Heat exchanger for exchanging heat between two fluids, use of the exchanger with liquid metal and gas, application to a fast neutron nuclear reactor cooled with liquid metal

Abstract

A heat exchanger for exchanging heat between two fluids, use of the exchanger with liquid metal and gas, and application to a fast neutron nuclear reactor cooled with liquid metal. The present invention concerns a heat exchanger (1) for exchanging heat between a first fluid (N.sub.2) and a second fluid (Na). According to the invention, the structure of the heat exchanger makes it possible to supply and recover the primary fluid, such as sodium (Na), to and from a given longitudinal end (2a) opposite the longitudinal end (2b) by which the secondary fluid, such as nitrogen (N.sub.2), is supplied and recovered. This allows a physical separation between the paths of the two fluids in the exchanger, with the possibility, in particular, of having restricted access for one of the fluids, such as sodium (Na) and non-restricted access for the other of the fluids, such as nitrogen (N.sub.2).

Claims

1. A heat exchanger exchanging heat between a first and a second fluid, comprising: a sealed enclosure having a central axis (X) and comprising, at one of its longitudinal ends, at least one inlet and one outlet for the first fluid and, at the other of its longitudinal ends, at least one inlet and one outlet for the second fluid, the sealed enclosure being adapted to be pressurized, at least one heat exchanger module incorporating a first and a second fluid circuit, extending parallel to the central axis (X) and arranged inside the enclosure, a structure for supporting and holding the at least one heat exchanger module, rigidly fixed to the enclosure, the at least one heat exchanger module being supported and held exclusively by the structure for supporting and holding, an inlet or outlet chamber for the first fluid, formed axially between the structure for supporting and holding and the sealed enclosure, and communicating with one of the inlet and the outlet of the first fluid circuit, a first central manifold extending around the central axis (X), entirely arranged axially opposite the chamber and communicating, on the one hand, with one of the inlet and the outlet for the first fluid of the enclosure and, on the other hand, with the other of the inlet and the outlet of the first fluid circuit, an annular manifold arranged around the first central manifold and the at least one heat exchanger module and extending to at least to the structure for supporting and holding, forming a guiding space for the first fluid and communicating, on the one hand, with the other of the inlet and the outlet for the first fluid of the enclosure and, on the other hand, with the chamber, at least one inlet conduit communicating on the one hand with the inlet for the second fluid of the enclosure, and, on the other hand, with the inlet of the second fluid circuit, at least one outlet conduit communicating on the one hand with the outlet for the second fluid of the enclosure, and, on the other hand, with the outlet of the second fluid circuit, the conduits not being supported by the structure for supporting and holding.

2. The heat exchanger as claimed in claim 1, comprising: a plurality of heat exchanger modules, each extending parallel to the central axis (X) and each arranged inside the outer enclosure, a plurality of inlet conduits each communicating on the one hand with the inlet for the second fluid of the enclosure, and on the other hand with the inlet of the second fluid circuit of one of the heat exchanger modules, a plurality of outlet conduits communicating on the one hand with the outlet for the second fluid of the enclosure, and on the other hand with the outlet of the second fluid circuit.

3. The heat exchanger as claimed in claim 2, the plurality of inlet conduits communicating with a second central manifold.

4. The heat exchanger as claimed in claim 2, the plurality of outlet conduits communicating with a third central manifold.

5. The heat exchanger as claimed in claim 2, a third central manifold being arranged coaxially around the second central manifold.

6. The heat exchanger as claimed in claim 1, the inlet of the first fluid circuit of each heat exchanger module being arranged at a longitudinal end of each heat exchanger module.

7. The heat exchanger as claimed in claim 1, the inlet of the second fluid circuit of each heat exchanger module being arranged at a longitudinal end of each heat exchanger module.

8. The heat exchanger as claimed in claim 1, the inlet of the first fluid circuit and the inlet of the second fluid circuit of each heat exchanger module being arranged at a longitudinal end of each heat exchanger module.

