EP0173586A1 - Cylindrical shell and tube heat exchanger, wherein the shell is radially held inside an external shell - Google Patents

Abstract

Steam generator, in particular nuclear pressurized water reactors comprising a bundle of tubes (2) arranged in a bundle envelope (5). The bundle envelope (5) has openings in its wall each corresponding to a support piece (20) along the edge of which are fixed sleeves (15) projecting radially in the space between the envelope (5) and the outer wall (3) of the heat exchanger. Each of the support pieces (20) has two cylindrical parts located in the extension of one another, a large diameter part (20a) welded by its lateral surface inside the sheath (15) and a part small diameter (20b) intended to come to bear on the casing (3). Shims (23) are interposed between the part (20a) of the support piece (20) and a spacer plate (8) of the heat exchanger.

Description

The invention relates to a heat exchanger comprising a bundle of tubes arranged in a cylindrical bundle envelope maintained radially inside an external cylindrical envelope.

Heat exchangers such as the steam generators of a pressurized water nuclear reactor comprise a tube bundle constituted by a very large number of small diameter tubes arranged vertically inside a bundle envelope of generally cylindrical shape. itself arranged inside the envelope in external rigid pressure of great thickness of the steam generator.

The pressurized water from the nuclear reactor circulates inside the small diameter tubes and the water to be vaporized is introduced inside the bundle envelope where it comes into contact with the external surface of the tubes. The vapor is recovered at the top of the bundle envelope and then it is generally dried in steam-water separators arranged in the outer envelope of the steam generator above the bundle envelope.

The steam generator is supplied with water to be vaporized by a means generally located towards the upper part of the bundle envelope. In addition, the water recovered in the vapor by the water-vapor separators is also returned to the envelope of the bundle for its vaporization. There is thus a permanent circulation of water inside the envelope of the steam generator. This circulation may require channeling means such as additional cylindrical envelopes arranged coaxially with the bundle envelope and the external envelope of the steam generator, on only part of their lateral surface.

Steam generators are very tall units in which the various coaxial envelopes are arranged with a generally small radial spacing.

It is known to use spacer plates through which the tubes of the bundle pass, distributed along the height of the bundle, to maintain the tubes in fixed radial positions with respect to each other. These spacer plates are interconnected by vertical tie rods, the assembly being placed inside the bundle envelope.

It is therefore important to maintain the various coaxial envelopes of the steam generators, and the entire bundle by the spacer plates in the radial directions, so as to avoid relative displacements and shocks between these envelopes and the bundle in the event of external stresses. such as those accompanying an earthquake.

French patent No. 2,511,491 has proposed holding devices in the radial and axial directions of the envelope of the bundle of a steam generator, inside its rigid outer envelope and of greater thickness. These holding devices are fixed to the bundle casing, according to several assemblies each arranged at a spacer plate, the various support devices of an assembly being distributed around the periphery of the spacer plate. supports are made up of parts having a thickness greater than the thickness of the bundle envelope fixed in the wall thereof, locally at the level of the spacer plates. These parts are pierced with tapped holes inside which one can screw threaded studs, the projecting end of which in the space existing between the bundle casing and the rigid external casing bears against the interior surface of this external casing. pui devices is made after adjusting the studs, by introducing wedging wedge-shaped parts between the outer edge of the spacer plates and the inner surface of the support device directed towards the beam.

Such support devices have the disadvantage of occupying a large part of the width of the space reserved between the bundle envelope and the external envelope and thus limiting, appreciably, the passage section for the water spray circulating in this space without ensuring a perfect seal. These support devices also have the drawback of requiring the introduction of wedging parts in notches machined at the peripheral part of the spacer plates. These notches decrease the distance between the peripheral tubes of the bundle and the edge of the spacer plates. If you want to keep a sufficient distance between the peripheral tubes and the plate, you must reduce the number of tubes in the bundle. On the other hand, the supporting parts must have shapes that do not facilitate their fixing by welding. in the wall of the bundle envelope.

In the case of a steam generator comprising several coaxial envelopes delimiting annular-shaped spaces which must be perfectly sealed against each other, there is practically no B 8488 GP not possible to use support devices as described in French patent 2,511,491, the use of which is accompanied by a risk of leakage.

