JPS6116882B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to tubular heat exchangers such as feedwater preheaters, condensers and steam generators. The problems with this tubular heat exchanger stem from the fact that the tubes are subject to severe vibrations caused by the turbulence and instability of the liquid flow around them. Sometimes the vibrations are so strong that the tubing fatigues rapidly, a condition that often occurs in condensers, for example. In addition, it may also occur that the tubes collide in the gap between the tube and the tube support plate with openings through which the tubes pass, which wears away the material of the tube at the interface between the tube and the tube support plate. The result is that. Wear can progress to such a degree that severe leakage occurs. Obviously, such leakage is unacceptable in a nuclear power plant. The main objective of the present invention is to solve this problem, especially in steam generator installations where tube wear has already been observed, or in new installations where such wear is expected, where feed water impinges on adjacent tubes. It is an object of the present invention to provide a nozzle structure for introducing feed water into a steam generator in such a way that it is deflected without any substantial resistance or turbulence. With this object in mind, the present invention provides a flow control device for providing a substantially uniform and swirl-free inflow and distribution of feed water to a steam generator, the flow control device comprising a secondary a plurality of tubes constituting a tube bundle for a primary fluid for heating the feed water as a fluid, and a steam generator shell surrounding the tube bundle and having an inlet nozzle and an outlet nozzle for the feed water, the inlet nozzle being In a flow control device having a diffuser structure therein, water from the shell of the steam generator passes through the inlet nozzle during a break in a water supply pipe connected to and located within the inlet nozzle. a number of diff user passages mounted to limit the flow of the inlet nozzle and extending from said diff user structure parallel to the axis of the inlet nozzle;
and having a radially extending portion between the downstream end of the diffuser passageway and the tube bundle surrounded by the shell, adapted to deflect the flow of feed water radially about the inlet nozzle axis in an uninterrupted flow path. It is characterized by having a butty-full structure which is curved as shown in FIG. The conditions associated with vibration in the tubes of a heat exchanger are roughly analogous to the action of wind in an unrestrained chimney. Inwardly directed vortices, the so-called Karman vortices, form in the windshadow behind the chimney, and these vortices generate lateral pulsating forces. This pulsating force has a frequency f _c that depends on the diameter D of the chimney and the speed U of the wind.
has. For chimneys with low attenuation,
When the resonant frequency of the chimney is within the range of f _c =0.2 to 0.7×U/D, there is a risk that the vibrations will have an amplitude that is large enough to damage the chimney. Here, the coefficients 0.2 to 0.7 are the dimensionless Struuhal number S. Therefore, S=f _c・D/U According to extensive research on heat exchanger tubes,
Due to the high velocities of fluid outside a tube bundle with one or more rows of tubes and of the fluid passing laterally through the tube bundle, S>2 based on the flow velocity in the cross-section between the tubes. In the case of a Struuhal number in the range, or a completely empty area in front of the tube bundle, the Struuhal number for the underlying normal tube pitch S > 0.7, substantially similar to the situation in the case of an unrestrained chimney. In contrast, it was shown that severe vibrations occur. If, in addition to this, the flow is pulsating in direction and intensity, the risk of tube vibrations increases significantly. Normally, vibrations have nodes on the support plate. However, relatively high frequencies with nodes between the support plates may also be present. The invention will become more apparent from the following description of a number of preferred embodiments, taken in conjunction with the accompanying drawings. FIG. 1 shows a conventional steam generator with a shell, in which hot pressurized water is passed from a heat source, e.g. a nuclear reactor, into a primary fluid system through a primary fluid inlet nozzle 1 of the steam generator. is supplied to the shell. In the left half of the steam generator, water flows upward through closely packed tubes with a relatively small diameter, for example 20 mm. Inside the top of the shell, a tube bends downward into the right half of the steam generator shell. The section of the downwardly curved tube through which the water flows downwards is represented by five tubes 2. flowing around the tube2
After providing heat to the primary water, the primary water returns to the reactor through the outlet nozzle 3 to be reheated. Water in the secondary fluid system having a pressure approximately half that of the primary fluid system is fed to the steam generator through a secondary water inlet nozzle 4 welded to the rigid shell 5 of the steam generator. The temperature of the feed water from the feed water supply pump of the secondary fluid system is significantly lower than the water vaporization temperature corresponding to the normal pressure in most of the secondary fluid system of the steam generator. Cold feed water is used to provide rapid cooling of the primary water passing through a tube section below the right half of the steam generator, said tube section thus acting like an economizer. In the left and upper right halves of the steam generator, hot primary water vaporizes water in the secondary fluid system. Steam exits the steam generator through a steam outlet nozzle (not shown) at the top of the steam generator, passes through a moisture separator, and then heads to the steam turbine. The water supply from the inlet nozzle 4 enters the space between the tubes of the tube bundle, traverses these tubes and flows between the tube support plates 6 and 7. A portion of the flow is directed downward and takes a zigzag path along support plates 8-11 through holes at each end thereof. Another portion of the flow flows upwardly along support plates 12-16. To illustrate the problems addressed by the present invention, FIG. 2 shows in more detail in horizontal section a conventional steam generator inlet nozzle 4 carrying a flow restriction member. The water supply pipe 20 is connected to the inlet nozzle by welding. In order to ensure that only the outflow of secondary water from the steam generator is limited to a pipe section that may burst in the water supply pipe, a flow restriction member 2 is installed.
1, that is, a diverging nozzle arrangement, as described below, is arranged in the inlet nozzle 4 in close proximity to the water supply pipe. The divergent nozzle arrangement (diff-user structure) 21 comprises a number (in this case four) of divergent nozzle passages (diff-user passages) having the smallest orifice 23 behind a smoothly rounded inlet surface 24.
22. In the diverging part of the nozzle, a high velocity at the smallest orifice 23 (this is 30
A portion of the gained momentum (which may be at a speed of the order of m/s) is restored. In order to prevent the water jet, which is still injected at high speed from the diverging nozzle passage, from impinging too quickly onto the tube bundle, two circular baffle plates 25 and 26 are placed in front of the inlet hole and spaced a small distance from it. ing. Conveniently, said buff-full plate is provided with supports 27, 28, for example.
It is fixed to the shell by means and is provided with a number of openings 29, 30 for distributing the flow of water. Despite these measures, the flow of water to the tubes 2 between the support plates 6 and 7 is limited to such an extent that the tube rows adjacent to the inlet holes are subjected to vibrations, sometimes very violent vibrations. Until now, they were unstable and strong in some cases, leading to wear on the support plate causing severe leakage. If radioactive primary coolant leaks into the secondary coolant due to a broken tube due to flow-induced vibrations, the entire secondary system will be radioactively contaminated and the steam generator will need to be repaired. It becomes necessary. Such repairs are costly and time consuming because they involve repairing internal components located within the steam generator shell that are not accessible through the inlet nozzle opening. According to the flow control device according to the invention, the water velocity behind the nozzle device 21, which has a water velocity of approximately 30 m/s at the smallest orifice cross-section of the nozzle, is such that the flow of the feed water as it enters the tube bundle is caused by wear or fatigue. This is reduced to such a degree that a low velocity is obtained that does not expose the tube to forced vibrations of a magnitude that would jeopardize the mechanical strength of the tube. For this purpose, the inlet velocity of the feed water should be reduced to about 2.5 m/s or less in order to obtain a sufficiently low Struuhal number. According to the invention, this is achieved by a device having the characteristic features as evident from the patent claims. In the following, the invention will be explained in more detail in connection with FIGS. 3-17. In order to investigate the possibility of obtaining a favorable liquid flow through the inlet cross-section of the steam generator by using a diverging nozzle of circular cross-section, the following calculations are performed. Starting from the premise that the velocity of the secondary water should be reduced from the maximum velocity at the throat of the nozzle to a velocity as low and uniform as possible along the entire inlet cross-section towards the tube bundle of the steam generator. Therefore, the number of diverging nozzles should be relatively large and the nozzle outlet should cover an area constituting as large a part of the inlet area as possible. The nozzle angle should not be greater than 2 x 4° to obtain a stable and uniform flow through the diff user portion of the nozzle, since the diameter increase or taper angle behind the smallest cross section of the nozzle is equal to the unit length. This means that it should not be larger than 2x7%. For different numbers of nozzles, there are many optimal shapes of the exit cross-section of the nozzle arrangement for a circular cross-section according to FIG. 2, and _FIG . The ratio between d and _y is shown. Let A _nio be the maximum allowable area for restricting the flow rate to the tube rupture, and let Z be the number of nozzles, then the diameter of the nozzles at the throat is becomes. If the taper angle is set to 2×7%, the length of the differential user portion of the nozzle is L= _dy − _di /0.14=7.14(d _y −d _i ). The effective range of the exit cross section is then Z· _dy ² /D _y ² . As an example, for a steam generator with a secondary water inlet nozzle having a diameter D _y =36 cm and an orifice area at the minimum cross-section of the nozzle of 0.2025 x cross-sectional area of the tube, i.e. 206.1 cm ² : Minimum length L
and effective range are obtained.

From this table it can be seen that a number of nozzles of at least 14 is preferred in order to reduce the required length of the nozzle device to less than the diameter of the device.
There is an interest in achieving as few nozzles as possible, as short a length as possible, and as high an effective range as possible. From the table, it can be seen that the increase in effective range is relatively small from 3 divergent nozzles to 37 nozzles, and since only about 3/4 of the inlet area is used, the increase is satisfactory for some purposes. Although you may not think so, the length of the differential user part is approximately 1.5 times the diameter of the nozzle device.
You can see that it decreases to 0.5 times. In a preferred embodiment of the invention, which will be explained in more detail below, it has been possible to reach values close to 100%. As is clear from the table, seven diverging nozzles obtain a relatively large effective range of more than 10% at the cost of a significantly longer length, but each passage of the nozzle device is shorter than the diameter of the supply pipe. To obtain a length of the diverging section of , the diverging nozzle passages of circular cross section should have at least 14. Therefore, by arranging the divergent user passages of the divergent nozzle device such that the velocity of the flow from the smallest cross-section of each divergent passage is reduced to the average velocity corresponding to the tube cross-section, water is allowed to pass through the nozzle device. A substantially uniform flow is then obtained. Also, as will be explained in more detail below, a number of diffusing rings constitute vanes that guide the flow and impart to said flow a radial velocity having a selected velocity component in the direction of flow toward the tube bundle. A further improvement can be obtained by arranging the For steam generators in which the secondary water supply when fed into a tube bundle should be spread along the tube bundle, the width of which is larger compared to the height, an acceptable uniform velocity distribution towards each tube row is required. The flow of water from the nozzle should be distributed radially in such a way that more water is guided horizontally than vertically to avoid high local velocities. According to a further feature of the invention, this comprises a separate section having dimensions and a circular part shape for a selected flow of water guided radially deflecting in the direction of the outlet of the nozzle arrangement. This is achieved by arranging a diffuser nozzle. As another example for a certain steam generator structure,
In one embodiment according to the invention, a single centrally located nozzle restricting the flow rate is provided in combination with a set of ring-shaped diffusers located downstream of the nozzles that substantially radially deflect the flow. It is being As in the embodiments described above, the flow is distributed in such a way that a greater proportion of the flow is distributed horizontally than vertically. FIG. 4 shows a horizontal cross section of a steam generator inlet nozzle 4 with a diverging nozzle arrangement 21, which is provided with 37 diverging nozzle ducts 22. This example is particularly suitable for secondary water inlets of steam generators where the height of the tube bundle is approximately as large as its width. Two plates (Batsuful structure 7
A cross-shaped plate member consisting of 1 and 72 is combined with the diverging nozzle device 21, and the two plates 71 and 7
2 extend in the direction from the diverging nozzle device toward the tube end as two mutually intersecting guide plates. Plates 71, 72 extending into the space within the steam generator shell
The lines are cut at about 45 degrees as shown and support at their top a member 73 having a number of substantially axial or slightly diverging holes 77. In order to avoid the inconvenience of interfering with the flow exiting from the diverging nozzle arrangement 21, the edges 75 of the plates 71, 72 facing the nozzle arrangement should be located at a certain distance from the nozzle arrangement. It is. The cross-shaped plate members 71, 72 support a plurality of diffuser vane rings (buttful structures) 76 which are spaced apart from each other and cover the flow cross section. The diffuser vane ring 76 has a vane-like cross-section and is oriented to substantially radially diverge the flow of water entering the steam generator, thereby reducing the flow velocity before the water reaches the tubes 78 of the tube bundle. decrease. 6th
The ring shown in the figure consists of four parts, each part being fixed between plates 71 and 72, radially spaced from each other. Preferably, the rings 76 are arranged with equal pitch and the vanes provide a uniform and substantial circumferential velocity with an axially selected component behind the rings and deflect the flow, and also The inflow and outflow angles are chosen to give a favorable inflow velocity toward . As mentioned above, the effective range, i.e. the ratio between the sum of the downstream areas of the diverging nozzles of the nozzle arrangement 21 and the inlet duct area, in some cases
In that only 3/4 of the secondary fluid tube is used,
It may not be considered satisfactory even for a very large number of nozzles with circular downstream openings. In order to improve the coverage ratio, the diverging nozzle passage of the nozzle device 21, which has a circular cross-section along its entire length, has several sections, which together form a substantially annular section, at the outlet end of the nozzle device. It can be replaced with the nozzle section of In order to avoid cavitation in the flow, the diffuser passage should be formed by walls inclined with respect to the flow direction at an angle of no more than 7°. The radius of the edge should be of the same order of magnitude as the radius of the smallest part. Under these circumstances, the minimum length compared to the circular nozzle cross-section must be increased by a factor of two to obtain optimal flow without cavitation at the edges. For six diverging nozzle passages in an annular row of passages outside the central circular nozzle passage, an unfavorable flow passage geometry is obtained having an outer edge-to-edge spacing of approximately 1.6×inlet diameter. A more favorable arrangement is obtained by arranging eight diverging nozzle passages instead of six around a central nozzle passage. Twelve passages would be optimal for adding an annular row around one row with eight passages. Therefore, a divergent nozzle arrangement 21 with 21 divergent nozzles is considered to be the optimal solution, and this divergent nozzle arrangement is illustrated in FIG. It is shown in the direction from the vessel. The nozzle device is a central circular diverging nozzle (diffuser passage) 3
0, and around this nozzle 30, two circular rows of 8 diverging nozzles (diff user passages) 31 and 12 diverging nozzles (diff user passages) 32 are arranged, respectively. All are arranged with a shaped outlet. The outlet is generally rectangular in shape with radial side walls 34, 35 and partial circular walls 36, 37 each extending along a circle about the center of the central diverging nozzle. The edge of the annular sector is rounded with a radius approximately the same as the inlet radius, as described above. Preferably, the wall of the adjacent diverging nozzle at the nozzle exit has a wall edge 4 along lines A, B, C in FIG. 6, for example as illustrated in FIGS.
It is cut diagonally, ending in a sharp edge as shown at 0, 50, 60. Preferably, the diverging nozzle device comprises a substantially cylindrical member of a material suitable for the purpose. For steam generators in which the space adjacent to the feedwater inlet nozzle 4 in front of the tube bundle has a width that is much greater than the distance between the tube support plates 6 and 7 of FIG. 1, which also serve as butthole plates. If so, the water supply should be distributed over the water inlet area of the bundle in such a way that the majority of the water volume is distributed horizontally rather than vertically. A device for providing such distribution of water supply is illustrated by FIGS. 10-15, in which a device is shown for directing different selected amounts of water in different directions to achieve this purpose. The wide-end nozzle directs the flow within individual annular sectors.
Guided into a space around the mouth of the nozzle with dimensions that optimally direct the inflow. FIG. 10 is a horizontal cross-sectional view of the diverging nozzle device and tube bundle according to the present invention, and FIG. 11 is a vertical cross-sectional view thereof. A cross section of the diverging nozzle arrangement 21 at the location where the diffuse user portion of the diverging nozzle arrangement ends is shown in FIG. Deflection portion (boutful structure) 8 that comes after the wide-spread nozzle device 21
0, the annular fan-shaped downstream end of the diverging nozzle duct 22 extends in the circumferential direction to the buff-full plate 81. As seen in the longitudinal and cross-section of Figure 10, the flow rate of the upper and lower nozzle outlets should be less than the flow rate of the side nozzles, and the flow of the side nozzles should be distributed as far as the corners of the tube bundle enclosure. It is. The water supply flowing through the longitudinal section should have more axial direction than the water supply flowing through the horizontal section, which corresponds to the axial view of the inlet nozzle 4 of sections A, D, E, F, respectively. The twelfth symbol represents
This is provided by arranging the nozzle outlet mouth as illustrated by FIGS. The flow deflection portion of the outlet passage from each diverging nozzle duct 22 terminates in a baffle plate 81 which directs the flow of water radially and horizontally with respect to passages 1, 4, 5, 8 in FIG. 13, while The flow from the central diverging nozzle and passages 2, 3, 6, 7 is
As can be seen in Figure 1, it is guided more axially. The substantially radial walls of the annular sector-shaped passageway in the flow deflecting portion of the passageway include the thirteenth, fourteenth,
As can be seen in Figure 15, it is formed to distribute the flow rate from the diverging nozzle in the direction towards the outer part of the tube bundle. The deflection part 80 is attached by welding to a diverging nozzle arrangement 21 which can be attached as one unit to the inlet nozzle 4 by means of a weld seam 79, said inlet nozzle 4 holding the diverging nozzle arrangement 21 in place in the event of a pipe rupture. arranged so that it can be maintained. FIG. 16 shows yet another embodiment in which the use of a single nozzle 90 with a plurality of annular diffuser rings 91 adjacent the minimum cross-sectional area Given a flow restriction of
is reduced to an acceptable speed. The diverging nozzle device 21 is mounted within the tubular inlet pedestal 93. In order to ensure a vortex-free inflow towards the flow-limiting nozzle 90, a flow regulating plate member 94 having several straight channels of square cross-section is arranged in front of the nozzle in the direction of flow. As shown in FIG. 16, downstream of the smallest portion of the nozzle 90, a large number (for example, 5 to 7) of diff user rings 91 having a shape capable of forming a diff user passage are arranged. The axial and radial pitch of the diffuser ring 91 is selected to provide a substantially uniform flow velocity as the water enters the tube bundle 78. As illustrated by FIG. 17, the annular diff user passage 92 is subdivided by substantially radial guide walls 97, which are directed toward the outer horizontal portion of the bundle and outwardly. The inlet nozzle is arranged to direct flow to the space 96 above and below the inlet nozzle and to direct less flow to the space 96 above and below the inlet nozzle. Said guide wall 97 supports the diffuser ring 91 and holds the diverging nozzle arrangement 21 together. The diff user ring may consist of several machined rings 91, each of which has a guide wall 97 attached to its uneven surface by welding. According to the invention, therefore, in particular in steam generator installations where tube wear is already observed or in new installations where such wear is to be expected,
The water supply does not collide with adjacent pipes, i.e.
A nozzle structure can be provided for introducing feed water into a steam generator in such a way that it is deflected without any substantial resistance or turbulence. Therefore,
A substantially uniform and swirl-free inflow and distribution of feed water towards the steam generator can be provided, such that the flow of feed water as it enters the tube bundle compromises the mechanical strength of the tubes due to wear or fatigue. The water velocity behind the diffuser structure is reduced to the extent that a low velocity is obtained that does not expose the tube to large magnitude forced vibrations, thereby preventing wear and fatigue of the tube.
Furthermore, in the past, when radioactive primary coolant leaked into the secondary coolant due to pipes being damaged by flow-induced vibrations, the entire secondary system became radioactively contaminated and the steam Generator repairs were required, and such repairs were costly and time consuming because they involved repairing internal components located within the steam generator shell that were not accessible through the inlet nozzle opening. According to the present invention, such repairs are not necessary.

[Brief explanation of the drawing]

1 is a partial sectional view of the lower part of a steam generator with a section into which the fluid to be heated, i.e. the secondary fluid, enters; FIG. 2 is a secondary fluid inlet nozzle as present in conventional installations of the known type; A horizontal cross-sectional view showing the
FIG. 3 shows a number of downstream cross-sectional views of a bench lily nozzle with a circular cross-section arranged as a diverging nozzle arrangement with different numbers of identical diverging nozzles; FIG. 5 is a partial sectional view illustrating an example of a secondary fluid inlet particularly suitable for a steam generator with 7, 8, and 9 are views of the downstream wall of the diverging nozzle device shown along lines A, B, and C, respectively, in FIG. 6. 10 and 11 are horizontal and longitudinal sections, respectively, of an embodiment according to the invention of a steam generator in which the tube bundle has a width substantially greater than the height between the tube support plates adjacent to the inlet nozzle. Figures 12 to 15 are Figures 10 and 1.
FIG. 16 is a longitudinal sectional view of another embodiment of the flow control device according to the present invention, and FIG. 17 is a longitudinal sectional view of the embodiment according to FIG. 16. FIG. 3 is a longitudinal cross-sectional view of the inlet nozzle in the axial direction. 1... Primary water inlet nozzle, 2... Tube bundle, 3... Outlet nozzle, 4... Secondary water inlet nozzle, 5... Shell, 6-16
... Pipe support plate, 20 ... Secondary water supply pipe, 21 ... Divergent nozzle device (diff user structure), 22 ... Divergent nozzle duct (diff user passage), 2 ... Orifice, 24 ... Inlet surface, 25, 26 ... Buff full plate,
29... Opening, 30... Central divergent nozzle (diff user passage), 31, 32... Divergent nozzle (diff user passage), 31'... Tube bundle, 34, 35... Radial side wall, 36, 37... Partial circular wall, 40, 50, 60...
Blades, 71, 72...Plates (batsufuru structure), 73...
Member (boutful structure), 75... Edge (boutful structure), 76... Diffuser blade ring (boutful structure), 77... Hole, 78... Tube bundle, 80... Deflection portion (boutful structure), 81... Boutful plate, 9
0...Flow rate restriction nozzle, 91...Diff user ring (buttful structure), 92...Diff user passage, 9
4...Flow control plate member, 96...Space, 97...Guide wall (buttful structure).

Claims (1)

[Claims] 1. A flow control device for providing a substantially uniform and swirl-free inflow and distribution of feedwater toward a steam generator, the flow control device heating the feedwater as a secondary fluid. a steam generator shell surrounding the tube bundle and having an inlet nozzle and an outlet nozzle for said water supply, said inlet nozzle having a diffuser structure therein; In the flow control device that
a number of diff user passages connected to and installed to limit the flow of water from the steam generator shell through the inlet nozzle during a break in a water supply pipe located within the inlet nozzle; , extending from said diff user structure parallel to the axis of the inlet nozzle, and directing the flow of feed water radially about the inlet nozzle axis in an uninterrupted flow path between the downstream end of the diffuse user passage and the tube bundle surrounded by the shell. a baffle structure that is curved to have a radially extending portion adapted to deflect.