2o.

FIG. 3 shows the output signal (
water supply pump rotation speed command). To explain this function curve, the output signal shows zero until the signal from the water supply header pressure transmitter 3 reaches a certain value p1, and during this time the rotation speed of the turbine-driven water supply pump 20 is maintained at the minimum rotation speed. ing. Then, when the water supply header pressure rises and the difference with the discharge pressure of the turbine-driven water supply pump 2o, that is, the differential pressure across the water supply control valve 22 becomes small, the output of the function generator 4 is increased according to a predetermined function. to ensure the necessary differential pressure across the water supply control valve 22. Thereafter, when the signal from the water supply header pressure transmitter 3 rises to a constant value p2, the output of the function generator 4 is held at a constant value p2. Furthermore, the opening degree of the water supply control valve 22 increases, and at the stage when it is near the fully open point, the water supply control valve bypass valve 24 is opened, and at the same time the switching device 2 is switched between a and c.
Switch to the side. Thereafter, water supply control is performed by controlling the rotational speed of the turbine-driven water supply pump 20 during normal operation as in the past.

Next, the operation of the water supply control device of the present invention will be explained using FIGS. 4 and 5.

FIG. 4 is a characteristic diagram showing the relationship between the water supply control valve opening degree and the Cv value. The relationship between the two can be replaced with the relationship between the water supply flow rate command value and the BFT discharge flow rate. Therefore, the control system of the water supply control device of the present invention can be controlled with an appropriate gain. Further, since the control system is composed of a subtracter and a PI controller for the water supply control valve, an appropriate control time can be set, and stable control can be realized.

Further, FIG. 5 is a characteristic curve diagram showing the operation of the present water supply control device on a water supply pump discharge flow rate-discharge pressure curve (QH curve). At the initial stage, the feed water flow rate and feed water header pressure are small, and the operating point of the turbine-driven feed water pump is yl,
The water supply header pressure is zl. At this time, the differential pressure across the water supply control valve is the difference (yl-z,) between the above values, and the water supply flow rate can be expressed as ε1.

After that, at a stage when the water supply flow rate increases and the water supply header pressure also rises, if the rotation speed of the turbine-driven water supply pump is maintained as it is, the operating point of the turbine-driven water supply pump becomes y2 and the water supply header pressure becomes z2. With the differential pressure across the water supply control valve (y 2 Z 2 ) at this time, the flow rate ε2 cannot be ensured even if the water supply control valve is fully opened.

Therefore, the rotation speed of the turbine-driven water pump is increased from the minimum rotation speed δ1 (rpm) to δ2 (rpm) by outputting the water supply pump rotation speed command as shown in FIG. 3, and the operating point is changed to y2. Increase the differential pressure across the water supply control valve to (
y2=-z2).

When the water supply control valve is close to being fully open, control is switched to control based on the rotation speed of the turbine-driven water supply pump. Therefore, the operating point is y21. From now on, the intersection point ()'3 between the water supply pump discharge flow rate-discharge pressure curve (Q-H curve) and the system head curve will be explained. Y4...).

Next, a control device that inputs the opening degree signal of the water supply control valve to the function generator will be described.

In FIG. 2, the PI controller 1 that receives a deviation signal between the water supply flow rate command and the discharge flow rate of the turbine-driven water pump is connected to the water supply control valve 22, as in the above-described invention. The water supply control valve 22 is also equipped with an opening detector 5, and an opening signal obtained by the opening detector 5 is input to a function generator 6.

FIG. 3 shows the output signal (
water supply pump rotation speed command). To explain this function curve, the output signal shows zero until the opening signal from the opening detector 5 of the water supply control valve 22 reaches a constant value p1,
During this time, the rotational speed of the turbine-driven water supply pump 20 is maintained at the minimum rotational speed. Then, when the opening degree of the water supply control valve 22 increases and the differential pressure across the water supply control valve 22 becomes small, the output of the function generator 6 is increased according to a predetermined function, and the output of the water supply control valve 22 is increased according to a predetermined function. Ensure a sufficient differential pressure between the front and rear. Thereafter, when the opening signal of the water supply control valve 22 rises to a constant value p2, the output of the function generator is held at a constant value. Furthermore, the opening degree of the water supply control valve 22 increases, and when the water supply control valve bypass valve 24 is opened at a stage near the full opening point, the switching device 2 is switched to the a-c side. From then on, in normal operation as before,
Water supply is controlled by controlling the rotation speed of the turbine-driven water supply pump.

