Installation and process for liquefying a cryogenic fluid
The gas injection line with a valve in the phase separator addresses the issue of liquid overflow by maintaining thermodynamic equilibrium, ensuring stable liquid level measurement and continuous supply in cryogenic fluid liquefaction installations.
Patent Information
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2024-01-30
- Publication Date
- 2026-04-03
AI Technical Summary
The phase separator in cryogenic fluid liquefaction installations can become completely filled with liquid, leading to operational issues such as inaccurate liquid level measurement and potential halting of liquid supply to downstream storage tanks due to the absence of a gaseous phase, especially when subcooling occurs without flash gas production.
A gas injection line equipped with a valve is connected to a pressurized gas reserve, allowing the injection of warmer gas into the phase separator to maintain thermodynamic equilibrium and control the liquid level, using an electronic control unit to regulate the valve based on pressure and thermodynamic conditions.
The solution ensures stable liquid level measurement and continuous supply to storage tanks by compensating for condensation in the phase separator, preventing operational disruptions and maintaining efficient liquefaction processes.
Smart Images
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Abstract
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 a cryogenic fluid liquefaction installation, for example hydrogen, comprising a feed gas circuit for the liquefied gas having an upstream end intended to be connected to a pressurized feed gas source at a first initial temperature and a downstream end intended to be connected to at least one liquefied feed gas collection device, the installation comprising a set of heat exchangers arranged in series in heat exchange with the feed 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 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 heat exchanger assembly and the downstream end, a device for expanding the cooled feed gas and a liquid and gas phase separator for the feed gas stream 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 device for recovering the gaseous phase in the installation, for example in the cycle circuit, ,
[0003] The hydrogen liquefaction process is generally carried out using a gas stream at ambient temperature and 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 might be a temperature of -251°C at a pressure of 24 bar abs.
[0004] Following 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 storage unit(s) can be used to fill delivery trucks (or another tank or downstream process). The truck filling pressure is defined by the operator. The truck filling pressure determines the pressure in the storage unit(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 final expansion, bringing the fluid to the pressure of the downstream storage. Typically, this flash gas is recovered within the installation, and only the liquid phase is sent to the 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 reached. The saturated liquid is sent from the separator to the storage tank(s). The gaseous phase from 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 gaseous 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 with the installation.
[0012] Thus, for example, a separator that no longer contains a gaseous phase can halt the supply of liquid to a downstream storage tank. Indeed, the liquid is supplied from the tank to the storage tank(s) by opening a valve that is controlled by the liquid level in the separator. This liquid level measurement is generally performed by measuring the gas pressure in the separator. If there is no gaseous phase in the separator, the level measurement is either unavailable or inaccurate.
[0013] One object 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, which also conforms to the generic definition given in the preamble above, is essentially characterized in that the installation comprises a gas injection line equipped 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 include one or more of the following features: - the injected pressurized gas is at a temperature higher than the temperature in the phase separator, - pressurized gas injected to a degree of purity exceeding a predetermined threshold, - the downstream end of the injection line is connected to at least one of the following: the gas supply circuit between the heat exchanger assembly and the expansion unit, the gas supply circuit between the expansion unit 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 heat exchanger assembly(ies) in which the feed gas is at a temperature higher than the target temperature, - the supply circuit includes, at an intermediate level between the upstream end and the outlet of the last of the heat exchanger assembly(ies), a cryogenic purification unit and possibly at least one catalysis section, the upstream end of the injection line being located downstream of the cryogenic purification unit and / or downstream of the catalysis section, for example at the outlet of the cryogenic purification unit 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 includes at least one cycle gas compression device such as at least one compressor, at least one compressed cycle gas cooling device, at least one cooled compressed cycle gas expansion device, for example at least one turbine and / or valve(s) and one expanded cycle gas heating device, - the upstream end of the injection line is connected to the outlet of the cycle gas expansion device, - the upstream end of the injection line is connected downstream to at least one device for heating the expanded cycle gas, - the feed gas is hydrogen, the cycle gas is or contains hydrogen, - the installation includes an electronic control unit comprising a microprocessor configured to control the opening or closing of the valve based on a pressure measurement in the phase separator and / or the thermodynamic conditions of the fluid at the outlet of the unit relaxation 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 conforming to any one of the above or below characteristics, 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 lower than 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 features: - The step of determining the pressure in the phase separator includes at least one of the following: a pressure measurement, a detection of an expansion in the expansion device without the 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 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 above or below features within the scope of the claims.
[0018] Other features and advantages will become apparent from the following description, given with reference to the figures in which: Brief description of the figures
[0019] The invention will be better understood upon reading the following description, given solely by way of example and made with reference to the accompanying drawings in which:
[0020] [Fig. 1] is a schematic and partial view illustrating an example of the structure and operation of an installation according to the invention. Detailed description
[0021] In all figures, the same references refer 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 from different embodiments can also be combined and / or interchanged to provide other embodiments.
