Fluid liquefaction method and device
Patent Information
- Application Number
- EP2023733348
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-07-08
- Filing Date
- 2023-06-20
- Publication Date
- 2025-05-14
AI Technical Summary
Existing devices for liquefying hydrogen and helium lack flexibility and efficiency, particularly when dealing with intermittent energies and unsatisfactory performance, as they require high shaft rotation speeds and are constrained by high cut-off temperatures, leading to reduced yield and complexity in leak management.
The device employs a dual refrigeration cycle system with centrifugal compressors and centripetal turbines, where at least one turbine is coupled to a compression stage to provide mechanical work during expansion, and a second refrigerator with a similar cycle gas composition, allowing for variable speed control of motors to adjust cold power and temperature settings, enhancing flexibility and efficiency.
This configuration allows for lower cut-off temperatures without compromising overall efficiency, increasing flexibility in the liquefaction process, and enabling better adaptation to varying energy sources while maintaining high performance.
Smart Images
Figure 1.1
Abstract
Description
[0001] Description
[0002] Title of the invention: Device and method for liquefying a fluid.
[0003] The invention relates to a device and a method for liquefying a fluid such as hydrogen and / or helium.
[0004] The invention relates more particularly to a device for liquefying a fluid such as hydrogen and / or helium comprising a circuit of 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 heat exchange with the circuit (3) of fluid to be cooled, the device comprising a pre-cooling system in heat exchange with at least a portion of the set of heat exchanger(s) configured to lower the temperature of the fluid to be cooled to a first temperature, for example between 30 and 110K, the device further comprising a cooling system in heat exchange with at least a portion 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 between 15 and 25K, in which the cooling system comprises a first refrigerator with a refrigeration cycle of a first cycle gas comprising helium and / or hydrogen, said first refrigerator comprising, arranged in series in a cycle circuit: a cycle gas compression mechanism, at least one cycle gas cooling member, a cycle gas expansion mechanism and at least one expanded cycle gas reheating member, in which the compression mechanism comprises several compression stages in series composed of a set of centrifugal type compressor(s), the compression stages being mounted on shafts driven in rotation by a set of motor(s), the expansion mechanism comprising several expansion stages composed of a set of centripetal type turbines.,
[0005] Devices for liquefying cryogenic fluids, particularly hydrogen, generally include a pre-cooling system using a cold source such as a liquid nitrogen reserve or a closed or semi-closed nitrogen cycle refrigerator.
[0006] The lowest pressure of the pre-cooling cycle determines the lowest temperature reached by the pre-cooling cycle gas (cut-off temperature). Thus, this low pressure of the pre-cooling cycle is imposed at the lowest possible value, to lower the cut-off temperature at the cold end of this pre-cooling cycle and thus effectively pre-cool the flow of gas to be liquefied before it exchanges heat with the refrigerator cycle gas which lowers the temperature to a liquefaction temperature.
[0007] This architecture generally uses multi-stage compression stations comprising a gear wheel or speed increase device between the speed provided by the electric motor typically at 50 or 60Hz and the rotating shafts, carrying the multiple compression stages, which themselves require for energy efficiency aspects a very high shaft rotation speed. This architecture does not allow a great capacity for flexibility in the liquefaction process as described below.
[0008] A known solution consists of using the so-called mobile "IGV" technology ("Inlet Guide Vanes") which allows the gas flow rates to be varied at the suction, typically of the first compression stage of the cycle which includes these IGVs. Generally, this technology is only installed at the inlet of the first compression stage of the refrigeration cycle concerned for cost reasons and limitation of mobile components which could generate a potential failure on the entire plant. This solution is only partially satisfactory. In particular, the overall efficiency and performance of the installation are not satisfactory. In particular, this solution does not allow the installation to be adapted to intermittent energies or only with unsatisfactory performance.
[0009] Another solution is to use a refrigeration cycle using refrigerant mixtures ("MR"). However, these solutions provide a higher cut-off temperature (mixture of hydrocarbon and nitrogen type components, the mixture of which induces cut-off temperatures 20 to 50 degrees higher than pure nitrogen pre-cooling cycles) which constrains the final cooling cycle more from a thermodynamic point of view. In addition, in the event of a leak, the mixture to be reconstituted is complex for operators (need to determine the component(s) that leak preferentially and to readjust the mixture step by step). If the cut-off temperature of this cycle is lowered (typically by adding nitrogen to the mixture in larger proportions), the efficiency of this process drops significantly (of the order of 10% if the cut-off temperature is lowered by 5K).An aim of the present invention is to overcome all or part of the drawbacks of the prior art noted above.
[0010] To this end, the device according to the invention, moreover in accordance with the generic definition given in the preamble above, is essentially characterized in that at least one of the turbines is coupled to the same shaft as at least one compression stage so as to provide the compression stage with mechanical work produced during expansion and in that the pre-cooling system comprises a second refrigerator with a refrigeration cycle of a second cycle gas, said second refrigerator comprising, arranged in series in a cycle circuit: a cycle gas compression mechanism, at least one cycle gas cooling member, a cycle gas expansion mechanism and at least one expanded cycle gas heating member, in which the compression mechanism comprises several compression stages in series composed of a set of centrifugal type compressor(s),the compression stages being mounted on shafts driven in rotation by a set of motor(s), the expansion mechanism comprising one or more expansion stages composed of a set of centripetal type turbine(s), at least one of which is coupled to the same shaft as at least one compression stage so as to provide the compression stage with mechanical work produced during expansion.,
[0011] Furthermore, embodiments of the invention may comprise one or more of the following features: the cycle gas of the second refrigerator comprises at least one of: nitrogen, neon, helium, hydrogen, oxygen, argon or carbon dioxide, 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, the first refrigerator and the second refrigerator comprise at least one common motor whose shaft is coupled to one or more compressors and / or one or more turbines of the first refrigerator and also coupled to one or more compressors of the second refrigerator and / or one or more turbines of the second refrigerator, the motor assembly of the first and / or the second refrigerator comprises at least one variable speed electric motor controlled by an electrical signal, for example by frequency variation,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 frequency variation and in that the cold power supplied by the second refrigerator determines the first temperature and is a function of the rotation speed of said at least one motor, 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 frequency variation and in that the cold power supplied by the first refrigerator determines the second temperature and is a function of the rotation speed of said at least one motor, the device comprises an electronic control member for at least one motor(s) of the first refrigerator and at least one motor of the second refrigerator, the control member being configured to jointly control the speed setpoint of the motors of the first and second refrigerators,the control member is configured to increase or decrease in an identical manner in percentages the speed setpoints of the motors of the first and second refrigerators. The invention also relates to a method for liquefying a fluid such as hydrogen and / or helium using a device according to any one of the characteristics above or below, the method comprising a step of cooling the fluid to be cooled to the first temperature, for example between 30 and 110K via the second refrigerator then a step of cooling the fluid to be cooled from the first temperature to the second temperature for example between 15 and 25K.,
[0012] According to other possible features: the method comprises a step of controlling the value of the first temperature via the control of the speed of at least one of the motors of the set of motor(s) of the second refrigerator, 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.
[0013] 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.
[0014] Other features and advantages will appear on reading the description below, made with reference to the figures in which:
[0015] Brief description of the figures
[0016] The invention will be better understood on reading the following description, given solely by way of example and with reference to the appended drawings in which:
[0017] [Fig. 1] is a partial and schematic view illustrating an example of structure and operation of an example of a liquefaction device according to the invention,
[0018] [Fig. 2] is a schematic and partial view of a detail of such a device in an alternative embodiment,
[0019] [Fig. 3] is a schematic and partial view of another detail of such a device in another variant embodiment.
[0020] Detailed description
[0021] In all figures, the same references refer to the same elements. 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. Single features of different embodiments may also be combined and / or interchanged to provide other embodiments.
[0022] The device 1 for liquefying a fluid such as hydrogen and / or helium illustrated in [Fig. 1] comprises a circuit 3 of 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.
