Apparatus and method for liquefying fluids such as hydrogen and / or helium

Abstract

A device for liquefying a fluid is disclosed, the device comprising a fluid circuit (3) to be cooled, the device (1) comprising a heat exchanger assembly (6, 7, 8, 9, 10, 11, 12, 13) in heat exchange with the fluid circuit (3) to be cooled, at least one first cooling system (20) in heat exchange with at least one portion of the heat exchanger assembly (6, 7, 8, 9, 10, 11, 12, 13), the first cooling system (20) being a refrigerator having a cycle for refrigerating a cycle gas mainly comprising helium, said refrigerator (20) comprising, 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 reheating the expanded cycle gas, wherein the compression mechanism comprises at least four compression stages (15) in series made up of a centrifugal compressor assembly (15), the compression stages (15) being mounted on a shaft (19, 190) driven in rotation by an electric machine assembly (18), the expansion mechanism comprises at least three expansion stages in series made up of a set of radial turbines (17), the at least one member (16, 5, 6, 8, 10, 12) for cooling the cycle gas is 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) in order to supply the compression stage (15) with mechanical work produced during expansion.

Description

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

[0002] The present invention more particularly relates to a device for liquefying a fluid such as hydrogen and / or helium, the device comprising a circuit for the fluid to be cooled, the circuit having an upstream end intended to be connected to a source of gaseous fluid and a downstream end intended to be connected to a means for collecting the liquefied fluid, the device comprising an assembly of one or more heat exchangers in heat exchange relationship with the circuit for the fluid to be cooled, the device comprising at least one first cooling system in heat exchange relationship with at least one portion of the assembly of one or more heat exchangers, the first cooling system being a refrigerator carrying out a refrigeration cycle of a circulating gas mainly comprising helium, said refrigerator comprising, arranged in series in a circulation loop: a mechanism for compressing the circulating gas, at least one means for cooling the circulating gas, a mechanism for expanding the circulating gas and at least one means for heating the expanded circulating gas, wherein the compression mechanism comprises at least four compression stages in series consisting of an assembly of one or more centrifugal-type compressors, the compression stages being mounted on a shaft driven in rotation by an assembly of one or more electric motors, the expansion mechanism comprising at least three expansion stages in series consisting of an assembly of radial-type turbines.

[0003] The solutions of the prior art for liquefying hydrogen (H2) combine a cycle compressor which obtains a relatively low isothermal efficiency (about 60% to 65%) and has a relatively limited volumetric capacity, but which is rather high in terms of investment cost and high in terms of maintenance cost.

[0004] Document EP 3368630 A1 describes a known method for liquefying hydrogen.

[0005] The aim of the present invention is to overcome all or some of the drawbacks of the prior art described above.

[0006] To this end, the essential characteristics of the device according to the invention, which also complies with the general definition given in the above preamble in other respects, consist in that the at least one means for cooling the circulating gas is configured to cool the circulating gas at the outlet of at least one of the turbines, and in that at least one of the turbines is coupled to the same shaft as at least one compression stage, so as to supply the mechanical work produced during expansion to the compression stage.

[0007] Thus, in contrast to the prior art methods which aim to achieve a significant compression ratio via a volumetric cycle compressor, the present invention uses centrifugal compression, which makes it possible to obtain a significantly higher isothermal efficiency (for example, greater than 70% and typically close to 75-80%) despite the relatively low compression ratio.

[0008] In addition, the application makes it possible to actively recover the expansion work, in particular of the circulating gas between 80 K and 20 K, thereby increasing the efficiency of the installation, compared to the prior art.

[0009] Preferably, the compression of the circulating gas is overall centrifugal and uses a circulating fluid comprising mainly helium or consisting of pure helium. This makes it possible to advantageously use this type of compressor and mechanical integration of the expansion work of the turbines directly connected to the compression station.

[0010] Furthermore, the embodiments of the application can have one or more of the following features:

[0011] - the compression means comprise only centrifugal-type compressors,

[0012] - the at least one means for cooling the circulating gas comprises a set of one or more heat exchangers arranged at the outlet of at least some of the turbines,

[0013] - the device comprises a system for cooling the circulating gas, such as a heat exchanger, arranged at the outlet of at least some of the turbines, in series along the circulation direction of the circulating gas, except for the last turbine,

[0014] - along the circulation direction of the circulating gas, at least two turbines in series are respectively coupled to a compression stage, considered in the reverse order of their arrangement in series, that is to say, for example, at least one turbine is coupled to a compression stage located upstream of the compression stage coupled to another turbine preceding it in the circulation loop,

[0015] - the working pressure of at least one turbine coupled to a compression stage is adjusted to the working pressure of the compressor comprising the compression stage coupled to said at least one turbine, that is to say the pressure of the circulating gas entering the turbine does not differ by more than 40% and preferably not more than 30% or 20% from the outlet pressure of the compressor coupled to said at least one turbine,

[0016] - the mechanical coupling of the turbine and the compression stage to the same shaft is configured to ensure the same rotational speed of the coupled turbine and compression stage,

[0017] - the device comprises more compression stages than turbines it comprises, each turbine coupled to a single corresponding compression stage to the same shaft driven by a corresponding electric machine, the other compression stages not coupled to a turbine being mounted only on a rotating shaft driven by a separate corresponding electric machine,

[0018] - the compression stages coupled to a turbine and the compression stages not coupled to a turbine alternate in series in the circulation loop,

[0019] - 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,

[0020] - the cycle circuit comprises a backflow pipe having a first end connected to an outlet of one of the turbines and a second end connected to an inlet of one of the compression stages other than the first compression stage, for backflowing a portion of the cycle gas flow to the compression stages at an intermediate pressure level between the low pressure at the inlet of the compression stages and the higher pressure at the outlet of the compression stages,

[0021] - the backflow pipe is in heat exchange relationship with the at least one means for cooling the cycle gas and / or the means for heating the expanded cycle gas,

[0022] - the cycle circuit comprises a local bypass pipe for the cycle gas flow, the local bypass pipe having a first end connected upstream of a turbine and a second end connected to an inlet of another turbine located downstream, said bypass pipe being configured to directly pass a portion of the cycle gas flow to the inlet of the coolest downstream turbine,

[0023] - the assembly of one or more heat exchangers comprises a plurality of heat exchangers arranged in series, and wherein two separate parts of the cycle circuit are simultaneously circulated in countercurrent operation, respectively for cooling and heating the cycle gas, said plurality of heat exchangers forming the means for cooling the cycle gas and the means for heating the cycle gas,

[0024] - the device comprises a second cooling system in heat exchange relationship with at least one part of the assembly of one or more heat exchangers, said second cooling system comprising a circuit for a heat transfer fluid such as liquid nitrogen or a refrigerant mixture,

[0025] - the cycle gas consists of helium or a mixture containing at least 50% of helium,

[0026] - the cycle circuit comprises an inlet guide vane ("IGV") at the inlet of at least one of the turbines, the inlet guide vane being configured to regulate the flow rate of the fluid to a determined operating point,

[0027] - the working pressures of the turbines are respectively set to the working pressures of the compressors coupled with said turbines, so that the pressure of the cycle gas entering a turbine differs by no more than 30% and preferably no more than 20% from the outlet pressure of the two compressors in series coupled with said turbine.

[0028] The application can also relate to a method for producing cryogenic hydrogen, in particular liquefied hydrogen, using a device according to any one of the above or below features, wherein the pressure of the cycle gas at the inlet of the mechanism for compressing the cycle gas is between two bar absolute and forty bar absolute, and in particular between eight bar absolute and thirty-five bar absolute.

[0029] The application can also relate to any alternative device or method comprising any combination of the above or below features within the scope of the claims.

[0030] Further specific features and advantages will become apparent from the description given below, which is made with reference to the drawings, in which:

[0031] [ Figure 1 ] shows a schematic partial view illustrating the structure and operation of a first possible exemplary embodiment of the application,

[0032] [ Figure 2 ] shows a schematic partial view illustrating the structure and operation of a second possible exemplary embodiment of the application,

[0033] [ Figure 3 ] shows a schematic partial view illustrating the structure and operation of a third possible exemplary embodiment of the application,

[0034] [ Figure 4 ] shows a schematic partial view illustrating the structure and operation of a fourth possible exemplary embodiment of the application,

[0035] [ Figure 5 ] shows a schematic partial view illustrating the structure and operation of a fifth possible exemplary embodiment of the application,

[0036] [ Figure 6 ] shows a schematic partial view illustrating a detail of a fourth possible exemplary embodiment of the application, which illustrates a possible instance of the structure and operation of the motor-driven turbo-compressor of the device.

[0037] [ Figure 1 ] The device 1 for liquefying a fluid illustrated in the figures is intended for liquefying hydrogen gas, but can also be applicable to other gases, in particular helium or any mixture.

[0038] The device 1 comprises a circuit 3 for the fluid to be cooled, in particular hydrogen, which has 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 can typically comprise an electrolyser, a hydrogen distribution network, a steam methane reforming (SMR) unit or one or more of any other suitable source.

[0039] The device 1 comprises an assembly of heat exchangers 6, 7, 8, 9, 10, 11, 12, 13 arranged in series in heat exchange relationship with the circuit 3 for the fluid to be cooled.

[0040] The device 1 comprises at least one cooling system 20 in heat exchange relationship with at least one portion of the assembly of heat exchangers 5, 6, 7, 8, 9, 10, 11, 12, 13.

[0041] This first cooling system 20 is a refrigerator carrying out a refrigeration cycle on the circulating gas mainly comprising helium. This refrigerator 20 comprises, arranged in series in the circulation circuit 14 (preferably in a closed loop), the following components: a mechanism 15 for compressing the circulating gas, at least one member 16, 5, 6, 8, 10, 12 for cooling the circulating gas, a mechanism 17 for expanding the circulating gas, and at least one member 13, 12, 11, 10, 9, 8, 7, 6, 5 for heating the expanded circulating gas.

[0042] The fluid to be liquefied (for example hydrogen) is thus a fluid separate from the fluid of the circulating gas (for example helium and possibly one or more other components).

