Fluid liquefaction method and device

Abstract

The invention relates to a device for liquefying a fluid such as hydrogen, comprising a pre-cooling system in a heat-exchange relationship with at least part of a set of heat exchanger(s) configured to lower the temperature of the fluid that is to be cooled to a first temperature and a cooling system in a heat-exchange relationship with at least part of the set of heat exchanger(s), wherein the cooling system and the pre-cooling system each comprise a refrigeration cycle refrigerator for a cycle gas comprising, in a cycle circuit: a compression mechanism, and an expansion mechanism, the compression mechanism comprising a set of centrifugal-type compressors mounted on shafts driven in rotation by a set of motors, the expansion mechanism comprising at least one of the turbines coupled to the same shaft as at least one compression stage.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a § 371 of International PCT Application PCT / EP2023 / 066537, filed Jun. 20, 2023, which claims the benefit of FR2207003, filed Jul. 8, 2022, both of which are herein incorporated by reference in their entireties.FIELD OF THE INVENTION

[0002] The invention relates to a device and a method for liquefying a fluid such as hydrogen and / or helium.BACKGROUND OF THE INVENTION

[0003] Devices for the liquefaction of cryogenic fluids, notably hydrogen, generally comprise a pre-cooling system using a cold source such as a reserve of liquid nitrogen or a closed-cycle or semi-closed-cycle refrigerator operating on nitrogen.

[0004] The lowest pressure in the pre-cooling cycle determines the lowest temperature that the pre-cooling cycle gas attains (cut-off temperature). Thus, this low pressure of the pre-cooling cycle is set to the lowest possible value in order to lower the cut-off temperature at the cold end of this pre-cooling cycle and thus effectively pre-cool the flow of gas that is to be liquefied before this gas exchanges heat with the cycle gas of the refrigerator which lowers the temperature down to a liquefaction temperature.

[0005] This architecture generally employs multi-stage compression stations comprising a gear wheel or other device for increasing speed between the speed supplied by the typically 50 or 60 Hz electric motor and the rotary shafts, bearing the multiple compression stages, which for energy-efficiency reasons require a far higher shaft rotational speed. This architecture does not allow for a great deal of flexibility in the liquefaction process as described below.

[0006] One known solution is to use the so-called mobile “IGV” (Inlet Guide Vanes) technology that enables the flow rates of gas on the intake side, typically of the first compression stage of the cycle that comprises these IGV to be varied. In general, for reasons of cost and to limit the number of moving parts that could potentially cause the entire installation to fail, this technology is installed only at the inlet of the first compression stage of the relevant refrigeration cycle. This solution is only partially satisfactory. In particular, the overall efficiency and output of the installation are not satisfactory. In particular, this solution does not allow the installation to cope with intermittent energy supplies, or if it does, it then does so with somewhat unsatisfactory output.

[0007] Another solution is to use a refrigeration cycle operating on mixed refrigerants (MR). However, these solutions provide a higher cut-off temperature (mixtures of constituents of hydrocarbon and nitrogen type which when mixed give rise to cut-off temperatures 20 to 50 degrees higher than pre-cooling cycles operating on pure nitrogen) and this imposes a greater thermodynamic demand on the final cooling cycle. In addition, in the event of a leak, the mixture that the operators have to top up is complicated for the operators to reconstitute (as it is necessary to determine which component or components have leaked the most and to readjust the mixture step-by-step). If the cut off temperature of this cycle is lowered (typically by adding greater proportions of nitrogen to the mixture), the output of this method drops significantly (by the order of 10% if the cut-off temperature is lowered by 5 K). It is an object of the present invention to alleviate all or some of the above-mentioned disadvantages of the prior art.SUMMARY OF THE INVENTION

