Facility and method for liquefying a cryogenic fluid

Abstract

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

Description

FACILITY AND METHOD FOR LIQUEFYING A CRYOGENIC FLUID

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

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

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

[0004] At the end of this cooling (in a series of heat 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 is going to be stored (pressure slightly higher than atmospheric pressure for example).

[0005] This or these storages can be used to fill delivery trucks (or another downstream tank or process). The filling pressure of the truck is defined by the operator. The filling pressure of the truck imposes the pressure in the storage(s).

[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 the storage.

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

[0009] In a second configuration, the final expansion does not produce "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 subcooled. In this case, the gas phase in the phase separator is going to condense progressively.

[0011] This can lead to completely filling the phase separator with liquid up to its gas outlet in the upper part. This creates operating problems of the installation.

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

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

[0014] To this end, the installation according to the invention, otherwise in accordance with the generic definition given in the preamble above, is essentially characterized in that the installation comprises a gas injection line provided with a valve, the injection line having an upstream end connected to a pressurized gas reserve 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 the following features: - the injected pressurized gas is at a temperature higher than the temperature in the phase separator, - the injected pressurized gas has a degree of purity higher than a determined threshold, - the downstream end of the injection line is connected to at least one among: the gas supply circuit between the set of heat exchangers and the expansion device, the gas supply circuit between the expansion device 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 feed 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 exchanger(s), a cryogenic purification device and optionally at least one catalysis section, the upstream end of the injection line being located downstream of the cryogenic purification device and / or downstream of the catalysis section, for example at the outlet of the cryogenic purification device 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 line is connected to the cycle circuit, - the cycle circuit comprises at least one compression device of the cycle gas such as at least one compressor, at least one cooling device of the compressed cycle gas, at least one expansion device of the cooled compressed cycle gas, for example at least one turbine and / or valve(s) and a reheating device of the expanded cycle gas, - the upstream end of the injection line is connected to the outlet of the expansion device of the cycle gas, - the upstream end of the injection line is connected downstream of at least one reheating device of the expanded cycle gas, - the feed gas is hydrogen, the cycle gas is or contains hydrogen, - the installation comprises an electronic control unit comprising a microprocessor configured to control the opening or the closing of the valve as a function of a measurement of the pressure in the phase separator and / or of the thermodynamic conditions of the fluid at the outlet of the expansion device and / or of the quantity or of the thermodynamic conditions of the fluid in the phase separator.

[0016] The invention also relates to a method for liquefaction of a cryogenic fluid, for example hydrogen, by means of an installation according to any one of the characteristics above or below, the method comprising a step of cooling a flow of feed gas under pressure and at an initial temperature, for example at ambient temperature, down to a target cryogenic temperature lower than its critical temperature, a step of expansion of the flow of feed gas cooled to the target cryogenic temperature, a step of transfer of the expanded flow of feed gas into the phase separator, the method comprising a step of determination of the pressure in the phase separator and a step of injection of 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 determination of the pressure in the phase separator comprises at least one among: a pressure measurement, a detection of an expansion in the expansion device without production of "flash" gas, - the injection step is carried out when the pressure in the phase separator (7) drops below a determined threshold and / or when the pressure in the phase separator (7) decreases according to a determined value, - the installation is configured to produce liquefied feed fluid at the outlet of the expansion device 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 device. - The invention may also relate to any alternative device or method comprising any combination of the characteristics above or below within the scope of the claims.

[0018] Other particularities and advantages will appear upon reading the description below, made with reference to the figures in which: Brief description of the figures

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

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

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

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

[0023] The illustrated liquefaction installation 1 comprises a supply circuit 3 of 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 ambient temperature and at a pressure between 5 and 30 bar.

[0024] The supply circuit 3 possesses a downstream end 23 intended to be connected to at least one collection member of the liquefied feed 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 down to a target cryogenic liquefaction temperature, for example a temperature lower than its critical temperature, for example lower than 25K in the case of hydrogen.

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

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

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

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

[0032] This precooling device 14 can comprise a cryogenic loop or fluid (nitrogen or other). In the non-limiting example illustrated, the precooling 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 can include a separator 18 separating the liquid and gas phases.

[0033] Of course, the installation 1 can comprise other (pre)refrigeration device(s).