9. The heat exchanger as claimed in claim 1, the outlet of the first fluid circuit being arranged at a longitudinal end of each heat exchanger module.

10. The heat exchanger as claimed in claim 1, the outlet of the second fluid circuit being arranged at a longitudinal end of each heat exchanger module.

11. The heat exchanger as claimed in claim 1, the outlet of the first fluid circuit and the outlet of the second fluid circuit being arranged at a longitudinal end of each heat exchanger module.

12. The heat exchanger as claimed in claim 1, the inlet of the first fluid circuit and the outlet of the second fluid circuit of each heat exchanger module being arranged at a same longitudinal end and the inlet of the second fluid circuit and the outlet of the first fluid circuit of each heat exchanger module being arranged at a same opposite longitudinal end.

13. A method for operating the heat exchanger as claimed in claim 1, the sealed enclosure being arranged substantially vertically with the inlet and the outlet for the first fluid at the top and the inlet and the outlet for the second fluid at the bottom.

14. The use of the heat exchanger as claimed in claim 1, the first fluid, as secondary fluid, being a gas or a gas mixture, and the second fluid, as primary fluid, being a liquid metal.

15. The use of the assembly as claimed in claim 10, the first fluid primarily comprising nitrogen and the second fluid being liquid sodium.

16. The use of the assembly as claimed in claim 10, the first or the second fluid originating from a nuclear reactor.

17. A nuclear installation comprising a fast neutron nuclear reactor cooled with liquid metal and a heat exchanger claimed in claim 1.

Description

DETAILED DESCRIPTION

(1) Other advantages and features of the invention will emerge more on reading the detailed description of exemplary implementations of the invention given in an illustrative and nonlimiting manner with reference to the following figures in which:

(2) FIG. 1 is a view in longitudinal cross section and in perspective of a heat exchanger according to the prior art;

(3) FIG. 1A is a perspective and cut-away view of the heat exchanger according to FIG. 1;

(4) FIGS. 1B and 1C are detail views of the heat exchanger according to FIG. 1;

(5) FIG. 2 is a perspective and cut-away view of a heat exchanger according to the invention;

(6) FIG. 2A is a perspective and cut-away view of the upper part of a heat exchanger according to FIG. 2;

(7) FIG. 2B is a perspective and cut-away view of the lower part of a heat exchanger according to FIG. 2;

(8) FIG. 3 is a perspective view of the plurality of exchanger modules and of a part of the support structure of the heat exchanger according to FIG. 2;

(9) FIG. 4 is a perspective view of the plurality of exchanger modules and of an additional part of the support structure of the heat exchanger according to FIG. 2;

(10) FIG. 5 is a perspective view of the plurality of exchanger modules and of another additional part of the support structure of the heat exchanger according to FIG. 2;

(11) FIG. 5A is a detail view of FIG. 5;

(12) FIG. 6 reprises FIG. 5 and also illustrates, in perspective, the first central manifold of the heat exchanger according to the invention;

(13) FIG. 7 reprises FIG. 6 and also illustrates, in perspective, the inlet and outlet conduits for one of the fluids and their central manifolds of the heat exchanger according to the invention;

(14) FIG. 8 is an isolated perspective view of the inlet and outlet conduits for one of the fluids and of their central manifolds shown in FIG. 7;

(15) FIG. 8A reprises FIG. 7 and also illustrates, in perspective, the arrangement of a part of the annular manifold and the arrangement of the inlet and outlet conduits and of their central manifolds in the bottom of the sealed enclosure of the exchanger according to the invention;

(16) FIG. 9 is a perspective and cut-away view of the relative arrangement between the cover of the sealed enclosure and another part of the annular manifold.

(17) Throughout the present application, the terms vertical, lower, upper, bottom, top, below and above should be understood by reference relative to a heat exchanger according to the invention with its sealed enclosure as it is in vertical operating configuration. Thus, in an operating configuration, the central axis X of the sealed enclosure 2 is vertical and the cover 20 is at the top.

(18) Similarly, throughout the present application, the terms inlet, outlet, downstream and upstream should be understood with reference to the direction of circulation of one or other of the two fluids through the heat exchanger according to the invention.

