JPS58170804A - Level control device for feedwater heater - Google Patents

Abstract

PURPOSE:To control the level of a feedwater heater nicely by a method wherein an emergency level adjusting valve is preceded to open and the forced closing of a normal level adjusting valve is delayed by a timer when the operation thereof is transferred to the independent load operation in a plant by a load interception. CONSTITUTION:The level of a first high-pressure feedwater heater 12 is detected by a level transmitter 20 while normal and emergency adjusting valves 23, 24 are controlled through normal and emergency adjusting meters 21, 22. When the operation is transferred to the independent load operation in the plant by the interception of the load, an FCB signal is introduced into a three-way solenoid valve 81 and the emergency level adjusting valve 24 is opened immediately to suppress the rise of the level. On the other hand, the FCB signal is introduced into the three-way solenoid valve 80 through the timer 82 and the normal level adjusting valve 23 is closed forcibly. Thus, the bypass operation of the feed water heater due to the rise of the levels of the first and second high-pressure feedwater heaters 11, 12 may be interrupted and the stable level control may be effected.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to water level control of feedwater heaters in thermal power plants and nuclear power plants, and relates to a water level control device for feedwater heaters operated in single-load operation in the plant due to load shedding. As an example, this will be explained with reference to FIG. 1, which is a piping system diagram mainly showing the area around the high-pressure feed heater.

The steam generated in the boiler 1 is passed through the main steam pipe 50 to the main steam stop valve 6.
0 to the high pressure turbine 2 to do work. The exhaust steam after work is led to the boiler 1 through a low temperature reheat pipe 51, where it is reheated and passed through a high temperature reheat pipe 52 to a reheat steam stop valve 65.
The water flows into the intermediate pressure turbine 3 via the turbulence turbine 3 to perform work, then flows into the low pressure turbine 4 to perform work, and is discharged to the condenser 6. The discharged steam is condensed, pressurized by the condensate pump 7, flows into the deaerator 9 via the low pressure feed water heater 8, is pressurized from the deaerator 9 by the feed water pump 10, and is then pressurized to the second high pressure. The water is heated by the feed water heater 11 and the first high-pressure feed water heater 12 and sent to the boiler 21 as feed water.

On the other hand, the first high-pressure heater 12 transfers the heated steam to the low-temperature reheat pipe 51.
The water is taken in through the bleed stop valve 63 and the feed water is heated.

The water level of the drain generated due to heat exchange is transmitted to the water level transmitter 2.
0 is detected, the regular water level control valve 23 is controlled via the regular water level controller 21, and the water is guided to the second high pressure feed water heater 11 while controlling the water level to be constant. If the drain discharge capacity in this regular line is insufficient and the water level rises, the emergency water level control valve 24 is controlled via the emergency water level controller 22 to control the water level to the specified value and discharge it to the condenser 6. do. In addition, the second high-pressure feed water heater 11 takes in steam as heating steam from the intermediate pressure turbine 3 through the bleed pipe 53 through the bleed air stop valve 66 and the bleed air check valve 67, heats the feed water, and heats the feed water. The generated drain is guided to the deaerator 9 or the condenser 6 while the water level is controlled in the same way as the first high-pressure feed water heater 12.

In recent years, in well-planned plants, when load shedding occurs due to external line cut-off, etc., in order to improve the plant's operating rate, it is necessary to move to single-load operation within the plant instead of shutting down the plant. This is often the case. In this case, the main blocking valve 60 is emergency closed and the high pressure turbine bypass valve 62 is closed.
is controlled to open the valve, and main steam is bypassed from the main steam pipe 50 to the low-temperature reheat pipe 51 via the high-pressure turbine bypass valve 62. Similarly, the reheat steam stop valve 65 is closed, the low-pressure turbine bypass valve 64 is controlled to open, and high-temperature reheat steam is discharged from the high-temperature reheat pipe 52 to the condenser 6 . This process prevents turbine overspeed due to load shedding. In addition, by closing the blocking valve 60 and the reheat steam stop valve 65, the pressure inside the turbine becomes negative pressure. As some of the remaining water remains, they try to flow backwards (saturated water flows back through the franchise) and into the turbine.

However, since the bleed pipe is equipped with a bleed check valve,
Actually no backflow to the turbine occurs. In the unlikely event that cold steam flows into the turbine, there is a risk of damaging the turbine, so to ensure safety, generally, at the same time as load shedding,
The bleed stop valve is often forced to close. The turbine then
Open the reheat steam stop valve 65, adjust it with the reheat steam control valve (not shown) provided there, and shift to in-house load operation.

On the other hand, boiler 1 reduces the fuel amount to the amount of fuel suitable for the load operation in the station based on a command to rapidly reduce the fuel at the same time as the load is cut off (hereinafter abbreviated as PCB signal). It takes a relatively long time, although it varies depending on the type of boiler, various limit values depending on the structure of the boiler, controllability, etc. The amount of water supplied to the boiler 1 is gradually reduced in accordance with changes in the load of the boiler, but it is desirable that the temperature of the water supply is also gradually lowered to avoid sudden changes in the temperature of the water supply to the boiler 2. In the example shown in FIG. 1, the first high-pressure feedwater heater 12, which obtains heated steam from the low-temperature reheat pipe 51, continues to operate even when the load is cut off to ensure the boiler feedwater temperature.

However, since the feed water heaters below this feed water heater have stopped operating, the inlet feed water temperature of the first high pressure feed water heater 12 is low, the heat load on the feed water heater is high, and the amount of extracted steam is reduced. The amount of drain increases rapidly. Therefore, the water level of the first high-pressure feedwater heater 12 and furthermore the second high-pressure feedwater heater 11 rises rapidly and reaches the set point of the high level switch 40, and the water level of the first high-pressure feedwater heater 12 and furthermore, the water level of the second high-pressure feedwater heater 11 rises to the set point of the high level switch 40, and the water level is transferred to the feedwater heater bypass valve via the feedwater heater bypass valve switching device 42. Switch valves 43 and 44 to the first
The high-pressure feedwater heater 12 and the second high-pressure feedwater heater 11 are bypassed, and low-temperature feedwater is sent to the boiler 1, so that it no longer plays the role of the first high-pressure feedwater heater 11, 12 described above. For this reason, it is necessary to perform stable water level control of the first high-pressure feed water heater 12 and the second high-pressure feed water heater 11 even during single-load operation within the station due to load shedding.
Conventional water level control methods have had the problem of not being able to provide sufficient control to deal with this problem.

SUMMARY OF THE INVENTION An object of the present invention is to provide a water level control device for a feed water heater that can perform good water level control even when switching to in-house single load operation due to load shedding.

In the present invention, when shifting to in-house single load operation due to load shedding,
As shown in FIG. 1, only the first high-pressure feedwater heater 12 that obtains heated steam from the low-temperature reheat pipe 51 is operated, and the other feedwater heaters 11.8, etc. (including the deaerator 9) are connected to the turbine. To prevent the inflow of water or cold steam, the bleed stop valve is closed and operation is stopped. For this reason,! 1 The inlet water temperature of the high-pressure feed water heater 12 decreases, the heat load on this feed water heater increases, and the water level rises. (Generally, the steam pressure in the low-temperature reheat pipe increases temporarily when the station shifts to single-load operation, and this pressure increase also increases the heat load on the feed water heater and the amount of condensate. In general, a rise in the water level due to an increase in pressure will not occur because the amount of water also increases.) If the water level in the feedwater heater rises, the emergency control valve 24 is opened (by a control signal) and the drain is closed. However, there is a delay in operation in response to a sudden rise in the water level, so the water level rises excessively and the high level switch is activated, causing the feedwater heater to operate in pinosu mode.

In order to prevent this problem from occurring, the emergency valve is activated at the same time as the signal to shift to in-house single load operation, and in order to avoid the water level of the low pressure side feed water heater 8 from rising excessively,
After a certain time limit (after waiting for the emergency control valve to reach the valve opening required for drain discharge), the regular control valve 23 is forcibly closed,
Aim to improve water level control throughout the feed water heater group.

An embodiment of the present invention will be described below with reference to FIG. Fig. 2 shows a first high-pressure feed water heater 1 in contrast to the conventional technology shown in Fig. 1.
2 is a control system diagram when one embodiment of the present invention is adopted for the drain control system of No. 2. FIG.

Similar to the prior art, the water level of the first high-pressure water heater 12 is detected by the water level transmitter 20 and sent as an air pressure signal to the regular water level controller 21 and the emergency controller 22. Regular water level controller 2
1, the water level signal and set value (normal water level control level NWL)
), a proportional/integral calculation is performed based on the deviation (Δ), and a control valve operation signal is transmitted to control the regular water level control valve 23. Further, the emergency water level controller 22 performs proportional calculation based on the deviation (Δ) between the water level signal and the set value (emergency water level control level DWL), and controls the emergency water level control valve 24. In the present invention, the emergency water level controller 22 can be used as a cascade setting type controller to switch the set value, and DWL during normal operation
The air signal set by the pressure reducing valve 72 for setting and the pressure reducing valve 73 for DWL setting during FCB (boiler fuel throttling) is
It is connected to the side solenoid valve 81, selects one of the signals, turns it on neutrally, and gives a setting signal to the emergency water level controller 22 via the throttle tank 83 for slowing changes when switching the signal. That's what I do. When shifting to in-house single load operation due to load shedding, the FCB signal is taken into the 3-way solenoid valve 81, and the set air signal from the DWL setting pressure reducing valve 72 during normal operation and the set air signal from the DWL setting pressure reducing valve 73 during 9PCB. Switch.

