JPH0122521B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a thermal power generation facility in which power cannot be transmitted from a generator due to an accident on the power system side, the generator is disconnected from the external system, and only the load of the power plant is operated by the generator. The present invention relates to operational control of a turbine-driven water supply pump when the plant is in so-called isolated operation.

Modern thermal power generation equipment can operate with only the on-site load without stopping the power generation equipment in the event of an accident in the power system, and when the power grid is restored, the power generation equipment can be connected to the power grid to quickly take the load off. This is aimed at stabilizing the power system.

Figure 1 shows a conceptual diagram of conventional thermal power generation equipment.

In FIG. 1, steam generated by a boiler 11 is guided to a turbine 12, which turns a generator 13 to generate electricity.

The steam that has done work in the turbine 12 is cooled by a condenser 14, turned into water, sent by a condensate pump 15, heated by a low-pressure feed water heater 16,
The water is temporarily stored in the deaerator 17.

The water stored in the deaerator 17 is sent as high-pressure water by a turbine-driven feedwater pump 18, further heated by a high-pressure feedwater heater 19, and sent to the boiler 11.

Here, the turbine-driven feedwater pump 18 is driven by a turbine 20 for driving the feedwater pump, but the steam source of the turbine 20 for driving the feedwater pump uses extracted steam from the turbine 12 during normal operation, and during low load, the steam source for the turbine 20 for driving the feedwater pump is used. 11 outlet steam is used.

The flow rate of water supplied to the boiler 11 is controlled by the rotation speed of the turbine-driven water pump 18. Therefore, by controlling the rotation speed of the water supply pump driving turbine 20, the flow rate can be changed.

FIG. 2 is a block diagram of an example of a conventional water supply control system in which an electro-hydraulic governor is used in the turbine 20 for driving the water supply pump.

In FIG. 2, the water supply flow rate setting value set by the setting device 22 is compared with the suction flow rate of the turbine-driven water supply pump 18, and the deviation is proportionally and integrally compensated by the regulator 23 and set as the rotation speed command value.

This rotation speed command value and the water supply pump drive turbine 2
The rotation speed of 0 is compared with the signal detected by the rotation speed detector 24, the deviation is gain compensated by the feedwater pump drive turbine controller 25, converted into a hydraulic signal by the electro-hydraulic converter 26, and the low-pressure steam By operating the control valve 27 and the high pressure steam control valve 28, the rotation speed of the water supply pump driving turbine 20 is controlled.

Here, the relationship between the low pressure steam control valve 27 and the high pressure steam control valve 28 has a characteristic as shown in FIG.

In other words, 300 indicates when the valve is fully open, and 30
1 represents the opening degree characteristics of the low-pressure air control valve 27 and 302 the opening characteristics of the high-pressure steam control valve 28 in response to the respective control signals. When the signal is increased from 0, first, the low pressure steam control valve 27 starts to open, and when it becomes fully open,
The high pressure steam control valve 28 is configured to begin to open.

Therefore, during normal operation, steam from the turbine bleed air is used to control the low pressure regulating valve 27, and when the load on the turbine 12 decreases and the turbine bleed air becomes insufficient,
The high pressure regulating valve 28 is opened and controlled.

If the station load independent operation occurs in this normal state, the load on the turbine 12 suddenly becomes only the station load, so the regulating valve of the turbine 12 is suddenly closed.

Then, the steam pressure at the outlet of the boiler 11 rises rapidly, and the discharge pressure of the turbine-driven water supply pump 18 also rises accordingly. At the same time, since the turbine bleed steam is almost completely exhausted, the low pressure steam source for the feedwater pump driving turbine 20 is eliminated.

At the moment when the predetermined load islanding operation occurs and the main steam pressure increases, the rotation speed of the turbine-driven water supply pump 18 is almost the same as before the station load islanding operation occurs, so the system loss, that is, the feedwater flow rate shown in Fig. 4, is reduced. As can be seen from the curve representing the relationship between
Water supply flow rate also decreases rapidly.

It is conceivable that this rapidly decreased feed water flow rate will become less than the minimum flow rate required by the boiler 11, and furthermore, since there will be no low pressure steam source for turbine extraction air, the rotation speed of the turbine driven water feed pump 18 will decrease, making matters worse. direction.

Therefore, in order to ensure the minimum water supply flow rate of the boiler 11 when the station load independent operation occurs, it is necessary to increase the rotation speed of the turbine-driven water supply pump 18.

However, in the conventional control device shown in FIG. 2, the proportional + integral circuit of the regulator 23 has a value that can compensate for load changes during normal operation. It is not possible to compensate for such large and sudden changes.

