EP0731328B1 - Heat exchanger with U-tubes, provided with a damping and anti- blowout device for securing tubes - Google Patents

Description

The invention relates to a heat exchanger comprising a bundle of bent U-shaped tubes and anti-vibration bars between the curved parts of the tubes as defined in the preamble of claim 1 and known for example from document EP-A-0 639 741. The invention applies in particular to a generator of steam from a pressurized water nuclear reactor.

Reactor steam generators pressurized water nuclear systems have tubes curved in U presenting two parallel straight branches crimped at their ends in a tubular plate.

The ends of the tubes being engaged in openings passing through the tube plate, regularly distributed according to a distribution rectangular or triangular, the bundle tubes are thus kept in a regular arrangement in which the straight branches are all parallel between them and the tubes arranged in layers planes parallel to each other in each of which the bent parts of the tubes have radii of decreasing curvature from outside to inside the tablecloth.

The curved parts of the tubes of each of the bundle layers have radii of curvature different and are juxtaposed so as to constitute a substantially hemispherical structure called a bun, at the top of the bundle of steam generator.

While the generator is operating steam, pressurized water at high temperature flows through the beam and water tubes food is brought into contact with the surface outer exchange tubes along which it moves in the vertical direction while heating up then by vaporizing, to come out as vapor at the top of the steam generator.

The circulation of fluids in contact with tubes can cause vibrations which are likely to cause damage to the tubes if these are not maintained effectively.

The right side of the tubes is engaged in spacers located at regular distances the of each other according to the height of the beam. These straight parts are therefore effectively maintained by rigid elements. The curved parts of the tubes of the bundle making up the bun should also be maintained and generally used for this anti-vibration bars which are inserted each between two plies of adjacent tubes of the bundle and arranged in substantially radial directions bun. These anti-vibration bars as described for example in US-A-3,007,679 are generally connected two by two from their ends to inside the bun and placed angularly to form V-shaped structures

The outer ends of the bars anti-vibration mounts opposite their central part are protruding from the tubes constituting the layer external of the bun and are connected to each other by connecting means ensuring the maintenance of the bars anti-vibration.

Various means of connecting the outer ends of anti-vibration bars using fasteners placed above the top surface of the bun.

We first proposed as for example in the US-A-3,007,679 to weld the ends of the anti-vibration bars on curved elements called pins arranged along meridian planes of the hair bun.

Devices have also been proposed. mechanical connection to connect the ends external anti-vibration bars by connections mechanics arranged so as to group together successive sets of bar ends anti-vibration.

All anti-vibration wedging devices with anti-vibration bars require a anti-theft device to ensure their retention at inside the bun.

In the patent US-A-3,007,679 already cited, we have used anti-theft stirrups made up of parts in U welded on the pins and coming to imprison several tubes of the tube bundle inside the U so as to make the pins and the bars antivibration integral with the tubes.

However, the anti-theft stirrups have the downside of keeping the device anti-vibration, by making the restraint effort carry on certain tubes of the bundle, the tubes being a sensitive element in the operation of the generator steam, so we tried to make the effort to retained from elements other than the tubes.

In EP 0639741 filed by the Company FRAMATOME, we have proposed means of fixing the anti-vibration bars to prevent their ejection at outside the bundle in the steam generator in service, which include a structure fixed on the nearest steam generator spacer plate curved parts of the tubes constituting the bun. The structure is made up of at least one arch of successive segments in the form of arcs of a circle, the end segments are fixed above the plate upper spacer through devices of fixation, the successive segments are connected between them end to end and to the anti-vibration bars by connecting devices.

This anti-theft device while removing the aforementioned drawback of emphasizing the effort of retained on the tubes, requires a fairly long, given the large number of connections mechanical to be put in place during mounting.

The object of the invention is therefore to propose a heat exchanger comprising a bundle of tubes curved in a U so as to present two branches straight and a curved part between the two branches straight, the bundle tubes being located in a regular arrangement in which the straight branches are all parallel to each other and the tubes arranged according to flat sheets parallel to each other, a bundle envelope surrounding the bundle of tubes, a plurality of interleaved anti-vibration bars between the adjacent plies of the tubes in their part curved, so as to present an end to outside the beam, connecting means between the parts of the outer ends of the bars anti-vibration and anti-theft device which is simpler mounting than known devices and which ensures complete support in position of the bars antivibration and their connecting means.

For this purpose, all of the so-called means of link is connected to at least one support integral with the beam envelope so as to constitute the anti-theft device for anti-vibration bars allowing limited movement of all anti-vibration bars and their connecting means in a direction parallel to the straight branches of tubes.

In order to clearly understand the invention, we will now describe, by way of nonlimiting example, with reference to the attached figures, a steam generator of a nuclear water reactor under pressure and a timing device according to the invention associated with this steam generator.

Figure 1 is an elevational view with partial section through a vertical plane of a generator steam from a pressurized water nuclear reactor.

Figure 2 is a schematic sectional view of the upper part of the bun in a plane perpendicular to that of Figure 1.

Figure 3A is a detailed sectional view of Figure 1 showing the ends of the bars antivibration on part of the bun with a schematic representation of the connecting means in the case of a steam generator having a network of tubes not square.

FIG. 3B is a view similar to the view of FIG. 3A, in the case of a steam generator having a bundle of triangular pitch tubes.

Figure 4 is a perspective view of a part of the tube support device according to the invention showing the connecting means and the anti-theft device.

FIG. 4A is a detailed view of a skate for supporting the connecting means on a tube.

Figure 5 is a perspective view of a detail of the tube support device.

Figure 5A is a sectional view of a detail of the central comb.

Figure 6 is a sectional view showing the anti-theft device.

In Figure 1, we see a generator of steam from a pressurized water nuclear reactor generally designated by the reference 1.

The steam generator has an envelope external 2 representing a lower part 2a having the shape of a cylindrical shell in which is arranged the bundle of tubes 3 of the steam generator, inside a beam envelope 4. The part upper 2b of the casing 2 of the steam generator 1 has a diameter greater than the diameter of the part lower 2a and contains means for separation and drying of the vapor produced in contact with the beam 3.

The lower end part of the ferrule 2a of the envelope 2 is integral with a tubular plate 5 thick which is crossed by openings in which the bundle 3 tubes are introduced and fixed by welding and crimping (mechanical or hydraulic for example). On plate tubular 5 is also fixed, opposite the ferrule 2a of envelope 2, a hemispherical envelope 6 delimiting the water box of the steam generator in two parts separated by a partition 7.

Each of the two parts of the water box is connected by tubing to the primary reactor circuit nuclear in which the pressurized water circulates cooling of the reactor core.

The bundle 3 consists of tubes 10 which are curved and have a U shape. Each tubes 10 has two straight branches 10a, 10b and a substantially semi-circular curved portion 10c between the straight branches 10a and 10b.

The ends of the branches 10a and 10b are engaged and set in openings crossing the tube plate 5, on either side of the partition 7.

The straight branches 10a, 10b of the tubes 10 of the beam are also engaged in openings passing through spacer plates 8 arranged with spaced depending on the height of the beam. The network of openings in each of the spacer plates reproduces the network of openings of the tube plate 5, so that the branches 10a and 10b are maintained in parallel arrangements.

In addition, the network of plate openings tubular 5 and spacer plates 8 includes straight rows in which the straight branches of tubes 10 including the curved part 10c has a decreasing radius of curvature from the outside towards the inside of the beam. Beam tubes thus constitute successive layers 12 which are visible in particular in Figure 2. In each layers, the radii of curvature of the curved parts 10c or tube hangers are decreasing by outside towards inside, i.e. from top to low; in addition, the radius of curvature of the outer tube of the sheet having the maximum radius of curvature decreases from the inner central part to the outside of the beam.

Therefore, the bun 9 constituted by the hangers 10c juxtaposed with tubes 10 has a shape substantially hemispherical. Opening networks of engagement of the tubes of the tube plate 5 and of the spacer plates 8 are interrupted at the party central plates in a diametrical direction, so as to define a free space or water street 11 to the central part of the beam between the branches of tubes with the smallest radii of curvature under the small hangers that are aligned in the direction diameter of the water street 11.

The steam generator 1 comprises a torus 13 arranged above the upper part of the envelope of beam 4 in which the bun 9 is placed.

When the steam generator is in operating, pressurized water reactor cooling enters one of the compartments of the water box so as to be distributed inside the branches 10a of the tubes 10 of the beam opening into this entry compartment. The water under pressure circulates inside the tubes to stand out in the second compartment of the water box by the second branches 10b of the tubes 10. The water recovered at the exit of the bundle tubes is returned to the nuclear reactor vessel through a primary circuit pipe.

Feed water introduced into the envelope of the steam generator 2 by the torus feed 13 flows up and down in a space annular formed between the bundle envelope 4 and the outer casing 2 of the steam generator then enters the inside of the beam envelope 4 for come into contact with the tubes 10 above the face top of the tube plate 5. Water feed flows from bottom to top inside the beam, in contact with the tubes and heats up then vaporizes by heat exchange with water under pressure circulating inside the tubes. Steam formed in contact with the bundle tubes is sent into the upper part 2b of the steam generator for be dried and then discharged through the upper end 14 of the steam generator.

The bundle tubes inside each flat sheets of tubes 12 are placed so that have a certain spacing and the layers are also arranged in relation to each other, with a certain spacing. Feed water from steam generator can thus flow in contact with the entire outer surface of the tubes.

Water circulating at high speed in contact with the surface of the tubes generates vibrations of these tubes 10 whose straight branches are perfectly maintained by the spacer plates 8.

To maintain the 10c hangers tubes, inside the bun 9, there are bars anti-vibration 15 in each of the free spaces between two adjacent layers 12, so that the branches anti-vibration bars are placed in radial directions and that two successive branches following the outline of the hangers 10c do between them a substantially constant angle.

We generally have between two layers adjacent 12 of the beam, three anti-vibration bars 15 V-shaped with six overall branches placed with an angular distribution substantially constant.

The outer ends 15b of the branches anti-vibration bars are protruding compared to the upper surface of the bun and allow secure the anti-vibration bars.

Thereafter, we will designate by bar anti-vibration any branch of a set 15 V-shaped

In FIGS. 3A and 3B, there is shown in a sectional view of the plies of tubes in their part upper part of a set of following shimming the invention, in the case of a bundle of tubes maintained in a mesh network arrangement square and in the case of a bundle of tubes maintained in a triangular mesh network layout, respectively.

The bundle tubes are held in a regular network layout through the openings in the tube plate 5 and through the through openings spacer plates 8 which include networks similar openings.

The arrangement of the tubes in the case of a triangular mesh network translates in particular by a space between the successive layers of tubes more weak than in the case of a square mesh network.

The device according to the invention applies as well in the case of a network of tubes tightened to triangular meshes that in the case of a network with square meshes.

In FIGS. 3A and 3B, the corresponding elements bear the same references with, however, the sign ' (prime) in the case of the elements in FIG. 3B relating to a triangular mesh network.

In FIGS. 3A and 3B, the tubes 10 or 10 'of the network of tubes constituting the outer layers of the steam generator bun.

The tubes 10 or 10 'constitute sheets successive parallels between which are inserted 15 or 15 'anti-vibration bars.

In the part of the tube bundle of the steam generator constituting the bun, the tablecloths of tubes consist of the upper parts curved juxtaposed tubes and decreasing radii from the outside to the inside of the bun.

The antivibration bars 15 include projecting ends 15b on the outside of the bun and arranged in alignment with each other to constitute alignments of variable length.

The protruding ends 15b of the bars anti-vibration are connected to each other by means link 20 allowing the connection of two or a greater number of anti-vibration bars constituting a set of aligned bars.

Likewise, the end portions of the bars 15 'anti-vibration mounts inserted between the sheets of tubes arranged in a mesh network triangular as shown in Figure 3B can be connected via connecting means 20 'allowing the ends of a set of two or more bars anti-vibration.

We will now refer to Figure 4 to describe the connecting means 20 of a wedging according to the invention making it possible to link between they the ends of the anti-vibration bars 15.

Each of the connecting means 20 is constituted an elongated piece 21 called a comb and comprising notches 21a, of a closure bar constituting the cover 22 intended to be positioned on the notches 21a, and means for fixing the cover to the comb made up of one or more screws 23. The notches 21a are dimensioned so as to receive the ends of the anti-vibration bars 15. A comb 21 has at least two notches to allow connection of anti-vibration bars. The central comb which happens to be the most important may involve up to thirty notches.

In order to improve the maintenance of the extremities anti-vibration bars 15 in the connecting means 20, bars are preferably used antivibration pads 15 having notches in their end part. The notches of the anti-vibration bars 15 are positioned opposite the notch of the comb so as to come to fit on the bottom of the notch in the comb, which ensures effective support from the end of the anti-vibration bar on the means 20. In all cases, the depth and the width of the notches of the comb are dimensioned so that the section of the anti-vibration bar 15 located in the notch 21a of the comb comes approximately fill in the said notch.

The comb 21 has one or more holes tapped arranged between the notches on the face where locate the notches openings and intended for receive the connecting screws 23.

The cover 22 has the shape of a bar elongated and has one or more holes for the passage of the connecting screws 23.

When the anti-vibration bars including ends are aligned, are introduced into the notches 21a of the comb 21, the cover is fixed above said notches by means of the screws 23 which are introduced into the tapped holes of the comb. One or two solder points between the head of each screw 23 and the cover 22 of the comb 21 locks the screws 23 in rotation.

Finally some combs have holes additional threaded fittings fitted in the face where locate the notches openings and also in the end face of said combs, as it will be explained further.

In order to ensure the correct positioning of connecting means 20 and anti-vibration bars 15 compared to tubes 10 of the beam and more particularly with respect to the bun 9, the stops 24 composed of a shoe 25, a rider 26 and a screw 27, are installed on the combs and come to take support on certain tubes 10 located towards the outside of the bun 9. The detailed drawing of the stopper 24 is shown in Figure 4A.

The pad 25 has the shape of a small plate elongated, it has a rounded profile 25a the size of the outer profile of a tube 10, this profile rounded represents the bearing surface on the tube; the width of said stopper is slightly greater than diameter of a tube except on a part where the stop has two recesses 25b; the said stopper has a oblong hole between the two recesses, arranged in the lengthwise to allow adjustment of the position of the stop during assembly.

Jumper 26 has a U-shaped section overturned, its length is appreciably that of skate recesses 25, it is equipped with an oblong hole and is positioned on the pad 25, at the level of the recesses.

The screw 27 secures the pad 25 and the rider 26 on the comb 21 by screwing in a hole existing thread on the comb.

A weld between the rider 26 and the comb 21 ensures the final positioning of the shoe 25. A solder point between the screw head 27 and the jumper 26 ensures the indessibility of the screw 27.

The connecting means 20 connecting the ends of the anti-vibration bars 15 located in a same meridian plane of the bun are all united each other by the fact that two connecting means 20 successive trap a bar end 15b anti-vibration 15 common which is therefore inserted in two successive combs 21.

In the case where the combs 21 have a number sufficient notches, preferably two ends of anti-vibration bars 15 in common, inserted in two successive connecting means so to obtain better rigidity of the assembly.

The ends of anti-vibration bars 15 connected to two successive connecting means have then two notches to be inserted in the notches of the two successive combs.

When all the connecting means 20 are installed, all ends 15b of the bars anti-vibration 15 are positioned in one or two comb notches 21.

In the current case where there are three anti-vibration bars 15 V-shaped openings different, but identical between each layer of tubes, thus connecting six sets of ends of anti-vibration bars 15 arranged substantially along meridians of the bun in perpendicular planes in terms of flat sheets 12. All of the means for bond 20 of the same meridian is called set of connection of the ends. Each of these sets of connection of the ends is integral with another set connecting ends located on the bars same opening antivibration, but it is independent of the 4 other linkage assemblies extremities.

In order to liaise between all end connection assemblies, we install hoops 30 arranged in parallels of the shape hemispherical of the bun, arranged outside the bun 9 and connecting the different sets together connecting ends.

The connection between the arches 30 and the means link 20 is achieved by the fact that each hoop is connected to a comb 21 of each connection assembly extremities. The connection between a hoop 30 and a comb 21 is produced by a screw 31 passing through the arch 30 in which a hole has been arranged and coming screw into the tapped hole in the face end of the comb 21 and described above.

For example, there will be seven arches 30 for keep all ends in a rigid set anti-vibration bars. The different arches 30 are of different radii depending on their location above bun.

There may be an additional central arch 30 large radius located in the plane of Figure 2, its connection with the central comb 21 of each set of connection of the ends takes place in the middle of the said comb.

