Titanium or titanium alloy heat exchanger

Abstract

Title of the invention: Titanium or titanium alloy heat exchanger. The invention relates to a plate and fin heat exchanger configured for heat exchange between at least one refrigerant and at least one heat transfer fluid. The heat exchanger comprises a plurality of plates (2) arranged parallel to each other and in a longitudinal direction (z) so as to define between said plates (2) a plurality of passages (3) adapted for the flow of the refrigerant or heat transfer fluid along the longitudinal direction (z). Fin-type heat exchange structures (8) (123) are arranged within at least a portion of the passages (3). The heat exchanger is characterized in that the plates (2) and the heat exchange structures (8) are formed entirely or partially of titanium or a titanium alloy. Figure for the abstract: 1

Description

Title of the invention: Titanium or titanium alloy heat exchanger

[0001] The present invention relates to a plate and fin type heat exchanger.

[0002] The present invention finds particular application in the field of separation of gas by cryogenics, in particular of cryogenic air separation (known by the English acronym "ASU" for air separation unit) used for the production of pressurized gaseous oxygen. In particular, the present invention can be applied to a heat exchanger that vaporizes a refrigerant, for example liquid oxygen, by exchanging heat with a heat source, for example gaseous nitrogen. If the heat exchanger is located in the vessel of a distillation column, it can constitute a thermosiphon vaporizer-condenser in which the exchanger is immersed in a bath of liquid oxygen flowing down the column, or a vaporizer operating by downward film vaporization fed directly by the liquid falling from the column and / or by a recirculation pump.

[0003] The present invention can also be applied to a heat exchanger which vaporizes at least one flow of liquid-gas mixture, in particular a flow of mixture of several constituents, for example a mixture of hydrocarbons, by heat exchange with at least one other fluid, for example natural gas.

[0004] The present invention can also find application in the field of hydrogen liquefaction. In particular, the invention can be applied to a heat exchanger, especially a catalytic exchanger, in which a flow of gaseous hydrogen is cooled, or even liquefied in whole or in part, by heat exchange with a flow of refrigerant fluid, as well as to the cooling and / or liquefaction process using said exchanger.

[0005] The present invention also applies to on-board cryogenic exchangers in which the fluids circulating in the exchanger can include neon, nitrogen, hydrogen, helium, oxygen, argon, carbon monoxide, methane.

[0006] In particular, one or more exchangers according to the invention can be used in a cryogenic refrigeration device, in particular a cryogenic refrigeration device using a Brayton cycle or an Ericsson cycle.

[0007] One technology used is that of brazed aluminum plate and fin or wave heat exchangers, which make it possible to obtain very compact devices offering a large exchange surface. These exchangers include separating plates and a stack of passages for the different fluids to be exchanged. thermal. Heat exchange structures, usually corrugated structures or waves formed from a succession of fins or wave legs, are inserted between the plates, delimiting in the passages channels in which fluids flow and forming additional heat exchange surfaces.

[0008] The role of heat exchange structures is to increase the contact area between the fluids and the walls of the exchanger in order to promote heat exchange. The performance of a heat exchanger is linked to the heat transfer coefficient of the heat exchange structures in contact with the fluids. The heat transfer coefficient of a structure depends in particular on the geometry of the structure, the nature of the material constituting it, the porosity of this material, its roughness, and the fluid flow regime.

[0009] Improving the thermal performance of a heat exchanger with constant volume and temperature difference can be achieved, in particular, by increasing the heat exchange surface area and / or by increasing the heat transfer coefficient. Increasing the heat exchange surface area is generally related to the density of the corrugated interlayer element used, usually expressed in terms of the number of fins per unit length.

