Removable closure for cryogenic tank, especially for aircraft, cryogenic tank, and aircraft

Abstract

To provide a removable closure for a cryogenic tank, which is improved to be capable of reducing the effort, time and costs required for maintenance of a tank and tank equipment.SOLUTION: A cryogenic tank 10 includes a tank interior 46 for storing a cryogenic medium, and an access opening 44 provided in a multiple tank wall 42, in which the multiple tank wall 42 includes a tank wall vacuum insulation space 54 between an inner side tank wall skin 50 and an outer side tank wall skin 52. A removable closure 48 comprises an outer side closure wall 2 and an inner side closure wall 3, and comprises a closure vacuum insulation volume 7 between the outer side closure wall 2 and the inner side closure wall 3. The removable closure 48 is configured for the installation of equipment 74 that is required for operating the cryogenic tank 10 in the closure vacuum insulation volume 7 formed in the interior of the removable closure 48. A cryogenic tank 10 includes the closure 10. An aircraft includes a cryogenic tank 10 with the closure 48.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a removable closure for a cryogenic (cryogenic; particularly from about the temperature of liquid natural gas (-162°C) to the temperature of liquid helium (-269°C)) tank, particularly for aircraft. The invention also relates to a cryogenic tank including such a closure. The invention also relates to an aircraft including such a cryogenic tank or closure. [Background technology]

[0002] According to a preferred embodiment, the cryogenic tank is a liquid hydrogen (LH2; liquid H2) tank for storing liquid hydrogen.

[0003] For technical background, reference is made to the following documents: [1] DE 10 2014 107 316 A1 [2] US 2021 / 0 078 702A1 [3] WO 2021 / 148 335A1 [4] US 2023 / 0 002 069 A1 [5] EP 4 119 834 A1 [6] EP 4 124 568 A1 [7] EP 4 124 790 A1 [8] Product sheet: Demaco-Cryogenics Johnston Coupling, downloaded May 23, 2023 [9] EP 4 279 392 A1

[0004] Documents [1] to [3] and [9] relate to hydrogen installations in aircraft. Documents [4] to [7] relate to cryogenic tanks for aircraft, in particular liquid hydrogen tanks (LH2 tanks), and aircraft equipped with such cryogenic tanks. Document [8] relates to the so-called Johnston coupling for connecting cryogenic piping sections.

[0005] Lightweight energy storage is a key challenge for next generation aircraft. Hydrogen offers high energy density, but storage techniques (cryogenic, compression, solid / absorption) are key challenges. Hydrogen can be compressed and / or cooled to cryogenic temperatures to increase its volumetric and gravimetric energy density. This typically requires complex tank systems with specific requirements regarding materials, design and operating principles (e.g., related to operational safety).

[0006] Compressed hydrogen and cryogenic hydrogen are the technologies of choice or of choice in today's vehicles, such as automobiles and aircraft. Cryogenic tanks allow for the lowest fuel volume / fuel mass ratio (ratio of volume per mass of fuel).

[0007] Cryogenic tanks, such as liquid hydrogen (LH2) tanks, require very good thermal insulation, so they usually have double-walled vacuum insulation, i.e. a double wall structure with a vacuum space surrounding the inside of the tank.

[0008] Hydrogen tanks are usually completely sealed by welding. However, maintenance on such cryogenic tanks requires access to the inside of the tank. Therefore, maintenance or replacement of equipment and facilities inside the tank requires a great deal of effort. As a result, the entire tank must be removed from, for example, the aircraft and repaired outside the aircraft, and the tank must be cut open to perform maintenance work inside the tank.

[0009] In addition, the insulating vacuum surrounding the inside of the tank is high vacuum (for example, 10-1 Pa~10 -5 Pa), which is difficult to achieve. Creating such a vacuum within the walls of a cryogenic tank can take days or even weeks, making cryogenic tank maintenance labor intensive and rendering the tank unusable for relatively long periods of time.

[0010] Additionally, cryogenic tanks are typically equipped with an equipment capsule that houses the tank equipment (e.g., valves, sensors, level gauges, etc.) required for handling and operation of the tank. The equipment capsule may be attached to the tank or installed separately from the tank. While some of the equipment may be housed within the tank, a significant portion is detached and installed in a protective housing or capsule.

[0011] To limit heat penetration, the protective housing or capsule (also called coldbox) is often evacuated or at least filled with an inert gas. For leak-proof reasons, valves, sensors, etc. and connecting pipes are welded together inside the protective housing, which complicates the maintenance of the equipment.

[0012] To perform maintenance on the protective housing or tank, it must be removed from the vehicle or aircraft on which it is installed.

[0013] Therefore, in addition to the considerable effort and time required for tank maintenance, maintaining the equipment within the capsule required for operating the cryogenic tank also requires an even greater amount of effort and time. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] German Patent Application Publication DE 10 2014 107 316 A1 [Patent Document 2] US Patent Application Publication US 2021 / 0 078 702A1 [Patent Document 3] International Publication WO 2021 / 148 335A1 [Patent Document 4] US Patent Application Publication US 2023 / 0 002 069 A1 [Patent Document 5] European Patent Application Publication No. EP 4 119 834 A1 [Patent Document 6] European Patent Application Publication No. EP 4 124 568 A1 [Patent Document 7] European Patent Application Publication No. EP 4 124 790 A1 [Patent Document 8] European Patent Application Publication No. EP 4 279 392 A1 [Non-patent literature]

[0015] [Non-Patent Document 1] Product sheets:Demaco-Cryogenics Johnston Couplinghttps: / / directories.gasworld.com / files / a81855a8ca / 4429 / documents / 4429-Demaco-Product-Sheet-combined.pdf Summary of the Invention [Problem to be solved by the invention]

[0016] The object of the present invention is to improve hydrogen tanks for use in aircraft and other vehicles, particularly to reduce the effort, time, and cost involved in maintaining the tanks and tank equipment. [Means for solving the problem]

[0017] According to a first aspect, the present invention provides a removable closure for a cryogenic tank. The cryogenic tank includes a tank interior for storing a cryogenic medium and an access opening in multiple (double-walled or more) tank walls, the multiple tank walls including a tank wall vacuum insulation space between an inner tank wall skin (an inner wall of the multiple tank walls) and an outer tank wall skin (an outer wall of the multiple tank walls). The removable closure includes an outer closure wall, an inner closure wall, and a closed vacuum space between the outer and inner closure walls. The removable closure is configured to accommodate installation of equipment required to operate the cryogenic tank within the closed vacuum insulation space formed inside the removable closure.

[0018] The main advantages of the present invention are as follows:

[0019] a) The installation space for the tank and capsule is reduced as space for the equipment capsule is reserved by a removable closure that houses the vacuum insulated space. b) Heat penetration into the equipment capsule is reduced. c) The risk of hydrogen (H2) leakage to the outside is reduced. d) Equipment can be replaced without cutting the tank structure or breaking the tank vacuum, for example by using a tank closure. e) The vacuum is not significantly affected by opening or closing the removable closure.

[0020] In particular, the removable closure of the cryogenic tank forms a protective housing or capsule that contains the tank equipment, i.e., the capsule is integral with the removable tank closure.

[0021] Preferably, a removable closure is inserted into the tank, which significantly reduces heat penetration into the capsule.

[0022] Preferably, when the tank is closed, the removable closure is located to a large extent or to a large extent inside the tank, which reduces the risk of hydrogen leaking, particularly to the outside.

[0023] Preferably, the inner closure wall is spaced a predetermined distance from the outer closure wall such that at least a portion of the enclosed vacuum insulated space is located within the cryogenic tank when the access opening is closed.

[0024] Preferably, the inner closure wall is located at the bottom of the removable closure, which creates a large vacuum space that can be used to install equipment therein instead of installing the equipment in a protective housing or equipment capsule outside the tank.

[0025] Preferably, the removable closure includes a ring wall that may form a tube, which connects the outer closure wall and the inner closure wall to form the enclosed vacuum insulated space.

[0026] Preferably, a closure flange, which may be formed as a flange ring, is attached to said ring wall in order to fasten the removable closure to a tank flange or tank flange ring mounted on the cryogenic tank.

[0027] Preferably, one or more pipes extend through the outer enclosure wall into the enclosed vacuum space.

[0028] Preferably, one or more pipes extend through the enclosed vacuum space and the inner enclosed wall.

[0029] Preferably, one or more pipes extend into or through the interior of the cryogenic tank when the cryogenic tank is closed.

[0030] Preferably, the removable closure includes a vacuum port for evacuating the enclosed vacuum insulated space.

[0031] Preferably, multiple layers of insulation are installed within the closed gap vacuum space.

[0032] Preferably, the closure comprises or can be formed as a panel, for example formed by an outer closure wall and / or an inner closure wall, in particular the panel is a double-walled access panel.

[0033] According to a second aspect, the present invention provides a cryogenic tank including: (1) a multi-layer tank wall; (2) an access opening in the multi-layer tank wall providing access to the interior of the cryogenic tank for maintenance, repair, and / or replacement service; and (3) a removable closure for closing the access opening, wherein the multi-layer tank wall includes: (i) an inner tank wall skin; (ii) an outer tank wall skin; and (iii) a tank wall vacuum insulation space between the inner tank wall skin and the outer tank wall skin, and wherein the removable closure is configured according to the first aspect of the present invention.

[0034] Preferably, the access opening in the multi-wall tank is defined by a multi-wall tank ring, which includes: (1) an outer tank ring wall arrangement; (2) an inner tank ring wall; and (3) a tank ring vacuum insulation space between the outer tank ring wall and the inner tank ring wall.

[0035] Preferably, the ends of the multi-walled tank ring are sealed to form a tank ring vacuum insulation space between the outer tank ring wall (outer tank wall) and the inner tank ring wall (inner tank wall).

[0036] Preferably, the outer tank ring wall arrangement comprises an inner / outer tank ring wall (outer tank wall located inside the tank) arranged on the inner side of the inner tank wall skin, and an outer / outer tank ring wall (outer tank wall located outside the tank) arranged on the outer side of the outer tank wall skin.

[0037] Preferably, the outer tank ring wall arrangement is hermetically connected to the outer tank wall skin and the inner tank wall skin, whereby the tank wall vacuum insulation space and the tank ring vacuum insulation space are in fluid communication with each other and / or form a single inter-tank wall vacuum space.

[0038] Preferably, the access opening has a tank flange and the closure has a closure flange that mates with the tank flange, so that in the closed state the closure flange is sealingly connected to the tank flange, in particular by an assembly of a plurality of bolts and screws.

[0039] According to a third aspect, the present invention provides an aircraft including a cryogenic tank fitted with a removable closure according to the first aspect of the invention.

[0040] The features and advantages described with respect to the removable closure also pertain to the cryogenic tank, and vice versa.

[0041] Exemplary embodiments of the present invention that will demonstrate further advantages and features are described in detail below with reference to the drawings. [Brief explanation of the drawings]

[0042] [Figure 1] 1 shows an aircraft equipped with a cryogenic tank. [Figure 2] 1 is a cross-sectional view of a portion (e.g., top) of a cryogenic tank with an access opening and a closure for the access opening, the access opening and closure being in a closed position. [Figure 3] 3 is a cross-sectional view similar to FIG. 2, with the access opening and closure in an open position. [Figure 4] FIG. 1 is a view of a cryogenic tank with the access opening and closure closed. [Figure 5] FIG. 10 is an enlarged cross-sectional view of the tank access portion in an open state. [Figure 6]FIG. 10 is an enlarged cross-sectional view of the tank access portion in a closed state. DETAILED DESCRIPTION OF THE INVENTION

[0043] In the drawings, similar or identical elements and features are marked with the same reference numbers.

[0044] 1, the aircraft 30 includes a fuselage 32. The aircraft 30 further includes a pair of wings 34 attached to the fuselage 32. Furthermore, each wing 34 has an engine 36 attached thereto.

[0045] The aircraft 30 includes an aft fuselage 38 that includes a horizontal stabilizer and a vertical stabilizer. Additionally, the aircraft 30 includes a tank arrangement 40 (a combined arrangement including tanks and ancillary equipment). The tank arrangement 40 preferably includes a cryogenic tank 10 located in the aft fuselage 38. It should be noted that the cryogenic tank 10 may have a different shape and / or be located in different parts of the aircraft 30.

[0046] Tank 10 contains hydrogen fuel that can be supplied to engine 36. The hydrogen fuel can be supplied to a fuel cell (not shown) where the hydrogen is converted to electrical energy that is supplied to engine 36. The hydrogen fuel is stored in tank 10 in the form of a cryogenic liquid, or liquid hydrogen (LH2).

[0047] 2-6, a preferred embodiment of the cryogenic tank 10 and a preferred embodiment of a removable closure 48 for the cryogenic tank will now be described in more detail.

[0048] Cryogenic tank 10 includes (1) a multi-layer tank wall 42, (2) an access opening 44 in multi-layer tank wall 42 that allows access to an interior 46 of cryogenic tank 10 for maintenance or repair, and (3) a closure 48 or cap for closing access opening 44.

[0049] In the illustrated embodiment, the cryogenic tank 10 is a double-walled tank 10, with the multiple tank walls 42 comprising (i) an interior tank wall skin 50, (ii) an exterior tank wall skin 52, and (iii) a tank wall vacuum insulation space 54 between the interior tank wall skin 50 and the exterior tank wall skin 52.

[0050] The closure 48 includes (i) an upper or exterior closure wall 2, (ii) a lower or interior closure wall 3, and (iii) a closure vacuum insulation space 7 between the exterior closure wall 2 and the interior closure wall 3.

[0051] The closure 48 is configured to accommodate equipment 74 required to operate the cryogenic tank 10 within the closure-vacuum insulation space 7 formed within the closure 48.

[0052] In the illustrated embodiment, the access opening 44 is located at the top of the cryogenic tank 10. Figure 2 shows a cross-sectional view of this top in a closed state, Figure 3 shows a cross-sectional view in an open state, Figure 4 shows a perspective view in a closed state, Figure 5 shows an enlarged cross-sectional view of the tank access in an open state, and Figure 6 shows an enlarged cross-sectional view of the tank access in a closed state.

[0053] In the illustrated embodiment, the closure 48 forms or includes a panel 56 (specifically, a double-walled access panel) that includes an exterior closure wall 2 and an interior closure wall 3 (also referred to as an outer panel wall and an inner panel wall). The closure vacuum insulated space 7 is also referred to as a panel vacuum insulated space.

[0054] The interior closure wall 3 is spaced a distance D from the exterior closure wall 2 such that when the access opening 44 is closed by the removable closure 48, at least a portion of the closure vacuum insulation space 7 is located within the interior 46 of the cryogenic tank 10. In this manner, at least a portion of the closure vacuum insulation space 7 is surrounded by the cryogenic medium within the interior 46 of the cryogenic tank 10 and is thereby fully insulated.

[0055] In the illustrated embodiment, the inner side closure wall 3 is located at the bottom of the removable closure 48. This creates a very large vacuum space that is used to install the equipment 74 of the cryogenic tank 10.

[0056] The removable closure 48 includes a ring wall 4 formed in a tubular (particularly cylindrical) shape, which connects the outer closure wall 2 and the inner closure wall 3 to form a closure vacuum insulation space 7.

[0057] The ring wall 4 is attached to a closure flange 1 formed as a flange ring and is used to fasten a removable closure 48 to a tank flange 11 also formed as a flange ring. The tank flange 11 is attached to a cryogenic tank 10.

[0058] The ring wall 4 of the closure 48, the outer closure wall 2 located at the upper end of the closure 10, and the inner closure wall 3 located at the lower end of the closure 10 are welded together to form a closure vacuum insulation space 7. This closure vacuum insulation space 7 is also called a panel vacuum space or a panel vacuum insulation space.

[0059] A plurality of pipes 20, 22 extend into the tank 10 and through the closure 48. These pipes 20, 22 extend from the exterior of the closure 48, through the exterior closure wall 2, and into the closure vacuum insulated space 7.

[0060] The equipment actuator 73 is located outside the tank 10 and closure 48 and is connected to the interior 46 of the tank 10 by pipes 20,22.

[0061] The pipe 22 extends through the closure / vacuum insulated space 7, through the inner side / closure wall 3 and into or through the interior 46 of the cryogenic tank.

[0062] The removable closure 48 further includes a vacuum port 8 for evacuating the closure / vacuum insulation space 7. Air is exhausted from the vacuum port 8, creating a vacuum in the vacuum insulation space 7 formed inside the closure 48.

[0063] A heat insulating material formed as a multilayer insulation (MLI) is fitted inside the closure / vacuum insulation space 7. The multilayer insulation (MLI) suppresses heat radiation by alternately stacking metal-coated plastic films, such as aluminum-deposited polyimide films, and spacers.

[0064] On one side of the multi-tank wall 42 is a tank flange 11. The tank flange 11 is attached to the multi-tank wall 42 and abuts against a closure flange 1. The closure flange 1 is also called a panel flange. Seals 12 (particularly cryogenic seals / gaskets) are installed between the tank flange 11 and the closure flange 1. These flanges 1, 11 are bolted together by a plurality of bolt and screw assemblies 13.

[0065] In some embodiments, the multi-wall tank wall 42 includes a multi-wall tank ring 64 (a cylindrical multi-wall, such as a double-walled cylinder, that defines the access opening 44 in the tank body), which includes (1) an outer tank ring wall arrangement 14, 15 (a combination of outer tank walls located outside and inside the tank, respectively), (2) an inner tank ring wall 16 (an inner tank wall), and (3) a tank ring vacuum insulation space 66 between the outer tank ring walls 14, 15 and the inner tank ring wall 16.

[0066] In some embodiments, the outer tank ring wall arrangement 14, 15 includes an inner tank ring wall 14 disposed on the inner side of the inner tank wall skin 50 and an outer tank ring wall 15 disposed on the outer side of the outer tank wall skin 52.

[0067] 5 and 6, the multi-walled tank ring 64 forms a kind of shaft connected to the tank flange 11. This shaft is composed of (1) an inner / outer tank ring wall 14 (e.g., a lower outer ring made from the tank wall material), (2) an outer / outer tank ring wall 15 (e.g., an upper outer ring made from the tank wall material), (3) an inner tank ring wall 16 (e.g., an inner ring made from the tank wall material), and (4) an inner closure plate 17 or end plate (e.g., a lower closure plate made from the tank wall material, which closes the end of the multi-walled tank ring 64 on the tank interior side). The other end of the multi-walled tank ring 64 (the end on the tank exterior side) is sealed and closed by the tank flange 11.

[0068] The surface of the closure ring wall 4 forming the outer cylinder surface or outer tube surface and the surface of the inner tank ring wall 16 forming the inner cylinder surface or inner tube surface are smooth surfaces, forming a tight fit similar to the fit used in so-called Johnston couplings for cryogenic fluid piping.

[0069] All of the face members 11, 14, 15, 16, 17, 50 and 52 that make up the tank body may be welded together to form the multi-layer tank wall 42. The access opening 44 is defined by a multi-wall tank ring 64.

[0070] Within the multiple tank walls 42, a single inter-tank wall space 18 is formed. In other words, the vacuum insulated spaces 54, 66 between the inner and outer tank wall skins 50, 52 and between the tank ring walls 14, 15, 16 are combined into the single inter-tank wall space 18. This inter-tank wall space 18 is also insulated by multi-layer insulation (MLI - details not shown).

[0071] The closure-insulating vacuum space 7 together with the tank wall-insulating vacuum spaces 54, 66 form part of the insulating structure of the cryogenic tank 10.

[0072] The piping 20, 22 extending into the cryogenic tank 10 extends through the access panel 56, i.e., through the closure 48 and the closure-insulated vacuum space 7 formed therein. Therefore, it is not necessary to double-wall the pipes 20, 22 to minimize heat ingress along the pipes 20, 22.

[0073] The pipes 20, 22 can also function as structural support, i.e., the pipes 20, 22 ensure the distance D between the exterior wall panel 2 and the interior wall panel 3.

[0074] A cryogenic tank 10 for an aircraft 30 is described above, which provides tank access for maintenance, inspection, and repair of the interior of the tank on board the aircraft 30. The access opening 44 is closed by a removable closure 48, which includes or forms a multi-wall panel 56. When closed, the multi-wall panel 56 forms a vacuum insulated space 7 for the tank 10, minimizing heat ingress into the cryogenic tank 10.

[0075] The equipment 74 associated with the cryogenic tank 10 is, for example, equipment necessary for the operation of the cryogenic tank 10, such as piping, sensors, level gauges, etc., and is placed within the vacuum insulated space 7 in the removable closure 48 of the cryogenic tank 10.

[0076] The present invention improves the installation of systems in liquid hydrogen tanks. Such tanks typically have an equipment capsule that houses tank equipment (valves, sensors, etc.), which is traditionally either attached to the tank or installed separately from the tank. The present invention provides an improved technical solution for such capsules. The present invention is particularly applicable to hydrogen-fueled aircraft. [Explanation of symbols]

[0077] 1 Closure flange 2 Upper Enclosure Wall / External Enclosure Wall 3 Lower or inner closing wall 4 Closure ring wall / tube 7 Closures and vacuum insulation spaces 8 vacuum ports 10 Cryogenic Tank 11 Tank flange 12 Seals 13 Bolt and screw arrangement 14 Inside of outer tank ring wall 15 Outside of outer tank ring wall 16 Inner tank ring wall 17 Inner Closure Plate 18 Vacuum space between tank walls 20, 22 Pipes 30 aircraft 32 Aircraft (fuselage) 34 Wings 36 Engine 38 Rear fuselage section 40 Tank Arrangement 42 Multiple tank walls (e.g. double tank walls) 44 Access opening 46 Inside the Tank 48 Obturator 50 Inner side tank wall skin 52 External side tank wall skin 54 Tank wall / insulation space 56 Panels 64 Multi-wall tank ring 66 Tank ring / vacuum insulation space 74 Equipment 73 Equipment Actuators D distance

Claims

1. A removable closure for a cryogenic tank (10), comprising: The cryogenic tank (10) a tank interior (46) for storing a cryogenic medium; an access opening (44) in the multiple tank wall (42); The multi-layer tank wall (42) includes a tank wall vacuum insulation space (54) between an interior tank wall skin (50) and an exterior tank wall skin (52); The removable closure (48) includes an exterior closure wall (2), an interior closure wall (3), and a closure vacuum insulation space (7) between the exterior closure wall (2) and the interior closure wall (3); The removable closure (48) is configured to install equipment (74) required to operate the cryogenic tank (10) within a closure-vacuum insulation space (7) formed within the removable closure (48).

2. 2. A removable closure according to claim 1, characterized in that the inner closure wall (3) is spaced a distance (D) from the outer closure wall (2) so that at least a portion of the closure vacuum insulation space (7) is located within the cryogenic tank (10) when the access opening (44) is closed.

3. 3. A removable closure according to claim 1 or 2, characterized in that the inner side closure wall (3) is arranged at the bottom of the removable closure (48).

4. The removable closure (48) a ring wall (4) connecting the outer closure wall (2) and the inner closure wall (3) to form a closure vacuum insulation space (7); A removable closure according to any one of claims 1 to 3, characterized in that it comprises a closure flange (1) attached to the ring wall (4) for fixing the removable closure (48) to a tank flange (11) attached to the cryogenic tank (10).

5. One or more pipes (20, 22) 5.

1. Extending through the exterior enclosure wall (2) into the enclosure vacuum insulation space (7), and / or 5.

2. Extending through the closure vacuum insulation space (7) and the interior closure wall (3), and / or 5.

3. A removable closure according to any one of claims 1 to 4, characterized in that it extends into or through the interior (46) of the cryogenic tank (10) when it is closed.

6. A removable closure according to any one of claims 1 to 5, characterized in that it comprises a vacuum port (8) for evacuating the closure vacuum insulation space (7).

7. A removable closure according to any one of claims 1 to 6, characterized in that a multi-layer insulation material is fitted into the closure vacuum insulation space (7).

8. a multi-layer tank wall (42); an access opening (44) in the multi-tank wall (42) that allows access to the interior (46) of the cryogenic tank (10) for maintenance, repair, and / or replacement work; a removable closure (48) for closing the access opening (44); The multi-layer tank wall (42) comprises an interior tank wall skin (50), an exterior tank wall skin (52), and a tank wall vacuum insulation space (54) between the interior tank wall skin (50) and the exterior tank wall skin (52); A cryogenic tank, wherein the removable closure (48) is configured as claimed in any one of claims 1 to 7.

9. The access opening (44) in the multi-wall tank wall (42) is surrounded and defined by a multi-wall tank ring (64); 9. The cryogenic tank according to claim 8, wherein the multi-wall tank ring (64) comprises an outer tank ring wall arrangement (14, 15), an inner tank ring wall (16), and a tank ring vacuum insulation space (66) formed between the outer tank ring wall (14, 15) and the inner tank ring wall (16).

10. 10.

1. The ends of the multi-walled tank ring (64) are sealed, and / or 10.

2. The outer tank wall arrangement (14, 15) comprises an inner outer tank wall (14) arranged on the inner side of the inner tank wall skin (50) and an outer outer tank wall (15) arranged on the outer side of the outer tank wall skin (52); and / or 10.

3. A cryogenic tank as claimed in claim 9, characterized in that the outer tank ring wall arrangement (14, 15) is hermetically connected to the outer tank wall skin (50) and the inner tank wall skin (52), so that the tank wall vacuum insulation space (54) and the tank ring vacuum insulation space (66) are in fluid communication with each other and / or form a single inter-tank wall vacuum space (18).

11. 11. The cryogenic tank according to any one of claims 8 to 10, characterized in that the access opening (44) comprises a tank flange (11) and the closure (48) comprises a closure flange (1) mating with the tank flange (11), so that in the closed state the closure flange (1) is sealingly connected to the tank flange (11), in particular by means of a plurality of bolt and screw assemblies (13).

12. A cryogenic tank (10) comprising a removable closure (48) according to any one of claims 1 to 7, and / or an aircraft comprising a cryogenic tank (10) according to any one of claims 8 to 11.

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