Device and method for liquefying a gas

Abstract

The invention relates to a device (200) for liquefying a gas (51), the device comprising: - a circuit (55) for conveying gas to be liquefied, the circuit comprising at least one heat exchanger (204) for exchanging heat between the gas (51) to be liquefied and a refrigerant flow (52) comprising at least dihydrogen refrigerant; - a closed refrigeration circuit (210) configured to convey the refrigerant flow, the closed refrigeration circuit comprising a means (215) for maintaining an internal composition of the dihydrogen refrigerant at a ratio of parahydrogen to orthohydrogen that is lower or higher than the ratio corresponding to a natural equilibrium composition in the refrigerant flow closed circuit, the means (215) comprising a catalytic reactor (220) configured to convert some of the orthohydrogen from the dihydrogen refrigerant flow into parahydrogen or vice versa.

Description

Technical field of the invention

[0001] The present invention relates to a device for liquefying a gas and a method for liquefying a gas. It is applicable, in particular, to the field of liquefying a dihydrogen stream. State of the art

[0002] The liquefaction of dihydrogen is an energy-intensive process with a theoretical minimum energy consumption of 3.9 kWh per kilogram of liquid hydrogen produced. Industrial cycles currently in operation consume between 11 and 13 kWh / kgLH₂. When dihydrogen is used as a coolant or refrigerant, more than half of the energy consumption can be attributed to its compression. Improving the energy efficiency of hydrogen compressors is therefore essential to reducing the overall cost of hydrogen liquefaction.

[0003] Dihydrogen exists naturally in two forms depending on the spin number of its two protons: orthohydrogen (o-H2) and parahydrogen (p-H2). The equilibrium composition of dihydrogen changes with temperature, as shown in figure 1 In the figure 1 The x-axis (110) represents temperature in Kelvin, and the y-axis (105) represents the percentage of parahydrogen in the hydrogen. At room temperature, dihydrogen is composed of 75% orthohydrogen and 25% parahydrogen (this composition is subsequently called normal hydrogen), while around 20 K, the liquefaction temperature, it is almost 100% parahydrogen. If normal hydrogen is liquefied and stored, a slow conversion to the parahydrogen form occurs (over several days). The heat generated by this conversion vaporizes some of the stored liquid, resulting in a loss.

[0004] When hydrogen is used as a refrigerant, its temperature varies throughout the refrigeration cycle, and its composition changes slowly due to natural conversion. Furthermore, although the volumetric properties of orthohydrogen and parahydrogen are similar, their calorimetric properties are significantly different. Thus, the exothermic natural conversion (orthohydrogen to parahydrogen) and the differences in physical properties between the two forms affect the performance of the refrigeration cycle and lead to increased energy consumption in the compressors of a closed-loop refrigeration system. This effect is even more pronounced when compression is performed at low temperatures and / or when the hydrogen is stored at low temperatures (for example, in an intermediate storage tank).

[0005] For open hydrogen liquefaction cycles, such as the one described in US patent 7559213, the composition of the dihydrogen used as a refrigerant depends directly on the state of conversion of the hydrogen stream to be liquefied, and this composition does not vary over time. This is because the hydrogen recycled in the cycle has a composition of 99% parahydrogen and mixes in a fixed proportion over time with the dihydrogen to be liquefied, which has a normal composition.

[0006] Some closed liquefaction cycles use dihydrogen as a refrigerant. Above 184 K (-89°C), the equilibrium composition varies little; therefore, changes in composition and their impact are largely negligible. Recent developments have highlighted liquefaction cycles where the average temperature of the hydrogen used as a refrigerant is below 184 K (-89°C). In "Advanced precooling for optimized hydrogen liquefaction," H2Tech, March 2021, Howe, Skinner, and Finn present a closed cycle compressing hydrogen at a low temperature, around 120 K (-153°C). Patent application FR2105720 proposes a closed cycle where the hydrogen used as a refrigerant does not exceed a temperature of 150 K (-123°C). Consequently, the hydrogen undergoes a slow conversion to a state other than normal hydrogen.In "Large scale hydrogen liquefaction in combination with LNG re-gasification", 2006, Kuendig mentions that the refrigerant will contain between 30% and 50% parahydrogen after a long operating time without giving an order of magnitude.

[0007] For informational purposes, other uses of the conversion have been proposed in the literature, such as patent application FR2006278, which presents a system converting parahydrogen from the boil-off gas of liquid hydrogen storage downstream of the liquefier in order to use the generated cooling to cool the flow of hydrogen to be liquefied, or the publication "Enhanced dormancy due to para-to-ortho hydrogen conversion in insulated cryogenic pressure vessels for automotive applications" in which JK Peng uses the conversion of parahydrogen to orthohydrogen to slow the pressure rise in a cryo-compressed hydrogen storage tank. Patent application EP3162871A1 discloses a device for liquefying a gas according to the preamble of claim 1 and a method for liquefying a gas according to the preamble of claim 15.

[0008] Open hydrogen liquefaction cycles solve the problem of hydrogen composition evolution through the conversion step of the hydrogen to be liquefied. However, these cycles exhibit low energy efficiency.

[0009] The literature offers no solution for controlling the composition of the refrigerant hydrogen in a closed refrigeration cycle. As a result, the refrigerant composition changes slowly, which has unforeseen and undesirable effects on heat exchange and the performance of the compression and expansion stages.

[0010] Furthermore, this evolution depends heavily on the processes considered, external conditions and the load factor of the installation. Presentation of the invention

[0011] The present invention aims to remedy all or part of these drawbacks.

[0012] Accordingly to a first aspect, the present invention relates to a device according to claim 1.

