JPS6161002B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method for automatically starting a boiler in a steam power generation plant, and its purpose is to provide a means for automatically preventing a drop in main steam temperature that may occur during the startup process of a steam power generation plant. The object of the present invention is to obtain a method for automatically starting a boiler that can completely automatically start the boiler properly by adding a new feature.

Boiler startup in large-capacity steam power plants is generally automated, and an example of a control system diagram is shown in FIG. In the figure, 1 is the boiler, 2
is a turbine, 3 is a condenser, 4 is a feed water pump, 5 is a main steam control valve, and 6 is a generator. On the other hand, the control system includes a central control panel 7 that is monitored and operated by the operator.
It consists of a unit control section 8 that controls load settings, etc., a turbine governor 9, an automatic starting device 10 having a computer system, a boiler control section 11, and the like. Each part of these control systems is interconnected,
The entire plant is automatically controlled from startup to steady operation based on central power supply instructions. Although the overall control system is well known and will not be described here, the method for starting the boiler, which is the subject of the present invention, will be explained as follows. Figure 2 shows the main parts of Figure 1 in more detail.
2 and 13 are a low temperature superheater and a high temperature superheater installed in the boiler 1, 14 is a flash tank, 1
5 and 16 are feed water heaters, and 17 is a deaerator. Also, low temperature superheater 12 (hereinafter referred to as low temperature SH)
and high temperature superheater 13 (hereinafter referred to as high temperature SH)
There is a superheater stop valve 18 and a superheater pressure reducing valve 19 between the
(hereinafter referred to as SH pressure reducing valve) are inserted in parallel, while a superheater bypass valve 20 is inserted between the flash tank 14 and the inlet and outlet sides of each superheater 12 and 13 as shown in the figure. , a steam monitor valve 21, and a superheater vent valve 22 are inserted. The startup of the boiler proceeds according to a predetermined program. The program control steps are: first, clean up of the low pressure system → system water circulation before boiler ignition via flash tank 14 → boiler ignition and start of deaeration → boiler heating circulation → ventilation to high temperature SH 13 and main steam pipe When each step such as warming progresses and the steam conditions of the main steam are established, the steam in the flash tank 14 is then used to ventilate the turbine 2 and start increasing the speed of the turbine.The generator is also synchronously turned on and the turbine 2 is the initial load. Next, when the temperature reaches a predetermined temperature at which the enthalpy of the outlet fluid of the low-temperature SH 12 becomes equal to the enthalpy of the steam generated in the flash tank, the SH pressure reducing valve 19 begins to open and enters the main steam pressure control mode. After that, the ventilation from the flash tank 14 is stopped, and the opening degree of the regulating valve 5 is set and maintained at a certain opening degree, for example, about 20%, according to a request from the boiler side, by a command from the governor 9.

After that, in order to increase the boiler pressure to the rated value while keeping the opening degree of the regulating valve constant, the load setting device (details of which will be described later) and the load change rate setting device are used to increase the boiler pressure to the rated value, based on the load request signal given via the governor 9. Then, the SH pressure reducing valve 19 is gradually opened toward full opening, and as a result, the load on the turbine is increased to the output corresponding to when the SH pressure reducing valve 19 is fully opened. In the next step, the SH stop valve 18 is opened, and from then on, the load request signal is returned to the main steam control valve 5, and the load is increased to a predetermined target load by operating the control valve. The startup ends here, and the subsequent operation is taken over by the steady operation control system.

By the way, in the process of gradually opening the SH pressure reducing valve 19 toward full opening when starting the boiler described above, it is necessary that the outlet steam temperature of the low-temperature SH 12 is maintained at a specified temperature or higher. Otherwise, the main steam conditions will not be appropriate and the operation of the turbine will be affected. However, during the startup process before steady operation of the boiler is established, transient unstable factors such as insufficient heat capacity of low-temperature SH12 cause SH
In the middle of opening the control valve 19, the superheating of the steam cannot be followed, and a phenomenon often occurs in which the outlet steam temperature of the low-temperature SH 12 drops to a temperature lower than the specified value. The timing at which such a phenomenon occurs is unique to each boiler, and occurs under approximately the same conditions each time it is started. However, in the past, no special consideration was given to the above-mentioned temperature drop in the operation control system, and each time the boiler was started, the operator would manually switch the SH pressure reducing valve 19 halfway open and then adjust the valve opening. hold temporarily,
Currently, the operation is switched to automatic mode again after waiting for the heat capacity of the low-temperature SH12 to rise sufficiently. This means that the advantages of the automatic startup method are not fully utilized, causing inconvenience in driving operations, and a solution to this problem is desired.

