Hydrogen storage system and aircraft with a hydrogen storage system

Description

[0001] The invention relates to the field of hydrogen storage and more particularly to its application to aircraft using an electric propulsion system powered by hydrogen. Such a system requires the installation, on board the aircraft, of a liquid hydrogen tank for supplying hydrogen to fuel cells or a hydrogen combustion propulsion engine. To remain in the liquid state in the tank, the hydrogen must be kept at a very low temperature, of the order of -253 °C. For this, the hydrogen tank is provided with very high-performance thermal insulation. However, despite this thermal insulation, some of the hydrogen is caused to evaporate in the tank.When hydrogen from the tank is used to operate the aircraft, in particular its propulsion, this evaporation phenomenon is not a problem since the hydrogen thus evaporated is used on board the aircraft, for example to power fuel cells or a hydrogen combustion engine. On the other hand, when the aircraft is parked on the ground, the fuel cells or the hydrogen combustion engine are no longer used for the operation of the aircraft and therefore no longer consume hydrogen. As a result, the pressure in the tank increases due to the aforementioned phenomenon of hydrogen evaporation. However, in order to guarantee the integrity of the tank and prevent it from exploding, it is necessary to limit the pressure inside the tank to a pressure value lower than a maximum pressure value, for example approximately 850 bars.

[0002] One solution to this problem, devised by the inventors, would be to install a pressure monitoring system in the tank, which would control the opening of a valve when the pressure in the tank is too high, so as to release into the atmosphere a portion of the hydrogen gas contained in the tank, so as to allow a reduction in the pressure in the tank. However, to function, this monitoring system must be powered by energy, for example electricity, while the aircraft can no longer be powered electrically by the fuel cells used for the aircraft's propulsion since these fuel cells are off when the aircraft is parked on the ground. A first solution could be to power this monitoring system by means of a battery.However, this solution would be difficult to implement safely, as it would be necessary to ensure that the battery capacity would be sufficient to power the surveillance system as long as the hydrogen tank was not empty. A second solution could be to power the surveillance system using a ground-based power source, for example a "ground power unit" at the airport where the aircraft is parked. However, this solution would make the aircraft dependent on available ground resources, which could lead to difficult-to-manage situations if an airport does not have a suitable power source.

[0003] Document US2016 / 159492A1 describes a system comprising a fuel cell supplied with hydrogen from a hydrogen tank. A hybrid regulator is mounted in series on a hydrogen pipe between the hydrogen tank and the fuel cell. This hybrid regulator, whose inlet is connected to the hydrogen tank, makes it possible to regulate the pressure of the hydrogen at its outlet, connected to the fuel cell. The hybrid regulator comprises a linear actuator making it possible to adjust the value of the pressure of the hydrogen at its outlet. The hybrid regulator regulates the pressure of the hydrogen at its outlet independently of the pressure of the hydrogen at its inlet, corresponding to the pressure of the hydrogen in the tank. Consequently, the hybrid regulator is of no use in limiting the pressure inside the hydrogen tank.

[0004] Document US 10,654,592 B2 describes a hydrogen storage system according to the prior art. DISCLOSURE OF THE INVENTION:

[0005] The present invention aims in particular to provide a solution to this problem. It relates to an assembly comprising an aircraft and a hydrogen storage system, in accordance with claim 1.

[0006] Thus, since the fuel cell is permanently connected to the hydrogen tank, the fuel cell is continuously supplied with hydrogen as long as there is hydrogen in the tank. Consequently, as long as there is hydrogen in the tank, the fuel cell produces electricity to power the processing unit. This makes it possible to power the hydrogen evaporation control system autonomously and therefore guarantee its operation as long as there is hydrogen in the tank. In addition, consuming hydrogen from the tank to power the fuel cell increases the time before tank depressurization, by controlling the valve, is necessary.

[0007] Claims 2 to 7 correspond to different embodiments of the invention. DETAILED DESCRIPTION:

[0008] The invention will be better understood by reading the following description and examining the attached figures. There figure 1 schematically illustrates a hydrogen storage system. The figure 2 illustrates an aircraft equipped with a hydrogen storage system. The figure 3 schematically illustrates a hydrogen storage system, connected to an aircraft propulsion system. figure 4 illustrates a variant of the hydrogen storage system connected to the propulsion system of an aircraft. The figure 5 schematically illustrates a particular embodiment of the hydrogen storage system connected to the propulsion system of an aircraft. figure 6 schematically illustrates another particular embodiment of the hydrogen storage system connected to the propulsion system of an aircraft. figure 7 schematically illustrates another particular embodiment of the hydrogen storage system connected to the propulsion system of an aircraft. figure 8 schematically illustrates a particular mode, in accordance with the invention, of integrating a hydrogen storage system with an aircraft.

[0009] The hydrogen storage system 10 shown in the figure 1 comprises a hydrogen tank 12 (labeled "H2" in the figure), a fuel cell 14 (labeled "FC" in the figure), a processing unit 16 (labeled "Proc" in the figure), as well as a pipe 18 on which a controllable valve 22 is mounted in series. A first end of the pipe 18 is connected to the hydrogen tank 12. A second end of the pipe 18 is provided to discharge hydrogen from the hydrogen tank 12 into the atmosphere when the valve 22 is open. The fuel cell 14 is permanently connected to the hydrogen tank 12 by a pipe 21, so as to allow the production of electricity by the fuel cell 14 as long as the tank 12 contains hydrogen. The processing unit 16 is connected to the fuel cell 14 by an electrical circuit 24 provided to enable the processing unit 16 to be supplied with electricity by the fuel cell 14.The processing unit 16 is also connected at the output to a control input of the valve 22, by a connection 26, so as to allow the control, by the processing unit 16, of the opening or closing of the valve 22. Advantageously, the processing unit 16 is also connected at the input to a pressure sensor 25 by a connection 23. The pressure sensor 25 is installed so as to allow the pressure of the hydrogen in the hydrogen tank 12 to be measured. According to a first alternative, the pressure sensor 25 is installed in the hydrogen tank 12. According to another alternative, the pressure sensor 25 is installed in a hydrogen pipe connected to the hydrogen tank. The processing unit 16 comprises for example a microprocessor or a microcontroller.

[0010] In a particular embodiment, the hydrogen tank 12 is installed on board an aircraft such as the aircraft 1 shown in the figure 2 The hydrogen tank 12 is then connected, for example, to a propulsion system 3 of the aircraft by a pipe 20, such that the propulsion system 3 is supplied with energy by hydrogen from the tank 12.

[0011] The operation of the hydrogen storage system is as indicated below. As long as the hydrogen tank 12 contains hydrogen, the fuel cell 14 receives hydrogen from the tank via the pipe 21, such that the fuel cell produces electricity continuously. Consequently, the processing unit 16, electrically connected to the fuel cell 14 by the electrical circuit 24, is continuously electrically powered as long as the hydrogen tank 12 contains hydrogen. This ensures the operation of the processing unit 16 as long as the hydrogen tank 12 contains hydrogen. The processing unit 16 controls the opening or closing of the valve 22 depending on the pressure inside the hydrogen tank 12.In one embodiment, the processing unit commands the opening of the valve 22 when said pressure is greater than or equal to a first predetermined pressure threshold and it commands the closing of the valve when the pressure is less than or equal to a second predetermined pressure threshold, lower than the first pressure threshold. Thus, when the pressure inside the tank reaches the first predetermined pressure threshold due to the evaporation of hydrogen in the tank, the opening of the valve 22 makes it possible to evacuate, via the pipe 18, a portion of the hydrogen contained in the tank in gaseous form. This portion of the hydrogen is thus released into the atmosphere, which makes it possible to reduce the pressure in the hydrogen tank. The pressure in the tank thus decreases until it reaches, downwards, the second predetermined pressure threshold.The processing unit 16 then controls the closing of the valve 22 so as to stop releasing hydrogen into the atmosphere. This operation makes it possible to ensure that the value of the pressure inside the hydrogen tank does not exceed the first predetermined pressure threshold. For this, the processing unit uses, for example, as a pressure value, a pressure value acquired from the pressure sensor 25. Preferably, the processing unit monitors the pressure repeatedly, for example over a period of approximately 1 second. The value of the first pressure threshold is, for example, chosen in the interval [5 bars; 25 bars], for example 10 bars, and the value of the second pressure threshold is, for example, chosen in the interval [5 bars; 10 bars], for example 5 bars.

[0012] In one embodiment, when the hydrogen storage system 10 is connected to the propulsion system 3, the propulsion system 3 comprises an engine operating by combustion of hydrogen from the hydrogen storage system 10 via the pipe 20.

[0013] In another embodiment illustrated in the figure 3 , the propulsion system 3 comprises a set of fuel cells 34, electrically connected, by a set of electrical connections 33, to at least one electric motor 32. A propulsion propeller 30 is mechanically coupled to the electric motor 32. The fuel cells of the set of fuel cells 34 are connected at the input to the hydrogen storage system 10 via the pipe 20. The propulsion system 3 further comprises a controller not shown in the figure 3 . To enable the propulsion system 3 to operate, the controller controls the hydrogen supply to the fuel cells of the fuel cell stack 34, for example by controlling the opening of a valve mounted in series on the pipe 20. The fuel cells then produce electricity, thus enabling the motor 32 to be electrically powered, which then drives the propulsion propeller 30 in rotation.

[0014] In a variant illustrated on the figure 4 , the fuel cell 14 of the hydrogen storage system is part of the fuel cell assembly 34 electrically powering the electric motor 32. As in the embodiment illustrated in the figure 3 , the fuel cell 14 is permanently connected to the hydrogen tank by the pipe 21. The other fuel cells of the fuel cell set 34 are supplied with hydrogen by the pipe 20. This hydrogen supply is controlled by the controller of the propulsion system 3, as indicated previously. An electrical output of the fuel cell 14 electrically supplies the processing unit 16 via the electrical connection 24.

[0015] In particular, the aircraft comprises an electrical circuit configured to electrically power the electric motor 32 by the fuel cell 14 of the hydrogen storage system 10, in addition to the electrical power supply of said motor by the set of fuel cells 34. In an example illustrated in the figure 5 , this electrical circuit comprises an electrical connection 24a, as well as a contactor 28a mounted in series on this electrical connection. A first end of the electrical connection 24a is connected to an electrical output of the fuel cell 14 and a second end of said electrical connection is connected to the electric motor 32 or to a controller of said motor. The contactor 28a is controlled by the controller of the propulsion system 3. For example, the controller controls the closing of the contactor 28a during phases of use of the propulsion system 3 requiring high propulsion power, in particular during takeoff of the aircraft. This makes it possible to avoid oversizing the fuel cell assembly 34 to allow a punctual supply of maximum power during takeoff of the aircraft.

[0016] In a particular way again, as represented on the figure 6 , the aircraft further comprises a non-propulsion system 29b (labeled S in the figure) normally powered with electricity by an on-board electrical source of the aircraft (not shown in the figure), called the main electrical source, independent of the fuel cell 14 of the hydrogen storage system and of the set of fuel cells 34. The aircraft also comprises an electrical circuit configured to electrically power the non-propulsion system 29b by the fuel cell 14 of the hydrogen storage system 10 in the event of a failure of the main electrical source, in particular when the aircraft is in flight. This electrical circuit comprises an electrical connection 24b between an electrical output of the fuel cell 14 and the non-propulsion system 29b, as well as a contactor 28b mounted in series on this electrical connection.The contactor 28b is controlled, for example by an electrical core (not shown) of the aircraft, so as to close the contactor in the event of a failure of the main electrical source.

[0017] In a particular way again, as illustrated on the figure 7 , the aircraft further comprises an electrical system 29c (labeled R in the figure) separate from the processing unit 16, as well as an electrical circuit configured to electrically power this electrical system by the fuel cell of the hydrogen storage system when the aircraft is parked on the ground. This electrical circuit comprises an electrical connection 24c between an electrical output of the fuel cell 14 and the electrical system 29c, as well as a contactor 28c mounted in series on this electrical connection. The electrical system 29c is for example a system for heating the set of fuel cells 34 of the propulsion system 3, as illustrated by the arrow F in the figure. The contactor 28c is for example controlled by the processing unit 16, via a connection 25c, so as to control the closing of said contactor when the fuel cells of the set of fuel cells 34 must be heated while the aircraft is parked on the ground.

[0018] In a variant, the electrical system 29c is an electrical system external to the aircraft. The electrical connection 28c then comprises an electrical socket installed on board the aircraft (for example fixed to a wall of the fuselage 2 of the aircraft), as well as a removable electrical cable connected between this electrical socket and the electrical system 29c when the aircraft is parked on the ground.

[0019] In the realization illustrated on the figure 8, in accordance with the invention, the hydrogen storage system 10 is partially installed on board the aircraft 1. Indeed, the fuel cell 14 is then external to the aircraft, for example installed on board a service vehicle of an airport on which the aircraft is parked. An electrical socket Pe and a hydrogen pipe connector Ph are installed on board the aircraft, for example fixed to its fuselage 2. The electrical line 24 extends between the electrical socket Pe and the processing unit 16. The hydrogen pipe 21 extends between the hydrogen tank 12 and the hydrogen pipe connector Ph. When the aircraft is parked on the ground, a removable hydrogen pipe 21a, connected to the fuel cell 14, is connected to the hydrogen pipe connector Ph and a removable electrical cable 24e, connected to an electrical output of the fuel cell 14, is connected to the electrical socket Pe.This particular embodiment has the advantage of not requiring the transport of the fuel cell 14 during the flight phases of the aircraft, which makes it possible to reduce the mass of the aircraft and therefore to reduce the energy consumption necessary for its propulsion.

Claims

1. Assembly comprising an aircraft (1) and a hydrogen storage system (10) that comprises a hydrogen tank (12) and a system for controlling the evaporation of hydrogen in the hydrogen tank, the control system comprising: - a hydrogen discharge pipe (18) connected, at one end, to the hydrogen tank and, at the other end, to a controllable valve (22); and - a processing unit (16) configured to control the valve on the basis of the pressure in the tank, so as to ensure that the value of the pressure inside the hydrogen tank does not exceed a first predetermined pressure threshold; said hydrogen storage system (10) comprising - a fuel cell (14), the processing unit being electrically powered by the fuel cell, characterized in that the fuel cell (14) is permanently connected to the hydrogen tank so as to permanently produce electricity as long as there is still hydrogen in the tank, and in that the hydrogen tank (12) is installed on board the aircraft and the fuel cell (14) of the hydrogen storage system is installed in a unit that is external to the aircraft and intended to be connected to the aircraft by a removable hydrogen pipe (21a) and by a removable electrical connection (24e).

2. Assembly according to Claim 1, characterized in that the aircraft comprises a propulsion system (3) supplied with power by hydrogen from the hydrogen storage system (10).

3. Assembly according to Claim 2, characterized in that the propulsion system comprises an engine operating by the combustion of hydrogen from the hydrogen storage system.

4. Assembly according to Claim 2, characterized in that the propulsion system comprises an electric motor (32) electrically powered by a fuel cell assembly (34) supplied with hydrogen by the hydrogen storage system (10).

5. Assembly according to Claim 4, characterized in that the aircraft has an electrical system (29c) that is separate from the processing unit (16), and an electrical circuit (24c, 28c) configured to electrically power this electrical system via the fuel cell (14) of the hydrogen storage system (10) when the aircraft is parked on the ground.

6. Assembly according to Claim 5, characterized in that this electrical system (29c) corresponds to a system for heating at least one of the fuel cells of the fuel cell assembly (34).

7. Assembly as claimed in any one of Claims 4 to 6, characterized in that the aircraft has an electrical circuit configured to allow an external electrical system to be connected to the aircraft when the aircraft is parked on the ground, and to electrically power this electrical system via the fuel cell (14) of the hydrogen storage system (10).