[0013] Thanks to these provisions, the hydrogen liquefaction cycle controls the composition of the hydrogen used as a refrigerant, for example by involving at least one catalytic reactor in the refrigeration cycle placed at a chosen temperature, in order to optimize the properties of the refrigerant and reduce the energy consumption of the device by having an operating equilibrium composition different from the natural equilibrium composition.

[0014] These provisions allow the normal hydrogen to be converted to a target composition at the start of the refrigeration cycle and counteract the natural conversion that occurs throughout the system's lifetime. As a result, the physical properties of the refrigerant remain unchanged and losses are reduced, preventing excessive energy consumption by the equipment. In optional embodiments, the closed refrigeration circuit is configured so that the hydrogen refrigerant, at the inlet of the catalytic reactor, has a temperature essentially equal to the average temperature of the hydrogen refrigerant in the closed circuit.

[0015] These embodiments minimize the thermal impact of the conversion of orthohydrogen to parahydrogen. In optional embodiments, the catalytic reactor is positioned on a hot branch of the closed cooling circuit.

[0016] These embodiments optimize the parahydrogen content by converting the majority of the refrigerant hydrogen with each pass through the reactor. These embodiments also reduce the thermal impact of the conversion if it takes place on the hot branch instead of the cold branch, which acts as the coolant.

[0017] In optional embodiments, the catalytic reactor is configured to operate at a temperature between 31 K and 184 K. These embodiments allow for optimal energy efficiency of the device.

[0018] In optional embodiments, the maintenance means is configured to maintain the proportion of parahydrogen in the internal composition of the refrigerant dihydrogen stream between 27% and 96%. These embodiments allow for optimal energy efficiency of the device.

[0019] In optional embodiments, the holding means includes a bypass of the catalytic reactor configured to operate a predetermined flow ratio between the flow through the reactor and the flow through the bypass. These embodiments allow for dynamic adjustment of the dihydrogen composition, proportional to the bypass and reactor flow rates.

[0020] In optional embodiments, the closed circuit of refrigerant hydrogen is configured to maintain an average temperature of the refrigerant hydrogen between 31 K and 184 K. These embodiments allow optimal energy efficiency of the device.

[0021] In optional embodiments, the device of the present invention includes a pre-cooling circuit for the gas to be liquefied, said pre-cooling circuit comprising a heat exchanger between a pre-cooling fluid stream and the refrigerant hydrogen stream. These embodiments allow for optimal energy efficiency of the device.

[0022] In optional embodiments, the gas to be liquefied is a stream consisting essentially of dihydrogen.

[0023] In optional embodiments, at least one catalytic reactor is integrated into a heat exchanger. Integrating the catalyst into a heat exchanger allows for continuous conversion during the cooling of the hydrogen to be liquefied, thus reducing the overall energy consumption of the liquefaction process.

[0024] Furthermore, this catalytic exchanger for the refrigerant dihydrogen flow eliminates the need for a catalytic reactor, thus reducing the cost and complexity of the overall process.

[0025] In optional embodiments, the closed refrigeration circuit includes an intercooling compression stage and at least one compression stage with a temperature below -40 °C for the refrigerant hydrogen. These arrangements limit the temperature rise of the refrigerant hydrogen and thus lower the average temperature in the cooling circuit.

[0026] In optional embodiments, the catalytic reactor is positioned on a cold branch of the closed refrigeration circuit. These embodiments allow for a reduction in the overall average temperature of the refrigerant flow in the closed transport circuit.

[0027] In optional embodiments, the closed refrigeration circuit includes at least one compressor for the ambient temperature refrigerant hydrogen and a storage tank for the liquid refrigerant hydrogen.

[0028] In optional embodiments, the catalytic reactor uses a catalyst comprising a member of the iron oxide family and preferably Fe2O3.

[0029] According to a second aspect, the present invention relates to a method for liquefying a gas according to claim 15.

[0030] The advantages of the process of the present invention are similar to those of the device of the present invention. Brief description of the figures

[0031] Other advantages, purposes and particular features of the invention will become apparent from the following non-limiting description of at least one particular embodiment of the device and method of the present invention, with reference to the accompanying drawings, in which: There figure 1 schematically represents the evolution of the proportion of parahydrodrene in the internal composition of dihydrogen as a function of temperature. figure 2 represents, schematically, a first particular embodiment of the device that is the subject of the invention, The figure 3 represents, schematically, a second particular embodiment of the device that is the subject of the invention, The figure 4 represents, schematically, a third particular embodiment of the device that is the subject of the invention, The figure 5 represents, schematically, a fourth particular embodiment of the device that is the subject of the invention, The figure 6represents, schematically, a fifth particular embodiment of the device that is the subject of the invention, The figure 7 represents, schematically, a sixth particular embodiment of the device that is the subject of the invention, The figure 8 represents, schematically, a seventh particular embodiment of the device that is the subject of the invention, The figure 9 represents, schematically and in the form of a flowchart, a succession of steps of a particular embodiment of the process that is the subject of the invention and The Figure 10 represents, schematically, an eighth particular embodiment of the device that is the subject of the invention. Description of the implementation methods

[0032] The present description is given by way of non-limiting attribution, each feature of an embodiment being able to be advantageously combined with any other feature of any other embodiment.

[0033] As can be understood from this description, various inventive concepts can be implemented by one or more of the methods or devices described below, several examples of which are provided herein. The actions or steps performed in implementing the method or device can be ordered in any appropriate manner. Consequently, it is possible to construct embodiments in which the actions or steps are performed in a different order than illustrated, which may include performing certain acts simultaneously, even if they are presented as sequential acts in the illustrated embodiments.

[0034] The indefinite articles "a" and "an", as used in the description and in the claims, should be understood as meaning "at least one", unless clearly stated otherwise.

[0035] The expression "and / or," as used in this document and in the claims, shall be understood as meaning "either or both" of the elements thus joined, that is, elements that are present conjunctively in some cases and disjunctively in others. Multiple elements listed with "and / or" shall be interpreted similarly, that is, "one or more" of the elements thus joined. Other elements may also be present, other than those specifically identified by the "and / or" clause, whether or not they are related to those specifically identified elements.Thus, by way of non-limiting example, a reference to "A and / or B", when used in conjunction with an open language such as "including", may refer, in one embodiment, to A only (possibly including elements other than B); in another embodiment, to B only (possibly including elements other than A); in yet another embodiment, to A and B (possibly including other elements); etc.

[0036] As used herein in the description and in the claims, "or" should be understood to have the same meaning as "and / or" as defined above. For example, when separating items in a list, "or" or "and / or" should be interpreted as inclusive, meaning the inclusion of at least one, but also more than one, of a number or list of items, and optionally, additional unlisted items. Only terms explicitly stating the contrary, such as "only one of" or "exactly one of," or, when used in the claims, "consisting of," refer to the inclusion of only one item from a number or list of items. In general, the term "or" as used here should only be interpreted as indicating exclusive alternatives (i.e., "either one but not both") when preceded by terms of exclusivity, such as "either", "one of", "only one of", or "exactly one of".

[0037] As used in this description and in the claims, the expression "at least one," with reference to a list of one or more elements, should be understood as meaning at least one element chosen from one or more elements in the list of elements, but not necessarily including at least one of each element specifically listed in the list of elements and not excluding any combination of elements in the list of elements. This definition also allows for the optional presence of elements other than those specifically identified in the list of elements to which the expression "at least one" refers, whether or not they are related to those specifically identified elements.Thus, by way of non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B", or, equivalently, "at least one of A and / or B") may refer, in one embodiment, to at least one, possibly including more than one, A, without B present (and possibly including elements other than B); in another embodiment, to at least one, possibly including more than one, B, without A present (and possibly including elements other than A); in yet another embodiment, to at least one, possibly including more than one, A, and at least one, possibly including more than one, B (and possibly including other elements); etc.

[0038] In the claims, as well as in the description below, all transitive expressions such as "comprising", "including", "carrying", "having", "containing", "implying", "holding", "composed of", and others, shall be understood as open, that is, as meaning including but not limited to. Only the transitive expressions "consisting of" and "consisting essentially of" shall be understood as closed or semi-closed transitive expressions, respectively.

[0039] It should be noted from the outset that the figures are not to scale.

[0040] The gas 51 to be liquefied can be of any type ordinarily liquefied. Preferably, this gas 51 is dihydrogen.

[0041] The refrigerant stream is defined as containing at least some hydrogen refrigerant. The proportion of hydrogen refrigerant depends on the specific application of the present invention. In some embodiments, the proportion of hydrogen refrigerant in the refrigerant stream is at least 30%. In some embodiments, the proportion of hydrogen refrigerant in the refrigerant stream is at least 50%. In some embodiments, the proportion of hydrogen refrigerant in the refrigerant stream is at least 70%. In some embodiments, the proportion of hydrogen refrigerant in the refrigerant stream is at least 90%. In some embodiments, the proportion of hydrogen refrigerant in the refrigerant stream is at least 99%. In the following description, the terms "refrigerant stream" and "hydrogen refrigerant" are used interchangeably.

[0042] The refrigerant dihydrogen 52 can originate from liquefied dihydrogen 51 or from a third source.

[0043] A "hot branch" of a closed circuit is at least a part of said circuit in which the temperature of the transported fluid decreases.

[0044] A "cold branch" of a closed circuit is at least a part of said circuit in which the temperature of the transported fluid increases.

[0045] We observe, on the figure 2 (not to scale) a schematic view of one embodiment of the device 200 that is the subject of the present invention. This device 200 for liquefying a gas 51 comprises: a circuit 55 for transporting gas to be liquefied comprising at least one heat exchanger 204 between the gas 51 to be liquefied and a refrigerant flow 52 comprising at least refrigerant dihydrogen, a closed refrigeration circuit 210 configured to transport essentially the refrigerant flow, the closed refrigeration circuit comprising a means 215 for maintaining an internal composition of the refrigerant dihydrogen in a ratio of parahydrogen to orthohydrogen lower or higher than said ratio corresponding to a natural equilibrium composition in the closed refrigerant flow circuit, said maintenance means comprising a catalytic reactor 220 configured to convert a portion of the orthohydrogen in the refrigerant dihydrogen flow into parahydrogen or vice versa.

[0046] The transport circuit 55, for example, is formed of a set of pipes configured to transport the gas 51 to be liquefied, the gas 51 originating from a source (not shown) and being transported to a fixed or mobile storage 56. This transport circuit 55 is configured to transport the gas 51 through at least one heat exchanger, 201, 202, 203, 204, 205, 206, 207, 208 and / or 209. Each heat exchanger, 201, 202, 203, 204, 205, 206, 207, 208 and / or 209, may belong to a pre-cooling and / or cooling circuit. The number and arrangement of heat exchangers, 201, 202, 203, 204, 205, 206, 207, 208 and / or 209, depends on the desired configuration for device 200, the desired specifications for gas 51 at the outlet of this device 200 and the desired energy performance for device 200.