FIG. 3 shows the set points and control characteristics of the emergency water level controller 22 during normal times and during FCB. After changing the setting value of the emergency water level controller 22, the emergency water level control valve 24 is controlled after waiting for the water level to rise to the normal setting point as in the normal DWL control shown in FIG. PC without doing anything
Since the set point B at time B is set below NWL, the output signal of the emergency water level controller 22 can be outputted at the same time as the set value is changed, and the emergency water level regulating valve 24 can be opened immediately.

This makes it possible to suppress the rise in water level.

On the other hand, for the regular water level control valve 23, the regular water level controller 2
A two-way solenoid valve 80 is installed between the regular water level controller 1 and the regular water level control valve 23, and the control signal of the regular water level controller 21 and the air signal set to the forced closing pressure reducing valve 71 are sent to the three-way solenoid valve 80. The timer 82 is set in response to the PCB signal, and the PCB
After a certain period of time has elapsed after the signal is generated, the control signal from the regular water level controller switches to a forced closing signal.

When shifting to in-house single load operation due to load shedding, the PCB signal is sent to the 3-way solenoid valve 80 using the timer 82 (wait until the emergency water level control valve reaches the valve opening required for drain discharge.The timer setting value is 1 to 5). (preferably, seconds), and is set by the forced closing pressure reducing valve 71 according to the control signal of the regular water level controller 21, and is switched to the 9 air signal, and the regular water level regulator 23 is forcibly closed. Figure 4 shows the internal pressure of each feedwater heater when the station shifts to single-load operation due to load shedding.

Conventionally, as shown in FIG. 4, if the front pressure of the regular water level control valve 23, that is, the internal pressure 90 of the first high-pressure feed water heater, suddenly increases,
The amount of drain flowing into the second high-pressure water heater 11 increases.

On the other hand, the internal pressure 91 of the first high-pressure feed water heaters decreases, and the internal pressure 9 of the deaerator, which is the drain destination of the second high-pressure feed water heater 11, decreases.
4, the drain discharge amount is insufficient and the water level rises, and the emergency line for discharging the condenser hedren is activated to discharge the condensate.
Since condensate flows in from the drain, there is insufficient discharge even in this emergency line, and the water level continues to rise, causing a problem in which the high level switch is activated and the feed water heater is switched to bypass operation. At the time of transition to single-load operation within the plant, the regular water level control valve 23 is forcibly closed and drain flow from the first high-pressure feed water heater is cut off, so that the above-mentioned problems can be prevented.

In addition, by delaying the forced closing of the regular water level control valve 23 by the timer 82,
It also has the effect of mitigating the rise in water levels in step 2.

In one embodiment of the present invention, a case has been described in which a pneumatic type is adopted as the feed water heater water level control system, but an electric type and a digital type can also be applied. Similarly, although the case where the emergency water level controller is set to proportional operation has been described, if the setting value is selected appropriately, this can be used in the case of proportional/integral operation. In addition, although we have described the case where the drain to the second high-pressure water heater is shut off by forcibly closing the regular water level control valve, it is also possible to install a connection valve before or after the regular water level control valve and forcibly close it. be.

In the figure, 2i1i is a high-pressure turbine, and 5 is a generator.

42 is a feed water heater bypass valve switching device, 61 is a low temperature reheat extraction air check valve, and 64 is a low pressure turbine bypass valve.

According to the present invention, when the station shifts to single-load operation due to load interruption, bypass operation of the feedwater heaters due to a rise in the water levels of the first high-pressure feedwater heater and the second high-pressure feedwater heater can be prevented, and stable water level control can be achieved.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of a thermal power plant showing conventional feedwater heater water level control, Fig. 2 is a system diagram of feedwater heater drain control according to an embodiment of the present invention, and Fig. 3 is an emergency control system according to the present invention. The needle control characteristic diagram and FIG. 4 are the pressure characteristic diagrams of the feed water heater. 6... Condenser, 11... Second high pressure water heater, 12
...First high-pressure water heater, 20...Water level transmitter, 2
DESCRIPTION OF SYMBOLS 1... Regular water level controller, 22... Emergency water level controller, 23... Regular water level regulating valve, 24... Emergency water level regulating valve, 40... Level high switch, 71... Pressure reducing valve for forced closing, 72... Pressure reducing valve for DWL setting during normal operation, 73... Pressure reducing valve for DWL setting during FCB, 80.81
...3 grass 3 eyes j゛ aromatic skin (-/,) $4 ward 1 single open (8r) e13

Claims (1)

[Claims] 1. In a power generation plant that generates electricity by driving a turbine using steam generated by a steam generator, a turbine bypass system that directly leads excess steam to the turbine to a condenser and a water supply line to the steam generator The feed water is heated by the steam that has done some work in the heater and/or the steam generator or the steam from the steam generator, and the drain generated by heat exchange raises the drain water level of the feed water heater. means for controlling fJ1 at a specified value by a first control valve and guiding it to the low-pressure side feed water heater; and a second control valve controlling at a second specified value set above the specified value for fJ1. and a means configured to be able to guide drainage through the device to equipment on the low-pressure side. A water level control device for a feed water heater, characterized in that it is provided with means for changing the setting below a specified value.