JP2015048981A - Droplet scattering prevention device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a droplet scattering prevention device capable of preventing reduction in wall thickness of a pipeline caused by droplet collision in the downstream of an orifice, and reducing reduction in wall thickness as a fail-safe.SOLUTION: Fluid flows in a pipeline 16. An orifice 18 is provided in the pipeline 16, and has a hole 18H through which the fluid flows. A circulation flow suppression part 20 is provided in the pipeline 16 on the downstream side of the orifice 18, and has a hole 20H through which the fluid flows. The circulation flow suppression part 20 is positioned between an end surface OW on the downstream side of the orifice 18, which is perpendicular to the shaft of the pipeline 16, and a surface S1, which is a surface perpendicular to the shaft of the pipeline 16, and on which the diameter of a jet flow 21 of fluid flowing out from the hole 18H of the orifice 18 is maximum.

Description

  The present invention relates to a droplet scattering prevention device for piping located downstream of an orifice in a nuclear power plant.

  In general, the orifice plays two roles.

  One is the role as a flow meter. When an orifice (a disc with a round hole in the center) created in accordance with JIS (Japanese Industrial Standards) is inserted into a pipe line in which fluid flows, the flow is throttled, and differential pressure is generated before and after the orifice.

  This differential pressure is theoretically determined from Bernoulli's theorem because it has a certain relationship with the flow rate. For actual fluids, the relationship between differential pressure and flow rate is given by an empirical formula, and the accuracy of flow rate measurement is guaranteed without flow rate calibration.

  The other is a role as a decompression mechanism. In the piping system of a boiling water nuclear power plant, the pressure difference from the reactor vessel to the condenser is about 7 MPa, so the flow velocity of steam into the condenser becomes very large and the steam is damaged in the condenser. There is a concern. For this reason, an orifice is installed upstream of the condenser to reduce the pressure and optimize the flow velocity flowing into the condenser.

  Here, a steam turbine plant provided with a plurality of orifices as a pressure reducing mechanism is known (see, for example, Patent Document 1).

JP 2007-182862 A

Masahiro UMEHARA, Shinji EBARA, Hidetoshi HASHIZUME, Analysis of generating mechanism of liquid droplet jet stream at the orifice downstream area, NUTHOS-8: The 8th International Topical Meeting on Nuclear Thermal-Hydraulics, Operation and Safety Shanghai, China, October 10-14 , 2010

  According to the technique shown in Patent Document 1, the pressure of the steam passing through the pipe can be reduced stepwise.

  However, regarding each orifice, the downstream of the orifice is a negative pressure, and the pressure ratio between the upstream and downstream of the orifice is large. Therefore, the flow becomes sonic when passing through the orifice and becomes supersonic downstream from the orifice. In general, it is known that the supersonic flow does not reach the entire pipe, but becomes an independent flow due to the formation of strong shear and shock waves as a jet around the center of the pipe.

  On the other hand, a circulating flow is formed downstream of the orifice obliquely rearward with respect to the traveling direction of the jet. Here, when a liquid film is present on the pipe wall surface downstream of the orifice, droplets that are torn off from the liquid film by the circulating flow accompany the circulating flow (see Non-Patent Document 1). Therefore, there is a concern that the pipe may be thinned by the collision of the droplets accompanying the circulation flow. Therefore, when there is a concern about pipe thinning due to droplet collision, it is necessary to take measures to prevent the thinning and reduce the thinning as a fail safe.

  The present invention has been made to solve the technical problem. An object of the present invention is to provide a droplet scattering prevention device capable of preventing pipe thinning due to droplet collision downstream of an orifice and reducing the thinning as a fail safe.

  In order to achieve the above object, the present invention is provided in a pipe through which a fluid flows, an orifice provided in the pipe and having a first hole through which the fluid flows, and the pipe downstream of the orifice, A circulation flow suppression portion having a second hole through which the fluid flows, and the circulation flow suppression portion includes an end face on the downstream side of the orifice perpendicular to the axis of the pipe and a plane perpendicular to the axis of the pipe. In this plane, the fluid jets flowing out from the first hole of the orifice are positioned between the plane having the maximum diameter.

  According to the present invention, it is possible to prevent the pipe from being thinned by the droplet collision downstream of the orifice, and to reduce the thinning as a fail safe. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

1 is a system diagram of a nuclear power generation system including a droplet scattering prevention device according to a first embodiment of the present invention. It is sectional drawing which cut | disconnected the droplet scattering prevention apparatus which is the 1st Embodiment of this invention by the plane containing the axis | shaft. It is sectional drawing which cut | disconnected the droplet scattering prevention apparatus shown to FIG. 2A by the plane perpendicular | vertical to the axis | shaft. It is sectional drawing which cut | disconnected the orifice which is a comparative example by the plane containing the axis | shaft. It is sectional drawing which cut | disconnected the orifice shown to FIG. 3A by the plane perpendicular | vertical to the axis | shaft. It is sectional drawing which cut | disconnected the droplet scattering prevention apparatus which is the 2nd Embodiment of this invention by the plane containing the axis | shaft. It is sectional drawing which cut | disconnected the droplet scattering prevention apparatus shown to FIG. 4A by the plane perpendicular | vertical to the axis | shaft. It is sectional drawing which cut | disconnected the droplet scattering prevention apparatus which is the 3rd Embodiment of this invention by the plane containing the axis | shaft. It is sectional drawing which cut | disconnected the droplet scattering prevention apparatus shown to FIG. 5A by the plane perpendicular | vertical to the axis | shaft.

(First embodiment)
Hereinafter, the configuration and operation of the droplet scattering prevention apparatus 100A according to the first embodiment of the present invention will be described with reference to FIGS. The droplet scattering prevention device 100A is a device that prevents droplets from scattering from a liquid film adhering to a pipe wall downstream of an orifice provided in a steam pipe used in a nuclear power plant, for example.

  Initially, the whole structure of the nuclear power generation system provided with the droplet scattering prevention apparatus 100A which is the 1st Embodiment of this invention is demonstrated using FIG. FIG. 1 is a system diagram of a nuclear power generation system including a droplet scattering prevention device 100A according to the first embodiment of the present invention.

  The nuclear power generation system of the present embodiment includes a core 1, a reactor vessel 2, a main steam system piping 3, a high pressure turbine 4, a moisture separator 5, a low pressure turbine 6, a shaft 7, a generator 8, a condenser 9, a condenser 9 It is mainly composed of a water pump 10, a feed and condensate system pipe 11, a feed water pump 12, a feed water heater 13, a feed water pump driving turbine 14, and an extraction system pipe 15.

  The core 1 contains a fissile material stored in a nuclear reactor vessel 2. The main steam system pipe 3 sends the steam flowing out from the reactor vessel 2 to the high pressure turbine 4 and the low pressure turbine 6. The feed water condensate system pipe 11 sends water in which the steam that has finished work is condensed in the condenser 9 to the reactor vessel 2.

  The generator 8 is connected to the shaft 7 of the high pressure turbine 4 and the low pressure turbine 6. The condensate pump 10, the feed water pump 12 and the feed water heater 13 are connected to the feed condensate system pipe 11 on the downstream side of the condenser 9. The moisture separator 5 between the high-pressure turbine 4 and the low-pressure turbine 6 sends steam to the feed water pump drive turbine 14 and the feed water heater 13.

  In the nuclear power generation system of the present embodiment, the steam heated in the core 1 is supplied to the main steam system pipe 3, the steam is guided to the high-pressure turbine 4 and the low-pressure turbine 6, and power is generated by the generator 8. The steam used for work is condensed in the condenser 9 to become water, and then heated and pressurized through the feed water pump 12 and the feed water heater 13 to be supplied.

  The steam extracted from the moisture separator 5 between the high pressure turbine 4 and the low pressure turbine 6 works in the feed water pump drive turbine 14 and rotates the feed water pump 12. Thereafter, the steam is sent to the condenser 9 and returned to the water. Further, in the shaft seal portion of the feed water pump driving turbine 14, the steam is sent back to the condenser 9 and returned to the water in order to prevent leakage from the seal portion to the outside of the casing.

  In the nuclear power generation system described above, the droplet scattering prevention device 100A according to the first embodiment of the present invention is provided, for example, in the main steam system pipe 3 and the extraction system pipe 15 connected to the condenser 9.

  Next, the configuration of the droplet scattering prevention apparatus 100A according to the first embodiment of the present invention will be described with reference to FIG. 2 (2A, 2B). FIG. 2A is a cross-sectional view of the droplet scattering prevention apparatus 100A according to the first embodiment of the present invention cut along a plane including its axis. 2B is a cross-sectional view of the droplet scattering prevention apparatus 100A shown in FIG. 2A cut along a plane perpendicular to the axis thereof. In the example of FIG. 2A, the main steam flow 17 flows in the right direction (y-axis direction).

  FIG. 2 (2A, 2B) shows the piping structure downstream of the orifice 18 of the present embodiment. As shown in FIGS. 2A and 2B, a circulation flow suppression mechanism 20 (circulation flow suppression unit) is installed in the circumferential direction of the pipe 16 in the flow path of the pipe 16 downstream of the orifice 18.

  The circulating flow suppression mechanism 20 is located between the position where the jet spread 22 is the largest in the radial direction and the wall surface OW on the downstream side of the orifice perpendicular to the flow direction.

  In other words, the circulating flow suppressing mechanism 20 is a downstream end face OW of the orifice 18 perpendicular to the axis of the pipe 16 and a plane perpendicular to the axis of the pipe 16, and on the surface from the hole 18H of the orifice 18. It is located between the surface S1 where the diameter of the jet 21 flowing out is the maximum.

  Here, the circulation flow suppression mechanism 20 is annular, and is provided on the intersection line between the surface S2 perpendicular to the axis of the pipe 16 and the inner peripheral surface 16W of the pipe 16. The surface S1, the surface S2, and the end surface OW of the orifice 18 are parallel. The distance between the surface S1 and the surface S2 is not more than a predetermined threshold value. In the example of FIG. 2A, the surface S1 overlaps the surface S2.

  The circulation flow suppression mechanism 20 is located between the jet 21 flowing out from the downstream of the orifice 18 and the pipe wall surface 16W.

  In other words, the diameter of the hole 20 </ b> H of the circulation flow suppression mechanism 20 is larger than the maximum value of the diameter of the jet 21.

  Further, the diameter of the hole 20H of the circulation flow suppressing mechanism 20 is larger than the diameter of the hole 18H of the orifice 18. The circulation suppression mechanism 20, the orifice 18 and the pipe 16 are coaxial.

  By providing the circulation suppressing mechanism 20 in this way, it is possible to suppress a circulating flow that causes droplets to scatter from the liquid film 19.

  As described above, according to this embodiment, by suppressing the circulation flow that scatters droplets from the liquid film 19, pipe thinning due to droplet collision is prevented in advance, and the thinning is reduced as a fail safe. can do.

(Comparative example)
Next, referring to FIG. 3 (3A, 3B), an orifice 18 without the circulation flow suppressing mechanism 20 will be described as a comparative example.

  FIG. 3A is a cross-sectional view of the orifice 18 as a comparative example cut along a plane including its axis. 3B is a cross-sectional view of the orifice 18 shown in FIG. 3A cut along a plane perpendicular to its axis.

  As shown in FIG. 3A, since the pressure ratio between the upstream and downstream of the orifice 18 is large in the pipe 16 near the orifice 18, an independent jet 21 is generated around the pipe center due to strong shear and shock wave formation.

  On the other hand, in the vicinity of the wall surface 16W on the pipe wall surface downstream of the orifice 18, it flows in the direction opposite to the jet 21 as indicated by the arrow 25a, returns at the corner constituted by the orifice 18 and the pipe 16, and as indicated by the arrow 25b. A circulating flow 25 is formed outside the jet 21 along the jet 21 in the same direction as the jet 21 and reattaches to the pipe wall surface 16W.

  When the liquid film 19 exists on the pipe wall surface 16 </ b> W downstream of the orifice 18, the droplets 24 that are torn off from the liquid film 19 by the circulation flow 25 accompany the circulation flow 25. When the spread 22 (jet diameter) of the jet 21 is large in the vicinity of the downstream of the orifice 18, the space between the wall surface 16 </ b> W of the pipe 16 and the jet 21 is narrowed, and the circulating flow 25 is near the corner formed by the orifice 18 and the pipe 16. Is small and strong. Since the circulating flow 25 is reattached at a fixed position on the piping wall surface 16W, there is a concern that the piping 16 may be thinned by the collision of the droplets 24 accompanying the circulating flow 25.

  On the other hand, according to the droplet scattering prevention device 100A according to the first embodiment described above, such a circulating flow 25 can be suppressed.

(Second Embodiment)
Next, the configuration and operation of the droplet scattering prevention device 100B according to the second embodiment of the present invention will be described with reference to FIG. 4 (4A, 4B).

  FIG. 4A is a cross-sectional view of the droplet scattering prevention device 100B according to the second embodiment of the present invention cut along a plane including its axis. FIG. 4B is a cross-sectional view of the droplet scattering prevention device 100B shown in FIG. 4A cut along a plane perpendicular to its axis. In FIG. 4 (4A, 4B), the same parts as those in FIG. 2 (2A, 2B) are denoted by the same reference numerals.

In FIG. 4, compared with FIG. 2, the circulation flow suppression mechanism 20 includes a gap 23 (hole) that penetrates in the axial direction of the pipe 16 and through which the liquid film 19 (liquid) attached to the pipe 16 passes. Is different. In the example of FIG. 4B, the four gaps 23 (23 ₁ to 23 ₄ ) are formed at regular intervals in the circumferential direction on the outer peripheral portion (portion adjacent to the inner peripheral surface of the pipe) of the annular circulation flow suppressing mechanism 20. Is done.

  As shown in FIG. 4A, due to the adiabatic expansion of the jet 21, the temperature may decrease downstream of the orifice 18, and moisture may be extracted from the wet steam. It is considered that the extracted water is accumulated as a liquid film 19 in the space of the pipe 16 to the orifice 18 and the circulation flow suppressing mechanism 20. When the amount of the liquid film 19 is increased, there is a concern that the liquid film 19 is blown off by the jet flow 21 flowing out from the orifice 18 and scattered as droplets 24.

  Since the flow stagnates in the space of the piping 16 to the orifice 18 and the circulation flow suppression mechanism 20, it is considered that the pressure is higher in the space of the piping 16 to the orifice 18 and the circulation flow suppression mechanism 20 than the downstream of the circulation flow suppression mechanism 20. It is done. By forming the gap 23 through which the liquid film 19 is passed through the circulation flow suppressing mechanism 20, the effect of removing the liquid film 19 accumulated in the space from the gap 23 can be obtained.

  As described above, according to the present embodiment, by suppressing the circulation flow 25 that scatters the droplets 24 from the liquid film 19, pipe thinning due to droplet collision is prevented in advance, and the thickness is reduced as fail-safe. Can be reduced. Further, the liquid film 19 does not accumulate in the space between the wall surface OW on the downstream side of the orifice 18 and the circulation flow suppressing mechanism 20. Thereby, the generation source of the droplet 24 which causes pipe thinning can be eliminated.

(Third embodiment)
Next, with reference to FIGS. 5 (5A, 5B), the configuration and operation of the droplet scattering prevention apparatus 100C according to the third embodiment of the present invention will be described.

  FIG. 5A is a cross-sectional view of a droplet scattering prevention apparatus 100C according to a third embodiment of the present invention cut along a plane including its axis. FIG. 5B is a cross-sectional view of the droplet scattering prevention device 100C shown in FIG. 5A cut along a plane perpendicular to its axis. In FIG. 5 (5A, 5B), the same parts as those in FIG. 2 (2A, 2B) are denoted by the same reference numerals.

  FIG. 5 (5A, 5B) shows the piping structure downstream of the orifice 18 of the present embodiment. As shown in FIG. 5A, the space of the pipe 16 to the orifice 18 and the circulation flow suppressing mechanism 20 is constituted by a pipe member 26 (connecting portion).

  Here, the piping member 26 has a conical surface 26 </ b> S that connects the hole 18 </ b> H of the orifice 18 and the hole 20 </ b> H of the circulation flow suppressing mechanism 20.

  According to such a member 26, it becomes possible to reduce the circulating flow 25, and the droplet 24 scattered from the liquid film 19 is accompanied by the circulating flow 25, and the thickness is reduced by the collision of the droplet with the wall surface 16W. Can be prevented, and the thickness reduction can be reduced as fail-safe.

  As described above, according to the present embodiment, by suppressing the circulation flow 25 that scatters the droplets 24 from the liquid film 19, pipe thinning due to droplet collision is prevented in advance, and the thickness is reduced as fail-safe. Can be reduced. Further, it is possible to suppress the liquid film from adhering to the pipe wall 16W downstream of the orifice 18.

  The present invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. A part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. It is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

  For example, in the member 26 used in the droplet scattering prevention apparatus 100C according to the third embodiment, the wall surface OW (end surface) of the orifice 18, the pipe wall surface 16W, the end surface of the circulation flow suppressing mechanism 20, and the conical surface 26S. The area surrounded by is filled, but it does not have to be filled. That is, the member 26 may be composed only of the conical surface 26S.

DESCRIPTION OF SYMBOLS 1 ... Core 2 ... Reactor vessel 3 ... Main steam system piping 4 ... High pressure turbine 5 ... Moisture separator 6 ... Low pressure turbine 7 ... Shaft 8 ... Generator 9 ... Condenser 10 ... Condensate pump 11 ... Supply condensate system Pipe 12 ... Feed pump 13 ... Feed heater 14 ... Feed pump driving turbine 15 ... Extraction system pipe 16 ... Pipe 17 ... Main flow 18 ... Orifice 19 ... Liquid film 20 ... Circulation flow suppression mechanism (circulation flow suppression unit)
21 ... Jet 22 ... Pipe radial spread 23 ... Gap (hole)
24 ... Droplet 25 ... Circulating flow 26 ... Piping member (connection part)

Claims (7)

Piping through which fluid flows;
An orifice provided in the pipe and having a first hole through which the fluid flows;
A circulation flow suppression unit provided in the pipe on the downstream side of the orifice, and having a second hole through which the fluid flows,
The circulating flow suppression unit is
An end face on the downstream side of the orifice perpendicular to the axis of the pipe;
It is a surface perpendicular to the axis of the piping, and is located between the first surface where the diameter of the jet of the fluid flowing out from the first hole of the orifice is the maximum on the surface. Droplet scattering prevention device. The droplet scattering prevention device according to claim 1,
The circulating flow suppression unit is
A droplet scattering prevention device, wherein the droplet scattering prevention device is provided on a line of intersection between a second surface perpendicular to the axis of the pipe and an inner peripheral surface of the pipe. The droplet scattering prevention device according to claim 2,
The diameter of the said 2nd hole of the said circulation flow control part is larger than the maximum value of the diameter of the said jet flow. The droplet scattering prevention apparatus characterized by the above-mentioned. The droplet scattering prevention device according to claim 3,
The diameter of the 2nd hole of the said circulation flow control part is larger than the diameter of the said 1st hole of the said orifice. The droplet scattering prevention apparatus characterized by the above-mentioned. The droplet scattering prevention device according to claim 1,
The circulating flow suppression unit is
A droplet scattering prevention device characterized by having a third hole that penetrates in the axial direction of the pipe and through which the liquid attached to the pipe passes. The droplet scattering prevention device according to claim 5,
The third hole is
It is formed in the outer peripheral part of the said circulation flow control part. The droplet scattering prevention apparatus characterized by the above-mentioned. The droplet scattering prevention device according to claim 1,
The droplet scattering prevention device, further comprising: a connecting portion having a conical surface connecting the first hole of the orifice and the second hole of the circulation flow suppressing portion.

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