JPS6239657B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a combined cycle load control device in which a gas turbine and a steam turbine are coupled to one shaft.

FIG. 1 shows an example of a combined cycle in which a gas turbine and a steam turbine are coupled to one shaft. In the figure, 1 is an air compressor;
2 is a combustor. The high temperature gas at the outlet of the combustor 2 causes the gas turbine 3 to generate mechanical power. Approximately 2/3 of this power becomes the driving force for air compressor 1, and approximately
1/3 is taken out as the electrical output of the generator 4.
However, just by doing the above, the energy of the exhaust gas 5 cannot be used effectively, so
A configuration in which an exhaust heat recovery boiler 6 is provided and a steam turbine cycle is utilized is widely used. That is, the steam turbine 7 is connected to the same shaft as the air compressor 1, the gas turbine 3, and the generator 4, and the steam generated from the exhaust heat recovery boiler 6 is input to the steam turbine 7 to generate larger mechanical power. I have to.
The exhaust gas from the steam turbine 7 is cooled by seawater or the like in a condenser 8 and becomes condensed water. This condensate is pressurized by a condensate water pump 9, the exhaust heat is recovered into a working fluid by an exhaust heat recovery boiler 6, and then enters a steam turbine 7 via a main steam pipe 10 to drive the steam turbine 7. do. Reference numeral 11 indicates a bypass pipe connected to the condenser 8, and reference numeral 12 indicates a bypass regulating valve.The bypass regulating valve 1 is used to prevent steam pressure from increasing due to nowhere for the recovered steam to go due to load interruption, etc.
2 will be opened. In this plant configuration, the inlet air of the air compressor 1 is controlled by an inlet guide vane 13, and the mechanical output of the gas turbine 3 is controlled by a fuel regulating valve. Further, the mechanical output of the steam turbine 7 is controlled by a steam control valve 15. The control of the inlet guide vane 13 of the air compressor 1 is interlocked with the control of the fuel adjustment valve 14, and is controlled to prevent inflow into the surge region of the air compressor 1. Therefore, control of the output of the generator 4 in this plant configuration substantially depends on the control of the fuel adjustment valve 14 and the steam control valve 15. Furthermore, the role of the steam turbine cycle is exclusively to recover the exhaust heat from the gas turbine 3 and use it as output, and in order to efficiently recover it, all the steam generated from the exhaust heat recovery boiler 6 must be properly heated. Generally, the steam control valve 15 is introduced into the steam turbine 7.
is fully open during normal load operation, and active control for load adjustment is performed by the fuel adjustment valve 14.

That is, in the plant configuration shown in FIG. 1, load adjustment is performed on the gas turbine side, that is, by adjusting the fuel supply to the combustor 2, and the steam control valve 15 is kept at a constant opening to efficiently recover exhaust heat. The usual method is to do so.

As a method for making the steam turbine 7 follow the gas turbine 3 by keeping the opening degree of the steam regulating valve 15 substantially constant, a method of placing the steam regulating valve 15 in the main steam pressure control loop can be considered. The amount of steam generated by the exhaust heat recovery boiler 6 is determined by the gas turbine load, so by controlling the pressure setting value by changing the load command, the steam turbine 7 can follow the steam turbine 7 with the opening degree almost constant in each load zone. can be done. However, with this alone, the load follow-up characteristic is determined exclusively by the output response of the gas turbine 3, so a very good load response cannot be expected. If the load response is to be greatly improved, the amount of fuel must be increased or decreased over a wide range, which causes instability in the combustion system.

An object of the present invention is to provide a combined cycle load control device with good load fluctuation characteristics.

The present invention provides a control loop that follows the gas turbine and shifts the pressure set value according to load deviation in the opening control loop of the steam regulating valve in the main steam pressure control system. This makes use of the boiler's stored energy.

FIG. 2 shows a load control system according to an embodiment of the present invention. In the figure, 21 is a fuel control signal, 22 is a steam control valve control signal, 23 is a plurality of gas turbine outlet temperature input signals, and a computing unit 24
calculates the gas turbine inlet temperature by averaging these. The calculator 25 calculates the gas turbine outlet temperature, and its output is combined by a low value priority circuit 27 with a fuel control amount 26 defined by the load request command. That is, the output of the calculator 25 limits the fuel signal, and has the role of limiting the fuel control signal 21 within a safe range.

Reference numeral 28 is a load setting value, and an adder 31 calculates a deviation 30 from the actual generator outlet 29. This deviation 30 is corrected by a load controller 32, and an adder 33 calculates a correction governor free value based on the system frequency deviation. effect) is modified by the signal 34 and becomes the fuel control command 26.

On the other hand, the steam regulating valve control signal 22 is the steam regulating valve 1
This signal 2 is used to control 5.
2 is formed as follows.

According to the load set value 28, the main steam pressure setter 3
5, a main steam pressure setting program is created, and the output at each instant becomes the main steam pressure setting value. In other words, the setting of the main steam pressure is changed depending on the load, resulting in variable pressure operation, and the opening degree of the steam control valve is set efficiently.

The main steam pressure set value 36 is compared with the actual main steam pressure 38 in an adder 37, and the steam control valve control signal 22 is determined based on this deviation. Thereby, the opening degree of the steam control valve 15 is efficiently controlled, and the exhaust heat recovery energy is recovered as the steam turbine output.

The load deviation signal 30 is also controlled by a limit limiter 39 and further modified by a controller 40. The output 41 of the controller 40 serves to shift the pressure setpoint by biasing the steam opening signal. For this reason, the steam control valve 15 is temporarily opened and closed to effectively utilize the boiler heat storage capacity. Therefore, the load response improves in advance of the gas turbine output. Note that the upper and lower limit value limiter 39 is the steam control valve 1
The load deviation signal 30 is controlled so that the opening/closing control is performed within a range close to the fully open state (for example, 100% ± 5%).
This method imposes upper and lower limits on the pressure setting value and limits the shift amount of the pressure setting value to a small amount. As a result, the steam regulating valve 15 does not deviate significantly from the fully open state even when performing opening/closing control, so that the entire plant can be operated efficiently.

Fig. 3 shows the operation of the control system shown in Fig. 2. When the load deviation △p occurs, the steam control valve 15
The overall load response is improved since the control is started in advance.

If we tried to control the load using only gas turn 3, a load deviation would occur and the result would be as shown by the solid line, but since we put the steam control valve in the pressure control loop and shifted the pressure set point due to the load deviation, the load response would be shown as the broken line. Improved as shown in .

FIG. 3 shows the effects of the present invention. As shown in the figure, since the steam control valve starts control in advance when the load deviation Δp occurs, the overall load response is improved. In other words, if you try to control the load using the gas turbine output, a load deviation will occur, as shown by the solid line, but by putting the steam control valve in the pressure control loop and shifting the pressure set value based on the load deviation. , the load response becomes as shown by the broken line, which is good.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an example of a combined cycle, FIG. 2 is a block diagram showing a load control device according to an embodiment of the present invention, and FIG. 3 is a diagram showing load response. 24, 25... Arithmetic unit, 27... Low value priority circuit, 3
2...Load controller, 35...Main steam pressure setting device, 39
...Upper/lower limit controller, 40...controller.

Claims (1)

[Claims] 1. When a load deviation occurs in a load control device for a combined cycle plant in which a gas turbine and a steam turbine are connected to a common shaft,
A control loop is installed in the main steam pressure control loop that guides this load deviation signal to the upper and lower limit value limiters and temporarily shifts the main steam pressure set value by a small amount in response to the load deviation signal that has been limited to the upper and lower limit values. A load control device characterized by: