JPS6114403A - Controlling method of turbine bypass valve - Google Patents

Abstract

PURPOSE:To prevent a variation in main steam pressure and a drum water level, a boiler trip, etc. from occurring, by controlling the opening of a high-pressure steam turbine bypass valve in a manner conformable to a boilder surplus energy value in time of a sudden drop in turbine load. CONSTITUTION:A bypass valve control parameter arithmetic unit 32 is installed in a control system which controls the opening of a high-pressure turbine bypass valve on the basis of a pressure setting signal 18 and a main steam pressure signal 19, and with this device 32, a second selector 25 and a constant generator 31 are controlled. In time of a sudden drop in turbine load, the arithemetic unit 32 takes in turbine output, boiler output, a boiler drum level, etc., then calculates boiler surplus energy, and generates an opening signal 26 for the specified time characteristic of the bypass valve so as to cause the bypass output to approximate to the surplus energy. With this constitution, a variation in the drum water level and a boiler trip are preventable from occuring.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for controlling high pressure steam turbine bypass valves installed in parallel to high pressure steam turbines in a steam turbine type thermal power generation system.

[Background of the invention]

Generally, in steam turbine thermal power generation systems,
The main shutoff valve is suddenly closed in order to prevent turbine overspeed that occurs when the turbine load (power generation load) suddenly decreases due to the opening of the main circuit breaker in the power transmission system. However, in this case, the steam energy generated from the boiler is no longer guided to the turbine, and the energy generated by the boiler does not decrease rapidly, so the boiler's retained energy becomes excessive, and if left as is, the boiler may trip due to high boiler pressure. will occur. In order to avoid this situation, a method has conventionally been adopted in which surplus energy is released by suddenly opening a high-pressure steam turbine bypass valve installed in parallel with the high-pressure steam turbine.

However, in this method, the bypass valve is suddenly opened uniformly at the fully open state, and then a PI (proportional integral) control system is used to maintain a constant opening for a certain period of time, and then the main steam pressure and the main steam pressure set value are Based on the deviation of <PI control. In this case, the rapid opening of the bypass valve and the subsequent control 'I
Since the bypass amount of boiler energy due to C does not correspond accurately to the boiler surplus energy, the boiler condition, that is, the drum level, and the main steam pressure fluctuate excessively, often resulting in boiler trips.

Here, an example of the above-mentioned conventional high-pressure steam turbine bypass valve control method will be explained in detail. Fig. 5 shows a system diagram of a general steam turbine type thermal power generation system.
In the figure, main steam generated by a boiler superheater 1 passes through a main blocking valve 9 and a main control valve 10 to a high-pressure steam turbine 3.
After being converted into rotational energy, it is heated again in the reheater 2, and then guided to the medium and low pressure steam turbine 4 via the reheat blocking valve 12 and the intercept valve 11, where it is converted into rotational energy. , is discharged to the condenser 5. The ventilator valve 16 is normally in a fully closed state.

If the output of the generator 6 suddenly decreases due to the opening of the main circuit breaker, etc.
The main blocking valve 9 is quickly closed to cut off steam to the high-pressure steam turbine 3 and prevent the turbine from over-rotating. At this time, since the boiler output does not decrease rapidly, the high pressure steam turbine bypass valve 7 is suddenly opened to bypass and release the energy supplied to the high pressure steam turbine 3.

Next, FIG. 6 shows a control system diagram of a conventional high pressure steam turbine bypass valve. The main steam pressure 19 is determined by the comparison calculator 20
This is compared with the pressure setting signal 18 from the boiler master control device, and the deviation between both signals is determined. A bypass valve opening command value is calculated by the PI calculator 21 based on the obtained deviation.

The first switch 24 switches between the command value from the second PI calculator 21 and the command value 22 in the analog memory based on the manual increase/decrease command 23 . The second switch 25 is the first switch gate 2
4 and the output value of the constant generator 31 are switched. The output value of the constant generator 31 is used to set a target value for performing PI constant value control after the bypass valve is suddenly opened. Based on the bypass valve opening command value 26 obtained in this way, the position comparator 28 compares the output of the valve position detector 27 with the command value 26, and the servo mechanism 29 controls the high-pressure steam turbine bypass valve so that the deviation becomes O. Drive 7. In addition, 1
7 is a coefficient unit, 30 is a Quiback, .

A signal generator is shown.

FIG. 7 shows the temporal response characteristics of the above control system. In FIG. 7, when the turbine load 36 suddenly decreases to O (FIG. 7(a)), a bypass valve opening command signal 26 is generated to quickly close the high-pressure steam turbine bypass valve 7 (see FIG. 7(a)).
Figure (b)). In response to this bypass valve opening command signal 26, the turbine bypass valve drive mechanism shown in FIG. 51 to fully open.