[0010] Another performance criterion for a heat exchanger concerns its portability. For example, cryogenic refrigeration devices used on satellites, such as Brayton cycle refrigeration machines, require heat exchangers that combine high energy efficiency with low weight. The exchangers used for this type of application are generally shell-and-tube heat exchangers comprising microtubes, typically with an outside diameter of around 0.5 mm. The advantage of microtubes lies in their small hydraulic diameter, which allows for very high heat transfer coefficients thanks to a Reynolds number (Re) that becomes laminar and a constant Nusselt number (Nu) for a laminar Reynolds number.

[0011] However, tubular heat exchangers are not entirely satisfactory. Indeed, these exchangers only allow the circulation of two fluids, which may be insufficient in certain processes. Furthermore, these primary surface heat exchangers offer few degrees of freedom to vary the heat exchange surface area according to the characteristics of the fluids involved. Finally, the need to weld the tubes into the tube sheet fixed to the end of the shell can lead to a complex and time-consuming manufacturing process.

[0012] The present invention aims to solve, in whole or in part, the problems mentioned above, in particular to propose a heat exchanger whose shipability and operational flexibility are improved.

[0013] The solution according to the invention is then a plate and fin type heat exchanger configured to connect at least one refrigerant and at least one heat transfer fluid, said exchanger comprising a plurality of plates arranged parallel to each other and in a longitudinal direction so as to define between said plates a plurality of passages adapted for the flow of the refrigerant or the heat transfer fluid along the longitudinal direction, finned heat exchange structures being arranged within at least a part of the passages, characterized in that the plates and the heat exchange structures are formed in whole or in part of titanium or a titanium alloy.

[0014] Depending on the case, the exchanger according to the invention may include one or more of the technical characteristics given below.

[0015] All the plates and heat exchange structures are made of titanium or a titanium alloy.

[0016] The exchanger includes inlet or outlet manifolds configured to introduce or expel the refrigerant or heat transfer fluid into or from the passages, said inlet or outlet manifolds being formed in whole or in part of titanium or a titanium alloy.

[0017] The titanium alloy comprises at least 50% by weight of titanium, preferably at least 90% by weight of titanium, and even more preferably at least 95% by weight of titanium.

[0018] The plates and heat exchange structures are assembled by brazing using a brazing agent comprising a eutectic copper-silver alloy.

[0019] The heat exchange structures and the plates are assembled by brazing using a brazing agent, the heat exchange structures and / or the plates having in whole or in part a surface coating formed of a material distinct from nickel, a nickel alloy or the brazing agent, in particular formed of a material comprising nickel.

[0020] The heat exchange structures are in the form of corrugated products comprising at least one corrugation with wave crests and wave bases arranged against the plates and connected alternately by fins, said fins succeeding one another in a corrugation direction of the heat exchange structures.

[0021] Said at least one corrugation has a fin density, defined as the number of fins per unit length measured along the corrugation direction, of at least 30 fins per inch or fins per inch (1 inch=2.54 centimeters), preferably a fin density of at most 80 fins per inch or fins per inch (1 inch=2.54 centimeters), preferably again a fin density of between 40 and 70 fins per inch or fins per inch (1 inch=2.54 centimeters).

[0022] The heat exchange structures have a thickness ranging from 0.03 to 0.1 mm.

[0023] The passages have a height ranging from 1 to 3 mm, said height being defined as the gap between two adjacent plates measured orthogonally to the plates.

[0024] The plates have a thickness ranging from 0.05 to 0.4 mm.

[0025] The exchanger comprises a body formed by the stacking of the plates (2), said body having a length, measured parallel to the longitudinal direction (z), less than or equal to 1 m, preferably between 0.1 and 0.8 m and / or said body having a width, measured parallel to the lateral direction (x), less than or equal to 0.1 m, preferably between 0.02 and 0.08 m and / or said body having a height, measured orthogonally to the longitudinal (z) and lateral (x) directions, less than 0.06 m, preferably between 0.01 and 0.05 m.

[0026] The passages are delimited by closure bars arranged between the plates and formed in whole or in part of titanium or a titanium alloy.

[0027] The closing bars have a cross-section of square, rectangular or U shape.

[0028] According to another aspect, the invention relates to an air separation installation by distillation or hydrogen liquefaction comprising at least one heat exchanger according to the invention, the heat exchanger comprising inlet or outlet manifolds for distributing or evacuating into or from passages of the exchanger liquid oxygen as a refrigerant and gaseous nitrogen as a heat source.

[0029] Furthermore, the invention relates to a cryogenic refrigeration device for transferring heat from a cold source to a hot source via a working fluid circulating in a closed working circuit, the working circuit comprising in series: a substantially isothermal compression portion of the working fluid, a substantially isobaric cooling portion of the working fluid, a substantially isothermal expansion portion of the working fluid and a substantially isobaric heating portion of the working fluid, the compression portion of the working circuit comprising at least two compressors arranged in series and at least one cooling exchanger for the compressed working fluid disposed at the outlet of each compressor, the expansion portion of the working circuit comprising at least one expansion turbine and at least one heating exchanger for the expanded working fluid,in which the compressed working fluid cooling exchanger and / or the expanded working fluid heating exchanger is according to the invention and includes inlet or outlet manifolds for distributing or discharging the compressed working fluid as a heat transfer fluid or the expanded working fluid as a refrigerant into or from passages of the exchanger.

[0030] Furthermore, the invention relates to the use of a heat exchanger according to the invention in which said at least one heat-generating fluid and / or said at least one refrigerant fluid includes at least one of: neon, krypton, xenon, nitrogen, argon, oxygen, hydrogen, helium, carbon monoxide, carbon dioxide, methane.

[0031] The present invention will now be better understood from the following description, given solely by way of non-limiting example and made with reference to the figures mentioned below.

[0032] [Fig-1] is a partial three-dimensional view of a heat exchanger according to a mode of realization of the invention.

[0033] [Fig.2] is a cross-sectional view of a heat exchange structure in a passage of an exchanger according to an embodiment of the invention.

[0034] [Fig.3] is a schematic view illustrating the structure and function of a example of an embodiment of a refrigeration device according to the invention.

[0035] As can be seen on [Fig. 1], a heat exchanger according to the invention comprises a set of plates 2 arranged parallel to each other with spacing and thus forming several series of parallelepiped-shaped and flat passages 3 for the flow of at least one refrigerant and at least one heat transfer fluid to be connected by indirect heat exchange via the plates 2.

[0036] The plates 2 are stacked parallel to each other and along a stacking direction y. They extend in two dimensions, length and width, respectively along the longitudinal direction z and the lateral direction x. The plates 4 thus define a plurality of passages 3 for the flow of fluids globally parallel to the longitudinal direction z. Preferably, each passage 3 has a parallelepiped and flat shape.

[0037] Over most of their height, the passages 3 contain heat exchange structures 8 comprising, in this example, corrugated sheets, also called heat exchange waves. These structures may or may not be perforated. These heat exchange structures 8 are preferably of the vertical generator type, or so-called "easyway" arrangement. In this case, the corrugated heat exchange structures 8 exhibit, during operation, an overall corrugation direction that is orthogonal to the longitudinal direction z and parallel to the lateral direction x. The heat exchange structures are brazed to the plates 2.

[0038] It is also conceivable that the heat exchange structures of the exchanger may have different directions, dimensions and / or undulation shapes than those of the embodiments described in this application.

[0039] At the ends of the passages 3, the exchange structures 8 can be extended respectively by so-called distribution waves used to distribute the fluids in the respective passages. All or part of the passages of the exchanger 1 can be provided with at least one heat exchange structure 8. Along their edges, the Passages 3 are closed respectively by closing bars 6. The plates 2 are spaced apart by these bars 6, which do not completely close the passages 3 but leave inlet and outlet openings. The inlets and outlets of each passage, used for the circulation of the same fluid, are joined by manifolds 4, 7 fitted with tubes 5 and used for the introduction and discharge of the fluid.

