JPS5825924B2 - Heat exchanger saturated water level detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a water level detection device, and particularly to a water level detection device suitable for use in a deaerator water storage tank, a tubular heat exchanger, and the like.

Conventional water level detection devices for deaerator water storage tanks include a method that measures the water level by detecting the difference in the static water head between the standard water gauge water level at the same pressure as the tank internal pressure and the tank water level, and a method that measures the water level using a float. There is a method to detect it.

However, in the former case, when the pressure in the tank changes over a wide range, the error increases with changes in the saturated water specific gravity, and in the latter case, the error in the water level detection piping and the water level increase due to a sudden drop in the pressure in the tank. Water in the detector sometimes caused a flash, making measurements impossible.

The purpose of the present invention is to keep the water in the piping always below the saturation temperature by replenishing the water level detection piping with water at a lower temperature than the water stored in the tank, even if a sudden drop in pressure occurs. It is an object of the present invention to provide a water level detection device that prevents flushing in a detection pipe and at the same time has a negligible measurement error due to water injection.

The present inventors have confirmed that the reason why the output signal of the water level detector generates pulsations even though the actual water level in the deaerator water storage tank is constant is as follows.

In other words, the water temperature in the water level detection piping and the water level detection meter is lower than the water temperature in the deaerator water storage tank under normal conditions due to the temperature drop due to heat radiation, but due to the sudden decrease in the pressure inside the water storage tank, the water temperature in the deaerator water storage tank is The temperature inside the air storage tank decreases and matches the water temperature inside the water level detection piping and water level detection meter.

If the pressure continues to drop further, the temperature drop due to heat dissipation from the water level detection piping cannot be followed up, causing a flash within the water level detection piping and the water level detector.

From this, it was confirmed through plant operation that the float of the water level detector pulsated up and down, and the output signal of the water level detector pulsated.

As a means to prevent this flushing, by injecting water at a temperature lower than the water temperature of the deaerator water storage tank and always keeping the temperature lower than the saturation temperature inside the tank, flushing within the piping can be prevented even when the pressure suddenly drops. Pulsation of the meter's output signal can be prevented.

Since the water in the deaerator water storage tank is heated by the turbine extraction, the water temperature increases in proportion to the turbine output, and the specific gravity decreases.

On the other hand, since the deaerator inlet condensate used for water injection is also heated in the low-box feed water heater by the turbine bleed air, the water temperature increases and its specific gravity decreases in proportion to the turbine output.

Therefore, although the difference between the water temperature in the deaerator water storage tank and the water injection temperature also changes in proportion to the turbine output, the amount of change is small, so there is little measurement error, and it can be put to practical use.

If the specific gravity difference corresponding to the temperature difference is corrected in advance, the measurement accuracy will be further improved.

In the case of a turbine trip, the flow rate of the turbine extraction air for the condensate heater and the turbine extraction air for deaerator heating becomes zero, and both the condensate temperature at the deaerator inlet and the temperature inside the deaerator water storage tank decrease. .

However, because the water capacity of the water level detection water side piping is not less than the water storage capacity of the deaerator water storage tank, and because the water temperature to be injected is relatively low, the water temperature in the water level detection piping is below the saturation temperature. Flushing does not occur in the water level detection piping.

An embodiment of the present invention will be described below with reference to the drawings.

Condenser 2 of a thermal power plant; Accumulated condensate is pumped up by a condensate pump 4, passes through a condensate pipe 3, is heated by 1T of extracted air from a turbine 1 in a condensate heater 5, and is then transferred to a deaerator 6. sent to.

The condensate sprayed in a mist form by the spray nozzle 7 in the deaerator is heated and degassed by the deaerator heating turbine bleed air 8, and is temporarily stored in the deaerator water storage tank 9.

The condensate stored in the deaerator water storage tank is supplied to the boiler 18 by the boiler feed pump 10.

The water level of the deaerator water storage tank 9 is determined by the water side piping 11 for water level detection.
and is led to a water level detector 13 by a steam side piping 12 for water level detection.

The water level transmitter 14 converts the detected water level into an air signal or an electric signal, and transmits the signal to a control instrument, a monitoring instrument, or the like.

For flash prevention water injection, the outlet condensate of the condensate heater 5 is adjusted to the required flow rate using the water injection flow control valve 16, the water injection pipe 15 is wrapped around the water level detector 13, the water level detector 13 is cooled, and the water level is detected. Water is injected into the water side piping 11.

