Facility and method for liquefying a fluid

Abstract

The invention relates to a facility for liquefying a fluid such as hydrogen, the facility comprising a supply circuit (2) having an end intended to be connected to a member for collecting the liquefied fluid, the facility (1) comprising a set of heat exchangers (4, 5) in heat exchange with the supply circuit (2) and a system for cooling the set of heat exchangers (4, 5) and comprising at least one refrigerator having a refrigeration cycle for a cycle gas, the refrigerator (6) comprising, in a cycle circuit (16): a compression mechanism (26), at least one cooling member (4, 5), an expansion mechanism (36, 46, 56, 66) and at least one warming member (5, 4), wherein the compression mechanism (26) comprises one or more compression stages made up of a set of compressors, the expansion mechanism comprising at least two expansion stages in series, each provided with at least one expansion turbine (36, 46, 56, 66), the last expansion stage being made up of two turbines (66) arranged in parallel, the cycle circuit (16) comprising a set of pipes and valves (106, 206, 306) configured to allow the cycle gas flow to bypass at least one of the two parallel turbines (66) of the last expansion stage and / or to bypass a turbine of a stage preceding the last expansion stage.

Description

Installation and process for liquefying a fluid

[0001] The invention relates to an installation and a method for liquefying a cryogenic fluid, for example hydrogen and / or helium.

[0002] The invention relates more particularly to a liquefaction installation for a fluid such as hydrogen and / or helium, comprising a supply circuit for the fluid to be cooled having an upstream end intended to be connected to a source of gaseous fluid and a downstream end intended to be connected to a collection device for the liquefied fluid, the installation comprising a set of heat exchanger(s) in thermal exchange with the supply circuit and a cooling system in thermal exchange with at least part of the set of heat exchanger(s) configured to cool the supply circuit, the cooling system comprising at least one refrigerator with a cycle refrigeration system for a cycle gas comprising, for example, predominantly helium and / or hydrogen, said refrigerator comprising, arranged in series in a cycle circuit: a cycle gas compression mechanism, at least one cycle gas cooling device,a cycle gas expansion mechanism and at least one heating element for the expanded cycle gas, in which the compression mechanism comprises one or more compression stages consisting of a set of compressor(s), for example of the centrifugal type, the expansion mechanism comprising at least two expansion stages in series, each equipped with at least one expansion turbine, for example of the centripetal type.

[0003] For the production of liquid hydrogen (H2) in facilities using an electrolyzer powered by renewable energy, liquefiers face non-linear operating modes (significant variations in the amount of available electricity and therefore hydrogen produced). In particular, liquefiers must be able to operate at increasingly reduced levels, almost to a complete shutdown ("turndown"). This necessitates the ability to reduce the liquefier load to match the electricity production levels of the renewable energy sources.

[0004] For a liquefier designed to liquefy approximately 100 tonnes per day, one possible architecture involves a refrigeration cycle using four expansion turbines in series coupled to cycle compressors. The four turbines are identical machines (similar power and expansion ratio).

[0005] Existing facilities make it imperfect or difficult to reduce the load on liquefiers to relatively low levels.

[0006] One aim of the present invention is to overcome all or part of the disadvantages of the prior art noted above.

[0007] 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 last expansion stage is composed of two turbines arranged in parallel and in that the cycle circuit includes a set of pipe(s) and valve(s) configured to allow the cycle gas flow to bypass at least one of the two parallel turbines of the last expansion stage and / or to bypass a turbine of a stage preceding the last expansion stage.

[0008] Furthermore, embodiments of the invention may include one or more of the following features: the installation is configured to operate with a thermal load of the fluid flow to be cooled in the supply circuit that is variable over time, the installation being configured to be switchable between a first operating configuration in which the cycle gas flow does not bypass one of the two parallel turbines of the last expansion stage when the thermal load is above a determined threshold and a second operating configuration in which the cycle gas flow bypasses at least one of the two parallel turbines of the last expansion stage when the thermal load is below the determined threshold,The installation includes a device for determining the thermal load of the fluid flow to be cooled in the supply circuit and a control device configured to control the installation and in particular the set of valve(s) of the cycle circuit so that, in response to a drop in the thermal load below a determined threshold, the cycle gas flow bypasses at least one of the two parallel turbines of the last expansion stage and / or a turbine of a previous stage; at least one of the turbines of the expansion mechanism is coupled to at least one of the following: a compressor of the compression mechanism, a brake device or an electric generator; the cycle circuit includes a bypass line for the two parallel turbines of the last expansion stage, said bypass line being fitted with a valve, for example of the Joule-Thomson type.The two parallel turbines of the last expansion stage are smaller than the size of the preceding turbines in series; the expansion mechanism consists of three or four or more expansion stages in series; the cycle circuit piping and valve assembly is configured to allow the cycle gas flow to bypass at least one of the two parallel turbines of the last expansion stage and to bypass the turbine of the stage preceding the last expansion stage; the cycle circuit does not include a passage through the heat exchanger assembly between the outlet of the turbine of the stage preceding the last expansion stage and the last expansion stage.