[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, an expansion device 6 of the cooled feed gas and a liquid and gas phase separator 7 of the flow of feed gas expanded in the expansion device 6.

[0036] The expansion device 6 can 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 recovery member of 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 line 8 provided with a valve 9. This injection line 8 possesses an upstream end 80 connected to a pressurized gas reserve 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 allows injecting 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 into the system.

[0041] The valve 9 on this injection line 8 is preferably a control valve, for example piloted, making it possible to regulate the flow rate 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 unit 12 comprising a microprocessor is configured to control the opening or the 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 of other conditions such as for example: the thermodynamic conditions of the fluid at the outlet of the expansion device 6 (temperature and / or pressure) and / or of the quantity (level) or of 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 reception of a subcooled liquid feed flow, the pressure in the phase separator 7 is going to 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 of the injection line 8 can be calculated by considering that the mixture inside the phase separator 7 (feed flow + gas injection flow) is at equilibrium.

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

[0047] [Fig. 1] 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 present relative advantages as regards for example the efficiency of the mixture obtained between the fluid present and the injection gas or as regards 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] Likewise, in the case of hydrogen, the injected fluid must have an Ortho / Para composition preferably close to that of the hydrogen at this location of the circuit.

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

[0053] For example, the upstream end 80 of the injection line 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 feed 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 higher than 99.999%). To this end, the injected gas can be taken downstream of a cryogenic purification system 11 of the supply circuit.

[0055] As illustrated, the supply circuit 3 can 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 a precooling to a temperature around 80K) a cryogenic purification device 11 (PSA type) and optionally at least one catalysis section 19. As illustrated, the upstream end 80 of the injection line 8 can be located downstream of this cryogenic purification device 11 and / or downstream of the catalysis section 19, for example at the outlet of the cryogenic purification device 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 warmer than the liquid fluid of the phase separator 7. The gas flow rate necessary 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 line 8 can be located further downstream of this cryogenic purification device 11 and catalysis section 19.

[0058] That is to say that the injection gas can be taken from the supply line 3 in the second cold box at a colder level (and with, if applicable, 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 line 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 feed gas).

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

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

[0062] The expansion device 6 can be composed of one or more turbines in series and / or in parallel. The temperature of the gases at the inlet or at the outlet of these turbines is relatively 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 H2 cycle gas which can vary.

[0063] For example, injection gas 8 can thus be taken at the outlet of an expansion stage 103 which supplies 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 line 8 can be connected to another location of the cycle of the refrigerator 10, for example at the level of an intermediate reheating of the expanded cycle gas before its return into the compression device 102. For example, the injection gas is taken at the outlet of a reheating exchanger 5, before its entry into the first cold box or just after the entry into the first cold box.

[0065] That is to say that the injection gas can be taken at the outlet of the 20K cold box of the medium pressure cycle. This gas is relatively warmer than the fluid of the separator 7. The necessary flow rate is therefore relatively low. In addition, the extraction of this gas at the outlet of a relatively cold exchanger 5 is more energy 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 line 8 (the injection point) can be located at different locations of the circuit.

[0067] For example, the downstream end 81 of the injection line 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 device 6.

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

[0069] As illustrated, as a variant or in combination, the injection gas can be injected at the level of the gas outlet of the phase separator 7. This injection of the warm gas on 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 warm gas near the gas outlet of the separator 7 will create a gas pocket in the head of the separator even if the bulk of this injected warm gas flow will leave towards the cycle circuit 101 of the refrigerator 10.

[0070] Thus, the installation provides the possibility of injecting relatively warmer gas into a gas / liquid separator 7 supplied by a cryogenic liquid which can be subcooled, in order to compensate for the condensation of the gas in the separator 7. This makes it possible to create a controllable liquid level in the phase separator 7.

[0071] The warm 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 this operation make it possible to operate a liquefier which can be configured to produce subcooled feed gas or not. In the case where subcooled feed gas is produced, the injection of warmer gas makes it possible to avoid the disadvantages described above.

[0073] In the examples above, the gas injected at the level of 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 can be hydrogen while the cycle gas can be helium or another component 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] Likewise, the feed gas can be another gas (helium or other), the cycle gas can be helium or a mixture containing helium, the gas injected into the phase separator can be helium or another component of the cycle gas (H2 for example).

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

Claims

1. Installation for liquefaction of a cryogenic fluid, for example hydrogen,comprising a supply circuit (3) of feed gas to be liquefied having an upstream end (13) intended to be connected to a source (2) of feed gas under pressure at a first initial temperature and a downstream end (23) intended to be connected to at least one collection member (30) of the liquefied feed 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 feed gas down to a target cryogenic temperature, for example a temperature lower than its critical temperature, for example lower than 25K, the cooling system comprising a cryogenic refrigerator (10) possessing a cycle circuit (101) containing a cycle gas for example comprising or consisting of at least one among: hydrogen, helium, the supply circuit (3) comprising, arranged in series between the set of heat exchangers (4, 5) and the downstream end (23), an expansion device (6) of the cooled feed gas and a liquid and gas phase separator (7) of the flow of feed gas expanded in the expansion device (6), the phase separator (7) comprising a liquid outlet configured to supply the downstream end (23) with liquefied feed gas and a gas outlet connected to a recovery member of the gas phase in the installation (1), for example in the cycle circuit (101), the installation (1) comprising a gas injection line (8) provided with a valve (9), the injection line (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 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) 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 exchanger(s) (4, 5), a cryogenic purification device (11) and at least one catalysis section (19), the upstream end (80) of the injection line (8) being located downstream of the catalysis section (19), at the outlet of the catalysis section (19).

2. Installation according to claim 1, characterized in that the injectedpressurized gas is at a temperature higher than the temperature in the phase separator (7).

3. Installation according to claim 1 or 2, characterized in that the injectedpressurized gas has a degree of purity higher than a determined threshold.

4. Installation according to any one of claims 1 to 3, characterized in thatthe downstream end (81) of the injection line (8) is connected to at least one among: the gas supply circuit (3) between the set of heat exchangers (4, 5) and the expansion device (6), the gas supply circuit (3) between the expansion device (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 thatthe upstream end (80) of the injection line (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 feed gas has a temperature higher than the target temperature.

6. Installation according to any one of claims 1 to 5, characterized in thatthe cycle gas is of the same nature as the feed gas.

7. Installation according to claim 6, characterized in that the upstream end(80) of the injection line (8) is connected to the cycle circuit (101).

8. Installation according to any one of claims 1 to 7, characterized in thatthe cycle circuit (101) comprises at least one compression device (102) of the cycle gas such as at least one compressor, at least one cooling device (4, 5) of the compressed cycle gas, at least one expansion device (103) of the cooled compressed cycle gas, for example at least one turbine and / or valve(s) and a reheating device (5, 4) of the expanded cycle gas.

9. Installation according to claims 7 and 8, characterized in that theupstream end (80) of the injection line (8) is connected to the outlet of the expansion device (103) of the cycle gas.

10. Installation according to claim 9 or according to claims 7 and 8,characterized in that the upstream end (80) of the injection line (8) is connected downstream of at least one reheating device (5, 4) of the expanded cycle gas.

11. Installation according to any one of claims 1 to 10, characterized in thatthe feed gas is hydrogen and in that the cycle gas is or contains hydrogen.

12. Installation according to any one of claims 1 to 11, characterized in thatit comprises an electronic control unit (12) comprising a microprocessor configured to control the opening or the closing of the valve (9) as a function of a measurement (13) of the pressurein the phase separator (7) and / or of the thermodynamic conditions of the fluid at the outlet of the expansion device (6) and / or of the quantity or of the thermodynamic conditions of the fluid in the phase separator (7).

13. Method for liquefaction of a cryogenic fluid, for example hydrogen, bymeans of an installation according to any one of the preceding claims, the method comprising a step of cooling a flow of feed gas under pressure and at an initial temperature, for example at ambient temperature, down to a target cryogenic temperature lower than its critical temperature, a step of expansion (6) of the flow of feed gas cooled to the target cryogenic temperature, a step of transfer of the expanded flow of feed gas into the phase separator (7), the method comprising a step of determination of the pressure in the phase separator (7) and a step of injection of 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).

14. Method according to claim 13, characterized in that the step ofdetermination of the pressure in the phase separator (7) comprises at least one among: a pressure measurement, a detection of an expansion in the expansion device (6) without production of "flash" gas.

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

16. Method according to any one of claims 14 to 16, characterized in thatthe installation (1) is configured to produce liquefied feed fluid at the outlet of the expansion device (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 device (6).

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