FR2581443A1 - HEAT EXCHANGER HAVING A STRAIGHT TUBE BEAM OF WHICH THE TRANSVERSE HOLD IS PROVIDED BY SPACED GRIDS AND ITS APPLICATIONS - Google Patents

Abstract

THE EXCHANGER INCLUDES A BEAM 2 OF TUBES 3, AN ENVELOPE 1 AND A SET OF SPACER GRILLS 18. THE SPACER GRILLS HAVE A FIRST SET OF OPENINGS FOR THE PASSAGE OF TUBES 3 OF BEAM 2 HELD BY THE GRIDS AND A SECOND SET OF OPENINGS FOR THE PASSAGE OF THE EXCHANGE FLUID FLOWING OUTSIDE THE TUBES 3. THE OPENINGS ARE ARRANGED SUCH AS THE THICKNESS OF THE WALLS OF THE METAL GRID BETWEEN THE OPENINGS IS SIGNIFICANTLY CONSTANT. THE INVENTION APPLIES, IN PARTICULAR, TO STEAM GENERATORS OF QUICK NEUTRON NUCLEAR REACTORS COOLED BY LIQUID SODIUM.

Description

2 5 8 1 4 4 3

  The invention relates to a heat exchanger with a bundle of straight tubes with circular pitch, the

  transverse support is provided by grids between-

  toises. Tu-beam heat exchangers

  bes rights are very often used as gener-

  steam generators in nuclear reactors in part

  especially those cooled by liquid metal. The fluid

  reactor cooling allows heating

  ment and the spraying of feed water which can be circulated inside the tubes or, on the contrary, in contact with the external surface of these tubes. The reactor coolant circulates either outside the tubes, inside the envelope of the steam generator containing the

  bundle, either inside the tubes, respectively-

is lying.

  In the case of large installations,

  the size of the steam generators can be

  considerable and in particular, in the case of genera-

  steam generator with straight tubes, the length of the tubes and of the envelope containing the bundle as well as the number of tubes can be very large. We must therefore use spacer grids fixed inside the envelope of the steam generator, spaced from each other along the length of the tubes, to ensure transverse support and bracing of the bundle tubes. Such spacer grids must allow not only the maintenance of the tubes

  against the stresses of circulating exchange fluids

  lant in contact with them at high speed but still the passage of the exchange fluid circulating outside

  tubes in the longitudinal direction of the genera-

  steam generator. The pressure drop in this coolant

  change must be as small as possible and it is therefore necessary to provide a large passage section for this fluid relative to the straight section

total steam generator.

  In an attempt to reconcile these imperatives, very often spacer grids made by assembling strips are used. rods or profiles of various shapes. Such devices are complex, difficult to set up and making them from many different elements does not allow

  obtain very good reliability.

  It has therefore been proposed to use flat metal plates pierced with openings, as spacer grids. The openings passing through the plate are arranged in a regular network corresponding to the arrangement of the tubes in the cross section planes of the steam generator. To allow both the maintenance of the tubes and the passage of the exchange fluid outside of these tubes, it has been proposed

  in French patent 2,150,826, to realize the or-

  grooves in the spacer plates in tri- form

  lobed, so as to provide three bearing surfaces of the tube projecting towards the inside of the opening and three sections for passage of the fluid outside the tube, between the projecting parts. This provision

  could be used for bundles of cons-

  constituting networks i not square, triangular or hexa-

  gonal, in the cross sections of the generator of va-

  fear. However, this provision is not used

  sand in the case of other types of network, for example-

  ple in the case of networks i not circular, that is i-

  say constituted by circular, coaxial and equidising rows of tubes, inside which the

  tubes are spaced a constant arc length.

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  In this case, in fact, it is necessary to do

  link the shape of the openings from one row to another to keep the thickness of the walls made in the metal of the plate substantially constant, between two adjacent openings. It is indeed necessary that these walls separating the openings have a substantially constant thickness, so that the spacer grid has good resistance to thermal shock. It

  therefore results from design and user difficulties

  who cannot be resolved, or who cannot

  be that by accepting construction costs pro-

  hibitives, the number of tube passages to be provided in each of the spacer grids being very high, for example of the order of several thousand. On the other hand, if we try to solve the problem by keeping openings whose outside contour is regular, we must, to maintain a constant thickness of the walls between the openings, provide for fluid passage sections around the non-uniform tubes, this

  which introduces prejudicial thermal imbalances

  for proper operation of the steam generator.

  The object of the invention is therefore to propose a heat exchanger with a bundle of straight tubes and

  with circular pitch whose transverse support is sufficient

  secured by spacer grids, comprising an envelope

  loppe containing the tubes inside which circulate

  a first exchange fluid, a second exchange fluid circulating in the envelope, outside the tubes, and a set of spacer grids for transversely holding the tubes, fixed inside the envelope, spaced of each other along the length of the tubes and constituted by plates

  metallic planes crossed by a set of openers

  tures arranged in a regular network with circular steps

  cular corresponding to the arrangement of the tubes in the cross section planes of the bundle, this heat exchanger operating under very good thermal conditions and using spacer grids whose design and machining are relatively simple

  and satisfactory thermal shock resistance.

  For this purpose, each of the spacer grids further comprises a second set of openings for the passage of the second exchange fluid. interposed between the openings of the first set, so that

  the thickness of the partition walls between the openings

  neighboring tures made in the metal of the plate

is substantially constant.

  In a preferred embodiment, the openings constituting the first assembly have a

  circular shape and a very slightly larger diameter

  laughing at the outside diameter of the tubes.

  In order to make it clear -the invention, we will now describe, with reference to the attached figures, several embodiments of a heat exchanger according to the invention and its spacer plates, this heat exchanger being used as a steam generator in a reactor

fast neutron nuclear.

  Fig. 1 is a sectional view through a vertical plane of symmetry, of the steam generator with straight tubes. Fig. 2 is a fragmentary top view

  a steam generator spacer grid shown

felt in FIG. 1.

  Fig. 3 is a fragmentary top view

  a steam generator spacer grid,

before a first variant.

  Fig. 4 is a fragmentary top view

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  of the peripheral part of a spacer grid

before a second variant.

  Fig. 5 is a sectional view along AA of FIG. 4 showing a support means for the spacer grid.

  In Fig. 1, we see a generator of va-

  fear comprising an external envelope 1 enclosing a bundle of straight tubes 2. Each of the tubes 3 of the bundle is fixed at one of its ends in a lower tubular plate 4 and at its other end in an upper tubular plate 5. The envelope 1 comprises a central cylindrical body constituting the envelope of the bundle 2 and two end parts

  6 and 7 with larger diameter on which are

  xed the tubular plates 4 and 5, respectively.

  The lower tube plate 4 is made of

  munication by its external face with a water collector 10 receiving the supply water of the steam generator by a pipe 11. The collector 10 makes it possible to distribute the supply water in the tubes 3 of the bundle 2, this water of food constituting the

  first steam generator exchange fluid.

  The upper part 7 of the envelope 1 re-

  receives, via an inlet tube 12, liquid sodium

  hot, which then flows up and down in the envelope

  beam beam 1, in contact with the outer surface

  of the tubes 3 and which constitutes the second exchange fluid. The feed water circulating in the tubes 3 is thus heated and then vaporized, the vapor formed being recovered by a vapor collector 14 then evacuated by a tube 15. The cooled liquid sodium, after its circulation in contact with the tubes of the bundle, spring from the casing 1 by a tube 13

  provided in part 6 of this envelope.

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  The tubes 3 of the bundle 2 are held and braced by spacer grids 18 fixed i

  inside the central body of the envelope. These grills

  the spacers 18 allow both the holding of the tubes in the transverse directions and the passage

  sodium wise, outside the tubes, in the di-

  vertical section, following arrows 19.

  In Fig. 2, we see a part of a spacer grid 18 comprising a first set

  openings 20 of circular shape and a second

  appears to be openings 21 of asymmetrical three-lobed form

  than. The openings 20 have diameters very slightly greater than the diameters of the tubes 3 and are arranged in successive rows 20a, b, 20c circular, equidistant and coaxial. In each of the rows, the successive openings 20 have

  identical spacings in arc distance. The tu-

  bes 3 of the bundle are engaged in the openings 20 and perfectly maintained inside these, the clearance between the tube 3 and the opening 20 being very small. In the case of a steam generator of a fast neutron nuclear reactor whose spacer grids 18 have a diameter of approximately 1.2 m and a spacing of 0.6 m in the longitudinal direction of the tubes of bundle 2 which have a diameter of 15. 10 m, the pitch of the circular network of tubes is

  35.10-3 m and the clearance between the tubes 3 and the openings

  res 20, from 0.2 to 0.5.10- 3 m, depending on tolerances.

  The openings 21 are interposed between the openings 20 along the successive rows of tubes

  and between these rows so that the walls 23 mena-

  between two neighboring openings, that these two or

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  vertures either two openings 21 or an opening 20 and an opening 21, have a substantially constant thickness. These walls are formed in the metal of the plate intended to constitute the spacer grid 18, during the machining of the openings 20 and 21. This machining is carried out by drilling and by broaching of

the metal plate.

  To obtain a practically constant thickness of the walls 23, the openings 21 have

  a three-lobed outline comprising three circular portions

  res 24 and three extensions 25 one of which has a di-

  radial direction and the other two of the circular directions

  conferences compared to the spacer grid 18

  and to the rows of tubes 20. The openings 21 asso-

  ciées to the same row of tubes 20 ipar example the

  appears to be openings 21a associated with row 20a)

  have identical shapes and dimensions; these for-

  my and dimensions can possibly be modified

  from row to row, or from one group of rows to another group of rows, going from the inside to the outside of the spacer grid. So we have the

  possibility, when machining the grid in-

  tretoise. to perform repetitive operations ran-

  row by row. In addition, the openings 21 each have

  ne, for axis of symmetry, a radius of the grid between

height 18.

  The plates used to make the spacer grids can be made of ferritic steel containing 2.25 Z of chromium and 1 Z of molybdenum or of steel with 5 Z or 9 Z of chromium and 1 Z of molybdenum

  or in austenitic steel of grade 316L.

  After machining the openings 20 allowing the passage of the tubes, it is possible to produce on the surface

  of these openings, in the thickness of the grid in

  tretoise, that is to say on the surface of the walls 23, a surface treatment such as a chrome plating or an aluminization. Such a surface treatment makes it possible to limit the wear of the tubes and the attack of these tubes by fretting corrosion, during operation.

steam generator.

  When the steam generator is running

  liquid sodium circulates according to the di-

  vertical section, outside the tubes, in the

  veloppe 1 and crosses the spacer plates through the openings 21 almost exclusively, the clearance between the

  tubes 3 and the openings 20 being very small. The re-

  partition of sodium flux in straight sections

  of the steam generator is thus perfectly homogeneous

  ne, which provides excellent thermal conditions

Operating.

  In addition, the small and substantially constant thickness of the walls 23 surrounding the openings 20 and 21 prevents the appearance of thermal gradients at the level of the spacer grids and reduces the risks.

  thermal shock damage.

  In Fig. 3, we see a variant of

  reading of the openings 20 and 21, the openings 20

  being made in three-lobed form and comprising each

  cune three cylindrical bearing surfaces 26 for the

  transverse holding of the corresponding tube 3. These or-

  trilobed vertices 20 have a single axis of symmetry

  sorts which is in the radial direction with respect to the plate 18. One of the extensions of the opening 20

  is of radial direction and the other two of direc-

  substantially circumferential, relative to the

  corresponding row of openings 20.

  The openings 21 are oblong and

  also have as direction of symmetry a direction ra-

2 5 8 1 4 4 3

  dial of the plate 18. These openings 21 are interca-

  strips between the three-lobed extensions of the openings

  to obtain a significant wall thickness 23-

  constant. This condition can be obtained with openings 20 which are all identical to each other and openings 21 constituting the second set of openings, varying from one row to another. In the embodiment shown in

  Fig. 3, the liquid sodium in the generator in operation

  both requires three-way extensions

  lobed openings 20 and through openings 21. In this case also, the distribution of the sodium flux is

  extremely homogeneous in the cross sections of the giant

  steam generator. The machining of the spacer grid shown in FIG. 3 can be made by drilling

and pinout.

  In Fig. 4. we see a second mode of re-

  alisation of a spacer grid 18 fixed to the interior

  of the envelope 1. The openings 20 of the first assembly allowing the passage of the tubes 3 all have a circular shape and a diameter very slightly

  greater than the outside diameter of the tubes 3. The or-

  vertices 21 have the shape of parallelograms with rounded or flattened angles. The shape and dimensions of these

  parallelograms are slightly changed by one ran-

  g & e i another and very strongly modified in the neighboring

  swims from the periphery of the spacer grid, where the

  openings 30 replacing the corresponding openings 21-

  lay approximately half the size of the openings 21. Likewise, the shape and distribution

  openings 21 are profoundly modified as

  sinage of the axis XX of the spacer grid 18 along which is placed a set of supports 32 of the

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  spacer grid 18 which will be described later in the text. The shape and distribution of the openings 20 and 21 make it possible to obtain a thickness of the walls 23 for the separation of the openings which is practically constant. This wall thickness corresponds to the thickness of

  metal between two neighboring openings, in a direction

  tion contained in the plane of the spacer grid 18.

  A spacer grid as shown in FIG. 4 can be obtained by molding or by

  electrochemical machining of a steel plate.

  In addition to the openings 20 and 21, the spacer grid 18 shown in FIG. 4 has notches such as 33 in the direction X'X. A notch 33 is formed on the spacer grid 18. i

  each of its ends, following the direction radia-

  the X'X and also at each of its ends,

  vant the radial direction perpendicular i X'X. As

  it is visible in Figs. 4 and 5. each of the

  support elements 32 of the plate 18 comprises an element

  support frame 34 welded at 35 on the internal surface

  envelope 1, through its

  lower part and engaged, by its upper part.

  inside the corresponding notch 33 of the

  grid 18. The upper part of the support element

  port 34 is notched so as to provide support edges for the spacer grid 18 engaged with play

  in element 34 by its part 33. The grid between

  height 18 is thus maintained in the directions ver-

  tical with respect to envelope 1 but remains free

  to expand in the radial direction.

  The main advantages of the heat exchanger according to the invention are therefore a very good

  thermal operation. grice i a re-

  1 1 homogeneous partition of the exchange fluid circulating outside the tubes, a precise arrangement and a

  efficient hold of the beam tubes, very good

  resistance to thermal shock of the grids between

  rods and easy design and machining of

these spacer grids.

  The invention is not limited to the modes of

  which have been described.

  This is how we can imagine openings.

  res of different forms from those which have been described

  tes, for example openings of polygonal shape to

  rounded corners to form the second set.

  The openings in the first set can be used

  sées only for the maintenance of the tubes or both for the maintenance of the tubes and the passage of the second exchange fluid. In all cases, complementary shapes of the openings belonging to one and the other of the two assemblies will be sought in order to obtain a wall thickness separating these most openings.

constant possible.

  One can also imagine a means of fixing

  tion of the spacer grids in the shell of the

  heat changer of a different type from that which has

been described.

  Finally, the heat exchanger according to the

  vention can be used not only as a general

  steam generator in a nuclear reactor but also for any heat exchange between two fluids in

  industries such as the chemical industry.

Claims (11)

  1.- Tube bundle heat exchanger   straight and with circular steps, the cross-maintenance of which   sal is provided by spacer grids, comprising a casing (1) enclosing the tubes (3) inside which circulates a first exchange fluid, a second exchange fluid circulating in the casing (1) at the outside of the tubes (3) and a set of spacer grids (18) for transversely holding the tubes (3) fixed inside the casing (1) spaced apart from one another along the length of the tubes (3) and   formed by flat metal plates crossing   seized by a set of openings (20) arranged following   in front of a regular network with corresponding circular pitch   at the disposal of the tubes (3) in the sec-   right beam (2). characterized in that each of the spacer grids (18) further comprises a second set of openings (21) for the passage of the second exchange fluid, interposed between the openings (20) of the first set, so that the thickness of the walls (23) of separation between the neighboring openings (20, 21) formed in the metal of   the plate is substantially constant.   2.- Heat exchanger according to the claim   cation 1. characterized in that the openings (20) of the first set are circular in shape and have a diameter very slightly greater than the diameter outside of the tubes (3).   3.- Heat exchanger according to which one   conch of claims 1 and 2. characterized by   the tubes (3) are arranged in sections   beam straight lines (2), following a circular pitch network constant ring.   4.- Heat exchanger according to the claim   cation 3, characterized in that the openings (20) of the first set have three-lobed sections with a single axis of symmetry in a radial direction of the plate (18).   5.- Heat exchanger according to the claim   cation 3, characterized in that the openings (21) of the second set have a three-lobed section with a single axis of symmetry in a radial direction of the plate (18).   6.- Heat exchanger according to which one   conch of claims 1 and 2, characterized by   that the openings (21) of the second series have   a section of general shape in parallelogram.   7.- Heat exchanger according to one which-   conch of claims 1 and 2, characterized by   that the openings (21) of the second series have   polygonal sections with rounded vertices.   8.- Heat exchanger according to which one   conch of claims 1 to 7, characterized by   each of the spacer grids (18) is sup-   carried by a set of support elements (32) provided   placed evenly around its periphery and   as a support element (34) welded by its lower part to the interior surface of the envelope (1) and engaged, by its notched upper part, in a notch (33) provided in the grid (18), the notch of the support element (34) providing support surfaces of the grid (18) by letting it move freely in the radial direction under the effect of expansion.   9.- Heat exchanger according to which one   conch of claims 1 to 8. constituting a general   steam generator whose feed water circulates inside the tubes (3) of the bundle (2) and whose   second exchange fluid is liquid sodium.   10.- Heat exchanger according to resale   dication 1, characterized in that the grids   spacers are obtained by machining a metal plate metallic.   11.- Heat exchanger according to resale   dication 1, characterized in that the grids-   spacers are obtained by molding.