Note that the operations shown in FIGS. 4 and 5 can also be obtained in the present invention.

〔Effect of the invention〕

As is clear from the above explanation, according to the present invention, since the feed water flow rate command is directly input to the feed water control valve at the time of plant startup, it is possible to obtain an appropriate gain and delay time, and also to obtain a turbine-driven water supply. Since the pump rotation speed increases functionally as the water supply header pressure rises, if it exceeds the control range of only the water supply control valve, the water supply control valve bypass valve should be fully opened and the opening of the steam control valve should be adjusted. This allows a smooth transition to control based only on the rotation speed of the turbine-driven water pump.

In addition, since the rotation speed of the turbine-driven water supply pump increases according to a predetermined function as the opening degree of the water supply control valve increases,
It is possible to stably secure a predetermined water supply flow rate from the low flow rate at startup to normal operation of the turbine-driven water supply pump, and when the flow rate exceeds the control range of the water supply control valve alone, the water supply control valve bypass valve can be activated. It is possible to fully open the steam control valve, adjust the opening degree of the steam control valve, and smoothly shift to control based only on the rotational speed of the turbine-driven water supply pump.

[Brief explanation of the drawing]

1 and 2 are water supply system diagrams showing one embodiment of the water supply control device according to the present invention, FIG. 3 is a function curve diagram showing an example of the output from the function generator according to the present invention, and FIG. A characteristic diagram showing the relationship between the opening degree and Cv value of the water supply control valve according to the present invention, and Fig. 5 is a water supply pump discharge flow rate-discharge pressure curve (Q-H curve) and system head curve of the water supply control device according to the present invention. Fig. 6 is a water supply system diagram showing an example of a conventional water supply control device, and Fig. 7 is a water pump discharge flow rate-discharge pressure curve (Q-H curve) of a conventional water supply control device. . 1.28...PI controller, 2...Switcher, 3
...Water supply header pressure transmitter, 4, 6...Function generator, 5...Opening degree detector, 20...Turbine drive pump, 21...Drive turbine, 22...Water supply control valve,
23... Water supply control device valve, 24... Water supply control valve bypass valve, 27... Subtractor, 29... Steam control valve, 3
0...Water supply flow rate command, 31...Minimum signal rotation speed generator, 32...Adder, 33...Pickup, 34
...P controller, 35...Turbine-driven water supply pump starting program, 36...Low value selection circuit.

Claims (1)

[Claims] 1. A water supply control valve, a post-water supply control valve, and a water supply control valve bypass valve are arranged on the discharge side of a turbine-driven water supply pump driven by a driving turbine, and water is supplied by adjusting the opening and closing of the water supply control valve. A first control unit that controls the flow rate, further detects a deviation between the feed water flow rate command and the feed water pump discharge flow rate, adjusts the opening degree of the steam control valve of the drive turbine, and controls the rotation speed of the feed water pump. a PI controller that sends an opening command to the water supply control valve; and a water supply header pressure provided downstream of the water supply control valve; It consists of a transmitter and a function generator that inputs the signal from this water supply header pressure transmitter and generates a predetermined output signal, and furthermore, a signal switch is installed in the water supply system, and by switching the signal switch, When starting up the plant, the rotation speed of the water supply pump is controlled by the output signal of the function generator of the first control section, and during normal operation, the rotation speed of the water supply pump is controlled by the second control section. water supply control device. 2. A first system in which a water supply control valve, a post-water supply control valve, and a water supply control valve bypass valve are arranged on the discharge side of a turbine-driven water supply pump driven by a driving turbine, and the water supply flow rate is controlled by adjusting the opening and closing of the water supply control valve. a second control unit that further detects a deviation between the feed water flow rate command and the feed water pump discharge flow rate, adjusts the opening degree of the steam control valve of the drive turbine, and controls the rotation speed of the feed water pump; A water supply control device comprising: a PI controller that sends an opening command to the water supply control valve; an opening detector of the water supply control valve; and a signal from the opening detector. Input,
A function generator that generates a predetermined output signal is further provided in the water supply system, and by switching this signal switch, the output signal of the function generator of the first control section is changed at the time of plant startup. A water supply control device, characterized in that the rotation speed of the water supply pump is controlled by the second control unit during normal operation.