Installation and process for liquefying a cryogenic fluid

Abstract

The invention relates to an installation and a method for liquefying a cryogenic fluid comprising a set of heat exchangers (4, 5) in heat exchange with a supply circuit (3), a cooling system in heat exchange with the set of heat exchangers (4, 5) comprising a cryogenic refrigerator (10) with cycle gas, the supply circuit (3) comprising an expansion member (6) and a phase separator (7) of which a liquid outlet supplies the downstream end (23) with liquefied supply gas and a gas outlet is connected to a gas phase recovery member, the installation (1) comprising an injection pipe (8) having an upstream end (80) connected to a pressurized gas reserve of the installation and supplying a gas of the same nature as the supply gas and / or a gas of the same nature as the cycle gas or a component of the cycle gas,and a downstream end (81) configured to allow the injection of said pressurized gas into the phase separator (7). Abstract figure: Fig. 1,

Description

Title of the invention: Installation and method for liquefying a cryogenic fluid

[0001] The invention relates to an installation and a method for liquefying a cryogenic fluid, for example hydrogen (H2).

[0002] The invention relates more particularly to an installation for liquefying a cryogenic fluid, for example hydrogen, comprising a supply circuit for supplying supply gas to be liquefied having an upstream end intended to be connected to a source of supply gas under pressure at a first initial temperature and a downstream end intended to be connected to at least one member for collecting the liquefied supply gas, the installation comprising a set of heat exchangers arranged in series in heat exchange with the supply circuit, the installation comprising a cooling system in heat exchange with the set of heat exchangers and configured to lower the temperature of the supply gas to a target cryogenic temperature, for example a temperature below its critical temperature, for example below 25K,the cooling system comprising a cryogenic refrigerator (10) having a cycle circuit containing a cycle gas, for example comprising or consisting of at least one of: hydrogen, helium, the supply circuit comprising, arranged in series between the set of heat exchangers and the downstream end, a device for expanding the cooled supply gas and a liquid and gas phase separator of the flow of supply gas expanded in the expansion device, the phase separator comprising a liquid outlet configured to supply the downstream end with liquefied supply gas and a gas outlet connected to a device for recovering the gas phase in the installation, for example in the cycle circuit, ,

[0003] The hydrogen liquefaction process is generally carried out from a gas stream at ambient temperature and at relatively high pressure (5 to 30 bar for example) in order to increase the dew point temperature of the feed gas. For example, liquefaction conditions for a hydrogen stream may be a temperature of -251°C for a pressure of 24 bar abs.

[0004] At the end of this cooling (in a series of exchanger(s) cooled by at least one refrigerator), the hydrogen undergoes a final expansion, for example via a valve and / or a liquid turbine to reach a relatively low pressure of the storage in which the liquid hydrogen will be stored (pressure slightly higher than atmospheric pressure for example).

[0005] This or these storages can be used to fill delivery trucks (or other tank or downstream process). The truck filling pressure is defined by the operator. The truck filling pressure dictates the pressure in the storage facility(ies).

[0006] Two operating configurations can occur.

[0007] In a first configuration, the installation produces dense hydrogen without subcooling. In this case, "flash" vaporization gas is produced after the last expansion, which brings the fluid to the pressure of the downstream storage. Usually, this flash gas is recovered in the installation and only the liquid phase is sent to storage.

[0008] The liquid and gas are separated in a pot or phase separator. In this separator, equilibrium between the gas and liquid phases is achieved. The saturated liquid is sent from the separator to the storage facility(ies). The gas phase from the separator can be recovered in the hydrogen-based refrigeration cycle.

[0009] In a second configuration, the final expansion does not produce a "flash" gas. This produces fluid at the pressure of the downstream storage.

[0010] In this second configuration (second operating case) without flash during the final expansion, the liquefied liquid is sub-cooled. In this case, the gas phase in the phase separator will gradually condense.

[0011] This can lead to the phase separator being completely filled with liquid up to its gas outlet at the top. This creates operational problems for the installation.

[0012] Thus, for example, a separator no longer containing gas phase can stop the supply of liquid to a downstream storage. In fact, the liquid is supplied from the pot to the storage(s) by opening a valve which is controlled by the liquid level in the separator. This liquid level measurement is generally carried out by measuring the gas pressure in the separator. In the absence of gas phase in the separator, the level measurement is not available or is erroneous.

[0013] An aim of the present invention is to overcome all or part of the drawbacks of the prior art noted above.

[0014] To this end, the installation according to the invention, moreover in accordance with the generic definition given in the preamble above, is essentially characterized in that the installation comprises a gas injection pipe provided with a valve, the injection pipe having an upstream end connected to a reserve of pressurized gas of the installation and supplying a gas of the same nature as the feed gas and / or a gas of the same nature as the cycle gas or a component of the cycle gas, and a downstream end configured to allow the injection of said pressurized gas into the phase separator.

[0015] Furthermore, embodiments of the invention may comprise one or more of several of the following characteristics: - the injected pressurized gas is at a temperature higher than the temperature in the phase separator, - pressurized gas injected at a degree of purity greater than a determined threshold, - the downstream end of the injection pipe is connected to at least one of: the gas supply circuit between the set of heat exchangers and the expansion member, the gas supply circuit between the expansion member and the phase separator, the gas outlet of the phase separator, - the upstream end of the injection line is connected to the gas supply circuit at an intermediate level between the upstream end and the outlet of the last of the set of heat exchanger(s) in which the supply gas has a temperature higher than the target temperature, - the supply circuit comprises, at an intermediate level between the upstream end and the outlet of the last of the set of heat exchangers, a cryogenic purification member and possibly at least one catalysis section, the upstream end of the injection pipe being located downstream of the cryogenic purification member and / or downstream of the catalysis section, for example at the outlet of the cryogenic purification member and / or at the outlet of the catalysis section, - the cycle gas is of the same nature as the feed gas, - the upstream end of the injection pipe is connected to the cycle circuit, - the cycle circuit comprises at least one member for compressing the cycle gas such as at least one compressor, at least one member for cooling the compressed cycle gas, at least one member for expanding the cooled compressed cycle gas, for example at least one turbine and / or valve(s) and a member for reheating the expanded cycle gas, - the upstream end of the injection pipe is connected to the outlet of the cycle gas expansion device, - the upstream end of the injection pipe is connected downstream of at least one expanded cycle gas reheating device, - the feed gas is hydrogen, the cycle gas is or contains hydrogen, - the installation comprises an electronic control member comprising a microprocessor configured to control the opening or closing of the valve as a function of a measurement of the pressure in the phase separator and / or the thermodynamic conditions of the fluid at the outlet of the expansion member and / or the quantity or thermodynamic conditions of the fluid in the phase separator.

[0016] The invention also relates to a method for liquefying a cryogenic fluid, for example hydrogen, by means of an installation in accordance with any one of the characteristics above or below, the method comprising a step of cooling a feed gas stream under pressure and at an initial temperature, for example at ambient temperature, to a cryogenic target temperature below its critical temperature, a step of expanding the cooled feed gas stream to the cryogenic target temperature, a step of transferring the expanded feed gas stream into the phase separator, the method comprising a step of determining the pressure in the phase separator and a step of injecting pressurized gas into the phase separator, said gas being at a temperature higher than the temperature of the fluid in the phase separator.

[0017] According to other possible particularities: - the step of determining the pressure in the phase separator comprises at least one of: a pressure measurement, a detection of an expansion in the expansion member without production of “flash” gas, - the injection step is carried out when the pressure in the phase separator (7) falls below a determined threshold and / or when the pressure in the phase separator (7) decreases by a determined value, - the installation is configured to produce liquefied feed fluid at the outlet of the expansion member in a first subcooled liquid state or in a second non-subcooled liquid state and in that the injection step is carried out when the installation produces liquefied feed fluid in the subcooled liquid state at the outlet of the expansion member. - The invention may also relate to any alternative device or method comprising any combination of the above or below features within the scope of the claims.

[0018] Other features and advantages will appear on reading the description below, given with reference to the figures in which: Brief description of the figures

[0019] The invention will be better understood on reading the following description given solely by way of example and with reference to the appended drawings in which:

[0020] [Fig. 1] is a schematic and partial view illustrating an example of structure and operation of an installation according to the invention. Detailed description

[0021] In all the figures, the same references refer to the same elements.

[0022] In this detailed description, the following embodiments are examples. Well that the description refers to one or more embodiments, this does not mean that the features apply only to a single embodiment. Single features of different embodiments may also be combined and / or interchanged to provide other embodiments.

[0023] The illustrated liquefaction installation 1 comprises a circuit 3 for supplying feed gas to be liquefied (hydrogen for example) having an upstream end 13 intended to be connected to a source 2 of feed gas under pressure at a first initial temperature. The source 2 is for example an electrolyzer, a reformer or a gas network. The gas is for example hydrogen at room temperature and at a pressure between 5 and 30 bar.

[0024] The supply circuit 3 has a downstream end 23 intended to be connected to at least one member for collecting the liquefied supply gas, for example at least one cryogenic storage 30.

[0025] The liquefaction installation 1 comprises a set of heat exchanger(s), for example a plurality of heat exchangers 4, 5 arranged in series in heat exchange with the supply circuit 3 and a cooling system in heat exchange with the heat exchangers 4, 5.

[0026] The cooling system is configured to lower the temperature of the feed gas to a target cryogenic liquefaction temperature, for example a temperature below its critical temperature, for example below 25K in the case of hydrogen.

[0027] The cooling system comprises a cryogenic refrigerator 10 having a cycle circuit 101 containing a cycle gas. The cycle gas comprises or consists of at least one of: hydrogen, helium.

[0028] The cryogenic refrigerator is configured to produce cold power at at least one cold end of its cycle and provide this cold power to lower the temperature of the hydrogen to the target cryogenic temperature.

[0029] The refrigerator 10 is illustrated schematically for the sake of simplification. The cycle circuit 101 comprises one or more compressors 102. The compressed fluid is cooled (exchangers 4, 5) then expanded (turbine(s) 103 and / or valve(s)) then reheated (exchangers 5, 4). The cycle circuit 101 thus subjects the cycle gas to a thermodynamic cycle to provide cold power.

[0030] All or part of the heat exchangers 4, 5 may be multi-pass exchangers (co-current or counter-current) to ensure the simultaneous heating and cooling of the flow(s).

[0031] As illustrated, the cooling system may further comprise a pre-cooling device 14 in heat exchange with a portion of the heat exchangers. This pre-cooling device 14 may be configured to lower the hydrogen temperature from the first temperature at the upstream end to a second intermediate temperature between the first temperature and the final target temperature. For example, this pre-cooling device 14 pre-cools the feed gas to a temperature between 70K and 150K, for example 80K.

[0032] This pre-cooling device 14 may comprise a cryogenic loop or fluid (nitrogen or other). In the non-limiting example illustrated, the pre-cooling device 14 comprises a nitrogen refrigeration loop 15 which subjects a nitrogen flow to a cycle of compression 15, cooling 4, expansion 17 and reheating 4. As illustrated, the refrigeration loop 15 may include a separator 18 separating the liquid and gas phases.

[0033] Of course, the installation 1 may include other (pre)refrigeration devices.

[0034] The pre-refrigeration system 14 and the corresponding elements of the installation can be housed in a first cold box (80K for example). The refrigerator 10 and the corresponding elements of the installation 1 can be housed in a second, colder cold box (20K for example).

[0035] The supply circuit 3 comprises, arranged in series between the heat exchangers 4, 5 and the downstream end 23, a member 6 for expanding the cooled supply gas and a separator 7 for the liquid and gas phases of the flow of supply gas expanded in the expansion member 6.

[0036] The expansion member 6 may comprise or consist of at least one cryogenic turbine and / or a valve, for example of the Joule Thomson type.

[0037] The phase separator 7 comprises a liquid outlet configured to supply the downstream end 23 with liquefied feed gas and a gas outlet connected to a member for recovering the gas phase in the installation 1.

[0038] In this example, the gas outlet of the phase separator 7 is connected to the cycle circuit 101, for example to a separator pot 104 of the cycle circuit 101.

[0039] The installation 1 comprises a gas injection pipe 8 provided with a valve 9. This injection pipe 8 has an upstream end 80 connected to a reserve of pressurized gas preferably of the same nature as the feed gas and a downstream end 81 configured to allow the injection of said pressurized gas into the phase separator 7.

[0040] The injection line 8 makes it possible to inject relatively hotter gas at the separator 7. This makes it possible to compensate, if necessary, for the condensation of the gas phase in the separator 7 by adding heat to the system.

[0041] The valve 9 on this injection pipe 8 is preferably a regulating valve, for example piloted, making it possible to regulate the flow of gas injected towards the separator 7.

[0042] For example, the pressure in the phase separator 7 controls the opening of this valve 9.

[0043] For example, an electronic control member 12 comprising a microprocessor is configured to control the opening or closing of the valve 9, for example as a function of a measurement 130 of the pressure in the phase separator 7 (sensor 130) and / or other conditions such as, for example: the thermodynamic conditions of the fluid at the outlet of the expansion member 6 (temperature and / or pressure) and / or the quantity (level) or the thermodynamic conditions of the liquid in the phase separator 7.

[0044] When the gas phase of the phase separator 7 condenses due to the receipt of a subcooled liquid feed flow, the pressure in the phase separator 7 will decrease. This valve 9 can be opened to compensate for this pressure drop.

[0045] The maximum flow rate considered for the sizing of the valve 9 and the injection pipe 8 can be calculated by considering that the mixture inside the phase separator 7 (feed flow rate + gas injection flow rate) is in equilibrium.

[0046] Several locations can be considered for the injection of this gas and for the source of this injection gas.

[0047] [Fig.l] illustrates several examples represented simultaneously but which can be combined according to all possible configurations (one or more source points combined with one or more injection points).

[0048] These different solutions have relative advantages with regard, for example, to the efficiency of the mixture obtained between the fluid present and the injection gas or with regard to the circuitry to be considered.

[0049] In order to limit the generation of entropy, the temperature difference between the source point and the phase separator 7 is preferably limited.

[0050] In addition, the injected fluid must have a composition similar to that in the supply circuit at the injected location. For example, an identical or close purity.

[0051] Similarly, in the case of hydrogen, the injected fluid must have an Ortho / Para composition preferably close to that of hydrogen at this point in the circuit.

[0052] In the non-limiting example, three distinct source points and three distinct potential injection points are illustrated.

[0053] For example, the upstream end 80 of the injection pipe 8 can be connected to the gas supply circuit 3 at an intermediate level between the upstream end 13 and the outlet of the last of the heat exchangers 4, 5 in which the supply gas has a temperature higher than the target temperature.

[0054] The injected gas preferably has a determined purity (for example hydrogen at a determined degree of purity, for example greater than 99.999%). For this purpose, the gas injected can be taken downstream of a cryogenic purification system 11 of the supply circuit.

[0055] As illustrated, the supply circuit 3 may comprise, at an intermediate level between the upstream end 13 and the outlet of the last of the heat exchangers 4, 5 (for example after pre-cooling to a temperature around 80K) a cryogenic purification member 11 (PSA type) and possibly at least one catalysis section 19. As illustrated, the upstream end 80 of the injection pipe 8 may be located downstream of this cryogenic purification member 11 and / or downstream of the catalysis section 19, for example at the outlet of the cryogenic purification member 11 and / or at the outlet of the catalysis section 19.

[0056] For example, feed gas is used just before its entry into the second cold box. This gas is hotter than the liquid fluid in the phase separator 7. The gas flow rate required to control the liquid level in the phase separator 7 is relatively low but the temperature differential is relatively large. This injection gas flow has not necessarily completed its Ortho / Para conversion at the same level as downstream (and therefore in the phase separator 7).

[0057] As also illustrated, the upstream end 80 of the injection pipe 8 may be located further downstream of this cryogenic purification member 11 and catalysis section 19.

[0058] That is to say that the injection gas can be taken from supply line 3 in the second cold box at a colder level (and with, if necessary, a higher Ortho / Para conversion). This solution has a higher energy efficiency than the previous solution. In addition, the stability of the hydrogen is higher (higher Ortho / Para conversion rate).

[0059] As illustrated, as a variant or in combination, the upstream end 80 of the injection pipe 8 can be connected to the cycle circuit 101. That is to say that the injection gas is cycle gas (when the cycle gas of the refrigerator 10 is preferably of the same nature as the supply gas.

[0060] As shown schematically, the cycle circuit 101 may comprise at least one member 102 for compressing the cycle gas such as at least one compressor, at least one member 4, 5 for cooling the compressed cycle gas (heat exchanger(s)), at least one member 103 for expanding the cooled compressed cycle gas, for example at least one turbine and / or valve(s) and one member 5, 4 for reheating the expanded cycle gas (heat exchanger(s)).

[0061] The upstream end 80 of the injection pipe 8 can thus be connected to the outlet of a cycle gas expansion member 103 (at the outlet of a turbine for example).

[0062] The expansion member 6 may be composed of one or more turbines in series or / and in parallel. The temperature of the gases at the inlet or outlet of these turbines is rela tively higher than the gas of the first example of sampling at the level of the supply circuit 3. This source of injection gas chosen at the level of an outlet of a turbine 103 of the cycle gas offers a higher energy efficiency. The Para hydrogen content of the gas will depend on the content of the cycle gas H2 which can vary.

[0063] For example, injection gas 8 can thus be taken from the outlet of an expansion stage 103 which feeds an intermediate compression stage 102 of the cycle.

[0064] In another illustrated configuration (as a variant or in combination), the upstream end 80 of the injection pipe 8 can be connected to another location in the cycle of the refrigerator 10, for example at the level of an intermediate reheating of the expanded cycle gas before its return to the compression member 102. For example, the injection gas is taken from the outlet of a reheating exchanger 5, before its entry into the first cold box or just after entering the first cold box.

[0065] That is to say that the injection gas can be taken from the outlet of the 20K cold box of the medium pressure cycle. This gas is relatively hotter than the fluid of the separator 7. The necessary flow rate is therefore relatively low. In addition, the extraction of this gas from the outlet of a relatively cold exchanger 5 is energetically more efficient since the gas has exchanged its cold before being injected into the phase separator 7. However, the energy efficiency will be lower because the temperature difference can be relatively large. The Para hydrogen content of the gas will depend on the nature of the cycle gas which can vary.

[0066] As also illustrated schematically, the downstream end 81 of the injection pipe 8 (the injection point) can be located at different points in the circuit.

[0067] For example, the downstream end 81 of the injection pipe 8 can be connected to the gas supply circuit 3, between the heat exchangers 4, 5 and the phase separator 7, upstream and / or downstream of the expansion member 6.

[0068] These two configurations make it possible to inject relatively hot gas directly into the liquid 7 of the phase separator 7. This ensures good gas-liquid mixing and makes it possible to achieve thermodynamic equilibrium.

[0069] As illustrated, alternatively or in combination, the injection gas may be injected at the gas outlet of the phase separator 7. This injection of the hot gas at the gas outlet of the phase separator 7 may require a lower injection flow rate due to the temperature stratification inside the phase separator 7. This injection of relatively hot gas near the gas outlet of the separator 7 will create a gas pocket in the head of the separator even if the majority of this injected hot gas flow will leave towards the cycle circuit 101 of the refrigerator 10.

[0070] Thus, the installation provides the possibility of injecting relatively hotter gas into a gas / liquid separator 7 supplied with a cryogenic liquid which can be sub-cooled, in order to compensate for the condensation of the gas in the separator 7. This allows to create a controllable liquid level in the phase separator 7.

[0071] The hot injection gas injected into the phase separator 7 is then recovered, for example in the circuit 101 of the refrigerator 10.

[0072] This configuration and operation makes it possible to operate a liquefier that can be configured to produce subcooled or non-subcooled feed gas. In the case where subcooled feed gas is produced, the injection of hotter gas makes it possible to avoid the disadvantages described above.

[0073] In the above examples, the gas injected at the phase separator 7 is of the same nature as the feed gas. For example, the feed gas is hydrogen (H2) and the cycle gas is hydrogen, the gas injected into the phase separator 7 being hydrogen. However, other configurations are possible. Thus, for example, the feed gas may be hydrogen while the cycle gas may be helium or another constituent or mixture containing or not containing helium.

[0074] In this case, the gas injected into the phase separator 7 can be helium (or hydrogen for example).

[0075] Similarly, the feed gas may be another gas (helium or other), the cycle gas may be helium or a mixture containing helium, the gas injected into the phase separator may be helium or another constituent of the cycle gas (H2 for example).

[0076] For example, the type of injected gas may be different from the "receiver" gas if it does not disturb any "purity" specifications of the "receiver" gas and / or the operation of the installation.

Claims

1.

2.

3. Claims Installation for liquefying a cryogenic fluid, for example hydrogen, comprising a circuit (3) for supplying supply gas to be liquefied having an upstream end (13) intended to be connected to a source (2) of supply gas under pressure at a first initial temperature and a downstream end (23) intended to be connected to at least one member (30) for collecting the liquefied supply gas, the installation (1) comprising a set of heat exchangers (4, 5) arranged in series in heat exchange with the supply circuit (3), the installation (1) comprising a cooling system in heat exchange with the set of heat exchangers (4, 5) and configured to lower the temperature of the supply gas to a target cryogenic temperature, for example a temperature below its critical temperature, for example below 25K,the cooling system comprising a cryogenic refrigerator (10) having a cycle circuit (101) containing a cycle gas, for example comprising or consisting of at least one of: hydrogen, helium, the supply circuit (3) comprising, arranged in series between the set of heat exchangers (4, 5) and the downstream end (23), a member (6) for expanding the cooled supply gas and a separator (7) for liquid and gas phases of the flow of supply gas expanded in the expansion member (6), the phase separator (7) comprising a liquid outlet configured to supply the downstream end (23) with liquefied supply gas and a gas outlet connected to a member for recovering the gas phase in the installation (1), for example in the cycle circuit (101), the installation (1) comprising a gas injection pipe (8) provided with a valve (9),the injection pipe (8) having an upstream end (80) connected to a reserve of pressurized gas of the installation and supplying a gas of the same nature as the feed gas and / or a gas of the same nature as the cycle gas or a component of the cycle gas, and a downstream end (81) configured to allow the injection of said pressurized gas into the phase separator (7)., Installation according to claim 1, characterized in that the injected pressurized gas is at a temperature higher than the temperature in the phase separator (7). Installation according to claim 1 or 2, characterized in that the gas under pressure injected at a degree of purity greater than a determined threshold.

4. Installation according to any one of claims 1 to 3, characterized in that the downstream end (81) of the injection pipe (8) is connected to at least one of: the gas supply circuit (3) between the set of heat exchangers (4, 5) and the expansion member (6), the gas supply circuit (3) between the expansion member (6) and the phase separator (7), the gas outlet of the phase separator (7).

5. Installation according to any one of claims 1 to 4, characterized in that the upstream end (80) of the injection pipe (8) is connected to the gas supply circuit (3) at an intermediate level between the upstream end (13) and the outlet of the last of the set of heat exchanger(s) (4, 5) in which the supply gas has a temperature higher than the target temperature.

6. Installation according to claim 5, characterized in that the supply circuit (3) comprises, at an intermediate level between the upstream end (13) and the outlet of the last of the set of heat exchangers (4, 5), a cryogenic purification member (11) and possibly at least one catalysis section (19), the upstream end (80) of the injection pipe (8) being located downstream of the cryogenic purification member (11) and / or downstream of the catalysis section (19), for example at the outlet of the cryogenic purification member (11) and / or at the outlet of the catalysis section (19).

7. Installation according to any one of claims 1 to 6, characterized in that the cycle gas is of the same nature as the feed gas.

8. Installation according to claim 7, characterized in that the upstream end (80) of the injection pipe (8) is connected to the cycle circuit (101).

9. Installation according to any one of claims 1 to 8, characterized in that the cycle circuit (101) comprises at least one member (102) for compressing the cycle gas such as at least one compressor, at least one member (4, 5) for cooling the compressed cycle gas, at least one member (103) for expanding the cooled compressed cycle gas, for example at least one turbine and / or valve(s) and a member (5, 4) for reheating the expanded cycle gas.

10. Installation according to claims 8 and 9, characterized in that the upstream end (80) of the injection pipe (8) is connected to the outlet of the cycle gas expansion member (103).

11. Installation according to claim 10 or according to claims 8 and 9, characterized in that the upstream end (80) of the injection pipe (8) is connected downstream of at least one member (5, 4) for reheating the expanded cycle gas.

12. Installation according to any one of claims 1 to 11, characterized in that the feed gas is hydrogen and in that the cycle gas is or contains hydrogen.

13. Installation according to any one of claims 1 to 12, characterized in that it comprises an electronic control member (12) comprising a microprocessor configured to control the opening or closing of the valve (9) as a function of a measurement (13) of the pressure in the phase separator (7) and / or of the thermodynamic conditions of the fluid at the outlet of the expansion member (6) and / or of the quantity or thermodynamic conditions of the fluid in the phase separator (7).

14. A method of liquefying a cryogenic fluid, for example hydrogen, by means of an installation according to any one of the preceding claims, the method comprising a step of cooling a feed gas stream under pressure and at an initial temperature, for example at ambient temperature, to a cryogenic target temperature below its critical temperature, a step of expanding (6) the feed gas stream cooled to the cryogenic target temperature, a step of transferring the expanded feed gas stream into the phase separator (7), the method comprising a step of determining the pressure in the phase separator (7) and a step of injecting pressurized gas into the phase separator (7), said gas being at a temperature higher than the temperature of the fluid in the phase separator (7).

15. Method according to claim 14, characterized in that the step of determining the pressure in the phase separator (7) comprises at least one of: a pressure measurement, a detection of an expansion in the expansion member (6) without production of “flash” gas.

16. Method according to claim 14 or 15, characterized in that the injection step is carried out when the pressure in the phase separator (7) falls below a determined threshold and / or when the pressure in the phase separator (7) decreases by a determined value.

17. Method according to any one of claims 14 to 16, characterized in that the installation (1) is configured to produce liquefied feed fluid at the outlet of the expansion member (6) in a first subcooled liquid state or in a second non-subcooled liquid state and in that the injection step is carried out when the installation (1) produces liquefied feed fluid in the subcooled liquid state at the outlet of the expansion member (6).

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