JPS6329082B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a turbine bypass cooperative control method for a drum boiler, and particularly to a turbine bypass cooperative control method optimal for performing variable pressure operation in a drum boiler.

While once-through boilers require changing the water and fuel to change the steam pressure, drum boilers have the characteristic of being able to change the pressure simply by changing the fuel. Therefore, it is suitable for relatively small-scale systems. Such drum boilers tend to require drum variable pressure operation in order to achieve high efficiency, and in addition, a turbine bypass system tends to be installed in order to shorten startup time.

The main steam pressure in a drum boiler is controlled by a boiler/hollow control method in which a turbine control valve is opened or closed in response to a load command, and the main steam pressure is controlled by changing the fuel flow rate. When variable pressure operation is performed, if the boiler fuel is changed and the boiler is characterized by a large response delay until the main steam pressure changes, the deviation of the main steam pressure will increase, resulting in excessive or insufficient boiler input, and further This will result in larger fluctuations in steam pressure, which will cause the high-pressure turbine bypass valve to open (opening the high-pressure turbine bypass valve during load operation will result in load fluctuations, main steam pressure fluctuations, and temperature fluctuations, so During load operation, the bypass valve must not be opened.Although it has a pressure relief function in the event of an abnormal pressure rise, it should not operate during normal operation.)

Due to the above-mentioned drawbacks, it has not been possible to improve load followability in plants using drum boilers having a turbine bypass system.

An object of the present invention is to provide a drum boiler turbine bypass cooperative control method that can improve load followability in a plant having a turbine bypass system using a drum boiler.

The present invention sets a limit value to prevent the turbine regulating valve opening from opening or closing too much beyond the specified limit when the load changes, thereby preventing the main steam pressure from rising or falling, and preventing too much or too little fuel. A limit value is set for the fuel command.

It is necessary to control the fuel command in this way in variable pressure operation, so for example, when lowering the load, the main steam pressure setting is lowered.
On the other hand, since the turbine control valve is closed, the actual main steam pressure increases. This is because, as a result, the pressure deviation becomes large, and there is a possibility that the amount of fuel becomes insufficient.

FIG. 1 is a schematic diagram of a thermal power plant using a drum boiler and a turbine bypass system to which the present invention is applied.

Basically, drum boiler 1, high pressure turbine (HP) 2, low/medium pressure turbine 3, generator (G)
Consists of 4. The drum boiler 1 consists of a superheater 5, a reheater 6, and a boiler drum 7, and the boiler drum 7 is heated by fuel (heavy oil, etc.) sent through a fuel flow control valve (FF-CV) 8 to generate steam. . The generated steam is superheated in the superheater 5 and then sent to the high pressure turbine 2 side. The reheater 6 superheats the exhaust steam that has been used in the high pressure turbine 2 and whose temperature has decreased, and sends it to the low/intermediate pressure turbine (LP/IP) 3 side. A turbine bypass valve (HPBV) 10 is connected in parallel with the high pressure turbine 2 . This turbine bypass valve 10 is used when starting up the plant and is used to speed up the start-up. A main stop valve (MSV) 11 and a turbine control valve (CV) 12 are provided between the superheater 5 and the high-pressure turbine 2, and supply and stop steam to the turbine and control the amount of steam. In addition, a reheat stop valve (RSV) 13 and an intercept valve (ICV) 14 are provided between the reheater 6 and the low/intermediate pressure turbine 3 to control the steam supplied to the low/intermediate pressure turbine 3. It's in control. Each of the valves described above may be operated independently, or the main blocking valve 11
The reheat stop valve 13, the turbine control valve 12, and the intercept valve 14 may be operated in conjunction with each other. A main steam pressure transmitter (PX) 15, which is used as one of the control signals and detects the main steam pressure, is provided on the inlet side of the main shutoff valve 11. Further, water is supplied to the boiler drum 7 by a water supply pump 16 via a water supply flow control valve 9 .

The output of the drum boiler 1, that is, the steam flow rate, is controlled by opening and closing a turbine control valve 12. At the time of starting, the main stop valve 11, the reheat stop valve 13, the control valve 12, and the intercept valve 14 are each closed. First, the turbine bypass valve 10 is opened, and the steam generated in the boiler 1 is bypassed through the high-pressure turbine 2. Next, the turbine bypass valve 10 is closed, the main stop valve 11 and the reheat stop valve 13 are fully opened, and the turbine control valve 12 and intercept valve 14 are gradually opened. Through this operation, steam is supplied to the high-pressure turbine 2, and the steam exiting the reheater 6 is supplied to the low- and intermediate-pressure turbines 3, thereby driving both turbines. As the turbine rotates, the connected generator 4 is driven to rotate. Generator output or load is proportional to the steam flow rate entering each turbine. In addition, the turbine bypass valve 10 can be opened at startup, and
It is opened when the main steam pressure rises above the set value and is used to prevent the main steam pressure from rising.

FIG. 2 is a pattern diagram of the pressure changing movement, showing the turbine control valve opening degree and the main steam pressure change with respect to load changes. The area where the main steam pressure shows a constant value under low load, as shown by the dotted line, is the startup area.
The region where the turbine regulating valve opening degree is constant is the variable pressure operation region, which is indicated by a solid line. As is clear from FIG. 2, it can be seen that the load, main steam pressure, and turbine regulating valve opening are determined as set values.

