JPH0539901A - Method and device for automatically controlling boiler - Google Patents

Abstract

PURPOSE:To control stably the process quantity for boiler against a rapid change in load by limiting the rate of change in the input instruction signals to boiler to a rate not to exceed the rate of change that is beforehand set and outputting it to a sub-loop control means. CONSTITUTION:If input instruction signals (BID) 13 to boiler that are outputted from a boiler master section 11 changes more than an allowable rate of change for the boiler, a deviation develops between the value of input instruction signal to boiler on the input side of a rate of change limiting device 13-1 connected to the output side of the boiler master section 11 and the value of input instruction signal to boiler on the output side of the rate of change limiting device 13-1. That deviation is detected by a limitation detector 13-2, and if it is larger than a value beforehand set, it is judged that the rate of change limiting device 13-1 has operated. Further, when the main steam pressure 12 that is detected by a main steam detection device 12-1 goes over a rated value by a certain value, the limitation detector 13-2 outputs opening signal to the drive sections of a primary superheater bypass valve 24 and secondary superheater bypass valve 25 to open both of them.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boiler control for a thermal power plant, and more particularly to a boiler automatic control method and apparatus suitable for controlling a once-through boiler whose load changes rapidly.

[0002]

2. Description of the Related Art Conventionally, a boiler automatic control system for a thermal power plant is "700 MW coal-fired power plant integrated digital control system" (thermal power nuclear power plant, 1985, January, vol.
36, No. As described in 1), normal load changes, load runback that reduces the load to a value commensurate with the capacity of the remaining auxiliary equipment when the main auxiliary equipment is stopped, and the generator was disconnected from the transmission grid during a power grid failure. At this time, the fast cut back (F
It had functions such as CB). However, in recent years, it has not been sufficient to cope with a situation in which the system frequency is rapidly changed due to a sudden increase in the demand amount, switching of the system operation, etc., along with a change in the power demand form.

The contents of the boiler control will be described below with reference to FIG. The boiler control unit uses the unit load command (M
WD) 8 for producing a unit master unit 9, a turbine master unit 10 connected to the output side of the unit master unit 8 for producing a command value to the turbine governor, and an output side of the unit master unit 9. A boiler master unit 11 that is connected and creates a boiler input command signal (BID) 13 is provided, and control sub-loops 14 and 16 that are connected to the output side of the boiler master unit 11 and that control each operating end. In the unit master unit 9, a frequency bias 7 is added to a central power supply command (hereinafter referred to as a medium supply command) 5 which is a load request command or a load target set in the power plant in order to correct a governor change with respect to a system frequency fluctuation. Then, the unit load command (MWD) 8 is created. Turbin master unit 1
0 creates a command value to the turbine governor on the basis of the unit load command 8, and the boiler master unit 11 operates on the basis of a change in the main steam pressure indicating an imbalance of energy between the turbine side and the boiler side. A correction signal is added to the unit load command 8 to create a boiler input command signal 13.

Based on this boiler input command signal 13,
Boiler input quantities such as water supply, fuel and air are controlled. The water supply control sub-loop 14 uses the boiler input command signal 13
And the feed water flow rate is controlled based on the output of the feed water flow rate detector 15, and the fuel control sub-loop 16 performs the water-fuel ratio correction 17 based on the change of the main steam temperature by the boiler input command signal 13
In addition to this, a combustion amount command (FRD) 18 is created, and the fuel flow rate is controlled based on the combustion amount command 18 and the output of the fuel flow rate detector 19. The combustion amount command 18 also serves as a request signal for the air flow rate.

In the once-through boiler, in order to protect the furnace water wall 20, the feed water flow rate is always 1/1 / the rated feed water flow rate.
It is necessary to maintain 4 or more. Therefore, at the time of start-up (until the load becomes about 1/4), a supply amount of water equal to or more than the amount of steam flowing into the turbine is supplied to the furnace water wall 20, and excess steam generated in the furnace water wall 20 is From the inlets of the primary superheater 21 and the secondary superheater 27, the primary superheater bypass valves 24 and 2
Flash tank 28 through the next superheater bypass valve 25
To be bypassed. The primary superheater bypass valves 24, 2
Secondary superheater bypass valve 25 and secondary superheater bypass valve 2
A system including a superheater pressure reducing valve 26 provided in the steam pipe on the secondary superheater side of the branch for 5 is called a start bypass system. Before the generator is installed, the superheater pressure reducing valve 26 is fully closed, the primary superheater bypass valve 24 sets the primary superheater outlet pressure 22 and the secondary superheater bypass valve 25 sets the primary superheater outlet. Excess steam is bypassed to the flash tank 28 while controlling the temperature 23 to a specified value. At the time of temperature rise and ramping, the superheater pressure reducing valve 26 is gradually opened, and the main steam pressure 12 rises accordingly. At the same time, the primary superheater bypass valve 24 and the secondary superheater bypass valve 25 are gradually closed, and the superheater pressure reducing valve 26 is fully opened at the time point when the startup bypass operation is switched to the once-through operation.
Secondary superheater bypass valve 24 and secondary superheater bypass valve 2
5 is fully closed. The primary superheater bypass valve 2
The 4th and 2nd superheater bypass valves 25 also have the function of a pressure relief valve, and during normal operation, the main steam pressure 12 or the 1st superheater outlet pressure 22 added the value (alpha) set to the rated value. When the value is exceeded, it is opened to lower the main steam pressure.

[0006]

In the conventional boiler control apparatus described above, there is a possibility that the behavior of the plant becomes unstable when the power transmission system side is abnormal and the plant is stopped as described below. ..

FIG. 6 shows a phenomenon when the system frequency is increased. When the system frequency rises due to an abnormality on the side of the power transmission system, the turbine rotation speed of the turbine is captured, and the turbine turbine in the turbine starts narrowing down the amount of steam flowing into the turbine rapidly. As a result, the generator output decreases, but in order to match this, the load is also narrowed down by the frequency bias 7 on the boiler control side. The setting 6 of the frequency bias is the same as the inclination of the narrowing of the turbine governor (adjustment rate), but the dead zone is provided because it is not necessary to adjust the load on the boiler side for the heat storage capacity of the boiler. The solid line of the generator output in FIG. 6 is the actual output (MW), and the broken line is the unit load command (MWD) 8. In order to suppress the rise of the main steam pressure 12 due to the narrowing of the turbine governor to the unit load command 8, a correction value 11 '(BID correction value in FIG. 6) based on the main steam pressure deviation is added to the boiler master section 11. Has been. A signal obtained by adding the correction value 11 'to the unit load command 8 is a boiler input command signal (BID) 13, which is represented by the solid line of the boiler input command in FIG. With this boiler input command signal 13,
Although the feed water flow rate, the fuel flow rate, etc., which are the input amounts of the boiler, are controlled, the change of the boiler input command signal 13 is abrupt when the system frequency fluctuation as described above is dealt with compared to the normal load change. For example, hunting of the feed water flow rate as shown in FIG. 6 may occur, and eventually the feed water flow rate becomes equal to or less than the minimum feed water flow rate, and the unit may stop due to the protective interlock of all fuel cutoff (MFT). The solid line in the water supply flow rate column of FIG. 6 shows the actual water supply flow rate, and the broken line shows the command value of the water supply flow rate.

As described above, in the prior art, the boiler input command signal is rapidly changed at a rate of, for example, 100% / minute with respect to a rapid load change such as a frequency change. There is a problem that hunting occurs and the operation of the plant becomes unstable. As a cause of the rapid load change, in the above example, the frequency fluctuation due to an abnormality on the power transmission system side was mentioned.However, since the predicted load fluctuation in the entire power transmission system is rapid, the unit load command signal itself may change. It may be sudden.

An object of the present invention is to stably control the process amount of a boiler against a rapid load change.

[0010]

Means for Solving the Problems The above-mentioned problems include means for creating a boiler input command signal based on a load request command,
A boiler automatic control device comprising a sub-loop control means for controlling a boiler input amount based on the boiler input command signal, is provided by being connected to an output side of the means for creating the boiler input command signal. A change rate limiter that limits the rate of change of the input command signal to a value that does not exceed a preset rate of change and outputs the change rate limiter to the sub-loop control means, and the change rate limiter is connected to the change rate limiter. The change rate limiter detects the output of the change rate of the boiler input command signal by limiting it to a value that does not exceed the preset change rate, and opens the superheater bypass valve. It is achieved by providing.

Further, a change rate of the boiler input command signal is provided to a boiler automatic control device having a sub-loop control means for controlling the boiler input amount based on the boiler input command signal.
This can also be achieved by providing a rate-of-change limiter that limits the rate of change at which each input quantity is stably controlled.

Further, means for generating a boiler input command signal based on the load request command, and sub-loop control means for controlling the boiler input amount based on the boiler input command signal,
In the boiler automatic control device provided with, is provided by connecting to the output side of the means for creating the boiler input command signal, the rate of change of the boiler input command signal is limited to a value not exceeding a preset rate of change. When the main steam pressure exceeds a preset value, the change rate limiter for outputting to the sub-loop control means, the main steam pressure detecting means, and the main steam pressure detecting means are provided so as to be connected to the main steam pressure detecting means. It is also achieved by providing a superheater bypass valve forced opening means for opening the superheater bypass valve.

Further, in a boiler automatic control method in which a unit load command is created based on the load request command and the boiler input amount is controlled based on the unit load command, the rate of change of the created unit load command is predetermined. The boiler automatic control method may be characterized by not exceeding the specified value.

[0014]

The maximum boiler input command signal change rate at which the boiler operation does not become unstable is preset as the allowable change rate. The change rate limiter connected to the output side of the means for creating the boiler input command signal does not exceed the preset allowable change rate for the rate of change of the boiler input command signal created by the means for creating the boiler input command signal. Limit to a value. Therefore, the rate of change of the boiler input command signal input to the sub-loop control means is equal to or less than the preset allowable change rate, and the boiler input amount is based on the boiler input command signal of the change rate equal to or lower than the allowable change rate. Once controlled,
The operation of the boiler plant will not become unstable.

On the other hand, the turbine governor is controlled by a unit load command created based on the load request command,
The rate of change of the unit load command is not limited by the rate of change limiter, so the rate of change of the turbine load is greater than the rate of change of the boiler load. Therefore, when the turbine load is rapidly narrowed down, the boiler load is narrowed down and the main steam pressure is expected to rise, but the rate of change of the boiler input command signal is limited and the sub-loop When it is output to the control means, the superheater bypass valve forced opening means detects this and opens the superheater bypass valve, so that an increase in main steam pressure can be avoided. This increase in main steam pressure is avoided by the superheater bypass valve forced opening means that detects that the change rate limiter has limited the change rate of the boiler input command signal, and the main steam pressure exceeds the preset pressure. It is also possible by the superheater bypass valve forced opening means which detects that and opens the superheater bypass valve.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. The boiler automatic control device of the present embodiment,
Unit load command (MWD) 8 based on the mid-pay command or load request command that is the load target set in the power plant
And a turbine master unit 1 that is connected to the output side of the unit master unit 9 and that generates a command value to the turbine governor based on the unit load command 8.
0 and a boiler input command signal (BI) based on a unit load command 8 connected to the output side of the unit master unit 9.
D) Boiler master unit 11 for creating 13 and change rate limiter 13-1 connected to the output side of the boiler master unit 11
A feed water control sub-loop 14 and a fuel control sub-loop 16 which are sub-loop control means connected to the output side of the rate-of-change limiter 13-1, and the input side of the rate-of-change limiter 13-1. And a limit detector 13-2 which is a superheater bypass valve forced opening means connected to the output side. The output side of the limit detector 13-2 is the primary superheater bypass valve 2
The difference between the value of the boiler input command signal on the input side of the change rate limiter 13-1 and the value of the boiler input command signal on the output side is determined. The secondary superheater bypass valve 24 and the secondary superheater bypass valve 25 are configured to open when the size is larger than the predetermined size. When the change rate of the input signal is larger than a predetermined value, the change rate limiter 13-1 limits the change rate to the predetermined change rate and outputs it. Unit master unit 9, turbine master unit 1
0, boiler master unit 11, Zaburupu control means 14, 1
The configuration and operation of 6 are the same as those described in the related art of FIG.