[0023] The illustrated liquefaction installation 1 comprises a feed gas supply circuit 3 (for example, hydrogen) having an upstream end 13 intended to be connected to a pressurized feed gas source 2 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 has a downstream end 23 intended to be connected to at least one liquefied feed gas collection device, 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 the following: 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 simplicity. The cycle circuit 101 includes one or more compressors 102. The compressed fluid is cooled (heat exchangers 4, 5) then expanded (turbine(s) 103 and / or valve(s)) and then reheated (heat exchangers 5, 4). The cycle circuit 101 thus subjects the cycle gas to a thermodynamic cycle to provide cooling power.
[0030] All or part of the heat exchangers 4, 5 may be multi-pass (co-current or counter-current) exchangers to ensure the simultaneous heating and cooling of the flow(s).
[0031] As illustrated, the cooling system may further include a pre-cooling device 14 in heat exchange with a portion of the heat exchangers Heat. This pre-cooling device 14 can be configured to lower the hydrogen temperature from the initial temperature at the upstream end to a second intermediate temperature between the initial 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 include a cryogenic loop or fluid (nitrogen or other). In the non-limiting example shown, the pre-cooling device 14 includes a nitrogen refrigeration loop 15 which subjects a nitrogen flow to a compression 15, cooling 4, expansion 17 and heating 4 cycle. As shown, the refrigeration loop 15 may include a separator 18 separating the liquid and gaseous phases.
[0033] Of course, installation 1 may include other (pre)refrigeration devices.
[0034] The pre-cooling system 14 and the corresponding components of the installation can be housed in a first cold box (80K for example). The refrigerator 10 and the corresponding components 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 cooled feed gas expansion device 6 and a liquid and gas phase separator 7 of the feed gas flow expanded in the expansion device 6.
[0036] The expansion member 6 may include or consist of at least one cryogenic turbine and / or a valve, for example of Joule Thomson type.
[0037] The phase separator 7 includes a liquid outlet configured to supply the downstream end 23 with liquefied feed gas and a gas outlet connected to a gaseous phase recovery device 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] Installation 1 includes a gas injection line 8 equipped with a valve 9. This injection line 8 has an upstream end 80 connected to a pressurized gas reservoir 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 relatively warmer gas to be injected at the separator 7. This makes it possible to compensate, if necessary, for the condensation of the gaseous phase in the separator 7 by adding heat to the system.
[0041] The valve 9 on this injection line 8 is preferably a regulating valve, for example piloted, allowing the flow of gas injected towards the separator 7 to be regulated.
[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 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: the thermodynamic conditions of the fluid at the outlet of the expansion unit 6 (temperature and / or pressure) and / or the quantity (level) or thermodynamic conditions of the liquid in the phase separator 7.
[0044] When the gaseous 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 line 8 can be calculated by considering that the mixture inside the phase separator 7 (supply 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. 1 illustrates several examples shown simultaneously but which can be combined in 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] Furthermore, the injected fluid must have a composition similar to that in the supply circuit at the injection point. For example, identical or close purity.
[0051] Similarly, in the case of hydrogen, the injected fluid should have an Ortho / Para composition preferably close to that of hydrogen at that point in the circuit.
[0052] In the non-limiting example, three distinct source points and three potential distinct injection points are illustrated.
[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 is at a temperature higher than the target temperature.
[0054] The injected gas preferably has a specific purity (for example, hydrogen with a specific degree of purity, for example greater than 99.999%). For this purpose, the injected gas can be taken downstream of a cryogenic purification system 11 of the supply circuit.
[0055] As illustrated, the supply circuit 3 may include, 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 80 K), a cryogenic purification unit 11 (PSA type) and optionally at least one catalysis section 19. As illustrated, the upstream end 80 of the injection line 8 may be located downstream of this cryogenic purification unit 11 and / or downstream of the catalysis section 19, for example, at the outlet of the cryogenic purification unit 11 and / or at the outlet of the catalysis section 19.
[0056] For example, feed gas is used just before it enters the second cold box. This gas is hotter than the liquid fluid in the 7-phase separator. The gas flow rate required to control the liquid level in the 7-phase separator 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 7-phase separator).
[0057] As also illustrated, the upstream end 80 of the injection line 8 can be located further downstream of this cryogenic purification organ 11 and catalysis section 19.
[0058] That is to say, the injection gas can be drawn from supply line 3 in the second cold box at a colder level (and with, where applicable, a higher Ortho / Para conversion). This solution offers a higher energy efficiency than the previous solution. Furthermore, the stability of the hydrogen is higher (higher Ortho / Para conversion rate).
