JPS6145121B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the temperature of steam generated in a boiler.

There are many types of boilers, depending on where they are installed, such as for land use, ship use, mobile use, etc., and depending on the purpose, there are use for power generation, factory use, etc. The following is an explanation using a boiler used in a thermal power plant as an example. A boiler supplies water and fuel (including air) to generate high-temperature, high-pressure steam, and its control device mainly controls the fuel flow rate and water supply flow rate to obtain the desired steam temperature or amount of steam. becomes.

Figure 1 shows a schematic diagram of the configuration around the boiler. Although not shown, the boiler 1 includes a furnace, a combustion device, a water tube and a drum, a superheater, a reheater, and the like. Water is supplied to the boiler 1 by a water supply pump 2, and high-pressure water determined by the desired pressure of the boiler 1 is supplied. The discharge flow rate of the water supply pump 2 is controlled by adjusting the water supply control valve 3, and the discharge flow rate of the water supply pump 2 is controlled by adjusting the water supply control valve 3 with a water supply control device 4.

On the other hand, fuel is supplied to the boiler 1 by a fuel pump 5, which supplies fuel such as heavy oil to the boiler 1.
The discharge flow rate of the fuel pump 5 is controlled by adjusting the fuel control valve 6 with a fuel control device 7. The temperature of the steam generated within the boiler 1 is then measured by a temperature measuring device 8.

In addition to liquid fuels such as heavy oil, fuels include solid fuels such as coal, and gaseous fuels such as natural gas and liquefied petroleum gas. In the following explanation, liquid fuels will be assumed.

Generally, the control of the boiler 1 includes combustion control, water supply control, steam temperature control, etc., and the control contents differ between startup and operation. For example, steam temperature control when starting up the boiler 1 is performed by a fuel control system shown in FIG. That is, when the boiler is started, the temperature of the steam generated in the boiler 1 is controlled by controlling the fuel. And, as shown in Figure 2,
The fuel control system when starting the boiler has automatic and manual control modes. If automatic is selected with the control mode changeover switch 9, the control flow will be as shown by the solid line in the figure, and if manual is selected, the control flow will be the one that includes the solid and broken lines in the figure.

In FIG. 2, a boiler input command 10 outputs the fuel flow rate necessary to raise the temperature of the steam generated in the boiler 1 to a predetermined final temperature at a predetermined steam temperature increase rate as a boiler input command Q _R. ,
In this case, the predetermined steam temperature increase rate and the predetermined final temperature are determined based on the structure and performance of the boiler 1.

The boiler input command Q _R is input to the adder 11,
It is added to the output of the water-fuel ratio setting device 12. The water-fuel ratio setting device 12 corrects the amount of fuel input in response to the boiler input command, and applies a bias to the boiler input command Q _R when the water supply amount fluctuates or during manual operation. For example, the bias applied during manual operation is determined by the deviation multiplier 13,
This is the deviation between the fuel flow rate Q detected by the fuel flow meter 14 and converted into a signal by the converter 15 and the boiler input command Q _R . This deviation is provided to the water-fuel ratio setting device 12 via the analog memory 16.

Next, the output of the adder 11 is inputted to the deviation amplifier 17 as a fuel flow rate command Q _O and compared with the fuel flow rate Q. If there is a deviation between these, the setting value of the fuel setting device 18 is changed according to the deviation. Therefore, the setting value of the fuel setting device 18 is set to such a value that the fuel flow rate Q matches the fuel flow rate command Q _O. Fuel control device 7
is to adjust the fuel control valve 6 so that the fuel flow rate Q becomes the set value. Here, normally, if the temperature rise of the steam is a specified value, the water-fuel ratio is kept constant, so the output of the water-fuel ratio setting device 12 is zero.

Suppose now that automatic control mode is selected. In this case, since the output of the water-fuel ratio setting device 12 is zero, the output of the adder 11, that is, the fuel flow rate command Q _O
becomes the boiler input command Q _R. Therefore, the output of the deviation amplifier 17 is the difference between the boiler input command Q _R and the fuel flow rate Q. From this, when the fuel flow rate Q is equal to the boiler input command value Q _R , the fuel setting device 1
The set value of No. 8 is maintained as it is, and when a deviation occurs, the set value is changed according to the deviation, thereby controlling the fuel flow rate Q to be equal to the boiler command value Q _R.

By the way, if the fuel flow rate Q is maintained equal to the boiler command value _QR , the steam temperature will theoretically increase at a predetermined steam temperature increase rate unless the amount of water supply changes. However, in reality, the boiler condition changes from time to time, so even if the heat flow rate Q is maintained at the boiler input command Q _R , there may be cases where you want to change the fuel flow rate Q due to constraints other than steam temperature, The temperature may not rise at the rate of increase. In such cases, a manual control mode may be selected and the fuel flow rate may be manually changed to remove the constraint.

If the manual control mode is selected to make this correction, the fuel setting device 18 will be directly operated manually to change its set value. Therefore, the fuel flow rate Q is controlled by the fuel control device 7 so as to be equal to the set value corrected by this manual operation. As a result, the fuel flow rate Q deviates from the boiler input command Q _R , which is the fuel flow command Q _O , by the amount of manual correction.

If this deviation occurs, the output of the deviation amplifier 17 will be generated to eliminate the deviation due to automatic control (the flow of control shown by the solid line). In that case, even if you manually make corrections, the fuel flow rate Q will be equal to the boiler input command Q _R
This will cause the manual operation to become meaningless.

Therefore, when the manual control mode is selected, the deviation between the fuel flow rate Q and the boiler input command value Q _R , that is, the correction amount due to manual operation, is detected by the deviation amplifier 13 and transmitted to the water-fuel ratio setting device through the analog memory 16 . A bias corresponding to the correction is added to 12. Therefore, the output of the comparator 11, that is, the fuel flow rate command Q _O , is the sum of the boiler input command Q _R and the correction amount, so the deviation amplifier 17
The output will no longer occur. In other words, even if manual correction is applied during manual operation, the manual operation will not be automatically pulled back and the manual operation can be performed smoothly.

However, such a fuel control system has the following problems when switching from manual control mode to automatic control mode. That is, during manual operation, the output of the water-fuel ratio setter 12 is not zero, but the amount corrected by the manual operation. Therefore, the fuel flow command Q _O is the boiler input command Q _R with manual correction added, and when switching from manual to automatic, the fuel flow command Q _O including the correction is It will be input to the deviation amplifier 17.

In other words, even after the manual correction is completed and the system is switched to automatic mode, the amount of correction still remains, and therefore, the extra fuel flow rate is continuously supplied to the boiler 1 by that amount. In this case, the rate of increase in steam temperature becomes higher than a predetermined rate of increase in steam temperature, which is undesirable as it causes unnecessary thermal fatigue to the boiler 1.

Therefore, an object of the present invention is to prevent manual fuel flow correction from being included in the fuel flow command when switching from manual control mode to automatic control mode, and to switch from manual control mode to automatic control mode. An object of the present invention is to obtain a steam temperature increase control method in which the steam temperature increase rate after switching to a mode becomes a predetermined steam temperature increase rate.

In order to achieve this objective, in the present invention, when switching from manual control mode to automatic control mode, the manual correction of fuel flow rate is canceled,
The fuel flow rate command of the automatic control mode at the time of switching is made to match the boiler input command.

FIG. 3 is a block diagram showing one embodiment of the present invention. Components that are the same as those in the fuel control system shown in FIG. 2 are designated by the same reference numerals, and a description thereof will be omitted.
When the automatic control mode is selected by the changeover switch 9, the initial setting means 19 detects the output of the water-fuel ratio setting device 12 at that time, that is, the manual correction amount, and sends a command to cancel the correction amount to the water-fuel ratio setting device. 1
This is what is output to 2.

As mentioned above, when the manual control mode is selected by the changeover switch 9, the set value of the fuel flow rate setting device 18 is directly changed by manual operation,
Since the fuel flow rate is corrected, the fuel flow rate Q includes the amount of manual correction.