[0009] The invention also relates to a method for liquefying a fluid such as hydrogen and / or helium using an installation according to any one of the preceding or below characteristics, comprising a step for controlling the cycle gas flow in the expansion mechanism including a bypass of at least one of the two parallel turbines of the last expansion stage and optionally of the turbine of a stage preceding the last expansion stage, to increase the expansion rate per turbine in case of a decrease in the cold thermal power to be supplied by the cycle refrigerator.

[0010] 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.

[0011] Other features and advantages will become apparent upon reading the description below, which refers to the figures in which: Brief description of the figures

[0012] 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:

[0013] is a schematic and partial view illustrating the structure and operation of an example of an installation according to the invention,

[0014] is a schematic and partial view illustrating a detail of the structure and operation of another embodiment of the turbines of the last expansion stage of the installation according to the invention

[0015] is a schematic and partial view illustrating a detail of the structure and operation of yet another example of the realization of a detail (cooling system in particular) of the installation according to the invention. Detailed description

[0016] In all the figures, the same references refer to the same elements.

[0017] 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.

[0018] The illustrated installation 1 for liquefying a fluid such as hydrogen and / or helium includes a circuit 2 for supplying the fluid to be cooled, having an upstream end intended to be connected to a source of gaseous fluid, for example, an outlet of an electrolyzer powered by a renewable and time-varying source of electricity.

[0019] The supply circuit 2 also has a downstream end 3 intended to be connected to a liquefied fluid collection device, for example a cryogenic storage.

[0020] Installation 1 comprises a set of heat exchangers 4, 5 in heat exchange with the supply circuit 2 and a cooling system 6 in heat exchange with at least part of the set of heat exchangers 4, 5. The cooling system 6 is configured to cool the supply circuit 2 to a liquefaction temperature (e.g., around 20 K).

[0021] The cooling system includes at least one refrigerator with a refrigeration cycle using a cycle gas comprising, for example, predominantly helium and / or hydrogen. The cooling system may further include at least one pre-cooling device to provide intermediate cooling of the gas flow in the supply circuit 2 between the initial temperature (for example, ambient) and an intermediate temperature (for example, around 80 K).

[0022] The refrigerator 6 which provides cooling up to the liquefaction temperature includes, arranged in series in a cycle circuit 16: a cycle gas compression mechanism 26, at least one compressed cycle gas cooling element (for example at least part of the aforementioned heat exchanger assembly(ies)), a cycle gas expansion mechanism and at least one expanded cycle gas heating element (for example at least part of the heat exchanger assembly, i.e. the heat exchanger(s) can provide both heating and cooling of the cycle gas in two separate ways, for example in counter-current.

[0023] The compression mechanism 26 comprises one or more compression stages consisting of a set of compressor(s), for example, of the centrifugal and / or positive displacement (piston) type. The expansion mechanism comprises at least two and preferably at least three expansion stages in series, each equipped with at least one expansion turbine 36, 46, 56, 66, for example, of the centripetal type.

[0024] Preferably, at least one of the turbines 36, 46, 56, 66 of the expansion mechanism is coupled to at least one of: a compressor 26 of the compression mechanism, a brake device or an electric generator.

[0025] According to the invention, the last expansion stage consists of two turbines 66 arranged in parallel and the cycle circuit 16 includes a set of pipe(s) and valve(s) 106, 206, 306 configured to allow the cycle gas flow to bypass at least one of the two parallel turbines 66 of the last expansion stage and / or to bypass a turbine of a stage preceding the last expansion stage.

[0026] Installation 1 can be configured to operate with a thermal load of the fluid flow to be cooled from the supply circuit 2 which is variable over time (variable flow rate of gas to be liquefied for example).

[0027] Installation 1 can thus be configured to be switchable between a first operating configuration in which the cycle gas flow does not bypass one of the two turbines 66 in parallel with the last expansion stage when the thermal load is above a determined threshold and a second operating configuration in which the cycle gas flow bypasses at least one of the two turbines 66 in parallel with the last expansion stage when the thermal load is below the determined threshold.

[0028] For example, the threshold may correspond to 50% of the maximum load or the usual nominal load of the installation.

[0029] Installation 1 may include a device 7 for determining the thermal load of the fluid flow to be cooled in the supply circuit 2, for example a flow sensor 7 for the gas flow to be cooled, and a control device 8 configured to control installation 1 and in particular the set of valve(s) 106, 206, 306 of the cycle circuit so that the cycle gas flow bypasses at least one of the two turbines 66 in parallel of the last expansion stage and / or a turbine 56 of a previous stage in response to a drop in the thermal load below a determined threshold.

[0030] For example, the thermal load determination element 7 of the supply circuit 2 is configured to determine the flow rate of the supply circuit 2 of the fluid to be cooled after pre-cooling to the intermediate temperature (e.g. around 80K) and / or the flow rate of the cooled fluid at the liquefaction temperature (e.g. around 20K) and / or the flow rate of vaporization gas (flash) produced within the liquefied fluid and / or the temperature of the liquefied fluid at the liquefaction temperature.

[0031] For example, the thermal load can be calculated based on several of these parameters, by calculating, for example, the balance on this flow rate (after removing the "flash" vaporization gas flow rate) and possibly also by measuring the temperature of the liquefied fluid at the liquefaction temperature.

[0032] At least one of the turbines can be coupled to a compressor to form a "turbocharger" or "turbobooster". The control unit 8 can be configured to control the installation 1 by operating the corresponding compressor(s) (for example, the speed). This can be in combination with, or as an alternative to, the valve control mentioned above.

[0033] As schematically illustrated in the figure, two turbines 66 in parallel of the last expansion stage can each be associated with a respective valve 206 arranged upstream.

[0034] The control of the installation in response to the load can ensure (for example via the control unit 8) control of the inlet valve 206 of each turbine 66 according to the load of the liquefier.

[0035] In the example of the, the circuit 2 for supplying the fluid to be cooled includes, after cooling to the liquefaction temperature, an expansion 202 (valve and / or turbine) then a phase separator pot 506 whose liquid outlet supplies, for example, a liquid storage 302.

[0036] The cycle circuit 16 includes, downstream of the third expansion stage, a phase separator pot 406 forming a thermosiphon. The separator pot 406 receives a portion of the cycle gas flow exiting the third turbine 56 with a final expansion at relatively low pressure (expansion by turbine and / or Joule-Thomson valve) before feeding the thermosiphon pot 406. This pot 406 also receives a fluid (gas) flow from the separator pot 506 located on the supply circuit 2.

[0037] For example, the charge of the liquefier can be determined as a given or function of the flow rate of gas to be liquefied (measured for example by a sensor 7 after pre-cooling of the gas from the supply circuit 2) from which is subtracted the flow rate of the gaseous phase generated by vaporization (flash) downstream (for example sensor 70 on the flow of gas transferred between the separator pot 506 of the supply circuit 2 to the separator pot 406 of the cycle circuit.

[0038] Adjusting the opening of valve 206 at the inlet of each turbine 66 allows the installation 1 to be adapted to the actual load.

[0039] For example, for a load greater than 50% of the maximum load that installation 1 can handle, all turbines can be operational simultaneously.

[0040] Preferably, a control loop is provided at the level of the compressor(s) of the cycle circuit 16. For example, a pressure controller 260 is configured to receive the compression setpoint via the control unit 8 (liquefier charge computer to control the pressure at the inlet of the high-pressure compressor).

[0041] The pressure at the discharge of the high-pressure compressor (downstream stage) can thus be a consequence of the pressure at the inlet of the compression (upstream stage).

[0042] The cycle gas pressure at the inlet of the first expansion turbine 36 is a consequence of the pressure at the compression outlet (due to the series arrangement).