[0008] In certain embodiments, the invention more particularly relates to a device for liquefying a fluid such as hydrogen and / or helium, comprising a circuit for 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 member for collecting the liquefied fluid, the device comprising a set of heat exchanger(s) in a heat-exchange relationship with the circuit (3) for fluid to be cooled, the device comprising a pre-cooling system in a heat-exchange relationship with at least part of the set of heat exchanger(s) and configured to lower the temperature of the fluid to be cooled to a first temperature, for example comprised between 30 and 110 K, the device further comprising a cooling system in a heat-exchange relationship with at least part of the set of heat exchanger(s) and configured to lower the temperature of the fluid to be cooled from the first temperature to a second temperature, for example comprised between 15 and 25 K, wherein the cooling system comprises a first refrigerator with a refrigeration cycle operating using a first cycle gas containing helium and / or hydrogen, said first refrigerator comprising, arranged in series in a cycle circuit: a compression mechanism for compressing the cycle gas, at least one cooling member for cooling the cycle gas, an expansion mechanism for expanding the cycle gas, and at least one heating member for heating the expanded cycle gas, wherein the compression mechanism comprises several compression stages in series, these being made up of a set of compressor(s) of the centrifugal type, the compression stages being mounted on shafts rotationally driven by a set of motor(s), the expansion mechanism comprising several expansion stages made up of a set of turbines of centripetal type.

[0009] In an effort to overcome the deficiencies of the prior art discussed, supra, the device according to the invention, in other respects in accordance with the generic definition thereof given in the above preamble, may include at least one of the turbines that is coupled to the same shaft as at least one compression stage so as to supply to the compression stage mechanical work produced during the expansion, and in that the pre-cooling system comprises a second refrigerator with a refrigeration cycle operating using a second cycle gas, said second refrigerator comprising, arranged in series in a cycle circuit: a compression mechanism for compressing the cycle gas, at least one cooling member for cooling the cycle gas, an expansion mechanism for expanding the cycle gas, and at least one heating member for heating the expanded cycle gas, wherein the compression mechanism comprises several compression stages in series, these being made up of a set of compressor(s) of the centrifugal type, the compression stages being mounted on shafts rotationally driven by a set of motor(s), the expansion mechanism comprising one or more expansion stages made up of a set of turbine(s) of centripetal type, at least one of which is coupled to the same shaft as at least one compression stage so as to supply to the compression stage mechanical work produced during the expansion.

[0010] Moreover, some embodiments of the invention may comprise one or more of the following features:

[0011] the cycle gas of the second refrigerator comprises at least one from among: nitrogen, neon, helium, hydrogen, oxygen, argon or carbon dioxide,

[0012] the first refrigerator and the second refrigerator comprise respective motors of the same type and / or respective compressors of the same type, and / or respective turbines of the same type,

[0013] the first refrigerator and the second refrigerator comprise at least one motor in common, the shaft of which is coupled to one or more of the compressors and / or one or more of the turbines of the first refrigerator and also coupled to one or more of the compressors of the second refrigerator and / or one or more of the turbines of the second refrigerator,

[0014] the set of motor(s) of the first and / or the second refrigerator comprises at least one variable-speed electric motor controlled by an electrical signal, for example by varying the frequency of the electrical signal,

[0015] the set of motor(s) of the second refrigerator comprises at least one variable-speed electric motor controlled by an electrical signal, for example by varying the frequency of the electrical signal, and in that the cold power supplied by the second refrigerator determines the first temperature and is dependent on the rotational speed of said at least one motor,

[0016] the set of motor(s) of the first refrigerator comprises at least one variable-speed electric motor controlled by an electrical signal, for example by varying the frequency of the electrical signal, and in that the cold power supplied by the first refrigerator determines the second temperature and is dependent on the rotational speed of said at least one motor,

[0017] the device comprises an electronic control member for controlling at least one of the motor(s) of the first refrigerator and at least one motor of the second refrigerator, the control member being configured to control jointly the speed setpoint for the motors of the first and second refrigerators,

[0018] the control member is configured to increase or decrease, by identical percentages, the speed setpoints for the motors of the first and second refrigerators.

