JPH07174304A - Water level controller for feed water heater - Google Patents

Abstract

PURPOSE:To stably hold water level control of a lowpressure feed water heater by limiting a drain amount to be fed from the heater of an upstream when the control of the heater falls in a trouble. CONSTITUTION:A water level signal from a water level detector is input to subtracters 40, 50, and subtracted between output signals (NWL) and (NWL+50 mm) from signal setters 41, 51. Obtained water level signals are PID-calculated by PID calculators 42, 52. An output of a signal setter 47 is input to an output limiter 43 via a signal switching unit 46 for switching in response to a load of a generator, an inner pressure of a condenser.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feed water heater water level control device attached to a feed water heater which heats feed water by extraction air from a steam turbine.

[0002]

2. Description of the Related Art Generally, in a steam turbine plant such as a thermal power plant or a nuclear power plant, steam that has finished work in a steam turbine is introduced into a condenser to be condensed, and the obtained condensate is heated by a plurality of stages of feed water. It is heated through a vessel to raise the temperature and then circulated into the boiler or reactor.

As the heat source of the feed water heater, steam extracted from a high-pressure or low-pressure turbine is used, and this steam is cooled by heat exchange with condensate in the feed water heater and becomes a drain inside the feed water heater. After being stored in the condensate, it is sent to the feed water heater and the condenser so as to sequentially exchange heat with the condensate.

By the way, as the feed water heater, since condensate water or feed water is generally at high pressure, a multi-tube heat exchanger is used, and the feed water is made to flow into the heating pipe, or the steam or drain extracted outside the pipe is made to flow. It is configured to perform heat exchange on the wall. Drain in which steam is condensed is stored in the drain cooling section of the feed water heater.

Further, the feed water heater is usually provided with a drain water level control device for controlling the drain water level to a predetermined level. FIG. 6 is a system diagram of a conventional general condenser or low-pressure feed water heater. A steam turbine 1 is directly connected to a condenser 2 and low-pressure feed water heaters 3 and 4.

A condensate pump 5, a gland steam condenser 6, a demineralizer 7 and a condensate booster pump 8 are sequentially connected to the condenser 2, and the condensate pressurized by the condensate booster pump is low pressure. It is heated by the feed water heaters 3 and 4, and is further supplied to the boiler or the reactor through a feed water pump and a high pressure feed water heater (not shown).

A water level detector 9 is installed in the low-pressure feed water heater 4, and a water level signal is guided to a water level controller 10 to control a control valve 11. The water level signal from the water level detector 9 is also guided to the water level controller 12 and controls the control valve 13.

The low-pressure feed water heater 3 has a water level detector 14
Is installed, the water level signal is guided to the water level controller 15, and the control valve
Control 16 The condenser 17 is provided between the condenser 2, the condensate pump 5, the gland steam condenser 6, the desalination device 7, the condensate booster pump 8, the low pressure feed water heaters 3 and 4 and the feed water pump (not shown). Are connected.

The drain pipe 18 guides the drain of the low-pressure feed water heater 4 to the condenser 2 via the control valve 11 and to the low-pressure feed water heater 3 via the control valve 13. The drain pipe 19 guides the drain of the low-pressure feed water heater 3 to the condenser 2 via the control valve 16. In addition, the middle stage of the steam turbine 1 and the low-pressure feed water heaters 3, 4
Turbine extraction pipes 20 and 21 are connected between and.

In the condensate system having the above-mentioned structure, part of the steam that has worked in the steam turbine 1 is introduced to the low-pressure feed water heater 4 via the turbine extraction pipe 20 and heated by a heating pipe (not shown). ) Heat is exchanged with the condensate flowing through the inside of the pipe) and is recovered as a feed water heater drain through the drain pipe 18 and the low pressure feed water heater 3 and the condenser 2 via the control valves 11 and 13.

Further, in the low-pressure feed water heater 3, the steam from the turbine extraction pipe 21 and the drain from the low-pressure feed water heater 4 perform heat exchange with the condensate, and the heat is drained to the condenser 2 as the drain of the feed water heater. Be recovered.

The condensate stored in the condenser 2 passes through the condensate pump 5 or the condensate booster pump 8 by the condensate pipe 17 and gradually rises by the low-pressure feed water heaters 3, 4 as described above. After being heated, it is sent to the boiler again, the obtained main steam is sent to the steam turbine 1, expanded, and then discharged to the condenser 2.

FIG. 7 illustrates the structure of the low pressure feed water heater 3 described with reference to FIG. Condensate introduced into the fuselage from the condensate inlet section 30 is heated steam flowing from the extraction inlet section 32 and the pre-stage drain inlet section 33 before reaching the condensate outlet section 31.
It is warmed by the drain flowing in from.