[0040] According to the invention, the plates 2 and the heat exchange structures 8 are formed in whole or in part of titanium or a titanium alloy.

[0041] First of all, thanks to its plate structure, the exchanger can connect more than two fluids for heat exchange, making it a compact device, offering a large exchange surface and more flexible operation, compared with a tubular heat exchanger.

[0042] Moreover, titanium and its alloys are characterized by low densities, lower than those of aluminium or steel, making it possible to manufacture lighter parts.

[0043] Titanium and its alloys also exhibit good mechanical strength, which is advantageous when the components are subjected to mechanical stresses during transport or use in embedded devices. Furthermore, titanium and its alloys exhibit good corrosion resistance, making them suitable materials for use in corrosive atmospheres, particularly in the presence of air or oxygen.

[0044] Another advantage is that titanium or its alloys have lower thermal conductivity than aluminum or aluminum alloys, particularly at low temperatures. This significantly reduces the phenomenon of heat conduction from the hot end to the cold end of the heat exchanger, particularly through the sealing bars, known as longitudinal conduction or longitudinal conduction heat loss, which poses a problem for relatively short heat exchangers and therefore those with a hot end close to the cold end.

[0045] The use of titanium or titanium alloy thus makes it possible to consider shorter, and therefore more compact and easier to ship, heat exchangers. In particular, the plates 2 of the heat exchanger have a length, measured parallel to the longitudinal direction z, less than or equal to 1 m, preferably between 0.1 and 0.8 m. According to one embodiment, the plates 2 of the heat exchanger have a width, measured parallel to the lateral direction x, less than or equal to 0.1 m, preferably between 0.02 and 0.08 m.

[0046] According to one embodiment, the plates 2 have a thickness ranging from 0.05 to 0.4 mm.

[0047] According to one embodiment, the exchanger comprises a stack of a plurality of plates 2, the stack having a height, measured parallel to the stacking direction y, of between 0.01 m and 0.05 m.

[0048] In one embodiment, all of the plates 2 and heat exchange structures 8 are made of titanium or a titanium alloy.

[0049] Preferably, the inlet or outlet manifolds 4, 7 are also formed in whole or in part of titanium or a titanium alloy. Even more preferably, all the constituent elements of the heat exchanger are formed of titanium or a titanium alloy.

[0050] By "constituent elements of the exchanger", we mean in particular the primary parts forming the body of the exchanger, in particular the heat exchange structures, the plates, the closing bars, as well as the inlet or outlet manifolds of fluids assembled to said body.

[0051] The titanium alloy preferably comprises at least 50% by weight of titanium, more preferably at least 90% by weight of titanium, and even more preferably at least 95% by weight of titanium. In particular, the titanium alloy may comprise titanium and at least one component selected from carbon, iron, vanadium, nitrogen, oxygen, and hydrogen.

[0052] According to a particular embodiment, the titanium alloy may comprise from 0 to 0.08% carbon, from 0 to 0.05% nitrogen, from 0 to 0.4% oxygen, from 0 to 0.015% hydrogen and titanium for the remainder.

[0053] According to another particular embodiment, the titanium alloy may comprise 0 to 0.1% carbon, 0 to 0.05% nitrogen, 0 to 0.2% oxygen, 0 to 0.01% hydrogen, 5.5 to 6.75% aluminum, 3.5 to 4.5% vanadium, 0 to 0.4% iron and titanium for the remainder.

[0054] According to another particular embodiment, the titanium alloy may comprise 0 to 0.08% carbon, 0 to 0.05% nitrogen, 0 to 0.13% oxygen, 0 to 0.012% hydrogen, 5.5 to 6.5% aluminum, 3.5 to 4.5% vanadium, 0 to 0.25% iron and titanium for the remainder.

[0055] According to one embodiment, the plates 2 and the heat exchange structures 8 are joined together by brazing using a brazing agent comprising a eutectic alloy, preferably a binary copper-silver (CuAg) eutectic alloy. For example, the eutectic alloy may comprise 25% by weight of copper and 75% by weight of silver. The use of a eutectic alloy makes it possible to limit the temperature required for the brazing operation and thus to limit the thermal and mechanical stresses on the constituent elements of the heat exchanger. The brazing agent may, in particular, be in the form of a coating deposited on the surfaces of the plates 2 and / or the heat exchange structures 18 or of one or more strips arranged between the surfaces of the plates 2 and / or the heat exchange structures 8 to be joined.

[0056] According to one embodiment, all or part of the constituent elements of the heat exchanger, in particular the heat exchange structures 8 and / or the plates 2 and / or the closing bars 6, have, in whole or in part, a surface coating made of a material other than nickel, a nickel alloy, or the brazing agent, in particular made of a material comprising nickel, preferably pure nickel or an alloy comprising at least 90%, or even at least 95% by weight, nickel. The surface coating is configured to limit the dissolution of the base metal forming the constituent elements of the heat exchanger during brazing. This limits the interaction between the brazing agent and the constituent metal of the heat exchanger elements so as to form as few brittle intermetallic phases as possible, thereby increasing the mechanical strength of the heat exchanger.

[0057] Preferably, the heat exchange structures are coated before being brazed with the plates 2. Preferably, at least 90%, more preferably at least 95%, more preferably at least 98% of the surface area of ​​the heat exchange structures 8 is coated.

[0058] [Fig.2] schematically illustrates an example of an embodiment in which the structures The heat exchangers 8 are in the form of corrugated products comprising at least one corrugation with wave crests 121 and wave bases 122 connected alternately by fins 123, also called wave legs. The fins 123 follow one another along a corrugation direction D which is parallel to the plates 2 and, in the illustrated example, orthogonal to the longitudinal direction z.

[0059] During operation, the fluid flowing in passage 3 is in indirect heat exchange via a plate 2, which forms a primary exchange surface, with another fluid flowing in an adjacent passage 3. The fins 123 form secondary exchange surfaces that intensify heat exchange between the fluids and also stiffen the exchange passages by acting as spacers.

[0060] The structures 8 can also take on other particular shapes defined according to the desired fluid flow characteristics. More generally, the term "fins" covers blades or other secondary heat exchange surfaces, which extend between the primary heat exchange surfaces, i.e. the plates of the exchanger, in the passages of the exchanger.

[0061] In the embodiment according to [Fig.2], the channels defined between each pair of consecutive fins 123 have a cross-section of overall rectangular shape, the fins extending globally parallel to the longitudinal direction z and parallel to the stacking direction y. It is also conceivable that the fins 123 form an angle of inclination with the y direction.

[0062] Note that, as a heat exchange structure 8 of the corrugated product type, the different types of waves commonly used in the plate and fin type heat exchangers, namely straight waves, partial offset waves (of the "serrated" type in English), wave or herringbone waves (of the "herringbone" type in English), perforated or not.

[0063] Preferably, the heat exchange structure 8 has a height h, corresponding approximately to the height of the passage in which it is arranged, of between 1 and 3 mm. The heat exchange structure 8 preferably has a thickness e of less than 0.15 mm, preferably ranging from 0.03 to 0.1 mm. This allows for increased compactness and / or a reduction in the weight of the exchanger. Note that the thickness of a corrugated product-type heat exchange structure refers to the thickness of the flat product from which the corrugated product is formed. This thickness corresponds to the thickness of the wave legs, wave crests, and wave bases once the corrugated product has been formed.

[0064] According to one embodiment, the heat exchange structure 8 has at least 40 fins per inch (1 inch = 2.54 centimeters), preferably a fin density of at most 70 fins per inch (1 inch = 2.54 centimeters). Since titanium or its alloys have a lower density than aluminum, it is possible to use higher fin densities without significantly increasing the weight of the exchanger. As in the example of [Fig. 2], the fins 123 are preferably arranged periodically with a pitch p between two successive fins. The fin density n, i.e., the number of fins per unit length, is expressed by the relation n = l / p.

[0065] According to one embodiment, the passages 3 are delimited by closure bars 6, which may have a square, rectangular, or U-shaped cross-section. The U-shaped closure bars 6 mechanically reinforce the heat exchanger and limit wave collapse during the brazing operation at high temperature. Indeed, in order to obtain high-quality, i.e., continuous, brazed joints, it is essential to apply a load to the assembly during brazing. Furthermore, the closure bars serve to isolate the fluids contained in the heat exchanger from the external atmosphere. The use of U-shaped closure bars 6 increases the cross-sectional area for the fluid circulating in the heat exchanger passages, thanks to the additional volume freed up in the U-shaped recess, and helps to minimize the size of the heat exchanger.

[0066] Preferably, all or part of the bars 6 are arranged so that the hollow of the U of the bars 6 is oriented towards the inside of the passages of the exchanger.

[0067] The hollow of the U can optionally be oriented towards the face of one of the plates located on either side of a bar.

[0068] Note that the locking bars 6 can also be formed entirely or partially from titanium or a titanium alloy. The bars 6 can also be assembled by brazing using a brazing agent comprising a eutectic copper-silver alloy.

[0069] [Fig. 3] schematically illustrates an embodiment in which at least one heat exchanger according to the invention is integrated into a cryogenic refrigeration device of the type using a Brayton cycle. These refrigeration devices have generally been used for the reliquefaction of methane vapors or the liquefaction of hydrogen, or for cooling superconducting elements. They can be devices installed on ships or satellites. The integration of one or more heat exchangers according to the invention has the advantage of reducing the mass and dimensions of the refrigeration devices. Referring to the example embodiment in [Fig. 3], the refrigeration device according to the invention is designed to transfer heat from a cold source 35 at a cryogenic temperature to a hot source 21, at ambient temperature, for example.

[0070] The cold source 35 can be, for example, liquid nitrogen to be cooled, and the hot source 21 water or air. To carry out this heat transfer, the refrigeration device illustrated in [Fig. 3] uses a working circuit 200 of a working fluid comprising the components listed below.

[0071] The circuit 200 comprises at least two centrifugal compressors 23, 25, 27 arranged in series and operating at ambient temperature. The circuit 200 comprises several heat exchangers 22, 24, 26 operating at ambient temperature, arranged respectively at the outlet of the compressors 23, 25, 27. The working fluid temperatures at the inlet and outlet of each compression stage (i.e., at the inlet and outlet of each compressor 23, 25, 27) are maintained by the heat exchangers at a substantially identical level.

[0072] The inlet and outlet temperatures of each compression stage are substantially the same.

[0073] The exchangers 22, 24, 26 may be separate or consist of separate portions of the same exchanger in heat exchange with the hot source 21. At least one of the exchangers 26, 24, 22 for cooling the compressed working fluid is according to the invention.

[0074] Downstream of the compression section comprising the series-connected compressors, the refrigerator includes a heat exchanger 28, preferably of the counter-current plate type, separating the ambient temperature elements (in the upper part of circuit 200 shown in [Fig. 3]) from the cryogenic temperature elements (in the lower part of circuit 200). The fluid is cooled. The cooling of the gas from ambient temperature to cryogenic temperature is achieved by counter-current exchange with the same working fluid at cryogenic temperature, which returns from the expansion section after heat exchange with the cold source 35. Downstream of this The cooling portion, consisting of the plate heat exchanger 28, comprises one or more expansion turbines 29, 31, 33, preferably of the centripetal type, arranged in series. The turbines 29, 31, 33 operate at cryogenic temperatures. The inlet and outlet temperatures of each expansion stage (turbine inlet and outlet) are maintained substantially identically by one or more cryogenic heat exchangers 30, 32, 34 located at the outlet of the turbine(s). This arrangement allows for near-isothermal expansion. The inlet and outlet temperatures of each expansion stage are substantially the same.

[0075] These heating exchangers 30, 32, 34 can be separate or consist of separate portions of the same exchanger in heat exchange with the cold source 35. At least one of the heating exchangers 30, 32, 34 of the expanded working fluid is in accordance with the invention.

[0076] Downstream of the expansion section and the heat exchange with the cold source 35, the working fluid exchanges heat again with the plate heat exchanger 28. The fluid exchanges heat in the exchanger 8 in the opposite direction to its flow after the compression section. After reheating, the fluid returns to the compression section and can begin the cycle again.

[0077] The refrigerator preferably uses a gaseous fluid circulating in a closed circuit as its working fluid. This fluid may consist, for example, of a pure gas or a mixture of pure gases. Gases best suited to this technology include helium, neon, nitrogen, oxygen, and argon. Carbon monoxide and methane, or any other fluid in a gaseous phase at the temperature of the cold source, may also be used.

[0078] According to one embodiment, the refrigerator is designed and controlled in such a way as to obtain a work cycle of the fluid approaching the Ericsson cycle, that is to say isothermal compression, isobaric cooling, isothermal expansion and isobaric heating.

[0079] According to another embodiment, the refrigerator is designed and controlled in such a way as to obtain a work cycle of the fluid approaching the Brayton cycle, that is to say an adiabatic compression, an isobaric cooling, an adiabatic expansion and an isobaric heating.

[0080] According to an advantageous feature, the refrigerator uses several so-called high-speed motors 70 to drive at least the compressors 23, 25, 27 (i.e., to drive the compressor wheels). A high-speed motor is usually defined as a motor whose rotational speed allows direct coupling with a centrifugal compression stage or a centripetal expansion stage. High-speed motors preferably use magnetic or dynamic gas bearings. A high-speed motor typically rotates at a speed A low-speed motor typically rotates at a speed of 10,000 revolutions per minute, or several tens of thousands of revolutions per minute.

Claims

Demands

1. A plate and fin type heat exchanger configured to connect at least one refrigerant and at least one heat transfer fluid, said exchanger comprising a plurality of plates (2) arranged parallel to each other and in a longitudinal direction (z) so as to define between said plates (2) a plurality of passages (3) adapted for the flow of the refrigerant or heat transfer fluid along the longitudinal direction (z), finned heat exchange structures (8) (123) being arranged within at least a part of the passages (3), the plates (2) and the heat exchange structures (8) being formed in whole or in part of titanium or a titanium alloy and characterized in that the plates (2) and the heat exchange structures (8) are assembled by brazing using a brazing agent comprising a eutectic alloy.

2. Heat exchanger according to claim 1, characterized in that all of the plates (2) and heat exchange structures (8) are made of titanium or a titanium alloy.

3. Heat exchanger according to any one of claims 1 or 2, characterized in that it comprises inlet or outlet manifolds (4, 7) configured to introduce or discharge the refrigerant or heat transfer fluid into or from the passages (3), said inlet or outlet manifolds (4, 7) being formed in whole or in part of titanium or a titanium alloy.

4. Heat exchanger according to any one of the preceding claims, characterized in that the titanium alloy comprises at least 50% by weight of titanium, preferably at least 90% by weight of titanium, and even more preferably at least 95% by weight of titanium.

5. Heat exchanger according to any one of the preceding claims, characterized in that the heat exchange structures (8) and the plates (2) are assembled by brazing using a brazing agent, the heat exchange structures (8) and / or the plates (2) having in whole or in part a surface coating formed of a material distinct from nickel, a nickel alloy or the brazing agent, in particular formed of a material comprising nickel.

6. Heat exchanger according to any one of the preceding claims, characterized in that the brazing agent comprises a eutectic copper-silver alloy.

7. Heat exchanger according to any one of the preceding claims, characterized in that the heat exchange structures (8) are in the form of corrugated products comprising at least one corrugation with wave crests (121) and wave bases (122) arranged against the plates (2) and connected alternately by fins (123), said fins (123) succeeding one another along a corrugation direction (D) of the heat exchange structures (8).

8. Exchanger according to claim 7, characterized in that said at least one corrugation has a fin density, defined as the number of fins per unit length measured along the corrugation direction (D), of at least 30 fins per inch or fins per inch (1 inch=2.54 centimeters), preferably a fin density of at most 80 fins per inch or fins per inch (1 inch=2.54 centimeters), preferably again a fin density of between 40 and 70 fins per inch or fins per inch (1 inch=2.54 centimeters).

9. Heat exchanger according to any one of the preceding claims, characterized in that the heat exchange structures (8) have a thickness ranging from 0.03 to 0.1 mm.

10. Exchanger according to any one of the preceding claims, characterized in that the passages (3) have a height ranging from 1 to 3 mm, said height being defined as the gap between two adjacent plates (2) measured orthogonally to the plates (2).

11. Heat exchanger according to any one of the preceding claims, characterized in that the plates (2) have a thickness ranging from 0.05 to 0.4 mm.

12. Exchanger according to any one of the preceding claims, characterized in that it comprises a body formed by the stacking of the plates (2), said body having a length, measured parallel to the longitudinal direction (z), less than or equal to 1 m, preferably between 0.1 and 0.8 m and / or said body having a width, measured parallel to the lateral direction (x), less than or equal to 0.1 m, preferably between 0.02 and 0.08 m and / or said body having a height, measured orthogonally to the longitudinal (z) and lateral (x) directions, less than 0.06 m, preferably between 0.01 and 0.05 m.

13. Heat exchanger according to any one of the preceding claims, characterized in that the passages (3) are delimited by closure bars (6) arranged between the plates (2) and formed in whole or in part of titanium or a titanium alloy, in particular the closure bars (6) have a cross-section of square, rectangular or U shape.

14. Air separation installation by distillation or hydrogen liquefaction comprising at least one heat exchanger according to any one of claims 1 to 13, the heat exchanger comprising inlet or outlet manifolds for distributing or evacuating into or from passages of the exchanger liquid oxygen as a refrigerant and gaseous nitrogen as a heat source.

15. Cryogenic refrigeration device for transferring heat from a cold source (35) to a hot source (21) via a working fluid circulating in a closed working circuit (200), the working circuit (200) comprising in series: a substantially isothermal compression portion of the working fluid, a substantially isobaric cooling portion of the working fluid, a substantially isothermal expansion portion of the working fluid and a substantially isobaric heating portion of the working fluid, the compression portion of the working circuit (200) comprising at least two compressors (27, 25, 23) arranged in series and at least one heat exchanger (26, 24, 22) for cooling the compressed working fluid disposed at the outlet of each compressor (27, 25, 23), the expansion portion of the working circuit (200) comprising at least one expansion turbine (29, 31, 33) and at least one heat exchanger (30, 32,34) for heating the expanded working fluid, wherein the compressed working fluid cooling exchanger (26, 24, 22) and / or the expanded working fluid heating exchanger (30, 32, 34) is as defined according to any one of claims 1 to 13 and includes inlet or outlet manifolds for distributing or discharging into or from passages of the exchanger the compressed working fluid as a heat transfer fluid or the expanded working fluid as a refrigerant.

16. Use of a heat exchanger according to any one of claims 1 to 13 wherein said at least one heat transfer fluid and / or said at least one refrigerant fluid comprises at least one of: neon, the krypton, xenon, nitrogen, argon, oxygen, hydrogen, helium, carbon monoxide, carbon dioxide, methane.

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