[0023] Source 2 may comprise a distribution unit (network) and / or a gas production unit (for example hydrogen). Source 2 may comprise in particular an electrolyser or a steam reforming unit.
[0024] The collection member 4 may comprise, for example, at least one cryogenic liquid storage. Upstream of the storage 4, the circuit 3 of fluid to be cooled preferably comprises a valve, for example an expansion valve 12 and / or an expansion turbine.
[0025] The liquefaction device 1 comprises a set of heat exchanger(s) 6, 7, 8, 9, 10 arranged in series and / or in parallel in heat exchange with the circuit 3 of fluid to be cooled and a pre-cooling system 20 in heat exchange with at least part of the set of heat exchanger(s) 6.
[0026] This pre-cooling system is typically configured to lower the temperature of the fluid to be cooled to a first temperature, for example between 30 and 110K, for example 80K.
[0027] The liquefaction device 1 further comprises a cooling system 21 in heat exchange with at least part of the set of heat exchanger(s) 6, 7, 8, 9, 10.
[0028] This cooling system is configured to further lower the temperature of the fluid to be cooled from the first temperature to a second temperature, for example between 15 and 25K, for example 20K to allow its liquefaction.
[0029] As illustrated, the cooling system comprises a first refrigerator 21 with a refrigeration cycle of a first cycle gas comprising helium and / or hydrogen. This first refrigerator 21 comprises, arranged in series in a cycle circuit 14: a mechanism 15 for compressing the cycle gas, at least one member for cooling the cycle gas, a mechanism 17 for expanding the cycle gas and at least one member for reheating the expanded cycle gas. That is to say that the first refrigerator 21 subjects the cycle gas to a thermodynamic cycle in which the cycle gas reaches at a cold end a very low (cryogenic) temperature constituting a cold power and which is put into heat exchange with the fluid to be liquefied.
[0030] The fluid to be liquefied (e.g. hydrogen) is a fluid which is preferably distinct from the cycle gas fluid (e.g. helium and possibly other component(s)).
[0031] Preferably these two circuits are therefore distinct.
[0032] As illustrated, the set of heat exchanger(s) which cools the fluid to be liquefied preferably comprises one or more counter-current heat exchangers 6, 7, 8, 9 arranged in series and in which two separate portions of the cycle circuit 14 circulate simultaneously in counter-current (respectively for the cooling and reheating of separate flows of the cycle gas).
[0033] That is to say that this plurality of counter-current heat exchangers forms both a cooling member for the cycle gas (after compression and after one or more expansion stages for example) and a heating member for the cycle gas (after expansion and before returning to the compression mechanism).
[0034] The compression mechanism comprises several compression stages 15 in series composed of a set of centrifugal compressor(s) 15. For example, the compression mechanism comprises at least four compression stages 15 composed of a set of centrifugal compressors arranged in series (and possibly in parallel).
[0035] A compression stage 15 may consist of a wheel of a motorized centrifugal compressor.
[0036] The compression stages 15 (i.e. the compressor wheels) are mounted on shafts 19 driven in rotation by a set of motor(s) 18 (at least one motor).
[0037] Preferably, all of the compressors 15 are of the centrifugal type.
[0038] The expansion mechanism preferably comprises several expansion stages composed of a set of centripetal turbine(s) 17, in which at least one of the turbines 17 is coupled to the same shaft 19 as at least one compression stage 15 so as to provide the compression stage 15 with mechanical work produced during expansion. For example, the expansion mechanism comprises three or more expansion stages formed of centripetal turbines 17 arranged at least partly in series.
[0039] Preferably, the number of compression stages (e.g., the number of compression wheels) is greater than the number of expansion stages (e.g., the number of expansion wheels). Preferably, all the turbines 17 are of the centripetal type and are mostly arranged in series.
[0040] The device 1 may comprise a member 8, 9 for cooling the cycle gas 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 between 2K and 30K.
[0041] 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 provide the compressor with mechanical work produced during expansion.
