JPH0230403B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a feedwater heater drain return system for returning feedwater heater drain to a condenser in a steam turbine plant.

[Technical background of the invention]

Generally, in a steam turbine plant, condensate generated in a feed water heater is introduced into a condenser flush device provided in a condenser via a condenser cooler or the like, and is then returned to the condenser.

FIG. 1 is a schematic diagram of a recirculation system to a condenser in a steam turbine plant, in which steam discharged from a steam turbine 1 is cooled by cooling water such as seawater in a tube bundle 3 of a condenser 2. It condenses, becomes condensate, and is temporarily stored in a hot well 4 formed below the tube bundle section 3. The condensate stored in this hot well 4 is pressurized by a condensate pump 5, and introduced into a drain cooler 7 through a condensate pipe 6, and further into a first feed water heater 8, a second feed water heater 9, and a second feed water heater 9 (not shown). The water is supplied to a boiler (not shown) through a third feedwater heater and the like, where it is turned into steam and supplied to the turbine 1 again.

On the other hand, the first feedwater heater 8, the second feedwater heater 9, and the third feedwater heater are provided with bleed air extracted from an intermediate stage of the steam turbine 1 through bleed pipes 10, 1.
1 and 12, respectively, and are supplied as heated steam, where the condensate is heated and then condensed to become drain.

By the way, the drain generated in the second feed water heater 9 is introduced into a drain tank 15 through a drain pipe 14 having a regulating valve 13, and further into a drain cooler 7 through a drain pipe 16. On the other hand, the drain generated in the first feed water heater 8 is guided to the drain pipe 16 by the drain pipe 17, and drain tank 15
It is supplied to the drain cooler 7 where it joins the drain from the drain, and after being cooled there, it passes through the drain pipe 18.
The drain is introduced into a drain receiving box 19 provided on one side of the condenser 2.

The drain receiving box 19 is partitioned into a drain introducing chamber 21 and a drain falling chamber 22 by a partition wall 20 extending perpendicularly from the bottom wall to a predetermined height, as particularly shown in an enlarged view in FIG. Falling chamber 22
A shelf board 23 consisting of several stages of perforated plates is provided inside, and an opening 24 communicating with the hot well 4 is provided at the lower end. Further, a space 25 that communicates the upper portions of the drain introducing chamber 21 and the drain falling chamber 22 with each other is communicated with the upper portion of the condenser 2 via a balance duct 26.

Therefore, the drain that has flowed into the drain introducing chamber 21 flows upward in the drain introducing chamber 21, overflows from the top edge of the partition wall 20, falls into the drain falling chamber 22, and sequentially passes through the shelf plate 23 to the opening. from the section 24 to the hot well 4 of the condenser 2.

The cross-sectional area of the drain introducing chamber 21 is sufficiently larger than the cross-sectional area of the drain pipe 18, and the free surface of the drain introducing chamber 21, that is, the height to the top of the partition wall 20, corresponds to the outlet temperature of the drain cooler 7. The drain tank 15 is configured to have a height equal to or higher than the water head corresponding to the difference between the saturation pressure and the internal pressure of the condenser 2.
The drain tank 15 is placed at a height such that the drain water level in the drain tank 15 appears balanced and stable in relation to the water level at the top of the drain, that is, at the free surface of the drain.

As a result, the drain rising inside the drain introduction chamber 21 begins to flash when the water level reaches a water depth corresponding to the difference between the saturation pressure of the drain temperature and the pressure inside the condenser 2, and the drain rises at the free surface. Become active.
The steam generated by the flash rises in a gas-liquid two-phase flow, is separated from the drain on the free surface, is discharged, and flows into the condenser 2 through the balance duct 26.

[Problems with background technology]

However, in such a device, the pressure inside the condenser 2 is about 0.05 ata, and the specific volume of steam in this state is about 30,000 times the specific volume of water. When a portion of the condensate flashes and becomes steam, the average specific volume of gas and liquid increases rapidly. Therefore, the flashed steam rises at high speed toward the free surface, escapes from the drain, and is discharged from the balance duct 26 into the condenser 2, but the speed at which this flashed steam escapes from the drain is If the speed is extremely high, the two-phase condensate and the flashed steam cannot be completely separated, and the condensate becomes water droplets and accompanies the flashed steam and enters the condenser 2 through the balance duct 26. It flows in and collides with the pipe bundle 3 and other internal structures at high speed, causing erosion.
In severe cases, there is a risk of damage.

