JPH11141465A - Feed water control device of drum boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control a boiler feed flow rate to the limited flow rate of a boiler feed water pump or lower by determining the valve opening signal of a regulating valve, and controlling the regulating valve so that valve opening speed gradually gets close to zero as a boiler feed water signal gets close to a boiler limited flow rate. SOLUTION: A composed deviation signal consisting of a drum level signal 1, a feed water flow rate signal 2 and a main steam flow rate signal 3 is formed by an adder 8, and the opening instruction signal of a feed water flow rate regulating valve 15 is formed by a proportional integrator 9 on the basis of the composed deviation signal to control the feed water flow rate. A change ratio limiter 20 effective for only the valve opening increasing direction is set on the output side of the opening instruction signal from the proportional integrator 9, and the valve opening speed is controlled to a value formed by a function generator as the change ratio set signal from the feed water flow rate signal 2. Namely, the valve opening side operating speed is controlled so as to start to be gradually reduced when it is close to a boiler feed water pump limit value, and be zero at the pump flow rate limit value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water supply control method and apparatus for a drum boiler, and more particularly to a method for controlling a water supply to a boiler by suppressing abnormalities such as a pump trip due to an overload of a boiler water supply pump. The present invention relates to a water supply control device for a drum boiler that can be used.

[0002]

2. Description of the Related Art In a conventional apparatus, as shown in FIG. 2, for example, a feed water flow signal to a boiler increases, and when a feed water flow 2 reaches a limit flow of a boiler feed pump, this is detected by a signal detector 16. Then, the feed water flow rate control valve opening signal at that time is switched by the signal switch 13 via the signal memory 12 and transmitted to the low value signal selector 10. That is, when the boiler feed water flow signal 2 becomes equal to or greater than a predetermined value, the signal detector 16 is turned on,
Instead of the signal from the signal generator 11, the signal from the signal storage 12 is output to the signal low value selector 10.

[0003] In a signal low value selector 10, a signal memory 12 having a lower value than a signal from the proportional integrator 9 is used.
Is selected and output. That is, since the opening command signal when the signal detector 16 is turned on is given by the signal storage unit 12, the valve is opened to a value equal to or greater than the opening of the water supply flow control valve when detected by the signal detector 16. A control method that does not increase the degree was adopted. However, since the detection delay of the measurement loop exists in the boiler feed water flow rate signal 2, there is a case in which the boiler feed water flow rate signal 2 is actually controlled to a predetermined value or more.

[0004] As described above, if the water supply flow rate is required to be higher than the boiler water supply pump limit flow rate, the boiler water supply pump will be overloaded and the plant operation cannot be continued. Needed. In other words, opening the feed water flow control valve increases the flow rate accordingly, causing an overload to the pump as described above. For that purpose, it has been desired to control the boiler feedwater flow rate with accuracy and at most the pump limit flowrate in any case.

[0005]

In the prior art, as described above, when it is detected that the flow rate of the boiler feedwater has reached the limit flow rate of the boiler feedwater pump, the opening degree of the boiler feedwater flow rate control valve is not changed for the first time. It is designed not to open beyond the opening.

On the other hand, since the boiler feed water flow rate control valve performs drum level control, when the drum level is rapidly lowered, the feed water flow rate control valve is opened so that the drum level can be normally maintained promptly. Operate. Also, it goes without saying that the feedwater flow rate detector has a detection delay.

Accordingly, when the limit value of the boiler feed water flow rate is detected by the boiler feed water flow rate signal detector 16, the opening of the boiler feed water flow control valve is set to the opening required to supply water above the boiler feed water flow limit value. It is highly likely that the boiler feed pump has an excessive flow rate due to overshoot due to a mechanical delay on the operation command side of the feedwater flow rate control valve, resulting in pump motor overload or pump stoppage due to drop in pump handling pressure. There was a risk of plant shutdown.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to reliably control the boiler feedwater flow rate below the limit flow rate of the boiler feedwater pump to prevent a pump trip due to an overload of the feedwater pump and to maintain a stable operation. An object of the present invention is to provide a boiler feedwater flow control device capable of continuing operation.

[0009]

In order to achieve the above object, the present invention mainly employs the following constitution.

In a water supply control device for a drum boiler provided with a boiler water supply pump and a control valve for adjusting the flow rate of water supplied to the boiler, a drum level setting signal, a drum level detection signal, a boiler water supply flow rate signal and a boiler steam flow rate signal are used. Only when the valve opening is in the increasing direction, the valve opening speed is gradually adjusted to zero as the boiler water supply signal approaches the boiler limited flow rate. A water supply control device for a drum boiler that controls a valve.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. Here, 1 is a drum level signal, 2 is a boiler feed water flow signal, 3 is a boiler main steam flow signal, 4 is a subtractor, 5 is a subtractor, 6 is a signal generator, 7 is a proportional integrator, and 8 is an adder. , 9 is a proportional integrator, 10 is a signal low value selector, 11 is a signal generator, 12 is a signal storage, 13
Is a signal switch, 14 is a manual automatic switch, 15 is a water supply flow rate control valve, 16 is a signal detector, 20 is a change rate limiter, 21
Represents a function generator.

As shown in FIG. 1, a drum boiler calculates a drum level setting signal from a signal generator 6 and a drum level signal 1 from a drum level detector as a deviation signal by a subtractor 4 and then a proportional integrator 7. Is converted into a boiler water supply control valve opening signal. Further, the main steam flow rate signal 3 and the feed water flow rate signal 2 which are the steam generated from each drum are calculated as a deviation signal by a subtracter 5, and this deviation signal and the boiler feed water flow rate control valve opening signal from the drum level deviation described above are calculated. Are added by the adder 8.

