Method for filling a tank with liquid hydrogen and associated storage device

Abstract

The present disclosure relates to a method for filling a tank (9) with liquid hydrogen, the tank comprising: o 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 tank (9), o a first wall (5) disposed around the internal wall (2) and delimiting an empty space (8) between the internal wall and the first wall (5), the method 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 starting before a step of filling the tank (9) with liquid hydrogen, the liquid nitrogen producing an internal wall temperature (TPI) greater than or equal to the temperature of the liquid hydrogen (TH) and lower than the ambient temperature (TA).

Description

[0001] DESCRIPTION

[0002] METHOD FOR FILLING A LIQUID HYDROGEN TANK AND ASSOCIATED STORAGE DEVICE

[0003] FIELD OF THE INVENTION

[0004] The invention relates to the storage and transport of liquid hydrogen in tanks, and more particularly to the management of thermal flows between the liquid hydrogen and the ambient air located around the tank.

[0005] STATE OF THE ART

[0006] Hydrogen occurs naturally in its diatomic form (H2), in liquid or gaseous form. In all that follows, the terms "liquid hydrogen" and "gaseous hydrogen" will be used to refer to dihydrogen in its liquid and gaseous form respectively.

[0007] In order to be able to store or transport a large mass of hydrogen in a limited volume, several solutions are known from the state of the art. Firstly, it is possible to store hydrogen in its gaseous form under high pressure, so as to increase its density, and to allow a given mass of hydrogen to be stored in a tank of limited volume. However, the compression of hydrogen consumes a lot of energy, and its storage in pressurized form presents risks of leaks, detonation or deflagration, so that particularly robust materials to form the tanks and strict control are necessary. In addition, compression presents constraints of use, particularly for large quantities of hydrogen (long and complex filling for tanks with a capacity greater than 100 kg for example)

[0008] 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, this reduces the volume required to store an equivalent mass of hydrogen in its gaseous form by nearly 800 times. The volume gain is significantly greater than that obtained by simple pressurization of gaseous hydrogen: at 700 bars, the density of gaseous hydrogen is only approximately 40 g / L. In addition, 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.

[0009] Storing and transporting hydrogen in liquid form, however, has its 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 liquid hydrogen, there is therefore a significant difference between the temperature of the tank before filling, close to ambient temperature, and the much lower temperature of liquid hydrogen. When 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 structure of the tank, the amount of hydrogen lost can be significant, typically up to a third to half of the volume of hydrogen stored, or even more when the tank used is particularly thick.

[0010] A known state-of-the-art solution consists of carrying out an initial cooling of the tank before filling it with liquid hydrogen: the tank is filled with liquid nitrogen so as to cool it to an intermediate temperature (around -200°C) between that of the liquid hydrogen and ambient temperature. When filling with liquid hydrogen, the wall of the tank is then at a temperature close to -200°C and is no longer at ambient temperature. The heat flow between the internal wall of the tank at -200°C and the liquid hydrogen at -250°C is then low, resulting in equally low losses of hydrogen by evaporation. However, the presence of residual liquid nitrogen in the tank can cause the formation of solid nitrogen crystals which contaminate the hydrogen.Before filling with liquid hydrogen and following the first cooling with liquid nitrogen, it is therefore necessary to purge the nitrogen used for cooling by using significant quantities of helium or gaseous hydrogen, which in itself represents a significant cost. The need to carry out a purge therefore tempers the advantage provided by the reduction of the heat flow between the internal wall and the liquid hydrogen.

[0011] STATEMENT OF THE INVENTION

[0012] An objective of the present application is to allow the filling of a liquid hydrogen tank by limiting the evaporation of the hydrogen due to the temperature difference between it and the internal wall of the tank during the cooling phase.

[0013] Another objective of the present application is to avoid the need to purge a gas used to cool the tank before filling it.

[0014] To this end, the present disclosure relates, according to a first aspect, to a liquid hydrogen storage device, comprising a liquid hydrogen tank and a cooling system, the tank comprising: o a cavity delimited by an internal wall, the cavity being configured to receive liquid hydrogen at a temperature lower than an ambient temperature of the air around the tank, o a first wall arranged around the internal wall and delimiting an empty space between the internal wall and the first wall, the cooling system comprising at least one pipe located outside the cavity and in contact with the internal wall, the pipe being configured to circulate liquid nitrogen at an internal wall temperature greater than or equal to the temperature of the liquid hydrogen and lower than the ambient temperature,the internal wall temperature being preferentially higher than the temperature of liquid hydrogen by less than 60 Kelvin.,

[0015] 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 an intermediate temperature between ambient temperature and the temperature of liquid hydrogen. According to one embodiment, the cooling system comprises several pipes, each pipe being either connected to a respective liquid nitrogen tank or connected to a single nitrogen tank common to all the pipes, the pipes being in contact with different parts of the internal wall.

[0016] 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 pipe.

[0017] A second aspect of the present disclosure relates to a method for filling a liquid hydrogen tank, the tank comprising: o a cavity delimited by an internal wall, the cavity being configured to receive liquid hydrogen at a temperature lower than an ambient temperature of the air around the tank, o a first wall arranged around the internal wall and delimiting an empty space between the internal wall and the first wall, the method comprising a step of circulating liquid nitrogen in at least one pipe located outside the cavity and in contact with the internal wall, the circulating step starting before a step of filling the tank with liquid hydrogen, the liquid nitrogen having an internal wall temperature greater than or equal to the temperature of the liquid hydrogen and lower than the ambient temperature.

[0018] According to one implementation of the method, 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.

[0019] According to one implementation of the method, the temperature of the hydrogen and / or the internal wall temperature is substantially equal to 20 Kelvin after completion of the filling step. According to one implementation of the method, the temperature of the liquid hydrogen is substantially equal to 20 Kelvin, the internal wall temperature being substantially equal to 77 Kelvin.

[0020] DESCRIPTION OF FIGURES

[0021] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which:

[0022] - Figure 1 schematically illustrates a liquid hydrogen storage device according to a first aspect of the invention,

[0023] - Figure 2 schematically illustrates a liquid hydrogen storage device according to a second aspect of the invention.

[0024] In all figures, identical reference signs designate the same elements.

[0025] DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0026] Figure 1 represents, according to a first aspect of the invention, a liquid hydrogen storage device 1. It comprises a tank 9 provided with an internal cavity 11, configured to accommodate a volume of liquid hydrogen at a temperature T lower than the ambient temperature TA of the air surrounding the tank 9, at least in a portion of the cavity 11. The hydrogen contained in the cavity 11 may be two-phase, that is to say contain a liquid hydrogen phase and a gaseous hydrogen phase, the gaseous hydrogen being in particular derived from the evaporation of the liquid hydrogen contained in the cavity 11. The internal cavity 11 is delimited by an internal wall 2.

[0027] In order to prevent the inner wall 2 from being subjected to a significant temperature gradient between, on the one hand, the temperature of the external ambient air TA and the temperature T of the hydrogen in the inner cavity 11, a first wall 5 surrounds the inner wall 2 so that an empty space 8 exists between the inner wall 2 and the first wall 5. This empty space 8 makes it possible to create 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 T 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 empty space 8, so as to limit the heat transfer by radiation between the inner wall 2 and the first wall 5.

[0028] 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.

[0029] The storage device 1 further comprises a cooling system. The cooling system comprises 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 TRI, so as to impose a desired temperature on the inner wall 2. This inner wall temperature TPI is intermediate between the liquid hydrogen temperature T and lower than the ambient temperature TA.

[0030] Liquid nitrogen is injected into line 13 before filling tank 9 with liquid hydrogen in order to carry out an initial cooling operation.

[0031] The pipe 13 may have several different geometries depending on the uses. The pipe 13 may have any geometry capable of passing liquid nitrogen and coming into contact with the internal wall 2. It may be a conduit wound around the internal wall 2, as shown in FIG. 1. Alternatively, it may be a honeycomb structure, and / or a waffle plate type structure.

[0032] Thus, when filling the tank 9 with liquid hydrogen, the cooling system makes it possible to reduce the temperature of the internal wall, in particular by approximately -200°C, and therefore to minimize the temperature difference between the internal 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 molecule is introduced into the internal cavity 11, so there is no risk of contamination of the liquid hydrogen by residues of such a molecule. It follows that no purging of the internal cavity 11 is necessary after completion of filling.

[0033] Preferably, the internal wall temperature TPI 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.

[0034] According to one embodiment, shown in Figure 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 T 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.

[0035] According to the Stefan-Boltzmann law, the radiative heat transfer between an object of absolute temperature T and its environment of absolute temperature TE is proportional to the difference between the fourth powers of these temperatures (T 4 - T E 4). Thus, thanks to the second pipe 13, the radiative heat transfer between the hydrogen and the first wall 5 is proportional to the value (Ti 4 - T 4 ), whereas in the absence of the cooling system, it is proportional to the value (TA 4 - T 4 ) which can be considerably higher. This prevents the evaporation of liquid hydrogen in the internal cavity 11 during its transport, which requires degassing to lower the pressure of the hydrogen in the internal cavity 11 - this degassing causing a mass loss of hydrogen during transport.

[0036] The first wall 5 may be the outer wall 12, or be an intermediate wall extending between the inner wall 2 and the outer wall 12, as shown in Figure 2. In this second case, a void exists on each side of the first wall 5.

[0037] The second pipe 13 may be fluidically connected to a liquid nitrogen tank 10. Alternatively, the cooling system may comprise several separate pipes 13, each pipe 13 being fluidically connected to a separate liquid nitrogen tank 10. In this case, the pipes 13 may be in contact with different parts of the inner wall 2. Alternatively, the cooling system may comprise several separate pipes 13, each pipe 13 being fluidically connected to a single liquid nitrogen tank 10 common to all the pipes 13.

[0038] The liquid nitrogen tank 10 may be removable. Indeed, once the tank 9 has been filled, it is not necessary for it to remain connected to the tank 10.

[0039] According to one embodiment, the hydrogen storage device comprises several tanks 9 as described previously, 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 pipe 13.

[0040] 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 T lower than the ambient temperature TA of the air around the tank 9. The tank further comprises a first wall 5 arranged around the internal wall, an empty space 8 extending between the internal wall 2 and the first wall 5. The method comprises a step of circulating liquid nitrogen at an internal wall temperature TPI in a pipe 13 - possibly 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 internal wall 2 to reach a desired temperature, significantly lower than the ambient temperature TA and preferably as close as possible to the temperature of the liquid hydrogen T. H .

[0041] According to one implementation of the method, the pipe 13 is connected to a liquid nitrogen tank 10 during circulation, this tank 10 being removable. In other words, the tank 10 can be disconnected from the pipe 13 after completion of circulation.

[0042] According to one implementation of the process, the temperature T 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.

[0043] According to one implementation of the method, the internal wall temperature T Pi is approximately 20 Kelvin when the tank is filled with liquid hydrogen, i.e. after completion of the filling step.

[0044] According to one implementation of the method, the internal wall temperature T Pi is approximately equal to 77 Kelvin, or -196°C. This temperature makes it possible to minimize 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 T Pi which remains more easily achievable than the temperature of hydrogen itself.

[0045] According to one implementation of the method, after completion of filling, the pipe 13 having received the liquid nitrogen is subjected to treatment. This treatment may include purging with nitrogen, or replacing the nitrogen with helium.

[0046] According to one implementation of the method, during filling, the pipe 13 is supplied with gaseous nitrogen so as to limit the difference between the pressure in the pipe 13 and the pressure in the tank 9.

[0047] 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

CLAIMS 1. Method for filling a tank (9) with liquid hydrogen, the tank comprising: o a cavity (11) delimited by an internal wall (2), the cavity (11) being configured to receive liquid hydrogen at a temperature (T H ) lower than an ambient temperature (TA) of the air around the tank (9), o a first wall (5) arranged around the internal wall (2) and delimiting an empty space (8) between the internal wall and the first wall (5), the method 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 starting before a step of filling the tank (9) with liquid hydrogen, the liquid nitrogen having an internal wall temperature (T P i) greater than or equal to the temperature of liquid hydrogen (T H) and lower than room temperature (RT).

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

3. Method for filling a tank (9) with liquid hydrogen according to one of claims 1 and 2, the temperature of the hydrogen (T H ) and / or the internal wall temperature (T P (i) being substantially equal to 20 Kelvin after completion of the filling step 4. Method for filling a tank (9) with liquid hydrogen according to any one of claims 1 to 3, the temperature of the liquid hydrogen (TH) being substantially equal to 20 Kelvin, the internal wall temperature (TPI) being substantially equal to 77 Kelvin.

5. Device (1) for storing liquid hydrogen for implementing the method according to claim 1, comprising a plurality of liquid hydrogen tanks and a separate cooling system for each tank, each tank (9) comprising: o a cavity (11) delimited by an internal wall (2), the cavity (11) being configured to receive liquid hydrogen at a temperature (T H ) lower than an ambient temperature (TA) of the air around the tank (9), o a first wall (5) arranged around the internal wall (2) and delimiting an empty space (8) between the internal 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 internal wall (2), the pipe (13) being configured to circulate liquid nitrogen at an internal wall temperature (T Pi) greater than or equal to the temperature of liquid hydrogen (T H ) and lower than the ambient temperature (TA), the internal wall temperature (T P i) being preferentially higher than the temperature of liquid hydrogen (T H ) of less than 60 Kelvin.

6. Liquid hydrogen storage device according to claim 5, further comprising at least one second pipe (4) in contact with the first wall (5) and configured to circulate liquid nitrogen at an intermediate temperature (Ti) between the ambient temperature (TA) and the temperature (T H ) liquid hydrogen.

7. Liquid hydrogen storage device according to any one of claims 5 and 6, the cooling system comprising several pipes (13), each pipe (13) being either connected to a respective liquid nitrogen tank (10) or connected to a single nitrogen tank (10). common to all the pipes (13), the pipes (13) being in contact with different parts of the internal wall (2).

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