JPH01131801A - Pressure controller in deaerator - Google Patents

Abstract

PURPOSE: To suppress flushing phenomenon of a deaerator by controlling an inner pressure regulation valve for the deaerator based on the output from a pressure regulator for proportionally integrating or differentiating the differential error between the outputs of a temperature/pressure conversion circuit and a pressure detector. CONSTITUTION: A temperature detector 12 detects the temperature of water stored in a water storage tank 8. The detected temperature is inputted to a temperature/pressure conversion circuit 13 outputting a corresponding pressure set value comprising a specified function. The pressure set value is inputted to a pressure regulator 6 along with the output from a pressure detector 5 for detecting actual pressure in a deaerator 1. They are compared with each other and an inner pressure regulation valve 3 for the deaerator is opened/closed by the output from the pressure regulator 6 thus controlling introduction of auxiliary steam to the deaerator. The inner pressure of the deaerator is controlled to a lower limit set level or to a level lower by a specified level than the saturated steam pressure of stored water for the range exceeding the lower limit set level.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) This invention relates to PCB (first cut back), which is a protective operation in steam turbine power generation equipment due to a sudden decrease in fire intensity of a boiler, for example. A deaerator that can suppress the backflow of evaporation from the deaerator water tank to the deaerator, known as flooding, which tends to occur when a turbine generator is load-shedded or when a turbine-generator is started immediately after load shedding. This invention relates to an internal pressure control device.

(Prior art) Conventionally, in steam turbine power generation equipment, a closed cycle called a Rankine cycle has been formed in order to reuse feed water, and there is generally no excess or deficiency of steam or water flowing through the closed cycle. However, even if a small amount of leakage force 1 occurs outside the closed cycle system, it is equipped with a make-up water system to replenish it. It is also taken into consideration that there may be a small amount of atmospheric air intrusion from systems that are closed cycles and reach low pressures below atmospheric pressure.

In such a Rankine cycle, makeup water from outside the closed cycle naturally takes in oxygen from the atmosphere when air enters the cycle, and exists as dissolved oxygen in the water flowing inside the closed cycle. This dissolved oxygen is removed from carbon steel piping,
In particular, it causes corrosion of boiler tubes. Therefore, in steam turbine power generation equipment, dissolved oxygen is degassed to below 14 PPb by vacuum degassing in the condenser, and then superheated and degassed to below 7 PPb in the deaerator.
The pressure is increased by a group of boiler feed water pumps, and water is supplied to the boiler via a several-stage high-pressure feed water heater (C).

By the way, the first-order principle is applied to remove dissolved oxygen. In other words, the solubility of a gas in a liquid is proportional to the partial pressure of the gas acting on the liquid surface. Methods of separating oxygen and liquid by evaporation are well known.

Conventionally, degassing methods used in steam turbine power generation equipment include vacuum degassing and heating degassing. Vacuum deaeration is generally used only when there is no heating source or when deaeration is performed at low temperatures.This method of deaeration in a condenser applies pressure on the vacuum side to -722mHg relative to atmospheric pressure. Lower and degas. Since there is still a lot of dissolved oxygen if this is done alone, further heat deaeration is performed in a deaerator.

In this method, condensate containing dissolved oxygen is atomized and atomized through a spray pulp, and heated steam is brought into direct contact with the water from beneath the spray, raising the water to its saturation temperature, thereby separating the gases. This method lowers the pressure and at the same time increases the surface area of the spray water to separate oxygen from the spray water.

Heated steam to separate oxygen from spray water is usually 1.

Steam extracted from the steam turbine is sent to the deaerator, but since the steam temperature is low from the time the steam turbine generator starts up to when the load is low, steam from other auxiliary steam sources is used. has been done.

FIG. 5 is a schematic system diagram of a conventional deaerator internal pressure control device.6 In FIG. It is connected to a pipe (or auxiliary steam source) 2. Also connected to the deaerator 1 are a condensate pipe 9 that sends condensate from a condenser (not shown) and a bleed pipe 10 that sends steam turbine bleed air. The water degassed in the deaerator 1 is sent to the deaerator water tank 8 through several downcomer pipes (not shown).
Further, the deaerator 1 and the deaerator water tank 8 are connected by several balance pipes (not shown) so that the internal pressures are equal during normal operation. The downcomer pipe 11 sends water from the water storage tank 8 to the boiler feed pump.The deaerator 1 is equipped with a pressure detector 5, which detects the actual pressure inside the deaerator 1. A predetermined output signal (
Normally, 0.35 kg/aJ The internal pressure of the deaerator 1 is controlled by adjusting the amount of auxiliary steam introduced into the deaerator 1 from the steam pipe 2.

Conventional deaerator internal pressure control devices work effectively because:
When the steam turbine generator starts up and the load increases, and the pressure of the steam turbine bleed air 10 exceeds the above-mentioned pressure setting of 0.35 kg/dg, the deaerator internal pressure control valve 3 is fully opened, and at higher loads, the steam turbine bleed air pressure also increases, and the deaerator 1 is degassed by the steam turbine bleed air 10.

(Problems to be Solved by the Invention) Here, during load shedding of the steam turbine generator or load shedding accompanying the occurrence of FC8, the pressure of the steam turbine bleed air 10 drops rapidly. On the other hand, the temperature of the water stored in the deaerator water tank 8 is slightly undercooled from the saturation temperature corresponding to the extraction pressure before the load is cut off, and as a result of the sudden drop in the pressure inside the deaerator, it evaporates (flash). ).

At this time, the pressure control device in the deaerator is set to 0.35k.
g/di, and the pressure (several kilograms) is sufficient to suppress flash.
The pressure setting is far from that (g/a1g to more than 10 kg/cd method). For this reason, the proportional and integral functions do not open the control valve until the pressure inside the deaerator falls below the set value, so the operation is delayed, but the differential function detects the pressure drop. The control valve 3 is opened to introduce auxiliary steam into the deaerator 1 to alleviate the drop in pressure inside the deaerator. However, since the amount of auxiliary steam is not introduced to ensure the internal pressure of the deaerator l sufficient to suppress the flash, the flash phenomenon continues.

On the other hand, due to the reduced steam turbine bleed air temperature, pressure, the heating effect of the feedwater heater (not shown) leading to the deaerator 1 is reduced and the heating effect of the lower hot well of the condenser (not shown) is reduced. Since the water (approximately 40° C.) flows into the deaerator 1 from the condensate pipe 9 in the form of cold condensate that is not heated much, the internal pressure of the deaerator 1 is further reduced. During flushing, when the pressure in the water tank 8 is higher than that in the deaerator 1, the water accumulated at the bottom of the deaerator 1 stops flowing into the water tank 8, but water continues to be supplied from the water tank 8 to the boiler in a relatively small amount. I'm here.

The water level in the water tank 8 becomes abnormally low.

A deaerator water level control device (not shown) sends a large amount of condensate to the deaerator in response to this water level drop, and the amount of water accumulated in the deaerator 1 continues to increase as the flush phenomenon continues. When the static water head and the pressure difference are balanced, water flows into the water tank 8, and the water storage tray also lowers, suppressing flushing. However, because this change is rapid, water falls all at once from the deaerator 1 to the water storage tank 8, causing water to accumulate. Although the flush phenomenon ends when the water level in the tank 8 is raised to an abnormally high level, the water level in the water storage tank 8 drastically changes from abnormally low to abnormally high, causing the deaerator water level control device to swing significantly.

Among the phenomena accompanying these series of flashes, the flush causes the deaerator 1 and water tank 8 to reach the saturated vapor pressure of cold condensate (maximum -722 amHg gauge), so the water head from the deaerator water tank 8 to the BFP increases. The difference is almost 10 meters, and there is a danger that water will not come down from downpipe 11.
There is also a risk that the required net suction head (NPSH) of BFP may not be secured. In addition, water that has accumulated abnormally in the deaerator 1,
If the water passes through the bleed pipe 10 and is not stopped by a check valve on the way, there is a risk that the water may flow into the steam turbine and cause unexpected troubles due to water induction.

