JPS6149491B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a combined cycle power generation plant in which a gas turbine plant generates electricity, and its exhaust gas is guided to an exhaust heat recovery boiler to generate high-pressure steam, and this steam drives a steam turbine to generate electricity. Regarding the control method.

If the amount of fuel in the gas turbine combustor is increased or decreased due to fluctuations in plant load, the steam pressure generated in the boiler will fluctuate, which is not desirable in a constant pressure operating plant. For this reason, conventionally, when pressure fluctuations become large, the first method switches the fuel amount control from load control to steam pressure control, and the second method controls the deviation of the steam turbine rotation speed that occurs due to steam pressure fluctuations. Measures were taken to detect this and operate the steam control valve using a regulating material to control the steam pressure.

For this reason, there was a drawback that output and steam pressure could not be controlled independently. Also, in the first method, either the output or the steam pressure will not be controlled at a certain point in time. Furthermore, in the second method, the correction operation is performed only after the pressure fluctuation appears as a change in the rotational speed, which causes a time delay and makes it difficult to improve controllability.

The object of the present invention is to provide a control system for a combined cycle power plant that independently controls plant output and steam output and has good controllability.

In a combined cycle power plant using a waste heat boiler, the amount of change in the flow rate, pressure, and temperature of steam generated in the heat generating boiler is F(s), P(s),
T(s), where s is determined by the Laplace operator, the amount of change in the fuel flow rate of the gas turbine combustor B(s), and the amount of change in the opening of the steam turbine control valve C(s), and the transmission is as follows. It can be expressed as a functional expression.

F(s)=Gfc(s)・B(s) +Gfc(s)・C(s)...(1) P(s)=Gpb(s)・B(s) +GPc(s)・C(s ) ...(2) T(s) = Gtb(s)・B(s) +Gtc(s)・C(s) ...(3) However, Gfb(s) is the transfer to steam flow rate due to fuel flow rate change The function, Gfc(s) is the transfer function to the steam flow rate due to the amount of change in the opening of the steam turbine control valve,
GPb(s) is a transfer function to steam pressure due to a change in fuel flow rate, GPc(s) is a transfer function to steam pressure due to a change in steam turbine regulator valve opening, and Gtb(s) is a transfer function to steam temperature due to a change in fuel flow rate. Transfer function, Gtc
(s) is a transfer function to the steam temperature due to the amount of change in the opening degree of the steam turbine control valve.

Therefore, in order to achieve constant pressure operation regardless of the fuel flow rate in the gas turbine, the amount of change in steam pressure p(s) = 0, that is, the amount of change in steam turbine regulator valve opening C(s) and During the fuel flow rate change B(s) of the gas turbine combustor, C(s)=G(s)・B(s) in equation (4), where G(s)=-Gpb(s)/Gpc(s) )...
(4) There should be a relationship. In other words, by converting the fuel flow rate signal into the steam turbine control valve opening signal through the element of the transfer characteristic G(s), constant pressure operation in which the steam pressure is kept constant can be realized.

For G(s), for example, Gpb(s)=
A/1+T ₁ s, Gpc(s)=1+T ₂ s/1+T ₁ s
In this case, G(s)=A/B·1/1+T ₂ s, and a first-order lag filter may be used. Furthermore, if pressure fluctuations during transient response due to changes in fuel flow rate are allowed and constant pressure operation can be achieved in a steady state, G(s)=A/B may be used, and a coefficient multiplier may be used.

If the relationship in equation (4) is satisfied, then equation (1) and (3)
The formula is F(s) = {Gfb(s) − Gfc(s)・Gpb(s)/G
pc(s)} ・B(s) ……(5) T(s)={Gtc(s)−Gtc(s)・Gpb(s)/G
pc(s)} ・B(s) ...(6), and the steam flow rate F(s) and steam temperature T
(s), therefore, the steam turbine output is uniquely determined by the fuel flow rate. Since the gas turbine output is determined by the fuel flow rate, the combined plant total output, which is the sum of the outputs of the steam turbine and the gas turbine, is It is uniquely determined by the fuel flow rate.

Therefore, a function indicating the correspondence between the fuel flow rate and the total plant output is determined theoretically or experimentally, and the plant load request signal is converted into a signal corresponding to the fuel flow rate of the gas turbine using this function. By operating the fuel valve, it is possible to generate a total plant output that matches the load demand.

The configuration of the first embodiment of the present invention will be explained with reference to the schematic diagram in FIG.

1 is a plant load request signal, 2 is a first converter,
3 is a combustion request signal, 4 is a combustion control system, 5 is a combustor, 6 is a gas turbine plant, 7 is its output,
8 is a second converter, 9 is a steam control valve opening request signal,
10 is exhaust gas, 11 is a boiler (heat exchanger), 12
is steam, 13 is a steam control valve, 14 is a steam turbine plant, and 15 is its output. The first one holds a function that determines the amount of combustion corresponding to the plant output.
It consists of a converter 2 and a second converter 8 having a transmission characteristic for transmitting a steam control valve opening signal 9 corresponding to the amount of combustion. Now, when a command to change the load to be shared by this combined cycle power plant is received, this signal 1 is converted into a combustion amount corresponding to the new required load by the first converter 2, and a combustion request signal is sent to the combustion control system 4. Send as 3. At the same time, this combustion request signal 3 is converted into a steam control valve opening signal 9 by a second converter 8, and the steam control valve 13 is converted to a steam control valve opening signal 9 to keep the steam pressure constant.
Send to.