In addition, the manual fuel flow rate correction is calculated by the deviation amplifier 13 and added to the boiler input command Q _R via the analog memory 16 and the water-fuel ratio setter 12, so the fuel flow rate command Q _O is calculated by the manual correction. It will include. In addition, the fuel flow rate command Q
The reason why _O includes the manual correction is that even if the fuel flow rate Q includes the manual correction, it is offset by the deviation amplifier 17 and the fuel is automatically set during the manual control mode. This is to prevent the device 18 from being manipulated.

The case of switching from manual control mode to automatic control mode in this state will be described. Figure 4 shows a characteristic diagram of the fuel flow rate Q at the time of switching, and the time before time _t2 is the manual control mode;
t ₂ and later are automatic control modes. During the manual control mode, the manual correction amount is represented by the deviation between the fuel flow rate Q and the boiler input command Q _R . Before time t ₁ , the manual correction is a negative value, and before time t ₁
The following cases are positive values. Normally, in steam temperature control at boiler startup, the manual correction value is a positive value, but in combustion control at boiler startup, the manual correction value may be a negative value. The case where the correction value is positive or negative is shown.

Assume that the operator manually operates the temperature measuring device 8 while monitoring it, and switches to automatic control mode at time _t2 . In this case, the manual fuel flow correction at switching time t ₂ is ΔQ ₂ . At the switching time t ₂ , the initial setting means 19 outputs a command to the water-fuel ratio running device 12 to cancel the correction amount ΔQ ₂ at that time t ₂ . Then, the output of the water-fuel ratio setting device 12 becomes zero, the output of the adder 11, that is, the fuel flow rate command Q _O becomes the boiler input command Q _R , an output is generated in the deviation amplifier 17, and the setting device of the fuel setting device 18 becomes The setting value is set to the boiler input command Q _R. As a result, the fuel control device 7 controls the fuel flow rate Q to match the boiler input command value Q _R . Then, at time _t3 , the actual fuel flow rate Q becomes equal to the boiler input command Q _R , and from then on, the fuel flow rate Q is controlled to be maintained equal to the boiler input command Q _R.
The steam temperature will rise at a predetermined steam temperature increase rate.

As described above, according to the present invention, when the fuel control system is switched from the manual control mode to the automatic control mode in steam temperature control at the time of boiler startup, the fuel flow rate is corrected by manual operation. Since the fuel flow rate command after switching matches the boiler input command to obtain a predetermined steam temperature increase rate, the temperature can be increased in line with the predetermined steam temperature increase rate after switching. .

In addition, even if manual operation intervenes during automatic steam temperature increase control, the steam temperature will increase at a predetermined rate after switching to automatic control mode, regardless of the fuel flow rate input by manual operation. This results in a fuel control system that allows easy manual intervention. That is, even if automatic control does not raise the steam temperature at a predetermined rate of increase, manual intervention can be easily performed, making it possible to control the temperature increase according to a predetermined temperature increase schedule.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the boiler and its surroundings, Fig. 2 is a control block diagram showing a conventional fuel control system, Fig. 3 is a control block diagram of a fuel control system showing an embodiment of the present invention, and Fig. 4 is a control block diagram of the boiler. FIG. 3 is a characteristic diagram of fuel control operation at startup. DESCRIPTION OF SYMBOLS 1... Boiler, 2... Water supply pump, 3... Water supply control valve, 4... Water supply control device, 5... Fuel pump, 6... Fuel control valve, 7... Fuel control device, 8... Temperature measurement device, 9... Changeover switch, 10 ... Boiler input command device, 11 ... Adder, 12 ... Water-fuel ratio setting device, 13,
17... Deviation amplifier, 14... Fuel flow meter, 15... Converter, 16... Analog memory, 18... Fuel setting device, 19... Initial setting means.

Claims (1)

[Claims] 1. When in automatic control mode, the fuel flow rate input to the boiler is controlled so as to match a predetermined boiler input command so that the temperature of the steam generated in the boiler increases at a predetermined steam temperature increase rate. , wherein when in manual control mode, the control is performed to match a fuel flow rate command obtained by adding a correction amount for the fuel flow rate to the boiler input command, from the manual control mode to the automatic control mode. A method for controlling a rise in steam temperature, characterized in that when switching, a correction amount of the fuel flow rate included in the fuel flow rate command is canceled so that the fuel flow rate command matches the boiler input command.