In view of this point, the present invention attempts to provide a solution to the above-mentioned problems that occur when starting a boiler, and the automatic boiler starting method of the present invention will be described below based on several embodiments.

First, in FIG. 3, 23 is a load setting device provided in the turbine governor 9, and 24 is a load change rate setting device. As is well known, to set the load such as the initial load mentioned above and the subsequent load increase to the output equivalent to fully opening the SH pressure reducing valve, a command is given to the load setting device 23 to increase the load to the set value. This is done by On the other hand, load change rate setting device 2
4, a mode such as cold start C or hot start H is selected by the operator when starting the power plant depending on the situation of the power plant and the period of suspension of operation. By the way, in the present invention, a setting stage 0 is provided which provides a mode in which the load change rate is zero, based on an embodiment described later. The load change rate setter 24 adds a limit to the load increase rate by mode selection to the set value set by the load setter 23, and outputs a load increase command signal up to the set output at the selected load change rate. S.H.
It is applied to the boiler control system including the pressure reducing valve 19 or the main steam control valve. Note that the reference numeral 25 indicates an output detector of the generator 6, and the reference numeral 26 indicates a steam temperature detector provided on the outlet side of the low temperature SH 12.

By the way, according to the boiler automatic starting method of the present invention, in the process of increasing the load by gradually opening the SH pressure reducing valve 19 until it is fully open while keeping the opening degree of the regulating valve 5 constant after taking the initial load upon starting, In the middle of this process, the progress of the opening command signal to the SH pressure reducing valve 19 is temporarily interrupted and stopped by automatic control means such as program control, and the valve opening is maintained in that state. is set. By setting this valve opening holding step, it is possible to sufficiently increase the amount of heat held in the low temperature SH12 during this step time, and the outlet steam temperature of the low temperature SH12 drops below the specified value during the opening operation of the SH pressure reducing valve. It is possible to prevent the boiler from dropping and to fully automatically start the boiler appropriately.

Next, some embodiments of automatic control means for setting the valve opening holding step of the SH pressure reducing valve described above will be described. First, in the first embodiment, the load setter 23 described above in FIG. 3 is automatically program-controlled in accordance with the program shown in FIG. That is, after the initial load is taken, the load increase command signal set by the load setting device 23 is divided into two stages and set. First, the load setter 23 is adjusted to a certain specified output value corresponding to a predetermined halfway opening of the SH pressure reducing valve 19.
When the load setting device 23 is operated, the load setting device 23 is temporarily stopped. Thereafter, from the time when the actual output value of the generator 6 increases to the specified output value with a time delay while being regulated by the selection mode of the load change rate setting device 24, the retained heat of the low-temperature SH 12 is further increased by the subsequent SH pressure reducing valve. 19
The load setter 23 is held as it is for a specified time (for example, about 5 to 10 minutes) required for the load to be sufficiently increased to follow the opening operation of the load setter 23. Next, when the specified holding time has elapsed, the load setter 23 is again operated to increase the set value to an output corresponding to fully opening the SH pressure reducing valve 19. The above operations are automatically program-controlled according to a preset program.

In the second embodiment, a specially provided setting stage 0 with a zero change rate is used in the load change rate setter 24 shown in FIG. Further, unlike the previous embodiment, the load setting device 23 sets the load to an output value corresponding to fully opening the SH pressure reducing valve 19 from the beginning. This load setting value is determined by the valve opening command signal SH at a predetermined rate of change specified by the mode selected by the load change rate setting device 24.
This is applied to the pressure reducing valve 19, but as in the previous embodiment, when the specified output value at a predetermined intermediate stage is reached, the load change rate setting is automatically changed to zero change rate stage 0. Can be switched. Due to this
The SH pressure reducing valve 19 is held at an intermediate opening position. The valve opening degree holding step is held for a specified time, and when this time has elapsed, the load change rate setting device 24 is returned from the zero setting stage to the initially selected mode setting stage. The above operations are automatically performed under automatic program control. Note that in the first and second embodiments, the generator output detector 2
The detected value of step 5 is used as a control input signal, and the control is controlled so that the valve opening holding step is performed when the output reaches a predetermined specified value.
Since it is proportional to the opening degree of the SH pressure reducing valve, it is also possible to use the valve opening degree of the SH pressure reducing valve 19 as it is as a control input signal to control switching to the valve opening degree holding step. In addition, the specified output value that determines the timing of switching to the valve opening holding step is determined based on test run data for each boiler to be operated.
It is determined at which output point the SH12 outlet steam temperature decrease phenomenon occurs, and based on this data.