[0047] In some embodiments, the gas 51 to be liquefied is dihydrogen in gaseous form, with a mass flow rate of 0.116 kg / s, a pressure of 21 bar, and a temperature of 298 K. The embodiments 200, 300, 400, 500, 600, 700, and 1100 are shown in figures 2 to 7 And 10 Each one contains nine heat exchangers in succession. In these figures 2 to 7 And 10 The heat exchangers are arranged as follows: The gas flow 51 first passes through a pre-cooling section, comprising: a first heat exchanger, 201, 301, 401, 501, 601, 701, a second heat exchanger, 202, 302, 402, 502, 602, 702 and a third heat exchanger, 203, 303, 403, 503, 603, 703, the gas flow 51 then passes through a cooling section, comprising: a fourth heat exchanger, 204, 304, 404, 504, 604, 704, a fifth heat exchanger, 205, 305, 405, 505, 605, 705, a sixth heat exchanger, 206, 306, 406, 506, 606, 706, a seventh exchanger, 207, 307, 407, 507, 607, 707, an eighth exchanger, 208, 308, 408, 508, 608, 708 and a ninth exchanger, 209, 309, 409, 509, 609, 709, the liquefied gas flow 51 then being conveyed to the storage 56, optionally by first passing through a pressure-reducing valve 53, known as a "Joule-Thomson" valve.

[0048] Storage 56 can be a temporary storage for separating the evaporation gas and the liquefied gas 51.

[0049] As can be seen, for example, the feed stream consists of normal hydrogen (25% parahydrogen and 75% orthohydrogen) at a pressure of 21 bar, a temperature of 298 K (25 °C), and a mass flow rate of 0.116 kg / s. The stream is first cooled to 83 K (-190 °C) by two heat exchangers. This stream then enters a catalytic heat exchanger, which performs the first stage of the ortho-to-para conversion. The stream exits the pre-cooling section at a temperature of 80 K (-193 °C) with a composition of 49% parahydrogen.

[0050] In the cooling section, the feed stream 51 reaches a temperature of 22 K (-251 °C) and a composition of 99% parahydrogen through a series of six catalytic heat exchangers. The final liquefaction stage is carried out with a pressure-reducing valve that lowers the pressure to 2 bar. The liquid portion of the stream (98%) exits the device, and the remaining gaseous portion is conveyed to an exhaust gas management system.

[0051] There figure 8 represents a variant of the gas transport circuit 55 51, which includes eight heat exchangers. In this variant, the heat exchangers are arranged as follows: The gas flow 51 first passes through a pre-cooling section, comprising: a first exchanger 801 and a second exchanger 802, the gas flow 51 then passes through a cooling section, comprising: a third exchanger 803, a fourth exchanger 804, a fifth exchanger 805, a sixth exchanger 806, a seventh exchanger 807 and an eighth exchanger 808, the liquefied gas flow 51 then being conveyed to the storage 56.

[0052] Regarding the embodiments illustrated in figures 2 to 8 And 10 Each heat exchanger is, for example, a plate heat exchanger between a so-called "hot" fluid and a so-called "cold" fluid. In each such heat exchanger, the gas 51 to be liquefied acts as the hot fluid. The cold fluid depends on the implementation variants. For example, in the figures 2 to 8 And 10, the heat exchangers in the cooling section use hydrogen refrigerant as the cold fluid, while the heat exchangers in the pre-cooling section use hydrogen refrigerant and a pre-cooling fluid.

[0053] Thus, as can be understood, all or part of the heat exchangers are traversed by the closed refrigeration circuit 210. The refrigeration circuit 210, for example, consists of a set of pipes configured to transport the refrigerant dihydrogen 52. This transport circuit 210 is configured to transport the dihydrogen 52 refrigerant through at least one heat exchanger, 201, 202, 203, 204, 205, 206, 207, 208 and / or 209. The configuration of the refrigeration circuit 210 depends on the desired performance of the device 200 and the operating conditions expected for this device 200.

[0054] In some embodiments, the refrigerant dihydrogen 52 is configured to have a temperature between 171 K and 22 K, this refrigerant dihydrogen 52 being configured to cool the gas 51 to be liquefied.

[0055] In the embodiment of device 200 shown in figure 2 The refrigeration circuit 210 is a closed circuit which includes: a so-called "hot" branch, in which the refrigeration circuit 210 passes successively through: the second heat exchanger 202, the third heat exchanger 203, the fourth heat exchanger 204, the means 215 for maintaining the internal composition of the dihydrogen, the fifth heat exchanger 205, the sixth heat exchanger 206, the seventh heat exchanger 207, the eighth heat exchanger 208, and an expansion valve 211; a so-called "cold" branch, formed of two parts: a first part, originating at the outlet of the expansion valve 211, in which the refrigeration circuit 210 passes successively through: the ninth heat exchanger 209, the eighth heat exchanger 208, the seventh heat exchanger 207, the sixth heat exchanger 206, the fifth heat exchanger 205, the fourth heat exchanger 204, and a first compressor 212, a second compressor 213,the refrigerant hydrogen at the outlet of the second compressor 213 being supplied to the second heat exchanger 202 and a second part, originating from a diversion located at the outlet of the holding means 215, in which the refrigeration circuit 210 passes successively through: a first expansion valve 214, the sixth heat exchanger 206, a second expansion valve 216, the seventh heat exchanger 207, the sixth heat exchanger 206, the fifth heat exchanger 205, the fourth heat exchanger 204, the refrigerant hydrogen at the outlet of the fourth heat exchanger 204 being supplied to the second compressor 213.

[0056] In the embodiment of device 300 shown in figure 3 The 310 refrigeration circuit is a closed circuit, similar to the 210 refrigeration circuit as shown in figure 2 , which has the following variants: The holding means 315 is positioned on the first part of the cold branch, between the sixth heat exchanger 306 and the fifth heat exchanger 305 and the second part of the cold branch originates from a diversion at the outlet of the fourth heat exchanger 304 along the hot branch.

[0057] In the embodiment of device 400 shown in figure 4 The 410 refrigeration circuit is a closed circuit, similar to the 210 refrigeration circuit as shown in figure 2 , in which the holding means 415 comprises two catalytic reactors, 420 and 421, located on either side of the fourth heat exchanger 404 along the hot branch.

[0058] In the embodiment of device 500 shown in figure 5 The 510 refrigeration circuit is a closed circuit, similar to the 210 refrigeration circuit as shown in figure 2, which has the following variants: The holding means 515 is positioned on the hot branch, between the fifth heat exchanger 505 and the sixth heat exchanger 506 and the second part of the cold branch originates from a diversion at the outlet of the fourth heat exchanger 304 along the hot branch.

[0059] In the embodiment of device 700 shown in figure 7 The 710 refrigeration circuit is a closed circuit, similar to the 210 refrigeration circuit as shown in figure 2 , which presents the following independent variants: on the second part of the cold branch, the flow 52 of dihydrogen at the outlet of the second expansion valve 216 is supplied to a fifth expansion valve 717, the flow from this fifth expansion valve 717 being supplied to the seventh heat exchanger 707, the first compressor 212 is replaced by a first compressor 712, the second compressor 213 is replaced by an intercooled compression stage 713, formed here of a succession of heat exchangers 719 and compressors 718, the flow 52 of dihydrogen at the outlet of the intercooled compression stage 713 being supplied to the fourth heat exchanger 704.

[0060] In the embodiment of device 800 shown in figure 8 The 810 refrigeration circuit is a closed circuit, similar to the 210 refrigeration circuit as shown in figure 2 , which has the following variants: The holding means 815 is positioned on the second part of the cold branch, between the sixth heat exchanger 806 and the fifth heat exchanger 805, the second part of the cold branch originates from a diversion at the outlet of the third heat exchanger 803 along the hot branch, the dihydrogen flow exiting the third expansion valve 214 is supplied to the fifth heat exchanger 805, the dihydrogen flow exiting the fifth heat exchanger 805 is supplied to the fourth expansion valve 216, the first compressor 212 is replaced by a succession consisting of a first compressor 812 and a heat exchanger 813 and the second compressor 213 is replaced by a succession consisting of a second compressor 817 and a heat exchanger 818.

[0061] In embodiments of device 800, such as that shown in figure 8, the catalytic reactor 820 is positioned on a cold branch of the closed refrigeration circuit 810.

[0062] In embodiments of device 800, such as that shown in figure 8 , the closed refrigeration circuit 810 comprising at least one compressor 817 of the refrigerant dihydrogen at ambient temperature and a tank 819 for storing the liquid refrigerant dihydrogen.

[0063] In particular embodiments, such as those illustrated in figures 2 to 8 And 10 , the closed circuit, 210, 310, 410, 510, 610, 710 and / or 810, of refrigerant dihydrogen is configured to maintain an average temperature of the refrigerant dihydrogen between 31 K and 184 K.

[0064] As can be understood, the closed circuit 210 includes a means 215 for maintaining the internal composition of the dihydrogen. Such a maintenance means 215 includes, for example, at least one catalytic reactor 220 configured to favor a predetermined ratio of parahydrogen to orthohydrogen. This ratio is selected so as to be lower or higher than the same ratio in a natural equilibrium state of a closed circuit 210 without a maintenance means 215. Increasing the relative proportion of parahydrogen in the composition of the dihydrogen improves the performance of the dihydrogen in the heat exchanges taking place within the device 100.

[0065] In particular 200 embodiments, as represented in figure 2 , the catalytic reactor 220 is positioned on a hot branch of the closed circuit 210.

[0066] In 300 particular embodiments, as represented in figure 3, the catalytic reactor 320 is positioned on a cold branch of the closed circuit 310.

[0067] In 400 particular modes of realization, as represented in figure 4 The holding means 415 comprises two catalytic reactors, 420 and 421, positioned on a hot branch of the closed circuit 210. These two catalytic reactors, 420 and 421, are positioned, for example, on either side of a heat exchanger with the flow 51 of gas to be liquefied. This heat exchanger is, for example, the fourth heat exchanger 404 in a general sequence of a pre-cooling section with three heat exchangers, which corresponds to the first heat exchanger in the cooling section.

[0068] In 500 particular modes of realization, as represented in figure 5 , the 520 catalytic reactor is a so-called “short” reactor positioned on a hot branch of the closed 510 circuit.

[0069] In 600 specific realizations, as represented in figure 6 , the maintenance means 615 comprises a catalytic reactor 620 and a bypass 616 of the reactor 620, positioned on a hot branch of the closed circuit 610.

[0070] The bypass 616 is, for example, a valve mounted on a pipe whose inlet is located upstream of reactor 620 and whose outlet is located downstream of reactor 620. This valve can be controlled in flow rate to the flow rate through reactor 620.

[0071] In variants, the 616 bypass is associated with a control unit, such as a PLC, configured to issue activation or deactivation commands to the 616 bypass according to predetermined activation criteria.

[0072] In embodiments such as that represented in Figure 10 , presented in a non-exhaustive manner as a variant of the figure 2The maintenance means 1115 includes at least one catalytic reactor 1120 integrated into a heat exchanger 204. The catalytic reactor 1120 can be integrated into any heat exchanger, 202, 203, 204, 205, 206, 207, 208 or 209, of the closed circuit 52.