In the present embodiment, the conventional boiler automatic control device is provided with a change rate limiter 13-1 for suppressing the change rate of the boiler input command signal 13, and a change exceeding the change rate allowed for the boiler is provided. Bypassing excess steam based on the imbalance of the load change of the turbine and the boiler by preventing the input change of the rate from being given to each sub loop control means and limiting the input change rate of the boiler. Limit detector 13 which is a superheater bypass valve forced opening means
2 is provided.

During the operation of the boiler, the maximum allowable change rate of the boiler input amount allowed as a boiler is grasped in advance by the maximum load change test, and the set value of the change rate limiter 13-1 is adjusted to this maximum allowable change rate. Is set. By setting in this way, even if a boiler input command signal for instructing a boiler input amount change equal to or higher than the maximum allowable change rate is output in order to cope with system frequency fluctuations, it is input to the sub loop control means. The change rate of the boiler input command signal is limited within the maximum allowable change rate by the change rate limiter 13-1, and the change in the input amount actually applied to the boiler does not make the operation of the boiler unstable. .. On the other hand, in order to cope with frequency fluctuations in the transmission system, rapid narrowing of the load on the turbine side is unavoidable, and if the boiler side limits the narrowing of its input amount as described above, excess energy will be generated on the boiler side. Occur. This energy is released to the flash tank 28 by forcibly opening the primary superheater bypass valve 24 and the secondary superheater bypass valve 25.

The above operation will be described with reference to FIG. When the boiler input command signal (BID) 13 output from the boiler master unit 11 changes more than the allowable change rate of the boiler, the change rate limiter 13-1 connected to the output side of the boiler master unit 11 changes the boiler input command signal. In order to limit the rate of change, a deviation occurs between the boiler input command signal input to the rate of change limiter 13-1 and the boiler input command signal output from the rate of change limiter 13-1. The deviation is detected by the limit detector 13-2, and when the value of the deviation becomes equal to or more than a preset set value, it is determined that the limit detector 13-1 has operated, and further the main vapor pressure detecting means 12-1. When the main steam pressure 12 detected at 7 becomes higher than the rated value by 7 kg / cm ² or more, the limit detector 13-2 sends an open signal to the drive parts of the primary superheater bypass valve 24 and the secondary superheater bypass valve 25. Is output and both are opened. In this example, the main steam pressure was 7 kg / cm ² higher than the rated value, but
It does not necessarily have to be 7 kg / cm ² . When the conventional main steam pressure is higher than the rated value by 14 kg / cm ² or more, the mechanism for opening the primary superheater bypass valve 24 and the secondary superheater bypass valve 25 operates as it is.

The above operation for coping with the fluctuation of the system frequency is shown in FIG. 4 in comparison with the case of the prior art. In the figure,
The solid line shows an example of values in the case of the conventional technique, and the alternate long and short dash line shows an example of values in the case of the embodiment of the present invention (the value of the system frequency is common to both). Although the turbine governor is narrowed down as the system frequency increases and the generator output decreases, in the case of the present embodiment, since the input amount on the boiler side is not narrowed down, the decrease in the generator output also decreases. The main steam pressure in this example is higher than that in the conventional example, but does not rise to a certain extent or more due to the opening operation of the superheater bypass valve. Further, since the movement of the boiler input command signal is small, the decrease in the main steam pressure from the rated value due to the reverse response is small. Further, the rate of change of the boiler input command signal is suppressed by the operation of the rate-of-change limiter, and as a result, changes in the feed water flow rate and fuel flow rate are slow and controlled stably.

In the above embodiment, as shown in FIG. 4, the superheater is operated on condition that the change rate limiter 13-1 operates and the main steam pressure rises from the rated value by 7 kg / cm ² or more. Although the bypass valve is opened, the limit detector 13-2 is not provided, the main steam pressure detecting means is the superheater bypass valve forced opening means, and the main steam pressure is rated regardless of the operation of the change rate limiter 13-1. than the value, when the rose 7 kg / cm ² or more,
The superheater bypass valve may be opened.

In another embodiment shown in FIG. 2, a rate-of-change limiter 13-1 is connected to the output side of the unit master section 9, and the rate of change of the unit load command 8 input to the turbine master section 10 is also This is an example in which the rate of change is limited to a predetermined rate or less. According to the present embodiment, since the turbine load and the boiler input amount are controlled based on the same rate of change, the amount of energy imbalance between the turbine and the boiler is small. There is no need for the superheater bypass valve forced opening means provided in the.

[0023]

According to the present invention, the change rate limiter
Since the rate of change of the boiler input command signal input to the sub-loop control means is equal to or less than the specified value, it is possible to prevent the boiler input command signal from becoming a disturbance to the sub-loop control means, and at the same time. Since excess steam is released due to the imbalance of input and output between the turbine and the boiler, the effect of ensuring stable operation of the thermal power plant even during rapid load changes such as system frequency fluctuations There is.

[Brief description of drawings]

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

FIG. 2 is a system diagram showing another embodiment of the present invention.

FIG. 3 is a block diagram showing details of the operation of the embodiment shown in FIG.

FIG. 4 is a conceptual diagram showing a relationship between a process amount and a control signal when the frequency changes in the embodiment shown in FIG.

FIG. 5 is a system diagram showing an example of a conventional technique.

FIG. 6 is a conceptual diagram showing a relation between a process amount and a control signal at the time of frequency fluctuation in the prior art.

[Explanation of symbols]

5 Load request command 8 Unit load command 11 Means for creating boiler input command signal (boiler master part) 12-1 Main steam pressure detecting means 13 Boiler input command signal 13-1 Change rate limiter 13-2 Superheater bypass valve forced open Means (limitation detector) 14,16 Sub-loop control means 24,25 Superheater bypass valve

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akio Matsuzaki 1-3-1 Uchisaiwaicho, Chiyoda-ku, Tokyo Tokyo Electric Power Company

Claims (4)

[Claims] 1. A boiler automatic control device comprising: means for generating a boiler input command signal based on a load request command; and sub-loop control means for controlling a boiler input amount based on the boiler input command signal. , Provided to be connected to the output side of the means for creating the boiler input command signal, and limiting the rate of change of the boiler input command signal to a value not exceeding a preset rate of change, to the sub-loop control means. A change rate limiter for outputting and a change rate limiter connected to the change rate limiter are provided.
A superheater bypass valve forcibly opening means for opening the superheater bypass valve by detecting that the change rate limiter has changed the rate of change of the boiler input command signal to a value not exceeding a preset change rate and outputting the value. , A boiler automatic control device characterized by being provided. 2. A boiler automatic control device comprising sub-loop control means for controlling a boiler input amount based on a boiler input command signal, wherein each input amount is stably controlled with respect to the rate of change of the boiler input command signal. An automatic boiler control device, characterized in that a change rate limiter for limiting the change rate is provided. 3. A boiler automatic control device comprising: means for generating a boiler input command signal based on a load request command; and sub-loop control means for controlling a boiler input amount based on the boiler input command signal. , Provided to be connected to the output side of the means for creating the boiler input command signal, and limiting the rate of change of the boiler input command signal to a value not exceeding a preset rate of change, to the sub-loop control means. A change rate limiter for outputting, a main steam pressure detecting means, and a superheater which is provided in connection with the main steam pressure detecting means and which opens a superheater bypass valve when the main steam pressure exceeds a preset value. An automatic boiler control device comprising: a bypass valve forced opening means. 4. In a boiler automatic control method in which a unit load command is created based on a load request command and the boiler input amount is controlled based on the unit load command, the rate of change of the created unit load command is predetermined. Boiler automatic control method characterized by not exceeding the specified value.