JPS6058361B2 - Water level control device for feed water heater - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a feedwater heater installed in a steam turbine plant.
The present invention relates to a water level control device that can maintain the drain water level in a feed water heater within an allowable range.

[Background of the invention]

In order to prevent deterioration of the heat exchange performance of the feed water heater of a steam turbine plant and to prevent the occurrence of cavitation, water hammer, etc. in the drain discharge device, the drain water level within the feed water heater is kept within a certain range. −
-11ι←n, Lele En-le, il, [-・１ー・ Police, Ru.

A conventional drain discharge control device opens and closes a drain control valve in response to a drain water level change signal in a feed water heater to keep fluctuations in drain water level within an allowable range. Although I am calm,
BACKGROUND ART In order to improve thermal efficiency during partial load operation, the extraction point of heated steam supplied from a steam turbine to a feedwater heater is switched at a certain load of a turbine plant.

By switching the bleed point, the heating steam pressure fluctuates rapidly in a stepwise manner. In such a case, it is considered impossible to control the fluctuation of the drain water level within an allowable range using the above-mentioned known method. Figure 1 is a diagram showing the relationship between the heating steam pressure of the feed water heater and the steam turbine load when the extraction point of the heating steam is switched at a load near 85% of the steam turbine rated load, which is proposed in the past. be. It is shown that heating steam 21 is used from the low pressure side (reheat point) at about 85% or more of the rated load, and heating steam 22 from the high pressure side (high pressure turbine stage) is used at about 85% or less of the load. Figure 2 shows the low pressure side heating steam 23 when corresponding to Figure 1.
and shows changes in the saturation temperature of the high-pressure side heating steam 24.
According to the characteristics shown in FIG. 1, when the load is switched around 85%, the heating steam pressure suddenly changes from about 31 to 9/clt to 43 to 9/ai, or in the opposite direction. In such cases, with conventional drain control devices, when the pressure drops, the second
As shown in the figure, the saturation temperature of the heating steam is about 2
The temperature changes to 35°C, and brushing of the drain occurs inside the drain cooler and at the drain cooler inlet. In addition, the inside of the drain cooler becomes a two-phase mixed flow of steam and water, and the resistance of the drain cooler section increases, making it impossible to completely discharge the drain even if the control valve is sufficiently opened. As a result, the drain water level rises abnormally to a dangerous level. Even in conventional steam turbine plants that do not perform bleed switching, abnormal water level fluctuations are often experienced due to brushing due to pressure fluctuations of heated steam when the load changes suddenly, and it is necessary to limit the turbine load change rate. has become a limiting factor in how turbines are operated. However, in the case of a feed water heater that performs bleed air switching, pressure fluctuations occur even more rapidly than in the past, so special consideration is required for the drain discharge device. [Object of the Invention] An object of the present invention is to suppress fluctuations in the drain water level to a small level even when brushing occurs due to a sudden decrease in pressure within the feed water heater, thereby preventing a decline in the performance of the feed water heater.

[Summary of the Invention] That is, the features of the present invention include a first drain pipe for discharging drain from the drain cooler section, and a first drain pipe provided in the drain pipe that opens and closes in response to fluctuations in the water level of the drain reservoir. In a feed water heater having a control valve, the control valve detects a sudden increase in pressure of heating steam introduced to heat the feed water, and causes the first control valve to open further than the opening determined by the water level. and a second drain line for directly discharging drain from the drain basin, and a second control valve that opens when the water level in the drain basin rises abnormally. This is because it was established.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIG.

Reference numeral 1 denotes a well-known feed water heater having a drain cooler section 2 and a drain reservoir section 3 inside.

A steam pipe 4 has a bleed air switching valve 6 in the middle and one end connected to the high pressure side of a steam turbine (not shown), and 5 also has an bleed air switching valve 7 in the middle and one end connected to a steam turbine (not shown). These steam pipes 4 and 5 are connected together after the extraction switching valves 6 and 7, and are thus connected to the feedwater heater 1.

8 is a pressure detector that detects the pressure inside the feed water heater 1, and 9 is a water level detector that detects the drain water level inside the feed water heater 1.

10 has one end connected to the drain cooler section 2, and the other end connected to the condenser (
(not shown), and this drain pipe 1
A control valve 11 for controlling the flow rate of drain is provided in the middle of the drain.

12 is a drain pipe whose one end is connected to the drain reservoir 3;
A control valve 13 for controlling the flow rate of drain is also provided in the middle of this drain pipe 12, and the other end is connected to the drain pipe 10 on the downstream side of the control valve 11.

A control signal line 14 connects the water level detector 9 and the control valve 11, and a water level regulator 15 and a regulator 16 are provided in the middle of the control signal line 14 to set a normal water level.

In addition, the control valve 1 branched from before the signal inlet of the water level regulator 15
A control signal line 17 is provided that connects to the water level 3, and a water level regulator 18 is provided in the middle of this control signal line 17 to set an abnormal water level that is slightly higher than the normal water level. Reference numeral 19 is a control signal line connecting the pressure detector 8 and the regulator 16.

Now, when the heated steam on the low pressure side enters the feed water heater 1 through the steam pipe 5, the heat is taken away by the feed water passing through the heat exchanger (not shown) and the steam becomes drain, and the drain reservoir It accumulates to 3.

When the heating steam pressure changes slowly, the drain passes through the drain cooler section 2, the drain pipe 10, and the control valve 11.
It is discharged to a condenser (not shown). Control valve 11 at this time
This control is performed via the regulator 16 so that the normal water level is set by the water level regulator 15 based on the water level signal from the water level detector 9. Said regulator 16
The control valve 11 also has the function of detecting the rate of change in the output of the pressure detector 8, that is, the rate of change in the heating steam pressure, but when the pressure change is gradual, it hardly intervenes in the control, and the control valve 11 only detects the water level. The valve 11 is controlled by a signal from the valve 9, and the opening degree of the valve 11 is adjusted to a steady setting level. When the drain water level is around the steady setting level, the control valve 13 is closed because it does not reach the setting level of the water level regulator 18, and the drain is discharged from the drain pipe 10 via the drain cooler section 2 from the drain reservoir 3. Ru. Next, when the turbine load changes and the load switching point changes from a high side to a low side, the bleed air switching valve 7 closes, the other bleed air switching valve 6 opens, and the heated steam on the high pressure side enters the feed water heater 1 and heats up. The pressure inside the chamber increases rapidly.

This rapid pressure change is detected by the pressure detector 8, and the pressure signal is converted into a pressure change rate signal by the regulator 16, so that the opening is larger than the opening determined by the water level change signal from the water level regulator 15. The control valve 11 is controlled accordingly. That is, when the steam pressure in the heater suddenly increases, the saturation temperature rises in a stepwise manner as shown in FIG. Increase this to prevent the drain water level from rising.

On the other hand, when the turbine load passes through the load switching point in an increasing direction, the pressure within the heater 1 drops rapidly.

Then, brushing occurs in the drain cooler section where the drain temperature is the lowest in the feed water heater. When brushing occurs in the drain cooler section 2, the fluid flowing there becomes a mixed flow of liquid and gas, which increases the flow resistance and reduces the amount of drain discharged outside the device through the drain pipe 10 and control valve 11. decreases rapidly, and the drain water level inside the vessel rises. Due to the rise in the drain water level, the water level detector 9 gives a signal in the direction of further opening the control valve 11, but due to the increase in flow resistance in the drain cooler section, the drain water level is not lowered. When the drain water level inside the vessel reaches the level set by the water level regulator 18, the control valve 13 opens and the drain in the drain reservoir 3 is directly discharged to the outside of the vessel through the drain pipe 12, so that the drain water level no longer rises any higher.

Therefore, the water level in the vessel will not rise above the level set by the water level regulator 18. In addition, the drain reservoir 3
Also, when brushing occurs, the water level in the drain reservoir 3 becomes apparently high, and the detection level of the water level detector 9 exceeds the set level of the water level regulator 18, so the control valve 13 is opened and the drain in the reservoir 3 is raised. is directly discharged through the drain pipe 12. Since the drain pipe 12 directly communicates with the drain reservoir 3, the drain can be quickly discharged even when brushing occurs, and the drain water level can be kept within an allowable range.

〔Effect of the invention〕

According to the present invention, even if rapid pressure fluctuation occurs in the feed water heater and brushing occurs, the internal drain water level can be maintained within an allowable range.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the heating steam pressure of the feed water heater and the steam turbine load when the extraction point is changed, and Figure 2 shows the change in the saturation temperature of the internal steam when corresponding to Figure 1. The diagram shown in FIG. 3 is a system diagram showing an embodiment of a water level control device for a feed water heater according to the present invention. 1... Feed water heater, 2... Drain cooler section, 3... Drain reservoir section, 8... Pressure detector, 9... Water level detection 10... Drain pipe, 11... Control valve, 12... Drain pipe, 13... Control valve, 16... Regulator .

Claims (1)

[Claims] 1. A feed water heater having a first drain pipe that discharges drain from the drain cooler to the outside, and a first control valve that is provided in the drain pipe and opens and closes in response to fluctuations in the water level of the drain reservoir, a regulator that detects a sudden increase in the pressure of the heating steam introduced into the feed water heater and controls the first control valve to open more than the opening determined by the water level; A second drain pipe is provided for directly discharging drain from the drain reservoir to the outside, and this drain pipe is provided with a second control valve that opens when the water level in the drain reservoir increases abnormally. Water level control device for feed water heater.