The object of the invention is therefore to propose a heat exchanger comprising a bundle of tubes arranged in a cylindrical bundle envelope held radially inside an external cylindrical envelope and placed coaxially with it, a set of plates spacers arranged transversely to the bundle inside the bundle envelope and spaced along its length and several sets of support parts integral with the bundle envelope, arranged radially at the level of the spacer plates and each inserted between the outer edge of the spacer plates and the inner surface of the outer envelope, with interposition of wedging means between the spacer plate and the support piece, heat exchanger whose bundle envelope is perfectly maintained in the external envelope by supporting parts which constitute only very limited obstacles to the circulation of fluids in the exchanger, which are perfectly nt adaptable in the case where the heat exchanger comprises more than two coaxial envelopes leaving spaces perfectly sealed with respect to each other and which can be set up by welding in a simple and rapid manner.

• - l'enveloppe du faisceau comporte des ouvertures dans sa paroi correspondant chacune à une pièce d'appui, suivant le bord desquelles sont fixés des fourreaux cylindriques saillants radialement dans l'espace entre l'enveloppe du faisceau et la paroi externe de l'échangeur de chaleur,
• - et chacune des pièces d'appui comporte deux parties cylindriques ayant un même axe de direction radiale, dans le prolongement l'une de l'autre, une partie à grand diamètre soudée par sa surface latérale externe à l'intérieur du fourreau correspondant et comportant une surface d'appui des moyens de calage dirigée vers le faisceau de tubes et inclinée radialement par rapport à l'axe de la pièce d'appui et une partie à plus faible diamètre destinée à venir en appui par son extrémité sur la surface intérieure de l'enveloppe externe de l'échangeur de chaleur.

For this reason :

• - The bundle envelope has openings in its wall each corresponding to a support piece, along the edge of which are fixed cylindrical sleeves projecting radially in the space between the bundle envelope and the external wall of the exchanger heat,
• each of the support pieces comprises two cylindrical parts having the same axis of radial direction, in the extension of one another, a large diameter part welded by its external lateral surface inside the corresponding sheath, and comprising a bearing surface of the wedging means directed towards the bundle of tubes and inclined radially with respect to the axis of the bearing piece and a part with a smaller diameter intended to come to bear by its end on the inner surface of the outer shell of the heat exchanger.

• La figure 1 est une vue en coupe par un plan vertical de symétrie de la partie centrale d'un générateur de vapeur renfermant le faisceau de tubes.
• La figure 2 est une vue en coupe suivant AA ou BB de la figure 1 montrant les dispositifs d'appui des enveloppes internes du générateur de vapeur.
• La figure 3 est une demi-vue en coupe du générateur de vapeur suivant CC de la figure 1.
• La figure 4 est une vue en coupe suivant DD de la figure 5, d'un dispositif d'appui tel que représenté sur la figure 2.
• La figure 5 est une vue en coupe suivant E de la figure 4.
• La figure 6 est une coupe suivant FF de la figure 4.
• Les figures 7, 8, 9 sont des vues similaires aux vues 4, 5 et 6 respectivement d'un dispositif d'appui suivant une variante de réalisation.

In order to clearly understand the invention, a non-limiting example will now be described, with reference to the attached figures, a steam generator of a pressurized water nuclear reactor of the preheating type comprising devices radial support of its internal envelopes.

• Figure 1 is a sectional view through a vertical plane of symmetry of the central part of a steam generator containing the bundle of tubes.
• Figure 2 is a sectional view along AA or BB of Figure 1 showing the support devices of the internal envelopes of the steam generator.
• FIG. 3 is a half-section view of the steam generator along CC of FIG. 1.
• FIG. 4 is a sectional view along DD of FIG. 5, of a support device as shown in FIG. 2.
• FIG. 5 is a sectional view along E of FIG. 4.
• FIG. 6 is a section along FF of FIG. 4.
• Figures 7, 8, 9 are views similar to views 4, 5 and 6 respectively of a support device according to an alternative embodiment.

In Figure 1, we see the central part of a steam generator of a pressurized water nuclear reactor. The steam generator comprises a tubular plate 1 in which the tubes of the bundle 2 are fixed, the ends of which open onto the underside of the plate 1. Only the axes of two end U-shaped tubes of the bundle are shown to show the arrangement of this beam.

The tubular plate 1 is secured at its lower part to a spherical bottom (not shown) constituting a chamber in two parts, one part of which receives water under pressure at high temperature coming from the nuclear reactor which penetrates into the tubes by one of their ends and the other of which receives the pressurized water which has circulated in the tubes of bundle 2 before its return to the nuclear reactor vessel.

The tubular plate 1 is integral at its upper part with the external casing 3 of the steam generator of cylindrical shape in its central part enclosing the bundle. At its upper part, the external cylindrical enclosure 3 is connected by means of a frustoconical part 3a to a steam dome not shown in which are placed the water-steam separators for drying the steam produced in the generator. steam.

The bundle 2 is entirely contained in a bundle envelope 5 also of cylindrical shape and disposed inside the outer envelope 3 and coaxial with it. This bundle envelope 5 provides a free space between its lower edge and the upper surface of the tube plate 1. The interior volume of the bundle envelope 5 is separated into two parts by a vertical partition 6 over a fraction of its height. The partition 6 disposed along the central space of the bundle tubes delimits in this bundle, up to a certain height, a hot branch which corresponds to the part of the tubes receiving pressurized water coming from the nuclear reactor and a branch cold which corresponds to the part of the tubes through which the pressurized water leaves the beam.

As can be seen in FIGS. 1, 2 and 3, it can be seen that the steam generator comprises an intermediate envelope 7 coaxial with the envelopes 3 and 5 and disposed between these envelopes on the part of their circumference corresponding substantially to the cold branch of the bundle . This cylindrical intermediate envelope 7 is connected at its upper part to a parallel frustoconical part 7a and opposite the frustoconical part 3a of the external envelope 3.

The steam generator shown in FIG. 1 is supplied with water to be vaporized by supply means opening into the space limited by the envelopes 5 and 7. The space between these envelopes closed at its ends as it is visible on the Figures 2 and 3 therefore allows a supply of water to be vaporized by the base of the cold branch of the bundle only. The lower part of the cold branch of the bundle up to the top of the partition 6 therefore allows this feed water to be preheated. On the other hand, the water recovered by the separators located in the vapor dome at the top of the generator returns to the base of the bundle both through the annular space between the outer casing 3 and the bundle casing 5 and through the annular space between the intermediate envelope 7 and the outer envelope 3 which are both in communication with the lower part of the hot branch of the bundle and through the annular space between the bundle envelope 5 and the intermediate envelope 7 which is in communication with the lower part of the cold branch of the bundle.

In this way the flow of water recovered by the separators at high temperature is only partially subjected to preheating.

All of the water coming into contact with the bundle inside the casing 5 heats up during its circulation from bottom to top in this casing 5 in contact with the bundle of tubes 2. This water vaporizes and the vapor is recovered at the top of the bundle envelope 5.

The bundle tubes are held laterally by spacer plates 8 arranged transversely inside the envelope 5. Tie rods 9 fixed to their lower part on the tubular plate 1 make it possible to maintain the axial spacing of the spacer plates 8.

The support devices 10 of the envelopes 5 and 7 on the external envelope 3 as well as the support devices 11 of the bundle envelope 5 on the external envelope 3 in its part where it is not doubled by the the intermediate envelope 7 are interposed between the edge of the spacer plates 8 and the interior surface of the external envelope 3.

In FIGS. 2 and 3 it can be seen that these support devices 10 and 11 are regularly distributed around the periphery of the spacer plates 8, the support axes in the radial direction of two successive devices making an angle of 26 °. There are thus around each of the spacer plates, seven support devices such as 10 and seven support devices such as 11. The support axes of radial direction of the devices 10 and 11 placed consecutively make an angle of 24 °.

The angular positions of the support devices are given in degrees in Figures 2 and 3 taking as axis 0-180 ° the axis of symmetry of the spacer plate.

The support devices placed around the two upper spacer plates and around the two lower half-spacer plates (Figure 2) differ from the support devices placed around the intermediate spacer plates (Figure 3) only by the width of the support area and by the number of wedging pieces between the spacer plate and the supporting piece.

In FIGS. 4, 5 and 6, there can be seen in more detail a support device such as 10 serving to hold in the radial direction the bundle casing 5 and the intermediate casing 7 relative to the external casing 3 of the steam generator. The envelope 5 is pierced with openings 14 which correspond to the intersection of the envelope 5 with a cylinder whose axis X'X has a radial direction and is located substantially at the level of the axis of the spacer plate 8. This axis X'X constitutes the support axis of the device 10. Along the openings 14, a cylindrical sheath with a circular base 15 having the axis X 'is fixed by welding to the wall of the bundle 5 X, slightly protruding in the annular space between the bundle envelope 5 and the outer envelope 3.

The intermediate envelope 7 has, like the envelope 5, an opening formed by the section of the envelope 7 by a cylinder with an axis XX '. Along this opening 16 of smaller diameter than the opening 14, is fixed by welding to the wall of the envelope 7, a sheath 17 sail lant in the space between the envelopes 7 and 5. An annular plate 18 welded to the free ends of the sleeves 15 and 17 allows to connect them.

The support piece is constituted by a single piece 20 of generally cylindrical shape with an axis XX '. This support piece 20 includes a large diameter part 20a whose outside diameter is very slightly less than the inside diameter of the sheath 15 and a small diameter part 20b whose outside diameter is very slightly less than the inside diameter of the sheath 17.

The face of the support piece 20 directed towards the inside of the steam generator, that is to say towards the bundle and the spacer plate 8 is machined so as to constitute a support surface 20c inclined with respect to the vertical of an angle close to 5 °. This bearing surface 20c is therefore inclined in the radial direction relative to the horizontal axis XX '. The angle of inclination of this support surface 20c corresponds to the machining angle of the shims 23 interposed between the spacer plate 8 and the support piece 20.

The end of the small-diameter part 20b of the part 20 directed towards the internal surface of the external envelope 3 is machined to constitute a spherical bearing surface between the part 20 and this internal surface.

For the installation of the support device 10, the support piece 20 is placed as shown in FIGS. 4 and 5 so that its spherical end surface is in contact with the internal surface of the envelope 3. A circular weld 24 is then produced between the external lateral surface of the part 20a of this part and the internal surface of the sheath 15. This operation is facilitated by the fact that a circular welding of parts of revolution is carried out.

We then place the set of shims 23 between the bearing surface 20c of the part 20 and the external lateral edge of the spacer plate 8 so as to achieve perfect retention of the envelope 5 in the radial direction XX 'by relation to the external envelope 3.

For the larger width support pieces shown in Figure 2, it is necessary to use six juxtaposed shims to achieve the setting of the support piece. For the parts shown in FIG. 3, of smaller width, it is necessary to use only three shims such as 23.

When the setting is made, the shims are fixed by welds on the bearing face 20c of the part 20.

The radial retention of the envelope 5 is thus achieved by recommencing these operations for each of the support devices 10 placed at the periphery of each of the spacer plates 8. The support devices 10 allow radial support at the same time of the bundle envelope 5 and of the intermediate envelope 7 fixed on the envelope 5 at the level of the support devices by the sleeves 17 and 15 and by the annular plate 18. It may also be noted that the space between the envelopes 5 and 7 remain perfectly isolated from the rest of the annular space between the bundle envelope 5 and the external envelope 3, by the fact that the parts of revolution are welded over their entire periphery, the support part being placed outside this isolated internal space.

The support devices 11 between the bundle envelope 5 and the external envelope 3, in the part of this envelope which is not surrounded by the intermediate envelope 7, consist of a support piece identical to the part 20 welded by its large diameter part to a sheath identical to the cylindrical sheath 15 fixed at an opening identical to the opening 14 in the wall of the envelope 5. A support device It comprises all of the elements shown in FIGS. 4, 5 and 6 with the exception of the sheath 17 and the annular plate 18.

In FIGS. 7, 8 and 9, an alternative embodiment of the support piece is seen, the latter no longer being in one piece but made up of two separate pieces 30a and 30b. The large diameter part 30a is welded inside a cylindrical sleeve with a circular base 25 itself welded to the casing 5 along an opening in this wall identical to the openings 14 of the embodiment shown in the figures 4 to 6.

The small diameter part 30b coming to bear on the internal surface of the external envelope 3 is itself fixed by welding on a cylindrical sleeve with circular base 27 fixed on the intermediate envelope 7 and coaxial with the sleeve 25. The parts 30a and 30b come to bear one on the other by flat faces, when shims 33 are interposed between the external lateral edge of the spacer plate 8 and the bearing surface 30c inclined relative to the vertical machined on the face of the part 30a directed inwards, that is to say towards the bundle of the steam generator.

For their installation, the parts 30a and 30b are connected by a circular weld to the sleeves 25 and 27 respectively. The support of the parts 30a and 30b on the spacer plate 8 and on the external wall 3 is then carried out by placing shims 33.

It can be seen that the main advantages of the heat exchanger according to the invention are to include support devices in the radial direction of its internal envelopes and spacer plates of the bundle on its rigid external envelope, which are extremely effective and do not introduce only a slight disturbance of the circulation of the fluids of the heat exchanger in the spaces between these envelopes. Indeed, the support piece comprises a part with a small section which can extend in the radial direction over the largest part of the space between the envelopes, the part with large diameter allowing the fixing of this support piece. on the beam envelope which can, conversely, be of reduced length. In addition, these support devices can be fixed only by circular welds which are easy to produce. The installation of these support devices on the envelopes is carried out by means of cylindrical sleeves and welded annular plates which make it possible to make absolutely watertight junctions between the envelopes, which makes it possible to maintain perfect insulation of the spaces between the envelopes one to another.