An adder 8 creates a combined deviation signal of three elements consisting of the drum level signal 1, the boiler feed water flow signal 2, and the boiler main steam flow signal 3. An opening command signal for the water supply flow rate control valve of each drum is created from the combined deviation signal via the proportional integrator 9 to control the water supply flow rate.

In the present invention, on the output side of the opening command signal of the boiler feed water flow control valve from the proportional integrator 9, a signal change rate limiter 20 effective only in the valve opening increasing direction is provided. The valve opening side speed is controlled to a value generated by the function generator 21 from the boiler feed water flow rate signal 2 as a rate setting signal.

More specifically, the function generator 21 has the following characteristics. The opening / closing speed of the boiler feedwater flow control valve normally operates at a speed sufficient to control, but when the boiler feedwater pump limit value is approached, the valve open-side operation speed starts to gradually decrease and the open flow speed starts at the pump flowrate limit value. Is controlled to be zero, that is, not to increase in the opening direction. FIG. 1B is a diagram showing the input / output relationship of the function generator 21. As long as the boiler feedwater flow, which is the input of the function generator 21, has not yet reached the pump limit flow, the function generator 2
The valve opening change rate which is the output of 1 operates at 100% (assuming the speed at which the valve is closed to open in 1 minute as 100%), but as the water supply flow rate approaches the pump limit flow rate, the valve opening speed is reduced. It is gradually approaching zero.

Eventually, the valve opening speed is set to zero when the flow rate of the supplied water reaches the pump limit flow rate. However, the valve opening speed is gradually decreased until reaching this limit. The feedwater flow rate does not overshoot, and the pump overload due to this overshoot disappears. FIG. 3 shows the relationship between these signals.

That is, the valve opening command signal (output signal of (P + I)) operates in the opening direction according to the drum level and the feed water deviation signal, but increases as the actual boiler feed water flow signal approaches the pump limit flow value. The rate of change of the opening degree in the direction is limited, and stops at the pump limit flow rate value. If the valve opening command signal ((P + I) output signal) becomes equal to or less than the above value, the signal after the change rate limiter is output as it is, and the pump is controlled so as not to reach the pump limited flow rate. Will be.

In FIG. 2, the function of the rate-of-change limiter 20 is to make the signal from the function generator 21 effective only when the valve opening increases.

As a result, the problems of the detection delay and the operation delay, which have conventionally occurred, are surely solved, so that the overload of the boiler feed pump can be avoided.

Next, another embodiment of the present invention will be described.
A method is also conceivable in which the boiler feedwater flow rate control valve opening upper limit signal corresponding to the boiler feedwater pump capacity is created in advance to limit the boiler feedwater flow rate control valve opening signal. Since an operation delay is inevitable, it is necessary to allow for this operation delay, that is, an overshoot amount of the feedwater flow rate. It is considered that such a method can provide the same effect as the present invention.

As described above, according to the present invention, the boiler feed water flow control valve opening signal can be controlled to be equal to or less than the limit flow rate of the boiler feed pump in any operation state. Pump stoppage due to load can be prevented, and stable operation continuation can be realized.

[0022]

According to the present invention, the operation speed of the boiler feed water flow rate control valve becomes slower as the flow rate approaches the boiler feed water pump flow limit value, so that the boiler feed water flow limit value can be detected without delay and moreover. At this point, it is possible to limit the opening of the feedwater flow control valve without overshoot of the feedwater flow.

Therefore, overload of the boiler feed pump can be reliably prevented, and stable plant continuation can be achieved.

[Brief description of the drawings]

FIG. 1 is a control system diagram showing one embodiment of the present invention.

FIG. 2 is a control system diagram according to the related art.

FIG. 3 is a diagram showing a relationship between an input signal and an output signal of a rate-of-change limiter according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Drum level signal 2 Boiler feed water flow signal 3 Boiler main steam flow signal 4 Subtractor 5 Subtractor 6 Signal generator 7 Proportional integrator 8 Adder 9 Proportional integrator 10 Signal low value selector 11 Signal generator 12 Signal storage 13 signal switch 14 manual automatic switch 15 feed water flow control valve 16 signal detector 20 change rate limiter 21 function generator

Claims (2)

[Claims] 1. A water supply control device for a drum boiler, comprising a boiler water supply pump and a control valve for adjusting a flow rate of water supplied to the boiler, comprising: a drum level setting signal, a drum level detection signal, a boiler water supply flow signal, and a boiler steam flow signal. The valve opening signal of the control valve is obtained by using only the direction in which the valve opening increases, so that the valve opening speed gradually approaches zero as the boiler water supply signal approaches the boiler limited flow rate. A water supply control device for a drum boiler, wherein the control valve controls the control valve. 2. A water supply control device for a drum boiler, comprising: at least one boiler water supply pump for supplying water to each of one or more drum boilers; and a boiler water supply flow rate control valve for adjusting a flow rate of the water supply corresponding to the evaporation amount of the boiler. Means for obtaining a level deviation signal between a drum level setting signal and a drum level detection signal of the boiler; means for obtaining a flow rate deviation signal between a steam flow rate signal taken out of the boiler and a water supply flow rate signal to the boiler; Means for obtaining a water supply flow rate control valve opening signal to each drum of the boiler based on the flow rate deviation signal; and as the water supply flow rate signal approaches a pump limit flow rate signal, the operating speed of the control valve gradually approaches zero. A function generating means for generating an appropriate signal, and when an output from the means for obtaining the feed water flow control valve opening signal is in a direction to increase the valve opening. A limiting means for validating the output from the function generation; and a water supply control device for a drum boiler, wherein a signal from the limiting means is output to the water supply flow rate control valve to control a water supply flow rate to the boiler. .