[0042] This architecture makes it possible to de-correlate (make independent) the heat transfer fluid process (helium-based cycle gas for example) from the delivery temperature of the fluid 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 known devices. This is possible despite a relatively low overall compression ratio of the cycle gas. This centrifugal compression technology was generally not recommended for hydrogen liquefaction in the prior art due to the limitation of the compression ratio per stage.
[0043] Thus, the device 1 may comprise one or more Moto-Turbo-Compressors on a part of the compression station. A Moto-Turbo-Compressor is an assembly comprising a motor whose shaft directly drives a set of compression stage(s) (wheel(s)) and a set of expansion stage(s) (turbine(s)). This utilizes mechanical expansion work directly on one or more compressors 15 of the cycle gas.
[0044] The pre-cooling system 21 comprises a second refrigerator 20 with a refrigeration cycle for a second cycle gas. This second refrigerator 20 also comprises, arranged in series in a cycle circuit 140: a mechanism 150 for compressing the cycle gas, at least one member 160 for cooling the cycle gas, a mechanism 170 for expanding the cycle gas and at least one member 6 for reheating the expanded cycle gas.
[0045] The compression mechanism comprises several compression stages 150 in series composed of a set of centrifugal compressor(s) 150. The compression stages 150 are mounted on shafts 190 driven in rotation by a set of motor(s) 180.
[0046] The expansion mechanism comprising one or more expansion stages composed of a set of centripetal turbine(s) 170. As for 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 provide the compression stage 150 with mechanical work produced during expansion.
[0047] That is, the first 21 and second 20 refrigerators preferably have the same general structure and technology.
[0048] This pre-cooling system 20 architecture allows for lower cut-off temperature of the pre-cooling system 20 compared to known devices and provides improved flexibility.
[0049] The cycle gas of the second refrigerator 20 may comprise at least one of: nitrogen, neon, helium, hydrogen, oxygen, argon or carbon dioxide. Preferably the cycle gas of this second refrigerator ensuring pre-cooling is composed of a mixture of helium and neon or helium and nitrogen for example. Preferably the device only uses rare and / or inert gases in the cycles.
[0050] This makes it possible to achieve lower temperatures in the pre-cooling system (typically below 80K) without affecting overall efficiency and without risking condensing or even freezing a component which would have a dramatic impact on the turbomachines and exchangers in the circuit.
[0051] As illustrated, at least one exchanger 6 may be common to the following flows: circuit 3 of fluid to be cooled, circuit 14 of the first refrigerator (in particular two flows: after and before compression) and circuit 140 of the second refrigerator (for example two flows: before and after expansion).
[0052] As mentioned above, the first 21 and second 20 refrigerators preferably have the same general structure and the same technology. In particular, these two refrigerators 20, 21 preferably comprise components of the same or identical nature. By “identical” or “of the same nature” is meant components (motor, turbine wheel, compressor wheel, bearings, casing, etc.) of the same technology but not necessarily strictly identical. For example, components of the same nature may be of different sizes.
[0053] 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).
[0054] The two cycles 14, 140 comprise, for example, centripetal turbines and centrifugal compressors coupled on the same shafts. These components of the same nature allow for the pooling of components or sub-components: for example, the same electric motors, the same electrical chain for the motor-compressors and motor-turbo-compressors, the same wheels, the same dimensions, the same designs. This allows for the pooling of supplies and in particular for the reduction of the references of components or organs of the device 1 (example: motor, bearings on the entire liquefaction unit, etc.).
[0055] This allows the use in the same device 1 (same installation) of machines of a single type both for pre-cooling (from 300K to 80K for example) and cooling between 80 and 20K for example). For example, only the turbines would be different.
[0056] Cryogenic components can be housed in separate thermally insulated (preferably vacuum) cold boxes or in a single cold box (e.g. with separate independent or non-independent volumes).
[0057] In addition, and as shown diagrammatically in [Fig. 2], the first refrigerator 21 and the second refrigerator 20 may comprise a motor 18, 180 common to the rotary shaft 19, 190 to 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 compressor wheel 15 and / or turbine wheel 17 of the first 21 refrigerator and also coupled to at least one compressor wheel 150 and / or turbine wheel 170 of the second 20 refrigerator.