As shown in FIG. 2, the condensate temperature 20 at the outlet of the condensate heater 5 is always lower than the water temperature 19 in the deaerator water storage tank, and has a substantially constant temperature difference 23.

This means that during normal operation, the water temperature in the pipe 11 is kept lower by a constant temperature 23 than the water temperature 19 in the deaerator tank, which has the effect of preventing measurement errors due to excessive cooling.

Considering the case where the turbine trips during normal operation, if there is no water injection piping, the flow rate of the deaerator heating turbine bleed air 8 and the condensate heater turbine bleed air 17 becomes zero at the same time as the turbine trips, as shown in Fig. 3. As shown, the water temperature 19 in the deaerator water storage tank drops rapidly.

At this time, the temperature 24 inside the pipe for water level detection without water injection is also
Although it decreases due to heat dissipation, the water temperature in the deaerator water storage tank is 19
The decline is more gradual than that of

Therefore, after the intersection 25, the temperature 24 inside the water level detection pipe becomes higher than that without water injection, and a flash occurs in the water level detection pipe 11.

Therefore, according to the present invention, a water injection pipe 15 is provided to inject condensate at the outlet of the condensate heater 5 which is lower than the water temperature 19 in the deaerator water storage tank indicated as the condensate temperature 20 at the outlet of the condensate heater 5. As a result, the temperature 26 inside the water level detection pipe when water is injected is always lower than the water temperature 19 inside the deaerator water storage tank by a temperature difference 23, which prevents flash from occurring in the water level detection pipe 11 and stabilizes the water level detection pipe 11. This has the effect of making it possible to detect the water level.

FIG. 4 shows another embodiment of the present invention. What is different from FIG. 1 is that FIG. The only point is that this is an example of a type heat exchanger.

In the case of a tube heat exchanger, the condensate generated in the condensate heater 5 and the condensate sent from the condensate pipe 3 are not mixed, but the condensate taken out from the condensate pipe 3 at the outlet is Wrap the water injection pipe 15 around the water level detector 13, and
After cooling, water is injected into the part of the water side piping for water level detection closest to the water level detector.

Using the condensate heater outlet condensate as water injection is the second
In the same manner as shown in the figure, it is possible to always inject water at a temperature lower than the saturation temperature inside the feed water heater, which has the effect that measurement errors can be ignored even during normal operation.

During a turbine trip, the water level in the condensate heater drops rapidly, but by injecting water at a temperature lower than the saturation temperature in the condensate heater, flushing in the water level detection piping is prevented and a stable This has the effect of enabling water level detection.

According to the present invention, the water temperature in the water level detection piping of the saturated water storage tank can always be maintained at a lower temperature than the water temperature in the water storage tank by a certain temperature difference, so that the deviation in water level measurement can always be kept constant. can.

Furthermore, even if the internal value of the saturated water tank suddenly decreases, there is an effect of preventing flushing within the water level detection piping and the water level detection meter.

[Brief explanation of the drawing]

Fig. 1 is a piping system diagram of the present invention, Fig. 2 is a diagram showing the relationship between turbine output and condensate temperature, water temperature in the deaerator water storage tank, and specific gravity, and Fig. 3 is a diagram showing the relationship between the turbine output and condensate temperature and the water temperature in the deaerator water storage tank and specific gravity. FIG. 4 is a diagram schematically showing changes in the water temperature in the air storage tank and the water temperature in the water level detection pipe, and is a system diagram showing an example in which the present invention is applied to a tubular heat exchanger. 1...Turbine, 2...Condenser, 3.
... Condensate pipe, 4 ... Condensate pump, 5 ...
... Condensate heater, 6 ... Deaerator, 11 ...
... Water side piping for water level detection, 12 ... Steam side piping for water level detection, 13 ... Water level detection meter, 14.
...Water level signal transmitter, 15...Water injection piping, 16...Water injection amount control valve, 17...
Bleeding pipe for condensate heating.

Claims (1)

[Claims] 1. Water level detection piping forming a U-shaped tube, which is disposed in a container containing saturated water provided in a heat exchanger, and whose ends communicate with the water side and the steam side of the container, respectively; A water level detector provided in the water level detection pipe, and a pipe branching from the condensate pipe that supplies condensate to the heat exchanger and guiding the condensate to the water level detection pipe as cooling water are provided. A water level detection device for saturated water in a heat exchanger, characterized by: