EP0544579A1 - U-tube heat exchanger with anti-blow-out supporting device - Google Patents

Abstract

In a heat exchanger such as a steam generator fitted to a nuclear power plant, the U-shaped tubes (14), grouped in a bundle forming parallel sheets, are held in their curved intermediate part (14c) by anti-vibration bars (36a , 36b ', 36c') placed between each pair of adjacent plies, these bars being connected to each other outside the bundle by connecting pins (38a, 38b, 38c). To prevent the flight of the assembly formed by the anti-vibration bars and the connecting pins, at least part of the anti-vibration bars (36a, 36b ', 36c') are hooked in notches formed in an elongated structure (40) fixed to the spacer plate (34a) closest to the curved part of the tubes. <IMAGE>

Description

The invention relates to a heat exchanger comprising a bundle of U-shaped tubes, the curved intermediate portion of which is held by a new type anti-flight support device.

The invention applies in particular to steam generators which are used in nuclear power plants to ensure the transfer of heat between the primary circuit and the secondary circuit of the pressurized water reactor.

In these steam generators, after it has been reheated in the reactor core, the water in the primary circuit (hereinafter called "primary water") circulates in a bundle of inverted U-shaped tubes, to transfer the heat that 'it conveys water to the secondary circuit (hereinafter called "secondary water"), in order to transform it into vapor.

More precisely, the inverted U-shaped tubes of the bundle are arranged in parallel layers and their rectilinear branches pass through horizontal spacer plates which ensure their relative positioning over most of the height of the bundle.

In the upper part of the bundle, that is to say in the curved intermediate part of the tubes, the relative positioning between the tubes is maintained by anti-vibration bars. More specifically, at least one more or less open V-shaped bar is usually placed between each pair of adjacent tube plies, to prevent the tubes from vibrating into this upper part of the bundle, which could result from the circulation of water inside and outside the tubes. All the anti-vibration bars are linked together, beyond the bundle of tubes, by connecting pins welded to the ends of the bars.

As illustrated in particular in document US-A-3 007 679, in a device for supporting the upper part of the bundle of tubes thus designed, the flight of the assembly formed by the connecting pins and by the anti-vibration bars is usually prevented by anti-theft stirrups which are fixed on the connecting pins and encircle some of the tubes located outside the bundle.

In a structure of this type, the anti-take-off stirrups have the disadvantage of joining together several tubes of the bundle, which creates constraints in the event of differential expansions between these tubes, in particular if one or more of them is are blocked during the life of the steam generator.

The invention specifically relates to a heat exchanger in which the maintenance of the bundle tubes in the upper part of the latter is ensured in a conventional manner by anti-vibration bars connected together by connecting pins, but in which the anti-stirrups -flight traditionally used are eliminated and replaced by anti-take-off means of a different nature, which do not have the drawbacks of anti-take-off stirrups and can be easily assembled during the manufacture of the exchanger.

According to the invention, this result is obtained by means of a heat exchanger comprising a bundle of U-shaped tubes arranged in layers, each tube comprising two straight parts and a curved intermediate part, spacer plates through which the straight parts of the tubes, at least one anti-vibration bar placed between each pair of sheets of adjacent tubes, in their curved intermediate part, pins for connection of the anti-vibration bars, and anti-take-off means of the assembly formed by the anti-vibration bars and the connection pins, characterized in that the anti-vibration means flights comprise an elongated structure fixed to the spacer plate closest to the curved intermediate parts of the tubes, inside these curved parts, perpendicular to said plies, this elongated structure comprising, between each pair of adjacent tube plies, at least one notch in which an anti-vibration bar is received.

Thanks to the fixing of the antivibration bars in notches formed on an elongated structure carried by the spacer plate closest to the curved parts of the tubes, the flight of the assembly formed by the antivibration bars and the connecting pins is prevented without 'it is necessary to provide anti-theft stirrups as in the prior art. Consequently, any risk of creating stresses between the tubes in the event of differential expansions is eliminated. Furthermore, the arrangement proposed in accordance with the invention makes it possible for the anti-vibration bars to support all of the tubes of each ply, that is to say from the smallest bending radius to the largest, which doesn was not always the case in the prior art.

In the case where at least two anti-vibration bars are placed between each pair of adjacent plies of tubes, the notches formed in the elongated structure comprise groups of notches receiving all the anti-vibration bars placed between two adjacent plies, these groups of notches regularly distributed all the n layers ( n being an integer at least equal to 2 and, for example, equal to 8), and unit notches each receiving the anti-vibration bar closest to the elongated structure, for the remaining sheets.

According to a preferred embodiment of the invention, the notches formed in the elongated structure open onto an edge of this structure turned towards the curved parts of the tubes by access slots, through which the anti-vibration bars can be introduced. In the case where the notches comprise groups of notches, all the notches of the same group open on this edge by a common access slot.

To allow easy mounting of the heat exchanger, for example in accordance with the method described in document FR-A-2 603 364, the access slots are offset radially towards the outside of the tube bundle, relative to the notches opening into these slots.

Preferably, the elongated structure comprises a rectilinear attachment rail, fixed to the spacer plate closest to the curved parts of the tubes, perpendicular to this plate. Depending on the nature of the materials which constitute the attachment rail and the spacer plate, the attachment rail can be welded directly to this plate or welded to at least one flange fixed to the spacer plate by fixing means such as screws. .

• la figure 1 est une vue de côté, illustrant schématiquement, en coupe verticale partielle, un générateur de vapeur réalisé conformément à l'invention ;
• la figure 2 est une vue en coupe selon un plan vertical perpendiculaire au plan de la figure 1, illustrant la partie haute du faisceau de tubes ;
• la figure 3 représente à plus grande échelle la partie supérieure du faisceau de tubes, en coupe selon le plan de la figure 1 ;
• la figure 4 est une vue en perspective illustrant plus précisément le montage des barres antivibratoires sur une structure allongée fixée à la plaque entretoise supérieure, conformément à l'invention ; et
• la figure 5 est une vue en coupe selon le même plan vertical que la figure 2, illustrant à plus grande échelle l'accrochage des barres antivibratoires sur la structure allongée qui est fixée sur la plaque entretoise supérieure du générateur de vapeur.

A preferred embodiment of the invention will now be described, by way of nonlimiting example, with reference to the appended drawings, in which:

• Figure 1 is a side view, schematically illustrating, in partial vertical section, a steam generator produced according to the invention;
• Figure 2 is a sectional view along a vertical plane perpendicular to the plane of Figure 1, illustrating the upper part of the bundle of tubes;
• Figure 3 shows on a larger scale the upper part of the bundle of tubes, in section along the plane of Figure 1;
• FIG. 4 is a perspective view illustrating more precisely the mounting of the anti-vibration bars on an elongated structure fixed to the upper spacer plate, in accordance with the invention; and
• Figure 5 is a sectional view along the same vertical plane as Figure 2, illustrating on a larger scale the attachment of the anti-vibration bars on the elongated structure which is fixed on the upper spacer plate of the steam generator.

In Figure 1, there is shown very schematically a steam generator for use in a nuclear power plant and produced according to the invention. It is recalled, however, that this application is only one embodiment of the invention, which can be applied equally to any heat exchanger comprising U-shaped tubes arranged in a bundle, whatever the primary and secondary fluids which circulate in and around the tubes, and whatever the orientation of the tubes, the main axis of the beam can be oriented vertically as in the example described, horizontally or even obliquely.

The steam generator illustrated in FIG. 1 comprises in a known manner a cylindrical outer casing 10, of vertical axis, the interior volume of which is divided into two parts by a horizontal plate 12, called a tube plate, in the immediate vicinity of the convex bottom of the outer casing 10. The tube plate 12 is traversed by a multitude of perforations in which the lower ends are fixed of a set of inverted U-shaped tubes 14, these tubes being arranged in a bundle in the part of the outer envelope 10 situated above the tube plate 12.

More precisely, the ends of each of the tubes 14 of the bundle are fixed to the tube plate 12 so that the two ends of each tube open below the tube plate 12 respectively in an inlet chamber 16 of primary water and in an outlet chamber 18 of primary water separated from each other by a vertical partition 20. An inlet pipe 22 of primary water and an outlet pipe 24 of primary water open respectively into the inlet chamber 16 and into the outlet chamber 18.

Secondary water is admitted into the outer casing 10 through an inlet pipe 26 for secondary water situated at a level higher than the high level of the bundle of tubes 14 and which is connected to the interior of the steam generator by a toroidal manifold 28 opening over its entire periphery by tubes 29 in the form of an inverted J.

The secondary water admitted into the outer casing 10 of the steam generator descends by gravity into an annular space formed between this outer casing 10 and an inner casing 30 which encircles the bundle of tubes 14 over its entire height and whose lower end is located near the tube plate 12. The secondary water then rises in the inner envelope 30, circulating around the tubes 14, so that it takes part of the calories conveyed by the primary water and is transforms into vapor in the upper part of the inner envelope 30.

Still in known manner, the vapor thus formed is taken up in the upper part of the envelope. interior 30 and passes through water-steam separation and steam drying devices well known to specialists and not shown in FIG. 1. The dried steam then leaves the steam generator by an outlet pipe 32 for secondary steam which opens axially in the dome of the outer casing 10.

Each of the tubes 14 in inverted U of the bundle of tubes through which the heat exchange takes place between the primary water and the secondary water comprises two rectilinear and vertical parts of great length 14a and 14b and an intermediate part curved in semicircle 14c located at the top of the beam.

As illustrated very diagrammatically in FIG. 1, the support of the straight parts 14a and 14b of the tubes 14 is ensured by a set of spacer plates 34 arranged horizontally at equal distance from each other over the entire height of the straight parts 14a and 14b of the beam tubes. These plates have perforations through which the tubes 14 pass and which ensure a controlled circulation of the secondary water around these tubes. The upper spacer plate, designated by the reference 34a, is situated slightly below the horizontal axis, perpendicular to the plane of FIGS. 1 and 3, on which all the curved parts 14c of the tubes 14 are centered.

As illustrated better in FIG. 2, it is important to observe that the tubes 14 are arranged in layers, that is to say that they are situated in vertical planes parallel to the planes of FIGS. 1 and 3 and perpendicular in the plane of FIG. 2. Each of these layers comprises a number of tubes 14 which increases progressively as we approach the vertical axis of the steam generator, the tubes of each sheet having curved intermediate parts 14c whose radius of curvature decreases radially towards the interior of the bundle, as illustrated in FIGS. 1 and 3.

To support the curved parts 14c of the tubes 14, which is not provided by the spacer plates 34, anti-vibration bars are used in known manner which are placed between each pair of adjacent plies of tubes 14. More precisely, in the embodiment illustrated in FIGS. 3 to 5, three anti-vibration bars 36a, 36b and 36c (or 36a, 36b 'and 36c') are placed between each pair of adjacent plies of tubes 14 three the shape of a V with a rounded top, arranged symmetrically with respect to the plane of symmetry of the bundle of tubes 14 passing through the vertical axis of the steam generator and oriented perpendicularly to FIGS. 1 and 3.

The three anti-vibration bars 36a, 36b and 36c (or 36a, 36b 'and 36c') which are placed between each pair of adjacent tube layers differ essentially in their apex angle and in their position. Thus, the antivibration bar 36a closest to the upper spacer plate 34a has an obtuse apex angle, while the intermediate antivibration bar 36b (or 36b ') has an apex angle close to 90 ° and that the antivibration bar 36c ( or 36c ') the farthest from the upper spacer plate 34a has an acute apex angle.

According to a known technique, all the anti-vibration bars 36a are connected together, beyond the outer tubes of the bundle of tubes 14, by connecting pins 38a welded to the ends of the bars 36a which project outside the bundle. Similarly, connecting pins 38b and 38c are welded respectively to the ends of the anti-vibration bars 36b, 36b 'and 36c, 36c', beyond the outer tubes of the tube bundle 14, so as to connect together all the anti-vibration bars 36b, 36b 'and all the anti-vibration bars 36c, 36c'.

The invention relates more precisely to an anti-takeoff device of a new type, which is associated with the assembly formed by the antivibration bars 36a, 36b, 36b ', 36c and 36c' and by the connecting pins 38a, 38b and 38c, to prevent this assembly from partially escaping between the plies of tubes 14 under the effect of vibrations generated in the latter by the circulation of water.

As illustrated in particular in FIGS. 3 to 5, this anti-flight device comprises an elongated structure 40 which is fixed to the upper spacer plate 34a, inside the curved parts 14c of the tubes 14 or bundle, perpendicular to the sheets formed by these tubes, that is to say in a direction perpendicular to the planes of Figures 1 and 3, passing through the vertical axis of the steam generator and on which are the centers of the curved parts 14c of the tubes.

This elongated structure 40 mainly comprises a rectilinear attachment rail 42. In the embodiment illustrated in particular in FIG. 5, the attachment rail 42 is welded on flanges 44, regularly distributed, themselves fixed on the spacer plate upper 34a by fixing means such as screws or bolts 46.

It should be noted that in a variant embodiment not shown, the soles 44 can be replaced by a single sole extending over the entire length of the attachment rail 42.

In another embodiment not shown, the hanging rail 42 can also be directly welded to the upper spacer plate 34a, if the materials constituting these two parts allow it.

As illustrated more precisely in FIGS. 4 and 5, the fastening rail 42 includes, over its entire length, notches in which the central parts of the anti-vibration bars 36a, 36b 'and 36c' are received.

Thus, the fastening rail 42 comprises, between certain pairs of plies of adjacent tubes 14, groups of three notches 48a, 48b and 48c and, between other pairs of plies of adjacent tubes, a single notch 50. More precisely , the groups of three notches 48a, 48b and 48c are regularly distributed every eight plies of tubes in the example shown, while the attachment rail 42 has a single notch 50 for all the other remaining plies.

Each of the groups of three notches 48a, 48b and 48c is placed in a plane containing a group of three anti-vibration bars 36a, 36b 'and 36c', and these three notches open onto an edge 42a of the hanging rail 42 facing the parts curved tubes 14c through a common access slot 52.

Furthermore, each unitary notch 50 is also placed in the same plane as a group of three anti-vibration bars 36a, 36b and 36c, but it receives only the central part of the anti-vibration bar 36a closest to the axis of the beam. of tubes. These unitary notches 50 are aligned with the notches 48c of the groups of notches 48a, 48b and 48c closest to the edge 42a of the rail 42.

The introduction of the anti-vibration bars 36a into the notches 50 is also carried out by an access slot 54 which opens onto the edge 42a of the attachment rail 42.

The access slots 52 and 54 are oriented parallel to the planes containing the groups of anti-vibration bars 36a, 36b ', 36c' and 36a, 36b, 36c which correspond to them, and offset radially outwards from the bundle of tubes with respect to these planes.

Thus, the anti-vibration bars 36a, 36b 'and 36c' can be introduced successively through the slot 52 and put in place in the corresponding notches 48a, 48b and 48c after the adjacent ply of tubes 14 closest to the beam axis of tubes has been installed. When the next ply of tubes is, in turn mounted on the device, the anti-vibration bars 36a, 36b 'and 36c' are automatically maintained.

Similarly, the anti-vibration bar 36a of each of the groups of bars 36a, 36b, 36c can be introduced into the notch 50 by the slot 54 after the adjacent ply of tubes closest to the beam axis has been implementation. Maintaining this anti-vibration bar 36a is ensured when the next layer of tubes is put in place.

It should be noted that the antivibration bars 36a closest to the axis of the tube bundle are almost the same when these bars are hooked in the notches 48a and when they are hooked in the notches 50. On the other hand, the antivibration bars 36b 'and 36c' which are hooked in the notches 48b and 48c have a smaller apex angle than the corresponding anti-vibration bars 36b, 36c which are not hooked in these notches. To distinguish these two types of anti-vibration bars, those which are not hung in notches have been designated by the references 36b and 36c, while the bars which are hung in the notches 48b and 48c have been designated by the references 36b 'and 36c 'in Figures 3 to 5.

The assembly of the tubes 14 of the steam generator according to the invention is advantageously carried out in the manner described in the document FR-A-2 603 364.

Thanks to the structure which has just been described in detail with reference to FIGS. 3 to 5, the assembly constituted by the anti-vibration bars 36a, 36b, 36c, 36b 'and 36c' and by the connecting pins 38a, 38b and 38c is attached to the upper spacer plate 34a, so that its flight is prevented, without it being necessary to have recourse to anti-flight stirrups which risk creating stresses in the event of differential expansions between the encircled tubes by these stirrups, in particular in the event of one or more of these tubes being blocked.

This structure also makes it possible for the antivibration bars 36a, 36b, 36c, 36b 'and 36c' to support all of the tubes 14 of each ply, that is to say of the smallest bending radius of the curved part 14c up to 'at the greatest.

Furthermore, the anti-take-off device according to the invention allows easy installation of the anti-vibration bars as and when the different layers of tubes 14 of the bundle are put in place. The assembly procedure of the steam generator therefore remains practically unchanged.

Of course, the invention is not limited to the embodiment which has just been described by way of example, but covers all its variants. Thus, as already mentioned, the invention applies to any heat exchanger comprising a bundle of U-shaped tubes, whatever the orientation of the bundle and the application concerned. Furthermore, the invention can be used regardless of the number of anti-vibration bars placed between the successive layers of tubes and the attachment of the bars may concern all of them or only a part of them as in the example described. In the latter case, groups of notches receiving all of the corresponding anti-vibration bars must be distributed among unitary notches, all of the n layers of tubes, so that the assembly is kept in place. This number n can then be any number greater than or equal to two.

Claims (8)

Heat exchanger comprising a bundle of U-shaped tubes (14) arranged in layers, each tube comprising two rectilinear parts (14a, 14b) and a curved intermediate part (14c), spacer plates (34) which pass through the rectilinear parts of the tubes , at least one anti-vibration bar (36a, 36b, 36c, 36b ', 36c') disposed between each pair of adjacent plies of tubes, in their curved intermediate part, connecting pins (38a, 38b, 38c) of the anti-vibration bars, and anti-take-off means of the assembly formed by the anti-vibration bars and the connecting pins, characterized in that the anti-take-off means comprise an elongated structure (40) fixed to the spacer plate (34a) closest to the curved intermediate parts (14c) of the tubes, inside these curved parts, perpendicular to said plies, this elongated structure comprising, between each pair of plies of adjacent tubes, at least one notch (48a, 48b, 48c, 50) in which is received an anti-vibration bar (36a, 36b ', 36c'). Heat exchanger according to claim 1, characterized in that at least two anti-vibration bars (36a, 36b, 36c, 36b ', 36c') being arranged between each pair of adjacent plies of tubes, the notches formed in the elongated structure (40) comprise groups of notches (48a, 48b, 48c) receiving all the anti-vibration bars (36a, 36b ', 36c') placed between two adjacent plies, these groups of notches being regularly distributed all the n plies, and unitary notches (50) each receiving the anti-vibration bar (36a) closest to the elongated structure, for the remaining plies. Heat exchanger according to any one of the preceding claims, characterized by fact that the notches (48a, 48b, 48c, 50) formed in the elongated structure (40) open onto the edge (42a) of this structure facing the curved parts (14c) of the tubes, by access slots (52 , 54). Heat exchanger according to claims 2 and 3 combined, characterized in that the notches (48a, 48b, 48c) of the same group of notches open onto said edge (42a) by a common access slot (52) . Heat exchanger according to any one of claims 3 and 4, characterized in that the access slots (52,54) are offset radially towards the outside of the tube bundle (14), relative to the notches (48a , 48b, 48c, 50) opening into these slots. Heat exchanger according to any one of the preceding claims, characterized in that the elongated structure (40) comprises a straight hooking rail (42) fixed to the spacer plate (34a) closest to the curved parts (14a ) tubes, perpendicular to this plate. Heat exchanger according to claim 6, characterized in that the attachment rail (42) is welded to at least one flange (44) fixed to the spacer plate (34a) by fixing means (46). Heat exchanger according to claim 6, characterized in that the attachment rail (42) is welded directly to the spacer plate (34a).

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