In the body of the low-pressure feed water heater 3, an overheat returning section Z1 for raising the condensate by turbine extraction steam, a condensing section Z2 for exchanging the steam heat with the condensate and draining it, and a drained state. Drain cooling section Z for further heat exchange
Divided into three.

The steam introduced from the extraction inlet 32 into the low-pressure feed water heater 3 exchanges heat with the condensate in the superheat returning section Z1 to raise the temperature of the condensate. The condensing part Z2 causes heat exchange between saturated steam and condensate in the largest part of the condensate heating area, and in the drain cooling part Z3, the drain generated in the condensing part Z2 enters the feed water heater. Cooling to a saturation temperature or lower by low-temperature condensate to cause heat exchange with the condensate and keeping the drain water level constant prevents steam from escaping through the drain outlet 4 to the next-stage heater.

Next, referring to FIG. 8, the low-pressure feed water heater 4
The drain level control of will be described. The water level signal of the low-pressure feed water heater 4 detected by the water level detector 9 is sent to the subtractor 40 in the controller 12 to control the drain control valve 13 on the low-pressure feed water heater 3 side, and the signal setter 41 outputs the signal. Output signal (NWL)
Is subtracted between the PID calculator 42 and the deviation signal.
Sent to.

The PID calculator 42 calculates the deviation signal, and the output limiter 43 limits the output to an appropriate output.
Further, this signal is input to the PID calculator 42 via the switch 44, and integral feedback is performed here.

The signal from the output limiter 43 is sent to the I / P converter 45 where signal conversion is performed and the opening of the control valve 13 is controlled to be appropriate. On the other hand, the water level signal of the low-pressure feed water heater 4 detected by the water level detector 9 is also sent to the subtractor 50 in the controller 10 to control the drain control valve 11 on the condenser side, and the signal setter. After being subtracted from the output signal (NWL + 50 mm) of 51, it is sent to the PID calculator 52 as a deviation signal.

In the PID calculator 52, the PID calculation is performed on the deviation signal in the same manner as the calculation in the controller 12 described above.
The output limiter 53 limits the output to a proper value. Further, this signal is input to the PID calculator 52 via the switch 54, and integral feedback is performed here. The output limiter 53 signal is I /
The signal is sent to the P converter 55 for signal conversion, and the opening of the control valve 11 is controlled to be appropriate.

[0020]

In the above-mentioned conventional feed water heater water level control device, the drain is discharged to the condenser 2 by a slight pressure difference due to the characteristics of the low pressure feed water heater 3. Most of the pressure is generated by the difference in hydrostatic head.

Therefore, if it is assumed that the seawater temperature is lowered, for example, in winter, and the internal pressure of the condenser 2 becomes a high vacuum (730 mmHg or more) due to heat exchange with this seawater, then it flows into the low-pressure feed water heater 3. The condensate temperature will decrease.

In order to warm this cold condensate, a large amount of turbine extraction air flows into the low pressure feed water heater 3. As described above, the inside of the low-pressure feed water heater 3 has an overheat returning section, a condensing section,
It is divided into drain cooling sections Z1, Z2 and Z3. In this drain cooling section Z3, in order to discharge the drain to the outside of the feed water heater, the drain water level accumulated in the drain cooling section Z3 is kept constant so that the discharged drain does not flash. However,
As the turbine extraction air increases, the amount of drain increases, and the internal pressure of the low-pressure feed water heater 3 decreases due to the decrease in the condensate temperature.

Further, as the amount of drain increases,
The pressure loss in the drain cooling section Z3 and the pressure loss in the drain pipe 18 increase as a square ratio. As described above, most of the differential pressure of the low-pressure feed water heater 3 is dominated by the hydrostatic head, so that the water level of the low-pressure feed water heater 3 rises to compensate for the pressure loss.

The rise of the water level is balanced at a certain place due to the relation with the drain amount, but at this time, the water level control valve 16 is fully opened and the control of the drain water level becomes incomprehensible. In the worst case, the water induction is performed. There is a risk of causing.

An object of the present invention is to keep the water level control of the low pressure feed water heater stable by limiting the amount of drain flowing from the upstream low pressure feed water heater when the water level control of the low pressure feed water heater fails. Another object of the present invention is to provide a feed water heater water level control device.

[0026]

According to the present invention, an upstream feed water heater and a downstream feed water heater are connected by a drain system through a drain system, and the drain system regulates the amount of drain flowing into the downstream feed water heater. In addition to installing a control valve, an emergency control valve that releases the drain of the upstream feed water heater to the outside in an emergency drain system that is independent of the drain system is provided. It is characterized in that means for limiting the pressure based on the internal pressure of the container is provided.