(19) In the interests of clarity, the same references denote the same elements both for a heat exchanger 1 according to the prior art already described with reference to FIGS. 1 to 1C, and for a heat exchanger 1 according to the invention described with reference to FIGS. 2 to 9.

(20) FIGS. 1 to 1C of the heat exchanger 1 according to the prior art, as disclosed in the publication [1], have already been commented on in the preamble. They are therefore not detailed hereinbelow.

(21) The inventors of the present invention have sought to retain the advantages of the heat exchanger 1 according to this publication [1], namely, essentially, a good compactness and a high unitary thermal power, while dispensing with its major drawback. Thereby, they'll have sought to guarantee the distribution of the fluids in an industrial manner.

(22) Thus, they have proposed the heat exchanger 1 illustrated in FIGS. 2 to 9, which is intended to transfer heat between a first fluid, which is nitrogen (N.sub.2) (cold fluid) and a second fluid which is the liquid sodium (Na).

(23) The heat exchanger 1 is represented in its vertical operating configuration with the cover 20 of the sealed enclosure on the top.

(24) The heat exchanger 1 of central axis X comprises a sealed enclosure 2 in which is housed a plurality 3 of exchanger modules 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8 arranged vertically and parallel to the axis X. In the embodiment illustrated in FIGS. 2 to 10, the number of identical exchanger modules is equal to eight.

(25) The sealed enclosure 2 is of essentially cylindrical general form and consists essentially of a cover 20, a bottom 21 and a lateral jacket 22 in the form of a shell. The cover 20 and the shell 22 are joined together by means of a first group of bolts 23. The bottom 21 and the shell 22 are also joined together by means of a second group of bolts 23.

(26) The sealed enclosure 2 comprises, at one 2a of its longitudinal ends, an inlet 10 and an outlet 11 for the nitrogen.

(27) At the other 2b of the longitudinal ends of the enclosure 2, there are provided an inlet 12 and an outlet 13 for the liquid sodium.

(28) Each exchanger module 3.1 to 3.8 incorporates two fluid circuits, one dedicated to the circulation of the sodium (Na) originating from a nuclear reactor SFR, as primary fluid for the exchanger module, and the other dedicated to the circulation of the nitrogen (N.sub.2) as secondary fluid.

(29) The plurality 3 of exchanger modules 3.1 to 3.8 is supported by a support and holding structure 4. The support and holding structure 4 is thus rigidly fixed to the outer enclosure 2.

(30) An inlet chamber 5 for the nitrogen is formed axially on the underside of the enclosure 2, at its lower longitudinal end 2b, between the support structure 4 and the bottom 21 of the enclosure 2. In other words, this chamber 5 is the space available between the support structure 4 and the bottom 21 of the enclosure 2.

(31) This chamber 5 communicates with each inlet, not represented, of the nitrogen circuit incorporated in one of the exchanger modules 3.1 to 3.8.

(32) Opposite the chamber 5, a first central manifold 6 is arranged axially around the central axis (X). The function of this first central manifold 6 is to recover the hot nitrogen to which the heat has been transferred from the sodium in the exchanger modules 3.1 to 3.8. This hot manifold 6 is thus common to the modules 3.1 to 3.8 but each independently feeds this manifold by the outlet 30.

(33) This central manifold 6 therefore communicates upstream with each outlet 30 of the nitrogen circuit incorporated in one of the exchanger modules 3.1 to 3.4. Downstream, this central manifold communicates with the outlet 11 for the nitrogen of the enclosure 2, i.e. through the cover 20.

(34) An annular manifold 7 is arranged coaxially around the central manifold 6 and the exchanger modules 3.1 to 3.8, forming a guiding space for the nitrogen. The function of this annular manifold 7 is to bring the cold nitrogen into the chamber 5.

(35) More specifically, this annular manifold 7 consists essentially of a deflector of flared form 70 and a shell of cylindrical form 71. The annular manifold 7 may consist of a single piece produced by sheet metalwork.