An object of the present invention is to provide a deaerator internal pressure control device that can suppress the highly dangerous deaerator flash phenomenon.

[Structure of the invention]

(Means for Solving the Problems) The deaerator internal pressure control device of the present invention directly contact heats condensate using turbine extraction or other auxiliary steam, and separates and removes dissolved gas in the condensate. The gas system includes a temperature/pressure conversion circuit that outputs a pressure setting value corresponding to the temperature of the deaerator water tank as a constant function, and a pressure detector that detects the actual pressure inside the deaerator, The output of this temperature/pressure conversion circuit and the output of the pressure detector are input, and when a deviation occurs between the two outputs, the error is proportional and integrated.

The present invention is characterized in that the pressure regulating valve in the deaerator is opened and closed in accordance with the output of the differentiating pressure regulator to control the introduction of auxiliary steam into the deaerator.

(Function) In the present invention, the output of the temperature/pressure conversion circuit and the output of the pressure detector that detects the actual pressure inside the deaerator are compared using a pressure regulator, and when a deviation occurs between the two outputs, The output obtained by proportionally, integrally, and differentiated the error amount opens and closes the pressure control valve in the deaerator, and auxiliary steam is introduced into the deaerator. As a result, the pressure inside the deaerator will be set to the lower limit pressure setting value when starting the plant, and in the range exceeding the lower limit pressure setting value, the pressure will be set to the saturated steam pressure value of the stored water minus a certain value. Pressure control.

(Example) The present invention will be described below with reference to FIG. FIG. 1 is a system diagram showing an embodiment of the present invention, and the same parts as in FIG. 5 are denoted by the same reference numerals, and the explanation thereof will be omitted. That is, in FIG. 1, reference numeral 12 indicates a temperature detector, which detects the temperature of water stored in the water tank 8. This detected temperature is input to a temperature/pressure conversion circuit (or temperature/pressure converter) 13, which outputs a pressure setting value that is a constant function and matches the storage water temperature.

This pressure set value is input to the pressure regulator (or calculation circuit) 6. In addition, the output of the pressure detector 5 that detects the actual internal pressure of the deaerator 1 is also input to this pressure regulator (or calculation circuit) 6, and the output is compared with the pressure setting value that matches the storage water temperature.
The output of this pressure regulator (or arithmetic circuit) 6 drives the deaerator internal pressure regulating valve 3 to open and close.

FIG. 2 is an embodiment showing the detailed configuration of the temperature/pressure conversion circuit 13. Reference numeral 14 denotes a temperature/pressure converter (or temperature/pressure converter) in which a function for outputting a saturated steam pressure value suitable for the storage temperature of the water tank 8 is incorporated. This output is sent to the adder 15, and the output from the bias setter 16 that adds a pressure drop bias is subtracted, or the lower limit pressure setter 18 that sets the lower limit of the pressure. It is sent to the pressure regulator (or calculation circuit) 6 via the selector 17.

Next, the operation of the deaerator internal pressure control device of the present invention having the above configuration will be explained. When starting or stopping the plant, the lower limit pressure set value (
Normally, the pressure inside the deaerator 1 is controlled at 35 kg/Jy). Further, when the steam turbine generator starts up and takes on a load and the steam turbine extraction pressure exceeds the lower limit set pressure, the deaerator internal pressure control valve 3 closes and the deaeration is switched to steam turbine extraction. In this way, during normal operation, it functions in exactly the same way as before.

By the way, when the steam turbine generator undergoes load shedding, the steam turbine extraction pressure rapidly decreases. On the other hand, since the water stored in the deaerator water tank 8 has a saturated steam temperature that matches the bleed pressure before load shedding, the saturated steam pressure that matches the bleed pressure before load shedding, that is, the water storage temperature, can be significantly increased. Introduce auxiliary steam to prevent a severe flash phenomenon from occurring.

