EP0056744B1 - Heat exchangers with bundles of straight or undulating tubes, especially on systems of supporting tubes, and method of realising such systems - Google Patents

Description

The present invention relates to a heat exchanger, and it relates to improvements in heat exchangers, in particular applicable to a steam generator, with straight tubes, preferably corrugated tubes, arranged in vertical sheets, parallel and maintained at certain levels. axial, by concentric support systems, each of which is constituted by a circular strip with alternating trapezoidal cells, welded to a support strip and closed, after fitting the tubes, by a closure strip to which the support strip is welded of the following support system in the radial direction of the grille. These support systems have been described in FR-A-2 420 735.

In the preferential case of the use of corrugated tubes having corrugations situated on the same side of the axis passing through the straight ends of the tubes held in the corresponding openings provided in the end plates of the grille, at the base of the two domes generally used in this kind of device, the tubes are arranged so that the planes containing their undulations are substantially tangent to the circles of the associated tubular bundles provided between the shell and a central tube of the heat exchanger.

Because of the temperature differences of the fluids present in the device, the corrugated tubes contract or expand, more particularly at the level of the corrugations whose arrows vary, which results in a tangential force which is exerted on the various support systems in the cells of which the corrugated parts of the tubes are trapped. And, in the same sector of concentric support systems located at the same level, the peripheral displacement of the different portions of the support systems of this sector increases from the center towards the grille.

The support systems located at the same level being welded to each other, harmful voltages can arise under certain thermal operating conditions and lead, at the very least, to a deterioration of said support systems.

Also, to remedy this drawback, it is provided, according to the invention, that at least some of the support systems, located at the same level, are independent of neighboring support systems and form groups of support systems, _and ue _bras radial are provided for the apptn said independent support systems, in the space between the grille and the central tube.

According to a preferred embodiment, ensuring total flexibility of all the support systems, all the mobile support systems of the same level are independent of each other, and radial arms are provided on both sides. on the other of all support systems of the same level.

Thanks to this arrangement, the support systems independent of one another and belonging to the same level, are held in place between the shell and the central tube of the heat exchanger which can therefore also be mounted and transported in horizontal position.

Advantageously, each radial arm is constituted by two flat bars welded on edge, with a certain spacing between them.

According to another embodiment, there are provided, at least at certain levels, two concentric rings, one of which is situated on the side of the internal face of the grille and the other on the side of the external face of the central tube, the first can be welded to the grille and the second to said central tube, which improves the retention of support systems.

In the case where it is desired to provide the apparatus, at least at certain levels, with a system of deflectors, in order to subject the circulation of the fluid in the grille to a certain trajectory, with a view to disciplining the flow thereof for to obtain a better heat transmission coefficient, it is provided, according to the invention, to combine, with at least certain circular bands with trapezoidal cells, circular bands in the form of combs, extending over arcs of appropriate length , and whose teeth which extend radially towards the center, pass respectively between two neighboring tubes so as to close as much as possible the intervals which may exist between the latter, said combs being laid flat on the alveolar strip and being welded to the neighboring support strip.

Advantageously, the combs arranged at a given level are angularly offset relative to the combs arranged at the next level and at the previous level, the angular offset being such that the projection on a horizontal plane of two combs located at two successive levels is a ring s' extending over 360 °. Preferably, the comb of each level extends in an arc of 300 °, but it can also extend over 180 °, or less. It is understood that combs extending over such arcs are formed by pieces of coextensive combs and welded together.

As a general rule, a heat exchanger, and more particularly a steam generator, is a large device, and for convenience, the radiator grille is placed horizontally on electric turners to allow the placement of the bundles and support by sectors of 60 ° or possibly 120 °.

In order to allow this to be put in place under good conditions, the invention proposes a method which consists in that the radial arms welded to the inner face of the grille or to the ring which is adjacent to it, are supported using of stiffening flat bars welded at their ends to the bottom plates in which the ends of the tubes are held and provided with openings for the passage of the free ends of the radial arms; after installation of the tube bundle and the support systems, said stiffening flat bars are dismantled and the central tube is put in place and is welded to said radial arms by openings which it comprises, said central tube possibly being able to be produced in the calender, by assembling and welding individual wall elements.