[0058] Similarly, motors of the two refrigerators 20, 21 may share common components, for example the same power circuitry and / or the same electronic variable speed drive (“VFD”).
[0059] Preferably, at least part of the motor assembly(s) 18, 180 of the first and / or second refrigerator 21, 20 are variable speed electric motors controlled by an electrical signal, for example by frequency variation.
[0060] In addition, the cooling power supplied by each refrigerator 20, 21 is preferably a function of the rotation speed of the motor(s), for example the cooling power supplied is proportional to the rotation speed of the motors.
[0061] In particular, the rotation speed of the motor(s) 180 of the second refrigerator 20 determines the lowest temperature provided by the second refrigerator 20 (cut-off temperature). This determines the second temperature in the process of cooling and liquefying the fluid to be liquefied.
[0062] As shown diagrammatically in [Fig. 3], the device 1 preferably comprises an electronic member 11 for controlling at least one motor(s) 18, 180. The electronic member 11 comprises, for example, a microprocessor or computer or any other suitable system.
[0063] As illustrated, the electronic member 11 can control at least one motor(s) 18 of the first refrigerator 21 and at least one motor 180 of the second refrigerator 20. This control member 11 can in particular be configured to jointly control the speed setpoint of 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.
[0064] For example, the control member 11 can be configured to increase or decrease identically (in percentage) the speed setpoints of the motors 18, 180 of the first 21 and second 20 refrigerators.
[0065] For example, the temperature conditions of the liquefied fluid can be controlled via the speed of the motors 18, 180. Thus, for example, if the speed of the motors of the first refrigerator 21 needs to be reduced (or increased) by 30%, the speed of the motors 20 of the second refrigerator is also reduced (or increased) by 30%. This can be achieved via a single control instruction (an identical or unique signal).
[0066] Preferably, the pre-cooling cycle is closed and the cooling cycle is also closed.
[0067] In a possible variant, the two cycles could be connected via a balancing valve (and a valve control system). This makes it possible to distribute the cooling powers produced by the two refrigerators 20, 21 without changing the speed of the corresponding motors.
[0068] The device 1 has great flexibility for controlling the cooling powers of the pre-cooling 20 and cooling 21 systems.
[0069] This makes it possible to control and set the temperatures at the junction between the two refrigerators in circuit 3 of fluid to be liquefied.
[0070] Device 1 also makes it possible to increase the cold production capacity at the cooling level while maintaining the same architecture, i.e. a liquefied gas at a lower temperature than at the nominal operating point. Indeed, it is possible to lower the cut-off temperature of the pre-cooling system at specific times. This makes it possible to reduce the thermal load for the cooling system and therefore to further subcool the liquefied fluid at the liquefier outlet. The cut-off temperature can be modified over a wider temperature range.
Claims
AMENDED CLAIMS received by the International Bureau on October 18, 2023 (10 / 18 / 2023)
1. Device for liquefying a fluid such as hydrogen and / or helium comprising a circuit (3) of 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, the device (1) comprising a set of heat exchanger(s) (6, 7, 8, 9, 10) in heat exchange with the circuit (3) of fluid to be cooled, the device (1) comprising a pre-cooling system (20) in heat exchange with at least a portion of the set of heat exchanger(s) (6) configured to lower the temperature of the fluid to be cooled to a first temperature, for example between 30 and 110K, the device (1) further comprising a cooling system (21) in heat exchange with at least a portion of the set of exchanger(s) (6, 7, 8, 9,10) of heat and configured to lower the temperature of the fluid to be cooled from the first temperature to a second temperature, for example between 15 and 25K, wherein the cooling system (21) comprises a first refrigerator (21) with a refrigeration cycle of a first cycle gas comprising helium and / or hydrogen, said first refrigerator (21) comprising, arranged in series in a cycle circuit (14): a mechanism (15) for compressing the cycle gas, at least one member (6, 7, 8, 9) for cooling the cycle gas, a mechanism (17) for expanding the cycle gas and at least one member (10, 9, 8, 7, 6) for reheating the expanded cycle gas, wherein the compression mechanism comprises several compression stages (15) in series composed of a set