In this way, in the control device of the present invention, the temperature of the water stored in the water storage tank 8 is constantly detected by the temperature detector 12, and the pressure set value is set by reducing the bias by a slight pressure drop to the saturated steam pressure that matches the storage water temperature. The auxiliary steam can be introduced into the deaerator 1 by driving the control valve 3 so that Furthermore, economical operation is possible in which the pressure in the deaerator is gradually reduced by the pressure drop bias, and the amount of auxiliary steam is gradually reduced.

In this way, the severe flash phenomenon during load shedding can be avoided, so the abnormal drop in water level in the deaerator water tank that accompanies the conventional severe flash phenomenon, the abnormally high water level that occurs subsequently, and the downcomer pipe It is possible to avoid the phenomenon in which water becomes difficult to fall, the NPSH of the boiler feed pump can be ensured, and water does not accumulate abnormally in the deaerator 1, so the risk of water induction can be avoided.

In addition, also in the other embodiment of the present invention shown in FIG. It may also be a downcomer pipe 11.

This detected temperature is sent to the temperature calculation circuit 19, which calculates an intermediate value or average value, and sends the output to the temperature/pressure conversion circuit 13.
This configuration improves the reliability of temperature detection.

Furthermore, in another embodiment shown in FIG. 4, the deaerator internal pressure control device of the present invention is additionally installed in the deaerator internal pressure control device of the conventional configuration (FIG. 5). A control system is created in which seven parts of the components shown in FIGS. 1 and 2 are rearranged and combined with a high selector (17') that gives priority to the opening direction signal of the control valve 3.

〔Effect of the invention〕

As described above, in the present invention, the temperature/
The output of the pressure conversion circuit is compared with the output of the pressure detector that detects the actual pressure inside the deaerator, and when a deviation occurs between them, the output of the pressure controller is used to proportionally, integrate, and differentiate the error. By opening and closing the deaerator internal pressure control valve to control the introduction of auxiliary steam into the deaerator.

The pressure inside the deaerator is controlled so that it reaches the lower limit pressure set value when starting the plant, and in the range that exceeds the lower limit pressure set value, the pressure is controlled so that it becomes the pressure value obtained by subtracting a certain value from the saturated steam pressure of the stored water. Rare.

If the pressure inside the deaerator does not drop significantly from the saturated steam pressure of the water stored in the water tank, the occurrence of a severe flash phenomenon can be avoided.

[Brief explanation of the drawing]

FIG. 1 is a system configuration diagram showing an embodiment of the deaerator internal pressure control device of the present invention, FIG. 2 is a configuration circuit diagram showing a temperature/pressure conversion circuit used in the present invention, and FIGS. Figure 4 is a system configuration diagram showing other different embodiments of the present invention;
The figure is a schematic system diagram showing a conventional deaerator internal pressure control device. 1... Deaerator 2... Auxiliary steam pipe 3... Deaerator internal pressure control valve 5.5'... Pressure detector 6.6'... Pressure regulator (or calculation circuit ) 7... Pressure setting device 8... Deaerator water tank 9... Condensate pipe 10... Bleed pipe 11... Downpipe pipes 12, 12', 12'... Temperature detector 13. ...Temperature/pressure conversion circuit 14...Temperature 1 degree/pressure converter 15...Adder 16...Bias setter 17, 17'...High selector 18...Lower limit pressure setter 19... ...Temperature calculation circuit Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5

Claims (1)

[Claims] (1) In a deaerator system that directly contacts and heats condensate using turbine extraction air or other auxiliary steam to separate and remove dissolved gas in the condensate, the pressure setting value corresponding to the temperature of the deaerator water tank is set. It is equipped with a temperature/pressure conversion circuit that outputs an output as a constant function and a pressure detector that detects the actual pressure inside the deaerator. When a deviation occurs in the output, it is configured to open and close the pressure control valve inside the deaerator based on the output of the pressure controller that proportionally, integrally, and differentiates the error to control the introduction of auxiliary steam to the deaerator. A deaerator internal pressure control device characterized by: