JPH06272808A - Temperature reducing device - Google Patents

Abstract

PURPOSE:To enable a thermal fatigue, a thermal deformation and a thermal buckling of a steam pipe to be prevented by a method wherein a spray ring is provided with a small number of large diameter injections ports opened toward a direction between a downstream direction and a central direction and a large number of small diameter injection ports opened toward a downstream direction. CONSTITUTION:There is provided a water feeding pipe 4 for feeding water at a hollow part of a spray ring 2 arranged in an annular form along a wall inner circumferential surface of a steam pipe 1. The spray ring 2 is provided with a small number of large diameter injection ports 5 opened toward a direction between a downstream direction and a central direction, a large number of small diameter injection ports 6 opened toward a downstream direction and then fed water is injected from these injections ports 5 and 6. In addition, an annular back-flow preventing plate 3 is arranged at an upstream side of the spray ring 2 along the wall inner circumferential surface of the steam pipe 1. With such an arrangement as above, it is possible to stabilize an interface between a wet region and a dry region and to prevent a back-flow of the fed water into the upstream side within the steam pipe.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a desuperheater for treating turbine bypass steam in a thermal power plant or a nuclear power plant.

[0002]

2. Description of the Related Art In a thermal power plant, when starting or stopping, steam generated in a boiler bypasses a turbine and is guided to a condenser for condensation treatment. At this time, in order to protect the condenser, the steam is cooled and cooled by the temperature reducer.

FIG. 5 is a vertical sectional view of a conventional desuperheater. In the figure, 1 is a steam pipe, and 7 is a spray nozzle that penetrates through the wall of the steam pipe and is inserted therein. The spray nozzles are provided at four locations on the circumference of the pipe at equal intervals, and water is injected to spray. It is for doing. A broken line arrow S is superheated steam, and M is a mist generated by water sprayed from the spray nozzle 7. L is a liquid film produced by the above mist coming into contact with the inner wall surface of the pipe.

In this apparatus, the injected water sprayed from the spray nozzle 7 toward the downstream side of the steam flow becomes the mist M and spreads in the downstream direction at a gradient of 1/10. As a result, the inside of the pipe is filled with mist M. Also, a thin liquid film L is generated on the tube wall. The mist M comes into contact with the superheated steam S and evaporates, and the superheated steam S lowers its temperature. W is a region where the liquid film L is formed, that is, a wet region, and D is a region where the liquid film is not formed, that is, a dry region.

[0005]

As shown in FIG. 5, in the conventional desuperheater, when the ratio of the amount of injected water to the amount of superheated steam flowing through the desuperheater changes, the wet region and the dry region are changed. There was a phenomenon in which the boundaries of were moved. When the amount of superheated steam decreases with respect to a certain amount of injected water, the wet area moves to the upstream side, and along with this, the wall surface of the steam pipe that has newly turned to the wet area is rapidly cooled, which causes large thermal stress. However, there was a defect that thermal fatigue cracks occurred there.

Further, particularly when the steam pipe is arranged horizontally, when the steam flow is stopped, the sprayed injection water accumulates at the bottom of the steam pipe without steaming, and it flows back to the upstream side. Therefore, the temperature of the steam pipe is lowered over a wide range only in the bottom portion thereof in the wet region. At this time, the long horizontal steam pipe has a drawback that it undergoes large thermal deformation due to the temperature difference between the upper side and the lower side, which causes buckling.

The present invention solves the above-mentioned drawbacks of the prior art,
Stabilize the boundary between the wet and dry areas to prevent thermal fatigue cracks in the steam pipe, and prevent backflow of injected water upstream in the steam pipe to prevent thermal deformation and thermal buckling of the steam pipe. It is something to prevent.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and in a desuperheater for injecting water into a steam pipe through which superheated steam flows to cool and reduce the temperature of the superheated steam, The present invention relates to a desuperheater having the characteristics of. (1) A hollow spray ring provided annularly along the inner peripheral surface of the wall of the steam pipe, and an injection water pipe for injecting water into the hollow portion of the spray ring are provided, and the spray ring has a downstream direction. And a small number of large-diameter jets that open in the direction between the center and the small-diameter jet that opens in the downstream direction are provided, and the injection water is jetted from these jets. To do. (2) In the desuperheater according to the item (1), an annular backflow prevention plate is provided on the upstream side of the spray ring along the inner peripheral surface of the wall of the steam pipe.

[0009]

[Operation] Since the injected water injected from a small number of large-diameter jets has a strong momentum, it penetrates into the steam flow to become a mist, diffuses to the downstream side of the steam flow, contacts the superheated steam, and evaporates. Reduce the temperature of superheated steam.

The water injected from a large number of small-diameter jets is pushed by the steam flow and adheres to the inner wall surface of the pipe, forming a liquid film. A part of the liquid film flows back to the splaying side and forms a stable wet region on the downstream side of the splaying or on the downstream side of the backflow prevention plate. This prevents thermal fatigue cracks in the steam pipe.

The backflow prevention plate prevents backflow of the injected water in the upstream direction when the flow of the superheated steam is stopped. This prevents thermal deformation and thermal buckling in the horizontally long steam pipe after the steam flow is stopped.

[0012]

1 is a longitudinal sectional view of a desuperheater according to an embodiment of the present invention, FIG. 2 is a sectional view taken along the line AA of FIG. 1, and FIG. 3 is a partially enlarged view of FIG. In FIG. 1, 1 is a steam pipe (inner diameter 1000
mm), 2 is a spray ring annularly provided on the inner circumference of the wall surface of the steam pipe (100 A, pipe outer diameter 114 mm), 3 is the spray ring on the upstream side of the spray ring on the inner circumference of the wall surface of the steam pipe. An annular backflow prevention plate (height 114
mm), 4 is an injection water pipe that is connected to the spray ring and injects water into the spray ring from the outside, and in FIG. 2, 5 is a large-diameter jet port (internal diameter 10 mm) provided in the spray ring 2 ) And is open toward the center direction by about 45 degrees from the downstream direction of the steam pipe. 6 is a small-diameter jet port (inner diameter 2 mm) provided in the spray ring, which opens in the downstream direction.

In the present apparatus, at the start of use, the injection of water injection is started first, and after a few seconds, the flow of superheated steam is started. At the end of use, superheated steam flow is stopped first, and injection water injection is stopped after a few seconds.

FIG. 3 shows a state in which the sprayed water is changed into a mist M and a liquid film L is formed. As shown in the figure, the flow of the superheated steam S is separated at the tip of the backflow prevention plate 3, adheres to the wall surface on the downstream side of the spray ring 2, and part of the flow flows back to the spray ring side. Since the injected water injected from the small number of large-diameter jets 5 has a strong momentum, it enters the steam flow to become the mist M, diffuses to the downstream side of the steam flow, contacts the superheated steam S, and evaporates, Reduce the temperature of superheated steam. The small-diameter liquid column injected from the small-diameter jet port 6 becomes unstable and becomes a mist at the downstream of about 50 times the liquid column diameter, and the mist is carried by the airflow and reaches the wall surface, where the liquid film L Is generated. A part of the liquid film is carried by the air flow that flows backward to the spraying side and flows to the spraying side. The thickness of the liquid film becomes a thickness that balances with the force received from the air flow, and even if the liquid film becomes thicker than that, the liquid scatters and is carried to the steam main stream and flows away downstream. In this way, the inner wall surface of the pipe on the downstream side of the backflow prevention plate 3 is covered with the liquid film and is always in the wet area W. On the other hand, the upstream side of the backflow prevention plate 3 is always in the dry region D because backflow is prevented. Therefore, the boundary between both areas is always constant and stable.

FIG. 4 is a comparative view of the effects of this embodiment and the prior art, showing the variation of the tube wall temperature. In the figure, the horizontal axis is the distance from the cooling water injection point toward the upstream side,
The vertical axis shows the tube wall temperature, the solid line shows the temperature distribution according to this embodiment, and the broken line shows the example of the temperature distribution in the state of several steam flow rates according to the prior art. In this embodiment, as is clear from this figure, since there is no fluctuation in the high temperature region upstream due to fluctuations in the steam flow rate, the thermal stress in the steam pipe is significantly reduced compared to the conventional one, and thermal fatigue The problem goes away.

Although the injection of water is continued for several seconds after the steam flow is stopped, the water that has reached the wall surface is blocked by the backflow prevention plate. It will not be dripping or cooled,
The problems of thermal deformation and thermal buckling during this time zone are resolved.

[0017]

In the desuperheater of the present invention, a hollow spray ring provided annularly along the inner peripheral surface of the wall of the steam pipe, and an injection water pipe for injecting water into the hollow portion of the spray ring. The spraying is provided with a small number of large-diameter outlets that open in the direction between the downstream direction and the center direction, and a large number of small-diameter outlets that open in the downstream direction, The injection water is injected from these jet outlets, or further, since an annular backflow prevention plate is provided on the upstream side of the spraying along the inner peripheral surface of the wall of the steam pipe, a wet area and a dry area are provided. Can be stabilized to prevent thermal fatigue cracks in the steam pipe, and to prevent backflow of injected water to the upstream side in the steam pipe to prevent thermal deformation and thermal buckling of the steam pipe.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a desuperheater according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a partially enlarged view of FIG.

FIG. 4 is a comparative diagram of the effects of the above-described embodiment and the prior art.

FIG. 5 is a vertical sectional view of a conventional desuperheater.

[Explanation of symbols]

 1 steam pipe 2 spraying 3 backflow prevention plate 4 injection water pipe 5 large diameter jet 6 small diameter jet 7 spray nozzle (conventional technology) S superheated steam M mist L liquid film D dry area W wet area

Claims (2)

[Claims] 1. A desuperheater for injecting water into a steam pipe through which superheated steam flows to cool and dehumidify the superheated steam, wherein a hollow space provided in an annular shape along an inner peripheral surface of a wall of the steam pipe. The spray ring is provided with an injection water pipe for injecting water into the hollow part of the spray ring, and the spray ring has a small number of large-diameter jet ports that open in the direction between the downstream direction and the center direction,
A desuperheater characterized in that it is provided with a large number of small-diameter jet outlets opening in the downstream direction, and the above-mentioned injected water is jetted from these jet outlets. 2. The desuperheater according to claim 1, wherein an annular backflow prevention plate is provided on an upstream side of the spray ring along an inner peripheral surface of a wall of the steam pipe. .