[0019] The invention also relates to a method for liquefying a fluid such as hydrogen and / or helium using a device having any one of the features described above or below, the method comprising a step of cooling the fluid to be cooled to the first temperature, for example comprised between 30 and 110 K using the second refrigerator and then a step of cooling the fluid to be cooled from the first temperature to the second temperature for example comprised between 15 and 25 K.

[0020] According to other possible specific features:

[0021] the method comprises a step of controlling the value of the first temperature by controlling the speed of at least one of the motors of the set of motor(s) of the second refrigerator,

[0022] the cycle circuits of the first refrigerator and of the second refrigerator contain the same cycle gas and are interconnected via at least one valve.

[0023] The invention may also relate to any alternative device or method comprising any combination of the features above or below that falls within the scope of the claims.

[0024] Further distinctive features and advantages will become apparent on reading the description below, provided with reference to the figures, in which:BRIEF DESCRIPTION OF THE DRAWINGS

[0025] These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it can admit to other equally effective embodiments.

[0026] The invention will be understood better from reading the following description, which is given solely by way of example and with reference to the appended drawings, in which:

[0027] FIG. 1 is a partial and schematic view illustrating an example of the structure and operation of one example of a liquefaction device according to the invention,

[0028] FIG. 2 is a partial and schematic view of a detail of such a device, in an embodiment variant,

[0029] FIG. 3 is a partial and schematic view of another detail of such a device, in another embodiment variant.DETAILED DESCRIPTION OF THE INVENTION

[0030] Throughout the figures, the same references relate to the same elements.

[0031] 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. Individual features of different embodiments can also be combined and / or interchanged to provide other embodiments.

[0032] The device 1 for liquefying a fluid such as hydrogen and / or helium and illustrated in FIG. 1 comprises a circuit 3 for fluid to be cooled, having an upstream end intended to be connected to a source 2 of gaseous fluid, and a downstream end 23 intended to be connected to a member 4 for collecting the liquefied fluid.

[0033] The source 2 may comprise a unit (network) for distributing and / or a unit for producing gas (for example hydrogen). The source 2 main in particular comprise an electrolyzer or a steam reforming unit.

[0034] The connecting member 4 may for example comprise at least one cryogenic liquid storage unit. Upstream of the storage unit 4, the circuit 3 for fluid to be cooled preferably comprises a valve, for example an expansion valve 12 and / or an expansion turbine.

[0035] The liquefaction device 1 comprises a set of heat exchanger(s) 6, 7, 8, 9, 10 arranged in series and / or in parallel in a heat-exchange relationship with the circuit 3 for fluid to be cooled, and a pre-cooling system 20 in a heat-exchange relationship with at least part of the set of heat exchanger(s) 6.

[0036] This pre-cooling system is typically configured to lower the temperature of the fluid to be cooled to a first temperature, for example comprised between 30 and 110 K, for example 80 K.

[0037] The liquefaction device 1 further comprises a cooling system 21 in a heat-exchange relationship with at least part of the set of heat exchanger(s) 6, 7, 8, 9, 10.

[0038] This cooling system is itself configured to lower still further the temperature of the fluid to be cooled from the first temperature to a second temperature, for example comprised between 15 and 25 K, for example 20 K, to allow said fluid to liquefy.

[0039] As illustrated, the cooling system comprises a first refrigerator 21 with a refrigeration cycle operating using a first cycle gas containing helium and / or hydrogen. This first refrigerator 21 comprises, arranged in series in a cycle circuit 14: a compression mechanism 15 for compressing the cycle gas, at least one cooling member for cooling the cycle gas, an expansion mechanism 17 for expanding the cycle gas, and at least one heating member for heating the expanded cycle gas.

[0040] What this means is that the first refrigerator 21 subjects the cycle gas to a thermodynamic cycle in which the cycle gas at a cold end attains a very low (cryogenic) temperature constituting a cold power which is then placed in the heat-exchange relationship with the fluid that is to be liquefied.

[0041] The fluid that is to be liquefied (for example hydrogen) is a fluid that is preferably distinct from the fluid of the cycle gas (for example helium with possibly one or more other component(s)).

[0042] Preferably, these two circuits are thus separate.

[0043] As illustrated, the set of heat exchanger(s) which cools the fluid to be liquefied preferably comprises one or a plurality of countercurrent heat exchangers 6, 7, 8, 9 which are arranged in series and in which two separate portions of the cycle circuit 14 perform circulation simultaneously in countercurrent operation (respectively for the cooling and the heating of separate flows of the cycle gas).

[0044] That is to say that this plurality of countercurrent heat exchangers forms both a member for cooling the cycle gas (after the compression and after one or more expansion stage(s), for example) and a member for heating the cycle gas (after the expansion and before the return to the compression mechanism).

[0045] The compression mechanism comprises a plurality of compression stages 15 in series made up of a set compressor(s) 15 of centrifugal type. For example, the compression mechanism comprises at least four compression stages 15 made up of a set of compressors of the centrifugal type which are arranged in series (and possibly in parallel).

[0046] A compression stage 15 may be made up of an impeller wheel of a motorized centrifugal compressor.

[0047] The compression stages 15 (that is to say the compressor impeller wheels) are mounted on shafts 19 that are rotationally driven by a set of motor(s) 18 (at least one motor).

[0048] Preferably, all the compressors 15 are of the centrifugal type.

[0049] The expansion mechanism preferably comprises several expansion stages made up of a set of turbine(s) 17 of centripetal type, wherein at least one of the turbines 17 is coupled to the same shaft 19 as at least one compression stage 15 so as to supply to the compression stage 15 mechanical work produced during the expansion. For example, the expansion mechanism comprises three or more expansion stages formed of turbines 17 of the centripetal type arranged at least partly in series.

[0050] As a preference, the number of compression stages (for example the number of compression impeller wheels) is greater than the number of expansion stages (for example the number of expansion turbine wheels). As a preference, all the turbines 17 are of centripetal type and are predominantly arranged in series.

[0051] The device 1 may comprise a cooling member 8, 9 for cooling the cycle gas and configured to cool the cycle gas at the outlet of at least one of the turbines 17. That is to say that, after expansion in a turbine 17, the cycle gas may be cooled by a value typically comprised between 2 K and 30 K.

[0052] In addition, at least one of the turbines 17 is coupled to the same shaft 19 as a compression stage 15 of a compressor so as to supply to the compressor mechanical work produced during the expansion.

[0053] This architecture makes it possible to decorrelate (make independent) the method with heat-transfer fluid (helium-based cycle gas, for example) in relation to the delivery temperature of the fluid that is to be liquefied (hydrogen, for example). This makes it possible in particular, in the cycle circuit 14, to increase the value of the low pressure level of the cycle gas to pressures which are higher than in the known devices. This is possible in spite of a relatively low overall cycle gas compression ratio. This centrifugal compression technology would generally not be recommended for the liquefaction of hydrogen in the prior art owing to the limitation of the compression ratio per stage.

[0054] As a result, the device 1 may comprise or more motor-driven turbocompressors in part of the compression station. A motor-driven turbocompressor is an assembly comprising a motor, the shaft of which directly drives a set of compression stage(s) (impeller wheel(s)) and a set of expansion stage(s) (turbine(s)). This makes use of the mechanical work of expansion directly at one or more of the compressors 15 of the cycle gas.

[0055] The pre-cooling system 21 comprises a second refrigerator 20 with a refrigeration cycle operating using a second cycle gas. This second refrigerator 20 likewise comprises, arranged in series in a cycle circuit 140: a compression mechanism 150 for compressing the cycle gas, at least one cooling member 160 for cooling the cycle gas, an expansion mechanism 170 for expanding the cycle gas, and at least one heating member 6 for heating the expanded cycle gas.