Therefore, in the conventional control device, when the station load is operated alone, the rotation speed of the turbine-driven water supply pump 18 is increased to the required rotation speed, or the low pressure control valve 27 is switched to the high pressure control valve 28 within the necessary time. As a result, the minimum water supply flow rate of the boiler 11 is interrupted, and the power generation equipment is stopped.

This will be explained with reference to the water supply flow rate Q-pressure H relationship curve shown in FIG.

In FIG. 4, N+2 to NO to N-4 indicate the rotational speed of the turbine-driven water supply pump 18, a is the outlet steam pressure of the boiler 11, and b is the discharge pressure of the turbine-driven water supply pump 18 corresponding to the steam pressure. be. Therefore, the difference between b and a represents the pressure loss from the turbine-driven feedwater pump 18 outlet to the boiler 11 outlet.

Now, in FIG. 4, if the operating state before the station load independent operation occurs is at point c, the water supply flow rate at this time is d, and the discharge pressure of the turbine-driven water supply pump 18 is at point e.

Assume that in this state, the station load independent operation occurs, the outlet pressure of the boiler 11 rises rapidly, and at the same time, the discharge pressure of the turbine-driven water pump 18 reaches point f.

At this time, if the rotation speed of the turbine-driven water supply pump 18 remains at NO, the water supply flow rate becomes O, as can be seen from FIG. If the minimum water supply flow rate of the boiler 11 is g at that time, the flow rate will be completely below that value.

Therefore, at this time, it is necessary to immediately increase the rotational speed to at least the speed corresponding to point h. and,
Finally, as the pressure drops, N corresponding to point j
- Must be rotated 3 times.

Looking at the steam source for the feedwater pump driving turbine 20 at this time, first, the extracted steam of the turbine 12 rapidly decreases, so the driving steam for the feedwater pump driving turbine 20 disappears, and the rotation speed decreases.

Therefore, in order to secure point h, in order to switch the steam source to boiler 11 outlet steam, the regulator valve of the feed water pump driving turbine 20 is changed to the low pressure regulator valve 27.
It is necessary to immediately switch from the high pressure regulating valve 28 to the high pressure regulating valve 28.

However, in the conventional control device, the regulator 23 cannot cope with such sudden movements, so the rotation speed temporarily decreases, making it difficult to ensure the minimum water supply flow rate g of the boiler 11. was impossible.

Therefore, in the present invention, the outlet pressure of the boiler 11 is detected when a predetermined load single operation occurs, and a command value is immediately set to the rotation speed of the water supply pump driving turbine 20 commensurate with the pressure, and this command value is used to set the rotation speed of the water supply pump driving turbine 20. By making a correction corresponding to the opening degree of the high pressure regulating valve 28 of the turbine 20 commensurate with the boiler outlet steam, the switching from the low pressure regulating valve 27 to the high pressure regulating valve 28 is accelerated, and the water supply flow rate to the boiler 11 is ensured. The purpose is to provide a pump control method.

FIG. 5 is a block diagram of one embodiment of the present invention.

As can be seen from FIG. 5, the conventional control system remains the same.

A switch 33 is provided on the output side of the conventional regulator 23, and during normal operation, the switch 33 is connected to the regulator 23 side, and when the station load independent operation occurs, the signal from the function converter 32 side is sent to the controller 25 of the water pump driving turbine 20. configured to be entered.

Now, during normal operation, as mentioned above, switch 3
3 is on the regulator 23 side, a certain flow rate setting is given by the setting device 22, this set value is compared with the signal of the suction flow rate transmitter 30 of the turbine-driven feed water pump 18, and the deviation is determined by the regulator 23. 23, which undergoes proportional + integral compensation to become a rotation speed command signal, which is then passed through a switch 33 and compared with the signal from the rotation detector 24 of the water supply pump driving turbine 20.

This deviation passes through the controller 25 of the water supply pump driving turbine 20, becomes a hydraulic pressure signal by the electro-hydraulic converter 26, and is transmitted to the control valves 27 and 28.

At this time, assuming that the power generation output of the turbine 12 is under periodic load operation, there is sufficient steam extracted from the turbine 12, so the turbine 20 for driving the water supply pump
The low pressure regulating valve 27 is open, and the high pressure regulating valve 28 is operated in a fully closed state.

When station load independent operation occurs from this operating state, the switch 33 is immediately switched to the side of the auxiliary boiler feed water control means comprising the pressure transmitter 31 and the function converter 32.

This function converter 32 detects the outlet steam pressure (main steam pressure) of the boiler 11 using the pressure transmitter 31, and uses the detected pressure signal as input to control the feedwater pump driving turbine 20, that is, the turbine-driven feedwater pump 18 at this time. It is a function that determines the rotation speed.

Furthermore, this function
The rotation speed determined by the outlet pressure of No. 8 is determined from the feed water flow rate Q-pressure H curve in FIG. In other words, energy from the pressure and temperature of the steam at the outlet of the boiler 11 is used to drive the water supply pump at the turbine 2.
It is a function corrected by a value calculated in advance so that the opening degree of the high pressure regulating valve 28 is necessary to obtain a rotation speed of 0.

The output signal of the function converter 32 passes through the switch 33 and becomes a rotation speed command value, which is compared with the current rotation speed, and the deviation is determined by the feedwater pump driving turbine 20.
The gain is compensated by the controller 25, converted into a hydraulic signal by the electro-hydraulic converter 26, and the control valve 27,
8.

At this time, since the low-pressure steam source, that is, the turbine extracted steam, is no longer present in the regulator valve, the high-pressure regulator valve 28 on the boiler outlet steam side opens immediately to the degree of opening given by the function converter 32.

At this time, the rotational speed of the water supply pump driving turbine 20 is determined by the discharge pressure and flow rate of the turbine-driven water supply pump 18, as explained above regarding the function converter 32.

Therefore, even if the steam pressure at the outlet of the boiler 11 increases due to the occurrence of isolated load operation in the plant, the flow rate required by the boiler 11 can be ensured, and the water can be supplied to the boiler 11 without stopping the boiler 11 and the turbine 12. It is possible to continue operation even in a transient unstable state when isolated load operation occurs in the plant, and it also leads to stabilization of the power system.

Since the main steam pressure is detected from the outlet side of the boiler 11 in this way, state changes can be detected without response delay. As a result, it is possible to prevent water level fluctuations in the boiler due to detection delays, overheating due to a drop in water level, and boiler tube rupture due to overheating. As mentioned earlier, the function stored in the function converter 32 is a function that takes into account the transient state at the time of isolated load operation in the station, so the boiler 11 and turbine 12 are not in a stable state. When the rotation speed of the water supply pump driving turbine 20 is determined by the given function, there will be a slight difference between the rotation speed and the stable rotation speed.

Therefore, the present invention also proposes that the rotational speed command value after this stable state is controlled by switching the switch 33 to the regulator 23 side for normal control.

According to experiments and simulation tests, it has been found that the appropriate switching time is about 1 to 3 minutes from the occurrence of the isolated load operation in the station.

As described above, according to the present invention, the command value for switching the steam source of the boiler feed water pump drive turbine and controlling the rotation speed can be applied in the case of a rapid load drop during isolated operation within a power plant, which occurs at the time of a power system accident, etc. A function converter is installed specifically for in-house independent operation, and a function is inserted into this function converter to determine the required pump rotation speed and the opening degree of the high pressure regulator valve of the feedwater pump drive turbine based on the boiler outlet pressure. By doing so, when isolated operation occurs in the plant, the output of the function converter is used as a command value to control the rotation speed, and even in a transient unstable state, the amount of water required by the boiler can be supplied.

Thus, according to the present invention, the load can be increased when the power system recovers from an accident without stopping the power generation equipment, and it can also be useful for stabilizing the power system.

[Brief explanation of drawings]

Figure 1 is a conceptual system diagram of conventional thermal power generation equipment, Figure 2 is a block diagram of a conventional water supply control system for a water pump drive turbine, and Figure 3 is a diagram of the relationship between the low pressure regulator and high pressure regulator of the water pump turbine. , FIG. 4 is an explanatory diagram of the relationship between water supply flow rate and pressure, and FIG. 5 is a block diagram of an embodiment of the present invention. 11... Boiler, 12... Turbine, 13...
Generator, 14... Condenser, 15... Condensate pump,
16...Low pressure feed water heater, 17...Deaerator, 18
...Water pump, 19...High pressure water heater, 20
...Water pump drive turbine, 22...Setting device,,
23...Adjuster, 25...Controller, 26...Electro-hydraulic converter, 27...Low pressure steam control valve, 28...High pressure steam control valve, 29...Orifice or flonose, 30...Suction flow rate transmitter , 31...pressure transmitter, 32...function converter, 33...switcher.

Claims (1)

[Claims] 1. When station load islanding occurs in thermal power generation equipment, the normal boiler water supply control means is switched to the auxiliary boiler water supply control means including a function converter, the main steam pressure from the boiler is detected, and the water supply is controlled based on this main steam pressure. 1. A water supply pump control method during station load independent operation, characterized by supplying water to a boiler by controlling the rotational speed of a pump-driving turbine, and returning to normal boiler water supply control means after a predetermined period of time.