FIG. 3 is a block diagram showing an embodiment of the present invention. The figure shows an example in which each of the turbine control valve 12, the fuel flow control valve 8, and the high pressure bypass valve 10 is controlled.

The load command signal (MWD) 31 is sent to the adder 32, and after being added to the output of the output detector (MW) 33 provided in the generator 4, P+
The signal is sent to the I calculator 34, where proportional and integral calculations are performed. The output signal of this P+I calculator 34 becomes an opening command for the turbine control valve 12. Upper and lower limit limiters 35 impose upper and lower limits on this opening command, and the setting range thereof is determined by the output signal of a function generator (FX) 36 based on the load command signal 1. This setting range is determined by the voltage transformation pattern shown in FIG.

Next, the fuel flow regulating valve 8 is controlled as follows. An adder 38 adds the output signal of the main steam pressure transmitter 15 and the output signal (preceding transmission) of the function generator 37, which generates the main steam pattern based on the load command signal 1, and calculates the fuel target. The value is calculated. Proportional and integral calculations of this target value are performed by the P+I calculator 39, and addition with the fuel command is performed by the adder 40. The fuel command is issued by converting the load command signal 1 by a function generator 41. It is assumed that the pattern of the function generator 37 matches the dotted line characteristics in FIG. When changing the load during variable pressure operation, the pressure set value and the actual pressure response (the pressure response resulting from the opening/closing operation of the turbine control valve) are reversed, resulting in a large pressure deviation and an excessive (under) command. Therefore, a limit is placed on the output of the adder 40, and this limit is performed by an upper/lower limiter 42. This limiter set value is determined by the function generator 43 based on the load command signal 1. The pattern of the function generator 43 is determined by calculating the relationship between load and fuel so that the boiler uses economical fuel. An adder 45 adds the actual fuel flow value, which is the output signal of the fuel flow transmitter (FF) 44, to the fuel command obtained by the upper/lower limiter 42, and a P+I calculator 46 calculates the proportional value. - Performs integration and controls the fuel flow control valve 8.

Further, the control of the high pressure bypass valve 10 is as follows. The output signal of the function generator 37 and the output of the bias setting device 47 are added by an adder 48, and the addition result and the main steam pressure transmitter 15 are added by the adder 4.
9, and the result is proportionally calculated by the P+I calculator 50.
The high pressure bypass valve 10 is controlled by performing integral calculations. In this way, the control operation of the high-pressure turbine bypass valve uses the set value of the main steam pressure as the set value of the main steam pressure plus a constant bias.
Therefore, if the main steam pressure is controlled within a certain range of fluctuations by the fuel, it will remain fully closed.

FIGS. 4A, B, C, and D are explanatory diagrams showing the responsiveness when the load is lowered according to the present invention. Figure 4A shows the load change, Figure 4B shows the turbine adjustment valve opening,
FIG. 4C shows changes in main steam pressure, and FIG. 4D shows changes in fuel flow rate. In each figure, the solid line indicates the set value (target value), and the dotted line indicates the response when the upper and lower limiters 35 and 42 are not provided (that is, in the conventional case). Further, the shaded area indicates the setting range of the limiter. This limiter setting is set to a value that prevents the turbine bypass valve from opening. When the load is reduced from 80% to 40% as shown in FIG. 4A, the turbine regulating valve opening and main steam pressure exhibit ideal changes in accordance with the characteristics shown in FIG. 2. On the other hand, in the conventional case, a sudden change occurs as shown by the dotted line, and the load followability deteriorates.

As is clear from the above, according to the present invention, load followability can be improved even in a plant with a drum boiler and a turbine bypass.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of a thermal power plant using a drum boiler and a turbine bypass system.
Figure 2 is a pattern diagram showing an example of variable voltage operation, Figure 3
The figure is a block diagram showing an embodiment of the present invention, and FIGS. 4A, B, C, and D are explanatory diagrams showing the responsiveness of the present invention and the conventional method when the load drops. 1...Drum boiler, 2...High pressure turbine, 3...
Low/medium pressure turbine, 4... Generator, 5... Superheater, 6
... Reheater, 8... Fuel flow control valve, 10... Turbine bypass valve, 12... Turbine control valve, 13... Intercept valve, 15... Main steam pressure transmitter, 32, 3
8, 40, 45... Adder, 33... Generator output detector, 34, 39, 46... P+I calculator, 35, 4
2...Upper/lower limiter, 36, 37, 41, 43
...Function generator, 44...Fuel flow rate transmitter.

Claims (1)

[Claims] 1. In a control method for performing variable pressure operation of a thermal power plant in which a turbine bypass system is added to a drum boiler while coordinating the control of a turbine control valve, a fuel flow control valve, and a turbine bypass valve based on a load command. , the drum is characterized in that the turbine regulating valve opening is limited within a specified opening range programmed based on the load command, and the fuel flow rate is limited within a specified fuel amount range programmed based on the load command. Boiler turbine bypass cooperative control method.