In addition, 47 is a hydraulic bypass part, 50 is a hydraulic pipe for driving in the closing direction, 52 is a hydraulic piston, and 54 is a hydraulic pipe for driving in the closing direction.

Now, while the bypass valve opening signal 26 is being generated, the bypass valve opening degree 39 rapidly opens to the full open position over the bypass valve opening command holding time T1 (FIG. 7(C)). After the time T1 has elapsed, the signal generated by the signal generator 31 is selected by the second switch 25 and output as the bypass valve opening command value 26.

The output of the signal generator 31 is maintained for 12 hours, after which the control shifts to <PI control based on the deviation between the main steam pressure 19 and the pressure setting signal 18. The behavior of the plant during this period is shown in FIG. 7, where the bypass valve opening 39 approaches the bypass valve opening constant control value A over time T1 (FIG. 7 (C)). Fixed value control is performed during time T2. The main steam pressure 19, which is the main control variable, rises after the turbine load 36 suddenly decreases because the energy retained in the boiler becomes excessive, and continues to rise during the bypass valve opening command holding time T1, but eventually the excess energy is released and it falls. (Figure 7(a)). On the other hand, as shown in FIG. 7(e), the boiler drum water level 41 will be affected by excessive energy being released from the boiler if the bypass valve opening 39 continues to be opened more than the amount required to release excess energy from the boiler, i.e. , too much steam was released from the drum, and the boiler drum water level was 4.
1 becomes the boiler drum water level low trip level 42 or lower, and boiler tri-tu No. 16 43 is issued (Fig. 7 (
f)). The above phenomenon does not realize the original purpose of temporarily opening the high-pressure steam turbine bypass valve 7 to release excess energy and avoid a boiler trip because the boiler output does not decrease in time when the turbine load suddenly decreases. It turns out.

In order to improve the above drawbacks of the conventional 11il control system,
There is a method based on "Japanese Patent Application No. 43-29882 Turbine Bypass Pressure Reducing Control Method", but this method stores the steam flow before the turbine trip and commands the bypass valve opening corresponding to that value. This is a mechanical control method. Although such a control method is effective in avoiding boiler trip after turbine trip,
Since the bypass valve opening degree is set as a function only of the main engine air flow rate, it is possible to set the bypass valve opening degree as a function only of the main engine air flow rate. There were limits to the ability to avoid boiler trips.

As soon as the turbine runback occurs, the turbine bypass steam power and main steam power are calculated based on the various conditions at that time, and the turbine bypass control valve opening degree is calculated based on these calculated values. There is a system that attempts to stabilize the plant by issuing a command to quickly open the turbine bypass valve when a runback occurs based on the bypass control valve opening value (Japanese Patent Application Laid-open No. 173509/1983).

This control method is basically similar to the control method shown earlier in that it stores the steam flow rate before the turbine trip and commands the bypass valve opening corresponding to that value. The difference is that the configuration that controls it is electrical.

Furthermore, the opening degree of the turbine bypass valve is detected, and this detection signal is compared with the sudden opening signal of the main steam stop valve or steam control valve. There is a device that avoids the occurrence of unnecessary scram by bypassing the reactor scram signal, that is, the trip signal, when the opening degree is commensurate with the turbine generator output when the valve is suddenly opened (Japanese Patent Application Laid-Open No. 56-150397 Publication No.).

In this example, control is performed based on the opening degree of the turbine bypass valve.

In this way, in all of the conventional examples, there is no effective means for detecting phenomena that should originally be understood using energy when preventing trips caused by too much or too little energy held in the boiler that occurs when the turbine load is reduced. , which was approximately controlled using the steam flow rate and valve opening degree.

[Purpose of the invention]

The present invention applies to a high-pressure steam turbine bypass system, when the turbine load suddenly decreases due to factors such as high or low water level in the drum due to too much or too little energy in the boiler, low water level in the drum, or high or low main steam pressure. Prevent boiler trips and improve power generation system availability and operational performance.
[Summary of the Invention] In order to achieve the above object, a method for controlling a turbine bypass valve according to the present invention provides a method for controlling a turbine bypass valve in a high-pressure steam turbine, an intermediate-low pressure steam turbine, and a control method for controlling a high-pressure steam turbine in the case of a sudden decrease in turbine load. In the method for controlling the high-pressure steam turbine bypass valve in a power generation system including a high-pressure steam turbine bypass valve installed in parallel, an opening amount of the high-pressure steam turbine bypass valve is determined as a function of a turbine load reduction amount, and It is characterized by the fact that it changes.

