JPS59115406A - Load controller of composite cycle power generating plant - Google Patents

Abstract

PURPOSE:To prevent the occurrence of hunting due to excessive control, by a method wherein, in a composite cycle power generating plant, a change in the output of a steam turbine as the result of a change in the flow rate of fuel to a gas turbine is previously detected, and control is effected in anticipation of a change in output. CONSTITUTION:An exhaust gas temperature detector 21 for a gas turbine is installed in a gas turbine 9. A signal from the temperature detector 21 is fed to a forecast computer 22. The forecast computer 22 consists of an imperfect differential computer including a wasteful time element, and through receipt of a signal from the detector 21, it forecasts a change in the output of a steam turbine 13 resulting from a change in fuel. In this case, a wasteful time is determined based on the delay of a waste heat recovery boiler 11, the gain of an imperfect differentiator is determined by the ratio of the output of the gas turbine 9 to that of the steam turbine 13, and the time constant thereof is determined by the time constant of the output of the steam turbine. An adder 23 is installed between a load detector 15 and a subtractor 17 to add a forecast computed value to a feedback system. Thus, a load control system is controlled according to a value to which a forecast value is also added.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a load control device for a combined cycle power plant (hereinafter referred to as a combined cycle plant) using a gas turbine and a steam turbine.

[Technical background of the invention] A combined cycle plant is a system in which fuel is combusted in a gas turbine, the exhaust heat is recovered in an exhaust heat recovery boiler to generate steam, and the steam is used to drive a steam turbine. be.

Therefore, the output of a combined cycle plant depends on the fuel of the gas turbine, and by controlling this fuel, the output can be controlled. Combined cycle plants can be roughly divided into single-shaft types in which a gas turbine, steam turbine, and generator are arranged on one shaft, and multi-shaft types in which the gas turbine and steam turbine are arranged separately on separate shafts.

A load control device for such a combined cycle plant will be described, and in the following explanation, a single-shaft type combined cycle plant will be used as an example. Figure 1 shows an overview of a conventional load control device.

In FIG. 1, output control of the gas turbine 9 will be described first. A gear setting signal from a speed setter 1 is applied to a subtracter 2. On the other hand, the rotation speed detection signals of the gas turbine 9 , the steam turbine 13 , and the five power generators 10 are fed back to the subtractor 2 from the rotation speed detector 6 provided in the compressor 8 . In this case, the rotation speeds of the gas turbine 9, the steam turbine 13, and the generator 10 are the same because this plant is a single-shaft type. The subtracter 2 calculates the deviation between the speed setting value and the feedback detection value, and outputs the deviation signal to the operational amplifier 3. The operational amplifier 3 performs a "proportional" or "proportional integral" calculation based on the input deviation signal, and sends the calculated value to the fuel regulating valve 5 via the servo amplifier 4 to control its opening. This opening adjustment controls the fuel flow rate supplied to the combustor 7 of the gas turbine 9, and as a result, the output of the gas turbine 9 is controlled to match the speed setting value.

Next, output control of the steam turbine 13 will be described. The enthalpy of steam supplied from the exhaust heat recovery boiler 11 to the steam turbine 13 is determined by the enthalpy of the exhaust gas from the gas turbine 9. Therefore, by keeping the steam control valve 12 fully open or at a constant opening degree, the turbine output is uniquely determined in relation to the degree of vacuum of the condenser 14.

For this reason, the output to the power system is a value obtained by multiplying the sum of the outputs of the gas turbine 9 and the steam turbine 13 by the efficiency of the generator 10. This is because the generator 10 is uniaxially connected to the gas turbine 9 and the steam turbine 13.

To control the load (am output), the subtracter 17 calculates the deviation between the load setting signal from the load setting device 16 and the actual load detection signal from the load detector 15, and the calculated deviation signal is sent to the speed setting device l. This is done by controlling the setting device 1 by giving the following information. As a result, control can be performed so that the deviation is finally equal to zero, that is, the load becomes equal to the load setting value.

[Problems with background technology]

In the combined cycle plant described above, there is a problem in that the output response of the steam turbine 13 is delayed while the output response of the gas turbine 9 is quick.

