JPH0278804A - Control device for water level in feed water heater - Google Patents

Abstract

PURPOSE:To prevent production of a sudden fluctuation in a level in a high pressure feed water heater by a method wherein drain flush occurring due to a drop in a generator load or a delay in a drain temperature drop when a plant is in a transient state is computed as a void amount, and the opening of a regulating valve is regulated in response to the computed void amount. CONSTITUTION:A temperature detector 15 and a pressure detector 16 are connected to a drain line 5 connected to a high pressure feed water heater 4, and detecting signals from the two detectors 15 and 16 are inputted to a void amount computing control device 17 togetherwith a detecting signal from a level detector 11. The openings of regulators 6, 7, and 9 are controlled by means of a control signal from the void amount computing control device 17. Namely, upon the occurrence of a state in which a plant load is dropped and a feed water temperature is reduced to generate drain flush, a void amount is computed by the void amount computing control device 17, a valve opening command signal is outputted, by means of the signal, the regulating valves 6, 7, and 9 are opened to respective proper openings, and a rapid increase in a level in a high pressure feed water heater is prevented from occurring.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a water level control device for a feed water heater that heats feed water by using air extracted from a steam turbine.

(Prior Art) Generally, in a steam turbine plant, a water supply system is provided with a plurality of stages of feed water heaters in order to increase the thermal efficiency of the plant by heating the water supplied to the boiler using turbine bleed air or pre-stage drain.

FIG. 3 is a schematic diagram of a water supply system that supplies condensate in a deaerator water storage tank to a boiler using a water supply pump. After the condensate is pressurized by the feedwater pump 3, it is passed through a plurality of high-pressure feedwater heaters 4 (only one of which is shown in the figure).
The water is then supplied to a boiler (not shown).

The high-pressure feedwater heater 4 is supplied with steam turbine bleed air and drain from the pre-stage feedwater heater, where it exchanges heat with the feedwater. The drain generated by the heat exchange is sent to the next high-pressure feed water heater via the drain line 5. Further, the drain line 5 is connected to the deaerator 1 via the first regulating valve 6, to the low pressure feed water heater 8 via the second regulating valve 7, and further via the third regulating valve 9. It is connected to the condenser 10.

By the way, the water level in the high-pressure feed water heater 4 is detected by a water level detector 11, and when the water level exceeds the normal standard water level (N, W, L), a first controller 12 turns on the first control valve. 6 is controlled in the open direction, and drain is discharged to the deaerator 3. In addition, the discharge amount is insufficient by the first control valve 6 alone, and the water level is normally lower than the standard water level α (N, W
, L0α), the second control valve 7 is controlled in the opening direction by the second controller 13, and the drain is discharged to the low-pressure feed water heater 8. Furthermore, the first control valve 6 and the second
Even if both of the control valves 7 are opened, the amount of drain discharged is insufficient, and when the normal water level reaches β (N, W, , L + β), the third control valve 9 is moved in the opening direction by the third controller 14. The condensate is discharged into the condenser 10 under controlled conditions. In this way, the water level in the feed water heater is always N, W, LSN,
Controlled by W, L+α, N, W, L+β.

(Problem to be Solved by the Invention) However, when a steam turbine plant has to suddenly reduce the power generation load from rated operation due to plant shutdown, etc., the internal pressure of the high-pressure feed water heater decreases due to the load drop. decreases in proportion to the decrease in bleed pressure, but since the temperature of the feed water stored in the deaerator water storage tank 2 falls slowly, the temperature of the drain that exchanges heat with the feed water also falls slowly. .

Therefore, the drain discharged from the high-pressure feed water heater 4 to the deaerator 1 may cause a flash phenomenon.

That is, as shown in FIG. 4, when the load W decreases, the feed water heater internal pressure P also decreases correspondingly. If this internal pressure P decreases, the drain saturation temperature T1
is also descending.

However, since a large amount of feed water is stored in the deaerator water storage tank, even if the load starts to drop, the feed water temperature T2 starts to drop after a delay of t seconds. Therefore, the temperature T of the drain whose temperature drops by exchanging heat with the feed water also exhibits the same temperature drop phenomenon as the feed water temperature T2. and drain temperature T
The re-drain flash phenomenon begins at the drain flash generation point a, where 3 and the drain saturation temperature TI intersect.

However, when a drain flush occurs in this way, the control of drain discharge by the first control valve 6 is disturbed, and the water level of the feed water heater drain rises rapidly, causing a high water level alarm and There are problems such as a low level warning being generated and the water level control system being greatly disturbed.

In view of these points, the present invention provides a feedwater heater water level control device that can prevent feedwater heater water level fluctuations due to drain flush as described above and perform stable control during generator load drops and plant transient changes. The purpose is to obtain.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides a feedwater heater water level control device for a steam turbine plant having a feedwater heater that heats feedwater using extracted air from a steam turbine. The drain flash that occurs due to the delay in the drop in drain temperature during operation is calculated as a void amount by a void amount calculator, and the back-up control valve attached to the feed water heater is controlled by the valve control device in accordance with the calculated void amount. It is characterized by adjusting the opening degree.