In this way, by determining the degree of opening of the high-pressure steam turbine bypass valve as a function of the amount of turbine load reduction and changing it over time, it is possible to prevent excessive or insufficient energy held by the boiler that occurs due to a sudden decrease in turbine load. It is possible to suppress abnormal fluctuations in the water level of the drum caused by this, thereby preventing boiler trips.

As the surplus energy of the boiler, which is the amount of energy generated corresponding to the amount of turbine load reduction, the main steam h1. The aim is to control the opening degree of the high-pressure steam turbine bypass valve as a function of the main steam pressure and boiler drum water level in a comprehensive manner.

[Embodiments of the invention]

Next, an embodiment of a method for controlling a turbine bypass valve according to the present invention will be described based on the drawings.

FIG. 1 shows a block diagram of a control system for carrying out the control method according to the present invention. In FIG. 1, parts that overlap with those in FIG. 6 are given the same reference numerals, and detailed explanation thereof will be omitted. Note that the configuration of the power generation system itself including the high-pressure steam turbine bypass valve to be controlled will be described below as being similar to that shown in FIG. 5.

The difference between the control system of FIG. 1 and the one of FIG. 6 according to the present invention is that a bypass valve control parameter calculation device (hereinafter abbreviated as parameter calculation device) 32 is provided, and this parameter calculation device 32 controls the second switch 25 and constant generator 31.

That is, the turbine bypass control method according to the present invention includes:
This system provides a means for releasing energy from the high-pressure electric turbine bypass valve 7 corresponding to the boiler excess energy due to a sudden decrease in the turbine load. (Fig. 4 (b)), determine to which opening degree the high-pressure steam turbine bypass valve 7 should be suddenly opened, and furthermore, after the high-speed sudden opening, to what value should the valve opening target value be set? determine whether the valve opening target value is to be maintained for a period of
These are the commands for each.

Now, if the turbine load 36 suddenly decreases (Fig. 4(a)
), the parameter calculation device 32 processes the data in the following procedure (see FIG. 2).

A. The start time T of sudden turbine load is T=O, and the input signal 35 for control parameter calculation is the turbine output PT (t), boiler output PR (t), turbine bypass valve passing output PBy (t), Let the boiler pressure be p, n(
t), Boiler output steam flow rate is TB(t), Boiler output steam temperature is Tn(t), Boiler drum level'&
Take in L (t).

B. Calculated turbine output p of boiler surplus energy PBX
, r(t), and boiler output P II (t) all decrease with time t, but the turbine output Pt(t) decreases more steeply, so the surplus energy P#X(t) is
It is given by the following formula and takes a positive value.

Pgx(t) = pH(t) PT(t) > 0
・・・・・・・・・(1) p-e:yAi/
<20(7)□1j 1. Iweka 1, 6. . ,
'With respect to the boiler drum level L(t), the bypass output p BF (t) is converted to the surplus energy P- under the following constraints.
The goal is to bring it closer to x(t).

P rB(t)<P, BUL...
...-Old-(2) LLL <L(t)<LUL
...Dan... (3) However, at 22, Prsτ
IL is the boiler pressure upper limit, IjLL is the boiler drum level lower limit, and LoL is the boiler drum level upper limit.

Calculation of C0 high-speed valve opening command time TI Next, the high-speed valve opening command time T1, that is, how far the bypass valve should be opened is determined using the following formula.

TI= f (P-x (0), L (0), P-
B (0), P'' B (0), L (0) ) --
(4) The method of determining the function f is that for the values of each of the above parameters, the boiler pressure P, ++(t) is the upper limit, and L(
A polynomial or an approximation function is found to determine the high-speed valve opening command time Tl so that t) does not exceed the limit value.

Bypass valve opening command holding time T determined in this way
During I, bypass valve opening command value 26 is output (4th
Figure (b)). This bypass valve opening command value 26 is input to a position comparator 28 and compared with the detected value of the pulp position detector 27, and the high pressure steam turbine bypass valve 7 is driven by the servo mechanism 29 so that the deviation becomes 0. Ru. This high pressure steam turbine bypass valve 7 is fully opened as shown in FIG. 4(C), while the main steam pressure 19 is
Due to the sudden decrease in 6, the energy retained in the boiler becomes excessive, so it rises and continues to rise with a predetermined time constant, but eventually the surplus energy is bypassed by the sudden opening of the high-pressure steam turbine bypass valve 7, so it gradually decreases ( Figure 4 (
d)).

In this way, the rapid opening of the high-pressure steam turbine bypass valve 7 is completed as the high-speed valve opening command time TI elapses, but if the high-pressure steam turbine bypass valve 7 is left open even after that, excessive boiler energy will be released. As a result, the drum water level 41 decreases. Therefore, it is necessary to determine the valve opening low value control setting value A and the constant value control holding time T2 by the following procedure, and control to gradually narrow down the high pressure steam turbine bypass valve 7.

D, boiler pressure Pry, boiler outlet steam flow rate FB.

The drum level L, the boiler outlet steam temperature 1fTB, and the bypass valve opening 39 are taken into the parameter calculation 71 and the wheat rack 32.

E, read out the boiler surplus energy integral value S P'=x (= fTP-x(t) old) after the sudden decrease in turbine load.

F, calculation to fixed value control set value A = g (f ” P, x (t) dt , L (Tt
), Prn ('r+), Fi (T1).

L ('rt), Pos (rll, ))
−・−・−−−−(s>G, calculation of constant value control holding time T2 Tz=h (,/”P−x(t)d t , L (T
+), Prn (Tt), FB (Tl).

L (T1), Pos (Tt))
---(6) The functions g and h are determined based on the integrated value of the boiler excess energy Fax(t) at the high-speed valve opening command time T1 and the drum level L at the high-speed valve opening command time T1.
(tt), boiler pressure P・x(tt), boiler main steam flow rate Fn(t), bypass valve opening, valve opening low value control setting value A (t), constant value control holding time T2, boiler drum level L (t), the boiler output PrB(t) is within the limit area, and the bypass output Pa(1) and the surplus energy r', x(t) are equal, that is, 1Tp, x(t) -fTP, (1) Old
......Set the approximation function so that it becomes (7).

By performing control in this way, the boiler drum water level 41 fluctuates slightly, as shown in FIG. 4(e), but has almost no effect, and therefore, as shown in FIG. , IJ knob signal is not generated.

〔Effect of the invention〕

As described above, according to the control method of the present invention, the opening degree of the one-pressure steam turbine bypass valve can be controlled in accordance with the amount of boiler surplus energy when the turbine load suddenly decreases.
Preventing fluctuations in main steam pressure and drum water level caused by too much or too little boiler energy released through the bypass valve, and preventing boiler trips caused by the fluctuations,
Improves the availability and operational performance of power generation systems.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the control system of the turbine exhaust valve according to the present invention, Fig. 2 is a flowchart showing the data processing procedure when the turbine load suddenly changes in the control method of the present invention), and Fig. 193 is the same control system. A flowchart showing the data processing procedure when the bypass valve is suddenly opened in the method, FIG. 4 is a time chart showing signal waveforms of each part of the control system according to the present invention, and FIG. 5 is an overview of a general steam turbine thermal power generation system. Fig. 6 is a block diagram showing the control system of the conventional turbine valve, Fig. 7 is a time chart showing the signal waveforms of each part of the conventional control system, and Fig. 8 is the high-pressure steam turbine bypass valve. Drive unit 1... superheater, 2... reheater, 3... high pressure steam turbine, 4... medium and low pressure steam turbine, 5... condenser, 6... generator, 7... High pressure steam turbine bypass jpsi8... Pressure setting signal, 19... Main steam pressure, 20... Comparison calculator, 21... PI calculator, 22
...Analog memory, 23...Manual increase/decrease command value, 2
4...first switch, 25...second switch, 26...
・Bypass valve opening command value, 27...Position detector, 28
...Position comparator, 29...Servo mechanism, 30...
Tieback signal generator, 31...constant generator, 32
... Bypass control parameter calculation device, 35 ... Bypass control parameter calculation device input signal, 36 ... Turbine load, 39 ... Bypass valve opening degree, 41 ... Boira drum water level, 42 ... Boiler drum water level low
Lip level, 43...Boiler trip No. 5, T1.
...High-speed valve opening command holding time, T2...Bypass valve opening constant value control holding time, A...Bypass valve opening constant value control value.

Claims (1)

[Claims] 1. A high-pressure steam turbine, a medium-low pressure steam turbine, and a high-pressure steam turbine bypass valve installed in parallel with the high-pressure steam turbine to bypass and rapidly reduce the steam flow rate to the high-pressure steam turbine when the turbine load suddenly decreases. The method for controlling the high pressure steam turbine bypass valve in a power generation system comprising: determining an opening amount of the high pressure steam turbine bypass valve as a function of a turbine load reduction amount and changing the amount over time; control method.