[0043] Preferably, a flow controller is also provided to adjust the cycle gas flow in the cycle circuit 16 according to the load.

[0044] For example, a bypass can be provided to transfer cycle gas to the supply circuit 2 or vice versa.

[0045] Alternatively or in combination, cycle gas can be purged to the atmosphere or recovered if the cycle gas flow rate is too high given the load.

[0046] If the cycle gas flow rate and the pressure within the cycle circuit 16 are adjusted in this way, the speed of the turbine(s) will adapt (pressure and cycle gas flow rate at the turbine inlet).

[0047] This is therefore a consequence of the aforementioned pressure and flow controls.

[0048] Generally, this coupling (pressure and flow rate) defines the turbine's efficiency. For a given thermal load (greater than 50 percent of the maximum or nominal load), it is thus possible to control the pressure and flow rate in the cycle circuit 16 to operate the turbine(s) at their optimal operating point as required by their manufacturer.

[0049] For a load less than 50% of the maximum thermal load, one or more turbines are bypassed (not supplied with cycle gas).

[0050] If the bypassed turbine(s) 56, 66 are coupled to a compressor, a braking mode is provided. This means that the corresponding compressors are not active in the cycle circuit 16. For example, a set of valve(s) is provided to bypass the compressor(s) in question. The corresponding compressors are then connected to a separate circuit independent of the cycle circuit's cooling system.

[0051] Similarly, in this case, the possible liquid turbine located at the cold end of the supply circuit 2 is preferably also bypassed with a Joule Thomson type valve.

[0052] As illustrated, the cycle circuit 16 may advantageously include a bypass pipe 166 for the two turbines 66 in parallel with the last expansion stage. This bypass pipe 166 is equipped with a valve 166, for example of the Joule-Thomson type.

[0053] Preferably, these two turbines 66 in parallel with the last expansion stage are smaller than the size of the other previous turbines 36, 56 in series.

[0054] The replacement of the fourth turbine 4 in series (and last turbine) of the known installations by two smaller turbines 66 arranged in parallel and the possibility of bypassing the previous turbine 56 (3 ème(turbine in series) allows the expansion rate per turbine to be increased in case of a decrease in the cooling power to be supplied.

[0055] The arrangement with two parallel 66 final turbines and the appropriate valve assembly allows at least one of the parallel 66 turbines to be isolated / bypassed. This increases the flexibility of the installation 1 when it is in operation.

[0056] The sizing of the last turbine in series in known installations is often limited or problematic due to the relatively higher volumetric flow rate it receives compared to the other upstream turbines. Often, the turbine in the last expansion stage is subject to more technical constraints; for example, it may be sized to generate a fluid at its outlet with a temperature difference of between 0.1 and 4°C relative to the dew point, to avoid producing liquid at the turbine outlet.

[0057] To maintain a turbine of the same class as the previous turbines, adjustment systems are incorporated into the existing installations. For example, a bypass of the last turbine may be installed, connecting the inlet of the fourth turbine directly to its outlet.

[0058] The claimed arrangement which subdivides the last expansion turbine into two turbines 66 in parallel with the bypasses of one or both turbines 66 makes it possible to efficiently adapt the refrigeration cycle to a significant drop in power / load.

[0059] In addition, preferably the cycle circuit allows the turbine 56 of the stage preceding the last expansion stage 66 to be bypassed.

[0060] Furthermore, preferably, the cycle circuit 16 does not include a passage through the heat exchanger assembly 5 between the turbine outlet 56 of the stage preceding the last expansion stage and the last expansion stage 66.

[0061] The bypass(s) of the turbine(s) concerned 66, 56 can be controlled by an electronic controller 8 comprising a microprocessor, for example based on a signal representative of the load of the installation 1, for example a flow sensor 7 in the supply circuit 2 (and / or any other appropriate parameter). The controller 8 can in particular control the opening / closing of the corresponding valves.

[0062] Thus, depending on the load conditions, the cycle gas flow passes through the last two parallel turbines 66 in which it is expanded (corresponding valves 106, 206 open or closed 406) or the cycle gas flow passes through only one of the last two parallel turbines 66 in which it is expanded (corresponding valves 106 open or closed 206, 406) or the cycle gas flow does not pass through either of the last two parallel turbines 66 (corresponding valve(s) open 406 / closed 106, 206).