[0043] Preferably, the two circuits are thus separate.

[0044] As illustrated, the assembly of one or more heat exchangers for cooling the hydrogen to be liquefied preferably comprises one or more counterflow heat exchangers 5, 6, 8, 10, 12 arranged in series, and in which two separate portions of the circulation circuit 14 circulate simultaneously in counterflow operation (for cooling and heating separate circulating gas flows, respectively).

[0045] That is to say, this plurality of counterflow heat exchangers forms both members for cooling the circulating gas (for example, after compression and after the expansion stage) and members for heating the circulating gas (after expansion and before returning to the compression mechanism).

[0046] The compression mechanism comprises at least four compression stages 15 constituted by an assembly of centrifugal-type compressors arranged in series (and possibly in parallel).

[0047] The compression stages 15 can be constituted by impellers of motorized centrifugal compressors.

[0048] The compression stages 15 (that is to say the compressor impellers) are mounted on shafts 19, 190 which are driven in rotation by an assembly of one or more electric motors 18 (at least one electric motor). Preferably, all the compressors 15 are of the centrifugal type.

[0049] The expansion mechanism itself comprises at least three expansion stages formed by at least partially series-arranged centrifugal turbines 17. For example, the number of compression stages (e.g. the number of compression impellers) is greater than the number of expansion stages (e.g. the number of expansion impellers). Preferably, all turbines 17 are centrifugal and mainly arranged in series.

[0050] The at least one means for cooling the circulating gas 16, 5, 6, 8, 10, 12 is in particular configured to cool the circulating gas at the outlet of at least one of the turbines 17. That is, after expansion in the turbine 17, the circulating gas can be cooled typically by a value between 2 K and 30 K.

[0051] In addition, at least one of the turbines 17 is coupled to the same shaft 19 as a compression stage 15 of the compressor, in order to supply the mechanical work produced during expansion to the compressor.

[0052] This combination of specific technical features (centrifugal compression, centrifugal expansion, transfer of work from turbine to compressor, etc.) is possible for a circulating gas containing helium. In particular, this makes it possible to decouple (make it independent) the method using the heat transfer fluid (helium-based circulating gas) from the delivery temperature of the fluid to be liquefied (for example, hydrogen). This makes it possible in particular to increase the value of the low pressure level of the circulating gas in the circulation loop 14 to a higher pressure than in known devices. This is possible despite the relatively low overall compression rate of the circulating gas. Due to the limitation of the compression rate per stage, this centrifugal compression technology is not generally recommended for the liquefaction of hydrogen in the prior art.

[0053] Thus, the device 1 can have one or more motor-driven turbo-compressors in a part of the compression station. A motor-driven turbo-compressor is an assembly comprising an electric motor whose shaft directly drives the assembly of one or more compression stages (one or more impellers) and the assembly of one or more expansion stages (one or more turbines). This directly exploits the mechanical expansion work at one or more compressors of the circulating gas.

[0054] For example, and as illustrated, the device 1 comprises more compression stages 15 than turbines 17, for example twice or approximately twice as many. Each turbine 17 can be coupled to a single respective compression impeller 15 to the same shaft 19 driven by a respective electric motor 18. One or more other compression impellers 15 (one or more stages) not coupled to a turbine 17 can be mounted only on a rotating shaft 190 driven by a separate respective electric motor 18 (motor-driven compressor).

[0055] As illustrated, the compression stages 15 coupled to a turbine 17 and the compressors not coupled to a turbine 17 can alternate in series in the circulation loop 14.

[0056] Preferably, the compression mechanism comprises more than six compression stages in series. Of course, this is by no means limiting, as less efficient configurations can be envisaged, for example with three compression stages in series, which make it possible to liquefy the hydrogen gas. The minimum compression ratio (by centrifugation technique) for achieving the liquefaction of the hydrogen gas should preferably be around 1.3 to 1.6.

[0057] The four compression stages 15 in series make it possible to obtain very good isothermal efficiency, in particular with respect to the known solutions of piston compression at the cost of a relatively significant helium mass flow.

[0058] In the non-limiting example illustrated in Figure 1 ], only four compression stages 15 and three turbines 17 are shown, but the device 1 can 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, etc.

[0059] The cooling can be provided downstream of all or some of the compression stages or downstream of all or some of the compressors 15 (for example by heat exchangers 16 cooled by a heat transfer fluid or any other refrigerant). This cooling can be provided after each compression stage, or as illustrated, after every two (or more) compression stages 15, or only downstream of the compression station. Surprisingly, this cooling distribution at every two (or three) compression stages 15, and not at the outlet of each of the compression stages 15 in series, makes it possible to obtain cooling performance while still limiting the cost of the device 1.

[0060] Similarly, the at least one means for cooling the circulating gas preferably comprises systems 8, 10, 12 for cooling the circulating gas, such as heat exchangers, provided in series at the outlet of at least some of the turbines 17.

[0061] This intermediate expansion intercooling makes it possible to limit the high pressure values required to reach the coldest temperature of the circulating gas.

