JPS6149488B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a front pressure control device for a steam turbine control valve in a combined cycle power plant, and particularly to a control device that improves pressure controllability during variable pressure operation.

The prepressure control system for the steam turbine control valve in a conventional combined cycle power plant is as shown in Figure 3.
Based on the steam turbine load, when the steam turbine load increases, when the steam turbine control valve opens to the specified opening A ₁ , the pressure setting value is changed from P ₁ to P ₂ , or from P ₂ to P _3.
A control method was adopted in which the pressure setting was changed from P ₃ to P ₂ , or from P ₂ to P ₁ after the regulating valve closed to the specified opening A ₂ when the load was lowered. When changing the value, the pressure change and the adjustment valve opening change are large, the adjustment valve opening tends to hunt, and furthermore, when the adjustment valve is throttled, the throttle loss is large.

An object of the present invention is to prevent hunting of a steam turbine control valve and obtain stable pressure control characteristics.

Embodiments of the present invention will be described below with reference to the drawings.
First, FIG. 1 shows the overall configuration of a plant to which the present invention is applied.

Combined cycle power plant has gas turbine 1
, a gas turbine generator 2, an exhaust heat recovery boiler 5 using the gas turbine exhaust gas 4, an exhaust heat recovery boiler 5, a steam turbine 6 using the steam generated by the exhaust heat recovery boiler, and a steam turbine generator 7. Configured as the main engine. The water/steam system includes a condenser 8, a condensate pump 9, a deaerator 10, a feed water pump 11, an exhaust heat recovery pump 5, a main steam pipe, and a steam turbine control valve 12, as in a general steam turbine cycle.
and then reaches the steam turbine 6. Generally, there are a plurality of gas turbines and exhaust heat recovery boilers, and a plurality of systems are arranged in parallel from the outlet header of the water supply pump 11 to the header in front of the steam turbine control valve.

In the load control method, a load control device 16 inputting gas turbine (hereinafter abbreviated as GT) load signals 20a, 20b and steam turbine (hereinafter abbreviated as ST) load signal 21 operates the gas turbine fuel pump 3 or fuel valve. The contents of the control device 16 are shown in FIG.

A target load signal is created for the target load set value 18 via the change rate limiter 19, and each gas turbine load 2
The sum and deviation of 0a, 20b and the steam turbine load 21 are determined by a subtractor 23, and a demand load signal for each gas turbine is created via a regulator 24. The demand load signal is further compared with each gas turbine load 20a or 20b in a subtractor 25 and passed through a regulator 26 to form a gas turbine fuel operation signal. In addition,
The subtractor and regulator that create the fuel operation signal for the No. 2 gas turbine are omitted in the drawing.

On the other hand, the steam turbine adopts a steam turbine control valve front pressure control system, which accepts all the steam generated by the exhaust heat recovery boiler in order to effectively utilize it.

As shown in Fig. 4, the conventional setting method for the pressure in front of the regulating valve is based on a setting function 27 in which the pressure setting is low at low loads and high at high loads, and a straight line connects the pressure settings. is desirable from the standpoint of improving steam turbine efficiency and reducing turbine humidity. The improved front pressure control device 17 for performing such control has a block configuration as shown in FIG. That is, the value of the steam turbine load obtained from the steam turbine load detector 15 is input to the function generator 28, and the deviation between the prepressure setting shown in FIG. and the regulator 30 controls the control valve 12.
Obtain the operation signal to. However, when controlling the adjustment valve with this setting, there are the following problems. In other words, when the steam turbine load L, the steam turbine setting P _L , and the gas turbine are operating stably at the corresponding loads, if the gas turbine load decreases, the amount of steam generated by the exhaust heat recovery boiler decreases, and the steam Turbine load is reduced. As the steam turbine load decreases, the pressure setting of FIG. 4 moves on the setting function 27 in the direction of and decreases. When the pressure setting decreases, the steam turbine adjustment valve opening degree opens in accordance with the block diagram of FIG. 5, and as the steam turbine load increases, the pressure setting moves in the direction of FIG. 4. This time, when the pressure setting increases, the opening degree of the regulating valve closes, and the steam turbine load decreases. The pressure setting decreases again in the same direction as , and a hunting phenomenon of the adjustment valve opening occurs below.

For this reason, in the present invention, hysteresis is provided for the steam turbine front pressure setting function 28 as shown in FIG.