But it is also conceivable, and generally more advantageous, to proceed with the installation of the tubular bundles, the support systems and the radial arms by operating from the exterior surface of the central tube, suitable supports being provided, if necessary , to temporarily support the radial arms and to ensure their radial position, supports which are then removed, to allow the establishment of the grille.

In the particular case of corrugated tubes having straight portions between the successive corrugations, it has been indicated that due to the dilations of the tubes at the level of the corrugations, the deflection of each of these can increase under certain thermal conditions and to hold In view of these conditions, it has been proposed that in these levels, the concentric support systems are independent of each other and rest on a radial arm or are located between pairs of pairs of radial arms located between the grille and the central tube. In what follows, these levels will be designated by “mobility levels” or more briefly by “mobile level”.

On the other hand, at the level of the straight portions of the tubes, situated between two corrugations, there is no expansion which can lead to mobility in the peripheral direction of the concentric support systems provided at this level, which will be designated by "fixed levels" . Also, it will be possible at these fixed levels to provide welds between the radial arms and at least some of the support systems; these welds can be made between the radial arm (s) on the one hand, and one or other of the constituent bands of the support systems on the other hand.

• La fig. 1 est une vue schématique d'un tube ondulé du type destiné à être mis en oeuvre dans le cadre de l'invention.
• La fig. 2 est une vue schématique et partielle d'un faisceau de tubes selon la fig. 1, montrant la déformation que peut subir un tube au niveau mobile.
• La fig. 3 représente schématiquement une coupe radiale au niveau d'un système de supportage de tubes.
• Les fig. 3A et 3B montrent respectivement en perspective l'agencement de deux portions de systèmes de supportage à un niveau mobile et à niveau fixe.
• La fig. 3C est une coupe de la fig. 3 selon la ligne III C-III C.
• La fig. 3D est une vue schématique partielle avec arrangement des déflecteurs constitués par des peignes.
• La fig. 4 est une vue axiale schématique d'un appareil selon l'invention, en position horizontale.
• La fig. 5 est une coupe axiale de la fig. 4 selon la ligne V-V montrant deux des vireurs électriques sur lesquels repose l'appareil de la fig. 4.
• La fig. 6 montre schématiquement la disposition des déflecteurs réalisés à l'aide de peignes.
• La fig. 7 montre une épure permettant de déterminer la répartition des tubes dans des secteurs de 60°.
• La fig. 8 est une coupe schématique et partielle montrant la disposition d'un faisceau tubulaire réparti par secteurs de 120° entre la calandre et le tube central.

By way of example, various embodiments of the subject of the invention have been described below, and shown in the accompanying drawing.

• Fig. 1 is a schematic view of a corrugated tube of the type intended to be used in the context of the invention.
• Fig. 2 is a schematic and partial view of a bundle of tubes according to FIG. 1, showing the deformation that a tube can undergo at the mobile level.
• Fig. 3 schematically represents a radial section at the level of a tube support system.
• Figs. 3A and 3B respectively show in perspective the arrangement of two portions of support systems at a mobile level and at a fixed level.
• Fig. 3C is a section of FIG. 3 along line III C-III C.
• Fig. 3D is a partial schematic view with arrangement of the deflectors constituted by combs.
• Fig. 4 is a schematic axial view of an apparatus according to the invention, in a horizontal position.
• Fig. 5 is an axial section of FIG. 4 along the line VV showing two of the electric turners on which the apparatus of FIG. 4.
• Fig. 6 schematically shows the arrangement of the deflectors produced using combs.
• Fig. 7 shows a diagram for determining the distribution of the tubes in sectors of 60 °.
• Fig. 8 is a schematic and partial section showing the arrangement of a tubular bundle distributed by sectors of 120 ° between the grille and the central tube.

In fig. 1, there is shown schematically the general appearance of a corrugated tube, suitable for implementing the invention. This tube is mounted by its two straight ends 1 and 2 in the plates 3 and 4 usually provided at the base of the upper and lower domes that comprise a steam generator or more generally a heat exchanger. Between these straight ends 1 and 2, the tube has undulations of which only two have been shown at 5 and 6. These undulations 5 and 6 are situated on the same side of a straight portion 7 which connects two successive undulations and which is aligned with the ends 1 and 2, and they are connected to it by curved portions 8 and 9, while they are connected respectively to the straight ends 1 and 2 by the curved portions 9 and 10.

As is apparent from FIG. 2, the corrugated tubes are arranged so that the plane containing the axis of the corrugations and that of the straight portions lies substantially in the plane tangential to the circle of the circumferential alignment of the tubes of the relevant circular row of the bundle. In this figure, the reference 5 designates the corresponding corrugation of FIG. 1, and there is indicated the arrow f of the ripple at rest. During a deformation, under the effect of temperature, the arrow f increases and takes the value f ', and it goes from 10 to 10'.

However, between the plates 3 and 4, it has been proposed to provide, in particular at the level (movable level) of the tops of the corrugations such as those designated by 5, concentric support systems, each of which is constituted by a support strip with which is welded a honeycomb strip with alternating successive cells in which are housed said undulations and to close the cells by a closure band to which is welded the following support band and thus step by step between the grille and a central tube disposed in this last.

Therefore, in one and the same mobi level the, the concentric support systems form between the calender and the central tube a whole in one piece and the portions of the concentric support systems and subtending a same angle in the center, undergo, for the same temperature, peripheral dilations which grow from the center to the grille.

To remedy this drawback, the invention proposes the arrangement of FIG. 3.

Below the level of the top of a corrugation such as 5 of FIG. 1, we weld in 12 and 13, a flat iron 14 mounted on edge whose other end 15 will be temporarily supported as will be explained later in connection with FIG. 4, to finally be welded at 16 to the central tube 17.

On this radial arm, a ring 19 is placed near the inner face 18 of the calender 11 in a vertical position. Against the inner face of the ring is placed an annular support band 20 and to this is welded a honeycomb band 21 as described in FR-A-2 420 735, and in the cells of which the tubes are placed such as that designated by 5, and held in place by a closure strip 22 welded to the cellular strip 21.

Inside this support system 20, 21, 22 for the tubes such as 5, there are the support systems 20 ', 21', 22 'for the tubes 5', and step by step the support system 20 _n , 21 _n , for tubes 5 _n whose cells are closed by the ring 22 _n which is the equivalent of the closure strips 22, 22 ', the ring 22 _n being welded to the wall of the central tube 17 .

Concentric support systems have thus been produced, independent of each other, so that the circumferential expansion of one of the systems is independent of the neighboring system or systems.

Preferably, a radial arm 14 _′ similar to the radial arm 14 is placed on the ply of the support systems thus produced, and advantageously each radial arm 14 and 14 ′ will be constituted by two flat bars such as those designated by 14 and 14 ′ and which will be arranged on either side of the radial row of tubes 5 ,, 5 '... 5n.

Fig. 3A shows in perspective two pieces of two successive support systems between the radial arms and arranged at a movable level. The external support system consists of the support strip 20 to which is welded, by welding points such as that indicated by S, the cellular strip 21 against which the closure strip 22 is freely applied. The internal support system is constituted in the same way by the support strip 20 ', by the honeycomb strip 21' and by the closure strip 22 _' , with the same weld point S, the assembly of the two support systems being disposed freely between the radial arms 14 and 14 '. And, according to the invention, no welding is provided between the two support systems. If desired, a welding point can be provided between 21 and 22 and between 21 'and 22'.

Fig. 3B shows an arrangement identical to that of FIG. 3A, but for a "fixed level", with this double difference that only the radial arm 14 and a weld S "are provided there between the arm 14 and the closure strip 22 ', it being understood that such weld S "may be provided between the arm 14 and the closure strip of each support system such as that designated by 22,22 '.

To discipline the flow of the fluid in the heat exchanger, with a view to obtaining a better coefficient of surface heat transmission, provision is made to have at least some of the support systems for strips 29 in the form of combs which are visible in fig. 3C, which is a section of FIG. 3 along line III C-III C.

As is apparent from FIGS. 3 and 3C, the combs 29, 29 '... 29n are associated respectively with the rows of the tubes 5, 5 _' ... 5n and are laid flat on the alveolar strips 21, 21 '... 21 n and held in place place by welding to the support strips 20, 20 _' ... 20n in a position such that the teeth of each comb 29, 29' ... 29n pass between the tubes held by the respective cellular strips 21, 2T ... 21 not.

Each of the combs 29, 29 _' ... 29n is in fact constituted by partial and coextensive combs, welded together by weld lines such as those indicated in fig. 3C par 29 ₁ , 29 ₂ ... 29n to extend over an arc whose value depends on the trajectory that one wishes to print on said fluid, and all of these combs constitute deflectors whose arrangement of a level of support systems to another will be explained using fig. 3D.

Between the calender 11 and the central tube, combs 29a, 29a _′ , 29a _’ are provided at the various mobile and fixed levels, represented schematically in the form of rings extending at an angle a, each of these rings forming deflectors by means of combs as shown in Fig. 3C In Fig. 3D, the angle a is equal to 300 ° and the path impressed on the fluid from one level to another is tilted as much as possible on the axis of the device so as to give a maximum heat transfer coefficient at the level of the tubes not shown in this figure. But the angle a can also be equal to 240 °, but in all cases, the arrangement of the rings or deflectors is symmetrical between two successive stages, and in the case of this arrangement, the fluid coming from a lower level in direction D is distributed at the next level in directions D and D _z .

The arrangement of the radial arms 14 and 14 _' of FIG. 3, on either side of all of the support systems provided at a given level so that a support system is independent of neighboring support systems, is particularly advantageous for mounting the tubular bundles and the support in the radiator grille placed horizontally, in particular on electric tackers as shown in figs. 4 and 5 in which only two tackers 23 and 24 have been shown tees, the presence of these turners allowing the mounting of the tube bundle in sectors of 60 °, for example delimited by the pairs of radial arms 14-14,14 _' -14' ... 14n-14n.

In this type of mounting, the inner ends 15, 15 ′ of the radial arms such as 14, 14 ′ are mounted in openings made in temporary flat irons 25, 26 fixed to the plates 3 and 4 and removed for the placement of the inner cylinder 17 (fig. 3). After setting up the bundle of tubes and support systems, the flat bars 25, 26 are removed and the central tube 27 is put in place as shown in FIG. 6.

This is an axial and schematic section of the device according to the invention and shows the presence of deflectors 29, 29 ₁ ... 29 _n produced by combs 29 to 29m placed flat as the honeycomb bands 21 to 21 n so that the teeth pass between the tubes in a circular row, as described in connection with figs. 3 and 3A.

Each deflector 29, 29, ... 29 _n can in this case extend over an arc of 306 ° and form a ring whose radial thickness is less than the radial distance between the grille and the central tube, with the particularity that successive rings are arranged alternately on the side of the radiator grille and on the side of the central tube to impart an undulating trajectory to the ascending fluid. It will be noted that the radial thicknesses of the successive rings are different from each other, while the radial thicknesses of the rings which have the same arrangement are equal to each other.

It emerges from the above that the mounting of the circular support systems and their lining in sectors of 60 °, 120 ° or 180 °, and that of the corresponding sections of the support strip to which the cellular strip is welded, can be prepared in advance, outside the grille, depending on the arrangement to be adopted for the distribution of the tube, which leads to a mass production of the support system.

Fig. 7 shows the sketch used to determine this distribution in the case where we adopt the assembly by secterus of 60 °.

We start by drawing a regular hexagon 29 with the center O as the origin of two axes of coordinates X, Y. On the sides 30, 31 we draw the perpendicular bisectors 30, 31. In the sector 30-O-31, we mark l location of a first tube 32 at the top of the hexagon, after drawing concentric circles with radial pitch p, the locations of the other tubes whose number increases by one unit per radial pitch are marked, between the perpendicular bisectors 30, 31 , with a symmetry with respect to the axis OY which is the bisector of the angle 30, 0, 31. We proceed in the same way to establish the sketch for the other sectors of 60 °, noting that the radial arms will be arranged parallel to the perpendicular bisectors 30, 31.

Once the tracing has been made, the diameter of the lower tube 37, traced in FIG. 8, in which there is no need to have corrugated tubes.

Claims (10)

1. An improvement in heat exchangers, applicable in particular to a vapour generator, of the type comprising straight tubes, preferably undulating tubes, which are disposed in vertical arrays, parallel and held at certain axial levels by concentric supporting systems, each of which is formed by circular band which has alternate trapezoidal openings therein and which is welded to a supporting band and which, after the tubes have been set in position, is closed off by a closure band to which is welded the supporting band of the supporting system, in the radial direction of the casing, characterised in that at least some of the supporting systems (20, 21 ... 20n, 21 n) which are disposed at the same level are independent of the supporting systems that are adjacent thereto in the radial direction, and form groups of supporting systems, and that radial arms (14, 14', 14n) are provided for supporting said independent supporting systems in the space between the casing and the central tube.

2. The improvement according to claim 1 characterised in that all the supporting systems at the same axial level are independent of each other and that radial arms (14, 14', 14n) are disposed above and below the assembly of supporting systems at the same level.

3. The improvement according to either one of claims 1 and 2 characterised in that the radial arms (14, 14_', 14n) extend radially between the casing (11) of the exchanger and a central tube (17), between two radial rows of tubes.

4. The improvement according to claim 3 characterised in that each radial arm is formed by two flat iron bars (14, 14') which are welded on edge with a certain spacing therebetween.

5. The improvement according to any one of claims 2 to 4 characterised in that two concentric rings are provided at least at certain levels, one of the rings being disposed on the side of the inward surface (19) of the casing and the other (22n) being disposed on the side of the outward surface of the central tube (17).

6. The improvement according to any one of claims 1 to 5 characterised in that associated with each supporting system is a comb-like member (29) which is disposed flat on the band forming said openings, and welded to the associated supporting band (20) in such a way that the teeth pass between the tubes (5 ... 5n) and provide maximum blocking of the passages between openings and tubes, the assembly forming a deflector.

7. The improvement according to any one of claims 1 to 6 characterised in that, at the same level, the combs (29) are disposed along circular arcs subtending angles at the centre of 300°, and the combs at successive levels are angularly displaced relative to each other in order to impart to the fluid flowing outside the tubes, an inclined flow path substantially perpendicular to the tubes.

8. The improvement according to any one of claims 1 to 6 characterised in that the deflectors are formed by rings extending over 360° and being of a radial thickness that is less than the radial distance between the casing and the central tube and that the successive rings are disposed successively on the casing side and on the central tube side.

9. A process for the production of a heat exchanger, applicable to a vapour generator, comprising the improvement according to any one of claims 1 to 7, of the type disposed in a casing disposed horizontally on electrical rotating means (23, 24), characterised in that the radial arms (14, ... 14n) which are welded to the inside surface of the casing (18) are supported by means of flat stiffening iron bar members (25, 26) which are welded by their ends to the end plates (3, 4) in which the ends of the tubes are held, and provided with openings for receiving the free ends of the radial arms (14 ... 14n), and that, after the tube nest and the supporting systems, optionally with the combs, have been set in position, the flat stiffening bar members are removed and the central tube (27) is set in position, and comprises openings for receiving the radial arms (14 ... 14n), said central tube possibly being produced by the assembly and welding of individual wall elements.

10. A process for the production of a heat exchanger applicable to a vapour generator, comprising the improvement according to any one of claims 1 to 7, characterised in that assembly of the supporting systems and the tube nests is effected from the central tube (27) in an outward direction, the casing being fitted last, possibly in the form of successive sections which are then welded together.

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