[0062] As illustrated, the device 1 preferably comprises systems for cooling the circulating gas, such as heat exchangers, at the outlet of all the turbines 17 in series along the circulation direction of the circulating gas, except for the last turbine 17. As illustrated, this cooling system can be provided by the respective counterflow heat exchangers 8, 10, 12 described above.

[0063] This expansion followed by cooling makes it possible to implement a temperature staging (that is to say, makes it possible to reach different, decreasing temperatures after each expansion stage) to extract cold at the fluid to be cooled. This temperature staging is obtained by this arrangement and via the minimum compression ratio obtained, for supplying these different turbines 17.

[0064] The arrangement of a plurality of centrifugal compression stages 15 in series upstream makes it possible to obtain this pressure difference, which makes it possible to implement a sufficient cooling staging downstream. In particular, for the same pressure difference, the more the temperature decreases, the more the constant entropy drop of the enthalpy during expansion decreases. The effect of the turbine 17 arrangement in series and the cooling 8, 10 at the outlet of the turbine is to increase the average mass flow in the turbine 17 relative to a known conventional staging. The theoretical isentropic efficiency thus tends to increase and thus makes it possible to obtain a better efficiency of the turbine 17.

[0065] In particular, the cooling 8, 10 between expansion stages allows the circulating fluid to reach the target liquefaction temperature without requiring even greater overall compression ratios. The expansion is preferably isentropic or virtually isentropic. That is to say, the circulating fluid is progressively cooled and the fluid is liquefied.

[0066] Thus, the minimum temperature is reached directly at the outlet of the last virtually isentropic expansion stage (that is to say, downstream of the last expansion turbine 17). Thus, for example, it is not necessary to additionally provide a Joule-Thomson type expansion valve downstream. The cold and in particular subcooled temperature of the hydrogen gas to be liquefied can be obtained with the turbine 17 alone (extracting work).

[0067] Preferably, most or all of the turbines 17 are coupled to one or more respective compressors 15.

[0068] For example, along the circulation direction of the circulating gas, the successive turbines 17 are preferably coupled to the compression stages 15 of the compressors, considered in the reverse order of their arrangement in series. That is to say, for example, a turbine 17 is coupled to a compressor 15 upstream of the compressor 15 coupled to the turbine 17 preceding it.

[0069] Thus, preferably, the order of connection of the coupled turbines 17 and compressors is at least partially reversed between the turbines and the compressors (in the circulation loop, the more upstream turbine is coupled to the more downstream compressor).

[0070] Thus, for example, in the case of a structure with six compression stages 15 in series and three expansion stages in series, the first turbine 17 (that is, the first turbine 17 following the compression mechanism) can be coupled in series to the fifth compressor 15 (fifth compression stage), while the second turbine 17 can be coupled in series to the third compressor 15 (third compression stage), and the third turbine 17 can be coupled in series to the first compressor 15 (first compression stage). The other compressors 15 forming the other compression stages can not be coupled to a turbine (motor-driven compressor system, rather than motor-driven turbo-compressor). Thus, the most powerful turbine 17 (the one most downstream) can be coupled to the first compression stage (the first compression stage intakes at a low pressure of the cycle). At this relatively low pressure level, the greater the compression ratio of the compressor 15, the less the impact of the pressure drop felt at its level (as for the other compressors 15).

[0071] Of course, this example above is by no means limiting. For example, the turbines 17 can be coupled respectively to the even-numbered compressors 15 (first turbine coupled to the sixth compressor, second turbine coupled to the fourth compressor, etc.) or directly in series with the compressors (for example, first turbine 17 coupled in series with the sixth compressor 15, tenth turbine coupled in series with the fifth compressor, etc.).

[0072] Preferably, the operating pressure of the turbines 17 is respectively set to the operating pressure of the compressors 15 to which they are coupled. That is, the pressure of the cycle gas entering the turbine 17 differs by no 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 load on the output shaft 19 of the said motor 18 directly coupling the compressor impeller 15 and the turbine 17.

[0073] For example, the at least one turbine 17 and the corresponding compression stage to which it is coupled have a structural configuration such that the pressure of the cycle gas leaving the turbine 17 differs by no more than 40% and preferably by no more than 30% or 20% from the pressure of the cycle gas at the inlet of the compression stage 15.

[0074] Similarly, the at least one turbine 17 and the corresponding compression stage to which it is coupled preferably also (or possibly alternatively) have a structural configuration such that the pressure of the cycle gas entering the turbine 17 differs by no more than 40% and preferably by no more than 30% or 20% from the pressure of the cycle gas at the outlet of the compression stage.

[0075] This combination of specific technical features (centrifugal compression, centripetal expansion, transmission of work from the turbine to the compressor, and pressure regulation between the coupled compression impeller and expansion impeller) improves the efficiency of the device with respect to known solutions.

[0076] This structural configuration of the turbomachines (for example, the turbomachine wheels) and of the compression stages (for example, the compression wheels) means that the two elements are dimensioned (if appropriate, the shape and / or the size of the wheels and / or of their volutes and / or of their inlet distributors) to carry out, respectively, the same or similar absolute values of compression and expansion as indicated above. That is, by design, the two coupled elements can reach these compression and expansion ratios (without using another active or passive element in the cycle loop), preferably independently of the conditions of the cycle gas flow.

[0077] For example, the expansion ratio at the end of at least one turbomachine 17 coupled to a compression stage can be configured to reduce the pressure of the cycle gas by a value that does not differ by more than 40% (or not more than 20%) from the value of the pressure increase at the end of the compression stage 15 to which it is coupled.

[0078] For example, if the compressor 15 is coupled to a turbomachine 17 and operates between 10 and 15 bars (compressing a flow initially at 10 bars to an exit pressure of 15 bars), it is advantageous for the turbomachine 17 to expand this flow to a pressure between 15 and 10 bars (inlet at 15 bars and outlet at 10 bars).

[0079] This improves the distribution and balance of the axial forces of the shaft 19 that supports them.

[0080] This tends to reduce the resultant of the axial forces, since the sign of the forces resulting from the pressure difference at the end of the wheels 15, 17 is opposite.

[0081] This is preferably also applicable to the case of a plurality of turbomachines coupled in series to one or more compressors 15.

[0082] Thus, as illustrated, the expansion mechanism can comprise at least two expansion stages in series constituted by the assembly of the centrifugal turbomachines 17 in series.

[0083] In addition, as mentioned above, the at least two turbomachines 17 in series are preferably coupled to the compression stages 15, respectively, in the opposite order to that in which they are arranged in series, along the direction of circulation of the cycle gas. That is, at least one turbomachine 17 is coupled to a compression stage 15 upstream of the compression stage 15 coupled to another turbomachine 17 that precedes it in the cycle loop 14.

[0084] Preferably, the device comprises n turbomachines (expansion wheels or stages) and k compressor wheels or stages, with k >= n. The expansion ratio selected at the end of each turbomachine 17 is thus preferably imposed as a function of the compressor to which they are coupled (as explained above).

[0085] In the example illustrated, in which the compressors 15 are alternately coupled to the turbines 17 and then uncoupled from the turbines, the working pressure of the turbines 17 can be set "one by one" or "two by two" to the working pressure of the compressors 15 (that is to say, the first turbine 17 works at the compression rate of the 5th or 6th compressor 15; similarly, the second turbine 17 works at the compression rate of the 3rd or 4th compressor, etc.). If one considers a pair of two compressors 15 in series (one compressor with a compression impeller coupled to a turbine, followed by one compressor with a compression impeller uncoupled from a turbine), the first of the two compressors will for example compress the cycle gas to a first pressure PA, while the second compressor will then compress this cycle gas to a second pressure PB, with PB > PA. The turbine 17 coupled to the first of the two compressors preferably expands the cycle gas from the second pressure PB to the first pressure PA. This can for example be obtained by adjusting the characteristics of this turbine 17 according to this constraint. For example, there is adjustment of the section of the distributor, calibrated to the flow rate reaching the turbine 17, which has an effect on the pressure drop generated in the distributor part and in the impeller part of the turbine.

[0086] Thus, for example when a turbine is coupled every two compression stages in series, the pressure relationship (inlet / outlet) described in detail above between the coupled expansion stage and the compression stage can thus apply separately to the compression stage supporting the turbine or to the assembly of two compressor impellers in series.

[0087] In addition, the mechanical coupling(s) of the turbines 17 and of the compression stages 15 to one and the same shaft 19 are configured to preferably ensure that the coupled turbines 17 and compression stages 15 have the same rotational speed. This makes it possible to directly and efficiently exploit the expansion work in the device. If appropriate, the rotational speeds of all the compressor and turbine impellers can be equal to one and the same determined value.

[0088] It can optionally be provided to equip all or some of the compression stages with control means. For example, a variable frequency drive ("VFD") can be provided for each motor 18 driving at least one compression stage. This makes it possible to independently adjust the speed of the compression stages or of each compression stage, and thus to adjust the expansion, without using complex gear systems or drives and specific control means connected to a variable blade set upstream of one or more compression stages. This speed control means can be provided for an assembly of compressors or for each compression stage.

[0089] Preferably, the device 1 does not comprise flow valves or valves for reducing the pressure (pressure drop) in the circuit between the compression stages, between the expansion stages or downstream of the expansion of the cycle. Thus, it is possible to provide only isolation valves for maintenance in the cycle circuit 14.

[0090] That is, the operating point (speed, pressure) of the turbine 17 can be regulated only by the dimensional characteristics of the turbine 17 (for example, without a throttle valve at the turbine inlet). This increases the reliability of the device (there are no potential problems of failure of valves involved in the control of the process, since they are not present). Furthermore, this makes it possible to eliminate expensive auxiliary circuits (safety valves, etc.) and simplifies manufacturing (reduction in the number of lines to be isolated, etc.).

[0091] The use of a helium-based cycle gas makes it possible to reach the temperature for supercooling the liquefied hydrogen without the risk of zones below atmospheric pressure within the process (which would be dangerous if the cycle fluid were hydrogen gas) and without the risk of freezing of the cold source (the maximum liquefaction temperature of helium gas is equal to 5.17 K). The effect of supercooling the liquefied hydrogen has very significant advantages for the transport chain of the hydrogen molecules and then, due to the reduction in the evaporated gas during transport, potentially very significant advantages for the user (typically a liquid station).

[0092] Thus, it is possible to reach the gel point of the hydrogen gas stream to be liquefied (13 K) without crystallizing the cold source.

[0093] The low-pressure part of the cycle circuit 14 can be operated at a relatively high pressure. This makes it possible to reduce the volumetric flow rate in the heat exchangers 6, 7, 8, 9, 10, 11, 12, 13. Thus, the working pressure of the cycle gas can be decoupled from the target pressure or temperature of the fluid to be cooled. Thus, this pressure of the cycle gas can be increased to accommodate the stresses of the turbine, but also to reduce the volumetric flow rate at low pressure, which is generally one of the main parameters that influences the size of the heat exchangers.

[0094] This low-pressure level in the cycle circuit 14 is for example greater than or equal to 10 bars, and can typically be between 10 bars and 40 bars. This reduces the volumetric flow rate in the heat exchangers, which balances the low compression rate of each compression stage.

[0095] As illustrated, the device 1 can comprise for example a second cooling system in heat exchange relationship with at least part of the assembly of one or more heat exchangers 5, which is in heat exchange relationship with the cycle gas. This second cooling system 21 comprises for example a circuit 25 for a heat transfer fluid such as liquid nitrogen or a refrigerant mixture, which cools the cycle gas and / or the hydrogen gas to be liquefied by a first counterflow heat exchanger or a plurality of counterflow heat exchangers and can also make it possible to prevent the displacement losses caused at the hot end by circulating the heat transfer fluid(s) in a closed loop as illustrated in Figure 1 ].

[0096] This second cooling system 21 enables pre-cooling of the fluid to be liquefied and / or the working gas, for example, at the outlet of the compression mechanism. This refrigerant, circulating in the circuit 25 for the heat transfer fluid (e.g., in a loop), is supplied, for example, by a unit 27 for generating and / or storing 28 of this refrigerant. If appropriate, the circuit 3 for the fluid to be cooled passes through this unit 27 so as to be pre-cooled upstream. It should be noted that it is conceivable that the device 1 may have one or more other additional cooling systems. For example, in addition to the systems described above, a third cooling circuit fed by a cooler (e.g., a cold source typically supplied at temperatures between 5°C and -60°C) may be provided. If desired, a fourth cooling system may also be provided to again supply cooling to the device 1 and increase the liquefaction capacity of the device 1. Figure 2 The embodiment differs from the previous embodiment only in that the recirculation loop 14 includes a return pipe 22 having a first end connected to the outlet of one of the turbines 17 (except for the last turbine in the downstream direction) and a second end connected to the inlet of one of the compressors 15 (except for the first compressor 15 in the upstream direction). This return pipe 22 enables some of the recirculated gas flow to return to the compressor at an intermediate pressure level between the low pressure at the compressor inlet and the high pressure at the compressor outlet.

[0097] The return pipe 22 can be in heat exchange relationship with at least some of the counter-current heat exchangers. Depending on the desired optimization level, multiple return pipes to the compression station at intermediate pressures can be advantageously installed. For example, the extraction point (at the turbine under consideration) and the injection point (at the compression stage under consideration) can be at different pressure levels. Figure 3 The embodiment differs from the previous embodiment only in that the recirculation loop 14 further includes a partial bypass pipe 24 having a first end connected upstream of turbine 17 (e.g., a first turbine 17 in the upstream direction) and a second end connected to the inlet of another turbine (e.g., a third turbine) located downstream. For example, bypass pipe 24 allows some of the recirculated gas flow leaving the compressor at high pressure to be diverted towards the coldest turbine further downstream. The remaining flow enters this hotter first upstream turbine 17. This allows the flow rate sent to different stages to be adjusted according to the positioning with respect to the specific speeds of the different turbines and compressors. For example, a compressor at a higher pressure draws in a lower volumetric flow rate than the first compression stage (closer to the low pressure of the process). One way to increase this volumetric flow rate and thus potentially increase its isentropic efficiency is to incorporate the return flow from the expansion stage at intermediate pressures, such as [ Figure 3 As shown in the image. Figure 4 The device 1 shown in the figure illustrates yet another non-limiting embodiment. Elements identical to those described above are indicated by the same reference numerals and will not be described in detail again.

[0098] [ Figure 4 ] The cycle 14 of the device shown in [

[0099] In this example, the device 1 has five expansion stages in series (six centripetal turbine wheels, of which two are arranged in parallel), for example one or two expansion stages per compressor. As shown, all turbines 17 can be coupled to the compressor shaft 19 (for example, two turbines 17 are mounted on the other end of the shaft 19 of each motor 18 to supply mechanical work to the compressor wheels 15 also mounted on this shaft 19). Of course, the turbines 17 can be on the same side of the shaft 19 as the compression wheels 15. For example, four first expansion stages are formed by four turbines 17 in series. The fifth expansion stage is formed, for example, by two turbines 17 arranged respectively in the two branches of the cycle 14 in parallel. Figure 5 ] The device 1 shown in [ Figure 4 ] differs from that of the device of [

[0100] This recirculation makes it possible to increase the volumetric flow of the compressors, which are thus supplied with an excess flow, and thus potentially increase their isentropic efficiency.