[0059] As illustrated, alternatively or in combination, the upstream end 80 of the injection line 8 can be connected to the cycle circuit 101. That is to say, 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 schematically shown, the cycle circuit 101 may include at least one cycle gas compression element 102 such as at least one compressor, at least one compressed cycle gas cooling element 4, 5 (heat exchanger(s)), at least one cooled compressed cycle gas expansion element 103, for example at least one turbine and / or valve(s) and one expanded cycle gas heating element 5, 4 (heat exchanger(s)).
[0061] The upstream end 80 of the injection line 8 can thus be connected to the outlet of a cycle gas expansion device 103 (at 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 outlet of these turbines is relatively higher than that of the gas in the first sampling example at the level of the supply circuit 3. This injection gas source, chosen at the outlet of a turbine 103 of the cycle gas, offers a higher energy efficiency. The hydrogen content Para of the gas will depend on the H2 content of the cycle gas, 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 (either alternatively or in combination), the upstream end 80 of the injection line 8 may be connected to another point in the refrigerator cycle 10, for example, at an intermediate heating point for the expanded cycle gas before its return to the compression unit 102. For example, the injection gas is taken from the outlet of a heating exchanger 5, before or just after it enters the first cold box.
[0065] That is to say, the injection gas can be taken from the outlet of the cold box 20K of the medium-pressure cycle. This gas is relatively warmer than the fluid in the separator 7. The required flow rate is therefore relatively low. Furthermore, extracting this gas from the outlet of a relatively cold heat 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 hydrogen content Para 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 in 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 allow relatively hot gas to be injected directly into the liquid 7 of the phase separator 7. This ensures good gas-liquid mixing and allows thermodynamic equilibrium to be reached.
[0069] As illustrated, alternatively or in combination, the injection gas can be injected at the gas outlet of the phase separator 7. This injection of hot gas at the gas outlet of the phase separator 7 may require a lower injection flow rate due to 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 separator head, even though most of this injected hot gas flow will go to the refrigerator cycle circuit 101.
[0070] Thus, the installation provides for 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 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 allows the use of a liquefier that can be configured to produce subcooled or uncooled feed gas. When subcooled feed gas is produced, injecting warmer gas avoids the drawbacks described above.
[0073] In the examples above, 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, so the gas injected into the phase separator 7 is hydrogen. However, other configurations are possible. Thus, for example, the feed gas could be hydrogen while the cycle gas could 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 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 constituent of the cycle gas (H2 for example).
[0076] For example, the type of gas injected may be different from the "receiving" gas if it does not interfere with any "purity" specifications of the "receiving" gas and / or the operation of the installation.
Claims
1. Demands Installation for the liquefaction of a cryogenic fluid, for example hydrogen, comprising a feed gas supply circuit (3) having an upstream end (13) intended to be connected to a source (2) of pressurized feed gas at a first initial temperature and a downstream end (23) intended to be connected to at least one liquefied feed gas collection device (30), 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 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 feed circuit (3) comprising, arranged in series between the heat exchanger assembly (4, 5) and the downstream end (23), a device (6) for expanding the cooled feed gas and a liquid and gas phase separator (7) of the feed gas stream 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 gas phase recovery device in the installation (1), for example in the cycle circuit (101), the installation (1) comprising a gas injection line (8) equipped with a valve (9),the injection line (8) having an upstream end (80) connected to a pressurized gas reservoir 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 heat exchanger assembly (4, 5), a cryogenic purification unit (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 injected pressurized 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 gas under pressure injected has 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 line (8) is connected to at least one of: the gas supply circuit (3) between the heat exchanger assembly (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 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 heat exchanger assembly (4, 5) in which the feed gas is at a temperature above the target temperature.
6. Installation according to any one of claims 1 to 5, characterized in that the 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 that the cycle circuit (101) comprises at least one cycle gas compression element (102) such as at least one compressor, at least one compressed cycle gas cooling element (4, 5), at least one cooled compressed cycle gas expansion element (103), for example at least one turbine and / or valve(s) and an expanded cycle gas heating element (5, 4).
9. Installation according to claims 7 and 8, characterized in that the upstream end (80) of the injection line (8) is connected to the outlet of the cycle gas expansion device (103).
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 (5, 4) device for heating the expanded cycle gas.
11. Installation according to any one of claims 1 to 10, characterized in that the 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 that it comprises an electronic control element (12) including 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 the thermodynamic conditions of the fluid at the outlet of the expansion element (6) and / or the quantity or thermodynamic conditions of the fluid in the phase separator (7).
13. A method for 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 above the temperature of the fluid in the phase separator (7).
14. Method according to claim 13, 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.
15. A method according to claim 13 or 14, 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 according to a determined value.
16. A method according to any one of claims 13 to 15, 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).