Liquid hydrogen storage device

Abstract

According to a first aspect, the present disclosure relates to a liquid hydrogen storage device (1), comprising a liquid hydrogen tank and a cooling system, the tank (9) comprising: a cavity (11) delimited by an inner wall (2), the cavity (11) being configured to receive liquid hydrogen at a temperature (TH) lower than an ambient temperature (TA) of the air around the tank (9), a first wall (5) disposed around the inner wall (2) and delimiting a void space (8) between the inner wall and the first wall (5), the cooling system comprising at least one pipe (13) located outside the cavity (11) and in contact with the inner wall (2), the pipe (13) being configured to circulate liquid nitrogen at an inner wall temperature (TPI) greater than or equal to the temperature of the liquid hydrogen (TH) and lower than the ambient temperature (TA),the internal wall temperature (TPI) being preferentially higher than the liquid hydrogen temperature (TH) by less than 60 Kelvin. Abbreviated figure: Fig. 1,

Description

Title of the invention: Liquid hydrogen storage device FIELD OF INVENTION

[0001] The invention relates to the storage and transport of liquid hydrogen in tanks, and more particularly to the management of heat flows between the liquid hydrogen and the ambient air located around the tank. STATE OF THE ART

[0002] Hydrogen occurs naturally in its diatomic form (H2), in liquid or gaseous form. In the following, the terms "liquid hydrogen" and "gaseous hydrogen" will be used to refer to dihydrogen in its liquid and gaseous forms, respectively.

[0003] In order to store or transport a large mass of hydrogen in a limited volume, several solutions are known from the prior art. First, it is possible to store hydrogen in its gaseous form under high pressure, thereby increasing its density and allowing a given mass of hydrogen to be stored in a tank of limited volume. However, compressing hydrogen consumes a great deal of energy, and storing it in pressurized form presents risks of leaks, detonation, or deflagration, so particularly robust materials for constructing the tanks and strict controls are necessary. Furthermore, compression presents operational constraints, especially for large quantities of hydrogen (for example, long and complex filling of tanks with a capacity exceeding 100 kg).

[0004] It is also known to store or transport hydrogen in liquefied form. Indeed, since the density of gaseous hydrogen is approximately 0.09 g / L, while that of liquid hydrogen is 71 g / L at atmospheric pressure, the volume required to store an equivalent mass of hydrogen in its gaseous form is reduced by nearly 800 times. The volume reduction is significantly greater than that obtained by simply pressurizing gaseous hydrogen: at 700 bar, the density of gaseous hydrogen is only about 40 g / L. Furthermore, storing hydrogen in liquid form solves some of the problems discussed previously: liquid hydrogen can be stored at ambient pressure, reducing the risks associated with the high pressure of pressurized gaseous hydrogen.

[0005] However, the storage and transport of hydrogen in liquid form have their own drawbacks. Indeed, the condensation point of hydrogen is approximately 20 Kelvin (equivalent to approximately -253°C) at a pressure of 1 bar (atmospheric pressure). When filling a tank with hydrogen Because the hydrogen is liquid, there is a significant difference between the temperature of the tank before filling, which is close to ambient temperature, and the much lower temperature of the liquid hydrogen. When the liquid hydrogen at -253°C is poured into the tank, this temperature difference creates a heat flow between the hydrogen and the inner wall of the tank, which vaporizes some of the liquid hydrogen. Depending on the tank's design, the amount of hydrogen lost in this way can be substantial, typically ranging from one-third to one-half of the stored hydrogen volume, or even more when the tank is particularly thick.

[0006] A known prior art solution consists of first cooling the tank before filling it with liquid hydrogen: the tank is filled with liquid nitrogen to cool it to an intermediate temperature (around -200°C) between that of the liquid hydrogen and the ambient temperature. During filling with liquid hydrogen, the tank wall is then at a temperature close to -200°C and is no longer at ambient temperature. The heat flux between the inner wall of the tank at -200°C and the liquid hydrogen at -250°C is therefore low, resulting in similarly low hydrogen losses by evaporation. However, the presence of residual liquid nitrogen in the tank can cause the formation of solid nitrogen crystals that contaminate the hydrogen.Before filling with liquid hydrogen and following the initial cooling with liquid nitrogen, it is therefore necessary to purge the nitrogen used for cooling using significant quantities of helium or gaseous hydrogen, which in itself represents a considerable cost. The need to perform this purging thus mitigates the advantage provided by the reduction in heat flow between the inner wall and the liquid hydrogen. Description of the invention

[0007] One objective of the present application is to enable the filling of a liquid hydrogen tank while limiting hydrogen evaporation due to the temperature difference between the hydrogen and the inner wall of the tank during the cooling phase

[0008] Another objective of the present application is to eliminate the need to purge a gas used to cool the tank prior to filling it.

[0009] To this end, the present disclosure relates, in a first aspect, to a liquid hydrogen storage device, comprising a liquid hydrogen tank and a cooling system, the tank comprising: • a cavity delimited by an internal wall, the cavity being configured to receive liquid hydrogen at a temperature lower than the ambient temperature of the air around the reservoir, • a first wall arranged around the inner wall and defining an empty space between the inner wall and the first wall,

[0010] the cooling system comprising at least one pipe located outside the cavity and in contact with the inner wall, the pipe being configured to circulate liquid nitrogen at an inner wall temperature greater than or equal to the temperature of liquid hydrogen and less than the ambient temperature, the inner wall temperature being preferably greater than the temperature of liquid hydrogen by less than 60 Kelvin.

[0011] According to one embodiment, the hydrogen storage device further comprises at least one second pipe in contact with the first wall and configured to circulate liquid nitrogen at a temperature intermediate between the ambient temperature and the temperature of the liquid hydrogen.

[0012] According to one embodiment, the cooling system comprises several pipes, each pipe being either connected to a respective liquid nitrogen reservoir, or connected to a single nitrogen reservoir common to all the pipes, the pipes being in contact with different parts of the inner wall.

[0013] According to one embodiment, the hydrogen storage device comprises several liquid hydrogen tanks, the hydrogen storage device further comprising a separate cooling system for each liquid hydrogen tank, the same liquid nitrogen tank being connected to each of the cooling systems by a separate pipeline.

[0014] A second aspect of this disclosure relates to a method for filling a liquid hydrogen tank, the tank comprising: • a cavity delimited by an internal wall, the cavity being configured to receive liquid hydrogen at a temperature lower than the ambient temperature of the air around the reservoir, • a first wall arranged around the inner wall and defining an empty space between the inner wall and the first wall,

[0015] the process comprising a step of circulating liquid nitrogen in at least one pipe located outside the cavity and in contact with the inner wall, the circulation step beginning before a step of filling the tank with liquid hydrogen, the liquid nitrogen having an inner wall temperature greater than or equal to the temperature of the liquid hydrogen and lower than the ambient temperature.

[0016] According to one embodiment of the process, the pipeline is connected to a liquid nitrogen tank during the circulation step, the liquid nitrogen tank being disconnected from the pipeline after completion of the circulation step.

[0017] According to one embodiment of the process, the hydrogen temperature and / or the internal wall temperature is substantially equal to 20 Kelvin after completion of the filling step

[0018] According to one embodiment of the process, the temperature of the liquid hydrogen is approximately equal to 20 Kelvin, the internal wall temperature being approximately equal to 77 Kelvin. DESCRIPTION OF THE FIGURES

[0019] Other features, objectives and advantages of the invention will become apparent from the following description, which is purely illustrative and not limiting, and which should be read in conjunction with the accompanying drawings on which: - Figure [1] schematically illustrates a liquid hydrogen storage device according to a first aspect of the invention, - Fig. 2 schematically illustrates a liquid hydrogen storage device according to a second aspect of the invention.

[0020] In all figures, identical reference symbols designate the same elements.

[0021] DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0022] Figure 1 represents, according to a first aspect of the invention, a liquid hydrogen storage device 1. It comprises a reservoir 9 having an internal cavity 11, configured to hold a volume of liquid hydrogen at a temperature TH lower than the ambient air temperature TA surrounding the reservoir 9, at least in a part of the cavity 11. The hydrogen contained in the cavity 11 may be two-phase, that is to say, contain a phase of liquid hydrogen and a phase of gaseous hydrogen, the gaseous hydrogen in particular resulting from the evaporation of the liquid hydrogen contained in the cavity 11. The internal cavity 11 is delimited by an internal wall 2.

[0023] To prevent the inner wall 2 from being subjected to a significant temperature gradient between, on the one hand, the ambient outside air temperature TA and the temperature TH of the hydrogen in the inner cavity 11, a first wall 5 surrounds the inner wall 2 such that a void 8 exists between the inner wall 2 and the first wall 5. This void 8 creates a buffer zone between the inner cavity 11 and the ambient air, this buffer zone having a temperature between the temperature of the liquid hydrogen TH and the ambient temperature TA, and ensuring thermal insulation between the liquid hydrogen and the air surrounding the first wall 5. It is possible to provide multi-layer insulation comprising a plurality of layers of thin sheets in the void 8, so as to limit the heat transfer by radiation between the inner wall 2 and the first wall 5.

[0024] Alternatively, the empty space 8 can be filled with perlite beads, which also provide radiative thermal insulation between the inner wall 2 and the first wall 5.

[0025] The storage device 1 further includes a cooling system. The cooling system includes at least one pipe 13, which is in contact with the inner wall 2, outside the inner cavity 11. The pipe 13 is configured to allow the circulation of liquid nitrogen at an inner wall temperature TP1, so as to impose a desired temperature on the inner wall 2. This inner wall temperature TP1 is intermediate between the temperature of liquid hydrogen TH and lower than the ambient temperature TA.

[0026] Liquid nitrogen is injected into the pipe 13 before filling the tank 9 with liquid hydrogen in order to carry out an initial cooling.

[0027] The conduit 13 can have several different geometries depending on the application. The conduit 13 can have any geometry suitable for carrying liquid nitrogen and coming into contact with the inner wall 2. It can be a conduit wound around the inner wall 2, as shown in [Fig. 1]. Alternatively, it can be a honeycomb structure, and / or a waffle plate type structure.

[0028] Thus, during the filling of the tank 9 with liquid hydrogen, the cooling system reduces the temperature of the inner wall, in particular by approximately -200°C, and therefore minimizes the temperature difference between the inner wall 2 and that of the liquid hydrogen, in particular by approximately 60°C, reducing the proportion of hydrogen that evaporates during filling. No foreign molecules are introduced into the internal cavity 11, so there is no risk of contamination of the liquid hydrogen by residues of such molecules. Consequently, no purging of the internal cavity 11 is necessary after filling is complete.

[0029] Preferably, the internal wall temperature TP1 is substantially equal to the temperature of the liquid hydrogen, so as to minimize as much as possible the heat flux between the internal wall 2 and the liquid hydrogen.

[0030] According to one embodiment, shown in [Fig. 2], the storage device 1 comprises a second pipe 4 independent of the pipe 13. The second pipe 4 is in contact with the first wall 5 and configured to allow the circulation of liquid nitrogen at an intermediate temperature Ti between the ambient temperature TA and the temperature TH of the liquid hydrogen. When it is desired to transport the storage device 1 in a vehicle, this pipe makes it possible to maintain the intermediate temperature Ti at a desired value.

[0031] According to the Stefan-Boltzmann law, the radiative heat transfer between an object at absolute temperature T and its environment at absolute temperature TE is proportional to the difference between the fourth powers of these temperatures (T4 - Te4). Thus, thanks to the second channel 13, the radiative heat transfer between the hydrogen and the first wall 5 is proportional to the value (T / - TH4), whereas in the absence of the cooling system, it is proportional to the value (TA4 - TH4), which can be considerably higher. This prevents the evaporation of liquid hydrogen in the internal cavity 11 during its transport, which necessitates degassing to reduce the hydrogen pressure in the internal cavity. These degassings result in a mass loss of hydrogen during transport.

[0032] The first wall 5 can be the outer wall 12, or be an intermediate wall extending between the inner wall 2 and the outer wall 12, as shown in [Fig. 2]. In this second case, a void exists on each side of the first wall 5.

[0033] The second pipe 13 can be fluidically connected to a liquid nitrogen reservoir 10. Alternatively, the cooling system can comprise several separate pipes 13, each pipe 13 being fluidly connected to a separate liquid nitrogen reservoir 10. In this case, the pipes 13 can be in contact with different parts of the inner wall 2. Alternatively, the cooling system can comprise several separate pipes 13, each pipe 13 being fluidly connected to a single liquid nitrogen reservoir 10 common to all the pipes 13.

[0034] The liquid nitrogen tank 10 can be removed. Indeed, once the tank 9 has been filled, it is not necessary for it to remain connected to the tank 10.

[0035] According to one embodiment, the hydrogen storage device comprises several tanks 9 as described above, each tank 9 being associated with a cooling system, the different cooling systems being connected to the same liquid nitrogen tank 10, each via a separate pipeline 13.

[0036] According to another aspect, the invention relates to a method for filling a liquid hydrogen tank. The tank comprises an internal cavity 11 delimited by an internal wall 2 and capable of receiving hydrogen at a temperature TH lower than the ambient temperature TA of the air around the tank 9. The tank further comprises a first wall 5 disposed around the internal wall, with a void space 8 extending between the internal wall 2 and the first wall 5. The method includes a step of circulating liquid nitrogen at an internal wall temperature TP1 in a pipe 13 – optionally several pipes 13 – located outside the internal cavity 11 and in contact with the internal wall 2. This circulation begins before filling the tank 9, so as to allow the inner wall 2 to reach a desired temperature, significantly lower than the ambient temperature TA and preferably as close as possible to the temperature of liquid hydrogen TH.

[0037] According to one embodiment of the process, the pipeline 13 is connected to a liquid nitrogen tank 10 during the circulation phase, this tank 10 being removable. In other words, the tank 10 can be disconnected from the pipeline 13 after the circulation phase is complete.

[0038] According to one embodiment of the process, the TH temperature of hydrogen is approximately 20 Kelvin (or -253 °C). This temperature, close to the boiling point of hydrogen, allows the hydrogen to be kept in a liquid state while minimizing heat transfer between it and the ambient air.

[0039] According to one embodiment of the process, the internal wall temperature TP1 is approximately 20 Kelvin when the tank is filled with liquid hydrogen, i.e. after completion of the filling step.

[0040] According to one embodiment of the process, the internal wall temperature TP1 is approximately equal to 77 Kelvin, or -196°C. This temperature minimizes the temperature difference between the internal wall and the liquid hydrogen, which is then approximately 57 Kelvin only for liquid hydrogen at 20 Kelvin, while having an internal wall temperature TP1 that remains more easily attainable than the temperature of the hydrogen itself.

[0041] According to one embodiment of the process, after completion of filling, the pipe 13 that received the liquid nitrogen is subjected to treatment. This treatment may include purging with nitrogen, or replacing the nitrogen with helium.

[0042] According to one embodiment of the process, during filling, the pipeline 13 is supplied with nitrogen gas so as to limit the difference between the pressure in the pipeline 13 and the pressure in the tank 9.

[0043] The storage device 1 and the method for filling a tank have been described in relation to liquid hydrogen. However, they can also be applied to liquid helium or liquid argon.

Claims

Demands

1. A liquid hydrogen storage device (1) comprising a plurality of liquid hydrogen tanks and a separate cooling system for each tank, each tank (9) comprising: • a cavity (11) delimited by an inner wall (2), the cavity (11) being configured to receive liquid hydrogen at a temperature (TH) lower than an ambient temperature (Ta) of the air around the tank (9), • a first wall (5) disposed around the inner wall (2) and delimiting a void (8) between the inner wall and the first wall (5), each cooling system comprising at least one pipe (13) connected to the same liquid nitrogen tank, the pipe (13) being located outside the cavity (11) and in contact with the inner wall (2),the pipeline (13) being configured to circulate liquid nitrogen at an internal wall temperature (TP1) greater than or equal to the temperature of liquid hydrogen (TH) and less than the ambient temperature (TA), the internal wall temperature (TP1) being preferably greater than the temperature of liquid hydrogen (TH) by less than 60 Kelvin.

2. Liquid hydrogen storage device according to claim 1, further comprising at least a second channel (4) in contact with the first wall (5) and configured to circulate liquid nitrogen at an intermediate temperature (TO) between the ambient temperature (TA) and the temperature (TH) of the liquid hydrogen.

3. Liquid hydrogen storage device according to any one of claims 1 and 2, the cooling system comprising several pipes (13), each pipe (13) being either connected to a respective liquid nitrogen reservoir (10), or connected to a single nitrogen reservoir (10) common to all the pipes (13), the pipes (13) being in contact with different parts of the inner wall (2).

4. A method for filling a liquid hydrogen tank (9), the tank comprising: • a cavity (11) delimited by an internal wall (2), the cavity (11) being configured to receive liquid hydrogen at a temperature (TH) lower than an ambient temperature (Ta) of the air around the reservoir (9), • a first wall (5) disposed around the internal wall (2) and delimiting a void space (8) between the internal wall and the first wall (5), the process comprising a step of circulating liquid nitrogen in at least one pipe (13) located outside the cavity (11) and in contact with the internal wall (2), the circulation step beginning before a step of filling the reservoir (9) with liquid hydrogen, the liquid nitrogen having an internal wall temperature (TP1) greater than or equal to the temperature of the liquid hydrogen (TH) and lower than the ambient temperature (TA).

5. Method of filling a liquid hydrogen tank (9) according to the preceding claim, the pipeline (13) being connected to a liquid nitrogen tank (10) during the circulation step, the liquid nitrogen tank (10) being disconnected from the pipeline (13) after completion of the circulation step.

6. A method for filling a liquid hydrogen tank (9) according to any one of claims 4 and 5, wherein the hydrogen temperature (TH) and / or the internal wall temperature (TP1) is substantially equal to 20 Kelvin after completion of the filling step

7. Method of filling a tank (9) with liquid hydrogen according to any one of claims 4 to 6, the temperature of the liquid hydrogen (TH) being substantially equal to 20 Kelvin, the internal wall temperature (TP1) being substantially equal to 77 Kelvin.

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