The support devices of the heat exchanger according to the invention are on the other hand of a shape such that they can be adapted to heat exchangers comprising any number of internal casings.

The invention is not limited to the embodiments which have been described; on the contrary, it includes all variants.

Thus the support pieces and the wedging pieces can be of a different shape from those which have been described. The number of support devices distributed around a spacer plate is not limited, each of these support devices producing only a small obstacle to the circulation of the fluid in the spaces between the envelope and the outer casing of the steam generator.

The shape and distribution of the support devices around the spacer plates over the height of the steam generator may be different from those which have been described.

Finally, the invention applies not only to the case of steam generators of pressurized water nuclear reactors but also to the case of other heat exchangers comprising a bundle of tubes disposed in a cylindrical bundle envelope itself placed at inside a rigid external cylindrical pressure casing.

Claims (6)

1.- Heat exchanger comprising a bundle of tubes (2) disposed in a cylindrical bundle envelope (5) held radially inside an external cylindrical envelope (3) and placed coaxially with it, a set of spacer plates (8) arranged transversely relative to the bundle (2) inside the envelope (5) and spaced along its length and several sets of support pieces (20, 30) integral with the envelope bundle (5) arranged radially at the level of the spacer plates (8) and each inserted between the outer edge of a spacer plate (8) and the inner surface of the outer casing (3), with interposition of wedging means (23, 33) between the spacer plate (8) and the support piece (20, 30),
characterized by the fact: - That the bundle envelope (5) has openings (14) in its wall each corresponding to a support piece (20, 30) along the edge of which are fixed cylindrical sleeves (15, 25) projecting radially in the space between the bundle casing (5) and the external wall (3) of the heat exchanger, - And that each of the support pieces (20, 30) comprises two cylindrical parts (20a, 20b - 30a, 30b) having the same radial direction axis, in the extension of one another, a large part diameter (20a, 30a) welded by its external lateral surface inside the corresponding sheath (15, 25) and comprising a bearing surface (20c, 30c) of the wedging means (23, 33) directed towards the beam of tubes (2) and inclined radially with respect to the axis XX 'of the support piece (20, 30) and a part (20b, 30b) of smaller diameter intended to come to bear by its end on the interior surface of the external casing (3) of the heat exchanger. 2. A heat exchanger according to claim 1, comprising on at least part of its periphery an intermediate envelope (7) disposed between the bundle envelope (5) and the external envelope (3) and coaxially with the latter. ,
characterized in that the sheath (15) integral with the bundle envelope (5) is connected to a sheath (17) coaxial with the sheath (15) fixed to the intermediate envelope (7) along an opening ( 16) thereof and projecting into the space between the bundle casing (5) and the intermediate casing (7), so as to pass the support piece (20) through the casings ( 5 and 7) while keeping tightly closed the space between the bundle envelope (5) and the intermediate envelope (7). 3.- heat exchanger according to any one of claims 1 and 2,
characterized by the fact that the support piece (20) is produced in the form of a single piece. 4. Heat exchanger according to claim 1, comprising an intermediate envelope (7) between the bundle envelope (5) and the external envelope (3) coaxial with these envelopes (3) and (5),
characterized by the fact that the support piece (30) has two independent parts (30a) and (30b), one of which has a large diameter (30a) fixed in the sheath (25) integral with the bundle envelope (5 ) and a small diameter part (30b) fixed inside a sheath (27) coaxial with the sheath (25) and integral with the intermediate envelope (7), these two independent parts (30a) and (30b) of the support piece coming into contact with each other by a flat face perpendicular to their radial support axis, when the part (30b) is pressed against the outer casing (3) of the heat exchanger and that at least one shim (33) coming to bear on the inner face of the part (30a) with a large diameter of the support piece (30) is interposed between the external lateral surface of the spacer plate (8) corresponding and the support piece (30) in two parts. 5- heat exchanger according to any one of claims 1 to 4,
characterized in that it comprises a set of support devices (10, 11) also spaced angularly around each of its spacer plates (8). 6. Heat exchanger according to claim 5,
characterized in that the support devices constituting the different assemblies each associated with a spacer plate (8) have widths in the circumferential direction of the spacer plates (8) varying according to the position of the spacer plate at which they are associated in the heat exchanger, these support devices comprising a number of wedging pieces (23, 33) also variable.

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