[0056] The compression mechanism comprises a plurality of compression stages 150 in series made up of a set compressor(s) 150 of centrifugal type. The compression stages 150 are mounted on shafts 190 that are rotationally driven by a set of motor(s) 180.

[0057] The expansion mechanism comprises one or more expansion stages made up of a set of turbine(s) 170 of centripetal type.

[0058] As was the case with the first refrigerator, at least one of the turbines 170 is coupled to the same shaft 190 as at least one compression stage 150 so as to supply to the compression stage 150 mechanical work produced during the expansion.

[0059] What that means is that the first refrigerator 21 and second refrigerator 20 preferably have the same general structure and technology.

[0060] This architecture of pre-cooling system 20 makes it possible to lower the cut-off temperature of the pre-cooling system 20 in comparison with the known devices, and offers greater flexibility.

[0061] The cycle gas of the second refrigerator 20 may comprise at least one from among: nitrogen, neon, helium, hydrogen, oxygen, argon or carbon dioxide. As a preference, the cycle gas for this second refrigerator that performs the pre-cooling is made up of a mixture of helium and neon or helium and nitrogen for example. As a preference, the device uses only rare and / or inert gases in the cycles.

[0062] This makes it possible to attain lower temperatures in the pre-cooling system (typically below 80 K) without adversely affecting the overall output and without the risk of causing the condensing or even freezing of a constituent which would have a dramatic impact on the turbomachines and exchangers of the circuit.

[0063] As illustrated, at least one exchanger 6 may be common to the following streams: circuit 3 for fluid to be cooled, circuit 14 of the first refrigerator (notably two streams: after and before compression) and circuit 140 of the second refrigerator (for example two streams: before and after expansion).

[0064] As mentioned hereinabove, the first refrigerator 21 and second refrigerator 20 preferably have the same general structure and the same technology. In particular, these two refrigerators 20, 21 preferably comprise components that are of the same type or identical. What is meant by “identical” or “of the same type” is components (motor, turbine wheel, compressor impeller wheel, bearings, housing, etc.) that employ the same technology but are not necessarily strictly identical. For example, the components that are of the same type may be of different sizes.

[0065] Thus, the first refrigerator 21 and the second refrigerator 20 comprise, for example, respective motors of the same type and / or respective compressors of the same type, and / or respective turbines of the same type, and / or bearings of the same type (magnetic or gas).

[0066] The two cycles 14, 140 comprise for example centripetal turbines and centrifugal compressors which are coupled on the same shafts. These components of the same type allow components or subcomponents to be shared: for example same electric motors, same electrotechnical system for the motor-compressors and motor-turbocompressors, same wheels, same dimensions, same designs, etc. This allows for shared sourcing and notably makes it possible to reduce the part numbers of components or of members of the device 1 (for example: motor, bearings across the entirety of the liquefaction unit, etc.).

[0067] This allows the one same device 1 (one same facility) to use machines of one single type both for pre-cooling (from 300 K to 80 K for example) and for cooling (between 80 K and 20 K for example). For example, only the turbines would differ.

[0068] The cryogenic components may be housed in separate thermally insulated (preferably vacuum) cold boxes or in the one same cold box (for example having, or not having, independent separate volumes).

[0069] In addition, and as schematically indicated in FIG. 2, the first refrigerator 21 and the second refrigerator 20 may comprise a motor 18, 180 in common, to the rotary shaft 19, 190 of which wheels of the two refrigerators 20, 21 are coupled. For example, the shaft 19, 190 of a motor 18, 180 is coupled to at least one impeller wheel of a compressor 15 and / or turbine wheel of a turbine 17 of the first refrigerator 21 and is also coupled to at least one impeller wheel of a compressor 150 and / or a turbine wheel of a turbine 170 of the second refrigerator 20.

[0070] Likewise, motors of the two refrigerators 20, 21 may share components in common, for example the same power circuitry and / or the same speed-the varying electronics (“VFD”).

