Cryogenic tank

Abstract

Cryogenic tank comprising a structure for holding an inner casing (2) in an outer casing (3), with a first connection (5) between the first end (21) of the inner casing (2) and the first end (31) of the outer casing (3), and a second connection (6) between the second end (22) of the inner casing (2) and the second end (32) of the outer casing (3), the first connection (5) being integral on the one hand with a curved region of the dome (31) of the first end of the outer casing (3) and on the other hand with a curved region of the dome (21) of the first end of the inner casing (2), the second connection (6) being integral on the one hand with a curved region of the dome (32) of the second end of the outer casing (3) and on the other hand with a curved region of the dome (22) of the second end of the inner casing (2). Abstract figure: Fig. 1

Description

Title of the invention: Cryogenic tank

[0001] The present invention relates to a cryogenic tank for storing liquefied fluid and to a method of assembling such a tank.

[0002] Cryogenic tanks are generally made up of two envelopes assembled one inside the other, separated from each other by a space allowing thermal insulation and possibly evacuated under vacuum. The cryogenic fluid is stored in the internal envelope. The implementation of the supports, that is to say the mechanical connection between the external envelope and the internal envelope, must fulfill the function of limiting thermal inputs by conduction while ensuring a resistance adapted to the mechanical stresses that the tank will undergo. It is known to produce cryogenic tanks comprising supports, generally made of steel, in the form of a neck (sliding or not) and / or tie rods.

[0003] These solutions are not suitable for the production of compact cryogenic tanks, in particular because they have large dead volumes that cannot be used to contain the fluid. Having to contain fluids that are particularly sensitive to thermal inputs, such as hydrogen and in particular in liquid form, the known solutions favor thermal performance to the detriment of the useful storage volume.

[0004] The present invention aims to effectively overcome these drawbacks by proposing a cryogenic tank for storing liquefied fluid comprising an inner casing delimiting a storage volume for liquefied fluid and an outer casing arranged spaced apart around the inner casing, the space between said inner and outer casings comprising thermal insulation, the inner and outer casings extending in a longitudinal direction between two longitudinal ends, the inner and outer casings having, at each longitudinal end, a dome-shaped portion, the tank comprising a structure for holding the inner casing in the outer casing, the holding structure comprising a first mechanical connection between the first longitudinal end of the inner casing and the first longitudinal end of the outer casing,and a second mechanical connection between the second longitudinal end of the inner envelope and the second longitudinal end of the outer envelope, the first mechanical connection being secured on the one hand to a curved region of the dome of the first end of the outer envelope and on the other hand to a curved region of the dome of the first end of the inner envelope, the second mechanical connection being secured on the one hand to a curved region of the dome of the second end of the outer envelope and on the other hand to a curved region of the dome of the second, end of the inner envelope.

[0005] The invention thus makes it possible to propose a more suitable compact architecture, with reduced dead volumes, an optimized cryogenic fluid storage volume, and which overcomes all or part of the drawbacks cited above.

[0006] The invention can be advantageously applied to fixed or mobile cryogenic tanks, in particular semi-trailers for transporting liquefied gases, on-board cryogenic fuel tanks. The fluids concerned are, for example, helium, hydrogen, methane, natural gas, or any other fluid or mixture of fluids at cryogenic temperatures.

[0007] According to one embodiment, each dome-shaped portion has a cross-section, in a plane orthogonal to the longitudinal direction, of width which varies between a minimum width, at the longitudinal end, and a maximum width, the first mechanical connection being integral with the dome of the first end of the outer envelope in a region where the width of the section of the dome of the outer envelope is between 50% and 100% of the maximum width, and integral with the dome of the first end of the inner envelope in a region where the width of the section of the dome of the inner envelope is between 50% and 100% of the maximum width.

[0008] According to one embodiment, the second mechanical connection is secured to the second end of the outer envelope in a region where the width of the section of the dome of the outer envelope is between 50% and 100% of the maximum width, and / or to the second end of the inner envelope in a region where the width of the section of the dome of the inner envelope is between 50% and 100% of the maximum width.

[0009] According to one embodiment, at least one of the mechanical connections is integral with the respective dome of the external envelope in a region where the width of the section of the dome of the external envelope is between 80% and 100% of the maximum width, and / or integral with the respective dome of the internal envelope in a region where the width of the section of the dome of the internal envelope is between 80% and 100% of the maximum width.

[0010] According to one embodiment, at least one of the mechanical connections is integral with the respective dome of the external envelope in a region where the width of the section of the dome of the external envelope is greater than 50% and strictly less than 100% of the maximum width, and / or integral with the respective dome of the internal envelope in a region where the width of the section of the dome of the internal envelope is greater than 50% and strictly less than 100% of the maximum width.

[0011] According to one embodiment, the first mechanical connection is rigidly fixed to the external envelope and fixed to the internal envelope so as to be able to move and / or deform in response to relative expansion and / or contraction of the internal envelope.

[0012] According to one embodiment, the first and / or the second mechanical connection comprises several support structures distributed angularly around a central axis.

[0013] According to one embodiment, the support structures are part of a connecting ring extending around the central axis and delimiting an open volume whose section, in a plane orthogonal to the central axis, exhibits a monotonic variation when moving along the central axis.

[0014] According to one embodiment, the connecting ring has an inner face facing the dome of the internal envelope and an outer face facing the dome of the external envelope, the inner face having a profile complementary to the profile of the dome of the internal envelope.

[0015] According to one embodiment, the outer face of the connecting ring has a profile complementary to the profile of the dome of the outer envelope.

[0016] According to one embodiment, the first and / or the second mechanical connection comprises at least three support structures, each comprising at least one internal protuberance projecting from the internal face of the connection ring and at least one external protuberance projecting from the external face of the connection ring, the connection ring being secured to the internal and respectively external envelope only at the level of these protuberances.

[0017] According to one embodiment, the support structures are distributed angularly around the central axis in a uniform manner.

[0018] According to one embodiment, the central axis is parallel or coincides with the longitudinal axis.

[0019] According to one embodiment, the open volume delimited by the connecting ring has a section of substantially elliptical shape.

[0020] According to one embodiment, the open volume delimited by the connecting ring has a section of substantially circular shape.

[0021] According to one embodiment, the outer protrusions are welded or glued to the outer casing, and the inner protrusions are welded or glued to the inner casing.

[0022] According to one embodiment, the holding structure comprises only the first and second mechanical connections.

[0023] According to one embodiment, the holding structure comprises at least one third mechanical connection positioned longitudinally, along the longitudinal axis, between the first mechanical connection and the second mechanical connection.

[0024] The invention further relates to a method of assembling a tank as described above, the longitudinal axis being horizontal during assembly, comprising the following successive steps - a. fixing the first mechanical connection to the dome of the first end of the internal envelope; - b. insertion of the assembly thus obtained into the external envelope; - c. fixing the first mechanical connection to the dome of the first end of the outer envelope.

[0025] The invention further relates to a method of assembling a tank as described above, the longitudinal axis being vertical during assembly, comprising the following successive steps - a. fixing the first mechanical connection to the dome of the first end of the outer casing; - b. insertion of the inner envelope into the outer envelope; - c. fixing the first mechanical connection to the dome of the first end of the internal envelope.

[0026] The invention will be better understood upon reading the following description and examining the accompanying figures. These figures are given only for illustrative purposes but in no way limit the invention.

[0027] [Fig-1] [Fig.l] represents a vertical and longitudinal sectional view, schematic and partial, illustrating a first example of possible embodiment of the invention;

[0028] [Fig.2] [Fig.2] represents a schematic and partial sectional view of a detail of any one of the longitudinal ends of the inner or outer envelope of [Fig.l];

[0029] [Fig.3] [Fig.3] represents a schematic and partial sectional view of a detail of a first end of the tank of the embodiment of [Fig.l];

[0030] [Fig.4] [Fig.4] represents a perspective, schematic and partial view, illustrating an example of the production of the supports of [Fig.l];

[0031] [Fig.5] [Fig.5] represents a schematic vertical and longitudinal sectional view and partial, illustrating a second example of possible embodiment of the invention.

[0032] The cryogenic tank 1 illustrated by way of example in [Fig.l] comprises an inner casing 2 delimiting a storage volume for liquefied fluid and an outer casing 3 arranged spaced apart around the inner casing 2. The space between said inner 2 and outer 3 casings comprises thermal insulation 4. The thermal insulation may in particular comprise multi-layer insulation, also known as MLI (“multi-layer insulation”), perlite, foam, glass beads or any other suitable insulation. The thermal insulation may also be under vacuum, the space between said casings then being evacuated to a pressure of less than 102 mbar, and preferably between 10 4 mbar and 107 mbar.

