JPS644043B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a variable voltage operation control device for a thermal power plant.

Conventional thermal power plants often operate under load at the rated pressure, but in this case, when the load starts to change and the main steam pressure deviation becomes large, there is a method that limits the opening of the turbine control valve. In other words, when you open the turbine control valve to remove the load,
In order to prevent the main steam pressure from dropping and temporarily opening the turbine regulator too much, once the main steam pressure has recovered, the main steam pressure should be adjusted so that the turbine regulator opens only to the point at which the required load is achieved. A method of limiting by deviation is adopted. That is, this is a cooperative control method in which the turbine is controlled based on the response of the boiler (recovery characteristics of the main steam pressure), that is, the opening degree of the turbine control valve is limited.

FIG. 1 shows a schematic configuration diagram of a thermal power plant to which such a cooperative control method is applied.

Liquid fuel such as heavy oil is supplied to the boiler 2 while its flow rate is controlled by a valve 1, and air that helps the combustion of this fuel is supplied to the boiler 2 by a forced draft fan 4 while its flow rate is controlled by an FDF (Force Draft Fan) inlet vane 3.
supplied to Further, water is supplied to the boiler 2 by a water supply pump 5, and the amount of water supplied is controlled by a water supply control valve 6. The feed water sent to the boiler 2 is heated by combustion of fuel, becomes steam, and is supplied to the turbine 8 via the turbine control valve 7. The amount of steam supplied to the turbine 8 is controlled by the control valve 7.
The rotation speed of the turbine 8 is controlled by the rotation speed of the turbine 8. At this time, the main steam pressure on the exit side of the boiler is measured by the pressure detector 10. A generator 9 is connected as a load of the turbine 8, and the power demand (generator output
MW) causes fluctuations in the turbine load.

By the way, when performing variable pressure operation in which the main steam pressure is changed to change the load, if the turbine adjustment valve opening degree is limited by the main steam pressure deviation, there is a drawback that load tracking is poor. The reason is that the main steam pressure deviation at the beginning of a load change is due to the increase in the pressure set value determined by the amount of load change, and the pressure drop caused by opening the turbine control valve to take up the load. If the opening degree of the turbine adjustment valve is limited by this deviation, the change in the opening degree of the turbine adjustment valve will be significantly restricted at the beginning of the load change. As a result, it takes time for the load to change as water and fuel increase and the main steam pressure increases. This means that the load followability is inferior.

An object of the present invention is to relate to a variable voltage operation control device for a thermal power plant that can improve load followability in variable voltage operation.

When performing variable pressure operation, the present invention programs the main steam pressure setting using a load command signal, and at intermediate loads, sets the main steam pressure in proportion to the load, temporarily changing the main steam pressure set value output. It was designed to be delayed.

FIG. 2 is a control block diagram showing an embodiment of the present invention. FIG. 2 shows an example of controlling three valves: a turbine control valve, a water supply control valve, and a fuel control valve.

The turbine control valve 7 is connected to the load command signal circuit 11
The adder 12 subtracts the load command signal (LD) that is the output of the (MWD) from the detection signal of the generator output detector 13 (MW), and the PI (proportional integral) calculator 14 calculates the PI. Controlled by results. This turbine control valve 7 is normally operated at a constant value, for example, 80% opening. On the other hand, the water supply control valve 6 and the fuel control valve 1 are similarly controlled by PI, but the main steam pressure or steam temperature is further added as a control condition. That is, the feed water control valve 6 converts the signal from the function generator 15 into the main steam pressure set value outputted via the first-order lag calculator 16 (not provided in the past) and converts it into the main steam pressure detector 10 using the adder 17. subtract the signal. The result of this subtraction is subjected to a PI calculation in a PI calculator 19, and then added to the load command signal LD in an adder 20 to obtain a boiler input command signal BD. The adder 22 subtracts this boiler input command signal BD from the detected value of the flow rate detector 21 that detects the feed water flow rate, and the result is subjected to PI calculation by the PI calculator 23, and then the valve opening is determined based on the calculation result. Control. On the other hand, the fuel control valve 1 receives the boiler input command signal
This is done by adding the steam temperature control signal to BD to generate the fuel command signal FD. That is,
The adder 2 adds the steam temperature signal of the steam temperature detector 25 from the steam temperature set value output from the function generator 24.
6, perform PI calculation on this using PI calculation unit 27,
This calculation result is added by an adder 28 and a fuel command signal is generated.
Get FD. An adder 29 subtracts the signal from the fuel flow rate detector 30 from the obtained fuel command signal FD. The output of the adder 29 is subjected to PI calculation by a PI calculation unit 31, and the fuel control valve 1 is controlled based on the result of this calculation. In this case, the output signal of the function generator 15 is output in proportion to the load command signal LD.

FIG. 3 is a characteristic diagram showing the relationship between the load, the adjustment valve opening, and the set value of the main steam pressure during variable pressure operation. In the figure, the solid line characteristic indicates the turbine regulating valve opening, and the dotted line characteristic indicates the main steam pressure. When the load is low, that is, when the turbine is started, the turbine control valve is opened (0 to 80%) until the load approaches 30%, for example. At this time, the main steam pressure remains at a relatively low value (for example, 30%) and remains almost constant until the opening of the regulating valve stops (opening of 80%), and then gradually increases until, for example, when the load is 80%. The main steam pressure is set to approximately 80%.