[0073] In particular embodiments, such as those represented in figures 2 to 8 , the reactor, 220, 320, 420, 520, 620, 720 and / or 820, catalytic is configured to operate at a temperature between 31 K and 184 K.

[0074] Any heterogeneous catalyst with paramagnetic activity, chemically compatible with dihydrogen, and physically compatible with cryogenic temperatures can be used. An example of such a catalyst is IONEX (registered trademark), a formulation containing Fe₂O₃ from the iron oxide family. Another functional example is OXYSORB (registered trademark), a formulation containing CrO₄. A non-exhaustive list of known and compatible catalysts from the literature is given below: Cr 2 O 3, Cr(OH) 3, Mn(OH) 4, Fe(OH) 4, Co(OH) 3 and Ni(OH) 2.

[0075] In preferred embodiments, the maintenance means, 215, 315, 415, 515, 615, 715 and / or 815, is configured to maintain the proportion of parahydrogen in the internal composition of the refrigerant dihydrogen stream between 27% and 96%.

[0076] As can be seen, for example, the cooling loop is a dual-pressure loop, known as a "Claude loop," and the refrigerant used is hydrogen. The refrigerant fluid 52 is first compressed to 29 bar by a multi-stage compressor 213. The temperature of the fluid 52 at the outlet of the compressor 213 is approximately 171 K (-102 °C). The fluid 52 is cooled to 80 K (-193 °C) with two heat exchangers, 202 and 203, by exchange with a pre-cooling fluid, such as nitrogen. The fluid 52 then enters a cooling section and is cooled to 69 K (-204 °C) in the first cooling heat exchanger 204. The hydrogen stream 52 passes through a catalytic conversion reactor 220 where the hydrogen reaches an equilibrium composition for the operating temperature considered. In this case, hydrogen is for example composed of 58% parahydrogen and 42% orthohydrogen.The hydrogen is thus slightly heated to between 0.1 K and 0.5 K in steady state. The refrigerant is then separated, and 89% of the total flow is expanded, by means of an expansion valve 214, to 18.5 bar and reaches 60 K (-213 °C). The stream 52 is then cooled to 51 K (-222 °C) in a heat exchanger 206, and then expanded with a two-stage expansion valve 216 to 4.5 bar to reach 31.5 K (-241.5 °C). From this point, the stream 52 is used as a refrigerant in the cooling heat exchangers 207, 206, 205, and 204. The remaining portion (11%) is cooled to 26 K through four heat exchangers, 205, 206, 207 and 208. This portion is then expanded with an expansion valve 211 to 1.5 bar to reach 22 K. The liquid refrigerant cools the supply stream to 22 K in two two-phase heat exchangers, 209 and 208, and four multi-flow heat exchangers, 207, 206, 205 and 204.The two refrigerant streams at 4.5 and 1.5 bar exit the cooling section at 78 K (-195 °C). The low-pressure stream is compressed to 4.5 bar in a first compressor 212. The stream from the first compressor 212 is then mixed with the medium-pressure stream before entering the second compressor 213.

[0077] In preferred embodiments, the closed refrigeration circuit, 210, 310, 410, 510, 610, 710 and / or 810, is configured so that the flow 52 of refrigerant dihydrogen has, at the inlet of the catalytic reactor, 220, 320, 420, 520, 620, 720 and / or 820, a temperature essentially equal to the average temperature of the refrigerant dihydrogen 52 in the closed circuit, 210, 310, 410, 510, 610, 710 and / or 810.

[0078] In particular embodiments, such as those represented in figures 2 to 8and 10, the device, 200, 300, 400, 500, 600, 700 and / or 800, includes a pre-cooling circuit 54 for the gas to be liquefied, said pre-cooling circuit including at least one heat exchanger, 203, 303, 403, 503, 603, 703 and / or 802, between a pre-cooling fluid flow and the refrigerant dihydrogen flow 52.

[0079] In some embodiments, the pre-cooling circuit 54 is configured to transport nitrogen with a temperature between 298 K and 80 K. The objective of such a pre-cooling circuit 54 is to cool the gas 51 to be liquefied and the refrigerant dihydrogen from 90 K to 80 K.

[0080] In the embodiments of the device, 200, 300, 400, 500 and / or 600, represented in Figures 2 to 6 The pre-cooling circuit 54 is a closed circuit which includes: a so-called "hot" branch, in which the pre-cooling circuit 54 passes successively through: the first heat exchanger, 201, 301, 401, 501 and / or 601, the second heat exchanger, 202, 302, 402, 502 and / or 602, and an expansion valve 56; a so-called "cold" branch, formed of two parts: a first part, originating from the outlet of the expansion valve 56, in which the pre-cooling circuit 54 passes successively through: the third heat exchanger, 203, 303, 403, 503 and / or 603, the second heat exchanger, 202, 302, 402, 502 and / or 602, the first heat exchanger, 201, 301, 401, 501 and / or 601, of heat, a compressor 57 and a dedicated heat exchanger 58, the pre-cooling fluid at the outlet of the dedicated heat exchanger 58 being supplied to the first heat exchanger, 201, 301, 401, 501 and / or 601, and a second part, originating from a diversion located at the outlet of the first heat exchanger, 201, 301, 401, 501 and / or 601,of heat, in which the pre-cooling circuit 54 passes through an expansion valve 59, the pre-cooling fluid at the outlet of the expansion valve 59 being supplied to the second heat exchanger, 202, 302, 402, 502 and / or 602.

[0081] In a particular embodiment of device 700, represented in figure 7 The pre-cooling circuit 54 is similar to the cooling circuit 54 shown in figures 2 to 6 , the compressor 57 being formed of a succession of compressors. In this embodiment, the refrigerant flow 54 is implemented in at least one heat exchanger 719 of the intercooled compression stage 713 and in at least one compression stage 718 at a temperature below -40°C.

[0082] In a particular embodiment of device 800, represented in figure 8 , the pre-cooling circuit 54 is an open circuit.

[0083] As can be seen, for example, pre-cooling from 300 K (27 °C) to 80 K (-193 °C) is achieved using a closed nitrogen loop. The nitrogen is first compressed from 1 bar to 50 bar by a multi-stage compressor 57. This nitrogen is then cooled to 200 K (-73 °C) in a heat exchanger 201. The nitrogen is then separated; 97% of the total flow is expanded to 1.1 bar in an expansion valve 59 and reaches 81 K (-192 °C). This nitrogen returns as refrigerant to the first pre-cooling heat exchanger 201. The remaining portion (3%) is cooled to 83 K (-190 °C). This portion is then partially liquefied by an expansion valve 56, reaching 78 K (-195°C), and functions in the third heat exchanger 203 as the primary refrigerant. The remaining cooling capacity of the nitrogen is used in the pre-cooling heat exchangers 202 and 201.

[0084] We observe, in Figure 10, a series of specific steps of process 1000, which is the subject of the present invention. This process 1000 for liquefying a gas comprises: a stage 1005 for transporting the gas to be liquefied, comprising at least one stage 1010 for heat exchange between the gas to be liquefied and a refrigerant stream comprising at least refrigerant dihydrogen, a stage 1015 for transporting the refrigerant stream in a closed-circuit refrigeration system, the transport stage comprising a stage 1020 for maintaining an internal composition of the refrigerant dihydrogen at a parahydrogen to orthohydrogen ratio lower or higher than said ratio corresponding to a natural equilibrium composition in the closed-circuit refrigerant stream, said maintenance means comprising a 1025 catalytic reaction step to convert some of the orthohydrogen from the refrigerant dihydrogen into parahydrogen or vice versa.

[0085] Methods for carrying out the steps of this process 1000 are described in relation to the figures 2 to 8 And 10 .

[0086] As can be understood, a particular composition of the refrigerant dihydrogen that is the subject of the present invention comprises 58% parahydrogen and 42% orthohydrogen, this composition not being the natural equilibrium composition. This constitutes a compromise to obtain the best match between the thermal properties of the gas both during its compression and as a refrigerant.

[0087] Indeed, increasing the parahydrogen content primarily results in an increase in hydrogen's specific heat capacity. This, in turn, increases the energy required to change its temperature. During compression, this reduces the temperature increase between the inlet and outlet, thus minimizing the decrease in hydrogen density. The denser a gas is, the easier it is to compress. Therefore, the compression power of hydrogen is reduced when it is compressed in a form that is most highly converted to parahydrogen.

[0088] As can be understood, the present invention exhibits high operating performance under the following operating conditions, with regard to device 200 shown in figure 2 : Table 1 Settings lower limit upper limit Pre-cooling temperature (K / °C) 60 / -213 150 / -123 Compression inlet temperature (K / °C) 31 / -242 250 / -23 Parahydrogen fraction (%) 27 % 96 % Catalysis temperature (K / °C) 31 / -232 184 / -89 Average refrigerant temperature (K) 31 / -232 184 / -89 Minimum operating time (days) 30 -

[0089] In the embodiment of device 300 shown in figure 3 The catalytic reactor 320 is positioned on a return branch of the cooling loop, which shifts the cycle equilibrium according to its associated temperature. A suitable position for reactor 320 is between the fifth heat exchanger 305 and the sixth heat exchanger 306. In this embodiment, the catalysis temperature is 54 K (-219 °C) (for a composition of 74% p-H2 and 26% o-H2).

[0090] In another embodiment of device 400, as represented in figure 4The catalytic conversion is carried out in several catalytic reactors, 420 and 421, arranged at different temperatures, thus aiming for a stepwise conversion of the refrigerant hydrogen. This is advantageous because the heat generated during the conversion increases inversely with temperature. In this embodiment, a first conversion is carried out at 80 K (-193 °C), bringing the hydrogen to a composition of 52% p-H2, and then a second conversion is carried out at 69 K (-204 °C), bringing the hydrogen to the target composition of 58% p-H2.

[0091] In another embodiment of device 500, as represented in figure 5A partial conversion at a temperature other than the target temperature associated with the target equilibrium composition is achieved. This is feasible provided that reactor 520 is sized so that the transit time or the reactivity of the catalyst does not allow thermodynamic equilibrium to be reached. For example, reactor 520 is placed at a catalysis temperature of 56 K (-217 °C), but shortening the length of reactor 520 allows the target composition of 58% p-H2 to be reached instead of the equilibrium composition of 70% p-H2 associated with the temperature of 56 K (-217 °C).

[0092] In another embodiment of device 600, as represented in figure 6The target composition can be selected using a partial bypass device of reactor 620. Thus the final composition corresponds to the average of the output compositions of reactor 620 and bypass 616 weighted by the respective flow rates passing through them.

[0093] In another embodiment of device 700, as represented in figure 7 The present invention is applied in the context of cryogenic compression with intermediate cooling (called "intercooler"), i.e. cooling the refrigerant fluid between each stage.