Next, another embodiment of the present invention will be explained with reference to the block diagram of FIG.

The characteristics of the second converter include the characteristics of the first converter and the characteristics of the second converter, that is, a characteristic that converts the plant load request signal into the corresponding steam control valve opening. 2′ converter 1
6, this is a control method in which the steam pressure reducing valve opening degree is determined directly from the plant load request signal 1 rather than from the combustion amount. FIG. 3 is a schematic diagram showing a configuration when the present invention is applied to a feedback control system. 17 is a mixer that subtracts the plant total output 28 from the plant load request signal 1;
18 is the plant output controller, 19 is its output, 2
0 is a mixer that adds combustion request signal 3 and output 19, 21 is a steam pressure set value, 23 is a mixer that subtracts steam pressure 22 from it, 24 is a steam pressure controller, and 26 is its output 25 and steam addition Mixer 27 adds output 7 and output 1 with valve opening request signal 9
This is a mixer that adds 5.

That is, when the control method of the present invention shown in FIG. 1 or 2 is applied to a plant in which a plant output feedback control system and a steam pressure feedback control system are incorporated as shown in FIG. The amount request signal 3 is added to the operation output 19 of the plant output controller, and the steam control valve opening request signal 9 is generated.
may be added to the operation output 25 of the steam pressure regulator. FIG. 4 is a block diagram when the present invention is applied to a system in which a control valve is controlled by a speed governor. 29 is a mixer that subtracts the rotation speed 31 of the gas turbine plant 6 from the combustion request signal 3 which is the setting value of the governor 30; 32 is the steam control valve opening request signal 9 which is the setting value of the governor 33; The rotational speed 34 of the steam turbine blunt 14 is subtracted. It is a mixer.

In other words, the fuel flow rate of the combustor 5 and the steam control valve 1
3 is operated by speed governors 30 and 33 as shown in FIG. It is sufficient to use a setting signal that takes into account the conversion characteristics.

In addition, if the response of the waste heat recovery boiler is slow and the follow-up of the plant power generation output to the plant load request is poor, a signal whose phase is advanced from the actual load request is used as the plant load request signal to adjust the load change. In some cases, the responsiveness of plant power generation output to

Thus, as explained above, the control method of the present invention utilizes the physical characteristics of a combined cycle power generation plant using an exhaust heat recovery boiler to make the control of plant output and steam pressure independent. It has the effect of controlling both.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the configuration of one embodiment of the present invention, FIG. 2 is a block diagram showing another embodiment of the present invention, and FIG. 3 is a diagram showing the structure of a feedback control system in which the present invention is applied. A schematic diagram showing the configuration, FIG. 4 is a block diagram when the present invention is applied to a system in which the control valve is controlled by a speed governor. 1... Plant load request signal, 2... First converter, 3... Combustion request signal, 4... Combustion control system, 5
... Combustor, 6 ... Gas turbine plant, 7 is its output, 8 ... Second converter, 9 ... Steam control valve opening request signal, 10 ... Exhaust gas, 11 ... Boiler (heat exchanger) , 12... Steam, 13... Steam control valve, 14... Steam turbine plant, 15 is its output, 16... 2' converter, 17, 20, 23,
26, 27, 29, 32... Mixer, 18... Plant output controller, 19 is its output, 21... Steam pressure set value, 24... Steam pressure regulator, 25 is its pressure, 30, 33... ...Governor, 31, 34...
...Rotation speed (voltage).

Claims (1)

[Scope of Claims] 1 Regarding load control and steam pressure control of a combined cycle power plant using an exhaust heat recovery boiler, a first converter that converts a plant load request signal into a combustion request signal of a gas turbine, and a combustion request signal. a second converter that converts the signal into a steam control valve opening request signal, and according to the load request for the plant, the plant output, which is the sum of the outputs of the gas turbine and the steam turbine, matches the load request value. The combustion amount of the gas turbine combustor is determined by the first converter and transmitted as a combustion request signal to the fuel control system, and the steam control valve opening degree for keeping the steam pressure constant is determined from the combustion request signal by the second converter. A method for controlling a combined cycle power plant, characterized in that the output and steam pressure of the combined cycle power plant are controlled by determining the signal using a converter, transmitting the signal as a steam control valve opening request signal, and operating the plant. 2. In what is stated in claim 1,
Controlling the output and steam output of a combined cycle power plant using means for converting a plant load request signal into a steam control valve opening request signal, which has the characteristics of a first converter and a second converter. A control method for a combined cycle power plant featuring features.