[0101] [ Figure 6 ] The device 1 shown in [

[0102] Of course, any other suitable type of arrangement (number and distribution) of compression stages 15 and expansion stages 17 can be envisaged (as well as for the number of electric machines).

[0103] Therefore, other modifications are possible.

[0104] Therefore, various configurations are possible for the turbo machines 17, and especially for the downstream turbo machines (the coldest ones).

[0105] For example, as already shown, the last two expansion stages (two turbo machines) can be installed in parallel instead of in series. This makes it possible to generate a greater enthalpy drop at the end of these turbo machines. This will be achieved at the expense of efficiency (as the two turbo machines will share 100% of the flow and the available pressure difference will almost be doubled). Although the efficiency of these last two expansion stages can decrease, achieving a greater enthalpy drop will make it possible to grade the expansion more efficiently.

[0106] This is because the same cold enthalpy difference results in a temperature change at the end of the turbo machines that is less than the temperature change of the hotter turbo machines. This improves the efficiency of the refrigeration and liquefaction process. Therefore, although the temperature difference at the end of the turbo machines is relatively reduced, the efficiency of the device makes it possible to liquefy the hydrogen gas with good energy efficiency.

[0107] The temperature difference induced by the turbo machines 17 can be a function of the temperature of the circulating gas upstream of the turbo machines 17.

[0108] A buffer tank (not shown) and an assembly of one or more valves can be provided, preferably at a low pressure level, the aim being to limit the maximum pressure with which the cooling circuit is filled with gas. Preferably, at the end of the compression station, the minimum compression ratio is between 1.3 and 1.6. For example, the circulating gas can consist of 100% or 99% helium gas and be supplemented with hydrogen gas.

[0109] The circulation circuit can comprise, at the inlet of at least one of the turbo machines 17, inlet guide vanes (“IGVs”) configured to regulate the flow of fluid to a determined operating point.

[0110] In addition, the arrangement of the compressor wheels 15 and / or of the turbo machines 17 is not limited to the above example. Therefore, the number and arrangement of the compressors 15 can be modified. For example, the compression can consist of only three compressors, each of which can be provided with a plurality of compression stages, for example three compression stages, that is to say three compressor wheels (with or without inter-stage cooling).

[0111] Similarly, two compression stages 15 can be arranged in parallel and in series with other compression stages (for example three in series). The two compression stages in parallel can be placed upstream of the other compression stages and thus supply a relatively high flow at low pressure in the downstream direction by using machines that can all be identical.

[0112] In the same way, the turbomachines 17 can be placed in parallel in the circulation circuit 14.

[0113] In addition, as has been shown, all the turbomachines can be coupled to one or more compressor impellers (for example one or more turbomachines 17 coupled to the same shaft 19 as one or more compression stages).

[0114] As shown, the circuit 3 for the fluid to be cooled can have one or more catalytic means (one or more tanks 280) at the outside of the exchanger or one or more portions 29 of one or more exchangers, for example for the conversion of hydrogen (ortho to para hydrogen).

Claims

1. An apparatus for liquefying a fluid, the apparatus comprising a circuit (3) for a fluid to be cooled, the circuit having an upstream end intended to be connected to a gaseous fluid source (2) and a downstream end (23) intended to be connected to a component (4) for collecting the liquefied fluid, the apparatus (1) comprising an assembly of one or more heat exchangers (5,6,7,8,9,10,11,12,13) ​​in heat exchange relationship with the circuit (3) for the fluid to be cooled, the apparatus (1) comprising an assembly of one or more heat exchangers (5,6,7,8,9,10,11,12) in heat exchange relationship with the one or more heat exchangers (5,6,7,8,9,10,11,12) At least one first cooling system (20) in which at least a portion of the components of (13) are in heat exchange relationship, the first cooling system (20) being a refrigerator for cooling a circulating gas consisting of helium or a mixture containing at least 50% helium, the refrigerator comprising the following components arranged in series in the circulation loop (14): a compression mechanism (15) for compressing the circulating gas, at least one heat exchanger (16, 5, 6, 8, 10, 12) for cooling the circulating gas, an expansion mechanism (17) for expanding the circulating gas, and at least one... The heat exchangers (13, 12, 11, 10, 9, 8, 7, 6, 5) for heating the expanded circulating gas, wherein the compression mechanism (15) comprises at least four compression stages in series, consisting of one or more centrifugal compressor assemblies mounted on shafts (19, 190) driven to rotate by one or more motor (18) assemblies, the expansion mechanism (17) comprises at least three expansion stages in series, consisting of multiple centripetal turbine assemblies, and the at least one heat exchanger (16, 5, 6, 8, 1) for cooling the circulating gas. 0,12) is configured to cool the circulating gas at the outlet of at least one of these turbines. The device includes more compression stages than the turbines it includes. Each turbine is coupled to a single corresponding compression stage to the same shaft (19) driven by a corresponding motor (18) so that the mechanical work generated during expansion is supplied to that compression stage. Other compression stages not coupled to the turbines are mounted only on a rotating shaft (190) driven by a separate corresponding motor (18). The compression stages coupled to the turbines and those not coupled to the turbines are alternated in series in the circulation loop.

