JPH0554002B2 - - Google Patents

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) This invention relates to FCB (first cut back), which is a protective operation for steam turbine power generation equipment, for example, when the fire intensity of a boiler suddenly decreases. A deaerator that can suppress the backflow of evaporation from the deaerator water tank to the deaerator, called flushing, which tends to occur when the turbine generator is load-shedded or when the 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. No, but
Even if a small amount of leakage 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 causes corrosion of carbon steel piping, especially boiler tubes. Therefore, in steam turbine power generation equipment, the dissolved oxygen is degassed to below 14 ppb by vacuum deaeration in the condenser, and then superheated and degassed to below 7 ppb in the deaerator, and then the pressure is increased by the boiler feed water pump group ( Water is supplied to the boiler via several stages of high-pressure feed water heaters).

By the way, the following 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 degassing is generally used only when there is no heating source or when degassing at low temperatures.This method of degassing in a condenser applies pressure on the vacuum side to -722 mmHg 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.

This method atomizes and atomizes condensate containing dissolved oxygen through a spray valve, and brings it into direct contact with the water as if blowing up heated steam from below the spray water, thereby raising the spray water to its saturation temperature. Therefore, while lowering the gas partial pressure, the surface area of the sprayed water is increased to separate oxygen from the sprayed water.

The heated steam that separates oxygen from the spray water is typically
The steam extracted from the steam turbine is sent to the deaerator, but since the steam turbine generator is started up and the load is low, the steam temperature is low.
Steam from other auxiliary steam sources is used.

FIG. 5 is a schematic system diagram of a conventional deaerator internal pressure control device. In FIG. 5, the deaerator 1 is connected to an auxiliary steam pipe (or auxiliary steam source) 2 via an electric valve 4 and a deaerator internal pressure control valve 3. 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. In addition, downpipe 11
The water in water tank 8 is pumped into the boiler feed pump (hereinafter referred to as BFP).
).

A pressure detector 5 is attached to the deaerator 1, and the pressure detector 5 detects the actual pressure inside the deaerator 1 and sends it to a pressure regulator (or pressure regulator) 6.
Here, it is compared with a predetermined output signal from the pressure setting device 7 (usually 0.35 kg/cm ² g), and the deviation is subjected to calculations such as proportionality, integration, and differentiation, and the calculated signal is sent to the deaerator. The amount of auxiliary steam introduced into the deaerator 1 from the auxiliary steam pipe 2 is controlled by applying it to the pressure regulating valve 3 to adjust the valve opening and adjusting the amount of auxiliary steam introduced into the deaerator 1 from the auxiliary steam pipe 2.

The conventional deaerator internal pressure control device operates effectively only when the plant starts and stops, and when the steam turbine generator starts and the load increases, the pressure of the steam turbine extracted air 10 reaches the above-mentioned pressure. Setting 0.35
When the load exceeds Kg/cm ² g, the deaerator internal pressure control valve 3 is fully closed, and at higher loads, the steam turbine bleed pressure also increases, and the steam turbine bleed air 10 degasses the deaerator 1. It is done.

(Problems to be solved by the invention) Here, load shedding of a steam turbine generator,
During the load shedding that accompanies the occurrence of FCB, 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, the water evaporates at once. Start (flash).

At this time, the pressure control device inside the deaerator is set to
The pressure setting is 0.35 kg/cm ² g, which is far from the pressure sufficient to suppress flashing (several kg/cm ² g to more than ten kg/cm ² g). For this reason, the proportional and integral functions do not open the control valve 3 until the pressure inside the deaerator falls below the set value, so the operation is delayed, but the differential function detects the pressure drop. Open the control valve 3 to introduce auxiliary steam into the deaerator 1,
Mitigates 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 1 sufficient to suppress flashing, the flashing phenomenon continues.

On the other hand, due to the decrease in steam turbine bleed air temperature and pressure, the heating effect of the feedwater heater (not shown) leading to the deaerator 1 is reduced, and the condensate in the lower hotwell of the condenser (not shown) is reduced. (approximately 40° C.) flows into the deaerator 1 from the condensate pipe 9 in the form of cold condensate that is not heated much, thereby further reducing the internal pressure of the deaerator 1. 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 does not flow down to the water tank 8, but water continues to be supplied from the water tank 8 to the boiler in a relatively small amount. As a result, the water level in the water tank 8 drops abnormally.

A deaerator water level control device (not shown) sends a large amount of condensate to the deaerator in accordance with this water level drop, and deaerator 1
As the flash phenomenon continues, the amount of water accumulated in the tank continues to increase, but when this static water head and the pressure difference are balanced, it flows into the water tank 8, which lowers the storage water temperature and suppresses the flash, but this change is rapid. , deaerator 1
Water suddenly falls from the water tank 8 to the water tank 8, causing the water level in the water tank 8 to reach an abnormally high level, and the flashing phenomenon ends. However, since the water level in the water tank 8 drastically changes from abnormally low to abnormally high, swings wide.

Among the phenomena accompanying these series of flashes,
The saturated vapor pressure of the cold condensate in the deaerator 1 and water tank 8 due to flushing (maximum -722mmHg gauge)
Therefore, there is a risk that the difference in water head from the deaerator water tank 8 to the BFP will approach 10 m, and water will no longer come down from the downcomer pipe 11, and that the required net suction head (NPSH) of the BFP will not be secured. In addition, if water that has accumulated abnormally in the deaerator 1 passes through the bleed pipe 10 and is not stopped by a check valve in the middle, there is a risk that it will flow into the steam turbine and cause unexpected trouble in the water induction. are doing.

An object of the present invention is to provide a deaerator internal pressure control device that can suppress the flashing phenomenon of condensate in a deaerator water tank.

[Structure of the invention]

(Means for Solving the Problems) The deaerator internal pressure control device of the present invention controls condensate by using auxiliary steam supplied via the deaerator internal pressure control valve when the turbine is started or stopped. Degassing involves direct contact heating, and when the turbine bleed air exceeds a predetermined pressure, the supply of auxiliary steam is cut off and the turbine bleed air is supplied to directly contact heat the condensate and separate and remove dissolved gases in the condensate. a temperature/pressure conversion circuit that determines the saturated steam pressure corresponding to the temperature of condensate in the deaerator storage tank and outputs it as a set value; a pressure detector that detects the actual pressure inside the deaerator; temperature/
Compare the output of the pressure conversion circuit and the output of the pressure detector, and when a deviation occurs, adjust the opening degree of the pressure control valve inside the deaerator so that the saturated steam pressure corresponds to the temperature of the condensate. The apparatus is characterized by comprising means for controlling the introduction of auxiliary steam into the deaerator.

(Function) In the present invention, the output of the temperature/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, the saturated vapor pressure corresponding to the temperature of the condensate is determined. Adjust the opening of the deaerator internal pressure control valve so that 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. Control pressure.

(Example) The present invention will be described below with reference to FIG. 1st
The figure is a system diagram showing one embodiment of the present invention, and the same parts as in FIG. 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, and a pressure set value corresponding to the storage water temperature, which is a constant function, is output.

This pressure setting value is determined by the pressure controller (or calculation circuit)
6 is input. 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 is compared with the pressure set value based on the storage water temperature and calculated. The opening degree of the deaerator internal pressure control valve 3 is adjusted by the output of this pressure regulator (or arithmetic circuit) 6.

FIG. 2 is an embodiment showing the detailed configuration of the temperature/pressure conversion circuit 13. Reference numeral 14 is a temperature/pressure converter (or temperature/pressure converter), and a water storage tank 8
It has a built-in function that outputs the saturated steam pressure value corresponding to the storage water temperature. 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 internal pressure of the deaerator 1 is controlled by the lower limit pressure set value (usually 0.35 kg/cm ² g) set by the lower limit pressure setting device 18. Further, when the steam turbine generator starts up and takes on a load and the extraction pressure of the steam turbine exceeds the lower limit set pressure, the deaerator internal pressure control valve 3 is closed 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 drops rapidly. On the other hand, the water stored in the deaerator water tank 8 has a saturated steam temperature that matches the bleed pressure before load shedding, so the saturated steam pressure that met 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 corresponding to the stored water temperature. The auxiliary steam can be introduced into the deaerator 1 by driving the control valve 3 so that In addition, economical operation is possible in which the pressure in the deaerator is gradually lowered by using the pressure drop bias, and the amount of auxiliary steam is gradually reduced.

In this way, the severe flashing phenomenon during load shedding can be avoided, and the abnormally low water level in the deaerator water tank that accompanies the conventional severe flashing 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 the other embodiment of the present invention shown in FIG. 3, reference numerals 12, 12', and 12'' are temperature detectors, respectively, and the detection locations are located at other locations where the temperature distribution of the water tank 8 has little difference or It may be a downcomer pipe 11.This detected temperature is sent to a temperature calculation circuit 19, an intermediate value or an average value is calculated, and the output thereof is sent to a temperature/pressure conversion circuit 13.
This configuration can improve 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 some 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 output of the temperature/pressure conversion circuit which calculates the saturated steam pressure corresponding to the temperature of the deaerator water tank and outputs it as a set value, and the output of the actual pressure inside the deaerator are combined. When a deviation occurs, adjust the opening degree of the pressure control valve in the deaerator so that the saturated steam pressure corresponds to the temperature of the condensate.
By controlling the introduction of auxiliary steam to the deaerator, the pressure inside the deaerator is set to the lower limit pressure set value at the time of plant startup, and in the range exceeding the lower limit pressure set value, the saturated steam pressure of the stored water is adjusted. If the pressure is controlled so that the pressure value is obtained by subtracting a certain value from the value, and the pressure inside the deaerator does not drop significantly from the saturated steam pressure of the water stored in the water tank, it is possible to avoid the occurrence of a severe flash phenomenon. can.

[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 FIG.
4 and 4 are system configuration diagrams showing other different embodiments of the present invention, and FIG. 5 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, 1
0...Bleed pipe, 11...Down pipe, 12,12',
12''... Temperature detector, 13... Temperature/pressure conversion circuit, 14... Temperature/pressure converter, 15... Adder, 16... Bias setting device, 17, 17'...
High selector, 18... Lower limit pressure setting device, 19
...Temperature calculation circuit.

Claims (1)

[Claims] 1 When the turbine is started or stopped, condensate is directly contacted and heated by auxiliary steam supplied through the deaerator internal pressure control valve, and after the turbine bleed air exceeds a predetermined pressure, the supply of the auxiliary steam is cut off. and in a deaerator which directly contact heats the condensate by supplying the turbine bleed air and separates and removes dissolved gas in the condensate, the temperature corresponds to the temperature of the condensate in the deaerator water tank. A temperature/pressure conversion circuit that determines saturated steam pressure and outputs it as a set value, a pressure detector that detects the actual pressure inside the deaerator, and an output of the temperature/pressure conversion circuit and an output of the pressure detector. and when a deviation occurs, adjust the opening degree of the pressure control valve in the deaerator so that the pressure becomes saturated steam pressure corresponding to the temperature of the condensate, and send the auxiliary steam to the deaerator. A deaerator internal pressure control device characterized by comprising means for controlling the pressure to be introduced into a deaerator.