[0071] As a preference, at least part of the set of motor(s) 18, 180 of the first and / or the second refrigerator 21, 20 are variable-speed electric motors controlled by an electrical signal, for example by varying the frequency of the electrical signal.

[0072] In addition, the cold power supplied by each refrigerator 20, 21 is preferably dependent on the rotational speed of the motor or motors, the cold power supplied being for example proportional to the rotational speed of the motors.

[0073] In particular, the rotational speed of the motor or motors 180 of the second refrigerator 20 governs the lowest temperature supplied by the second refrigerator 20 (cutoff temperature). This determines the second temperature in the process for cooling and liquefying the fluid that is to be liquefied.

[0074] As schematically indicated in FIG. 3, the device 1 preferably comprises an electronic control member 11 for controlling at least one motor(s) 18, 180. The electronic controller 11 comprises, for example, a microprocessor or computer or any other appropriate system.

[0075] As illustrated, the electronic member 11 may control at least one of the motor(s) 18 of the first refrigerator 21 and at least one motor 180 of the second refrigerator 20. This control member 11 may in particular be configured to control jointly the speed setpoint for the motors of the first and second refrigerators 20, 21. That is to say that the control of one of the refrigerators 20 or 21 determines (is dependent on) the control of the other refrigerator 21 or 20.

[0076] For example, the control member 11 may be configured to increase or decrease, by identical percentages, the speed setpoints for the motors 18, 180 of the first refrigerator 21 and second refrigerator 20.

[0077] For example, the temperature conditions of the liquefied fluid may be controlled through the speed of the motors 18, 180. Thus, for example, if the speed of the motors of the first refrigerator 21 has to be lowered (or increased) by 30%, the speed of the motors 20 of the second refrigerator is lowered (or increased) likewise by 30%. This may be achieved via one single control setpoint instruction (an identical or single signal).

[0078] As a preference, the pre-cooling cycle is a closed cycle and the cooling cycle is likewise a closed cycle.

[0079] In one possible variant, the two cycles could be connected via an equalizing valve (and a control system for operating the valve). This allows the cold powers produced by the two refrigerators 20, 21 to be apportioned without changing the speed of the corresponding motors.

[0080] The device 1 offers a great deal of flexibility in the control of the cold powers of the pre-cooling system 20 and cooling system 21.

[0081] Thus it is possible to control and set the temperatures at the junction between the two refrigerators in the circuit 3 for fluid to be liquefied.

[0082] The device 1 also makes it possible to increase the capacity to produce cold in the cooling system while maintaining the same architecture, namely a liquefied gas at a temperature lower than at the nominal operating point. Specifically, it is possible to lower the cut-off temperature of the pre-cooling system on an ad-hoc basis. This makes it possible to reduce the thermal load on the cooling system and therefore have the liquefied fluid even more sub-cooled as it leaves the liquefier. The cut-off temperature can be modified over a wider range of temperatures.

[0083] While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

[0084] The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

[0085] “Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of “comprising”). “Comprising” as used herein may be replaced by the more limited transitional terms “consisting essentially of” and “consisting of” unless otherwise indicated herein.

[0086] “Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

[0087] Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

[0088] Ranges may be expressed herein as from about one particular value, and / or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and / or to the other particular value, along with all combinations within said range.

[0089] All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.