[0094] In another embodiment of device 800, as represented in figure 8The placement of the catalytic reactor 820 is configured so that compression takes place at ambient temperature. If the average temperature of the refrigerant dihydrogen remains below 184 K (-89 °C), as is the case, for example, if a liquid hydrogen buffer storage is used after valve 53, then in this embodiment, increasing the parahydrogen content reduces the natural conversion in the liquid buffer storage, thereby reducing and shifting some of the losses associated with the process to a location less sensitive to heat release.

[0095] The present invention is particularly suitable for the production of liquid hydrogen in excess of five tonnes per day because the reduction in investment requirements and the stability of the process in operation allow for savings on the final cost of hydrogen liquefaction.

Claims

1. Device (200, 300, 400, 500, 600, 700, 800, 1100) for liquefying a gas (51), this device comprising: - a circuit (55) for transporting gas to be liquefied, the circuit comprising at least one exchanger (204, 304, 404, 504, 604, 704, 804) exchanging heat between the gas (51) to be liquefied and a refrigerant flow (52) comprising at least dihydrogen refrigerant; - a closed refrigeration circuit (210, 310, 410, 510, 610, 710, 810) configured to transport the refrigerant flow; characterised in that the closed refrigeration circuit comprises a means (215, 315, 415, 515, 615, 715, 815, 1115) for maintaining an internal composition of the dihydrogen refrigerant at a ratio of parahydrogen to orthohydrogen that is lower or higher than said ratio corresponding to a natural equilibrium composition in the closed refrigerant flow circuit, this maintenance means comprising a catalytic reactor (220, 320, 420, 520, 620, 720, 820, 1120) configured to convert a portion of the orthohydrogen from the refrigerant flow into parahydrogen or vice versa.

2. Device (200, 400, 500, 600, 700, 800, 1100) according to claim 1, wherein the closed refrigeration circuit (210, 310, 410, 510, 610, 710, 810) is configured such that the dihydrogen refrigerant has, on input to the catalytic reactor (220, 320, 420, 520, 620, 720, 820), a temperature essentially equal to the mean temperature of the dihydrogen refrigerant in the closed circuit.

3. Device (200, 400, 500, 600, 1100) according to one of claims 1 or 2, wherein the catalytic reactor (220, 420, 520, 620) is positioned on a hot leg of the closed refrigeration circuit (210, 410, 510, 610).

4. Device (200, 300, 400, 500, 600, 700, 800, 1100) according to one of claims 1 to 3, wherein the catalytic reactor (220, 320, 420, 520, 620, 720, 820) is configured to operate according to a temperature between 31 K and 184 K.

5. Device (200, 300, 400, 500, 600, 700, 800, 1100) according to one of claims 1 to 4, wherein the maintenance means (215, 315, 415, 515, 615, 715, 815) is configured to maintain the proportion of parahydrogen in the internal composition of the dihydrogen refrigerant between 27% and 96%.

6. Device (600) according to one of claims 1 to 5, wherein the maintenance means (615) comprises a bypass (616) of the catalytic reactor configured to operate a predetermined throughput ratio between the flow passing through the reactor (620) and the flow passing through the bypass.

7. Device (200, 300, 400, 500, 600, 700, 800, 1100) according to one of claims 1 to 6, wherein the closed refrigerant circuit (210, 310, 410, 510, 610, 710, 810) is configured to maintain a mean temperature of the dihydrogen refrigerant between 31 K and 184 K.

8. Device (200, 300, 400, 500, 600, 700, 800, 1100) according to one of claims 1 to 7, which comprises a circuit (54) for pre-cooling the gas to be liquefied, this pre-cooling circuit comprising a heat exchanger (203, 303, 403, 503, 603, 703, 802) for exchanging heat between a pre-cooling fluid flow and the dihydrogen refrigerant flow (52).

9. Device (200, 300, 400, 500, 600, 700, 800, 1100) according to one of claims 1 to 8, wherein the gas to be liquefied is a flow comprised essentially of dihydrogen.

10. Device (1100) according to one of claims 1 to 9, wherein at least one catalytic reactor (1120) is integrated into a heat exchanger (204).

11. Device (700) according to one of claims 1 to 10, wherein the closed refrigeration circuit (710) comprises a stage (713) of intercooling compression and at least one stage (718) of compression at a temperature below -40°C for the dihydrogen refrigerant.

12. Device (800) according to one of claims 1 to 11, wherein the catalytic reactor (820) is positioned on a cold leg of the closed refrigeration circuit (810).

13. Device (800) according to one of claims 1 to 12, wherein the closed refrigeration circuit (810) comprises at least one compressor (817) of the dihydrogen refrigerant at ambient temperature and a storage tank (819) for the liquid dihydrogen refrigerant.

14. Device (200, 300, 400, 500, 600, 700, 800, 1100) according to one of claims 1 to 13, wherein the catalytic reactor (220, 320, 420, 520, 620, 720, 820) utilises a catalyser comprising a member of the iron oxide family, preferably Fe2O3.

15. Method (1000) for liquefying a gas, the method comprising: - a step (1005) of transporting gas to be liquefied, the step comprising at least one step (1010) of exchanging heat between the gas to be liquefied and a refrigerant flow comprising at least dihydrogen refrigerant; - a step (1015) of transporting the refrigerant flow in a closed refrigeration circuit; characterised in that the step of transporting the refrigerant flow comprises a step (1020) of maintaining an internal composition of the dihydrogen refrigerant at a ratio of parahydrogen to orthohydrogen that is lower or higher than said ratio corresponding to a natural equilibrium composition in the closed refrigerant flow circuit, this maintenance step comprising a catalytic reaction step (1025) to convert a portion of the orthohydrogen from the refrigerant flow into parahydrogen or vice versa.

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