Figure 4 shows 80% load from 50% load during variable voltage operation.
This is the main steam pressure setting value and load target value characteristics when the load is changed at a rate of 3%/min. The desired control can be achieved by maintaining the turbine control valve opening at a set value (TV) of 80% opening and increasing the main steam pressure set value (MPS) in accordance with the load command signal (LD).

Figure 5 shows the main steam pressure set value (MPS), turbine adjustment valve opening change (ATV), and actual main steam pressure (AMP) when the load command signal is changed as shown in Figure 4. This is a characteristic diagram for a conventional configuration, that is, a case without the temporary delay calculator 16 shown in FIG. When changing the load at 3%/min from 50% load, the main steam pressure setting value will change in proportion to the load command signal.
MPS increases, water supply control valve 6 and fuel control valve 1
is controlled in the direction of opening the valve, and the opening degree (ATV) of the turbine control valve 11 is opened as shown in FIG.

Therefore, as shown in Figure 5, the actual main steam pressure
AMP decreases. However, as time passes, the steam pressure gradually recovers as the fuel water supply increases due to the load command signal (LD), and finally reaches the main steam pressure set value MPS. However, the PI calculator 19 returns the main steam pressure deviation (MPS-AMP) to 0.
As a result, fuel and water supply are increased excessively, which causes excessive control to exceed the main steam pressure set value, resulting in meandering control characteristics as shown in FIG.

Although such meandering of the main steam pressure can be reduced by suppressing the rate of change, in reality, a rapid change of about 7%/min is desired.

However, as shown in FIG. 2, by providing the primary lag calculator 16 to delay the main steam pressure set value, as shown in FIG. The output signal DMG is delayed by several minutes (for example, about 1 to 2 minutes). This delay time is selected so that the amount of heat stored in the boiler can be discharged. During the first 1 to 2 minutes of the load change,
Compared to the load increase due to the opening of the turbine control valve, the drop ratio of main steam pressure is small, and the deviation signal (DMS-AMP)
is small, excessive fuel supply by PI calculator 19,
Prevents water supply. The actual main steam pressure AMP changes slowly. As a result, the overresponse of the main steam pressure AMP disappears, and the main steam pressure AMP becomes 1 to 2 minutes behind the set value (MPS). Furthermore, since changes in main steam pressure are stabilized, main steam temperature is also stabilized. In the first-order lag control, the specified pressure is reached at the load change end point (load settling area). In such control, only during load changes, a value slightly different from the specified pressure and the specified turbine adjustment valve opening is taken, resulting in worse than maximum efficiency, but the amount is extremely small and does not pose a problem.

As is clear from the above, according to the present invention, due to the first-order lag control, the turbine control valve has good responsiveness at the beginning of the load change, and during the load change, the fuel and water supply can be stably adjusted, and the boiler side input (water supply, fuel ), it is possible to suppress the excessive response of

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of a thermal power plant;
The figure is a control block diagram showing an embodiment of the present invention.
The figure shows the main steam pressure and turbine control valve opening characteristics with respect to the load in a stable state during variable pressure operation, and Figure 4 shows the characteristics of the main steam pressure and turbine control valve opening during variable pressure operation from 50% load to 80% load.
Main steam pressure set value and load target value characteristic diagram when changing by %/min. Figure 5 is a characteristic diagram showing conventional main steam pressure change. Figure 6 is main steam pressure change and turbine control valve according to the present invention. FIG. 3 is a characteristic diagram showing changes. 1... Fuel control valve, 2... Boiler, 3...
FDF inlet vane, 6... Water supply control valve, 7... Turbine control valve, 8... Turbine, 9... Generator,
11...Load command signal circuit, 12, 17, 20,
22, 26, 28, 29... Adder, 13... Generator output detector, 14, 19, 23, 27, 31
...PI calculator, 15...Function generator, 16...
First-order delay calculator, 21...Water supply flow rate detector, 24
...Function generator, 25 ...Main steam temperature detector, 3
0...Fuel flow rate detector.

Claims (1)

[Scope of Claims] 1. Main steam pressure setting means that outputs a main steam pressure set value signal that follows load changes; and a water supply control valve and a fuel control valve that follow the main steam pressure set value signal to the boiler. a water supply/fuel control means for controlling the opening degree of the turbine; and a turbine control valve control means for controlling the opening degree of the turbine control valve in accordance with load changes. In a variable pressure operation control device for a thermal power plant that performs variable pressure operation by changing the boiler pressure while coordinating the feed water control valve, the fuel control valve, and the turbine regulator valve opening, the main steam pressure set value is set at the beginning of a load change. It is characterized by being provided with a primary delay means for delaying the change in main steam pressure for a predetermined time with respect to a change in the main steam pressure set value that follows a load change by delaying the output of the signal for a predetermined time. A variable voltage operation control device for thermal power plants. 2. The variable voltage operation control device for a thermal power plant according to claim 1, wherein the predetermined time delayed by the primary delay means is a time during which the amount of heat stored in the boiler can be discharged.