2. The apparatus as claimed in claim 1, characterized in that, The fluid is hydrogen and / or helium.

3. The apparatus as described in claim 1 or 2, characterized in that, The compression mechanism consists only of centrifugal compressors.

4. The apparatus according to any one of claims 1 to 3, characterized in that, The at least one heat exchanger (16,5,6,8,10,12) for cooling the circulating gas includes components of one or more heat exchangers (8,10,12) disposed at the outlet of at least some of these turbines.

5. The apparatus as described in any one of claims 1 to 4, characterized in that, The device includes heat exchangers (8, 10, 12) for cooling the circulating gas, which are disposed at the outlets of at least some of the turbines connected in series along the circulation direction of the circulating gas, excluding the last turbine.

6. The apparatus as claimed in any one of claims 1 to 5, characterized in that, Along the circulation direction of the circulating gas, at least two turbines connected in series are respectively connected to the compression stage, in the reverse order of their series connection.

7. The apparatus as claimed in claim 6, characterized in that, At least one turbine is connected to a compression stage located upstream of another turbine connected to it in the circulation loop (14).

8. The apparatus as claimed in any one of claims 1 to 7, characterized in that, The operating pressure of at least one turbine connected to the compression stage is adjusted to the operating pressure of the compressor that includes the compression stage connected to the at least one turbine.

9. The apparatus as claimed in claim 8, characterized in that, The pressure of the circulating gas entering the turbine differs from the outlet pressure of the compressor connected to the at least one turbine by no more than 40%.

10. The apparatus as claimed in claim 9, characterized in that, The pressure of the circulating gas entering the turbine differs from the outlet pressure of the compressor connected to the at least one turbine by no more than 30%.

11. The apparatus as claimed in claim 10, characterized in that, The pressure of the circulating gas entering the turbine differs from the outlet pressure of the compressor connected to the at least one turbine by no more than 20%.

12. The apparatus according to any one of claims 1 to 11, characterized in that, The mechanical connection between the turbine and the compression stage and the same shaft (19) is configured to ensure that the connected turbine and compression stage rotate at the same speed.

13. The apparatus according to any one of claims 1 to 12, characterized in that, The device includes 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.

14. The apparatus according to any one of claims 1 to 13, characterized in that, The circulation loop (14) includes a return pipe (22) having a first end connected to an outlet of one of the turbines and a second end connected to an inlet of one of the compression stages other than the first compression stage, for returning a portion of the circulating gas flow to the compression stage at an intermediate pressure level between the low pressure at the inlet of the compression stage and the higher pressure at the outlet of the compression stage.

15. The apparatus as claimed in claim 14, characterized in that, The return pipe (22) is in heat exchange relationship with at least one heat exchanger (16,5,6,8,10,12) for cooling the circulating gas and / or the heat exchanger (13,12,11,10,9,8,7,6,5) for heating the expanded circulating gas.

16. The apparatus according to any one of claims 1 to 15, characterized in that, The circulation loop (14) includes a local bypass pipe (24) for the circulating gas flow, the local bypass pipe having a first end connected to the upstream of a turbine and a second end connected to the inlet of another turbine located downstream, the bypass pipe (24) being configured to directly deliver a portion of the circulating gas flow to the inlet of the coldest downstream turbine.

17. The apparatus according to any one of claims 1 to 16, characterized in that, The assembly of the one or more heat exchangers (5,6,7,8,9,10,11,12,13) ​​includes a plurality of heat exchangers arranged in series, wherein two separate portions of the circulation loop (14) are simultaneously circulated in countercurrent operation for cooling and heating the circulating gas, respectively, the plurality of heat exchangers forming a heat exchanger (16,5,6,8,10,12) for cooling the circulating gas and a heat exchanger for heating the circulating gas.

18. The apparatus as claimed in any one of claims 1 to 17, characterized in that, The device includes a second cooling system that is in heat exchange relationship with at least a portion of the components of the one or more heat exchangers (5,6,7,8,9,10,11,12,13), the second cooling system (21) including a loop (25) for heat transfer fluid.

19. The apparatus as claimed in claim 18, characterized in that, The heat transfer fluid is liquid nitrogen or a mixture of refrigerants.

20. A method for producing cryogenic hydrogen using the apparatus (1) as described in any one of the preceding claims, wherein, The pressure of the circulating gas at the inlet of the compression mechanism (15) used to compress the circulating gas is between two bar absolute pressure and forty bar absolute pressure.

21. The method of claim 20, wherein, The low-temperature hydrogen gas is liquefied hydrogen.

22. The method of claim 20 or 21, wherein, The pressure of the circulating gas at the inlet of the compression mechanism (15) used to compress the circulating gas is between eight bar absolute pressure and thirty-five bar absolute pressure.

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