In this setting, when ST load is increasing, set curve 2
7 and set curve 32 during load drop.
descend along the

For example, the steam turbine pressure is P _L The steam turbine load is L and the corresponding gas turbine load. If the gas turbine load drops during stable operation, the amount of steam generated by the heat recovery boiler decreases, and the steam turbine load decreases. . As the steam turbine load decreases, the pressure setting moves on the setting function 32 in the direction of and decreases. As the pressure setting decreases, the steam turbine control valve tends to open, and the steam turbine load tends to increase, but the pressure setting moves in the direction for the hysteresis effect, keeping the pressure setting constant. Since the gas turbine load decreases, the amount of steam generated by the exhaust heat recovery boiler decreases, and the steam turbine again decreases in load with the pressure setting constant, and further decreases according to the setting curve 32.

According to this method, stable pressure control is possible without hunting in the opening degree of the regulating valve due to changes in the amount of generated steam due to fluctuations in the gas turbine load.

FIG. 7 shows an embodiment of a front pressure control device 17' for performing such pressure control of the present invention. In FIG. 7, numeral 42 is a hysteresis circuit having an insensitive region of a predetermined width for input rises and falls, and various electrical or mechanical configurations are possible. This hysteresis circuit is inserted on the output side of the function generator 28, and its output is used as the pressure setting value. The other blocks are the same as those shown in FIG.

FIG. 8 shows a further improvement of the control valve control described above. According to the front pressure control device shown in FIG. 7, by inserting the hysteresis circuit 42, even if the gas turbine load fluctuates and the amount of steam generation changes somewhat, the steam turbine regulator valve front pressure setting does not change. Hunting of the adjustment valve opening can be prevented, but
The front pressure control device 17'' shown in Figure 9 further prevents the slight change in the opening degree of the adjustment valve that occurs at this time
This is to match the return signal of the adjustment valve opening with the opening target signal corresponding to the pressure setting shown in FIG.

The steam turbine front pressure setter 28 and the hysteresis circuit 42 are similar to those shown in FIG. 7 to obtain the functions shown in FIG. 6 for the steam turbine load obtained by the load detector 15. The control valve represented by the function shown in FIG. 8 is determined by the setting function unit 35 for the steam turbine front pressure set value determined from this. At this time, the steam turbine front pressure setting in Fig. 6 is set to curve 27.
Corresponding to the above case and the case above curve 32, the adjustment valve opening degree setting is made to correspond to curves 33 and 34, respectively. The above adjustment valve opening setting value and the actual adjustment valve opening 3
Adder 3 adds the result of proportional or proportional integration to the deviation from 6 by the regulator to the signal of steam turbine front pressure setting device 28.
Add at 9. The signal of the calculator 38 is turned on and off by a switch 41, but the content of the pressure setting interval discriminator 40 that operates the switch 41 is to turn on the signal when the steam turbine front pressure setting value is between _P4 and _P5 . pressure
This is to cause an off signal to be output during other sections including P ₄ and P ₅ .

According to this device, since the specified opening corresponding to the set pressure is taken in the pressure changing section, the movement in the straight line and direction in the explanation of FIG.

If a digital controller or the like is used as the control device, the functions of the present invention can be provided relatively easily.

As described above, according to the present invention, since the pressure setting in front of the steam turbine regulator changes stably, the regulator valve control can be stabilized.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a combined cycle plant to which the present invention is applied, Figure 2 is a load control system diagram of Figure 1,
Figure 3 is a characteristic diagram showing a conventional steam turbine front pressure setting method, Figure 4 is a characteristic diagram showing a steam turbine front pressure setting method that is an improved version of the conventional method, and Figure 5 is a characteristic diagram showing the front pressure setting method shown in Figure 4. A control block diagram for implementing the setting method, FIG. 6 is a characteristic diagram showing the steam turbine front pressure control method of the present invention, and FIG. 7 is a control block diagram showing an embodiment of the front pressure setting device shown in FIG. FIG. 8 is a characteristic diagram of the adjustment valve opening degree setting when the pressure is set in FIG. 6, and FIG. 9 is a control block diagram showing another embodiment of the present invention. 1...Gas turbine, 5...Exhaust heat recovery boiler,
6...Steam turbine, 13...Main steam pressure detector, 15...Steam turbine load detector, 17',
17″...Steam turbine front pressure control device, 28...
Function generator, 29...subtractor, 30...adjuster,
42...Hysteresis circuit.

Claims (1)

[Claims] 1. Opening of the steam turbine control valve of a combined cycle power plant consisting of a gas turbine generator, an exhaust heat recovery boiler that generates steam from its exhaust gas, and a steam turbine that is driven by the steam generated by the exhaust heat recovery boiler. The device for controlling the front pressure of the steam turbine regulator by temperature control includes a function generator that generates the set value of the front pressure as a function according to the value of the steam turbine load, and a function generator that has a hysteresis characteristic in the output of the function generator. A pressure control device for a steam turbine in a combined cycle plant, characterized in that the pressure setting for the front pressure control is a function having hysteresis characteristics with respect to the steam turbine load.