[0027]

In the feed water heater water level control device of the present invention,
It is possible to prevent malfunction of the low-pressure feed water heater due to rise of the water level of the feed water heater and backflow of the drain to the steam turbine, and to obtain stable water level control.

[0028]

Embodiments of the present invention will now be described with reference to the drawings. In FIG. 1, as in the conventional case, the water level signal from the water level detector 9 is input to the subtracters 40 and 50, and subtracted between the output signal (NWL) of the signal setting device and the signal setting device 51 (NWL + 50 mm), Further, PID calculation is performed by PID calculators 42 and 52.

The output of the signal setting device 47 is input to the output limiter 43 via the signal switching device 46 which switches according to the generator load and the internal pressure of the condenser 2. That is, the water level controller 12
A command signal for narrowing the opening of the water level control valve 13 set by the signal setter 47 is input to the output limiter 43 on the side. The timing of switching the set value to the output of the signal setter 47 will be described with reference to FIG. When the generator load is equal to or higher than the predetermined value and the degree of vacuum of the condenser 2 is equal to or higher than the predetermined value, the signal switch 46 is switched to input the set value of the signal setter 47 to the output limiter 43.

As a result, the opening of the water level control valve 13 is limited by the set value. As a result, the water level of the low-pressure feed water heater 4 gradually rises, the water level control valve 11 is opened, and the drain is discharged to the condenser 2 through the drain pipe 18. By discharging a part of the drain of the low-pressure feed water heater 4 to the condenser 2 in this way, it is possible to prevent the rise of the water level in the low-pressure feed water heater 3.

Another embodiment will be described with reference to FIG. Also in this embodiment, the signal switch 56 is operated in accordance with the load of the generator and the internal pressure of the condenser 2. Output limiter
The set value from the signal setter 57 is input to 53. That is, the output of the water level controller 10 is regulated by the set value of the output limiter 53, and the opening degree of the water level control valve 11 is limited.

The switching timing from the normal control to the set value is the same as in FIG. In this case, the signal switch 56 is operated. As described above, by switching a part of the drain of the low-pressure feed water heater 4 to the condenser side, it is possible to prevent the drain water level from rising.

Still another embodiment will be described with reference to FIG. A water level control valve 69 is provided in parallel with the water level control valve 11.
The method shown in FIG. 2 can be applied to the opening / closing timing.

In the above structure, by opening the water level control valve 69, a part of the low-pressure feed water heater 4 is discharged to the condenser 2, so that the water level rise of the drain can be prevented.

Instead of the method shown in FIG. 2, the method shown in FIG. 5 is possible. It is added that the opening degree command value of the water level control valve 16 of the low-pressure feed water heater 3 is not less than a predetermined value with the signal switch 46 as an operating condition. The condition that the generator load is equal to or higher than the predetermined value and the degree of vacuum of the condenser 2 is equal to or higher than the predetermined value is the same as the case of FIG. Even in the case of applying the present embodiment, the drain can be discharged at an appropriate timing as in the case of applying the embodiment of FIG.

[0036]

As described above, in the feed water heater water level control device according to the present invention, the water level control malfunctions and the drain flows back to the steam turbine as the amount of drain increases.
It is possible to prevent problems such as so-called water induction.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a feed water heater water level control device according to the present invention.

FIG. 2 is a block diagram showing the function of the signal switch shown in FIG.

FIG. 3 is a block diagram showing another embodiment of the present invention.

FIG. 4 is a system diagram showing another embodiment of the present invention.

FIG. 5 is a block diagram showing functions of a signal switch according to another embodiment.

FIG. 6 is a system diagram showing a conventional low pressure feed water heater drain system.

FIG. 7 is a sectional view of a conventional low-pressure feed water heater.

FIG. 8 is a block diagram showing a conventional feed water heater water level control device.

[Explanation of symbols]

 3, 4 ... Low-pressure feed water heater 11, 13, 16 ... Control valve 40, 50 ... Subtractor 41, 47, 51, 57 ... Signal setter 42, 52 ... PID calculator 43, 53 ... Output limiter 46, 56 ... Signal switch

Claims (2)

[Claims] 1. A drain system is provided for connecting the upstream side feed water heater and the downstream side feed water heater by a drain system, and the drain system is provided with a control valve for adjusting the amount of drain flowing into the downstream side feed water heater. In the one provided with an emergency control valve for releasing the drain of the upstream side feed water heater to the outside in the emergency drain system independent of the drain system, the water level control signal for the control valve is used for the plant operating state and the pressure inside the condenser. A water level controller for controlling the water level of the feed water heater, which is provided with a means for limiting the water level based on the above. 2. The feed water heater water level control device according to claim 1, wherein the water level control signal to the control valve is limited based on the control valve opening together with the plant operating state and the pressure inside the condenser.