[0033] In the example illustrated, the inner 2 and outer 3 envelopes extend in a longitudinal direction 100 between two longitudinal ends. The inner and outer envelopes have, at each longitudinal end, a dome-shaped end portion 21, 31, 22, 32. A main body, called a shell, extends between the two longitudinal ends of the tank. The shell is preferably a cylinder of circular section, but alternatively it could have an elliptical section or another shape adapted to the needs.

[0034] Other shapes are also possible for at least one of the end portions 21, 31, 22, 32 of the internal envelope 2 and / or of the external envelope 3, for example a cylinder, a parallelepiped or other polyhedron, and in particular in the case where a valve box is associated with the reservoir.

[0035] The tank 1 comprises a structure for holding the inner casing 2 in the outer casing 3. The holding structure comprises a first mechanical connection 5 between the first longitudinal end 21 of the inner casing 2 and the first longitudinal end 31 of the outer casing 3, and a second mechanical connection 6 between the second longitudinal end 22 of the inner casing 2 and the second longitudinal end 32 of the outer casing 3.

[0036] The first mechanical connection 5 is secured, on the one hand, to a curved region of the dome of the first end 31 of the external envelope 3 and, on the other hand, to a curved region of the dome of the first end 21 of the internal envelope 2.

[0037] The second mechanical connection 6 is secured, on the one hand, to a curved region of the dome of the second end 32 of the external envelope 3 and, on the other hand, to a curved region of the dome of the second end 22 of the internal envelope 2.

[0038] As illustrated in [Fig.2], each of the end portions 21, 31, 22, 32 may have a cross-section, in a plane orthogonal to the longitudinal axis 100, of width which varies between a minimum width, at the longitudinal end, and a maximum width at the junction with the ferrule. In the case of a cylindrical ferrule and two dome-shaped ends, the maximum width thus corresponds to the diameter of the ferrule.

[0039] The first mechanical connection 5 may be integral with the dome of the first end 31 of the external envelope 3 in a region where the width of the section of the dome 31 of the external envelope 3 is between 50% and 100% of the maximum width, and preferably between 80% and 100% of the maximum width.

[0040] The first mechanical connection 5 may be integral with the dome of the first end 21 of the internal envelope 2 in a region where the width of the section of the dome 21 of the internal envelope 2 is between 50% and 100% of the maximum width, and preferably between 80% and 100% of the maximum width.

[0041] The second mechanical connection 6 can be secured to the second end 32 of the outer envelope 3 in a region where the width of the dome section 32 of the outer envelope 3 is between 50% and 100% of the maximum width, and preferably between 80% and 100% of the maximum width.

[0042] The second mechanical connection 6 may be secured to the second end 22 of the internal envelope 2 in a region where the width of the section of the dome 22 of the internal envelope 2 is between 50% and 100% of the maximum width, and preferably between 80% and 100% of the maximum width.

[0043] That is to say that the mechanical connections 5, 6 are mechanically attached to the dome 31, 32 of the end of the external envelope 3, respectively to the dome 21, 22 of the end of the internal envelope 2, in a peripheral zone thereof and that at least a part of this attachment is located in a region where the width of the section of the dome 21, 22, 31, 32 is strictly less than the maximum width. Thus, as illustrated in [Fig. 3], the mechanical connection 5, 6 can be integral with the external envelope 3, respectively with the internal envelope 2, in a region which extends between the dome and the shell.

[0044] Such a positioning of the mechanical connections 5, 6 makes it possible in particular to reduce the dimension of the space between the internal casing 2 and the external casing 3, thus reducing the total size and increasing the volumetric efficiency of the system. That is to say that the ratio between the useful volume for containing the cryogenic fluid and the total volume of the tank is higher than for a cryogenic tank of the state of the art. Thus, for example, a tank produced according to the invention, and having the same size as a tank of the state of the art, will have a larger useful volume. Alternatively, a tank according to the invention, and having the same useful volume as a tank according to the state of the art, will have a smaller total size.

[0045] Increased resistance of the system to radial forces and stresses is also obtained, while maintaining a low level of thermal inputs.

[0046] In addition, by shifting the mechanical connections, for example in the form of rings, from the shell to the domes, the thermal insulation of the shell is more effective and simpler to implement. All thermal inputs are in fact moved to the level of the dome.

[0047] In other embodiments, all the mechanical connections 5, 6, or at least some of them, are mechanically attached to the dome 31, 32 of the end of the outer casing 3, respectively to the dome 21, 22 of the end of the inner casing 2, in a peripheral zone thereof and the whole of this attachment is located in a region where the width of the section of the dome 21, 22, 31, 32 is strictly less than the maximum width. In this case, the mechanical connections 5, 6 are not in direct contact with the shell and the size can be subsequently reduced.

[0048] In order to minimize thermal inputs, the mechanical connections 5,6 are preferably made of a material with low thermal conductivity, in particular less than 1 W m1 K1. Examples of suitable materials are fiberglass composites, for example epoxy such as types G10 or G11.

[0049] The first mechanical connection 5 can be rigidly fixed to the outer casing 3, and fixed to the inner casing 2 so as to be able to move and / or deform in response to a relative expansion and / or contraction of the inner casing.

[0050] The second mechanical connection 6 can then be rigidly fixed to both the external casing 3 and the internal casing 2. Preferably, the fluid supply and / or withdrawal pipe(s) are mounted at the second longitudinal end, where the connection 6 is rigidly fixed.

[0051] Thus the first mechanical connection 5 constitutes a connection between the two envelopes 2, 3 which is more deformable (relatively more flexible connection) than the second mechanical connection 6 (relatively more rigid connection). That is to say that the first mechanical connection 5 is configured to allow, during a temperature differential between the two envelopes 2, 3 generating a relative retraction or expansion of the envelopes 2, 3, a relative longitudinal displacement between the two envelopes 2, 3 at the first end which is greater than the relative longitudinal displacement allowed by the second mechanical connection 6 at the second end.

[0052] These relative degrees of flexibility or rigidity can be chosen by adapting the dimensions of the mechanical connections 5, 6 and / or their materials. For example, the most deformable connection can be made of foam or other suitable composite material, and the most rigid connection can be made of epoxy.

[0053] Compared to state-of-the-art stainless steel mechanical connections, it is thus possible to lighten the system, while guaranteeing that the internal casing 2 is held in the external casing 3 and optimum resistance to mechanical stresses.

[0054] Thus, the inner casing 2 can be supported in the outer casing 3 by two mechanical connections 5, 6, one of which is relatively more deformable and configured in particular to deform during the relative contraction of the inner casing 2 when cold. This deformation is configured to allow the relative dimensional variations of the two casings 2, 3 to be absorbed without harming the maintenance of the inner casing in the outer casing 3 and without affecting the thermal insulation. This also makes it possible to prevent the relative contraction of the inner casing from causing excessive mechanical stresses on the pipes.

[0055] In particular, this architecture allows a deformation of the first mechanical connection 5 which is close to the relative longitudinal contraction of the internal envelope 2 (and which allows this contraction of the internal envelope 2).

[0056] When filling the inner envelope 2 with cryogenic liquid, the thermal gradient (from the outside ambient temperature to the temperature of the liquid cryogenic inside: for example between -269°C and -180°C) that this first mechanical connection 5 will undergo will allow to accompany the relative thermal contraction of the internal envelope 2 at the level of the first end while the second end (at the level of the second mechanical connection 6, considered as a fixed point), will undergo a zero or weaker deformation. During its contraction, the internal envelope 2 (at least one end connected to the internal envelope 2) will move longitudinally relatively towards the second end (relatively fixed).

[0057] Note that the term “flexible” used above does not necessarily mean that the first mechanical connection 5 is intrinsically “flexible”. On the other hand, this first mechanical connection 5 is configured to deform (longitudinal displacement) in response to changes in temperature while allowing resistance to radial forces. In particular, the first mechanical connection 5 is thus capable and configured to maintain sufficient rigidity in the radial (transverse) directions for the absorption of forces.

[0058] In another embodiment, not shown, the first and second mechanical connections 5, 6 may both be rigidly fixed to the outer casing and fixed to the inner casing so as to be able to move and / or deform in response to a relative expansion and / or contraction of the inner casing. In this case, the fluid supply and / or withdrawal pipe(s) are preferably mounted at the end corresponding to the least flexible mechanical connection 5, 6.

[0059] The first and / or the second mechanical connection may comprise a plurality of support structures 7, 8, for example at least three support structures, distributed angularly around a central axis 200. These support structures 7, 8 may be separate or form part of a connecting ring 9 extending around the central axis 200.

[0060] The support structures are intended to come into contact with the internal and / or external casing. They may be welded, glued or bonded to the casings 2, 3 by another suitable means. Alternatively, they may be force-mounted and embedded between the casings 2, 3. In all cases, the assembly of the tank is simplified. For example, the total welding or bonding surface may be reduced compared to state-of-the-art tanks comprising one or two necks.

[0061] The support structures 7, 8 may each comprise at least one inner protrusion 8 projecting from the inner face of the connecting ring and / or at least one outer protrusion 7 projecting from the outer face of the connecting ring. In this case, the connecting ring is secured to the outer casing 3 and respectively the inner casing 2 only at the level of these respective protrusions. The surface of the protrusions 7, 8 which is in contact respectively with the outer casing 3 or the inner casing 2 may have a complementary profile respec- tively from the surface of the outer envelope 3 or the inner envelope 2.

[0062] The junction between the outer protrusions 7 and the outer casing 3, respectively between the inner protrusions 8 and the inner casing 2, can for example be made by welding or gluing. In order to obtain different rigidities or flexibilities, it is conceivable that the outer protrusions 7 and inner protrusions 8 are joined to the respective casing by different technical means. For example, the outer protrusions 7 can be welded to the outer casing 3, while the inner protrusions are glued to the inner casing 2, or vice versa.

[0063] Depending on the level of mechanical stresses to be tolerated, the thickness of the ring can be modified: thinner for expected moderate stresses, thicker for expected greater loads.

[0064] According to the embodiment illustrated in [Fig.4], the connecting ring 9 delimits an open volume 300 whose section, in a plane orthogonal to the central axis 200, has a monotonic variation when moving along the central axis 200. That is to say, when considering successive sections in successive planes orthogonal to the central axis 200, the surface area of ​​the section of the open volume 300 increases or decreases monotonically depending on whether one moves respectively from the longitudinal end towards the ferrule or from the ferrule towards the longitudinal end. The inner face of the ring 9 here has a surface which converges towards the opening of the ring, and the protuberances 7, 8 have a uniform thickness.

[0065] Alternatively, the surface of the inner face of the ring 9 may be cylindrical and the protrusions 7, 8 may have a thickness that varies monotonically along the central axis 200. That is to say, the inner face of the ring 9 has a surface parallel to the central axis 200 and the protrusions 7, 8 a profile converging towards the opening of the ring. Even in this case, when considering successive sections in successive planes orthogonal to the central axis 200, the surface area of ​​the section of the open volume 300 increases or decreases monotonically depending on whether one moves respectively from the longitudinal end towards the ferrule or from the ferrule towards the longitudinal end.

[0066] The inner face of the connecting ring 9 may be located, when the tank is assembled, opposite the dome of the internal casing 2.

[0067] The outer face of the connecting ring 9 may be located, when the tank is assembled, opposite the dome of the external casing 3.

[0068] The inner face of the connecting ring 9 may have a profile complementary to the profile of the dome of the inner envelope. For example, the surface of the inner face of the ring 9 may correspond to a homothety of the surface of the inner envelope 2.

[0069] The outer face of the connecting ring 9 may also have a profile complementary to the profile of the dome of the outer envelope 3. For example, the surface of the outer face of the ring 9 may correspond to a homothety of the surface of the outer envelope 3.

[0070] In order to maximize the thermal path between the inner envelope and the outer envelope and thus reduce thermal losses, the support structures are offset and preferably distributed angularly around the central axis 200 in a uniform manner. The angular distance between an inner protrusion and an adjacent outer protrusion is in particular equal to 360° divided by the total number of inner and outer protrusions. To define this distance, the angle having its apex on the central axis 200 is considered.

[0071] In another embodiment not shown, for the same mechanical connection 5, 6 the number of internal protrusions 8 may not be equal to the number of external protrusions 7.

[0072] The central axis 200 of the connecting ring is preferably parallel or coinciding with the longitudinal axis 100. In this way, the mechanical forces are distributed in a more balanced manner.

[0073] The section of the open volume 300 in a plane orthogonal to the central axis 200 has a shape which preferably corresponds to that of the section of the internal envelope 2. For example, this section of the open volume 300 may be substantially elliptical or circular. To define this shape, the protuberances 7, 8 are not taken into account. Corresponding (or conjugate) shapes of this section of the open volume 300 of the ring and of the section of the internal envelope 2 make it possible in particular to facilitate the alignment and assembly of these two elements.

[0074] In a possible embodiment of the invention illustrated in [Fig.l], the holding structure comprises only the first 5 and second 6 mechanical connections, i.e. the holding structure is constituted by the two aforementioned connections. Alternatively, as illustrated in [Fig.5], the holding structure may comprise one or more additional mechanical connections 16, for example when the length of the tank is particularly great, or when there is an increased need for mechanical strength. In particular, there may be at least one third mechanical connection 16 positioned longitudinally, along the longitudinal axis 100, between the first mechanical connection 5 and the second mechanical connection 6. Preferably, the distribution of the mechanical connections along the longitudinal axis 100 is uniform, in order to optimize the thermal paths and minimize thermal losses. Preferably, the at least one third mechanical connection is of the flexible type.

[0075] The invention also relates to methods of assembling a tank as described above. Methods of producing the internal casing being known by elsewhere, the description will be limited to the mounting of the inner envelope in the outer envelope and to its suspension by means of the first and second mechanical connections.

[0076] The inner casing, comprising a dome at each longitudinal end, must be positioned and suspended inside the outer casing. To do this, the outer casing initially comprises only the shell and a dome at one longitudinal end. The dome at the other longitudinal end is subsequently assembled, once the inner casing is suspended inside the outer casing.

[0077] According to a first manufacturing method, the longitudinal axis 100 of the tank is horizontal during assembly. The method then comprises the following successive steps: fixing the first mechanical connection 5 to the dome of the first end of the internal casing 2; insertion of the assembly thus obtained into the external casing; fixing the first mechanical connection 5 to the dome of the first end of the external casing 2.

[0078] According to a second manufacturing method, the longitudinal axis 10 of the tank is vertical during assembly. The method then comprises the following successive steps: fixing the first mechanical connection 5 to the dome of the first end of the internal casing 2; insertion of the assembly thus obtained into the external casing; fixing the first mechanical connection 5 to the dome of the first end of the external casing 2.

[0079] The fixing of the mechanical connections to the external envelope and to the internal envelope can be carried out, as described above, by any suitable means and in particular by welding or by gluing.

[0080] Thus a cryogenic tank 1 according to the invention is simpler to manufacture, has better volumetric efficiency and optimizes the compromise between the absorption of mechanical stresses and the limitation of thermal inputs.

Claims

1.

2.

3. Claims Cryogenic tank for storing liquefied fluid comprising an inner casing (2) delimiting a storage volume for liquefied fluid and an outer casing (3) arranged spaced apart around the inner casing (2), the space between said inner (2) and outer (3) casings comprising thermal insulation (4), the inner (2) and outer (3) casings extending in a longitudinal direction (100) between two longitudinal ends, the inner and outer casings having, at each longitudinal end, a dome-shaped portion, the tank (1) comprising a structure for holding the inner casing (2) in the outer casing (3), the holding structure comprising a first mechanical connection (5) between the first longitudinal end (21) of the inner casing (2) and the first longitudinal end (31) of the outer casing (3),and a second mechanical connection (6) between the second longitudinal end (22) of the inner casing (2) and the second longitudinal end (32) of the outer casing (3), the first mechanical connection (5) being integral on the one hand with a curved region of the dome (31) of the first end of the outer casing (3) and on the other hand with a curved region of the dome (21) of the first end of the inner casing (2), characterized in that the second mechanical connection (6) is integral on the one hand with a curved region of the dome (32) of the second end of the outer casing (3) and on the other hand with a curved region of the dome (22) of the second end of the inner casing (2)., Cryogenic tank according to claim 1, characterized in that each dome-shaped portion (21, 22, 31, 32) has a cross-section, in a plane orthogonal to the longitudinal direction (100), of width which varies between a minimum width, at the longitudinal end, and a maximum width, the first mechanical connection (5) being integral with the dome (31) of the first end of the outer casing (3) in a region where the width of the section of the dome of the outer casing is between 50% and 100% of the maximum width, and integral with the dome of the first end of the inner casing (2) in a region where the width of the section of the dome (21) of the inner casing is between 50% and 100% of the maximum width. Cryogenic tank according to claim 2, characterized in that the second mechanical connection (6) is secured to the second end of the outer casing (3) in a region where the width of the section of the dome (32) of the outer casing (3) is between 50% and 100% of the maximum width, and / or to the second end of the inner casing (2) in a region where the width of the section of the dome (22) of the inner casing is between 50% and 100% of the maximum width.

4. Cryogenic tank according to claim 3, characterized in that at least one of the mechanical connections (5, 6) is integral with the respective dome (31, 32) of the outer casing (3) in a region where the width of the section of the dome (31, 32) of the outer casing is greater than 50% and strictly less than 100% of the maximum width, and / or integral with the respective dome (21, 22) of the inner casing (2) in a region where the width of the section of the dome (21, 22) of the inner casing (2) is greater than 50% and strictly less than 100% of the maximum width.

5. Cryogenic tank according to one of the preceding claims, characterized in that the first mechanical connection (5) is rigidly fixed to the external casing (3) and fixed to the internal casing (2) so as to be able to move and / or deform in response to a relative expansion and / or contraction of the internal casing (2).

6. Cryogenic tank according to one of claims 2 to 5, characterized in that the first (5) and / or the second mechanical connection (6) comprises several support structures (7, 8) distributed angularly around a central axis (200).

7. Cryogenic tank according to claim 6, characterized in that the support structures (7, 8) are part of a connecting ring (9) extending around the central axis (200) and preferably delimiting an open volume (300) whose section, in a plane orthogonal to the central axis (200), exhibits a monotonic variation when moving along the central axis (200).

8. Cryogenic tank according to claim 7, characterized in that the connecting ring (9) has an inner face facing the dome (21, 22) of the inner casing (2) and an outer face facing the dome (31, 32) of the outer casing (3), the inner face having a profile complementary to the profile of the dome (21, 22) of the inner casing, and / or the outer face of the connecting ring (9) has a profile complementary to the profile of the dome (31, 32) of the outer casing.

9. Cryogenic tank according to claim 8, characterized in that the first (5) and / or the second mechanical connection (6) comprises at least three support structures (7, 8), each comprising at least one inner protrusion (8) projecting from the inner face of the connecting ring and at least one outer protrusion (7) projecting from the outer face of the connecting ring, the connecting ring (9) being integral with the inner (2) and respectively outer (3) casing only at the level of these protrusions.

10. Cryogenic tank according to one of claims 6 to 9, characterized in that the support structures (7, 8) are distributed angularly around the central axis (200) in a uniform manner.

11. Cryogenic tank according to one of claims 7 to 10, characterized in that the ring (9) delimits an open volume (300) whose section, in a plane orthogonal to the central axis (200), presents a monotonous variation when moving along the central axis (200), this open volume (300) having a section of substantially elliptical or circular shape.

12. Cryogenic tank according to one of the preceding claims, characterized in that the holding structure comprises only the first (5) and second (6) mechanical connections.

13. Cryogenic tank according to one of claims 1 to 11, characterized in that the holding structure comprises at least one third mechanical connection (16) positioned longitudinally, along the longitudinal axis (100), between the first mechanical connection (5) and the second mechanical connection (6).

14. Method of assembling a tank according to one of the preceding claims, the longitudinal axis (100) being horizontal during assembly, comprising the following successive steps - a. fixing the first mechanical connection (5) to the dome of the first end of the inner casing (2); - b. inserting the assembly thus obtained into the outer casing; - c. fixing the first mechanical connection (5) to the dome of the first end of the outer casing (2).

15. Method of assembling a tank according to one of claims 1 to 13, the longitudinal axis (100) being vertical during assembly, comprising the following successive steps a. fixing the first mechanical connection (5) to the dome of the first end of the external casing (2); b. insertion of the inner envelope into the outer envelope; c. fixing the first mechanical connection (5) to the dome of the first end of the internal envelope (2).

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