(36) A relative arrangement between the deflector 70 and the cover 20 of the enclosure is shown in FIG. 9.

(37) The guiding space 72 for the cold nitrogen originating from the inlet 10 is delimited from upstream to downstream, outside by the enclosure 2 and inside only by the annular manifold 7, that is to say by the deflector 70 and the shell 71. Thus, the function of the shell 71 is to guide the cold nitrogen along the wall of the sealed enclosure 2, in order to distribute by the bottom ends of the modules 3.1 to 3.8. In other words, the cold nitrogen distributed in the annular space 72 sets the temperature of the wall of the sealed enclosure 2, typically at approximately 330 C.

(38) The annular manifold 7 therefore communicates upstream with the inlet 10 for the nitrogen of the enclosure 2 and downstream with the chamber 5.

(39) A plurality 8 of inlet conduits 81, 82, 83, 84, 85, 86, 87, 88 is arranged to bring the hot sodium into each of the inlets 31, 32, 33, 34, 35, 36, 37, 38 of the sodium circuit incorporated in one of the exchanger modules 3.1 to 3.8.

(40) Thus, each inlet conduit 81 to 88 communicates upstream with the inlet 12 for the sodium of the enclosure 2, and downstream with each inlet 31 to 38 of the sodium circuit incorporated in one of the exchanger modules 3.1 to 3.8. Advantageously, the plurality 8 of inlet conduits communicates with a second central manifold 14.

(41) As better illustrated in FIG. 2, each inlet 31 to 38 is produced on the top of a module 3.1 to 3.8: the plurality 8 of inlet conduits 81 to 88 is therefore curved inward to be able to emerge into these longitudinal inlets 31 to 38.

(42) As a variant not represented, provision can be made for each inlet 31 to 38 to be produced on a longitudinal side in the top part of a module 3.1 to 3.8. A plurality 9 of outlet conduits 91, 92, 93, 94, 95, 96, 7, 98 is arranged to extract the cold sodium from each of the outlets of the sodium circuit incorporated in one of the exchanger modules 3.1 to 3.8.

(43) Thus, each outlet conduit 91 to 98 communicates upstream with an outlet of the sodium circuit incorporated in one of the exchanger modules 3.1 to 3.8 and downstream with the outlet 13 for the sodium of the enclosure 2. The outlet 13 for the cold sodium is made toward the bottom of the enclosure 2 through the bottom 21. Advantageously, the plurality 9 of outlet conduits communicates with a third central manifold 17.

(44) An exemplary advantageous embodiment of the plurality of inlet 8 and outlet 9 conduits and their relative arrangement is shown in FIG. 7A: the coaxial arrangement of the third central manifold 17 around the second central manifold 14 can be seen clearly.

(45) As better illustrated in FIG. 3, the support and holding structure 4 comprises a support platform 40 which bears against a peripheral shoulder inside the bottom 21 of the enclosure 2. In accordance with the invention, no relative sealing function between the supply of the cold nitrogen and the recovery of the hot nitrogen needs to be produced for the platform 40. Thus, as emerges more clearly hereinbelow, no flexibility by metal bellows between the inlet 8 and outlet 9 conduits for the sodium is required.

(46) The platform 40 can thus be open-work, notably to reduce the weight. When clearance is required for access to the bottom surfaces of the exchanger modules 3.1 to 3.8, openings of large dimension can be produced. Thus, by way of example, the platform 40 can be an assembly of beams produced by mechanized welding. The modules 3.1 to 3.8 are placed on the platform 40 and are held in position by virtue of angle irons fixed onto the platform 40 (FIG. 3).

(47) The support and holding structure 4 also comprises means 41 for laterally holding the exchanger modules 3.1 to 3.8, also fixed onto the platform 40 (FIG. 4). By way of example, the lateral holding means 41 can be an assembly of beams produced by mechanized welding which closely follows the outer form of the modules. It can be two groups of beams at 90 to one another and dividing the modules 3.1 to 3.8 into four equal groups (FIG. 4).