In addition, if the flashed steam blows up at high speed accompanied by condensate, it becomes a resistance to the condensate flowing upward in the condensate introduction chamber 21, and the liquid level fluctuates, causing the condensate overflowing from the partition wall 20 to become extremely unstable. The drain flow rate becomes stable, and this fluctuation in the drain flow rate is transmitted to the drain tank 15 via the drain cooler 7, resulting in abnormal fluctuations in the water level and causing problems such as noise generation within the system.

By the way, in order to solve such problems, it is necessary to create a structure that allows the flash phenomenon to occur gently and stably on the free surface of the drain in the drain receiving box 19, that is, to reduce the amount of steam generated per unit area of the drain surface. In order to reduce the amount as much as possible, the cross-sectional area of the drain introduction chamber 21 needs to be sufficiently wide. However, the drain introduction chamber 21
If it is widened, the entire drain receiving box becomes very large and has a structure that protrudes from the condenser 2, which has disadvantages such as difficulty in implementation due to limitations of the plant building and problems with seismic design.

[Purpose of the invention]

In view of these points, it is an object of the present invention to provide a highly reliable feed water heater drain recirculation device that stabilizes the flow of drain and prevents water level fluctuations, erosion, and noise in the drain tank.

[Summary of the invention]

The present invention has a drain introduction chamber that constitutes a path for refluxing feed water heater drain to a condenser, and the feed water heater drain led to the bottom of the drain introduction chamber becomes a gas-liquid two-phase flow from the middle. flows towards the top,
In the feedwater heater drain reflux device in which the separated steam is collected in the condenser, a portion whose cross-sectional area gradually increases upward is formed in the upper part of the drain introduction chamber, and a horizontal section is formed at the maximum area portion. It is characterized by connecting drain storage parts that maintain sufficient expansion in the direction, and the average specific volume of the flow becomes a gas-liquid two-phase flow due to the portion where the cross-sectional area gradually increases. This structure absorbs the increase in water pressure, prevents the rising speed of drain from increasing rapidly, reduces the amount of flash steam per unit area of the surface of the drain reservoir, and suppresses fluctuations of the water surface.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 3 to 5. Note that the same parts in the figure as in FIGS. 1 and 2 are designated by the same reference numerals, and the explanation thereof will be omitted.

In FIGS. 3 and 4, reference numeral 21 is a drain introduction chamber provided on the outer wall of the condenser 2, which has a slightly larger cross-sectional area than the drain pipe 18 connected to its lower part. A drain reservoir 30 is connected to the top of the drain introduction chamber 21 and extends in the left-right direction and has a cross-sectional area sufficiently larger than the cross-sectional area of the drain introduction chamber 21.

That is, the bottom plate 31 of the drain water storage section 30
The enclosure plate 32 is composed of a slope portion 31a that expands left and right upward, and a horizontal portion 31b that extends outward from the top end of the slope portion 31a, and a lower end of the slope portion 31a forms the drain introduction chamber 21. A weir plate 33 is erected at the outer end of the horizontal portion 31b of the bottom plate 31.

That is, the upper part of the drain introduction chamber 21 is connected to the drain water storage part 30 which has a sufficient width in the horizontal direction through the part where the cross-sectional area gradually increases upward.
communicated within.

Further, on both sides of the drain introducing chamber 21, a drain falling chamber 22 is provided, which is provided with a plurality of shelves 23 made of perforated plates inside. Drain flows into the drain falling chamber 22 from above, and the lower end of the drain falling chamber 22 is communicated with the hot well 4 of the condenser 2 through an opening 24. Furthermore, the space above the drain storage section 30 is communicated with the inside of the condenser 2 via a balance duct 26.