According to yet another embodiment, as shown in FIG. 3, a steam temperature detector 26 is installed on the outlet side of the low-temperature SH 12, and the detected value is used as a control input signal to control the steam temperature at that part to a specified temperature. to avoid further decline
The valve opening degree holding step operation is performed by means for automatically controlling the valve opening degree of the SH pressure reducing valve 19 at intermediate stages. In addition, when carrying out this embodiment, if the steam temperature detection value is to be transferred to the valve opening holding step as a control input signal, the load setting device 2 is of course
3. The load change rate setting device 24 receives the control signal from the steam temperature detector and is temporarily suspended while maintaining the valve opening command signal at that point.

As described above, according to the boiler automatic startup method of the present invention, the steam temperature at the outlet of the low-temperature superheater can be raised to a specified value or higher by the automatic control means without requiring any frequent manual operations by the operator when starting the boiler. The boiler can be maintained and the boiler can be started in a fully automatic manner, which provides excellent operational effects.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the control system of a steam power generation plant that is the subject of the present invention, Fig. 2 is a detailed view of the main parts in Fig. 1, and Fig. 3 is a control system for the superheater pressure reducing valve for implementing the present invention. FIG. 4 is a control program diagram showing a system according to an embodiment of the present invention. 1: Boiler, 2: Turbine, 5: Main steam control valve, 6: Generator, 7: Central control panel, 8: Unit control section, 9: Turbine governor, 10: Automatic start device, 11: Boiler control section, 12 :Low temperature superheater, 1
3: High temperature superheater, 18: Superheater stop valve, 19: Superheater pressure reducing valve, 23: Load setting device, 24: Load change rate setting device, 25: Output detector, 26: Main steam temperature detector.

Claims (1)

[Scope of Claims] 1. A superheater pressure reducing valve is provided between a low temperature superheater and a high temperature superheater in a boiler, and after the main steam is vented to the turbine during the startup process of the boiler to take the initial load,
The load is increased by gradually opening the superheater pressure reducing valve until it is fully open based on a command signal specified by a load setting device and a load change rate setting device while keeping the opening degree of the main steam control valve constant. In the boiler automatic startup method, when the superheater pressure reducing valve is fully opened, an automatic control means is used to prevent the main steam temperature at the outlet of the low-temperature superheater from dropping below the specified temperature. A method for automatically starting a boiler in a steam power generation plant, characterized in that a valve opening holding step is set in which the progress of an opening command signal given to a pressure reducing valve is temporarily interrupted and the valve opening is held in that state. 2. In the boiler automatic start-up method according to claim 1, the valve opening degree holding step of the superheater pressure reducing valve adjusts the command value given to the superheater pressure reducing valve from the load setting device at a predetermined intermediate stage. It is characterized by being set by an automatic program control means to hold the specified output value for a specified holding time, and to increase the output command value again to the output command value corresponding to fully opening the superheater pressure reducing valve after the specified holding time has elapsed. A method for automatically starting a boiler in a steam power generation plant. 3. In the method for automatically starting a boiler according to claim 1, the step of maintaining the opening degree of the superheater pressure reducing valve includes providing a setting stage for a zero change rate in the load change rate setting device, and setting the load change rate at the beginning. The point in time when the turbine output, which increases while being limited to a predetermined load change rate, reaches the specified output at a predetermined intermediate stage under the condition that the command value of the setting device is set to the output value equivalent to fully opening the superheater pressure reducing valve. The load change rate setting device is switched to the zero setting command for a specified holding time, the valve opening is maintained as it is, and after the specified holding time has elapsed, the load change rate setting device is set again to the specified load change rate command. A method for automatically starting a boiler in a steam power plant, characterized in that the method is as follows. 4. In the boiler automatic start-up method according to claim 1, the valve opening degree holding step of the superheater pressure reducing valve uses the main steam temperature at the outlet side of the low-temperature superheater as a control input signal to reduce the main steam temperature to a predetermined temperature or below. 1. A method for automatically starting a boiler in a steam power plant, characterized in that the opening degree of a superheater pressure reducing valve is set by an automatic control means that regulates and controls the degree of opening of a superheater pressure reducing valve in the middle of the process to fully open so as not to decrease the opening degree of a superheater pressure reducing valve.