[0063] These three configurations can correspond respectively, for example, to three load levels for installation 1.

[0064] When the charge (the flow of gas to be liquefied) of the installation 1 is greater than or equal to the normal or nominal operating level, the cycle gas flow of the refrigerator cycle circuit 6 is expanded in the two final expansion turbines 66 arranged in parallel (bypass valves 406 closed and valves 106, 206 associated with the turbines 66 open).

[0065] Conversely, when energy and hydrogen production decrease, the liquefier load is reduced. The cycle gas flow rate can be reduced.

[0066] At least part of the cycle gas flow can bypass one or both of the last 66 turbines in series (by closing a valve associated with a turbine and opening the bypass valve 406).

[0067] Of course, the invention is not limited to the examples mentioned. For example, three, four, five or more than five expansion stages may be provided.

[0068] As schematically illustrated in the figure, two turbines 66 in parallel of the last expansion stage can each be associated with a respective valve 206 arranged upstream.

[0069] The control of the installation in response to the load can ensure (for example via the control unit 8) control of the inlet valve 206 of each turbine 66 according to the load of the liquefier.

[0070] In the example of the, the circuit 2 for supplying the fluid to be cooled includes, after cooling to the liquefaction temperature, an expansion 202 (valve and / or turbine) then a phase separator pot 506 whose liquid outlet supplies, for example, a liquid storage 302.

[0071] The cycle circuit 16 includes, downstream of the third expansion stage, a phase separator pot 406 forming a thermosiphon. The separator pot 406 receives a portion of the cycle gas flow exiting the third turbine 56 with a final expansion at relatively low pressure (expansion by turbine and / or Joule-Thomson valve) before feeding the thermosiphon. This pot 406 also receives a fluid (gas) flow from the separator pot 506 located on the supply circuit 2.

[0072] For example, the liquefier charge can be determined as a given or function of the flow rate of gas to be liquefied (measured for example by a sensor 7 after pre-cooling) from which is subtracted the flow rate of the gaseous phase generated by vaporization (flash) downstream (for example sensor 70 on the gas flow transferred between the pot 506 separator of the supply circuit 2 to the pot 406 separator of the cycle circuit.

[0073] Adjusting the opening of valve 206 at the inlet of each turbine 66 allows the installation 1 to be adapted to the actual load.

[0074] For example, for a load greater than 50% of the maximum load that installation 1 can handle, all turbines can be operational simultaneously.

[0075] Preferably, a control loop is provided at the level of the compressor(s) of the cycle circuit 16. For example, a pressure controller 126 is configured to receive the compression setpoint via the control unit 8 (liquefier charge computer to control the pressure at the inlet of the high-pressure compressor).

[0076] The pressure at the discharge of the high-pressure compressor (downstream stage) can thus be a consequence of the pressure at the inlet of the compression (upstream stage).

[0077] The cycle gas pressure at the inlet of the first expansion turbine 36 is a consequence of the pressure at the compression outlet (due to the series arrangement).

[0078] Preferably, a flow controller is also provided to adjust the cycle gas flow in the cycle circuit 16 according to the load.

[0079] For example, a bypass can be provided to transfer cycle gas to the supply circuit 2 or vice versa.

[0080] Alternatively or in combination, cycle gas can be purged to the atmosphere or recovered if the cycle gas flow rate is too high given the load.

[0081] If the cycle gas flow rate and the pressure within the cycle circuit 16 are adjusted in this way, the speed of the turbine(s) will adapt (pressure and cycle gas flow rate at the turbine inlet).

[0082] This is therefore a consequence of the aforementioned pressure and flow controls.

[0083] Generally, this coupling (pressure and flow rate) defines the turbine's efficiency. For a given thermal load (greater than 50 percent of the maximum or nominal load), it is thus possible to control the pressure and flow rate in the cycle circuit 16 to operate the turbine(s) at their optimal operating point as required by their manufacturer.

[0084] For a load less than 50% of the maximum thermal load, one or more turbines are bypassed (not supplied with cycle gas).

[0085] If the bypassed turbine(s) 56, 66 are coupled to a compressor, a braking mode is provided. This means that the corresponding compressors are not active in the cycle circuit 16. For example, a set of valve(s) is provided to bypass the compressor(s) in question. The corresponding compressors are then connected to a separate circuit independent of the cycle circuit's cooling system.