Referring to Figure 5, there is shown the connection between a central comb 21 and the arch 30 central.

The placement of the bundle tubes and anti-vibration bars can be realized according to the process described in patent FR-A-2 603 364 of the FRAMATOME company. According to this process the tubes are mounted in successive layers from the layer la largest located in the center according to the plan of the figure 1 towards the tablecloths of decreasing sizes and in progressively inserting the bars anti-vibration, when half the beam is mounted, the generator is rotated 180 ° steam along its axis then located in a horizontal position and we go up the other half of the beam starting from the largest dimension tablecloth towards the tablecloths of decreasing sizes.

In order to be able to install the central arch 30 and the central comb 21, we have a central comb composed of two half-combs whose assembly longitudinal is carried out by a tail-like assembly dovetail as shown in Figure 5A. Each half-comb is equipped with a support console 28 which is screwed with the cover 22 of the comb.

When we start the assembly phase of the tubes of the second half of the tubes, we insert the second half comb on the first half comb using of the dovetail.

The support brackets 28 are mounted with the covers of each half-comb and have a hole threaded to receive a fixing screw. The hoop is fitted with lugs 29 which are fixed by means of a fixing screw, crossing the tab and coming to be screwed in the tapped hole of the support brackets 28.

Referring now to Figures 4 and 6, we see that the entire wedging device antivibration consisting of antivibration bars 15, the end connection assemblies and the hoops 30, is held by an anti-flight device.

Indeed, the previously wedging device described can move as a whole between the plies of tubes. The initial positioning of the device made during assembly could be caused to modify especially during generator operation steam. As indicated in the presentation of the invention of devices with anti-theft stirrups retained by the tubes or with a rail on the plate spacer located near the bun were used.

In the case of the present invention, uses supports 40 fixed on the envelope of harness 4 and connected to the timing device antivibration.

The anti-theft device we are going to make the description could be used with a anti-vibration wedging device different from that described above and in particular at the level of the links the ends of the anti-vibration bars. Support 40 intended to ensure the anti-theft function consists a metal tab 41 rigidly fixed, by welding on the beam envelope 4. The support tab 41 has at its end opposite the envelope of bundle 4, a hinge 42 intended to receive a dowel 44. The pin 44 is arranged in one direction parallel to the axis of the steam generator.

At each end of the arches 30 is disposed a lug 32, rigidly fixed by welding and integral of the roll bar.

In the most common case the generator steam is arranged with its axis in vertical position as shown in Figure 1. The description which follows is therefore made in this configuration. If the steam generator was in a horizontal position the positioning terms should be adapted in result.

The tab 32 is substantially flat and arranged in a substantially horizontal position, below the hinge 42 and the support leg 41, which are located in the extension of each other with their faces lower lying in the same horizontal plane 43.

The tab 32 has an opening 33 of dimensions slightly larger than that of the section ankle 44.

Ankle 44 longer than the length of the hinge 42 is introduced into hinge 42 so as to protrude a few millimeters above the hinge 42, and several centimeters below the hinge 42 in coming through the opening of tab 32. It is then welded, in the upper part, by a weld 45 on the upper face of the hinge 42.

During assembly, there is a clearance J between the underside of the hinge 42, located in a plane horizontal 43 and the upper face of the tab 32. This game can be materialized by positioning provisional of a wedge (not shown) between the faces mentioned above.

Set J at assembly, at room temperature decreases during operation at high temperature. We will therefore make a game J so that it remains still a game, weaker, in the conditions of operation.

The device thus constituted with the supports ensures that the entire anti-vibration device will be well maintained in a position close to that established during the mounting, and limits both the vertical movement of the anti-vibration device to the top of the generator steam and its tilting. In order to give the system freedom of movement sufficient, the opening 33 in the tab 32 is larger than the anchor 44 and allows therefore a limited displacement of the support device in a horizontal plane.

Finally, to complete the system, a washer 46 is positioned at the lower end of the ankle 44 and fixed to the said ankle by a solder 47, this ensures that the tab 32 of the arch 30 can in no case be released from its position on the ankle 44.

The support device thus described is reproduced at both ends of the arch 30. When there are seven arches 30 as indicated previously, preferably fourteen distributed supports will be installed around the perimeter of the bundle envelope 4.

The invention is not limited to the mode of achievement which has been described.