(48) A sealing plate 42 is screwed onto the holding structure 41 (FIG. 5). Its function is to produce the seal between the cold nitrogen brought into the heat exchanger and the hot nitrogen leaving each exchanger module 3.1 to 3.8 is recovered by the first central manifold 6.

(49) The first central manifold 6 or hot nitrogen manifold is fixed directly onto the sealing plate 42.

(50) An exemplary advantageous embodiment of the sliding sealing system between central manifold 6 and modules 3.1 to 3.8 is shown in FIG. 5A: a flange 43 is fixed onto the sealing plate 42 by means of screws 44 and segmented seals 45 between the outlet 30 of the modules and the manifold 6 are arranged. Seals 46 are also arranged between flange 43 and sealing plate 42. As a variant, metal bellows could be provided.

(51) The operation of the heat exchanger 1 which has just been described will now be briefly explained in relation to the path of the nitrogen and of the sodium.

(52) The cold nitrogen arrives, at a temperature of the order of 330 C. and a pressure of the order of 180 bar, through the inlet 10 and then is brought by the annular manifold 7 to the bottom of the enclosure 2 to the inlet chamber 5 above the bottom 21, as illustrated by the lateral arrows in FIG. 2.

(53) The nitrogen then circulates through the heat exchanger modules 3.1 to 3.8 in which the heat originating from the hot sodium is transferred to it.

(54) The nitrogen which has become hot, at a temperature of the order of 515 C., leaves the modules 3.1 to 3.8 and is then extracted from the enclosure by the outlet 11 via the first central manifold 6.

(55) For its part, the hot sodium is brought, at a temperature of the order of 530 C., by the second central manifold 14 through the inlet 12 and is then distributed in each exchanger module 3.1 to 3.8 by the inlet conduits 81 to 88, as illustrated by the upward vertical arrows in FIG. 2.

(56) The sodium then passes through the heat exchanger modules 3.1 to 3.8 in which it transfers its heat to the nitrogen.

(57) The sodium which has become cold, at a temperature of the order of 345 C., leaves the modules 3.1 to 3.8 by their bottom ends and is then is extracted from the enclosure 2 by the outlet 13 via the outlet conduits 91 to 98.

(58) In a heat exchanger 1 according to the invention, the cold gas (cold N.sub.2) circulates from top to bottom and in counter-flow with the hot sodium. Thus, as better illustrated in FIGS. 2A and 2B, the cold gas (cold N.sub.2) arrives in the chamber 5, enters in the bottom part of the modules 3.1 to 3.8 then leaves hot through the outlets 30 of the modules to feed the manifold 6 and finally leaves the exchanger by the outlet 11. As illustrated in FIG. 2A, in the heat exchanger 1 according to the invention, there is no gas inlet manifold for each module: the gas channels delimited between the deflector 7 and the enclosure 2 emerge directly into the latter, in the chamber 5. Thus, the chamber 5 defined by the enclosure 2 acts as gas inlet manifold.

(59) The circulation of the fluids is compatible with a natural convection circulation.

(60) In practice, a forced convection is provided for nominal operation, in other words to initiate the movement of the gas and of the liquid sodium in the exchanger 1. Then, in case of accident (stopping of the pumps for example), the circulation can continue by natural convection. Indeed, the cooling sodium tends to drop naturally and, when it is cooled in an exchanger module 3.1 to 3.8, its extraction is facilitated by gravity. Thus, the sodium that has become cold is discharged in the bottom part of the device which improves its gravity draining.

(61) For its part, the cold gas (N.sub.2) descends along the wall of the sealed enclosure 2 and it rises up again when it is reheated to be extracted by the central manifold 6. The heat favors its progression toward the top of the exchanger 1.

(62) Other variants and enhancements can be provided without in any way departing from the scope of the invention.

REFERENCE CITED

(63) [1]: Innovative power conversion system for the French SFR prototype, ASTRID, L. Cachon and al. Proceeding of ICAPP'12, Chicago, USA, Jun. 24-28, 2012, Paper 12300.