DEVICE AND METHOD FOR LIQUEFIING A FLUID SUCH AS HYDROGEN AND / OR HELIUM

Description

[0001] The invention relates to a device and a method for liquefying a fluid such as hydrogen and / or helium.

[0002] 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 of fluid to be cooled, the device comprising at least a first cooling system in heat exchange with at least part of the set of heat exchanger(s), the first cooling system being a refrigerator with a refrigeration cycle of a cycle gas comprising mainly helium, said refrigerator comprising, arranged in series in a cycle circuit: a mechanism for compressing the cycle gas, at least one member for cooling the cycle gas,a cycle gas expansion mechanism and at least one member for reheating the expanded cycle gas, in which the compression mechanism comprises at least four 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 at least three expansion stages in series composed of a set of centripetal type turbines.,

[0003] State-of-the-art hydrogen (H2) liquefaction solutions incorporate cycle compressors that achieve relatively low isothermal efficiencies (around 60% to 65%) and with a relatively limited volume capacity, but at the cost of a fairly substantial investment and high maintenance costs.

[0004] Document EP3368630 A1 describes a known hydrogen liquefaction process.

[0005] Document JP2007205667A describes a device for liquefying a fluid 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 of fluid to be cooled, the device comprising at least a first cooling system in heat exchange with at least a portion of the set of heat exchanger(s), the first cooling system being a refrigerator with a refrigeration cycle of a cycle gas comprising predominantly helium, said refrigerator comprising, arranged in series in a cycle circuit: a mechanism for compressing the cycle gas, at least one member for cooling the cycle gas, a mechanism for expanding the cycle gas and at least one member for reheating the expanded cycle gas.

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

[0007] To this end the present invention provides an apparatus according to claim 1.

[0008] Furthermore, embodiments of the invention may include one or more of the following features: the compression mechanism comprises only centrifugal type compressors, the device comprises a cycle gas cooling system, such as a heat exchanger, arranged at the outlet of at least some of the turbines excluding the last turbine in series according to the direction of circulation of the cycle gas, according to the direction of circulation of the cycle gas, at least two turbines in series are coupled respectively with compression stages taken in the reverse order of their arrangement in series, that is to say that, for example, at least one turbine is coupled with a compression stage located upstream of a compression stage coupled to another turbine which precedes it in the cycle circuit, the working pressure of at least one turbine coupled to a compression stage is set to the working pressure of the compressor comprising the compression stage to which it is coupled,that is to say that the pressure of the cycle gas entering the turbine does not differ more than 40% and preferably not more than 30% or 20% from the inlet pressure of the compressor to which it is coupled, the mechanical coupling of the turbines and the compression stages to the same shaft is configured to ensure an identical rotational speed of the turbine and the coupled compression stages, the device comprises more compression stages than turbines, each turbine being coupled to the same shaft as a single respective compression stage driven by a respective motor, the other compression stages not coupled to a turbine being mounted alone on rotating shafts driven by separate respective motors, the compression stages coupled to a turbine and the compression stages not coupled to a turbine are alternated in series in the cycle circuit,the device comprises sixteen compression stages and eight turbines or twelve compression stages and six turbines or eight compression stages and four turbines or six compression stages and three turbines or four compression stages and three turbines, the return pipe is in heat exchange with the at least one cycle gas cooling member and / or the expanded cycle gas heating member, the cycle circuit comprises a partial bypass pipe of the cycle gas flow having a first end connected upstream of a turbine and a second end connected to the inlet of another turbine located downstream, said bypass pipe being configured to transfer a portion of the cycle gas flow directly to the inlet of the cooler downstream turbine,the heat exchanger assembly comprises a plurality of heat exchangers arranged in series and in which two separate portions of the cycle circuit circulate simultaneously in counter-current for respectively cooling and heating the cycle gas, said plurality of heat exchangers forming a cycle gas cooling member and a cycle gas heating member, the device comprises a second cooling system in heat exchange with at least part of the heat exchanger assembly, said second cooling system comprising a heat transfer fluid circuit such as liquid nitrogen or a mixture of refrigerants, the cycle circuit comprises at the inlet of at least one of the turbines an inlet guide vane (IGV) device configured to adjust the fluid flow rate to a determined operating point,the working pressures of the turbines are set respectively to the working pressures of the compressors to which they are coupled, so that the pressure of the cycle gas entering the turbine does not differ by more than 30% and preferably by no more than 20% from the outlet pressure of two compressors in series to which it is coupled,

[0009] The invention also relates to a method for producing hydrogen at cryogenic temperature, in particular liquefied hydrogen, using a device according to any one of the preceding characteristics or below, in which the pressure of the cycle gas at the inlet of the cycle gas compression mechanism is between two and forty bar abs and in particular between eight and thirty-five bar abs.

[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 appear on reading the description below, made with reference to the figures in which: [ Fig.1 ] represents a schematic and partial view illustrating the structure and operation of a first exemplary embodiment which is not according to the invention, [ Fig.2 ] represents a schematic and partial view illustrating the structure and operation of a first possible embodiment of the invention, [ Fig.3 ] represents a schematic and partial view illustrating the structure and operation of a second possible embodiment of the invention, [ Fig.4 ] represents a schematic and partial view illustrating the structure and operation of a fourth exemplary embodiment which is not according to the invention, [ Fig.5 ] represents a schematic and partial view illustrating the structure and operation of a fourth possible embodiment of the invention, [ Fig.6 ] represents a schematic and partial view illustrating a detail of the fourth exemplary embodiment illustrating an example of structure and possible operation of a motor-turbocharger of the device.

[0012] The device 1 for liquefying a fluid shown in [ Fig.1 ] is intended for the liquefaction of hydrogen but can be applied to other gases, including helium or any mixture.

[0013] The device 1 comprises a circuit 3 of fluid to be cooled (typically hydrogen) 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 source 2 may typically comprise an electrolyzer, a hydrogen distribution network, a methane reforming unit (SMR) or any other suitable source(s).

[0014] The device 1 comprises a set of heat exchangers 6, 7, 8, 9, 10, 11, 12, 13 arranged in series in heat exchange with the circuit 3 of fluid to be cooled.

[0015] The device 1 comprises at least a first cooling system 20 in heat exchange with at least part of the set of heat exchangers 5, 6, 7, 8, 9, 10, 11, 12, 13.

[0016] This first cooling system 20 is a refrigerator with a refrigeration cycle of a cycle gas comprising mainly helium. This refrigerator 20 comprises, arranged in series in a cycle circuit 14 (preferably closed in a loop): a mechanism 15 for compressing the cycle gas, at least one member 16, 5, 6, 8, 10, 12 for cooling the cycle gas, a mechanism 17 for expanding the cycle gas and at least one member 13, 12, 11, 10, 9, 8, 7, 6, 5 for reheating the expanded cycle gas.

[0017] Thus the fluid to be liquefied (example hydrogen) is a fluid which is distinct from the cycle gas fluid (example helium and possibly other component(s)).

[0018] Preferably these two circuits are therefore distinct.

[0019] As illustrated, the set of heat exchanger(s) which cools the hydrogen to be liquefied preferably comprises one or more counter-current heat exchangers 5, 6, 8, 10, 12 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).

[0020] 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 expansion stages for example) and a heating member for the cycle gas (after expansion and before returning to the compression mechanism).

[0021] The compression mechanism comprises at least four compression stages 15 composed of a set of centrifugal type compressors arranged in series (and possibly in parallel).

[0022] A compression stage 15 may consist of a wheel of a motorized centrifugal compressor.

[0023] The compression stages 15 (i.e. the compressor wheels) are mounted on shafts 19, 190 driven in rotation by a set of motor(s) 18 (at least one motor). Preferably, all the compressors 15 are of the centrifugal type.

[0024] The expansion mechanism comprises at least three expansion stages formed of centripetal turbines 17 arranged at least partly in series. For example, the number of compression stages (for example the number of compression wheels) is greater than the number of expansion stages (for example number of expansion wheels). Preferably, all the turbines 17 are centripetal and are mostly arranged in series.

[0025] The at least one member 16, 5, 6, 8, 10, 12 for cooling the cycle gas is in particular 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 can be cooled by a value typically between 2K and 30K.

[0026] 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.

[0027] This combination of technical features (centrifugal compression, centripetal expansion, transfer of work from the turbines to the compressors, etc.) is possible with a cycle gas comprising helium. Indeed, this makes it possible to de-correlate (make independent) the heat transfer fluid process (helium-based cycle gas) 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.

[0028] 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 of the cycle gas.

[0029] For example, and as illustrated, the device 1 comprises more compression stages 15 than turbines 17, for example twice as many or about twice as many. Each turbine 17 may be coupled to the same shaft 19 as a single respective compressor wheel 15 driven by a respective motor 18. The other compressor wheel(s) 15 (stage(s)) not coupled to a turbine 17) may be mounted alone on rotating shafts 190 driven by separate respective motors 18 (Motor-compressor).

[0030] As illustrated, the compression stages 15 coupled to a turbine 17 and the compressors not coupled to a turbine 17 can be alternated in series in the cycle circuit 14.

[0031] Preferably, the compression mechanism comprises more than six compression stages in series. Of course, this is in no way limiting since it is possible to envisage, for example, a less efficient configuration with three compression stages in series which would make it possible to liquefy hydrogen. The minimum compression ratio (by centrifugal technology) to achieve hydrogen liquefaction should preferably be in the order of 1.3 to 1.6.

[0032] Four compression stages 15 in series make it possible to achieve very good isothermal efficiency compared to known piston compression solutions, at the cost of a relatively high helium mass flow rate.

[0033] In the non-limiting example illustrated in [ Fig.1 ], only four compression stages 15 and three turbines 17 are shown, but the device 1 could comprise eight compression stages 15 and four turbines 17. Any other distribution can be envisaged, for example sixteen compression stages 15 and eight turbines 17 or twelve compression stages and six turbines or six compression stages and three turbines or four compressors and three turbines...

[0034] Cooling may be provided downstream of all or part of the compression stages or downstream of all or part of the compressors 15 (for example via a heat exchanger 16 cooled by a heat transfer fluid or any other refrigerant). This cooling may be provided after each compression stage or, as illustrated, every two (or more) compression stages 15 or only downstream of the compressor station. Surprisingly, this distribution of the cooling not at the outlet of each of the compression stages 15 in series but every two (or three) compression stages 15 makes it possible to achieve the cooling performance while limiting the costs of the device 1.

[0035] Likewise, the at least one cycle gas cooling member preferably comprises a cycle gas cooling system 8, 10, 12, such as a heat exchanger, arranged at the outlet of at least some of the turbines 17 in series.

[0036] This inter-expansion intermediate cooling makes it possible to limit the value of the high pressure necessary to reach the coldest temperatures in the cycle gas.

[0037] As illustrated, the device 1 preferably comprises a cycle gas cooling system, such as a heat exchanger, at the outlet of all the turbines 17 excluding the last turbine 17 in series according to the direction of circulation of the cycle gas. As illustrated, this cooling system can be provided by respective counter-current heat exchangers 8, 10, 12 mentioned above.

[0038] This cooling after expansion allows a temperature staging (i.e. reaching distinct temperatures which are lower and lower after each stage of expansion) to extract cold from the fluid to be cooled. This temperature staging is obtained by this arrangement and via a minimum compression ratio obtained to power these different turbines 17.

[0039] The arrangement of several centrifugal compression stages 15 in series upstream makes it possible to obtain this pressure differential allowing adequate staging of the cooling downstream. Indeed, for the same pressure difference, the more the temperature decreases, the more the enthalpic drop at constant entropy during expansion decreases. The arrangement of the turbines 17 in series and the cooling 8, 10 at the outlet of the turbines has the effect of increasing the average mass flow rate of the turbines 17 compared to a conventionally known staging. The theoretical isentropic efficiency thus tends to increase and therefore makes it possible to achieve better efficiencies of the turbines 17.

[0040] In particular, the cooling 8, 10 between the expansion stages allows the cycle fluid to reach the target liquefaction temperatures without requiring an even greater overall compression ratio. The expansions are preferably isentropic or quasi-isentropic. That is, the cycle fluid is cooled as it progresses and the fluid is liquefied.

[0041] Thus, the minimum temperature is reached directly at the outlet of the last quasi-isentropic expansion stage (i.e. downstream of the last expansion turbine 17). It is therefore not necessary to additionally provide a Joule-Thomson type expansion valve downstream, for example. The cold and in particular a subcooling temperature of the hydrogen to be liquefied can be obtained exclusively with turbines 17 (work extraction).

[0042] Preferably, most or all of the turbines 17 are coupled with one or more respective compressors 15.

[0043] For example, depending on the direction of circulation of the cycle gas, the successive turbines 17 are preferably coupled respectively with compression stages 15 of compressors taken in the reverse order of their arrangement in series. That is to say, for example, a turbine 17 is coupled with a compressor 15 located upstream of a compressor 15 coupled to the turbine 17 which precedes it.

[0044] The order of association of the coupled turbines 17 and compressors is therefore preferably at least partly reversed between the turbines and the compressors (in the cycle circuit, a turbine further upstream is coupled with a compressor further downstream).

[0045] Thus, in the case for example of an architecture with six compression stages 15 in series and three expansion stages in series, the first turbine 17 (i.e. the first turbine 17 after the compression mechanism) can be coupled to the fifth compressor 15 in series (fifth compression stage) while the second turbine 17 can be coupled to the third compressor 15 in series (third compression stage), the third turbine 17 can be coupled to the first compressor 15 in series (first compression stage). The other compressors 15 forming the other compression stages may not be coupled to a turbine (motor-compressor system and not motor-turbo-compressors). Thus, the most powerful turbine 17 (the furthest downstream) can be coupled to the first compression stage (the first compression stage draws at the low pressure of the cycle).At this level of relative low pressure, the greater the compression ratio of compressor 15, the less the impact of pressure losses at its level is felt (and so on with the other compressors 15).

[0046] This example above is of course in no way limiting. For example, the turbines 17 could be coupled respectively to the compressors 15 of even order number (the first turbine with the sixth compressor, the second turbine with the fourth compressor etc.) or with compressors directly in series (for example the first turbine 17 with the sixth compressor 15, the second turbine with the fifth compressor etc.).

[0047] Preferably, the working pressures of the turbines 17 are respectively set to the working pressures of the compressors 15 to which they are coupled. That is to say, the pressure of the cycle gas which enters the turbine 17 does not differ by more than 40% and preferably by no more than 30 or 20% from the outlet pressure of the compressor 15 to which it is coupled. This makes it possible to reduce the axial loads at the output shafts 19 of the engines 18 concerned which directly couple the compressor wheels 15 and turbines 17.

[0048] For example, the at least one coupled turbine 17 and corresponding compression stage are structurally configured such that the pressure of the cycle gas exiting the turbine 17 differs by no more than 40% and preferably by no more than 30% or no more than 20% from the pressure of the cycle gas entering the compression stage 15.

[0049] Likewise, the at least one coupled turbine 17 and the corresponding compression stage are preferably structurally configured also (or possibly alternatively) so that the pressure of the cycle gas entering the turbine 17 does not differ by more than 40% and preferably by no more than 30% or no more than 20% from the pressure of the cycle gas leaving the compression stage.

[0050] This combination of technical features (centrifugal compression, centripetal expansion, transfer of work from the turbines to the compressors and adjustment of pressures between the coupled compression and expansion wheels) improves the efficiency of the device compared to known solutions.

[0051] This structural configuration of the turbine (e.g. turbine wheel) and compression stage (e.g. compression wheel) means that these two elements are dimensioned (shape and / or dimension of the wheel and / or their volute and / or their inlet distributor where applicable) to respectively achieve compressions and expansions of the same absolute value or close to it as specified above. That is to say that, by design, these two coupled elements will be able to achieve these compression and expansion ratios (without using any other active or passive element in the cycle circuit), preferably whatever the conditions of the cycle gas flow.

[0052] For example, the expansion ratio across the at least one turbine 17 coupled to a compression stage may be configured to achieve a cycle gas pressure drop of the value not differing by more than 40% (or not more than 20%) from the value of the pressure increase across the compression stage 15 to which it is coupled.

[0053] For example, if the compressor 15 is coupled to the turbine 17 and it works between 10 bar and 15 bar (compression of the flow initially at 10 bar at an outlet pressure of 15 bar), it is advantageous to have this flow expanded by the turbine 17 to pressures between 15 and 10 bar (inlet at 15 bar and outlet at 10 bar).

[0054] This improves the distribution and balancing of the axial forces of the shaft 19 which carries them.

[0055] The signs of the forces generated by the pressure differences at the terminals of the wheels 15, 17 being opposite, this tends to reduce the resultant of the axial forces.

[0056] This preferably also applies in the case of several turbines in series coupled to one or more compressors 15.

[0057] Thus, as illustrated, the expansion mechanism may comprise at least two expansion stages in series composed of a set of centripetal type turbines 17 in series.

[0058] Furthermore, as mentioned above, depending on the direction of circulation of the cycle gas, preferably at least two turbines 17 in series are coupled respectively with compression stages 15 taken in the reverse order of their arrangement in series. That is to say, at least one turbine 17 is coupled with a compression stage 15 located upstream of a compression stage 15 coupled to another turbine 17 which precedes it in the cycle circuit 14.

[0059] Preferably the device comprises n turbines (stages or expansion wheels) and k stages or compressor wheels, with k >= n. The expansion ratios chosen at the terminals of each turbine 17 are preferably thus imposed according to the compressor to which they are coupled (as explained above).

[0060] In the example illustrated with alternation of a compressor 15 coupled to a turbine 17 then a compressor 15 not coupled to a turbine, the working pressures of the turbines 17 can be set to the working pressures of the compressors 15 "one by one" or "two by two" (that is to say the first turbine 17 works on the compression ratio of the 5th or 6th compressors 15; likewise the second turbine 17 works on the compression ratio of the 3rd or 4th compressors, etc. If we consider a pair of two compressors 15 in series (a compressor with a compression wheel coupled to a turbine followed by a compressor with a compressor wheel not coupled to a turbine), the first of these two compressors compresses for example the cycle gas to a first pressure PA while the second compresses this cycle gas then to a second pressure PB with PB > PA.The turbine 17 which will be coupled to the first of these two compressors will preferentially expand the cycle gas from the second pressure PB to the first pressure PA. This can be obtained for example by adjusting the characteristics of this turbine 17 according to this constraint. For example, there is adjustment of the section of the distributor calibrating the flow arriving at the turbine 17, which has an effect on the pressure drop occurring in the distributor part and the wheel part of the turbine.

[0061] Thus, for example when turbines are coupled every two compression stages in series, the pressure relationships detailed previously (inlet / outlet) between the coupled expansion and compression stages can therefore apply either to the compression stage alone which carries the turbine or to a set of two compressor wheels in series.

[0062] In addition, the mechanical coupling(s) of the turbines 17 and compressor wheels 15 to the same shaft 19 is (are) configured to preferably ensure an identical rotational speed of the turbine 17 and the coupled compressor wheels 15. This makes it possible to obtain a direct and efficient use of the expansion work in the device. Where appropriate, the rotational speeds of all the compressor wheels and turbines may be equal to a single, determined value.

[0063] A control member may optionally be provided for all or some of the compression stages. For example, a variable frequency drive (“VFD”) may be provided for each motor 18 driving at least one compression stage. This makes it possible to independently adjust the speeds of several or each compression stage and therefore the expansion without using a complex gear system or a motorization and a specific control means linked to variable blades upstream of one or more compression stages. This speed control member may be provided for all of the compressors or for each compression stage.

[0064] Preferably, the device 1 does not include a flow valve or a valve for reducing the pressure in the circuit (pressure drop) between the compression stages, between the expansion stages or downstream of the cycle expansion. Thus, only isolation valves for maintenance can be provided in the cycle circuit 14.

[0065] That is to say, the operating point of the turbines 17 (speed, pressure) can be adjusted solely by the dimensional characteristics of the turbine 17 (no throttle valve at the turbine inlet, for example). This increases the reliability of the device (no potential problem of failure of control valves on the process, since they are absent). This also allows the elimination of costly ancillary circuits (safety valves, etc.) and simplifies manufacturing (reduction in the number of lines to be insulated, etc.).

[0066] The use of a helium-based cycle gas makes it possible to reach temperatures for subcooling liquefied hydrogen without the risk of a subatmospheric zone in the process (which would be dangerous if the cycle fluid were hydrogen) and without the risk of freezing the cold source (the maximum liquefaction temperature of helium is equal to 5.17K). The subcooling effect of liquefied hydrogen presents a very notable advantage on the hydrogen molecule transport chain and then potentially at users (typically liquid stations) thanks to the reduction of vaporization gases ("Boil-off") during the journeys.

[0067] It is thus possible to reach the freezing point (13K) on the side of the hydrogen flow to be liquefied without crystallizing the cold source.

[0068] The low-pressure part of the cycle circuit 14 can be operated at a relatively high pressure. This makes it possible to reduce the volume flow rates in the heat exchangers 6, 7, 8, 9, 10, 11, 12, 13. The working pressure of the cycle gas can thus be de-correlated from the target pressure or temperature of the fluid to be cooled. This pressure of the cycle gas can thus be increased to adapt to the constraints of the turbomachine but also to reduce the low-pressure volume flow rate which is, as a general rule, one of the major parameters sizing the heat exchangers.

[0069] This low pressure level in the cycle circuit 14 is for example greater than or equal to 10 bar and can typically be between 10 and 40 bar. This reduces the volume flow in the heat exchangers which counterbalances the low compression ratio per compression stage.

[0070] As illustrated, the device 1 may comprise a second cooling system in heat exchange with at least a portion of the heat exchanger assembly 5 in exchange with the cycle gas for example. This second cooling system 21 comprises for example a circuit 25 of heat transfer fluid such as liquid nitrogen or a mixture of refrigerants which cools the cycle gas and / or the hydrogen to be liquefied through the first heat exchanger(s) in counter-current, and may also make it possible to combat losses by hot end deviation caused by the closed-loop circulation of the heat transfer fluid(s), as illustrated in the [ Fig.1 ] via at least one pre-cooling exchanger 5.

[0071] This second cooling system 21 makes it possible, for example, to pre-cool the fluid to be liquefied and / or the working gas at the outlet of the compression mechanism. This refrigerant which circulates in the heat transfer fluid circuit 25 (for example in a loop) is for example supplied by a unit 27 for producing and / or storing 28 this refrigerant. If necessary, the circuit 3 of fluid to be cooled passes through this unit 27 for upstream pre-cooling. Note that it is conceivable that the device 1 has other additional cooling system(s). For example, a third cooling circuit supplied by a refrigeration unit (for example providing a cold source at a temperature typically between 5°C and -60°C) can be provided in addition to the aforementioned system. A fourth cooling system could also be provided to further supply cold to the device 1 and increase the liquefaction power of the device 1 if necessary.The embodiment of the [. Fig.2 ] differs from the previous one only in that the cycle circuit 14 comprises a return pipe 22 having a first end connected to the outlet of one of the turbines 17 other than the last one downstream and a second end connected to the inlet of one of the compressors 15 other than the first compressor 15 upstream. This return pipe 22 makes it possible to return a portion of the cycle gas flow into the compression mechanism at an intermediate pressure level between the low pressure at the inlet of the compression mechanism and the high pressure at the outlet of the compression mechanism.

[0072] The return line 22 may be in heat exchange with at least some of the countercurrent heat exchangers. Several return lines to the intermediate pressure compressor station may advantageously be installed depending on the expected level of optimization of the process. For example, the sampling points (at the turbines considered) and injection points (at the compression stages considered) may be located at different pressure levels. The embodiment of the [ Fig.3 ] differs from the previous one only in that the cycle circuit 14 further comprises a partial bypass pipe 24 having a first end connected upstream of a turbine 17 (for example the first upstream turbine 17) and a second end connected to the inlet of another turbine 17 located downstream (for example the third turbine). For example, the bypass pipe 24 allows the diversion of a part of the cycle gas flow leaving the compression mechanism at high pressure to colder turbines further downstream. The rest of the flow passes into this first, hotter upstream turbine 17. This allows, depending on the specific speed positioning of the different turbines and compressors, to adjust the flow rates sent to the different stages. For example, the compressors located at higher pressure draw in a lower volume flow rate than the first compression stages (located close to the low pressure of the process).One way to increase this volume flow rate and thus potentially increase their isentropic efficiency is to integrate an intermediate pressure return from the expansion stages as shown in [. Fig.3 ]. The device 1 shown in [ Fig.4 ] illustrates yet another non-limiting embodiment. Elements identical to those described above are designated by the same reference numerals and are not described in detail again.

[0073] The 14 cycle circuit of the device of the [ Fig.4 ] comprises three compressors (driven respectively by three motors 18). As illustrated, each compressor may have four compression stages 15 (i.e., four compression wheels in series). These compressor wheels 15 may be mounted by direct coupling to one end of a shaft 19 of the motor 18 concerned. In this example, the device therefore has twelve centrifugal compression stages in series. As shown, cooling 26 of the cycle gas may be provided every two compression stages.

[0074] The device 1 has in this example five expansion stages in series (six centripetal turbine wheels, two of which are arranged in parallel), for example one or two expansion stages per compressor. As illustrated, all the turbines 17 can be coupled to a compressor shaft 19 (for example two turbines 17 are mounted at the other end of the shaft 19 of each engine 18 to provide mechanical work to the compressor wheels 15 also mounted on this shaft 19). Of course the turbines 17 could be on the same side of the shaft 19 as the compression wheels 15. For example, the first four expansion stages are formed of four turbines 17 in series. The fifth expansion stage is for example formed of two turbines 17 arranged respectively in two parallel branches of the cycle circuit 14. The device 1 shown in [ Fig.5 ] is distinguished from that of the [ Fig.4 ] in that it comprises cycle gas return lines 122, 123, 124 transferring a portion of the cycle gas leaving turbines 17 at intermediate pressure levels (medium pressure) within the compression mechanism. For example, a line 124 connects the outlet of the first turbine to the outlet of the eighth compression stage. Similarly, a line 123 connects the outlet of the second turbine to the outlet of the sixth compression stage. Similarly, a line 122 connects the outlet of the third turbine 17 to the outlet of the fourth compression stage. Of course, the device could comprise only one or only two of these medium pressure return lines. Similarly, other return lines could be envisaged. In addition, the ends of these lines could be changed (outlet of other turbine(s) and outlet(s) of other compression stages).

[0075] This or these returns make it possible to increase the volume flow rate of the compressors thus supplied with a surplus flow rate and thus potentially increase their isentropic efficiency.

[0076] Device 1 shown in [ Fig.6 ] illustrates a detail of the device 1 illustrating a non-limiting example of the structure and possible operation of a motor-turbocharger arrangement. One end of the shaft 19 of the engine 18 drives four compressor wheels (four compression stages 15). The other end of the shaft 19 is directly coupled to two expansion stages (two turbines 17).

[0077] Of course, any other type of arrangement of the compression stages 15 and expansion stage 17 (number and distribution) suitable can be considered (same for the number of engines).

[0078] So other modifications are possible.

[0079] Different configurations are therefore possible for the 17 turbines, particularly for the downstream turbines (the coldest).

[0080] For example, as already illustrated, the last two expansion stages (two turbines) can be installed in parallel rather than in series. This allows for a greater enthalpy drop across these turbines. This would be achieved at the expense of efficiency (because two turbines would share 100% of the flow rate and the available pressure difference would be almost doubled). Despite this potential drop in efficiency for these last two expansion stages, achieving a greater enthalpy drop could allow for more efficient expansion staging.

[0081] Indeed, the same cold enthalpy differential induces a smaller temperature variation at the terminals of a turbine than for a hotter turbine. This improves the efficiency of the refrigeration and liquefaction process. Thus, despite a relatively small temperature differential at the turbine terminals, the efficiency of the device allows hydrogen to be liquefied with good energy efficiency.

[0082] The temperature differential caused by the turbine 17 may be a function of the temperature of the cycle gas upstream of the turbine 17.

[0083] A buffer tank (not shown) and a set of valve(s) may be provided, preferably at the low pressure level, in order to limit the maximum gas filling pressure of the cooling circuit. Preferably, the minimum compression ratio is between 1.3 and 1.6 at the terminals of the compressor station. The cycle gas may be composed of 100% or 99% helium and supplemented with hydrogen, for example.

[0084] The cycle circuit may comprise at the inlet of at least one of the turbines 17 an inlet guide vane (IGV) device configured to adjust the fluid flow rate to a determined operating point.

[0085] Furthermore, the arrangement of the compressor wheels 15 and / or turbines 17 is not limited to the previous examples. Thus, the number and arrangement of the compressors 15 can be modified. For example, the compression mechanism could be composed of only three compressors, each compressor could be provided with several compression stages for example three compression stages i.e. three compressor wheels (with or without inter-stage cooling).

[0086] Similarly, two compression stages 15 could be arranged in parallel and in series with other compression stages (e.g. three in series). The two compression stages in parallel can be placed upstream of the others and thus provide downstream a relatively large flow at low pressure using machines which can all be identical.

[0087] Similarly, turbines 17 can be placed in parallel in the cycle circuit 14.

[0088] Furthermore, as already illustrated, all the turbines could be coupled to one or more compressor wheels (for example one or more turbines 17 coupled to the same shaft 19 as one or more compression stages).

[0089] As illustrated, the circuit 3 of fluid to be cooled may comprise one or more catalysis members (pot(s) 280) outside of exchangers or section(s) 29 of exchanger(s) for example for the conversion of hydrogen (ortho to para).

Claims

1. Device for liquefying a fluid such as hydrogen and / or helium, comprising a circuit (3) for fluid that is 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 an assembly of heat exchanger(s) (6, 7, 8, 9, 10, 11, 12, 13) in a heat exchange relationship with the circuit (3) for fluid that is to be cooled, the device (1) comprising at least one first cooling system (20) in a heat exchange relationship with at least part of the assembly of heat exchanger(s) (6, 7, 8, 9, 10, 11, 12, 13), the first cooling system (20) being a refrigerator that performs a refrigeration cycle on a cycle gas mainly comprising helium, said refrigerator (20) comprising the following disposed in series in a cycle circuit (14): a mechanism (15) for compressing the cycle gas, at least one member (16, 5, 6, 8, 10, 12) for cooling the cycle gas, a mechanism (17) for expanding the cycle gas and at least one member (13, 12, 11, 10, 9, 8, 7, 6, 5) for heating the expanded cycle gas, wherein the compression mechanism comprises at least four compression stages (15) in series composed of an assembly of compressor(s) (15) of the centrifugal type, the compression stages (15) being mounted on shafts (19, 190) that are driven in rotation by an assembly of one or more motors (18), the expansion mechanism comprising at least three expansion stages in series composed of an assembly of turbines (17) of the centripetal type, the at least one member (16, 5, 6, 8, 10, 12) for cooling the cycle gas being configured to cool the cycle gas at the outlet of at least one of the turbines (17) and 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 mechanical work produced during the expansion to the compression stage (15), and in that the cycle circuit (14) comprises a return pipe (22) having a first end connected to the outlet of one of the turbines (17) other than the last downstream turbine and a second end connected to the inlet of one of the compression stages (15) other than the first upstream compression stage (15), for returning part of the flow of cycle gas to the compression mechanism at an intermediate pressure level between the low pressure at the inlet of the compression mechanism and the higher pressure at the outlet of the compression mechanism.

2. Device according to Claim 1, characterized in that the return pipe (22) is in a heat exchange relationship with the at least one member (5, 6, 8, 10, 12) for cooling the cycle gas and / or the member (13, 12, 11, 10, 9, 8, 7, 6, 5) for heating the expanded cycle gas.

3. Device according to Claim 1 or 2, characterized in that the compression mechanism comprises solely compressors (15) of the centrifugal type.

4. Device according to any one of Claims 1 to 3, characterized in that the at least one member for cooling the cycle gas comprises an assembly of heat exchanger(s) (8, 10, 12) disposed at the outlet of at least some of the turbines (17).

5. Device according to any one of Claims 1 to 4, characterized in that it comprises a system (8, 10, 12) for cooling the cycle gas, such as a heat exchanger, disposed at the outlet of at least some of the turbines (17) except for the last turbine (17) in series along the direction of circulation of the cycle gas.

6. Device according to any one of Claims 1 to 5, characterized in that, along the direction of circulation of the cycle gas, at least two turbines (17) in series are coupled respectively to compression stages (15) considered in the reverse order of their disposition in series, that is to say that, for example, at least one turbine (17) is coupled to a compression stage (15) located upstream of a compression stage (15) coupled to another turbine (17) which precedes it in the cycle circuit (14).

7. Device according to any one of Claims 1 to 6, characterized in that the working pressure of at least one turbine (17) coupled to a compression stage (15) is adjusted to the working pressure of the compressor (15) comprising the compression stage to which said at least one turbine is coupled, that is to say that the pressure of the cycle gas entering the turbine (17) differs from the inlet pressure of the compressor (15) to which said turbine is coupled by no more than 40% and preferably no more than 30% or 20%.

8. Device according to any one of Claims 1 to 7, characterized in that the mechanical coupling of the turbines (17) and of the compression stages (15) to one and the same shaft (19) is configured to ensure an identical rotational speed of the turbine (17) and of the compression stages (15) that are coupled.

9. Device according to any one of Claims 1 to 8, characterized in that it comprises more compression stages (15) than it does turbines (17), each turbine (17) being coupled to the same shaft (19) as a single respective compression stage (15) driven by a respective motor (18), the other compression stages (15) that are not coupled to a turbine (17) being mounted only on rotary shafts (190) driven by separate respective motors (18).

10. Device according to Claim 9, characterized in that the compression stages (15) that are coupled to a turbine (17) and the compression stages that are not coupled to a turbine (17) alternate in series in the cycle circuit.

11. Device according to any one of Claims 1 to 10, characterized in that it comprises sixteen compression stages (15) and eight turbines (17), or twelve compression stages (15) and six turbines (17), or eight compression stages (15) and four turbines (17), or six compression stages (15) and three turbines (17), or four compression stages (15) and three turbines (17).

12. Device according to any one of Claims 1 to 11, characterized in that the cycle circuit (14) comprises a partial bypass pipe (24) for the flow of cycle gas, having a first end connected upstream of a turbine (17) and a second end connected to the inlet of another turbine (17) located downstream, said bypass pipe (24) being configured to transfer part of the flow of cycle gas directly to the inlet of the coldest downstream turbine.

13. Device according to any one of Claims 1 to 12, characterized in that the assembly of heat exchanger(s) comprises a plurality of heat exchangers (5, 6, 7, 8, 9, 10, 11, 12, 13) which are disposed in series and in which two separate portions of the cycle circuit (14) perform circulation simultaneously in countercurrent operation for respectively the cooling and the heating of the cycle gas, said plurality of heat exchangers forming a member for cooling the cycle gas and a member (16, 5, 6, 8, 10, 12) for heating the cycle gas.

14. Device according to any one of Claims 1 to 13, characterized in that it comprises a second cooling system in a heat exchange relationship with at least part of the set of heat exchanger(s) (5, 6, 7, 8, 9, 10, 11, 12, 13), said second cooling system (21) comprising a circuit (25) for heat transfer fluid such as liquid nitrogen or a mixture of refrigerants.

15. Process for preparing hydrogen at cryogenic temperature, notably liquefied hydrogen, using a device (1) according to any one of the preceding claims, wherein the pressure of the cycle gas at the inlet of the mechanism (15) for compressing the cycle gas ranges between two and forty bar abs and notably ranges between eight and thirty five bar abs.