When condensate whose temperature is several degrees higher than the saturation temperature of the internal pressure of the condenser 2 flows from the drain cooler into the drain introduction chamber 21 through the drain pipe 18, the condensate flows upward while decreasing its speed. A flash begins to occur at the water level corresponding to the difference between the saturation pressure of the drain temperature and the pressure inside the condenser.
It rises in a gas-liquid two-phase flow. The drain that has reached the upper end of the drain introduction chamber 21 is divided into right and left sides along the slope portion 31a of the bottom plate 31 in the drain storage section 30, and flows into the drain storage section 30 while further decreasing the speed. The drain flows toward the weir plate 33 at a very slow speed on the horizontal portion 31b.

By the way, as described above, due to the occurrence of the flash phenomenon in the upper part of the drain introduction chamber 21, the flow inside the drain introduction chamber becomes a gas-liquid two-phase flow and the average specific volume increases. The increase in the specific volume is gradually absorbed by the portion formed by the slope portion 31a of which the cross-sectional area gradually increases, and the flow rate of the drain is not accelerated, and the surface area of the drain storage portion 30 is Since it is formed sufficiently wide, the amount of flash steam per unit area of the drain surface is small, and the flash phenomenon completely ends by the time it reaches the weir plate 33.

Therefore, the flashing phenomenon of condensate on the surface of the condensate reservoir occurs very slowly and stably, and when the flashed steam escapes from the condensate, it does not accompany the condensate, and the steam and condensate are separated. Completely separated. Therefore, the liquid level in the drain water storage section 30 hardly fluctuates and is maintained at a substantially constant level, and the drain overflowing from the weir plate 33 also has a stable flow. Similarly, the fluid state within the drain pipe 18 is always stable, and no abnormal fluctuations occur in the water level in the drain tank.

FIG. 5 shows another embodiment of the present invention, in which the drain falling chamber 22 may be provided only on one side of the drain introduction chamber 21 when the drain flow rate is small, and the slope portion 31a may be provided on one side of the drain introduction chamber 21. It may be shaped like a curved plate to smooth the flow.

〔Effect of the invention〕

As explained above, in the present invention, a portion where the cross-sectional area gradually increases upward is formed in the upper part of the drain introduction chamber, and the drain water storage is maintained with sufficient horizontal expansion above the maximum area portion. Since the parts are connected, the increase in the average specific volume of the gas-liquid two-phase flow due to the occurrence of flash is absorbed by the part whose cross-sectional area gradually expands, and the temperature rise of the drain does not increase rapidly. Flows at a low speed and takes a sufficiently long time to reach the weir plate, reducing the amount of flash steam per unit area on the surface of the drain reservoir. Therefore, the movement of the water surface is suppressed, and drain accompanying the flash steam does not flow into the condenser, thereby preventing erosion and noise inside the condenser. In addition, since the water surface in the drain water storage section does not fluctuate, the flow condition in the drain pipe becomes stable, and fluctuations in flow rate are not transmitted to the drain tank, etc., causing abnormal noise. Enables stable overall operation.

[Brief explanation of drawings]

Fig. 1 is a schematic system diagram of a conventional feed water heater drain recirculation system, Fig. 2 is a vertical cross-sectional side view of a conventional drain introduction chamber, Fig. 3 is a longitudinal cross-sectional view of the drain introduction chamber in the present invention, and Fig. 4 This figure is a perspective view of the same as above, and FIG. 5 is a longitudinal sectional view showing another embodiment of the present invention. 2... Condenser, 4... Hotwell, 21...
Drain introduction chamber, 22... Drain fall chamber, 30...
Drain storage part, 31... bottom plate, 31a... slope part, 31b... horizontal part, 33... weir plate.

Claims (1)

[Claims] 1. It has a drain introduction chamber that forms a path for refluxing feed water heater drain to the condenser, and the feed water heater drain led to the bottom of the drain introduction chamber becomes a gas-liquid two-phase flow from the middle and flows to the top In the feed water heater drain reflux device, the steam flowing towards the drain and separated in the upper space is collected in the condenser, in which a portion whose cross-sectional area gradually expands upward is formed in the upper part of the drain introduction chamber. A drain recirculation device for a feed water heater, characterized in that a drain water storage section that maintains sufficient horizontal expansion is connected to the upper part of the largest area section.