JPH0217764B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention makes it possible to perform stable control by preventing the main steam temperature and reheat steam temperature from rising or falling even when operating a drum boiler at variable pressure in a low negative region. This invention relates to a main steam temperature control device for a boiler.

Conventionally, STC (Steam
Temperature Control - Main Steam Temperature Control) The following is used as the compensation signal.
The first method uses the difference signal between the load (main steam flow rate signal) SF and the fuel flow rate as a compensation signal. In this case, as shown in Figure 1, the main steam flow rate signal SF
The difference signal between FF and fuel flow rate FF is used as a compensation signal. That is, the function generator 1 uses the function generator 1 as a signal equivalent to the spray flow rate obtained from the static characteristics, and the arithmetic unit 2 generates a difference signal between SF and FF, and assumes that the difference indicates the unbalance of the boiler. This was used as a feed forward signal. In addition, 3 in the figure is a controller that measures the PV value (Process Value - measured value) and SV value (Setting value) of the main steam temperature.
Value - target value) is input. A computing unit 4 receives the output of the controller 3 and the outputs of the function generator 1 and computing unit 2. The output of the calculator is used as a spray control signal to adjust the temperature inside the boiler.

The second method is to use a signal obtained by dividing the load and the fuel flow rate as a compensation signal, as shown in FIG. That is, SF and FF are divided by the arithmetic unit 5, and this is used as a compensation signal as it indicates the imbalance of the boiler. Part 3 is the boiler master signal BM
This uses the integral control output of the main steam pressure PT as the compensation signal. That is, as shown in FIG. 3, the main steam pressure PT is input to the controller 6, and its control output is used as a compensation signal to feed-forward to the calculator 4.

4, as shown in FIG. 4, the output of the signal generator 7 is inputted to the rate limiter 9 via the transfer contact 8 so that its value can be arbitrarily set. The output of the rate limiter 9 is fed forward to the arithmetic unit 4. Also,
The boiler master signal BM is input into the arithmetic unit after being gain-adjusted by a gain adjustment circuit 10. In this case, the input signal of controller 3 is the reheat steam temperature signal.
These are PV value and SV value. By appropriately setting the value of the signal generator 7, the GRF damper can be forcibly throttled down by X percent after transformation, thereby preventing the temperature rise of the inlet metal of the desuperheater. The timing is that PT starts narrowing down at 123K.
It will be canceled if it exceeds 140K. In the figure,
11 is a function generator receiving the main steam flow rate SF; 12;
13 is a function generator that commonly receives the air flow signal AF; 14 is a low limiter that receives the outputs of the arithmetic unit 4 and the function generator 12; and 15 is a high limiter that receives the outputs of the function generator 13 and the low limiter 14. The output of the high limiter drives the GRF damper. FIG. 5 is a diagram showing the operation of each part at this time. In the figure, a shows the SF (main steam flow rate) signal, b shows the pressure change in the boiler, c shows the output of the rate limiter 9, and d shows the opening degree of the GRF damper. In the figure c, x indicates the setting value of the signal generator 7.

The so-called variable pressure operation, in which the main steam pressure in the boiler is changed according to the load, has rapidly become popular in recent years as a technology for increasing the efficiency of boilers in the low load range from the perspective of energy conservation. Main steam temperature control (Steam
Temperature Control (hereinafter simply referred to as STC)
However, manual operation or manual altitude during voltage transformation required techniques. When performing STC operation of a boiler, the time constant and gain change in the low load region even at low pressure, making control difficult.
If voltage transformation is added to this, control becomes even more difficult. This is true of the recent ABC (Automatic
Boiler Control) has become a problem when replacing control systems. The reason is as follows. In other words, when performing STC during variable voltage operation,
It is necessary to perform manual operations in a pattern as shown in FIG. In the figure, a represents the change in main steam flow rate, b represents the change in main steam pressure, c represents the operation output MV of the GRF damper manual operation signal, and d represents the operating signal at that time.
The PV value and SV value are shown respectively. In Figure d, the solid line indicates the PV value and the wavy line indicates the SV value.
When performing such an operation, a high input gain is required during transformation, which may cause noise in the medium to high load region after transformation is completed, so conventional technology uses a simulation method as shown in Figure 6. I couldn't get a suitable signal to do so. For this reason, if you try to perform variable voltage operation in a low load area, the 4th
This required complex logic as shown in the figure.

The present invention has been made in view of the above points, and is designed to generate a signal equivalent to the target value of main steam pressure.
The differentiated signal is input to the STC system and used as a feed forward signal for the spray flow rate control valve and GRF damper opening, ensuring stable operation even when the drum boiler is operated at variable pressure in a low load range. This is a boiler main steam temperature control device that can perform ABC.

The present invention will be described in detail below with reference to the drawings.

FIG. 7 is a configuration diagram showing an embodiment of the present invention. In the figure, 100 is the combustion control system (ACC
system), 200 is the main steam temperature control system (STC system), 3
00 is a reheat steam temperature control system. First, ACC
The system will be explained. The main steam pressure signal is input to a calculator 101 and a rate limiter 102. The output of the arithmetic unit 101 is sent to the arithmetic unit 1 as a PV value.
03, the output of rate limiter 102 is SV
It is entered into the arithmetic unit 103 as a value. On the other hand, the main steam flow rate signal SF is input to the arithmetic unit 103 via the function generator 104 and is also input to the arithmetic unit 106 . The outputs of the arithmetic unit 103 and the function generator 104 are input to a controller 105, and the output of the controller is input to the arithmetic unit 106. Arithmetic unit 106
The output is auto/manual switching calculator 1
07 and is output as the boiler master signal BM. This BM signal controls combustion within the boiler. Further, the main steam flow rate signal SF enters the function generator 108 and is converted into a predetermined value, and then enters the transfer contact 109. The transfer contact has an auto mode control (AMC)
The output of analog memory 110 is also included to provide set target values. The output of the transfer contact 109 is input to the rate limiter 102.
Furthermore, an analog memory 111 for providing an AMC rate of change and a signal generator 112 for providing a program mode control (PMC) rate of change.
The output is input to the transfer contact 113. The output of the transfer contact is input to a gain matching circuit 114, and the output of the gain matching circuit is input to the rate limiter 102. Here, the output of the transfer contact 109 and the output of the gain matching circuit 114 are used as control signals for the main steam temperature control system STC, which will be described later. The output of the transfer contact 109 is used as the main steam pressure setting target value PS, and the gain adjustment circuit 1
The outputs of 14 are respectively used as pressure change rate signals PR.

Next, the STC system 200 will be explained. The PV value and SV value of the main steam temperature signal are input to a computing unit 201, and the output values thereof are input to computing units 202 and 203. Further, the PV value of the main steam temperature signal is also input to the calculator 204. On the other hand, the main steam flow rate signal SF is commonly input to function generators 205 to 207, and the output of 205 is sent to the arithmetic unit 202.
The output of 206 is sent to the arithmetic unit 203 and the controller 2.
At 08, the outputs of 207 are input to the arithmetic unit 209, respectively. The controller 208 is the function generator 20
6 and the outputs of the arithmetic unit 203 are received and the outputs are input to the arithmetic unit 209. function generator 205,
The outputs of the arithmetic units 202 and 204 are input to the arithmetic unit 210, and the outputs of the arithmetic units are input to the arithmetic unit 209. The output of the calculator 209 is input to a controller 211, which receives the signal and the attemperator outlet temperature signal and outputs a spray control signal. On the other hand, the control signal PS generated by the ACC system 100 and
PR is the rate limiter 212 in the STC system 200.
is being entered. The output of the rate limiter is differentiated by a differential calculator 213 and then input to calculators 214 and 215. The output of the arithmetic unit 214 is input to the arithmetic unit 209 as a feed forward signal. The SF signal and the fuel flow signal FF enter a computing unit 216, and the output of the computing unit enters the computing units 214 and 215. Also, SF
The differential signal d/dt (SF) of the signal is sent to the computing unit 214, 2.
It's in 15. The output of the calculator 215 is sent to the reheat steam temperature control system 3 via the rate limiter 217.
Connected to 00.

In the reheating steam temperature control system 300, in response to the PV value and SV value of the reheating steam temperature signal, calculation units 301 and 30
2, a predetermined calculation is performed, and then the controller 303 performs a control calculation, and then enters the calculation unit 304. The arithmetic unit contains the PV value of the rate limiter 217 and reheat steam temperature signal differentiated by the arithmetic unit 305 as a feed forward signal. Arithmetic unit 3
The output of 04 passes through a low limiter 306 and a high limiter 307 and is output as a control signal for the GRF damper opening degree. The operation of the device configured as described above will be explained as follows.

As mentioned above, the main steam pressure setting target value PS and pressure change rate signal PR created by the ACC system 100 are
By incorporating it into the rate limiter 212 of the STC system 200, the rate limiter can be transferred to the ACC system 1.
An SV signal equivalent to that used in 00 can be obtained. By differentiating this SV signal with the differential calculator 213, a signal MV' close to the manual operation pattern as shown in FIG. 6c can be obtained.
This pseudo operation pattern signal MV' is sent to the computing unit 214.
By sending the feed forward to the computing unit 209 via the controller 211, the optimum spray control signal can be outputted from the controller 211. Here, the reason why the SV value of the main steam pressure signal is not used as it is is because
If you import this directly into the STC system, the ACC system will be 100.
This is because disturbances occur due to the logic of Further, the above-mentioned MV' is fed forward to the calculator 304 of the reheat steam temperature control system 300 via the calculator 215 and the rate limiter 217 to obtain the optimum value.
Provides GRF damper opening control output.

FIG. 8 is a diagram showing the operation of each part at this time. In the figure, a shows the change in the main steam flow rate SF, b shows the change in the main steam pressure PT, c shows the differential output waveform MV' at this time, d shows the change in the spray flow rate, and e shows the change in the GRF damper opening. ing. In Figure d, the solid line shows the actual spray flow rate, and the broken line shows the correction signal given as a feed forward. It can be seen that this correction signal corresponds to the differential output shown in c. eThe solid line in the figure is
The broken lines indicate the changes in the GRF damper opening degree, and the respective correction signals are also given as feed forwards.

In both figures d and e, due to the correction signal indicated by the broken line, the change is reduced by the amount of the correction signal, so the fluctuation can be suppressed to a low level. During variable voltage operation
The reason why STC is difficult is that the temperature rise or fall due to the isenthalpy change due to the main steam pressure change is large, which makes STC in the low load region even more difficult.
In such cases, skilled operators perform manual operations relying on experience and intuition. The present invention was made based on the fact that similar effects can be obtained by using a differential signal of the main steam pressure set value as an alternative to such manual operation. The reason for this is that this differential signal is output only when the signal changes, that a signal with a level corresponding to the set rate of pressure change is obtained, and that when using a method of controlling the control mode depending on the load, As the load increases or decreases, the pressure setting increases or decreases, and this is the STC.
Although this is a disturbance to the system, using the differential signal effectively compensates for such disturbance, thereby further improving the controllability of the STC control system. In particular, since the opening degree of the GRF damper can be greatly changed at the start and end of transformation, it can have a positive effect on the ABC as a whole. Note that, as shown in FIG. 9, if high and low limiters 220 are provided after the rate limiter 212 so that the timing of the signal can be changed arbitrarily, a signal that matches the characteristics of the plant can be created. In particular, these timing adjustments are essential for boilers with large furnace volumes, such as coal-fired boilers. FIG. 10 is a diagram showing the operation of each part when timing adjustment is provided in this manner. In the figure, a shows the output of the rate limiter 212, b shows the output of the high/low limiter 220, and c shows the differential signal waveform.
In the figure, t1 in c indicates the start, t2 indicates the low limit, and t3 indicates the high limit.

As explained above in detail, according to the present invention, a signal equivalent to the target value of main steam pressure is input to the STC system,
The signal obtained by differentiating this signal is sent to the spray flow control valve and
By using it as a feed forward signal for the GRF damper opening, stable ABC can be achieved even when the drum boiler is operated at variable pressure in the low load range.
It is possible to realize a main steam temperature control device for a boiler that can perform the following steps.

[Brief explanation of drawings]

Figures 1 to 4 are diagrams showing the configuration of a conventional main steam temperature control system, Figure 5 is a diagram showing the operation of each part, Figure 6 is a diagram showing the operation of each part during manual operation, and Figure 7 8 is a diagram showing an embodiment of the present invention, FIG. 8 is a diagram showing the operation of each part according to the present invention, FIG. 9 is a diagram showing another embodiment of the invention, and FIG. 10 is a diagram showing the operation of each part in this case. FIG. 1, 4, 11-13, 108, 205-207
...Function generator, 2, 5, 101, 103, 10
6,107,201-204,209,210,
214-216, 301, 302, 304, 30
5... Arithmetic unit, 3, 6, 105, 208, 21
1,303...Controller, 7,112...Signal generator, 8,109,113...Transfer contact, 9,102,212,217...Rate limiter, 10,114...Gain adjustment circuit, 1
4,306...Lorimitsuta, 15,307...
High limit, 110...Analog memory, 21
3...differential calculator, 220...high/low limiter.

Claims (1)

[Claims] 1. When performing variable pressure operation of a drum boiler in a low load region, a rate limiter means of the STC (main steam temperature control) system that inputs the main steam pressure set target value signal and pressure change rate signal, and the output of this rate limiter means. A main steam temperature control device for a boiler, characterized in that a signal obtained by differentiating the above is used as a feedforward signal for a spray flow rate control valve and a GRF damper opening.