of centrifugal compressor(s) (15), the compression stages (15) being mounted on shafts (19) driven in rotation by a set of motor(s) (18),the expansion mechanism comprising several expansion stages composed of a set of centripetal type turbines (17), in which at least one of the turbines (17) is coupled to the same shaft (19) as at least one compression stage (15) so as to provide the compression stage (15) with mechanical work produced during expansion and in that the pre-cooling system (21) comprises a second cycle refrigerator (20), AMENDED SHEET (ARTICLE 19) refrigeration of a second cycle gas, said second refrigerator (20) comprising, arranged in series in a cycle circuit (140): a mechanism (150) for compressing the cycle gas, at least one member (160, 6) for cooling the cycle gas, a mechanism (170) for expanding the cycle gas and at least one member (6) for reheating the expanded cycle gas, in which the compression mechanism comprises several compression stages (150) in series composed of a set of centrifugal type compressor(s) (150), the compression stages (150) being mounted on shafts (190) driven in rotation by a set of motor(s) (180), the expansion mechanism comprising one or more expansion stages composed of a set of centripetal type turbine(s) (170) of which at least one is coupled to the same shaft (190) as at least one compression stage (150) so as to provide the compression stage (150) of the mechanical work produced during expansion characterized in that,the assembly of motor(s) (18) of the first refrigerator (21) comprises at least one variable speed electric motor controlled by an electrical signal, by frequency variation and in that the cold power supplied by the first refrigerator determines the second temperature and is a function of the rotation speed of said at least one motor (18), the assembly of motor(s) (180) of the second refrigerator (20) comprises at least one variable speed electric motor controlled by an electrical signal, by frequency variation and in that the cold power supplied by the second refrigerator determines the first temperature and is a function of the rotation speed of said at least one motor (180), and in that it comprises an electronic member (11) for controlling at least one motor(s) (18) of the first refrigerator (21) and at least one motor of the second refrigerator (20),the control member (11) being configured to jointly control the speed setpoint of the motors of the first and second refrigerators (20, 21), that is to say that the control of one of the refrigerators determines or is dependent on the control of the other refrigerator.,
2. Liquefaction device according to claim 1, characterized in that the cycle gas of the second refrigerator (20) comprises at least one of: AMENDED SHEET (ARTICLE 19) nitrogen, neon, helium, hydrogen, oxygen, argon or carbon dioxide.
3. Liquefaction device according to claim 1 or 2, characterized in that the first refrigerator (21) and the second refrigerator (20) comprise respective motors of the same type and / or respective compressors of the same type, and / or respective turbines of the same type.
4. Liquefaction device according to any one of claims 1 to 3, characterized in that the first refrigerator (21) and the second refrigerator (20) comprise at least one common motor (18, 180) whose shaft (19, 190) is coupled to one or more compressors (15) and / or one or more turbines of the first (21) refrigerator and also coupled to one or more compressors (150) of the second (20) refrigerator and / or one or more turbines (170) of the second (20) refrigerator.
5. Liquefaction device in any one of claims 1 to 4, wherein the control member (11) is configured to increase or decrease in identical percentages the speed setpoints of the motors of the first and second refrigerators (20, 21).
6. A method of liquefying a fluid such as hydrogen and / or helium using a device according to any one of claims 1 to 5, the method comprising a step of cooling the fluid to be cooled to the first temperature, for example between 30 and 110K via the second refrigerator (20) then a step of cooling the fluid to be cooled from the first temperature to the second temperature, for example between 15 and 25K.
7. Liquefaction method according to claim 6, characterized in that it comprises a step of controlling the value of the first temperature via the control of the speed of at least one of the motors of the set of motor(s) (180) of the second refrigerator (20). AMENDED SHEET (ARTICLE 19)
8. Liquefaction method according to any one of claims 1 to 7, characterized in that the cycle circuits (14, 140) of the first refrigerator (21) and of the second refrigerator (20) contain the same cycle gas and are interconnected via at least one valve. AMENDED SHEET (ARTICLE 19)