Claims

1-8. (canceled)9. A device for liquefying a fluid, the device comprising:a circuit for fluid to be cooled, having an upstream end configured to be connected to a source of gaseous fluid, and a downstream end configured to be connected to a member for collecting the liquefied fluid;a set of heat exchanger(s) in a heat-exchange relationship with the circuit for fluid to be cooled;a pre-cooling system in a heat-exchange relationship with at least part of the set of heat exchanger(s) and configured to lower the temperature of the fluid to be cooled to a first temperature between 30 K and 110 K;a cooling system in a heat-exchange relationship with at least part of the set of heat exchanger(s) and configured to lower the temperature of the fluid to be cooled from the first temperature to a second temperature between 15 and 25 K,wherein the cooling system comprises a first refrigerator with a refrigeration cycle operating using a first cycle gas containing helium and / or hydrogen, said first refrigerator comprising, arranged in series in a cycle circuit: a compression mechanism configured to compress the cycle gas, at least one cooling member configured to cool the cycle gas, an expansion mechanism configured to expand the cycle gas, and at least one heating member configured to heat the expanded cycle gas,wherein the compression mechanism comprises a plurality of compression stages in series, said plurality of compression stages being comprised of a set of centrifugal compressor(s),wherein the plurality of compression stages are mounted on shafts rotationally driven by a set of motor(s),wherein the expansion mechanism comprises several expansion stages comprised of a set of centripetal turbines, wherein at least one of the centripetal turbines is coupled to a same shaft as at least one compression stage so as to supply to the compression stage mechanical work produced during the expansion,wherein the pre-cooling system comprises a second refrigerator with a refrigeration cycle operating using a second cycle gas, said second refrigerator comprising, arranged in series in a second cycle circuit: a second compression mechanism configured to compress the second cycle gas, at least one cooling member configured to cool the second cycle gas, a second expansion mechanism configured to expand the second cycle gas, and at least one heating member configured to heat the expanded second cycle gas,wherein the second compression mechanism comprises a second plurality of compression stages in series, said plurality of compression stages being comprised of a second set of centrifugal compressor(s),wherein the second plurality of compression stages are mounted on shafts rotationally driven by a second set of motor(s),wherein the second expansion mechanism comprises one or more expansion stages comprising a second set of centripetal turbine(s), at least one of which is coupled to a same shaft as at least one second compression stage so as to supply to the second compression stage mechanical work produced during the expansion,wherein the set of motor(s) of the first refrigerator comprises at least one variable-speed electric motor controlled by an electrical signal by varying the frequency of the electrical signal, andwherein the cold power supplied by the first refrigerator determines the second temperature and is dependent on a rotational speed of at least one motor in the set of motors of the first refrigerator(18),wherein the second set of motor(s) of the second refrigerator comprises at least one variable-speed electric motor controlled by an electrical signal by varying the frequency of the electrical signal,wherein the cold power supplied by the second refrigerator determines the first temperature and is dependent on a rotational speed of said at least one motor in the second set of motors of the second refrigerator),the device further comprising:an electronic control member configured to control at least one of the motor(s) of the first refrigerator and at least one motor of the second refrigerator, the electronic control member being configured to control jointly a speed setpoint for the motors of the first and second refrigerators, such that the control of one of the refrigerators determines, or is dependent on, the control of the other refrigerator.

10. The device as claimed in claim 9, wherein the second cycle gas of the second refrigerator comprises one or more of: nitrogen, neon, helium, hydrogen, oxygen, argon, and carbon dioxide.

11. The device as claimed in claim 9, wherein the first refrigerator and the second refrigerator comprise respective motors of the same type and / or respective compressors of the same type, and / or respective turbines of the same type.

12. The device as claimed in claim 9, wherein the first refrigerator and the second refrigerator comprise at least one motor in common, the shaft of which is coupled to one or more of the compressors and / or one or more of the turbines of the first refrigerator and also coupled to one or more of the compressors of the second refrigerator and / or one or more of the turbines of the second refrigerator.

13. The device as claimed in claim 9, wherein the control member is configured to increase or decrease, by identical percentages, the speed setpoints for the motors of the first and second refrigerators.

14. A method for liquefying a fluid using the device as claimed in claim 9, the method comprising:cooling the fluid to be cooled to the first temperature using the second refrigerator; andcooling the fluid to be cooled from the first temperature to the second temperature.

15. The method as claimed in claim 0, further comprising controlling the value of the first temperature by controlling the speed of at least one of the motors of the set of motor(s) of the second refrigerator.

16. The method as claimed in claim 0, wherein the cycle circuit of the first refrigerator and the second cycle circuit of the second refrigerator contain the same cycle gas and are interconnected via at least one valve.

Images