[0086] Similarly, in this case, the possible liquid turbine located at the cold end of the supply circuit 2 is preferably also bypassed with a Joule Thomson type valve.

Claims

Liquefaction installation for a fluid such as hydrogen and / or helium comprising a supply circuit (2) for the fluid to be cooled having an upstream end intended to be connected to a source of gaseous fluid and a downstream end (3) intended to be connected to a collection device for the liquefied fluid, the installation (1) comprising a set of heat exchanger(s) (4, 5) in heat exchange with the supply circuit (2) and a cooling system in heat exchange with at least a portion of the set of heat exchanger(s) (4, 5) configured to cool the supply circuit (2), the cooling system comprising at least one refrigerator with a cycle refrigeration system for a cycle gas comprising, for example, predominantly helium and / or hydrogen, said refrigerator (6) comprising, arranged in series in a cycle circuit (16): a cycle gas compression mechanism (26), at least one component (4,5) cycle gas cooling, a cycle gas expansion mechanism (36, 46, 56, 66) and at least one expanded cycle gas heating device (5, 4), wherein the compression mechanism (26) comprises one or more compression stages consisting of a set of compressor(s), for example, of the centrifugal type, the expansion mechanism comprising at least two expansion stages in series, each equipped with at least one expansion turbine (36, 46, 56, 66), for example, of the centripetal type, the last expansion stage being composed of two turbines (66) arranged in parallel, the installation being characterized in that the cycle circuit (16) comprises a set of pipe(s) and valve(s) (106, 206,306) configured to allow the cycle gas flow to bypass at least one of the two turbines (66) in parallel with the last expansion stage and / or to bypass a turbine of a stage preceding the last expansion stage and in that the installation is configured to operate with a thermal load of the fluid flow to be cooled from the supply circuit (2) which is variable over time,the installation (1) being configured to be switchable between a first operating configuration in which the cycle gas flow does not bypass either of the two turbines (66) in parallel with the last expansion stage when the thermal load is above a predetermined threshold and a second operating configuration in which the cycle gas flow bypasses at least one of the two turbines (66) in parallel with the last expansion stage when the thermal load is below the predetermined threshold and in that the installation includes a device (7) for determining the thermal load of the fluid flow to be cooled in the supply circuit (2) and a control device (8) configured to control the installation and in particular the set of valve(s) (106, 206, 306) of the cycle circuit so that, in response to a decrease in the thermal load below a predetermined threshold,The cycle gas flow bypasses at least one of the two parallel turbines (66) of the last expansion stage and / or one turbine (56) of a previous stage. Installation according to claim 1, characterized in that at least one of the turbines (36, 46, 56, 66) of the expansion mechanism is coupled to at least one of: a compressor (26) of the compression mechanism, a brake device or an electric generator. Installation according to any one of claims 1 to 2, characterized in that the cycle circuit (16) comprises a bypass pipe (166) for the two turbines (66) in parallel with the last expansion stage, said bypass pipe (166) being equipped with a valve (166), for example of the Joule Thomson type. Installation according to any one of claims 1 to 3, characterized in that the two turbines (66) in parallel of the last expansion stage have a smaller size than the size of the other preceding turbines (36, 56) in series. Installation according to any one of claims 1 to 4, characterized in that the decompression mechanism consists of three or four or more decompression stages in series. An installation according to any one of claims 1 to 5, characterized in that the assembly of pipe(s) and valve(s) (106, 206, 306) of the cycle circuit is configured to allow the cycle gas flow to bypass at least one of the two turbines (66) in parallel with the last expansion stage and to bypass the turbine (56) of the stage preceding the last expansion stage (66), and in that the cycle circuit (16) does not include a passage through the heat exchanger assembly (5) between the outlet of the turbine (56) of the stage preceding the last expansion stage and the last expansion stage (66). A method for liquefying a fluid such as hydrogen and / or helium using an installation according to any one of the preceding claims comprising a step for controlling the cycle gas flow in the expansion mechanism comprising a bypass of at least one of the two turbines (66) in parallel with the last expansion stage and optionally of the turbine of a stage preceding the last expansion stage, to increase the expansion rate per turbine in the event of a decrease in the cooling thermal power to be supplied by the cycle refrigerator.

Images