This is because the output of the gas turbine 9 changes directly in response to changes in the fuel flow rate, whereas the output of the steam turbine 13 changes from "change in exhaust gas energy from the gas turbine" → "steam volume of the exhaust heat recovery boiler" → " This is because there is a large time constant in energy transmission due to the intervention of a system called "steam turbine output", and as a result, there is a time delay before the steam turbine output responds to changes in fuel flow rate. Note that, in general, the ratio between the gas turbine output and the steam turbine output is characterized as being approximately constant. This state is shown in FIG.

As shown in FIG. 2, the temporal change 19 in the gas turbine output with respect to the step change 18 in the fuel flow rate results in a TGT time lag, but the steam turbine output 20 results in a TNT time lag.6TGT is a few seconds. order, and TST is approximately 1
It is a phase change. In FIG. 2, the shaded characteristic is the output response of the combined cycle plant in open loop to a step change in fuel amount.

As a result of these characteristics, there is a long time delay when controlling the output of a complex plant to match the required load.
The steam turbine output 20 generated with rs'r causes problems such as excessive control and output hunting.

[Object of the Invention] Therefore, the present invention solves the above-mentioned problems in complex plants, and provides load control that can improve the stability of control operation during transient control, that is, control operation in response to load requests. The purpose is to provide the device to Buddha.

[Summary of the Invention] In order to achieve the above object, a load control method according to the present invention predicts a change in output of a steam turbine that may occur in the future based on the change in output of a gas turbine, and adjusts gas turbine fuel based on the predicted value. It is characterized by suppressive control. This is because gas turbine fuel determines the output of the entire combined cycle plant. [Embodiments of the Invention] Hereinafter, with reference to the drawings, load control of a combined cycle plant according to the present invention will be explained. An example of the i11 device will be described. FIG. 3 shows a first example of a load control device according to the present invention, and FIG. 5 shows a second example. In FIGS. 3 and 5, parts that overlap those in FIG. 1 are given the same reference numerals and will be described below.

Configuration In FIG. 3, the gas turbine 9 is provided with a gas turbine exhaust gas temperature detector 21. As shown in FIG.

This gas turbine exhaust gas temperature detector 21 is for detecting a signal related to a change in the output of the steam turbine 13, and is used to predict a change in the output of the steam turbine 13 that will occur in the future due to a change in fuel.

A detection signal from this exhaust gas temperature detector 21 is sent to a prediction calculator 22.

The prediction calculator 22 is composed of an incomplete differential calculator including a dead time controller 22, and receives a detection signal from the exhaust gas temperature detector 21 to predict the output change of the steam turbine 3 due to a change in fuel. The calculation result is sent to the adder 23 and added to the load control feedback loop of the combined cycle plant.

Here, the dead time is determined based on the delay of the exhaust heat recovery boiler 11, the gain of the incomplete differentiator is determined by the output ratio of the gas turbine 9 and the steam turbine 13, and its time constant is the time constant of the steam turbine output (the Figure 2, TST).

The adder 23 is located between the load detector 15 and the subtracter 17, and adds the predicted calculated value to the feedback system. Therefore, the load-side control system is controlled not only by the detected amount from the load detector 15 but also by the predicted value.

Operation Next, the control operation of the load control device according to the present invention will be explained. First, to give an overview, when a load target value is given from the load setter 16, the fuel flow rate to the gas turbine 9 is controlled according to the deviation between the load target value and the actual load detection value. The fuel of the gas turbine 9 flows in the direction of the obtained deviation (
+ or -), and as a result, the output of the gas turbine 9 increases or decreases. The change in the output of the steam turbine 13 that will occur in the future due to the change in the output of the gas turbine 9 is captured in advance by the change in exhaust gas temperature, predicted by the prediction calculator 22, and the predicted value is added to the actual load via the adder 23. By increasing or decreasing gas turbine fuel at an early stage, the final output of the combined cycle plant (=gas turbine output and steam turbine output) is stably controlled to match the target load.

The above will be described in more detail with reference to FIG. In FIG. 4, when the load command 1B changes, the turbine output 19 starts to increase in response, but just before the steam turbine output 20 is generated, the actual load feedback value 24
Since the predicted calculation value 25 is added to the subtracter 17, the feedback value given to the subtracter 17 becomes 24A as a whole, and is controlled by this feedback value 24A. As a result, since the fuel to the gas turbine 9 is suppressed, the output response of the gas turbine 9 takes the form shown in 19. In this way, since the fuel is throttled, the overall output of the combined cycle plant changes cleanly as shown in 26, preventing excessive control due to response delay and enabling stable load control.

Next, a second example shown in FIG. 5 will be explained. In this second example, the drum-generated steam pressure value of the exhaust heat recovery boiler 11 is used as a parameter for predicting the output of the steam turbine 13 instead of the exhaust gas depth shown in FIG. Therefore, the exhaust heat recovery boiler 11 is provided with a drum-generated steam pressure detector (hereinafter referred to as a pressure detector) 27. The pressure detection signal from the pressure detector 27 is input to the prediction calculator n, which is thereafter controlled in the same manner as in the case of FIG. Note that in this case, the dead time of the prediction calculator 22 becomes a considerably small value.

Furthermore, the load command value from the load setter 16 can be given to the prediction calculator 22 as a final parameter for the prediction calculation, as shown by a broken line 28 in FIG.

Furthermore, although the above embodiment has been described as adding the predicted calculated value to the load feedback value, the predicted calculated value may be given to the load command value from the load setting device 16 via a subtractor. The rest of the configuration is the same as described above, so a description thereof will be omitted.

〔Effect of the invention〕

As described above, according to the present invention, in a combined cycle plant, changes in the steam turbine output that will occur in the future due to changes in the fuel flow rate to the gas turbine are detected in advance, and the output is controlled in anticipation of the output changes in advance. Therefore, control stability can be improved, such as preventing output hunting due to excessive control.

[Brief explanation of drawings]

Figure 1 is a block diagram showing an example of the configuration of a load control device for a conventional combined cycle plant. Figure 2 shows the gas turbine output, steam turbine output, and output as a combined cycle plant in response to changes in gas turbine fuel in a conventional combined cycle plant. 3 is a block diagram showing a first configuration example of the load control device for a combined cycle plant according to the present invention, and FIG. 4 is an explanatory diagram showing the oven loop characteristics of Explanatory diagram showing each output response characteristic. FIG. 5 is a block diagram showing a second configuration example of a load control device for a combined cycle plant according to the present invention. ! ...Speed setter 2...Subtractor 3...
Operational amplifier 4... Servo booster 5... Fuel adjustment valve 6... Rotation speed detector 7... Gas turbine combustor 8... Compressor 9... Gas turbine 10... Starting am11 ...Exhaust heat recovery boiler
12...Steam control valve 13...Steam turbine
14... Condenser 15... Load detector 16.
...Load setter 17...Subtractor 21...
・Gas turbine exhaust gas 22...prediction calculator
Temperature change detector 23... adder

Claims (1)

[Claims] 1. In a load control device for a combined cycle power plant that drives a steam turbine with steam generated using exhaust heat of a gas turbine, an output change that detects a signal related to a change in the output of the steam turbine. a detector, a prediction calculator that predicts a change in the output of the steam turbine based on the detection signal, and an adder that adds the calculation result signal to a feedback loop or a load setting loop of the load detection amount of the load control device. A load control device for a combined cycle power plant, characterized by comprising: 2. A load control device for a combined cycle power plant according to claim 1, wherein the signal related to the output change of the steam turbine is a temperature change of the exhaust gas of the gas turbine. 3. % Permissible The device according to claim 1, wherein the signal related to the output change of the steam turbine is a drum-generated steam pressure of an exhaust heat recovery boiler of the gas turbine. load control device. 4. A load control device for a combined cycle power generation plant, wherein the device according to claim 1, wherein the signal related to the change in output of the steam turbine is a load command value of the load control device. . 5.Claims 1, 2, and 3 (4)
2. A load control device for a combined cycle power generation plant, wherein the prediction calculator is an incomplete differential calculator having a dead time element.