The device for fixing the ends of the anti-vibration bars could be realized according to a already known device and be associated with supports anti-theft such as that which has been described.

The anti-theft device could be produced differently, provided you allow the realization of a limited clearance for moving all of the connecting means.

The anti-vibration bars can be of a form different from that which has been described.

The invention applies in the case of any steam generator or heat exchanger comprising a regular network of tubes with parts curved between which bars are inserted anti-vibration.

Claims (14)

1. Heat exchanger comprising a bundle of tubes (10) bent in U-shaped manner, so as to provide two straight branches (10a, 10b) and a curved part (10c) between the two straight branches (10a, 10b), the tubes of the bundle being in a regular arrangement in which the straight branches (10a, 10b) are all parallel to one another and the tubes (10) arranged in parallel planar layers, a bundle envelope (4) surrounding the tube bundle (10), a plurality of damping rods (15) placed between adjacent layers of tubes in the curved part thereof, so as to have an end outside the bundle, linking means (20) between the outer end parts of the damping rods (15) and an anti-blowout device, characterized in that the assembly of said linking means (20) is connected to at least one support (40) integral with the bundle envelope (4), so as to form the damping rod anti-blowout device, whilst permitting a limited displacement of all the damping rods and their linking means in a direction parallel to the straight branches of the tubes.
2. Heat exchanger according to claim 1, characterized in that the linking means (20) of the ends of the damping rods (15) comprise first linking means (20) linking the ends of the rods located substantially in planes perpendicular to the planes of the planar layers and constituting end linking assemblies and second linking means linking the end linking assemblies.
3. Heat exchanger according to claim 2, characterized in that the second linking means linking the end linking assemblies comprise an arch (30) placed in a plane substantially parallel to the planes of the planar layers.
4. Heat exchanger according to claim 3, characterized in that at least one arch (30) is connected to the support (40) integral with the bundle envelope.
5. Heat exchanger according to any one of the preceding claims, characterized in that the anti-blowout device also permits a limited relative displacement in all directions between each support (40) integral with the envelope and the linking means (20) of the ends of the damping rods.
6. Heat exchanger according to claim 4, characterized in that the arch (30) has a substantially horizontal lug (32) with a window (33), in which is inserted a pin (44) substantially parallel to the straight branches of the tubes and integral with the support (40), said support being located on the same side of the lug as the linking means assembly.
7. Heat exchanger according to claim 6, characterized in that the window (33) has larger internal dimensions than the external dimensions of the pin (44), in order to permit a displacement in the two dimensions located in the plane perpendicular to the straight branches of the tubes.
8. Heat exchanger according to claim 6, characterized in that a clearance when cold J is provided in adequate form between the lug (32) of the arch (30) and the part of the support (40) facing the lug, so that there is still a clearance when hot when the heat exchanger is operating.
9. Heat exchanger according to any one of the preceding claims, for which the outer end parts of the damping rods (15) are distributed in accordance with a plurality of assemblies having at least two rods, in which the rods are aligned, characterized in that the linking means (20) for each of the assemblies of aligned damping rods comprise a cleat (21) having notches (21a) able to receive the ends of the damping rods (15), a cleat cover (22) for closing spaces constituted by notches and means (23) for fixing the cover to the cleat.
10. Heat exchanger according to claim 9, characterized in that the means for fixing the cover to the cleat are constituted by tapped holes located in the cleat and screws (23) placed in said tapped holes.
11. Heat exchanger according to either of the claims 9 and 10, characterized in that the damping rods (15) have notches for positioning facing corresponding notches of the cleats, so as to permit a securing effect preventing any relative movement between the damping rods and the linking means (20).
12. Heat exchanger according to any one of the claims 9 to 11, characterized in that the linking means (20) located in the same plane perpendicular to the planes of the planar layers are interconnected by means of the ends of certain damping rods (15), which are inserted in two successive cleats.
13. Heat exchanger according to any one of the claims 9 to 12, characterized in that the cleats (21) are positioned with respect to the tubes of the tube bundle by means of a support device (24) fixed to the cleat and having a bearing surface cooperating with the external profile of certain tubes (10).
14. Heat exchanger according to claim 13, characterized in that the support device (24) is constituted by a pad (25) maintained on the cleat (21) by a staple (26) and fixed by a screwed connection (27).

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