(Function) When the pressure inside the high-pressure feed water heater decreases when the generator load drops or the plant is in a transient state, the drain flash that occurs due to the delay in the drain temperature drop due to the drain temperature and drain pressure is calculated as the void amount. The control valve is controlled in the opening direction by the valve opening command value obtained by the calculation, and a sudden rise in the water level of the high pressure feed water heater is prevented.

(Example) Hereinafter, an example of the present invention will be described with reference to FIGS. 1 and 2. Note that the same parts in FIG. 1 as in FIG. 3 are designated by the same reference numerals, and detailed explanation thereof will be omitted. 6 In FIG. 1, a temperature detector 15 and a pressure detector 16 are connected to the drain line 5 connected to the high-pressure feed water heater 4, and the detection signals from the rain detectors 15 and 16 are used to detect the water level. The detection signal from the detector 11 is input to the void amount calculation control device 17, and the control signal from the void amount calculation control device 17 controls the first controller 6, the second controller 7, and the third controller. A total of nine opening degree controls are performed.

In other words, when the plant load begins to drop and the feed water temperature drops, causing a drain flush,
The void amount calculation control device 17 calculates the void amount and outputs a valve opening command signal, and the valve opening command signal is used for each control valve 6. 7. 9 is opened to an appropriate opening degree, thereby preventing a sudden rise in the water level of the high pressure feed water heater and preventing disturbances in the control system.

FIG. 2 is a block diagram showing the configuration of the void amount calculation and control device 17, in which the detection signal from the temperature detector 15 is converted into specific enthalpy in the function generator 20, and the output signal is sent to the flash rate calculation and control device. 21.

Further, the detection signal from the pressure detector 16 is compared with the static water head in the adder 22, the pressure signal is converted into the specific enthalpy of saturated water in the function generator 23, and the output signal is sent to the flash rate calculator 21. is input. The pressure signal is further converted into specific enthalpy of saturated steam by the function generator 24, and its output signal is also input to the flash rate calculator 21.

The flash rate calculator 21 calculates a flash rate based on the specific enthalpy of the drain temperature, the specific enthalpy of saturated water, and the specific enthalpy of saturated steam, and this flash rate signal is input to the void rate calculator 25.

On the other hand, the pressure signal is converted into a specific volume of steam by the function generator 26, and is also converted into a specific volume of drain by the function generator 27, and the specific volume of steam and the specific volume of drain signal 1 are also calculated by the above-mentioned void ratio calculation. The signal is input to the device 25.

The void ratio calculator 25 calculates the void ratio based on the specific volume of steam and drain converted by the function generators 26 and 27, and the output signal from the flash ratio calculator 21.

Further, the generator load signal is input to the function generator 28, where it is converted into a drain amount, and the void amount is calculated by the void amount calculator 29 based on the drain amount signal and the void ratio signal from the void ratio calculator 25. be done.

Further, the detection signal from the temperature detector 15 is also input to a function generator 30, where it is converted into a saturated pressure, and by this saturated pressure signal and the pressure signal obtained by the pressure detector 16, A corrected differential pressure is calculated in the corrected differential pressure calculator 31, and this corrected differential pressure signal is input to the valve capacity calculator 32.

On the other hand, the temperature signal from the temperature detector 15 is converted into a drain specific gravity by a function generator 33, and the drain specific gravity signal is also input to the valve capacity calculator 32, where the valve capacity is calculated together with the corrected differential pressure signal. be done.

This valve capacity signal is then input to the light control device 34,
The valve opening command signal from the valve control device 34 is transmitted to each control valve 7.
, 9, and the opening degree of each control valve 7, 9 is controlled.

As a result, stable control of the high-pressure feedwater heater water level can be obtained at all times, regardless of generator load drops and transient phenomena.

〔Effect of the invention〕

As explained above, in the present invention, the drain flash that occurs due to a delay in lowering the drain temperature during a generator load drop or a transient state of the plant is calculated as a void amount, and the amount of voids is adjusted according to the calculated void amount. By adjusting the opening degree of the valve, it is possible to prevent sudden fluctuations in the water level of the high-pressure feedwater heater, and it is possible to maintain stable water level control of the high-pressure feedwater heater when the plant load drops. .

[Brief explanation of the drawing]

FIG. 1 is a schematic system diagram of the feed water heater water level control device of the present invention, FIG. 2 is a block diagram of the void Mke1 calculation control device, FIG. 3 is a schematic system diagram of the conventional feed water heater water level control device, and FIG. The figure is an explanatory diagram of the operation. 1... Deaerator, 2... Deaerator water storage tank, 3...
Water supply pump, 4... High pressure water heater, 5... Drain line, 6... First control valve, 7... Second control valve, 9... Third control valve, 15・・Temperature detector, 16・
...Pressure detector, 2 u...Flash rate calculator, 25
...Void ratio calculator, 29...Void amount calculator, 3
2...Valve capacity calculator. Applicant's agent Mr. Sato Figure 1 Figure 3

Claims (1)

[Claims] In a feedwater heater water level control system for a steam turbine plant that has a feedwater heater that heats the feedwater using extracted air from the steam turbine, the drain flash that occurs due to a delay in the drop in drain temperature during a generator load drop or during a transient state of the plant is controlled. It has a void amount calculator that calculates the void amount, and a valve control device that adjusts the opening degree of the backup control valve attached to the feed water heater in accordance with the void amount calculated by the void amount calculator. A feed water heater water level control device characterized by: