Equipment and method for liquefying hydrogen

Abstract

The invention relates to an installation for the liquefaction of hydrogen in a cryogenic liquefied hydrogen storage device (8) via a downstream end (22) of a circuit (2) for hydrogen to be cooled, the cryogenic storage device (8) being equipped with an outlet pipe (11) configured to be able to supply liquefied hydrogen to at least one tank (19) to be filled, in particular a mobile tank, the installation (1) comprising a set of heat exchangers (3, 4, 5) in a heat exchange relationship with the circuit (2) for hydrogen to be cooled, and a cooling device in a heat exchange relationship with the set of heat exchangers (3, 4, 5), the cooling device being a refrigerator with a cyclic gas refrigeration cycle. (7), the installation (1) comprises at least a first pipe (12) for recovering boil-off gas, the first pipe (12) comprising a first end intended to be connected to a tank (19) and a second end connected to a downstream end (22) of a circuit for hydrogen to be cooled, the first recovery pipe (12) comprising at least a cryogenic compressor (13) and a part in a heat exchange relationship with at least a part of the set of heat exchangers (3, 4, 5), the first recovery pipe (12) being configured to recover, compress and then cool the boil-off hydrogen and mix it with liquefied hydrogen at the downstream end (22) of the hydrogen circuit (2).

Description

[Technical field]

[0001] The present invention relates to an installation and a method for the liquefaction of hydrogen.

[0002] The invention more particularly relates to an installation for the liquefaction of hydrogen, comprising a circuit for hydrogen to be cooled, comprising an upstream end for connection to a hydrogen source and a downstream end connected to at least one cryogenic storage unit for liquefied hydrogen, the cryogenic storage unit being equipped with an outflow line configured to be able to supply liquefied hydrogen to at least one tank to be filled, in particular a mobile tank, the installation comprising a set of heat exchangers in a heat exchange relationship with the circuit for hydrogen to be cooled, the installation comprising a cooling device in a heat exchange relationship with the set of heat exchangers, the cooling device comprising a refrigerator having a cycle for refrigerating a cycle gas in its working circuit, the cycle gas comprising at least one of hydrogen, helium, the working circuit of the refrigerator comprising a member for compression of the cycle gas, a member for cooling the cycle gas, a member for expansion of the cycle gas and a member for reheating the cycle gas, the installation comprising at least a first line for recovery of boil-off gas comprising a first end for connection to a tank. [Background technology]

[0003] Liquefaction of hydrogen in a liquefaction facility generally uses a stream of gaseous hydrogen under pressure, typically at pressures between 10 and 30 bar absolute.

[0004] To reach the hydrogen liquefaction temperature, this stream may undergo a step of pre-cooling by heat exchange with a first refrigeration cycle, which may use a refrigerant (for example nitrogen) and / or a refrigerant composed of a mixture ("MR" for "mixed refrigerant").

[0005] The stream to be liquefied is then cooled in a cold box to a liquid state by a refrigeration cycle using a refrigerant composed of or including helium and / or hydrogen. It should be noted that optionally, one or more intermediate cooling steps can be provided between the above-mentioned pre-cooling and cooling.

[0006] The liquefied hydrogen that is produced is typically transferred to at least one cryogenic storage unit that is used, for example, to fill mobile tanks (eg, trucks or other mobile tanks).

[0007] One issue with this type of facility is the management of boil-off gas ("BOG").

[0008] Cryogenic storage units are the first potential source of boil-off gas for pre-liquefied hydrogen. Storage units for liquefied hydrogen generally produce a relatively constant flow of boil-off gas at relatively low pressure and relatively low temperature (typically around 20 K, but could be even higher), which is the result of heat input in the storage unit. When little or no liquid is withdrawn from the storage unit, this flow may be intermittently increased significantly by the piston effect of liquid coming from the liquefier.

[0009] The reuse of these boil-off gases is typically carried out in the refrigeration cycle with hydrogen (at relatively low pressure) and under cryogenic conditions (i.e., reusing the hydrogen molecules and hydrogen molecules frigory), provided that the pressure differential between the cryogenic storage unit pressure and the refrigeration cycle pressure is sufficient and valves for redistribution of the cryogenic gas are provided in the liquefaction plant.

[0010] Another solution is to suppress or reduce that flow of boil-off gas by producing subcooled liquid hydrogen at the outlet of the liquefier (especially in configurations using a helium-based refrigeration cycle).

[0011] The tanks to be filled with the liquid hydrogen produced by the installation are another source of boil-off gas. In fact, these transfer tanks or containers for liquid hydrogen generally produce the boil-off gas at a relatively low or moderate pressure (typically between 7 and 1.1 bara) and at a slightly higher temperature (typically between 20K and 40K, or even just above 40K). This other source of boil-off gas is more discontinuous and also highly variable in terms of quantity and thermodynamic state depending on the tank conditions. The boil-off gas recovered from this second source of boil-off gas is generally reheated to approximately ambient temperature and reused in the refrigeration cycle with hydrogen. If the pressure difference between the pressure of these gases and the pressure of the cycle is sufficient, this reuse can be carried out without additional equipment provided for that purpose. Otherwise, additional equipment (for example blowers, boosters, compressors, etc., such as cryogenic ejectors) is necessary.

[0012] If the refrigerant constituting the cycle gas is not pure hydrogen (e.g. helium or other gas), the gaseous boil-off hydrogen cannot be reused in the cycle (risk of contamination of the refrigerant), in which case the boil-off gas must be avoided (by producing subcooled liquid hydrogen) or recovered using ambient temperature compression equipment.

[0013] Therefore, management of boil-off gas becomes an issue. Summary of the Invention [Problem to be solved by the invention]

[0014] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to obviate all or part of the above-mentioned disadvantages of the prior art. [Means for solving the problem]

[0015] To this end, an installation according to the invention, which otherwise complies with the general definition given in the preamble above, is substantially characterised in that at least a first line for recovery of boil-off gas comprises a second end connected to the downstream end of the circuit for hydrogen to be cooled, this first recovery line comprising a part in heat exchange relationship with at least one cryogenic compressor and with at least a part of the set of heat exchangers, the first recovery line being configured so that the evaporated hydrogen can be recovered, compressed and then cooled and mixed with liquefied hydrogen at the downstream end of the hydrogen circuit.

[0016] Furthermore, embodiments of the invention can include one or more of the following features. the portion of the first recovery line in heat exchange relationship with at least a portion of the set of heat exchangers includes at least one dedicated passage for boil-off gas in the heat exchanger, the passage being arranged in parallel with the cooling passages for the hydrogen circuit in the exchanger. the installation comprises a second line for recovery of boil-off gas comprising a first end connected to a cryogenic storage unit (8) and a second end connected to a downstream end of the circuit for hydrogen to be cooled, the second recovery line comprising a part in heat exchange relationship with the cryogenic compressor and at least a part of the set of heat exchangers, the second recovery line being configured so that the evaporated hydrogen can be recovered, compressed, cooled and then mixed with the liquefied hydrogen at the downstream end. the first and second lines for the recovery of boil-off gas have a common part downstream of the first end, in particular the first and second lines for the recovery of boil-off gas share the same common cryogenic compressor, the same passages of a set of heat exchangers forming part of the heat exchange relationship, and the same second end. the circuit for hydrogen to be cooled comprises at least one final expansion element (e.g. a turbine or an expansion valve) downstream of the last heat exchange with the set of heat exchangers, and the second end of the first line for recovery of boil-off gas is connected downstream of the final expansion element, i.e. between the final expansion element and the cryogenic storage unit. The equipment includes a bypass line for the cryogenic compressor including a first end connected to at least a first recovery line downstream of the cryogenic compressor and downstream of a portion in heat exchange relationship with at least a portion of the set of heat exchangers, the bypass line including a second end connected to a suction inlet of the cryogenic compressor, the equipment including a member for adjusting a flow rate of a fluid in the bypass line configured to control a flow of boil-off gas reinjected into the cryogenic compressor. The arrangement includes a member for guiding a flow regulating member to maintain a pressure or flow rate at the suction inlet of the cryogenic compressor greater than a specified value. the first recovery line comprises, between its first end and the cryogenic compressor, at least one of a member for analyzing the composition of the boil-off gas, in particular a device for measuring the impurity / impurities, and a member for purifying the boil-off gas configured to remove at least one impurity. The first recovery line includes a plurality of cryogenic compressors arranged in series and / or parallel. The installation includes a bypass line provided between the recovery line on one side and a set of valves provided to regulate the flow of gas that is or is not allowed to pass through the bypass line. - compressing the boil-off gas using at least one cryogenic compressor of the facility, when the pressure and / or flow rate at the inlet of the cryogenic compressor is below a specified threshold, the method includes a step of recirculating at least a portion of the compressed boil-off gas flow to the inlet of the cryogenic compressor.

[0017] Furthermore, the present invention relates to a method for liquefying hydrogen using an installation according to any of the above or below characteristics, comprising the steps of recovering boil-off gas in at least one cryogenic hydrogen tank, compressing the recovered boil-off gas, cooling the compressed gas and transferring the cooled gas to a cryogenic storage unit.

[0018] Other possible different characteristics are as follows: The method includes the steps of recovering boil-off gas from a cryogenic storage unit, compressing the recovered boil-off gas, cooling the compressed gas, and transferring the cooled gas to the cryogenic storage unit. The boil-off gas recovered in the recovery step has an absolute pressure of between 1 and 7 bar, preferably between 1 and 2 bar, and a boil-off gas temperature of between 20K and 50K. In a compression step, the pressure of the boil-off gas is increased to reach a value between 1.3 and 6 bara, in particular 2 bara, and the temperature is increased by, for example, 5 to 10 K.

[0019] Furthermore, the invention may relate to any alternative device or method including any combination of the above or below features within the context of the claims.

[0020] Further particular features and advantages will become apparent from the following description, given with reference to the drawings. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 shows a schematic partial view illustrating the structure and operation of an example of an installation according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The exemplary installation 1 for liquefying hydrogen comprises a circuit 2 for hydrogen to be cooled, including an upstream end 21 for connection to a source 23 of gaseous hydrogen. The source 21 may, for example, provide a stream of pure dry gaseous hydrogen having an absolute pressure (for example between 10 and 80 bar) at ambient temperature.

[0023] The circuit 2 for hydrogen to be cooled has at least one downstream end 22 connected to at least one cryogenic storage unit 8 for liquefied hydrogen for storing the product liquefied hydrogen in the cryogenic storage unit 8 .

[0024] The cryogenic storage unit 8 is for example an insulated cryogenic tank under vacuum which stores liquefied hydrogen, for example at a pressure of about 1.5 bar absolute and at a temperature of about 20K.

[0025] The cryogenic storage unit 8 may be equipped with outflow lines 11 or orifices configured to be able to supply liquefied hydrogen to one or more tanks 19 (in particular one or more mobile tanks) to be filled. This transfer of the liquefied hydrogen may be performed by differential pressure and / or by gravity and / or via a transfer member (e.g. a pump).

[0026] The installation 1 comprises a set of heat exchangers 3, 4, 5 in heat exchange relationship with a circuit 2 for hydrogen to be cooled, and a cooling device in heat exchange relationship with the set of heat exchangers 3, 4, 5 for cooling the hydrogen circuit 2.

[0027] The cooling device comprises at least one refrigerator 7 having a cycle for refrigerating a cycle gas in a working circuit, the cycle gas comprising at least one of hydrogen, helium. The working circuit of the refrigerator 7 comprises a member 9 for compression of the cycle gas (e.g. one or more compressors), a member 3, 4 for cooling the cycle gas (e.g. one or more cooling heat exchangers), a member 10 for expansion of the cycle gas (one or more turbines and / or expansion valves) and a member 5, 4, 3 for reheating the cycle gas (one or more heat exchangers). In particular, the reheating and cooling can be achieved at least in part by countercurrent exchangers 3, 4, 5 in which two separate parts of the cycle gas circulate under different thermodynamic conditions (in particular temperatures).

[0028] That is, the working circuit of the refrigerator 7 is configured to subject the working gas to a thermodynamic cycle which produces at one end of the working circuit a cooling capacity which is transferred via one or more heat exchangers to the circuit 2 to be cooled.

[0029] As illustrated diagrammatically, upstream of the cooling of the refrigerator 7, the hydrogen circuit 2 can be pre-cooled to an intermediate temperature (for example, about 80 K) before liquefaction of the hydrogen. This pre-cooling is carried out by at least one pre-cooling device 24 by heat exchange with a set of heat exchangers 3 for pre-cooling. For example, the pre-cooling device 24 comprises a refrigeration cycle with a refrigerant (for example, nitrogen) and / or a refrigerant composed of a mixture ("MR" for "mixed refrigerant"). Of course, any other type of pre-cooling device 24 can be envisaged, for example a stream of a cryogenic fluid, a source of a liquefied gas (for example, nitrogen).

[0030] Furthermore, the installation 1 comprises at least a first line 12 for recovery of boil-off gas (hydrogen) having a first end for connection to at least one (in particular mobile) tank 19 to be filled and a second end connected to the downstream end 22 of the circuit 2 for hydrogen to be cooled.

[0031] This first recovery line 12 includes at least one cryogenic compressor 13 and, downstream of the cryogenic compressor 13, a portion in heat exchange relationship with at least a portion of the set of exchangers 3, 4, 5 in the cold box.

[0032] This first recovery line 12 is configured so that the evaporated hydrogen can be recovered, compressed and then cooled (in particular liquefied) and mixed with the liquefied hydrogen produced at the downstream end 22 of the hydrogen circuit 2.

[0033] Illustratively, this first recovery line 12 may have a portion in heat exchange relationship with one or more of the set of exchangers 3 , 4 , 5 cooled by the refrigerator 7 .

[0034] That is, for example, the first recovery line 12, which is in heat exchange relationship with at least a part of the set of heat exchangers 3, 4, 5, can include at least one dedicated passage for boil-off gas in the heat exchangers 3, 4, 5. This or these passages can be arranged in parallel with the cooling passages for the hydrogen circuit 2 in the exchangers 4, 5. For example, the evaporated hydrogen circulates in a dedicated passage parallel to the flow of the circuit 2 for the hydrogen to be liquefied, for example between that flow of the hydrogen circuit 2 and a flow of cycle gas. The exchanger or exchangers 4, 5 are for example plate or other exchangers which include dedicated passages for these different flows of fluids. The dedicated passages can have one or more catalytic parts which convert ortho-hydrogen to para-hydrogen.

[0035] For example, the first recovery line 12 may be adapted to operate at an absolute pressure of between 1.1 bar and 10 bar (particularly 5 bar) and at a temperature of between about 20 K and 40 K (e.g. 35 K) and with a maximum flow rate of 1000 Nm 3 Evaporated hydrogen can be withdrawn from tank 19 at a flow rate which can be on the order of 1000 s / h.

[0036] The cryogenic compressor 13 is configured to compress the cryogenic gas flow to produce a gaseous hydrogen flow, for example at a pressure sufficient to overcome the pressure losses in the downstream circuit, i.e. for example at a pressure of about 2 bar absolute starting from an evaporated gas flow at an absolute pressure of the order of 1.3 bar.

[0037] For example, the pressure of the boil-off gas stream at the inlet of the cryogenic compressor 13 may be between 1.0 and 2.0 bar absolute, preferably between 1.0 and 1.5 bar absolute, while at the outlet of the compressor its pressure of the gas may be, for example, between 1.3 and 6 bar absolute, preferably between 1.3 and 2.5 bar absolute.

[0038] The cryogenic compressor can be a centrifugal or positive displacement type compressor.

[0039] As illustrated by the dashed line, a bypass line 25 may be provided between at least the first recovery line 12 (or the outlet of the tank 19) on the one hand and the downstream end of the compressor 13 on the other hand. This allows the compressor 13 to be released when there is no need to use it when the boil-off gas is at sufficient pressure. A set of valves (not shown for simplicity) may be provided to regulate the flow of gas that is or is not allowed to pass through the bypass line 25. The method may thus include the step of at least a portion of the evaporated hydrogen bypassing the compressor 13 when the evaporated hydrogen is at a pressure greater than a specified level.

[0040] Thus, in any liquefaction cycle, the boil-off gas from the tank or tanks 9 can be directly recycled in a low temperature state (typically at a temperature between 50 K and 20 K) via the cryogenic compressor 13. These boil-off gases are compressed and therefore optionally slightly reheated (for example to +5 K to 10 K by the effect of quasi-adiabatic compression depending on the capacity of the cryogenic compressor 13). The low temperature compressed boil-off gas is then introduced into one or more dedicated passages of the main exchange line of the refrigerator to be cooled in parallel to the line for the hydrogen to be liquefied. This flow of cooled gaseous hydrogen (in particular at least partially liquefied) is then mixed with the flow of liquefied hydrogen of the circuit 2.

[0041] This structure allows efficient recovery and reuse of boil-off gas from the tanks 19 (particularly trucks), which can be variable over time in terms of temperature conditions and the flow rates to be treated.

[0042] By way of example, the circuit 2 for hydrogen to be cooled may comprise a final expansion element 15 (e.g. a turbine or an expansion valve (e.g. Joule-Thomson type)) downstream of the last heat exchanger 5 of the set of heat exchangers. Preferably, the second end of the first line 12 for recovery of boil-off gas is connected downstream of the final expansion element 15, i.e. between the final expansion element 15 and the cryogenic storage unit 8.

[0043] The cold boil-off hydrogen mixed with the liquefied hydrogen in circuit 2 may be substantially liquid (optionally partially two-phase: liquid-gas).

[0044] The installation 1 can be provided for similarly reusing the boil-off gas of the cryogenic storage unit 8 for liquefied hydrogen according to the same principle (compression, cooling, then mixing with the product liquefied hydrogen). For this purpose, the installation 1 can comprise at least a second recovery line 14 equipped with a first end connected to the cryogenic storage unit 8 and a second end connected to the downstream end 22 of the circuit 2 for the hydrogen to be cooled.

[0045] As an example, this second recovery line 14 and the first recovery line 12 can share the cryogenic compressor 13 and the parts in heat exchange relationship as described above. That is, the first line 12 and the second line 14 for recovery of boil-off gas can have separate upstream ends but share the same common parts downstream of the first end. In particular, the boil-off gas collected in the first line 12 and the second line 14 for recovery of boil-off gas preferably share the same cryogenic compressor 13 and use the same passages of the set of heat exchangers 3, 4, 5 for cooling.

[0046] That is, the boil-off gases of the tank 19 and the cryogenic storage unit 8 may be collected and mixed in a common collector which provides the inlet to the cryogenic compressor 13 .

[0047] Advantageously, such an installation 1 can simultaneously and / or continuously recover and reuse the boil-off gas of the mobile tank 19 and / or the storage unit 8 by adapting to flows that are variable in terms of quantity and in terms of temperature and pressure conditions.

[0048] Of course, the installation 1 can be configured to be able to simultaneously (and / or sequentially) recover boil-off gas from multiple tanks 19. Thus, the installation 1 can have multiple first recovery lines 12 (or first recovery lines 12 including multiple first ends).

[0049] Similarly, the installation 1 can be configured so that boil-off gas can be withdrawn from multiple storage units 8, if required.

[0050] As illustrated diagrammatically, the first recovery line 12 may comprise, between the first end and the cryogenic compressor 13, at least one of a member 18 for analyzing the composition of the boil-off gas, in particular a device for measuring the impurity / impurities, a member 18 for purifying the boil-off gas configured to remove at least one impurity. For example, this analysis and / or purification may be performed upon connection of a tank 19.

[0051] As illustrated generally, the installation 1 can include a bypass line 16 for the cryogenic compressor 13 that can recycle at least a portion of the compressed flow to the suction of the cryogenic compressor 13 to ensure a minimum pressure or flow rate at the suction.

[0052] The bypass line 16 has a first end connected to the recovery lines 12, 14, e.g., downstream of the portion in heat exchange relationship with at least a portion of the set of heat exchangers 3, 4, 5. The bypass line 16 includes a second end connected to the suction of the cryogenic compressor 13.

[0053] Furthermore, the installation 1 includes a member 17 for regulating the flow of fluid in the bypass line 16 that is configured to control the flow of boil-off gas reinjected into the cryogenic compressor 13 in order to maintain a pressure or flow rate at the suction of the cryogenic compressor 13 greater than a specified value. This regulating member 17 can, for example, include or consist of a set of valves.

[0054] Thus, when there is little or insufficient boil-off gas (e.g., less than the minimum input flow rate required to supply the cryogenic compressor 13), a portion of the gaseous hydrogen is removed to allow the cryogenic compressor 13 to operate under optimal conditions and avoid premature wear and tear, and in particular shutdown of the cryogenic compressor 13, in the event of insufficient supply.

[0055] This cryogenic bypass flow (if required) is therefore preferably cooled in the exchanger lines in cycles 4 and 5 before being reinjected into the suction of the cryogenic compressor 13. When the boil-off gas flow rate is sufficient, the bypass can be shut off and the performance of the cryogenic compressor 13 can be controlled (guided) by the flow rate to be processed (directly or indirectly), i.e. the cryogenic compressor 13 can be controlled or guided as a function of the pressure at the inlet of the cryogenic compressor 13. As shown diagrammatically, the regulating member 17 can be guided by a programmable electronic controller 20 which can include a microprocessor. This controller 20 can be part of the compressor 13 if required.

[0056] Of course, the invention is not limited to the examples described below. Thus, for example, the device 1 can include several cryogenic compressors 13 arranged in series and / or in parallel in a return line. In particular, several cryogenic compressors arranged in series (with or without intercooling of the compressed flow) can increase the compression ratio.

[0057] Similarly, the installation 1 may have an intermediate gas storage unit (buffer) upstream of the suction of the cryogenic compressor 13 for storing boil-off gas at cryogenic temperature levels, so as to decouple the compressor function from the variable return of boil-off gas.

Claims

1. An installation for the liquefaction of hydrogen, comprising a circuit (2) for hydrogen to be cooled, comprising an upstream end (21) for connection to a hydrogen source (23) and a downstream end (22) connected to at least one cryogenic storage unit (8) for liquefied hydrogen, said cryogenic storage unit (8) being equipped with an outlet (11) configured to be able to supply liquefied hydrogen to at least one tank (19) to be filled, in particular a mobile tank, said installation (1) comprising a set of heat exchangers (3, 4, 5) in a heat exchange relationship with said circuit (2) for hydrogen to be cooled, said installation (1) comprising a cooling device in a heat exchange relationship with said set of heat exchangers (3, 4, 5), said cooling device comprising a refrigerator (7) having a cycle for refrigerating a cycle gas in its working circuit, said cycle gas comprising at least one of hydrogen, helium, the working circuit of the refrigerator (7) comprises a member (9) for compression of the cycle gas, a member (3, 4) for cooling the cycle gas, a member (10) for expansion of the cycle gas and a member (5, 4, 3) for reheating the cycle gas; the installation (1) comprises at least a first line (12) for recovery of boil-off gas comprising a first end and a second end connected to the downstream end (22) of the circuit (2) for hydrogen to be cooled, the first line (12) for recovery, the second end comprising at least one cryogenic compressor (13) and a part in heat exchange relationship with at least a part of the set of heat exchangers (3, 4, 5); the first recovery line (12) is configured so that evaporated hydrogen can be recovered, compressed and then cooled and mixed with the liquefied hydrogen at the downstream end (22) of the hydrogen circuit (2); the first end of the first return line (12) is to be connected to a tank (19), the installation comprises a bypass line (16) of the cryogenic compressor (13) comprising a first end connected to the at least first return line (12, 14) downstream of the cryogenic compressor (13) and downstream of a portion in heat exchange relationship with at least a portion of the set of heat exchangers (3, 4, 5), the bypass line (16) comprising a second end connected to a suction inlet of the cryogenic compressor (13), the installation (1) comprising a member (17) for regulating the flow of a fluid in the bypass line (16) configured to control the flow of boil-off gas reinjected into the cryogenic compressor (13).

2. 2. The installation according to claim 1, characterized in that the portion of the first recovery line (12) in heat exchange relationship with at least a portion of the set of heat exchangers (3, 4, 5) comprises at least one dedicated passage for the boil-off gas in the heat exchangers (3, 4, 5), said passage being arranged in parallel with cooling passages for the hydrogen circuit (2) in the exchangers (4, 5).

3. 3. The installation according to claim 1 or 2, further comprising a second line (14) for recovery of boil-off gas comprising a first end connected to the cryogenic storage unit (8) and a second end connected to the downstream end (22) of the circuit (2) for hydrogen to be cooled, the second recovery line (14) comprising a cryogenic compressor (13) and a part in a heat exchange relationship with at least a part of the set of heat exchangers (3, 4, 5), characterized in that the second recovery line (14) is configured to be able to recover, compress, cool and then mix evaporated hydrogen with the liquefied hydrogen at the downstream end (22).

4. 4. Installation according to claim 3, characterized in that the first line (12) and the second line (14) for recovery of boil-off gas have a common part downstream of the first end, in particular the first line (12) and the second line (14) for recovery of boil-off gas share the same common cryogenic compressor (13), the same passages of the set of heat exchangers (3, 4, 5) forming the part in heat exchange relationship, and the same second end.

5. 3. Installation according to claim 1 or 2, characterized in that the circuit (2) for hydrogen to be cooled comprises at least one final expansion element (15) (e.g. a turbine or an expansion valve) downstream of the last heat exchange with the set of heat exchangers (3, 4, 5), and the second end of the first line (12) for recovery of boil-off gas is connected downstream of the final expansion element (15), i.e. between the final expansion element (15) and the cryogenic storage unit (8).

6. 3. The installation according to claim 1 or 2, characterized in that it includes a member (20) for guiding a flow regulating member (17) to maintain a pressure or flow rate at the suction inlet of the cryogenic compressor (13) greater than a specified value.

7. 3. The installation according to claim 1 or 2, characterized in that the first recovery line (12) comprises at least one of the following between the first end and the cryogenic compressor (13): a member (18) for analyzing the composition of the boil-off gas, in particular a device for measuring an impurity / impurities, a member (18) for purifying the boil-off gas configured to remove at least one impurity.

8. 3. Installation according to claim 1 or 2, characterized in that the first return line (12) comprises a number of cryogenic compressors (13) arranged in series and / or in parallel.

9. 3. Installation according to claim 1 or 2, characterized in that it includes a bypass line (25) provided on the one hand between said first recovery line (12) and a set of valves provided to regulate the flow of gas that is or is not allowed to pass through the bypass line (25).

10. 3. A method for liquefying hydrogen using an installation according to claim 1 or 2, comprising the steps of recovering boil-off gas in at least one cryogenic hydrogen tank (19), compressing the recovered boil-off gas, cooling the compressed gas and transferring the cooled gas to a cryogenic storage unit (8).

11. 11. The method according to claim 10, comprising the steps of recovering boil-off gas from the cryogenic storage unit (8), compressing the recovered boil-off gas, cooling the compressed gas, and transferring the cooled gas to the cryogenic storage unit (8).

12. 11. The method according to claim 10, characterized in that the boil-off gas recovered in the recovery step has an absolute pressure between 1 and 7 bar, preferably between 1 and 2 bar, and a boil-off gas temperature between 20 and 50 K.

13. 11. A method according to claim 10, characterized in that in the compression step the pressure of the boil-off gas is increased to reach a value between 1.3 and 6 bara, in particular 2 bara, and the temperature is increased, for example by 5 to 10 K.

14. 11. The method according to claim 10, characterized in that in the step of compressing the boil-off gas using at least one cryogenic compressor (13) of the installation (1), it comprises the step of recirculating at least a portion of the flow of compressed boil-off gas to the inlet of the cryogenic compressor (13) if the pressure and / or flow rate at the inlet of the cryogenic compressor (13) is below a specified threshold value.

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